F− substituted Bi2WO6 (Bi2WO6−XF2X) photocatalysts with high activity have been successfully synthesized by a two-step process. The effects of F− substitution on the crystal structure and photocatalytic activity of Bi2WO6 were investigated. F− substitution could change the original coordination around the W and Bi atoms. Comparing with Bi2WO6, the photocatalytic activity of Bi2WO6−XF2X increased about 2 times for degradation of MB under visible-light (λ > 420 nm) irradiation. Density functional calculations revealed that Bi2WO6−XF2X has a wider valence bandwidth and lower valence band position. The high activities of Bi2WO6−XF2X photocatalysts come from its valence band which increase the mobility of photoexcited charge carriers and possess a stronger oxidation power.

Nanoporous g-C3N4 (npg-C3N4) with high surface area was prepared by a bubble-templating method. A higher calcination heating rate and proportion of thiourea can result in a larger surface area and better adsorption and photodegradation activities of npg-C3N4. Compared with the bulk g-C3N4, the adsorption capacity for the target pollutants and photocatalytic degradation and photocurrent performances under visible light irradiation of npg-C3N4 were greatly improved. The optimal photodegradation activity of npg-C3N4 was 3.4 times as high as that of the bulk g-C3N4. The enhanced activities of npg-C3N4 can be attributed to the larger number of surface active sites, improved separation of photogenerated electron–hole pairs, and higher efficiency of charge immigration.

The dramatic enhanced visible light photocatalytic activity and excellent antiphotocorrosion performance of CdS photocatalysts were obtained after hybridized by monolayer polyaniline. The as-prepared PANI-CdS hybrid photocatalysts reveal the outstanding photocatalytic activity and photoelectrical conversion efficiency which can improve about 2.5 and 1.8 times that of the pure CdS, respectively. Significantly, the issue of photocorrosion, a congenital disadvantage of CdS photocatalysts, has been solved completely after hybridization. The mechanisms on enhancement of photocatalytic activity and antiphotocorrosion performance have been emphasized. Under visible light irradiation, photogenerated electrons in LUMO of PANI injected into the conduction band of CdS, photogenerated holes in the valence band of CdS transferred to the photocatalysts surface through HOMO of PANI. The rapid transferring of hole and high separation efficiency of electron−hole pairs lead to the dramatically enhanced photoactivity and completely inhibited photocorrosion.

•One-dimensional supramolecular organic nanofibers self-assembled by a carboxy-substituent perylene diimide (PDI) molecule through H-type π-π stacking and hydrogen bonding.•PDI supramolecular nanofibers show highly efficient and stable photocatalytic activity under visible light.•The highly efficient and stable activity was attributed to the well-defined H-type π-π stacking and the internal electric field caused by terminal carboxyl group.•The electronic properties of PDI supramolecular nanofibers were elucidated.The development of organic materials for visible light driven photocatalytic is regarded as one of the most promising avenues to solve environment and solar-energy utilization issue. Here, we present that one-dimensional supramolecular organic nanofibers, self-assembled by a carboxy-substituent perylene diimide (PDI) molecule through H-type π-π stacking and hydrogen bonding, can act as a robust and effective photocatalyst for both organic pollutants degradation and water oxidation under visible light without the apparent need for an added metal co-catalysts. We corroborate that the highly efficient and stable activity of such supramolecar photocatalyst are attributed to the introduction of terminal carboxyl group, which leads to well-defined and stable H-type π-π stacking, and constructs the internal electric field in supramolecular nanofibers, thereby resulting in the deepening of valence band (VB) and the enhancement of migration and separation efficiency of photo-induced charge carriers. Our findings may help the development of semiconducting-based organic supramolecular materials for applications in environment protection and water splitting.Download high-res image (175KB)Download full-size image

•TiO2/g-C3N4 thin film electrode was fabricated via a surface hybridization and dip-coating method.•The surface hybrid heterojunction of TiO2/g-C3N4 greatly improves its photocatalytic and photoelectrocatalytic activity.•The synergistic effects between the electrocatalytic and photocatalytic oxidation processes in photoelectrocatalytic were illustrated.•Coking wastewater and phenol can be mineralized by TiO2/g-C3N4 photoelectrocatalytic processes.TiO2/g-C3N4 (TCN) thin film electrode was fabricated via a surface hybridization and dip-coating method. Phenol could be completely mineralized and the pollutants in coking wastewater could be degraded quickly by TCN under simulated solar light and electric field. The characteristics of the photoelectrocatalytic (PEC) degradation of phenol-containing coking wastewater were investigated under visible light, ultraviolet light and simulated solar irradiation. The results showed that phenol was degraded completely by the TCN-0.3 with a 1.5 V bias in 1.5 h under simulated solar irradiation with 100% TOC removal rate. 45% of the TOC for the coking wastewater was removed by the TCN-0.3 with a 1.5 V bias under 5.0 h simulated solar irradiation, which was 2.45 and 5.69 times as high as that of the pure TiO2 and g-C3N4, respectively. The surface hybrid heterojunction formed between TiO2 and g-C3N4 promotes the migration of the photogenerated electrons and holes and greatly improves the degradation efficiency with applied potential. The significant synergistic effect between the electrocatalytic and photocatalytic oxidation processes in PEC is conducive to electron-hole pair separation, producing the more active substances, such as hydroxyl radicals, and increases the degree of degradation and mineralization of phenolic compounds.Download high-res image (133KB)Download full-size image

•The 3D ZnIn2S4/TiO2 composite photocatalyst is prepared by two steps for CO2 reduction.•The CH4 production rate of ZnIn2S4/TiO2 is about 38-times higher than pure ZnIn2S4.•The supposed mechanism of the excellent performance is due to a Z-Scheme system.A 3-dimensional (3D) ZnIn2S4/TiO2 Z-scheme system has been designed and constructed for photocatalytic reduction of CO2 into renewable hydrocarbon fuels without the use of a solid-state electron mediator. The unique 3D morphology, achieved by assembling 2D ZnIn2S4 nanosheets onto 1D TiO2 nanobelts, not only provides large surface area but also improves the separation and transfer efficiency of photogenerated electrons and holes. The 3D ZnIn2S4/TiO2 Z-scheme photocatalysts show excellent light-harvesting properties demonstrated in photocatalytic reduction of CO2, resulting in generation of desired hydrocarbons. The CH4 production rate of the 3D ZnIn2S4/TiO2 can reach up to 1.135 μmol g−1 h−1, which is about 39-times higher than that of bare ZnIn2S4 (0.029 μmol g−1 h−1). The enhanced photocatalytic activity is attributed to effective separation of the charge carriers between ZnIn2S4 and TiO2 through the direct Z-scheme instead of a type-II heterojunction. The photogenerated electrons in TiO2 nanobelts recombine with the holes in ZnIn2S4 nanosheets, and the unrecombined electrons/holes on different active sites have stronger reduction/oxidation abilities, leading to higher photocatalytic activity for CO2 reduction.Download high-res image (263KB)Download full-size image

