•Bi2S3 nanorod films were successfully fabricated by a multi-step preparation route.•Bi2S3 nanorod films can produce H2 through the photocatalytic splitting of H2S.•Our route can be used to prepare other Bi based films for various applications.Photocatalytic splitting of H2S into H2 is beneficial for environmental remediation and clean energy production. However, the conventional photocatalyst in powder form is difficult to recover. In this work, Bi2S3 nanorod films are fabricated via the conversion of Bi films by annealing and hydrothermal treatment. The hydrothermal reaction time has a significant influence on the performance of photocatalytic splitting H2S to H2 over these samples. The optimized hydrothermal treatment time is 24 h. Photocurrent and electrochemical impedance spectroscopy confirm that the Bi2S3 nanorod film obtained under this condition has an effective separation of electron-hole pairs, leading to enhanced photocatalytic activity.Download high-res image (142KB)Download full-size image

•BN-modified PVA aerogel was successfully fabricated through direct frozen-drying of PVA and BN solution.•The introduction of BN nanosheets significantly changes the wettability from hydrophily to hydrophobicity.•PVA connects with BN nanosheets through the formation of hydrogen bonds.•BN-modified PVA aerogel shows great promising application in wastewater treatment.•PVA aerogel can be modified by different inorganic materials with various functions.Macroscopic polyvinyl alcohol (PVA) aerogel is of great interest in environmental remediation due to its low cost and easy fabrication. However, the hydrophily of PVA aerogel limited its application in oil-water separation. In this work, boron nitride (BN)-modified PVA aerogel has been successfully prepared by a cost-effective frozen-drying method. PVA plays a role as a scaffold of aerogel to support BN nanosheets which can modify the surface properties of PVA aerogel, resulting in a dramatic change of wettability from hydrophily (0°) to hydrophobicity (94.9°–100.8°). Moreover, the obtained BN-modified PVA aerogel possesses a favorable porous structure, low density (41.8–60.0 mg/cm3) and good adsorption capacity (12–38 g/g), which make it a promising wastewater treatment material. Importantly, PVA aerogel with other functions can be easily fabricated through coupling with other inorganic materials by this strategy, which can provide various promising applications for environmental remediation.Download high-res image (115KB)Download full-size image

•MnS/In2S3 composites present impressive high activity and superior stability for H2 production from H2S.•A maximum H2 production rate of 8360 μmol g−1 h−1 can be achieved over MnS/In2S3.•The addition of SO32− and S2− can suppress the formation of yellow S22− and solid S, favoring the long-term H2 production.Large amounts of sulfide or sulfite have been extracted from fossil energy resources, which call for green strategies to utilize them. In this study, hydrogen production and H2S removal are simultaneously achieved over MnS/In2S3 composite photocatalysts. Highly active MnS/In2S3 composite photocatalysts were synthesized via a solvothermal route. The photocatalytic activities depend on their compositions. A maximum H2 production rate of 8360 μmol g−1 h−1 can be achieved over a MnS/In2S3 with optimized composition, which is approximately 2090 times higher than that of pristine α-MnS and 50 times higher than that of β-In2S3 alone. The corresponding quantum efficiency of this sample is as high as 34.2% at 450 nm even in the absence of any noble-metal co-catalysts. Importantly, MnS/In2S3 composite displays a good stability and anti-photocorrosion, which provides a strategy for scaling up the H2 production from byproducts at petrochemical plants for energy applications.Download high-res image (180KB)Download full-size image

Layered bismuth oxychloride (BOC) exhibits highly efficient activity for photocatalytic environmental remediation due to the confinement effect induced excitonic photocatalytic process. However, the strong excitonic process suppresses catalytic reactions with photo-induced electrons, such as hydrogen generation, CO2 conversion and nitrogen fixation. Moreover, the wide band gap of BiOCl limits its application under visible light. In this study, flexible BiOCl nanosheets with oxygen vacancies (BOC-OV) were successfully prepared. Molecular oxygen activation, electronic spin resonance (ESR), transient photocurrent, transient absorption spectroscopy, and transient fluorescence spectroscopy indicated that oxygen vacancies induced exciton dissociation of flexible BiOCl nanosheets. Moreover, oxygen vacancies induced wide spectrum (UV-Vis) absorption. The enhanced exciton dissociation resulted in the superior CO2 conversion of BOC-OV under UV-Vis light irradiation, where the light to carbon monoxide (LTCO) conversion efficiency reached up to 26.5 × 10−6. Theoretical calculations and in situ Fourier transform infrared spectrometry (FT-IR) analysis revealed that the mechanism of oxygen vacancies improves the photocatalytic CO2 conversion with BOC-OV via the CO2 hydrogenation pathway. This study indicates that oxygen vacancies have a great influence on photocatalytic CO2 reduction due to their special surface and electron structure properties.

