Jamie Ford

Graphene Oxide Framework Materials: Theoretical Predictions and Experimental Results†

A series of idealized model systemswith various diboronic acid linker concentrations (and con-sequently different pore size, pore volume, and surface areas)were examined (see Supporting Information for details).Structural optimization yielded a circa 1.1 nm interlayerseparation for these ideal structures. The simulated absolute

Nanoconfinement and Catalytic Dehydrogenation of Ammonia Borane by Magnesium‐Metal–Organic‐Framework‐74

Ammonia borane (NH3BH3, AB) has recently received much attention as a promising hydrogen-storage medium among a very large number of candidate materials because of its satisfactory air stability, relatively low molecular mass (30.7 gmol ), and remarkably high energy-storage densities (gravimetric and volumetric hydrogen capacities are 19.6wt% and 140 gL , respectively). However, the direct use of pristine AB as a hydrogen energy carrier in onboard/fuel-cell applications is prevented by its very slow dehydrogenation kinetics below 100 8C and the concurrent release of detrimental volatile by-products such as ammonia, borazine, and diborane. Many different methods have been adopted to promote efficient H2 generation from AB, including catalytic hydrolysis in aqueous solution, ionic liquids, organic solvents, and thermodynamic modifications by formation of hybrid structures with transition metals, alkali-, or alkaline-earth metal/hydrides, 12] or nanoconfined phases using porous scaffolds. However, many of these methods rely on the usage of heavy metal catalysts, aqueous or nonaqueous solutions, and ionic liquids, all of which make the hydrogen density of the systems unacceptably low for practical applications. Furthermore, the vigorous reactions, hygroscopic properties, and water solubility of borohydrides have negative impacts on the dehydrogenation performance and make it difficult to control the release of hydrogen. The other approach is made, in particular, nanocomposition of AB within porous scaffoldings. However, systems still suffers one or more of the followings: either the nanocomposite is heavier or cannot prevent the generation of all the volatile by-products. Hence, more work needs to be done to explore the potential role that catalysts can play to further improve the controllable H2-release kinetics under moderate conditions while at the same time preventing the generation of detrimental byproducts. Over the past few years, porous metal–organic frameworks (MOFs) have emerged as promising multifaceted materials, combining such functions as catalytic activity, 24] shape-selectivity, templating, and purification. Crystalline MOF structures are composed of metal sites linked to organic ligands, yielding three-dimensional extended frameworks that often possess considerable porosity. In principle, the combination of nanoporosity and active metal sites in MOFs makes them potentially useful materials for promoting the decomposition of AB. However, until now, such a use of MOFs has been rare and any future success would depend crucially on the particular choices of a suitable metal center, pore structure, and thermal stability. For instance, Li et al. were the first to show that Y-based MOF as a solid state decomposition agent for AB. The main drawback of AB-Y-MOF is largely added weight due to the heavy Y metal. In addition, for the given very narrow pore structure of Y-MOF, as low as approximately 8 wt% of AB loading is achieved for the reported 1:1 mole ratio. Thus, it is highly desirable to have a light weight MOF with stable and suitable nanopore channels that can hold more than one AB molecule. Herein, we show that the porous MgMOF-74 (Mg2ACHTUNGTRENNUNG(DOBDC), DOBDC=2, 5-dioxido-1, 4-benzenedicarboxylate) is a promising candidate for nanoconfinement and catalytic decomposition of AB for clean and efficient H2 generation. Mg-MOF-74 has a rigid framework, composed of one-dimensional (1D) hexagonal channels (Figure 1a) with a nominal diameter of approximately 12 running parallel to the DOBDC ligands. In as-synthesized material, the Mg cations are coordinated with five oxygen atoms from the DOBDC ligands and one oxygen atom from a terminal water molecule. However, upon heating under vacuum, the terminal water molecules can be easily removed, leading to unsaturated (open) Mg metal sites (decorated on the edges of the hexagonal pore channels) with an open pore structure of high surface area (>1000 mg ). The open Mg metal sites play a vital role in enhanced binding of various gas molecules (H2, CH4, C2H2, NO, etc. ) and successfully used to promote molecular separation. Figure 1b represents AB confinement within the MOF pores as obtained [a] Dr. S. Gadipelli, Dr. J. Ford, Dr. W. Zhou, Dr. H. Wu, Dr. T. J. Udovic, Dr. T. Yildirim NIST Center for Neutron Research Gaithersburg MD 20899-6102 (USA) Fax: (+1)301-921-9847 E-mail : taner@seas.upenn.edu gsrini@seas.upenn.edu [b] Dr. S. Gadipelli, Dr. J. Ford, Dr. T. Yildirim Department of Materials Science and Engineering University of Pennsylvania, Philadelphia PA, 19104 (USA) [c] Dr. W. Zhou, Dr. H. Wu Department of Materials Science and Engineering University of Maryland, College Park MD, 20742 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100090.