•The graphene/ZnO has been prepared via a simple one-step hydrothermal method.•There is 99% of DON could be photodegraded within 30 min by GZ0.3 totally.•Photocatalysis can be used to detoxification firstly and systematically.•The active species on the surface were superoxide radicals and holes.Water-soluble deoxynivalenol (DON) pose a major threat as a potential organic pollutant to water environmental quality. DON is a toxic secondary metabolite produced by molds of the Fusarium genus and one of the most important mycotoxins in cereal commodities, which can be enriched from the contaminated grain by deoxynivalenol in the process of wet processing. In this work, graphene/ZnO hybrids has been successfully prepared via a simple one-step hydrothermal method and exhibited superior photocatalytic activity for the photodegradation of DON under the irradiation of UV light. The UV light photocatalytic activity of graphene/ZnO hybrid GZ0.3 was 3.1 times than pure ZnO and about 99% of DON (15 ppm) could be photodegraded within 30 min totally while there were three peaks of intermediate products appeared. The ESI/MS analysis confirmed the presence of DON and degradation product with the secondary mass spectrogram in the positive ESI mode. Overall, this work could provide new insights into the fabrication of graphene/ZnO hybrids composite as high performance photocatalysts and facilitate their application in the mycotoxin detoxification and environmental protection issues.Schematic drawing illustrating synthetic route and the mechanism of charge separation and adsorption-photocatalytic process over graphene/ZnO hybrid photocatalysts under UV light irradiation.Download high-res image (289KB)Download full-size image

•One-pot method is proposed to prepare C/Bi/Bi2O3 composite with enhanced photocatalytic activity.•In this method, no reduction agent is used to reduce metallic Bi.•Metallic Bi and remaining organic carbon can improve light absorption and accelerate the separation of electron-hole pairs.In this work, a novel C/Bi/Bi2O3 composite photocatalyst was prepared by a facile one-pot method, using EDTA-Bi as a precursor. The C/Bi/Bi2O3 composite photocatalyst exhibited higher photocatalytic activity than Bi2O3 on the degradation of 2,4-dichlorophenol (2,4-DCP) under both simulated sunlight and visible light irradiation. Metallic Bi and the remaining organic carbon cannot only enhance the absorption of lights, but also accelerate the seperation of photogenerated charge carriers. As a result, the photocatalytic activity is enhanced. More importantly, this paper provides a facile method for the preparation of C/Bi/Bi2O3 composite materials, which is suitable for mass production.Download high-res image (315KB)Download full-size image

Bismuth molybdate photocatalysts with different phase structures and morphologies were controllably synthesized via a refluxing method by adjusting the pH in the reaction system. Bi2MoO6 nanosheets were easily obtained under acidic conditions, while Bi3.64Mo0.36O6.55 nanoparticles were formed in circumneutral and basic solutions. The mechanism for the formation and phase transition of these two bismuth molybdates is based on tuning the pH value, which can control the growth rate along different crystal axes and the formation of different hydrolysis products that act as the initial seeds of the crystallographic phases. The photocatalytic activity of the Bi2MoO6 nanosheets for MB and MO degradation was higher than that of the Bi3.64Mo0.36O6.55 nanoparticles under visible light irradiation, and the highest photocatalytic activity was observed for the Bi2MoO6 nanosheets prepared at pH 6.0. The high visible-light photocatalytic activity of the Bi2MoO6 nanosheets arises from the easy separation and transfer of photogenerated electron–holes in the nanosheet’s structure as well as the narrow band gap, which leads to an improvement in the visible absorption ability. Electron spin resonance (ESR) and a photogenerated carrier trapping experiment suggested that both Bi2MoO6 and Bi3.64Mo0.36O6.55 had the same photocatalytic mechanism and the main oxidative species for these samples was the hydroxyl radical.

Highly dispersed BiPO4 with surface oxygen vacancies was synthesized via a solvothermal–calcination method. It can disperse uniformly in water for more than three days and the optimum photocatalytic activity of this highly dispersed BiPO4 was more than twice as high as that of Degussa P25 due to the oxygen vacancies. The high dispersibility is attributed to a layer of organic matter formed on the surface of BiPO4via the solvothermal approach. Most of the organic matter can be removed by calcination at 450 °C, but a small amount remains, thus the calcined BiPO4 retained its high dispersibility. This high dispersibility maintains a good contact between BiPO4 and the pollutants, resulting in the efficient removal of the pollutants by BiPO4. Besides, calcination at 450 °C also induced the formation of oxygen defects in BiPO4, which promotes the separation of photogenerated charge carriers and thus improves the photocatalytic activity of BiPO4.

P3HT-g-C3N4 photocatalysts with high activity have been fabricated by assembling p-type P3HT particles on n-type g-C3N4 nanoplates via a ball milling method. The photocatalytic activity of the P3HT-g-C3N4 photocatalysts for the degradation of MB was 2 times higher than that of pure g-C3N4. The formation of a heterojunction interface of P3HT-g-C3N4 photocatalysts enhanced the separation efficiency of photogenerated electron–hole pairs and resulted in the enhancement of photocatalytic performance. The potential difference in the heterojunction is the main driving force for efficient charge separation and transfer.

Semiconductor photocatalysts used for environmental applications have attracted a lot of attention due to their ability to completely convert pollutants into CO2 and H2O. For a simple and economical treatment, more efficient photocatalysts are highly desired compared to widely used TiO2. A non-metallic oxyacid type photocatalyst, BiPO4, was first discovered by the author's group and is now commonly accepted as a superior photocatalyst compared to TiO2 in the UV region. Because of its excellence, this paper has reviewed the recent progress on BiPO4, specifically on the efforts from the author's group, including the preparation as well as the modification methods involved in activity enhancement. The description of the physical properties and typical degradation pathways of the photocatalyst are also given for better comprehension of the origin of its high activity. Furthermore, as a represented non-metallic oxyacid photocatalyst, research into BiPO4 will offer guidelines for designing effective photocatalysts of the same type for environmental applications.