Layered bismuth oxychloride (BOC) exhibits highly efficient activity for photocatalytic environmental remediation due to the confinement effect induced excitonic photocatalytic process. However, the strong excitonic process suppresses catalytic reactions with photo-induced electrons, such as hydrogen generation, CO2 conversion and nitrogen fixation. Moreover, the wide band gap of BiOCl limits its application under visible light. In this study, flexible BiOCl nanosheets with oxygen vacancies (BOC-OV) were successfully prepared. Molecular oxygen activation, electronic spin resonance (ESR), transient photocurrent, transient absorption spectroscopy, and transient fluorescence spectroscopy indicated that oxygen vacancies induced exciton dissociation of flexible BiOCl nanosheets. Moreover, oxygen vacancies induced wide spectrum (UV-Vis) absorption. The enhanced exciton dissociation resulted in the superior CO2 conversion of BOC-OV under UV-Vis light irradiation, where the light to carbon monoxide (LTCO) conversion efficiency reached up to 26.5 × 10−6. Theoretical calculations and in situ Fourier transform infrared spectrometry (FT-IR) analysis revealed that the mechanism of oxygen vacancies improves the photocatalytic CO2 conversion with BOC-OV via the CO2 hydrogenation pathway. This study indicates that oxygen vacancies have a great influence on photocatalytic CO2 reduction due to their special surface and electron structure properties.

In this study, we report a self-template hydrothermal method for the synthesis of ATiO3 (A = Ba, Pb, and Sr) perovskites using anatase TiO2 nanosheets as precursors. Under hydrothermal conditions, ATiO3 with different structures and morphology can be obtained. These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The growth mechanism of ATiO3 was explored by XRD evaluation over different reaction time, and it was observed that PbTiO3 grows most slowly among all the samples including BaTiO3, SrTiO3, BaxPb1−xTiO3 and SrxPb1−xTiO3. The diffusion of A site sources to the solid surface and the reaction at solid/liquid interface could dominate the growth of ATiO3. All the as-prepared samples exhibited activities toward photocatalytic oxidation of NO at ppb level. Specifically, PbTiO3 has revealed the highest activity under both full spectrum and visible-light irradiation (λ > 420 nm), whereas BaTiO3 exhibited best selectivity for the formation of ionic species (NO3−), which could be ascribed to different electronic structures and charge separation efficiency of ATiO3. This study provides some important hints to tune the photocatalytic performances (activity and selectivity) of ATiO3 through the modification of A site elements.

Recently, non-noble metals with plasmonic properties have attracted great attention due to their potential applications in photocatalytic solar-energy conversion. However, in contrast to the well-studied plasmonic noble metals (mainly Au and Ag), which have distinct absorption peaks, the understanding of light absorption and the photocatalytic reaction mechanism of non-noble metals is far less. In this study, semimetal bismuth films are deposited on fluorine-doped tin oxide substrates by a dc magnetron sputtering method. Both theoretical calculation and UV-vis absorption spectra confirm that the field enhancement and location of plasmonic resonance peaks are strongly correlated with the size of Bi particles. Through tuning the sputtering power, for the first time, four distinct absorption peaks are observed over isolated Bi particles. Moreover, it is found that the energy barrier for the conversion of NO into NO2 over Bi is even lower than that with Au nanoclusters. Thus, Bi films are highly active for photocatalytic oxidation of NO. Moreover, the low NO2 desorption energy over Bi indicates that Bi films can be the main active sites during the reaction process and that they possess good stability.

In this study, DFT-D calculations were performed to explore the role of Cu and Mo loading in the CO2 conversion mechanism on a two-dimensional g-C3N4(001) surface. The introduced transition metals, Cu and Mo, significantly changed the electron distribution and band structures of g-C3N4. Moreover, two possible mechanisms for the reduction of CO2 to CO have been discussed in detail. We found that the energy barriers of the two mechanisms were largely reduced by Cu and Mo loading, and the dominant reaction path changed on different transition metal-loaded surfaces. Cu/g-C3N4(001) prefers to directly dissociate CO2 into CO, whereas cis-COOH is the preferred product of CO2 reduction on Mo/g-C3N4(001). Considering the activation barrier and reaction route selectivity, Mo-doped g-C3N4(001) was identified as a promising candidate for CO2 conversion. It is concluded that suitable transition metal doping can efficiently reduce the energy barrier and control route selectivity along the reaction paths over the g-C3N4 surface. These findings could provide a helpful understanding of the CO2 reduction mechanisms and aid in the molecular design of novel g-C3N4 catalysts for CO2 conversion.

