Magnetizing Calixarene: Azo Dye Removal from Aqueous Media by Fe3O4 Nanoparticles Fabricated with Carboxylic-Substituted Calix[4]arene

Calix[4]arene was reacted with isonipecotic acid to synthesize the Mannich base derivative, and Fe3O4 magnetic nanoparticles were bonded to the lower rim of the calix[4]arene derivative through ether linkage to obtain carboxylic calix[4]arene magnetic nanoparticles (CCMN). After characterization with transmission electron microscopy and Fourier transform infrared spectroscopy, adsorption studies were carried out for the removal of azo dyes (Evans Blue and Chicago Sky Blue 6 B). Adsorption parameters such as effects of pH, dosage, concentration, temperature, and time were optimized. Results showed that adsorption equilibrium was achieved within 15 min, and maximum % adsorption was calculated as 95% for both dyes at pH 2.5. An equilibrium isotherm study suggests that the adsorption mechanism follows a chemical ion exchange process with an adsorption capacity value of 13.9 and 17.5 mmol g–1 for Evans Blue and Chicago Sky Blue 6 B, respectively. The adsorption kinetic follows pseudo-second-order kinetics as anticipated from R2 values, whereas thermodynamic parameters suggest an endothermic reaction that can also be evident from ΔG° values, which decreased with an increase in temperature suggesting a spontaneous reaction. In addition, the dye removal efficiency of CCMN was hardly effected after 10 consecutive cycles. The study suggests that the magnetically retrievable calix[4]arene is a promising adsorbent for removal of azo dyes from aqueous solution.