The new role of graphene (GR) in boosting the two-electron reduction of O2 to H2O2 has been first identified in the GR–WO3 nanorod (NR) nanocomposite photocatalysts, which are fabricated by a facile, solid electrostatic self-assembly strategy to integrate the positively charged branched poly(ethylenimine) (BPEI)-GR (BGR) and negatively charged WO3 NRs at room temperature. Photoactivity test shows that, as compared to WO3 NRs, BGR–WO3 NRs with an appropriate addition ratio of GR exhibit remarkably enhanced and stable visible-light photoactivity toward the degradation of Rhodamine B. Besides the common roles of GR observed in the GR-based composite photocatalysts in the literature, including enhancing the visible-light absorption intensity, improving the lifetime and transfer of photogenerated charge carriers, and increasing the adsorption capacity for reactants, we have observed the new role of GR in boosting the two-electron reduction of O2 to H2O2 in this specific BGR–WO3 NR photocatalyst system. Importantly, this new role of GR does contribute to the overall photoactivity enhancement of BGR–WO3 NR nanocomposites. The synergistic contribution of GR on improving the photoactivity of WO3 NRs and the underlying reaction mechanism have been analyzed by the structure–photoactivity correlation analysis and controlled experiments using radicals scavengers.

A carbon nanotubes (CNT)/TiO2 nanocomposite photocatalyst has been prepared by a simple impregnation method, which is used, for the first time, for gas-phase degradation of benzene. It is found that the as-prepared CNT/TiO2 nanocomposite exhibits an enhanced photocatalytic activity for benzene degradation, as compared with that over commerical titania (Degussa P25). A similar phenomenon has also been found for liquid-phase degradation of methyl orange. The characterization of photocatalysts by a series of joint techniques, including X-ray diffraction, transmission electron microscopy, ultraviolet/visible (UV/vis) diffuse reflectance spectra, and photoluminescence spectra, discloses that CNT has two kinds of crucial roles in enhancement of photocatalytic activity of TiO2. One is to act as an electron reservoir, which helps to trap electrons emitted from TiO2 particles due to irradiation by UV light, therefore hindering electron−hole pairs recombination. The other is to act as a dispersing template or support to control the morphology of TiO2 particles in the CNT/TiO2 nanocomposite, and this important role was neglected in previous studies. Accordingly, a reasonable model is proposed to expain the role of CNT in CNT/TiO2 composites as a photocatalyst for degradation of organic pollutants.

We report an efficient and easily accessible self-assembly route to synthesize In2S3–GR nanocomposites via electrostatic interaction of positively charged In2S3 nanoparticles with negatively charged graphene oxide (GO) followed by a hydrothermal process for reduction of GO to graphene (GR). The as-synthesized In2S3–GR nanocomposites exhibit much higher visible light photocatalytic activity toward selective reduction of nitroaromatic compounds in water than bare In2S3 nanoparticles and In2S3–GR–H that is obtained from the simple “hard” integration of GR nanosheets with solid In2S3 nanoparticles without modification of surface charge. On the basis of the joint characterizations and structure–photoactivity correlation it is disclosed that the enhanced photocatalytic performance of In2S3–GR is mainly ascribed to the more efficient interfacial contact between In2S3 and the GR nanosheets than In2S3–GR–H, which would amplify the use of electron conductivity and mobility of GR to improve the lifetime and transfer of photogenerated charge carriers more efficiently and thus boost the photoactivity more effectively. This work highlights the significant effect of preparation methods on the photoactivity of GR–semiconductor nanocomposites. It is expected that such a simple electrostatic self-assembly strategy could aid to rationally fabricate more efficient GR–semiconductor nanocomposites with improved interfacial contact and photocatalytic performance toward various photocatalytic selective transformations.

Coverage-dependent behavior for chemical functionalization of the semiconductor X(100) (X = C, Si, and Ge) surface by cycloadditions of organic molecules, including carbene (CH2), silylene (SiH2), germylene (GeH2), and nitrene (NH), has been investigated using density functional theory (DFT) coupled with periodic slab models. In particular, we have performed calculations on models with 1, 2, 4, and 8 of these organic molecules, corresponding to coverages of θ = 0.125, 0.25, 0.5, and 1, respectively. The results demonstrate that the adsorption energies decrease when coverage is increased, being attributed to the intermolecular repulsion at high coverage. For the NH molecule, due to its smaller molecular size than CH2, SiH2, and GeH2, the adsorption energy is relatively insensitive to the variation of coverage. Interestingly, at the saturated coverage, the structure of as-formed monolayer organic film among C(100), Si(100), and Ge(100) is different. The large adsorption energies at the saturated coverage clearly suggest the feasibility of forming organic layer films of carbenes and nitrenes onto the semiconductor X(100) surface, thus leading to new hybrid multifunctional materials. In addition, it has also been found that the band gaps can be finely tuned by addition of organic layers onto the X(100) surface; for example, the band gap is significantly widened for the CH2/C(100) and NH/C(100) systems at the saturated coverage in comparison to that of bare C(100). These suggest that there is a promising flexibility for engineering the semiconductor C(100), Si(100), and Ge(100) surfaces by tuning the coverage and type of organic molecules, given the well-known abundance of carbene and nitrene chemistry.

•1D CdS@MoS2 (CM) core-shell nanowires are prepared by a facile hydrothermal strategy.•1D CM composites show the large and intimate coaxial interfacial contact.•1D CM composites show distinctly enhanced visible-light photoactivity for H2-evolution.•A probable photocatalytic mechanism over the 1D CM composites is proposed.The well-defined one-dimensional (1D) CdS@MoS2 (CM) core-shell nanowires are constructed by employing CdS nanowires (CdS NWs) as nanobuilding blocks via a facile hydrothermal strategy. The synergistic interaction, stemming from the large and intimate coaxial interfacial contact between MoS2 thin shell and 1D CdS core, can efficiently retard the charge carrier recombination and the MoS2 as noble-metal-free cocatalyst enriches the active sites for H2 evolution from water. Consequently, in comparison to bare CdS nanowires, the resultant 1D core-shell CM composite exhibits distinctly enhanced visible light activity for the evolution of H2. Notably, the activity of 1D CM with the optimized 2 wt% of MoS2 exceeds that of pure CdS and CdS–1 wt% Pt composite by a factor of 64 and 4 times, respectively, under identical reaction conditions, while the apparent quantum yield (A.Q.Y.) at 420 nm over 1D CM reaches 28.5%. This work provides a simple paradigm for facile and finely controlled synthesis of well-shaped 1D-based composite photocatalysts towards boosted solar energy conversion.One-dimensional CdS@MoS2 core-shell nanowires with large and intimate coaxial interfacial contact have been fabricated via a simple hydrothermal methodology, which exhibit boosted performance for visible-light photocatalytic H2 evolution.Download high-res image (284KB)Download full-size image

The obvious incongruity between the increasing depletion of fossil fuel and the finite amount of resources has motivated us to seek means to maintain sustainability in our society. Developing renewable and highly efficient energy conversion and storage systems represents one of the most promising and viable methods. Although the efficiency of energy conversion and storage devices depends on various factors, their overall performances strongly rely on the structure and functional properties of materials. Graphene and its derivatives as versatile templates for materials synthesis have garnered widespread interest because of their flexible capability to tune the morphology and structure of functional materials. Herein, we have demonstrated recent progress on graphene and its derivatives as versatile templates for materials synthesis, particularly highlighting the basic fundamental roles of graphene in the materials preparation process. Then, a concise overview of the functional applications of materials obtained from graphene-templated approaches has been presented with a few selected examples to show the wide scope of potential in energy storage and conversion. Finally, a brief perspective and potential future challenges in this burgeoning research area have been discussed.

There is still an ongoing effort to search for sustainable, clean and highly efficient energy generation to satisfy the energy needs of modern society. Among various advanced technologies, electrocatalysis for the oxygen evolution reaction (OER) plays a key role and numerous new electrocatalysts have been developed to improve the efficiency of gas evolution. Along the way, enormous effort has been devoted to finding high-performance electrocatalysts, which has also stimulated the invention of new techniques to investigate the properties of materials or the fundamental mechanism of the OER. This accumulated knowledge not only establishes the foundation of the mechanism of the OER, but also points out the important criteria for a good electrocatalyst based on a variety of studies. Even though it may be difficult to include all cases, the aim of this review is to inspect the current progress and offer a comprehensive insight toward the OER. This review begins with examining the theoretical principles of electrode kinetics and some measurement criteria for achieving a fair evaluation among the catalysts. The second part of this review acquaints some materials for performing OER activity, in which the metal oxide materials build the basis of OER mechanism while non-oxide materials exhibit greatly promising performance toward overall water-splitting. Attention of this review is also paid to in situ approaches to electrocatalytic behavior during OER, and this information is crucial and can provide efficient strategies to design perfect electrocatalysts for OER. Finally, the OER mechanism from the perspective of both recent experimental and theoretical investigations is discussed, as well as probable strategies for improving OER performance with regards to future developments.

Over the past few decades, layer-by-layer (LbL) assembly of multilayer thin films has garnered considerable interest on account of its ability to modulate nanometer control over film thickness and its extensive choice of usable materials for coating planar and particulate substrates, thus allowing for the fabrication of responsive and functional thin films for their potential applications in a myriad of fields. Herein, we provide elaborate information on the current developments of LbL assembly techniques including different properties, molecular interactions, and assembly methods associated with this promising bottom-up strategy. In particular, we highlight the principle for rational design and fabrication of a large variety of multilayer thin film systems including multi-dimensional capsules or spatially hierarchical nanostructures based on the LbL assembly technique. Moreover, we discuss how to judiciously choose the building block pairs when exerting the LbL assembly buildup which enables the engineering of multilayer thin films with tailor-made physicochemical properties. Furthermore, versatile applications of the diverse LbL-assembled nanomaterials are itemized and elucidated in light of specific technological fields. Finally, we provide a brief perspective and potential future challenges of the LbL assembly technology. It is anticipated that our current review could provide a wealth of guided information on the LbL assembly technique and furnish firm grounds for rational design of LbL assembled multilayer assemblies toward tangible applications.

The depletion of the Earth's fossil fuel reserves and the rapid increase in the emission of greenhouse gases and other environmental pollutants are driving the development of renewable energy technologies. Lignin is one of the three main subcomponents of lignocellulosic biomass in terrestrial ecosystems and makes up nearly 30% of the organic carbon sequestered in the biosphere. As a result of its rich content of aromatic carbon, lignin has the potential to be decomposed to yield valuable chemicals and alternatives to fossil fuels. However, the complex and stable chemical bonds of lignin make the depolymerization of lignin a difficult challenge with regard to its valorization. In this review, we highlight recent advances in the selective decomposition of lignin-based compounds via photocatalysis into other value-added chemicals and the treatment of waste water containing lignin. The photocatalytic transformation of lignin under mild conditions is particularly promising.

The current rapid industrial development generates a high need for alternative sustainable sources of energy. Artificial photosynthesis, which can directly convert solar energy into usable or storable energy resources, provides such a promising alternative. Semiconductor nanowires have gained growing interest in artificial photosynthesis due to their unique geometrical and electronic characteristics, which can provide large aspect-ratios, direct pathways for charge transport, decoupling the direction of charge carrier collection, and low reflectance induced by light scattering and trapping. In particular, heterostructured semiconductor nanowire arrays (NWAs) have recently been of great interest in artificial photosynthesis because of their unique structural and physicochemical properties. Nanowire structure can lower the electrochemical over-potential while the heterojunctions can enhance light absorption and charge separation, which thus increase the artificial photosynthesis efficiency of heterostructured semiconductor NWAs. In this review, we will highlight recent advances in the application of heterostructured semiconductor NWAs to artificial photosynthesis. An emphasis will be placed on the unique characteristics and benefits of using heterostructured semiconductor NWAs with different heterojunctions for artificial photosynthesis, as well as the associated challenges and directions for future research in this area.

Graphene (GR)–semiconductor composite-based photocatalytic systems have received ever-increasing attention due to the attractive possibilities they provide to alleviate environmental and energy issues. Extensive endeavours have been made to construct high-performance GR–semiconductor composite photocatalysts for solar energy conversion. In this review, recent advances in developing strategies to assemble efficient GR–semiconductor composite photocatalysts are highlighted. These advances can be mainly classified into three aspects. The first is the optimization of individual components, including maximization of the functions of graphene and optimization of the photoactive semiconductors. The second is interface engineering between graphene and semiconductors. The third is the design and optimization of GR–semiconductor composite photocatalysts from a system-level consideration. Finally, it is proposed that combining these advances together with theoretical investigations will take us further along the road to advancing GR–semiconductor composite-based photocatalysis. Truly smart GR–semiconductor composite photocatalysts with robust structural and functional infrastructure are anticipated to be forthcoming.

Progress in photochemistry and concomitant significant advances in flow chemistry, nanochemistry, and solid state lighting from the past decade hold the potential to make visible-light photocatalysis part of the synthetic tools used by the fine chemical and pharmaceutical industries for the production of active ingredients. This study identifies key advances and remaining gaps toward the widespread adoption of heterogeneously catalyzed processes using visible photons for manufacturing functional molecules on a large scale.

The continuous rise in the atmospheric CO2 level and the ever-increasing demand of energy have raised serious concerns about the ensuing effects on the global climate change and future energy supply. Photocatalytic conversion of CO2, which uses solar light energy to recycle CO2 into fuels and chemicals, provides a promising and straightforward strategy to simultaneously reduce the atmospheric CO2 level and fulfil the future energy demand. However, the lack of substantial development of state-of-the-art materials remains a major bottleneck of this technology. In recent years, graphene-based composite photocatalysts have gained increasing interest in CO2 conversion due to the introduction of graphene with a series of unique physicochemical properties, which has shown to play a significant role in promoting the photocatalytic solar energy conversion efficiency. In this review, we comprehensively summarize the typical literature reports on graphene-based composites for photocatalytic conversion of CO2 to produce solar fuels and chemicals. The main types of the reported graphene-based composites and the role of graphene in the composites in improving the photocatalytic performance have been elaborated. In particular, we have highlighted the possible role of graphene in tuning the product selectivity of photocatalytic reduction of CO2. Finally, perspectives on the existing problems and future research on graphene-based composites toward photocatalytic conversion of CO2 are critically discussed.

•An overview on the structural diversity, tunable properties, and synthetic strategies of graphene materials are summarized.•The multifarious roles of graphene materials in heterogeneous photocatalysis are highlighted.•Comparisons on graphene materials with different size/dimension are disclosed.•The perspectives on future research direction in the construction of graphene materials-enhanced photocatalysis systems are proposed.•The overview on graphene materials with all dimensions promotes the understanding of processing-structure-properties-applications relationships.Recent years have seen the rocket rise of graphene as the unique two-dimensional carbon nanosheets and its outstanding promise in materials science. In particular, because of its diverse, tunable structural and electronic properties, graphene has been well recognized to be an ideal co-catalyst to optimize the photocatalytic performance of semiconductors. Given that the conductive, optical, chemical and mechanical performances of graphene are closely linked to its structural diversity, tremendous efforts have been devoted to designing and tailoring the graphene nanosheets to construct the desirable architecture. The tailored graphene materials (GMs), such as zero-dimensional graphene quantum dots, one-dimensional graphene nanoribbons and three-dimensional graphene frameworks show a variety of fascinating features, thereby offering a fertile and flexible ground for the further development of GMs-enhanced photocatalysis. This review aims to provide an overview on the structural diversity, tunable properties, and synthetic strategies of these GMs, followed by highlighting their multi-functionality in heterogeneous photocatalysis. Finally, the perspectives on future research trends and challenges in constructing more efficient GMs-enhanced systems for solar energy conversion are presented. The integral comprehension of GMs with all dimensions would further guide the fundamental processing-structure-properties-applications relationships of GMs.

