Matthew R. Hill

Synthesis and Hydrogen Storage Properties of Be12(OH)12(1,3,5-benzenetribenzoate)4

The first crystalline beryllium-based metal-organic framework has been synthesized and found to exhibit an exceptional surface area useful for hydrogen storage. Reaction of 1,3,5-benzenetribenzoic acid (H(3)BTB) and beryllium nitrate in a mixture of DMSO, DMF, and water at 130 degrees C for 10 days affords the solvated form of Be(12)(OH)(12)(1,3,5-benzenetribenzoate)(4) (1). Its highly porous framework structure consists of unprecedented saddle-shaped [Be(12)(OH)(12)](12+) rings connected through tritopic BTB(3-) ligands to generate a 3,12 net. Compound 1 exhibits a BET surface area of 4030 m(2)/g, the highest value yet reported for any main group metal-organic framework or covalent organic framework. At 77 K, the H(2) adsorption data for 1 indicate a fully reversible uptake of 1.6 wt % at 1 bar, with an initial isosteric heat of adsorption of -5.5 kJ/mol. At pressures up to 100 bar, the data show the compound to serve as an exceptional hydrogen storage material, reaching a total uptake of 9.2 wt % and 44 g/L at 77 K and of 2.3 wt % and 11 g/L at 298 K. It is expected that reaction conditions similar to those reported here may enable the synthesis of a broad new family of beryllium-based frameworks with extremely high surface areas.

Dynamic Photo‐Switching in Metal–Organic Frameworks as a Route to Low‐Energy Carbon Dioxide Capture and Release

For post-combustion carbon dioxide capture technology to realize widespread viability, the energy costs must be drastically reduced. Current adsorbent technologies that rely on pressure, temperature, or vacuum swings consume as much as 40% of the production capacity of a power plant, most of which is associated with the liberation of CO2 from the capture medium. Ultimately this penalty, or parasitic energy load, must be brought closer to the thermodynamic minimum of about 4% to avoid prohibitive cost increases. Given that the triggers for release of adsorbed carbon dioxide, such as vacuum and heating, are so energy intensive, 3] requiring energy from the power plant, there is strong motivation to develop new release triggers that do not require extra energy from the plant, using renewable energy sources such as the sun. In conjunction with this, adsorbents with maximum gas sorption efficiency can further reduce the costs compared to the conventional energy-intensive CO2 gas separation process. Light, and in particular concentrated sunlight, is an extremely attractive stimulus for triggering CO2 release. If used with an adsorbent material that strongly absorbs sunlight concomitant with the desorption of large amounts of CO2, it may be possible to drastically reduce the energy costs. Perhaps the most attractive adsorbent candidates are metal–organic frameworks (MOFs), because of their large adsorption capacities, and the potential for incorporation of light-responsive organic groups within the pore structure. MOFs are an important class of 3D crystalline porous materials comprised of metal centers and organic ligands, joined periodically to establish a crystalline porous array. The large internal surface areas can be used to adsorb unprecedented quantities of gases, with particular interest in hydrogen, methane, 8] and carbon dioxide emergent. 7b,h,9] Methods for the incorporation of light-responsive groups within MOFs include the use of pendant groups pointing into the pores, and filling of pores with light-responsive guest molecules. The responsive groups within these materials may then alter their conformation when exposed to filtered light which results in a change in adsorption capacity, as reported thus far for static conditions. The responsive groups within these MOFs can be statically set to one position or another. For use in photoswing carbon dioxide capture, MOFs that can respond dynamically, or to the broadband radiation found in sunlight whilst loaded with adsorbed gas, are ideal. This will increase the speed of operation and lower the energy costs (see Figure 1)

Post-synthetic structural processing in a metal-organic framework material as a mechanism for exceptional CO2/N2 selectivity

Here we report the synthesis and ceramic-like processing of a new metal-organic framework (MOF) material, [Cu(bcppm)H2O], that shows exceptionally selective separation for CO2 over N2 (ideal adsorbed solution theory, S(ads) = 590). [Cu(bcppm)H2O]·xS was synthesized in 82% yield by reaction of Cu(NO3)2·2.5H2O with the link bis(4-(4-carboxyphenyl)-1H-pyrazolyl)methane (H2bcppm) and shown to have a two-dimensional 4(4)-connected structure with an eclipsed arrangement of the layers. Activation of [Cu(bcppm)H2O] generates a pore-constricted version of the material through concomitant trellis-type pore narrowing (b-axis expansion and c-axis contraction) and a 2D-to-3D transformation (a-axis contraction) to give the adsorbing form, [Cu(bcppm)H2O]-ac. The pore contraction process and 2D-to-3D transformation were probed by single-crystal and powder X-ray diffraction experiments. The 3D network and shorter hydrogen-bonding contacts do not allow [Cu(bcppm)H2O]-ac to expand under gas loading across the pressure ranges examined or following re-solvation. This exceptional separation performance is associated with a moderate adsorption enthalpy and therefore an expected low energy cost for regeneration.

