Three-dimensional covalent organic frameworks with nia nets for efficient separation of benzene/cyclohexane mixtures.

The synthesis of three-dimensional covalent organic frameworks with highly connected building blocks presents a significant challenge. In this study, we report two 3D COFs with the nia topology, named JUC-641 and JUC-642, by introducing planar hexagonal and triangular prism nodes. Notably, our adsorption studies and breakthrough experiments reveal that both COFs exhibit exceptional separation capabilities, surpassing previously reported 3D COFs and most porous organic polymers, with a separation factor of up to 2.02 for benzene and cyclohexane. Additionally, dispersion-corrected density functional theory analysis suggests that the good performance of these 3D COFs can be attributed to the incorporation of highly aromatic building blocks and the presence of extensive pore structures. Consequently, this research not only expands the diversity of COFs but also highlights the potential of functional COF materials as promising candidates for environmentally-friendly separation applications.

Three-dimensional microporous and mesoporous covalent organic frameworks based on cubic building units.

Covalent organic frameworks (COFs) have attracted extensive interest due to their unique structures and various applications. However, structural diversities are still limited, which greatly restricts the development of COF materials. Herein, we report two unusual cubic (8-connected) building units and their derived 3D imine-linked COFs with bcu nets, JUC-588 and JUC-589. Owing to these unique building blocks with different sizes, the obtained COFs can be tuned to be microporous or mesoporous structures with high surface areas (2728 m2 g-1 for JUC-588 and 2482 m2 g-1 for JUC-589) and promising thermal and chemical stabilities. Furthermore, the high selectivity of CO2/N2 and CO2/CH4, excellent H2 uptakes, and efficient dye adsorption are observed. This research thus provides a general strategy for constructing stable 3D COF architectures with adjustable pores via improving the valency of rigid building blocks.

Design and Synthesis of a Zeolitic Organic Framework.

The development of novel zeolite-like materials with large channel windows and high stability is of importance but remains a tremendous challenge. Herein, we report the first example of a 3D covalent organic framework with zeolitic network, namely the zeolitic organic framework (ZOF). By combining two kinds of tetrahedral building blocks with fixed or relatively free bond angles, ZOF-1 with the zeolitic crb net has been successfully synthesized. Its structure was determined by the single-crystal 3D electron diffraction technique. Remarkably, ZOF-1 shows high chemical stability, large pore size (up to 16 Å), and excellent specific surface area (≈2785 m2 g-1 ), which is superior to its analogues with the same network, including traditional aluminosilicate zeolites and zeolitic imidazole frameworks. This study thus opens a new avenue to construct zeolite-like materials with pure organic frameworks and will promote their potential applications in adsorption and catalysis for macromolecules.

Three-Dimensional Radical Covalent Organic Frameworks as Highly Efficient and Stable Catalysts for Selective Oxidation of Alcohols.

With excellent designability, large accessible inner surface, and high chemical stability, covalent organic frameworks (COFs) are promising candidates as metal-free heterogeneous catalysts. Here, we report two 3D radical-based COFs (JUC-565 and JUC-566) in which radical moieties (TEMPO) are uniformly decorated on the channel walls via a bottom-up approach. Based on grafted functional groups and suitable regular channels, these materials open up the application of COFs as highly efficient and selective metal-free redox catalysts in aerobic oxidation of alcohols to relevant aldehydes or ketones with outstanding turn over frequency (TOF) up to 132 h-1 , which has exceeded other TEMPO-modified catalytic materials tested under similar conditions. These stable COF-based catalysts could be easily recovered and reused for multiple runs. This study promotes potential applications of 3D functional COFs anchored with stable radicals in organic synthesis and material science.

Cytosine-Co assemblies derived CoNx rich Co-NCNT as efficient tri-functional electrocatalyst.

