The improvement of photocatalytic efficiency under an abundant natural resource, sun light, presents the next step in the large-scale application of photocatalysis for the treatment of dissolved organic and inorganic pollutants in wastewater. In this study, a composite catalyst of TiO2 and Graphene synthesised by a hydrothermal treatment method is used to photo-reduce Zn2+, the most abundant heavy metal found in combined sewer overflows (CSOs). The performance of this composite photo-catalyst was assessed under various process conditions such as pH, light intensity, catalyst loading and light source. The TiO2-Graphene composite photo-catalyst showed a 20.3 +/- 0.04% increase in the photo-reduction of Zn2+ under solar light compared to un-doped TiO2 when reaction rate constants are compared. This enhancement is a result of the availability of more sorption sites, decrease in band-gap of the TiO2, and effectiveness of the charge separation in the TiO2-G composite catalyst. (C) 2016 Elsevier B.V. All rights reserved.