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<p>The limited availability of multifunctional biopolymer-based hydrogels capable of removing both heavy metal ions and dyes remains a significant challenge, as most reported systems focus on single-pollutant adsorption and rely mainly on conventional functional groups. In the present study, we designed a Chitosan Xanthate-modified hydrogel (CSXAN hydrogel) incorporating diverse active sites to enhance metal coordination, electrostatic interaction, and secondary binding mechanisms, thereby enabling effective removal of Co(II) and methylene blue from synthetic wastewater. CSXAN hydrogel was synthesized using a free radical polymerization method. The CSXAN hydrogel was characterized through Ultraviolet-Visible, Fourier Transform Infrared Spectroscopy, Thermogravimetric analysis, point of zero charge, X-ray diffraction, scanning electron microscope, Derivative Thermogravimetry, Brunauer-Emmett-Teller (BET) surface area analyses. The BET analysis showed that CSXAN hydrogel possesses a specific surface area of 18.678&#xa0;m²/g, an average pore diameter of 2.976&#xa0;nm, and a total pore volume of 0.008&#xa0;cm³/g, respectively. Optimization studies were conducted by preparing four grades of CSXAN hydrogel. Among them, CSXAN-3 hydrogel achieved maximum swelling capacities of 225.11&#xa0;g/g in distilled water at pH 7 over 24&#xa0;h, proving to be the best grade(referred as CSXAN only afterwards). The studies revealed that removal of Co(II) ion and MB dye were optimized at temperature of 25 ℃, with dosage of 1.2&#xa0;g/L, pH of 7, time of 60&#xa0;min and original concentration of 400&#xa0;mg/L (for Co(II)) and 100&#xa0;mg/L (for MB dye). The adsorption kinetics were best described by intra-particle diffusion kinetic model for Co(II)(R<sup>2</sup> = 0.9931) and MB dye(R<sup>2</sup> = 0.9919) and Langmuir adsorption isotherm with adsorption capacity(q<sub>e</sub>)-386.7048(±60.7194) mg/g for Co(II)(R<sup>2</sup> = 0.9695) and 150.5810(±10.2430) mg/g for MB dye(R<sup>2</sup> = 0.9950) respectively. The negative values of ΔH specify that adsorption process is exothermic and negative ΔG values obtained at temperatures (298, 308 and 318&#xa0;K) show spontaneous adsorption nature. The calculated thermodynamic parameters for Co(II) ions were ΔH = − 67.2143 (±6.1126) kJ/mol and ΔS = − 201.9190 (±19.4995) J/mol·K, with a correlation coefficient (R²=0.9768). Similarly, for methylene blue (MB) dye, ΔH and ΔS were −72.4386 (±8.5216) kJ/mol and −215.4618 (±27.2360) J/mol·K, with a correlation coefficient (R²=0.9520) respectively. These results demonstrate that both Co(II) ions and MB dye adsorption is thermodynamically feasible and predominantly exothermic in nature. The CSXAN hydrogel exhibited high adsorption efficiencies of 96.8% for MB dye and 92.11% for Co(II) ions, with corresponding desorption efficiencies of 95.35% and 89.35%, while maintaining reusability over five consecutive adsorption–desorption cycles. Additionally, catalytic reduction of MB dye was tracked by UV-visible spectroscopy. Additionally, the work integrates adsorption with NaBH₄-assisted catalytic reduction, CSXAN hydrogel attained 97.57%(pH = 11) reduction efficiency in 180&#xa0;s. Therefore, the CSXAN hydrogel exhibits excellent adsorption as well as catalytic properties.</p>

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Eco-friendly Development of Chitosan Xanthate-modified(CSXAN) Hydrogel for Effective Removal of Co(II) ion and Methylene Blue Dye from Water: Adsorption and Catalytic behaviour

  • 期刊论文

  • 发表日期：

    2026年7月11日

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  • Kopal Kashaudhan,
  • Poorn Prakash Pande,
  • Jyoti Sharma,
  • Amar Nath,
  • Aradhana Chaudhary

摘要

The limited availability of multifunctional biopolymer-based hydrogels capable of removing both heavy metal ions and dyes remains a significant challenge, as most reported systems focus on single-pollutant adsorption and rely mainly on conventional functional groups. In the present study, we designed a Chitosan Xanthate-modified hydrogel (CSXAN hydrogel) incorporating diverse active sites to enhance metal coordination, electrostatic interaction, and secondary binding mechanisms, thereby enabling effective removal of Co(II) and methylene blue from synthetic wastewater. CSXAN hydrogel was synthesized using a free radical polymerization method. The CSXAN hydrogel was characterized through Ultraviolet-Visible, Fourier Transform Infrared Spectroscopy, Thermogravimetric analysis, point of zero charge, X-ray diffraction, scanning electron microscope, Derivative Thermogravimetry, Brunauer-Emmett-Teller (BET) surface area analyses. The BET analysis showed that CSXAN hydrogel possesses a specific surface area of 18.678 m²/g, an average pore diameter of 2.976 nm, and a total pore volume of 0.008 cm³/g, respectively. Optimization studies were conducted by preparing four grades of CSXAN hydrogel. Among them, CSXAN-3 hydrogel achieved maximum swelling capacities of 225.11 g/g in distilled water at pH 7 over 24 h, proving to be the best grade(referred as CSXAN only afterwards). The studies revealed that removal of Co(II) ion and MB dye were optimized at temperature of 25 ℃, with dosage of 1.2 g/L, pH of 7, time of 60 min and original concentration of 400 mg/L (for Co(II)) and 100 mg/L (for MB dye). The adsorption kinetics were best described by intra-particle diffusion kinetic model for Co(II)(R2 = 0.9931) and MB dye(R2 = 0.9919) and Langmuir adsorption isotherm with adsorption capacity(qe)-386.7048(±60.7194) mg/g for Co(II)(R2 = 0.9695) and 150.5810(±10.2430) mg/g for MB dye(R2 = 0.9950) respectively. The negative values of ΔH specify that adsorption process is exothermic and negative ΔG values obtained at temperatures (298, 308 and 318 K) show spontaneous adsorption nature. The calculated thermodynamic parameters for Co(II) ions were ΔH = − 67.2143 (±6.1126) kJ/mol and ΔS = − 201.9190 (±19.4995) J/mol·K, with a correlation coefficient (R²=0.9768). Similarly, for methylene blue (MB) dye, ΔH and ΔS were −72.4386 (±8.5216) kJ/mol and −215.4618 (±27.2360) J/mol·K, with a correlation coefficient (R²=0.9520) respectively. These results demonstrate that both Co(II) ions and MB dye adsorption is thermodynamically feasible and predominantly exothermic in nature. The CSXAN hydrogel exhibited high adsorption efficiencies of 96.8% for MB dye and 92.11% for Co(II) ions, with corresponding desorption efficiencies of 95.35% and 89.35%, while maintaining reusability over five consecutive adsorption–desorption cycles. Additionally, catalytic reduction of MB dye was tracked by UV-visible spectroscopy. Additionally, the work integrates adsorption with NaBH₄-assisted catalytic reduction, CSXAN hydrogel attained 97.57%(pH = 11) reduction efficiency in 180 s. Therefore, the CSXAN hydrogel exhibits excellent adsorption as well as catalytic properties.