Uniform and magnetic recyclable mesocrystalline Zn-doped Fe3O4 hollow submicrospheres (HSMSs) were successfully synthesized via a simple one-pot solvothermal route and were used for efficient heterogeneous photo-Fenton catalyst. XRD, XPS, Raman spectroscopy, Mössbauer spectroscopy, SEM, HRTEM, and EDX analyses revealed that the shell of HSMSs is highly porous and assembled by oriented attachment of magnetite nanocrystal building blocks with Zn-rich surfaces. Furthermore, a possible formation mechanism of mesocrystalline hollow materials was proposed. First, Fe3O4 mesocrystals were assembled by oriented nanocrystals, and a Zn-rich amorphous shell grew on the surfaces. Then, Zn gradually diffused into Fe3O4 crystals to form Zn-doped Fe3O4 due to the Kirkendall effect with increasing the reaction time. Meanwhile, the inner nanocrystals would be dissolved, and outer particles would grow larger owing to the Ostwald ripening process, leading to the formation of a hollow structure with porous shell. The Zn-doped Fe3O4 HSMSs exhibited high and stable photo-Fenton activity for degradation of rhodamine B (RhB) and cephalexin under visible-light irradiation in the presence of H2O2, which results from their hollow mesocrystal structure and Zn doping. It could be easily separated and reused by an external magnetic field. The results suggested that the as-obtained magnetite hollow mesocrystals could be a promising catalyst in the photo-Fenton process.Keywords: cephalexin; magnetite; mesocrystal; oriented attachment; photo-Fenton activity; Zn-doped Fe3O4;

•The iron sludge-graphene composite was used as heterogeneous Fenton catalyst.•The graphene significantly enhanced the catalytic activity of the composite.•The catalyst was efficient for the degradation of RhB, ARG and metronidazole.•The catalyst showed negligible iron leaching and good stability during the reaction.•The enhanced activity resulted from mesoporous structure and raised Fe3+/Fe2+ cycle.Fenton process has emerged as one of the most promising alternative strategies for wastewater treatment. Unfortunately, it is still challenging to deal with iron sludge generated during the process, which is of great importance for practical application. Here, we report a green way to modify iron sludge with low amount (0–2 wt%) of graphene as a heterogeneous Fenton catalyst. XRD, FESEM, TEM, Raman and XPS results suggested that the iron sludge existed as FeOOH particles that were mainly entrapped inside the graphene sheet. BET results confirmed the mesoporous structure of the composites. Under the optimal conditions, the degradation rate of rhodamine B, acid red G and metronidazole by the iron sludge-graphene catalyst reached 99.0%, 98.5% and 91.8%, respectively, within 120 min. Moreover, the as-prepared catalyst exhibited wide pH operating range, excellent stability and reusability. The enhanced heterogeneous Fenton property of the composite as compared to bare iron sludge could be ascribed to the mesoporous structure, increased adsorption ability and the promoted ≡FeIII/≡FeII cycle. This work not only provides a new idea of fabricating heterogeneous Fenton catalysts, but may also promote the application of homogeneous Fenton process for wastewater treatment.

A stable and efficient Fe2O3/expanded perlite (Fe2O3-Ep) composite catalyst was synthesized by a simple hydrothermal method for degradation of refractory contaminants in heterogeneous photo-Fenton system. X-ray diffraction and FT-IR analyses confirmed the presence of the Fe2O3 in the synthesized catalyst. The catalytic activity of the Fe2O3-Ep catalyst was evaluated by the degradation of rhodamine B (RhB, 5 mg/L) and metronidazole (MET, 5 mg/L) in the presence of H2O2 under visible light irradiation. The Fe2O3-Ep catalyst exhibited high efficiency for degradation of RhB at a wide pH range from 2 to 10 and showed excellent catalytic property for decomposition of MET as well. The degradation ratio of RhB was achieved 99%, and the removal ratio of COD was 62% within 90 min at the best experimental conditions (0.5 g/L of Fe2O3-Ep catalyst, 2 mL/L of H2O2). Furthermore, iron leaching of the Fe2O3-Ep catalyst during the catalytic degradation reaction was negligible and the catalyst still exhibited high catalytic activity and stability after five cycles. These results show that the catalyst can be used as a highly efficient heterogeneous photo-Fenton catalyst for the degradation of non-biodegradable refractory pollutants in water.

Correction for ‘Controlled synthesis of Bi25FeO40 with different morphologies: growth mechanism and enhanced photo-Fenton catalytic properties’ by Wenda Ji et al., Dalton Trans., 2017, DOI: 10.1039/c6dt04864a.

Bi25FeO40 microtetrahedra, microcubes and microspheres were successfully synthesized by a simple hydrothermal process and by adding different additive agents. The formation mechanism of Bi25FeO40 microcrystals was proposed; the additive agents had important influences on the morphology and facet exposure of the products. The catalytic activity of these materials was evaluated by the degradation of RhB in a heterogeneous photo-Fenton process. The Bi25FeO40 microcubes showed enhanced photo-Fenton catalytic activity, which can be attributed to an exposed {001} facet with the active O atoms. The hydroxyl radicals are the main active group in the heterogeneous photo-Fenton catalytic degradation. This study may provide a new method to design and synthesize novel nanoscale and microscope functional materials.

The La-Fe montmorillonite (La-Fe MMT) composite was synthesized by a simple precipitation method and was used for the degradation of dyes in both batch and fixed bed experiments. X-ray diffraction (XRD) and high-resolution transmission electron microscope analysis (HRTEM) confirmed the existence of Fe2O3 and La2O3 in the composite. The presence of La enhanced the degradation efficiency of dyes by the composite at neutral pH and results in little iron leaching consequently increasing the lifetime. More than 97% and 96% removal of the MB and RhB (100 mg/L each) by the La-Fe MMT Fenton system could be achieved in less than 1 h. The catalyst also exhibited excellent efficiency in fixed bed reactor with 91% MB degradation corresponds to 65% COD removal, even after 200 h of use. The factors such as solution pH, catalyst dosage, H2O2 dosage and temperature on the degradation of dyes were investigated. Fluorescence and quenchers experiments indicated that OH was the main reactive species for the degradation of dyes. Due to the low cost, efficient reactivity, high stability and low metal leaching, the La-Fe MMT possesses a great potential to be a green catalyst for the heterogeneous Fenton-like degradation of hazardous dyes.Download high-res image (99KB)Download full-size image

With the tunable and flexible physicochemical properties, tantalate photocatalysts with tungsten bronze structure are worth being studied. In this work, we successfully synthesized a novel potassium tantalate K6Ta10.8O30 with tungsten bronze structure using a facile solid-state reaction route. The effects of calcination time on the phase composition, morphology and crystallinity of the obtained samples were studied by XRD and SEM analyses. In addition, the photocatalytic activity of the samples was evaluated by the degradation of ARG dye under UV light irradiation. The results indicated that the K6Ta10.8O30 showed high photocatalytic activity for degradation of ARG and the photocatalytic degradation of ARG followed the first order kinetics. Furthermore, the possible photocatalytic mechanism of the K6Ta10.8O30 photocatalyst was proposed based on tungsten bronze structure feature and the scavengers experimental results. This study would give a new insight into tantalate photocatalysts.

