Green ZnO nanorod material for dye degradation and detoxification of pharmaceutical wastes in water

Abstract

Nanorods of zinc oxide photocatalyst are fabricated through a facile microwave-assisted hydrothermal method as a green preparation process in comparison with the conventional hydrothermal method. The influence of the preparation method on the morphological, structural, and optical properties of the prepared materials is investigated. Moreover, the photocatalytic activity of ZnO nanorod is tested against the degradation of some dyes and pharmaceuticals under the solar simulator. XRD data showed that ZnO NRs exhibited a hexagonal wurtzite phase. Photoluminescence of ZnO-S2 revealed a noticeable separation of photo-generated charged carriers and delaying their recombination. The bandgaps of samples ZnO-S1 and ZnO-S2 are calculated by using UV-DRS spectroscopic measurements and found to be 3.22 and 2.96 eV, respectively. All results confirmed that the microwave-assisted hydrothermal method is a more effective and green preparation process than hydrothermal one for ZnO nanorods production. It is found that samples prepared by microwave-assisted hydrothermal method (ZnO-S2) showed a higher degradation rate for MB than that prepared by hydrothermal one (ZnO-S1). Microwave-assisted ZnO-S2 showed complete degradation of other different dyes; Acid red, Remazol red, and Rhodamine B (RhB) under simulated sunlight indicating non-selectivity of photocatalytic activity for ZnO nanorods. However, the analgesic pharmaceuticals and antibiotics compounds are completely degraded over microwave-assisted ZnO-S2 after 90 min of light irradiation. Furthermore, it is found that the degradation activity of prepared ZnO nanorods fitted with the first-order kinetic. As well, the result displayed that inorganic ions hinder the photocatalytic degradation of dyes with the following the order; phosphate ions > chloride ions > sulfate ions ≈ nitrate ions.