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Supported nanoparticles of platinum on a wide variety of substrates, including carbon aerogel, carbon black, silica aerogel, silica, γ-alumina, and Nafion 112 film, were synthesized via a supercritical fluid route. The porous substrates and Nafion film were impregnated with an organometallic precursor, dimethyl(1,5-cyclooctadiene)platinum(II) (PtMe 2 COD), from a supercritical carbon dioxide (scCO 2 ) solution at 80 °C and 27.6 MPa. After depressurization, the impregnated organometallic precursor was reduced to elemental platinum by heat treatment in the presence of nitrogen gas. The resulting nanocomposites were investigated by transmission electron microscopy (TEM), which revealed uniformly dispersed platinum particles on each of the substrates with average particle sizes ranging from 1.2 to 6.4 nm and a narrow particle size distribution. A comparison of nanocomposites produced under different conditions showed that both the metal contents and the particle sizes are controllable.

Low‐cost, large‐scale production of highly photoluminescent semiconductor nanocrystals (NCs) is desirable for a variety of applications. In this paper we report the realization of highly photoluminescent zinc‐blende CdSe nanocrystals from room‐temperature water‐phase synthesis, followed by low‐temperature (80 ± 5 °C) chemical etching in a solution of 3‐amino‐1‐propanol/H2O (v/v = 10/1). X‐ray diffraction (XRD) and transmission electron microscopy (TEM) data indicate that these CdSe NCs exhibit a cubic, zinc‐blende crystal structure. After etching, these CdSe nanocrystals show strong band‐edge photoluminescence (with quantum efficiency as high as 50 %) and lack of deep‐trap emissions. A high‐resolution TEM investigation suggests that this etching not only removes surface irregularities, but also attacks grain boundaries. Moreover, the size distribution reduces upon progressive etching to allow photoluminescence full‐width‐at‐half‐maximum (FWHM) values as low as 30 nm.

Carbon-aerogel-supported ruthenium nanoparticles were synthesized by impregnating carbon aerogels with Ru(acac)3 or Ru(cod)(tmhd)2 from supercritical carbon dioxide (scCO2) solutions, followed by thermal reduction of these precursors. Two different carbon aerogels with pore diameters of 4 and 21 nm were synthesized. The kinetics and the thermodynamics of impregnation of carbon aerogels with the ruthenium coordination complexes were studied. The approach-to-equilibrium data indicated very fast adsorption, and the adsorption isotherms were found to follow the Langmuir model. The impregnated carbon aerogel complexes were reduced thermally at different temperatures between 300 and 1000 degrees C in the presence of nitrogen. The resulting nanocomposites were characterized using transmission electron microscopy (TEM) and hydrogen chemisorption. TEM micrographs showed that the ruthenium nanoparticles were dispersed homogeneously throughout the porous carbon aerogel matrix, and the average sizes obtained under different conditions ranged from 1.7 to 3.8 nm. Once complete decomposition of the precursor had been achieved, the mean size of the ruthenium particles increased with increasing reduction temperature.

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