Direct imaging of the pores and cages of three-dimensional mesoporous materials

Mesostructured composite materials, with features ranging from 20 to 500 An gstrom in size, are obtained by the kinetically controlled competitive asse mbly of organic and inorganic species into nanostructured domains. Short-ra nge order is limited, and long-range order is determined by weak forces suc h as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materi als obtained by removing the organic phase are of particular interest for a pplications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered ma terials because of the difficulty in obtaining large (>10 mum) single cryst als, and because large repeat spacings cause diffraction intensities to fal l off rapidly with scattering angle so that only limited small-angle data a re available. Here we present a general approach for the direct determinati on of three-dimensional mesoporous structures by electron microscopy. The s tructure solutions are obtained uniquely without pre-assumed models or para metrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials(1,2), which reveal a highly or dered dual micro- and mesoscale pore structure.