Preparation and infrared emissivities of alkali metal doped ZnO powders

Alkali metal(Li, Na, K) doped ZnO powders were synthesized by solid-state reaction at different calcination temperatures and holding time. Effects of holding time and K sources on the infrared emissivity of ZnO were investigated. The structure and surface morphologies of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The UV-Vis absorption and infrared emissivities were investigated by a UV-Vis spectrophotometer and an infrared emissometer, respectively. XRD patterns confirm the wurtzite structure of the as prepared samples with single phase. Smooth grain surfaces are detected in all doped ZnO samples, while ZnO:Li and ZnO:Na present the aggregation of grains. The redshifts in the optical band-gap are observed in K-, Na-, and Li-doped ZnO with the values 3.150, 3.144, and 3.142 eV. Due to better crystalline quality, ZnO:K shows a lower emissivity than others. The emissivity of K-doped ZnO decreases to the minimum value(0.804), at 1200 °C and holding 2 h. Compared with KNO3 as K source, K2CO3 doped ZnO has lower emissivities.

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 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.

Improvement of mechanical properties, microscopic structures, and antibacterial activity by Ag/ZnO nanocomposite powder for glaze-decorated ceramic

With the increase in the international trade of ceramics, improvement in the physical and chemical properties of ceramics has become a market demand in recent years. The addition of nanomaterials in glaze can simultaneously improve the mechanical and corrosion resistance properties of ceramics. In this study, the effect of nano-sized Ag/ZnO in glazed ceramic was investigated considering the hardness, whiteness, and microscopic structures of the products. Results showed that the Ag/ZnO nanocomposite powder significantly affects the performance of glaze. Glaze hardness reached the highest value (96.6 HV) at the low sintering temperature of 1130 ℃ with the addition of 10% Ag/ZnO nanocomposite powder. Furthermore, the Ag/ZnO nanocomposite powder improved crack resistance and whiteness. Ag as AgO and Ag2O in the glaze was effective for antibacterial activity of ceramic. In addition, the Ag/ZnO nanocomposite powder could also promote the shrinkage of bubbles in the glaze layer and smooth the glaze. These results indicated that the nanoparticles could act as an active center for melting raw materials, which is crucial for ceramic properties.

A versatile defect engineering strategy for room-temperature flash sintering

In this study,we reported that flash sintering(FS)could be efficiently triggered at room temperature(25℃)by manipulating the oxygen concentration within ZnO powders via a versatile defect engineering strategy,fully demonstrating a promising method for the repaid prototyping of ceramics.With a low concentration of oxygen defects,FS was only activated at a high onset electric field of~2.7 kV/cm,while arcs appearing on the surfaces of samples.Strikingly,the onset electric field was decreased to<0.51 kV/cm for the activation of FS initiated,which was associated with increased oxygen concentrations coupled with increased electrical conductivity.Thereby,a general room-temperature FS strategy by introducing intrinsic structural defect is suggested for a broad range of ceramics that are prone to form high concentration of point defects.