Improving Permeation and Antifouling Performance of Polyamide Nanofiltration Membranes through the Incorporation of Arginine

Inspired by the hydrophilicity effect of arginine (Arg) in water channel aquaporins (AQPs), Arg was incorporated into the polyamide layer during interfacial polymerization to enhance the permeation and antifouling performance of the nanofiltration (NF) membranes. Due to the presence of active amine groups, Arg became another aqueous phase monomer along with piperazine (PIP) to react with trimesoyl chloride (TMC) during interfacial polymerization, which was incorporated into the polyamide network. The resulting polyamide NF membranes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), static water contact angle, zeta potential, and positron annihilation spectroscopy (PAS) measurement. The effects of incorporating Arg in aqueous phase on water permeability and the rejection of dyes and inorganic salts of the NF membranes were studied, respectively. Similar to its function in AQPs, Arg apparently increased the hydrophilicity and the negative charges of the membrane surface and, consequently, the permeation performance. When the addition of Arg reached 40% to PIP, the water flux was doubled and the rejection ratios of Congo red and Orange GII were still > 90%. Meanwhile, the antifouling experiments verified that the modified polyamide NF membranes possessed excellent fouling-resistant performance for negatively charged foulants of BSA, emulsified oil droplet, and humic acid. The flux was decreased below 15%, and recovery even rose to 89%.