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Crystallization experiments performed with highly supercooled solutions produced highly pure (> 99 wt%) and highly crystalline mesocrystals of curcumin from impure solution (~22% of two structurally similar impurities) in one step. These mesocrystals exhibited a crystallographic hierarchy and were composed of perfectly or imperfectly aligned nanometer thick crystallites. X-ray diffraction and spectroscopic analysis confirmed that the spherulites are a new solid form of curcumin. A theoretical hypothesis based on particle aggregation, double nucleation and a repeated secondary nucleation is proposed to explain the spherulite formation mechanism. The experimental results provide for the first time evidence for an organic molecule to naturally form spherulites without the presence of any stabilizing agent. Control experiments performed with highly supercooled pure solutions produced spherulites confirming the formation of spherulites is attributed to the high degree of supercooling and not due to the presence of impurities. Likewise control experiments performed with a lower degree of supercooling produced impure crystals of curcumin via the classical molecular addition mechanisms. These experimental observations all together provide first time evidence for particle mediated crystallization as an alternate and efficient method to purify organic compounds.

ispartof: ENERGY STORAGE MATERIALS vol:15 pages:380-387 status: published

Neutron scattering has been used to reveal the structure and dynamics of molecular H2 physisorbed into the two-dimensional pores of sparingly hydrated Ca-laponite clay. Thermal pretreatment of the clay at 415 K under vacuum yielded an interlayer composition in the 1.0–1.5 water molecules per Ca2+ cation range and provided a vacant gallery height of 2.82 A. This value is very well matched to the diameter of molecular hydrogen and allows intercalation of H2 up to the point where a liquid-like monolayer is formed within the clay. At a low coverage of 0.1 H2 per cation the isosteric heat of adsorption is 9.2 kJ mol–1. Quasielastic neutron scattering experiments conducted at 40–100 K reveal two populations of H2 within the clay. First, we find molecules that are localized close to the partially hydrated Ca2+ cations. Second, we identify a more mobile liquid-like population whose motion is captured by jump diffusion. At 40 K, the H2 diffusion coefficient is 2.3 ± 0.5 × 10–5 cm2 s–1. This is an order of magnitud...

A new type of hierarchically porous carbon (HPC) structures of simultaneously high surface area and high pore volume has been synthesised from carefully controlled carbonization of in-house optimised metal–organic frameworks (MOFs). Changes in synthesis conditions lead to millimetre-sized MOF-5 crystals in a high yield. Subsequent carbonization of the MOFs yield HPCs with simultaneously high surface area, up to 2734 m2 g−1, and exceptionally high total pore volume, up to 5.53 cm3 g−1. In the HPCs, micropores are mostly retained and meso- and macro- pores are generated from defects in the individual crystals, which is made possible by structural inheritance from the MOF precursor. The resulting HPCs show a significant amount of CO2 adsorption, over 27 mmol g−1 (119 wt%) at 30 bar and 27 °C, which is one of the highest values reported in the literature for porous carbons. The findings are comparatively analysed with the literature. The results show great potential for the development of high capacity carbon-based sorbents for effective pre-combustion CO2 capture and other gas and energy storage applications.

We report controllable and enhanced hydrogen release kinetics at reduced temperatures in ammonia borane (AB) catalyzed by Zn-MOF-74. AB is loaded into the unsaturated Zn-metal coordinated one-dimensional hexagonal open nanopores of MOF-74 (ABMOF) via solution infiltration. The ABMOF system provides clean hydrogen by suppressing the release of detrimental volatile byproducts such as ammonia, borazine and diborane. These byproducts prevent the direct use of AB as a hydrogen source for polymer electrolyte membrane fuel cell applications. The H2 release temperature, kinetics, and byproduct generation are dependent on the amount of AB loading. We show that nanoconfinement of AB and its interaction with the active Zn-metal centers in MOF are important in promoting efficient and clean hydrogen generation.

We report the hydrogenation temperature and pressure dependence of hydrogen absorption capacity in CaC6. In addition, the structure and phase stability of hydrogenated CaC6, LiC6 and KC8 has been investigated using X-ray diffraction and Raman spectroscopy. It is found that the hydrogen chemisorption in both CaC6 and LiC6 leads to either metastable or higher stage intermediate compounds but eventually leaves completely deintercalated graphite by forming stable metal hydrides. In contrast hydrogenation of KC8 generates a restaged ternary hydride compound. The phase stability of hydrogenated compounds is discussed in the text based on the observed experimental results and correlated to the thermodynamic and kinetic aspects of intercalated metal.

