钙镁离子改性TiO₂对水中氟离子的吸附行为

This paper investigates the applicable pH value ranges for TiO₂ to remove F- from water. First, TiO₂-Ca and TiO₂-Mg nanoparticles modified by Ca²⁺ and Mg²⁺ are successfully gained by in-situ hydrolysis and doping. Then field emission scanning electron microscopy(FESEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), N₂ adsorption-desorption analysis and Zeta potential analysis are carried out for characterization. The results show that the modified anatase phase TiO₂ was successfully synthesized, and that the isoelectric points of TiO₂-Ca and TiO₂-Mg were increased to 4.51 and 5.08 respectively. The modified TiO₂ samples were applied to remove the low-concentration fluoride ions from water. The results show that the adsorption of fluoride ions by TiO₂-Ca and TiO₂-Mg can reach equilibrium within 20 min, with the adsorption capacity reaching 22.51 mg·g^-1 and 20.87 mg·g^-1 respectively. Compared with the raw TiO₂, the applicable pH value ranges of TiO₂-Ca and TiO₂-Mg are expanded to 5 and 6 respectively, and their sedimentation performance is greatly improved. Among the common coexisting ions, only high-concentrations PO^3-4 and CO^2-3 can significantly affect their adsorption performance. After the desorption and regeneration cycle was repeated 20 times, the adsorption of F- in water by TiO₂-Ca and TiO₂-Mg did not decrease significantly. This shows that modification by Ca²⁺ and Mg²⁺ has obvious effects on the physicochemical properties and fluorine ion adsorption of TiO₂ samples. In addition, the adsorption is a spontaneous exothermic process and the removal of F^- by TiO₂-Ca and TiO₂-Mg mainly involves ion exchange. The research results will provide theoretical and technical support for the application of the environmental-friendly TiO₂ in the removal of low-concentration fluoride ions from water.