Green synthesis of TiO₂ phases for efficient photocatalytic degradation of oxytetracycline in real aquaculture wastewater

Abstract

The increasing use of antibiotics, particularly oxytetracycline (OTC), in aquaculture has raised concerns about environmental pollution and the spread of antibiotic-resistant bacteria. This study investigates the photocatalytic removal of OTC in real aquaculture wastewater using green-synthesized titanium dioxide (TiO₂) derived from Neem leaves. Three phases of TiO₂ were successfully synthesized, namely anatase, rutile, and brookite, with their properties evaluated using XRD, FESEM, photocurrent response, EIS, and photoluminescence. Among the phases studied, Neem-Anatase TiO₂ demonstrated superior performance, achieving 86.63 % ± 2.7 % antibiotic degradation in pure OTC aqueous solution. With a band gap of 3.15 eV, Neem-Anatase TiO₂ exhibited light absorption capability 1.5 and 6 times greater than Neem-rutile (3.4 eV) and Neem-brookite (3.71 eV), respectively. Neem-Anatase TiO₂ maintained a 69.3 % ± 1.2 % degradation efficiency over four recycling cycles, and hole radicals was determined as the primary radical species involved in the photocatalytic process. In real aquaculture water, the Neem-Anatase TiO₂ OTC degradation performance could achieve 69.63 % ± 3.4 % after optimizing experimental parameters including the initial Neem-Anatase TiO₂ dosage (0.6 mg/mL), initial OTC concentration (10 ppm), pH (pH 6) and hydrogen peroxide concentration (5 mM) using the Design Expert software. Factors contributing to the reduction of OTC removal efficiency in aquaculture water include the screening and scavenging effect by the dissolved solids, organic and inorganic components in the water. This work demonstrates the potential of green-synthesized TiO₂, particularly the anatase phase, as a sustainable solution for antibiotic pollution in aquaculture wastewater thereby mitigating environmental impacts and limiting antibiotic resistance in aquatic ecosystems.