Graphene as an electron-conductive medium has been widely used to construct efficient photocatalysts for solar energy conversion, while the discovery of photosensitizer role of graphene further enriches our understanding of the multifunctional facets of graphene in graphene-based composite photocatalysis. However, the photosensitive efficiency of graphene remains relatively low, and the photosensitization mechanism has yet to be elucidated. Herein, we report a facile wet chemistry strategy to enhance the photosensitive efficiency of graphene via oxidation treatment of graphene oxide and particularly reveal the underlying origin of such boosted photosensitive efficiency of graphene. Graphene derived from graphene oxide with enhanced oxidation degree shows remarkably improved photosensitive efficiency for wide-bandgap ZnO toward visible-light-driven photoreduction process. Controlled experiments disclose that the residual content of oxygenated functional groups is the main factor affecting the photosensitive efficiency of graphene. Furthermore, theoretical calculations indicate that increasing the content of oxygenated functional groups in graphene is able to widen the bandgap of graphene with the upshift of its conduction band, which endows the electrons in the photocatalytic system with enhanced reduction capacity and thus boosts the photosensitive efficiency of graphene. These encouraging results would provide instructive guidelines for the utilization of multifunctional roles of graphene toward designing advanced graphene-based composite photocatalysts for solar energy conversion.

Artificial photosynthesis that mimics the natural photosynthetic protocol is now regarded as a promising candidate for chemical conversion of CO2 to renewable solar fuels. In this work, core–shell structured TiO2@SiO2 composites have been synthesized via a simple sol–gel method under ambient temperature and pressure and applied to photocatalytic reduction of CO2 with H2O in the gas-phase under simulated solar light irradiation. The results show that compared with bare TiO2, TiO2@SiO2 composites exhibit significantly enhanced adsorption capacity for CO2 and facilitate photogenerated charge carrier separation and thereby enhanced photoactivity toward CO2 reduction. Although the insulating nature of SiO2 inhibits the charge injection from inner TiO2 core through the silica layer to the outer surface, the separation efficiency of charge carriers within the inner pore structure of TiO2@SiO2 is facilitated due to the as-formed Ti–O–Si bonds. In particular, TiO2@30%SiO2, which balances the combined influence of CO2 adsorption and charge carrier separation, acquires the best photoactivity and high selectivity for CO formation. This can be ascribed to the enriched density of adsorbed CO2 and relatively lower electron density on the reactive sites of the samples. In addition, in contrast to bare TiO2, the competitive process of H2 formation is greatly inhibited over TiO2@SiO2 composites. It is hoped that our work could inspire ongoing interest in utilizing the SiO2 coating method as well as other proper core–shell strategies to tune the activity and selectivity of semiconductor-based materials for artificial photoreduction of CO2 to value-added solar fuels.

The severe consequences of fossil fuel consumption have resulted in a need for alternative sustainable sources of energy. Conversion and storage of solar energy via a renewable method, such as photocatalysis, holds great promise as such an alternative. One-dimensional (1D) nanostructures have gained attention in solar energy conversion because they have a long axis to absorb incident sunlight yet a short radial distance for separation of photogenerated charge carriers. In particular, well-ordered spatially high dimensional architectures based on 1D nanostructures with well-defined facets or anisotropic shapes offer an exciting opportunity for bridging the gap between 1D nanostructures and the micro and macro world, providing a platform for integration of nanostructures on a larger and more manageable scale into high-performance solar energy conversion applications. In this review, we focus on the progress of photocatalytic solar energy conversion over controlled one-dimension-based spatially ordered architecture hybrids. Assembly and classification of these novel architectures are summarized, and we discuss the opportunity and future direction of integration of 1D materials into high-dimensional, spatially organized architectures, with a perspective toward improved collective performance in various artificial photoredox applications.

Considerable effort has been made to fabricate graphene (GR)/semiconductor composite photocatalysts, by using graphene oxide (GO) as the most widely used precursor of GR, toward an improved efficacy of solar energy conversion. However, thus far, the role of GO in the preparation and photocatalytic activity of GR/semiconductor composites has remained rather elusive. Herein, we report a simple yet efficient approach to significantly improve the photocatalytic activity of GR/semiconductor CdS composites via the acid treatment of GO, which downsizes GO sheets into smaller ones with enhanced colloidal stability and oxygenated functional groups. The graphene/CdS composites, which are prepared using this type of downsized GO as the precursor of GR, exhibit remarkably higher visible-light photoredox activity than those prepared from the direct reduction of GO without acid treatment. Our comparative results directly highlight the important effect of physico-chemical features of GO on the preparation and thus photoactivity of GR/semiconductor composites; in particular, the rational tailoring of GO could open a new doorway to optimize the activity of GO-derived GR/semiconductor composite photocatalysts.

A ternary hybrid structure of one-dimensional (1D) silver nanowire-doped reduced graphene oxide (RGO) integrated with a CdS nanowire (NW) network has been fabricated via a simple electrostatic self-assembly method followed by a hydrothermal reduction process. The electrical conductivity of RGO can be significantly enhanced by opening up new conduction channels by bridging the high resistance grain-boundaries (HGBs) with 1D Ag nanowires, which results in a prolonged lifetime of photo-generated charge carriers excited from the CdS NW network, thus making Ag NW–RGO an efficient co-catalyst with the CdS NW network toward artificial photosynthesis.

Carbon in its single layer atomic morphology has exceptional thermal, optical, electronic and mechanical properties, which may form the basis for several functional products and enhanced technologies that go from electricity storage to polymer nanocomposites of so far unsurpassed characteristics. Due to the high cost, however, the current global production of graphene does not exceed 120 tonnes. New chemical and physical methods to exfoliate graphite, however, were recently engineered and commercialized, which open the route to massive adoption of graphene as the “enabler” of numerous important technologies, including enhanced electricity storage. This feature article presents an updated, critical overview that will be useful to nanochemistry and nanotechnology research practitioners and to entrepreneurs in advanced materials.

The extraordinary electrical conductivity of graphene has been widely regarded as the bible in literature to explain the activity enhancement of graphene–semiconductor composite photocatalysts. However, from the viewpoint of an entire composite-based artificial photosynthetic system, the significant matter of photocatalytic performance of graphene–semiconductor composite system is not just a simple and only issue of excellent electrical conductivity of graphene. Herein, the intentional design of melamine resin monomers functionalized three-dimensional (3D) graphene (donated as MRGO) with significantly deteriorated electrical conductivity enables us to independently focus on studying the geometry effect of MRGO on the photocatalytic performance of graphene–semiconductor composite. By coupling semiconductor CdS with graphene, including MRGO and reduced graphene oxide (RGO), it was found that the CdS-MRGO composites exhibit much higher visible light photoactivity than CdS-RGO composites although the electrical conductivity of MRGO is remarkably much lower than that of RGO. The comparison characterizations evidence that such photoactivity enhancement is predominantly attributed to the restacking-inhibited 3D architectural morphology of MRGO, by which the synergistic effects of boosted separation and transportation of photogenerated charge carriers and increased adsorption capacity can be achieved. Our work highlights that the significant matter of photocatalytic performance of graphene–semiconductor composite is not a simple issue on how to harness the electrical conductivity of graphene but the rational ensemble design of graphene–semiconductor composite, which includes the integrative optimization of geometrical and electrical factors of individual component and the interface composition.Keywords: composite photocatalyst; electrical conductivity; geometry effect; graphene; semiconductor

A bottom-up strategy based on graphene (GR) template is developed to synthesize free-standing TiO2 nanosheets. A cross-link of GR nanosheets and a homogeneous coating of TiO2 onto the self-assembled GR surfaces are simultaneously achieved by functionalizing the GR surface with benzyl alcohol. Followed by thermal treatment in air, the 2D TiO2 structure with ultralarge lateral size far beyond the size of original GR nanosheets (several hundred nanometers) has been built with GR as a sacrificial template. The resultant TiO2 nanosheets (TiO2–NS) are then homogeneously photodeposited with CdS nanocrystals, and thus the CdS–TiO2 composite nanosheets (CdS–TiO2–NS) are obtained. Using simulated solar light as energy source, the CdS–TiO2–NS exhibits much higher activity than that of bare TiO2–NS toward selective gas-phase reduction of CO2 and liquid-phase reduction of nitroaromatics. The improved photocatalytic activities of CdS–TiO2–NS benefits from (1) the deposition of narrow-band gap CdS can effectively extend the light absorption range of wide-band gap TiO2–NS and (2) the unique 2D structure of TiO2–NS provides abundant coupling interface for CdS decoration, which is beneficial for photogenerated charge-carrier transport across the interfacial domain. It is hoped that our work will promote further interest in the fabrication of new 2D materials using functional GR as a sacrificial template for diverse photoredox applications.

Myriad materials with desirable functional property resulting from their unique structures ignite enormous interest in synthesizing materials with controlled structural morphology toward achieving novel or enhanced properties for target applications. Herein, the novel and unique two-dimensional (2D) MoS2 nanosheet-coated Bi2S3 discoids composites, which feature a Bi2S3-core/MoS2-shell structure, have been elaborated via a facile anion-exchange strategy. Using the MoS2 nanosheets to coat the surface of Bi2S3 discoids boosts the light-harvesting efficiency and charge separation and promotes faster charge transport and collection, thus leading to the higher activity of the photocatalytic reduction of Cr(VI) under visible light irradiation (λ > 400 nm). In particular, the phase evolution and possible formation mechanism of the MoS2–Bi2S3 core–shell structure have been explored by virtue of temperature- and time-dependent experiments. It is anticipated that this work could promote further interest in adopting an anion-exchange strategy to fabricate semiconductor-based composite materials with controlled architectural morphology and enhanced photocatalytic performance toward diverse applications.

Designing a semiconductor CdS-based photocatalyst for H2 evolution from water with high activity and stability is extremely desirable for practical application. We report the important morphological and structural influence of MoS2 cocatalyst on the photocorrosion and photoactivity of CdS that is carpeted on a graphene (GR) surface. Homogeneous dispersion of MoS2 nanoparticles by a controlled photodeposition (PD) method produces the GR–CdS–MoS2 (PD) composite, which does not have the characteristic stacked layer structure of MoS2. However, this GR–CdS–MoS2 (PD) composite exhibits much higher activity and particularly antiphotocorrosion than the hydrothermal synthesized GR–CdS–MoS2 (HT) counterparts, which feature the characteristic MoS2 layer structure, toward photocatalytic water splitting under visible light irradiation. The characterization results indicate that homogeneous dispersion of tiny MoS2 for GR–CdS–MoS2 (PD) markedly improves the separation and transfer of charge carriers and provides the increased number of catalytic active sites afforded by the absence of the stacked layer structure of the MoS2 cocatalyst. This work provides direct evidence of the negative effect of the stacked layer structure of MoS2 on boosting the activity and photostability of CdS on the GR surface, which would guide the more rational use of MoS2 and GR as cocatalyst toward achieving a highly active and stable semiconductor-based composite photocatalyst for H2 evolution.

Tremendous interest is devoted to fabricating numerous graphene (GR)–semiconductor composites toward improved conversion of solar energy, resulting from the observation that the photogenerated electrons from semiconductors (e.g., TiO2, CdS) can be readily accepted or shuttled in the two-dimensional (2D) GR sheet. Yet although the hunt is on for GR–semiconductor composite based photoredox applications that aim to exploit the remarkable electronic conductivity of GR, the work necessary to find out how it could best be harnessed to improve the photocatalytic performance of semiconductors remains scanty. In this review, we highlight a few problems associated with improving the photocatalytic performance of semiconductors via methodological coupling with GR. In particular, we address strategies for harnessing the structure and electronic conductivity of GR via strengthening the interfacial contact, optimizing the electronic conductivity of GR, and spatially optimizing the interfacial charge carrier transfer efficiency. Additionally, we provide a brief overview of assembly methods for fabricating GR–semiconductor composites with controllable film infrastructure to meet the requirements of practical photocatalytic applications. Finally, we propose that, only with the principle of designing and understanding GR–semiconductor composites from a system-level consideration, we might get better at imparting the power of GR with unique and transformative properties into the composite system.

Low cost and easily made bismuth tungstate (Bi2WO6) could be one of the key technologies to make chemicals and fuels from biomass, atmospheric carbon dioxide and water at low cost using solar radiation as an energy source. Its narrow band gap (2.8 eV) enables ideal visible light (λ > 400 nm) absorption. Yet, it is the material's shape, namely the superstructure morphology wisely created via a nanochemistry approach, which leads to better electron–hole separation and much higher photoactivity. Recent results coupled to the versatile photochemistry of this readily available semiconductor suggest that the practical application of nanochemistry-derived Bi2WO6 nanostructures for the synthesis of value-added fine chemicals and fuel production is possible. We describe progress in this important field of chemical research from a nanochemistry viewpoint, and identify opportunities for further progress.

In2S3–carbon nanotube (In2S3–CNT) nanocomposites have been prepared via a facile refluxing wet chemistry process. The as-synthesized In2S3–CNT nanocomposites can be used as selective and active visible-light-driven photocatalysts toward hydrogenation of nitroaromatics to amines in water. Photoirradiation (λ > 420 nm) of In2S3–CNT photocatalysts suspended in water containing nitroaromatics produces the corresponding amines with high yields. The control experiments reveal that an inert atmosphere and the addition of a hole scavenger are both indispensable for the visible-light-driven photocatalytic hydrogenation of nitroaromatics over In2S3–CNT. In comparison with blank In2S3, the obviously enhanced photocatalytic performance of the In2S3–CNT photocatalyst is mainly ascribed to the unique physicochemical properties of CNTs, which enhances the adsorptivity of the substrate and performs as an electron reservoir to trap electrons, thereby hindering the recombination of photogenerated electron–hole pairs. It is hoped that the current work on the facile synthesis of semiconductor In2S3–CNT nanocomposites can broaden the applications of semiconductor-carbon based composite photocatalysts in the field of photocatalytic selective organic transformations under mild conditions.

A series of uniform ZnO nanospheres–reduced graphene oxide nanocomposites (ZnO–RGO NCs) with different weight addition ratios of RGO are successfully synthesized via a facile yet efficient method by intimately coating ZnO nanospheres (NSs) with RGO, which is afforded by electrostatic attraction between positively charged ZnO NSs and negatively charged graphene oxide (GO) in an aqueous medium at room temperature. The photocatalytic test of degradation of Rhodamine B shows that the optimal ZnO–10% RGO NCs exhibit a 5-fold enhancement of photoactivity than bare ZnO NSs, which is ascribed to the integrative synergetic effect of enhanced adsorption capacity, the decreased recombination of the electron–hole pairs and the enhanced ultraviolet light absorption intensity. Significantly, the recycled photoactivity tests show that, for ZnO–RGO NCs, the anti-photocorrosion of ZnO NSs is improved remarkably which is attributed to the effective hybridization of ZnO NSs with the RGO sheet via intimate surface coating. Such a significant photoactivity enhancement and anti-photocorrosion phenomenon can not be obtained by simply integrating RGO with ZnO NSs that are not subject to surface charge modification, which thus indicates the importance of intimate surface coating of ZnO with RGO toward the efficiency of enhancement of photoactivity and particularly the anti-photocorrosion of ZnO.

