Nanoscale Hierarchically Micro- and Mesoporous Metal–Organic Frameworks for High-Resolution and High-Efficiency Capillary Electrochromatographic Separation

Abstract

Metal−organic frameworks (MOFs) have been widely applied in a variety of fields. However, most of the developed MOFs are micrometer scale in crystal size and contain only micropores, which will limit the mass transport and diffusion of various analytes into their internal interaction sites, severely restricting the potential of MOFs in separation science. Herein, nanoscale hierarchically porous MOFs (NHP-MOFs) were first explored as a novel MOF-based stationary phase with excellent mass transfer performance and abundant accessible interaction sites for high-performance chromatographic separation. As a proofof-concept demonstration, the nanoscale hierarchically micro-and mesoporous UiO-66 (NHP-UiO-66) was firmly immobilized on the capillary inner surface and utilized as the porous stationary phase for high-resolution and high-efficiency electrochromatographic separation. A wide range of low-, medium-, and highmolecular-weight analytes, including substituted benzenes, chlorobenzenes, polycyclic aromatic hydrocarbons, nucleosides, polypeptides, and proteins were all separated well on a NHP-UiO-66-coated column with excellent resolution and repeatability, exhibiting significantly improved column efficiency and separation ability compared to those of a microporous UiO-66-modified column. The maximum column efficiencies for all the six kinds of analytes reached up to 1.2 × 10 5 plates/m, and the relative standard deviations of the migration times of substituted benzenes for intraday, interday, and column-to-column were all lower than 5.8%. These results reveal that NHP-MOFs can effectively combine the advantages of the high specific surface area of microporous MOFs and the excellent mass transfer performance and abundant accessible interaction sites of NHP materials, possessing great prospect for high-performance chromatographic separation.

High-Efficiency and Versatile Approach To Fabricate Diverse Metal–Organic Framework Coatings on a Support Surface as Stationary Phases for Electrochromatographic Separation

“…As shown in Figure and Figure S12, baseline separation of the five types of analytes with high column efficiency, including neutral, acidic, and alkaline compounds, could be easily achieved on all the three MOF-modified columns under their respective optimal conditions. Interestingly, in our previous study, the UiO-66-modified capillary fabricated using the postmodified strategy showed relatively low column efficiency for the separation of two types of aromatic compounds. The distinct difference in the separation effects of the two methods indicated that the preparation method of the MOF coating inside the capillary has a significant impact on the coating quality and electrochromatographic separation performance.…”

“…Therefore, the excellent separation performance and column capacity of Cys-MIL-100­(Fe)@capillary were mainly because of the high porosity and unique pore structure of MIL-100­(Fe). More specifically, compared with the other three MOF-modified columns, the larger pore size of MIL-100­(Fe), which contains mesoporous cages (25–29 Å) and microporous windows (5.5–8.6 Å) simultaneously, contributes to reducing the mass transfer resistance of various analytes entering and leaving its internal cavities, thus greatly improving the electrochromatographic separation performance . In contrast, even though Cys-HKUST-1@capillary had the highest BET surface area, its normalized column capacity was the lowest among all the four capillaries, which might be due to the smallest cavity diameter of HKUST-1.…”

Metal–Organic Frameworks-Based Immobilized Enzyme Microreactors Integrated with Capillary Electrochromatography for High-Efficiency Enzyme Assay

“…At the beginning, the uncoated new capillary columns (33 cm total length) were pretreated using the same processes as our previous study. 23 Subsequently, the prepared columns were premodified with Cys and further utilized for the in situ growth of UiO-66-NH 2 nanocrystals via the ICISG strategy. 22 Briefly, ZrCl 4 (8 mg, 0.0343 mmol) and BDC-NH 2 (6.2 mg, 0.0343 mmol) were codissolved in DMF (2 mL) at room temperature to prepare the precursor solution.…”

“…The fabrication process of UiO-66-NH 2 –IMER is illustrated in Figure . At the beginning, the uncoated new capillary columns (33 cm total length) were pretreated using the same processes as our previous study . Subsequently, the prepared columns were premodified with Cys and further utilized for the in situ growth of UiO-66-NH 2 nanocrystals via the ICISG strategy .…”

Recent trends on the implementation of reticular materials in column‐centered separations

“…Alternatively, smaller voids can be introduced in the MOF crystal network by adding a modulator in the MOF synthesis [ 42 ]. This approach has been explored adding dodecanoic acid in the synthesis of the MOF UiO‐66 (Figure 3a ) [ 43 ]. The resulting nanoscale hierarchically micro‐ and mesoporous MOF (NHP‐UiO‐66) was immobilized on the capillary inner surface and applied as stationary phase for capillary electrochromatography for substituted benzenes obtaining column efficiencies of up to 1.2 × 10 5 plates/m with migration time RSDs lower than 5.8% for intraday, interday, and column‐to‐column comparisons.…”