Preparation and Properties of Nanocomposite MWCNTs/Polyamide Reverse Osmosis Membrane for Desalination by Interfacial Polymerization

Abstract

Thin film nanocomposite (TFN) polyamide (PA) reverse osmosis (RO) membranes incorporating carboxylic multiwall carbon nanotubes (c-MWCNTs) were successfully synthesized by interfacial polymerization with aqueous solution of m-phenylenediamine (MPD) containing c-MWCNTs and Isopar G solution of trimesoly chloride (TMC). In order to improve the dispersion of MWCNTs in polymer matrix, carboxylic groups was modified onto the pristine MWCNTs by acid mixture (sulfuric acid and nitric acid of 3:1 volume ratio) and mixture of sulfuric acid and hydrogen peroxide (4:1 volume ratio). The feasibility of carboxylic on MWCNTs was evaluated by FT-IR, SEM, TEM and Raman spectroscopy analysis. Apparent size distribution and suspension of c-MWCNTs showed the well dispersion condition of c-MWCNTs in water which also proved the successful carboxylic of MWCNTs. The effect of c-MWCNTs incorporation into the PA selective layer on the surface morphology, separation performance and antifouling properties of the membranes were investigated and discussed. The “leaf-like” and granules outgrowth morphology of nanocomposite was observed by SEM and the c-MWCNTs incorporated in PA layer were observed by TEM. After doping c-MWCNTs, the water flux of TFN membranes increased due to higher hydrophilicity and additional water pathways of c-MWCNTs. It is noteworthy that the TFN membrane with 0.005 wt% c-MWCNTs could exhibit water flux as high as 68.3 L·m-2·h-1 and the NaCl rejection maintained at 96.0%. Meanwhile, the TFN membrane with 0.005 wt% c-MWCNTs showed better antifouling affinity than c-MWCNTs free membrane due to the increased in hydrophilicity as well as surface negative charge. Based on the result, it can be concluded that incorporating an appropriate amount of c-MWCNTs into PA rejection layer could potentially improve the performance of TFN membrane during RO applications.