Effect And Mechanism Of Crystal Plane Regulation On Photocatalytic Dissolution Of Precious Metals With Porous Single Crystal Titanium Dioxide

Due to its excellent physical and chemical properties,precious metals are widely used in the manufacture of electronics and catalysts,which greatly promotes the development of industry,agriculture and medicine.However,the low abundance of these precious metals on Earth and their limited availability pose a huge challenge for sustainability.Among them,photocatalytic technology has the advantages of low energy consumption and environmental friendliness,and has become an effective way to realize energy conversion,storage and environmental governance.Therefore,using photocatalytic technology to dissolve and recover precious metals is mild and effective,and has been verified.TiO₂ is widely used as photocatalyst due to its unique characteristics and has been applied in the photocatalytic dissolution of precious metals.At the same time,the photocatalytic performance of TiO₂ crystals varies with the physical and chemical properties of surface such as size,shape,crystal structure and number of exposed crystal surfaces.Controlling the size,shape and surface structure of crystals on the nanoscale is a possible method to improve the efficiency and selectivity of chemical reactions in catalysis.The ordered mesoporous structure can be used in thermal insulation,battery,catalyst and other fields due to its high specific surface area.Based on this,this paper will rely on the existing photocatalytic noble metal dissolution technology to achieve the selective dissolution of noble metal by regulating the TiO₂crystal plane,and further improve the selectivity and catalytic performance according to the unique properties of porous single crystal TiO₂.Meanwhile,the dissolution mechanism in the reaction process will be studied as follows:（1）Selective dissolution of precious metals by crystal plane regulation of single crystal TiO₂Single crystal TiO₂ was synthesized by hydrothermal method,and the main exposed crystal planes were{001},{101}and{100},respectively.The morphology and structure of the materials were analyzed by various characterization methods.The dissolution experiment was carried out by using waste catalyst containing precious metal at room temperature and pressure,and the precious metal ions in the solution were quantitatively studied.In addition,the selective dissolution of precious metals was investigated by adjusting the reaction conditions during the photocatalytic reaction.Different crystal faces of TiO₂ have different surface structures.In the noble metal dissolution experiment,the nature of oxidation and the surface active site for adsorption are determined.Meanwhile,precious metal itself has specificity,which determines the possibility of selective dissolution of precious metal by crystal faces.Solvent modulation showed that the active sites of different precious metals would be transferred on the crystal plane during the dissolution process,indicating that the distribution of active sites existed in various situations and would change accordingly.（2）Controlled preparation of mesoporous TiO₂ and selective dissolution of noble metalsPorous single crystal TiO₂ was prepared by roasting method,and TiO₂ with different exposure ratios of{001}crystal surface was prepared by titanium source modulation.The presence of mesopores and crystal surface exposure were verified by multiple characterization methods.Under the same experimental conditions,mesoporous TiO₂ can effectively improve the catalytic performance of noble metal dissolution,in which the dissolution rate of Au increases by more than 2 times.Through the modulation and characterization of the catalyst,the main reasons for the improvement of catalytic performance were explored,and the active species of the reaction were designed to capture experiment and EPR test.The photogenerated electrons and holes in the photocatalytic reaction participate in the reaction and react with solvents and gases during the reaction to form chloromethyl radical and superoxide radical.The improvement of catalytic performance is related to the larger specific surface area and higher porosity of mesoporous TiO₂.By increasing the amount of noble metal adsorbed,the active site of noble metal in catalytic reaction was increased,and the dissolution activity was improved.