A high concentration of surface oxygen vacancies were successfully introduced on the BiPO4−x nanorods via controllable hydrogen reduction. The BiPO4−x sample with surface oxygen vacancies shows a light-gray color, although the absorption sharp edge is not changed (still about 300 nm), the absorbance enhances in the range of 300–800 nm. The enhanced level of photocatalytic performance and photocurrent are both influenced by the concentration and extent of oxygen vacancies, which can be controlled by tuning hydrogen reduction temperature and time. Only high-concentration oxygen vacancies formed on the surface layers of BiPO4 can greatly improve the photocatalytic performance and photocurrent, while bulk oxygen vacancies will decrease the performance. The increasing of surface oxygen vacancies can results in broadening of the valence band width and narrowing of the bandgap, which can effect enhancement of the photoactivity and photocurrent, and extending the photoresponse wavelength range.

Tailored nanostructures offer a new way to facilitate electron–hole separation and offer additional opportunities to generate unique photocatalysts that demonstrate novel light absorption, thermodynamic and kinetic properties. A simple and efficient approach to the synthesis of a large variety of g-C3N4 tailored nanostructures is reported. Herein, NH3 and H2O2 were used as controllable chemical scissors to tailor bulk g-C3N4 to a large variety of g-C3N4 nanostructures, which include exfoliated porous, quantum dot, nanomites and nanospindles. The tailored g-C3N4 shows a photoreactivity of H2 evolution 3.0 (pure water) and 4.1 (saturated KCl solution) times higher than bulk g-C3N4 under λ > 420 nm. We believe this strategy affords new opportunities for structural tuning of X-doped (X = N, S, P, and O) carbon materials, as well as their exploration in catalysis, organic synthesis, nanomedicine and energy storage.

A phase junction over a Bi2SiO5 photocatalyst with the orthorhombic Bi2SiO5 and the tetragonal Bi2SiO5 structure was successfully synthesized via an ion exchange method using BiOBr solid microspheres as the sacrificial template. In the meantime, the as-prepared Bi2SiO5 phase junction possesses a novel morphology of a flower-like microsphere with nanoparticles evenly embedded in its nano-petals. It was found that the Bi2SiO5 phase junction not only showed a highly enhanced photocatalytic activity and excellent durability under UV or simulated solar irradiation, but also showed a remarkable visible-light activity for photo-degradation of phenol. Experimental results reveal that the tetragonal Bi2SiO5 phase in this phase junction possesses a narrower band gap, thus leading to its extended light absorption. The efficient charge separation via a phase junction would make a great contribution to its highly enhanced photocatalytic activity under UV or simulated solar irradiation. The high efficiency in the degradation of organic pollutants makes the as-prepared photocatalyst a promising candidate for photocatalytic environmental purification.

BiPO4 with a phase junction was synthesized by calcinating hexagonal BiPO4(HBIP) at different temperatures. The phase structures of BiPO4 were gradually transformed from HBIP to monazite monoclinic BiPO4 (nMBIP) and monoclinic BiPO4 (mMBIP) with increasing calcination temperature. The enhancement of the photocatalytic performance and photocurrent were ascribed to the formation of phase junction. A nMBIP–mMBIP surface-phase junction was formed in BiPO4 when HBIP was calcined at 500 °C, and its photocatalytic activity was 28.7 times as high as that of HBIP. Moreover, radical trapping experiments confirmed that the hole was the active species for BiPO4 on the degradation of methylene blue.

The ZnO/mpg-C3N4 composite photocatalyst with high visible light activity was successfully synthesized by a facile solvothermal method and characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectroscopy (DRS). The results indicated that ZnO particles dispersed uniformly on the mpg-C3N4 sheet. The photocatalytic activity of ZnO/mpg-C3N4 for photodegradation of MB was much higher than that of pure mpg-C3N4 both under the visible light and simulated solar irradiation. The optimal ZnO content for the photocatalytic activity of the ZnO/mpg-C3N4 composites is 24.9%, which is almost 2.3 times as high as that of pure mpg-C3N4 under visible light, and 1.9 times higher than that under simulated solar irradiation. The enhancement in photocatalytic activity should be assigned to the effective separation and transfer of photogenerated charges coming from the well-matched overlapping band-structure between mpg-C3N4 and ZnO. Radical trap experiments show that both ZnO/mpg-C3N4 composites and mpg-C3N4 have the same photodegradation mechanism, and the holes are their main oxidative species for MB degradation.

A visible-light-sensitive Bi2MoO6–BiOCl heterojunction photocatalyst was synthesized via a hydrothermal process. The as-prepared Bi2MoO6–BiOCl composite shows an irregular multi-plate structure with length ranging from 100 nm to 1 μm, indicating a possibility of the plate-on-plate structure by placing Bi2MoO6 and BiOCl nanoplates over each other. The Bi2MoO6–BiOCl photocatalyst not only had a good visible-light photocatalytic performance, but also exhibited higher photocatalytic activity than pure BiOCl and Bi2MoO6. The optimal Bi2MoO6 content for the photocatalytic activity of the Bi2MoO6–BiOCl composites is 30%. Compared to pure Bi2MoO6 the photoactivity of the Bi2MoO6–BiOCl composites is almost 2.0 times higher for the RhB photodegradation, and 1.5 times higher for the phenol photodegradation under visible light irradiation. The photocatalytic mechanism was elucidated via active species trapping experiments and ESR. The ˙OH and ˙O2− played the key roles in the degradation of RhB via the Bi2MoO6–BiOCl composite. Finally, the possible charge transfer mechanism of the enhanced visible light photocatalytic activity was proposed.

