Characterization and testing of periodic mesoporous organosilicas as potential selective benzene adsorbents.

The effects of surface imprinting on the adsorption and desorption properties of benzene- and diethylbenzene-bridged periodic mesoporous organosilicas (PMOs) acting as GC stationary-phase preconcentration sorbents for benzene and xylene were examined. Surface-imprinted and nonimprinted PMOs with diethylbenzene (DEB), benzene (BENZ), and ethane (BTSE) bridges and nonimprinted mesoporous silica (MCM-41) were prepared via well-established surfactant templating synthetic methods. The imprinted materials were synthesized using a surfactant demonstrated to produce trinitrotoluene (TNT) selective sorbents with increased adsorption capacity for cresol and 4-nitrophenol as well as TNT. Powder XRD and nitrogen sorption measurements revealed that all of the materials were mesoporous with the DEB materials having a random pore structure and lower surface area than the other materials which had ordered pore structures. Results for maximum uptake of benzene and p-xylene indicate a small but consistent positive effect on the adsorption of benzene and p-xylene due to surface imprinting. Comparing the surface area normalized uptakes (mg/m(2)) for materials having the same organic bridge with and without imprinting (DEB vs TDMI-DEB and BENZ vs TDMI-BENZ) shows that in seven of eight comparisons the imprinted analogue had a higher aromatic uptake. The imprinted samples showed higher weight normalized uptakes (mg/g) in five of eight cases. When used as a GC stationary phase, the organosilica materials yield more symmetrical chromatographic peaks and better separation than MCM-41, indicating superior trapping of BTX analytes, particularly at low concentrations. Additionally, these materials rapidly desorb the preconcentrated compounds.

Atomic scale characterization of the Pt/TiO2 interface.

We present results from an investigation of the Pt/TiO(2) catalyst system using a combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope. Evidence of a strong interaction between the Pt particles and the support is found to be dependent on the Pt cluster size, being manifested either as an encapsulation of the Pt particles by the support or a distortion of the structure of the Pt particles. In the case of clusters that are only a few atoms in size, we show direct evidence of an epitaxial nucleation relationship between Pt and Titania. The results also show unexpectedly that Pt particles exhibit a preferential nucleation on rutile rather than anatase.

Energy-loss near-edge fine structure and compositional profiles of cryomilled oxide-dispersion-strengthened aluminum.

Spatially resolved electron energy-loss spectroscopy (SREELS) makes possible the identification of small second-phase particles in an oxide-dispersion-strengthened aluminum alloy produced by mechanical alloying in a liquid-nitrogen slurry. Near-edge fine structure profiles based on aluminum L23 features that are characteristic of Al-Al or Al-O bonding yield the metal/oxide fraction as a function of probe position. Profiles of nitrogen fraction are derived from linear sequences of spectra so that detection limits can be analyzed at each point in a scan. Quantitative analysis of these linear profiles shows that particles with diameters in the range 10 to 30 nm are rich in nitrogen. A combination of statistical analysis of background removal results with visual inspection of derivative spectra is used to estimate detection limits.

High spatial resolution analysis using parallel detection eels.

The application of parallel detection electron energy loss spectroscopy to the characterization of small particles or interfaces is demonstrated. Data are presented that show variations of low energy loss plasmons, Al L23 edge near edge fine structure, and oxygen concentration with spatial resolution better than 10 nm. The use of this technique for chemical and electronic structure measurements from very small specimen volumes is discussed.