Synthesis And Application Of SnO₂@TiO₂/Graphene Composite Areogels

In this paper,we first prepared graphene oxide from graphite by modified Hummers method.The SiO₂ microspheres（280 nm）were synthesized by St?ber method,which was used as hard template in the subsequent studies,and Na₂SnO₃·3H₂O was used as tin source.The SiO₂@SnO₂ composite was synthesized by a one-step solvothermal method in the solvent of water and ethanol mixture.Subsequently,SiO2 template was etched by NaOH solution to obtain hollow SnO2spheres（HSSs）.Then,TiO₂ shell was anchored on the surface of HSSs by a sol-gel reaction using tetrabutyl titanate as titanium source,and calcined at a high temperature to obtain hollow SnO2@TiO2 spheres（HSTSs）.Finally,after one step hydrothermal treatment,hollow SnO₂@TiO₂ spheres and graphene oxide nanosheets self-assembled to form a three-dimensional（3D）SnO2@TiO2/graphene composite hydrogel,followed by freeze-drying to obtain hollow SnO2@TiO2/graphene composite hydrogel aerogels（HSTGAs）.The hollow SnO2@TiO2 spheres have an average size of 360 nm and a cavity size of about 280 nm.SnO₂ is rutile phase with a shell thickness of 10¹5 nm,and TiO₂ is anatase phase with a shell thickness of20³5 nm.The synthesized HSTGAs possess the characteristic of 3D network microstructure,large specific surface area(156.8 m² g^-1)and porous structure.The composite hold both the advantages of graphene and metal oxide hollow structure.In order to further explore the application of HSTGAs in environmental field,photocatalytic capability towards methylene blue（MB）was tested.The rate of MB remove could reach about 96%after 180 min irradiation,which was much higher than HSTSs and HSSs.The results show that HSTGAs have strong adsorption capacity and high degradation efficiency.Among them,the 3D structure of HSTGAs can provide a larger specific surface area that provides more active sites for dyes degradation.The synergistic effect between graphene,SnO2 and TiO2 significantly enhanced the photocatalytic efficiency of the composite.In order to investigate the electrochemical performance of HSTGAs,the application of HSTGAs as anode for lithium ion storage was explored.The electrochemical results showed that HSTGAs exhibited superior electrochemical performance compared to HSTSs and HSSs.The HSTGAs electrode showed an extremely high initial discharge capacity(1560.3 mAh g^-1)at a current density of 100mA g^-1.After 200 cycles,the retention of discharge capacity of HSTGAs is about668.2 mAh g^-11 and a Coulombic efficiency of approximately 100%,much higher than HSTSs(138 mAh g^-1)and HSSs(109.1 mAh g^-1).HSTGAs have excellent lithium storage performance,cycling performance and rate performance,due to the synergistic effect of metal oxide hollow spheres and graphene oxide nanosheets.