Heterojunctions between reduced graphene oxide (RGO) and titania nanosheets and their electrochemical properties were investigated. Graphene oxide (GO) was synthesized by Hummers' method, then activated by nitric acid and chloroacetic acid, respectively. They were photocatalytically converted to RGO, RGO-N, RGO-C via TiO2 nanosheets reduction, simultaneously forming heterojunctions of TG, TG-N, TG-C, respectively. Effect of nitric and chloroacetic acid on the RGO and heterojunctions were studied via photoelectrochemcial and photocatalytic measurements. The results revealed RGO was an n-type semiconductor and formed an n/n heterojunction of TG. GO-N was p-type doped after nitric acid treatment, and TG-N was an n/p heterojunction which had a less negative apparent Fermi energy (6), higher conductivity and lower charge transfer resistance in comparison with that of TG. On the other hand, after chloroacetic acid treatment, an n-type semiconductor RGO-C had been modified with more COOH. As a result TG-C n/n heterojunction had a more negative E;, lower effective donor concentration comparing with that of TG. (C) 2014 Elsevier B.V. All rights reserved.