Nanowires of metal oxides for gas sensing applications

Nanowires of different metal oxides (SnO2, ZnO) have been grown by evaporation-condensation process. Their chemical composition has been investigated by using XPS. The standard XPS quantification through main photoelectron peaks, modified Auger parameter and valence band spectra were examined for the accurate determination of oxidation state of metals in the nanowires. Morphological investigation has been conducted by acquiring and analyzing the SEM images. For the simulation of working conditions of sensor, the samples were annealed in ultra high vacuum (UHV) up to 500°C and XPS analysis repeated after this treatment. Finally, the nanowires of SnO 2 have were used to produce a novel gas sensor based on Pt/oxide/SiC structure and operating as Schottky diode. Copyright © 2008 John Wiley & Sons, Ltd.

Reduction of functionalized graphite oxides by trioctylphosphine in non-polar organic solvents

Graphene, functionalized with oleylamine (OA) and soluble in non-polar organic solvents, was produced on a large scale with a high yield by combining the Hummers process for graphite oxidation, an amine-coupling process to make OA-functionalized graphite oxide (OA-GO), and a novel reduction process using trioctylphosphine (TOP). TOP acts as both a reducing agent and an aggregation-prevention surfactant in the reduction of OA-GO in 1,2-dichlorobenzene (DCB). The reduction of OA-GO is confirmed by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectroscopy. The exfoliation of GO, OA GO, and OA-functionalized graphene (OA-G) is verified by atomic force microscopy. The conductivity of TOP-reduced OA G, which is deduced from the current–voltage characteristics of a vacuum-filtered thin film, shows that the reduction of functionalized GO by TOP is as effective as the reduction of GO by hydrazine.

Nitrous oxide emissions from subtropical horticultural soils : a time series analysis

Time series regression models were used to examine the influence of environmental factors (soil water content and soil temperature) on the emissions of nitrous oxide (N2O) from subtropical soils, by taking into account temporal lagged environmental factors, autoregressive processes, and seasonality for three horticultural crops in a subtropical region of Australia. Fluxes of N2O, soil water content, and soil temperature were determined simultaneously on a weekly basis over a 12-month period in South East Queensland. Annual N2O emissions for soils under mango, pineapple, and custard apple were 1590, 1156, and 2038 g N2O-N/ha, respectively, with most emissions attributed to nitrification. The N2O-N emitted from the pineapple and custard apple crops was equivalent to 0.26 and 2.22%, respectively, of the applied mineral N. The change in soil water content was the key variable for describing N2O emissions at the weekly time-scale, with soil temperature at a lag of 1 month having a significant influence on average N2O emissions (averaged) at the monthly time-scale across the three crops. After accounting for soil temperature and soil water content, both the weekly and monthly time series regression models exhibited significant autocorrelation at lags of 1–2 weeks and 1–2 months, and significant seasonality for weekly N2O emissions for mango crop and for monthly N2O emissions for mango and custard apple crops in this location over this time-frame. Time series regression models can explain a higher percentage of the temporal variation of N2O emission compared with simple regression models using soil temperature and soil water content as drivers. Taking into account seasonal variability and temporal persistence in N2O emissions associated with soil water content and soil temperature may lead to a reduction in the uncertainty surrounding estimates of N2O emissions based on limited sampling effort.

