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.