Graphene-like nanosheets have been synthesized by the reduction of a colloidal suspension of exfoliated graphite oxide. The morphology and structure of the graphene powder sample was studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The graphene sheets are found to be in a highly agglomerated state, with many wrinkles. The sample has a BET surface area of 640 m 2 /g as measured by nitrogen adsorption at 77 K. Hydrogen adsorption–desorption isotherms were measured in the temperature range 77–298 K and at pressures of up to 10 bar. This gives hydrogen adsorption capacities of about 1.2 wt.% and 0.1 wt.% at 77 K and 298 K, respectively. The isosteric heat of adsorption is in the range of 5.9–4 kJ/mol, indicating a favourable interaction between hydrogen and surface of the graphene sheets. The estimated room temperature H 2 uptake capacity of 0.72 wt.% at 100 bar and the isosteric heat of adsorption of our sample are comparable to those of high surface area activated carbons, however significantly better than the recently reported values for graphene and a range of other carbon and nanoporous materials; single and multi walled carbon nanotubes, nanofibers, graphites and zeolites.

The structure and superconducting properties of high temperature hydrogenated calcium-graphite intercalation compound, CaC 6 have been investigated using room temperature X-ray diffraction, and temperature and field dependence of magnetisation. It is found that the hydrogenation can only decompose the CaC 6 phase, and generate a mixture of CaH 2 and graphite as the final compound. The hydrogenation of CaC 6 also reveals a degradation of its superconducting properties. The experimental results are discussed in detail and it is found that the formation of stable CaH 2 and deintercalation are the main source for observed phase separation and suppression in superconductivity.

A doubly interpenetrated semiconducting MOF Zn(4)O(2,6-NDC)(3)(DMF)(1.5)(H(2)O)(0.5)·4DMF·7.5H(2)O (UTSA-38) of a cubic net has been constructed, which exhibits photocatalytic activity for the degradation of methyl orange in aqueous solution.

A 3D porous metal-organic framework and method of making are described. In some embodiments, a 3D porous metal-organic framework may be based on a trinodal (3,3,4) net of zyg topology by the self-assembly of the nonlinear hexacarboxylate (BHB) with the paddle-wheel Cu 2 (COO) 4 cluster. Although its porosity and surface area are moderate, the open copper sites and optimal pore spaces enable the pore spaces to be fully utilized for methane storage, resulting in a high methane storage density and high absolute volumetric methane storage at room temperature and 35 bar. By the immobilization of high density open metal sites and the deliberate control of the pore space for their efficient methane storage, this porous MOF functions as an efficient media for methane and natural gas storage.

We report the temperature and filed dependence of magnetic behaviour of the Ho1-xMmxCo2 (x = 0, 0.1, 0.2, 0.3 and 0.4; Mm = mischmetal) alloys and their crystalline hydrides. The change of magnetic transition temperature (TC), order of magnetic transition and total magnetization of the alloys with increasing Mm content is studied. The alloys exhibit strong composition and field dependence of thermal hysteresis and spin-reorientation below TC. The effect of hydrogen absorption on the magnetic behaviour of alloys is studied, and the results are correlated to the unit cell volume expansion and decrease in the conduction electron density. � 2010 Elsevier B.V. All rights reserved.

We report the synthesis of nanostructured stage-2 potassium graphite, KC24, by intercalation of turbostratic graphite nanofibers produced from an electrospun polymer, and compare its properties with exfoliated graphite-based KC24. The nanostructured KC24sample has low crystalline order and slightly increased interlayer spacing of 8.76 Å, compared with 8.65 Å in the bulk sample, indicating minimal registration of the graphite planes. Time-resolved time-of-flight neutron diffraction on both nanostructured and bulk KC24under ammoniation is suggestive of a more homogeneous and faster pressure-modulated phase transition to the ternary ammoniated potassium-graphite in the nanostructured material. Following ammoniation, negligible hydrogen uptake is observed at 50 K.

We show that the MOF NU-111 exhibits equally high volumetric and gravimetric methane uptake values, both within ≈75% of the DOE targets at 300 K. Upon reducing the temperature to 270 K, the uptake increases to 0.5 g g(-1) and 284 cc(STP) per cc at 65 bar. Adsorption of CO2 and H2 is also reported. Simulated isotherms are in excellent agreement with those obtained from experiments.

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.

We report the synthesis of a range of high surface area graphene oxide derived carbons (GODCs) and their applications toward carbon capture and methane storage. We obtain largely increased surface areas up to nearly 1900 m2 g−1 for GODC samples from 10 m2 g−1 of precursor graphene oxide (GO). Our GODCs reveal favourable gas adsorption capacities compared to other high surface area carbons. We show that producing high surface area carbons from GO precursor is a viable method, and the porosity parameters are easily tuneable for their potential gas adsorption applications.

