Green electrochemical synthesis of Zn-doped TiO2 with mechanistic and ecotoxicological insights into oxytetracycline degradation
摘要
The persistence of oxytetracycline (OTC) in water and the potential toxicity of its transformation intermediates highlight the need for sustainable photocatalysts that ensure both effective degradation and environmental safety. A green and facile electrochemical route was developed for the synthesis of Zn-doped TiO2 (Z2T2) photocatalysts using industrial titanium bars in 1 M KCl electrolyte under direct current, followed by calcination at 250–700 °C to tune the anatase–rutile phase ratio. Zn doping (0–5 mol%) further modified the optical and surface properties, yielding a 2 mol% Zn-TiO2 catalyst (Z2T2, 350 °C) with mixed anatase–rutile structure, mesoporous aggregates, nanosized crystallites (~ 9.7 nm), and a narrowed band gap of 2.65 eV. Under UVA irradiation (365 nm, 10 mg/L of OTC, 200 mg/L of photocatalyst), Z2T2 achieved 94% removal of OTC within 120 min through combined adsorption and photocatalytic degradation without added oxidants; persulfate addition further enhanced degradation via •SO4− radicals. Radical trapping revealed •O2− and h+ as dominant reactive species, following Langmuir–Hinshelwood surface‐reaction kinetics during the early adsorption-controlled stage. LC–MS/MS analysis identified over twenty intermediates formed via hydroxylation, deamination, decarboxylation, and ring‐opening pathways leading toward mineralization. Ecotoxicity modeling (ECOSAR v2.2) indicated several intermediates and low-molecular‐weight products exhibited acute aquatic toxicity (LC50/EC50 ≤ 1 mg/L, PNEC ≈ 0), highlighting that high removal efficiency does not ensure ecological safety. The Zn‐doped TiO2 synthesized by this facile and sustainable electrochemical approach thus offers an efficient and environmentally friendly method for antibiotic removal from water systems.