Ultra-High Adsorption Capacity of Core–Shell-Derived Magnetic Zeolite Imidazolate Framework-67 as Adsorbent for Selective Extraction of Theophylline

Abstract

A core–shell-derived structural magnetic zeolite imidazolate framework-67 (Fe3O4-COOH@ZIF-67) nanocomposite was fabricated through a single-step coating of zeolite imidazolate framework-67 on glutaric anhydride-functionalized Fe3O4 nanosphere for the magnetic solid-phase extraction (MSPE) of theophylline (TP). The Fe3O4-COOH@ZIF-67 nanocomposite was characterized through scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, Fourier transform infrared spectroscopy, Zeta potential analysis, X-ray diffraction, Brunauer–Emmett–Teller, and vibrating sample magnetometer. The material has a high specific surface area and good magnetism, which maintains the regular dodecahedron structure of ZIF-67 without being destroyed by the addition of Fe3O4-COOH nanospheres. The Fe3O4-COOH@ZIF-67 can rapidly adsorb TP mainly through the strong coordination interaction between undercoordinated Co2+ on ZIF-67 and –NH from imidazole of TP. The adsorption and desorption conditions, such as the amount of adsorbent, adsorption time, pH value, and elution solvent, were optimized. The kinetics of TP adsorption on Fe3O4-COOH@ZIF-67 was found to follow pseudo-second-order kinetics. The Langmuir model fits the adsorption data well and the maximum adsorption capacity is 1764 mg/g. Finally, the developed MSPE-HPLC method was applied in the enrichment and analysis of TP in four tea samples and rabbit plasma. TP was not detected in oolong tea and rabbit plasma, and its contents in jasmine tea, black tea, and green tea are 5.80, 4.31, and 1.53 μg/g, respectively. The recoveries of spiked samples are between 74.41% and 86.07% with RSD in the range of 0.81–3.83%. The adsorption performance of Fe3O4-COOH@ZIF-67 nanocomposite was nearly unchanged after being stored at room temperature for at least 80 days and two consecutive adsorption–desorption cycles. The results demonstrate that Fe3O4-COOH@ZIF-67 nanocomposite is a promising magnetic adsorbent for the preconcentration of TP in complex samples.

Applications of magnetic solid‐phase extraction in the sample preparation of natural product analysis (2020–2023)

“…ZIF‐67 is one of the most representative ZIFs, which has served as the SPE adsorbent to enrich different small‐molecule compounds, including antibiotics [27], insecticides [28], and dyes [29], on account of its extraordinary chemical and thermal stability in water, weakly acidic or alkaline solutions. In our previous study, through a single‐step coating method, a core‐shell‐derived structural magnetic ZIF‐67 (Fe 3 O 4 ‐COOH@ZIF‐67) nanocomposite was synthesized for the MSPE of theophylline (TP) [30]. After the characterization of MNPs and the optimization of adsorption and elution process conditions, the adsorption kinetics of TP on Fe 3 O 4 ‐COOH@ZIF‐67 were found to follow pseudo‐second‐order kinetics.…”

“…The recoveries in the real rabbit plasma sample are between 74.41% and 86.07% with a relative standard deviation (RSD, n = 3) from 0.81 to 3.83%. The interaction mechanisms (Figure 3 [30]), such as coordination interaction, π‐stacking, hydrogen bond interaction, and molecular‐sieving effect, may play crucial parts in the adsorption of TP by Fe 3 O 4 ‐COOH@ZIF‐67. However, the prepared sorbent does not have a relatively high recovery and reusability.…”

“…The adsorption of canthin-6-one alkaloids F I G U R E 3 Possible interactions between Fe 3 O 4 -COOH@ZIF-67 and TP, including coordination interaction, hydrogen bond interaction, π-stacking interaction, molecular-sieving effect, and electrostatic interaction. Reprint with permission [30].…”

Magnetic materials as adsorbents for the pre‐concentration and separation of active ingredients from herbal medicine

“…Chen et al. [72] have successfully synthesized a novel core‐shell structured magnetic Fe 3 O 4 ‐COOH@ZIF‐67 nanocomposite through a one‐step coating process, where ZIF‐67 is coated on glutaric anhydride‐functionalized Fe 3 O 4 nanospheres initially prepared via solvothermal method. The surface modification of Fe 3 O 4 nanoparticles with glutaric anhydride facilitated the introduction of carboxyl groups to coordinate with Co 2+ of ZIF‐67, serving as core‐shell linkers between Fe 3 O 4 and ZIF‐67.…”