Comparative Study on Morphology-Controlled Zinc Stannate Photocatalysts for Efficient H2O2-Assisted Degradation of Methylene Blue and Tetracycline

Abstract The widespread occurrence of organic dyes and antibiotic contaminants in aquatic systems has raised serious environmental concerns due to their toxicity and persistence, leading to significant interest in the development of efficient photocatalysts. In this work, the visible-light-driven photocatalytic degradation of methylene blue (MB) and tetracycline (TC) is investigated in the presence of hydrogen peroxide (H2O2) using zinc stannate (Zn2SnO4, ZTO) with three distinct morphologies: spherical nanoparticles (ZTO-NPs), urchin (ZTO-Urch), and octahedron (ZTO-Oct), synthesized via the hydrothermal method. Among these morphologies, ZTO-NPs exhibit superior photocatalytic performance with degradation efficiencies of 80% for MB after 180 min of irradiation and 88% for TC after 90 min, surpassing ZTO-Urch (51.4% for MB and 76% for TC) and ZTO-Oct (57.2% for MB and 40% for TC). This improved activity is mainly due to the larger surface area and higher density of active sites in ZTO-NPs. Adding H2O2 significantly improves the photocatalytic activity of ZTO-NPs, increasing MB degradation from 39% to 80% and TC from 78% to 88% by effectively reducing electron−hole recombination. The rate constants from pseudo-first-order kinetics are 0.0083 min−1 for MB and 0.0072 min−1 for TC. Furthermore, ZTO-NPs demonstrate excellent stability and reusability over five cycles. These findings underscore the synergistic impact of morphology and H2O2 in enhancing the degradation of organic pollutants under visible-light irradiation despite zinc stannate’s wide band gap.