Controllable Doping of Mn into Ni 0.075-x Mn x Al 0.025 (OH) 2 (CO 3 ) 0.0125 ·yH 2 O for Efficient Adsorption of Fluoride Ions.

Here, the structural, optical, and adsorptive behaviors of Ni _0.075-x Mn _x Al _0.025 (OH) ₂ (CO ₃ ) _0.0125 ·yH ₂ O (Ni-Mn/Al) layered double hydroxides (LDHs) are investigated to capture fluoride from aqueous media. The 2D mesoporous plate-like Ni-Mn/Al LDHs are successfully prepared via a co-precipitation method. The molar ratio of divalent to trivalent cations is maintained at 3:1 and the pH at 10. The X-ray diffraction (XRD) results confirm that the samples consist of pure LDH phases with a basal spacing of 7.66 to 7.72 Å, corresponding to the (003) planes at 2 θ of 11.47 ^o and the average crystallite sizes of 4.13 to 8.67 nm. The plate-like Mn-doped Ni-Al LDH consists of many superimposed nanosheets with a size of 9.99 nm. Energy-dispersive X-ray and X-ray photoelectron spectroscopies confirm the incorporation of Mn ²⁺ into the Ni-Al LDH. UV-vis diffuse reflectance spectroscopy results indicate that incorporating Mn ²⁺ into LDH enhances its interaction with light. The experimental data from the batch fluoride adsorption studies are subjected to kinetic models such as pseudo-first order and pseudo-second order. The kinetics of fluoride retention on Ni-Mn/Al LDH obey the pseudo-second-order model. The Temkin equation well describes the equilibrium adsorption of fluoride. The results from the thermodynamic studies also indicate that fluoride adsorption is exothermic and spontaneous.
Competing Interests: The authors declare no conflict of interest.
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