Hybrid of carbon quantum dots modified g-C3N4 nanosheets and MoS2 nanospheres: Indirectly promote hydroxyl group production for efficient degradation of methyl orange

Abstract

Azo dye molecules represented by methyl orange (MO), widely exist in industrial wastewater, and their efficient degradation requires hydroxyl groups with high oxidation activity. g-C3N4/MoS2 heterojunctions are widely used in many photocatalytic applications. However, typical type-II narrow bandgap heterojunctions have holes that cannot be directly oxidized to hydroxyl groups, which is an important barrier to MO degradation. In this work, g-C3N4 nanosheets were modified with carbon quantum dots (CQDs) and combined with spherical MoS2 nanoparticles to form CCN/MS composite photocatalysts. CQDs can be used as electronic reservoir to efficiently separate photogenerated carriers and facilitate the indirect generation of hydroxyl radicals. The results showed that the CCN/MS (10:1) sample had the most excellent degradation performance, with 93 % MO degradation in 120 min, while the control sample of CN/MS (10:1) without introducing CQDs had a degradation rate of only 24 % within the same time interval. In the mixed MO/MB degradation experiments, the degradation of MO was preferred to that of MB, suggesting the existence of a competitive mechanism between the two molecules. Our work proposes a possible pathway for the generation of hydroxyl groups using narrow bandgap semiconductor heterojunction catalysts, which provides a new perspective for understanding the degradation mechanism of pollutant molecules in real industrial wastewater.