The demand for the development of metal-free, visible-light-active photocatalysts is increasing. This study reports the solvothermal synthesis of carbon nitride (C3N4) photocatalysts by using acetonitrile as a solvent and solvothermal temperatures of 150-220 degrees C. The crystalline structures of the resulting C3N4 samples were obtained following a conversion from a mixed pseudocubic/beta phase to a graphitic phase by increasing the solvothermal temperature and the filling fraction of the autoclave. The interlayer spacing of tri-s-triazine units in the (100) direction within graphitic C3N4 (g-C3N4) was obtained from Xray diffraction measurements and was observed to decrease because of pressurization, leading to improved interlayer stacking of the tri-s-triazine units and a high degree of overlap between the n states and antibonding pi orbitals. The prepared catalysts had band gap energies of 1.5-2.5 eV, and the g-C3N4 samples had high photocatalytic activity during the degradation of methyl orange solutions under visible light irradiation. The g-C3N4 samples obtained at high temperatures and filling fractions exhibited lower photoluminescence emission intensities than did the C3N4 specimens with mixed phases (i.e., pseudocubic- and beta-C3N4), suggesting that these active g-C3N4 catalysts with compact planar tri-s-triazine units had efficient charge separation. The present study demonstrated the influence of the experimental conditions used in the synthesis of C3N4 on the subsequent photocatalytic degradation activity of the specimens under visible light irradiation. (C) 2017 Elsevier Ltd. All rights reserved.