Surfactant-free preparation of nickel carbonate hydroxide in aqueous solution and its toxic ion-exchange properties

In this paper, we have demonstrated a simple surfactant-free solution method for the synthesis of sea urchin-like nickel carbonate hydroxide, which was characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermal gravimetric analysis, nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Two types of carbonate species, a surface unidentate carbonate-like species and a crystal lattice carbonate species, were proposed based on the FTIR and symmetry analysis. The toxic ion-exchange properties towards As(V), Cd(II), and Cu(II) ions were investigated. At pH 5.0, the exchange capacities of Cd(II) and Cu(II) ions were 120.5 and 109.3 mg g(-1), respectively, through the ion-exchange between nickel ions with them, which was confirmed by XPS. For As(V) ion removal, the maximum exchange capacity was 49.6 mg g(-1) without any pH adjustment, which should be of importance for water treatment. Furthermore, a novel ion-exchange mechanism between the surface unidentate carbonate-like species and As(V) ions was proposed, which was revealed by XPS and FTIR.