Compared in Fig. 4 are the hydrophilicities of the TiO2–GO membrane and three control membranes (i.e., a virgin PSf mem- brane and two PSf membranes that were modified with GO and TiO2, respectively). Clearly all surface-modified membranes exhib- ited enhanced hydrophilicity, with a water contact angle about one- third to two-thirds that of the virgin PSf membrane ( "' 601), a result directly due to the hydrophilic properties of the deposited GO and/ or TiO2. Besides, neither UV nor sunlight irradiation practically changed the water contact angle of PSf or GO-modified membranes. In contrast, both UV and sunlight irradiations further reduced the water contact angles of TiO2 and TiO2–GO modified membranes. The increased hydrophilicity was most likely attributed to the photo-induced superhydrophilicity of TiO2.