Mesoporous semiconducting films consisting of preferentially orientated monoclinic-phase nanocrystals of tungsten trioxide have been prepared using a novel version of the sol-gel method. Transformations undergone by a colloidal solution of tungstic acid, stabilized by an organic additive such as poly(ethylene glycol) (PEG) 300, as a function of the annealing temperature have been followed by means of a confocal Raman microscope. The shape and size of WO3 nanoparticles, the porosity, and the properties of the films depend critically on preparation parameters, such as the tungstic acid/PEG ratio, the PEG chain length, and the annealing conditions. Well-crystallized WO3 films combine excellent photoresponse to the blue region of the solar spectrum, up to 500 nm, with good transparency at wavelengths larger than 550 nm. Particular applications of these nanocrystalline WO3 films include photoelectrochemical and electrochromic devices.

Lithium bis(trifluoromethylsulfone)imide (LiTFSI), a promising electrolyte for high energy lithium batteries, forms several stable solvates having low melting points in aprotic solvents. In a previous study (D. Brouillette, G. Perron and J. E. Desnoyers, J. Solution Chem., 1998, 27, 151), it was suggested, based on thermodynamic studies, that such stable solvates may persist in solution and influence their properties. To verify this hypothesis, phase diagrams and Raman spectra have been measured for solutions of LiTFSI in acetonitrile, propylene carbonate and glymes (n(ethyleneglycol) dimethyl ether or Gn), which have the chemical structure CH 3 -O-(CH 2 -CH 2 -O) n -CH 3 for n ¼ 1 to 4 and 10. The relative intensities of the LiTFSI and solvent Raman bands are proportional to the concentration for systems without solvates. The systems for which stable solvates were identified in the phase diagram show important changes in the relative intensities for both the LiTFSI and the solvent Raman bands at concentrations corresponding to particular stoichiometries and support the conclusion that stable solvates are present in the solutions. The structure of the crystalline G1:LiTFSI solvate was determined by X-ray crystallography. Structures for (G2) 2 :LiTFSI and (G1) 3 :LiTFSI solvates are proposed.

No abstract

No abstract

Laboratory batch and column tests were conducted to examine the reduction pathways and kinetics of Nnitrosodimethylamine (NDMA) by iron (Fe) and nickelenhanced iron (Ni/Fe). A decrease in NDMA concentration and increases in dimethylamine (DMA) and ammonium were observed in both Fe and Ni/Fe columns. In the Fe column, the transformation process of NDMA appeared to follow pseudo-first-order kinetics with respect to NDMA, with an average half-life of 13(2 h. A small amount of nickel (0.25%) plated onto the iron greatly enhanced NDMA transformation rates. At early time the NDMA half-life in the Ni/Fe column was 2 min but as time progressed the halflife increased to 4 min, and departures from first-order kinetics were observed. The mass balances of carbon in DMA and nitrogen in DMA and ammonium improved over time and reached 100% and 90%, respectively, after NDMA had passed through the column for more than 50 pore volumes (PV). No 1,1-dimethylhydrazine, nitrous oxide, or methane were detected. Based on the electrochemical properties of NDMA, the transformation mechanism of NDMA with Fe and Ni/Fe is postulated to be catalytic hydrogenation, resulting in N-N bond breakdown to form DMA and ammonium as final products. Nickel, being a much stronger catalyst than Fe for catalytic hydrogenation, resulted in a much faster reduction rate of NDMA. Of several methods tested, flushing the Ni/Fe column with 0.01 N sulfuric acid proved to be the most effective in restoring the Ni/Fe activity. The rapid transformation rate on Ni/Fe and the formation of nontoxic products indicate that this material may be applicable for treating NDMA contaminated water, both in-situ and above ground.

A needle trap device (NTD) and commercial poly(dimethylsiloxane) (PDMS) 7-microm film thickness solid-phase microextraction (SPME) fibers were used for the sampling and analysis of aerosols and airborne particulate matter (PM) from an inhaler-administered drug, spray insect repellant, and tailpipe diesel exhaust. The NTD consisted of a 0.53-mm o.d. stainless steel needle having 5 mm of quartz wool packing section near the needle tip. Samples were collected by drawing air across the NTD with a Luertip syringe or via direct exposure of the SPME fiber. The mass loading of PM was varied by adjusting the volume of air pulled through the NTD or by varying the sampling time for the SPME fiber. The air volumes ranged from 0.1 to 50 mL, and sampling times varied from 10 s to 16 min. Particulates were either trapped on the needle packing or sorbed onto the SPME fiber. The devices were introduced to a chromatograph/mass spectrometer (GC/MS) injector for 5 min desorption. In the case of the NTD, 10 microL of clean air was delivered by a gas-tight syringe to aid the introduction of desorbed analytes. The compounds sorbed onto particles extracted by the SPME fiber or trapped in the needle device were desorbed in the injector and no carry-over was observed. Both devices performed well in extracting airborne polycyclic aromatic hydrocarbons (PAHs) in diesel exhaust, triamcinolone acetonide in a dose of asthma drug and DEET in a dose of insect repellant spray. Results suggest that the NTDs and PDMS 7-microm fibers can be used for airborne particulate sampling and analysis, providing a simple, fast, reusable, and cost-effective screening tool. The advantage of the SPME fiber is the open-bed geometry allowing spectroscopic investigations of particulates; for example, with Raman microspectroscopy.