Carbon-metal composites are promising multifunctional electrocatalysts, but it is still challenging to prepare carbon-metal composites with tunable structure and strong metal-carbon interactions. Here, we present a unique gas-foaming assembly strategy to prepare cytosine-Co chelate derived Co and N codoped carbon nanotube (Co-NCNT). The structure for Co-NCNTs could be easily controlled by regulating cytosine-Co coordination or the carbonization temperature. The optimal Co-NCNT possesses homogeneous distributed NCNTs (10 nm), CoOx (5 nm) and CoNx moieties to synergistically boost electrochemical processes, and offer mesoporous nanosheet architecture to guarantee fast mass migrate and electron transfer. As a result, Co-NCNT shows remarkable ORR performance (onset potential of 0.93 V in 0.1 M KOH electrolyte) along with significant OER and HER activity. More important, it was found that CoNx moieties are responsible for the remarkable electrocatalytic activity in Co-NCNTs, because CoNx could alter active center, enhance metal-carbon synergy, decrease interfacial resistance and reinforce the strength of composites. Therefore, this paper not just demonstrates an advanced multi-functional electrocatalyst, but could also give deep understanding on the designing of multifunctional electrocatalysts.

Three-Dimensional Large-Pore Covalent Organic Framework with stp Topology.

Three-dimensional (3D) covalent organic frameworks (COFs) are excellent crystalline porous polymers for numerous potential applications, but their building units and topological nets have been limited. Herein we report the design and synthesis of the first 3D large-pore COF with the stp topology constructed from a 6-connected triptycene-based monomer. The new COF (termed JUC-564) has a high specific surface area (up to 3300 m2 g-1), the largest pore size among 3D COFs (43 Å), and record-breaking low density among crystalline materials reported to date (0.108 g cm-3). The large pore size of JUC-564 was confirmed by the incorporation of a protein. This study expands the structural varieties of 3D COFs based on the deliberate symmetry-guided design principle as well as their applications for adsorption and separation of large biological molecules.

Metal-Free Thiophene-Sulfur Covalent Organic Frameworks: Precise and Controllable Synthesis of Catalytic Active Sites for Oxygen Reduction.

Defective or heteroatom-doped metal-free carbon materials (MFCMs) have been regarded as efficient oxygen reduction reaction (ORR) catalysts in the past decade. However, the active centers for ORR in MFCMs are hard to confirm precisely and synthesize controllably through common methods such as high-temperature pyrolysis or heteroatom doping. To verify the precise structure acting as the active center for the ORR, we first report two crystalline metal-free thiophene-sulfur covalent organic frameworks (MFTS-COFs) as ORR catalysts. The MFTS-COFs show more positive catalytic capability than the thiophene-free COF, indicating that pentacyclic thiophene-sulfur building blocks act as active centers to induce ORR catalytic activity. MFTS-COFs with higher contents of thiophene-sulfur exhibit better ORR performance. The experimental identification is supported by density functional theory calculations. These results thus demonstrate that rational design and precise synthesis of metal-free crystalline organic materials can promote the development of new ORR catalysts.

Cross-Linking between Sodalite Nanoparticles and Graphene Oxide in Composite Membranes to Trigger High Gas Permeance, Selectivity, and Stability in Hydrogen Separation.

Thin membranes (900 nm) were prepared by direct transformation of infiltrated amorphous precursor nanoparticles, impregnated in a graphene oxide (GO) matrix, into hydroxy sodalite (SOD) nanocrystals. The amorphous precursor particles rich in silanols (Si-OH) enhanced the interactions with the GO, thus leading to the formation of highly adhesive and stable SOD/GO membranes via strong bonding. The cross-linking of SOD nanoparticles with the GO in the membranes promoted both the high gas permeance and enhanced selectivity towards H2 from a mixture containing CO2 and H2 O. The SOD/GO membranes are moisture resistance and exhibit steady separation performance (H2 permeance of about 4900 GPU and H2 /CO2 selectivity of 56, with no degradation in performance during the test of 50 h) at high temperature (200 °C) under water vapor (4 mol %).

Oral Colon-Targeted Konjac Glucomannan Hydrogel Constructed through Noncovalent Cross-Linking by Cucurbit[8]uril for Ulcerative Colitis Therapy.

