Tuning band structure of graphitic carbon nitride for efficient degradation of sulfamethazine: Atmospheric condition and theoretical calculation

Numerous approaches have been used to modify graphitic carbon nitride (g-C_(3)N_(4)) for improving its photocatalytic activity. In this study, we demonstrated a facial post-calcination method for modified graphitic carbon nitride (g-C_(3)N_(4)-Ar/Air) to direct tuning band structure, i.e., bandgap and positions of conduction band (CB)/valence band (VB), through the control of atmospheric condition without involving any additional elements or metals or semiconductors. The synthesized g-C_(3)N_(4)-Ar/Air could efficiently degrade sulfamethazine (SMT) under simulated solar light, i.e., 99.0% removal of SMT with rate constant k1 = 2.696 h-1 within 1.5 h (4.9 times than pristine g-C_(3)N_(4)). Material characterizations indicated that the damaged/partial-collapsed structure and decreased nanosheet-interlayer distance for g-C_(3)N_(4)-Ar/Air resulted in the shift of band structure due to the denser stacking of pristine g-C_(3)N_(4) through oxidative exfoliation and planarization by air calcination. In addition, the bandgap of g-C_(3)N_(4)-Ar/Air was slightly shrunk from 2.82 eV (pristine g-C_(3)N_(4)) to 2.79 eV, and the CB was significantly upshifted from -0.44 eV (pristine g-C_(3)N_(4)) to -0.81 eV, suggesting the powerful ability for donating the electrons for O_(2) to form ^(·)O_(2)^(-). Fukui index (f -) based on theoretical calculation indicated that the sites of SMT molecule with high values, i.e., N9, C4 and C6, preferred to be attacked by ^(·)O_(2)^(-) and ^(·)OH, which is confirmed by the intermediates’ analysis. The tuning method for graphitic carbon nitride provides a simple approach to regulate the charge carrier lifetime then facilitate the utilization efficiency of solar light, which exhibits great potential in efficient removal of emerging organic contaminants from wastewater.