Microwave-synthesized ZrO2/ZnO heterostructures: fast and high charge separation solar catalysts for dyes-waste degradation

Abstract

In 60 min, microwave-synthesized ZrO2/ZnO heterostructures exhibited high and fast sunlight photodegradation efficiencies for 50 ppm Congo red (CR) and 50 ppm methylene blue (MB) pollutants. ZrO2/ZnO heterostructures were characterized by XRD, SEM, EDX, FTIR, and diffuse reflectance (DR) techniques. The XRD analysis showed that these heterostructures have combined components of tetragonal ZrO2 and hexagonal ZnO phases. The SEM micrographs of all ZrO2/ZnO nanocomposites demonstrate the formation of nanospherical particles (major) and rod-like (minor) structures. The EDX spectra verified the presence of Zr, Zn and O elements with percentage ratios equivalent or close to that used during the experimental preparation. The FT-IR spectra showed the vibrational characteristic absorption modes of ZrO2 and ZnO bonds around 400–600 cm−1. Two band gap energies were estimated corresponding to ZrO2 (5.05–5.16 eV) and ZnO (3.1–3.16 eV) components. Remarkably, in presence of ZrO2/ZnO (30/70 at%) heterostructure, the free solar energy initiated photodegradation efficiencies of 87% and 98% for 50 ppm CR and 50 ppm MB dyes after 60 min, respectively, which indicates the fast and superior photocatalytic activity of microwave-synthesized ZrO2/ZnO heterostructure. As well, this composition reveals good reusability and stability for three photocatalytic cycles. This uppermost photodegradation performance can be assigned to the high separation of charge carriers, especially for the ZrO2/ZnO (30/70 at%) nanocomposite.Graphical abstract