Ending Aging in Super Glassy Polymer Membranes

Aging in super glassy polymers such as poly(trimethylsilylpropyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP), and polymers with intrinsic microporosity (PIM-1) reduces gas permeabilities and limits their application as gas-separation membranes. While super glassy polymers are initially very porous, and ultra-permeable, they quickly pack into a denser phase becoming less porous and permeable. This age-old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super glassy polymers through absorbing a portion of the polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super glassy polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super glassy polymers to be revisited for commercial application in gas separations.

A route to drastic increase of CO2 uptake in Zr metal organic framework UiO-66

CO2 uptake in zirconium MOF UiO-66 almost doubles with post-synthetic exchange of Zr by Ti. This was due to smaller pore size and higher adsorption enthalpy, with good complementarity between experiment and simulation. Furthermore, the full effect is obtained with ~50% Ti loading, precluding the need to fully substitute frameworks for CO2 capture.

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art.

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

Metal-organic frameworks impregnated with magnesium-decorated fullerenes for methane and hydrogen storage.

A new concept is described for methane and hydrogen storage materials involving the incorporation of magnesium-decorated fullerenes within metal-organic frameworks (MOFs). The system is modeled using a novel approach underpinned by surface potential energies developed from Lennard-Jones parameters. Impregnation of MOF pores with magnesium-decorated Mg(10)C(60) fullerenes, denoted as Mg-C(60)@MOF, places exposed metal sites with high heats of gas adsorption into intimate contact with large surface area MOF structures. Perhaps surprisingly, given the void space occupied by C(60), this impregnation delivers remarkable gas uptake, according to our modeling, which predicts exceptional performance for the Mg-C(60)@MOF family of materials. These predictions include a volumetric methane uptake of 265 v/v, the highest reported value for any material, which significantly exceeds the U.S. Department of Energy target of 180 v/v. We also predict a very high hydrogen adsorption enthalpy of 11 kJ mol(-1) with relatively little decrease as a function of H(2) filling. This value is close to the calculated optimum value of 15.1 kJ mol(-1) and is achieved concurrently with saturation hydrogen uptake in large amounts at pressures under 10 atm.

Methane storage in metal organic frameworks

In this applications article (116 references), the use and viability of metal organic frameworks (MOFs) for natural gas storage is critically examined through an overview of the current state of the field. These smart materials can be tuned to deliver best performance according to demand, as a function of temperature, desired storage pressure and mandated fill/release rates. Whilst the chemistry behind optimising natural gas storage performance in MOFs is highlighted, it is contextualised to the specific application in vehicular transport, and the best means of testing performance parameters are canvassed. Future applications of MOFs with natural gas are also discussed.

Kinetically controlled porosity in a robust organic cage material

Microporous materials are of significant interest owing to their central role in gas storage, separation processes, and catalysis. Recently, microporous molecular solids composed of discrete, shape-persistent organic cages have received growing attention because they possess unique properties that set them apart from conventional, extended network materials, such as zeolites, metal–organic frameworks, and covalent organic frameworks. For example, molecular solids are readily solution-processable, provide facile access to multicomponent materials by mix-and-match synthesis, and, by virtue of their noncovalent intermolecular packing, can exhibit advanced properties, such as adsorbatetriggered on/off porosity switching. Unlike extended networks, where solvent-accessible voids are linked through rigid covalent framework solids composed of discrete organic cages predominantly aggregate by relatively weak dispersion forces. Predicting the crystal structures of such weakly aggregating materials is a long-standing challenge in solid-state chemistry, and is, in this field, inherently coupled to estimating the ultimate porosity of a molecular solid from its building units, as different polymorphs can afford solids with dramatically different surface areas. Accordingly, relatively few examples of porous organic solids have been reported. Nevertheless, recent work from the laboratories of Cooper and Mastalerz have demonstrated that the porosity of such materials can be modified through crystal engineering strategies and synthetic processing. 10] Herein we describe the synthesis and characterization of a novel, permanently porous, shape-persistent cage molecule (C1) that is constructed entirely from thermodynamically robust carbon–carbon bonds and has the molecular formula C112H62O2 (Scheme 1). Furthermore, we demonstrate kinetically controlled access to two crystalline polymorphs C1a and C1b that possess dramatically different N2 porosities: polymorph C1a, which is nonporous to N2, and polymorph C1b, which affords a BET surface area of 1153 m g .

Gas‐Separation Membranes Loaded with Porous Aromatic Frameworks that Improve with Age

Porosity loss, also known as physical aging, in glassy polymers hampers their long term use in gas separations. Unprecedented interactions of porous aromatic frameworks (PAFs) with these polymers offer the potential to control and exploit physical aging for drastically enhanced separation efficiency. PAF-1 is used in the archetypal polymer of intrinsic microporosity (PIM), PIM-1, to achieve three significant outcomes. 1) hydrogen permeability is drastically enhanced by 375% to 5500 Barrer. 2) Physical aging is controlled causing the selectivity for H2 over N2 to increase from 4.5 to 13 over 400 days of aging. 3) The improvement with age of the membrane is exploited to recover up to 98% of H2 from gas mixtures with N2 . This process is critical for the use of ammonia as a H2 storage medium. The tethering of polymer side chains within PAF-1 pores is responsible for maintaining H2 transport pathways, whilst the larger N2 pathways gradually collapse.