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.
Yue LiuLong ChenXiaona LiuTianwei QianMeng YaoWen LiuHaodong Ji
A niobate/titanat nanoflakes(Nb/TiNFs)composite was synthesized via the hydrothermal method and used to remove Pb(Ⅱ)from water.XRD,TEM,and SEM results indicate that Nb/TiNFs appear as nanoflakes,of which the primary crystal phase is tri-titanate.Nb/TiNFs show rapid adsorption kinetics and the result fits well with the pseudo-second order model.The key mechanism of adsorption is ion-exchange between metal and-ONa/H.According to the Langmuir isotherm model,the maximum capacity of Pb(Ⅱ)is 488.323 mg·g^-1.The relatively low RL values indicate that Nb/TiNFs exhibit favorable adsorption of Pb(Ⅱ).Nb/TiNFs indicate high adsorption capacity over a broad pH range.Co-existing inorganic ions(Na+and Ca^2+)have a slight inhibition effect on adsorption,and HA moderately inhibits the adsorption of Pb(Ⅱ)on Nb/TiNFs.Because of the simple method of synthesis and high removal efficiency for heavy metals,Nb/TiNFs are a promising material in remediation of heavy metal polluted water.
