Facile synthesis of ZnO nanoparticles for the photocatalytic degradation of methylene blue

ZnO nanoparticle photocatalysts with a grain size range of 20-100 nm were prepared via a simple sol-gel method and characterized by X-ray powder diffractometry, scanning electron microscopy, gas adsorption, photoluminescence, UV-visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. As-synthesized ZnO samples were highly crystallized with hexagonal wurtzite structure, and the grain size was between 20 and 100 nm and increased with the annealing temperature. It was found that the band gap of ZnO nanoparticles narrowed to visible light region, i.e., 2.69 eV, which increased with the calcining temperature. The sample with a high concentration of oxygen vacancy exhibits excellent photocatalytic activity toward methylene blue (MB) degradation under solar light irradiation, at which the highest photodegradation with a react constant k value of 0.12 min(-1) was achieved. In addition, MB solution was decomposed within 30 min, and after 9 cycles, the catalyst maintains more than 95% photodegradation. Moreover, the intermediate process experiment demonstrated that aEuro cent O-2 (-) and h(+) are the main active intermediate species during the photocatalytic processes.