Improved antifouling performance of a polyamide composite reverse osmosis membrane by surface grafting of dialdehyde carboxymethyl cellulose (DACMC)

Antifouling properties are considered to be essential to polyamide (PA) composite reverse osmosis (RO) membranes for their industrial applications. In this work, an antifouling material, dialdehyde carboxymethyl cellulose (DACMC), was prepared by the oxidation of carboxymethyl cellulose (CMC) and then grafted onto the surface of a nascent PA RO membrane to improve its antifouling properties. The results showed that DACMC grafting could endow the membrane with improved hydrophilicity, surface smoothness and NaCl retention, while the permeability was decreased slightly after DACMC grafting. The zeta potentials of the membrane could be adjusted by changing the DACMC concentration. In addition, three typical surfactants with various charge properties, including sodium dodecyl sulfate (SDS), polyoxyethylene octylphenol ether (OP-10) and cetyltrimethylammonium bromide (CTAB), were used as feed foulants to evaluate the antifouling property of membranes. The results showed that, for the anionic SDS and nonionic OP-10 surfactants, the modified membranes with more DACMC had better antifouling performance because the membrane hydrophilicity dominated the interaction between foulants and the membrane surface. For the cationic CTAB, however, the pristine membrane showed better antifouling performance than the modified membrane with low DACMC grafting concentrations (5 and 10 g/L). This difference was attributed to the stronger electrostatic adsorption between the cationic CTAB and the modified membranes with more negative charges. The modified membrane with high DACMC grafting concentrations (20 g/L) exhibited the best antifouling performance for all the surfactants thanks to its high hydrophilicity and low negative charge. Therefore, the charge and hydrophilic properties of the RO membrane must be designed rationally to enhance the antifouling performance of the RO membrane when treating surfactant-containing wastewater.

Automated summary

Antifouling properties of polyamide composite reverse osmosis membranes are crucial for industrial applications. In this study, a new antifouling material, DACMC, was grafted onto a PA RO membrane to improve its hydrophilicity and NaCl retention. The presence of DACMC enhanced the membrane's antifouling performance against anionic and nonionic surfactants, while the pristine membrane showed better performance against cationic surfactants due to stronger electrostatic adsorption at low DACMC concentrations. A high DACMC concentration resulted in the best antifouling performance for all surfactants, highlighting the importance of rational design of charge and hydrophilic properties for RO membranes treating surfactant-containing wastewater.