Polyhedral Crystal Films of Covalent Organic Frameworks.

Porous crystal films offer great potential for tackling energy and environmental challenges. However, despite over a decade of intensive research, covalent organic framework (COF) films exhibiting polyhedral textures reflective of their crystalline nature remain exceedingly rare. Here we present a scalable and adaptable biphasic strategy to synthesize pyrene (Py)-COF polyhedral crystal films with exceptional crystalline order under ambient conditions.

Isomeric Separation of C6 Alkanes via Organic Solvent Reverse Osmosis with Covalent Organic Framework Membranes.

Membrane separation represents cutting-edge technology for the isomeric separation of C6 alkanes in the petrochemical sector. However, it remains challenging to design membranes with sub-0.1 nm resolution that can effectively discriminate between C6 alkane isomers.

Solvent-responsive covalent organic framework membranes for precise and tunable molecular sieving.

Membrane-based nanofiltration has the potential to revolutionize the large-scale treatment of organic solvents in various applications. However, the widely used commercial membranes suffer from low permeability, narrow structural tunability, and limited chemical resistance. Here, we report a strategy for fabricating covalent organic framework (COF) membranes with solvent-responsive structural flexibility.

Dual-layer spectral-detector CT for detecting liver steatosis by using proton density fat fraction as reference.

Objectives: To evaluate the diagnostic accuracy of liver dual-layer spectral-detector CT (SDCT) derived parameters of liver parenchyma for grading steatosis with reference to magnetic resonance imaging-based proton density fat fraction (MRI-PDFF).

Methods: Altogether, 320 consecutive subjects who underwent MRI-PDFF and liver SDCT examinations were recruited and prospectively enrolled from four Chinese hospital centers. Participants were classified into normal (n = 152), mild steatosis (n = 110), and moderate/severe(mod/sev) steatosis (n = 58) groups based on MRI-PDFF.

Temperature-dependent rearrangement of gas molecules in ultramicroporous materials for tunable adsorption of CO and CH.

The interactions between adsorbed gas molecules within porous metal-organic frameworks are crucial to gas selectivity but remain poorly explored. Here, we report the modulation of packing geometries of CO and CH clusters within the ultramicroporous CUK-1 material as a function of temperature. In-situ synchrotron X-ray diffraction reveals a unique temperature-dependent reversal of CO and CH adsorption affinities on CUK-1, which is validated by gas sorption and dynamic breakthrough experiments, affording high-purity CH (99.

Covalent organic framework atropisomers with multiple gas-triggered structural flexibilities.

Covalent organic frameworks (COFs) are emerging crystalline porous polymers, showing great potential for applications but lacking gas-triggered flexibility. Atropisomerism was experimentally discovered in 1922 but has rarely been found in crystals with infinite framework structures. Here we report atropisomerism in COF single crystals.

Insertion of CO in metal ion-doped two-dimensional covalent organic frameworks.

Carbon capture is one of the essential low-carbon technologies required to achieve societal climate goals at the lowest cost. Covalent organic frameworks (COFs) are promising adsorbents for CO capture because of their well-defined porosity, large surface area, and high stability. Current COF-based CO capture is mainly based on a physisorption mechanism, exhibiting smooth and reversible sorption isotherms.

Tunable Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks Triggered by CO Sorption.

Two-dimensional covalent organic frameworks (2D COFs) have been widely viewed as rigid porous materials with smooth and reversible gas sorption isotherms. In the present study, we report an unusual hysteresis step in the CO adsorption isotherm of a 2D COF, TAPB-OMeTA. powder X-ray diffraction (PXRD) measurements, computational modeling, and Pawley refinement indicate that TAPB-OMeTA experiences slight interlayer shifting during the CO adsorption process, resulting in a new structure that is similar but not identical to the AA stacking structure, namely, a quasi-AA stacking structure.

Efficient Splitting of Alkane Isomers by a Bismuth-Based Metal-Organic Framework with Auxetic Reentrant Pore Structures.

The isolation of di-branched alkanes from their isomers is vital in gasoline upgrading to achieve high octane numbers but is significantly challenging and energy-intensive. Here, we report the highly efficient separation of hexane isomers by combing molecular recognition and size-sieving in a bismuth-based MOF, UU-200. The unique auxetic structure with reentrant honeycomb-like pore cavities connected by narrow pore windows endows UU-200 with a complete rejection of di-branched alkanes and high capacities for linear and mono-branched isomers.

Efficient Adsorption of Acetylene over CO in Bioinspired Covalent Organic Frameworks.

Rational design of covalent organic frameworks (COFs) to broaden their diversity is highly desirable but challenging due to the limited, expensive, and complex building blocks, especially compared with other easily available porous materials. In this work, we fabricated two novel bioinspired COFs, namely, NUS-71 and NUS-72, using reticular chemistry with ellagic acid and triboronic acid-based building blocks. Both COFs with AB stacking mode exhibit high acetylene (CH) adsorption capacity and excellent separation performance for CH/CO mixtures, which is significant but rarely explored using COFs.

Growing single crystals of two-dimensional covalent organic frameworks enabled by intermediate tracing study.

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Here, we take a different perspective to explore the 2D COF growth process by tracing growth intermediates.

Aggregated Structures of Two-Dimensional Covalent Organic Frameworks.

Covalent organic frameworks (COFs) have found wide applications due to their crystalline structures. However, it is still challenging to quantify crystalline phases in a COF sample. This is because COFs, especially 2D ones, are usually obtained as mixtures of polycrystalline powders.

