Low-cost and scalable preparation,high photocatalytic activity,and convenient recycle of Zn O 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 H_2O 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 Zn O NPs are composed of nanoparticles with 100–150 nm in diameter,and have a small Brunauer-Emmett-Teller surface area of 6.85 m~2/g.The formation of Zn O nanoparticles is relative to the peeling of H_2 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 Zn O NPs.As a comparison with P25,the obtained dust gray Zn O 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 Zn O 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 Zn O 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 Zn O NPs endow themselves with promising application in purifying wastewater. Low-cost and scalable preparation, high photocatalytic activity, and convenient recycle of Zn O 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 H 2 O 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 Zn O NPs are composed of nanoparticles with 100-150 nm in diameter, and have a small Brunauer-Emmett-Teller surface area of ​​6.85 m 2 / g. The formation of Zn O nanoparticles is relative to the peeling of H 2 release. , 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 Zn O NPs.As a comparison with P25, the resulting dust gray Zn O 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 Zn O NPs show excellent photocatalytic activity on the degradation of rhodamine B (Rh-B) under solar light irradiation, close to that under UV irradiation. Implantantly, the Zn O NPs could be well recycled in water due to the quick sedimentation in themselves in solution. low-cost and scalable preparation, high photocatalytic activity, and convenient recycle of Zn O NPs endow themselves with promising applications in purifying wastewater.