Controllable Construction And Hydrogen Production Mechanism Research Of Tin-based Photocatalysts

Under the background of the"double carbon"strategy,it is the general trend to accelerate the pace of reducing carbon emissions,vigorously develop renewable energy and promote the adjustment of Chinese industrial structure and energy system.Benefiting from energy-saving,low cost and mild conditions,semiconductor photocatalysis technology has broad application prospects in upgrading energy system.In this field,it is the most important research direction to develop and prepare photocatalysts with excellent performance.In this work,SnS₂ and Sn O₂semiconductor materials with wide sources and high chemical stability are explored,whose carrier behavior is regulated by introducing defect energy levels and constructing built-in electric field.By means of theoretical calculation and experimental verification,the main factors affecting the photogenerated carrier separation efficiency of the catalyst are deeply analyzed.The necessary and sufficient conditions for increasing the half reaction rate and completing the whole reaction process are explored from the perspective of kinetics and thermodynamics.After a series of modification methods such as doping ions and forming heterojunctions,the hydrogen production rate of water decomposition of tin based 2D semiconductor catalyst has been significantly improved,and the purpose of pure water decomposition in the visible light range has been realized.SnS₂ flower-like photocatalyst modified by vacancy was successfully prepared by Cu²⁺doping strategy,which inhibited the inside recombination of photogenerated carriers.During the hydrothermal reaction,Cu²⁺released by the dissolution of Cu S precursor entered the lattice of SnS₂ to replace position of Sn⁴⁺,resulting in formation of S^2-vacancy defects.The generated sulfur vacancy formed a stable defect energy level near the bottom of the conduction band of the catalyst,reduced the band gap and increased the transfer path of photogenerated electrons,thus improving the carrier density and separation efficiency of photogenerated carrier.The addition of Cu²⁺and S vacancy reduced the surface work function of SnS₂,making it easier for photogenerated electrons to react with water molecules.Finally,the hydrogen production rate of 5%Cu/SnS_2-x under visible light was 1.37 mmol h^-1 g^-1,which was more than 6 times higher than that of the sample before doping.A face-to-face bonded g-C₃N₄/SnS₂ heterojunction was constructed by self-assembly method,and the migration direction of photogenerated carrier inSn-based semiconductor catalyst was optimized.Heterojunction interface charge recombination and staggered energy band structure promoted the transfer of photogenerated carrier following the mechanism of type II heterojunction,improved the separation efficiency of photogenerated electron hole pairs and reduced the probability of recombination in bulk phase.Results of DFT revealed that thanks to the smaller hydrogen adsorption free energy of heterojunction system,the interaction between catalyst and water molecules was enhanced,and the adsorption-desorption rate of reaction intermediates was faster,so as to further improve the hydrogen production rate of water decomposition to 1.69 mmol h^-1 g^-1.Taking full advantage of the structural advantages of two-dimensional materials and the anisotropy of charge transfer,Sn O₂/Cd S in-plane heterojunction catalyst was prepared by foaming vulcanization method,which improved the conductivity of heterojunction interface.The positive and negative charges accumulated at the interface of the two-phase heterojunction,and finally formed a built-in electric field pointing to Sn O₂,driving the two-phase photogenerated carrier to separate and transfer following the mechanism S-scheme.This S-scheme heterojunction could significantly improve the carrier separation efficiency of tin based catalysts and ensure that electrons and holes with high energy to participate in photocatalytic reactions.The modified Sn-based catalyst showed higher quantum efficiency,whose hydrogen production rate of water decomposition reached 2.54 mmol h^-1 g^-1.An efficient 2D rGO/SnS₂/Ag nanostructure photocatalyst was designed and prepared,which realized bidirectional separation of photogenerated carriers inSnS₂,and achieved purpose of decomposing pure water into H₂ and O₂ under visible light.In this system,rGO nanosheets was closely combined with SnS₂ through C-S bond and worked as electron transmission medium exacting photogenerated holes.Ag nanoparticles were modified on surface of SnS₂ in the form of cocatalyst and induced the transfer of photogenerated electrons.The recombination of interfacial charges accelerated the interfacial transport of charge to achieve higher carrier separation efficiency and quantum yield.Therefore,under synergistic action of each component,overall water splitting hydrogen and oxygen production rates of rGO/SnS₂/Ag photocatalyst in the visible region were as high as 137 and 68μmol h^-1 g^-1。...