β-Cyclodextrin modified chitosan and κ-carrageenan composites for acid fuchsin dye removal: mechanism insight and adsorption performance

This study is aimed at developing a highly effective adsorbent by physically crosslinking chitosan (CH), kappa-carrageenan (KCG), and β-cyclodextrin (β-CD) for removing acid fuchsin (AF) dye from water. Various analytical techniques, such as PXRD, FTIR, FE-SEM, and EDS, were utilized to analyze the interactions and morphology of the crosslinked biosorbents. The adsorption performance of CH/KCG and CH/β-CD/KCG biosorbents was assessed under diverse reaction conditions. The adsorption capacity increased with agitation time, reaching equilibrium at 240 min for CH/β-CD/KCG and 300 min for CH/KCG. CH/β-CD/KCG demonstrated the highest adsorption capacity among the two adsorbents studied. The maximum adsorption efficiencies were found to be 9.979 mg/g for CH/KCG and 10.98 mg/g for CH/β-CD/KCG biosorbents under neutral pH and at 30 °C (optimum temperature). Comparing CH/KCG with CH/β-CD/KCG, a notable increase of approximately 13.6% in AF adsorption was observed. Kinetics revealed a pseudo-second-order mechanism, and isotherm models suggested monolayer adsorption following Langmuir isotherm. Thermodynamic analysis indicated a low temperature, spontaneous, and exothermic adsorption process. The activation energy values were calculated as 47.515 and 18.269 kJ/mol for CH/β-CD/KCG and CH/KCG, respectively, indicating physical interactions as the driving force for adsorption. Acid fuchsin adsorption was primarily attributed to physical interactions and hydrogen bonding, facilitated by polymer and inclusion formation mediated by β-CD through host–guest interactions. Furthermore, the biosorbents showed remarkable reusability after three cycles of adsorption and desorption, indicating their promising potential as natural biosorbents for the removal of cationic dyes.