Sulfur-doped g-C₃N₄ with enhanced photocatalytic CO₂-reduction performance

Graphitic carbon nitride (g-C₃N₄) is the most stable phase of all carbon nitride allotropes under ambient conditions. In this study, sulfur-doped g-C₃N₄ was fabricated by simply calcinating thiourea at 520 °C. Sulfur-doped g-C₃N₄ (TCN) was found to absorb light up to 475 nm corresponding to a band gap of 2.63 eV, which was narrower than that of un-doped g-C₃N₄ (MCN) with a band gap of 2.7 eV. First-principle calculations based on spin-polarized density functional theory were utilized to investigate the theoretical partial density of states of the TCN and MCN, indicating that the band gaps of TCN and MCN were the same, but impurities existed in the TCN sample. Consequently, photogenerated electrons could easily jump from the impurity state to the conduction band or from the valence band to the impurity state. Photocatalytic CO₂ reduction was further used to evaluate the photoactivity of samples, and the CH₃OH yield using TCN and MCN were 1.12 and 0.81 μmol g⁻¹, respectively. PL spectrum analysis and transient photocurrent responses were also carried out to verify the suggested photocatalysis mechanism. Copyright © 2015 Elsevier B.V. All rights reserved.