Katie A. Cychosz

Carbon-Based Supercapacitors Produced by Activation of Graphene

Activated microwave-exfoliated graphite oxide combined with an ionic liquid can be used to make an enhanced capacitor. Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp2-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

Synthesis of self-pillared zeolite nanosheets by repetitive branching

Go with the Flow Effective absorption or filtration can be achieved by having a material with multiple levels of porosity, so that the main flow can occur in the larger channels, while smaller passageways can be used to sequester a secondary material. It can be difficult to make these materials because the pores need to be different sizes, but still fully connected to each other. Zhang et al. (p. 1684) show that a hierarchical zeolite can be made through a simple process using a single structure-directing agent that causes repetitive branching. This leads to a material with improved transport and catalytic properties. Single-step synthesis of pillared zeolite nanosheets is achieved with a common structure-directing agent. Hierarchical zeolites are a class of microporous catalysts and adsorbents that also contain mesopores, which allow for fast transport of bulky molecules and thereby enable improved performance in petrochemical and biomass processing. We used repetitive branching during one-step hydrothermal crystal growth to synthesize a new hierarchical zeolite made of orthogonally connected microporous nanosheets. The nanosheets are 2 nanometers thick and contain a network of 0.5-nanometer micropores. The house-of-cards arrangement of the nanosheets creates a permanent network of 2- to 7-nanometer mesopores, which, along with the high external surface area and reduced micropore diffusion length, account for higher reaction rates for bulky molecules relative to those of other mesoporous and conventional MFI zeolites.

Liquid Phase Adsorption by Microporous Coordination Polymers: Removal of Organosulfur Compounds

The utility of microporous coordination polymers (MCPs) for the adsorption of large organosulfur compounds (benzothiophene, dibenzothiophene, 4,6-dimethyldibenzothiophene) found in fuels is demonstrated. Large capacities are obtained at both low and high sulfur concentrations. For 4,6-dimethyldibenzothiophene, the compound most difficult to remove using current industrial techniques, a capacity of 41 g S/kg MCP at 1500 ppmw S is achieved by UMCM-150. It was determined that the size/shape of the pores in the MCP, rather than the surface area or pore volume, is the most important factor controlling adsorption capacity.

Enabling cleaner fuels: desulfurization by adsorption to microporous coordination polymers.

Microporous coordination polymers (MCPs) are demonstrated to be efficient adsorbents for the removal of the organosulfur compounds dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from model diesel fuel and diesel fuel. For example, packed bed breakthrough experiments utilizing UMCM-150 find capacities of 25.1 g S/kg MCP for DBT and 24.3 g S/kg MCP for DMDBT from authentic diesel indicating that large amounts of fuel are desulfurized before the breakthrough point. Unlike activated carbons, where selectivity has been a problem, MCPs selectively adsorb the organosulfur compounds over other, similar components of diesel. Complete regeneration using toluene at modest temperatures is achieved. The attainment of high selectivities and capacities, particularly for the adsorption of the refractory compounds that are difficult to remove using current desulfurization techniques, in a reversible sorbent indicates that fuel desulfurization may be an important application for MCPs.

Physical adsorption characterization of nanoporous materials: progress and challenges

AbstractWithin the last two decades major progress has been achieved in understanding the adsorption and phase behavior of fluids in ordered nanoporous materials and in the development of advanced approaches based on statistical mechanics such as molecular simulation and density functional theory (DFT) of inhomogeneous fluids. This progress, coupled with the availability of high resolution experimental procedures for the adsorption of various subcritical fluids, has led to advances in the structural characterization by physical adsorption. It was demonstrated that the application of DFT based methods on high resolution experimental adsorption isotherms provides a much more accurate and comprehensive pore size analysis compared to classical, macroscopic methods. This article discusses important aspects of major underlying mechanisms associated with adsorption, pore condensation and hysteresis behavior in nanoporous solids. We discuss selected examples of state-of-the-art pore size characterization and also reflect briefly on the existing challenges in physical adsorption characterization.

Liquid phase separations by crystalline microporous coordination polymers

Crystalline microporous coordination polymers (MCPs) are highly ordered, porous materials that have recently seen increasing attention in the literature. Whereas gas phase separations using MCPs have been extensively studied and reviewed, studies on applications in the liquid phase have lagged behind. This review details the work that has previously been reported on liquid phase separations using MCPs. Both enantioselective separations and separations of complex mixtures have been achieved using either adsorptive selectivities or size exclusion effects. Molecules that have been adsorbed include those as small as water to large organic dyes. In many cases, MCPs outperform their zeolite and activated carbon counterparts both kinetically and in efficiency of separation. The future outlook for the field is discussed in the context of current challenges in separations technologies.

CO2-filling capacity and selectivity of carbon nanopores: synthesis, texture, and pore-size distribution from quenched-solid density functional theory (QSDFT).