•Oxygen vacancies enriched BiOX (X = Cl, Br, I) were prepared at room temperature.•The induction of oxygen vacancy extended the visible light absorption capability.•BiOCl and BiOBr exhibited long visible light induced NO removal activity.•Up-conversion phosphors were coupled with BiOBr to fulfill NIR response.•UV, visible and NIR lights induced NO removal activity were achieved by composite.With the deterioration of air quality, photocatalysis as a green chemical method has attracted increasing attention. Herein, oxygen vacancies enriched BiOX (X = Cl, Br, I) nanoparticles, which were prepared by a facile precipitation method at room temperature, are employed for photocatalytic removal of toxic NO gas. By introducing glycerol in the reaction solution, more oxygen vacancies are produced in BiOX nanoparticle, finally extending light absorption of the samples to longer-wavelength light. The as-prepared BiOCl and BiOBr nanoparticles presented excellent UV, short and long wavelengths of visible lights (>510 nm) induced photocatalytic NO gas removal activity, which are comparable to those of the popular C-TiO2 and N-TiO2. Furthermore, the up-conversion phosphors were coupled with the representative BiOBr nanoparticles by simple method at room temperature to fulfill UV, visible and NIR lights responsive photocatalysis. Owing to the closely contact, narrowed band gap of BiOBr and nice energy conversion from up-conversion phosphor to BiOBr, the up-conversion phosphors/BiOBr composites not only exhibited excellent UV, short and long wavelengths of visible lights driven photocatalytic activity, but also showed promising NIR light induced one. Under the irradiation of NIR light, the calculated apparent quantum efficiencies of NO removal by B-UP/BiOBr and G-UP/BiOBr composites are about 2.52 and 1.92%, respectively. The up-conversion phosphors coupled BiOBr composites in this work provide potential materials for the high efficiency of UV, visible and NIR lights induced photocatalysis toward air decontamination.Download high-res image (183KB)Download full-size image

•{1 1 1} and {1 0 0} facets exposed Bi24Ga2O39 were synthesized by hydrothermal method.•Bi24Ga2O39 enclosed by {1 0 0} facets exhibited enhanced photocatalytic activity.•The removal ratio of Cr(VI) by BGO-C was 100% within 120 min.•DFT calculations show that {1 0 0} facet of Bi24Ga2O39 has lower surface energy.•The electronic structure of {1 0 0} surface results in high photocatalytic activity.The sillenite-type Bi24Ga2O39 photocatalysts with different exposed facets were successfully synthesized using a controlled hydrothermal method and their facet-dependent photocatalyic activity was confirmed by DFT calculation. Bi24Ga2O39 micro-tetrahedrons (BGO-T) enclosed by {1 1 1} facets were obtained at 1 M NaOH and micro-cubes (BGO-C) enclosed by {1 0 0} facets were obtained with ammonium hydroxide as mineralizer. The photocatalytic performances of the catalysts were evaluated by the reduction of Cr(VI) in water under irradiation of visible light (λ > 400 nm). The BGO-C enclosed by {1 0 0} facets showed higher photocatalytic activity toward Cr(VI) reduction than the other samples. XPS analysis revealed the reduction of Cr(VI) into Cr(III) happened over Bi24Ga2O39 photocatalyst under visible light illumination. The surface energy calculated by VASP showed that the cleavage energy of (1 0 0) surface was lower than that of (1 1 1) surface, which was consistent with our experimental results. The mechanism on the facet-dependent photocatalytic property of Bi24Ga2O39 has been investigated by the surface electronic structures and photoluminescence spectra.Download high-res image (135KB)Download full-size image

•Ag@Pt/sepiolite catalysts were prepared by a successive reduction method.•Core-shell Ag@Pt nanoparticles were highly dispersed on sepiolite nanofibers.•The Ag@Pt core-shell structure enhanced the reduction of nitrophenols with NaBH4.•DFT calculations confirmed the contribution of Ag@Pt core-shell structure.•s-d Hybridization and charge redistribution existed between Ag cores and Pt shells.We reported the enhanced catalytic property of core-shell Ag@Pt nanoparticles supported on sepiolite nanofibers for the reduction of nitrophenols in the presence of NaBH4. Furthermore, we confirmed the contribution of core-shell structure to the enhanced catalytic performance of Ag@Pt nanoparticles by DFT calculations. The Ag@Pt/sepiolite catalysts were prepared using a successive reduction method, in which core-shell Ag@Pt nanoparticles were highly dispersed on sepiolite nanofibers. DFT calculations showed that the charge redistribution and s-d hybridization between Ag cores and Pt shells contributed to the unique electronic structure of Ag@Pt nanoparticles. More importantly, 2 wt.% Ag@Pt/sepiolite catalyst exhibited much higher catalytic activity toward nitrophenols reduction than Ag/sepiolite and Pt/sepiolite, and relatively high catalytic stability even after 5 cycles. The enhanced catalytic performance of Ag@Pt/sepiolite catalysts was primarily owing to the large surface area and high porosity of sepiolite nanofibers and the unique electronic structure of core-shell Ag@Pt nanoparticles, which resulted in the effective adsorption of nitrophenols and the electron transfer from BH4− to nitrophenols, respectively. This study probably provides new insights into the catalytic reduction of nitrophenols in water by forming the composite between bimetallic core-shell nanoparticles and natural low-cost supports.Download high-res image (103KB)Download full-size image