Interstellar titanium-oxides in interplanetary dust

Interstellar gas abundances (Clayton et al., 1986) suggest that titanium may be bound up in dust and indeed, excess titanium in carbonaceous chondrites is attributed to mixing of interstellar and Solar System materials (Morton, 1974). Fine-grained chondritic interplanetary dust particles (lOPs) of cometary origin are relatively pristine early Solar System materials (Mackinnon and Rietmeijer, 1987; Rietmeijer, 1987) and show chemical and mineralogical signatures related to a pre-solar or nebular origin. For example, large OtH ratios suggest a presolar or interstellar dust component in some chondritic lOPs(Mackinnon and Rietmeijer, 1987). Ti/Si ratios (normalized to bulk CI) in lOPs and carbonaceous chondrite matrices exceed solar abundances but are similar to dust from comet Halley (Jessberger et al., 1987). The Ti-distribution in chondritic lOPs shows major, small-scale « 0.1 urn) variations (Flynn et al., 1978) consistent with heterogeneously distributed Ti-bearingphases. Analytical electron microscope (AEM) studies, in fact, have identified platey grains of Ti-metal, Ti407 and Ti s09 in two different lOPs (Mackinnon and Rietmeijer, 1987). The occurrence of Ti407 was related in situ low-temperature aqueous alteration and therefore implied the presence of BaTi03 (Rietmeijer and Mackinnon, 1984). Yet, the presence ofTis09 in an lOp which shows no evidence of aqueous alteration (Rietmeijer.and McKay, 1986) requires a different interpretation. The distribution of Ti-oxides in chondritic lOPs were investigated with ultra-microtomed thin sections of fluffy chondri tic lOP U2011*B (lSC allocation U2011C2) using a lEOL 2000FX AEM operating at an accelerating voltage of 200kV and with an attached Tracor Northern TN5500 energy dispersive spectrometer.

Nitrous oxide emissions from irrigated wheat in Australia : impact of irrigation management

Background and Aims: Irrigation management affects soil water dynamics as well as the soil microbial carbon and nitrogen turnover and potentially the biosphere-atmosphere exchange of greenhouse gasses (GHG). We present a study on the effect of three irrigation treatments on the emissions of nitrous oxide (N2O) from irrigated wheat on black vertisols in South-Eastern Queensland, Australia. Methods: Soil N2O fluxes from wheat were monitored over one season with a fully automated system that measured emissions on a sub-daily basis. Measurements were taken from 3 subplots for each treatment within a randomized split-plot design. Results: Highest N2O emissions occurred after rainfall or irrigation and the amount of irrigation water applied was found to influence the magnitude of these “emission pulses”. Daily N2O emissions varied from -0.74 to 20.46 g N2O-N ha-1 day-1 resulting in seasonal losses ranging from 0.43 to 0.75 kg N2O N ha-1 season -1 for the different irrigation treatments. Emission factors (EF = proportion of N fertilizer emitted as N2O) over the wheat cropping season, uncorrected for background emissions, ranged from 0.2 to 0.4% of total N applied for the different treatments. Highest seasonal N2O emissions were observed in the treatment with the highest irrigation intensity; however, the N2O intensity (N2O emission per crop yield) was highest in the treatment with the lowest irrigation intensity. Conclusions: Our data suggest that timing and amount of irrigation can effectively be used to reduce N2O losses from irrigated agricultural systems; however, in order to develop sustainable mitigation strategies the N2O intensity of a cropping system is an important concept that needs to be taken into account.

Spatiotemporal modelling in estimation of nitrous oxide emissions from soil

Nitrous oxide is a major greenhouse gas emission. The aim of this research was to develop and apply statistical models to characterize the complex spatial and temporal variation in nitrous oxide emissions from soils under different land use conditions. This is critical when developing site-specific management plans to reduce nitrous oxide emissions. These studies can improve predictions and increase our understanding of environmental factors that influence nitrous oxide emissions. They also help to identify areas for future research, which can further improve the prediction of nitrous oxide in practice.

