It is observed in Fig. 10(b) that MB permeation rates for both membranes in the dark experiments fluctuated at about 90%, the 10% removal being most likely attributed to the adsorption by PSf. Under sunlight, while the MB permeation of the virgin PSf membrane remained almost constant, the MB permeation of the TiO2–GO membrane decreased by about 10%, which could be explained by the sunlight-activated photodegradation of MB by the TiO2–GO membrane. The subsequent exposure of the TiO2–GO membrane to UV further decreased the MB permeation in the filtration experiment. Therefore, the photocatalytic properties of the TiO2–GO membrane enhanced the rejection of small organic molecules.