In this work, the influence of the terminating or exposed crystal planes of anatase TiO2 support on the catalytic activity of Pt/TiO2 catalysts is reported. Strong effects were observed when using CO oxidation as a probe reaction. The CO oxidation activity over these catalysts ranks in the following order: Pt/TiO2-{101} > Pt/TiO2-{100} > Pt/TiO2-{001}. The combination of in situ X-ray absorption spectroscopy, X-ray emission spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory calculations unravelled a strong interaction between platinum particles and different dominating facets of anatase. The catalytic activity of the Pt/TiO2 catalysts can be correlated with the spectroscopic/structural results. Compared to {001} facets, the {100} and {101} facets of TiO2 can stabilize active highly dispersed Pt species and avoid sintering Pt particles. This finding provides some important insights into understanding the metal–support interfacial interactions of Pt/TiO2 catalysts for tuning their catalytic performance.Keywords: CO oxidation activity; crystal facets; metal−support interaction; operando XAS/DRIFTS; Pt/TiO2 catalyst

The development of efficient visible-light responsive macroscopic photocatalysts is crucial for the commercialization of photocatalysis due to the difficult recovery process of photocatalyst nanoparticles. However, it remains a great challenge to achieve macroscopic photocatalysts which cannot only be successfully recycled, but also possess admirable visible-light driven photocatalytic activity. Here we report a one-step cryodesiccation route to fabricate ultra-light and recyclable C3N4/graphene oxide (GO) aerogel. This simple and mild synthesis means that it can be carried out in various containers, which greatly extends the shape and size of C3N4/GO aerogel. The obtained aerogel exhibits both an excellent adsorption capacity for oil, organic solvents, and dyes, and an enhanced visible-light photocatalytic activity toward the degradation of dyes and the oxidation of NO at a ppb level. The successful fabrication of such a fascinating multifunctional aerogel paves the way to integrate 2D lamellar powders into 3D macroscopic photocatalysts for commercial applications in photocatalysis as well as oil remediation.

•The residual precursor ions affect the charge/discharge performances of WO3.•Lithiated monoclinic WO3 reveals the best discharge capacity.•Lithiation can enhance the conductivity of WO3.Suitable host structure for lithium insertion and extraction is crucial for lithium-ion batteries. Tungsten trioxides (WO3) are particularly interesting materials for this purpose. In this work, the influences of structure and composition of WO3 on the charge/discharge performances of Li-ion batteries are systematically investigated. Firstly, lithiated tungsten trioxides (Li-WO3) are successfully synthesized by a hydrothermal method followed by annealing at different temperatures (200–600 °C). It is found that the hexagonal framework collapses and gradually transforms to the monoclinic phase due to the release of NH4+ and NH3 molecules. Unexpectedly, monoclinic WO3 reveals better performances than that of hexagonal WO3. Among all the investigated samples, the lithiated WO3 annealed at 500 °C exhibits the highest discharge capacity and cycle performance (703 mAh g−1 after 10 cycles). We believe that the Li+ remained in the solid structure of WO3 can lead to a more stable structure. In addition, Li+ could inhibit the oxidation of W5+ during the heat treatment process, which increases the electron conductivity of WO3. Our results indicate that the electrochemical properties of WO3 are strongly related to the residual precursor and crystal structure.

Hydrogen evolution through photocatalysis is promising with respect to the environmental problems and challenges of energy shortage that we encounter today. In this paper, we have combined graphene quantum dots (GQDs) and {001} faceted anatase TiO2 (with an exposed percentage of 65–75%) together for effective photocatalytic hydrogen evolution. A series of characterizations including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and UV-visible absorption spectroscopy have been carried out to study the structure of the as-prepared GQDs/{001}TiO2 composite. It turns out that GQDs could be effectively decorated on {001}TiO2 sheet without changing its intrinsic structure. With an optimum loading amount of GQDs (0.5 wt% to {001}TiO2), GQDs/{001}TiO2 exhibits a hydrogen evolution efficiency 8 times higher than that of bare {001}TiO2, which is a significantly more obvious improvement than many other photocatalytic systems relevant to GQDs and TiO2 hybrids. In addition, GQDs/{001}TiO2 could stand long-term photocatalytic experiments. Photocurrent tests show that such an improvement of the photocatalytic efficiency over GQDs/{001}TiO2 may originate from a higher charge separation efficiency. The present study could offer reference for the construction of photocatalytic hydrogen evolution systems with low cost and long term stability.

