(701d) Surfactant-Assisted Interfacial Polymerization for Polyamide Reverse Osmosis Membranes

Thin film composite polyamide reverse osmosis (TFC-PA-RO) membranes are commonly employed for desalination. The fabrication of TFC-PA-RO occurs through interfacial polymerization (IP) of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) to form a highly cross-linked polyamide layer. However, the rapid reaction rate and semi-self-limiting behavior of this IP reaction inhibit the control over distribution of free volume elements/pores which reduces the selectivity towards small, neutral solutes. These limitations can be overcome by enhancing the cross-linking degree of polyamide membrane through the incorporation of surfactants as interfacial regulators during IP. Surfactants regulate IP via their self-assembled network to increase amine diffusion and minimize interfacial tension between the aqueous and organic phases. This leads to the formation of ultra-permselective membranes with a uniform polyamide density distribution. In this study, different anionic, cationic, and non-ionic surfactants have been employed in concentrations ranging from 7.5 % to 100% of their critical micelle concentration (CMC) to investigate the effect of these surfactants on MPD diffusion, polyamide membrane formation, and membrane performance. We achieved more than 95% NaCl rejection and pure water permeance greater than 1 LMH/bar. Additionally, molecular weight cutoff studies were conducted by using various salts and small organic solutes. The surfactant-based membranes exhibited rejections of 70% for urea (1.8 Å) and 95% for glycerol (2.61 Å), significantly outperforming commercial XLE RO membranes, which showed 30% and 89% rejection for urea and glycerol, respectively. Characterization such as FTIR, contact angle, zeta potential, and SEM were used to investigate the polyamide's chemical and physical attributes.