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<p>Nowadays, environmental treatment researchers are focusing on utilizing solid biomass to fabricate eco-friendly solid adsorbents for water remediation. This work aims to synthesize a novel composite as an adsorbent to remove hexavalent chromium ions (Cr<sup>6+</sup>) from an aqueous medium effectively. Shrimp shells are abundant, accessible throughout the year, safe, beneficial to the environment, and readily transform into the valuable chitosan material. Chitosan/activated kaolinite nanocomposite (CK) was prepared by mixing the initial adsorbents and chitosan (CS) with kaolinite (K), and characterized by different tools. The synthesized CK adsorbent demonstrated distinctive characteristics, including a high surface area of 725.1 m<sup>2</sup>/g, an average pore radius of 2.92&#xa0;nm, a point of zero charge at pH 6.3, and a variety of surface chemical functional groups. The behavior of CK adsorbent was investigated by studying the effect of shaking time, pH, adsorbent dosage, the initial concentration of Cr<sup>6+</sup>, temperature, and ionic strength on the Cr<sup>6+</sup> removal process. Kinetic analysis revealed that the pseudo-second-order (PSO) model best described the adsorption behavior, with a high correlation coefficient (<i>R</i><sup>2</sup> = 0.9916–0.9963) and an average rate constant of 1.7 × 10⁻<sup>4</sup>&#xa0;g/mg·min. Thermodynamic parameters indicated an endothermic and spontaneous adsorption process, with Δ<i>H°</i>&#xa0;ranging from 13.81 to 17.39&#xa0;kJ/mol, Δ<i>S°</i>&#xa0;from 0.0107 to 0.1002&#xa0;kJ/mol·K, and negative Δ<i>G°</i>&#xa0;values between − 1.060 and − 3.681&#xa0;kJ/mol. A good increase in the adsorption capacity from 136.7 to 173.8&#xa0;mg/g was made by the incorporation of kaolinite into chitosan matrix under pH 4, 20&#xa0;°C, and an adsorbent dose of 0.8&#xa0;g/L. The CK adsorbent showed remarkable reusability after six consecutive adsorption–desorption cycles for Cr⁶⁺. Its adsorption capacity decreased only slightly, from 174 to 162&#xa0;mg/g, or an overall fall of around 6.9%. Therefore, CK composite could be a considerable candidate for Cr<sup>6+</sup> removal and a promising material in terms of economics and resource efficiency.</p>

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Utilization of chitosan/activated kaolinite nanocomposite based on shrimp shells for effective removal of hexavalent chromium ions: kinetic and thermodynamic studies

  • 期刊论文

  • 发表日期：

    2025年7月1日

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  • Sarah A. Felemban

摘要

Nowadays, environmental treatment researchers are focusing on utilizing solid biomass to fabricate eco-friendly solid adsorbents for water remediation. This work aims to synthesize a novel composite as an adsorbent to remove hexavalent chromium ions (Cr6+) from an aqueous medium effectively. Shrimp shells are abundant, accessible throughout the year, safe, beneficial to the environment, and readily transform into the valuable chitosan material. Chitosan/activated kaolinite nanocomposite (CK) was prepared by mixing the initial adsorbents and chitosan (CS) with kaolinite (K), and characterized by different tools. The synthesized CK adsorbent demonstrated distinctive characteristics, including a high surface area of 725.1 m2/g, an average pore radius of 2.92 nm, a point of zero charge at pH 6.3, and a variety of surface chemical functional groups. The behavior of CK adsorbent was investigated by studying the effect of shaking time, pH, adsorbent dosage, the initial concentration of Cr6+, temperature, and ionic strength on the Cr6+ removal process. Kinetic analysis revealed that the pseudo-second-order (PSO) model best described the adsorption behavior, with a high correlation coefficient (R2 = 0.9916–0.9963) and an average rate constant of 1.7 × 10⁻4 g/mg·min. Thermodynamic parameters indicated an endothermic and spontaneous adsorption process, with ΔH° ranging from 13.81 to 17.39 kJ/mol, ΔS° from 0.0107 to 0.1002 kJ/mol·K, and negative ΔG° values between − 1.060 and − 3.681 kJ/mol. A good increase in the adsorption capacity from 136.7 to 173.8 mg/g was made by the incorporation of kaolinite into chitosan matrix under pH 4, 20 °C, and an adsorbent dose of 0.8 g/L. The CK adsorbent showed remarkable reusability after six consecutive adsorption–desorption cycles for Cr⁶⁺. Its adsorption capacity decreased only slightly, from 174 to 162 mg/g, or an overall fall of around 6.9%. Therefore, CK composite could be a considerable candidate for Cr6+ removal and a promising material in terms of economics and resource efficiency.