Abstract

The presence of tetracycline antibiotics in aquatic environments is particularly concerning due to their persistence, ability to disrupt microbial communities, and contribution to the spread of antibiotic resistance, making their removal a complex environmental challenge. In this study, zinc oxide (ZnO) powders were synthesized via a sol-gel method with different nitrogen doping levels (30-50 wt%) and calcination temperatures (400 and 600 degrees C). The influence of doping and calcination temperature on the structural, morphological, optical and photocatalytic properties was investigated. The sample doped with 40 wt% urea and calcined at 400 degrees C exhibited the highest photocatalytic activity, achieving 79 % removal of tetracycline hydrochloride (TC-HCl) under visible-light irradiation. Detailed analysis showed that this optimal sample crystallized in a single-phase hexagonal wurtzite structure with high crystallinity. Nitrogen incorporation was confirmed by characteristic N-H bonding, while the surface displayed aggregated morphologies with roughness and porosity. It also presented the highest surface area and roughness among the series, together with an estimated band gap of 3.28 eV. These features indicate that surface defect states and enhanced pollutant-catalyst interactions, rather than simple band gap narrowing, were the main contributors to the improved activity. Overall, the findings highlight the potential of defect-engineered ZnO photocatalyst as a sustainable alternative for the removal of TC-HCl from wastewater, with performance comparable to that of commercial TiO2 catalysts.