A catalyst composed of monolayer nonstoichiometric titanate nanosheets (denoted as TN) and Pd clusters is constructed for precise synthesis of cyclohexanone from phenol hydrogenation with high conversion (>99%) and selectivity (>99%) in aqueous media under light irradiation. Experimental and DFT calculation results reveal that the surface exposed acid and basic sites on TN could interact with phenol molecules in a nonplanar fashion via a hexahydroxy hydrogen-bonding ring to form a surface coordination species. This greatly facilitates the adsorption and activation of phenol molecules and suppresses the further hydrogenation of cyclohexanone. Moreover, the surface Pd clusters serve as the active sites for the adsorption and dissociation of hydrogen molecules to provide active H atoms. The synergistic effect of the surface coordination species, TN and Pd clusters remarkably facilitate the high yield of cyclohexanone in photocatalysis. Finally, the possible thermo/photocatalytic mechanisms on Pd/TN are proposed. This work not only highlights the great potential for monolayer nonstoichiometric composition nanosheets in the construction of catalysts for precise organic synthesis but also provides insight into the inherent catalytic behavior at a molecular level.Keywords: green photocatalysis; hydrogenation of phenol; monolayer titanate nanosheet; precision synthesis;

•CdS-MIL-68(Fe) photocatalysts are prepared by a facile photodeposition method.•The product exhibits excellent photoactivity for 4-nitroaniline (4-NA) reduction.•Hole scavengers and N2 atmosphere are indispensable for the reduction.•Photoexcited electrons and CO2− are the main active species in this reaction.•MOFs-based materials are firstly applied to the photoreduction of 4-NA.Visible-light-initiated organic transformations have received much attention because of low cost, relative safety, and environmental friendliness. In this work, a series of CdS-decorated MIL-68(Fe) nanocomposites (CdS-M68 NCs) have been prepared via a facile room-temperature photodeposition technique in a controlled manner. Importantly, the CdS-M68 NCs exhibit remarkably enhanced photoactivity toward selective reduction of 4-nitroaniline (4-NA) to p-phenylenediamine (PPD) in water under visible light irradiation (λ ≥ 420 nm) as compared to bare CdS and MIL-68(Fe), giving a 4-NA conversion of ∼100% after irradiation for 8 min. The significantly enhanced photoactivity is attributed to the integrated factors of the effective transportation of the photogenerated electron-hole pairs and the enhanced visible light absorption intensity. Combining with trapping experiments and ESR analysis, it could be revealed that the photoexcited electrons and CO2− radicals should be the main active species in the present system. In addition, a possible photocatalytic reduction mechanism has been investigated.Download high-res image (170KB)Download full-size image

Creating two-dimensional (2D) crystal–metal heterostructures with an ultrathin thickness has spurred increasing research endeavors in catalysis because of its fascinating opportunities in tuning the electronic state at the surface and enhancing the chemical reactivity. Here we report a novel and facile Nb4+-assisted strategy for the in situ growth of highly dispersed Pd nanoparticles (NPs) on monolayer HNb3O8 nanosheets (HNb3O8 NS) constituting a 2D Pd/HNb3O8 NS heterostructure composite without using extra reducing agents and stabilizing agents. The Pd NP formation is directed via a redox reaction between an oxidative Pd salt precursor (H2PdCl4) and reductive unsaturated surface metal (Nb4+) sites induced by light irradiation on monolayer HNb3O8 NS. The periodic arrangement of metal Nb nodes on HNb3O8 NS leads to a homogeneous distribution of Pd NPs. Density functional theory (DFT) calculations reveal that the direct redox reaction between the Nb4+ and Pd2+ ions leads to a strong chemical interaction between the formed Pd metal NPs and the monolayer HNb3O8 support. Consequently, the as-obtained Pd/HNb3O8 composite serves as a highly efficient bifunctional catalyst in both heterogeneous thermocatalytic and photocatalytic selective reduction of aromatic nitro compounds in water under ambient conditions. The achieved high activity originates from the unique 2D nanosheet configuration and in situ Pd incorporation, which leads to a large active surface area, strong metal–support interaction and enhanced charge transport capability. Moreover, this facile Nb4+-assisted synthetic route has demonstrated to be general, which can be applied to load other metals such as Au and Pt on monolayer HNb3O8 NS. It is anticipated that this work can extend the facile preparation of noble metal/nanosheet 2D heterostructures, as well as promote the simultaneous capture of duple renewable thermal and photon energy sources to drive an energy efficient catalytic process.

A hybrid of CdS/HCa2Nb3O10 ultrathin nanosheets was synthesized successfully through a multistep approach. The structures, constitutions, morphologies and specific surface areas of the obtained CdS/HCa2Nb3O10 were characterized well by XRD, XPS, TEM/HRTEM and BET, respectively. The TEM and BET results demonstrated that the unique structural features of CdS/HCa2Nb3O10 restrained the aggregation of CdS nanoparticles as well as the restacking of nanosheets effectively. HRTEM showed that CdS nanocrystals of about 25–30 nm were firmly anchored on HCa2Nb3O10 nanosheets and a tough heterointerface between CdS and the nanosheets was formed. Efficient interfacial charge transfer from CdS to HCa2Nb3O10 nanosheets was also confirmed by EPR and photocurrent responses. The photocatalytic activity tests (λ > 400 nm) showed that the optimal hydrogen evolution activity of CdS/HCa2Nb3O10 was about 4 times that of the bare CdS, because of the efficient separation of photo-generated carriers.

Monolayer Bi2MoO6 nanosheets have been successfully prepared for the first time via a bottom-top approach with surfactant assistance, and show 8 times higher activity than bulk Bi2MoO6 for the selective oxidation of benzyl alcohol. Ultrafast charge separation and more acid–base active sites on the monolayer nanosheets are considered to be responsible for the robust photoactivity.

•HNbxTa1-xWO6 nanosheets with the thicknesses of 1.50–2.00 nm were prepared.•The band energy of monolayer nanosheet can be tunable via solid-solution strategy.•The photocatalytic H2 generations were found dependent on their compositions.•Solid-solution strategy is a useful method for developing efficient photocatalysts.HNbxTa1-xWO6 monolayer nanosheets solid solutions were successfully synthesized through a top-down method. The crystal structure and morphology of the prepared materials were investigated by X-ray diffraction patterns (XRD), Raman spectra, and transmission electron microscopy (TEM). Atomic force microscopy (AFM) further confirmed that the thicknesses of the nanosheets solid solutions were at a range of 1.50–2.00 nm. As the ratios of Nb increased from x = 0.0 to 1.0 in HNbxTa1-xWO6 nanosheets solid solutions, the photo-absorption spectra were red-shifted, showing a decrease in the band gaps (from 3.26 to 3.10 eV), and the flat band potentials were shifted positively (from −0.78 to −0.68 eV). The photocatalytic activities of hydrogen evolution from water for these samples were found to be strongly dependent on their composition, which would increase as the mole ratios of Nb to Ta increases. Among the prepared nanosheets solid solutions, HNb0.7Ta0.3WO6 nanosheets showed the highest photocatalytic activity for H2 evolution with a rate constant of 1320.0 μmol h−1 g−1. Combining with the photo-electrochemical analyses, precise control of the energy band structure via a solid solution strategy is a useful method for band engineering to develop an efficient photocatalyst.Download high-res image (173KB)Download full-size image

