Nanoscale zeolitic imidazolate framework-8 as a selective adsorbent for theophylline over caffeine and diprophylline

Abstract

In this work, we firstly explored zeolitic imidazolate framework-8 (ZIF-8) as a novel adsorbent for selective adsorption of theophylline (TPE) over its structure-related analogs involving caffeine (CFE) and diprophylline (DPE) in aqueous solution in view of sole and mixed adsorption, desorption, and solid phase extraction. The adsorption kinetics of TPE on ZIF-8 obeyed pseudo-second-order kinetics. Analysis of the intraparticle diffusion plots revealed that more than one process affected the adsorption, and film (boundary layer) diffusion controlled the adsorption rate at the beginning. The adsorption isotherms of TPE on ZIF-8 followed the Freundlich model, and enthalpy rather than entropy controlled its adsorption. Evidence from FT-IR and X-ray photoelectron spectroscopic data showed that the adsorption of TPE was also driven by coordination of unsaturated zinc species in ZIF-8 with the carbonyl groups in TPE besides π–π interaction and molecular size. All these interactions made the ZIF-8 a promising candidate for the selective adsorption and extraction of structure-related analogs.