By embedding noble metal palladium (Pd) into the interfacial layer matrix of graphene (GR) and semiconductor CdS, we have successfully constructed ternary CdS–(GR–Pd) nanocomposites with intimate interfacial contact. The CdS–(GR–Pd) nanocomposites show remarkably enhanced photocatalytic activity toward selective redox reactions under visible light irradiation as compared to blank-CdS and the optimum binary CdS–GR. It is revealed that the photocatalytic performance enhancement of CdS–(GR–Pd) is ascribed to the optimized spatial charge carrier transfer across the interface resulting from the introduction of Pd nanoparticles as mediators into the interfacial layer between GR and CdS. One role of Pd is to serve as electron reservoir to directly trap photogenerated electrons from CdS and the other role is as interfacial mediator to promote electron relay in the ternary CdS–(GR–Pd) photocatalysts along with conductive graphene as dual co-catalysts. Moreover, the negative light “shielding effect” of GR can be partially counterbalanced through such a facile strategy. This work substantiates the feasibility of adopting the “interfacial-mediator” strategy to optimize the interfacial charge carriers transfer pathway and efficiency for improved photoactivity of GR–semiconductor nanocomposites toward target photoredox reactions.

ZnIn2S4–graphene (GR) nanocomposites have been fabricated by a low-temperature and one-step wet chemistry process, during which the formation of ZnIn2S4 nanosheets, the reduction of graphene oxide (GO) and intimate interfacial contact between them were achieved simultaneously. The as-prepared ZnIn2S4–GR exhibited remarkably enhanced visible light photocatalytic performance toward selective reduction of nitroaromatics to amines in water compared to blank ZnIn2S4. Controlled experiments have been carried out and revealed that an inert atmosphere and the addition of a hole scavenger are two important conditions for photocatalytic selective reduction of nitroaromatics over ZnIn2S4–GR. In comparison with blank ZnIn2S4, the remarkably enhanced photocatalytic performance of ZnIn2S4–GR can be mainly attributed to the integrative effect of the unique physicochemical properties of GR and the intimate interfacial contact between ZnIn2S4 and GR. Specifically, the introduction of GR into the matrix of ZnIn2S4 can significantly influence the morphology and structure of the samples owing to the “structure-directing” role of GO, enhance the adsorptivity of the substrate, and effectively promote the separation and transfer of photogenerated charge carriers, thereby contributing to the photoactivity enhancement. It is hoped that the current work on the facile synthesis of ZnIn2S4–GR nanocomposites can broaden the applications of ZnIn2S4–GR and other GR-based nanocomposites as visible-light-driven photocatalysts toward selective organic transformations under mild conditions.

Ternary hybrids of (reduced graphene oxide)–(CdS nanowire)–TiO2 nanocomposites (CTG) featuring a large two-dimensional (2D) flat structure have been successfully synthesized via a simple surface charge promoted self-assembly method. Compared to the curly (reduced graphene oxide)–(CdS nanowire) nanocomposites (CG) synthesized by a similar approach, CTG possesses a large 2D flat structure, which not only provides high optical transparency and a large surface area but also facilitates the migration of photogenerated electrons. This large 2D flat structure of CTG leads to increased optical absorption of visible light and increased electrical conductivity as compared to the curly CG, which is attributed to the fact that the large 2D flat structure of reduced graphene oxide (RGO) in CTG provides more efficient contact between light and the RGO sheets and facilitates the transfer of charge carriers. Experimental evidence has proven that negatively charged TiO2 nanoparticles (NPs) both on the surfaces of the CdS nanowires (CdS NWs) and on the RGO sheets can prevent the RGO sheets from becoming curly or aggregated as a result of electrostatic repulsion, thereby forming the large 2D flat structure of CTG. In addition to using RGO as an electron “sink” to improve the transfer of photogenerated electron–hole pairs (EHPs) from CdS NWs, the TiO2 NPs on CdS NWs are able to further boost the transfer of charge carriers in the ternary CTG system due to the suitable energy band match between TiO2 and CdS. Such efficient, spatially separated charge carriers make CTG a versatile visible light photocatalyst for photo-redox processes. This work provides a new, simple strategy to construct these large 2D flat structured RGO-based multi-component composites by using the surface charge properties of materials to efficiently utilize their respective unique electronic properties toward diverse photo-redox processes in both energy conversion and environmental purification.

Branched hierarchical CdS/ZnO nanocomposites have been synthesized for application toward photocatalytic fine-chemical synthesis. Growing ZnO nanorods on the surface of CdS nanowires boosts the light harvesting efficiency and charge separation as well as fast charge transport and collection. A Z-scheme mechanism under artificial solar light is also proposed.

A two-dimensional (2D) SnNb2O6 nanosheet–graphene (SnNb2O6–GR) nanocomposite featuring a typical 2D–2D structure has been synthesized via a simple surface charge modified self-assembly approach. The method is afforded by electrostatic attractive interaction between negatively charged SnNb2O6 nanosheets and modified graphene nanosheets with a positively charged surface in an aqueous solution. The SnNb2O6–GR nanocomposite exhibits a distinctly enhanced visible light photocatalytic performance toward degradation of organic dye in water as compared to blank SnNb2O6 nanosheets. The enhanced photoactivity is attributed to the integrated factors of the intimate interfacial contact and unique 2D–2D morphology associated with SnNbO6 and GR, which are beneficial for harnessing the electron conductivity of GR, facilitating the transfer and separation of photogenerated charge carriers over SnNbO6–GR upon visible light irradiation, and thereby contributing to the photoactivity enhancement. It is hoped that this work could enrich the facile, efficient fabrication of various 2D–2D semiconductor nanosheet–graphene composite photocatalysts toward target photocatalytic applications.

Pd nanoparticles supported on defective TiO2 with oxygen vacancies (TiO2-OV) have been prepared by an oxygen vacancies mediated reduction strategy. The resulting Pd–TiO2-OV catalyst with uniform Pd nanoparticles deposition demonstrates a remarkably thermocatalytic activity toward rapid, efficient reduction of nitroaromatics in water. The reaction proceeds efficiently using HCOONH4 as a hydrogen source under ambient conditions. The controlled experiments show that the •CO2– radicals produced by dehydrogenation of HCOONH4 are the main active species for the selective nitro reduction. Moreover, defective TiO2 nanostructures deposited with Pd nanoparticles, featuring excellent visible-light absorption via the creation of oxygen vacancies, can take advantage of the solar and thermal energy to drive catalytic reduction reactions more efficiently at room temperature. During this process, the oxygen vacancies and Pd nanoparticles play synergetic roles in the photoreduction of nitro compounds. Our work would be beneficial for implementation of a novel defect-mediated catalytic system in which solar light energy can be coupled with thermal energy to drive an energy efficient catalytic process.Keywords: oxygen vacancies; Pd nanoparticles; photocatalyst; selective reduction; thermocatalyst;

Coupling ZnO with carbon materials using a suitable integration method to form ZnO–carbon composites has been established as a promising strategy to ameliorate the photocatalytic performance of semiconductor ZnO. In this perspective article, we describe the recent advances and current status of enhancing the photocatalytic activity and anti-photocorrosion of semiconductor ZnO by coupling with versatile carbon materials, e.g., C60, carbon nanotube, graphene and other carbon materials. The primary roles of carbon materials in boosting the photoactivity and photostability of ZnO have been outlined and illustrated with some selected typical examples. In particular, the three main kinds of mechanisms with regard to anti-photocorrosion of ZnO by coupling with carbon have been demonstrated. Finally, we give a concise perspective on this important research area and specifically propose further research opportunities in optimizing the photocatalytic performance of ZnO–carbon composites and widening the scope of their potential photocatalytic applications.

Zinc oxide (ZnO) nanostructured materials have received significant attention because of their unique physicochemical and electronic properties. In particular, the functional properties of ZnO are strongly dependent on its morphology and defect structure, particularly for a semiconductor ZnO-based photocatalyst. Here, we demonstrate a simple strategy for simultaneous morphology control, defect engineering and photoactivity tuning of semiconductor ZnO by utilizing the unique surfactant properties of graphene oxide (GO) in a liquid phase. By varying the amount of GO added during the synthesis process, the morphology of ZnO gradually evolves from a one dimensional prismatic rod to a hexagonal tube-like architecture while GO is converted into reduced GO (RGO). In addition, the introduction of GO can create oxygen vacancies in the lattice of ZnO crystals. As a result, the absorption edge of the wide band gap semiconductor ZnO is effectively extended to the visible light region, which thus endows the RGO–ZnO nanocomposites with visible light photoactivity; in contrast, the bare ZnO nanorod is only UV light photoactive. The synergistic integration of the unique morphology and the presence of oxygen vacancies imparts the RGO–ZnO nanocomposite with remarkably enhanced visible light photoactivity as compared to bare ZnO and its counterpart featuring different structural morphologies and the absence of oxygen vacancies. Our promising results highlight the versatility of the 2D GO as a solution-processable macromolecular surfactant to fabricate RGO–semiconductor nanocomposites with tunable morphology, defect structure and photocatalytic performance in a system-materials-engineering way.

We report a simple, in situ hydrothermal way to fabricate In2S3–graphene (GR) nanocomposites in which hierarchical In2S3 “petals” spread over the surface of GR sheets in virtue of the “structure directing” role of graphene oxide (GO) as the precursor of GR in a solution phase. With the addition of an appropriate amount of GO, the hierarchical petal-like In2S3 structures have been successfully grown on the two-dimensional (2D) GR “mat”. The as-synthesized In2S3–GR nanocomposites featuring good interfacial contact exhibit much higher photocatalytic activity toward selective oxidation of alcohols under visible light irradiation than blank In2S3. A series of characterization results disclose that the significantly enhanced photocatalytic performance of In2S3–GR nanocomposites can be ascribed to the integrative effect of the increased separation and transfer efficiency of photogenerated electron–hole pairs and the larger surface area. This work highlights the wide scope of fabricating GR-based semiconductor nanocomposites with specific architectural morphology by rationally utilizing the “structure directing” property of GO and extending their applications toward photocatalytic selective transformations.

Heterogeneous photocatalysis offers a promising route to realize green oxidation processes in organic synthesis because such selective organic transformation processes can be enabled under solar light irradiation with ambient conditions. In this research, graphene–TiO2 nanocomposites have been utilized for aerobic selective oxidation of benzylic alcohols to corresponding aldehydes and acids in water under simulated solar light irradiation. The photocatalytic performance and related properties of solvent exfoliated graphene–TiO2 (SEG–TiO2) and reduced graphene oxide–TiO2 (RGO–TiO2) have been comparatively studied. It has been found that decreasing the defect density of graphene, by using SEG instead of graphene oxide (GO) as the precursor of RGO, can enhance the photoactivity of graphene–TiO2 nanocomposites due to the improved electron conductivity of SEG as compared to that of RGO. It is hoped that this work would stimulate further interest in utilizing graphene–semiconductor nanocomposite photocatalysts in the field of green-chemistry-oriented photocatalytic selective organic transformation.

One-dimensional (1D) nanostructures are believed to play a significant role on the horizon of material science, and are a promising class of ideal high performance candidates for energy storage and conversion owing to their unique optical, structural and electronic properties. In particular, 1D nanostructure-based photocatalysts have been attracting ever-growing research attention. In this review article, we mainly focus on systematically summarizing the applications of 1D-based nanocomposites in photocatalysis, including nonselective processes for the degradation of pollutants, direct solar energy conversion to storable fuels and selective transformations for organic synthesis. Particularly, we explore the new directions for boosting the photocatalytic performances of 1D nanostructures, including graphene-1D nanocomposites, surface modification, 1D core–shell nanostructures and different exposed facet effects. It is hoped that this article will promote the efficient harnessing and rational development of the outstanding structural and electronic properties of 1D nanostructures to design more efficient 1D-based photocatalysts towards numerous applications in the field of solar energy conversion.

Photocatalytic selective organic transformation in water using visible light as the driving force represents an environmentally benign strategy for synthesis of fine chemicals under the framework of green chemistry. We herein report the photocatalytic aerobic oxidation of benzylic alcohols to corresponding aldehydes with high selectivity in water over a flower-like Bi2WO6 semiconductor using oxygen as an oxidant under visible light irradiation and mild conditions. A collection of joint techniques, in terms of electron spin resonance (ESR) spectra and controlled experiments using radicals scavengers, have been employed to explain the origin of the high selectivity for oxidation of benzylic alcohols achieved over the flower-like Bi2WO6 photocatalyst in an aqueous phase. The possible reaction mechanism for photocatalytic selective oxidation of alcohols over Bi2WO6 has also been discussed.

We report a simple and general approach to improve the transfer efficiency of photogenerated charge carriers across the interface between graphene (GR) and semiconductor CdS by introducing a small amount of metal ions (Ca2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) as “mediator” into their interfacial layer matrix, while the intimate interfacial contact between GR and CdS is maintained. This simple strategy can not only significantly improve the visible-light-driven photoactivity of GR–CdS semiconductor composites for targeting selective photoredox reaction, including aerobic oxidation of alcohol and anaerobic reduction of nitro compound, but also drive a balance between the positive effect of GR on retarding the recombination of electron–hole pairs photogenerated from semiconductor and the negative “shielding effect” of GR resulting from the high weight addition of GR. Our current work highlights that the significant issue on improving the photoactivity of GR–semiconductor composites via strengthening interfacial contact is not just a simple issue of tighter connection between GR and the semiconductor, but it is also the optimization of the atomic charge carrier transfer pathway across the interface between GR and the semiconductor.Keywords: graphene; interfacial composition engineering; mediator; selective photoredox; semiconductor

Ultralarge graphene-based TiO2 nanosheet composites are successfully fabricated by a noncovalent functionalization approach with use of benzyl alcohol as the linking agent. In the synthetic procedure, the aromatic molecules of benzyl alcohol direct themselves onto graphene (GR) surface via π–π interaction. Therefore, the basal planes of GR nanosheets are uniformly functionalized with hydroxyl groups derived from benzyl alcohol, which not only improves the dispersion of GR in solution but also induces a finely homogeneous coating of TiO2 nanocrystals onto the surface of GR nanosheets. The resulting GR@TiO2 nanocomposites, which feature unique ultralarge 2D sheet-like morphology with the lateral size far larger than the original GR and densely interfacial contact, are able to act as highly active photocatalysts toward selective reduction of aromatic nitro compounds to amines in water under ambient conditions. The higher photoactivity of GR@TiO2 than blank TiO2 is attributed to the efficient charge carriers separation and transfer by the GR platform. It is hoped that the facile synthesis strategy in this work could contribute to fabricating other ultralarge functional GR-based 2D sheet-onto-sheet composites with tunable morphology toward target photocatalytic applications.