•MoS2/CdS-TiO2 nanofibers were prepared by an electrospinning mediated photodeposition method.•This synthetic method was facile and rapid.•The products exhibited considerable photocatalytic activity for H2 evolution.•This work provided a new doorway of synthesis of MoS2/semiconductor nanocomposites.MoS2/CdS-TiO2 nanofibers have been successfully prepared by an electrospinning mediated photodeposition method for improving the interfacial contact between MoS2 and CdS-TiO2 nanofibers. The structural features, morphologies, and photo-absorption performances of the as-prepared samples were investigated in detail. The photocatalytic activity of a typical sample 1%MoS2/CdS-TiO2(60) nanofibers for H2 evolution under visible light irradiation exhibits 3.0 and 4.0 times higher than that of 1%MoS2/CdS-P25(60) and 1%Pt/CdS-TiO2(60), respectively. Based on the above results, it reveals that one dimensional TiO2 nanofibers can serve as excellent substrates for improving the dispersion of CdS and MoS2. Moreover, the intimate interaction among MoS2, CdS and TiO2 may be suggested by HRTEM images and elements mapping patterns. Further photoelectrochemical analyses show that the effective separation of photogenerated carriers can be markedly accelerated. Finally, a tentative photocatalytic reaction mechanism has also been investigated. This work demonstrates that the method of combining electrospinning and photodeposition is feasible for the preparation of an effective MoS2/CdS-TiO2 nanofibers composite photocatalyst.Download high-res image (97KB)Download full-size image

•A nickel polyoxometalate was synthesized by a simple aqueous solution method.•It was used as a carbon-free catalyst for the H2 evolution from water splitting.•It showed efficient catalytic activity for the visible-light-driven H2 evolution.•The electron-transfer steps for the H2 evolution had also been investigated.A simply as-prepared nickel phosphotungstate complex was used as a carbon-free homogeneous catalyst for the H2 evolution from water splitting under visible light irradiation (λ ≥ 400 nm). Its catalytic activity, the rate of the H2 evolution about 237 μmol h−1, was much higher than those of the Ni2+ ions and cobalt phosphotungstate complex. Spectroscopic studies suggested that the Ni2+ ions could react with Na8HPW9O34 to form a complex with a unique double-sandwich structure in the as-prepared sample. And the electrochemical experimental results revealed that it possessed two satisfactory redox potentials, which were in favor of the electrons transfer in our photoinduced hydrogen production system. Furthermore, the electron-transfer steps for the H2 evolution from water splitting in the present system were investigated in detail. On the basis of the luminescence analysis results, it was found that the reductive quenching pathway was dominant for the photosensitizer in the present system.Download high-res image (229KB)Download full-size image

A ultrathin HNb3O8 nanosheet was successfully prepared through a top-down approach. Atomic force microscopy (AFM) further confirmed that the thickness of the nanosheet was about 1.30 nm. The structure and the surface chemical state of the HNb3O8 nanosheet were well-characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray absorption fine structure (XAFS), Raman and X-ray photoelectron spectroscopy (XPS). The photocatalytic hydrogen evolution activity of the HNb3O8 nanosheet was about 4 times higher than that of layered HNb3O8 under ultraviolet irradiation. The enhanced activity was ascribed to the unique two-dimensional structure with a molecular thickness that leads to the effective separation of the photogenerated carriers. Moreover, a considerable variation in the photocatalytic hydrogen evolution activity of the HNb3O8 nanosheet was observed when suitable metals were loaded on the nanosheet via in situ photodeposition.

The defect degree of MoS2 ultrathin nanoplates are tailored easily via a facile one-pot hydrothermal method. The defect-rich MoS2 ultrathin nanoplates show excellent promotion of photocatalytic hydrogen evolution over CdS; 5.4 times as much as that of the CdS/Pt (1%), which arises from the dual-functional effect of the unique defect-decorated MoS2 ultrathin nanoplates.

A CdS/H2Ti5O11 ultrathin nanobelt nanocomposite (CdTi) was fabricated successfully by a two-step process. It was confirmed by SEM and TEM/HRTEM that the highly dispersed CdS about 15 nm in size was firmly anchored on the ultrathin nanobelt. The as-prepared CdTi-5 with an optimal loading of 81.3% CdS converted 4-nitroaniline to p-phenylenediamine, giving almost 100% yield with a selectivity of about 98% in 3 min under visible light irradiation. Its photocatalytic activity was much higher than that of the bare CdS and P25/CdS composition. The highly efficient performance was attributed to the synergetic effects of the formed heterojunction between titanate, nanobelt and CdS as well as the unique features of the titanate nanobelt, which makes the photo-generated electron to transfer smoothly and promotes the separation of photo-induced carriers. Finally, based on the experimental results of Mott–Schottky, UV-vis DRS and EPR, a possible reaction mechanism for the hydrogenation of 4-nitroaniline over the CdTi was proposed.

Ultrathin monolayer HNbWO6 nanosheets have been successfully prepared through a simple and ultrafast ion intercalation assisted exfoliation method. These obtained highly dispersed nanosheets present enhanced photocatalytic hydrogen evolution activity compared to the nanosheets prepared by the traditionally time-consuming process.

In this work, MIL-53(Fe)-reduced graphene oxide (M53-RGO) nanocomposites have been successfully fabricated by a facile and efficient electrostatic self-assembly strategy for improving the interfacial contact between RGO and the MIL-53(Fe). Compared with D-M53-RGO (direct synthesis of MIL-53(Fe)-reduced graphene oxide nanocomposites via one-pot solvothermal approach), M53-RGO nanocomposites exhibit improved photocatalytic activity compared with the D-M53-RGO under identical experimental conditions. After 80 min of visible light illumination (λ ≥ 420 nm), the reduction ratio of Cr(VI) is rapidly increased to 100%, which is also higher than that of reference sample (N-doped TiO2). More significantly, the M53-RGO nanocomposites are proven to perform as bifunctional photocatalysts with considerable activity in the mixed systems (Cr(VI)/dyes) under visible light, which made it a potential candidate for industrial wastewater treatment. Combining with photoelectrochemical analyses, it could be revealed that the introduction of RGO would minimize the recombination of photogenerated electron–hole pairs. Additionally, the effective interfacial contact between MIL-53(Fe) and RGO surface would further accelerate the transfer of photogenerated electrons, leading to the enhancement of photocatalytic activity of M53-RGO toward photocatalytic reactions. Finally, a possible photocatalytic reaction mechanism is also investigated in detail.Keywords: Cr(VI); dyes; graphene; MIL-53(Fe); photocatalysis; self-assembly; visible light;

We demonstrate a facile and general approach for the fabrication of highly dispersed Au, Pd, and Pt nanoparticles (NPs) on MIL-125(Ti) without using extra reducing and capping agents. Noble-metal NP formation is directed by an in situ redox reaction between the reductive MIL-125(Ti) with Ti3+ and oxidative metal salt precursors. The resulting composites function as efficient photocatalysts.

UiO-66-X (X = H, NH2, NO2, Br) have been successfully synthesized and tested for their photocatalytic activity in water treatment. Results show that electronic effect of the ligand substituents greatly affects the photocatalytic activity of UiO-66. The rates obtained by different substituents are linearly correlated with their Hammett coefficients.