Spin-polarized DFT+U computations have been performed to investigate the role of oxygen vacancies in dissociating H2S on the rutile TiO2(110) surface. A bridged O2c atom is demonstrated to be the most energetically favorable oxygen vacancy site, which makes V(O2c) an electron donator center and induces an isolated defect level with narrowed band gaps. A H2S molecule is adsorbed dissociatively over V(O2c), but molecularly on the perfect surface. For H2S dissociation, the HS/H intermediate state reveals the best thermal stability on both defected and perfect surfaces. Moreover, potential energy surface analysis shows that V(O2c) reduces markedly the energy barriers for the paths along H2S dissociation. This indicates oxygen vacancies to be efficient trap centers for H2S dissociation, as evidenced by a significant interfacial charge transfer promoted by vacancies. This work could provide insights into the role of oxygen vacancies in facilitating the decomposition of H2S on rutile TiO2(110) surface.

Graphene aerogels (GAs) are widely studied in the oil contamination field in recent years. Among the preparation approaches, hydrothermal treatment employing a certain reducing agent has attracted much attention owing to the environmentally friendly and facile synthesis process. In this work, we systematically investigate the effects of various reducing agents including ammonia, ethanediamine (EDA) and vitamin C (VC) at different hydrothermal temperatures (80, 100, 120, 140, 160 and 180 °C) and reaction times (4, 8, 12, 16, 20 and 24 h) on the density, specific surface area (SSA), strength, morphology and adsorption performance of GAs. The results reveal that GAs reduced by VC possess the most outstanding performance for mechanical strength and re-utilization but have poor adsorption capacity (Qwt), whereas the sample obtained with ammonia exhibits the highest Qwt for both lube (160 g g−1) and n-hexane (105 g g−1). However, this sample not only reveals the worst mechanical strength which leads to a sharp decrease of the Qwt during the adsorption–squeezing experiments, but GA reduced by ammonia is also very sensitive to the reaction time and temperature. Therefore, EDA is a very promising reducing agent for the hydrothermal process as the resulting GA can maintain a high Qwt and reveals a wide hydrothermal preparation window.

•BiOCl is more active towards photodegradation of RhB under visible light than UV–visible light.•The oxygen vacancy is in situ formed during the UV–vis or UV light irradiation in BiOCl.•The acceptor level formed by oxygen vacancy inhibits the formation of O2−·O2−·.BiOCl nanoplates with exposed {001} facets exhibited ∼3 times higher efficiency (k = 0.034 min−1) towards photodegradation of Rhodamine B under visible light (183 mW/cm2) than that (k = 0.012 min−1) under UV–visible light (196 mW/cm2) irradiation. It is found that oxygen vacancy could be easily in situ formed in the {001} facets of BiOCl under UV–visible or UV light irradiation. Hence, the acceptor level under the conduction band (CB) of BiOCl formed by oxygen vacancy could trap the energetic electrons and inhibit the creation of O2−·O2−· due to its weaker reductive ability. Our current work reveals oxygen vacancy does not always play a positive role for photodegradation of organic dyes.BiOCl nanoplates with exposed {001} facets revealed ∼3 times faster towards photodegradation of RhB under visible light than that under UV–visible light, which could be attributed to the in situ generation of oxygen vacancy under UV light irradiation.

•A facile route for MoS2-PVP aerogels by direct frozen-drying was reported.•PVP plays a significant role in the modification of MoS2 and formation of aerogels.•The density of aerogels can be tuned through changing the concentrations of precursors.•This route can be applied to prepare aerogels from many 1D or 2D materials.Three-dimensional (3D) aerogels with low density, high porosity and large surface area have attracted increasing attention and exhibit numerous applications. However, the material types of aerogels are still very limited. Herein, we report a facile synthesis route to prepare MoS2-polyvinylpyrrolidone (PVP) aerogels via direct frozen-drying from primitive solution with PVP, which plays a key role to obtain aerogels. The good wettability both on water and oil of PVP makes it easily cover on the surface of MoS2 nanosheets, which promotes the sheets connection with each other. The density of the obtained MoS2-PVP aerogels can be tuned from 9.2 to 33.8 mg/cm3 via simply changing the concentrations of the precursors. Importantly, our current approach has been successfully applied to prepare other 2D or 1D material-PVP aerogels, taking boron nitride-PVP and carbon nanotubes-PVP aerogels as examples.

