Impact of Molecular Structure on Superoxide Radical Generation in Biochar-Based D–A Heterojunction Photocatalysts for Rapid Chloramphenicol Degradation under Visible Light

Chloramphenicol (CAP) has evolved from a widely used antibiotic to a persistent pollutant that is difficult to manage. We employed photocatalysis to address the pollution that it caused. Given the similarity in requirements for active layer materials between photocatalysis and solar cells, we selected outstanding materials already employed in bulk heterojunction organic solar cells (BHJ-OSCs) to construct the catalyst. We selected PTQ10, which is low-cost and readily synthesized, as the donor and ITIC-Th and IEICO-4F, which can broaden the absorption range, as the acceptors, thereby constituting two distinct D-A heterojunction active layers. We immobilized them onto coconut shell charcoal (CSC) obtained from agricultural byproduct recycling, yielding two catalysts: PTQ10:ITIC-Th/CSC and PTQ10:IEICO-4F/CSC. They were able to degrade 97% of high-concentration CAP within 15 min under visible light irradiation and remained stable for over 20 cycles. We further investigated the influence of molecular structure on photocatalytic processes as follows: 1) ITIC-Th exhibits a larger dipole moment and more favorable band structure, resulting in enhanced charge separation efficiency; 2) ITIC-Th possesses reduced steric hindrance, exposing more active reaction sites; and 3) ITIC-Th demonstrates a broader light absorption range with more complete absorption of visible light. The above three points enable PTQ10:ITIC-Th/CSC to generate more •O₂^- and degrade CAP more efficiently. This work is expected to provide some ideas and help with environmental pollution control and photocatalyst design.