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.