Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.

Lithium-ion batteries are current power sources of choice for portable electronics, offering high energy density and longer lifespan than comparable technologies. Significant improvements in rate and durability for inexpensive, safe and non-toxic electrode materials may enable utilization in hybrid electric or plug-in hybrid electric vehicles (PHEVs). Furthermore, recent efforts for hybrid electric vehicle applications have been focused on new anode materials with slightly more positive insertion voltages with respect to Li/Li þ to minimize any risks of high-surface-area Li plating while charging at high rates, a major safety concern.[1] In hybrid electric vehicles, batteries are cycled with $10% charge/discharge from the point where the cell is at 50% capacity. when cycled in a voltage window of 3.0-0.005 V, but this material suffered from poor cycling stability, with the capacity degrading to 400 mA h g À1 in $100 cycles. [8] By increasing the cut-off potential to 0.2 V and employing a slow rate (discharge and charge at C/15 and C/20, respectively), the cycling was more stable, ranging from 600-400 mA h g À1 in 100 cycles.[8] A tin-doped MoO 3 system was also explored, and the average charge potential was lowered, but at the expense of capacity fading.[9] Here we report on anodes fabricated from crystalline MoO 3 nanoparticles that display both a durable reversible capacity of 630 mA h g À1 and durable high rate capability.The nanoparticle anodes show no capacity degradation for 150 cycles between 3.5 to 0.005 V with both charge and discharge at C/2, compared to micrometer-sized particles where the capacity quickly fades. (Typically both decreased capacity and rapid degradation are observed when deep cycles are employed at higher rates.) Upon cycling, long-range order in the MoO 3 nanostructures is lost. First-principle calculations are employed in order to explain the nanoparticle durability despite the loss of structural order. The crystalline molybdenum oxide nanoparticles are grown at high density by a previously described economical hot-wire chemical vapor deposition (HWCVD) technique.[10] Figure 1a shows a representative transmission electron microscopy (TEM) image of the as-synthesized nanoparticles. Extensive TEM analyses reveal that the bulk powder contains almost exclusively nanospheroids with diameters of 5-20 nm, thus providing a short solid-state Li-ion diffusion path. A highresolution TEM image of a nanoparticle where the lattice fringes are visible is shown in Figure 1b. A simple electrophoresis deposition process [11] is employed to fabricate high-surface area porous nanoparticle films on a stainless steel electrode with a thickness of $2 mm. Figure 1c displays a scanning electron microscopy (SEM) image of an electrophoresis-deposited film. The mass density of the nanoparticle film was found to be $3.3 g cm À3 from mass and thickness data compared to 4.7 g cm À3 for the bulk material. Furthermore, the electrode is comprised of entirely COMMUNICATION

Hydrogen holds promise as a clean alternative automobile fuel, but its on-board storage presents significant challenges due to the low temperatures and/or high pressures required to achieve a sufficient energy density. The opportunity to significantly reduce the required pressure for high density H 2 storage persists for metal-organic frameworks due to their modular structures and large internal surface areas. The measurement of H 2 adsorption in such materials under conditions most relevant to on-board storage is crucial to understanding how these materials would perform in actual applications, although such data have to date been lacking. In the present work, the metalorganic frameworks M 2 (m-dobdc) (M = Co, Ni; m-dobdc 4− = 4,6-dioxido-1,3benzenedicarboxylate) and the isomeric frameworks M 2 (dobdc) (M = Co, Ni; dobdc 4− = 1,4dioxido-1,3-benzenedicarboxylate), which are known to have open metal cation sites that strongly interact with H 2 , were evaluated for their usable volumetric H 2 storage capacities over a range of near-ambient temperatures relevant to on-board storage. Based upon adsorption isotherm data, Ni 2 (m-dobdc) was found to be the top-performing physisorptive storage material with a usable volumetric capacity between 100 and 5 bar of 11.0 g/L at 25 °C and 23.0 g/L with a temperature swing between −75 and 25 °C. Additional neutron diffraction and infrared spectroscopy experiments performed with in situ dosing of D 2 or H 2 were used to probe the hydrogen storage properties of these materials under the relevant conditions. The results provide benchmark characteristics for comparison with future attempts to achieve improved adsorbents for mobile hydrogen storage applications.

The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels production. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data analysis technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state 13 C NMR and subtraction of the spectrum of a standard amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addition of water increased cellulose order for all the cellulose samples studied.

ABSTRACT:We have synthesized, characterized, and computationally validated the high Brunauer−Emmett− Teller surface area and hydrogen uptake of a new, noncatenating metal−organic framework (MOF) material, NU-111. Our results imply that replacing the phenyl spacers of organic linkers with triple-bond spacers is an effective strategy for boosting molecule-accessible gravimetric surface areas of MOFs and related high-porosity materials.T he chemical and structural diversity of metal−organic frameworks (MOFs) is one of the most notable characteristics of these materials. MOFs are hybrid materials composed of inorganic nodes and organic struts. 1−3 The most intriguing examples exhibit large internal surface areas; ultralow densities; uniform channels, cavities, and voids; and permanent porosity. Because of these exceptional properties, MOFs are being investigated for many potential applications, including gas storage, 4−8 gas and chemical separations, 9−12 chemical catalysis, 13,14 sensing, 15 ion exchange, 16 drug delivery, 17 and light harvesting. 18,19 Furthermore, the availability of singlecrystal structures of MOFs allows the use of computational modeling to calculate guest adsorption capabilities and other properties, which can help in screening MOFs for particular applications and improving our understanding of their performance. 20 The fact that these computational methods can be usefully applied gives MOFs a significant advantage over their amorphous counterparts.Rising concerns about climate change have intensified the search for environmentally friendly and renewable fuels such as water-derived H 2 , cellulosic ethanol, and photo-or electrochemically generated methane. Although molecular hydrogen is a compelling alternative to gasoline in many respects, highdensity storage is a significant challenge for the viability of hydrogen-powered vehicles. In order to drive 300 miles, 5 to 13 kg of H 2 are needed. Therefore, technologies that can efficiently concentrate gases at lower pressures, such as adsorption on porous materials, are desirable. The U.S. Department of Energy (DOE) has set targets for on-board H 2 storage systems for the year 2017: 5.5 wt % in gravimetric capacity and 40 g/L of volumetric capacity at an operating temperature in the range −40 to 60°C under a maximum delivery pressure of 100 atm. 21 Recently, automobile manufacturer Mercedes-Benz has announced its intention to use MOFs for mobile hydrogen storage at cryogenic temperatures. 22 Required are materials with surface areas of ∼24 million square feet of surface area per pound (4900 m 2 /g) and the ability to store substantial hydrogen at 435 psi (30 bar). MOFs are powerful contenders relative to other porous materials in meeting these conditions.We set out to make a MOF that satisfies both of the aforementioned requirements (∼4900 m 2 /g and high hydrogen uptake at 30 bar). We turned our attention to (3,24)-paddlewheel-connected MOF networks (rht topology), 23 for which catenation (interpenetration or interweaving of multiple frameworks)...