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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.