Synthesis and Characterization of Allyl Polysulfone Derivatives for Membrane Application and Polystyrene Sulfonate Derivatives for Draw Solute Application

Abstract

This study presents synthesis and characterization of novel polymeric materials and their application to water treatment. Firstly, A series of ultrafiltration (UF) membranes based on polysulfone and mussel-inspired poly(dopamine methacrylamide) (PDMA) were prepared by a versatile in situ process composed of grafting-through polymerization and consecutive non-solvent induced phase separation. Nisin, a low molecular weight antimicrobial peptide, was subsequently immobilized on the surface of the UF membrane through the reaction between its N-terminal NH2 group and the catechol group in PDMA for microbial mitigation. The resulting nisin containing UF membranes showed outstanding fouling resistance and flux recovery ability due to the hydrophilic characteristics of PDMA moiety in the membrane. Furthermore, it is worth noting that the resulting membranes exhibit the antimicrobial activity against the Staphylococcus aureus (ATCC 6538) due to the nisin moiety. Second, thin film composite (TFC) polyamide membrane with tailored support structure was prepared for forward osmosis (FO) application. The porous polysulfone-based substrate was fabricated using the grafting-through polymerization of allyl polysulfone and dimethylaminoethyl methacrylate (DMAEMA), followed by non-solvent induced phase separation. 1,3,5-tricarbonyl trichloride and m-phenylene diamine were employed as the monomers for the interfacial polymerization to form a thin polyamide selective layer. poly(dimethylaminoethyl methacrylate) (PDMAEMA) moieties in the substrate was then convert into zwitterionic sulfobetaine moieties to impart fouling resistance. When the TFC membrane prepared in this study was tested in the FO system, a remarkably large water permeation flux value (~63.2 LMH) was observed with a small ratio of reverse solute flux to water permeation flux (Js/Jv) of < 0.02 g/L in the active layer against draw solution (AL-DS) mode using 2 M NaCl solution as a draw solution and DI water as a feed solution. Especially, the zwitterionic substrate in the TFC membrane exhibited fouling resistance against synthetic wastewater feed stream. Third, a series of oligomeric poly(tetrabutylphosphonium styrenesulfonate)s (PSSP#, where # is the number of monomer units in the oligomer) were prepared from tetrabutylphosphonium styrenesulfonate (SSP) as a monomer for application as a draw solute in a FO system. Although the water permeation flux values in the FO system using the oligomeric PSSP as a draw solute were slightly smaller than those using the monomeric SSP, the reverse solute flux values using the PSSPs were found to be much smaller than those using the SSP, indicating that the oligomers are more efficient draw solute materials in the FO system than the low molecular weight monomer. For example, when 20 wt% of the PSSP5 aqueous solution is used as the draw solution, the water permeation flux and reverse solute flux values are 14.50 LMH and 0.14 gMH, respectively, and when 20 wt% of the SSP aqueous solution is used, they are 16.28 LMH and 0.53 gMH, respectively. Since PSSPs have a lower critical solution temperature (LCST), the PSSP in water could be simply separated by heating to above the LCST without any other separation process. Moreover, it was found that the PSSPs have excellent bactericidal property above 99.9 % against Escherichia coli (ATCC 8739).