Fabrication of structural defects and carboxyl groups on graphitic carbon nitride with enhanced visible light photocatalytic activity

Abstract

Structural defects and surface functional group defects engineering in graphitic carbon nitride (g-C3N4) have great significance for optimizing its electron structure and photocatalytic activity. In this study, g-C3N4 was prepared via a solvothermal method without high-temperature calcination, and then carboxyl group defects-containing g-C3N4 was synthesized through post-modification. FTIR and XPS verified the presence of highly favorable carboxyl groups. Morphological and photoelectrical experiments verified that adding branched chains with carboxyl groups onto g-C3N4 effectively increased the specific surface area and pore volume of g-C3N4, improved the absorption of visible light and enhanced the separation and migration of photogenerated carriers. As a result, the modified g-C3N4 (CN-COOH) had a high bisphenol A (BPA) photocatalytic degradation of 99.6% at 60 min and a high kinetics constant of 0.067 min−1, which was 13.4 times that of the original g-C3N4 under visible light irradiation. In addition, CN-COOH showed high photocatalytic stability with photocatalytic activity decreased by only 1.5% after 5 cycles. Active species capture experiments have demonstrated that •O2− and holes are the main active substances in the BPA photocatalytic process. These findings open a new avenue for precise carboxyl modification of g-C3N4 via an environmentally-friendly post-modification approach and provide the mechanism of carboxyl defects of g-C3N4 photocatalysts on prompting photogenerated charge separation.