C3N4@ZnO hybrid materials with visible light photocatalytic performance have been prepared by facile mechanical milling. The dispersion of conjugated molecule g-C3N4 on the surface of ZnO improved during mechanical process, and the multilayer hybrid structure of g-C3N4@ZnO materials with remarkable visible light photocatalytic activity was formed by ball milling. The photocatalytic activity and photocurrent intensity of g-C3N4@ZnO under visible light irradiation was 3.0 and 2.0 times higher than those of pure C3N4, respectively. The great enhancement of visible light response originates from the increase of separation and immigration efficiency of photogenerated electron–hole pairs. Furthermore, a synergistic photocatalysis mechanism between ZnO and g-C3N4 was proposed. The enhanced visible light photocatalytic properties originate from the injection of excited electrons from the LUMO of C3N4 to the CB of ZnO. However, the photocatalytic activity of the photocatalyst is much lower than that of ZnO under UV light, which is caused by the lattice defect of ZnO formed during milling.

A new type of layered oxy-acid salt of bismuth oxynitrate was synthesized by a simple hydrothermal method. The obtained bismuth oxy-nitrates consist of a Bi2O22+ layered module inserted into the interlamellar anion modules of NO3− and OH−. Varying amounts of NO3− and OH− complexes on the surface of the bismuth oxynitrate were also obtained by adjusting the precursor pH before hydrothermal treatment. It was found that the sample prepared with the precursor pH = 5.00 presented the highest photocatalytic activity, with a rate constant of 0.05 min−1, which is 2 and 6.7 times higher than those presented by the samples with the precursor pH = 7.00 and 1.22, respectively. The largest cathodic to anodic photocurrent switching was also presented by the sample with the precursor pH = 5.00, which can be reasonably attributed to NO3− complexes on the surface of the bismuth oxynitrate. The NO3− complexes could efficiently migrate the photo-induced holes to the surface of the semiconductor.

The influence of defects on the photoactivity of ZnO has been revealed. The defects can be formed via ball-milling treatment, and part of the defects can be repaired via annealing treatment. The photocatalytic activity of the ZnO sharply decreased as the ball-milling speed and milling time increased. After the annealing treatment, the photocatalytic activity recovered partly but could not return to the activity of the pristine ZnO. The bulk defects such as oxygen vacancies (VO), zinc vacancies (VZn) and a lot of nonradiative defects were formed after the milling treatment. The annealing treatment can only repair part of the bulk defects and nonradiative defects. Thus, only part of the photoactivity was recovered. The species trapping experiments showed that the introduction of the bulk defects did not change the photocatalytic mechanism. The main oxidative species for the pristine ZnO, the milled ZnO, and the annealed ZnO are photogenerated holes and hydroxyl radicals.

A ZnO1−x photocatalyst with surface oxygen vacancies was fabricated by the controllable reduction of H2. After surface oxygen vacancies were introduced into the ZnO photocatalyst, a high visible-light-driven activity and photocurrent was produced. The UV activity for the degradation of MB and the photocurrent was enhanced about 2.2 times and 2.5 times, respectively. The visible-light activity resulted from the narrowed band gap due to the overlap of the valance band (VB) of the surface oxygen vacancy with O2p. The main active species are photoinduced holes and MB can be mineralized completely under visible-light irradiation. The overlap of the VB of the surface oxygen vacancy with O2p also extended the width of the VB and resulted in the increase of the separation efficiency of the photoinduced electron–hole pairs and the enhancement of the UV photoactivity greatly. The surface oxygen vacancy only increased the separation efficiency and did not change the photocatalytic degradation process, and the main oxidative species was still the photoinduced holes. The bulk oxygen vacancy can be formed via depth reduction at 700 °C for 5 h and resulted in the loss of photoactivity due to bulk defects.

The transformation of graphitic carbon nitride (g-C3N4) from nanoplates to nanorods was realized by a simple reflux method. The photocatalytic activity and the intensity of the photocurrent response of g-C3N4 nanorods under visible light were about 1.5 and 2.0 times those of g-C3N4 nanoplates, respectively. The formation mechanism of g-C3N4 from nanoplates to nanorods was demonstrated that g-C3N4 nanoplates undergo a possible exfoliation and regrowth process and a rolling mechanism of lamellar structure, which is responsible for elimination of the surface defects in the reflux process. During the transformation of g-C3N4 from nanoplates to nanorods, the enhancement of photocatalytic activity and photocurrent intensity in g-C3N4 nanorods was mainly attributed to the increase of active lattice face and elimination of surface defects.

ZnO1–x/graphene hybrid photocatalyst was prepared via a facile in-situ reduction of graphene oxide and ZnO1–x surface defect oxide. The hybrid photocatlayst showed enhanced photocatalytic activity for the photodegradation of methylene blue. The photocorrosion of ZnO1–x was successfully inhibited by graphene hybridation. ZnO1–x/graphene hybrid photocatalyst with 1.2 wt % graphene showed the optimized photocatalytic activity. The photocatalytic activity of ZnO1–x/graphene-1.2 wt % under visible and UV light was about 4.6 and 1.2 times that of ZnO1–x sample, respectively. The photocurrent intensity of ZnO1–x under visible and UV light irradiation can be enhanced by 2 and 3.5 times by graphene hybridization. The enhancement of photocatalytic activity and photocurrent intensity in ZnO1–x/graphene was attributed to the synergistic effect between graphene and ZnO1–x for high separation efficiency of photoinduced electron–hole pairs mainly resulting from the promotion of HOMO orbit of graphene and the Oi″ defect level of ZnO1–x in ZnO1–x/graphene.

The electronic structures of ZnO were calculated using density functional theory, in which the electronic interactions are described within the GGA+U (GGA = generalized gradient approximation) formalism, where on-site Coulomb corrections are applied on the Zn 3d orbitals (Ud) and O 2p orbitals (Up). The relaxed GGA+U calculation can correct completely the band gap, the position of Zn 3d states, the transition levels of O vacancy in band gap, and so on, which is different from other GGA+U (equivalent LDA+U) calculations partially correcting the energy band structure for fixed lattice constants. By comparing with experimental data, the pair of Ud = 10 and Up = 7 eV was identified as an optimum choice for the energy band structure of W-ZnO. Then, the proper pair of Ud and Up parameters was taken to predict the energy band structure of ZB- and RS- ZnO, of which the former is in good agreement with experimental values, and the latter is in dispute, relating to the decrease of the octahedral symmetry. Subsequently, we pay special attention to the possible causes of the decrease of lattice constants deriving from the +U correction. Further, the formation energies and transition levels of O vacancy in W-ZnO were calculated using three different schemes to address possible routes to presenting the defect states in band gap. Our results provide some guidance for improving electronic structure of ZnO using the GGA+U approach.

