In Situ Transformation of an Amorphous Supramolecular Coating to a Hydrogen-Bonded Organic Framework Membrane to Trigger Selective Gas Permeation.

We introduce a "solution-processing-transformation" strategy, deploying solvent vapor as scaffolds, to fabricate high-quality hydrogen-bonded organic framework (HOF) membranes. This strategy can overcome the mismatch in processing conditions and crystal growth thermodynamics faced during the facile solution processing of the membrane. The procedure includes the vapor-trigged in situ transformation of dense amorphous supramolecules to crystalline HOF-16, with HOF-11 as the transient state. The mechanism involves a vapor-activated dissolution-precipitation equilibrium shifting and hydrogen bonding-guided molecule rearrangement, elucidated through combined experimental and theoretical analysis. Upon removal of the molecular scaffolds, the resulting HOF-16 membranes showcase significant improvement in hydrogen separation performance over their amorphous counterparts and previously reported HOF membranes. The method's broad applicability is evidenced by successfully extending it to other substrates and HOF structures. This study provides a fundamental understanding of guest-induced ordered supramolecular assembly and paves the way for the advanced manufacture of high-performance HOF membranes for gas separation processes.

One-step Ethylene Purification from an Acetylene/Ethylene/Ethane Ternary Mixture by Cyclopentadiene Cobalt-Functionalized Metal-Organic Frameworks.

The separation of ethylene (C2 H4 ) from a mixture of ethane (C2 H6 ), ethylene (C2 H4 ), and acetylene (C2 H2 ) at normal temperature and pressure is a significant challenge. The sieving effect of pores is powerless due to the similar molecular size and kinetic diameter of these molecules. We report a new modification method based on a stable ftw topological Zr-MOF platform (MOF-525). Introduction of a cyclopentadiene cobalt functional group led to new ftw-type MOFs materials (UPC-612 and UPC-613), which increase the host-guest interaction and achieve efficient ethylene purification from the mixture of hydrocarbon gases. The high performance of UPC-612 and UPC-613 for C2 H2 /C2 H4 /C2 H6 separation has been verified by gas sorption isotherms, density functional theory (DFT), and experimentally determined breakthrough curves. This work provides a one-step separation of the ternary gas mixture and can further serve as a blueprint for the design and construction of function-oriented porous structures for such applications.

Micelles of Mesoporous Silica with Inserted Iron Complexes as a Platform for Constructing Efficient Electrocatalysts for Oxygen Reduction.

Iron, N-codoped carbon materials (Fe-N-C) are promising electrocatalysts toward oxygen reduction reactions due to their high atom utilization efficiency and intrinsic activity. Nanostructuring of the Fe-N-C materials, such as introducing porosity into the carbon structure, would be conducive to further increasing the exposure of active sites as well as improving the mass transfer. Herein, we explore the potential of iron complex-functionalized micelles of mesoporous SiO2 as a platform for constructing porous Fe-N-C materials. The classical three-dimensional MCM-48 was selected as a proof-of-concept example, which was utilized as the hard template, and cetyltrimethylammonium bromide micelles inside it played the role of the main carbon source. Fe-Nx sites were derived from Fe-1,10-phenanthroline complexes in the micelles introduced by in situ incorporation of 1,10-phenanthroline and post Fe2+ insertion in an aqueous solution. After thermal annealing in a nitrogen atmosphere and subsequent removal of the MCM-48 framework, a carbon material that possesses porous structural features with uniformly dispersed Fe-Nx sites (MPC@PhFe) was obtained, which shows superior ORR activity in a 0.1 M KOH solution and great potential for Zn-air battery applications as well. This work demonstrates the feasibility as well as the effectiveness of turning micelles of mesoporous SiO2 into porous carbon structures and might offer a universal strategy for manufacturing carbon materials for future application in energy storage and conversion.

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 %).

Fabrication of a Hydrogen-Bonded Organic Framework Membrane through Solution Processing for Pressure-Regulated Gas Separation.

