Alpha-calcium sulfate hemihydrate used as a water-soluble template for the synthesis of ZnO hollow microspheres

A template-assisted strategy is an effective method to obtain hollow nano/microspheres with uniform shape and size. However, acid, alkali, organic solvent and calcination are always required for the removal of the template, resulting in the pollution of chemicals, VOC emission or high energy-consumption. Here we report a water-soluble template prepared from alpha-calcium sulfate hemihydrate (alpha-HH) microspheres for the synthesis of ZnO particles with a dense core-shell structure by a two-step deposition-precipitation method. After the template of alpha-HH microspheres was removed simply by rinsing with water, the core-shell structured ZnO particles were turned into hollow microspheres of dimension 0.8-1.2 mu m. The ZnO hollow microspheres possessed large specific surface area and achieved a photocatalytic reaction rate constant which was 5.59 times that of ZnO solid particles, which was assessed by the photodegradation of Rhodamine B (RhB) under UV light irradiation. This work develops alpha-HH microspheres into a water-soluble template for the green synthesis of catalysts with hollow architecture so as to avoid chemical pollution and high energy-consumption during template removal.

Automated summary

A template-assisted strategy is an effective method to obtain hollow nano/microspheres with uniform shape and size. However, the removal of the template often requires acid, alkali, organic solvent and calcination, causing pollution and high energy consumption. In this study, water-soluble α-calcium sulfate hemihydrate microspheres were used as a template to synthesize ZnO particles with a dense core-shell structure. After simply rinsing the α-calcium sulfate hemihydrate microspheres with water, hollow microspheres of ZnO with enhanced photocatalytic activity were obtained.