Carbon nanotubes (CNTs) have good toughness and hydrophobicity. The embedding of CNTs into a graphene aerogel (GA) network could modify various properties of the GA. In this work, we report a facile and green approach to synthesize graphene–CNT aerogels (GCAs) by a one-step hydrothermal redox reaction. The prepared aerogels possess ultra-light densities ranging from 6.2–12.8 mg cm−3. The incorporation of CNTs into the GA could not only improve the morphologies, specific surface areas and hydrophobic properties but also enhance the adsorption capacity and mechanical properties of the GA. Under optimized GO/CNT mass ratio (7:1 and 3:1) conditions, adsorption capacities 100–270 times of their own weight could be achieved depending on the density of the adsorbed organics. The same trend also appeared in the adsorption of dyes including methylene blue (MB) and methyl orange (MO). Especially, the obtained GCAs exhibited excellent reusability and mechanical strength on the basis of absorption–combustion and adsorption–squeezing experiments. Even after 10 cycles, the macroscopic shape of the aerogels is well kept and almost no decrease in adsorption capacity was observed. Based on the facile preparation process, high adsorption capacity and stable cyclic performance, the GCAs could have promising widespread applications in practical water purification and oil remediation.

Polyaniline (PANI)-decorated {001} facets of Bi2O2CO3 nanosheets were synthesized by a low-temperature chemical method. We demonstrate that the strong interfacial interactions between Bi2O2CO3 {001} facets and PANI could promote in situ formation of oxygen vacancy at the interface confirmed by both density functional theory calculations and electron spin resonance experiments, which is due to the high oxygen density characteristic of Bi2O2CO3 {001} facets. In addition, such interfacial interaction also leads to a 0.38 eV positive shifting of the valence band of Bi2O2CO3. Importantly, the decorated PANI can stabilize these interfacial oxygen vacancies. Therefore, the migration and separation of photogenerated carriers have been improved significantly evidenced by electrochemical impedance spectroscopy, photoluminescence, and nanosecond time-resolved fluorescence-decay spectra, resulting in a 4.5 times higher activity toward photodegradation of Rhodamine B and a 6 times higher photocurrent density compared to their corresponding bare Bi2O2CO3. The finding of the in situ oxygen vacancy formation at the interface could provide some hints for the deep understanding of the interactions between PANI and crystal facets of semiconductors to develop highly efficient photocatalysts.Keywords: Bi2O2CO3/PANI; crystal facets; interfacial interaction; oxygen vacancy; photocatalysis

Herein, β-Bi2O3 nanosheets exposed with active {001} facets were facilely prepared through annealing Bi2O2CO3 with thermally stable {001} facets. The enhanced photocatalytic activity of β-Bi2O3 was ascribed to the high energy of {001} facets and the efficient charge separation. This 2D surface transformation strategy could shed new light on the fabrication of energetic facets and the development of highly active photocatalysts.

Reduced graphene oxide (RGO) has been demonstrated to be effective in enhancing the photocatalytic activity of various semiconductors. However, an important issue that has been overlooked is the role of RGO in UV-induced photocatalysis of RGO-based nanocomposites. In the present work, novel BiOIO3/RGO nanocomposites were prepared by a simple one-pot hydrothermal method, during which BiOIO3 nanoplates were formed in situ on RGO sheets resulting from partial reduction of RGO. The two components of the composite displayed intimate interfacial contact. The as-prepared BiOIO3/RGO nanocomposites exhibited highly enhanced visible photocatalytic activity, relative to that of pure BiOIO3, toward removal of NO from air. However, the BiOIO3/RGO nanocomposites showed only slightly increased photocatalytic activity, relative to pure, under UV irradiation. The limited enhancement of UV activity can be ascribed to the fact that BiOIO3 would be expected to compete with RGO with regard to absorption and utilization of UV light. Evidence shows that RGO can act as a semiconductor rather than a photosensitizer or electron reservoir in BiOIO3/RGO nano-composites. In addition, the active species responsible for photoactivity have been investigated by a DMPO spin-trapping electron spin resonance technique. Photo-generated holes were found to be the main active species inducing the photo-oxidation of NO under visible light, whereas holes and OH radicals are considered to be responsible for photo-activity under UV light. This work points to BiOIO3/RGO nano-composites as new and efficient visible light photocatalysts for environmental remediation applications, and also as a source of new insights into the pivotal role of RGO in photocatalysis of RGO-based nanocomposites under visible as well as UV light.

