Mechanistic insights into enrofloxacin degradation via Ti3+-engineered TiO2/g-C3N4 heterojunction photoanodes

To address the escalating antibiotic contamination in aquatic environments, this study developed Ti 3+ self-doped TiO 2 nanotube arrays/g-C 3 N 4 heterojunction photoanodes (TiO 2-x NTAs/g-C 3 N 4 ) via an integrated in situ synthesis strategy combining electrochemical oxidation, reduction, and chemical vapor deposition. Comprehensive characterization verified g-C 3 N 4 being uniformed dispersed on TiO 2 nanotube surfaces, with Ti 3+ doping significantly improving charge carrier separation efficiency. The photoelectrocatalytic system, utilizing the composite material and platinum as the photoanode and the cathode, respectively, achieved outstanding performance in the degradation of enrofloxacin (ENR). Compared with photocatalytic (72.4%) and electrocatalytic (10.4%) process within 120 min, photoelectrocatalytic process demonstrated the strongest degradation activity (85.4%) with significant synergy. The prepared TiO 2-x NTAs/g-C 3 N 4 photoanode showed robust stability, maintaining nearly unchanged ENR degradation efficiency over 10 cycles. Radical quenching experiments and electron paramagnetic resonance analysis identified the photogenerated holes (h⁺) and superoxide radicals ( • O 2 ⁻) as the dominant reactive species. The synergistic interplay between Ti 3+ doping and heterojunction engineering enabled dual optimization of photon utilization and interfacial charge dynamics. Density functional theory calculations coupled with product analysis elucidated three primary degradation pathways: piperazine ring cleavage, quinolone group oxidation, and defluorination. This work provides mechanistic insights into antibiotic degradation and advances material paradigms for photoelectrocatalytic water remediation.