Removal of Ni²⁺ from Aqueous Solutions by Adsorption Onto Magnetic Multiwalled Carbon Nanotube Nanocomposite

The removal of Ni²⁺ from aqueous solution by magnetic multiwalled carbon nanotube nanocomposite (MMWCNTs-C) was investigated. MMWCNTs-C was characterized by X-ray Diffraction method (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), surface area (BET), and Fourier Transform-Infrared Spectroscopy (FTIR). The effects of initial concentration, contact time, solution pH, and temperature on the Ni²⁺ adsorption onto MMWCNTs-C were studied. The Langmuir and Freundlich isotherm models were applied to fit the adsorption data. The results showed that the adsorption isotherm data were fitted well to the Langmuir isotherm model with the maximum monolayer adsorption capacity of 2.11 mg g^–1. The adsorption kinetics was best described by the pseudo-second-order model. The thermodynamic parameters, such as ΔH^o, ΔG^o and ΔS^o, were also determined and evaluated. The adsorption of Ni²⁺ is generally spontaneous and thermodynamically favorable. The values of ΔH^o and ΔG^o indicate that the adsorption of Ni²⁺ onto MMWCNTs-C was a physisorption process.