Traditional ways for the synthesis of bimetallic alloyed nanoparticles involve successive or simultaneous reduction of metallic precursors either in an organic solvent phase or in an aqueous phase. However, these two approaches generally require the use of surfactants or polymers, dendrimers, or ligands as protecting or capping agents in order to achieve stable colloidal bimetallic nanoalloys for potential use, for example, loading them onto supports as heterogeneous catalysts. Here, we report the direct synthesis of stabilizing-molecules-free bimetallic Au–Pd nanoalloys promoted by graphene oxide (GO) in an aqueous phase. Formation of Au–Pd nanoalloys and loading onto the reduced GO (denoted as GR) are accomplished simultaneously. Controlled experiments suggest that GO vividly acts as a unique “solution processable macromolecular surfactant” and 2D “flat-mat” support to promote formation and loading of alloyed Au–Pd bimetallic nanoparticles onto the GR sheet. The as-formed Au–Pd/GR exhibits higher photocatalytic activity than both monometallic Au/GR and Pd/GR, prepared by the same approach toward degradation of dye, Rhodamine B (RhB), which thus demonstrates the promising potential of bimetallic nanoalloys rather than the monometallic one in promoting visible light photocatalysis. It is anticipated that our work could boost further interest for harnessing the versatile soft materials features of GO in solution to synthesize other bimetallic alloy catalysts and exploring their applications in photocatalysis.

The new role of graphene (GR) in boosting the two-electron reduction of O2 to H2O2 has been first identified in the GR–WO3 nanorod (NR) nanocomposite photocatalysts, which are fabricated by a facile, solid electrostatic self-assembly strategy to integrate the positively charged branched poly(ethylenimine) (BPEI)-GR (BGR) and negatively charged WO3 NRs at room temperature. Photoactivity test shows that, as compared to WO3 NRs, BGR–WO3 NRs with an appropriate addition ratio of GR exhibit remarkably enhanced and stable visible-light photoactivity toward the degradation of Rhodamine B. Besides the common roles of GR observed in the GR-based composite photocatalysts in the literature, including enhancing the visible-light absorption intensity, improving the lifetime and transfer of photogenerated charge carriers, and increasing the adsorption capacity for reactants, we have observed the new role of GR in boosting the two-electron reduction of O2 to H2O2 in this specific BGR–WO3 NR photocatalyst system. Importantly, this new role of GR does contribute to the overall photoactivity enhancement of BGR–WO3 NR nanocomposites. The synergistic contribution of GR on improving the photoactivity of WO3 NRs and the underlying reaction mechanism have been analyzed by the structure–photoactivity correlation analysis and controlled experiments using radicals scavengers.

Glycerol, being either a primary by-product of biodiesel manufacture or a platform molecule from sugars, is of significant interest as a renewable biomass because it is a highly functionalized and versatile organic building block for the synthesis of value-added fine chemicals. In particular, selective oxidation of glycerol to various industrially valuable products by heterogeneous photocatalysis using solar light as free energy and molecular oxygen as benign oxidant under ambient conditions is extremely attractive. However, a highly selective, heterogeneous visible-light photocatalyst utilized for aerobic oxidation of glycerol has been unavailable. To date, the discovery or design of a visible-light-driven, highly selective photocatalyst for selective oxidation of glycerol to a specific product is particularly challenging in heterogeneous photocatalytic selective transformation. Herein, we for the first time, report the identification of flower-like Bi2WO6 as a highly selective visible-light photocatalyst toward aerobic selective oxidation of glycerol to dihydroxyacetone using oxygen as oxidant in water at room temperature and atmospheric pressure. A rationale for the observed high selectivity over photocatalyst flower-like Bi2WO6 is provided.

To develop various strategies to prevent the aggregation, sintering, or leaching of noble metal nanoparticles (NPs) represents a crucial issue for efficient synthesis and utilization of supported noble metal NPs with highly active and stable catalytic performance. Here, we report a facile synthesis approach to obtain a Pd@hCeO2 hollow core–shell nanocomposite that is composed of tiny Pd nanoparticles cores encapsulated within CeO2 hollow shells. The core–shell strategy efficiently prevents the aggregation of Pd NPs in the high temperature calcination process and the leaching of Pd NPs for the catalytic reaction in a liquid phase. This anti-aggregation and anti-leaching behavior is not able to be achieved for traditional supported Pd/CeO2 catalyst. Such a Pd@hCeO2 composite can serve as an efficient multifunctional nanocatalyst in both heterogeneous thermocatalytic and photocatalytic selective reduction of aromatic nitro compounds in water under ambient conditions. Each component, namely Pd metal core or semiconductor CeO2 shell, makes a necessary but totally dissimilar reactive contribution to achieving the same end product during these two different catalytic processes. Importantly, Pd@hCeO2 exhibits an excellent reusable and much higher catalytic performance than supported Pd/CeO2. This work provides a generic concept example on inhibiting aggregation of noble metal NPs during high temperature calcination and leaching of noble metal nanoparticles into solution via a hollow core–shell strategy and, more significantly, on sufficiently harnessing the specific metal core or semiconductor shell function integrated in a core–shell nanoarchitecture toward a multifunctional catalytic use in both thermocatalytic and photocatalytic selective green transformation in water.Keywords: anti-aggregation; hollow core−shell; leaching-resistance; photocatalysis; selective reduction; thermocatalysis;

Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addition, we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial minireview would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.

A series of CdS nanowire–Au nanocomposites (CdS NW–Au NCs) with different weight addition ratios of Au nanoparticles (NPs) are successfully synthesized by using a simple and efficient electrostatic self-assembly method at room temperature for utilizing the natural surface charge properties of the CdS NWs and Au NPs. These natural surface charge properties are dependent on the synthesis approaches. The probe reactions for photocatalytic selective reduction of nitroaromatic compounds in the aqueous phase under visible light irradiation are utilized to evaluate the photoactivity of this series of as-prepared CdS NW–Au NCs. The CdS NW–Au NCs exhibit significantly enhanced photoactivity as compared to the CdS nanowires (CdS NWs). The addition of Au NPs into the CdS NW domain enables efficient enhancement of the lifetime and transfer of photogenerated charge carriers from CdS NWs under visible light irradiation. However, the addition of excess amounts of Au NPs not only influences the penetration of light but the Au NPs also become the recombination centers, and result in decreased photoactivity. The optimal proportion of the Au NPs is proved to be 1 wt%, which indicates the synergistic effect between the CdS NWs and Au NPs. In addition, the surface plasmon resonance (SPR) effect of Au NPs is proved to not play an efficient role in the reaction and the possible photocatalytic reaction mechanism is proposed. It is hoped that this work could aid in the fabrication of 1-D semiconductor–metal nanocomposites by using such a simple and efficient electrostatic self-assembly strategy. In addition, it is also expected to enrich and supplement their application as visible light photocatalysts toward selective organic transformations through our investigation.

Development of various strategies for controllable fabrication of core–shell nanocomposites (CSNs) with highly active photocatalytic performance has been attracting ever-increasing research attention. In particular, control of the ultrathin layer TiO2 shell in constructing CSNs in an aqueous phase is a significant but technologically challenging issue. Here, this paper demonstrates the interface assembly synthesis of CdS nanospheres@TiO2 core–shell photocatalyst via the electrostatic interaction of negatively charged water-stable titania precursor with positively charged CdS nanospheres (CdS NSPs), followed by the formation of the ultrathin-layer TiO2 shell through a facile refluxing process in aqueous phase. The as-formed CdS NSPs@TiO2 core–shell nanohybrid exhibits a high visible-light-driven photoactivity for selective transformation and reduction of heavy metal ions. The ultrathin TiO2 layer coated on CdS NSPs results in excellent light transmission property, enhanced adsorption capacity, and improved transfer of charge carriers and lifespan of photoinduced electron–hole pairs, which would prominently contribute to the significant photoactivity enhancement. It is anticipated that this facile aqueous-phase synthesis strategy could be extended to design a variety of more efficient CSN photocatalysts with controllable morphology toward target applications in diverse photoredox processes.Keywords: core−shell nanocomposites; electrostatic interaction; interface assembly; selective photoredox; ultrathin layer coating;

A series of TiO2–graphene (GR), −carbon nanotube (CNT), and −fullerene (C60) nanocomposite photocatalysts with different weight addition ratios of carbon contents are synthesized via a combination of sol–gel and hydrothermal methods. Their structures and properties are determined by the X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), transmission electron microscopy (TEM), nitrogen adsorption–desorption, and photoelectrochemical measurements. Photocatalytic selective oxidation of benzyl alcohol to benzaldehyde is employed as a model reaction to evaluate the photocatalytic activity of the TiO2–carbon (GR, CNT, and C60) nanocomposites under visible light irradiation. The results reveal that incorporating TiO2 with carbon materials can extend the adsorption edge of all the TiO2–carbon nanocomposites to the visible light region. For TiO2–GR, TiO2–CNT, and TiO2–C60 nanocomposites, the photocatalytic activities of the composites with optimum ratios, TiO2–0.1% GR, TiO2–0.5% CNT, and TiO2–1.0% C60, are very close to each other along with the irradiation time. Furthermore, the underlying reaction mechanism for the photocatalytic selective oxidation of benzyl alcohol to benzaldehyde over TiO2–carbon nanocomposites has been explored using different radical scavenger techniques, suggesting that TiO2–carbon photocatalysts follow the analogous oxidation mechanism toward selective oxidation of benzyl alcohol. The addition of different carbon materials has no significant influence on the crystal phase, particle size, and the morphology of TiO2. Therefore, it can be concluded, at least for nanocomposites of TiO2–carbon (GR, CNT, and C60) obtained by the present approach, that there is no much difference in essence on affecting the photocatalytic performance of semiconductor TiO2 among these three different carbon allotropes, GR, CNT, and C60. Our findings point to the importance of a comparative study of semiconductor–carbon photocatalysts on drawing a relatively objective conclusion rather than separately emphasizing the unique role of GR and joining the graphene gold rush.Keywords: carbon nanotube; fullerene; graphene; selective oxidation; TiO2; visible light irradiation;

We report the self-assembly of uniform CdS nanospheres/graphene (CdS NSPs/GR) hybrid nanocomposites via electrostatic interaction of positively charged CdS nanospheres (CdS NSPs) with negatively charged graphene oxide (GO), followed by GO reduction via a hydrothermal treatment. During this facile two-step wet chemistry process, reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between CdS NSPs and the GR sheets are achieved. Importantly, the CdS NSPs/GR nanocomposites exhibit a much higher photocatalytic performance than bare CdS NSPs toward selective reduction of nitro organics to corresponding amino organics under visible light irradiation. The superior photocatalytic performance of the CdS NSPs/GR nanocomposites can be attributed to the intimate interfacial contact between CdS NSPs and the GR sheets, which would maximize the excellent electron conductivity and mobility of GR that in turn markedly contributes to improving the fate and transfer of photogenerated charge carriers from CdS NSPs under visible light irradiation. Moreover, the photocorrosion of CdS and the photodegradation of GR can be efficiently inhibited. The excellent reusability of the CdS NSPs/GR nanocomposites can be attributed to the synergetic effect of the introduction of GR into the matrix of CdS NSPs and the addition of ammonium formate as quencher for photogenerated holes. It is hoped that our current work could promote us to efficiently harness such a simple and efficient self-assembly strategy to synthesize GR-based semiconductor composites with controlled morphology and, more significantly, widen the application of CdS/GR nanocomposite photocatalysts and offer new inroads into exploration and utilization of GR-based semiconductor nanocomposites as visible light photocatalysts for selective organic transformations.Keywords: aromatic nitro organics; CdS nanospheres (CdS NSPs); electrostatic self-assembly; graphene (GR); photocatalytic reduction;

The charm embedded in nature is its inherent power to create a myriad of materials, for example, a spider web and lotus leaf, with ordinary composition but exhibiting fascinating functional property owing to their unique structures. Such intricate natural designs inspire immense research in synthesizing materials with controlled structure and morphology toward achieving novel or enhanced properties for target applications. Herein, we report a rotary vacuum evaporation and support-driven nanoassembly of tiny Pd noble metal particles on nanosized CeO2, which features a remarkable unique silk “mat-like” morphology with significant anti-aggregation of Pd nanoparticles during a high temperature calcination process, whereas the obvious aggregation phenomenon of Pd nanoparticles occurs when using commercial CeO2 as a support. This nanocomposite with unique structural and morphology composition is able to act as a highly selective and active visible light photocatalyst toward organic redox transformations in water, including aerobic oxidation of alcohols and anaerobic reduction of nitro-compounds under ambient conditions, representing a typical tenet of photocatalytic green chemistry.Keywords: CeO2; Nanoassembly; Pd nanoparticles; Selective redox; Silk mat ; Water

Graphene (GR) has proven to be a promising candidate to construct effective GR-based composite photocatalysts with enhanced catalytic activities for solar energy conversion. During the past few years, various GR-based composite photocatalysts have been developed and applied in a myriad of fields. In this perspective review, compared with the traditional applications of GR-based nanocomposites for the “non-selective” degradation of pollutants, photo-deactivation of bacteria and water splitting to H2 and O2, we mainly focus on the recent progress in the applications of GR-based composite photocatalysts for “selective” organic transformations, including reduction of CO2 to renewable fuels, reduction of nitroaromatic compounds to amino compounds, oxidation of alcohols to aldehydes and acids, epoxidation of alkenes, hydroxylation of phenol, and oxidation of tertiary amines. The different roles of GR in these GR-based nanocomposite photocatalysts such as providing a photoelectron reservoir and performing as an organic dye-like macromolecular photosensitizer have been summarized. In addition, graphene oxide (GO) as a co-catalyst in GO–organic species photocatalysts and GO itself as a photocatalyst for selective reduction of CO2 have also been demonstrated. Finally, perspectives on the future research direction of GR-based composite photocatalysts toward selective organic redox transformations are discussed and it is clear that there is a wide scope of opportunities awaiting us in this promising research field.

A facile, one-step clean strategy has been utilized for anchoring noble metal (Au, Ag, Pd) nanoparticles onto the flat surface of two-dimensional (2D) graphene oxide (GO) nanosheets. Without using any additional reductants, surfactants or protecting ligands, the deposition of metallic noble metal (Au, Ag, Pd) nanoparticles on the partially reduced graphene oxide (PRGO) mat has been realized by a simple redox reaction between the noble metal precursors and GO in an aqueous solution. The main size distributions of the Au, Ag and Pd particles are centered on 1–20 nm, 3–10 nm and 0.5–3 nm, respectively. The as-obtained Au, Ag and Pd–PRGO nanocomposites display superb catalytic activities for the selective reduction of nitroaromatic compounds into the corresponding amino compounds under ambient conditions. The rates of reduction follow the sequence, Pd–PRGO > Ag–PRGO > Au–PRGO, suggesting that the smallest noble metal particles size affords the highest catalytic activity. In addition, considering that the Au, Ag and Pd–PRGO nanocomposites still hold the abundant functional groups of the original GO, these noble metal–PRGO composites maintain the excellent hydrophilic nature of GO, which provides a flexible platform for the further fabrication of PRGO–metal-based multicomponent functional materials by a wet-chemistry approach.

A series of graphene–ZnO (GR–ZnO) nanorod nanocomposites with different weight addition ratios of graphene (GR) have been prepared via a facile hydrothermal reaction of graphene oxide (GO) and ZnO nanorods. X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectra, and electron spin resonance (ESR) spectra are employed to determine the properties of the samples. It is found that GR–ZnO nanorod nanocomposites with a proper addition amount of GR exhibit higher photocatalytic activity and improved anti-photocorrosion than ZnO nanorods toward liquid-phase degradation of dye under ultraviolet (UV) light irradiation. The improved photoactivity and anti-photocorrosion of GR–ZnO nanorods can be ascribed to the integrative synergistic effect of enhanced adsorption capacity, the prolonged lifetime of photogenerated electron–hole pairs and effective interfacial hybridization between GR and ZnO nanorods. This study also shows that graphene sheets act as electronic conductive channels to efficiently separate the photogenerated charge carriers from ZnO nanorods. It is hoped that our current work could promote increasing interest in designing the nanocomposites of one-dimensional (1D) semiconductor and two-dimensional (2D) graphene for different photocatalytic applications.

