Structure-controlled Interpenetrated MOF@COF via C-C Linkage for Enhanced Photocatalysis.

Diversifying the connecting junctions will be feasible for the controllable collaboration of metal organic frameworks (MOFs) and covalent organic frameworks (COFs) to rationally design multifunction-integrated heterostructures with enhanced performance, yet it is in the nascent stage. Herein, by intelligently exploiting the polymerization of vinyl group, C-C bond is innovatively introduced to construct the core-shell MOF@COF heterostructures with adjustable shell thickness and rare interpenetrated structure. The unique structure endows prepared C-C-linked MIL-68@COF-Vs with more superior visible-light harvesting and photogenerated carrier separation capability, leading to significantly higher photocatalytic activity and faster degradation rate than pristine MIL-68-C=Cs, COF-V, and imine-linked MIL-68-NH2@COF-V. Further, the customized MIL-68@COF-V is in-situ grown as reusable films with significantly boosted performance under ambient condition, which realize the highly efficient degradation of tetracycline within 15 min (96.5%), rhodamine 6G within 25 min (97.6%), and phenol within 40 min (95.3%) by solar drive. This work exhibits the distinctive advantages of C-C junction in the MOF@COF construction, and highlights the application prospect of rational-designed heterostructure in the treatment of persistent organic pollutants.

[Research progress of stationary phase of gas chromatography based on chiral organic frameworks].

Enantiomers typically show different pharmacological, toxicological, and physiological properties. Thus, the preparation of enantiopure compounds is of great significance for human health and sustainable development. Compared with asymmetric catalysis, enantiomeric separation is simpler, faster, and more efficient; as such, it has become the preferred method for obtaining pure enantiomers. At present, enantiomeric separation methods mainly include chromatography, nanochannel membrane separation, selective adsorption, and recrystallization. In particular, gas chromatography (GC) plays an important role in enantioseparation because of its high sensitivity, excellent reproducibility, and outstanding processing capacity for various enantiomers. The stationary phase is key to the separation efficiency of GC, and more efficient, stable, and cost-effective materials that could serve as stationary phases are constantly being explored. Organic frameworks, such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs), porous organic cages (POCs), metal-organic cages (MOCs), and hydrogen-bonded organic frameworks (HOFs), possess large specific surface areas, high porosities, tunable pore sizes, and easy functionalization, rendering them promising candidates for the separation of mixed analytes. Research has shown that the use of organic frameworks as stationary phases for GC results in excellent column efficiency and high resolution for various analytes, including n-alkanes, n-alcohols, polycyclic aromatic hydrocarbons, positional isomers, and organic fluorides. Furthermore, organic frameworks can be prepared as chiral stationary phases for GC by the intelligent introduction of a chiral moiety, thereby enabling the efficient separation of enantiomers. Synthetic strategies for chiral organic frameworks are primarily categorized as post-synthesis or bottom-up approaches. In general, the post-synthesis strategy can introduce various chiral sites to the framework; however, the distribution of chiral sites may not be uniform, and the ordered framework may be destroyed during the post-synthesis process. The bottom-up strategy allows for the uniform and precise distribution of chiral sites in the framework, but the synthesis of chiral monomers and the constraint between asymmetry and crystallinity limit its development. Chiral induction has been proposed as an alternative strategy for synthesizing chiral organic frameworks. The use of this strategy has led to the successful preparation of organic frameworks with abundant chiral sites and excellent crystallinity. Dynamic coating and in situ growth are the main approaches used to transform the as-prepared chiral organic frameworks into stationary phases. Notably, the in situ growth approach can yield chiral COF/MOF-coated capillary columns that provide high resolution for the separation of enantiomers with excellent repeatability and reproducibility. Nevertheless, owing to the slightly complex pretreatment process and the difficulty of synthesizing chiral organic frameworks, the in situ growth approach has not yet been widely applied. Owing to their excellent solvent processing performance, POCs, MOCs, and HOFs can be easily coated on the inner walls of columns to form membranes via dynamic or static coating. A series of enantiomers have been successfully separated and analyzed by immobilizing chiral COFs, MOFs, POCs, MOCs, and HOFs on GC capillary columns, demonstrating the great potential of chiral organic frameworks for enantiomeric separation. In general, the mechanisms by which chiral organic frameworks recognize enantiomers could be mainly categorized as van der Waals interactions, hydrogen bonding, π-π interactions, and size-exclusion effects. While molecular simulations can offer some insights into these recognition mechanisms, clarifying these mechanisms based on effective characterization remains challenging. In summary, organic frameworks show outstanding advantages for enantiomer separation. Given breakthroughs in synthetic strategies for chiral organic frameworks and the in-depth study of chiral recognition mechanisms, chiral organic frameworks may be expected to become an important aspect in the field of chiral materials, further realizing the large-scale analysis and production of chiral analytes. A total of 64 references, most of which are from the American Chemical Society, Springer Nature, Wiley Online Library, and Elsevier databases, are cited in this review.