Nanoporous g-C3N4 (npg-C3N4) with high surface area was prepared by a bubble-templating method. A higher calcination heating rate and proportion of thiourea can result in a larger surface area and better adsorption and photodegradation activities of npg-C3N4. Compared with the bulk g-C3N4, the adsorption capacity for the target pollutants and photocatalytic degradation and photocurrent performances under visible light irradiation of npg-C3N4 were greatly improved. The optimal photodegradation activity of npg-C3N4 was 3.4 times as high as that of the bulk g-C3N4. The enhanced activities of npg-C3N4 can be attributed to the larger number of surface active sites, improved separation of photogenerated electron–hole pairs, and higher efficiency of charge immigration.

The BiPO4–x nanorod with surface oxygen vacancy was fabricated via vacuum deoxidation. The concentration and kind of oxygen vacancy could be controlled by tuning the deoxidation temperature and time in vacuum. The photocatalytic activity depended on the concentration and kind of surface oxygen vacancy, and the optimum photocatalytic activity and photocurrent of the BiPO4–x nanorod was about 1.5 and 2.5 times as high as that of pure BiPO4, respectively. Besides, the photocatalytic response wave range of the BiPO4–x nanorod has been expanded to more than 365 nm. The enhancement of photocatalytic activity is attributed to the high separation efficiency of photoinduced electron–hole pairs due to the broadening of the valence band (VB) induced by surface oxygen-vacancy states, and the extending of photoresponse is considered to be the narrowing of energy band gap resulting from the rise of the valence band maximum (VBM).

ZnWO4/graphene hybride (GZW-X) photocatalysts were synthesized via a facile in situ reduction of graphene oxide and ZnWO4 in water. High efficiency for the degradation of methylene blue (MB) under both UV light and visible light was obtained for the GZW-X photocatalysts. The photocatalytic efficiency of ZnWO4/graphene-0.2 wt % under visible-light and UV-light irradiation was ∼7.1 and 2.3 times that of pristine ZnWO4, respectively. The visible photocatalytic activity originated from the •OH and O2•–, which were formed by photosensitization of graphene in ZnWO4/graphene. The enhancement of UV photocatalytic light activity in ZnWO4/graphene was attributed to the high separation efficiency of photoinduced electron–hole pairs resulting from the promotion of HOMO orbit of graphene in ZnWO4/graphene.Keywords: graphene; hybridization; photocatalysis; ZnWO4;

Heterogeneous photocatalysts offer great potential for converting photon energy into chemical energy and for decomposing organic contaminants. Many efficient photocatalysts have been proposed, unfortunately, most of these photocatalysts work only in the UV light region. It is necessary to develop visible-light-active photocatalysts to effectively utilize solar energy. This paper reviews a novel non-TiO2 photocatalyst, Bi2WO6, which shows high activity under visible light irradiation. The controllable synthesis of Bi2WO6 nanoplates and highly porous films of Bi2WO6, as well as several methods for improving the photocatalytic activity of Bi2WO6, specifically the efforts from the authors' group are reviewed.

ZnWO4 photocatalysts doped with chlorine were synthesized by a simple hydrothermal process. The influences of chlorine doping on the crystal structure, optical properties and photocatalytic activities of the ZnWO4 photocatalyst were investigated. ZnWO4 doped with chlorine showed enhanced photocatalytic activity for the degradation of methylene blue (MB), rhodamine B and 4-chlorophenol. The photocatalytic activity of ZnWO4 with RCl = 0.3 can be enhanced approximately 4 times for the degradation of MB. The enhanced photocatalytic activity originated from the increase of the transfer rate of photogenerated electrons to the photocatalyst surface, which was promoted by chlorine doping. The photodegradation process of MB can be described as N-demethylation and oxidative degradation. In the case of chlorine doping, an effective separation of the photogenerated electron–hole pairs and the fast interfacial charge transfer to the electron donor/electron acceptor occurred.

Phase-pure Bi2MoxW1–xO6 (0 ≤ x ≤ 1) photocatalysts were synthesized via a hydrothermal method. The as-prepared Bi2MoxW1–xO6 photocatalysts had an Aurivillius crystal structure and showed special anisotropic growth. The optical absorption spectra of Bi2MoxW1–xO6 were red-shifted monotonically as the value of x increased. On the basis of theoretical calculations, the introduction of Mo atom into Bi2WO6 could reduce the conduction band level of Bi2WO6, so the band gap energy was reduced. The curvature of the conduction band became smaller with an increase in the Mo content due to the different electronegativities of Mo 4d and W 5d. The photocatalytic activities determined by rhodamine B degradation under visible light irradiation (λ > 420 nm) of Bi2MoxW1–xO6 photocatalysts were significantly improved as compared with Bi2MoO6. The higher efficiency of Bi2WO6 was attributed to more effective photoelectron transfer in the conduction band with larger curvature. The photocatalytic activities under visible light irradiation (λ > 450 nm) of Bi2MoxW1–xO6 photocatalysts were much higher than that of Bi2WO6. The mechanism was discussed on the basis of the cystal structure, morphology, and electronic stucture. This work provides a strategy for developing active photocatalysts with more utilization of visible light.Keywords: Bi2MoO6; Bi2WO6; photocatalysis; substitution; visible light

Floriated like and nanobelt nanostructures of Zn3V2O7(OH)2(H2O)2 were successfully synthesized by a template-free hydrothermal route. The as-prepared floriated nanostructures were composed of 2D nanosheets, which intercrossed with each other through self-assembly. The influence of the hydrothermal temperature on the morphology and photocatalytic activities of products was systematically investigated. Significantly, this is the first time that Zn3V2O7(OH)2(H2O)2 was used as a photocatalyst for organic pollutant degradation under UV light irradiation. Moreover, Zn3V2O8 with porous nanostructures could be formed viacalcination of the corresponding Zn3V2O7(OH)2(H2O)2. It was found that the Zn3V2O8 nanostructure still possessed floriated like morphology and the pore sizes within the floriated were about 4 nm. All these characteristics were beneficial for the improvement of photocatalytic activity. The reaction constant (k) of the best quality Zn3V2O8 nanostructure was three times that of the sample prepared by solid-state reaction under visible-light irradiation.

