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Abstract: Three polymorphs of Ga2O3 (α-, β-, and γ-Ga2O3) were prepared, and their photocatalytic activities were evaluated by the decomposition of volatile aromatic compounds (e.g., benzene, toluene, and ethylbenzene) in dry air stream under UV light illumination at room temperature. It was found that the Ga2O3 catalysts exhibited much higher photocatalytic activity than commercial TiO2. The photocatalytic activities of the Ga2O3 polymorphs were strongly influenced by their crystal structure, and their specific activities decreased in the following order: β-Ga2O3 > α-Ga2O3 > γ-Ga2O3. The reasons for the differences in photocatalytic activity of the Ga2O3 polymorphs are discussed in terms of crystallinity, geometric structure, and electronic properties of the polymorphs. [Copyright &y& Elsevier]

Efficient visible-light-driven selective oxidation of benzyl alcohol to benzaldehyde over Pt/5MnNS. [Display omitted] • Multicomponent Pt/Mn-Bi 4 Ti 3 O 12 ultrathin nanosheets were successfully constructed. • Pt/5MnNS exhibited high benzaldehyde yield rate (1180 μmol·g−1·h−1). • Surface Ti4+δ sites as stronger Lewis acid sites effectively activated benzyl alcohol. • The structure–function relationship for the multicomponent Pt/5MnNS was revealed. Herein, a series of Pt nanoparticles modificatory Mn doped Bi 4 Ti 3 O 12 ultrathin nanosheets (Pt/MnNS) are constructed as a surface functionalized photocatalyst for the visible-light-driven selective benzyl alcohol (BA) oxidation. Especially, Pt/5MnNS shows the best performance with a benzaldehyde (BD) yield rate of 1180 μmol·g−1·h−1 and a selectivity of 99.9 %. More importantly, experimental results reveal that Mn doping not only extends the optical absorption range of the photocatalyst to the visible region, but also induces the formation of more surface Ti4+δ atoms. Those Ti4+δ atoms as stronger Lewis acid centers achieve more conspicuous adsorption and activation of BA via the C O⋯Ti coordination. It makes the deprotonation of BA by photogenerated holes be easier. Meanwhile, Pt nanoparticles significantly promote the separation and transfer of the photogenerated carriers for supporting the formation of superoxide and carbon-centered radicals. Thus, the photocatalytic BA oxidation efficiency is markedly improved by surface multicomponent synergistic effect. [ABSTRACT FROM AUTHOR]

