Preparation And Application Of The Functional Polymer Nanofiber Membrane

Water pollution is attracting more and more attention; especially theheavy metal ions pollution, which is harmful to human being. Many methodshave been developed by researchers, among which adsorption is a simple andeffective method compared to others. Several kinds of macro or nanoparticals have been widely used in the heavy metal ions removal, and havepresented good performance. However, the application of this kind ofmaterials was limited for its requirement of later separation from the solutionafter adsorption. Therefore we propsed a method that the adsorption materialsmakes into membrane style to solve this problem. Polymer nanofibermembrane obtained by electrospinning was used as the base material for itshigh porosity and great surface area to make functionanl polymer nanofibermembrane. The functional polymer nanofiber membrane was used for theremoval of heavy metal ion from aqueous solution. And we also used thefunctional polymer nanofiber membrane as sensor for acid and base gases.1. Since polypyrrole materials have the ability of adsorpting Cr（VI） ions from solution, PAN/PPy core/shell nanofiber membrane was prepared using asimple chemical oxidation method followe by electrospinning. This core/shellnanofiber membrane can adsorb Cr（VI） from aqueous solution. It can removeup to70%Cr（VI） from200mg L^-1aqueous solution at the condition of pH2.0. PAN/PPy core/shell nanofiber membrane presented well reuseperformance, the adsorption capacity can still retain80%of its originalamount after5times of regeneration. The adsorption process consist of twosteps, one is the ion exchange between Cr（VI） and Cl-, and the other is theredox proess. Cr（VI） was adsorbed onto the surface of nanofibers and thenabout82.7%of Cr（VI） was reduced to Cr（III）.2. Polyaniline （PANI） can also be used in the adsorption removal of Cr（VI）from solutions. Therefore, PAN/PANI core/shell nanofiber membrane wasprepared using a simple chemical oxidation method followe byelectrospinning. Its Cr（VI） removal performance and the adsorptionmechanism was carefully discussed. The morphology of the core/shellnanofibers was affected by the reaction temperature; coarser morphology canbe obtained at lower temperature. This membrane has higher adsorptioncapacity for Cr（VI） compared to PAN/PPy nanofiber membrane. Theadsorption capacity kept almost unchanged when the ion strength increased.The adsorption rate was fast, and the adsorption equilibrium can be reachedwithin30min when the Cr（VI） ions ranged from100to200mg L^-1. Thedynamic adsorption process can be better described using the pseudo-second-order model. Isotherom data fitted well to the Langmuirisotherm model. The nanofiber membrane has a strong ability of reduction forCr（VI）, almost86.2%of Cr（VI） can be reduced to Cr（III） after adsorption.And also the core/shell nanofiber membrane has great resue ability after5times of usage.3. Poly （acrylic acid） was grafted onto the surface of PAN nanofibers viaatom transfer radical polymerization （ATRP） method. Firstly, polydopaminewas coated onto the surface of PAN nanofibers, then the ATRP initiators wereanchored by the reaction between2-BIB and polydopamine, and finally thepoly （acrylic acid） can be grafted via ATRP onto the surface of the nanofibers.The surface modified PAN nanofiber membrane was used for the removal ofCu2+ions from aqueous solution. The adsorption performance was mainlyaffected by the solution pH, initial concentration and contact time. Theadsorption rate was fast, and the adsorption equilibrium can be reachedwithin15min when the concentration of Cu2+ions ranged from108to268mg L^-1. The modified PAN nanofiber membrane has a great regenerationperformance at acid condition after5times of usage.4. Poly （glycidyl methacrylate） was grafted onto the surface of PANnanofibers via atom transfer radical polymerization （ATRP） method. Firstly,polydopamine was coated onto the surface of PAN nanofibers, and then theATRP initiators were anchored by the reaction between2-BIB andpolydopamine, finally the poly （glycidyl methacrylate） can be grafted via ATRP onto the surface of the nanofibers. Vicinal polyalcohol groups wereintroduced onto the nanfiber surface via the reaction betweenN-methyl-D-glucamine and epoxy groups. The modified nanofiber membranewas used for the removal of boric acid form aqueous solution. The boronconcentration can decrease to0.59mg L^-1and0.29mg L^-1after72hadsorption when the initial concentration wasd1.1mg L^-1 and0.5mg L^-1,respectively. The boron concentration can be reduced below the WHOstandard (0.5mg L^-1) within4h by changing the nanofiber membrane everytwo hours. Meanwhile, the modified membrane has good reuse ability.