Fe5(PO4)4(OH)3·2H2O has been successfully synthesized by a simple hydrothermal process. The effects of hydrothermal temperature and pH value on the morphologies and sizes of the Fe5(PO4)4(OH)3·2H2O particles were investigated. The Fe5(PO4)4(OH)3·2H2O photocatalyst showed lower photocatalytic activity for the degradation of methylene blue under visible light irradiation. But the heterogeneous Fenton-like Fe5(PO4)4(OH)3·2H2O with H2O2 showed highly efficient photocatalytic activity in the photocatalytic decomposition of methylene blue. Effective electron transfer from the visible light-excited dyes to Fe(III), which leads to regeneration of Fe(II) and an easy cycle of Fe(III)/Fe(II), results in much faster degradation and mineralization of methylene blue in the photo-Fenton reaction under visible light irradiation.

ZnWO4 nanorod photocatalysts with various aspect ratios were synthesized by a hydrothermal method. The aspect ratio of the ZnWO4 nanorods was governed by the hydrothermal temperature and pH value. ZnWO4 nanorod photocatalysts showed highly efficient photocatalytic activity for the degradation of methylene blue under ultraviolet light irradiation. The photocatalytic activity and the effective separation of photogenerated electron–hole pairs were promoted by the increasing aspect ratio of the ZnWO4 nanorods. The amount of electron donors in the ZnWO4 increased with the aspect ratio of ZnWO4, which was in good agreement with photocurrent results. The enhancement of photocurrent density and photocatalytic activity resulted from the reduction of charge-transfer resistance and capacitive reactance, which were deduced by the high aspect ratio of ZnWO4 nanorods.

BiTaO4 photocatalyst for methylene blue (MB) degradation, which worked under visible-light irradiation, was systematically investigated for the first time. BiTaO4 possess similar degradation ability of TiO2−XNX under visible-light irradiation (λ > 420 nm). Density functional calculations revealed that Bi 6s orbitals contributed to the formation of valence band, resulting in narrowing the band gap. Moreover, comparing with BiNbO4, we found BiTaO4 showed photocorrosion suppression performance during the photocatalytic process. The differences in the photocorrosion suppression between BiTaO4 and BiNbO4 could be attributed to the conduction curvature and bandwidth, leading to differences in the mobility of photogenerated electrons formed in the conduction bands, which mainly consisted of Ta 5d and Nb 4d orbitals, respectively.

Monomolecular-layer polyaniline (PANI) was dispersed on the surface of zinc oxide (ZnO) and formed the hybrid effect between ZnO and PANI. The hybrid photocatalysts showed dramatic photocatalytic activity for the degradation of the methylene blue (MB) both under ultraviolet and visible light irradiation, and the photocorrosion of ZnO was successfully inhibited. The enhanced photocatalytic activity for PANI-hybridized ZnO originated from the high separation efficiency of photogenerated electrons and holes on the interface of PANI and ZnO, which was produced by the hybrid effect of PANI and ZnO. The photocorrosion inhibition of ZnO could be attributed to the rapidly transferring of photogenerated holes by the PANI monolayer. The relationship between the PANI content of the samples and their photocatalytic performance shows that an optimal PANI weight percent (1.0%) can significantly enhance the photocatalytic efficiency and anticorrosion of ZnO particles. In particular, the mechanisms on the enhancement of photocatalytic activity and antiphotocorrosion performance have been emphasized. Under ultraviolet light irradiation, photogenerated holes in the ZnO valence band could transfer to the HOMO orbital of PANI and then emigrate to the photocatalysts surface and oxidize the adsorbed contaminants directly. Under visible light irradiation, PANI generated a π−π* transition, delivering the excited electrons to the conduction band of ZnO, and then the electrons transferred to an adsorbed electron acceptor, yielding oxygenous radicals to degrade pollutants.

A method to suppress the photocorrosion of ZnO nanoparticles was developed by surface hybridization of ZnO with graphite-like carbon layers. The presence of carbon on the surface of the ZnO could significantly suppress the coalescence and crystal growth of ZnO nanoparticles during high-temperature treatment. The nanosized structure of ZnO was well preserved even after high-temperature calcination. The photocatalytic activity of ZnO was enhanced by hybridization with carbon layers attributed to the improved adsorption ability and crystallinity. The as-prepared samples exhibited high activity even after 720 h of photocatalysis reaction, while the pure ZnO nanoparticle was almost deactivated in 100 h due to serious photocorrosion. The as-prepared samples also showed much better activity under extreme pH conditions than that of pure ZnO. The mechanism of photocorrosion suppression and higher stability was then systematically investigated based on the crystal structure and the photocatalysis degradation process.

La1−xSrxMnO3 (x = 0, 0.2, 0.5, 0.8) nanoparticles were synthesized and their chemiluminescence (CL) and catalytic properties of CO oxidation were determined. We mainly investigated the influences of filter band length, flow rate of gas, test temperature, catalyst compositions, and particle size on CL intensities and catalytic activities of the catalysts. The catalysts were characterized by means of XRD, TEM, N2 adsorption isotherm, CO-TPD, and O2-TPD, etc. It was found that the strong CL response signals occurred over these perovskites nanoparticles; and that CL properties of the catalysts were well correlated with the reaction activities. These nanoparticles can be used to fabricate a stable gas detector due to a high activity and stability of perovskite structure. CL mode could be a rapid and effective method for the selection of new catalysts from thousands of materials, as well as for the detection of environmental deleterious gases.

The dramatic visible light photocatalytic activity was obtained for the degradation of Methylene Blue (MB) and Rhodamine B (RhB) under visible light irradiation (λ > 450 nm) after TiO2 photocatalysts were modified with monolayer dispersed polyaniline (PANI ) via a facile chemisorption approach. Under visible light irradiation, PANI generated π−π* transition, delivering the excited electrons into the conduction band of TiO2, and then the electrons transferred to an adsorbed electron acceptor to yield oxygenous radicals to degrade pollutants. Also, the ultraviolet photocatalytic performance was enhanced to about two times compared with that of P-25 TiO2 photocatalyst. The high photocatalytic activity came from the synergetic effect between PANI and TiO2, which promoted the migration efficiency of photogenerated carriers on the interface of PANI and TiO2. Under ultraviolet light irradiation, photoinduced holes in TiO2 valence band could transfer into HOMO orbital of PANI and then emigrate to the photocatalyst surface and oxidize the adsorbed contaminants directly. The optimum synergetic effect was found at a weight ratio of 3.0 wt % (PANI/TiO2).

