Synthesis and characterisation of Ni(OH)2 and NiO nanosheets and their removal properties of azo dyes from aqueous solution

Abstract

The degradation of various kinds of synthetic dyestuffs, such as dyestuff, textiles, leather, paper and plastics, stimulated a particular research interest in recent years. Nickel hydroxide and nickel oxide compounds stimulated a large interest in industrial and technical applications, for example as the active materials in electrochemical cycling and as a photocatalyst to remove organic dyes. In this paper, the mainly research is focused on the preparation process and removal properties of azo dye pollutants from aqueous solutions using Ni(OH)2 nanosheets or NiO nanosheets. The proposed research investigates the Ni(OH)2 nanosheets or NiO nanosheets that are important in understanding the structure, morphology and the photocatalytic performances. Ni(OH)2 nanosheets were synthesised by a simple chemical precipitation method using nickel chloride as precursors and ammonia as precipitating agent. The obtained Ni(OH)2 nanosheets can be successfully converted to NiO nanosheets via calcination under appropriate conditions. Analytical methods, such as X-ray diffraction spectra, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy and Fourier transformed infrared spectra, were employed to characterise the morphology and microstructure of the final products. The results reveal that Ni(OH)2 nanosheets were shape preserved transformed to NiO nanosheets at 250°C for 24 h. The removal performances for azo dyes Congo red, methyl orange, methylene blue, rhodaming B using the as prepared and commercial samples from aqueous solutions were investigated respectively. The as synthesised Ni(OH)2 nanosheets is found to have high efficiency for the removal of Congo red pollutant as a result of their unique structures, make them to be promising candidates for wastewater treatment.