Theoretical Study On The Effect Of Gold-copper Bimetallic Promoter On The Photocatalytic Performance Of Titanium Dioxide

Titanium dioxide?TiO₂?is a widely used semiconductor photocatalytic material,and its high-efficiency application is limited by its wide band gap and high recombination rate of photogenerated carriers.In many modification studies,noble-metal loading has attracted much attention due to its plasmonic resonance effect.The Au/TiO₂ composite photocatalytic materials have received a lot of attention due to its excellent photocatalytic performance.To reduce costs and maintain its original co-catalysis activity as much as possible,consider using an AuCu bimetal with bimetallic synergy to replace Au.In this work,the effect of Cu on the photocatalytic performance of Au/TiO₂ was analyzed from the microscopic view of atoms and electrons using theoretical calculations.The similarities and differences in photocatalytic performance between Au/TiO₂ and AuCu/TiO₂ were compared.The research results have important theoretical significance for the development and design of novel bimetallic AuCu/TiO₂ photocatalytic materials.The study includes a total of four parts:First,verify the interaction between Au and TiO₂,and then compare the catalytic performance of Au and AuCu surfaces.After that,the adsorption of AuCu bimetallic clusters on the surface of TiO₂ was studied.Finally,a large-sized AuCu/TiO₂ heterojunction was constructed to study the interfacial properties.The effect of Cu on the photocatalytic performance of Au/TiO₂ was also discussed.The main research contents and results are as follows:?1?The interactions and related properties of three different Au₉ isomers supported on TiO₂ substrates were investigated.The differences in the structure and property of Au₉ with two-dimensional and three-dimensional configurations were analyzed systematically.The calculated results showed that the interaction between Au₉ clusters and the substrate is closely related to the adsorption site of Au₉ and the stability of Au₉ in the gas phase.The two-dimensional Au₉ clusters have the strong interaction with the substrate and have the large adsorption energy.Besides,the stable adsorption site for Au₉ clusters deposited on the anatase TiO₂?001?surface tends to the O_2c-O_2c hollow site.The appearance of metal induced gap states,the disappearance of surface states of TiO₂?001?surface,and the shift of the Fermi level suggest the strong interaction between Au₉ cluster and TiO₂?001?surface.Meanwhile,the interaction and electron transfer between the Au₉ clusters and the TiO₂ support are mainly through the Au-O_2c bonds.The strong interaction and the large amount of charge transfer are favorable for photocatalytic reaction.?2?The adsorption and decomposition reaction paths of single H₂O molecule on Au,Cu and AuCu alloy were studied,and the catalytic performances of different surfaces were compared.The calculated results showed that the catalytic activity of the considered four surface models,using the active energy as comparison standard,is on the following order:Au?111?<AuCu?111?-Cu<AuCu?111?-Au<Cu?111?.The molecular adsorption energies of H₂O on AuCu?111?-Au and Cu?111?surfaces are relatively small,while the adsorption energies of the decomposed OH+H group are relatively large.Besides,the overlapping or hybridization between the metal-d states and the 1b₁ states of H₂O or lb₁-like states of OH+H group determines this interaction.Therefore,using AuCu alloy to replace Au as catalyst or co-catalyst reduces cost,and enhances the catalytic activity.?3?The metal-support interactions between the Au_xCu_y?x+y=1,2,3?nanoclusters and the clean anatase TiO₂?101?surface were systematically investigated,and the growth mechanisms and the transfer of active growth sites of AuCu clusters on TiO₂?101?surface were clarified.The calculated results showed that the AuCu/TiO₂ system always has the large adsorption energy and binding energy,and the interaction between the AuCu clusters and the substrate are also strong.The strength of the interaction between the clusters and the substrate has a linear correlation with the amount of charge transfer of the adsorbed clusters,and with the bond length of m_h-O_2c.Meanwhile,the interaction and electron transfer between the clusters and TiO₂ support are mainly through the m-O_2c bonds.The calculated results of catalytic activity showed that the Au_xCu_y?x+y=2?/TiO₂ system cannot decompose H₂O molecule spontaneously.However,the initial decomposition of H₂O can be promoted by replacing Au₃ or Cu₃ cluster with bimetallic Au₁Cu₂ or Au₂Cu₁cluster.Based on this result,it can be speculated that the AuCu/TiO₂ composite system has better photocatalytic properties than the Au/TiO₂ composite system in some cases.?4?The interfacial microstructures and electronic properties of AuCu/TiO₂hetero-structures were investigated.Calculation results of interfacial structures showed that,except AuCu?111?/TiO₂?101?,the interface spacings of AuCu/TiO₂ hetero-structures are smaller than that of Au/TiO₂ hetero-structure.The formations of AuCu?111?/TiO₂?101?and AuCu?100?-Cu/TiO₂?101?hetero-structures are easier than that of Au/TiO₂.Calculation results of electronic structures indicated that the AuCu?001?/TiO₂?101?and AuCu?100?-Cu/TiO₂?101?hetero-structures have more pronounced interface states and charge transfer,indicating that AuCu?001?and AuCu?100?-Cu surface have the strong interactions with the substrate.Besides,the Schottky barrier heights of AuCu/TiO₂hetero-structures are smaller than that of the Au/TiO₂ hetero-structure,which promotes electron transfer from Ti O₂ substrate to AuCu layer,and it is favorable for photocatalytic reaction.