Orally administered colon-targeted formulations of drugs are of great importance in managing diseases in the colon. However, it is often challenging to maintain the integrity of such formulations during delivery, particularly in the gastric environment, which may lead to premature drug release before reaching the targeted colon. Herein, an oral colon-targeted drug delivery hydrogel (OCDDH) was developed through cucurbit[8]uril (CB[8])-mediated noncovalent cross-linking of phenylalanine (Phe)-modified Konjac glucomannan (KGM), in which berberine (BBR), a natural anti-inflammatory product originating from Chinese medicine, was loaded into the hydrogel matrix. With the strong host-guest complexation mediated cross-linking and the inherent reversibility of such interactions, KGM-Phe@CB[8] hydrogel exhibited a readily tunable degree of cross-linking and an excellent self-healing capability, and therefore the hydrogel retained ultrahigh stability in the gastric environment, which is important for orally administered formulations to target the colon. In the colon, KGM may get degraded by colon-specific enzymes, ß-mannanase or ß-glucosidase, resulting in burst release of the loaded cargoes on site. The structure and specific payload release of the hydrogel, with and without BBR, have been fully characterized in vitro, and the therapeutic effect of BBR-loaded KGM-Phe@CB[8] hydrogel was evaluated against dextran sulfate sodium (DSS) induced ulcerative colitis (UC) in a mouse model. Very interestingly, the BBR-loaded KGM-Phe@CB[8] hydrogel exhibited significantly improved therapeutic efficacy in treating colitis, without causing any systemic toxicity, when compared with free BBR. This strategy may pave a new way in the development of advanced supramolecular OCDDH.

A simple matrine derivative for the facile syntheses of mesoporous zeolites ITQ-37 and ITQ-43.

ITQ-37 and ITQ-43 possessing mesoporous structures have aroused great interest because of their promising applications involving large molecules. However, it is challenging to synthesize these zeolites. Herein, MAS-ITQ-37 and MAS-ITQ-43 with enhanced Si/Ge ratios of 1.7 and 3.0 have been synthesized by using a simple matrine-derived organic structure-directing agent.

Ambient aqueous-phase synthesis of covalent organic frameworks for degradation of organic pollutants.

The development of a mild, low cost and green synthetic route for covalent organic frameworks (COFs) is highly desirable in order to open the door for practical uses of this new family of crystalline porous solids. Herein, we report a general and facile strategy to prepare a series of microporous or mesoporous COFs by a ß-ketoenamine based Michael addition-elimination reaction in aqueous systems at ambient temperature and pressure. This synthesis method not only produces highly crystalline and porous COFs, but also can be carried out with a high reaction rate (only 30 min), high yields (as high as 93%) and large-scale preparation (up to 5.0 g). Furthermore, an Fe(ii)-doped COF shows impressive performance in the oxidative degradation of organic pollutants in aqueous medium. This research thus provides a promising pathway to large-scale green preparation of COFs and their potential application in environmental remediation.

Construction of an Fe, N and S-codoped ultra-thin carbon nanosheet superstructure for the oxygen reduction reaction.

A novel 3D superstructure containing Fe, N, and S-codoped ultra-thin carbon nanosheets was prepared. The newly developed superstructure possessed a hierarchical porosity and a high dopant content, and served as an efficient noble-metal free ORR electrocatalyst (onset potential 0.95 V vs. RHE).

Evolving mechanism of organotemplate-free hierarchical FAU zeolites with house-of-card-like structures.

Hierarchical FAU zeolites with house-of-card-like (HCL) structures were synthesized through a one-pot organotemplate-free route in the Na2O-Al2O3-SiO2-H2O system. The structure details and formation mechanism of HCL zeolites were determined by the combination of electron crystallography and synthesis chemistry. The results revealed that the unique HCL morphology was attributed to large solution viscosity, and the evolution process obeyed a skeleton crystal growth model due to the limited vortexing effect, which was different from those of the HCL zeolites obtained using organic templates.

Guidance from an in situ hot stage in TEM to synthesize magnetic metal nanoparticles from a MOF.

