Self-reduced Co-TiO2 photocatalysts for peroxymonosulfate activation: efficient ciprofloxacin degradation and dynamic charge transfer

Abstract

Co ions have been widely recognized as highly effective catalysts for peroxymonosulfate (PMS) activation. However, their practical utility is frequently compromised by diminished catalytic performance resulting from oxidative deactivation processes. To overcome this limitation, a defective Co-doped TiO₂ photocatalyst (CoTO) was developed through a facile solvothermal synthesis approach. Owing to its exceptional photoinduced charge separation efficiency, the CoTO photocatalyst facilitated spontaneous reduction of oxidized Co³⁺ to Co²⁺ through photogenerated electrons. The self-regenerative mechanism enabled sustained and efficient PMS activation, thereby conferring outstanding cycling stability to the catalytic system. Under visible light irradiation, the CoTO photocatalyst demonstrated exceptional catalytic performance, achieving 81.5% ciprofloxacin (CIP, 20 mg L⁻¹) degradation within just 5 min. Femtosecond transient absorption spectroscopy (fs-TAS) revealed that synergistic interplay between Co²⁺/Co³⁺ clusters and oxygen vacancies established stable charge separation and transport pathways, effectively doubling photogenerated carrier lifetimes and thereby ensuring highly efficient catalytic performance. In-depth mechanism investigations have revealed that the CoTO/PMS system facilitated the efficient oxidation and degradation of CIP through a synergistic interplay of multiple reactive oxygen species.