Multi-layer ZnO assembled microspheres, microstars and microflowers with high photocatalytic performance

Hierarchical ZnO microspheres, microstars and microflowers were synthesized via hydrothermal process. After calcination, the zinc nitrate and urea reacted and formed into microspheres. Addition of sucrose made the consisting layers with porosity and assembled to microstars. Surfactant trisodium citrate further altered the hierarchical structure to microflowers. The phase structure, surface morphology and optical absorption of the as prepared samples were analyzed by X-ray diffraction, field emission scanning electron microscopy and ultraviolet–visible spectrophotometer. It turned out that the samples were hexagonal ZnO with high purity and crystalinity, and showed intense absorption in the UV region. Photocatalytic studies indicated that the samples exhibited excellent photocatalytic activity towards methyl orange (MO) under UV light irradiation. The sample with microflowers performed the best in the photodegradation, and its recycling tests also gave satisfactory results for five cycles, which could be attributed to the large specific surface area and strong UV absorption. We expect this work could widen the application of the promising ZnO-based photocatalyst in environmental protection and control.