Preparation Of Tin-based Pseudocapacitive Materials And Application In Capacitive Deionization

Due to the rapid growth of population and the aggravation of global groundwater pollution,the development of desalination technology to obtain fresh water is particularly critical.Capacitive deionization（CDI）is a noval desalination technology,which has the advantages of no secondary pollution,environmental friendliness and low operating voltage（<1.6 V）,and has been widely concerned in recent decades.Currently,the electrode materials of CDI are mainly carbon materials.However,due to the limited specific surface area of the carbon material for ion storage based on the double electric layer,the salt adsorption capacity of carbon material is limited.In addition,due to the anodic oxidation of the carbon material electrode,the cycling stability of carbon electrode is poor.Beyond that,the carbon material electrode cannot be applied in the high-concentration brine test.Based on these,hybrid capacitive deionization（HCDI）emerges as the times require.HCDI combines the traditional CDI system with the battery system to store ions based on the redox reaction of pseudocapacitor materials,which has high salt adsorption capacity and good cycling stability.Aimed at building negative materials of HCDI,this dissertation revolves around tin oxygen and tin sulfide with a high capacity,combining with the advantages of excellent electrical conductivity of carbon material,SnO₂/CNT composite and SnS₂/RGO composite were prepared respectively,and applied in the HCDI system,an excellent desalination performance are obtained.The specific work is shown below.（1）Tin dioxide,with its high theoretical capacity and low operating voltage（<0.6 V）,but its large volume expansion（>400%）and poor conductivity preclude its direct use in HCDI.Carbon materials have good conductivity and are commonly used as conductive substrates.The composite of tin dioxide and carbon nanotubes can effectively solve the defects of tin dioxide.In this dissertation,tin dioxide and carbon nanotubes composites were prepared by one step hydrothermal method with tin dichloride as the tin source.Sn-C bonds were formed between tin dioxide and carbon nanotube,which is conducive to the transport and storage of sodium ions,and the composite has excellent electrical conductivity.It was assembled with activated carbon elecerode into an asymmetric module and used in HCDI,which shows a salt adsorption capacity of 9 mg g^-1 and excellent cycling stability of keeping 120%salt adsorption capacity after 100 cycles,and the system also shows different adsorption performance for different cations.（2）Compared with tin dioxide,tin disulfide has higher theoretical capacity and larger layer spacing,so it has a broader prospect for sodium ion storage.However,tin disulfide also faces the problem of huge volume expansion during the process of sodium ion insertion and release,and it has poor conductivity,resulting in a low reversible capacity.Graphene is a common two-dimensional sheet material with good electrical conductivity and stable chemical properties.The in-situ growth of tin disulfide particles on the graphene sheet layer can greatly alleviate the volume expansion of tin disulfide during the process of sodium ion insertion and release,and improve the electrical conductivity of the composite material.In this dissertation,the composite of tin disulfide and graphene was prepared by one-step hydrothermal method,which was used as a negative electrode material in hybrid capacitive deionization,and demonstrates a high salt adsorption capacity of 14.1 mg g^-1 and the salt adsorption capacity can keep 130%after 100 cycles.The system was applied to the study removal performance of other main cations in seawater,which also shows excellent desalination performance.