Synthesis and characterisation of alkali metal (Mn, Fe) oxide–ZnO nanorod composites and their photocatalytic decolourization of rhodamine B under visible light

Abstract

Semiconductor photocatalyst has attracted a great deal of attention in environmental wastewater treatment. As versatile semiconductor materials, ZnO nanocomposites composed of two or more oxide particles with different energy levels exhibit better photocatalytic activity due to more efficient charge separation. The alkali metal (Mn,Fe) oxide–ZnO nanocomposites have reported little work on the photodegradation of organic contaminants under visible light irradiation. In this paper, the main research is focused on the preparation process and the removal properties of organic pollutants rhodamine B (RB) from the wastewater using the alkali metal (Mn,Fe) oxide–ZnO nanorod composites. The proposed research investigates the alkali metal (Mn,Fe) oxide–ZnO nanorod composites with varied Mn or Fe content that are important in understanding structure, morphology and photocatalytic performances. The well crystalline phase alkali metal (Mn,Fe) oxide–ZnO nanorod composites have been directly synthesised at low temperature (90°C) by a simple water bath method. The thorough structural characterization included X-ray diffraction, scanning electron microscopy and ultraviolet–visible spectroscopy were used to examine the morphology and microstructure of the final products. The photoactivity of nanostructured composites was tested by the degradation of RB under visible light. The results show that the removal of RB follows a Langmuir–Hinshelwood first order kinetic law over the initial stage of the reaction time by using the composites as photocatalyst. The composites are found to be efficient and generating less toxic secondary pollutants, which can easily be eliminated from the system by subjecting further to traditional physical, chemical and biologic treatments. The well crystalline phase and the excellent removal capacity for organic pollutants RB from wastewater make them promising candidates for wastewater treatment.