ZnO2–SnO2: a new, efficient heterojunction composite for the rapid and enhanced photocatalytic degradation of rhodamine B dye and moxifloxacin under UV irradiation and sunlight

Abstract

In this study, ZnO₂ nanoparticles and a neoteric ZnO₂–SnO₂ composite were successfully prepared for the investigation of photocatalytic degradation of dye and pharmaceutical contaminants. Various characterization techniques were employed to analyse the as-prepared photocatalysts. The degradation involves the irradiation of light on materials, resulting in the generation of charge-carrier pairs (e⁻–h⁺), which react with O₂ and H₂O to produce reactive oxygen species (ROS), namely, ˙O₂⁻ and ˙OH, which decontaminate pollutants. The photocatalytic activity of the as-prepared catalysts was tested for the degradation of rhodamine B (Rh B) dye and the pharmaceutical antibiotic moxifloxacin (MOX). Results indicate that the new composite-catalyst outperforms ZnO₂ in the degradation of Rh B and MOX, which can be attributed to the better separation and transfer of photoexcited charge carriers, thereby achieving degradation percentages of 96.4% in 30 minutes for Rh B and 95.1% in 20 minutes for MOX after UV light irradiation. However, under natural sunlight, the degradation percentages of Rh B and MOX were 96.2% in 105 minutes and 77.5% in 90 minutes, respectively. The degradation rates of the composite-catalyst were found to be 2.3 and 4.75 times higher than that of ZnO₂ for Rh B and MOX, respectively. Furthermore, scavenging activity was tested, which reveals that ˙OH radicals predominantly contribute to the degradation of the contaminants. The Rh B degradation pathway was studied using HR-MS technique, and toxicity assessment was performed using ECOSAR software. More importantly, the present study highlights the performance of the catalyst ZnO₂–SnO₂, which is reported for the first time.