•W/Mo co-doped BiVO4 were prepared by hydrothermal method.•W/Mo co-doping could promote the effective separation of photogenerated carriers compared to pure BiVO4.•W/Mo co-doped BiVO4 exhibited higher photocatalytic activity toward the degradation of HPAM.Polymer flooding is an effective way to enhance oil recovery (EOR). However, the treatment of the oily wastewater becomes an urgent issue. Photocatalysis is a promising approach for this purpose. In this report, W/Mo co-doped BiVO4 particles are synthesized by hydrothermal method. W/Mo co-doping could promote an effective separation of photogenerated carriers reflecting from the 6 times higher photocurrent density compared to pure BiVO4. The photodegradation of partially hydrolyzed polyacrylamide (HPAM) over 0.5 at.% W and 1.5 at.% Mo co-doped BiVO4 is 43% under UV–vis light irradiation for 3 h, which is much higher than that of pure BiVO4 (18%).W/Mo co-doping could promote the effective separation of photogenerated carriers reflecting from the 6 times higher photocurrent compared to pure BiVO4. Therefore, W/Mo co-doped BiVO4 exhibited higher photocatalytic activity toward the degradation of partially hydrolyzed polyacrylamide.

Elemental photocatalysts have recently been proposed as interesting materials to be used as alternatives to conventional semiconductor compounds. In this study, we demonstrate that not only elements with semiconducting properties are photocatalytically active by introducing semimetallic bismuth for the photooxidation of NO. Black Bi films were prepared via an electrochemical deposition approach. Both density functional theory (DFT) calculations and temperature dependence electrical resistivity measurements pointed out that the obtained films exhibited semimetallic behavior. The Bi films were easily oxidized upon exposure to air. However, electrochemical reduction of the surface amorphous oxide layer led to a more than 4-fold enhancement of the photocurrent density of the Bi films. The detection of hydroxyl radicals with electron spin resonance (ESR) investigations further confirmed the photogeneration of electrons and holes. A 37.7% removal ratio of NO over Bi films was observed under UV light irradiation with no significant reduction of photocatalytic activity after five cycles. Given that the conduction and valence bands of semimetallic Bi overlap, the associated excitation processes are more complex in comparison with semiconductor photocatalysts, thereby indicating a different photocatalytic mechanism. The present study points out new directions for developing semimetallic photocatalysts.

The photocatalytic performance of Bi2WO6 was limited by slow electron transfer and fast charge recombination. In this report, Bi2WO6/graphene (2 wt%) composites were fabricated by a two-step approach using graphene as precursor, which can maintain the crystallinity, morphology and particle size of pristine hierarchical Bi2WO6 microspheres, providing unique opportunities to correlate interfacial interaction with photocatalytic activity. The interfacial electronic interaction between Bi2WO6 and graphene evidenced by X-ray photoelectron spectroscopy (XPS) resulted in positive shifting of the Fermi level and broadening of the valence band (VB) of Bi2WO6. These reveal a stronger oxidative power and faster mobility of photogenerated holes upon excitation, in combination with radical trapping and electron spin resonance (ESR) experiments providing clear evidence for this key property. Compared to pristine Bi2WO6, the composites exhibited not only higher photocatalytic activity toward the oxidation of NO, but also better selectivity for the formation of ionic species (NO3−) as well as a ninefold enhancement of the photocurrent density. The significantly improved charge separation and migration in the Bi2WO6/graphene composite was demonstrated by electrochemical impedance spectroscopy (EIS). Moreover, the interfacial electron transfer rate determined for the composite was 7.97 × 108 s−1via time-resolved fluorescence decay spectra. It was therefore proposed that the enhanced photocatalytic activity of Bi2WO6/graphene could be directly ascribed to the deeper VB edge position as well as efficient charge transfer across the interface. The present study points out the key role of graphene in tuning electronic structure and interfacial charge transfer processes for the development of highly efficient photocatalysts.

•Hierarchical Bi2WO6 microshperes as photocatalyst.•Enhancing photocatalytic activities and PEC performances under acidic condition.•Energy band diagram of Bi2WO6 at different pHs.Visible-light induced degradation of Rhodamine B (RhB) over hierarchical Bi2WO6 microspheres at different pHs was studied. It was observed that the initial pH values have a significant effect on the photodegradation efficiency of RhB. The photoelectrochemical experiments were performed to understand the influences of pH values. Both the enhanced efficiency of photoinduced electron–hole separation and more positive of the valence band top of Bi2WO6 under acidic conditions favor the enhancement of photocatalytic activities.The initial pH values have a significant effect on the photodegradation efficiency of Rhodamine B over hierarchical Bi2WO6 microspheres. Photoelectrochemical studies indicate that both the enhanced efficiency of photoinduced electron–hole separation and more positive EVB of Bi2WO6 under acidic conditions favor the enhancement of photocatalytic activities.