H3PMo12O40 molecules have been successfully encapsulated in the cavities of MIL-100(Fe) via a facile hydrothermal method (denoted as HPMo@MIL-100(Fe)). A series of characterization has corroborated the insertion of H3PMo12O40 within the cavities of MIL-100(Fe). The resulting HPMo@MIL-100(Fe) nanocomposites have exhibited much higher photoactivity than the original-MIL-100(Fe) toward the photocatalytic selective oxidation of benzylic alcohols and the reduction of Cr(VI) under visible light irradiation (λ ≥ 420 nm). The higher photoactivity of HPMo@MIL-100(Fe) can be attributed to the integrative effect of enhanced light absorption intensity and more efficient separation of photogenerated electron–hole pairs. The host porous structure of MIL-100(Fe) can achieve a uniform composition with H3PMo12O40, which is significantly important for producing highly reactive dispersed H3PMo12O40 molecules and enhancing the photocatalytic activity of HPMo@MIL-100(Fe) nanocomposites. And the immobilized H3PMo12O40 molecules are more convenient for recycling. Importantly, almost no Fe and Mo ions leach from the MIL-100(Fe) during the reaction, which verifies the photostability of the HPMo@MIL-100(Fe). In addition, possible photocatalytic redox reaction mechanisms have been investigated.

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed noble-metal nanoparticles (Au, Pd, Pt) were immobilized on MIL-100(Fe) (denoted M@MIL-100(Fe)) using a facile room-temperature photodeposition technique. The resulting M@MIL-100(Fe) (M = Au, Pd, and Pt) nanocomposites exhibited enhanced photoactivities toward photocatalytic degradation of methyl orange (MO) and reduction of heavy-metal Cr(VI) ions under visible-light irradiation (λ ≥ 420 nm) compared with blank-MIL-100(Fe). Combining these results with photoelectrochemical analyses revealed that noble-metal deposition can effectively improve the charge-separation efficiency of MIL-100(Fe) under visible-light irradiation. This phenomenon in turn leads to the enhancement of visible-light-driven photoactivity of M@MIL-100(Fe) toward photocatalytic redox reactions. In particular, the Pt@MIL-100(Fe) with an average Pt particle size of 2 nm exhibited remarkably enhanced photoactivities compared with those of M@MIL-100(Fe) (M = Au and Pd), which can be attributed to the integrative effect of the enhanced light absorption intensity and more efficient separation of the photogenerated charge carrier. In addition, possible photocatalytic reaction mechanisms are also proposed.

CdS/TiO2 heterojunction nanofibers have been successfully synthesized through the photodeposition of CdS on 1D TiO2 nanofibers that were prepared via a facile electrospinning method. The as-synthesized samples showed high photocatalytic activities upon selectively oxidizing a series of alcohols into corresponding aldehydes under visible light irradiation. TEM observations revealed that CdS was closely grown on the TiO2 nanofibers. Moreover, it was found that the CdS/TiO2 nanofibers that were photodeposited for 4 h exhibited the highest catalytic activity, with a conversion of 22% and a selectivity of 99%, which were much higher than those of commercial CdS. In addition, we also discuss the photoabsorption performance and the reaction mechanism of the photocatalytic oxidation of alcohols.

A Ternary composite UiO-66/CdS/1% reduced graphene oxide (RGO) was successfully prepared, with a photocatalytic hydrogen evolution rate 13.8 times as high as that of pure commercial CdS. It shows great advantages over the perfect composite photocatalyst-P25/CdS/1%RGO.

Novel photocatalysts RGO-UiO-66(NH2) were synthesized via an electrostatically derived self-assembly of UiO-66(NH2) with graphene, followed by hydrothermal reduction. Such nanocomposites exhibit enhanced photocatalytic activity for the reduction of Cr(VI) compared with the pristine UiO-66(NH2).

CdS nanorods have been successfully decorated on the surface of MOF (metal–organic framework) UiO–66(NH2) via a facile room-temperature photodeposition technique in a controlled manner. Electrochemical measurements indicate that the CdS photodeposition proceeds via the preferential reduction of Cd ions to Cd0 followed by chemical reaction with S8. The photocatalytic performances of the obtained CdS–UiO–66(NH2) nanocomposites have been evaluated by selective oxidation of various alcohol substrates using molecular oxygen as a benign oxidant. The results show that such CdS–UiO–66(NH2) nanocomposites exhibit considerable photocatalytic activity and stability, which may be due to the large specific surface area and the charge injection from CdS into UiO–66(NH2) leads to efficient and longer charge separation by reducing the recombination of electron–hole pairs. This work represents the first example of using MOFs not only as supports but also as electron providers to trigger the reaction for coupling MOFs with metal sulfides, thus fabricating novel MOF–CdS nanocomposite systems and improving their photocatalytic activity. It is hoped that our findings could offer useful information and open a new window for the design of novel MOF–semiconductor nanocomposites as efficient visible light driven photocatalysts.

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed Pd nanoparticles of about 3–6 nm in diameter are immobilized in the metal-organic framework (MOF) UiO-66(NH2) via a facile one-pot hydrothermal method. The resulting Pd@UiO-66(NH2) nanocomposite exhibits an excellent reusable and higher visible light photocatalytic activity for reducing Cr(VI) compared with UiO-66(NH2) owing to the high dispersion of Pd nanoparticles and their close contact with the matrix, which lead to the enhanced light harvesting and more efficient separation of photogenerated electron–hole pairs. More significantly, the Pd@UiO-66(NH2) could be used for simultaneous photocatalytic degradation of organic pollutants, like methyl orange (MO) and methylene blue (MB), and reduction of Cr(VI) with even further enhanced activity in the binary system, which could be attributed to the synergetic effect between photocatalytic oxidation and reduction by individually consuming photogenerated holes and electrons. This work represents the first example of using the MOFs-based materials as dual functional photocatalyst to remove different categories of pollutants simultaneously. Our finding not only proves great potential for the design and application of MOFs-based materials but also might bring light to new opportunities in the development of new high-performance photocatalysts.

Metal–organic frameworks (MOFs) have been arousing a great interest owing to their unique physicochemical properties. In this work, Zr-benzenedicarboxylate (UiO-66) and its derivative, Zr-2-NH2-benzenedicarboxylate (UiO-66(NH2)), are successfully prepared via a facile solvothermal method and applied to photocatalytic reactions. Powder X-ray diffraction (XRD) confirms the isoreticular nature of UiO-66 and UiO-66(NH2), while Fourier transformed infrared spectra (FTIR) prove the effective presence of amino group. UV-vis diffuse reflectance spectra (DRS) show the photoabsorption edge of UiO-66 could be shifted to the visible light region by simply introducing the amino group (–NH2) on the organic ligand. Importantly, UiO-66(NH2) is proved to perform as an efficient multifunctional visible-light-driven photocatalyst with high stability and considerable recyclability in both the photocatalytic selective oxidation of alcohols to aldehydes using molecular oxygen as oxidant and catalytic reduction of aqueous Cr(VI) to Cr(III) under ambient conditions. Furthermore, the possible reaction mechanism has also been investigated in detail. This work makes a systematic attempt to understand the reaction of photocatalytic selective oxidation of alcohols over MOFs and represents the first example to report the identification of MOFs as promising visible-light photocatalysts toward reduction of aqueous Cr(VI). More significantly, our finding also provides a new way to design MOFs-based photocatalysts, that is, by tuning the predesigned ligands with specific functional groups, the optical absorption properties of MOFs can be flexibly modulated, and then the effective solar energy conversion can be expected.

