Titanium(IV) hydrate based on chitosan template for defluoridation from aqueous solution

A cost effective bio-adsorbent, titanium(IV) hydrate based on chitosan template (Ti-CHI), was synthesized using Ti(SO4)2 and chitosan for defluoridation from aqueous solutions. The Ti-CHI material was characterized using FTIR, SEM with EDX, XRD, XPS and Zeta potential. The adsorption kinetics of fluoride onto Ti-CHI followed pseudo-second-order and intra-particle diffusion models. The Ti-CHI was effective for defluoridating systems with low fluoride concentrations (4.52 mg/L), exhibiting a 87.50% removal rate and permitting a residual fluoride concentration (0.55 mg/L). The most stable pH range for fluoride removal was from 4 to 9. After combining the results of pH effects, FTIR and Zeta potential, the NH groups and TiOH groups were revealed as the fluoride adsorption sites on Ti-CHI. In addition, the carbonate ions present in the aqueous solutions adversely impact the fluoride adsorption. The Langmuir, Freundlich, and Langmuir-Freundlich models were used to illustrate the isotherms of the adsorption process. The adsorption of fluoride onto Ti-CHI fits the Langmuir and Langmuir-Freundlich isotherm models well. The maximum adsorption capacity for fluoride on the Ti-CHI was 16.12 mg/g. Thermodynamic studies revealed that the adsorption process was spontaneous.