Nanoconfined ammonia borane in a flexible metal–organic framework Fe–MIL-53: clean hydrogen release with fast kinetics

We demonstrated the dehydrogenation behaviour of nanoconfined ammonia borane (AB) in Fe–MIL-53, a flexible metal–organic framework (MOF) by solid state thermolysis. We observed clean hydrogen release with fast kinetics at reduced temperatures.

Synthesis of photoacid crosslinkable hydrogels for the fabrication of soft, biomimetic microlens arrays

Soft, biomimetic microlens arrays were fabricated by interference lithography from the copolymers of poly(2-hydroxyethyl methacrylate), whose hydroxyl groups were crosslinked by photoacids and external crosslinkers.

A highly practical route for large-area, single layer graphene from liquid carbon sources such as benzene and methanol†

Through a detailed systematic study, we determined the parameters critical for high-quality, single-layer graphene formation and developed a straightforward synthesis that requires no explosive hydrogen or methane gas flow. The synthesis is further simplified by using only a liquid carbon source such as methanol. Of over a dozen liquid carbon sources studied, methanol is found to be unique in that it acts as both a carbon/hydrogen source and an inhibitor to amorphous carbon growth. No deposition of amorphous carbon was observed, regardless of vapor pressure, unlike methane and other hydrocarbons. Finally, we describe a protocol to control graphene growth to a single side or selected location on the copper substrate, which is required for most device applications. Using our novel methods, we have prepared high-quality, single-layer graphene samples at the inch scale that have been thoroughly characterized with Raman spectroscopy, optical transmittance, scanning electron microscopy and sheet resistance measurements. Our method is safe, simple, and economical and will be of value to both fundamental researchers and nanodevice engineers.

Probing the Structure, Composition, and Spatial Distribution of Ligands on Gold Nanorods

The structure and size of ligands attached to the surfaces of gold nanorods, such as adsorbed surfactants or grafted polymers, are important considerations that facilitate the use of such nanoparticles in the human body, in advanced materials for energy harvesting, or in devices for single molecule detection. Here, we report small-angle neutron scattering (SANS) measurements from surfactant or poly(ethylene glycol) (PEG) coated gold nanorods in solution, which quantitatively determine the location, structure, and composition of these surface layers. In addition, by synthesizing gold nanorods using seed crystals which are coated with deuterated cetyltrimethylammonium bromide (dCTAB), we are able to exploit the isotopic sensitivity of SANS to study, for the first time, the retention of surfactant from the seed crystals to the final gold nanorod product, finding that very little exchange of the deuterated with hydrogenated surfactant occurs. Finally, we demonstrate that, when Au NRs are PEGylated using standard techniques, the surfactant bilayer remains intact, and while mass spectrometry detects the presence of both surfactant and PEG, the composition as measured from SANS is predominantly that of the surfactant. These measurements not only provide new insight into the synthesis and functionalization of gold nanorods but provide a quantitative picture of the structure of grafted polymer and surfactant layers on gold nanorod surfaces which has implications for the fabrication of plasmonic and biomedical materials.

Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation

We report a variety of experiments and calculations and their interpretations regarding methyl group (CH3) rotation in samples of pure 3-methylglutaric anhydride (1), pure 3-methylglutaric acid (2), and samples where the anhydride is slowly absorbing water from the air and converting to the acid [C6H8O3(1) + H2O → C6H10O4(2)]. The techniques are solid state 1H nuclear magnetic resonance (NMR) spin-lattice relaxation, single-crystal X-ray diffraction, electronic structure calculations in both isolated molecules and in clusters of molecules that mimic the crystal structure, field emission scanning electron microscopy, differential scanning calorimetry, and high resolution 1H NMR spectroscopy. The solid state 1H spin-lattice relaxation experiments allow us to observe the temperature dependence of the parameters that characterize methyl group rotation in both compounds and in mixtures of the two compounds. In the mixtures, both types of methyl groups (that is, molecules of 1 and 2) can be observed independently and simultaneously at low temperatures because the solid state 1H spin-lattice relaxation is appropriately described by a double exponential. We have followed the conversion 1 → 2 over periods of two years. The solid state 1H spin-lattice relaxation experiments in pure samples of 1 and 2 indicate that there is a distribution of NMR activation energies for methyl group rotation in 1 but not in 2 and we are able to explain this in terms of the particle sizes seen in the field emission scanning electron microscopy images.