Kinetics, isotherm, mechanism, and recyclability of novel nano-sized Ce4+-doped Ni–Al layered double hydroxide for defluoridation of aqueous solutions

Abstract

Excessive uoride removing from aqueous solutions is of utmost importance as it has adverse impact on human health. This study investigates the de uoridation e ciency of a novel nano-sized Ce +4 -doped Ni/Al layered double hydroxide (Ni-Al-Ce LDH) for aqueous solutions. The synthesized Ni-Al-Ce LDH exhibited a well-de ned nanoscale plate-like morphology and a high surface area with an average size of 11.51 nm, which contributed to its enhanced uoride adsorption capacity. XRD, SEM, HRTEM, and BET studies con rmed these characteristics. XPS analysis con rmed the presence of Ce 4+ ions within the Ni-Al LDH. The experimental results indicated that the process of de uoridation followed a pseudo-second order model of kinetics, suggesting a chemisorption mechanism. The uoride adsorption isotherms demonstrated well ts to the Freundlich, Langmuir and Jovanovic models, indicating both monolayer and multilayer uoride adsorption on the Ce-doped Ni-Al LDH. The maximum adsorption capacity was found to be 238.27 mg/g (Langmuir) and 130.73 mg/g (Jovanovic) at pH 6.0 and 25°C. The proposed mechanisms for uoride adsorption on the LDH include ion exchange, surface complexation, hydrogen bonding, and ligand exchange. The Ni-Al-Ce LDH nanomaterial exhibited good recyclability, maintaining 71% of the uoride adsorption e ciency even after four consecutive cycles. This study highlights the signi cant role of Ce doping in improving the performance of Ni-Al LDH as a de uoridation adsorbent.