Bioelectronic and photogenerated electron synergistic catalyzed removal of chlorhexidine: Degradation and mechanism

The extensive use of the antimicrobial compound chlorhexidine (CHD) has emerged as a significant threat to both the ecological environment and human health. To address this concern, a photo-electrochemical cell-microbial fuel cell (PMFC) system was studied for CHD removal by incorporating, for the first time, the photocatalysts black phosphorus/carbon nitride (BPCN) and Cu₂O into the bioanode and air cathode of an MFC, respectively. By combining electrochemical, macro-genomic, and intermediate product analyses, the underlying mechanisms of bioelectronic and photoelectronic synergies were elucidated. Specifically, the bioanode and the energy band difference between BPCN and Cu₂O accelerated the bioelectronic and photoelectronic transfer, reduced the reaction barrier, and enhanced the cathodic dechlorination pathway. Consequently, the PMFC showed a 31.4-fold and 8.0-fold increase in CHD removal rate compared to the MFC and PEC, respectively. The photogenerated electrons, on the other hand, acted as key cofactors, replacing cytochrome c and facilitating electron transfer at the microbial-electrode interface, which improved the system's energy yield by 53.9 %. Additionally, illumination selectively enhanced the abundance of anode functional species, carbon metabolism, and interspecific cooperation, resulting in a 4.03-fold increase in the removal of CHD and its intermediates. These findings offer new perspectives on biochemically sustainable environmental remediation for recalcitrant pollutants.