A synergistic strategy involving oxygen-vacancy generation and noble-metal deposition is developed to improve the photocatalytic performance of TiO2 under visible-light irradiation. Through a redox reaction between the reductive TiO2 with oxygen vacancies (TiO2-OV) and metal salt precursors, noble-metal nanoparticles (Ag, Pt, and Pd) are uniformly deposited on the defective TiO2-OV surface in the absence of any reducing agents or stabilizing ligands. The resulting M-TiO2-OV (M = Ag, Pt, and Pd) nanocomposites are used as visible-light-driven photocatalysts for selective oxidation of benzyl alcohol and reduction of heavy metal ions Cr(VI). The results show that the oxygen vacancy creation obviously enhances the visible-light absorption of semiconductor TiO2. Meanwhile, the noble-metal deposition can effectively improve charge-separation efficiency of TiO2-OV under visible-light irradiation, thereby enhancing the photoactivity. In particular, Pd-TiO2-OV, having the average Pd particle size of 2 nm, shows the highest visible-light photoactivity, which can be attributed to the more efficient charge-carrier separation of Pd-TiO2-OV than Ag-TiO2-OV and Pt-TiO2-OV. The possible reaction mechanism for photocatalytic selective oxidation of benzyl alcohol and reduction of Cr(VI) over M-TiO2-OV (M = Ag, Pt, and Pd) has also been studied. It is hoped that our work could offer a simple strategy on fabricating defect-based nanostructures and their applications in solar energy conversion.

The CdS nanowires–reduced graphene oxide nanocomposites (CdS NWs–RGO NCs) combining one-dimensional (1-D) with two-dimensional (2-D) structures are successfully synthesized by a simple and efficient electrostatic self-assembly method, followed by a hydrothermal reduction process. The probe reactions for photocatalytic selective reduction of aromatic nitro organics in water under visible light irradiation are utilized to evaluate the photoactivity of the as-prepared CdS NWs–RGO NCs. The CdS NWs–RGO NCs exhibit significantly enhanced photoactivity as compared with the CdS nanowires (CdS NWs). The addition of RGO into the matrix of CdS NWs in a controlled manner is able to efficiently enhance the lifetime and transfer of photogenerated charge carriers from CdS NWs under visible light irradiation. Furthermore, the presence of RGO also improves the adsorption capacity of CdS NWs–RGO NCs toward aromatic nitro organics. These two primary factors result in the drastic photoactivity improvement of CdS NWs–RGO NCs toward selective reduction of nitro organics to the corresponding amino organics in water under visible light irradiation. In addition, the possible photocatalytic reaction mechanism is proposed. It is hoped that our work could not only offer useful information on the fabrication of various specific 1-D semiconductor–2-D RGO nanocomposites but also open a new window of such 1-D semiconductor–2-D RGO nanocomposites as visible light photocatalyst in the promising field of selective organic transformations.

The graphene–ZnO (GR–ZnO) nanocomposites have been fabricated via a facile, low-temperature in situ wet chemistry process, during which the reduction of graphene oxide and intimate interfacial contact between ZnO nanoparticles and GR nanosheets are achieved simultaneously. The GR–ZnO nanocomposites exhibit visible light photoactivity toward reduction of Cr(VI) in aqueous solution under ambient conditions. The large band gaps of GR–ZnO composites suggest that the visible light irradiation cannot photoexcite electrons in the valence band (VB) to conduction band (CB) of ZnO, thus ruling out the possibility that the visible light photoactivity of GR–ZnO is induced by the band gap photoexcitation of ZnO. Instead, under visible light irradiation, the GR sheet in GR–ZnO can be photoexcited from ground-state GR to excited-state GR* to generate electrons, which then inject into the CB of ZnO to make the GR–ZnO composites exhibit visible light photoactivity. Our results provide new robust proof of the role of GR as a macromolecular photosensitizer for semiconductors. Along with the fact that the photosensitization efficiency of GR is generally low, we propose that three basic principles are required to experimentally observe the exact photosensitizer role of GR in the GR–semiconductor composites under visible light. We hope that this work could boost further study on the photosensitizer role of GR and on how to improve the photosensitization efficiency of GR and inform ongoing interest in deep thinking of the microscopic charge carrier transfer pathway across the interface between GR and the semiconductor.

We report an efficient and easily accessible self-assembly route to synthesize In2S3–GR nanocomposites via electrostatic interaction of positively charged In2S3 nanoparticles with negatively charged graphene oxide (GO) followed by a hydrothermal process for reduction of GO to graphene (GR). The as-synthesized In2S3–GR nanocomposites exhibit much higher visible light photocatalytic activity toward selective reduction of nitroaromatic compounds in water than bare In2S3 nanoparticles and In2S3–GR–H that is obtained from the simple “hard” integration of GR nanosheets with solid In2S3 nanoparticles without modification of surface charge. On the basis of the joint characterizations and structure–photoactivity correlation it is disclosed that the enhanced photocatalytic performance of In2S3–GR is mainly ascribed to the more efficient interfacial contact between In2S3 and the GR nanosheets than In2S3–GR–H, which would amplify the use of electron conductivity and mobility of GR to improve the lifetime and transfer of photogenerated charge carriers more efficiently and thus boost the photoactivity more effectively. This work highlights the significant effect of preparation methods on the photoactivity of GR–semiconductor nanocomposites. It is expected that such a simple electrostatic self-assembly strategy could aid to rationally fabricate more efficient GR–semiconductor nanocomposites with improved interfacial contact and photocatalytic performance toward various photocatalytic selective transformations.

Selective activation of saturated sp3 C–H bonds to high-value-added chemicals remains a significant but challenging task for the sustainable exploitation of available feedstocks. However, the selective oxidation of C–H bonds with environmentally benign oxygen is often very difficult to control. Research works available in thermal heterogeneous catalysis often involve the use of transition metal particles together with harsh reaction conditions, e.g., high temperature and high pressure, which results in the difficulty in controlling the selectivity. Here, we report a very simple room temperature method to prepare a cubic phase, sheet structured semiconductor CdS sample. The as-prepared CdS is able to be used as a visible-light-driven photocatalyst for the selective oxidation of saturated primary C–H bonds in alkyl aromatics with high activity and selectivity using molecular oxygen as a benign oxidant and benzotrifluoride as the solvent under ambient conditions, i.e., room temperature and atmospheric pressure. The superior photocatalytic performance of CdS can be attributed to its unique assembly of sheet structure with cubic phase, high surface area and efficient separation of photogenerated charge carriers. The possible reaction mechanism for the photocatalytic selective oxidation of such C–H bonds over the CdS semiconductor has also been proposed.

Graphene (GR) has become a sparkling rising star on the horizon of material science. Due to its unique planar structure, excellent transparency, superior electron conductivity and mobility, high specific surface area, and high chemical stability, GR is regarded as an ideal high performance candidate to prepare GR-based nanocomposites for energy storage and conversion. During the past few years, GR-based photocatalysts have been attracting ever-increasing research attention. In this tutorial review, the applications of GR-based nanocomposites in photocatalysis, including nonselective processes for degradation of pollutants, selective transformations for organic synthesis and water splitting to clean hydrogen energy, are summarized systematically. In particular, in addition to discussing opportunities offered by GR, we will also describe the existing challenges for future exploitation and development of GR-based nanocomposites, which we hope would significantly advance us to rationally and efficiently harness the outstanding structural and electronic properties of GR to design smarter and more efficient GR-based photocatalysts instead of joining the graphene “gold rush”.

Coenocytic Pd@CdS nanocomposite has been successfully prepared via a facile wet chemistry approach. Its structure and properties have been characterized by a series of techniques, including field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ultra-violet/visible diffuse reflectance spectroscopy (DRS), nitrogen adsorption–desorption and electron spin resonance spectroscopy (ESR). The results demonstrate that the Pd nanoparticles as multiple cores are evenly distributed inside the photoactive CdS shell, forming a coenocytic nanostructure. It is found that the concentration of precursors and the intrinsic nature of noble metal colloids play essential roles in the growth process for such noble metal@semiconductor nanocomposite. Accordingly, a possible formation mechanism for the coenocytic Pd@CdS nanocomposite is proposed. The visible light photocatalytic activity of Pd@CdS has been evaluated by selective oxidation of a range of alcohols using molecular oxygen as oxidant under mild conditions. The results show that the coenocytic Pd@CdS exhibits enhanced photocatalytic activity as compared to blank-CdS obtained by the same procedure in the absence of Pd colloid nanoparticles as seeds. The enhanced photocatalytic performance of the coenocytic Pd@CdS can be ascribed to the coupling interaction of enhanced light absorption intensity, the longer lifetime of photogenerated charge carriers and its favorable adsorptivity. It is expected that our work could provide useful information for fabricating other core-shell nanocomposites and open an avenue to utilizing them in the field of photocatalytic selective organic transformations.

One-dimensional (1D) CdS@TiO2 core–shell nanocomposites (CSNs) have been successfully synthesized via a two-step solvothermal method. The structure and properties of 1D CdS@TiO2 core–shell nanocomposites (CdS@TiO2 CSNs) have been characterized by a series of techniques, including X-ray diffraction (XRD), ultraviolet–visible-light (UV-vis) diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FESEM), photoluminescence spectra (PL), and electron spin resonance (ESR) spectroscopy. The results demonstrate that 1D core–shell structure is formed by coating TiO2 onto the substrate of CdS nanowires (NWs). The visible-light-driven photocatalytic activities of the as-prepared 1D CdS@TiO2 CSNs are evaluated by selective oxidation of alcohols to aldehydes under mild conditions. Compared to bare CdS NWs, an obvious enhancement of both conversion and yield is achieved over 1D CdS@TiO2 CSNs, which is ascribed to the prolonged lifetime of photogenerated charge carriers over 1D CdS@TiO2 CSNs under visible-light irradiation. Furthermore, it is disclosed that the photogenerated holes from CdS core can be stuck by the TiO2 shell, as evidenced by controlled radical scavenger experiments and efficiently selective reduction of heavy-metal ions, Cr(VI), over 1D CdS@TiO2 CSNs, which consequently leads to the fact that the reaction mechanism of photocatalytic oxidation of alcohols over 1D CdS@TiO2 CSNs is apparently different from that over 1D CdS NWs under visible-light irradiation. It is hoped that our work could not only offer useful information on the fabrication of various specific 1D core–shell nanostructures, but also open a new doorway of such 1D core–shell semiconductors as visible-light photocatalysts in the promising field of selective transformations.Keywords: core−shell nanocomposite; mild conditions; one-dimensional; selective oxidation; visible-light photocatalyst;

Incessant interest has been shown in the synthesis of graphene (GR)–semiconductor nanocomposites as photocatalysts aiming to utilize the excellent electron conductivity of GR to lengthen the lifetime of photoexcited charge carriers in the semiconductor and, hence, improve the photoactivity. However, research works focused on investigating how to make sufficient use of the unique electron conductivity of GR to design a more efficient GR–semiconductor photocatalyst have been quite lacking. Here, we show a proof-of-concept study on improving the photocatalytic performance of GR–TiO2 nanocomposites via a combined strategy of decreasing defects of GR and improving the interfacial contact between GR and the semiconductor TiO2. The GR–TiO2 nanocomposite fabricated by this approach is able to make more sufficient use of the electron conductivity of GR, by which the lifetime and transfer of photoexcited charge carriers of GR–TiO2 upon visible light irradiation will be improved more efficiently. This in turn leads to the enhancement of visible-light-driven photoactivity of GR–TiO2 toward selective transformation of alcohols to corresponding aldehydes using molecular oxygen as a benign oxidant under ambient conditions. It is anticipated that our current work would inform ongoing efforts to exploit the rational design of smart, more efficient GR–semiconductor photocatalysts for conversion of solar to chemical energy by heterogeneous photocatalysis.

We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS–GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure–photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS–GR nanocomposites acts as an organic dye-like macromolecular “photosensitizer” for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR–semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept of the reaction mechanism in graphene–semiconductor photocatalysts could provide a new train of thought on designing GR-based composite photocatalysts for targeting applications in solar energy conversion, promoting our in-depth thinking on the microscopic charge carrier transfer pathway connected to the interface between the GR and the semiconductor.Keywords: graphene; nanocomposite; photosensitizer; selective oxidation; ZnS

The ternary CdS–graphene–TiO2 hybrids (CdS–GR–TiO2) have been prepared through an in situ strategy on the flatland of graphene oxide (GO). The structure and properties have been characterized by a series of techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), UV–vis diffuse reflectance spectra (DRS), electrochemical analysis, photoluminescence spectra (PL), nitrogen adsorption–desorption, and electron spin resonance spectra (ESR). Combined with our previous results, it is found that the introduction of the third-component TiO2 can maintain the morphology and porosity of the samples, whereas it is able to tune the energy band, increase the surface area, and facilitate the electron transfer, thus prolonging the lifetime of photogenerated carriers. Taking photocatalytic selective oxidation of various alcohols to their corresponding aldehydes as model reactions, the ternary CdS–GR–TiO2 hybrid exhibits enhanced photocatalytic activity compared with its foundation matrix binary CdS–GR. The improved photocatalytic performance can be attributed to the combined interaction of the longer lifetime of photogenerated electron–hole pairs, faster interfacial charge transfer rate, and larger surface area. In addition, a possible reaction mechanism has been proposed. This work indicates that the careful design of graphene–based composites by coupling graphene to suitable, multiple semiconductors allows the achievement of more efficient photocatalysts, which may have the great potential to improve the capacity for photocatalytic processes significantly. As a proof-of-concept, it is expected that this work could offer new inroads into exploration and utilization of graphene–based nanocomposites as a fertile ground for energy conversion.

We report a very facile and green template-free hydrothermal approach to synthesize Pt@CeO2 nanocomposite in an aqueous phase with tunable core-shell and yolk-shell structure. The formation of such core-shell and yolk-shell Pt@CeO2 nanocomposites can be reasonably explained by a novel mechanism of combined synergy interaction of heterogeneous seeded growth process and Ostwald ripening process, which is distinctly different from the well-known physical phenomena, such as nanoscale Kirkendall effect, Ostwald ripening and oriented attachment, employed in wet-chemistry fabrications of core/yolk-shell inorganic nanostructures. Interestingly, we show that, using selective oxidation of benzyl alcohol as a probe reaction at room temperature and ambient pressure, the incorporation of Pt into the shell of semiconductor CeO2 can remarkably enhance the photocatalytic performance of CeO2 for selective oxidation of alcohol. This represents a first example on the application of metal core@semiconductor-oxide shell nanostructured composite materials as visible-light-driven photocatalyst to selective oxidation reactions. Therefore, our findings could not only offer a useful direction on scale-up fabrication of other metal-oxide-coated noble metal nanocomposites with tunable core/yolk-shell structure, but also point to promising vistas of such metal core@oxide shell semiconductor nanocomposites as a novel class of materials platform as visible-light-driven photocatalyst in selective organic transformations.