Porous carbons synthesized by KOH activation of petroleum coke can have high surface areas, over 3000 m(2)/g, and high CO(2) sorption capacity, over 15 wt % at 1 bar. This makes them attractive sorbents for carbon capture from combustion flue gas. Quenched solid density functional theory (QSDFT) analysis of high-resolution nitrogen-sorption data for such materials leads to the conclusion that it is the pores smaller than 1 nm in diameter that fill with high-density CO(2) at atmospheric pressure. Upon increasing pressure, larger and larger pores are filled, up to about 4 nm at 10 bar. An ideal CO(2)/N(2) selectivity of such carbon materials tends to decrease substantially upon increasing pressure, for example, from about 8-10 at 1 bar to about 4-5 at 10 bar. All in all, this work confirms the robust CO(2)-filling properties of porous carbon sorbents, their low-pressure selectivity advantages, and points to the critical role of <1 nm pores that can be controlled with activation conditions.

Linker-Directed Vertex Desymmetrization for the Production of Coordination Polymers with High Porosity

Five non-interpenetrated microporous coordination polymers (MCPs) are derived by vertex desymmetrization using linkers with symmetry inequivalent coordinating groups, and these MCPs include properties such as rare metal clusters, new network topologies, and supramolecular isomerism. Gas sorption in polymorphic frameworks, UMCM-152 and UMCM-153 (based upon a copper-coordinated tetracarboxylated triphenylbenzene linker), reveals nearly identical properties with BET surface areas in the range of 3300-3500 m(2)/g and excess hydrogen uptake of 5.7 and 5.8 wt % at 77 K. In contrast, adsorption of organosulfur compounds dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) shows remarkably different capacities, providing direct evidence that liquid-phase adsorption is not solely dependent on surface area or linker/metal cluster identity. Structural features present in MCPs derived from these reduced symmetry linkers include the presence of more than one type of Cu-paddlewheel in a structure derived from a terphenyl tricarboxylate (UMCM-151) and a three-bladed zinc paddlewheel metal cluster in an MCP derived from a pentacarboxylated triphenylbenzene linker (UMCM-154).

Carbide-Derived Carbon Monoliths with Hierarchical Pore Architectures†

Porous carbon materials are crucial components in catalysis, gas storage, electronics, and biochemistry. A hierarchical pore architecture in these materials is essential to achieve high surface areas combined with advanced mass transport kinetics. Widely used approaches for the generation of microor mesopores are activation and nanocasting. In contrast, macroporous carbon materials are primarily obtained by carbonization of polymeric precursor gels or replication of larger templates. A relatively new class of microand mesoporous carbon material with tunable porosity are carbide-derived carbon materials (CDCs). High-temperature chlorination of carbides leads to selective removal of metalor semi-metal atoms and allows control over the pore size of the resulting CDCs in a subngstrcm range by changing synthesis conditions or the carbide precursor. These materials have been studied for applications in gas storage and as electrode materials in supercapacitors because of their high specific surface areas. Recently, metal etching from pyrolyzed pre-ceramic components (polysilsesquioxanes or polysilazanes) was found to be a useful route towards carbide-derived carbon materials with enhanced porosity and gas-storage properties. A significant step towards ultrahigh specific surface area combined with a hierarchical mesoporous–microporous system was achieved using nanocasting of silica templates (SBA-15 or KIT-6) with polycarbosilane precursors and subsequent chlorine treatment of the resulting ordered mesoporous silicon carbides. These ordered mesoporous CDCs offer specific surface areas as high as 2800 mg 1 and total pore volumes of up to 2 cmg . Their mesostructure can be easily controlled by changing the silica hard template, resulting in excellent performance in protein adsorption, gas storage, and as electrodes for supercapacitors. However, such carbon materials are available only as nonstructured micrometer-sized powders and cannot be shaped into films without the addition of binders or the use of high mechanical stress, leading to structural deformation. Chlorine treatment of mechanically mixed Si/SiC precursors was found to be a useful route towards monolithic CDC with a hierarchical pore system. The presence of a free metal phase in the precursor system provides the opportunity to introduce a secondary macroporosity of 3 mm sized channels with a volume of 0.23 cmg 1 along with the microporous carbide-derived carbon material system. The introduction of large transport pores in polymerbased CDCs might be an alternative way to form materials that combine high surface areas with efficient fluid transport. The current literature describes a variety of routes for the production of highly macroporous ceramics from precursor polymers with controllable cell and window sizes. In particular, direct blowing of polycarbosilanes was found to be a useful approach for the generation of silicon carbide foams that might be suitable materials for the production of hierarchical CDCs. In the following, we describe a novel synthesis route for monolithic carbide-derived carbon materials, including micro-, meso-, and macroporous structures with extremely high specific surface area. They can be obtained by hightemperature chlorination of macroporous polymer-derived silicon carbide (SiC-PolyHIPE). A soft-templating approach starting from a high internal phase emulsion (HIPE) was used with an external oil phase consisting of liquid polycarbosilane SMP-10 and the cross-linker paradivinylbenzene. Using Span-80 as surfactant to stabilize the internal water phase, the application of oxidic or carbon hard templates and the corresponding template removal under harsh conditions is no longer necessary. After cross-linking the polymer chains, the resulting PolyHIPEs were pyrolyzed to silicon carbides at maximum temperatures of 700, 800, and 1000 8C and subsequently converted into CDCs by chlorine treatment at the maximum pyrolysis temperature (Supporting [*] M. Oschatz, L. Borchardt, Dr. I. Senkovska, N. Klein, Dr. R. Frind, Prof. Dr. S. Kaskel Department of Inorganic Chemistry Dresden University of Technology Bergstrasse 66, 01062 Dresden (Germany) E-mail: stefan.kaskel@chemie.tu-dresden.de

