The intrinsic morphology and basal plane defects on g-C3N4 nanosheet have important influences on its electronic structures and photocatalytic activity. In this work, we report extending thermal treatment time of g-C3N4 at 550 degrees C not only change the morphology of g-C3N4 but also element composition of g-C3N4. The morphology variation results in largely increased SSA from 40.22 to 117.27 m(2) g(-1), obviously reduced pore size from 3.99 to 2.77 nm for g-C3N4 and formation of in-plane holes. Moreover, composition variation of g-C3N4 has also been found to have changed as the pyrolysis time extended. These changes have significant impact on the optical properties and photoelectrical characters of g-C3N4, which were investigated by UV-DSR, PL and Photocurrent measurement. The photocatalytic activity of g-C3N4 obtained via 9 h thermal treatment at 550 degrees C has shown highest photocatalytic activity, which is 1.77 times than that of g-C3N4 obtained via 3 h thermal treatment under visible irradiation and 1.99 times under UV irradiation respectively. (C) 2016 Elsevier B.V. All rights reserved.