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<p>Methylene blue is a widely used cationic dye whose persistence and toxicity necessitate efficient and regenerable adsorbents for wastewater treatment. Here, novel MgCr<sub>2</sub>O<sub>4</sub>/Mg<sub>6</sub>MnO<sub>8</sub>/C nanocomposites were synthesized by a facile Pechini sol–gel route at 600 °C (MCM600) and 800 °C (MCM800) and applied for methylene blue removal from aqueous media. The structural and morphological properties were characterized by XRD, EDS, FE-SEM, and HR-TEM, revealing cubic MgCr<sub>2</sub>O<sub>4</sub> and Mg<sub>6</sub>MnO<sub>8</sub> phases with temperature-dependent crystallite size and grain/particle growth. Batch adsorption experiments were used to evaluate the effects of pH, contact time, temperature, and initial dye concentration, as well as adsorption kinetics, isotherms, thermodynamics, and desorption/reusability. Under optimized conditions (pH 10, 298 K), Langmuir isotherm analysis gave high maximum adsorption capacities of 350.88 mg/g for MCM600 and 273.22 mg/g for MCM800, exceeding many reported methylene-blue adsorbents. The outstanding performance is attributed to the synergistic effect between the obtained phases and the carbonaceous matrix, which provides abundant active sites and favorable surface properties. The adsorption process followed the pseudo-first-order kinetic model and was found to be spontaneous, exothermic, and predominantly physical in nature. Regeneration tests using HCl solutions achieved desorption efficiencies above 99% at 2.0 M, with MCM600 retaining 85.29% of its initial removal efficiency after five adsorption–desorption cycles.</p>

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Facile design of MgCr2O4/Mg6MnO8/C novel nanocomposites with exceptional capacity and reusability for methylene blue removal

  • 期刊论文

  • 发表日期：

    2026年5月31日

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  • N. S. Al-Kadhi,
  • E. A. Abdelrahman,
  • R. K. Shah

摘要

Methylene blue is a widely used cationic dye whose persistence and toxicity necessitate efficient and regenerable adsorbents for wastewater treatment. Here, novel MgCr2O4/Mg6MnO8/C nanocomposites were synthesized by a facile Pechini sol–gel route at 600 °C (MCM600) and 800 °C (MCM800) and applied for methylene blue removal from aqueous media. The structural and morphological properties were characterized by XRD, EDS, FE-SEM, and HR-TEM, revealing cubic MgCr2O4 and Mg6MnO8 phases with temperature-dependent crystallite size and grain/particle growth. Batch adsorption experiments were used to evaluate the effects of pH, contact time, temperature, and initial dye concentration, as well as adsorption kinetics, isotherms, thermodynamics, and desorption/reusability. Under optimized conditions (pH 10, 298 K), Langmuir isotherm analysis gave high maximum adsorption capacities of 350.88 mg/g for MCM600 and 273.22 mg/g for MCM800, exceeding many reported methylene-blue adsorbents. The outstanding performance is attributed to the synergistic effect between the obtained phases and the carbonaceous matrix, which provides abundant active sites and favorable surface properties. The adsorption process followed the pseudo-first-order kinetic model and was found to be spontaneous, exothermic, and predominantly physical in nature. Regeneration tests using HCl solutions achieved desorption efficiencies above 99% at 2.0 M, with MCM600 retaining 85.29% of its initial removal efficiency after five adsorption–desorption cycles.