Portable desalinator using graphene oxide functionalized microporous membranes

Commercial microporous polyamide (PA) membranes were smoothly coated with different aliquots of graphene oxide (GO) water solution and crosslinked with polyvinyl alcohol (PVA)/citric acid (CA). The functionalized membrane was attached to a low-cost and easy-to-assemble portable filtration unit for the removal of mono- and bivalent salt from brackish water. The structure and morphology of GO, which was synthesized via a modified Hummers method, and the as-prepared membranes, were characterized through X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). FTIR revealed the same bands for GO and the modified membranes, typical of oxygenated groups vibrations. XRD of crosslinked membranes exhibited traces of crystalline phases probably induced by GO-PVA interactions. SEM images revealed that the PA membranes exhibited an irregular porous geometry and that the GO sheets were uniformly deposited on them, forming a multilayer coat ranging from ∼0.3 to ∼0.5 µm thickness, depending on the amount of GO deposited. Tests using ultrasonic bath showed that the PVA/CA reticulation enhanced the mechanical stability of the membranes, by promoting esterification crosslinking reactions of the carboxyl groups, from the citric acid, with the hydroxyl groups, from the PVA and GO. The membranes were evaluated through salt rejection capacity for magnesium sulfate (MgSO4) and sodium chloride (NaCl) ions in aqueous solutions. Polyamide membranes modified with GO aliquots of 0.75 mg exhibited the best performance, with rejection of 55 % and permeability of 1.42 L/m².h.bar for Mg+2, and rejection of 37 % and permeability of 2.08 L/m².h.bar for Na+. Furthermore, they can guarantee> 29 % retention for Mg+2 ions on the third reuse. These results indicate 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.