The fluorine doped ZnWO4 photocatalyst was synthesized by hydrothermal synthesis and annealing treatment. The existing states of fluorine in the crystal were elucidated, and the effects of fluorine on the crystal structure, photocatalytic activity, and degradative intermediates were investigated. The doping concentration of fluorine in the interstitial lattice of ZnWO4 crystal can be controlled by the annealing conditions. The photocatalytic activity can be enhanced about 50% after the doped ZnWO4 was annealed at 450 °C for 1 h due to perfect crystal structure. The enhancement of photocatalytic activity after fluorine doping could be attributed to the higher separation efficiency of electron-hole pairs, which results in a large number of holes participated in the photocatalytic process. The fluorine doping does not change the degradation pathway of 4-chlorophenol (4-CP) in our system. 4-CP was mainly transformed into hydroxylated aromatic intermediates such as benzoquinone (BQ), hydroquinone (HQ), and 4-chlorocatechol (4-CC). The photodegradation of 4-CP in powdered F-doped ZnWO4 system proceeded via direct holes oxidation reactions.

C60 molecules with monomolecular layer state dispersed on the surface of ZnO and formed the hybridized interaction between ZnO and C60. C60-hybridized ZnO photocatalyst showed enhanced photocatalytic activity for the degradation of the organic dye and the photocorrosion of ZnO was successfully inhibited by the hybridization of C60 molecules. The photocorrosion inhibition of ZnO by C60 molecule could be attributed to the reduced activation of surface oxygen atom. The enhanced photocatalytic activity for C60-hybridized ZnO was originated from the high migration efficiency of photoinduced electrons on the interface of C60 and ZnO, which was produced by the interaction of C60 and ZnO with a conjugative π-system. The enhancement degree of photocatalytic activity was strongly depended on the coverage of C60 molecules on the surface of ZnO nanoparticles, and the optimum hybridization effect was found at a weight ratio of 1.5% (C60/ZnO). The hybridization of C60 with semiconductors could be used to improve the photocatalytic activity as well as the photostability.

Semiconductor photocatalysts used for environmental applications have attracted a lot of attention due to their ability to completely convert pollutants into CO2 and H2O. For a simple and economical treatment, more efficient photocatalysts are highly desired compared to widely used TiO2. A non-metallic oxyacid type photocatalyst, BiPO4, was first discovered by the author's group and is now commonly accepted as a superior photocatalyst compared to TiO2 in the UV region. Because of its excellence, this paper has reviewed the recent progress on BiPO4, specifically on the efforts from the author's group, including the preparation as well as the modification methods involved in activity enhancement. The description of the physical properties and typical degradation pathways of the photocatalyst are also given for better comprehension of the origin of its high activity. Furthermore, as a represented non-metallic oxyacid photocatalyst, research into BiPO4 will offer guidelines for designing effective photocatalysts of the same type for environmental applications.

Heterogeneous photocatalysts offer great potential for converting photon energy into chemical energy and for decomposing organic contaminants. Many efficient photocatalysts have been proposed, unfortunately, most of these photocatalysts work only in the UV light region. It is necessary to develop visible-light-active photocatalysts to effectively utilize solar energy. This paper reviews a novel non-TiO2 photocatalyst, Bi2WO6, which shows high activity under visible light irradiation. The controllable synthesis of Bi2WO6 nanoplates and highly porous films of Bi2WO6, as well as several methods for improving the photocatalytic activity of Bi2WO6, specifically the efforts from the authors' group are reviewed.

BiPO4 with a phase junction was synthesized by calcinating hexagonal BiPO4(HBIP) at different temperatures. The phase structures of BiPO4 were gradually transformed from HBIP to monazite monoclinic BiPO4 (nMBIP) and monoclinic BiPO4 (mMBIP) with increasing calcination temperature. The enhancement of the photocatalytic performance and photocurrent were ascribed to the formation of phase junction. A nMBIP–mMBIP surface-phase junction was formed in BiPO4 when HBIP was calcined at 500 °C, and its photocatalytic activity was 28.7 times as high as that of HBIP. Moreover, radical trapping experiments confirmed that the hole was the active species for BiPO4 on the degradation of methylene blue.

Tailored nanostructures offer a new way to facilitate electron–hole separation and offer additional opportunities to generate unique photocatalysts that demonstrate novel light absorption, thermodynamic and kinetic properties. A simple and efficient approach to the synthesis of a large variety of g-C3N4 tailored nanostructures is reported. Herein, NH3 and H2O2 were used as controllable chemical scissors to tailor bulk g-C3N4 to a large variety of g-C3N4 nanostructures, which include exfoliated porous, quantum dot, nanomites and nanospindles. The tailored g-C3N4 shows a photoreactivity of H2 evolution 3.0 (pure water) and 4.1 (saturated KCl solution) times higher than bulk g-C3N4 under λ > 420 nm. We believe this strategy affords new opportunities for structural tuning of X-doped (X = N, S, P, and O) carbon materials, as well as their exploration in catalysis, organic synthesis, nanomedicine and energy storage.

A new type of layered oxy-acid salt of bismuth oxynitrate was synthesized by a simple hydrothermal method. The obtained bismuth oxy-nitrates consist of a Bi2O22+ layered module inserted into the interlamellar anion modules of NO3− and OH−. Varying amounts of NO3− and OH− complexes on the surface of the bismuth oxynitrate were also obtained by adjusting the precursor pH before hydrothermal treatment. It was found that the sample prepared with the precursor pH = 5.00 presented the highest photocatalytic activity, with a rate constant of 0.05 min−1, which is 2 and 6.7 times higher than those presented by the samples with the precursor pH = 7.00 and 1.22, respectively. The largest cathodic to anodic photocurrent switching was also presented by the sample with the precursor pH = 5.00, which can be reasonably attributed to NO3− complexes on the surface of the bismuth oxynitrate. The NO3− complexes could efficiently migrate the photo-induced holes to the surface of the semiconductor.

