Photocatalytic conversion of polystyrene under mild conditions using surface-modified BiOBr/g-C3N4 heterojunction with strong interfacial interactions

Abstract

Polystyrene (PS) waste constitutes an increasingly urgent environmental issue. Existing chemical recovery methods generally suffer from harsh reaction conditions and difficult catalyst recovery. In this study, a BiOBr/g-C₃N₄ 2D/2D heterojunction modified with potassium stearate (PST) was proposed for heterogeneous photocatalytic conversion of polystyrene under mild conditions, achieving a 32.63 % yield of benzoic acid. The introduction of PST induced the formation of strong interfacial interactions between g-C₃N₄ and BiOBr nanosheets, thereby enhancing the separation and transfer of photo generated carriers. Furthermore, the PST hydrophobic chains on the heterojunction surface effectively aggregate and adsorb PS molecules and their degradation intermediates, significantly enhancing the chemical recovery efficiency of polystyrene. Quenching experiments and electron paramagnetic resonance (EPR) analyses identified superoxide anion radicals and singlet oxygen as the primary oxidizing species in the conversion process, with alkyl and alkoxy radicals acting as intermediates in the photo degradation of polystyrene. Furthermore, this strategy was successfully applied to commercial plastics, achieving benzoic acid yields of 29–32 %. This work presents a promising strategy for the development of an environmentally friendly conversion system for polystyrene.