Membranas poliméricas modificadas com nanomateriais de grafeno para descontaminação/dessalinização de água

Abstract

The scarcity of water, as well as the pollution of rivers, is a common problem for a large part of the world population, and more specifically for the inhabitants of the Agreste and Sertão regions of Pernambuco, in Brazil. Therefore, it is necessary to search for solutions for the treatment and reuse of effluents and desalination technologies for brackish or salt water.In this work, modifications were proposed in two types of commercial microfiltration membranes: mixed cellulose esters (MCE) and polyamide (PA) with graphene oxide (OG) in the membranes, from the filtration of an aqueous solution of OG, with concentrations of 1 mg/l, 2.5 mg/l and 5 mg/l. Because of the need to create mechanical stability on the modified surface, a process known as polymeric crosslinking was carried out, using polyvinyl alcohol (PVA) and citric acid (AC) as crosslinking agents, followed by heat treatment to cure and anchor the polymer in the OG/membrane system. For morphological and structural analysis of graphene oxide, membranes and manufactured composites, the following characterization techniques were used: scanning electron microscopy (SEM), X-ray diffraction (DRX), thermogravimetry (TG), infrared spectroscopy by fourier transform (FTIR), ultraviolet-visible spectroscopy (UV-Vis), in addition to the stability test to evaluate the modified surfaces. It was possible to observe characteristics such as the morphology and porosity of pure and modified membranes, in addition to estimating the thickness of the deposited GC layers (ranging from 0.1 to 0.3 μm) by SEM. FTIR analisys also verified the presence of oxygenated functional groups on both,the membranes and graphene oxide. The application of the membranes, in the decontamination of the dye methylene blue (AM) and in the desalination of aqueous solutions, took place through the direct filtration process, with rejection and permeate flow tests. For dyes, maximum rejections of >90% AM and flux of 2 L/m².h were obtained with the modified MCE membranes, and average rejection close to 50%, and permeate flux of 5 L/m².h with the PA membranes. Initial desalination tests, using a Na2SO4 solution, showed a probable immediate reaction between the OG and the salts contained in the water, and consequent removal of part of the membrane cover. Subsequent crosslinking inhibited this initial removal, but the results of both tests did not indicate an acceptable percentage (>98%) of saline rejection as compared to other works. The crosslinking efficiency between PVA, AC and OG, through covalent bonds, was investigated with a comparative test of exposure to ultrasound, in membranes only modified with OG and in crosslinked ones. The results obtained showed that crosslinked membranes have greater stability and adherence.