Jifu Zheng

Synthesis and characterization of a novel poly(arylene ether sulfone) containing pendent imidazole groups for high temperature proton exchange membranes

A series of poly(arylene ether sulfone) containing pendent imidazole groups (PSf-Im-x) have been successfully synthesized based on a novel monomer 2,2′-bis-(2-methyl-imidazol-1-yl-methyl)-biphenyl-4,4′-diol (MIPO). The pendent imidazole groups along the polymer chain were expected to provide functional sites for the acid–base interaction with the doping phosphoric acid (PA) when they are used as polymer electrolyte membranes for high temperature fuel cell applications. The PA content of the linear PSf-Im-x membranes is about 172.3–235.8% in 85 wt% H3PO4 at room temperature. The volume swelling of these membranes is 114.4–194.0%, lower than that of polybenzimidazole (PBI) with similar PA content. The proton conductivities of the membranes are 0.021–0.053 S cm−1 at 140 °C under absolutely dehydrated state. The low volume swelling and good proton conductivity may be attributed to the “side-chain-type” structures of pendent imidazole groups, which facilitate ion transport. To obtain higher acid doping while maintaining mechanical properties, cross-linked membranes were prepared by the reaction of the imidazole group of the polymer and p-xylene dichloride. The PA content of the membranes with 20% cross-linking is 313.2% in 85 wt% H3PO4 at 80 °C. The stress at breaking and the proton conductivity of the membrane is 3.2 MPa at room temperature and 0.063 S cm−1 at 140 °C in an absolutely dehydrated state.

Ultrathin films of organic networks as nanofiltration membranes via solution-based molecular layer deposition.

Ultrathin films of organic networks on various substrates were fabricated through the solution-based molecular layer deposition (MLD) technique. The rigid tetrahedral geometries of polyfunctional amine and acyl chloride involved in the reaction ensure the continuity of the polymerization process. A linear increase in film thickness with respect to cycle number was observed by UV-vis adsorption, ellipsometry, and quartz crystal microbalance. The growth rate per MLD cycle is 1.6 nm, which can be controlled at the single molecular level. For the first time, we develop the MLD method on the top of hydrolyzed PAN substrate, resulting in nanofiltration (NF) membranes. The stepwise growth was monitored via attenuated total reflectance infrared studies. The separation performance of the obtained membrane for various solutes was sensitive to the terminated layers and number of cycles. The rejection of NH(2)-terminated membranes follows the order of CaCl(2) > Na(2)SO(4) > NaCl, while the order for COOH-capped surface is Na(2)SO(4) > CaCl(2) > NaCl. The absolute value of zeta potential for the MLD membranes decreases with the addition of deposition layers. The moderate water flux for the resulting membrane is due to the reduced porosity of the support as well as the low roughness and hydrophilicity of the membrane surface. This bottom-up process provides a promising approach for construction of long-term steady NF membranes with nanoscale dimensions.

Integrated antimicrobial and antifouling ultrafiltration membrane by surface grafting PEO and N-chloramine functional groups

Ultrafiltration membranes with integrated antimicrobial and antifouling properties were fabricated using an engineering thermoplastic (carboxylated cardopoly(aryl ether ketone, PEK-COOH). Different molecular weights of PEO (Mw: 120, 350, 550) were grafted to the PEK-COOH membrane surface via EDC/NHS methodology. N-chloramine modified membranes then were prepared by simple exposure to dilute sodium hypochlorite solution. The surface grafting processes were all performed in water (i.e. without organic solvent). With this surface modification, the hydrophilicity of membranes improved significantly and the pure water flux increased compared to the unmodified PEK-COOH membrane. Furthermore, the PEO and N-chloramine modified membranes were resistant not only to both protein adsorption and bacterial adhesion, but also to microbial proliferation. The results of this work suggest that PEO and N-chloramine modified membranes are promising as fouling-resistant membranes.

Nanofiber mats electrospun from composite proton exchange membranes prepared from poly(aryl ether sulfone)s with pendant sulfonated aliphatic side chains

A series of cardo poly(aryl ether sulfone) copolymers bearing pendant sulfonated aliphatic side chains were synthesized and electrospun into nanofibers. The sulfonated poly(aryl ether sulfone) nanofibrous mats were filled with appropriate amounts of Nafion solution. The composite membranes showed significantly reduced swelling and excellent mechanical properties as well as appropriate proton conductivity. These membranes in particular exhibited much lower methanol permeability, in the range of 10−7 cm2 s−1, and higher selectivity, at about 105 S s cm−3, than did Nafion 117 in our experiments. The results show that the fabricated nanofiber-based composite membranes can be used as a promising proton exchange membrane for direct methanol fuel cell applications.

Preparation and characterization of an antibacterial ultrafiltration membrane with N-chloramine functional groups

In this study, a cardo poly(aryl ether ketone) ultrafiltration membrane containing an N-chloramine functional group (PEK-N-Cl membrane) was easily obtained via exposure of a cardo poly(aryl ether ketone) ultrafiltration membrane (PEK-NH membrane) to dilute sodium hypochlorite solution. The chlorination process did not harm membrane performance. In addition, the PEK-N-Cl membrane was stable in both air and water. The PEK-N-Cl membrane exhibited excellent antimicrobial properties against both Gram-negative and Gram-positive bacteria (i.e. E. coli and Bacillus subtilis, respectively). The PEK-N-Cl membrane provided 94.2% and 100% reduction of E. coli and Bacillus subtilis, respectively, within 30min of contact times. Moreover, nearly 100% of the E. coli was killed after 2h during the filtration process for the PEK-N-Cl membrane. In addition, the water flux decreased by 42% for the PEK-N-Cl membrane compared to 77.6% for the PEK-NH membrane after filtration of the E. coli solution and incubation on LB nutrient agar plate, indicating that the PEK-N-Cl membrane enhibits antifouling. Furthermore, the PEK-N-Cl membrane is recyclable via subsequent exposure to a sodium hypochlorite solution.