Abstract
The mixed-ligand strategy was selected as an approach to tailor a metal–organic framework (MOF) with microextraction purposes. The strategy led to the synthesis of up to twelve UiO-66-based MOFs with different amounts of functionalized terephthalate ligands (H-bdc), including nitro (-NO2) and amino (-NH2) groups (NO2-bdc and NH2-bdc, respectively). Increases of 25% in ligands were used in each case, and different pore environments were thus obtained in the resulting crystals. Characterization of MOFs includes powder X-ray diffraction, infrared spectroscopy, and elemental analysis. The obtained MOFs with different degrees and natures of functionalization were tested as sorbents in a dispersive miniaturized solid-phase extraction (D-µSPE) method in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD), to evaluate the influence of mixed functionalization of the MOF on the analytical performance of the entire microextraction method. Eight organic pollutants of different natures were studied, using a concentration level of 5 µg· L−1 to mimic contaminated waters. Target pollutants included carbamazepine, 4-cumylphenol, benzophenone-3, 4-tert-octylphenol, 4-octylphenol, chrysene, indeno(1,2,3-cd)pyrene, and triclosan, as representatives of drugs, phenols, polycyclic aromatic hydrocarbons, and disinfectants. Structurally, they differ in size and some of them present polar groups able to form H-bond interactions, either as donors (-NH2) or acceptors (-NO2), permitting us to evaluate possible interactions between MOF pore functionalities and analytes’ groups. As a result, extraction efficiencies can reach values of up to 60%, despite employing a microextraction approach, with four main trends of behavior being observed, depending on the analyte and the MOF.
Highlights
Metal–organic frameworks (MOFs) are having enormous success as novel sorbent materials in analytical solid-phase extraction (SPE) approaches, when performing in dispersive and miniaturized modes (D-μSPE) [1,2,3,4,5]
Taima-Mancera et al showed the positive effects of incorporating polar functionalities in the organic ligand of the MOFs used in D-μSPE when intending to extract polar analytes of a small size [12], with this idea having been further expanded by Boontongto et al to other application studies for polar analytes [14]
Likewise, infrared spectra were utilized to identify nitro- and amino-functional groups in the MOFs, and the elemental analysis was carried out to evaluate whether the degree of functionalization was correctly introduced in the resulting MOFs
Summary
Metal–organic frameworks (MOFs) are having enormous success as novel sorbent materials in analytical solid-phase extraction (SPE) approaches, when performing in dispersive and miniaturized modes (D-μSPE) [1,2,3,4,5]. MOFs have been studied the most, given their superior chemical and hydrothermal stability, together with their simple (and mild) preparation [23] and green aspects [24] They have appeared as sorbents in a number of recent D-μSPE studies [12,25,26,27]. The incorporation of different contents of -NH2 functionalization into UiO-66 has been proposed, resulting in a thermally-stable superior material, and permitting the porosity to be tuned by varying the ratios of non-functionalized ligand versus -NH2 -functionalized ligand [31] Given these considerations, the current study intends to prepare and characterize UiO-66 derivatives incorporating different contents of non-functionalized and functionalized-organic ligand—including -NH2 and -NO2 groups—in the MOF structure through the mixed-linker approach. The selected analytes present a low to high size (to evaluate their influence when entering or when not entering the MOFs’ pores), while incorporating or not incorporating polar groups in their structures (to evaluate possible interactions between MOF pore functionalities and analytes’ groups)
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