Under sunlight, the combination of GO and TiO2 apparently generated a significant synergistic effect (Fig. 8(b)): the MB photodegradation kinetics for the TiO2–GO membrane was 4–5 times those for the TiO2 and GO-modified membranes, respec- tively. The additive photocatalytic effect of GO and TiO2, however, is not sufficient to explain the significantly enhanced photocata- lytic efficiency. We believe that such an enhanced efficiency of photodegradation under sunlight was due to the lowering of band- gap energy of TiO2 by GO and hence the expanding of the light- response range of TiO2 from UV only to both UV and sunlight