•A new sillenite-type Bi12MnO20 photocatalyst was prepared by a facile sol-gel route.•The Bi12MnO20 exhibited strong UV, visible and NIR lights absorption capability.•The hybrid of O 2p and Mn 3d orbits led to excellent light absorption properties.•The DFT calculation and DRS confirmed the existence of intermediate band.•Bi12MnO20 showed high full spectrum photocatalytic activity for reduction of Cr(VI).Although UV and visible lights induced photocatalysis has been well developed in recent years, the full spectrum of UV, visible and NIR lights responsive photocatalysis is still few, which is beneficial for energy utilization and practical application. Herein, we report a new sillenite-type Bi12MnO20 photocatalyst prepared by a facile sol-gel method. Through incorporating the Mn4+ ions into tetrahedral sites of metastable cubic γ-Bi2O3 to split the 3d orbits of Mn4+, the new-produced Bi12MnO20 crystal presents peculiar and strong absorption capability, covering the full spectrum of UV, visible and NIR lights in the range of 200–1300 nm. The DFT calculation further confirms the existence of intermediate band state in the band gap of Bi12MnO20, which was formed by the hybrid of O 2p and Mn 3d orbits. More importantly, under the irradiation of UV, visible and NIR lights, Bi12MnO20 product exhibits excellent photocatalytic reduction activity for Cr(VI), which is mainly due to the relatively good charge separation enhanced by unique electronic structure of the Bi3+ 6s2 lone pair, the suitable band positions and the introduction of intermediate band state. In addition, the Bi12MnO20 specimen also displays good visible light driven photocatalytic oxidation property for acid red G, which is mainly caused by h+ and O2− species. The as-prepared Bi12MnO20 semiconductor would provide a new potential to fulfill the full spectrum responsive photocatalysis.Download high-res image (211KB)Download full-size image

•Novel Z-scheme visible-light-driven Bi12GeO20/g-C3N4 photocatalysts were prepared.•The Bi12GeO20/g-C3N4 composites exhibited enhanced photocatalytic activities.•The degradation of microcystin-LR and RhB is an oxygen-induced reaction.•The reduction of aqueous Cr(VI) is a proton assisted electron transfer reaction.We successfully synthesized novel solid state Z-scheme visible-light-driven Bi12GeO20/g-C3N4 composite photocatalysts and investigated their photocatalytic activities for degradation of microcystin-LR and RhB, and for reduction of aqueous Cr(VI). The TEM and HRTEM images clearly showed the heterogeneous nanostructures at the interface between Bi12GeO20 and g-C3N4. The as-prepared Bi12GeO20/g-C3N4 composites exhibited enhanced photocatalytic activities for the degradation of microcystin-LR and RhB aqueous solution and reduction of aqueous Cr(VI) as compared to the pure Bi12GeO20 and g-C3N4 under visible-light irradiation. On the basis of the radical species trapping experiments and ESR analyses, O2− and h+ were confirmed to be the mainly active species involved in the degradation of organic pollutants and this reaction was identified to be an oxygen-induced pathway. Meanwhile, combined with the in situ ATR-FTIR spectroscopy and kinetic isotope effect investigations, the photocatalytic reduction of aqueous Cr(VI) was identified as a proton assisted electron transfer reaction. Moreover, the enhanced photocatalytic activities of the Bi12GeO20/g-C3N4 composites can be attributed to the improved photo-absorption properties and effective separation of photo-induced charge carriers caused by the Z-scheme system of the as-prepared Bi12GeO20/g-C3N4 composites.Download high-res image (151KB)Download full-size image

•TiO2 microspheres with exposed {001} facets were successfully synthesized.•Pt-TiO2 catalyst combined the properties of Pt nanoparticles and TiO2 {001} facet.•The catalyst exhibited an enhanced visible-light photocatalytic activity.•The formation mechanism of TiO2 microspheres with exposed {001} facets was studied.In this study, TiO2 microspheres with exposed {001} facets were successfully synthesized by a low-temperature hydrothermal method without using any organic solvents as morphology controlling agent. Furthermore, an active Pt-TiO2 catalyst was prepared by impregnation and deposition-precipitation methods with reduction processes. The photocatalytic activity of the samples was evaluated by degradation of formaldehyde in air under visible light irradiation at room temperature. After modification with Pt, the optical absorption property of the Pt-TiO2 microspheres was extended to visible light range. More importantly, the Pt-TiO2 microspheres exhibited excellent photocatalytic performance for formaldehyde degradation under visible light irradiation, being superior to pure TiO2 microspheres and even Pt-P25. The formation mechanism of the TiO2 microspheres with exposed {001} facets was studied. Moreover, the proper photocatalytic mechanism was also proposed. This work provided new insight into the improvement of photocatalytic activity by special high-energy facet exposing and noble metal depositing.Download high-res image (124KB)Download full-size image

Engineering exposed facets for improving the activation of molecular oxygen into O2˙− species and charge separation is a promising way to improve photocatalytic oxidation activity. Herein, SrTiO3 nanocrystals with controllably exposed {001} and {110} facets are prepared as a proof-of-concept candidate to study the effect of exposed facets on the activation of molecular oxygen into O2˙− species, finally acting on the photocatalytic oxidation of gaseous HCHO. The photocatalytic test demonstrates that {110} facet exposed SrTiO3 nanoparticles present a HCHO photocatalytic degradation rate about 6.8 times faster than that of the {001} facet exposed one. The experiments and theoretical calculations together confirm that as compared to the {001} facet exposed sample, the {110} facet exposed sample is favorable for activating molecular oxygen to produce O2˙− species under the irradiation of light, owing to the relatively higher conduction band position and lower surface adsorption energy for O2 molecules as well as advantageous charge accumulation on adsorbed O2 molecules. Finally, the new production of O2˙− species and the higher charge separation contribute to the superior HCHO photocatalytic oxidation activity of {110} facet exposed SrTiO3. This interesting finding is probably useful for the design of highly efficient single crystal photocatalysts for photocatalytic oxidation reactions.

•The nZVI/R composite was used for the removal of MO under ultrasound (US).•US irradiation apparently enhanced the degradation ratio of MO by nZVI/R system.•The degradation ratio of MO by the nZVI/R under US was 93% within 20 min.•The composite was efficient for the degradation of MO over a wide pH range of 2–9.•The US/nZVI/R system was also efficient for the degradation of metronidazole.In this study, the rectorite-supported nanoscale zero-valent iron (nZVI/R) was synthesized through a reduction method. X-ray diffraction analysis showed the existence of the nZVI in the nZVI/R composite and X-ray photoelectron spectroscopy analysis indicated that the nZVI particles were partly oxidized into iron oxide. Scanning electron microscopy analysis revealed that the nZVI particles were highly dispersed on the surface of the rectorite. The specific surface area of the nZVI/R composite is 21.43 m2/g, which was higher than that of rectorite (4.30 m2/g) and nZVI (17.97 m2/g). In the presence of ultrasound (US), the degradation of methyl orange and metronidazole by the nZVI/R composite was over 93% and 97% within 20 min, respectively, which is much higher than that by the rectorite and the nZVI. The degradation ratio of methyl orange and metronidazole by the nZVI/R composite under US was 1.7 and 1.8 times as high as that by the nZVI/R composite without US, respectively. The mechanism of the enhanced degradation of methyl orange and metronidazole under US irradiation was studied. These results indicate that the US/nZVI/R process has great potential application value for treatment of dye wastewater and medicine wastewater.

