104 research outputs found
Hierarchical porous metal-organic framework monoliths
Hierarchical porous crystalline metal-organic framework (MOF) monoliths are prepared by powder-packing synthesis. The resulting MOF monolithic column shows fast and efficient chromatographic separation
Aligned macroporous monoliths with intrinsic microporosity via a frozen-solvent-templating approachd
Aligned macroporous monoliths of an organic cage, a polymer of intrinsic microporosity (PIM-1), and a metalâorganic framework (HKUST-1) are prepared by a controlled freezing approach. In addition to macropores, all the monoliths contain the intrinsic micropores.</p
Metal-organic conjugated microporous polymer containing a carbon dioxide reduction electrocatalyst
A metal-organic conjugated micorporous polymer (CMP) containing a manganese carbonyl electrocatalyst for CO2 reduction has been synthesised and electrochemically characterised. Incorporation in a rigid framework changes the behavior of the catalyst, preventing reductive dimerization. These initial studies demonstrate the feasibility of CMP electrodes that can provide both high local CO2 concentrations and well defined electrocatalytic sites
Aromatic polymers made by reductive polydehalogenation of oligocyclic monomers as conjugated polymers of intrinsic microporosity (C-PIMs)
Reductive dehalogenation polycondensation of a series of penta-or hexacyclic, bisgeminal tetrachlorides with dicobalt octacarbonyl leads to the formation of homopolymers and copolymers with very different optical spectra. While the formation of tetrabenzoheptafulvalene connectors introduces efficient conjugation barriers due to their strongly folded structure, linking of 5-membered ring-based pentacyclic building blocks via bifluorenylidene connectors allows for an extended Ï-conjugation along the main chain. A comparison of homopolymer P57 and copolymer P55/77 indicates a quite different reactivity for dichloromethylene functions if incorporated into 5-or 7-membered rings. Interestingly, all investigated (co)polymers show an intrinsic microporosity in the solid-state (forming so-called Conjugated Polymers of Intrinsic Microporosity C-PIMs) and have SBET values of up to 760 m2 g-1 for homopolymer P77. This value is one of the highest reported values to date for C-PIMs
Powder-Bot: A Modular Autonomous Multi-Robot Workflow for Powder X-Ray Diffraction
Powder X-ray diffraction (PXRD) is a key technique for the structural
characterisation of solid-state materials, but compared with tasks such as
liquid handling, its end-to-end automation is highly challenging. This is
because coupling PXRD experiments with crystallisation comprises multiple solid
handling steps that include sample recovery, sample preparation by grinding,
sample mounting and, finally, collection of X-ray diffraction data. Each of
these steps has individual technical challenges from an automation perspective,
and hence no commercial instrument exists that can grow crystals, process them
into a powder, mount them in a diffractometer, and collect PXRD data in an
autonomous, closed-loop way. Here we present an automated robotic workflow to
carry out autonomous PXRD experiments. The PXRD data collected for polymorphs
of small organic compounds is comparable to that collected under the same
conditions manually. Beyond accelerating PXRD experiments, this workflow
involves 13 component steps and integrates three different types of robots,
each from a separate supplier, illustrating the power of flexible, modular
automation in complex, multitask laboratories.Comment: 11 pages, 4 figures plus Supporting Information (2 videos, 13
supporting figures and one table
Porous organic cages for sulfur hexafluoride separation
A series of porous organic cages is examined for the selective adsorption of sulfur hexafluoride (SF6) over nitrogen. Despite lacking any metal sites, a porous cage, CC3, shows the highest SF6/N2 selectivity reported for any material at ambient temperature and pressure, which translates to real separations in a gas breakthrough column. The SF6 uptake of these materials is considerably higher than would be expected from the static pore structures. The location of SF6 within these materials is elucidated by X-ray crystallography, and it is shown that cooperative diffusion and structural rearrangements in these molecular crystals can rationalize their superior SF6/N2 selectivity
Experimental Confirmation of a Predicted Porous HydrogenâBonded Organic Framework
AbstractHydrogenâbonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structureâproperty predictions to generate energyâstructureâfunction (ESF) maps for a series of triptyceneâbased molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown lowâenergy HOF (TH5âA) with a remarkably low density of 0.374â
gâcmâ3 and threeâdimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5âA polymorph experimentally. This material has a high accessible surface area of 3,284â
m2âgâ1, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date.</jats:p
Controlling gas selectivity in molecular porous liquids by tuning the cage window size
Control of pore window size is the standard approach for tuning gas selectivity in porous solids. Here, we present the first example where this is translated into a molecular porous liquid formed from organic cage molecules. Reduction of the cage window size by chemical synthesis switches the selectivity from Xe-selective to CH4 -selective, which is understood using 129 Xe, 1 H, and pulsed-field gradient NMR spectroscopy
3D Cage COFs: A Dynamic Three-Dimensional Covalent Organic Framework with High-Connectivity Organic Cage Nodes.
Three-dimensional (3D) covalent organic frameworks (COFs) are rare because there is a limited choice of organic building blocks that offer multiple reactive sites in a polyhedral geometry. Here, we synthesized an organic cage molecule (Cage-6-NH2) that was used as a triangular prism node to yield the first cage-based 3D COF, 3D-CageCOF-1. This COF adopts an unreported 2-fold interpenetrated acs topology and exhibits reversible dynamic behavior, switching between a small-pore (sp) structure and a large-pore (lp) structure. It also shows high CO2 uptake and captures water at low humidity (<40%). This demonstrates the potential for expanding the structural complexity of 3D COFs by using organic cages as the building units
Sulfone-containing covalent organic frameworks for photocatalytic hydrogen evolution from water
Nature uses organic molecules for light harvesting and photosynthesis, but most man-made water splitting catalysts are inorganic semiconductors. Organic photocatalysts, while attractive because of their synthetic tunability, tend to have low quantum efficiencies for water splitting. Here we present a crystalline covalent organic framework (COF) based on a benzo-bis(benzothiophene sulfone) moiety that shows a much higher activity for photochemical hydrogen evolution than its amorphous or semicrystalline counterparts. The COF is stable under long-term visible irradiation and shows steady photochemical hydrogen evolution with a sacrificial electron donor for at least 50 hours. We attribute the high quantum efficiency of fused-sulfone-COF to its crystallinity, its strong visible light absorption, and its wettable, hydrophilic 3.2 nm mesopores. These pores allow the framework to be dye-sensitized, leading to a further 61% enhancement in the hydrogen evolution rate up to 16.3 mmol g â1 h â1 . The COF also retained its photocatalytic activity when cast as a thin film onto a support
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