Glutaraldehyde and terephthaldehyde-crosslinked chitosan for cationic and anionic dyes removal from aqueous solutions: Experimental, DFT, kinetic and thermodynamic studies

Novel chitosan polymers were synthesized using two cross-linkers, Glutaraldehyde and Terephthaldehyde, to enhance stability and efficiency. Characterization techniques (XRD, FTIR, FE -SEM, TGA, DTG, BJH, and BET) confirmed successful synthesis. These polymers were employed as adsorbents for removing Malachite Green (MG) and Congo Red (CR) dyes from water. Batch experiments and DFT calculations investigated the adsorption process, thermodynamics, and kinetics. Results showed the CSGT-III polymer achieved the highest removal efficiency. For initial dye concentrations ([CR]o = 50 mg/L, [MG]o = 20 mg/L) and adsorbent doses (0.8 g/L for CR, 0.4 g/L for MG), removal efficiencies were 96.99 % for CR and 99.07 % for MG. Thermodynamic analysis confirmed the spontaneous nature of adsorption, and the process was endothermic for both dyes. The Langmuir model fitted adsorption isotherms well, indicating a homogeneous surface. Kinetic analysis revealed a pseudosecond-order model for both dyes.