Increasing interest has been devoted to synthesizing graphene (GR)-semiconductor nanocomposites as photocatalysts for potential applications, which is very similar to its forebear carbon nanotube (CNT)-semiconductor photocatalysts. Unfortunately, a thoughtful and inevitable comparison between GR- and CNT-semiconductors as photocatalysts is often neglected in literature. This situation may give incomplete or exaggerated information on the contribution role of GR to enhance the semiconductor photocatalytic activity, as compared to CNT. Thus, our knowledge regarding the specific advantage of GR over CNT on how to design more efficient GR-semiconductor nanocomposites and understanding the origin of their enhanced photocatalytic performance is far from satisfactory. By taking the TiO2 semiconductor as an example, we conceptually demonstrate how to synthesize a more efficient GR-TiO2 nanocomposite as a visible light photocatalyst toward selective oxidation of alcohols under mild conditions. Comparison between GR-TiO2 and CNT-TiO2 discloses the prominent advantage of GR over CNT on both controlling the morphology of GR-TiO2 nanocomposite and enhancing the photocatalytic activity of TiO2. This work clearly highlights the importance and necessity for a comparison investigation between GR- and CNT-semiconductors as photocatalysts, which will promote our in-depth fundamental understanding on the analogy and difference between GR and CNT on controlling the morphology of GR (or CNT)-semiconductor nanocomposites and enhancing the photocatalytic performance. Therefore, we appeal the photocatalysis community to pay attention to this respect rather than separately imposing hype on the miracle of GR in much the same way as its carbon forebears, which could significantly advance our rational fabrication of smart GR-semiconductor nanocomposites for artificial photosynthesis.Keywords: graphene; nanocomposite; selective oxidation; TiO2; visible light photocatalysis

The core–shell nanocomposites of M@TiO2 (M = Au, Pd, Pt) have been synthesized successfully via a facile hydrothermal treatment of TiF4 precursor and noble metal colloid particles. Their properties were determined by a collection of joint techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectra (XRD), ultraviolet/visible diffuse reflectance spectra (DRS), photoluminescence spectra (PL), and electron spin resonance spectra (ESR). Photocatalytic degradation of Rhodamine B (RhB) in the liquid phase served as a probe reaction to evaluate the activity of the as-prepared M@TiO2 (M = Au, Pd, Pt) core–shell nanocomposites under the irradiation of both visible light and ultraviolet (UV) light. The results reveal that these core–shell nanocomposites possess tunable photoreactivity. It is interesting to find that the incorporation of noble metal core into the shell of TiO2 only contributes to enhancement of visible light photocatalytic activity of TiO2. The noble metal cores are believed to play an essential role in affecting the photoreactivity because they are able to trap electrons, improve the electron–hole pairs life, and enhance the visible light absorption intensity that are all beneficial for enhancement of the visible light photocatalytic activity of TiO2. However, the incorporation of noble metal core significantly lowers the UV light absorption intensity, thus leading to the obervation that, under UV light irradiation, the bare TiO2 still exhibits higher activity than M@TiO2 core–shell nanocomposites. The possible radical species involved in the degradation of RhB were analyzed by means of the PL and ESR techniques. Recycled activity tests demonstrate that the incorporation of metal core into the shell of TiO2 will inhibit the photocorrison behavior and provide much better photocatalytic stability of M@TiO2 (M = Au, Pd, Pt) nanocomposites than the bare TiO2. It is hoped that our work could render guided information for steering toward the design and application of TiO2-coated core–shell nanomaterials with tunable photocatalytic activity.

By means of density functional theory in conjunction with periodic slab models, coverage-dependent behavior for chemical functionalization of the semiconductor X (100) (X = C, Si, and Ge) surface by traditional cycloaddition of transition metal oxides (OsO4 and RuO4) has been investigated. We found that the transition-metal-mediated oxygen transfer reaction for cycloaddition of OsO4 and RuO4 onto X (100) is quite favorable. The adsorption energies decrease as the coverage is increased, and the band gap is widened or reduced depending on both the type of model molecules and the coverage. Furthermore, it is feasible to form organic layer films of transition metal oxides onto the semiconductor X (100) surface as reflected by the high adsorption energies at the saturated coverage, which could lead to new hybrid multifunctional materials. In addition, interestingly, two distinct and competitive monolayer structures are simultaneously observed on both the Si (100) and the Ge (100) surfaces, but only one stable monolayer geometry is found on the C (100) surface, indicating the flexibility of controlling the self-assembled molecular binding configuration using transition metal oxides on the semiconductor X (100) surface. It is hoped that our results may help to seek appropriate chemical modification methods to widen the application fields of the group IV semiconductor-based hybrid materials.

The Pd@CeO2 semiconductor nanocomposite with “plum-pudding” structure has been fabricated successfully via a facile low-temperature hydrothermal reaction of polyvinylpyrrolidone (PVP)-capped Pd colloidal particles and cerium chloride precursor followed by a calcination process in air. Different characterization techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), UV–vis diffuse reflectance spectra (DRS), X-ray photoelectron spectra (XPS), photoluminescence spectra (PL), nitrogen adsorption–desorption, and electron spin resonance spectra (ESR), have been used to investigate the structure and properties of the Pd@CeO2 nanocomposite. It is found that the nanosized Pd particles are evenly dispersed into the matrix of CeO2, thus forming a plum-pudding structure, i.e., multi-Pd core@CeO2 shell configuration. This unique nanostructure endows the Pd@CeO2 nanocomposite with enhanced activity and selectivity toward the visible-light-driven oxidation of various benzylic alcohols to corresponding aldehydes using dioxygen as oxidant at room temperature and ambient pressure compared with a supported Pd/CeO2 nanocomposite and nanosized CeO2 powder. The formation of the multi-Pd core@CeO2 shell structure can be understood by a synergistic interaction of heterogeneous seeded growth process, monolayer-capped core coalescence, and shell re-encapsulation. Together with the previous report, it can be concluded that the intrinsic structure nature of noble metal colloids is able to play a key role in affecting the formation process of noble metal core@semiconductor shell nanocomposites, by which we can realize the design and preparation of different specific core–shell nanostructures with atomic scale accuracy. It is hoped that our current work could open promising prospects of the fabrication of multimetal core@semiconductor shell nanocomposites and their application to visible-light-driven selective organic transformations.

A series of cadmium sulfide–graphene (CdS–GR) nanocomposites with different weight addition ratios of graphene (GR) have been synthesized via a facile one-step hydrothermal approach, during which the formation of CdS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), nitrogen adsorption–desorption, photoluminescence spectra (PL), and electron spin resonance spectra (ESR) are employed to determine the properties of the samples. It is found that the CdS nanoparticles evenly overspread on the graphene scaffold, and the properties of the samples, including morphology, pore structure, optical, and electronic nature, are able to be tuned by the addition of GR as compared with blank-CdS prepared in the absence of GR. The photocatalytic activities of the as-prepared CdS–GR nanocomposites are evaluated by selective oxidation of a range of alcohols under mild conditions. To our best knowledge, it is the first time to use CdS–GR nanocomposites as visible light photocatalyst for selective organic transformation. Our results demonstrate that the as-prepared CdS–GR nanocomposites can serve as a promising visible-light-driven photocatalyst for selective oxidation of alcohols to corresponding aldehydes. The high photoactivity of CdS–GR can be ascribed to the integrative effect of enhanced light absorption intensity, high electron conductivity of GR, and its significant influence on the morphology and structure of the samples. It is hoped that our current work could widen the application of CdS–GR nanocomposites and open promising prospects for the utilization of GR-based semiconductor nanocomposites as visible light photocatalyst for selective organic transformations.

Mesoporous Ti-HMS is able to be used as an active “single-site” photocatalyst for the gas-phase heterogeneous degradation of benzene, a notorious aromatic organic pollutant. In particular, it has been found that Ti-HMS shows enhanced activity and stability toward degradation of benzene as compared with commercial titania (Degussa, P25), which could be attributed to its unique features of large surface area, highly dispersion state of Ti oxide species and mesoporous channel structure. This suggests that there is a promising potential in using Ti-containing molecular sieves as a photocatalyst for degradation of volatile aromatic organic pollutants in air, therefore advancing the applications of such “single-site” photocatalyst in environment cleanup.Mesoporous Ti-HMS can be used as a “single-site” photocatalyst for gas-phase degradation of benzene. The abundance of various redox molecular sieves other than HMS and easiness of incorporating various metals (such as Cr, V, Mo, Zr, Mn, Sn and Al) into molecular sieves suggests a wide scope to optimize the performance of such “single-site” photocatalysts.

The nanocomposites of TiO2−graphene (TiO2−GR) have been prepared via a facile hydrothermal reaction of graphene oxide and TiO2 in an ethanol−water solvent. We show that such a TiO2−GR nanocomposite exhibits much higher photocatalytic activity and stability than bare TiO2 toward the gas-phase degradation of benzene, a volatile aromatic pollutant in air. By investigating the effect of different addition ratios of graphene on the photocatalytic activity of TiO2−GR systematically, we find that the higher weight ratio in TiO2−GR will decrease the photocatalytic activity. Analogous phenomenon is also observed for the liquid-phase degradation of dyes over TiO2−GR. In addition, the key features for TiO2−GR including enhancement of adsorptivity of pollutants, light absorption intensity, electron−hole pairs lifetime, and extended light absorption range have also been found in the composite of TiO2 and carbon nanotubes (TiO2−CNT). These strongly manifest that TiO2−GR is in essence the same as other TiO2−carbon (carbon nanotubes, fullerenes, and activated carbon) composite materials on enhancement of photocatalytic activity of TiO2, although graphene by itself has unique structural and electronic properties. Notably, this key fundamental question remains completely unaddressed in a recent report ( ACS Nano 2010, 4, 380) regarding liquid-phase degradation of dyes over the TiO2−GR photocatalyst. Thus, we propose that TiO2−GR cannot provide truly new insights into the fabrication of TiO2−carbon composite as high-performance photocatalysts. It is hoped that our work could avert the misleading message to the readership, hence offering a valuable source of reference on fabricating TiO2−carbon composites for their application as a photocatalyst in the environment cleanup.Keywords: graphene; nanocomposite; photocatalysis; TiO2; volatile aromatic pollutant

The viability of functionalization of the semiconductor surfaces of diamond (100), Si (100), and Ge (100) by traditional [3 + 2] cycloaddition of transition metal oxides has been predicted using effective cluster models in the framework of density functional theory. The cycloaddition of transition metal oxides (OsO4, RuO4, and MnO4−) onto the X (100) (X = C, Si, and Ge) surface is much more facile than that of other molecular analogues including ethylene, fullerene, and single-walled carbon nanotubes because of the high reactivity of surface dimers of X (100). Our computational results demonstrate the plausibility that the well-known [3 + 2] cycloaddition of transition metal oxides to alkenes in organic chemistry can be employed as a new type of surface reaction to functionalize the semiconductor X (100) surface, which offers the new possibility for self-assembly or chemical functionalization of X (100) at low temperature. More importantly, the chemical functionalization of X (100) by cycloaddition of transition metal oxides provides the molecular basis for preparation of semiconductor-supported catalysts but also strongly advances the concept of using organic reactions to modify the solid surface, particularly to modify the semiconductor C (100), Si (100), and Ge (100) surfaces for target applications in numerous fields such as microelectronics and heterogeneous photocatalysis.

Graphene (GR)-CdS nanocomposites with different weight addition ratios of GR have been assembled by a facile solvothermal treatment. The GR-CdS nanocomposite photocatalyst with an appropriate ratio of GR exhibits enhanced photoactivity for selective reduction of aromatic nitro compounds to the corresponding aromatic amines in water under visible light irradiation as compared with blank-CdS. The characterization of GR-CdS nanocomposite photocatalysts by a collection of techniques discloses that: i) GR can tune the microscopic morphology of CdS nanoparticles and improve light absorption intensity in the visible light region; ii) GR scaffolds act as an electron reservoir to trap and shuttle the electrons photogenerated from CdS semiconductor under the visible light illumination; iii) the introduction of GR enhances the adsorption capacity of GR-CdS nanocomposites toward the substrates, aromatic nitro compounds. The synergistic effect of these factors should account for the photoactivity advancement of GR-CdS nanocomposites toward the probe reactions. Furthermore, because the photogenerated holes in the system are trapped by the quenching agent ammonium oxalate, the as-obtained GR-CdS photocatalyst is stable during the photocatalytic reduction reactions. A reasonable model has also been proposed to illustrate the reaction mechanism.Graphene (GR)-CdS nanocomposites are utilized as visible-light-induced photocatalysts for selective reduction of aromatic nitro compounds to the corresponding aromatic amines in water.Download full-size image

A systematic comparison between graphene (GR)–semiconductor CdS and its analogs fullerene (C60) and carbon nanotube (CNT)–semiconductor CdS composite photocatalysts for selective oxidation of alcohols has been carried out based on a reasonable benchmark framework. The results reveal that GR cannot manifest its unique advantage over its carbon allotropes in enhancing the photoactivity of semiconductor CdS. The primary roles of these carbon allotropes (C60, CNT, and GR) are found to be quite similar in terms of structure–photoactivity correlation analysis. Overall, this work highlights that (i) the exponential increase in publications on GR–semiconductor photocatalysts has not been matched by increases in our knowledge regarding the similarity and difference of these carbon allotropes in relation to improving the photocatalytic performance of semiconductors; (ii) efforts should be more rationally focused on how to make the best use of remarkable properties of GR in designing more efficient GR-based semiconductor composite photocatalysts, thereby advancing the sufficient realization of GR’s potential in constructing efficient GR–semiconductor photocatalysts for solar energy conversion.Graphical abstractA critical and systematic comparison between graphene-semiconductor and its analog (carbon nanotube, fullerene)-semiconductor composite photocatalysts has been carried out, taking CdS as an example semiconductor and selective oxidation of alcohols under ambient conditions as model reactions, revealing that the primary roles of these carbon allotropes are quite similar, and graphene cannot manifest its unique and prominent advantage over its carbon forebears in enhancing the photoactivity of semiconductor CdS.Download high-res image (248KB)Download full-size imageHighlights► Intimate interfacial contact for CdS–carbon composite photocatalysts is achieved. ► A first systematic and critical comparison study in a reasonable benchmark framework is presented. ► The primary role of these carbon allotropes is found to be quite similar. ► Graphene fails to show prominent advantage over its carbon forebears in this study. ► Mismatch exists in the increase degree in publications and our knowledge on graphene-semiconductor composites photocatalysis.

