Porous, Crystalline, Covalent Organic Frameworks
18 Nov 2005-Science (American Association for the Advancement of Science)-Vol. 310, Iss: 5751, pp 1166-1170
TL;DR: Covalent organic frameworks (COFs) have been designed and successfully synthesized by condensation reactions of phenyl diboronic acid and hexahydroxytriphenylene to form rigid porous architectures with pore sizes ranging from 7 to 27 angstroms.
Abstract: Covalent organic frameworks (COFs) have been designed and successfully synthesized by condensation reactions of phenyl diboronic acid {C6H4[B(OH)2]2} and hexahydroxytriphenylene [C18H6(OH)6]. Powder x-ray diffraction studies of the highly crystalline products (C3H2BO)6.(C9H12)1 (COF-1) and C9H4BO2 (COF-5) revealed expanded porous graphitic layers that are either staggered (COF-1, P6(3)/mmc) or eclipsed (COF-5, P6/mmm). Their crystal structures are entirely held by strong bonds between B, C, and O atoms to form rigid porous architectures with pore sizes ranging from 7 to 27 angstroms. COF-1 and COF-5 exhibit high thermal stability (to temperatures up to 500 degrees to 600 degrees C), permanent porosity, and high surface areas (711 and 1590 square meters per gram, respectively).
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TL;DR: In this article , Covalent organic frameworks (COFs) have emerged as a promising platform for designing brilliant photocatalyst candidates, however, their photocatalytic performances are still poor.
Abstract: Owing to the high structural designability and functional tunability, covalent organic frameworks (COFs) have emerged as a promising platform for designing brilliant photocatalyst candidates. However, their photocatalytic performances are still...
5 citations
01 Jan 2015
TL;DR: In this paper, the synthesis of two-dimensional organic nanostructures on metal surfaces is studied by means of scanning tunneling microscopy and X-ray photoelectron spectroscopy.
Abstract: The synthesis of two-dimensional organic nanostructures on metal surfaces is studied under ultra-high vacuum conditions by means of scanning tunneling microscopy and X-ray photoelectron spectroscopy. The surface-supported structures are stabilized by various different intermolecular interactions resulting in the formation of self-assembled structures and covalent networks. For on-surface polymerization of covalent nanostructures different coupling reactions, substrate materials, and reaction parameters are investigated.
5 citations
Cites background from "Porous, Crystalline, Covalent Organ..."
...The single layers are shifted relative to each other obtaining an AB-stacking order similar to graphite.[125]...
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...Additionally, the nucleation of crystalline materials is facilitated by the use of solvents with sparse solubility for the precursor monomer.[125] The combination of poor solvents and a closed reaction system results in the growth of crystalline 2D and 3D materials with high yield....
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...Covalent organic frameworks (COFs) such as porous bulk crystals are particularly promising for many applications in gas storage, catalysis, and as molecular sieves.[125] Implementation of boronate chemistry in a solvothermal synthesis yielded versatile COF structures,[17] including first demonstrations of the application potential in organic electronics....
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...In this context, especially the condensation of bronic acid building blocks gained research interest for the solvothermal synthesis of 2D and 3D covalent organic frameworks (COFs).[125, 126] Thereby, three boronic acid groups cyclotrimerize to a six-membered boroxine ring (B3O3) accompanied by the elimination of three water molecules (Fig....
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TL;DR: In this paper, the hydrogen storage capacity of the light transition metal (TM)-decorated metal organic frameworks (MOFs) was investigated by performing ab initio density functional theory calculations.
Abstract: We investigate the hydrogen storage capacity of the light transition metal (TM)-decorated metal organic frameworks (MOFs) by performing ab initio density functional theory calculations. We find that among all the light TM elements, divalent Ti and Fe are suitable for decorating MOFs to enhance the hydrogen uptake, considering the H2 binding energy on the TM atom and the reversibly usable number of H2 molecules attached to the metal site. In general, the magnetization of metal atoms undergoes a high-spin to low-spin state transition when H2 molecules are adsorbed, which helps to stabilize the system energetically. By analyzing the projected density of states on each TM atom, it is shown that the d-level shift induced by the ligand field of the adsorbed H2 molecules contributes substantially to the H2 binding strength. We also study the stability of selected TM-decorated nanostructures against the attack of foreign molecules by examining the energetics of those contaminating molecules around the metal sites.
