Enhanced and efficient capture of Cd(II) through functionalized metal-organic frameworks embedded in a biopolymer (carboxymethyl cellulose/polyethylenimine): Thermodynamics, kinetics, and optimization via Box-Behnken methodology.

To establish a technique for the adsorption of cadmium (II) ions from aqueous solutions, we undertook modifications of thorium metal-organic frameworks (Th-MOF) through the incorporation of sulfonamide. This process created a functionalized of Th-MOF, referred to as NH-Th-MOF. This material was encapsulated in a biopolymer blend of carboxymethyl cellulose and polyethylenimine, then crosslinked with epichlorohydrin to form functionalized thorium metal-organic frameworks within carboxymethyl cellulose/polyethylenimine (FTMCP) hydrogel beads. The synthesis process demonstrated a high degree of accuracy, while characterization methods including SEM with EDX, FTIR, XRD, and nitrogen adsorption/desorption isotherm study indicated a significant surface area of 368.7 m/g. Following this, an evaluation was conducted on the potential application of wastewater systems as a medium for deploying novel adsorbents targeted at the removal of Cd(II) ions. In this context, experiments conducted in batch mode aimed to assess the ideal parameters, which encompass adsorbent dosage, Cd(II) ion concentration, temperature, and pH level. The data revealed that optimal adsorption performance was achieved at a pH level of 6, utilizing a dosage of 0.02 g per 25 mL of solution, coupled with a interaction duration of 100 min. The highest recorded adsorption capacity (Q) for Cd(II) when employing the FTMCP hydrogel bead adsorbent was noted to be 432.6 mg·g. The analysis revealed that the adsorption phenomenon aligns with the Langmuir isotherm model, and is further characterized by pseudo-second-order kinetics. Moreover, the findings indicated that the nature of the adsorption procedure is chemisorption, supported by an adsorption energy measurement of 32.42 kJ·mol. Thermodynamic evaluations indicate that the elimination of Cd(II) ions is an endothermic and spontaneous procedure, as evidenced by a positive ΔS value, which implies a rise in disorder at the boundary of the solid solution during the adsorption process. Furthermore, with a rise in temperature, the ΔG° value exhibits a trend towards becoming more negative. An analysis of the adsorption mechanisms reveals the significance of π-π interactions, electrostatic interactions, hydrogen bonding, and pore filling in the process. This particular adsorbent is deemed economically advantageous owing to its efficiency over an extended usage, capable of sustaining performance through up to five cycles. The chemical stability of the adsorbent is critical for its capacity for reuse, which is supported by the XRD patterns that show no significant differences before and after the regeneration process. In order to improve adsorption efficiency, the optimization was showed using the Box-Behnken design (BBD).