High-performance thin-film composite membranes with surface functionalization by organic phosphonic acids

Forward osmosis (FO), a novel promising technology for water treatment, has not progressed significantly beyond the conceptualization. A bottleneck is the lack of suitable membranes with high separation performance, good antifouling properties and chemical stability. In this work, a 3-step surface modification approach is employed to develop a thin-film composite polyamide (TFC PA) membrane, i.e., PEI grafting, acid functionalization (organic phosphonic acid or carboxylic acid), and the calcium mineralization. Effects of the organic acid type on membrane properties are investigated with various characterizations, in terms of chemical changes, surface properties, and morphology. The separation performance, antifouling properties and chemical stability of modified membranes are studied systematically. In comparison with the control membrane and those modified by organic carboxylic acids, membranes modified by organic phosphonic acids exhibit the higher FO water flux, lower reverse salt flux, lower fouling propensity, a better pH tolerance, as well as a superior chlorine resistance. The surface functionalized TFC membrane developed in this work therefore holds a great potential for wide membrane-based separation applications in various harsh environments.