Visible light driven S-scheme GQDs/BiOBr heterojunction with enhanced photocatalytic degradation of Rhodamine B and mechanism insight

A crucial and desirable objective in the wastewater treatment field is to design photocatalysts that can efficiently remove emerging pollutants while also being environmental-friendly. This work proposed a novel graphene quantum dots/BiOBr (GQDs/BiOBr) heterojunction with strong interfacial interactions through a hydrothermal method. Consequently, in just 140 min, RhB was almost entirely photodegraded by the GQDs/BiOBr and a rate constant 3.26 times higher than pristine BiOBr. The enhanced photocatalytic activity of GQDs/BiOBr was primarily associated with strengthened visible light absorption and improved charge transfer efficiency, as demonstrated through both experimental characterizations and density functional theory (DFT) calculation. Furthermore, with only a minor alteration in the surface chemical structure, GQDs/BiOBr retained strong photocatalytic ability after five cycles (RhB degradation of 85.17 %). The construction mechanism of S-scheme heterojunction, photogenerated carriers' transfer and photocatalytic mechanism were deduced by DFT calculation. The results derived from the radical trapping experiments as well as electron spin resonance (ESR) indicated that the presence of h+ and ·O2− were crucial for the degradation process of RhB. Finally, possible degradation intermediates had been identified and pathways of RhB were proposed, and the results of the toxicity assessment showed that ecotoxicity could be reduced or even eliminated. This effective and reliable visible-light-driven photocatalyst may be applied to build a photocatalytic degradation system for the environmentally friendly and energy-efficient removal of organic pollutants.