Enhanced photocatalytic hydrogen evolution over coal-based carbon quantum dots modified CoMoO4/g-C3N4

Abstract

In pursuit of exploring functional applications of coal, this study ultrasound-assisted hydrogen peroxide was used to transform cheap coal into environmentally friendly and high-value coal-based carbon quantum dots (CQDs). These CQDs are then harnessed to synergistically assist the photocatalytic water splitting for hydrogen evolution, in collaboration with CoMoO4 (CM) and g-C3N4 (CN). The results indicated that the novel composite photocatalyst, CMCN-11/8%SCQDs, exhibited high hydrogen evolution activity, reaching a maximum hydrogen production rate of 4916.63 μmol g−1 h−1 at pH 9. At a wavelength of 420 nm, the apparent quantum efficiency (AQE) was 1.78%. The conduction and valence band positions of CM were determined to be −1.03 eV and 1.65 eV, respectively, while those of CN were −0.83 eV and 1.72 eV, suggesting the formation of an S-type heterojunction between CM and CN. The significant role of SCQDs in enhancing the photocatalytic hydrogen evolution was extensively investigated, demonstrating that the synergistic effect between SCQDs, CM, and CN could enhance the hydrogen evolution activity. SCQDs exhibited excellent electron transfer capabilities, serving as bridges for electron transport, functioning both as electron acceptors and donors, effectively impeding the rapid recombination of electron-hole pairs and enhancing their separation efficiency. This study provides crucial insights into the utilization of coal-based CQDs for photocatalytic water splitting, offering an economically viable and sustainable option for the functional application of coal and opening new avenues for the rational design of efficient and cost-effective photocatalysts.