B. Pauwels

Structure Determination of Spherical MCM-41 Particles

Nitrogen sorption measurements show that template-direct- ed materials obtained via a modified Stber procedure typi- cally have a narrow pore-size distribution. The characteriza- tion of these spherical particles by means of XRD reveals a diffraction pattern that can be indexed as hexagonal. Scanning electron microscopy (SEM) confirms the morphology of the particles as spherical. (19,22) In spite of these characterizations, one crucial question remains: how can an array of hexagonally packed pores be placed in a spherical particle? In this commu- nication, (sub-)micrometer spheres of silica are investigated with nitrogen sorption measurements, SEM, XRD, and trans- mission electron microscopy (TEM). The results are com- pared with the experimental observations from conventional MCM-41 material. Based on these results, a model for the pore ordering of spherical particles is proposed and discussed. In Figure 1a, an SEM image of spherical MCM-41 particles (MCM-41 (SPH)) shows their perfectly spherical shape, with sizes ranging from 0.2 to 1 lm. The average size of the parti-

Au particles supported on (110) anatase-TiO2

Abstract Au particles were prepared by evaporation in ultra high vacuum at high temperature, on the surfaces of TiO2 micro-spheres with the anatase structure. The morphology and the structural deformation in Au deposits were studied by high resolution transmission electron microscopy and image simulations by the multislice technique. The particles were polyhedral, limited by (100) and (111) faces. Patches with a hexagonal lattice were found around the particles, which was interpreted as thin Au islands on the surface. In these islands the Au lattice was deformed and perfectly accommodated to the (110) surface of TiO2.

Non-ionic surfactant (C13EOm, m = 6, 12 and 18) for large pore mesoporous molecular sieves preparation

Abstract Polyoxyethylene tridecylethers (C13EOm, m=6, 12 and 18) have been used as templating agents for synthesis of large pore mesoporous materials. The effect of surfactant/silicium molar ratio, heating time, and temperature, and the number of oxyethylene units on the mesoporous material syntheses has been studied in detail. Final compounds were characterized by different techniques such as SEM, TEM and nitrogen adsorption–desorption analysis. The present work shows that the surfactant/tetramethoxysilane molar ratio has a strong effect on the pore diameter for a given surfactant. It is evidenced that both tetramethoxysilane (TMOS) and surfactant can play a role of swelling agent depending on the surfactant/TMOS molar ratio. It is also shown that the pore diameter depends strongly on the heating time and temperature, oxyethylene unit number and surfactant/TMOS molar ratio. All these factors can affect jointly or separately the pore diameter of obtained materials. It is revealed that the surfactant conformation can be changed with the heating temperature. At higher temperature, a more extended molecular conformation can be obtained, which leads to materials with larger pore size.

Multiply twinned C60 and C70 nanoparticles

Abstract Nanoparticles of C 60 and C 70 prepared by aerosol flow reactor method show a well developed morphology when produced at sufficiently high temperatures. Hexagonal plate shaped, icosahedral and decagonal particles of C 60 and C 70 are formed. Morphology and internal structure are studied by scanning and transmission electron microscopy. The plate-like particles are lamellar–twinned and grow preferentially on the side-faces by nucleation of new molecular layers along re-entrant corners. The decagonal multiply twinned nanoparticles are strained and show a distinct deviation from cubic symmetry. Some of the C 70 particles exhibit a modulated structure to accommodate the internal stress; this is possible because of the ellipsoidal shape of the C 70 molecule.

Unexpected microgravity effect during the self-organization of silicalite-1 nanoslabs

Silicalite-1 zeolite was synthesized from clear solutions prepared from tetraethylorthosilicate, tetrapropylammonium hydroxide and water. Crystallization was performed in a unit composing 30 miniautoclaves programmed to heat to 145 or 155°C and to quench sequentially. The synthesis under microgravity condition was conducted aboard the MAXUS 4 sounding rocket. A reference experiment under normal gravity was executed using the same temperature and time profiles. The evolution of the particle size populations was determined using X-ray scattering. The microgravity condition significantly slowed aggregation but did not change the overall aggregation mechanism. Surprisingly, aggregation of the smallest entities, expected to be the least influenced by absence of convection, were most retarded under microgravity conditions. A considerable fraction of the original nanoslabs persisted even at the end of crystallization. An explanation for this unusual microgravity effect was found in the observation of strong physical interaction between groups of individual particles.