Adsorptive performance of fly ash-derived zeolite modified by β-cyclodextrin for ibuprofen, bisphenol A and caffeine removal from aqueous solutions – equilibrium and kinetic study

Abstract

In this paper synthetic zeolite of NaX structure type was modified with β-cyclodextrin (CD) in order to enhance the adsorption of ibuprofen (IBU), bisphenol A (BPA) and caffeine (CFN) from aqueous solutions. CHN elemental analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal analysis (TG/DTA), infrared Fourier spectroscopy (FT-IR) and N2 adsorption isotherm were done to obtain surface characteristic of the hybrid material. The batch adsorption tests were performed to study adsorbent-adsorbate interaction at molecular level. IBU, BPA and CFN adsorption kinetics on NaX-CD followed the pseudo-second order model indicating the mechanism of electron sharing/exchange. IBU and BPA adsorption was best fitted to the Langmuir isotherm, suggesting monolayer adsorption and the formation of host–guest complexes with hydrogen bond formation. For CFN the best adjustment was achieved for Temkin model and the adsorption mechanism was mainly attributed to the π-π interactions. The maximum adsorption capacities were 31.3, 32.7 and 11.8 mg/g for IBU, BPA and CFN, respectively. The adsorption behaviour of NaX-CD indicates that it can constitute an efficient adsorbent for the removal of organic micropollutants from aqueous media.