Preparation, characterization and scaling propensity study of a dopamine incorporated RO/FO TFC membrane for pesticide removal

The poor permeability of prevalent thin film composite (TFC) membranes impedes their application in forward osmosis (FO). In this study, a high-flux TFC membrane was prepared by incorporating dopamine (DA) into an aqueous solution with various concentrations of m-phenylendiamine (MPD) in interfacial polymerization with trimesoyl chloride (TMC) on a fabricated polysulfone (PSF) substrate. SEM, AFM, XPS, ATR-FTIR, and water contact angle measurement (WCA) and Zeta potential were exploited to characterize synthesized membranes. The optimized TFC membrane (TFC-2; MPD: 2 wt%, DA: 0.1 wt%) attained a nearly five-fold water flux improvement (33.3 LMH (L.m⁻².h⁻¹) versus 7.1 LMH for control membrane), an acceptable reverse salt flux of 4.1 g/m²h and a reduced structural parameter (125 μm) in FO with 1 M NaCl draw solution. Membranes were then employed for pesticide removal from water in both reverse osmosis (RO) and FO resulting in high rejection values of >92% in RO and >91% in FO by the optimal membrane for all studied pesticides. Furthermore, the optimized DA-incorporated sample exhibited a better performance compared to the control membrane in terms of anti-scaling behavior and the scaling propensity of RO and FO processes was studied through flux decline measurement in supersaturated solutions with different concentrations of gypsum as model scalant. This study suggests that the FO process, regardless of the membrane material, is per se more resistant against scaling with a threshold gypsum concentration of 25–30 mM compared to RO starting to scale within 20–25 mM of gypsum solution within 24 h.