Nanoscale-controlled organicinorganic hybrid spheres for comprehensive enrichment of ultratrace chlorobenzenes in marine and fresh water.

The size of the adsorbent has the potential to influence extraction performance, but the size effect at the nanoscale is still poorly understood. In this study, organic-inorganic hybrid nanospheres (OIHNs) with controllable nanoscale sizes of 30, 50, and 100 nm were successfully prepared. These materials were further fabricated as solid phase microextraction (SPME) coatings with similar thicknesses, and coupled with gas chromatography-mass spectrometry (GC-MS) to investigate their extraction performance. The results showed that the extraction capacities of OIHNs for chlorobenzenes (CBs) and polycyclic aromatic hydrocarbons (PAHs) were much better than those of their corresponding derived carbon materials, despite the smaller specific surface areas and lower porosities of them. In addition, the enrichment performance increased significantly with decreasing particle size, and the OIHN-30 coating demonstrated the best performance, with enrichment factors ranging from 1098 to 6853 for CBs. Finally, a highly sensitive and practical analytical method was established with a wide linear range of 0.5-5000 ng·L-1, and the limits of quantification (LOQs) were 0.43-1.7 ng·L-1. The determinations of ultratrace CBs in five marine water samples and five fresh water samples were realized successfully. This study is expected to contribute to a deep understanding of the environmental effects of nanoparticles and the design of high-performance adsorbents.

Nitrogen-rich covalent organic framework as a practical coating for effective determinations of polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) are high-profile organic pollutants to be poisonous, carcinogenic, and mutagenic, and widely distributed at trace levels in the environment. In order to effectively enrich PAHs, two stable covalent organic frameworks (COFs, TAPT-OMe-PDA and TPB-DMTP) were prepared by combining 2,4,6-tri(4-aminophenyl)-1,3,5-triazine (TAPT) and 1,3,5-tri(4-aminophenyl) benzene (TAPB) with 2,5-dimethoxy-phenyl-1,4-diformaldehyde (OMe-PDA), respectively. Even though the surface area of TAPT-OMe-PDA was much lower than that of TPB-DMTP, it still demonstrated much better extraction efficiencies towards PAHs as the solid phase microextraction (SPME) coating. Therefore, the TAPT-OMe-PDA coated fiber was coupled with gas chromatography-mass spectrometry (GC-MS) to establish a practical and sensitive method, after the extraction parameters (extraction time, extraction temperature, desorption temperature, desorption time, salt concentration and pH) were optimized. This developed analytical method showed wide linear ranges, low limits of detection, good repeatability and reproducibility. Finally, five PAHs in three water samples were detected and quantified precisely (2.72-38.7 ng·L-1) with satisfactory recoveries (88.3%-118%).

Customized oxygen-rich biochar with ultrahigh microporosity for ideal solid phase microextraction of substituted benzenes.

The synergistic effect of high microporosity and abundant heteroatoms is important for improving the performance of biochar in various fields. However, it is still challenging to create enough micropores for biochar, while simultaneously retaining the heteroatoms from biomass. A series of biochar with variable microstructures was successfully prepared by carbonization and following ball milling on lotus pedicel (LP), watermelon rind (WR), and litchi rind (LR). The pore structures and heteroatoms of biochar were characterized in detail. Notably, high microporosity could be realized by the carbonization of LR, and further ball milling resulted in a higher microporous surface area (1323.4 m2·g-1) and richer oxygen. Furthermore, the obtained biochar was fabricated as solid phase microextraction (SPME) coatings with uniform morphologies and similar thicknesses to deeply investigate the relationships between the microstructures and extraction performance. The best performance was demonstrated by the LR800BM, with enrichment factors from 1780 to 155,217. Finally, it was coupled with gas chromatography-mass spectrometry (GC-MS) to develop an analytical method with a wide linear range (1-50,000 ng·L-1), low limits of detection (0.10-1.4 ng·L-1), good repeatability (0.83 %-7.5 %) and reproducibility (4.2 %-8.9 %). This work provides valuable insights into the structure-performance relationship of biochar, which is important for the design of high-performance biochar-based adsorbents and their applications in the environment.

