Application of the soluble salt-assisted route to scalable synthesis of ZnO nanopowder with repeated photocatalytic activity.

In this paper, the soluble salt-assisted route has been extended to the low-cost and scalable preparation of ZnO nanostructures via the simple oxidation of Zn-Na2SO4 mixture followed by washing with water. The as-prepared ZnO nanopowders are of nanoscaled size, hexagonal phase, and pure, without being stained by Na2SO4. Their optical band gap is 3.22 eV, exhibiting a red-shift of 0.15 eV in comparison with pure ZnO bulk, and their optical absorbance is strong in the region of 200-400 nm, suggesting their full utilization of most of the UV light in sunlight. The product shows evident photocatalytic activity in degradation of RhB under solar light irradiation, and then its solar light degradation efficiency is close to that under UV irradiation, indicating that there is a possibility of practical application. More importantly, the obtained ZnO nanoparticles, because of the quick precipitation by themselves in solution with no stirring, could be easily recycled without any accessorial means such as high-speed centrifuge. The low-cost and scalable preparation, high photocatalytic activity, and convenient recycling of this ZnO nanomaterial gives it potential in purifying waste water. Hence the interesting results in this study indicate the wide range of the soluble salt-assisted route for the industrial preparation of many other advanced nanomaterials.