Preparation, Characterizations And Application Of Organic-inorganic Hybrid Anion-exchange Membranes

Compared with organic or inorganic membranes,organic-inorganic hybrid membranes have favorable strength and flexibility,membrane formation ability, thermal and chemical stabilities,and also new synergetic properties.Hence,hybrid membranes can be potentially widely used.Ion-exchange hybrid membranes can introduce the merits of inorganic material into the organic polymers,thus is widely applied to various fileds.As the anion-exchange hybrid membranes have irreplaceable effects in some important applications,further development is quite necessary and meaningful.Anion-exchange hybrid membranes are widely needed on some important occasions such as retention of multi-valent ions,recovery of valuable metals, pressure-driven liquid separation,protein separation and gas separation,etc, eapecially on alkaline membrane fuel cells(AMFCs).In the filed of AMFCs,the performances of anion-exchange hybrid membranes are comparable with those of fluorinated polymer membranes.The hybrid membranes show excellent mechanical properties,chemical and thermal stabilities,as well as favorable electrical properties. The hybrid membranes can be prepared by various methods,including in-situ polymerization,adulteration,polymer modification and grafting.One of the most important methods is the copolymerization.This method can overcome organic-inorganic phase separation or reduce the degree of phase separation,obtain membranes with both favorable strength and flexibility,adjust the ratios between organic and inorganic phases more easily,introduce ion-exchange groups more conveniently,and make the ion-exchange groups more stable.Hence, copolymerization route is the main adopted method in this dissertation.This dissertation includes seven chapters.Chapterâ… gives an overview on the research background through the introduction of organic-inorganic hybrid materials and membranes.Subsequently,chapterâ… generalizes the development,application and preparation of ion-exchange hybrid membranes.Then the chapter focuses on the application and development,especially preparation of anion-exchange hybrid membranes.Finally,the research ideas and outline of the dissertation are proposed.As the method of copolymerization has excellent merits,In chapterâ…¡,the copolymer of glycidylmethacrylate andγ-methacryloxypropyl trimethoxy silane (poly(GMA-co-KH-570)) is prepared firstly.The copolymer is dip-coated on ceramic plate,and then undergos the ring-opening and sol-gel reaction,respectively. Finally,ceramic supported anion-exchange hybrid membranes are obtained. Effects of the copolymer composition are fully discussed on membrane hydrophilicity,water flux,electrical properties,thermal stability and membrane morphology.Results show that the membranes are suitable for potential application in pressure driven process,such as UF and NF.In order to develop hybrid membranes that can be used in electro-driven process, chapterâ…¢selects flexible polyethylene oxide(PEO) as the starting material.PEO is endcapped and quaternized to obtain precursor PEO-[Si(OCH₃)₃](+).The precursor undergoes the sol-gel reaction together with charged and non-charged alkoxysilanes of small molecular weight.Finally,free-standing anion-exchange hybrid membranes are obtained.The membranes are compact and homogenous.They have relatively high thermal stability,proper conductivity and excellent mechanical properties,thus can be potentially applied to AMFCs.Chapterâ…£adopts the method of copolymerization.The copolymer of vinylbenzyl chloride and KH-570(poly(VBC-co-KH-570)) undergoes the quaternization,and sol-gel reaction with alkoxysilanes of small molecular weight.The obtained anion-exchange hybrid membranes are compact and dense,with relatively high ion-exchange capacities(IECs) but low conductivity.The membranes have excellent chemical and thermal stabilities.They are intended for application in AMFCs.Chapterâ…¤utilize the polymer of poly(2,6-dimethyl-l,4-phenylene oxide)(PPO). PPO is modified by bromination,hydroxylation and quaternization in sequence, subsequent sol-gel reaction with alkoxysilanes,followed by heat treatment,yields two series of anion-exchange hybrid membranes.(1) Through varying the conditions of heat treatment,the hydrophilicity,flexibility,electrical properties and thermal stabilities of the hybrid membranes can be adiusted effectively.Membranes endured proper heat treatment(130℃4-6 h) can have relatively high alkaline resistance, thermal stability and acceptable conductivity.Generally speaking,the hybrid membranes can be potentially applied to AMFCs;(2) An optimized condition of heat treatment is selected(130℃5 h).The dosages of alkoxysilanes are varied,and the impacts of inorganic content on the membrane properties are investigated.Results show that proper silica content can improve the membrane performances.Compared with the membranes of part(1),the membranes here have significantly improved swelling resistance and electrical properties.Hence,they are more suitable for application in AMFCs.The above membrane formation processes all involve sol-gel reactions.To investigate the relations between sol-gel reaction and membrane properties,chapterâ…¥selects poly(GMA-co-KH-570).The copolymer is used to investigate the relations among materials,membrane formation process and membrane properties. Poly(GMA-co-KH-570) undergoes the sol-gel reaction together with charged and non-charged alkoxysilanes of small molecular weight.After the sol-gel process, anion-exchange hybrid membranes are obtained.Primary studies indicate that,the copolymer of high molecular weight is disadvantage to the sol-gel reaction,and the obtained membranes are always inhomogenous.The membranes prepared from the copolymer of low molecular weight have relatively high crosslinking degree,and are highly homogenous and flexible.The crosslinking degree affects their thermal stability significantly,while the dosage of charged alkoxysilane controls their electrical properties.