Trifluoromethyl-Functionalized 2D Covalent Organic Framework for High-Resolution Separation of Isomers

Development of novel functional materials for effective isomer separation is of great significance in environmental science, chemical industry, and life science due to the different functions of isomers. However, the similar physicochemical properties of isomers make their separation greatly challenging. Here, we report the fabrication of trifluoromethyl-functionalized 2D covalent organic framework (COF) TpTFMB with 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 1,3,5-triformylphloroglucinol (Tp) for the separation of isomers. TpTFMB was in situ-grown on the inner surface of a capillary for the high-resolution separation of isomers. The introduction of hydroxyl and trifluoromethyl functional groups with uniform distribution in 2D COFs is a powerful tactic to endow TpTFMB with various functions such as hydrogen bonding, dipole interaction, and steric effect. The prepared TpTFMB capillary column enabled the baseline separation of positional isomers such as ethylbenzene and xylene, chlorotoluene, carbon chain isomers such as butylbenzene and ethyl butanoate, and cis-trans isomers 1,3-dichloropropene. The hydrogen-bonding, dipole, and π-π interactions as well as the structure of COF significantly contribute to the isomer separation. This work provides a new strategy for designing functional 2D COFs for the efficient separation of isomers.

Particle Size Regulation of Single-Crystalline Covalent Organic Frameworks for High Performance of Gas Chromatography

Although polycrystalline covalent organic frameworks (PCOFs) have already shown great potential as stationary phases for chromatography, irregular shape and size distribution of PCOFs make regulation of particle size of PCOFs for high separation performance impossible, which is accessible by the application of single-crystalline COFs (SCOFs). Herein, we showed preparation of three-dimensional SCOF (SCOF-303) bonded capillaries (SCOF-303-capillary) with different particle sizes (about 0.4-1.6 μm) and further investigated gas chromatographic separation ability of these SCOF-303-capillaries for isomers of xylene, dichlorobenzene, and pinene. It was found resolution and column efficiency of SCOF-303-capillaries for isomers decreased with the increase in particle size, mainly resulting from the weaker size-exclusion effect and higher mass transfer resistance of the larger particle size of flexible SCOF-303. The obtained SCOF-303-capillary (particle size of ∼0.4 μm) offered baseline separation of xylene isomers with the high resolution of 2.26-3.52, great efficiency of 7879 plates m^-1 for p-xylene, better than PCOF-303-capillary, and commercial DB-5 and HP-FFAP capillary columns as well as many reported capillaries. This work not only shows the great potential of SCOFs for gas chromatography but also provides the theoretical direction for the design of the efficient COF based stationary phase by adjusting the particle sizes.

Hydrogen isotope separation on nickel-containing metal-organic framework@gama-alumina-based multicomponent composite packed column: Identification of individual role of each component

A new optimized multicomponent composite, Na₂Cr₂O₇/Na₂CrO₄/NaCl/MOF-74(Ni)@γ-Al₂O₃ (S₁/S_2/S₃/MOF-74(Ni)@γ-Al₂O₃. Na₂Cr₂O₇ = S₁, Na₂CrO₄ = S₂, NaCl = S₃), was prepared and used as a gas chromatography stationary phase for the separation of H₂ and D₂ isotopes. Under the optimal chromatographic separation conditions, the resolution of the packed column for the separation of H₂/D₂ was 2.87, and the separation time was 7.15 min at 77 K. The control experiments showed that in the multicomponent composite, MOF-74(Ni), which has a chemical affinity quantum sieving effect, played a major role in the separation of H₂/D₂. As the support of MOF-74, γ-Al₂O₃ enhanced the mechanical strength of MOF-74 and reduced the gas resistance. The presence of Na₂CrO₄ in the column increased the H₂/D₂ separation resolution, while the presence of NaCl reduced the separation time, produced more symmetrical and narrow chromatographic peaks of Gaussian distribution. Furthermore, by optimizing the ratio of NaCl and Na₂CrO₄, (S₂/S₃/MOF-74(Ni)@γ-Al₂O₃) composite with a NaCl/Na₂CrO₄ mass ratio of 0.7:1 was synthesized and used to realize the high-resolution separation of H₂/D₂ (R = 2.56) with a short separation time (t = 5.91 min). Both composites also showed excellent repeatability/reproducibility for separation.

Impact of the Preparation Procedure on the Performance of the Microporous HKUST-1 Metal-Organic Framework in the Liquid-Phase Separation of Aromatic Compounds

To date, metal-organic frameworks (MOFs) have been recognized as promising solid phases in high-performance liquid chromatography (HPLC). This research aimed to elucidate the role of the physico-chemical characteristics of the microporous HKUST-1 metal-organic framework in its operation as a selective adsorbent in HPLC. For this, the HKUST-1 samples were prepared by microwave-assisted synthesis and a solvothermal procedure. According to the chromatographic examinations, the HKUST-1 material synthesized in the microwave fields shows an efficient performance in the selective adsorption of aromatic compounds with different functionalities. This study revealed a significant impact of the preparation procedure on the mechanism of the liquid-phase adsorption on the HKUST adsorbents under conditions of the HPLC. An effect of the elution solvent with the different coordination ability to the Cu²⁺ sites in the HKUST-1 structure on the adsorption selectivity was observed.

