Smart nanocomposite of carbon quantum dots in double hydrogel (carboxymethyl cellulose/chitosan) for effectively adsorb and remove diquat herbicide: Characterization, thermodynamics, isotherms, kinetics, and optimizing through Box-Behnken Design.

This research synthesized carbon quantum dots (CQDs) encapsulated in a chitosan (CS) and carboxymethyl cellulose (CMC) matrix. The crosslinking with epichlorohydrin formed (CQDs-CS/CMC) hydrogel beads for effective removal of diquat (DQ) herbicides. Various techniques like XRD, FT-IR, FESEM, EDX, XPS, and nitrogen adsorption/desorption isotherm analysis were used to evaluate the textural properties. The textural properties of the CQDs-CS/CMC were investigated through nitrogen adsorption/desorption isotherms. The surface area was found to be 95.72 m/g, pore size 6.57 nm, and pore volume 0.313 cc/g. Post-DQ adsorption, these values decreased to 68.44 m/g, 4.2 nm, and 0.162 cc/g, indicating DQ blocked mesopores and adsorption sites. The study also examined the effects of dosage, pH, temperature, and initial DQ concentration on adsorption, employing equilibrium and kinetic studies. The system conformed to pseudo-second-order kinetics and Langmuir isotherm models. Chemisorption was the main adsorption process, with an energy of 32.3 kJ/mol. Increased metal uptake at higher temperatures shows the process is spontaneous and endothermic. The Box-Behnken Design software identified optimal adsorption parameters: a pH of 8 and a dosage of 0.02 g of CQDs-CS/CMC per 25 mL of DQ solution, achieving 449.6 mg/g adsorption capability. Extensive testing using Design-Expert software substantially improved the adsorption procedure. The assessment of adsorbent stability involved six cycles of adsorption/desorption. Results showed consistent reusability with no significant reduction in removal efficacy. It maintained its initial chemical configuration before and after repurposing, exhibited consistent performance, and reliable XRD results.