CdS photocatalysts with tunable band gaps (2.17–2.32 eV) were successfully prepared by a solvothermal method. Photocatalytic hydrogenation of 4-nitroaniline over the obtained samples was evaluated in the presence of HCO2NH4 as a hole scavenger upon purging with N2 under visible light irradiation (λ ≥ 420 nm). The CdS sample prepared by CdCl2 and sulfur powder in ethylenediamine showed excellent catalytic activity, giving 100% of 4-nitroaniline conversion and 95% of p-phenylenediamine selectivity after 35 min of visible light irradiation. The results of electron spin resonance revealed that its photoexcited holes could efficiently react with HCO2− ions within HCO2NH4 molecules to produce ˙CO2− radicals with strong reductive abilities. Furthermore, photoexcited electrons of the obtained sample exhibited relatively strong reductive abilities as compared to other CdS samples. Therefore, this sample showed the highest catalytic activity among the CdS samples for the photocatalytic hydrogenation of 4-nitroaniline.

TaON nanoparticles with low surface reduction defect sites were successfully constructed by a simple nitridation approach using Ta2O5·nH2O as a precursor. Large amounts of crystal water in Ta2O5·nH2O are considered as a parclose to prohibit Ta5+ from being reduced in the nitridation process with NH3 gas. Urea was also used in the synthesis, acting as a co-nitridation agent together with NH3 but also as a porogen for creating nanopores in TaON frameworks. The as-prepared TaON catalyst was evaluated by environmental purification of organic pollutants in water, as exemplified here by mineralization of phenol and its chloroderivatives in aqueous phase under visible light irradiation. Results revealed that a lower defect density of TaON, as well as its nanopore structure and smaller particle size, contribute to the promotion in both electron–hole separation and interfacial charge-transfer in materials surface/interface, being the main reasons for the enhanced photocatalytic performance.

Highly efficient visible-light-induced photocatalytic hydrogenation of nitrobenzene to aniline in water was observed over a Bi2MoO6 photocatalyst under N2 atmosphere in the presence of (NH4)2C2O4 as a hole scavenger. 100% of the nitrobenzene was converted and the selectivity of aniline was ∼97% after 20 min of visible light irradiation (λ ≥ 400 nm). The Bi2MoO6 photocatalyst showed good catalytic stability for the hydrogenation of nitrobenzene. Further experimental results revealed that both (NH4)2C2O4 and the N2 atmosphere were indispensable for the photocatalytic hydrogenation of nitrobenzene to aniline over the Bi2MoO6 photocatalyst. On the basis of the electron spin resonance analysis results, photoinduced electrons of the Bi2MoO6 photocatalyst were found to be the main active species for the hydrogenation of nitrobenzene. Moreover, a mechanism was proposed to explain the visible-light-induced photocatalytic hydrogenation of nitrobenzene to aniline over the Bi2MoO6 photocatalyst.

•Porous Sr0.25H1.5Ta2O6·H2O nanosphere were successfully prepared for the first time.•In the synthesis, PVP played an important role in formation of porous nanosphere.•The nanosphere exhibited a significantly improved photocatalytic activity.•Comparison on photocatalytic activities between TiO2 and tantalate was carried out.•Relationship between the morphologies and photocatalytic activity was investigated.Porous Sr0.25H1.5Ta2O6·H2O (HST) nanosphere with high surface area has been prepared by a PVP-assisted hydrothermal method for the first time. In the synthesis, PVP played an important role in formation of porous nanosphere. This approach could also be used to prepare other nanostructured tantalate efficiently without rigorous reaction conditions. The photocatalytic activities were evaluated by the decomposition of benzene in gaseous phase. Results showed that benzene could be effectively degraded and mineralized over the HST samples. Due to the unique porous structure, larger surface area, and stronger oxidizing ability of the photogenerated holes, HST nanosphere exhibited a superior photocatalytic activity for the degradation of benzene compared with HST nanopolydera and TiO2 (Degussa P25). The effect of the crystallinity of the samples on the photocatalytic activities was also discussed.

Highly efficient photocatalytic reduction of 4-nitroaniline to p-phenylenediamine over a commercial CdS photocatalyst was observed under visible light irradiation (λ ≥ 420 nm) in water. The conversion of 4-nitroaniline and the selectivity of p-phenylenediamine were ∼100% and ∼98% after 9 min of visible light irradiation, respectively. The photoreduction efficiency of 4-nitroaniline over the CdS photocatalyst remained above 95% in the 5th cycle of testing. Its photocatalytic activity was much higher than those of nitrogen-doped TiO2 and commercial TiO2 photocatalysts. Further experimental results revealed that the ammonium formate and N2 atmosphere were indispensable for the photocatalytic reduction of 4-nitroaniline over the CdS photocatalyst. On the basis of the results of electron spin resonance, photoexcited electrons and ·CO2− radicals were detected in the present system. These species had strong reductive powers, and were therefore able to efficiently reduce 4-nitroaniline to p-phenylenediamine.

Visible light-activated SnNb2O6 nanosheets (NSs) with high surface area and small crystallites have been prepared by a microwave-assisted template-free hydrothermal method without exfoliation for the first time. This approach could be used to prepare the functional materials efficiently and extended to synthesizing two-dimensional nanosheet materials directly as well. The crystalline phases, photoabsorption performances, and surface areas and porosity of the samples are characterized by XRD, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and N2-adsorption. Results show that a hypsochromic shift of the photoabsorption edge is observed, which reflects an obvious quantum size effect. TEM images reveal SnNb2O6 nanosheets with a thickness of 1–4 nm versus several hundred nanometres in lateral size. Based on the experimental results, the formation mechanism of SnNb2O6 nanosheets is also studied and proposed, which reasonably follows a synergy interaction of reaction–crystallization and dissolution–recrystallization processes. Due to the unique morphology, larger surface area, smaller crystallites and stronger redox ability of the photogenerated hole–electron pair, these photocatalysts show much higher photocatalytic activities for the degradation of rhodamine B (RhB) compared with their counterparts prepared by the traditional solid-state reaction. The reaction rate is enhanced by over 4 times and the RhB molecule can be mineralized into CO2 and H2O over SnNb2O6 NSs. The decomposition mechanism of RhB over SnNb2O6 under visible light irradiation and the active species in the photocatalytic process have also been discussed.

