Adsorption of Ni²⁺ from aqueous solution by magnetic Fe@graphite nano-composite

The removal of Ni²⁺ from aqueous solution by iron nanoparticles encapsulated by graphitic layers (Fe@G) was investigated. Nanoparticles Fe@G were prepared by chemical vapor deposition CVD process using methane as a carbon source and nanocrystalline iron. The properties of Fe@G were characterized by X-ray Diffraction method (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), Fourier Transform-Infrared Spectroscopy (FTIR), BET surface area and zeta potential measurements. The effects of initial Ni²⁺ concentration (1–20 mg L⁻¹), pH (4–11) and temperature (20–60°C) on adsorption capacity were studied. The adsorption capacity at equilibrium increased from 2.96 to 8.78 mg g⁻¹, with the increase in the initial concentration of Ni²⁺ from 1 to 20 mg L⁻¹ at pH 7.0 and 20oC. The experimental results indicated that the maximum Ni²⁺ removal could be attained at a solution pH of 8.2 and the adsorption capacity obtained was 9.33 mg g⁻¹. The experimental data fitted well with the Langmuir model with a monolayer adsorption capacity of 9.20 mg g⁻¹. The adsorption kinetics was found to follow pseudo-second-order kinetic model. Thermodynamics parameters, ΔHO, ΔGO and ΔSO, were calculated, indicating that the adsorption of Ni²⁺ onto Fe@G was spontaneous and endothermic in nature.