5 citations
TL;DR: In this paper, the electronic structures and energies of neutral and anionic (LiBH4)x clusters have been systematically studied by using density functional theory with the B3LYP/6-311++G(d, p) level.
Abstract: Summary
The electronic structures and energies of neutral and anionic (LiBH4)x clusters (x = 1 – 5) have been systematically studied by using density functional theory with the B3LYP/6-311++G(d, p) level. For investigating the importance of excess electrons on hydrogen storage capacity, the interactions between hydrogen atoms and the anionic (LiBH4)x clusters are also examined. The calculated formation energies of the anionic clusters show that the anionic clusters have a high thermal stability. It is found that hydrogen atoms are adsorbed on the anionic (LiBH4)x clusters chemically with adsorption energies in the range of −69.13 – −153.73 kcal/mol. The hydrogen storage capacity can be improved from 18.51% to 19.26 – 22.12% in weight percent depending on the size of various anionic (LiBH4)x clusters. Our calculation results show that the existence of excess electrons on the (LiBH4)x clusters can enhance the hydrogen storage capacity. The Mulliken charge analysis was performed to illustrate the interactions between H atoms and the anionic (LiBH4)x clusters. Copyright © 2016 John Wiley & Sons, Ltd.
5 citations
TL;DR: A covalent organic framework (COF) has been designed and synthesized successfully by a condensation reaction between hexahydroxytriphenylene hydrate and tetrahydroxydiborane.
Abstract: A covalent organic framework (COF) has been designed and synthesized successfully by a condensation reaction between hexahydroxytriphenylene hydrate and tetrahydroxydiborane. The characterisation studies reveal that it has good thermal stability and high crystallinity. This is a mesoporous material having a pore size of 2.8 nm and also having a B–B linkage with prospect of potential applications in future. Synopsis. A covalent organic framework (COF) has been synthesized successfully by the condensation reaction of hexahydroxytriphenylene hydrate and tetrahydroxydiborane. The characterisation studies reveal that it has good thermal stability and high crystallinity. This is a mesoporous material having a pore size of 2.8 nm and also having a B–B linkage.
5 citations
References
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Book•
05 Oct 1998
TL;DR: In this paper, the authors provide an introductory review of the various theoretical and practical aspects of adsorption by powders and porous solids with particular reference to materials of technological importance.
Abstract: The declared objective of this book is to provide an introductory review of the various theoretical and practical aspects of adsorption by powders and porous solids with particular reference to materials of technological importance. The primary aim is to meet the needs of students and non-specialists, who are new to surface science or who wish to use the advanced techniques now available for the determination of surface area, pore size and surface characterization. In addition, a critical account is given of recent work on the adsorptive properties of activated carbons, oxides, clays and zeolites. Key Features * Provides a comprehensive treatment of adsorption at both the gas/solid interface and the liquid/solid interface * Includes chapters dealing with experimental methodology and the interpretation of adsorption data obtained with porous oxides, carbons and zeolites * Techniques capture the importance of heterogeneous catalysis, chemical engineering and the production of pigments, cements, agrochemicals, and pharmaceuticals
3,128 citations
"Porous, Crystalline, Covalent Organ..." refers background in this paper
...At higher pressures, a slow rise in the isotherm occurs because of the existence of a small population of external mesopores between the crystallites; this feature is not uncommon for particles with platelet morphologies (19)....
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...These values surpass those of other layered materials, including graphite (10 m(2) g), clays (10 to 100 m(2) g), and pillared clays (50 to 300 m(2) g) and are in the range of the most porous zeolites and many porous carbons (19)....
