Microwave-assisted synthesis of ZnO structures for effective degradation of methylene blue dye under solar light illumination

Abstract

The presence of dyes in wastewater poses a high risk to both human health and the environment due to their potential toxicity and ecological impacts. Zinc(II) oxide is a low-cost, non-toxic material that can serve as a sustainable and effective solution to the global water pollution crisis. In this study, we propose a facile one-step synthesis of various ZnO structures by microwave irradiation. The primary goal of this study was to explore the morphology-dependent photocatalytic activity of various ZnO structures, as well as the impact of interfering anions on the Methylene Blue (MB) photodegradation under solar light illumination. Photocatalytic activity studies show that the sample denoted as 0.56 M-ZnO with a sheet-like structure has remarkable catalytic activity under solar light illumination, reaching ∼96.6% degradation of 30 mL MB solution (3 × 10⁻⁵ M) within 40 minutes. The BET specific surface area and band gap of the optimal 0.56 M-ZnO sample were observed to be 12.42 m² g⁻¹ and 2.89 eV, respectively. It was shown that the presence of anions like Cl⁻, NO₃⁻, and HCO₃⁻ can reduce the catalytic activity of 0.56 M-ZnO structure to some extent, although more than 70% MB degradation can still be obtained under neutral pH conditions. The superior catalytic efficacy observed in the 0.56 M-ZnO photocatalyst can be attributed to its improved crystallinity, large surface area, and enhanced production of hydroxyl radicals. The low-cost synthesis, combined with high photocatalytic activity collectively underscores the efficiency and practical usability of produced ZnO photocatalysts for dye degradation.