A novel Fe–MMT-I composite was synthesized during the degradation of rhodamine B (RhB) through Fenton's method, which could degrade RhB (concentration as high as 1000 mg L−1), reuse iron sludge and obtain a highly efficient bifunctional composite at the same time. X-ray diffraction analysis confirmed the existence of FeOOH in the composite. It is interesting to observe that the introduction of RhB leads to more FeOOH inserted into the layer of MMT, which enhanced both the adsorption and heterogeneous photo-Fenton activities of the composite. The Fe–MMT-I was efficient for the adsorption of RhB over a wide pH range (2.06–9.72). The Fe–MMT–RhB still exhibited a high adsorption capacity toward RhB even after five recycles using the heterogeneous Fenton method to regenerate the spent adsorbent. Furthermore, the Fe–MMT-I composite showed high efficiency for photo-Fenton discoloration of RhB with a wide operating pH range (2.01–11.67). Photoluminescence measurement and a leaching test demonstrated that the discoloration of RhB by the composite could be attributed to the synergetic effects of the enhanced adsorption power of the composite and the hydroxyl radicals initiated through the heterogeneous photo-Fenton process. This green method could lead to the construction of combined homogeneous and heterogeneous Fenton processes, which gives new insight into fabricating novel bifunctional composites for environmental remediation.

•Facet coupled tetrahedronal Bi12TiO20/g-C3N4 was synthesized by ultrasonic method.•DFT calculations show that {111} facet of Bi12TiO20 has the highest surface energy.•A facet coupling exists among Bi12TiO20-{111} facet and g-C3N4-{002} facet.•A well matched band alignment structure is formed between Bi12TiO20 and g-C3N4.•The facet coupling and the band alignment enhanced the photocatalytic activity.Uniform Bi12TiO20 microtetrahedrons exposed by {111} facets were synthesized by a controlled hydrothermal method. Well resolved density functional theory (DFT) calculations showed that {111} facet was the most active facet with the highest surface energy among the low index facets of Bi12TiO20. Series of facet coupled microtetrahedronal Bi12TiO20/g-C3N4 composites were prepared via a simple two-step method. The interface structure of composite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), and fourier transform infrared (FT-IR) spectroscopy analyses, showing that the interface of Bi12TiO20/g-C3N4 composite was connected by the {111} facets of Bi12TiO20 and the {002} facets of g-C3N4. Owing to this typical structure, the Bi12TiO20/g-C3N4 composite with mass ratio 0.5:0.02 of Bi12TiO20 to g-C3N4 presented higher photocatalytic activity for degradation of gaseous formaldehyde under visible light irradiation (λ ≥ 400 nm) as compared to the pure g-C3N4 and the as-obtained Bi12TiO20. Furthermore, the band structure calculations were employed to investigate the photocatalytic mechanism of Bi12TiO20/g-C3N4 composite.

Novel Bi2SiO5/AgI nanoplate photocatalysts with exposed {100} facets on the surfaces of Bi2SiO5 nanoplates were synthesized via an in situ precipitation method. Acid red G aqueous solution and gaseous formaldehyde were chosen as model organic pollutants to evaluate the photocatalytic activities of the as-prepared catalysts. Under visible light irradiation (>420 nm), the Bi2SiO5/AgI nanoplates exhibited enhanced photocatalytic activities as compared to pure Bi2SiO5 or AgI. X-ray photoelectron spectroscopy (XPS) reveals that a small amount of metallic Ag was formed on the surface of AgI during the photocatalytic reaction, thus leading to the transformation from Bi2SiO5/AgI to Bi2SiO5/AgI@Ag. The excellent photocatalytic activities of the Bi2SiO5/AgI nanoplates can be ascribed to the photocatalytic system composed of Bi2SiO5, AgI and metallic Ag and the inner electric field caused by the exposure of {100} facets on the Bi2SiO5 nanoplates. The as-prepared catalysts retained good photocatalytic activity after four recycles and the radical species involved in the degradation process have been investigated by using PL spectra and trapping experiments.

A series of graphene oxide (GO)–FePO4 composites with different GO weight ratios (2.5%, 5%, 10%, w/w) were prepared using a simple precipitation process and were firstly used as heterogeneous photo-Fenton catalysts. FESEM images prove the loose structure of the 5GO–FePO4 composite. UV–vis analysis demonstrates that the introduction of GO could enhance solar energy utilization of the composites. Under visible light irradiation, the degradation rate of rhodamine B (RhB) by the 5GO–FePO4 composite was 2.87 times more than that by the pure FePO4 in the presence of hydrogen peroxide. The composite was highly effective for the degradation of RhB in a wide pH range of 2.18–10.40 with negligible iron leaching. Moreover, the composite still showed high catalytic activity after six cycles, which makes it a promising heterogeneous catalyst for wastewater treatment. The introduction of GO promotes the photo-Fenton reaction of GO–FePO4 via three roles: offering more active sites, increasing adsorption capacity and accelerating the Fe3+/Fe2+ cycle by improving the utilization of solar energy. Our work may provide new insights for the development of new effective heterogeneous photo-Fenton catalyst.

•Micro/nanostructured Ag2ZnGeO4 hollow spheres were synthesized by a facile method.•The formation mechanism for the Ag2ZnGeO4 hollow spheres was investigated.•The catalyst exhibited an enhanced visible-light photocatalytic activity.•The reactive species in the photocatalytic process were studied.Micro/nanostructured Ag2ZnGeO4 hollow spheres were successfully synthesized by a one-step and low-temperature route under ambient pressure. The micro/nanostructured Ag2ZnGeO4 hollow spheres have a diameter of 1–2 μm and their shells are composed of numerous nanoparticles and nanorods. The growth process of the micro/nanostructured Ag2ZnGeO4 hollow spheres was investigated in detail. The results indicated that the morphologies and composition of Ag2ZnGeO4 samples were strongly dependent on the dose of the AgNO3 and reaction time. Excessive AgNO3 was favorable for the nucleation and growth rate of Ag2ZnGeO4 crystals and the formation of pure Ag2ZnGeO4. Moreover, the formation mechanism of the micro/nanostructured Ag2ZnGeO4 hollow spheres is related to the Ostwald ripening. Under the same conditions, the photocatalytic activity of micro/nanostructured Ag2ZnGeO4 hollow spheres is about 1.7 times and 11 times higher than that of bulk Ag2ZnGeO4 and Degussa P25, respectively. These interesting findings could provide new insight on the synthesis of micro/nanostructured ternary-metal oxides with enhanced photocatalytic activity.

