Hydrothermal synthesis of ZnO microspheres and hexagonal microrods with sheetlike and platelike nanostructures.

Unusual ZnO microspheres constructed of interconnected sheetlike nanostructures were prepared by the hydrothermal synthesis approach. These microspheres possess high surface areas (28.9 m(2)/g) and are amorphous. Trisodium citrate plays a key role in directing the formation of these microstructures. By increasing the reaction time, these microspheres gradually dissolved to form short hexagonal microrods with stacked nanoplate or nanosheet structure. The microrods were also formed under the influence of trisodium citrate. They are crystalline and show a strong (002) X-ray diffraction peak of wurtzite ZnO structure. Both microsphere and microrod samples show near-band-edge emission at approximately 385 nm, but only the microrod sample exhibits yellow luminescence at approximately 560 nm. Due to their high surface areas, these ZnO microstructures were examined for their ability to photodecompose phenol. The as-prepared samples did not display photocatalytic activity due to possible surface adsorption of solution species. However, microspheres with heat treatment to 300 degrees C can substantially enhance the photodecomposition of phenol under direct sunlight irradiation and still maintain their high surface area nanosheet structure.