A series of Fe-based MOFs MIL-68(Fe) with different defect contents were prepared and modulated by doping different amounts of Cu2+ ions for photocatalytic N 2 fixation by converting N 2 and H 2 O into NH 3 and O 2. [Display omitted] • MIL-68(Fe) with various OVs defect contents were prepared by Cu2+ doping for photocatalytic N 2 fixation. • Cu2+ doping induces crystal distortion to produce OVs defect and form coordinated unsaturated Fe2+ sites. • Coordinatively unsaturated Fe2+ sites can behave as active sites for the adsorption and activation of N 2. • Activated N 2 is reduced to NH 3 by the synergistic action of protonated hydrogen and photogenerated electrons. Photocatalytic N 2 fixation is a green process for ammonia synthesis by converting N 2 and H 2 O to NH 3 and O 2 directly using solar energy. Its efficiency is largely limited by the chemisorption and activation of N 2. This work adopts defect engineering strategy to develop a series of MIL-68(Fe) MOFs with varying concentrations of defects by doping Cu2+ on the metal nodes of MOFs. Upon Cu2+ doping, a larger number of oxygen vacancy defects are created due to the induced crystal distortion to form coordinatively unsaturated Fe2+ sites, which can serve as the active sites for promoting the chemisorption and activation of N 2. The photogenerated holes oxidize H 2 O to O 2 and H+, and the photogenerated electrons combine with formed H+ to reduce the activated N 2 to NH 3. It was found that the sample with 10 mol% Cu2+ doping shows the highest NH 3 production rate (21.0 μmol·g−1·h−1), which is 8.4 times higher than that (2.50 μmol·g−1·h−1) of the pristine MIL-68(Fe). The excellent performance is ascribed to the adequate Fe2+ active sites to chemisorb and activate N 2 and the optimal mobility of photogenerated charges. Finally, a mechanism is proposed to illustrate how the number of defects affects the photocatalytic N 2 fixation performance at the molecular level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nickel disulfide decorated CdS nanosheets (NiS 2 /CdS) are synthesized. • NiS 2 can serve as the active sites for hydrogen evolution reaction and dehydrogenation reaction. • The integrated photocatalytic redox cycles for H 2 production and imine synthesis are achieved on NiS 2 /CdS. Photocatalytic hydrogen (H 2) evolution integrated with selective oxidation to produce fine chemicals is a promising strategy for solar energy conversion and storage; however, the efficiency of such coupled photocatalytic redox cycles is greatly limited by the poor surface kinetics of hydrogen evolution reaction (HER) and/or dehydrogenation reaction (DHR) on heterogenous photocatalysts. Herein, we demonstrate that the immobilization of ultrafine nickel disulfide (NiS 2) nanoparticles on CdS nanosheets (NiS 2 /CdS) is a simple yet efficient approach to kinetic improve the surface redox reactions for H 2 production and dehydrogenative coupling of amines to imines. The NiS 2 nanoparticles loaded on CdS not only function as the HER active sites to speed up charge separation and to boost H 2 release, but also enhance the adsorption of amines to facilitate the dissociation of C-H and N-H bonds to form aldimines intermediates, which are readily coupled with other amines to afford a high selectivity toward imine synthesis. Benefiting from such unique bifunctional catalytic behavior of NiS 2 in proton (H+) reduction and substrate activation, NiS 2 /CdS exhibits a remarkable enhanced photocatalytic performance toward simultaneous production of H 2 and imines. The apparent quantum efficiency (AQE) at 420 nm is calculated to be 54.7%. This strategy using bifunctional cocatalysts to kinetic improve the surface redox reactions will have broad implications in the development of high-performance photocatalysts for integrated production of solar hydrogen and value-added solar chemicals. [ABSTRACT FROM AUTHOR]

The multifunctional photocatalysts (Au-Pd/SnNb 2 O 6 ultrathin nanosheets) are developed for selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde under visible light. The superior catalytic performance is attributed to a synergistic effect of Au, Pd nanoparticles, and SnNb 2 O 6 ultrathin nanosheets. [Display omitted] • Au-Pd/SnNb 2 O 6 (SN) as photocatalysts for selective hydrogenation of cinnamaldehyde. • The C = C of cinnamaldehyde would be absorbed on the surface Lewis acid sites of SN. • Photogenerated electrons promoted H 2 dissociation on Pd, Au reduced overhydrogenation. • The superior performance is attributed to a synergistic effect of catalyst component. Au-Pd bimetallic nanoparticles (NPs) supported on SnNb 2 O 6 ultrathin nanosheets (SN) were developed as multifunctional photocatalysts for the selective hydrogenation of cinnamaldehyde (CAL) to hydrocinnamaldehyde (HCAL) under visible light irradiation. A representative catalyst (Au 6 -Pd 1 /SN) exhibits optimum performances with 99.8% conversion and 91.0% selectivity. The structure and surface properties of the prepared samples were revealed by SEM, TEM, BET, TPD, XPS, and EPR. The results of in situ FTIR spectra and NH 3 -TPD reveal that the rich surface Lewis acid sites on SN can chemisorb and activate CAL via the C = C...Nb coordination. EPR experiments indicate that H 2 would dissociate to activated H atoms on Pd NPs following a photopromoted surface catalytic process. Experimental results suggest that Au NPs reduce the over hydrogenation of HCAL by inhibiting the formation of Pd-H species. The superior catalytic performance is attributed to a synergistic effect of Au, Pd NPs and SN. Finally, a possible synergetic mechanism for Au-Pd/SN is proposed to illustrate the photocatalytic process. This work offers a reference to guide a novel and more effective photocatalyst design for precise organic synthesis driven by sunlight. [ABSTRACT FROM AUTHOR]

