Study On The Organic - Inorganic Smart Nanocomposites Of PNIPAAm / Nano - TiO 2

Nano-TiO₂ is widely used as a kind of photocatalyst, but it is difficult to recycle due to its powder form, so that nano-TiO₂ immobilization technology gained more and more attention .At present, nano-TiO₂ is usually immobilized by high temperature methods on heat-resistant substrate. The immobilizations on organic substrate generally use doping method, bonding method, coupling method and etc. But most organic materials cannot be used a long time due to the photocatalysis of nano-TiO₂. Furthermore, organic film and adhesives will debase the photocatalysis of nano-TiO₂.Poly（N-isopropyl acrylamide） （PNIPAAm） hydrogel is a kind of intelligent polymer materials. When the environment temperature is higher than its lowest critical solution temperature （LCST）, the hydrogel will shrink quickly and lose water. While the temperature is lower than the LCST, the hydrogel will reswell and turn to porous and transparent. The micropore will provide channel for water molecules.In this paper, PNIPAAm/nano-TiO₂ organic-inorganic nano-compersite was synthesized to improve the recyclability of nano-TiO₂ with the temperature sensitivity of the PNIPAAm hydrogel. Furthermore, the porous structure and swelling properties of the PNIPAAm hydeogel would be able to minish the baffle to the photocatalisis of nano-TiO₂ to exhibit the superiority of organic-inorganic material.Because the LCST of normal PNIPAAm/nano-TiO₂ hydrogel was so low that it baffled its application, large-sized P（NIPAAm-co-AAc）/nano-TiO₂ hydrogel was prepeared was prepared to expand the temperature scope of the hydrogel. In order to minish the baffle of PNIPAAm and P（NIPAAm-co-AAc） to the photocatalisis of nano-TiO₂, pore-forming agent was used to introduce porous structure to prepare large-sized porous PNIPAAm/nano-TiO₂ hydrogel and large-sized porous P（NIPAAm-co-AAc）/nano-TiO₂ hydrogel. The micropore structure, chemical constitution, nano-TiO₂ load effect, temperature sensitivity, swelling property, deswelling property, photocatalysis, recyclability and photochemistry stability of the four large-sized PNIPAAm/nano-TiO₂ hydrogels were studied. Futhermore, the preparation process and basic properties of PNIPAAm/nano-TiO₂ microgel was preliminarily studied.The result showed that, the large sized PNIPAAm/nano-TiO₂ hydrogel could be prepared by aqueous solution radical polymerization successfully, and the nano-TiO₂ ratio could be ranged from 0% to 50% freely, and nano-TiO₂ physically loaded in the pore structure. The performance of hydrogel would be affected by the copolymerization of acrylic acid, nano-TiO₂ loading ratio, crosslinker dosage, dosage and molecular weight of PEG.The copolymerization of acrylic acid could enhance the LCST from 33℃to 38℃, and the swelling property and deswelling property could be improved too, but the photocatalysis of the P（NIPAAm-co-AAc）/nano-TiO₂ would be reduced.PEG played the role of introducing porous structure, so that the two kind of porous hydrogels had more pores than normal PNIPAAm/nano-TiO₂ hydrogel and P（NIPAAm-co-AAc）/nano-TiO₂, and the micropore structure, swelling proerty, deswelling property and photocatalysis could be improved, and the reduction of photocatalisis of P（NIPAAm-co-AAc）/nano-TiO₂ could be offseted.The photocatalitic experiment improved that there were many factors affected the photocatalisis of the hydrogel. However, when the nano-TiO₂ ratio reached 35% or 50%, all of hydrogels had good photocatalisis. Futhermore, after three repeated photocatalitic experiments, the photocatalisis of the four kinds of hydrogel wouldn’t be reduced. And PNIPAAm and P（NIPAAm-co-AAc） polymer chain wouldn’t be degraded substantially, and the chemical constitution hadn’t changed significantly after radiated 72h by UV.PNIPAAm/nano-TiO₂ microgel could be prepared by inverse suspension polymerization, and the microgel had large size and ruled shape. There were porous structure on the microgel surface, and nano-TiO₂ loaded in the microgel physically. Furthermore, the microgel had better phtocatalisis and recycliability than the large-sized hydrogel at the same nano-TiO₂ ratio. However, the preparation process would be influenced by many factors, so the preparation process was difficult to control.The stability of the reaction system was poor,so the nano-TiO₂ loading ratio and monomer conversion of the microgel was low, and this baffled the improve of the photocatalisis of the microgels.