A simple and green method of depositing platinum-based bimetallic nanoparticles (Pt−Ru, Pt−Cu, Pt−Au, Pt−Pd, and Pt−Ni) on multiwalled carbon nanotubes (MWCNTs) in supercritical fluid carbon dioxide (sc-CO2) is described. CO2-soluble metal precursors, such as metal acetylacetonates or hexafluoroacetylacetonates, were used in the experiments. Suitable temperature and pressure conditions for synthesizing each kind of bimetallic nanoparticle are studied. Characterizations of these nanocomposites, performed by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD), all confirmed their presence. These MWCNT-supported bimetallic nanoparticles have average sizes varying from 2.8 to 9.3 nm. The application of these nanocomposites is demonstrated by using them as electrocatalysts for direct methanol fuel cell (DMFC). Their electrochemical activities are studied by using cyclic voltammetry (CV), and their efficiency to oxidize methanol to carbon dioxide is at least 60% better than the MWCNT-supported monometallic Pt nanoparticle catalyst reported previously.

Semiconductor nanopaparticles of CdS and ZnS were synthesized by mixing two water-in-CO 2 microemulsions with one containing S 2ions and the other containing Cd 2+ or Zn 2+ ions in the water core. Nanoparticle formation was monitored in situ by measuring their absorption spectra in the UV−vis range using a high-pressure fiber-optic system. The size of the nanoparticles formed in the microemulsion was found to depend on the water-to-surfactant ratio (W). At W ) 6 and 12, the band gaps of CdS were calculated to be 3.50 and 3.15 eV, corresponding to particle radii of 1.4 and 1.7 nm, respectively. The ZnS particles synthesized at W ) 12 showed a band gap of 4.26 eV, corresponding to a mean particle radius of 1.6 nm. This microemulsion-plus-microemulsion approach offers a simple method for synthesizing various nanoparticles in supercritical CO 2 using water-soluble reagents as starting materials.

Minerals are rarely homogeneous and often display multiple generations of crystal growth and complex chemical zonation that are difficult to observe with standard microscopic techniques. tm VP FESEM at the University of Idaho is equipped with a variable pressure secondary electron detector (VP SE) that collects photons generated by cascade collisions between secondary electrons and gas molecules within the sample chamber. When a luminescent sample is imaged under routine high voltage conditions the VP SE photon detector functions as a monochromatic CL detector. The quality and usefulness of monochromatic CL images are subjective. The objective is to produce images with sufficient information for use with other micro beam techniques [i.e. laser-ablation ICP-MS]. Acceptability depends on the judgment and skill of the operator. In our comparative study, gray-scale sensitivity was lower in the VP SE CL images on the Supra 35 tm as compared to CL images collected on the AMRAY with the miniCL tm detector but otherwise were of comparable resolution and quality [ Fig. 1]. Although designed for the collection of secondary electron images, the VP SE detector functions well for the collection of CL images. The growing popularity of the VP SEM makes them a potentially untapped resource for CL imaging. The caveat here is that not all VP SEMs use a photon-based detector for VP SE imaging. For reasons of initial instrument cost and ease of use, a dedicated CL detector system on a SEM or EPMA is preferred as a method for routine CL imaging. However, when this tool is unavailable, a VP SEM with a VP SE photon detector offers a practical alternative.

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