HYDROTHERMAL SYNTHESIS AND PHYSIOCHEMICAL PROPERTIES OF Ni-HECTORITE

Abstract

Hectorite containing Ni²⁺ instead of Mg²⁺ in the trioctahedral sheets has been synthesized at 300°C for 12 h under autogenous water vapor pressure by hydrothermal reaction of four kinds of starting slurry with the initial molar ratios Na: Ni: Li: Si=0.7: 5.4: 0.6: 8.0, 1.4: 5.4: 1.2: 8.0, 1.4: 4.8: 1.2: 8.0 and 1.4: 4.8: 1.2: 7.5 made from Ni-Si homogeneous precipitates, lithium fluoride and sodium hydroxide. The resulting Ni-hectorite has been characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR), thermogravimetry and differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. The Ni-hectorite is relatively large massive plate-like particles with a characteristic tint of green and has similar structure to other hectorites, a smaller cation exchange capacity (CEC) and lower adsorptive ability of methylene blue (MB) compared to a commercial Mg-hectorite and a synthetic Znhectorite as reference. It has also been clarified that the Ni-hectorite modified electrode shows a redox reaction Ni²⁺ to Ni³⁺ and Ni³⁺ to Ni²⁺ in cyclic voltammetry.