Photocatalytic thin film composite forward osmosis membrane for mitigating organic fouling in active layer facing draw solution mode

Abstract

As a high-flux operation mode of thin film composite-forward osmosis (TFC-FO) membrane, active layer facing draw solution (AL-DS) mode suffers from the severe membrane fouling tendency, which is not addressed well. Here, we introduced a photocatalyst (Anatase titanium dioxide, A-TiO2) onto the support layer of TFC-FO membrane via the bonding of polydopamine (PDA) and polytetrafluoroethylene (PTFE), and prepared two photocatalytic membranes, A-TiO2/PDA@TFC and A-TiO2/PTFE@TFC. Compared with the pristine TFC-FO membrane, both A-TiO2/PDA @TFC and A-TiO2/PTFE@TFC had an improved water permeability (10.5 L m−2h−1 and 9.5 L m−2 h−1, respectively) and reduced reverse NaCl flux salt (0.8 g m−2 h−1 and 0.7 g m−2 h−1, respectively) in the AL-DS mode using 1 mol/L NaCl as draw solution and pure water as feed solution. Moreover, in the 16 h fouling experiment using 200 ppm bovine serum albumin (BSA) solution as a representative pollutant, the flux decline rate of both photocatalytic membranes was dramatically alleviated from 39.7% and 21.7% in the darkness to 8.5% and 9.7% under UV irradiation, respectively, indicating a significant anti-fouling capacity of photocatalytic effect. In all, the presence of A-TiO2 endowed membrane with high permeability, high rejection efficiency and excellent anti-fouling capacity under UV spotlight. As bonding agent, PTFE provided the modified membrane with a high photocatalytic effect and high self-cleaning capacity, while PDA increased the membrane permeability and protected membrane against photocatalytic damage. This work provides a simple and feasible method to improve the anti-fouling capacity of TFC-FO membrane in AL-DS mode.