Ammonium phosphomolybdate–titanium dioxide composite material as a catalyst for antibiotic degradation under ambient conditions†

Abstract

A composite material (designated as AT) of ammonium phosphomolybdate (APM) and titanium dioxide (TiO₂) was synthesized and evaluated for its catalytic ability to degrade tetracycline (TC) via an advanced oxidation process (AOP) under ambient dark conditions in a neutral solution. The catalyst was characterized using BET, XRD, FTIR, XPS, XRF, UV-DRS, and FESEM. Unlike pristine APM, the AT composite eliminated pH constraints in antibiotic degradation. Among various compositions, the 9AT catalyst (APM : TiO₂ = 9 : 1 w/w) exhibited the highest TC removal efficiency. Under optimal conditions (1.2 g L⁻¹ catalyst dose, pH 7.1, and 20 mg L⁻¹ initial TC concentration), 9AT achieved 96.5% TC degradation. Here, TiO₂ acted as a coating/stabilizing material to protect APM, which was only stabilized under acidic conditions and dissolved even in a near-neutral solution. The composite facilitated in situ production of H₂O₂, which generated hydroxyl radicals (˙OH) and singlet oxygen (¹O₂) via Mo⁵⁺ redox cycling, with ¹O₂ being the dominant reactive species. Transformation products (TPs) and plausible degradation pathways were identified. The developed catalyst demonstrated excellent stability, maintaining over 65% efficiency after eight cycles. Additionally, 9AT proved effective in degrading TC in real wastewater, underscoring its practical applicability. Notably, unlike pristine APM, which could be used only under acidic conditions, 9AT remained effective at neutral pH. To the best of our knowledge, this is the first study to fabricate and utilize such a composite as a heterogeneous catalyst for TC degradation under aerobic conditions.