Preparation And Photocatalytic Performance Of SnO₂ And Composite Microspheres

Tin dioxide has attracted a lot of attention because of its excellent chemical stability and the special thermodynamic position of valence band and conduction band edge.It is widely used in sensitized solar cells,gas sensor,photocatalytic materials and other fields.The performance of the material depends not only on its own chemical composition,but also on the morphology,structure and size of the material.However,in the past,the effect of most researchers on the preparation of monodisperse SnO₂ microspheres with controllable morphology is not ideal,the main reason is that Sn（OH）₄ precursors are formed by directly adding water or alkaline substances,which will lead to the hydrolysis rate of tin source is too fast,nucleation and growth can not be carried out separately,so that the concentration of tin dioxide precursor is always higher than the critical concentration,thus nucleation continues to form agglomerated products.And the prepared SnO₂ has high photogenerated electron-hole recombination rate,which will lead to low photocatalytic activity.In this study,in order to solve the problem that it is difficult to control the synthesis of monodisperse SnO₂ microspheres,firstly,monodisperse SnO₂ microspheres can be obtained by hydrothermal method by adding surfactants to reduce the surface free energy of the microspheres.And the improved St（?）ber method means that a suitable water production reaction is introduced before the hydrolysis reaction,that is,the alkyd esterification reaction is used to produce water,which provides a"water source"for the hydrolysis reaction of anhydrous tin chloride,so that the hydrolysis rate of anhydrous tin chloride is controlled by the esterification reaction to solve the problem tha t the hydrolysis rate of tin source is too fast and avoid the interaction between nucleation and growth process,thus obtaining monodisperse SnO₂ microspheres.The test of laser nanoparticle size analyzer（DLS）showed that the polydispersity index（PDI）of the SnO₂ microspheres was less than 6%.The results of photocatalytic degradation experiments showed that compared with the SnO₂ microspheres prepared by hydrothermal method,the degradation rate of rhodamine B by SnO₂ microspheres prepared by St（?）ber method was increased by26%.By means of specific surface area measurement（BET）,surface photovoltage spectrum（SPS）,transient photocurrent response（OTCS）and electron spin resonance（ESR）,it is concluded that the high activity of SnO ₂ prepared by St（?）ber method is due to its higher specific surface area,more micropore structure,larger photoelectric separation efficiency,more oxygen vacancies and more active free radicals.In order to restrain the high recombination rate of photogenerated electron-hole pairs of SnO₂,TiO₂-SnO₂ composites were constructed by adding a small amount of TiO ₂ to the synthesis system under hydrothermal conditions.UV-visible diffuse reflectance spectroscopy（UV-vis DRS）showed that TiO₂-SnO₂ composite photocatalyst had stronger UV absorption ability than pure SnO₂.SPS and OTCS results showed that the separation rate of photogenerated charge pair of TiO₂-SnO₂ photocatalyst was significantly improved.Under the irradiation of mercury lamp,the photocatalytic performance of differ ent proportions of TiO₂-SnO₂ composite microspheres was studied.The results showed that0.5:1-TS photocatalyst had better photocatalytic activity,and the degradation rate of rhodamine B increased from 47.20%to 94.54%.And when the amount of photocatalys t was 30 mg,the concentration of rhodamine B was 10 mg/L,and the p H value was under acidic conditions,0.5-TS photocatalyst showed the best photocatalytic activity,and the degradation rate could reach 98%.