Controllable Doping of Mn into Ni0.075‐xMnxAl0.025(OH)2(CO3)0.0125·yH2O for Efficient Adsorption of Fluoride Ions

Abstract

AbstractHere, the structural, optical, and adsorptive behaviors of Ni0.075‐xMnxAl0.025(OH)2(CO3)0.0125·yH2O (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 2θ of 11.47o 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 Mn2+ into the Ni‐Al LDH. UV–vis diffuse reflectance spectroscopy results indicate that incorporating Mn2+ 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.