Quantitative analysis of the contribution of hydroxyl functional groups to the characteristics of thin-film composite membrane via in-situ regulation

This study systematically investigates the regulatory effect and underlying mechanism of hydroxyl (-OH) content within the polyamide (PA) layer of thin film composite (TFC) membranes on membrane performance and fouling behavior. For this purpose, -OH-rich cellulose nanocrystals (CNCs) were employed as in-situ -OH donors, with incorporation concentrations ranging from 0.05 to 0.4 wt% during interfacial polymerization. X-ray photoelectron spectroscopy (XPS) quantitative analysis revealed that the surface -OH content of TFC-CNC membranes with CNC concentrations ranging from 0.05 to 0.4 wt% was 4.21 %, 4.25 %, 4.42 %, and 4.45 %, respectively. These values were significantly higher than the 0.56 % surface -OH content of the TFC-control membrane. The water contact angles (WCA) of TFC-CNC membranes with CNC concentrations of 0.05 to 0.4 wt% were 54.8°, 42.5°, 31.0°, and 23.6°, respectively. These values were exhibited a significant reduction relative to the water contact angle (WCA) of the TFC-control membrane (63.7°). Increasing surface -OH content enhanced membrane hydrophilicity and significantly improved water flux. This flux enhancement stems from the formation of multiple hydrogen bonds between -OH groups and water molecules. Specifically, the TFC-CNC (0.4) membrane attains a water flux of 42.65 LMH, approximately 2.2 times that of the TFC-control membrane (19.02 LMH). Moreover, nanomaterial incorporation reduced the crosslinking density of the PA layer, increased pore size, and enhanced surface roughness. These changes collectively exacerbated membrane fouling. Nevertheless, surface -OH groups alleviated these adverse effects: their week chelation Ca 2+ bridging between the membrane surface and organic pollutants, while their excellent hydration properties effectively minimized pollutant adsorption. These synergistic effects enhanced the antifouling capacity of TFC-CNC membranes, with the TFC-CNC (0.4) membrane achieving a flux recovery ratio (FRR) of 83.33 % (29.38 % for the TFC-control membrane). This finding underscores the critical role of –OH groups in regulating TFC membrane performance.