Modulating covalent organic frameworks with accessible carboxyl to boost superior extraction of polar nitrobenzene compounds from matrix-complicated beverages.

The wide use and high polarity of nitrobenzene compounds (NBCs) have caused a concern for their residues in daily beverages. Herein, the covalent organic frameworks (COFs) with abundant carboxyl were ingeniously designed by introducing a novel modulator, and further developed as solid phase microextraction (SPME) coatings. Due to the enhanced polar interaction, the extraction efficiencies of modified COF for NBCs were sharply increased. After coupling the high-performance SPME fiber with gas chromatograph-mass spectrometry (GC-MS), an ultrasensitive analytical method was developed, with a wide linear range (0.50-5000 ng/L), and low limits of detection (0.15-3.0 ng/L). More importantly, the method was highly feasible and practical, leading to the precise determinations of trace NBCs from variously matrix-complicated samples. This work provides a viable and efficacious approach for the extraction and analysis of polar pollutants form complicated matrices, and is of great significance for mild COF modification and its extended applications in analytical chemistry.

Melamine-participant hydrogen-bonded organic frameworks with strong hydrogen bonds and hierarchical micropores driving extraction of nitroaromatic compounds.

Enrichment and detection of trace pollutants in the real matrix are essential for evaluating water quality. In this study, benefiting from the good affinities of 1,3,6,8-tetra(4-carboxylphenyl)pyrene) (H4TBAPy) with itself and melamine (MA) respectively, the composite hydrogen-bonded organic frameworks (HOFs, MA/PFC-1), PFC-1 self-assembled by 1,3,6,8-tetra(4-carboxylphenyl)pyrene), were successfully constructed by the mild strategy of solvent evaporation at room temperature. Through a series of characterizations, such as Fourier transform infrared spectra, X-ray diffraction, thermal gravimetric analyses, and N2 adsorption-desorption, etc., the MA/PFC-1 was confirmed to be a stable and excellent material. In addition, it possessed high surface area, hierarchical micropores, strong hydrogen bonds, and rich function groups containing N and O heteroatoms, since the newly introduced MA could be another hydrogen bonding motif, as well as increased the polarity of reaction solvent. These advantages make MA/PFC-1 be an ideal coating material for solid phase microextraction (SPME). Satisfactory enrichment factors for nitroaromatic compounds (NACs) were got by the MA/PFC-1 fiber under the optimized conditions obtained by the control variables (extraction time of 60 min, extraction temperature of 80 °C, desorption time of 6 min, desorption temperature of 260 °C, pH value of 7, and stirring speed of 250 rpm). MA/PFC-1 was further used to develop an analytical method for NACs based on head-space SPME coupled with gas chromatography‒mass spectrometry (GC‒MS). The developed method with low limits of detection (4.30-20.83 ng L-1) and good reproducibility (relative standard deviations <8.6%). The excellent performance allowed the successful application of the developed method in the determinations of trace NACs in real water samples with recoveries of 80.1%-119%. This study proposed a mild approach to synthesize composite HOFs via doping MA and developed an environmentally friendly method for the precise determinations of NACs in the environment.

A robust and ultra-high-surface hydrogen-bonded organic framework promoting high-efficiency solid phase microextraction of multiple persistent organic pollutants from beverage and tea.

Persistent organic pollutants (POPs) are widely distributed in the environment and are toxic, even at low concentrations. In this study, we first used hydrogen-bonded organic framework (HOF) to enrich POPs, based on solid phase microextraction (SPME). The HOF called PFC-1 (self-assembled by 1,3,6,8-tetra(4-carboxylphenyl)pyrene) has an ultra-high specific surface area, excellent thermochemical stability, and abundant functional groups, making it potential to be an excellent coating in SPME. And the as-prepared PFC-1 fiber have demonstrated outstanding enrichment abilities for nitroaromatic compounds (NACs) and POPs. Furthermore, the PFC-1 fiber was coupled with gas chromatography-mass spectrometry (GC-MS) to develop an ultrasensitive and practical analytical method with wide linearity (0.2-200 ng·L-1), low detection limits for organochlorine pesticides (OCPs) (0.070-0.082 ng·L-1) and polychlorinated biphenyls (PCBs) (0.030-0.084 ng·L-1), good repeatability (6.7-9.9%), and satisfactory reproducibility (4.1-8.2%). Trace concentrations of OCPs and PCBs in drinking water, tea beverage, and tea were also determined precisely with the proposed analytical method.

