Influence of zeolite crystal size on zeolite-polyamide thin film nanocomposite membranes

Zeolite-polyamide thin film nanocomposite membranes were coated onto polysulfone ultrafiltration membranes by interfacial polymerization of amine and acid chloride monomers in the presence of Linde type A zeolite nanocrystals. A matrix of three different interfacial polymerization chemistries and three different-sized zeolite crystals produced nanocomposite thin films with widely varying structure, morphology, charge, hydrophilicity, and separation performance (evaluated as reverse osmosis membranes). Pure polyamide film properties were tuned by changing polymerization chemistry, but addition of zeolite nanoparticles produced even greater changes in separation performance, surface chemistry, and film morphology. For fixed polymer chemistry, addition of zeolite nanoparticles formed more permeable, negatively charged, and thicker polyamide films. Smaller zeolites produced greater permeability enhancements, but larger zeolites produced more favorable surface properties; hence, nanoparticle size may be considered an additional "degree of freedom" in designing thin film nanocomposite reverse osmosis membranes. The data presented offer additional support for the hypothesis that zeolite crystals alter polyamide thin film structure when they are present during the interfacial polymerization reaction.