Process and catalysts for the methanation of oxides of carbon

The present invention is directed to catalysts for the conversion of oxides of carbon to methane and/or other hydrocarbons and to precursors of such catalysts. The catalyst precursors include one or more refractory oxides selected from the group consisting of rare earth oxides and rare earth contg. perovskites, the precursor including nickel or nickel cations sufficient for a catalyst obtainable by reducing the precursor to be capable of at least partially reducing an oxide of carbon to a hydrocarbon product. Processes for the prepn. of such catalysts and catalyst precursors are also disclosed, as are processes for the conversion of oxides of carbon to methane and/or other hydrocarbons. [on SciFinder(R)]

Method of making metal oxides

A method for producing particles having at least regions of at least one metal oxide having nano-sized grains comprises providing particles of material having an initial, non-equiaxed particle shape, making a mixture of the particles of material and one or more precursors of the metal oxide, and treating the mixture such that the one or more precursors of the metal oxide react with the particles of material to thereby form at least regions of metal oxide on or within the particles, wherein atoms from the particles of material form part of a matrix of the at least one metal oxide and the at least one metal oxide has nano-sized grains and wherein at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.

Method for the production of porous complex metal oxides using a porogen

A method of producing porous complex oxides includes the steps of providing a mixt. of (a) precursor elements suitable to produce the complex oxide, or (b) one or more precursor elements suitable to produce particles of the complex oxide and one or more metal oxide particles; and (c) a particulate carbon-contg. pore-forming material selected to provide pore sizes in the range of 7-250 nm, and treating the mixt. to (i) form the porous complex oxide in which two or more of the precursor elements from (a) above or one or more of the precursor elements and one or more of the metals in the metal oxide particles from (b) above are incorporated into a phase of the complex metal oxide and the complex metal oxide has grain sizes in the range of 1-150 nm, and (ii) removing the pore-forming material under conditions such that the porous structure and compn. of the complex oxide is substantially preserved. The method may be used to produce nonrefractory metal oxides as well. The mixt. further includes a surfactant, or a polymer. [on SciFinder(R)]

Production of porous metal oxides

Porous complex oxides are produced by reacting metal oxide precursors in the presence of a pore-forming material to provide pore sizes in the range of 7-250 nm, followed by removal of the pore-forming material under conditions preserving the structure and compn. of the formed oxides. The pore-forming material are carbon black particles having a particle size of 10-100 nm. The carbon particles are removed from the formed oxide by heating at 100-300°. A surfactant can be added to the reaction mixt. [on SciFinder(R)]

Mechanism of ferromagnetism in non-magnetic ion-doped zinc oxides

Zinc oxide (ZnO) that contains non-magnetic ionic dopants, such as nitrogen (N)-doped zinc oxide (ZnO:N), has been observed to exhibit ferromagnetism. Ferromagnetism is proposed to arise from the Coulomb excitation in the localized states that is induced by the oxygen vacancy, V O. A model based on the Coulomb excitation that is associated with the electron–phonon interaction theoretically explains the ferromagnetic mechanism of ZnO:N. This study reveals that the ferromagnetism will be induced by either deep localized states with a small V O concentration or shallow localized states with a high V O concentration. Additionally, electron–phonon coupling either suppresses the ferromagnetism that is induced by the deep donor states of V O or enhances the ferromagnetism that is induced by the shallow donor states of V O.

Modeling nitrous oxide emissions from irrigated agriculture : testing DayCent with high-frequency measurements

A unique high temporal frequency dataset from an irrigated cotton-wheat rotation was used to test the agroecosystem model DayCent to simulate daily N2O emissions from sub-tropical vertisols under different irrigation intensities. DayCent was able to simulate the effect of different irrigation intensities on N2O fluxes and yield, although it tended to overestimate seasonal fluxes during the cotton season. DayCent accurately predicted soil moisture dynamics and the timing and magnitude of high fluxes associated with fertilizer additions and irrigation events. At the daily scale we found a good correlation of predicted vs. measured N2O fluxes (r2 = 0.52), confirming that DayCent can be used to test agricultural practices for mitigating N2O emission from irrigated cropping systems. A 25 year scenario analysis indicated that N2O losses from irrigated cotton-wheat rotations on black vertisols in Australia can be substantially reduced by an optimized fertilizer and irrigation management system (i.e. frequent irrigation, avoidance of excessive fertiliser application), while sustaining maximum yield potentials.