[Research progress on the application of derived porous carbon materials in solid-phase microextraction].

The concentrations of target analytes in samples are low, and complex matrices can lead to a variety of interferences. Therefore, it is important to pretreat the samples before analysis. Compared to the time-consuming, tedious, and environmentally unfriendly solvent-based sample pretreatment methods, pretreatment techniques based on adsorption have more promising applications. Adsorption-based pretreatment technologies include solid-phase extraction, dispersive solid-phase extraction, magnetic solid-phase extraction, and solid-phase microextraction. Among them, solid-phase microextraction integrates sampling, extraction, enrichment, and injection into a single step. It has the advantages of being solvent-free, highly efficient, time efficient, and labor efficient. The extraction efficiency of solid-phase microextraction is closely related to the coating materials. There are various types of coating materials, including metal-organic frameworks, covalent organic frameworks, molecular imprinted polymers, porous carbon materials and so on. Porous carbon materials include traditional porous carbon materials such as activated carbon, carbon nanotubes, carbon molecular sieves, and derived porous carbon materials. Given their advantages of large specific surface area, controllable porous structure, large number of active sites, as well as good physical and chemical stability, porous carbon materials have been widely used in batteries, supercapacitors, catalysis, adsorption, and separation. Porous carbon materials are also popular coating materials for solid-phase microextraction. In particular, derived porous carbon materials find widespread use given their variety and designability. Most of these materials are derived from biomass and metal-organic framework precursors. In addition, past studies have mainly focused on the structural optimization of derived porous carbon materials. However, the applications of derived porous carbon materials in solid-phase microextraction are restricted by the following problems. (1) The preparation of porous carbon materials derived from covalent organic frameworks has seen great progress. However, there are only a few studies on their applications in solid-phase microextraction. (2) The prepared-derived porous carbon materials have excellent extraction abilities as when applied to solid-phase microextraction coatings. However, there is less systematic and clear mechanism to explain it. (3) Most derived porous carbon materials when used as solid-phase microextraction coatings show nice extraction performance only for specific analytes such as polar or non-polar substances. Therefore, in this paper, the research progress of derived porous carbon materials in solid-phase microextraction over the past three years has been summarized, and future research prospects have been prospected. Covalent organic frameworks can be used as precursors to prepare derived porous carbon materials with a narrow pore size distribution and a large specific surface area. It is necessary to further develop porous carbon materials derived from covalent organic frameworks as solid-phase microextraction coatings. The specific mechanism underlying this extraction effect should also be clarified. In addition, it is necessary to develop high-performance derived porous coating materials for broad-spectrum and high-sensitivity analysis of pollutants with different physical and chemical properties. Therefore, hierarchical porous carbon materials should be widely studied in solid-phase microextraction because of their multimodal pore sizes. A total of 56 references are cited in this paper, most of which are from the Elsevier database.

High-surface ß-Ketoenamine linked covalent organic framework driving broad-spectrum solid phase microextraction on multi-polar aromatic esters.

Aromatic esters have been widely used in daily life with non-ignorable dangers, such as plasticizer, flavor, and preservative. Their wide applications and corresponding hazards caused by overuse have promoted the rapid development of sensitively analytical method for effective regulation. However, the variety makes it challenging for broad-spectrum and simultaneous extraction of diverse aromatic esters from the highly complex cosmetic samples. To our delight, a covalent organic framework, named DaTp (1, 3, 5-triformylphloroglucinol-2, 6-diaminoanthracene), possessing high specific surface, excellently thermochemical stability, and abundant electron-rich heteroatoms, has been synthesized and fabricated as a competitive solid phase microextraction coating for extracting the trace analytes with diverse polarity, through the hydrophobic interaction, π-π conjugation and hydrogen bond. Herein, this self-made SPME fiber has been further coupled with gas chromatography-tandem mass spectrometry (GC-MS) to determine the multi-polar aromatic esters in cosmetics packaged with plastic. This developed analytical method showed wide liner ranges, low limits of detection, good repeatability and reproducibility. Finally, the aromatic esters in four cosmetic samples were quantified precisely with satisfactory recoveries (80.7%-118%).