[Display omitted] • The sulfur vacancies (SVs) could be generated on ultrathin CdS nanosheet (CdS-NS) through visible light irradiation. • The light-induced SVs on CdS-NS can function as typical Lewis acid sites to adsorb and activate silanes. • Photocatalytic dehydrogenative coupling of silanes with alcohols has been achieved on CdS-NS with in-situ generated SVs. Photocatalytic organosilicon transformation is a green and emerging synthetic strategy toward silyl ethers production. This approach takes advantage of the highly reactive photogenerated electron-hole pairs to trigger redox reactions for chemical transformations under mild conditions. However, the development of heterogenous photocatalysts for silyl ethers synthesis is greatly hampered by the lack of sufficient reactive sites on the catalyst surface for the adsorption and activation of silanes. Herein, we demonstrate that the light-induced sulfur vacancies (SVs) in-situ generated on ultrathin CdS nanosheet (CdS-NS) can function as typical Lewis acid sites to adsorb and activate silanes via the formation of Si H···Cd coordination species. In addition, these electron-deficient SVs can also trap the photogenerated electrons to promote charge separation. The CdS-NS with SVs exhibits an excellent photocatalytic performance toward silyl ethers synthesis while producing H 2 simultaneously. This synthetic strategy based on in-situ creation of abundant Lewis acid sites on photocatalyst surface to activate silanes will have broad implications in the development of high-performance photocatalysts for organosilicon transformations. [ABSTRACT FROM AUTHOR]

The exposed Lewis acid sites in BiOCl nanosheets would efficiently chemisorb benzylamine. The synthesis of N-benzyleneamine from benzylamine was achieved via surface coordination activation mediated photocatalysis. • Rich oxygen vacancies in BiOCl nanosheets result in abundant surface Lewis acid sites. • The coordination of benzylamine with surface Lewis acid sites of BiOCl nanosheets. • The interface charges transfer from benzylamine to BiOCl nanosheet via surface coordination species. • A synergistic mechanism was proposed via surface coordination activation mediated photocatalysis. Ultrathin BiOCl nanosheets (NST) with the thickness about 1.5 nm was prepared as a photocatalyst for the oxidation of benzylamine (BA) to N-benzyleneamine under visible light. The photocatalytic activity of NST is over 2.5 times higher than that of its bulk counterpart. More oxygen vacancies (OVs) in NST were revealed by EPR and XPS. UV-DRS result indicates that light adsorption of NST can be extended to visible light due to the presence of OVs. In addition, rich OVs result in Bi atoms in sublayer to be exposed as Lewis acid sites. In situ FTIR spectrum shows that BA is chemosorbed on the Lewis acid sites forming surface -N∙∙∙Bi- coordination species, resulting in the activation of BA. The surface coordination species would also result in the red shift of the photo-absorption spectrum. Finally, a synergistic mechanism based on surface coordination activation and photocatalysis was proposed to explain the enhanced photocatalytic activity over NST. [ABSTRACT FROM AUTHOR]

