A comparative study in single- and binary-contaminant systems: the photodegradation of tetracycline and imidacloprid on flower-shaped Ag/AgBr/BiOBr under visible-light irradiation

Abstract

To compare photodegradation processes in single- and binary-contaminant systems, a representative antibiotic (tetracycline) and insecticide (imidacloprid) were employed as two contaminants of emerging concern. Ag/AgBr modified BiOBr was synthesized hydrothermally in an ionic-liquid/water medium and characterized via various techniques to support mechanistic studies. As-prepared flower-shaped Ag/AgBr/BiOBr exhibits superior photocatalytic activity to Ag/AgBr and BiOBr. Parallel experiments were conducted in single-contaminant systems to optimize the solution chemistry for comparison studies; these suggested that the photodegradation rate (DR) is highest at 1.0 g L⁻¹ at catalyst dosages ranging from 0.6 to 1.4 g L⁻¹, while raising the initial concentration reduces the DR. Additionally, electrostatic interactions between the reactants and photocatalyst cause DR fluctuations at different pH values. In the mechanistic studies, the contributions of the dominant active species (˙O₂⁻ and h⁺) were analysed quantitatively through quenching tests with scavengers. Furthermore, electrostatic interactions between the reactants and the active species result in non-equilibrated contributions from ˙O₂⁻ and h⁺ in single-contaminant systems. Comparison studies distinctly demonstrated a synergistic effect in binary-contaminant systems, which is caused by the mutually complementary utilization of h⁺ and ˙O₂⁻ during the photodegradation of tetracycline and imidacloprid.