Preparation Of SnO₂/TiO₂/PVDF Composite Membranes And Studing Of Photocatalytic Degradation Of RhB Dye

In recent years,with the continuous development of printing and dyeing chemical industry,the pollution of water environment has become more and more serious.Rhodamine B（RhB）,as one of the triphenylmethane dyes,has caused great harm to the environment because of its low biodegradability,stable physical and chemical properties,high toxicity and easy bioaccumulation,which seriously threatened the living environment and health safety of human beings.The combination of photocatalytic degradation technology and membrane separation technology,can both photocatalytic degradation and membrane separation,meanwhile the presence of photocatalyst improves the hydrophilicity of the membrane.It solves the problems such as the difficulty recovery of photocatalyst and easy pollution of organic membrane in every single process.It has been widely concerned by researchers and has broad research prospects.In this paper,SnO₂/TiO₂composite nano-photocatalysts were prepared by sol-gel method,and the composite nano-photocatalyst with the best photocatalytic performance was selected first.Then,the SnO₂/TiO₂composite nanoparticles were used to hydrophilic modify PVDF membrane by the method of blending modification,and the preparation of nano SnO₂/TiO₂/PVDF composite membrane which can play a role the dual functions of photocatalytic degradation and membrane separation.The effect of the addition of SnO₂/TiO₂composite nanoparticles on the structure and properties of composite membranes and the photocatalytic degradation of RhB dye were examined,and the composite membrane were studied in the process of photocatalytic degradation kinetics equation and mechanism.At the same time,the main active species in the photocatalytic degradation process of RhB by composite membranes were researched through free radical trapping experiment,then the degradation products of RhB were speculated.In addition,the experimental parameters of photocatalytic degradation of RhB by composite membranes were optimized.The results were as follows:（1）The photocatalytic performance of SnO₂/TiO₂composite nanoparticles increases at first and then decreases with the increase of sintering temperature and time.Therefore,the optimal conditions for the preparation of SnO₂/TiO₂composite nanoparticles by sol-gel method were as follows:the sintering temperature was 450°C,and the sintering time was 2 h.At this time,the prepared SnO₂/TiO₂composite nanoparticles contain both SnO₂tetragonal rutile crystal structure and TiO₂tetragonal anatase structure under the optimal conditions.The apparent morphology was nano cluster shape,and the surface of the nanoparticles contains hydrophilic hydroxyl functional groups,which mainly absorb ultraviolet light below 390 nm.The average pore size of SnO₂/TiO₂composite nanoparticles were about 24.22 nm through BET analysis.It was a kind of porous materials with a large specific surface area(43.98 m²·g^-1).When it was put under the ultraviolet irradiation for 4.5 h,the photocatalytic degradation efficiency of RhB reached 96.85%.The PVDF organic membrane was modified with SnO₂/TiO₂composite nanoparticles by blending method.Among them,the SnO₂/TiO₂/PVDF-7 composite membrane had the best comprehensive properties when the doping amount of SnO₂/TiO₂composite nanoparticles was7wt%:The pure water flux of the composite membrane was 119.92 L·m^-2·h^-1,which was242.63%higher than that of pure PVDF membrane;The water contact angle of the composite membrane was 62.61°,which was 35.80%lower than that of pure PVDF membrane;Compared with pure PVDF membrane,the mechanical strength of the composite membrane was improved by 23.70%,the inhibition rate of Escherichia coli was increased by 68.75%.Obviously,doping a certain amount of nanophotocatalyst in PVDF membrane can effectively improve the permeability,bacteriostatic performance,hydrophilicity,mechanical properties and thermal stability of the composite membrane.（2）The addition of SnO₂/TiO₂composite nanoparticles has improved the photocatalytic degradation rate of RhB in water by SnO₂/TiO₂/PVDF composite membranes.In particularly,the photocatalytic degradation efficiency of RhB as high as 91.84%when SnO₂/TiO₂/PVDF-7composite membrane was put under the condition of ultraviolet irradiation for 4.5 h.After five times recycles,the photocatalytic degradation rate of RhB by the SnO₂/TiO₂/PVDF-7 composite membrane can reach 83.51%,which still maintains a good repeatable usability and photocatalytic degradation stability.The experimental results showed that the photocatalytic degradation of RhB by SnO₂/TiO₂/PVDF composite membranes were in accordance with the quasi-first-order reaction kinetics law under ultraviolet irradiation.The free radical capture experiment showed that the main active species in the photocatalytic degradation of RhB by SnO₂/TiO₂/PVDF composite membranes were hydroxyl radical（·OH）and holes（h⁺）.Therefore,it was speculated that the intermediate products of RhB degradation were benzoic acid,terephthalic acid,etc.The optimum conditions for photocatalytic degradation of RhB in water by SnO₂/TiO₂/PVDF composite membranes were as follows:initial p H value was 6,initial concentration of RhB was 10 mg·L^-1,and H₂O₂concentration was 1 mmol·L^-1.