Impact of nitrification inhibitor (DMPP) on soil nitrous oxide emissions from an intensive broccoli production system in sub-tropical Australia

Vegetable cropping systems are often characterised by high inputs of nitrogen fertiliser. Elevated emissions of nitrous oxide (N2O) can be expected as a consequence. In order to mitigate N2O emissions from fertilised agricultural fields, the use of nitrification inhibitors, in combination with ammonium based fertilisers, has been promoted. However, no data is currently available on the use of nitrification inhibitors in sub-tropical vegetable systems. A field experiment was conducted to investigate the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N2O emissions and yield from broccoli production in sub-tropical Australia. Soil N2O fluxes were monitored continuously (3 h sampling frequency) with fully automated, pneumatically operated measuring chambers linked to a sampling control system and a gas chromatograph. Cumulative N2O emissions over the 5 month observation period amounted to 298 g-N/ha, 324 g-N/ha, 411 g-N/ha and 463 g-N/ha in the conventional fertiliser (CONV), the DMPP treatment (DMPP), the DMMP treatment with a 10% reduced fertiliser rate (DMPP-red) and the zero fertiliser (0N), respectively. The temporal variation of N2O fluxes showed only low emissions over the broccoli cropping phase, but significantly elevated emissions were observed in all treatments following broccoli residues being incorporated into the soil. Overall 70–90% of the total emissions occurred in this 5 weeks fallow phase. There was a significant inhibition effect of DMPP on N2O emissions and soil mineral N content over the broccoli cropping phase where the application of DMPP reduced N2O emissions by 75% compared to the standard practice. However, there was no statistical difference between the treatments during the fallow phase or when the whole season was considered. This study shows that DMPP has the potential to reduce N2O emissions from intensive vegetable systems, but also highlights the importance of post-harvest emissions from incorporated vegetable residues. N2O mitigation strategies in vegetable systems need to target these post-harvest emissions and a better evaluation of the effect of nitrification inhibitors over the fallow phase is needed.

Nitrous oxide emissions from fertilized, irrigated cotton (Gossypium hirsutum L.) in the Aral Sea Basin, Uzbekistan : influence of nitrogen applications and irrigation practices

Nitrous oxide emissions were monitored at three sites over a 2-year period in irrigated cotton fields in Khorezm, Uzbekistan, a region located in the arid deserts of the Aral Sea Basin. The fields were managed using different fertilizer management strategies and irrigation water regimes. N2O emissions varied widely between years, within 1 year throughout the vegetation season, and between the sites. The amount of irrigation water applied, the amount and type of N fertilizer used, and topsoil temperature had the greatest effect on these emissions. Very high N2O emissions of up to 3000 μg N2O-N m−2 h−1 were measured in periods following N-fertilizer application in combination with irrigation events. These “emission pulses” accounted for 80–95% of the total N2O emissions between April and September and varied from 0.9 to 6.5 kg N2O-N ha−1.. Emission factors (EF), uncorrected for background emission, ranged from 0.4% to 2.6% of total N applied, corresponding to an average EF of 1.48% of applied N fertilizer lost as N2O-N. This is in line with the default global average value of 1.25% of applied N used in calculations of N2O emissions by the Intergovernmental Panel on Climate Change. During the emission pulses, which were triggered by high soil moisture and high availability of mineral N, a clear diurnal pattern of N2O emissions was observed, driven by daily changes in topsoil temperature. For these periods, air sampling from 8:00 to 10:00 and from 18:00 to 20:00 was found to best represent the mean daily N2O flux rates. The wet topsoil conditions caused by irrigation favored the production of N2O from NO3− fertilizers, but not from NH4+ fertilizers, thus indicating that denitrification was the main process causing N2O emissions. It is therefore argued that there is scope for reducing N2O emission from irrigated cotton production; i.e. through the exclusive use of NH4+ fertilizers. Advanced application and irrigation techniques such as subsurface fertilizer application, drip irrigation and fertigation may also minimize N2O emission from this regionally dominant agro-ecosystem.