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 Fe 3 O 4 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 R 2 values, whereas thermodynamic parameters suggest an endothermic reaction that can also be evident from Δ G ° 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.