A series of group IIIA metal ion electron acceptors doped into Sr0.25H1.5Ta2O6·H2O (HST) samples have been prepared by an impregnation and calcination method for the first time. The samples are characterized by XRD, TEM, DRS and XPS. The variations in the electronic structure and photoelectric response after metal ion doping are investigated by theoretical calculations and photocurrent experiments, respectively. Results show that the metal ions can be efficiently incorporated into the HST crystal structure, which is reflected in the lattice contraction. Meanwhile, the photoabsorption edges of the metal-doped HST samples are red shifted to a longer wavelength. Taking into account the ionic radii and electronegativities of the dopants, as well as the XRD and XPS results, it is concluded that Ta5+ ions may be partially substituted by the Al3+ and Ga3+ ions in the framework, while In3+ ions are the favourable substitutes for Sr2+ sites in the cavity. The first-principles DFT calculations confirm that the variation of the band structure is sensitive to the type of group IIIA metal ion. Introducing the dopant only at the Ta site induces an obvious variation in the band structure and the band gap becomes narrow. Meanwhile, an ‘‘extra step’’ appeared in the band gap, which can trap photogenerated electrons from the valance band (VB) and could enhance the charge mobility and the photocurrent. For the photocatalytic degradation of methyl orange in an aqueous solution and in benzene in the gas phase, the doped samples show superior photocatalytic activities compared with both undoped samples and TiO2. The enhanced photocatalytic activities can be well explained by their electronic structure, photoabsorption performance, photoelectric response, and the concentration of the active species. Due to the fact that Ga ion doping can create an acceptor impurity level and change the electronic band, efficiently narrowing the band gap, the Ga-doped sample shows the highest photocatalytic activity.

Nanosized ZnNb2O6 photocatalysts (band gaps ~4.0 eV) were successfully synthesized via a citrate complex method. Their particle sizes ranged from 50 to 150 nm. The result of Mott–Schottky measurement revealed that the flat-band potential of ZnNb2O6 was ca. −1.3 V versus Ag/AgCl at pH 6.6. The photocatalytic activities of the samples for the degradation of methyl orange were evaluated under UV-light (λ = 254 nm). It was found that the sample obtained at 850 °C showed the highest photocatalytic activity due to its opportune crystallinity and surface area. Furthermore, ·OH radicals were detected as the major oxidation agents responsible for the decomposition of methyl orange.

A new photocatalyst Sr0.25H1.5Ta2O6·H2O (HST) with high surface area was successfully prepared by a facile and mild hydrothermal reaction using Ta2O5·nH2O as a precursor. TEM images revealed that their different morphologies, from nanoplate to nanopolyhedron, were formed under different pH values of the reactive solutions. The formation mechanism of HST was also studied and proposed. Growth of HST nanocrystallites followed a reaction-crystallization model. By analyzing the results of XRD, DRS, XPS, electrochemistry and theoretical calculation, the crystal and electronic structural characterizations of HST was established. Compared with isostructural Sr0.4H1.2Nb2O6·H2O (HSN), the Ta 5d orbitals were the main contribution to the bottom of the conduction band of HST, inducing the energy level more negative while the top of valence band, which was dominated by O 2p states, remained almost unchanged. Due to the more suitable electronic band structure and various morphologies, the photocatalyst showed superior photocatalytic activities for water splitting to generate H2 and for degrading benzene as compared with HSN. The rate of H2 evolution and the conversion ratio of benzene were 81 times and 4 times higher than that of TiO2 (Degussa P25), respectively. The proposed mechanisms for photocatalytic reactions based on the experimental results were discussed.

Nanocrystalline ZnTa2O6 photocatalysts with different crystal structures were prepared via a simple and facile sol–gel method in a temperature range of 650–950 °C. The absorption edges and particle sizes of the samples were located at about 285 nm (corresponding a band gap of 4.35 eV) and ranged from 25 to 150 nm, respectively. The photocatalytic activities of the samples were tested by the degradation of methyl orange under UV light irradiation. The results indicated that the crystal structure of ZnTa2O6 was a main factor for the different photocatalytic activities of the ZnTa2O6 samples. Moreover, the effects of crystallinities and surface areas of the obtained samples on the catalytic activities were also discussed.

A water-soluble niobium-citrate-peroxo compound was synthesized by using Nb2O5 as a precursor. This niobium compound solution was successfully applied to the preparation of microcrystalline ZnNb2O6 photocatalysts via a water-based sol-gel method. The results indicated that pure ZnNb2O6 could be obtained in a temperature range from 750 to 950 °C. The absorption edge of ZnNb2O6 located at about 305 nm, corresponding to a band gap of ca. 4.06 eV. The photocatalytic activities of the as-prepared samples for the methyl orange degradation were evaluated under UV light (λ = 254 nm). It was found that the sample obtained at 850 °C showed the highest photocatalytic activity due to its suitable surface area and crystallinity.Highlights► A water-soluble niobium peroxo compound was synthesized with Nb2O5 as a precursor. ► The niobium compound was applied to the preparation of ZnNb2O6 photocatalysts. ► The samples showed excellent performances in the degradation of methyl orange. ► The catalytic activity of ZnNb2O6 is dominated by the surface area and crystallinity.

Microcrystalline ABi2Nb2O9 (A=Sr, Ba) photocatalysts were successfully synthesized by a citrate complex method. The as-prepared samples were characterized by the X-ray diffraction technique, BET surface area analysis, UV–vis diffuse reflectance spectrum, transmission electron microscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectrometry. The results indicated that single-phase orthorhombic SrBi2Nb2O9 could be obtained after being calcined above 650 °C, while BaBi2Nb2O9 was tetragonal. Based on the diffuse reflectance spectra, the band gaps of the obtained samples were calculated to be around 3.34–3.54 eV. For the photocatalytic redox reaction of methyl orange under UV-light irradiation, SrBi2Nb2O9 exhibited higher photocatalytic activity than that of BaBi2Nb2O9. The effects of the crystallinities, BET surface areas and crystal structures of the samples on the photocatalytic activities were discussed in detail.Graphical abstractAurivillius-type ABi2Nb2O9 (A=Sr, Ba) photocatalysts were successfully synthesized by a citrate complex method. SrBi2Nb2O9 and BaBi2Nb2O9 showed different photocatalytic performances in the redox reaction of methyl orange (MO) under UV-light (λ=254 nm), due to the different crystal structures of ABi2Nb2O9 (A=Sr, Ba).

A photocatalyst Sr0.4H1.2Nb2O6·H2O (HSN) nanopolyhedra with high surface area has been successfully prepared by a simple hydrothermal method. The as-prepared samples were characterized by XRD, BET, SEM, TEM and XPS. The electronic structure of HSN determined by DFT calculations and electrochemical measurement revealed that HSN is an indirect-bandgap and n-type semiconductor, respectively. HSN samples showed high photocatalytic activities for both pure water splitting and the decomposition of benzene. The rate of H2 evolution over HSN was 15 times higher than that of P25 and the conversion ratio of benzene exceeded twice that of P25. The photocatalytic activities for water splitting can be greatly improved by loading various co-catalysts on HSN, such as Au, Pt, and Pd. The photocatalytic mechanisms were proposed based on the band structure and characterization results of the photocatalyst.

A novel solution-phase route using Nb2O5·nH2O as precursor was developed to selectively synthesize single-crystalline Sr0.4H1.2Nb2O6·H2O nanopolyhedrons and SrNb2O6 nanorods photocatalysts via simply adjusting pH values of the reactive solutions.

