ZnO nanopowders and their excellent solar light/UV photocatalytic activity on degradation of dye in wastewater

Low-cost and scalable preparation, high photocatalytic activity, and convenient recycle of ZnO nanopowders (NPs) would determine their practical application in purifying wastewater. In this contribution, ZnO NPs were scalably synthesized via the simple reaction of Zn powder with H₂O vapor in autoclave. The structural, morphological and optical properties of the samples were systematically characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, transmission electron microscopy, Micro-Raman, photoluminescence, and ultraviolet-visible spectroscopy. The as-prepared ZnO NPs are composed of nanoparticles with 100–150 nm in diameter, and have a small Brunauer-Emmett-Teller surface area of 6.85 m²/g. The formation of ZnO nanoparticles is relative to the peeling of H₂ release. Furthermore, the product has big strain-stress leading to the red-shift in the band gap of product, and shows a strong green emission centered at 515 nm revealing enough atomic defects in ZnO NPs. As a comparison with P25, the obtained dust gray ZnO NPs have a strong absorbance in the region of 200–700 nm, suggesting the wide wave-band utilization in sunlight. Based on the traits above, the ZnO NPs show excellent photocatalytic activity on the degradation of rhodamine B (Rh-B) under solar light irradiation, close to that under UV irradiation. Importantly, the ZnO NPs could be well recycled in water due to the quick sedimentation in themselves in solution. The low-cost and scalable preparation, high photocatalytic activity, and convenient recycle of ZnO NPs endow themselves with promising application in purifying wastewater.