•The Fe2O3–Kaolin composite was synthesized as heterogeneous photo-Fenton catalyst.•The efficient degradation of RhB and MB was achieved by using Fe2O3–Kaolin and H2O2.•The degradation of RhB by the Fe2O3–Kaolin catalyst could occur over a wide pH range.•The catalyst is efficient, inexpensive, stable and showed negligible iron leaching.An efficient Fe2O3–Kaolin was synthesized as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants. X-ray photoelectron spectroscopy analysis and high-resolution transmission electron microscope analysis confirmed the existence of Fe2O3 nanoparticles in the Fe2O3–Kaolin composite. The specific surface area of the Fe2O3–Kaolin catalyst increased from 19.47 to 39.32 m2/g compared to kaolin. The catalytic activity of the Fe2O3–Kaolin catalyst was evaluated by the photo-Fenton degradation of rhodamine B (RhB) under visible light irradiation and the results showed that the catalyst was highly effective for the degradation of RhB in a wide pH range of 2.21–10.13. At optimal conditions, 98% discoloration and 66% mineralization of RhB were achieved in 120 min. The catalyst was efficient for the degradation of methylene blue as well. Leaching test indicated that the leached iron from the catalyst was negligible and the catalyst still showed high photocatalytic activity after five reaction cycles, which all showed that the Fe2O3–Kaolin catalyst is a promising heterogeneous photocatalyst for the degradation of various dyes in wastewater. Finally, a possible photocatalytic mechanism was proposed based on photoluminescence measurements and a series of operating conditions.

The ability to suppress the recombination of the photoinduced charges is the key prerequisite for an excellent photocatalyst, which has attracted extensive and continuous interest in the field of photocatalysis. Herein, we presented a convenient strategy for the one-step selective synthesis of ultrathin BiOBr nanosheets with atomic thickness through a simple solvothermal method. These ultrathin BiOBr nanosheets not only show high exposure percentage of active (001) facets but also have an optimized band structure, which synergistically facilitates the electron–hole pair separation to realize significantly promoted visible-light photocatalytic activity. Our results provide a new avenue and direction for the design of photocatalysts with high visible-light photocatalytic performance.

Clay materials including clay minerals and layered double hydroxides (LDHs) have attracted great attention because of their special layer structures, large specific surface areas, and remarkable adsorption capacities. In the past few decades, they have been regarded as important components or precursors for making various functional materials. This paper aims to review and summarize the recent advances in the synthesis and photocatalytic applications of clay-based photocatalysts. Moreover, the effects of surface and structural characteristics of clay-based photocatalysts on photocatalytic properties are also discussed. The clay-based photocatalysts show good application prospects for environmental remediation and energy conversion. Especially, H2 generation and reduction of CO2 into carbon sources can be easily achieved using the LDH-based photocatalysts. Meanwhile, the role of clay materials in the photocatalysis is discussed in detail.

In this study, Zn2GeO4 hollow spheres were successfully fabricated by a template-engaged approach using zinc hydroxide carbonate (Zn4CO3(OH)6·H2O, ZHC) spheres as the template. During the hydrothermal process, Zn2+ dissolved from the surface of the ZHC spheres could rapidly react with the HGeO3− in solution and the Zn2GeO4 outer shell was formed in situ. Moreover, the building units of the Zn2GeO4 hollow spheres could gradually transform from the nanoparticles into nanobundles with the increase of the reaction time. The photocatalytic degradation results indicate that the Zn2GeO4 hollow spheres exhibited high photocatalytic activity and excellent stability for the degradation of antibiotic metronidazole in solution. Finally, the radical species involved in the degradation process have been investigated by using the scavenger experiments.

Hierarchical Zn2GeO4 microspheres have been successfully synthesized via a simple template-free and mild hydrothermal method, using Zn(NO3)2·6H2O and GeO2 as Zn and Ge sources, respectively. The as-prepared samples were characterized by XRD, SEM, FESEM, TEM, nitrogen adsorption, UV-vis diffuse reflectance spectrum, and FTIR. The hierarchical Zn2GeO4 microspheres were found to be constructed of randomly aggregated nanorods which have dimensions of about 0.5–1 μm in length and 200–500 nm in width. A formation mechanism of hierarchical Zn2GeO4 microspheres was proposed. The hierarchical Zn2GeO4 microspheres exhibited relatively high photocatalytic activities and stability for degradation of organic pollutants under UV light irradiation. In addition, the radical species involved in the degradation process have been investigated by using the PL spectra and scavenger experiments.

The heat-activated sepiolite, which was prepared using sepiolite by thermal treatment at different temperatures, was used as an absorbent for the removal of rhodamine B (RhB) from aqueous solutions. The structure and morphology of the as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The adsorption capacity of RhB onto the heat-activated sepiolite has been examined with pH, adsorbent dosage, contact time, initial dye concentration, and temperature. Kinetic studies showed that the equilibrium was attained within 40 min, and the kinetic data were well described by the pseudo-second-order kinetic model. Besides, the experimental data (R2>0.999) fitted the Freundlich model better than the Langmuir model. The as-prepared sample showed higher adsorption capacity (8.33 mg/g) for the removal of RhB than that of sepiolite, which could be attributed to more adsorption sites caused by appropriate heat treatment. The adsorbent can be well regenerated by calcination at 400 °C for 2 h and regenerated sepiolite did not exhibited significant loss of adsorption activity after five recycles.

In this study, we prepared a new visible light induced plasmonic photocatalyst AgAgClTiO2/rectorite using a facile deposition–photoreduction method. The catalysts were characterized using X-ray diffraction (XRD), UV–visible diffused reflectance spectra (UV–vis DRS), Raman spectra, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The as-prepared AgAgClTiO2/rectorite powders exhibited an efficient photocatalytic activity for the degradation of acid orange (ARG) and 4-nitrophenol (4-NP) under visible light irradiation (λ > 400 nm). Moreover, the mechanism suggested that the high photocatalytic activity is due to the charge separation and the surface plasmon resonance of metallic Ag particles in the region of visible light. The active species measurements suggested that HOHO is not the dominant photooxidant. Direct hole transfers and O2- were involved as the active species in the photocatalytic reaction.Graphical abstractHighlights► AgAgClTiO2/rectorite composite was prepared by a deposition–photoreduction method. ► The composite exhibited excellent visible light photocatalytic activity. ► h+ and O2- were considered the major reactive species in the photocatalytic process.

