Facile synthesis of sheet-like ZnO assembly composed of small ZnO particles for highly efficient photocatalysis

We report an effective and green precursor-based route for preparing a sheet-like ZnO assembly composed of small ZnO particles, which showed good photocatalytic performance under UV light irradiation. The process involved first preparing a zinc glycerol precursor and then calcination to transform it into a sheet-like ZnO assembly. The microstructure of the sheet-like ZnO assembly, including the crystallite size, crystallinity degree and Brunauer-Emmett-Teller (BET) specific surface area, could be easily tuned by changing the calcination temperature. With an increase in calcination temperature, the crystallinity degree could be improved along with an increase in the crystallite size. Photocatalytic tests indicated that the as-prepared ZnO sheets showed good activity for photo-degradation of organic dye under UV light irradiation. ZnO-600 (calcination at 600 degrees C) exhibited the best photocatalytic activity, which was superior to that of P25 TiO2, a commercial benchmark photocatalyst. Furthermore, the sheet-like ZnO assembly could be readily separated from the reaction system by filtration or low-speed centrifugation (or natural sedimentation) after photocatalytic use due to the large particle size of 10 mu m, which is favorable for separation and reuse. After 5 recycles, the ZnO-600 did not exhibit an obvious loss in activity, confirming its good activity upon recycling. By combining X-ray photoelectron spectroscopy (XPS) and BET tests, we found that the synergy of the BET surface areas and crystallinity resulted in the good performance of the sheet-like ZnO photocatalyst. In particular, due to the sheet-like structure, the ZnO could effectively combine with Ag particles, resulting in a large increase in the photocatalytic activity by more than 3 time by compounding with a small amount of Ag NPs (about 1% by mass). The present route is promising for the application of ZnO-based photocatalysts due to its easy handling process, good reproducibility, high yield and the good performance of the resulting materials.