Studies On Structural Design And Photocatalytic Performance Of Single Metal Atoms-Decorated ZnIn₂S₄ Semiconductor Materials

In recent years,the overexploitation and massive burning of fossil resources has resulted in severe energy crisis and environmental problems.Nowadays,how to efficiently alleviate the energy crisis and solve environmental problems has become the focus of researchers.Photocatalysis using inexhaustible solar energy is considered to be a competitive green energy conversion pathway.Specifically,photocatalytic reactions can generate photogenerated electron-hole pairs by solar excitation of semiconductor catalysts,which transfer to the catalyst surface and selectively convert reactants into high value-added products.However,most photocatalytic reactions still suffer from low reaction efficiency and poor selectivity,which are mainly due to the rapid recombination of photogenerated electron-hole pairs,low utilisation of catalytic sites and unsuitable binding strength between reactants/intermediates and catalytic sites.The rapid development of single-atom catalysts in recent years has attracted the interest of researchers due to their unique electronic structure and high atom utilisation,providing a new opportunity for the development of photocatalysis.In this paper,ZnIn₂S₄ semiconductors with visible-light response are used as the target of this study to promote photogenerated charges separation and surface reaction kinetics by constructing suitable metal single atoms on the surface,thus significantly enhancing the photocatalytic reaction efficiency,and combining in situ spectroscopy and theoretical calculations to investigate the mechanism of the catalytic reaction process,uncovering the structure-activity correlations between single-atom structure design and photocatalytic performance.The main research contents of this paper are as follows:1.Low-coordination Au single atom loaded ZnIn₂S₄ to achieve efficient photocatalytic CO₂ reduction to CH₄:A complex-exchange strategy is employed to anchor single Au atoms to ultrathin ZnIn₂S₄（ZIS）nanosheets with S vacancies,resulting in the Au1-S2 low coordination structure.Under visible-light irradiation（λ>420 nm）,the as-prepared single Au atoms on ultrathin ZIS nanosheets（Au1/ZIS）catalyst can achieve a CH₄ yield of 275 μmol g-1 h-1 and a CH₄ selectivity of 77%for photocatalytic CO₂ reduction in the presence of photosensitizer and hole sacrificial agent.The characterization of carrier kinetics showed that the introduction of Au single atoms enhances the carrier separation and transfer efficiency,thereby exhibiting excellent activity in the photocatalytic CO₂ reduction process.In situ diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）and density functional theory（DFT）calculations confirm that low-coordination single Au atoms can significantly enhance the activation of CO₂ molecules and improve stability for absorption of*CO intermediates compared to Au nanoparticles,which rapidly protonates to CH₄.In conclusion,we have innovatively constructed an ultrathin ZnIn₂S₄ nanosheet loaded with a low coordination structure Au single-atom catalyst using a complex-exchange method for the first time,and the catalyst can efficiently achieve photocatalytic CO₂ reduction to CH₄.This find may open up new avenues for selective artificial photosynthesis to targeted product with single metal atoms catalysts.2.Solar-driven selective oxidation of 5-hydroxymethylfurfural coupled with hydrogen evolution via atomically dispersed Ni sites loaded ZnIn₂S₄:A simple one-step solution method was used to modify atomically-dispersed Ni atoms onto the surface of ultrathin ZnIn₂S₄ nanosheets,resulting in the construction of O atoms coordinated single Ni atom structure model for photocatalytic 5-hydroxymethylfurfural（HMF）oxidation coupled with hydrogen evolution reaction.Notably,under visible-light irradiation,the optimal Ni species anchoring photocatalyst（Ni-ZIS-3）for photocatalytic HMF oxidation coupled with hydrogen evolution reactions can achieve>96%selectivity from HMF to DFF while generating DFF(387.4 μmol g^-1 h^-1)and H₂(333.5 μmol g^-1 h^-1)in a near stoichiometric ratio.Photoelectrochemical measurements display that the introduction of atomically-dispersed Ni species can significantly improve carrier separation efficiency,thereby exhibiting excellent activity in the photocatalytic HMF oxidation and H₂ evolution.In situ electron spin resonance（ESR）measurements combined with radical trapping experiments demonstrated that both photogenerated holes and hydroxyl radicals were involved in the photocatalytic HMF oxidation coupled with H₂ evolution,with holes predominating.Density functional theory（DFT）calculations reveal that the active sites for selective oxidation of HMF are atomically-dispersed Ni species,while S atoms are more preferred as H₂ evolution reaction（HER）sites.In summary,we propose a simple solutionbased strategy to achieve atomically-dispersed Ni species loading on ultrathin ZnIn₂S₄ nanosheets,and the as-prepared catalyst can efficiently achieve photocatalytic HM selective conversion of HMF coupled with H₂ evolution via photocatalysis.This work provides new insights for the development of artificial photosynthesis of high value-added chemicals from biomass resources.