Fluoride adsorption on manganese carbonate: Ion-exchange based on the surface carbonate-like groups and hydroxyl groups.

Manganese carbonate (MnCO3) nanowires and microcubes were controlled synthesized by a simple ethylene glycol (EG) mediated solution method. The volume ratios of EG and water has a decisive impact on the morphology of MnCO3 products. With a decreased water volume, MnCO3 products were transformed from microcubes to nanowires. The obtained MnCO3 nanowires were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherm. The adsorption properties of the MnCO3 products towards fluoride were investigated. The adsorption capacities of the nanowires were higher than that of the microtubes. According to the Langmuir model, the maximum adsorption capacity was 46.80mgg-1 at pH 7.0. The adsorption capacity was 11.58mgg-1 when the equilibrium fluoride concentration was just below the WHO guideline of 1.5mgL-1. The kinetic data were well fitted to pseudo-second-order model. The fluoride removal was attributed to the ion-exchange based on the surface hydroxyl groups and carbonate-like groups, which was revealed by Fourier transform infrared absorption spectroscopy and X-ray photoelectron spectroscopy.