Enhanced visible light photocatalytic activity and oxidation ability of porous graphene-like g-C₃N₄ nanosheets via thermal exfoliation

Graphene-like porous g-C₃N₄ nanosheets were synthesized via direct pyrolysis of thiourea followed by a thermal exfoliation. With increased exfoliation temperature, the color of the resulting samples gradually became shallow, and the thickness and size of the layers were decreased. A formation mechanism involving layer-by-layer exfoliation coupled with layer splitting was proposed. The band structure of the g-C₃N₄ nanosheets was continuously tuned because of quantum size effect. Time-resolved decay spectra indicated that the radiative lifetime of charge carriers (τ1 and τ2) increased from 4.13 and 26.23 ns for bulk g-C₃N₄ to 5.36 and 36.57 ns for graphene-like g-C3N4 nanosheets. The g-C₃N₄ nanosheet samples were applied for visible light photocatalytic removal of NOx in air. The performance of porous g-C₃N₄ nanosheets was significantly enhanced with increased exfoliation temperature from 450 to 550 °C. Moreover, photochemical and structural stability was well maintained after multiple reaction cycles. By monitoring the reaction intermediate NO₂, it was found that the generation of NO₂ was inhibited. The activity enhancement of graphene-like g-C₃N₄ nanosheets can be predominantly ascribed to the prolonged lifetime and improved photo-oxidation ability of charge carriers arising from the unique electronic structure. As the synthesis method for graphene-like g-C₃N₄ nanosheets with high a performance is simple, the g-C₃N₄ nanosheets can be envisioned to be applicable in environmental remediation and solar energy conversion. © 2015 Elsevier B.V. All rights reserved.