The micro/nano-structured CaWO4/Bi2WO6 composite was successfully synthesized by a one-step hydrothermal route without using any templates or surfactants. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry-differential scanning calorimetry (TG-DSC) and Brunauer–Emmet–Teller (BET) theory. The results indicated that the composite has a two-phase composition: CaWO4 and Bi2WO6. The photocatalytic activities of the CaWO4/Bi2WO6 composite were evaluated for the degradation of Rhodamine B (RhB) dye and 4-nitrophenol (4-NP) in aqueous solution under visible-light irradiation (>420 nm), which were 4.5 times and 2.5 times higher than that of the pure Bi2WO6, respectively. On the basis of the calculated energy band positions, the mechanism of enhanced photocatalytic activity for the micro/nano-structured CaWO4/Bi2WO6 composite can be attributed to the effective separation of electron–hole pairs.

A new photocatalyst, namely single-crystalline Bi5O7NO3 nanofibers, was prepared by a facile hydrothermal method in the presence of Triton X-100 and ammonia. Bi5O7NO3 possessing a crystalline sheet morphology could be dissolved and transformed into nanofibers by controlling the reaction time. Samples were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy. The Bi5O7NO3 nanofiber growth mechanism is discussed in detail. The band gap energy of the as-prepared Bi5O7NO3 photocatalyst was about 2.70–2.90 eV. Results of first-principle density functional theory calculations confirmed that Bi5O7NO3 had a narrow band gap. They revealed that the conduction band bottom was predominantly composed of Bi 6s, Bi 6p, N 2p and O 2p orbitals, while the valence band (VB) top primarily consisted of Bi 6p, Bi 6s and O 2p orbitals. The as-obtained Bi5O7NO3 nanofibers showed good photocatalytic activity and stability for the degradation of Rhodamine B (RhB) under visible light irradiation, which may be ascribed to the highly mobile conduction band (CB) and VB charge carriers.Graphical abstractSingle-crystalline Bi5O7NO3 nanofibers were prepared and showed a high visible-light photocatalytic efficiency for the degradations of RhB..Research highlights► Single-crystalline Bi5O7NO3 nanofibers were prepared by a facile hydrothermal method. ► Bi5O7NO3 sheets could be dissolved and transformed into nanofibers. ► Bi5O7NO3 nanofiber material exhibited a high visible-light photocatalytic activity. ► The charge carriers in the CB and VB were highly mobile.

Cu-doped KNb3O8 photocatalysts were prepared using a simple solid-state method. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectrum. XRD and SEM analyses suggest that Cu doping can induce the formation of the compound K6Nb10.8O30 with tungsten–bronze structure and the relative content of K6Nb10.8O30 in the Cu-doped samples increased with increasing Cu doping amount. When the Cu doping amount reaches 2 wt.%, the as-prepared sample is mainly composed of K6Nb10.8O30. The photocatalytic properties of the catalysts were evaluated using the degradation of acid red G. The results showed that Cu-doping significantly increased the photocatalytic activity of the KNb3O8 catalyst. The optimum dopant concentration range of Cu was found to be 0.3–1 wt.%. The synergistic effect of Cu doping and mixed phase niobate compounds is responsible for the enhanced photocatalytic activity.Highlights► Cu-doped KNb3O8 photocatalysts were prepared by a simple solid-state method. ► Cu doping can induce the formation of mixed phase niobates with KNb3O8 and K6Nb10.8O30. ► Cu doping and mixed phase niobates synergistically enhanced the photocatalytic activity.

In this study, monodisperse porous ZnO spheres were fabricated by a facile and low-cost soluble-starch-assisted method. The as-obtained samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV−vis diffuse reflectance spectroscopy (DRS), thermogravimetric and differential scanning calorimetry (TG−DSC), Fourier transform infrared (FTIR) spectroscopy, and Brunauer−Emmett−Teller (BET) analysis. The Raman spectra revealed that the uncalcined powders were composed of ZnO and starch. The BET analysis showed that mesopores (25 nm) and macropores (180 nm) coexisted in the typical porous ZnO spheres. The photocatalytic activities of the as-obtained ZnO samples were evaluated in the photocatalytic degradations of aqueous solutions of rhodamine B (RhB) and 4-nitrophenol (4-NP) at room temperature. A possible growth mechanism of the as-obtained porous ZnO spheres is also discussed.

H+-rectorite clay, which was prepared by modifying the raw rectorite with 10% hydrochloric acid at 60 °C for 24 h, was used as an absorbent for removal of methyl blue (MB) from aqueous solutions. The morphology and the structure and crystallinity of the pristine rectorite and the H+-rectorite were characterized by scanning electron microscopy (SEM) technique and X-ray diffraction (XRD) technique, respectively. The results showed that the H+-rectorite exhibited high adsorption ability than the raw rectorite, and it was found that the removal percentage of MB increased with increasing in adsorbents dose, whereas the adsorption amount qe (mg/g) decreased. The equilibrium was attained within 30 min in adsorption process, and the maximum adsorption capacity of H+-rectorite for methylene blue reached as high as 37 mg/g. Besides, the effect of temperature on the adsorption of MB with H+-rectorite was investigated and the equilibrium data were well fitted to Freundlich equations. The H+-rectorite absorbent saturated with MB can be regenerated by calcinating at 400 °C for 2 h and the regenerated absorbent still showed higher percentage removal of MB.

The TiO2/rectorite composites with a bicrystalline (anatase and rutile) framework were synthesized by a facile sol–gel method using titanium tetraisopropoxide as a TiO2 precursor at different temperatures. The as-obtained composites were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectrum, and Brunauer–Emmett–Teller (BET). XRD and HRTEM analyses confirm that the layered structure of rectorite in the TiO2/rectorite composites was destroyed to some extent. The TiO2/rectorite composites prepared at low temperature (80 °C) without calcination exhibited strong adsorbility for acid red G (ARG), and showed a high photocatalytic activity for the decomposition of ARG and the persistent organic pollutant 4-nitrophenol (4-NP) under UV irradiation. The excellent photocatalytic activity of the as-obtained composites can be attributed to the synergetic effect of the anatase–rutile mixed phase and bimodal pore structure in the composites. A possible mechanism of the photocatalysis over the TiO2/rectorite composites was proposed.Graphical abstractUV–vis absorption spectral changes of ARG during the photocatalytic process over the TiO2/rectorite composites obtained at 80 °C under UV light irradiation.Highlights► TiO2/rectorite composites with bicrystalline framework were prepared successfully. ► The mixed-phase titania contributes to high photocatalytic activity of composites. ► The OH was considered the main reactive species in the photocatalysis process.