Three-dimensional (3D) carbon-based architectures with their macroscopic monolithic shapes, well-defined interconnected porous networks, large surface areas and excellent adsorption capacities have received extensive attention in the field of environmental remediation. Given the frequent occurrence of oil spills, the demand for 3D carbon materials for oil remediation has increased very rapidly in recent years; however, considerable synthesis and functionalization studies remain to be performed to fully exploit their applications. This review aims to give an overview of the synthesis, modification and functionalization of 3D carbon-based architectures for oil remediation. In particular, we highlight novel monolithic materials with multifunctions such as photocatalytic activity, which can not only play a role as adsorbents but can also photocatalytically degradate oil.

Elemental photocatalysts have recently been proposed as interesting materials to be used as alternatives to conventional semiconductor compounds. In this study, we demonstrate that not only elements with semiconducting properties are photocatalytically active by introducing semimetallic bismuth for the photooxidation of NO. Black Bi films were prepared via an electrochemical deposition approach. Both density functional theory (DFT) calculations and temperature dependence electrical resistivity measurements pointed out that the obtained films exhibited semimetallic behavior. The Bi films were easily oxidized upon exposure to air. However, electrochemical reduction of the surface amorphous oxide layer led to a more than 4-fold enhancement of the photocurrent density of the Bi films. The detection of hydroxyl radicals with electron spin resonance (ESR) investigations further confirmed the photogeneration of electrons and holes. A 37.7% removal ratio of NO over Bi films was observed under UV light irradiation with no significant reduction of photocatalytic activity after five cycles. Given that the conduction and valence bands of semimetallic Bi overlap, the associated excitation processes are more complex in comparison with semiconductor photocatalysts, thereby indicating a different photocatalytic mechanism. The present study points out new directions for developing semimetallic photocatalysts.

The development of efficient visible-light responsive macroscopic photocatalysts is crucial for the commercialization of photocatalysis due to the difficult recovery process of photocatalyst nanoparticles. However, it remains a great challenge to achieve macroscopic photocatalysts which cannot only be successfully recycled, but also possess admirable visible-light driven photocatalytic activity. Here we report a one-step cryodesiccation route to fabricate ultra-light and recyclable C3N4/graphene oxide (GO) aerogel. This simple and mild synthesis means that it can be carried out in various containers, which greatly extends the shape and size of C3N4/GO aerogel. The obtained aerogel exhibits both an excellent adsorption capacity for oil, organic solvents, and dyes, and an enhanced visible-light photocatalytic activity toward the degradation of dyes and the oxidation of NO at a ppb level. The successful fabrication of such a fascinating multifunctional aerogel paves the way to integrate 2D lamellar powders into 3D macroscopic photocatalysts for commercial applications in photocatalysis as well as oil remediation.

Spin-polarized DFT+U computations have been performed to investigate the role of oxygen vacancies in dissociating H2S on the rutile TiO2(110) surface. A bridged O2c atom is demonstrated to be the most energetically favorable oxygen vacancy site, which makes V(O2c) an electron donator center and induces an isolated defect level with narrowed band gaps. A H2S molecule is adsorbed dissociatively over V(O2c), but molecularly on the perfect surface. For H2S dissociation, the HS/H intermediate state reveals the best thermal stability on both defected and perfect surfaces. Moreover, potential energy surface analysis shows that V(O2c) reduces markedly the energy barriers for the paths along H2S dissociation. This indicates oxygen vacancies to be efficient trap centers for H2S dissociation, as evidenced by a significant interfacial charge transfer promoted by vacancies. This work could provide insights into the role of oxygen vacancies in facilitating the decomposition of H2S on rutile TiO2(110) surface.

