Hydrogen bond interactions within OH-CQDs/fiber-like carbon nitride for enhanced photodegradation and hydrogen evolution

Graphitic carbon nitride (g-C3N4) possess great potential applications in photocatalytic wastewater purification and hydrogen production. However, its activity is moderate because of the sluggish electron transfer and insufficient light absorption. Here, a series of hydroxyl carbon quantum dots modified with fiber-like carbon nitride composites (OH-CQDs/CNF) were synthesized by a solvothermal approach to enhance the photocatalytic activity. Compared to g-C3N4, the prepared OH-CQDs/CNF exhibited significantly improved visible light absorption (UV-VIS), low recombination electron-hole pairs (PL), and dramatically enhanced conductivity (EIS). Therefore, the optimized OH-CQDs/CNF-4 composite (derived from 4 mL OH-CQDs) displayed excellent photodegradation activity, and its rate constant for tetracycline degradation was 11.3 times higher than that in the presence of g-C3N4, even higher than some noble metal or metal oxides modified g-C3N4. In addition, OH-CQDs/ CNF-4 rendered around 4 times H-2 evolution rate than CNF, mainly because the OH-CQDs were highly dispersed on the CNF surface and formed an intact interface through hydrogen bond interactions. Quenching experiments and ESR results indicated that center dot O-2(-) and h(+) were the main free radicals generated during TC degradation. This study provides guidance for the design of hydrogen bonding-based metal-free photocatalysts for wastewater purification and hydrogen evolution.