Carboxylic acid calix[4]arene grafted on magnetic chitosan as a novel and reusable bio-based nanosorbent for efficient dyes removal from aqueous solutions

A novel nanocomposite was prepared by functionalizing magnetic chitosan (MCS) with a carboxylic acid calix[4]arene derivative (CACA) for the removal of Eriochrome-Blue-Black-R (ECBBR) and Naphthol Green B (NG) dyes from aqueous solutions. The successful synthesis of the nanocomposite was confirmed by FT-IR (identification of functional groups), FE-SEM and PXRD (particle size and morphological/structural changes), TGA (increase in weight loss indicating successful modification), VSM (preservation of magnetic properties), and BET analysis (confirmation of the mesoporous structure), collectively demonstrating the formation of the CACA@MCS nanosorbent. Comparing to its constituent parts, the CACA@MCS nanocomposite exhibited superior removal efficiency (>94% and >91% for ECBBR and NG, respectively). The adsorption studies showed the dye removal using CACA@MCS followed the Langmuir isotherm and pseudo -second-order kinetic model. Positive ΔH values (+2.036 kJ mol -1 for ECBBR and +3.807 kJ mol -1 for NG) were found in thermodynamic studies, suggesting that both dyes' sorption processes are endothermic ( ΔG < 0). The non-covalent interactions, such as hydrogen bonding, π-π stacking, and electrostatic interactions, resulted in high maximum adsorption capacity (Q m ) values for dyes removal (1381 mg g -1 / 3.07 mmol g -1 for EBBR and 913 mg g -1 / 2.13 mmol g -1 for NG) as well as selective dye removal even in complicated environments containing competing dyes. The reusability study showed that the removal efficiency of CACA@MCS was not affected even after 8 consecutive cycles (<10% and <15% for ECBBR and NG, respectively). The results show that CACA@MCS is a promising nanomaterial for dye removal from the polluted solutions.