Graphical abstract The Lewis acid sites (Ti) in TNS would selectively adsorb OH in cinnamyl alcohol forming surface C O···Ti O coordination species. Under visible light irradiation, interface charge transfer occurs from C O to Ti O , resulting in the activation of cinnamyl alcohol and the charge enrichment in Ti atoms of TiO 6. The molecule O 2 would be adsorbed on the electron enriched Ti atoms and reduced to O 2 − for the oxidation of alcohol. Due to the hybrid electronic states of Cu-Cu 2 O, the interface electronic transfer kinetics are tuned to inhibit the intramolecular hydrogen transfer for dominating the selectivity towards cinnamaldehyde. The synergistic effect of surface coordination-activation-photocatalysis enables an efficient and green synthesis. Highlights • The coordination of hydroxyl in alcohol with surface Lewis acid sites of H 1.4 Ti 1.65 O 4 ·H 2 O nanosheets. • Directional interface charges transfer from alcohol to nanosheet occur via surface coordination species. • The hybrid electronic states of Cu-Cu 2 O tune interface charges transfer kinetics. • Synergistic surface coordination-activation-photocatalysis for precies synthesis. Abstract A multifunctional photocatalyst is constructed based on Cu-Cu 2 O hybrid and monolayer H 1.4 Ti 1.65 O 4 ·H 2 O nanosheets via an in situ photo-deposition process (Cu-Cu 2 O/TNS). The prepared sample enables the oxidation of cinnamyl alcohol to cinnamaldehyde with over 95% of selectivity under visible light irradiation using molecule O 2 as the oxidant. In situ FTIR spectra suggest that the Lewis acid sites in TNS would selectively adsorbed the hydroxyl of cinnamyl alcohol forming surface C O∙∙∙Ti O coordination species. UV-DRS spectra reveal that light adsorption of TNS can be extended to visible light region due to the interface charges transfer from C OH to Ti O via the surface coordination, resulting in the activation of OH in alcohol. In situ ESR further indicates that directional interface charge transfer induces the charge enrichment in Ti atoms of TiO 6 , facilitating O 2 adsorption. XAFS results reveal that the hybrid electronic states of Cu-Cu 2 O efficiently improve the interface electronic transfer kinetics to inhibit the intramolecular hydrogen transfer for dominating the selectivity towards cinnamaldehyde. This work highlights the synergistic effect of surface coordination-activation-photocatalysis for selective photosynthesis of fine chemicals. [ABSTRACT FROM AUTHOR]

The photoalkylation of nitroarenes with benzyl alcohols in one pot at room temperature and 1 atm N 2 was achieved over the Pd/H 1.07 Ti 1.73 O 4 ·H 2 O nanosheets. The sample shows efficient photocatalytic activity with high conversion of nitrobenzene (99%) and selectivity of secondary amine (85%). This flexible photocatalytic system is also applicable to other nitroarenes with high efficiency. Results of in situ FTIR, DRS, and in situ ESR revealed that the benzyl alcohol and nitrobenzene molecules can bind with the surface Lewis and Brønsted acid sites in the catalyst via the H O⋯Ti and NO 2 ⋯H O Ti species. The formation of surface coordination species results in not only the activation of reactant molecules via surface electron transfer, but also the expanded visible light absorption of the catalyst. Moreover, in situ ESR suggested that the surface coordination can also facilitate the formation of oxygen vacancies in catalysts, which can greatly promote the exposure of Lewis sites and enhance the activation of reactant molecules. Finally, a possible hydrogen transfer strategy over the sample is proposed on a molecular level. [ABSTRACT FROM AUTHOR]

Cu was loaded on ultrathin HNb 3 O 8 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 H 2 evolution activity of (0.5%) Cu/HNb 3 O 8 was about 23.6 times higher than that of the bare HNb 3 O 8 nanosheets under simulated solar light irradiation. The role of Cu in promoting photocatalytic hydrogen evolution activity over HNb 3 O 8 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 HNb 3 O 8 nanosheets with and without Cu modification were proposed, which might provide insights into the photocatalytic hydrogen evolution mechanism over niobate-based metal oxides. [ABSTRACT FROM AUTHOR]

Abstract: 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 150min, which was much higher than those of bulk PbBi2Nb2O9 and TiO2− x N x 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. [Copyright &y& Elsevier]

Postnitridation annealing has a remarkable effect on the surface property and photocatalytic performance of N-doped TiO2 for photocatalytic oxidation of ethylene. The activity of N-doped TiO2 under visible light illumination () can be enhanced fourfold by annealing the sample at 400 °C. Characterization results show that the thermal annealing reduces surface oxygen vacancies, removes surface-adsorbed NH3, and facilitates the adsorption of molecular oxygen on catalyst surface. Such a surface reconstruction contributes to the enhanced photocatalytic activity of the N-doped TiO2. The postcalcination also improves the photocatalytic stability of the N-doped TiO2 by stabilizing nitrogen atoms in the TiO2 lattice. A N-doped TiO2 sample without postcalcination suffers from a gradual deactivation, due mainly to the passivation of the catalyst surface by oxidized nitrogen species (e.g., hyponitrite, nitrite ions, and nitrate ions) formed during the photocatalytic degradation of ethylene. [Copyright &y& Elsevier]