Preparation of carbon nanotube polymeric membranes with cross-linkable and antimicrobial agents for water applications

The incorporation of carbon nanotubes (CNTs) along with cross-linkable and antimicrobial agents into polymeric membranes represents a cutting-edge approach to enhance water purification. Nevertheless, CNT-polymeric membranes should accomplish uniform dispersion along with stable integration of CNTs in the membrane matrix, as at the same time should ensure antimicrobial functionality and high-water flux. Current reports have studied the incorporation of CNTs into membranes, but concerns like poor dispersion, aggregation, and lack of effective cross-linking mechanisms continue to be hurdles in the optimization of membranes’ performance.

In this work, different vinylic monomers -either hydrophobic methyl methacrylate (MMA) or cross-linkable glycidyl methacrylate (GMA)- were polymerized on properly modified CNTs using Atom Transfer Radical Polymerization (ATRP). The resulting CNTs, either multiwalled or thin-multiwalled, were embedded into porous PET/PES (polyethylene terephthalate/polyethersulfone) membranes. The influence of the attached groups on their dispersion efficiency and embedment into the pores was studied. The polymer-functionalized CNTs were further modified by incorporating antimicrobial quaternized salts through non-covalent attachment. The cross-linking reaction between CNTs modified with epoxy groups was thoroughly tested using ethylene diamine (EDA) as a cross-linker for the reaction between epoxide groups of GMA attached to CNT surfaces and the amines of EDA. Various cross-linking methods and the parameters temperature, reaction time and phase of cross-linker were tested through thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM) to establish the optimal conditions. The results revealed successful embedding of CNTs with good distribution, as observed in the cross-section of the membranes, and effective cross-linking between GMA moieties and amines in the membrane pores. The incorporation and the cross-linking of CNTs into the PES membrane resulted in increased water flux, up to 572.4 L/m²h, of similar order of magnitude as those reported in relevant CNTs embedded membranes. The systematic optimization of the cross-linking conditions establishes a more robust method in terms of CNTs integration related to conventional embedding methods.