Preparation Of Nafion/TiO₂Hybrid Membranes And It’s Photocatalytic Degradation Process Of PCBs

As one of the12Persistent Organic Pollutants (abbreviated as POPs) which were put in the first batch of being controlled by the "Stockholm Convention on Persistent Organic Pollutants", PCBs had been banned worldwide for many years. However, as their stability physical and chemical properties, and the difficulty of the chemical or biological degradation, PCBs are still remaining widely in current environment. Because PCBs are extremely lipophilic and hydrophobic, while concentration through food chains brings potential toxicity as well as carcinogenicity, therefore, they pose great threats to ecological environment and human health.Numerous studies had shown that using TiO2as a photocatalyst to degrade PCBs was a convenient, effective and energy-saving way to control the pollution, and it was one of the current research focuses in this field. Preparing Nafion/TiO2hybrid film by compounding Nation and TiO2can not only avoid the wastage of TiO2and improve its recycling rate but also increase the exposure of the Nation’s acidic center, thereby enhancing its catalytic ability.This paper focused on the immobilizing of TiO2, which used the perfluorinated sulfonic acid resin (Referred to as Nafion) as a carrier and modifier, preparation of Nafion/TiO2hybrid membranes as well as the photocatalytic degradation process of PCBs.Nafion/TiO2hybrid membranes with different TiO2contents were prepared via recasting and in-situ reaction, using TiO2anatase hydrosol or powder and Nafion solution as raw materials, to incorporate TiO2particles within the Nafion matrix to obtain better photocatalytic efficiency. The microstructure and photocatalytic properties of the hybrid membranes were characterized by XRD、SEM、FT-IR. TG-DTA、XPS、UV/vis. The photocatalytic degradation process of2,4,5-PCB and Aroclor1254solution were characterized by GC-MS. Furthermore, the preparation and application of Nafion/TiO2photocatalytic filter cloth with non-woven base were explored preliminarily as well. The main results are as follows:The reaction formula with water as primary solvent was designed (where mass ratio of Ti(OC4H9)4:H2O:C2H5OH:HNO3=8:100:4:0.8) to synthesize TiO2nanocrystal hydrosol with the average particles size of47.5nm through the sol-gel method. Due to the containing of anatase TiO2, the hydrosol got the excellent photocatalytic properties without the conventional annealing.The Nafion/TiO2hybrid membranes prepared via recasting got better strength, toughness and transparency compared with the membranes prepared via in-situ reaction, which were very fragile. The surface and microstructure of the Nafion/TiO2hybrid membranes prepared via recasting were flat and porous while the surface of the membranes prepared via in-situ reaction were uneven and lacunosis. With the preparing method of recasting with TiO2hydrosol, TiO2powder and in-situ reaction, the hydrophobic properities of the Nafion/TiO2hybrid membranes were increasing, constant and decreasing respectively.The addition of TiO2hydrosol or powder will not destroy the PTFE skeleton structure of Nafion membranes, and the polymorphs of TiO2maintained as well. But with the increasing content of TiO2, the toughness of Nafion/TiO2hybrid films decreased. TiO2hydrosol improved the thermostability of the Nafion/TiO2hybrid membranes while the TiO2powder didn’t.The hybrid membranes possessed excellent and persistent photocatalytic activities. In the same photocatalytic degradation reaction system, the contents of TiO2has little effect on the adsorption and degradation rates of methyl orange solution with Nafion/TiO2hybrid membranes. With the content of TiO2increasing, the rates rose at first and then decreased, reaching the best point at15%TiO2hydrosol and20%TiO2powder.The obtained Nafion/TiO2hybrid membranes possessed excellent photocatalytic abilities to PCBs. The photocatalytic degradation rates of the2,4,5-PCB solution (640p.g/L) and the Aroclor1254solution (1000μg/L) were97.3%and98%. The photocatalytic degradation reaction of the2,4,5-PCB solution with the concentration of6.4mg/L consists of isomerization and dechlorination reaction.Nafion/TiO2-coated non-woven fabric filter cloth, which was prepared by dip-coating method, exhibited excellent UV resistance after long-time exposure to intensive ultraviolet radiation. Theoretically, the cloth could filter, adsorb and degrade toxic and hazardous substances in water,which showed its great potential in sewage treatment, industrial wastewater reuse and soilless cultivation.