An efficient Fe2O3-pillared rectorite (Fe-R) clay was successfully developed as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants. X-ray diffraction analysis and high-resolution transmission electron microscope analysis clearly showed the existence of the Fe2O3 nanoparticles in the Fe-R catalyst. The catalytic activity of the Fe-R catalyst was evaluated by the discoloration and chemical oxygen demand (COD) removal of an azo-dye rhodamine B (RhB, 100 mg/L) and a typical persistent organic pollutant 4-nitrophenol (4-NP, 50 mg/L) in the presence of hydrogen peroxide (H2O2) under visible light irradiation (λ > 420 nm). It was found that the discoloration rate of the two contaminants was over 99.3%, and the COD removal rate of the two contaminants was over 87.0%. The Fe-R catalyst showed strong adsorbability for the RhB in the aqueous solution. Moreover, the Fe-R catalyst still showed good stability for the degradation of RhB after five recycles. Zeta potential and Fourier transform infrared spectroscopy were used to examine the photoreaction processes. Finally, a possible photocatalytic mechanism was proposed.

Most of tantalate photocatalysts are mainly synthesized by solid-state (SS) reaction methods and only show photocatalytic activity under UV light irradiation. Ta2O5 as a raw material shows an extremely high chemical stability, limiting its application to a few systems. A novel nanometer Bi3TaO7 photocatalyst was synthesized by a facile and low-cost sol–gel method using Ta2O5 and Bi(NO3)3·5H2O as the Ta and Bi sources, respectively. The as-obtained samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The band gap energy of the as-obtained nanometer Bi3TaO7 photocatalyst was determined to be about 2.75–2.86 eV. The Bi3TaO7 nanopowders show a strong adsorbability and a high visible-light photocatalytic activity for the degradation of 4BS, which can be ascribed to the surface physicochemical properties and structure of the Bi3TaO7 nanometer catalyst. The degradation of 4BS is attributed to the photocatalysis but not to the adsorption of 4BS on the as-prepared catalyst.A novel nanometer Bi3TaO7 photocatalyst was synthesized by a facile and low-cost sol–gel method, which showed a strong adsorbability and a high visible-light photocatalytic activity for the degradation of 4BS.

N-doped TiO2/rectorite (NTR) mesoporous materials were synthesized and characterized by XRD, TEM, BET, XPS, FTIR, and UV–vis DRS. The XRD analysis indicated that the layered structure of rectorite was destroyed to some extent. TiO2 in the composites exists in anatase phase. The XPS and FTIR analyses confirm that nitrogen was doped into TiO2 lattices successfully. The UV absorption edges of the NTR samples showed a red shift as compared to that of the undoped TiO2. The NTR photocatalyst prepared at 400 °C showed a strong adsorption capability and a high visible light photocatalytic activity, which could be attributed to the synergetic effects of the rectorite structure and the N-doping.Graphical abstractResearch highlights► The N-doped TiO2/rectorite mesoporous composites were prepared successfully. ► The composites with large specific surface area showed a strong adsorption. ► The N-doping resulted in a red shift of the UV absorption edges of the composites. ► The composites showed a high visible light photocatalytic activity

Nanometer Bi2WO6 catalyst with visible-light responsive was prepared by a sol–gel method in the presence of EDTA. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectrum, Fourier transform infrared (FTIR) spectrum, Brunauer–Emmet–Teller (BET). The UV–vis diffuse reflectance spectrum of the as-prepared sample shows a markedly blue-shift as compared to that of the sample obtained by a solid-state reaction. The as-prepared samples exhibited higher activities than that synthesized by the solid-state reaction for 4BS photodegradation under visible-light irradiation (λ>400 nm) and the sample prepared at 450 °C exhibited the highest photocatalytic activity.

Nanosized Bi3NbxTa1−xO7 photocatalysts were prepared by a facile and low-cost sol−gel method using stable, less toxic Ta2O5, Nb2O5, and Bi(NO3)3·5H2O as the raw materials. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectroscopy. The Bi3NbxTa1−xO7 nanoparticles exhibited an efficient photocatalytic activity in the decomposition of acid red G (ARG) dye solution under visible light irradiation. Besides decoloring, the typical sample Bi3Nb0.6Ta0.4O7 also showed an excellent photocatalytic property for the removal of the cyanotoxin, microcystin-LR (MC-LR, an emerging contaminant from the Contaminant Candidate Lists (CCLs 1-3) of the USEPA). The excellent visible light photocatalytic activity of the samples was mainly attributed to their narrow band gaps, small particle size, and the oxygen vacancies on the surface of the catalysts. According to experimental results, a possible mechanism of the photocatalysis over Bi3NbxTa1−xO7 was proposed.

The nanometer potassium niobate powders with tungsten bronze (TB)-type structure were synthesized by a wet chemical method and characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). X-ray photoelectron spectroscopy (XPS) analysis confirmed the niobium with mixed valence states exists in the crystal structure of the photocatalyst, which may be advantage for increasing the photocatalytic activity. The band gap of K6Nb10.8O30 powders was estimated to be about 2.92 eV and shows a markedly blue-shift as compared to that of the sample obtained by the solid-state reaction. The photocatalytic activity of the samples was evaluated by degradation of acid red G under UV irradiation and the photocatalytic reaction follows first-order kinetics. The photocatalytic activity of the as-prepared sample is much higher than that of sample synthesized by solid-state reaction, and slightly higher than that of P25-TiO2.The K6Nb10.8O30 powders with TB-type structure were synthesized by a wet chemical method at lower temperature. The particle size of the as-prepared powders is much smaller than that of the sample by obtained solid-state method and its photocatalytic activity is much higher than that of the latter and slightly higher than that of P25-TiO2.

The photocatalytic activities of nitrogen and sulfur codoped TiO2 pillared montmorillonite (N,S-TiO2-PILM) for the degradation of 4BS dye under visible-light irradiation (λ >400nm) were studied. The catalysts were synthesized by impregnating doped titania sol into the interlayer of montmorillonite (MMT) and characterized by the UV−vis diffuse reflectance spectra, transmission electron microscopy, and the FT-IR absorption spectra. The ordered structure of MMT was destroyed to some extent and the size of TiO2 particles is about 2−6 nm. The absorption edge of the doped samples shows a red-shift as compared to that of pure TiO2. The photocatalyic activity of N,S-TiO2-PILM with a mole ratio of Ti:S of 1:4 and obtained at 350 °C for 2 h is higher than that of the other samples and Degussa P25 under visible light irradiation. The chromophore in the molecular structure of 4BS was destroyed completely by the photocatalytic reaction and the naphthalene rings and benzene rings were also decomposed partly.

