Selective layer reconstruction of deteriorated polyamide membrane by surface chemical deposition for desalination performance restoration and simultaneous antifouling and anti‑chlorine

This work focused on salt rejection restoration and simultaneous anti-fouling and anti‑chlorine functionalization of partially deteriorated polyamide-based reverse osmosis membrane by surface chemical deposition of tannic acid (TA) followed with polyethyleneimine (PEI). TA molecules were chemically deposited onto membrane surface with glutaraldehyde as bridging and cross-linking agent. The deposited TA molecules were then employed for sequential chemical deposition of PEI molecules through Schiff base reaction under hot alkaline condition. Restoration process was optimized and its influences on membrane physico-chemical properties were systematically studied. Under desired restoring conditions, deposition of TA molecules was found to recover NaCl rejection from 93.2 % to 96.5 %, the sequential deposition of PEI molecules further improved NaCl rejection up to 98.6 %. The depositions of TA and PEI were found to greatly improve membrane surface hydrophilicity and make the membrane hardly charged under neutral pH. The fouling resistance of restored membrane was better than the new polyamide based membrane for its excellent hydrophilicity and surface brushes induced by the PEI molecules grafted. Chlorination tests proved that the antioxidant structures of the deposited TA and PEI molecules endowed the restored membrane with better chlorine stability compared to the new polyamide membrane.