In this study, DFT-D calculations were performed to explore the role of Cu and Mo loading in the CO2 conversion mechanism on a two-dimensional g-C3N4(001) surface. The introduced transition metals, Cu and Mo, significantly changed the electron distribution and band structures of g-C3N4. Moreover, two possible mechanisms for the reduction of CO2 to CO have been discussed in detail. We found that the energy barriers of the two mechanisms were largely reduced by Cu and Mo loading, and the dominant reaction path changed on different transition metal-loaded surfaces. Cu/g-C3N4(001) prefers to directly dissociate CO2 into CO, whereas cis-COOH is the preferred product of CO2 reduction on Mo/g-C3N4(001). Considering the activation barrier and reaction route selectivity, Mo-doped g-C3N4(001) was identified as a promising candidate for CO2 conversion. It is concluded that suitable transition metal doping can efficiently reduce the energy barrier and control route selectivity along the reaction paths over the g-C3N4 surface. These findings could provide a helpful understanding of the CO2 reduction mechanisms and aid in the molecular design of novel g-C3N4 catalysts for CO2 conversion.

The photocatalytic performance of Bi2WO6 was limited by slow electron transfer and fast charge recombination. In this report, Bi2WO6/graphene (2 wt%) composites were fabricated by a two-step approach using graphene as precursor, which can maintain the crystallinity, morphology and particle size of pristine hierarchical Bi2WO6 microspheres, providing unique opportunities to correlate interfacial interaction with photocatalytic activity. The interfacial electronic interaction between Bi2WO6 and graphene evidenced by X-ray photoelectron spectroscopy (XPS) resulted in positive shifting of the Fermi level and broadening of the valence band (VB) of Bi2WO6. These reveal a stronger oxidative power and faster mobility of photogenerated holes upon excitation, in combination with radical trapping and electron spin resonance (ESR) experiments providing clear evidence for this key property. Compared to pristine Bi2WO6, the composites exhibited not only higher photocatalytic activity toward the oxidation of NO, but also better selectivity for the formation of ionic species (NO3−) as well as a ninefold enhancement of the photocurrent density. The significantly improved charge separation and migration in the Bi2WO6/graphene composite was demonstrated by electrochemical impedance spectroscopy (EIS). Moreover, the interfacial electron transfer rate determined for the composite was 7.97 × 108 s−1via time-resolved fluorescence decay spectra. It was therefore proposed that the enhanced photocatalytic activity of Bi2WO6/graphene could be directly ascribed to the deeper VB edge position as well as efficient charge transfer across the interface. The present study points out the key role of graphene in tuning electronic structure and interfacial charge transfer processes for the development of highly efficient photocatalysts.

Carbon nanotubes (CNTs) have good toughness and hydrophobicity. The embedding of CNTs into a graphene aerogel (GA) network could modify various properties of the GA. In this work, we report a facile and green approach to synthesize graphene–CNT aerogels (GCAs) by a one-step hydrothermal redox reaction. The prepared aerogels possess ultra-light densities ranging from 6.2–12.8 mg cm−3. The incorporation of CNTs into the GA could not only improve the morphologies, specific surface areas and hydrophobic properties but also enhance the adsorption capacity and mechanical properties of the GA. Under optimized GO/CNT mass ratio (7:1 and 3:1) conditions, adsorption capacities 100–270 times of their own weight could be achieved depending on the density of the adsorbed organics. The same trend also appeared in the adsorption of dyes including methylene blue (MB) and methyl orange (MO). Especially, the obtained GCAs exhibited excellent reusability and mechanical strength on the basis of absorption–combustion and adsorption–squeezing experiments. Even after 10 cycles, the macroscopic shape of the aerogels is well kept and almost no decrease in adsorption capacity was observed. Based on the facile preparation process, high adsorption capacity and stable cyclic performance, the GCAs could have promising widespread applications in practical water purification and oil remediation.

Hydrogen evolution through photocatalysis is promising with respect to the environmental problems and challenges of energy shortage that we encounter today. In this paper, we have combined graphene quantum dots (GQDs) and {001} faceted anatase TiO2 (with an exposed percentage of 65–75%) together for effective photocatalytic hydrogen evolution. A series of characterizations including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and UV-visible absorption spectroscopy have been carried out to study the structure of the as-prepared GQDs/{001}TiO2 composite. It turns out that GQDs could be effectively decorated on {001}TiO2 sheet without changing its intrinsic structure. With an optimum loading amount of GQDs (0.5 wt% to {001}TiO2), GQDs/{001}TiO2 exhibits a hydrogen evolution efficiency 8 times higher than that of bare {001}TiO2, which is a significantly more obvious improvement than many other photocatalytic systems relevant to GQDs and TiO2 hybrids. In addition, GQDs/{001}TiO2 could stand long-term photocatalytic experiments. Photocurrent tests show that such an improvement of the photocatalytic efficiency over GQDs/{001}TiO2 may originate from a higher charge separation efficiency. The present study could offer reference for the construction of photocatalytic hydrogen evolution systems with low cost and long term stability.