We report detailed synthesis of a range of porous graphene oxide frameworks (GOFs) by expansion of graphene oxide (GO) sheets with various linear boronic acid pillaring units in a solvothermal reaction. The GOF structures develop through boronate-ester formation as a result of B–O bonding between boronic acids and oxygen functional groups on the GO layers. Synthesized GOFs exhibit periodic layered structures with largely expanded interlayer spacing as characterized by X-ray powder diffraction (XRD). The boronate-ester link formation is further evidenced by Fourier transform infrared (FTIR) and Raman spectroscopy. Furthermore, the strong boronate-ester bonds between GO layers results in improved thermal stability over the precursor GO. The solvent-free, evacuated frameworks provide highly increased accessible surface area for nitrogen adsorption compared to GO alone, which depends on the type and length of the boronic acid, indicating the importance of pillaring unit. Both isosteric heat of adsorption (Qst) and the adsorbed hydrogen capacity per surface area are twice as large as typical porous carbon materials and comparable to metal–organic frameworks (MOFs) with open metal centers. This enhanced Qst and adsorption capacity is attributed to optimum interlayer spacing between graphene planes such that hydrogen molecules interact with both surfaces. Finally, our systematic study reveals the profound effect of both synthesis and activation temperatures to obtain porous framework structures.

The magnetic behaviour in Dy1-xMmxCo2 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5; Mm = mischmetal) compounds is reported using temperature and field dependence of magnetization (M-T and M-H respectively) measurements. A strong composition dependent irreversibility is observed in both the M-T and M-H scans below the magnetic ordering temperature (TC). A clear change of the first-order magnetic transition of DyCo2 to a second-order one in Dy0.5Mm0.5Co2 is evidenced by M-T and a series of Arrott (M2 versus H/M) plots, obtained from the M-H isotherms around TC. The variation in induced moments of the Co sublattice is estimated. It is found that the Mm substitution can only lead to a considerable reduction in the TC, saturation magnetization, and Co moment. The observed behaviour of M-T and M-H plots with increasing Mm content is discussed in detail. � 2010 IOP Publishing Ltd.

We report the first two examples of borohydride ammonia borane complexes: Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2. Their structures are successfully determined using a combination of X-ray diffraction and first-principles calculations. Both structures are composed of alternating layers of borohydride and ammonia borane. Examination of bond lengths indicates that this arrangement is stabilized via dihydrogen bonding between ammonia borane and their surrounding BH4−, and the interactions between ammonia borane ligands and cations. Our experimental results show that more than 10 wt% and 11 wt% hydrogen can be released from Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2, respectively. Negligible ammonia was detected compared to ammonia borane and its ammidoborane derivatives. Further improvements are needed to reduce borazine emission. Cycling studies show that decomposed Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2 can be partially hydrogenated under hydrogen pressures at high temperatures.

We report the effects of hydrogenation on the structure and superconducting properties of good quality bulk superconducting CaC6 samples prepared from Madagascar graphite single crystals using a Ca-metal vapour transport method. The hydrogenation of a CaC6 sample takes several hours during which, at different hydrogen exposure times, the structural and superconducting studies were carried out using X-ray diffraction, Raman scattering, and temperature and field dependence of magnetization measurements. These studies reveal that only a mixture of CaH2 and graphite is obtained upon hydrogenation of CaC6. The successive suppression of superconducting volume fraction and critical temperature is observed when increasing the hydrogenation time. The results reveal that there is a definite relation between structure and superconductivity in the hydrogenated CaC6 samples. The changes in stoichiometry and inevitable Ca-sub-lattice disorder during the deintercalation process are considered to be the main sources for the change in the superconducting transition temperature.

Reduced graphene-oxide (RGO)-based electrodes in supercapacitors deliver high energy/power capacities compared to typical nanoporous carbon materials. However, extensive critical analysis of literature reveals enormous discrepancies (up to 250 F g-1 ) in the reported capacitance (variation of 100-350 F g-1 ) of RGO materials synthesized under seemingly similar methods, inhibiting an understanding of capacitance variation. Here, the key factors that control the capacitance performance of RGO electrodes are demonstrated by analyzing and optimizing various types of commonly applied electrode fabrication methods. Beyond usual data acquisition parameters and oxidation/reduction properties of RGO, a substantial difference of more than 100% in capacitance values (with change from 190 ± 20 to 340 ± 10 F g-1 ) is found depending on the electrode preparation method. For this demonstration, ≈40 RGO-based electrodes are fabricated from numerous distinctly different RGO materials via typically applied methods of solution (aqueous and organic) casting and compressed powders. The influence of data acquisition conditions and capacitance estimation practices are also discussed. Furthermore, by optimizing electrode processing method, a direct surface area governed capacitance relationship for RGO structures is revealed.