Study On Photocatalytic Performance And Mechanism Of Transition Metal Doping Modified Silver-based Semiconductor

With the rapid development of industry,problems such as global warming and energy shortage caused by industrial pollution are becoming more and more serious.Therefore,human society urgently needs to find ideal methods to degrade organic pollutants.Photocatalysis technology using solar energy has received wide attention since 1972.In particular,TiO₂ and ZnO photocatalysts have been extensively studied because of their high activity under ultraviolet irradiation.Unfortunately,due to the wide band gap（>3.0 eV）,photocatalysts represented by TiO₂ can only absorb the ultraviolet band of sunlight and have a low utilization rate of solar energy,which greatly limits their development and practical application.Therefore,researchers have tried to use a large number of modification methods to improve the photocatalytic ability of TiO₂,such as deposition of precious metals,element doping,construction of heterojunction and surface modification.In addition,in order to maximize the use of sunlight,the search for new semiconductor catalysts has never stopped;for instance,graphene oxide,carbon nitride,Ag-based,etc.It is found that element doping modification is one of the most simple and effective methods to improve the degradation ability of photocatalyst.Due to the existence of a variety of valence states,transition metal elements can be used as electronic reservoirs.Compared with other metal cations,transition metal elements have the advantages of non-toxicity,low cost and variable valence,which has become a research hotspot of doping modification.However,there are still some limitations in the research of transition metal element doping,such as the modification of simple structure semiconductors and the synergistic effect with other modification methods.Therefore,it is of great significance to explore these two aspects in depth to extend the practical application range of this modification method.In this paper,a series of Mn²⁺-AgBr samples were prepared by simple ice bath deposition method for the first time to explore the effect of transition metal doping modification on simple structure semiconductors.Under simulated sunlight irradiation,Mn²⁺doped AgBr possessed good degradation activity to rhodamine B（RhB）and Ciprofloxacin（CIP）.Notably,the optimal sample AM-2（the mole ratio of Mn element in the whole sample is 0.014%）can degrade RhB at a reaction rate constant of 0.10334min^-1,which was 7.72 times that of pure AgBr.In light of density functional theory（DFT）,the improvement of photocatalytic performance was due to the incorporation of Mn ions that induced lattice strain,affected the charge distribution,and generated an intermediate Mn 2p-Br 3d two-dimensional energy level in the AgBr band gap.Photoelectrochemical experiments verified that Mn²⁺doping promoted the transfer efficiency of photogenerated electron-hole pairs and enhanced light absorption.In addition,the practical application ability of the photocatalyst is studied,and it is found that the new photocatalysts own excellent photocatalytic activity in the actual environment.Therefore,transition metal doping may provide a new way to improve the photocatalytic performance of simple structure Ag-based photocatalysts.Another novel of Bi₂SiO₅/Ni²⁺-Ag₆Si₂O₇ semiconductor was prepared by ice bath deposition and hydrothermal method to explore whether transition metal doping modification and semiconductor composite can play a synergistic role in photocatalytic reaction.XPS tests showed that electrons were transferred from Bi₂SiO₅ to Ni²⁺-Ag₆Si₂O₇ under light conditions.Through SEM and BET tests,it was observed that Bi₂SiO₅ can disperse Ag₆Si₂O₇ particles to a certain extent,and the addition of Ni²⁺can effectively reduce the particle size of the sample and increase the specific surface area.Under simulated sunlight,the degradation rate of the optimal samples for MO reached0.03743 min^-1,which was 7.28 times and 3.15 times of that of pure Bi₂SiO₅ and Ag₆Si₂O₇,respectively.The formation of Z-type heterojunction effectively inhibited the photo-induced carrier recombination,promoted the generation of active free radicals,and preserved the high redox capacity of photogenerated carriers.The doping of Ni²⁺increased the valence band position of Ag₆Si₂O₇,which further promoted the electron transfer in the Z-type transfer mechanism.Therefore,the enhanced photocatalytic ability was attributed to the synergistic effect of Ni²⁺doping and Bi₂SiO₅/Ni²⁺-Ag₆Si₂O₇Z-type heterojunction.