•CdS–graphene (GR) nanocomposites are synthesized by a facile solvothermal treatment.•The effect of GR defects density on improving semiconductor photoactivity is studied.•CdS–GR photocatalysts are used for selective oxidation and reduction in water.•CdS–graphene nanocomposites can serve as selective visible light photocatalysts.•The introduction of graphene can inhibit the photocorrosion of CdS effectively.A series of CdS–graphene (GR) nanocomposites with different weight addition ratios of GR have been fabricated via a facile one-step solvothermal approach. CdS–GR nanocomposites are proven to serve as selective visible light photocatalysts toward aerobic selective oxidation of alcohols and reduction of heavy ions Cr(VI), instead of being nonselective in water. Furthermore, we find that decreasing the defect density of GR by using the solvent-exfoliated graphene (SEG) instead of graphene oxide (GO) as the precursor of GR can efficiently enhance the photocatalytic activity of CdS–GR nanocomposites due to its improved electron conductivity as compared to reduced GO (RGO). In addition, the hybridization of CdS with GR (RGO, SEG) via an intimate interfacial interaction can also effectively inhibit the photocorrosion of CdS during the photocatalytic redox reaction. It is hoped that this work can draw attention to making better use of graphene to synthesize more efficient GR-based nanocomposite photocatalysts for solar energy conversion, especially in the field of diverse redox processes in water in the framework of green chemistry.CdS–graphene (GR) nanocomposites have been fabricated via a facile one-step solvothermal approach using graphene oxide (GO) and solvent-exfoliated graphene (SEG) as the precursors of GR. The activity of the optimum samples and blank-CdS in terms of conversion follows the order CdS–5% SEG > CdS–5% RGO > blank-CdS toward both photocatalytic selective oxidation of alcohols and reduction of heavy ions Cr(VI) in water under visible light irradiation due to the improved electron conductivity of SEG as compared to RGO.Download high-res image (273KB)Download full-size image

•CdS nanowires (NWs)-carbon nanotube (CNT) nanocomposites are synthesized by a simple self-assembly method at room temperature.•CdS NWs-CNT exhibits remarkably enhanced photoactivity toward selective reduction of aromatic nitro organics in water.•The origin of CNT on enhancing the photoactivity of CdS NWs is investigated.•The effect of different carbon materials, including CNT and graphene, on improving CdS NWs photoactivity is studied comparatively.•Simple CdS NWs-CNT nanocomposites can serve as highly efficient, visible light photocatalysts for selective organic transformation.One-dimensional CdS nanowires-carbon nanotubes nanocomposites (1D–1D CdS NWs-CNT NCs) with different weight addition ratios of CNT have been synthesized by a very simple room temperature self-assembly method, which is afforded by electrostatic attractive interaction between positively charged CdS NWs and negatively charged CNT in an aqueous solution. Importantly, the CdS NWs-CNT NCs exhibit remarkably enhanced photoactivity toward selective reduction of aromatic nitro organics in water under visible light irradiation as compared to bare CdS NWs. The significantly enhanced photoactivity is attributed to the integrated factors of the unique 1D–1D morphology associated with CdS NWs and CNT, the efficient retardation of recombination of the photoexcited electron–hole pairs, and the enhanced visible light absorption intensity. Besides, the CdS NWs-CNT NCs exhibit higher photoactivity than CdS NWs-reduced graphene oxide (CdS NWs-RGO NCs), toward selective reduction of aromatic nitro organics. Therefore, this work not only offers a very simple room temperature approach to synthesize highly efficient 1D semiconductor-1D CNT composite photocatalyst, but also gives an example that RGO cannot readily manifest its unique and prominent advantage over CNT for specific photocatalytic application, thus underpinning the importance of rationally utilizing the carbon materials (e.g., 1D CNT, 2D RGO) to design more efficient carbon-semiconductor composite photocatalyst.CdS nanowires (NWs)-carbon nanotube (CNT) 1D–1D nanocomposites (CdS NWs-CNT NCs) have been fabricated via a very simple, room temperature self-assembly method, which is afforded by electrostatic attractive interaction between positively charged CdS NWs and negatively charged CNT in an aqueous solution. The CdS NWs-CNT NCs exhibit enhanced photoactivity toward selective reduction of aromatic nitro organics as compared to CdS NWs and their analogue CdS NWs-graphene, thus promoting us to rationally utilize carbon materials to design more efficient carbon-semiconductor composite photocatalyst instead of plunging into the “graphene gold rush,” similar to the case of CNT.Download high-res image (90KB)Download full-size image

•A generalized method of fabricating robust and metal-free graphene–dyes 3D aerogel photocatalysts is developed.•3D aerogels show higher dye-sensitized activity and long-term stability than powder systems.•The photoactivity of aerogels can be regenerated easily by replenishing fresh dyes.•Advantages of the 3D aerogels over their powder counterparts are disclosed.•The work opens a new doorway to designing novel metal-free visible light photocatalysts.The design of efficient visible-light-driven photocatalysts that use low-cost and earth-abundant materials with easy recyclability is a significant and enduring theme for solar energy conversion with practical applications. Here we report a facile and generalized synthesis of metal-free 3D macroscopic graphene–organics aerogels in which the organic dyes as photosensitizers are spatially confined and distributed in the graphene framework. This 3D bulk aerogel with an interconnected conductive porous structure displays fast spatial separation and transportation of photogenerated charge carriers, high adsorptivity of target reactants, and efficient visible-light-driven photocatalytic activity, as well as easy separability and recyclability from the reaction medium. In addition, such a bulk aerogel manifests excellent regenerability via simple replenishment of fresh dyes, which guarantees the long-term photoactivity of the 3D aerogel. This universal approach for fabricating 3D graphene–organics aerogels is expected to open a new vista for constructing a novel type of metal-free and robust visible-light photocatalysts for artificial photoredox, as well as offering a generic way to improve the photosensitization efficiency of traditional organic dyes.Download high-res image (98KB)Download full-size image

Au/Ti-HMS was prepared by in situ method, NH3 deposition–precipitation (NH3 DP) and urea deposition–precipitation (Urea DP), respectively. The catalysts were characterized by a series of techniques including ICP, powder XRD, N2 sorption, UV–visible spectroscopy, TEM and H2-TPR. Using n-octane containing BT, DBT and 4,6-DMDBT as model compound, the performance of the catalysts in oxidative desulfurization (ODS) using in situ generated H2O2 from H2 and O2 were investigated. The results show that preparation method influences porous structure of the support and gold particles size. In situ sample has maintained the intrinsic structure of Ti-HMS, whereas, the gold particles are not as uniform and small as that of DP sample. NH3 DP sample still possesses the wormhole structure of HMS despite the absence of typical XRD peak. The mesoporous structure of urea DP sample has been damaged seriously. Au3+ on outer surface of the support is easier to be reduced than that in pores, as confirmed by H2-TPR. In addition, the three samples exhibit different catalytic activities in ODS using in situ H2O2 as oxidant. For the removal of BT and DBT, Au/Ti-HMS (NH3 DP) exhibits the highest catalytic activities. Regarding the removal of 4,6-DMDBT, the optimum catalyst is Au/Ti-HMS (In situ); however, Au/Ti-HMS (Urea DP) nearly loses catalytic activity.

Incessant interest has been shown in the synthesis of graphene (GR)–semiconductor nanocomposites as photocatalysts aiming to utilize the excellent electron conductivity of GR to lengthen the lifetime of photoexcited charge carriers in the semiconductor and, hence, improve the photoactivity. However, research works focused on investigating how to make sufficient use of the unique electron conductivity of GR to design a more efficient GR–semiconductor photocatalyst have been quite lacking. Here, we show a proof-of-concept study on improving the photocatalytic performance of GR–TiO2 nanocomposites via a combined strategy of decreasing defects of GR and improving the interfacial contact between GR and the semiconductor TiO2. The GR–TiO2 nanocomposite fabricated by this approach is able to make more sufficient use of the electron conductivity of GR, by which the lifetime and transfer of photoexcited charge carriers of GR–TiO2 upon visible light irradiation will be improved more efficiently. This in turn leads to the enhancement of visible-light-driven photoactivity of GR–TiO2 toward selective transformation of alcohols to corresponding aldehydes using molecular oxygen as a benign oxidant under ambient conditions. It is anticipated that our current work would inform ongoing efforts to exploit the rational design of smart, more efficient GR–semiconductor photocatalysts for conversion of solar to chemical energy by heterogeneous photocatalysis.

Coupling ZnO with carbon materials using a suitable integration method to form ZnO–carbon composites has been established as a promising strategy to ameliorate the photocatalytic performance of semiconductor ZnO. In this perspective article, we describe the recent advances and current status of enhancing the photocatalytic activity and anti-photocorrosion of semiconductor ZnO by coupling with versatile carbon materials, e.g., C60, carbon nanotube, graphene and other carbon materials. The primary roles of carbon materials in boosting the photoactivity and photostability of ZnO have been outlined and illustrated with some selected typical examples. In particular, the three main kinds of mechanisms with regard to anti-photocorrosion of ZnO by coupling with carbon have been demonstrated. Finally, we give a concise perspective on this important research area and specifically propose further research opportunities in optimizing the photocatalytic performance of ZnO–carbon composites and widening the scope of their potential photocatalytic applications.

Zinc oxide (ZnO) nanostructured materials have received significant attention because of their unique physicochemical and electronic properties. In particular, the functional properties of ZnO are strongly dependent on its morphology and defect structure, particularly for a semiconductor ZnO-based photocatalyst. Here, we demonstrate a simple strategy for simultaneous morphology control, defect engineering and photoactivity tuning of semiconductor ZnO by utilizing the unique surfactant properties of graphene oxide (GO) in a liquid phase. By varying the amount of GO added during the synthesis process, the morphology of ZnO gradually evolves from a one dimensional prismatic rod to a hexagonal tube-like architecture while GO is converted into reduced GO (RGO). In addition, the introduction of GO can create oxygen vacancies in the lattice of ZnO crystals. As a result, the absorption edge of the wide band gap semiconductor ZnO is effectively extended to the visible light region, which thus endows the RGO–ZnO nanocomposites with visible light photoactivity; in contrast, the bare ZnO nanorod is only UV light photoactive. The synergistic integration of the unique morphology and the presence of oxygen vacancies imparts the RGO–ZnO nanocomposite with remarkably enhanced visible light photoactivity as compared to bare ZnO and its counterpart featuring different structural morphologies and the absence of oxygen vacancies. Our promising results highlight the versatility of the 2D GO as a solution-processable macromolecular surfactant to fabricate RGO–semiconductor nanocomposites with tunable morphology, defect structure and photocatalytic performance in a system-materials-engineering way.

We report a very facile and green template-free hydrothermal approach to synthesize Pt@CeO2 nanocomposite in an aqueous phase with tunable core-shell and yolk-shell structure. The formation of such core-shell and yolk-shell Pt@CeO2 nanocomposites can be reasonably explained by a novel mechanism of combined synergy interaction of heterogeneous seeded growth process and Ostwald ripening process, which is distinctly different from the well-known physical phenomena, such as nanoscale Kirkendall effect, Ostwald ripening and oriented attachment, employed in wet-chemistry fabrications of core/yolk-shell inorganic nanostructures. Interestingly, we show that, using selective oxidation of benzyl alcohol as a probe reaction at room temperature and ambient pressure, the incorporation of Pt into the shell of semiconductor CeO2 can remarkably enhance the photocatalytic performance of CeO2 for selective oxidation of alcohol. This represents a first example on the application of metal core@semiconductor-oxide shell nanostructured composite materials as visible-light-driven photocatalyst to selective oxidation reactions. Therefore, our findings could not only offer a useful direction on scale-up fabrication of other metal-oxide-coated noble metal nanocomposites with tunable core/yolk-shell structure, but also point to promising vistas of such metal core@oxide shell semiconductor nanocomposites as a novel class of materials platform as visible-light-driven photocatalyst in selective organic transformations.

Coenocytic Pd@CdS nanocomposite has been successfully prepared via a facile wet chemistry approach. Its structure and properties have been characterized by a series of techniques, including field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ultra-violet/visible diffuse reflectance spectroscopy (DRS), nitrogen adsorption–desorption and electron spin resonance spectroscopy (ESR). The results demonstrate that the Pd nanoparticles as multiple cores are evenly distributed inside the photoactive CdS shell, forming a coenocytic nanostructure. It is found that the concentration of precursors and the intrinsic nature of noble metal colloids play essential roles in the growth process for such noble metal@semiconductor nanocomposite. Accordingly, a possible formation mechanism for the coenocytic Pd@CdS nanocomposite is proposed. The visible light photocatalytic activity of Pd@CdS has been evaluated by selective oxidation of a range of alcohols using molecular oxygen as oxidant under mild conditions. The results show that the coenocytic Pd@CdS exhibits enhanced photocatalytic activity as compared to blank-CdS obtained by the same procedure in the absence of Pd colloid nanoparticles as seeds. The enhanced photocatalytic performance of the coenocytic Pd@CdS can be ascribed to the coupling interaction of enhanced light absorption intensity, the longer lifetime of photogenerated charge carriers and its favorable adsorptivity. It is expected that our work could provide useful information for fabricating other core-shell nanocomposites and open an avenue to utilizing them in the field of photocatalytic selective organic transformations.

By embedding noble metal palladium (Pd) into the interfacial layer matrix of graphene (GR) and semiconductor CdS, we have successfully constructed ternary CdS–(GR–Pd) nanocomposites with intimate interfacial contact. The CdS–(GR–Pd) nanocomposites show remarkably enhanced photocatalytic activity toward selective redox reactions under visible light irradiation as compared to blank-CdS and the optimum binary CdS–GR. It is revealed that the photocatalytic performance enhancement of CdS–(GR–Pd) is ascribed to the optimized spatial charge carrier transfer across the interface resulting from the introduction of Pd nanoparticles as mediators into the interfacial layer between GR and CdS. One role of Pd is to serve as electron reservoir to directly trap photogenerated electrons from CdS and the other role is as interfacial mediator to promote electron relay in the ternary CdS–(GR–Pd) photocatalysts along with conductive graphene as dual co-catalysts. Moreover, the negative light “shielding effect” of GR can be partially counterbalanced through such a facile strategy. This work substantiates the feasibility of adopting the “interfacial-mediator” strategy to optimize the interfacial charge carriers transfer pathway and efficiency for improved photoactivity of GR–semiconductor nanocomposites toward target photoredox reactions.

Over the past few decades, layer-by-layer (LbL) assembly of multilayer thin films has garnered considerable interest on account of its ability to modulate nanometer control over film thickness and its extensive choice of usable materials for coating planar and particulate substrates, thus allowing for the fabrication of responsive and functional thin films for their potential applications in a myriad of fields. Herein, we provide elaborate information on the current developments of LbL assembly techniques including different properties, molecular interactions, and assembly methods associated with this promising bottom-up strategy. In particular, we highlight the principle for rational design and fabrication of a large variety of multilayer thin film systems including multi-dimensional capsules or spatially hierarchical nanostructures based on the LbL assembly technique. Moreover, we discuss how to judiciously choose the building block pairs when exerting the LbL assembly buildup which enables the engineering of multilayer thin films with tailor-made physicochemical properties. Furthermore, versatile applications of the diverse LbL-assembled nanomaterials are itemized and elucidated in light of specific technological fields. Finally, we provide a brief perspective and potential future challenges of the LbL assembly technology. It is anticipated that our current review could provide a wealth of guided information on the LbL assembly technique and furnish firm grounds for rational design of LbL assembled multilayer assemblies toward tangible applications.

Low cost and easily made bismuth tungstate (Bi2WO6) could be one of the key technologies to make chemicals and fuels from biomass, atmospheric carbon dioxide and water at low cost using solar radiation as an energy source. Its narrow band gap (2.8 eV) enables ideal visible light (λ > 400 nm) absorption. Yet, it is the material's shape, namely the superstructure morphology wisely created via a nanochemistry approach, which leads to better electron–hole separation and much higher photoactivity. Recent results coupled to the versatile photochemistry of this readily available semiconductor suggest that the practical application of nanochemistry-derived Bi2WO6 nanostructures for the synthesis of value-added fine chemicals and fuel production is possible. We describe progress in this important field of chemical research from a nanochemistry viewpoint, and identify opportunities for further progress.

