Preparation Of La/TiO₂-CdS Composite Fiber Membrane And Degradation Of Toluene Gas By Visible Light Combined Plasma

The treatment of volatile organic compounds(VOCs)is the focus in the field of air pollution control.Toluene gas is one of the representative components of VOCs,which is a common carcinogenic pollutant and has great harm to human health and the environment.Photocatalytic oxidation technology can decompose a variety of VOCs into CO₂ and H₂O without pollution and the reaction conditions are mild.It is a green,economic and effective degradation technology and has broad application prospects.The commonly used TiO₂photocatalysts have the advantages of stable properties,safety,non-toxicity and low price,but there are also shortcomings such as easy recombination of photogenerated electron pairs,only using ultraviolet light and easy agglomeration of nanoparticles.In this paper,aiming at the above problems,rare earth La doping and CdS semiconductor photocatalyst composite method were used to reduce the recombination rate of photogenerated electrons of TiO₂ photocatalyst and broaden its spectral response range.At the same time,polyvinyl alcohol(PVA)fiber membrane carrier material was prepared by electrospinning technology.The catalyst particles were fixed on the surface of PVA fiber by impregnation precipitation method to prepare nano-scale shell-core La/TiO₂-CdS composite fiber membrane.Finally,in order to improve the degradation rate of toluene,the photocatalytic degradation combined with plasma technology was used for joint degradation,and the degradation process was explored.1.PVA fiber membrane was prepared by electrospinning using 2488 type PVA with high alcoholysis and polymerization degree as template agent.The effects of spinning voltage,spinning distance,spinning solution injection speed and PVA mass fraction on the morphology of the fiber were discussed by SEM characterization and fiber diameter analysis.When the spinning conditions were 13KV,16cm,0.9m L and 4.5%,the fiber surface was smooth,there was no adhesion between fibers,and the diameter was 120-140nm.Then epoxy chloropropane was used to cross-link the PVA fiber membrane to avoid the hydrolysis of PVA fiber membrane in the impregnating solution.2.TiO₂ photocatalyst was prepared by sol-gel method with tetrabutyl titanate,ethanol and acetic acid as raw materials,and then the shell-core TiO₂ fiber membrane photocatalyst was prepared by impregnation and precipitation with the modified PVA fiber membrane as the carrier.Through the characterization of SEM,XRD,FTIR and TGA,TiO₂ particles were successfully loaded on the surface of PVA fiber,and the loading amount was about 25.4%.At the same time,the crystal structure of TiO₂ was not changed.The fiber structure reduced the agglomeration and accumulation of particles,and improved the effective contact area of the catalyst.The results of simulated photocatalytic degradation of toluene showed that TiO₂ composite fiber membrane still had good degradation ability,and the degradation rate of toluene reached 82.5%after 2 hours.In the kinetic study,the influence of toluene concentration conformed to the pseudo-first-order kinetic equation,and the correlation coefficients R² reached 0.9.3.La-TiO₂/CdS dual-modified photocatalyst was prepared by sol-gel method and hydrothermal method with tetrabutyl titanate,lanthanum nitrate,thiourea and cadmium chloride as raw materials in two steps,and then La-TiO₂/CdS composite fiber membrane was prepared by impregnation and precipitation.DRS characterization showed that the optical absorption band edge of doped TiO₂ was red shifted,and the spectral response range was broadened to visible light range.SEM,XRD and XPS characterization showed that La/TiO₂-CdS particles were successfully loaded onto the surface of PVA fibers.The effects of La doping amount and CdS composite amount on toluene degradation by TiO₂ fiber membrane were investigated.The best catalyst for toluene degradation was LTC-3 composite fiber membrane,i.e.the amount of lanthanum nitrate was 1.5 g and the amount of Cd Cl₂ was 0.20 g.Photocatalytic degradation of toluene by La/TiO₂-CdS composite fiber membrane under visible light for 1h was 57.3%.4.The comparative experiments of different photocatalytic and plasma degradation of toluene show that the synergistic effect of photocatalytic combined with plasma improves the degradation rate of toluene.The best process of photocatalytic combined with plasma degradation of toluene in the experiment is:the power of plasma generator is 33W,the best catalyst dosage is6g,and the initial content of toluene is 3.464g/L.In the stability experiment of La/TiO₂-CdS composite fiber membrane,it was also shown that the degradation rate did not decrease significantly after five cycles.La/TiO₂-CdS composite fiber membrane had good stability and recycling performance.