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...The total surface area was calculated to be 711 m(2) g, with a micropore contribution of 587 m(2) g (83%) and mesopore contribution of 124 m(2) g (17%) from de Boer statistical thickness (t-plot) analysis (19)....
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TL;DR: The surfactant-mediated synthesis of an ordered benzene–silica hybrid material has an hexagonal array of mesopores and crystal-like pore walls that exhibit structural periodicity, and it is expected that other organosilicas and organo-metal oxides can be produced in a similar fashion, to yield a range of hierarchically ordered mesoporous solids with molecular-scale pore surface periodicity.
Abstract: Surfactant-mediated synthesis strategies are widely used to fabricate ordered mesoporous solids in the form of metal oxides, metals, carbon and hybrid organosilicas. These materials have amorphous pore walls, which could limit their practical utility. In the case of mesoporous metal oxides, efforts to crystallize the framework structure by thermal and hydrothermal treatments have resulted in crystallization of only a fraction of the pore walls. Here we report the surfactant-mediated synthesis of an ordered benzene-silica hybrid material; this material has an hexagonal array of mesopores with a lattice constant of 52.5 A, and crystal-like pore walls that exhibit structural periodicity with a spacing of 7.6 A along the channel direction. The periodic pore surface structure results from alternating hydrophilic and hydrophobic layers, composed of silica and benzene, respectively. We believe that this material is formed as a result of structure-directing interactions between the benzene-silica precursor molecules, and between the precursor molecules and the surfactants. We expect that other organosilicas and organo-metal oxides can be produced in a similar fashion, to yield a range of hierarchically ordered mesoporous solids with molecular-scale pore surface periodicity.
1,216 citations
TL;DR: In this paper, a unified approach to pore size characterization of microporous carbonaceous materials such as activated carbon and carbon fibers by nitrogen, argon, and carbon dioxide adsorption at standard temperatures, 77 K for N2 and Ar and 273 K for CO2, was presented.
Abstract: We present a unified approach to pore size characterization of microporous carbonaceous materials such as activated carbon and carbon fibers by nitrogen, argon, and carbon dioxide adsorption at standard temperatures, 77 K for N2 and Ar and 273 K for CO2. Reference isotherms of N2, Ar, and CO2 in a series of model slit-shaped carbon pores in the range from 0.3 to 36 nm have been calculated from the nonlocal density functional theory (NLDFT) using validated parameters of intermolecular interactions. Carbon dioxide isotherms have also been generated by the grand canonical Monte Carlo (GCMC) method based on the 3-center model of Harris and Yung. The validation of model parameters includes three steps: (1) prediction of vapor−liquid equilibrium data in the bulk system, (2) prediction of adsorption isotherm on graphite surface, (3) comparison of the NLDFT adsorption isotherms in pores to those of GCMC simulations, performed with the parameters of fluid-fluid interactions, which accurately reproduce vapor−liqui...
657 citations
TL;DR: In this paper, the pore size of MCM-41 materials was estimated based on geometrical considerations of the ratio of pore volume to pore wall volume for an infinite hexagonal array of cylindrical pores.
Abstract: Nitrogen adsorption measurements were performed over a wide range of relative pressures (10-6−0.995) for a series of siliceous MCM-41 samples obtained using alkyltrimethylammonium surfactants with different chain length. Both high- and low-pressure adsorption data were analyzed. The pore size was shown to increase in a regular way with the chain length of the surfactant used. Moreover, a very good correlation between the pore size and the interplanar spacing of the MCM-41 samples was observed. Methods used to calculate the pore diameter were critically compared, and a new procedure to estimate the pore size of MCM-41 materials was proposed. This new procedure is based on geometrical considerations of the ratio of the pore volume to the pore wall volume for an infinite hexagonal array of cylindrical pores. Adsorption measurements showed that the amount adsorbed in the low-pressure region increases with a decrease in the pore size of the samples probably because of the enhancement of the gas−surface interac...
465 citations