The severe consequences of fossil fuel consumption have resulted in a need for alternative sustainable sources of energy. Conversion and storage of solar energy via a renewable method, such as photocatalysis, holds great promise as such an alternative. One-dimensional (1D) nanostructures have gained attention in solar energy conversion because they have a long axis to absorb incident sunlight yet a short radial distance for separation of photogenerated charge carriers. In particular, well-ordered spatially high dimensional architectures based on 1D nanostructures with well-defined facets or anisotropic shapes offer an exciting opportunity for bridging the gap between 1D nanostructures and the micro and macro world, providing a platform for integration of nanostructures on a larger and more manageable scale into high-performance solar energy conversion applications. In this review, we focus on the progress of photocatalytic solar energy conversion over controlled one-dimension-based spatially ordered architecture hybrids. Assembly and classification of these novel architectures are summarized, and we discuss the opportunity and future direction of integration of 1D materials into high-dimensional, spatially organized architectures, with a perspective toward improved collective performance in various artificial photoredox applications.

Selective activation of saturated sp3 C–H bonds to high-value-added chemicals remains a significant but challenging task for the sustainable exploitation of available feedstocks. However, the selective oxidation of C–H bonds with environmentally benign oxygen is often very difficult to control. Research works available in thermal heterogeneous catalysis often involve the use of transition metal particles together with harsh reaction conditions, e.g., high temperature and high pressure, which results in the difficulty in controlling the selectivity. Here, we report a very simple room temperature method to prepare a cubic phase, sheet structured semiconductor CdS sample. The as-prepared CdS is able to be used as a visible-light-driven photocatalyst for the selective oxidation of saturated primary C–H bonds in alkyl aromatics with high activity and selectivity using molecular oxygen as a benign oxidant and benzotrifluoride as the solvent under ambient conditions, i.e., room temperature and atmospheric pressure. The superior photocatalytic performance of CdS can be attributed to its unique assembly of sheet structure with cubic phase, high surface area and efficient separation of photogenerated charge carriers. The possible reaction mechanism for the photocatalytic selective oxidation of such C–H bonds over the CdS semiconductor has also been proposed.

Glycerol, being either a primary by-product of biodiesel manufacture or a platform molecule from sugars, is of significant interest as a renewable biomass because it is a highly functionalized and versatile organic building block for the synthesis of value-added fine chemicals. In particular, selective oxidation of glycerol to various industrially valuable products by heterogeneous photocatalysis using solar light as free energy and molecular oxygen as benign oxidant under ambient conditions is extremely attractive. However, a highly selective, heterogeneous visible-light photocatalyst utilized for aerobic oxidation of glycerol has been unavailable. To date, the discovery or design of a visible-light-driven, highly selective photocatalyst for selective oxidation of glycerol to a specific product is particularly challenging in heterogeneous photocatalytic selective transformation. Herein, we for the first time, report the identification of flower-like Bi2WO6 as a highly selective visible-light photocatalyst toward aerobic selective oxidation of glycerol to dihydroxyacetone using oxygen as oxidant in water at room temperature and atmospheric pressure. A rationale for the observed high selectivity over photocatalyst flower-like Bi2WO6 is provided.

There is still an ongoing effort to search for sustainable, clean and highly efficient energy generation to satisfy the energy needs of modern society. Among various advanced technologies, electrocatalysis for the oxygen evolution reaction (OER) plays a key role and numerous new electrocatalysts have been developed to improve the efficiency of gas evolution. Along the way, enormous effort has been devoted to finding high-performance electrocatalysts, which has also stimulated the invention of new techniques to investigate the properties of materials or the fundamental mechanism of the OER. This accumulated knowledge not only establishes the foundation of the mechanism of the OER, but also points out the important criteria for a good electrocatalyst based on a variety of studies. Even though it may be difficult to include all cases, the aim of this review is to inspect the current progress and offer a comprehensive insight toward the OER. This review begins with examining the theoretical principles of electrode kinetics and some measurement criteria for achieving a fair evaluation among the catalysts. The second part of this review acquaints some materials for performing OER activity, in which the metal oxide materials build the basis of OER mechanism while non-oxide materials exhibit greatly promising performance toward overall water-splitting. Attention of this review is also paid to in situ approaches to electrocatalytic behavior during OER, and this information is crucial and can provide efficient strategies to design perfect electrocatalysts for OER. Finally, the OER mechanism from the perspective of both recent experimental and theoretical investigations is discussed, as well as probable strategies for improving OER performance with regards to future developments.

Carbon in its single layer atomic morphology has exceptional thermal, optical, electronic and mechanical properties, which may form the basis for several functional products and enhanced technologies that go from electricity storage to polymer nanocomposites of so far unsurpassed characteristics. Due to the high cost, however, the current global production of graphene does not exceed 120 tonnes. New chemical and physical methods to exfoliate graphite, however, were recently engineered and commercialized, which open the route to massive adoption of graphene as the “enabler” of numerous important technologies, including enhanced electricity storage. This feature article presents an updated, critical overview that will be useful to nanochemistry and nanotechnology research practitioners and to entrepreneurs in advanced materials.

Ternary hybrids of (reduced graphene oxide)–(CdS nanowire)–TiO2 nanocomposites (CTG) featuring a large two-dimensional (2D) flat structure have been successfully synthesized via a simple surface charge promoted self-assembly method. Compared to the curly (reduced graphene oxide)–(CdS nanowire) nanocomposites (CG) synthesized by a similar approach, CTG possesses a large 2D flat structure, which not only provides high optical transparency and a large surface area but also facilitates the migration of photogenerated electrons. This large 2D flat structure of CTG leads to increased optical absorption of visible light and increased electrical conductivity as compared to the curly CG, which is attributed to the fact that the large 2D flat structure of reduced graphene oxide (RGO) in CTG provides more efficient contact between light and the RGO sheets and facilitates the transfer of charge carriers. Experimental evidence has proven that negatively charged TiO2 nanoparticles (NPs) both on the surfaces of the CdS nanowires (CdS NWs) and on the RGO sheets can prevent the RGO sheets from becoming curly or aggregated as a result of electrostatic repulsion, thereby forming the large 2D flat structure of CTG. In addition to using RGO as an electron “sink” to improve the transfer of photogenerated electron–hole pairs (EHPs) from CdS NWs, the TiO2 NPs on CdS NWs are able to further boost the transfer of charge carriers in the ternary CTG system due to the suitable energy band match between TiO2 and CdS. Such efficient, spatially separated charge carriers make CTG a versatile visible light photocatalyst for photo-redox processes. This work provides a new, simple strategy to construct these large 2D flat structured RGO-based multi-component composites by using the surface charge properties of materials to efficiently utilize their respective unique electronic properties toward diverse photo-redox processes in both energy conversion and environmental purification.

In2S3–carbon nanotube (In2S3–CNT) nanocomposites have been prepared via a facile refluxing wet chemistry process. The as-synthesized In2S3–CNT nanocomposites can be used as selective and active visible-light-driven photocatalysts toward hydrogenation of nitroaromatics to amines in water. Photoirradiation (λ > 420 nm) of In2S3–CNT photocatalysts suspended in water containing nitroaromatics produces the corresponding amines with high yields. The control experiments reveal that an inert atmosphere and the addition of a hole scavenger are both indispensable for the visible-light-driven photocatalytic hydrogenation of nitroaromatics over In2S3–CNT. In comparison with blank In2S3, the obviously enhanced photocatalytic performance of the In2S3–CNT photocatalyst is mainly ascribed to the unique physicochemical properties of CNTs, which enhances the adsorptivity of the substrate and performs as an electron reservoir to trap electrons, thereby hindering the recombination of photogenerated electron–hole pairs. It is hoped that the current work on the facile synthesis of semiconductor In2S3–CNT nanocomposites can broaden the applications of semiconductor-carbon based composite photocatalysts in the field of photocatalytic selective organic transformations under mild conditions.

ZnIn2S4–graphene (GR) nanocomposites have been fabricated by a low-temperature and one-step wet chemistry process, during which the formation of ZnIn2S4 nanosheets, the reduction of graphene oxide (GO) and intimate interfacial contact between them were achieved simultaneously. The as-prepared ZnIn2S4–GR exhibited remarkably enhanced visible light photocatalytic performance toward selective reduction of nitroaromatics to amines in water compared to blank ZnIn2S4. Controlled experiments have been carried out and revealed that an inert atmosphere and the addition of a hole scavenger are two important conditions for photocatalytic selective reduction of nitroaromatics over ZnIn2S4–GR. In comparison with blank ZnIn2S4, the remarkably enhanced photocatalytic performance of ZnIn2S4–GR can be mainly attributed to the integrative effect of the unique physicochemical properties of GR and the intimate interfacial contact between ZnIn2S4 and GR. Specifically, the introduction of GR into the matrix of ZnIn2S4 can significantly influence the morphology and structure of the samples owing to the “structure-directing” role of GO, enhance the adsorptivity of the substrate, and effectively promote the separation and transfer of photogenerated charge carriers, thereby contributing to the photoactivity enhancement. It is hoped that the current work on the facile synthesis of ZnIn2S4–GR nanocomposites can broaden the applications of ZnIn2S4–GR and other GR-based nanocomposites as visible-light-driven photocatalysts toward selective organic transformations under mild conditions.

A series of uniform ZnO nanospheres–reduced graphene oxide nanocomposites (ZnO–RGO NCs) with different weight addition ratios of RGO are successfully synthesized via a facile yet efficient method by intimately coating ZnO nanospheres (NSs) with RGO, which is afforded by electrostatic attraction between positively charged ZnO NSs and negatively charged graphene oxide (GO) in an aqueous medium at room temperature. The photocatalytic test of degradation of Rhodamine B shows that the optimal ZnO–10% RGO NCs exhibit a 5-fold enhancement of photoactivity than bare ZnO NSs, which is ascribed to the integrative synergetic effect of enhanced adsorption capacity, the decreased recombination of the electron–hole pairs and the enhanced ultraviolet light absorption intensity. Significantly, the recycled photoactivity tests show that, for ZnO–RGO NCs, the anti-photocorrosion of ZnO NSs is improved remarkably which is attributed to the effective hybridization of ZnO NSs with the RGO sheet via intimate surface coating. Such a significant photoactivity enhancement and anti-photocorrosion phenomenon can not be obtained by simply integrating RGO with ZnO NSs that are not subject to surface charge modification, which thus indicates the importance of intimate surface coating of ZnO with RGO toward the efficiency of enhancement of photoactivity and particularly the anti-photocorrosion of ZnO.

Graphene (GR) has proven to be a promising candidate to construct effective GR-based composite photocatalysts with enhanced catalytic activities for solar energy conversion. During the past few years, various GR-based composite photocatalysts have been developed and applied in a myriad of fields. In this perspective review, compared with the traditional applications of GR-based nanocomposites for the “non-selective” degradation of pollutants, photo-deactivation of bacteria and water splitting to H2 and O2, we mainly focus on the recent progress in the applications of GR-based composite photocatalysts for “selective” organic transformations, including reduction of CO2 to renewable fuels, reduction of nitroaromatic compounds to amino compounds, oxidation of alcohols to aldehydes and acids, epoxidation of alkenes, hydroxylation of phenol, and oxidation of tertiary amines. The different roles of GR in these GR-based nanocomposite photocatalysts such as providing a photoelectron reservoir and performing as an organic dye-like macromolecular photosensitizer have been summarized. In addition, graphene oxide (GO) as a co-catalyst in GO–organic species photocatalysts and GO itself as a photocatalyst for selective reduction of CO2 have also been demonstrated. Finally, perspectives on the future research direction of GR-based composite photocatalysts toward selective organic redox transformations are discussed and it is clear that there is a wide scope of opportunities awaiting us in this promising research field.

The development of high-performance artificial photosynthesis systems is central to taking advantage of solar energy to alleviate the environmental and energy crises. Integrating different functional materials ingeniously into an oriented nanoarchitecture holds great promise for constructing more efficient photocatalytic systems with additional structure-directing merits. Here we report an all-solid-state vectorial Z-scheme photosynthetic system composed of vertically aligned ZnO–Au@CdS core–shell nanorod arrays prepared via a heteroepitaxial growth process. Resulting from the synergistic effects of the three functional components integrated in this nanoarray structured system, the photocatalytic efficiency of the optimal ternary ZnO–Au@CdS hybrid is ca. 79 and 28 times higher than that of ZnO and ZnO–Au counterparts, respectively, toward selective reduction of aromatic nitro compounds in water under simulated sunlight irradiation, and even 1.5 times as high as that of the direct Z-scheme featured ZnO@CdS system due to the effective vectorial Z-scheme electron transfer process. Furthermore, the ZnO–Au@CdS nanorod arrays with a film structure are readily recycled and highly stable under the present reaction conditions. This work demonstrates a paradigm for constructing an all-solid-state Z-scheme artificial photosynthetic system favoring enhanced light harvesting, efficient charge separation and transfer, easy recycling and good photostability toward solar energy conversion.

The morphological characteristics of metal play a pivotal role in affecting the activity of metal–semiconductor composite photocatalysts for solar energy conversion. In this article, geometry- and size-controlled sub-20 nm Pd nanocubes (NCs) have been fabricated and hybridized with 2D TiO2 nanosheets (TNS) to explore how the geometry and size of Pd influences the photocatalytic efficiency of Pd-based semiconductor composites. The photoactivity results evaluated by the dual-function photocatalytic system for simultaneous H2 evolution and 1,1-diethoxyethane (DEE) production suggest that Pd NCs endow TNS with a greatly enhanced photoactivity compared to Pd nanoparticles (NPs) supported on 2D TNS. The activation energy for H2 generation and the adsorption affinity between Pd and hydrogen molecules can be modulated by the geometry differences between Pd NCs and Pd NPs. Meanwhile, the activity of TNS–Pd NCs composites can be increased by decreasing the size of the Pd NCs from 17 to 7 nm, which is predominantly attributed to the more efficient capability of small Pd NCs to boost the separation and transportation of photoexcited electron–hole pairs. Our work not only fundamentally elucidates the relationship between the morphological characteristics of metal Pd and the photoactivity of Pd-based semiconductor composites, but also supplies a dual-purpose sustainable way for simultaneous H2 evolution and organic synthesis of fine chemicals.

Tremendous interest is devoted to fabricating numerous graphene (GR)–semiconductor composites toward improved conversion of solar energy, resulting from the observation that the photogenerated electrons from semiconductors (e.g., TiO2, CdS) can be readily accepted or shuttled in the two-dimensional (2D) GR sheet. Yet although the hunt is on for GR–semiconductor composite based photoredox applications that aim to exploit the remarkable electronic conductivity of GR, the work necessary to find out how it could best be harnessed to improve the photocatalytic performance of semiconductors remains scanty. In this review, we highlight a few problems associated with improving the photocatalytic performance of semiconductors via methodological coupling with GR. In particular, we address strategies for harnessing the structure and electronic conductivity of GR via strengthening the interfacial contact, optimizing the electronic conductivity of GR, and spatially optimizing the interfacial charge carrier transfer efficiency. Additionally, we provide a brief overview of assembly methods for fabricating GR–semiconductor composites with controllable film infrastructure to meet the requirements of practical photocatalytic applications. Finally, we propose that, only with the principle of designing and understanding GR–semiconductor composites from a system-level consideration, we might get better at imparting the power of GR with unique and transformative properties into the composite system.