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<p>Heavy metal contamination of aquatic systems is a long-standing threat to both the environment and human health. This issue requires the development of effective, reusable, and clear adsorbents. In this study, we created a rare-earth bimetallic metal-organic framework-hydrogel composite called Ce-Sm-Tz@Alginate Beads. We synthesized it using in situ alginate gelation, followed by the solvothermal incorporation of a nitrogen-rich tetrazole ligand. The hybrid beads combine the structural stability of sodium alginate with the strong binding and adjustable chemistry of cerium and samarium centers. We confirmed the successful formation of a Ce-Sm-tetrazole coordination network embedded in the alginate matrix through comprehensive characterization using FTIR, XPS, SEM-EDAX, and PXRD. Batch adsorption experiments showed that the beads efficiently removed Pb(II), Cu(II), and Cr(VI) ions across various conditions. The maximum adsorption capacities were 2993.82&#xa0;mg·g⁻¹ for Pb(II), 895.20&#xa0;mg·g⁻¹ for Cu(II), and 1587.90&#xa0;mg·g⁻¹ for Cr(VI) under optimized conditions. Kinetic analysis indicated that adsorption followed pseudo-second-order behavior. This means that the uptake was controlled by site availability on a varied surface rather than by strong chemical bonding. Isotherm modeling showed that the Freundlich, Sips, and Hill models best described the adsorption behavior, while Dubinin-Radushkevich energies (less than 0.4&#xa0;kJ·mol⁻¹) indicated that physisorption was the main mechanism. The thermodynamic parameters suggested a spontaneous and endothermic process, with Pb(II) and Cr(VI) adsorption mainly driven by physical interactions, while Cu(II) showed some stronger interactions. To better understand the factors driving adsorption, we used explainable artificial intelligence techniques, including Principal Component Analysis (PCA) and Local Interpretable Model-agnostic Explanations (LIME). PCA identified the initial metal concentration and adsorption capacity as the main contributors, while LIME analysis showed that the sensitivities to contact time and adsorbent dosage varied by metal. Reusability studies demonstrated excellent stability for Pb(II) and moderate retention for Cr(VI), emphasizing the practical use of the composite beads. Overall, this work presents a scalable, clear, and sustainable rare-earth MOF-hydrogel system for multi-metal wastewater treatment. </p> Graphical Abstract <p></p>

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Heavy Metal Sequestration of Pb²⁺, Cr6+, and Cu²⁺ by Cerium–Samarium Bimetallic RE-Tetrazole MOF/Alginate Beads (Ce–Sm–Tz@Alginate Beads): A Multivariate and Explainable AI Framework Using PCA and LIME

  • 期刊论文

  • 发表日期：

    2026年3月11日

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  • M. G. Darsana,
  • D. G. Arya,
  • V. S. Dhanya,
  • Lincy S. Baby,
  • B. R. Bijini

摘要

Heavy metal contamination of aquatic systems is a long-standing threat to both the environment and human health. This issue requires the development of effective, reusable, and clear adsorbents. In this study, we created a rare-earth bimetallic metal-organic framework-hydrogel composite called Ce-Sm-Tz@Alginate Beads. We synthesized it using in situ alginate gelation, followed by the solvothermal incorporation of a nitrogen-rich tetrazole ligand. The hybrid beads combine the structural stability of sodium alginate with the strong binding and adjustable chemistry of cerium and samarium centers. We confirmed the successful formation of a Ce-Sm-tetrazole coordination network embedded in the alginate matrix through comprehensive characterization using FTIR, XPS, SEM-EDAX, and PXRD. Batch adsorption experiments showed that the beads efficiently removed Pb(II), Cu(II), and Cr(VI) ions across various conditions. The maximum adsorption capacities were 2993.82 mg·g⁻¹ for Pb(II), 895.20 mg·g⁻¹ for Cu(II), and 1587.90 mg·g⁻¹ for Cr(VI) under optimized conditions. Kinetic analysis indicated that adsorption followed pseudo-second-order behavior. This means that the uptake was controlled by site availability on a varied surface rather than by strong chemical bonding. Isotherm modeling showed that the Freundlich, Sips, and Hill models best described the adsorption behavior, while Dubinin-Radushkevich energies (less than 0.4 kJ·mol⁻¹) indicated that physisorption was the main mechanism. The thermodynamic parameters suggested a spontaneous and endothermic process, with Pb(II) and Cr(VI) adsorption mainly driven by physical interactions, while Cu(II) showed some stronger interactions. To better understand the factors driving adsorption, we used explainable artificial intelligence techniques, including Principal Component Analysis (PCA) and Local Interpretable Model-agnostic Explanations (LIME). PCA identified the initial metal concentration and adsorption capacity as the main contributors, while LIME analysis showed that the sensitivities to contact time and adsorbent dosage varied by metal. Reusability studies demonstrated excellent stability for Pb(II) and moderate retention for Cr(VI), emphasizing the practical use of the composite beads. Overall, this work presents a scalable, clear, and sustainable rare-earth MOF-hydrogel system for multi-metal wastewater treatment.

Graphical Abstract