B-doped Carbon Quantum Dots Anchored n/n-Junctioned Graphitic Carbon Nitride (g-C3N4) for CO2 Photoreduction

The abundant use of fossil fuel resources, accompanied by climate change and global energy demands, has motivated the search for sustainable transformations of greenhouse gas CO2 into value-added chemical fuels. In present work, the production of methane (CH4) gas by photocatalytic CO2 reduction over a boron (B)-doped CQD (BCQD)-hybridized graphitic carbon nitride (g-C3N4) homojunction (CNH) nanocomposite was investigated. The CNH and undoped CQD-based g-C3N4 were also synthesized for the comparison of photoactivity towards CO2 conversion. All photoactivity assessments were performed under the irradiation of two 200 W LED lights at ambient temperature and pressure. The results revealed that BCQD/CNH obtained the highest photocatalytic efficiency by achieving a total CH4 yield of 28.12 μmol/(hr-gcatalyst) in 6 h, which was 49.61% and 30.99% higher than the pristine g-C3N4 and undoped CQD/CNH, respectively. A series of control experiments was also carried out in the absence of either photocatalysts, water or light for 6 h. BCQD/CNH was able to yield 54.56% of CH4 as compared to the control experiment without water. In contrast, the lowest CH4 yield of 1.122 μmol/hr was obtained in the absence of BCQD/CNH. The surface morphologies of CNH, CQD/CNH, and BCQD/CNH were also investigated via FESEM and TEM analysis.