To elucidate the reduction mechanism of N-nitrosodimethylamine (NDMA) by granular iron, various electrochemical experiments using a mercury electrode were conducted. The studies included differential pulse voltammetry and exhaustive potentiostatic electrolysis. The results of the NDMA electroreduction experiments were compared with the results obtained in the column and batch experiments of Part 1 of this study. The results show that (1) electroreduction of NDMA occurs at potentials more negative than -1.3 V and this potential cannot be achieved under the conditions of the column and batch experiments and (2) different reduction products of NDMA were observed in the electrochemical tests relative to the column and batch tests. That is, dimethylamine (DMA) and nitrous oxide were formed in the electrochemical reduction experiments, whereas ammonia and DMA were produced in the column and batch experiments. The difference in product formation and more importantly the fact that the iron cannot reach the potentials required for electroreduction indicate that the reduction of NDMA on iron cannot take place by direct electron transfer. The process of catalytic hydrogenation was found to be consistent with all experimental observations and is proposed as the alternative mechanism.

The conversion of a Cu 2 O film on copper to Cu 2 S in aqueous sulfide solutions has been followed using a combination of electrochemical techniques and in situ Raman spectroscopy. Oxide films were electrochemically grown in alkaline solutions and their composition and morphology determined using Raman spectroscopy and scanning electron microscopy. Although corrosion potential measurements indicate that the aqueous sulfide solution rapidly penetrates the porous Cu 2 O layer, the oxide-to-sulfide reaction appears to proceed chemically at the oxide/solution interface rather than via the galvanic coupling of Cu oxidation to Cu 2 S and Cu 2 O reduction to Cu. In situ Raman spectroscopy confirms that the sulfide formed is Cu 2 S, and cathodic stripping voltammetry shows that the reaction is initially rapid and then proceeds at a constant rate until the conversion is complete. Comparison of the amounts of oxide initially present and sulfide eventually formed demonstrates that the conversion is 100% efficient. These studies are part of a larger project to determine the important corrosion processes on copper high-level nuclear waste containers exposed to anoxic aqueous sulfide containing groundwaters.A proposed method for the permanent disposal of Scandinavian/ Canadian high-level nuclear waste is to bury it 500-1000 m deep in granitic host rock. 1-3 The canisters were placed in vertical boreholes and surrounded by a self-sealing bentonite clay buffer material of very low hydraulic permeability. Vaults and tunnels would then be backfilled with a mixture of bentonite and crushed granite. The choice of container material depends largely on the redox conditions and the aqueous environment of the repository. 4 The material of choice for the fabrication of waste canisters is copper, a metal which should be thermodynamically stable under the saline, anoxic conditions anticipated over the large majority of the container lifetime. 5 The proposed container design has an outer copper liner ͑ϳ5 cm thick͒ and an inner wall of nodular cast iron, primarily for structural support. 3,6,7 The design of these containers has been discussed in detail elsewhere. 5 The evolution of geochemical conditions within the proposed repository environment has been well studied. 8 Initially, atmospheric O 2 , trapped within the repository upon sealing, and heat from radioactive decay creates warm, dry, oxidizing conditions. However, the dissolved O 2 is consumed by a number of processes including corrosion of the container, oxidation of dissolved copper corrosion products ͓e.g., Cu I ͑Cl 2 ͒ − → Cu II salts͔, and reaction with microbes and redox-sensitive materials dispersed in the backfill. 9 Thus, redox conditions at the container surface evolve relatively rapidly from warm and oxidizing to cool and anoxic as the O 2 is consumed and the heat-producing radioactivity decays. O 2 concentrations are predicted to be depleted after ϳ2600 years due to various scavenging mechanisms, 10 over which time the temperature at the canister surface will have decrea...