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The purpose of this study is to synthesize a semiconductor photocatalyst which responds to both UV light and visible light in removal of organic dyes.

ZnO nanoparticles were pre-synthesised via sol-gel method using zinc nitrate tetrahydrate and methanamine at 90°C for 20 h. Subsequently, the as-synthesised ZnO nanoparticles were filtered, washed and dried. To synthesize ZnO-MnO₂ core shell nanocomposites (CSNs), 2:3 M ratio of KMnO₄ and MnSO₄ solution was stirred for an hour. Next, ZnO nanoparticles were added into the solution. The solution was heated at 160°C for 3 h for the formation of ZnO-MnO₂ CSNs. The structural, optical and photocatalytic properties of ZnO-MnO₂ CSNs were characterised by field emission scanning electron microscope, transmission electron microscopy (TEM), X-ray diffractometer and PL spectroscopy, respectively.

The photodegradation efficiencies of rhodamine B (RhB) dye by ZnO-MnO₂ CSNs as photocatalysts are 87.1 per cent under UV irradiation and 76.6 per cent under visible light irradiation, respectively. Their corresponding rate constants are 0.016 min⁻¹ under UV irradiation and 0.013 min⁻¹ under visible light irradiation. It can be concluded that N-deethylation was the dominant step during the photodegradation of RhB dye as compared to cycloreversion. The ZnO-MnO₂ CSNs demonstrated good photostability after three consecutive runs.

ZnO-MnO₂ CSN photocatalyst which could response to UV and visible light in degradation of RhB dye was synthesised using sol-gel method. The analysis shows that N-deethylation was the key photodegradation mechanism of RhB by ZnO-MnO₂ CSN.

This paper aims to investigate the reusability of metal/metal oxide-coupled ZnO nanorods (ZnO NRs) to degrade rhodamine B (RhB).

ZnO NRs particles were synthesized by precipitation method and used to remove various types of metal ions such as Cu²⁺, Ag⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺ and Cr²⁺ ions under UV illumination. The metal/metal oxide-coupled ZnO NRs were characterized by scanning electron microscope, X-ray diffraction and UV-Vis diffuse reflectance. The photodegradation of RhB dye by these metal/metal oxide-coupled ZnO NRs under UV exposure was assessed.

The metal/metal oxide-coupled ZnO NRs were successfully reused to remove RhB dye in which more than >90% of RhB dye was degraded under UV exposure. Furthermore, the coupling of Ag, CuO, MnO₂, Cd and Ni particles onto the surface of ZnO NRs even enhanced the degradation of dye. The dominant reactive species involved in the degradation of RhB dye were ^•OH- and ^•O₂⁻-free radicals.

The coupling of metal/metal oxide onto the surface of ZnO NRs after metal ions removal could affect the photocatalytic performance of ZnO NRs in the degradation of organic pollutants in subsequent stage.

A good reusability performance of metal/metal oxide-coupled ZnO NRs make ZnO NRs become a desirable photocatalyst material for the treatment of wastewater, which consists of both heavy metal ions and organic dyes.

Metal/metal oxide coupling onto the surface of ZnO NRs particles improved subsequent UV-assisted photocatalytic degradation of RhB dye.