Nanostructured β-Ga2O3 samples were prepared by a combination of the solvothermal processes and subsequent heat treatments. β-Ga2O3 samples with various morphologies were obtained by using different kinds of solvent, including water, isopropanol and ethylene glycol. One-dimensional β-Ga2O3 nanorods were obtained in water medium, while β-Ga2O3 spheres were prepared in alcohol. The possible mechanism related to the phase formation and morphology of the as-prepared materials was discussed. Photocatalytic performance of the synthesized β-Ga2O3 samples was also examined. Results revealed that β-Ga2O3 sample prepared with ethylene glycol showed the highest photocatalytic activity for the degradation of salicylic acid. This could be ascribed to the high surface area, abundant hydroxyl groups, and wide band gap of β-Ga2O3 sample synthesized in ethylene glycol.β-Ga2O3 with various morphologies were prepared by a solvothermal method using different kinds of solvent. The photocatalytic activity of the synthesized β-Ga2O3 materials toward the photodegradation of salicylic acid is susceptible to their morphology and size.

Orthorhombic Bi2SiO5 nanosheets with thicknesses of 10−20 nm were first synthesized by a template-free hydrothermal synthesis process using Bi(NO3)3 and different Si sources as raw materials. The as-prepared samples were characterized by X-ray diffraction, Brunauer−Emmett−Teller (BET) surface area analysis, UV−vis diffuse reflectance spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and a photoluminescence technique with terephthalic acid. The results showed that different precursors led to samples with different morphologies, particle sizes, and BET surface areas. As a novel photocatalyst, the photocatalytic performances of Bi2SiO5 samples were evaluated by the photocatalytic degradation of salicylic acid and gaseous benzene. The results revealed that the sample obtained from Na2SiO3 as a precursor exhibited higher activity than that from (C2H5O)4Si due to its biscuit-like morphology, a smaller particle size, and a higher BET surface areas.

One-dimensional Bi2GeO5 nanobelts were first directly prepared by a surfactant-templated hydrothermal process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV−vis diffuse reflectance spectroscopy were used to characterize the obtained samples. By use of cetyltrimethyl ammonium bromide as the structure-directing template, Bi2GeO5 nanobelts with widths of about 70−180 nm were obtained. The mechanisms related to the morphology control of Bi2GeO5 are proposed and discussed. The UV−vis absorption spectra show that the as-prepared nanomaterials have a strong absorption edge in UV light and that their band gaps are somewhat relevant to the size and morphology. As a novel photocatalyst, the prepared Bi2GeO5 samples exhibit relatively high photocatalytic activity for the decomposition of azo dye methyl orange under UV irradiations. The samples obtained under different amounts of cetyltrimethyl ammonium bromide exhibited different photocatalytic performances. The effects of the crystallinity, specific surface area and morphology of the samples on the photocatalytic activities are also discussed.

 A novel photocatalyst CaSnO3 with microcube morphology was prepared by a facile hydrothermal process and subsequent heat treatment. The influence of pH and subsequent calcination temperature on the synthesis of CaSnO3 were investigated. CaSnO3 was found to be an effective photocatalyst, and exhibited high photocatalytic performance in the degradation of universal organic pollutants. The effects of the crystallinity, morphology and specific surface area of CaSnO3 samples on photocatalytic performance are also discussed.

Efficient upconversion Yb3+ and Tm3+ codoped β-NaYF4 is firstly synthesized via a novel and rapid microwave hydrothermal process. The as-prepared sample is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The sample shows a microtube morphology, which may be formed by the curliness of flakes. It is found that NaYF4:Yb3+, Tm3+ microtubes can be synthesized using microwave hydrothermal method in a much shorter reaction time compared with conventional hydrothermal method, and the upconversion fluorescent intensity is also greatly enhanced under 976 nm laser excitation. The energy transfer upconversion mechanisms and the possible reason for the enhancement of the fluorescent intensity are also proposed.

•Highly dispersed Cu was loaded onto ultrathin HNb3O8 nanosheets via in situ photodeposition.•Competing reduction reactions between Nb5+/Nb4+ and H+/H2 over HNb3O8 nanosheets were investigated.•Insights were obtained into the role of Cu in promoting H2 evolution over HNb3O8.Cu was loaded on ultrathin HNb3O8 nanosheets via a facile photodeposition method. The oxidation state of the Cu was further verified by XPS. TEM and STEM-EDX mapping demonstrated that the Cu cluster was highly dispersed on the nanosheets. The photocatalytic H2 evolution activity of (0.5%) Cu/HNb3O8 was about 23.6 times higher than that of the bare HNb3O8 nanosheets under simulated solar light irradiation. The role of Cu in promoting photocatalytic hydrogen evolution activity over HNb3O8 nanosheets was attributed to the reduction of hydrogen evolution potential and the improvement of separation of photogenerated carriers. These results were confirmed by a series of electrochemical characterizations, such as CV, LSV, I-t, and EIS. Finally, photocatalytic hydrogen evolution processes over HNb3O8 nanosheets with and without Cu modification were proposed, which might provide insights into the photocatalytic hydrogen evolution mechanism over niobate-based metal oxides.Download high-res image (125KB)Download full-size image

Nanocrystalline PbBi2Nb2O9 was successfully prepared by a modified sol–gel method. The as-prepared nanocrystalline PbBi2Nb2O9 was an active visible-light-driven photocatalyst for the photoreduction of 4-nitroaniline to p-phenylenediamine in aqueous solution upon purging with N2. Its photocatalytic activity was determined by the balance between the surface area and crystallinity. The best sample was obtained after calcination at 650 °C, giving 4-nitroaniline conversion of ∼100% and p-phenylenediamine selectivity of ∼99% after irradiation for 150 min, which was much higher than those of bulk PbBi2Nb2O9 and TiO2−xNx photocatalysts. Further experiments revealed that oxalate anion (as a hole scavenger) was indispensable for the photocatalytic reduction of 4-nitroaniline. Moreover, on the basis of the electron spin resonance analysis result, a mechanism was proposed to explain the photoreduction of 4-nitroaniline over nanocrystalline PbBi2Nb2O9.Graphical abstractNanocrystalline PbBi2Nb2O9 was successfully prepared by a sol–gel method. The as-prepared sample showed efficient photocatalytic activity for the reduction of 4-nitroaniline to p-phenylenediamine under visible light irradiation (λ ⩾ 420 nm).Download high-res image (65KB)Download full-size imageHighlights► Nanocrystalline PbBi2Nb2O9 photocatalyst was prepared by a sol–gel method. ► It showed visible light photocatalytic activity for the reduction of 4-nitroaniline. ► The crystallinity and surface area determined its photocatalytic activity. ► Hole scavengers and deaerated condition were indispensable for the reduction of 4-NA. ► Mechanism for the photoreduction of 4-nitroaniline to p-phenylenediamine was studied.

