The Preparations And Applications Of Novel Ion Exchange Hollow Fiber Membranes

Ion exchange hollow fiber membranes exhibit unique advantages during the preparation and application processes, such as self-supporting, large effective mass transfer area and high flux, modules with low weight and cost, etc. Therefore, they are widely used in the areas of industry, environment engineering, food and biomedical.Since the hollow fiber membranes need to be self-supported with no reinforcing materials, improvement of the mechanical strength is very important. For example, anion exchange membranes, especially those prepared by quaternization, generally show poor mechanical stability when the ion exchange capacity values are high. Furthermore, due to the inherent limit of the polymer materials for base membrane in chemical stability, harsh operation conditions should be avoided and thus application under severe conditions such as high temperature, strongly oxidizing conditions or organic solvents cannot be achieved. For enhancement of the membranes chemical and mechanical properties, two modification methods are mainly applied. They are organic-inorganic hybridization and guanidylation. And the author has investigated the applications of the obtained hollow fiber ion exchange membranes in protein adsorption, controlled drug release, noble metal ion adsorption and separation, catalytic oxidation, etc.A series of hybrid anion exchange hollow fiber membranes based on brominated poly (2,6-dimethyl-1,4-phenylene oxide)(BPPO) have been prepared through sol-gel process of different organic silanes and quaternization. Membrane properties are characterized to show that the hybrid membranes generally exhibit improved thermal stability, mechanical stability and dimensional stability as compared with the membranes without hybridization. And hybrid membranes can demonstrate excellent performance during the adsorption-washing-elution procedures in the permeation mode and the elution percentage can reach～95%.Hybrid anion exchange hollow fiber membrane modified by γ-MPS is proposed for the first time as potential drug carriers. The performances of the membranes in controlled release of the anionic drugs are improved after hybridization process. Loading and release experiments illustrate that the membranes can bind salicylates at a high loading efficiency (2.5mmol NaSA/g,1.4mmol NaMAS/g dry membrane), and the retention of the drug on the membrane matrix is significantly prolonged (drug released in7days under physiological condition:NaSA56.8%, NaMAS37.7%). Meanwhile, the membrane is biocompatible and can support the adherence, growth, and survival of human cells.1H-pyrazole-1-carboxamidine hydrochloride (HPCA) is employed for the guanidylation of the BPPO base membrane to prepare a novel type of guanidylated hollow fiber membrane. The guanidylation is conducted in aqueous solution under room temperature. The obtained guanidylated PPO hollow fiber membranes (GPPO HFMs) show high affinity to tetrachloroauric anions (AuCl4-) in acid solutions and can separate gold ions from multicomponent solution containing Mg(Ⅱ), Fe(Ⅲ), Co(Ⅱ), Ni(Ⅱ), Cu(Ⅱ), Zn(Ⅱ) and Pb(Ⅱ). Driving forces for the high adsorption of gold include ion exchange mechanism and complexation mechanism. And the formation of gold complexes is revealed to be the main interaction pattern.The GPPO membrane with saturated adsorption of gold ions can be in situ reduced by different reducing agents, such as NaBH4, ascorbic acid, D-glucose and citric acid to produce gold nano-particles attatched hollow fiber membranes (GPPO-Au). The GPPO-Au membrane modified by NaBH4shows the most uniform distributed gold nanoparticles in the membrane. And the size of the gold nanoparticles is also the smallest among the membranes obtained from different reducing ways. The GPPO-Au membrane modified by NaBH4is used as the catalysis of the reaction of benzyl alcohol catalyzed oxidation. Benzoic acid production increased16times with the catalysis of the membrane. And after6times’ usage, the catalytic efficiency of the membrane remained at around80%.In conclusions, hybridization and guanidylation are two alternative methods for the modification of BPPO base hollow fiber membrane to avoid the high swelling degree and low mechanical strength brought by quaternization. The author has not only researched the applications of the ion exchange hollow fiber membranes in biomedical, noble metal separation and catalytic oxidation, but also investigated the interactions between the membrane and the proteins, ionic drugs and metal ions. The results and priciples are meaningful for the future study and potential applications.