Graphitic carbon nitride (g-C3N4) photocatalysts were synthesized by thermal polycondensation of melamine at different temperatures (450 degrees C, 550 degrees C and 650 degrees C). The crystalline structure, morphology, porosity, composition and light absorption of the materials were thoroughly investigated. Furthermore, their photocatalytic activity was evaluated by NO oxidation under UV and visible light irradiation. The results showed that the structural and optical properties highly depend on the process temperature and thus the degree of polycondensation. The best photocatalytic activity was exhibited by the sample prepared at 450 degrees C and the possible reasons were discussed. (C) 2015 Elsevier BV. All rights reserved.