Multivariate Polycrystalline Metal-Organic Framework Membranes for CO/CH Separation.

Membrane technology is attractive for natural gas separation (removing CO, HO, and hydrocarbons from CH) because of membranes' low energy consumption and small environmental footprint. Compared to polymeric membranes, microporous inorganic membranes such as silicoaluminophosphate-34 (SAPO-34) membrane can retain their separation performance under conditions close to industrial requirements. However, moisture and hydrocarbons in natural gas can be strongly adsorbed in the pores of those membranes, thereby reducing the membrane separation performance.

Optimal Pore Chemistry in an Ultramicroporous Metal-Organic Framework for Benchmark Inverse CO /C H Separation.

Isolation of CO from acetylene (C H ) via CO -selective sorbents is an energy-efficient technology for C H purification, but a strategic challenge due to their similar physicochemical properties. There is still no specific methodology for constructing sorbents that preferentially trap CO over C H . We report an effective strategy to construct optimal pore chemistry in a Ce -based ultramicroporous metal-organic framework Ce -MIL-140-4F, based on charge-transfer effects, for efficient inverse CO /C H separation.

Efficient Trapping of Trace Acetylene from Ethylene in an Ultramicroporous Metal-Organic Framework: Synergistic Effect of High-Density Open Metal and Electronegative Sites.

Acetylene (C H ) removal from ethylene (C H ) is a crucial step in the production of polymer-grade C H but remains a daunting challenge because of the similar physicochemical properties of C H and C H . Currently energy-intensive cryogenic distillation processes are used to separate the two gases industrially. A robust ultramicroporous metal-organic framework (MOF), Ni (pzdc) (7 Hade) , is reported for efficient C H /C H separation.

Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks.

Layer-stacking structures are very common in two-dimensional covalent organic frameworks (2D COFs). While their structures are normally determined under solvent-free conditions, the structures of solvated 2D COFs are largely unexplored. We report herein the in situ determination of solvated 2D COF structures, which exhibit an obvious difference as compared to that of the same COF under dried state.

A Diversity of Asymmetric Nano-/Microcolloidal Architectures Grown by ATRP from Janus Seeds.

The fabrication of colloids has witnessed significant progress during the last decade, however, fabrication of anisotropic colloidal particles with complex geometries still represents a challenging task. Here, we present nano-/micro-sized colloidal architectures which 'grow' directly from nanoparticle seeds by controlled radical polymerization, resembling the growth of plants from seeds in the natural world. Specifically, we use the atom transfer radical polymerization (ATRP) technique to grow colloidal architectures from snowman-shaped Janus nanoparticle seeds (JNPS).

Combined Experimental and Simulation Studies of Cross-Linked Polymer Brushes under Shear.

We have studied the effect of cross-linking on the tribological behavior of polymer brushes using a combined experimental and theoretical approach. Tribological and indentation measurements on poly(glycidyl methacrylate) brushes and gels in the presence of dimethylformamide solvent were obtained by means of atomic force microscopy. To complement experiments, we have performed corresponding molecular dynamics (MD) simulations of a generic bead-spring model in the presence of explicit solvent and cross-linkers.

Modulation of Surface-Initiated ATRP by Confinement: Mechanism and Applications.

The mechanism of surface-initiated atom transfer polymerization (SI-ATRP) of methacrylates in confined volumes is systematically investigated by finely tuning the distance between a grafting surface and an inert plane by means of nanosized patterns and micrometer thick foils. The polymers were synthesized from monolayers of photocleavable initiators, which allow the analysis of detached brushes by size-exclusion chromatography (SEC). Compared to brushes synthesized under "open" polymerization mixtures, nearly a 4-fold increase in brush molar mass was recorded when SI-ATRP was performed within highly confined reaction volumes.

Influence of Geometries on the Assembly of Snowman-Shaped Janus Nanoparticles.

The self-assembly of micro/nanoparticles into suprastructures is a promising way to develop reconfigurable materials and to gain insights into the fundamental question of how matter organizes itself. The geometry of particles, especially those deviating from perfectly spherical shapes, is of significant importance in colloidal assembly because it influences the particle "recognition", determines the particle packing, and ultimately dictates the formation of assembled suprastructures. In order to organize particles into desired structures, it is of vital importance to understand the relationship between the shape of the colloidal building blocks and the assembled suprastructures.

Self-Assembly of Janus Nanoparticles into Transformable Suprastructures.

One of the greatest challenges in colloidal self-assembly is to obtain multiple distinct but transformable suprastructures from the same particles in monophasic solvent. Here, we combined deformable and rigid lobes in snowman-shaped amphiphilic Janus nanoparticles (JNPs). These JNPs exhibited excellent ability to self-assemble into micelles, worms, mini-capsules, giant- and elongated-vesicles.

Ultrathin, freestanding, stimuli-responsive, porous membranes from polymer hydrogel-brushes.

The fabrication of freestanding, sub-100 nm-thick, pH-responsive hydrogel membranes with controlled nano-morphology, based on modified poly(hydroxyethyl methacrylate) (PHEMA) is presented. Polymer hydrogel-brush films were first synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequently detached from silicon substrates by UV-induced photo-cleavage of a specially designed linker within the initiator groups. The detachment was also assisted by pH-induced osmotic forces generated within the films in the swollen state.