•Fe(III)-based MOF was firstly applied to the photocatalytic reduction reaction.•MIL-53(Fe) exhibited an outstanding photocatalytic activity for reduction of Cr(VI).•A first systematic study of the Fe(III)-based MOF as bifunctional photocatalyst.•Dyes and Cr(VI) could be also converted simultaneously over MIL-53(Fe).•MIL-53(Fe) was performed a stable and reusable visible-light-driven photocatalyst.A bifunctional photocatalyst-Fe-benzenedicarboxylate (MIL-53(Fe)) has been synthesized successfully via a facile solvothermal method. The resulting MIL-53(Fe) photocatalyst exhibited an excellent visible light (λ ≥  420 nm) photocatalytic activity for the reduction of Cr(VI), the reduction rate have reached about 100% after 40 min of visible light irradiation, which has been more efficient than that of N-doped TiO2 (85%) under identical experimental conditions. Further experimental results have revealed that the photocatalytic activity of MIL-53(Fe) for the reduction of Cr(VI) can be drastically affected by the pH value of the reaction solution, the hole scavenger and atmosphere. Moreover, MIL-53(Fe) has exhibited considerable photocatalytic activity in the mixed systems (Cr(VI)/dyes). After 6 h of visible light illumination, the reduction ratio of Cr(VI) and the degradation ratio of dyes have been exceed 60% and 80%, respectively. More significantly, the synergistic effect can also be found during the process of photocatalytic treatment of Cr(VI) contained wastewater under the same photocatalytic reaction conditions, which makes it a potential candidate for environmental restoration. Finally, a possible reaction mechanism has also been investigated in detail.Download full-size image

Trinuclear Fe (III) acetato complex intercalated montmorillonite Fenton catalysts with large surface areas were prepared by a facile ion exchange process. The obtained samples were characterized by FT-IR, TGA-DSC, N2-sorption and XPS in detail. To understand the microstructure of the active iron species in the montmorillonite, the Fe K-edge X-ray absorption spectra (XAFS) technique was also employed. The results showed that the trinuclear iron cluster was successfully intercalated into the layers of montmorillonite and the structure of the active iron species was an amorphous FeO(OH)-like structure after 500 °C post-treatment. When the prepared catalysts were used for the photo-Fenton reaction at room temperature, excellent activities were observed for degradation of phenol. Moreover, their activities were much higher than those of the traditional iron hydroxyl compound intercalated montmoillonite Fenton catalyst. The stable intercalated structure and the low leaching Fe concentration induced that the obtained catalyst can be operated for a long time. Meanwhile, the consumption of H2O2 and the change of pH in solution were also investigated in detail.Graphical abstractDownload high-res image (122KB)Download full-size imageHighlights► An amorphous FeO(OH) microstructure of the active iron species. ► Excellent photo-Fenton activities of the as-prepared catalysts. ► The stable intercalated structure and the low leaching Fe concentration. ► Layered Fenton catalyst with higher activity by intercalating larger iron cluster.

Monolayer Bi2MoO6 nanosheets have been successfully prepared for the first time via a bottom-top approach with surfactant assistance, and show 8 times higher activity than bulk Bi2MoO6 for the selective oxidation of benzyl alcohol. Ultrafast charge separation and more acid–base active sites on the monolayer nanosheets are considered to be responsible for the robust photoactivity.

UiO-66-X (X = H, NH2, NO2, Br) have been successfully synthesized and tested for their photocatalytic activity in water treatment. Results show that electronic effect of the ligand substituents greatly affects the photocatalytic activity of UiO-66. The rates obtained by different substituents are linearly correlated with their Hammett coefficients.

CdS nanorods have been successfully decorated on the surface of MOF (metal–organic framework) UiO–66(NH2) via a facile room-temperature photodeposition technique in a controlled manner. Electrochemical measurements indicate that the CdS photodeposition proceeds via the preferential reduction of Cd ions to Cd0 followed by chemical reaction with S8. The photocatalytic performances of the obtained CdS–UiO–66(NH2) nanocomposites have been evaluated by selective oxidation of various alcohol substrates using molecular oxygen as a benign oxidant. The results show that such CdS–UiO–66(NH2) nanocomposites exhibit considerable photocatalytic activity and stability, which may be due to the large specific surface area and the charge injection from CdS into UiO–66(NH2) leads to efficient and longer charge separation by reducing the recombination of electron–hole pairs. This work represents the first example of using MOFs not only as supports but also as electron providers to trigger the reaction for coupling MOFs with metal sulfides, thus fabricating novel MOF–CdS nanocomposite systems and improving their photocatalytic activity. It is hoped that our findings could offer useful information and open a new window for the design of novel MOF–semiconductor nanocomposites as efficient visible light driven photocatalysts.

A ultrathin HNb3O8 nanosheet was successfully prepared through a top-down approach. Atomic force microscopy (AFM) further confirmed that the thickness of the nanosheet was about 1.30 nm. The structure and the surface chemical state of the HNb3O8 nanosheet were well-characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray absorption fine structure (XAFS), Raman and X-ray photoelectron spectroscopy (XPS). The photocatalytic hydrogen evolution activity of the HNb3O8 nanosheet was about 4 times higher than that of layered HNb3O8 under ultraviolet irradiation. The enhanced activity was ascribed to the unique two-dimensional structure with a molecular thickness that leads to the effective separation of the photogenerated carriers. Moreover, a considerable variation in the photocatalytic hydrogen evolution activity of the HNb3O8 nanosheet was observed when suitable metals were loaded on the nanosheet via in situ photodeposition.

A series of group IIIA metal ion electron acceptors doped into Sr0.25H1.5Ta2O6·H2O (HST) samples have been prepared by an impregnation and calcination method for the first time. The samples are characterized by XRD, TEM, DRS and XPS. The variations in the electronic structure and photoelectric response after metal ion doping are investigated by theoretical calculations and photocurrent experiments, respectively. Results show that the metal ions can be efficiently incorporated into the HST crystal structure, which is reflected in the lattice contraction. Meanwhile, the photoabsorption edges of the metal-doped HST samples are red shifted to a longer wavelength. Taking into account the ionic radii and electronegativities of the dopants, as well as the XRD and XPS results, it is concluded that Ta5+ ions may be partially substituted by the Al3+ and Ga3+ ions in the framework, while In3+ ions are the favourable substitutes for Sr2+ sites in the cavity. The first-principles DFT calculations confirm that the variation of the band structure is sensitive to the type of group IIIA metal ion. Introducing the dopant only at the Ta site induces an obvious variation in the band structure and the band gap becomes narrow. Meanwhile, an ‘‘extra step’’ appeared in the band gap, which can trap photogenerated electrons from the valance band (VB) and could enhance the charge mobility and the photocurrent. For the photocatalytic degradation of methyl orange in an aqueous solution and in benzene in the gas phase, the doped samples show superior photocatalytic activities compared with both undoped samples and TiO2. The enhanced photocatalytic activities can be well explained by their electronic structure, photoabsorption performance, photoelectric response, and the concentration of the active species. Due to the fact that Ga ion doping can create an acceptor impurity level and change the electronic band, efficiently narrowing the band gap, the Ga-doped sample shows the highest photocatalytic activity.

A novel solution-phase route using Nb2O5·nH2O as precursor was developed to selectively synthesize single-crystalline Sr0.4H1.2Nb2O6·H2O nanopolyhedrons and SrNb2O6 nanorods photocatalysts via simply adjusting pH values of the reactive solutions.

Ultrathin monolayer HNbWO6 nanosheets have been successfully prepared through a simple and ultrafast ion intercalation assisted exfoliation method. These obtained highly dispersed nanosheets present enhanced photocatalytic hydrogen evolution activity compared to the nanosheets prepared by the traditionally time-consuming process.

