Funcionalização de membranas microporosas com nanomateriais de grafeno e reticulação polimérica para dessalinização de água

Abstract

Polyamide membrane and mixed cellulose ester were functionalized with graphene oxide and polyvinyl alcohol and cross-linked with citric acid. A practical nanofiltration system, using these membranes, was tested to retain ions of magnesium sulfate and sodium chloride in aqueous solutions. The membranes were evaluated through percent salt removal capacity and mechanical stability assays. To analyze the structural and morphological characteristics of graphene oxide and the membranes produced were used scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The nanofiltration system was stable at working pressures between 4-5 bar. The results showed that graphene oxide, obtained by the modified hummers method, was more effective in coating PA porous membranes than MCE. The mechanical stability was high due to the adhesion of the amine groups, present in the PA membranes, to the hydroxyl groups present in the basal plane of the OG. Polyamide membranes modified with 0.75 mg of OG showed the best performance in filtrations, and were responsible for an average retention of approximately 55% and permeability of 1.42 L/m².h.bar for Mg+2 , in addition to retention of 37% and permeability of 2.08 L/m².h.bar for NaCl. Furthermore, they can guarantee > 29% retention for Mg+2 ions on the third reuse. SEM images showed that polyamide membranes coated with 0.25, 0.5 and 0.75 mg OG exhibited an OG/PVA surface film of approximately 0.3, 0.4 and 0.5 μm, respectively, in which its magnification increases the salt rejection. It was found that the carboxyl group, present in the citric acid structure, reacts and forms cross-links with the hydroxyl groups, present in PVA and OG, through esterification. These results indicate that the mechanism that dominates the retention process in the produced membranes is size exclusion and showed the potential for desalination of solutions with divalent and monovalent ions. The advances achieved during this work showed practical potentialities to be applied in portable desalination systems.