A series of in situ hot stage experiments using transmission electron microscopy (TEM) were studied to directly observe the transition of a Ni-MOF to Ni nanoparticles wrapped in carbon (Ni-NPC) over temperatures ranging from ambient temperature to 700 °C. Ni-NPC-600 displays high catalytic activity in 4-nitrophenol reduction and high conversion, even after 10 cycles.

Synthesis of chiral polymorph A-enriched zeolite Beta with an extremely concentrated fluoride route.

Chiral zeolitic materials with intrinsically chiral frameworks are highly desired because they can combine both shape selectivity and enantioselectivity. In the field of zeolite, the synthesis of chiral polymorph A of zeolite Beta or chiral polymorph A-enriched zeolite Beta is one of the biggest challenges. We demonstrate here a generalized extremely concentrated fluoride route for the synthesis of chiral polymorph A-enriched zeolite Beta in the presence of five achiral organic structure-directing agents. The polymorph A-enriched Ti-Beta shows a higher enantioselectivity for the asymmetric epoxidation of alkenes than the normal Ti-Beta.

Creating extra pores in microporous carbon via a template strategy for a remarkable enhancement of ambient-pressure CO2 uptake.

In this work, we illustrate a template strategy to create extra pores in microporous carbon for enhancing ambient-pressure CO2 uptake, as exemplified in the context of carbonizing the silicon-containing POP, PPN-4, followed by removal of the silicon template. The resultant PPN-4/C600 demonstrates a remarkable enhancement of CO2 uptake capacity at 295 K and 1 bar by a factor of 2.3 compared to the parent PPN-4.

Metal-organic framework based upon the synergy of a Brønsted acid framework and Lewis acid centers as a highly efficient heterogeneous catalyst for fixed-bed reactions.

We report a strategy of combining a Brønsted acid metal-organic framework (MOF) with Lewis acid centers to afford a Lewis acid@Brønsted acid MOF with high catalytic activity, as exemplified in the context of MIL-101-Cr-SO3H·Al(III). Because of the synergy between the Brønsted acid framework and the Al(III) Lewis acid centers, MIL-101-Cr-SO3H·Al(III) demonstrates excellent catalytic performance in a series of fixed-bed reactions, outperforming two benchmark zeolite catalysts (H-Beta and HMOR). Our work therefore not only provides a new approach to achieve high catalytic activity in MOFs but also paves a way to develop MOFs as a new type of highly efficient heterogeneous catalysts for fixed-bed reactions.

An aluminophosphate molecular sieve with 36 crystallographically distinct tetrahedral sites.

The structure of the new medium-pore aluminophosphate molecular sieve PST-6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X-ray powder diffraction, and computer modeling. PST-6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure-directing agent, which is thought to contain bridging hydroxy groups. PST-6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved.

Highly mesoporous single-crystalline zeolite beta synthesized using a nonsurfactant cationic polymer as a dual-function template.

Mesoporous zeolites are useful solid catalysts for conversion of bulky molecules because they offer fast mass transfer along with size and shape selectivity. We report here the successful synthesis of mesoporous aluminosilicate zeolite Beta from a commercial cationic polymer that acts as a dual-function template to generate zeolitic micropores and mesopores simultaneously. This is the first demonstration of a single nonsurfactant polymer acting as such a template. Using high-resolution electron microscopy and tomography, we discovered that the resulting material (Beta-MS) has abundant and highly interconnected mesopores. More importantly, we demonstrated using a three-dimensional electron diffraction technique that each Beta-MS particle is a single crystal, whereas most previously reported mesoporous zeolites are comprised of nanosized zeolitic grains with random orientations. The use of nonsurfactant templates is essential to gaining single-crystalline mesoporous zeolites. The single-crystalline nature endows Beta-MS with better hydrothermal stability compared with surfactant-derived mesoporous zeolite Beta. Beta-MS also exhibited remarkably higher catalytic activity than did conventional zeolite Beta in acid-catalyzed reactions involving large molecules.