No abstract

A facile development of highly efficient Pt-TiO(2) nanostructured films via versatile gas-phase deposition methods is described. The films have a unique one-dimensional (1D) structure of TiO(2) single crystals coated with ultrafine Pt nanoparticles (NPs, 0.5-2 nm) and exhibit extremely high CO(2) photoreduction efficiency with selective formation of methane (the maximum CH(4) yield of 1361 μmol/g-cat/h). The fast electron-transfer rate in TiO(2) single crystals and the efficient electron-hole separation by the Pt NPs were the main reasons attributable for the enhancement, where the size of the Pt NPs and the unique 1D structure of TiO(2) single crystals played an important role.

No abstracts.

Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2787972͔ Nanothermite materials are comprised of a physical mixture of inorganic fuel and oxidizer nanoparticles. Nonhomogenous distribution of fuel and oxidizer has been observed in the microstructures. 1 This produces random hot spot density distribution and decreases the propagation speed of the combustion wave front. It is, therefore, important to achieve homogenous mixing of the oxidizer and fuel components for faster reaction kinetics. This can be achieved by selfassembly of fuel around the solid oxidizer. Enhancement in the combustion wave speed has already been reported for composites containing porous oxidizers and fuel nanoparticles, 2,3 and also for electrostatically charged selfassembled composites. 4 Recently, we reported that higher combustion wave speeds were achieved for the composites of ordered porous Fe 2 O 3 oxidizer and Al nanoparticles 5 as compared with the one containing porous oxidizer with no ordering of the pores and Al nanoparticles. We have also reported the composite of CuO nanorods and Al nanoparticles exhibiting a combustion wave speed of 1500Ϯ 100 m / s, which enhances to 2200 m / s for the self-assembled composites. 6-8 Interestingly, these higher combustion wave speeds are comparable to the lower end values of the detonation velocities ͑e.g., 2000 m / s for hydrocarbon/alkylene-air mixtures, 9 1500-2700 m / s for metallic azides and fulminates, 10 and about 3000 m / s for ammonium nitrate fuel oil͒ for explosives. 11 In conventional explosives, the gases produced during the chemical reaction develop turbulence due to a combined effect of high pressure and rapid shearing of molecular layers generating a shock wave. In a process called deflagration-todetonation transition ͑DDT͒, the wave propagates in the reactive medium creating localized high pressure at the hot spots and, after a certain run-up distance, rapid deflagration can transition to full detonation. 9 This distance depends on the dimensions of the shock tube and also the level of confinement. 9 In the case of low density superthermites, as the adiabatic reaction temperatures are several thousand degrees, the reaction products can volatilize rapidly 12 resulting in an increased level of turbulence and high localized pressures. Because of the low density and multiphase nature of reaction materials, the corresponding Chapman-Jouguet ͑CJ͒ pressure can be much lower ...

Optical sensors have proven to be a useful method in identifying explosive devices by recognizing vapors of explosive compounds that become airborne and emanate from the device. To detect high explosive compounds such as TNT, a molecularly imprinted polymer (MIP) sensing mechanism was developed. This mechanism consists of MIP microparticles prepared using methacrylic acid as the functional monomer. The MIP microparticles are then combined with fluorescent quantum dots via a simple cross-linking procedure. The result is a highly robust optical sensing scheme that is capable of functioning in an array of environmental conditions. To study the sensing mechanisms's ability to detect nitroaromatic analytes, the fluorescent-labeled MIP particles were tested for their performance in detecting aqueous 2,4-dinitrotoluene (DNT), a nitroaromatic molecule very similar to TNT, as well as TNT itself. These preliminary data indicate that the system is capable of detecting nitroaromatic compounds in solution with high sensitivity, achieving lower limits of detection of 30.1 and 40.7 microM for DNT and TNT, respectively. The detection mechanism also acted rapidly, with response times as low as 1 min for TNT. Due to the results of this study, it can be concluded that the fluorescent-labeled MIP system is a feasible method for detecting high explosives, with the potential for future use in detecting vapors from explosive devices.