Aqueous-phase synthesis of HEC half-ester–modified Na-Bentonite for selective Ni(II) ion separation from metal mixtures

Abstract

In this study, novel biocomposites based on sodium-bentonite (Be-Na) and hydroxyethyl cellulose (HEC) acid half-esters were developed through an environmentally friendly, aqueous-phase synthesis. A strategy combining solution blending, hydrothermal treatment, and freeze-drying was employed to promote the intercalation of anionic HEC derivatives into the interlayer galleries of Be-Na. The selected acid half-esters were chosen for their anionic and amphiphilic nature, enabling improved compatibility between hydrophilic clay and organic polymer matrices while enhancing dispersion and structural uniformity. A comprehensive morphological characterization was conducted on the synthesized materials, revealing an intercalated structure in the synthesized biocomposites, facilitated by the hydrothermal process. The incorporation of Be-Na nanofillers led to an enhancement in the thermal properties of the polymer chains, and a synthesis mechanism for the biocomposites was anticipated. Subsequently, these biocomposites were evaluated for their effectiveness in the separation of Ni(II) ions from complex mixtures. The Be-Na/HEC-AP biocomposite proved to be particularly promising, demonstrating increased adsorption efficiency compared to other biocomposites, even at acidic pH levels. Kinetic studies revealed an adsorption process consistent with PFO kinetics, while the Langmuir model with a chemisorption process better described the adsorption behavior of Ni(II) ions. Furthermore, the adsorption capacity of the Be-Na/HEC-AP biocomposite was determined to be 3.27 mmol/g. Significant selectivity towards Ni(II) ions was observed, and the material remained stable even after 5 cycles of adsorption–desorption. The Be-Na/HEC-AP biocomposite, with its high Ni(II) adsorption capacity, stability over multiple cycles, and green scalable synthesis, shows strong potential for industrial wastewater treatment applications.