Fast removal of Congo red from aqueous solution by adsorption onto micro/nanostructured NiO microspheres

Abstract Micro/nanostructured nickel carbonate hydroxide microspheres were synthesized by a ethylene glycol ((CH2OH)2, EG) mediated solvothermal method. The chemical composition of it was determined by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. After calcination, mesoporous micro/nanostructured NiO microspheres with a large surface area of 185.1 m2 g−1 were prepared. The adsorption properties towards Congo red (CR) were revealed. The adsorption of CR was well fitted by the Langmuir model, and the maximum adsorption capacity was 456.8 mg g−1. Kinetic experiment results can be described by the pseudo-second-order model. Furthermore, with the initial concentration of 300 mg L-1 of CR, over 99.41% of CR was removed within 1 min. The calculated thermodynamic parameters including the enthalpy change, change in the free Gibbs energy, entropy change revealed that the adsorption of CR on NiO microspheres was a feasible, spontaneous and endothermic process.