Heterogenization of manganese porphyrin via hydrogen bond in zeolite imidazolate framework-8 matrix, a host–guest interaction, as catalytic system for olefin epoxidation

A heterogenized meso-tetrakis(2,3-dihydroxyphenyl)porphyrinatomanganese(III) acetate at zeolite imidazolate framework-8 (T(2,3-OHP)PorMn@ZIF-8) is investigated for the catalytic olefin epoxidation reactions at room temperature. Heterogenization is accomplished through a non-classical hydrogen bond proposed between T(2,3-OHP)PorMn bearing O–H groups and C–H of the 2-methylimidazolate linkers in the ZIF-8 structure. The aforementioned compound is characterized by X-ray powder diffraction (XRD), atomic absorption spectroscopy (AAS), nitrogen adsorption−desorption, FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The catalytic system with rather high potential of reusability is proposed as a fairly efficient epoxidation catalyst compared to reports in homogeneous media.

Selective Adsorption and Separation of Xylene Isomers and Benzene/Cyclohexane with Microporous Organic Polymers POP-1

The separation of chemical substances with analogous chemical structures and physical properties remains a great challenge. In this work, triptycene-like microporous organic polymers (MOPs), POP-1, was synthesized via choosing 1,4-dimethoxybenzene (DMB) and triptycene as external cross-linkers and building blocks, respectively, and POP-1 was employed to separate xylene isomers and benzene (Bz)/cyclohexane (Cy). Results show that POP-1 has a higher uptake for m-xylene (0.29 g/g) and Bz (1.02 g/g); more intriguingly, their complete separation can be realized within 0.6 min using a column packed with POP-1. The interaction between POP-1 networks and adsorbates was also investigated using theoretical (density functional theory together with noncovalent interaction analysis) and experimental (inverse gas chromatography) approaches. Especially, both results present a good agreement, that is, weak interactions such as CH/π interactions play a dominant role in defining the separation performance of POP-1 for xylene isomers and Bz/Cy mixtures. Our findings suggest that MOPs may open up a new route for separating the chemicals that are similar in structure and size.

Preparation of a magnetic multiwalled carbon nanotube@polydopamine/zeolitic imidazolate framework-8 composite for magnetic solid-phase extraction of triazole fungicides from environmental water samples

A novel magnetic zinc-based zeolitic imidazolate framework (MMP/ZIF-8) has been prepared using a magnetic multiwalled carbon nanotube@polydopamine nanocomposite as the magnetic core and support. It was then used as an adsorbent for magnetic solid-phase extraction of triazole fungicides from environmental water samples. Successful synthesis of MMP/ZIF-8 was confirmed by material characterization, and the results showed that the synthetic composite has a high Brunauer–Emmett–Teller surface area (141.56 m² g⁻¹), large total pore volume (0.636 mL g⁻¹), and high superparamagnetism with a saturation magnetization of 44.1 emu g⁻¹. To evaluate the extraction performance of MMP/ZIF-8, the main parameters that affect the extraction efficiency were optimized. Under the optimal conditions, the developed method shows good linearity (R² ≥ 0.9915) in the concentration range 1–400 μg L⁻¹. Low limits of detection (0.08–0.27 μg L⁻¹, signal/noise = 3 : 1) and good precision (intraday relative standard deviation ≤ 7.73%, interday relative standard deviation ≤ 9.65%) are also achieved. The developed method was applied for analysis of triazole fungicides in environmental water samples.

A magnetic ZIF-8 composite was prepared based on Fe₃O₄/MWCNT@PDA and used as an adsorbent for MSPE of triazoles from environmental water samples.

Cationic Ionic Liquids Organic Ligands Based Metal-Organic Frameworks for Fabrication of Core-Shell Microspheres for Hydrophilic Interaction Liquid Chromatography

In this study, new metal-organic frameworks (MOFs) nanocrystals modified SiO2 core-shell microspheres were designed with cationic ionic liquids (ILs) 1,3-bis(4-carboxybutyl)imidazolium bromide (ILI) as organic ligands. By further adjustment the growth cycles, the new ILI-01@SiO2 core-shell stationary phase was facilely fabricated. The developed stationary phase was respectively characterized via element analysis, thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry. Because the introduction of cationic imidazolium-based ILs ILI for fabrication of the MOFs nanocrystals shell, the new stationary phase exhibits the retention mechanism of hydrophilic interaction liquid chromatography (HILIC). Many polar samples, such as amides, vitamins, nucleic acid bases, and nucleosides, were utilized to investigate the performance of the prepared ILI-01@SiO2 column. Compared to the conventional aminosilica column, the new ILI-01@SiO2 column displays high separation selectivity in a shorter separation time. Furthermore, the new ILI-01@SiO2 column was also used for detection of illegal melamine addition in the baby formula. All the above results demonstrate the new ILI-01@SiO2 core-shell stationary phase is of good potentials for high-selectivity separation the polar samples.

Novel nanoporous carbon derived from metal–organic frameworks with tunable electromagnetic wave absorption capabilities

Core–shell ZIF-8@ZIF-67 crystals, which integrate the properties of single ZIF-8 and ZIF-67, are elaborately designed for the first time by applying a seed-mediated growth technique.