Influence of citric acid on formation of Ni/NiO nanocomposite by sol–gel synthesis

Nickel/nickel oxide (Ni/NiO) nanocomposite was synthesized by simple sol–gel process by using nickel nitrate as a precursor and citric acid as a gelling agent. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis, Fourier transformed infra-red spectroscopy and vibrating sample magnetometer studies. The influence of citric acid on the formation of Ni/NiO composition was primarily studied by varying the mole ratios of nickel nitrate and citric acid ((N:C) : 1:1, 1:2, 1:4, 1:6 and 1:8). The XRD studies confirmed that the synthesized samples had a mixture of Ni and NiO or single phase of NiO. The SEM observations confirmed that the composites were spherical in shape with an average size of about 70 nm for 1:1 mole ratio and about 40 nm for 1:8 mole ratio samples. At lower N:C mole ratios, the obtained samples had mixture of ferromagnetic Ni and NiO, while at high N:C mole ratios, the sample consisted of almost single phase of NiO. The formation of ferromagnetic Ni was attributed to reduction of some amount of NiO by residual carbon.