A Microporous Copper Metal–Organic Framework with High H2 and CO2 Adsorption Capacity at Ambient Pressure

Metal–organic frameworks (MOFs) as highly porous materials have gained increasing interest because of their distinct adsorption properties. They exhibit a high potential for applications in gas separation and storage, as sensors as well as in heterogeneous catalysis. In the last few years, the H2 storage capacity of MOFs has been considerably increased. Mesoporous MOFs show high adsorption capacities for CH4, CO2, and H2 at high pressures. [2, 3, 7–10] To increase the uptake of H2 and CO2 by physisorption at ambient pressure, adsorbents with small micropores as well as high specific surface areas and micropore volumes are required. 12] Such microporous materials seem to be more appropriate for gas-mixture separation by physisorption than mesoporous materials. For gas separation in MOFs the interactions between the fluid adsorptive and “open metal sites” (coordinatively unsaturated binding sites) or the ligands are regarded as important. Industrial processes, such as natural-gas purification or biogas upgrading, can be improved with those materials during a vapor-pressure swing adsorption cycle (VPSA cycle) or a temperature swing adsorption cycle (TSA cycle). The microporous MOF series CPO-27-M (M = Mg, Co, Ni, Zn), for example, shows very high CO2 uptakes at low pressures (< 0.1 MPa). Concerning H2 adsorption, the microporous MOF PCN-12 offers with 3.05 wt % the highest uptake at ambient pressure and 77 K reported to date. Herein, we present a novel microporous copper-based MOF 3 1[Cu(Me-4py-trz-ia)] (1; Me-4py-trz-ia 2 = 5-(3methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl)isophthalate) with extraordinarily high CO2 and H2 uptakes at ambient pressure, the H2 uptake being similar to that in PCN-12. The ligand Me-4py-trz-ia (Figure 1 a), which can be obtained from cheap starting materials by a three-step synthesis in good yield, combines carboxylate, triazole, and pyridine functions and is adopted from a recently presented series of linkers, for which up to now only a few coordination polymers are known. Single crystals of 1 that are suitable for X-ray crystal structure analysis were prepared by diffusion of copper sulfate and H2(Me-4py-trz-ia). Larger quantities of microcrystalline 1 are obtained not only by solvothermal synthesis, but also in multigram scale by simple reflux of the starting materials in water/acetonitrile (see Supporting Information). According to the single crystal X-ray structure analysis, 1 crystallizes in the monoclinic space group P21/c (no. 14) with four formula units per unit cell. The asymmetric unit contains one linker anion and two crystallographically independent Cu ions residing on inversion centers. The copper ion Cu1 is coordinated in a square-planar fashion by two monodentate carboxylate and two pyridine functions in trans position leaving two accessible open metal sites per Cu1 atom (Figure 1b), whereas the second copper ion Cu2 is coordinated by monodentate triazole and chelating carboxylate groups forming a distorted octahedron (Figure 1 c). For this reason, both copper ions represent planar fourfold nodal points and the ligands act as tetradentate linkers in a 3D network with pts topology and a 3D pore system (Figure 1d). With narrow channels of about 250 600 pm in crystallographic c direction connecting the micropores with a diameter of approximately 550 pm, the structure has a calculated porosity of about 55% according to PLATON. Powder X-ray diffraction (PXRD) studies on the assynthesized microcrystalline sample 1a confirm both, the agreement with the simulated powder pattern of 1 based on [*] D. L ssig, J. Lincke, Prof. Dr. R. Gl ser, Prof. Dr. H. Krautscheid Universit t Leipzig, Fak. f r Chemie und Mineralogie Johannisallee 29, 04103 Leipzig (Germany) E-mail: krautscheid@rz.uni-leipzig.de