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<p>Cr (VI) is recognized as a highly toxic and carcinogenic heavy metal species that poses significant risks to both human health and the environment. Recent advancements in nanotechnology have introduced zero-valent iron nanoparticles as an encouraging alternative for heavy metal remediation. The eco-friendly synthesis method leverages the bioactive compounds in bael leaves to stabilize the zero-valent iron nanoparticles, eliminating the need for hazardous chemicals. Characterization of the synthesized zero-valent iron nanoparticles using SEM, and XRD confirmed their nanoscale size, porous morphology, and crystalline structure. To evaluate the consequences of distinct factors, such as pH, zerovalent iron nanoparticles dosage, duration of contact, and initial Cr (VI) concentration, research on batch adsorption was conducted. Optimal conditions—pH 2, zero-valent iron nanoparticle dosage of 0.2&#xa0;g/100 mL, Cr (VI) concentration of 25&#xa0;mg/L, and contact time of 40&#xa0;min—achieved a highest removal rate of 97.5% for Cr (VI). Adsorption followed pseudo-second-order kinetics (R² = 0.97) and was best described by the Langmuir isotherm model (R² = 0.99), indicating monolayer chemisorption with a maximum adsorption capacity of 6.6&#xa0;mg/g. Thermodynamic analysis revealed the process to be spontaneous (ΔG⁰ = − 3.64&#xa0;kJ/mol), endothermic (ΔH⁰ = 19.4&#xa0;kJ/mol), and driven by increased randomness (ΔS⁰ = 0.074&#xa0;kJ/mol·K). Desorption studies demonstrated that HCl effectively recovered 72.2% of Cr, primarily in the reduced Cr (III) form, supporting a dual mechanism of Cr (VI) removal involving both reduction and adsorption. Reusability experiments showed the regenerated NPs retained ~ 59% of their original efficiency, affirming their potential for repeated application. This work highlights <i>Aegle marmelos</i>-derived ZVI-NPs as a sustainable, low-cost, and regenerable adsorbent with high Cr (VI) removal efficiency and fast kinetics, suitable for practical wastewater treatment applications.</p>

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Kinetics, isotherms and thermodynamics studies of Cr (VI) removal using zero-valent iron nanoparticles synthesized from Aegle marmelos (Bael) plant extract

  • 期刊论文

  • 发表日期：

    2025年8月5日

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  • Vartika Nishad,
  • Shravan Kumar,
  • S.V.A.R. Sastry

摘要

Cr (VI) is recognized as a highly toxic and carcinogenic heavy metal species that poses significant risks to both human health and the environment. Recent advancements in nanotechnology have introduced zero-valent iron nanoparticles as an encouraging alternative for heavy metal remediation. The eco-friendly synthesis method leverages the bioactive compounds in bael leaves to stabilize the zero-valent iron nanoparticles, eliminating the need for hazardous chemicals. Characterization of the synthesized zero-valent iron nanoparticles using SEM, and XRD confirmed their nanoscale size, porous morphology, and crystalline structure. To evaluate the consequences of distinct factors, such as pH, zerovalent iron nanoparticles dosage, duration of contact, and initial Cr (VI) concentration, research on batch adsorption was conducted. Optimal conditions—pH 2, zero-valent iron nanoparticle dosage of 0.2 g/100 mL, Cr (VI) concentration of 25 mg/L, and contact time of 40 min—achieved a highest removal rate of 97.5% for Cr (VI). Adsorption followed pseudo-second-order kinetics (R² = 0.97) and was best described by the Langmuir isotherm model (R² = 0.99), indicating monolayer chemisorption with a maximum adsorption capacity of 6.6 mg/g. Thermodynamic analysis revealed the process to be spontaneous (ΔG⁰ = − 3.64 kJ/mol), endothermic (ΔH⁰ = 19.4 kJ/mol), and driven by increased randomness (ΔS⁰ = 0.074 kJ/mol·K). Desorption studies demonstrated that HCl effectively recovered 72.2% of Cr, primarily in the reduced Cr (III) form, supporting a dual mechanism of Cr (VI) removal involving both reduction and adsorption. Reusability experiments showed the regenerated NPs retained ~ 59% of their original efficiency, affirming their potential for repeated application. This work highlights Aegle marmelos-derived ZVI-NPs as a sustainable, low-cost, and regenerable adsorbent with high Cr (VI) removal efficiency and fast kinetics, suitable for practical wastewater treatment applications.