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<p>Mn<sup>2+</sup>-doped Ni–Al layered double oxide (LDO) nanoplates were synthesized via co-precipitation and calcination, aiming to develop an efficient adsorbent for fluoride removal from aqueous solutions. Comprehensive characterization using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HRTEM), Energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) confirmed the successful incorporation of Mn<sup>2+</sup>, formation of well-defined crystalline structures, plate-like morphology, and high surface area with mesoporosity. The adsorption performance of MNAOs was evaluated under varying conditions, including pH, initial fluoride concentration, adsorbent dose, contact time, temperature, and agitation speed. MNAO-20 exhibited the highest adsorption capacity, reaching a maximum modeled value of 411.97 mg/g, with rapid adsorption kinetics and equilibrium achieved within 30 min. The introduction of Mn<sup>2+</sup> dopant represented the key innovation of this study, as it significantly enhanced the surface area, mesoporosity, and density of active sites, thereby improving fluoride adsorption efficiency compared with undoped Ni–Al LDO. Kinetic studies indicated that adsorption was governed by a combination of mass transfer and chemical reaction mechanisms, while isotherm analyses suggested heterogeneous, multi-layer adsorption. Thermodynamic parameters revealed spontaneous, exothermic adsorption accompanied by decreased system randomness, consistent with the formation of ordered fluoride–adsorbent complexes. Regeneration experiments showed that MNAO retained 73.82% of its capacity after five adsorption–desorption cycles, demonstrating structural stability and reusability. The presence of coexisting anions (Cl<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, NO<sub>3</sub><sup>−</sup>) moderately reduced fluoride removal efficiency. Although the removal efficiency at neutral pH limits direct applicability to drinking water, the study provided important insights into the role of Mn<sup>2+</sup> doping in enhancing adsorption performance. These findings highlight MNAOs as a promising adsorbent for further surface modifications and development of scalable fluoride adsorbents for water treatment.</p>

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Synthesis and Characterization of Mn2+-Doped Ni–Al Layered Double Oxides Nanoplates for Fluoride Adsorption: Studies on Adsorption Isotherms, Kinetics, Thermodynamics and Regeneration

  • 期刊论文

  • 发表日期：

    2026年1月23日

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  • Ararso Nagari Wagassa,
  • Enyew Amare Zereffa,
  • Tofik Ahmed Shifa,
  • Amit Bansiwal

摘要

Mn2+-doped Ni–Al layered double oxide (LDO) nanoplates were synthesized via co-precipitation and calcination, aiming to develop an efficient adsorbent for fluoride removal from aqueous solutions. Comprehensive characterization using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HRTEM), Energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) confirmed the successful incorporation of Mn2+, formation of well-defined crystalline structures, plate-like morphology, and high surface area with mesoporosity. The adsorption performance of MNAOs was evaluated under varying conditions, including pH, initial fluoride concentration, adsorbent dose, contact time, temperature, and agitation speed. MNAO-20 exhibited the highest adsorption capacity, reaching a maximum modeled value of 411.97 mg/g, with rapid adsorption kinetics and equilibrium achieved within 30 min. The introduction of Mn2+ dopant represented the key innovation of this study, as it significantly enhanced the surface area, mesoporosity, and density of active sites, thereby improving fluoride adsorption efficiency compared with undoped Ni–Al LDO. Kinetic studies indicated that adsorption was governed by a combination of mass transfer and chemical reaction mechanisms, while isotherm analyses suggested heterogeneous, multi-layer adsorption. Thermodynamic parameters revealed spontaneous, exothermic adsorption accompanied by decreased system randomness, consistent with the formation of ordered fluoride–adsorbent complexes. Regeneration experiments showed that MNAO retained 73.82% of its capacity after five adsorption–desorption cycles, demonstrating structural stability and reusability. The presence of coexisting anions (Cl−, SO42−, NO3−) moderately reduced fluoride removal efficiency. Although the removal efficiency at neutral pH limits direct applicability to drinking water, the study provided important insights into the role of Mn2+ doping in enhancing adsorption performance. These findings highlight MNAOs as a promising adsorbent for further surface modifications and development of scalable fluoride adsorbents for water treatment.