Development and characterization of Rh-MOF encapsulated on double layer hydrogel of carboxymethyl cellulose/chitosan for enhanced and reusable adsorptive removal of brilliant green dye: Kinetics, isotherms, thermodynamic evaluation and process of optimization via Box-Behnken Design.

Abstract

This research investigates the creation and optimization of a dual-layer hydrogel composite formed from carboxymethyl cellulose (CMC) and chitosan (CS), which incorporates a rhodium-based metal-organic framework (Rh-MOF). The composite is designed to facilitate the efficient elimination of the cationic dye Brilliant Green (BG) from solutions. The structural stability of the Rh-MOF/CMC-CS hydrogel beads was significantly improved over the use of epichlorohydrin cross-linking. This modification played a vital character in attractive the mechanical strength of the hydrogel, thereby facilitating its ability to efficiently withstand numerous sequences of adsorption and desorption. The composite underwent extensive characterization through a range of analytical methods, such as XRD, FT-IR, XPS, EDX, nitrogen adsorption-desorption isotherms, and FESEM. This comprehensive approach facilitated a detailed examination of the composite's physical and chemical properties, alongside its morphological characteristics. A sequence of methodical batch adsorption experimentations was directed to analyze the influence of several operational factors on performance. These factors include pH level, dosage of the adsorbent, period of contact, initial concentration of dye, and temperature. Kinetic analyses revealed that the adsorption processes were consistent with a pseudo-second-order model. Furthermore, the equilibrium data aligned most closely with the isotherm of Langmuir, suggesting that chemisorption takes place in a monolayer arrangement. Furthermore, the thermodynamic evaluation provided parameters (ΔH° = +77.67 kJ/mol and ΔS° = +268.5 J/mol.K) indicating that the adsorption mechanism is both endothermic as well as spontaneous in nature. The enhancement of the process was achieved by using a Box-Behnken design in combination with response surface methodology (RSM). This approach successfully determined the ideal parameters for adsorption, specifically under conditions of pH 8, a dosage of 0.02 g per 25 mL, resulting in an impressive maximum adsorption capacity of 529.2 mg/g. Evaluations of the hydrogel's reusability across six adsorption and desorption processes showed its high capacity for regeneration and stable structure. These results demonstrate that Rh-MOF/CMC-CS hydrogel beads have the potential to be a practical and effective treatment of wastewater solution.