C3N4@ZnO hybrid materials with visible light photocatalytic performance have been prepared by facile mechanical milling. The dispersion of conjugated molecule g-C3N4 on the surface of ZnO improved during mechanical process, and the multilayer hybrid structure of g-C3N4@ZnO materials with remarkable visible light photocatalytic activity was formed by ball milling. The photocatalytic activity and photocurrent intensity of g-C3N4@ZnO under visible light irradiation was 3.0 and 2.0 times higher than those of pure C3N4, respectively. The great enhancement of visible light response originates from the increase of separation and immigration efficiency of photogenerated electron–hole pairs. Furthermore, a synergistic photocatalysis mechanism between ZnO and g-C3N4 was proposed. The enhanced visible light photocatalytic properties originate from the injection of excited electrons from the LUMO of C3N4 to the CB of ZnO. However, the photocatalytic activity of the photocatalyst is much lower than that of ZnO under UV light, which is caused by the lattice defect of ZnO formed during milling.

A high concentration of surface oxygen vacancies were successfully introduced on the BiPO4−x nanorods via controllable hydrogen reduction. The BiPO4−x sample with surface oxygen vacancies shows a light-gray color, although the absorption sharp edge is not changed (still about 300 nm), the absorbance enhances in the range of 300–800 nm. The enhanced level of photocatalytic performance and photocurrent are both influenced by the concentration and extent of oxygen vacancies, which can be controlled by tuning hydrogen reduction temperature and time. Only high-concentration oxygen vacancies formed on the surface layers of BiPO4 can greatly improve the photocatalytic performance and photocurrent, while bulk oxygen vacancies will decrease the performance. The increasing of surface oxygen vacancies can results in broadening of the valence band width and narrowing of the bandgap, which can effect enhancement of the photoactivity and photocurrent, and extending the photoresponse wavelength range.

P3HT-g-C3N4 photocatalysts with high activity have been fabricated by assembling p-type P3HT particles on n-type g-C3N4 nanoplates via a ball milling method. The photocatalytic activity of the P3HT-g-C3N4 photocatalysts for the degradation of MB was 2 times higher than that of pure g-C3N4. The formation of a heterojunction interface of P3HT-g-C3N4 photocatalysts enhanced the separation efficiency of photogenerated electron–hole pairs and resulted in the enhancement of photocatalytic performance. The potential difference in the heterojunction is the main driving force for efficient charge separation and transfer.

The ZnO/mpg-C3N4 composite photocatalyst with high visible light activity was successfully synthesized by a facile solvothermal method and characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectroscopy (DRS). The results indicated that ZnO particles dispersed uniformly on the mpg-C3N4 sheet. The photocatalytic activity of ZnO/mpg-C3N4 for photodegradation of MB was much higher than that of pure mpg-C3N4 both under the visible light and simulated solar irradiation. The optimal ZnO content for the photocatalytic activity of the ZnO/mpg-C3N4 composites is 24.9%, which is almost 2.3 times as high as that of pure mpg-C3N4 under visible light, and 1.9 times higher than that under simulated solar irradiation. The enhancement in photocatalytic activity should be assigned to the effective separation and transfer of photogenerated charges coming from the well-matched overlapping band-structure between mpg-C3N4 and ZnO. Radical trap experiments show that both ZnO/mpg-C3N4 composites and mpg-C3N4 have the same photodegradation mechanism, and the holes are their main oxidative species for MB degradation.

A ZnO1−x photocatalyst with surface oxygen vacancies was fabricated by the controllable reduction of H2. After surface oxygen vacancies were introduced into the ZnO photocatalyst, a high visible-light-driven activity and photocurrent was produced. The UV activity for the degradation of MB and the photocurrent was enhanced about 2.2 times and 2.5 times, respectively. The visible-light activity resulted from the narrowed band gap due to the overlap of the valance band (VB) of the surface oxygen vacancy with O2p. The main active species are photoinduced holes and MB can be mineralized completely under visible-light irradiation. The overlap of the VB of the surface oxygen vacancy with O2p also extended the width of the VB and resulted in the increase of the separation efficiency of the photoinduced electron–hole pairs and the enhancement of the UV photoactivity greatly. The surface oxygen vacancy only increased the separation efficiency and did not change the photocatalytic degradation process, and the main oxidative species was still the photoinduced holes. The bulk oxygen vacancy can be formed via depth reduction at 700 °C for 5 h and resulted in the loss of photoactivity due to bulk defects.

A visible-light-sensitive Bi2MoO6–BiOCl heterojunction photocatalyst was synthesized via a hydrothermal process. The as-prepared Bi2MoO6–BiOCl composite shows an irregular multi-plate structure with length ranging from 100 nm to 1 μm, indicating a possibility of the plate-on-plate structure by placing Bi2MoO6 and BiOCl nanoplates over each other. The Bi2MoO6–BiOCl photocatalyst not only had a good visible-light photocatalytic performance, but also exhibited higher photocatalytic activity than pure BiOCl and Bi2MoO6. The optimal Bi2MoO6 content for the photocatalytic activity of the Bi2MoO6–BiOCl composites is 30%. Compared to pure Bi2MoO6 the photoactivity of the Bi2MoO6–BiOCl composites is almost 2.0 times higher for the RhB photodegradation, and 1.5 times higher for the phenol photodegradation under visible light irradiation. The photocatalytic mechanism was elucidated via active species trapping experiments and ESR. The ˙OH and ˙O2− played the key roles in the degradation of RhB via the Bi2MoO6–BiOCl composite. Finally, the possible charge transfer mechanism of the enhanced visible light photocatalytic activity was proposed.

Floriated like and nanobelt nanostructures of Zn3V2O7(OH)2(H2O)2 were successfully synthesized by a template-free hydrothermal route. The as-prepared floriated nanostructures were composed of 2D nanosheets, which intercrossed with each other through self-assembly. The influence of the hydrothermal temperature on the morphology and photocatalytic activities of products was systematically investigated. Significantly, this is the first time that Zn3V2O7(OH)2(H2O)2 was used as a photocatalyst for organic pollutant degradation under UV light irradiation. Moreover, Zn3V2O8 with porous nanostructures could be formed viacalcination of the corresponding Zn3V2O7(OH)2(H2O)2. It was found that the Zn3V2O8 nanostructure still possessed floriated like morphology and the pore sizes within the floriated were about 4 nm. All these characteristics were beneficial for the improvement of photocatalytic activity. The reaction constant (k) of the best quality Zn3V2O8 nanostructure was three times that of the sample prepared by solid-state reaction under visible-light irradiation.