MOF-5-like crystals were studied by small-angle X-ray scattering (SAXS) to reveal, both quantitatively and qualitatively, their real structural details, including pore surface characteristics, pore shape, size distribution, specific surface area (SSA), spatial distribution, and pore-network structure. A combined SAXS and wide-angle X-ray scattering (WAXS) experiment was conducted to investigate the variation of the pore structure with the MOF-5 crystalline phase produced at different cooling rates. The SSA of the MOF-5 crystals synthesized herein spanned a broad range from approximately 3100 to 800 m2/g. The real pore structures were divided into two regimes. In regime I the material consisted mainly of micropores of radius approximately 8 A as well as mesopores of radius 120 approximately 80 A. The structure in regime II was a fractal network of aggregated mesopores with radius >or=32 A as the monomer, reducing SSA and hydrogen uptake capacity at room temperature. The two regimes can be manipulated by controlling the synthesis parameters. The concurrent evolution of pore structure and crystalline phase during heating for solvent removal was also revealed by the in-situ SAXS/WAXS measurement. The understanding of the impact of the real pore structure on the properties is important to establish a favorable synthetic approach for markedly improving the hydrogen storage capacity of MOF-5.

The metal-organic frameworks (MOF) with low and medium specific surface areas (SSA) were shown to be able to adsorb hydrogen via bridged spillover at room temperature (RT) up to an amount of full coverage of hydrogen in the MOF. Anomalous small-angle X-ray scattering was employed to investigate the key relationship between the structures and storage properties of the involved materials. It was found that the tunable imperfect lattice defects and the 3D pore network in the MOF crystal are the most critical structures for RT hydrogen uptake rather than the known micropores in the crystal, SSA, and Pt catalyst structure.

There are two regimes that exhibit two distinctive behaviors of spillover. The present study used small-angle X-ray scattering (SAXS) to measure size distribution of Pt nanoparticles in the bulk Pt-impregnated active carbon sample. The peak position of the size distribution as determined by SAXS turns out to be at ∼1 nm, which is rarely discussed in this field. SAXS technique is complementary to the other characterization methods. The experimental clue coming from SAXS measurement and our hydrogen storage capacity study shows that the impregnated Pt nanoparticles of ∼1 nm in size can enhance the hydrogen spillover effect. It can significantly increase the room temperature hydrogen uptake compared to currently studied similar systems. The mass loading of catalyst is not a critical factor. Tuning the pore-confined Pt sizes (<2 nm) in combination with an optimum activation method should play an effective role in further enhancement via the spillover effect. SECTION Nanoparticles and Nanostructures

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