Theory Study Of Optical Properties Of Metal Clusters And Metal/TiO₂ System

In the redox reaction which O₂ involved in,the reduction course of O₂ usually determines the reaction rate in the whole experiment.Recent reports show that,many noble metal involving Pt,Ag and Au nanoparticle clusters as well as binary alloy clusters including Pt Cu,AuPt and AuPd,acting as photocatalysts,not only provide high reaction rate,but also exhibit high catalyzed properties under visible light.During photocatalyzed reaction,however,it is extremely obvious that the electronic transfer between O₂ and noble metal clusters,as well as mechanism of light absorbance are not clear.Besides,the direction of electronic transfer between the noble metal and TiO₂ under light absorbance has been controversial.With the fast development in the field of modern electronic computer technology and theoretical chemistry,exporing the mechanism from a micro perspective become possible.In this work,the electron transfer mechanism between Pt metal clusters and O₂,as well as Pt Cu alloy clusters and O₂ under light conditions were studied by using the density functional method combined with time-dependent density functional mothed.We also explored the electron transfer direction between Pt metal and TiO₂.The main research contents are as follows: 1.The interaction between Pt_n?n=1,2,4,6,9,10,14,18,22,27?metal clusters and O₂ under visible lightFirstly,we studied the adsorption behavior of O₂ on Pt metal clusters,as well as the optical properties of Pt metal clusters and Pt-O₂ system with the method of time-dependent density functional.The calculations proves that O₂ tends to adsorb Pt_n cluster through bridge site.With the decrease of bond length between Pt atom and O atom,O₂ easily transits from superoxo to peroxo species.The adsorbed O₂ greatly change the optical absorption properties of the platinum clusters,especially in lower energy areas.The electron transition at this time includes not only the transition from d orbit to sp orbit of Pt,but also d orbit of Pt to p orbit of O.The analysis of DOS in the whole system fully illustrates why the optical absorption of Pt clusters enhanced under the adsorption of O₂ in the visible light.2.The interaction between Pt_nCu?n=1-6?alloy clusters and O₂ under visible lightUsing the same method,we studied the electronic transfer between Pt_n Cu?n=1-6?alloy clusters and O₂ under visible light.We find that there exsist single electrons in the alloy clusters with doped Cu atoms.With the increase of n,the number of electrons also increases.O₂ molecule bond with Pt atoms in the way of bridge site.Adsorbed O₂ basically form superoxo species.In the meantime,the doped Cu atoms greatly change the optical absorption properties of the platinum clusters,especially in higher energy areas.The electron transition at this time includes not only the transition from d orbit to sp orbit of Pt atom,but also d orbit to p orbit of Cu atom.Adsorption of O₂ also enhances the light absorption in the lower energy region of the entire spectrum.There exsist not only the transition from d orbit to sp orbit of Pt,but also the transition from d orbit of Pt to p orbit of O in the lower energy areas.We explain this phenomenon through the analysis of DOS.3.Charge transfer of Pt_n/TiO₂?n=1-4?under visible lightThe last part,we studied the problem of electronic transfer direction of Pt metal clusters and TiO₂ under visible light.The calculations show that Pt atoms creat a bond with 5 coordinated Ti atoms and 2 coordinated O atoms to form a stable adsorption configuration.The loading of Pt metal clusters does greatly change the light absorption properties of TiO₂,so that the entire system of light absorption extended to the visible region.Whether in the high energy area or in the low energy area,electrons from Pt metal clusters transit to TiO₂.This result illustrates the problem of electron transfer direction between Pt metal clusters and TiO₂ from a microscopic point of view.In conclusion,the above research results will lay a theoretical foundation for the study of the mechanism of photocatalytic oxidation and reduction on Pt metal clusters,PtCu binary alloy clusters and Pt/TiO₂ system.