Adsorbed Explosive Molecules

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

The second ORNL microcantilever project, funded by the ATF and technically co-directed hy TSA, involves polymer-coated micro cantilevers. In this case, the explosive molecule would be adsorbed on the surface of the polymer, and the swelling or change in physical properties would be measured indicating the presence of an explosive. Several polymers are currently being developed to provide the necessary selectivity for the different types of explosives signatures. The sensitivity is similar to the non-coated cantilever estimated limit of detection of low parts-per-billion (with proper collection and preconcentration system, LOD should approach low parts-per-trillion). Figure 6 illustrates two modes of detection for the coated cantilevers beam stress response and beam resonant frequency response. 

Quite complex kinetic behavior has been identified on some surfaces. For instance, on Ir(100), the TPD data from NO-saturated surfaces display two N2 desorption peaks, one at 346 K from the decomposition of bridge-bonded NO, and a second at 475 K from the decomposition of atop-bonded NO molecules [13], Interestingly, the first feature is quite narrow, indicating an autocatalytic process for which the parallel formation of N20 appears to be the crucial step. An additional complication arises from the fact that this Ir(100) surface undergoes a (1x5) reconstruction, and that NO adsorbed on the metastable unreconstructed (lxl) phase leads to N2 desorption at lower temperatures. In another example, on the reconstructed hexagonal Pt(100) surface, when a mixed NO + CO adsorbed layer is heated, a so-called surface explosion is observed where the reaction products (N2, C02 and N20) desorb simultaneously in the form of sharp peaks with half-widths of only 7 to 20 K. The shape of the TPD spectra suggests again an autocatalytic mechanism [14],... 

Overall the period since the 1980s can be described as a period of explosion in the discovery of new compositions and structures of molecular sieves. This can perhaps be seen most vividly by comparing the numbers of structure types contained in the various editions of the Atlas of Zeolite Structure Types [4]. The first edition (1978) contained 38 structure types, the second edition (1987) 64, the third edition (1992) 85 and the most recent edition (2007) 176. Thus 112 new structure types have been discovered since 1978. However, the reader should be cautioned that a significant number of the structure types included in the Atlas are not truly microporous or molecular sieve materials (i.e., they are not stable for the removal of as-synthesized guest species, typically water or organic templates) and therefore carmot reversibly adsorb molecules or carry out catalytic reactions. Unfortunately, the Atlas gives only limited information on the stability of the structures described. 

Editor That seems to correlate with our observation that the molecules tend to adsorb on soil particles and dust, rather than remain in the air as explosive vapor. I take it that you mean that some wind is needed to move these particles in order to make them available above ground level to the animal. So, a pure vapor plume in air is not as rich a source as wind carried dust and soil particles. Is that correct ... 

Materials synthesis is a necessary component in the development of advanced technologies for national security and homeland defense. For instance, new composites, nanoscale molecules and compounds, and polymers are needed for tougher, explosion- or puncture-resistant materials that can be employed in buildings, garments, bridges, and other products and structures. Personal protective materials could be enhanced with new chemical adsorbents filter materials, impermeable membranes, artificial sutures, and improved energetic materials for... 

The optimized GNR-1, its bilayer and trilayer (Bernal and rhombohedral) clusters, are used as sensors of molecules. For the sake of proof-of-concept experiment, O2 and N2 are adsorbed in the surface, their small size facilitates the calculations, but this approach can be extended to any molecule (or explosive). Each cluster is optimized with the adsorbed molecule. 

Early studies with many types of enzymes failed to find evidence for intermediate products between large polymers and the ultimate products of an enzymatic degradation. From these studies a concept developed of explosive reaction, in which a large molecule was thought to be adsorbed to an enzyme, and held until completely digested. Currently, there is no basis for such a hypothesis. In some cases it has been found that the affinity of smaller molecules for the enzyme is greater than that of the parent compound, so that accumulation of intermediates is minimized, but where adequate methods (as chromatography) are available, it can usually be shown that each bond split is caused by an independent reaction. ... 

The ambient air is diluted with numerous hydrocarbon components. Some of these molecules are fully or at least partly retained by the molesieve. This is important for the safety of the air separation unit, since all hydrocarbons are less volatile than nitrogen and oxygen and accumulate in the liquid oxygen formed in the bath of the main evaporator (13). Here their concentration must remain far below the solubility and explosion hmit. In particular, the molesieve adsorbs acetylene, which has a solubility hmit of only 6 ppm, completely. The adsorbers (6/6 ) are arranged pairwise and are automatically switched between adsorption and regeneration mode. 

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