Graphene quantum dots/carbon nitride heterojunction with enhanced visible-light driven photocatalysis of nitric oxide: An experimental and DFT study

Abstract

Visible light-driven photocatalysis for the degradation of nitric oxide (NO) has attracted considerable attention. Graphene quantum dots/graphite phase carbon nitride (GQDs/CN) heterojunctions were proposed as efficient visible-light responsive photocatalysts for NO treatment under the guidance of density function theory (DFT) simulation. Then, the GQDs/CN was synthesized via hydrothermal combination of GQDs and g-C3N4 (CN) produced from pyrolysis of citric acid (CA) and melamine, respectively. Afterwards, the GQDs/CN composite samples were characterized using XRD, XPS, FE-SEM, TEM, HR-TEM, BET, UV–Vis DRS, PL, photocurrent tests, and EIS. Later, the photocatalytic activity of the prepared GQDs/CN composites was evaluated by degrading NO at ppm level under visible light irradiation at conditions of 20 ppm of NO, 5% of O2, and 50% of relative humidity. Results show that 9GQDs/CN outperforms its counterparts. Compared to CN, the 9GQDs/CN increases the NO conversion rate from 61% to 90%, the selectivity of nitrate formation from 53% to 74%, and the value of DeNOx index from −0.25 to 0.19. The enhanced performance results from the inclusion of GQDs, which increases the specific surface area, promotes the absorption of light, boosts the separation of photogenerated electrons and holes, and inhibits their recombination. Furthermore, we used active species detection experiment, IC, in-situ DRIFTS, ESR measurement, XPS VB, Mott-Schottky, and DFT calculations to systematically explore the mechanism behind the degradation of NO using GQDs/CN, and confirmed the formation of Type-Ⅱ heterojunction between GQDs and g-C3N4. In addition, 9GQDs/CN maintains a high NO conversion rate after 5 cycles of experiments, indicating its potential in industrial applications.