Synthesis and Characterization of ZnO/NiO and Its Photocatalytic Activity

Abstract

Bimetallic ZnO/NiO was synthesized by a simple one-pot solvothermal method with zinc nitrate hexahydrate and nickel nitrate hexahydrate in ethanol medium. Material was characterized by X-ray diffraction, Field emission scanning electron microscope, UV-Vis and FTIR. The proposed mixed oxide was investigated as a suitable photocatalytic material for the degradation of organic dyes under visible light irradiation. The formation of ZnO/NiO hetero-junction improved the separation rate of photogenerated electrons and holes and therefore yields enhanced photocatalytic efficiency. Introduction. Nanostructured metal oxide materials fascinated the lot of attention due to their multifunctional activities including optical, magnetic, electrical and catalytic properties. These interesting features increases the wide utility of the materials to many promising applications. Zinc oxide (ZnO) as n–type semiconductor with a direct wide band gap of (Eg = 3.2 eV), has high photosensitivity, photocatalytic activity, quantum efficiency, non-toxicity and low cost [1]. Its extraordinary structural and microstructural benefits further extends their applications to gas sensors, solar cells, light-emitting diodes, field effect transistors, varistors and piezoelectric devices. To date several morphologies such as nanotubes, nanoflowers, nanowires and nanorods of ZnO have developed and studied as the photocatalysts for degradation of organic pollutants. Recent years it has been well established that the coupling of two different semiconductors with different energy levels of photogenerated electron–hole pairs enhanced their functional properties due to their interfacial activity. In particular, the combination of p and n type binary semiconductor oxides could form the p-n junction at the interface and lead to the effective separation of electron-hole pairs. Among various p-type oxides nickel oxide (NiO) is a highly active material with wide band gap (3.6eV to 4.0 eV) and extensively studied for various applications such as catalysis, gas sensing, battery cathodes, magnetic materials, electrochromic films, chemical sensors and photovoltaic devices [2]. In this study, the NiO–ZnO binary composite oxide has been synthesized by one-pot solvothermal synthesis and investigated as the visible light catalyst for photodegradation. The photogenerated electron–hole pairs were effectively separated, which facilitates to enhance their photocatalytic activity.