An efficient visible light photocatalyst of AgAgBr/attapulgite nanocomposite was prepared via the reaction between Ag+ and Br- ions in the presence of attapulgite and then reducing partial Ag+ ions to Ag0 species via the light-induced chemical reduction. Characterization methods, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–visible diffused reflectance spectroscopy (UV–vis DRS) were employed to study the phase structure, chemical state and optical properties of the nanocomposite. The AgAgBr/attapulgite nanocomposite exhibited an efficient photocatalytic activity for the degradation of Rhodamine B (RhB) aqueous solution under visible light radiation (λ > 400 nm). In addition, the photoactive radical species involved in the degradation reaction have been investigated by using the HO‐trapping photoluminescence (PL) spectra and quenching experiments. A possible photodegradation mechanism of RhB dye by the AgAgBr/attapulgite nanocomposite was postulated.Highlights► The AgAgBr/attapulgite nanocomposite photocatalyst was prepared. ► The nanocomposite exhibited excellent visible-light photocatalytic activity. ► The possible photocatalytic mechanism was postulated.

ZnMoO4 with a rhombus sheet or flower-like structure, α-ZnMoO4 and needle-like ZnMoO4·0.8 H2O were successfully synthesized by simple hydrothermal crystallization processes with citric acid. ZnMoO4·0.8 H2O was easily synthesized in a shorter reaction time (2 h) at a higher reactant concentration. It gradually transformed into ZnMoO4 with a monoclinic wolframite tungstate structure with an increased reaction time, and pure ZnMoO4 was obtained with a longer reaction time (8 h). Citric acid (CA) played an important role in controlling the morphology of the as-obtained molybdates. The α-ZnMoO4 and ZnMoO4 were synthesized by heating ZnMoO4·0.8 H2O at 130 °C for 4 h and 8 h, respectively, under hydrothermal conditions. With transforming of ZnMoO4·0.8 H2O to α-ZnMoO4 and further to ZnMoO4, the needle-like crystals gradually disappeared and were transformed into crystals with rhombus sheet morphology and then further to pentacle or flower-like crystals that can be ascribed to continuous splitting and growing of the rhombus sheets.

The micro/nano-structured CaWO4/Bi2WO6 composite was successfully synthesized by a one-step hydrothermal route without using any templates or surfactants. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry-differential scanning calorimetry (TG-DSC) and Brunauer–Emmet–Teller (BET) theory. The results indicated that the composite has a two-phase composition: CaWO4 and Bi2WO6. The photocatalytic activities of the CaWO4/Bi2WO6 composite were evaluated for the degradation of Rhodamine B (RhB) dye and 4-nitrophenol (4-NP) in aqueous solution under visible-light irradiation (>420 nm), which were 4.5 times and 2.5 times higher than that of the pure Bi2WO6, respectively. On the basis of the calculated energy band positions, the mechanism of enhanced photocatalytic activity for the micro/nano-structured CaWO4/Bi2WO6 composite can be attributed to the effective separation of electron–hole pairs.

Clay materials including clay minerals and layered double hydroxides (LDHs) have attracted great attention because of their special layer structures, large specific surface areas, and remarkable adsorption capacities. In the past few decades, they have been regarded as important components or precursors for making various functional materials. This paper aims to review and summarize the recent advances in the synthesis and photocatalytic applications of clay-based photocatalysts. Moreover, the effects of surface and structural characteristics of clay-based photocatalysts on photocatalytic properties are also discussed. The clay-based photocatalysts show good application prospects for environmental remediation and energy conversion. Especially, H2 generation and reduction of CO2 into carbon sources can be easily achieved using the LDH-based photocatalysts. Meanwhile, the role of clay materials in the photocatalysis is discussed in detail.

Correction for ‘Controlled synthesis of Bi25FeO40 with different morphologies: growth mechanism and enhanced photo-Fenton catalytic properties’ by Wenda Ji et al., Dalton Trans., 2017, DOI: 10.1039/c6dt04864a.

The ability to suppress the recombination of the photoinduced charges is the key prerequisite for an excellent photocatalyst, which has attracted extensive and continuous interest in the field of photocatalysis. Herein, we presented a convenient strategy for the one-step selective synthesis of ultrathin BiOBr nanosheets with atomic thickness through a simple solvothermal method. These ultrathin BiOBr nanosheets not only show high exposure percentage of active (001) facets but also have an optimized band structure, which synergistically facilitates the electron–hole pair separation to realize significantly promoted visible-light photocatalytic activity. Our results provide a new avenue and direction for the design of photocatalysts with high visible-light photocatalytic performance.

Novel Bi2SiO5/AgI nanoplate photocatalysts with exposed {100} facets on the surfaces of Bi2SiO5 nanoplates were synthesized via an in situ precipitation method. Acid red G aqueous solution and gaseous formaldehyde were chosen as model organic pollutants to evaluate the photocatalytic activities of the as-prepared catalysts. Under visible light irradiation (>420 nm), the Bi2SiO5/AgI nanoplates exhibited enhanced photocatalytic activities as compared to pure Bi2SiO5 or AgI. X-ray photoelectron spectroscopy (XPS) reveals that a small amount of metallic Ag was formed on the surface of AgI during the photocatalytic reaction, thus leading to the transformation from Bi2SiO5/AgI to Bi2SiO5/AgI@Ag. The excellent photocatalytic activities of the Bi2SiO5/AgI nanoplates can be ascribed to the photocatalytic system composed of Bi2SiO5, AgI and metallic Ag and the inner electric field caused by the exposure of {100} facets on the Bi2SiO5 nanoplates. The as-prepared catalysts retained good photocatalytic activity after four recycles and the radical species involved in the degradation process have been investigated by using PL spectra and trapping experiments.

In this study, Zn2GeO4 hollow spheres were successfully fabricated by a template-engaged approach using zinc hydroxide carbonate (Zn4CO3(OH)6·H2O, ZHC) spheres as the template. During the hydrothermal process, Zn2+ dissolved from the surface of the ZHC spheres could rapidly react with the HGeO3− in solution and the Zn2GeO4 outer shell was formed in situ. Moreover, the building units of the Zn2GeO4 hollow spheres could gradually transform from the nanoparticles into nanobundles with the increase of the reaction time. The photocatalytic degradation results indicate that the Zn2GeO4 hollow spheres exhibited high photocatalytic activity and excellent stability for the degradation of antibiotic metronidazole in solution. Finally, the radical species involved in the degradation process have been investigated by using the scavenger experiments.