Carbon quantum dots-modified tetra (4-carboxyphenyl) porphyrin/BiOBr S-scheme heterojunction for efficient photocatalytic antibiotic degradation

Solar-powered photocatalysis for treating pharmaceutical wastewater is a promising approach for tackling environmental issues and energy crisis. However, its efficiency is hindered by unsatisfactory light-absorption efficiency, rapid charge recombination, and weak photo-redox potential. Here, an organic/inorganic ternary S-scheme system of carbon quantum dots (CDs)/tetra (4-carboxyphenyl) porphyrin/BiOBr (TCPP/CDs/BOB) was ingeniously built by depositing CDs and TCPP onto BOB microspheres for effective purification of tetracycline hydrochloride (TC) under visible light. The Fermi level difference triggers electron delivery from TCPP to BOB upon hybridization, thereby creating an internal electric field (IEF) at the interface. This impels the effective separation of powerful photo-induced carriers. Moreover, CDs perform as electron reservoirs to further promote S-scheme carrier separation. Thus, more powerful photoelectrons in the CDs and holes in the BOB valence band are reserved for participation in photocatalytic reactions. The optimized TCPP/CDs/BOB-2 heterostructure exhibits an enhanced TC degradation capacity of 83.6% within 40 min and the rate constant of TCPP/CDs/BOB-2 is roughly 2.3, 1.8 and 2.0 times that of BOB, CDs/BOB, and TCPP/BOB, respectively. This work provides a new perspective for exploring organic/inorganic ternary S-scheme photocatalysts for water purification.