Photocatalytic degradation properties of Ni(OH)2 nanosheets/ZnO nanorods composites for azo dyes under visible-light irradiation

A new visible-light sensitive photocatalyst, Ni(OH)2 nanosheets/ZnO nanorods composites with different Ni(OH)2 contents, was synthesized via a facile water bath route. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopy were used to examine the morphology and microstructure of the composites. XRD analysis revealed that the two phases were composed of well crystallized ZnO and poorly crystallized Ni(OH)2·0.75H2O. Ni(OH)2/ZnO composites showed a red shift in band edge absorption peak in the UV–vis absorbance spectrum, which enhanced their photocatalytic activity. The composites were used for the photodecolourization of water solution of representative organic azo dyes (rhodamine B (RB), Congo red (CR), methylene blue (MB) and methyl orange (MO)) under visible light. All synthesized composites showed better photodegradation performance compared to either pure ZnO or Ni(OH)2. It was noted that composites removal rate strongly depended on the Ni(OH)2 content. When Ni(OH)2 fraction was 10 wt% composites exhibited maximum photodegradation performance for all organic azo dyes. Finally, the possible formation mechanism of the Ni(OH)2/ZnO composites and their photocatalytic decomposition mechanism were also proposed and discussed.