Ordered and flexible porous frameworks with solution processability are highly desirable to fabricate continuous and large-scale membranes for the efficient gas separation. Herein, the first microporous hydrogen-bonded organic framework (HOF) membrane has been fabricated by an optimized solution-processing technique. The framework exhibits the superior stability because of the abundant hydrogen bonds and strong π-π interactions. Thanks to the flexible HOF structure, the membrane possesses the unprecedented pressure-responsive H2 /N2 separation performance. Furthermore, the scratched membrane can be healed by the treatment of solvent vapor, achieving the recovery of separation performance.

An ultrafast responsive NO2 gas sensor based on a hydrogen-bonded organic framework material.

We report the development of a new type of organic semiconductor gas sensor based on a porphyrin-based hydrogen-bonded organic framework (HOF). Owing to the orderly porous structures, the decoration with rich amino sites and the n-type semiconductor nature, this HOF-based sensor exhibits selective NO2 sensing performance with ultra-fast response/recovery rates (17.6 s/15.4 s over 100 ppb) and a limit of detection lower than 40 ppb, together with high sensitivity, good reproducibility, and long-term stability at room temperature. This study demonstrates that HOF-based materials have potential application prospects in gas sensing, thereby offering a new way of thinking for the design and development of sensors.

TiO2-Coated Interlayer-Expanded MoSe2/Phosphorus-Doped Carbon Nanospheres for Ultrafast and Ultralong Cycling Sodium Storage.

Based on multielectron conversion reactions, layered transition metal dichalcogenides are considered promising electrode materials for sodium-ion batteries, but suffer from poor cycling performance and rate capability due to their low intrinsic conductivity and severe volume variations. Here, interlayer-expanded MoSe2/phosphorus-doped carbon hybrid nanospheres coated by anatase TiO2 (denoted as MoSe2/P-C@TiO2) are prepared by a facile hydrolysis reaction, in which TiO2 coating polypyrrole-phosphomolybdic acid is utilized as a novel precursor followed by a selenization process. Benefiting from synergistic effects of MoSe2, phosphorus-doped carbon, and TiO2, the hybrid nanospheres manifest unprecedented cycling stability and ultrafast pseudocapacitive sodium storage capability. The MoSe2/P-C@TiO2 delivers decent reversible capacities of 214 mAh g-1 at 5.0 A g-1 for 8000 cycles, 154 mAh g-1 at 10.0 A g-1 for 10000 cycles, and an exceptional rate capability up to 20.0 A g-1 with a capacity of ≈175 mAh g-1 in a voltage range of 0.5-3.0 V. Coupled with a Na3V2(PO4)3@C cathode, a full cell successfully confirms a reversible capacity of 242.2 mAh g-1 at 0.5 A g-1 for 100 cycles with a coulombic efficiency over 99%.

Reversed thermo-switchable molecular sieving membranes composed of two-dimensional metal-organic nanosheets for gas separation.

It is highly desirable to reduce the membrane thickness in order to maximize the throughput and break the trade-off limitation for membrane-based gas separation. Two-dimensional membranes composed of atomic-thick graphene or graphene oxide nanosheets have gas transport pathways that are at least three orders of magnitude higher than the membrane thickness, leading to reduced gas permeation flux and impaired separation throughput. Here we present nm-thick molecular sieving membranes composed of porous two-dimensional metal-organic nanosheets. These membranes possess pore openings parallel to gas concentration gradient allowing high gas permeation flux and high selectivity, which are proven by both experiment and molecular dynamics simulation. Furthermore, the gas transport pathways of these membranes exhibit a reversed thermo-switchable feature, which is attributed to the molecular flexibility of the building metal-organic nanosheets.

"Single nickel source" in situ fabrication of a stable homochiral MOF membrane with chiral resolution properties.

A homochiral MOF membrane was successfully and facilely synthesized using an in situ growth method, which had the advantages of cheap raw materials, simple operation and high thermal stability. A diol isomer mixture was used to test the separation efficiency of the membrane at different temperatures and pressures.