Metal–organic frameworks (MOFs) have been arousing a great interest owing to their unique physicochemical properties. In this work, Zr-benzenedicarboxylate (UiO-66) and its derivative, Zr-2-NH2-benzenedicarboxylate (UiO-66(NH2)), are successfully prepared via a facile solvothermal method and applied to photocatalytic reactions. Powder X-ray diffraction (XRD) confirms the isoreticular nature of UiO-66 and UiO-66(NH2), while Fourier transformed infrared spectra (FTIR) prove the effective presence of amino group. UV-vis diffuse reflectance spectra (DRS) show the photoabsorption edge of UiO-66 could be shifted to the visible light region by simply introducing the amino group (–NH2) on the organic ligand. Importantly, UiO-66(NH2) is proved to perform as an efficient multifunctional visible-light-driven photocatalyst with high stability and considerable recyclability in both the photocatalytic selective oxidation of alcohols to aldehydes using molecular oxygen as oxidant and catalytic reduction of aqueous Cr(VI) to Cr(III) under ambient conditions. Furthermore, the possible reaction mechanism has also been investigated in detail. This work makes a systematic attempt to understand the reaction of photocatalytic selective oxidation of alcohols over MOFs and represents the first example to report the identification of MOFs as promising visible-light photocatalysts toward reduction of aqueous Cr(VI). More significantly, our finding also provides a new way to design MOFs-based photocatalysts, that is, by tuning the predesigned ligands with specific functional groups, the optical absorption properties of MOFs can be flexibly modulated, and then the effective solar energy conversion can be expected.

CdS photocatalysts with tunable band gaps (2.17–2.32 eV) were successfully prepared by a solvothermal method. Photocatalytic hydrogenation of 4-nitroaniline over the obtained samples was evaluated in the presence of HCO2NH4 as a hole scavenger upon purging with N2 under visible light irradiation (λ ≥ 420 nm). The CdS sample prepared by CdCl2 and sulfur powder in ethylenediamine showed excellent catalytic activity, giving 100% of 4-nitroaniline conversion and 95% of p-phenylenediamine selectivity after 35 min of visible light irradiation. The results of electron spin resonance revealed that its photoexcited holes could efficiently react with HCO2− ions within HCO2NH4 molecules to produce ˙CO2− radicals with strong reductive abilities. Furthermore, photoexcited electrons of the obtained sample exhibited relatively strong reductive abilities as compared to other CdS samples. Therefore, this sample showed the highest catalytic activity among the CdS samples for the photocatalytic hydrogenation of 4-nitroaniline.

H3PMo12O40 molecules have been successfully encapsulated in the cavities of MIL-100(Fe) via a facile hydrothermal method (denoted as HPMo@MIL-100(Fe)). A series of characterization has corroborated the insertion of H3PMo12O40 within the cavities of MIL-100(Fe). The resulting HPMo@MIL-100(Fe) nanocomposites have exhibited much higher photoactivity than the original-MIL-100(Fe) toward the photocatalytic selective oxidation of benzylic alcohols and the reduction of Cr(VI) under visible light irradiation (λ ≥ 420 nm). The higher photoactivity of HPMo@MIL-100(Fe) can be attributed to the integrative effect of enhanced light absorption intensity and more efficient separation of photogenerated electron–hole pairs. The host porous structure of MIL-100(Fe) can achieve a uniform composition with H3PMo12O40, which is significantly important for producing highly reactive dispersed H3PMo12O40 molecules and enhancing the photocatalytic activity of HPMo@MIL-100(Fe) nanocomposites. And the immobilized H3PMo12O40 molecules are more convenient for recycling. Importantly, almost no Fe and Mo ions leach from the MIL-100(Fe) during the reaction, which verifies the photostability of the HPMo@MIL-100(Fe). In addition, possible photocatalytic redox reaction mechanisms have been investigated.

The defect degree of MoS2 ultrathin nanoplates are tailored easily via a facile one-pot hydrothermal method. The defect-rich MoS2 ultrathin nanoplates show excellent promotion of photocatalytic hydrogen evolution over CdS; 5.4 times as much as that of the CdS/Pt (1%), which arises from the dual-functional effect of the unique defect-decorated MoS2 ultrathin nanoplates.

TaON nanoparticles with low surface reduction defect sites were successfully constructed by a simple nitridation approach using Ta2O5·nH2O as a precursor. Large amounts of crystal water in Ta2O5·nH2O are considered as a parclose to prohibit Ta5+ from being reduced in the nitridation process with NH3 gas. Urea was also used in the synthesis, acting as a co-nitridation agent together with NH3 but also as a porogen for creating nanopores in TaON frameworks. The as-prepared TaON catalyst was evaluated by environmental purification of organic pollutants in water, as exemplified here by mineralization of phenol and its chloroderivatives in aqueous phase under visible light irradiation. Results revealed that a lower defect density of TaON, as well as its nanopore structure and smaller particle size, contribute to the promotion in both electron–hole separation and interfacial charge-transfer in materials surface/interface, being the main reasons for the enhanced photocatalytic performance.

A CdS/H2Ti5O11 ultrathin nanobelt nanocomposite (CdTi) was fabricated successfully by a two-step process. It was confirmed by SEM and TEM/HRTEM that the highly dispersed CdS about 15 nm in size was firmly anchored on the ultrathin nanobelt. The as-prepared CdTi-5 with an optimal loading of 81.3% CdS converted 4-nitroaniline to p-phenylenediamine, giving almost 100% yield with a selectivity of about 98% in 3 min under visible light irradiation. Its photocatalytic activity was much higher than that of the bare CdS and P25/CdS composition. The highly efficient performance was attributed to the synergetic effects of the formed heterojunction between titanate, nanobelt and CdS as well as the unique features of the titanate nanobelt, which makes the photo-generated electron to transfer smoothly and promotes the separation of photo-induced carriers. Finally, based on the experimental results of Mott–Schottky, UV-vis DRS and EPR, a possible reaction mechanism for the hydrogenation of 4-nitroaniline over the CdTi was proposed.

Visible light-activated SnNb2O6 nanosheets (NSs) with high surface area and small crystallites have been prepared by a microwave-assisted template-free hydrothermal method without exfoliation for the first time. This approach could be used to prepare the functional materials efficiently and extended to synthesizing two-dimensional nanosheet materials directly as well. The crystalline phases, photoabsorption performances, and surface areas and porosity of the samples are characterized by XRD, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and N2-adsorption. Results show that a hypsochromic shift of the photoabsorption edge is observed, which reflects an obvious quantum size effect. TEM images reveal SnNb2O6 nanosheets with a thickness of 1–4 nm versus several hundred nanometres in lateral size. Based on the experimental results, the formation mechanism of SnNb2O6 nanosheets is also studied and proposed, which reasonably follows a synergy interaction of reaction–crystallization and dissolution–recrystallization processes. Due to the unique morphology, larger surface area, smaller crystallites and stronger redox ability of the photogenerated hole–electron pair, these photocatalysts show much higher photocatalytic activities for the degradation of rhodamine B (RhB) compared with their counterparts prepared by the traditional solid-state reaction. The reaction rate is enhanced by over 4 times and the RhB molecule can be mineralized into CO2 and H2O over SnNb2O6 NSs. The decomposition mechanism of RhB over SnNb2O6 under visible light irradiation and the active species in the photocatalytic process have also been discussed.

A Ternary composite UiO-66/CdS/1% reduced graphene oxide (RGO) was successfully prepared, with a photocatalytic hydrogen evolution rate 13.8 times as high as that of pure commercial CdS. It shows great advantages over the perfect composite photocatalyst-P25/CdS/1%RGO.