Ag3PO4 composite nanofiltration membrane and its visible-light photocatalytic properties

Ag3PO4 and AgBr–Ag3PO4 were deposited on the surface of nanofiltration membrane (FT) with tannic acid (TA) and toluene-2,4 diisocyanate (TDI) as functional layers by alternate impregnation method to obtain composite NF membranes (FTA and FTAB) with visible catalytic activity. Under optimal conditions, the catalyst loads on the surfaces of FTA and FTAB were uniform, the initial water contact angle was lower than 28°, the zeta potential was close to −17 mV, the fluxes with FTA and FTAB were respectively 16 and 17.5 L m−2 h−1 (0.4 MPa), and the rejection of Na2SO4 and sulfamethoxazole (SMZ) were more than 75% and 90%, respectively. FTA and FTAB had good photochemical properties, strong absorption of visible light, low electrochemical impedance and sensitive transient photocurrent response. FTA and FTAB with an effective area of 16 cm2 had a static degradation rate of over 90% for 100 mL of 10 mg L−1 SMZ and ciprofloxacin and can achieve dynamic degradation in NF within 300 min under visible light. FTAB effectively alleviated the photo-corrosion behaviour of FTA, maintained the degradation rate of Congo red above 85% after four cycles and had good stability and anti-pollution self-cleaning performances.