Deterministic control of structural and optical properties of plasma-grown vertical graphene nanosheet networks via nitrogen gas variation

The effect of nitrogen on the growth of vertically oriented graphene nanosheets on catalyst-free silicon and glass substrates in a plasma-assisted process is studied. Different concentrations of nitrogen were found to act as versatile control knobs that could be used to tailor the length, number density and structural properties of the nanosheets. Nanosheets with different structural characteristics exhibit markedly different optical properties. The nanosheet samples were treated with a bovine serum albumin protein solution to investigate the effects of this variation on the optical properties for biosensing through confocal micro-Raman spectroscopy and UV-Vis spectrophotometry. © 2012 Optical Society of America.

Enhancement of electron field emission of vertically aligned carbon nanotubes by nitrogen plasma treatment

The electron field emission (EFE) characteristics from vertically aligned carbon nanotubes (VACNTs) without and with treatment by the nitrogen plasma are investigated. The VACNTs with the plasma treatment showed a significant improvement in the EFE property compared to the untreated VACNTs. The morphological, structural, and compositional properties of the VACNTs are extensively examined by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and energy dispersive X-ray spectroscopy. It is shown that the significant EFE improvement of the VACNTs after the nitrogen plasma treatment is closely related to the variation of the morphological and structural properties of the VACNTs. The high current density (299.6 μA/cm2) achieved at a low applied field (3.50 V/μm) suggests that the VACNTs after nitrogen plasma treatment can serve as effective electron field emission sources for numerous applications.

Plasma/ion-controlled metal catalyst saturation : enabling simultaneous growth of carbon nanotube/nanocone arrays

It is shown that the simultaneous saturation of Ni nanoparticles used as catalyst for vertically aligned carbon nanotube and nanocone arrays can be improved in low-temperature plasma- or ion-assisted processes compared with neutral gas-based routes. The results of hybrid multiscale numerical simulations of the catalyst nanoarrays (particle sizes of 2 and 10 nm) saturation with carbon show the possibility of reducing the difference in catalyst incubation times for smallest and largest catalyst particles by up to a factor of 2. This approach is generic and provides process conditions for simultaneous nucleation and growth of uniform arrays of vertically aligned nanostructures. © 2008 American Institute of Physics.

Plasma-controlled metal catalyst saturation and the initial stage of carbon nanostructure array growth

The kinetics of the nucleation and growth of carbon nanotube and nanocone arrays on Ni catalyst nanoparticles on a silicon surface exposed to a low-temperature plasma are investigated numerically, using a complex model that includes surface diffusion and ion motion equations. It is found that the degree of ionization of the carbon flux strongly affects the kinetics of nanotube and nanocone nucleation on partially saturated catalyst patterns. The use of highly ionized carbon flux allows formation of a nanotube array with a very narrow height distribution of half-width 7 nm. Similar results are obtained for carbon nanocone arrays, with an even narrower height distribution, using a highly ionized carbon flux. As the deposition time increases, nanostructure arrays develop without widening the height distribution when the flux ionization degree is high, in contrast to the fairly broad nanostructure height distributions obtained when the degree of ionization is low.

Carbon saturation of arrays of Ni catalyst nanoparticles of different size and pattern uniformity on a silicon substrate

The kinetics of saturation of Ni catalyst nanoparticle patterns of the three different degrees of order, used as a model for the growth of carbon nanotips on Si, is investigated numerically using a complex model that involves surface diffusion and ion motion equations. It is revealed that Ni catalyst patterns of different degrees of order, with Ni nanoparticle sizes up to 12.5 nm, exhibit different kinetics of saturation with carbon on the Si surface. It is shown that in the cases examined (surface coverage in the range of 1-50%, highly disordered Ni patterns) the relative pattern saturation factor calculated as the ratio of average incubation times for the processes conducted in the neutral and ionized gas environments reaches 14 and 3.4 for Ni nanoparticles of 2.5 and 12.5 nm, respectively. In the highly ordered Ni patterns, the relative pattern saturation factor reaches 3 for nanoparticles of 2.5 nm and 2.1 for nanoparticles of 12.5 nm. Thus, more simultaneous saturation of Ni catalyst nanoparticles of sizes in the range up to 12.5 nm, deposited on the Si substrate, can be achieved in the low-temperature plasma environment than with the neutral gas-based process.

On natures of sub-gap photoelectric and optical spectra in nitrogen-contaminated nanocrystalline diamond

Experimentally observed optical and photoelectrical spectra of nitrogen-contaminated (unintentionally doped) nano-crystalline CVD diamond films are simulated using semi-empirical adiabatic General Skettrup Model (GSM), which presumes dominant contributions of defect states from sp 3-coordinated intra-granular carbon atoms to intra-band single electron spectrum N(E) of the material. This picture disagrees with a common viewpoint that the N(E) spectrum of the gap states in diamond powders and polycrystalline CVD films mainly originates from π and π* bonds of sp2-coordinated carbon atoms, which are distributed nearly uniformly over outer surfaces and/or interfaces of the diamond grains. The GSM predicts as well strong effect of granular morphology on the density of intra-band defect states in polycrystalline diamonds.

Reactive Oxygen Species and Reactive Nitrogen Species in Epigenetic Modifications

For the normal homeostasis of a cell, there must be a balance between radical oxygen species/radical nitrogen species (ROS/RNS) production and the neutralization of these species by antioxidant scavenging. In times of stress, this balance is not maintained, and the result is oxidative stress. This stress can affect many pathways in the body and result in pathological consequences. Recent evidence suggests that ROS/RNS can affect the epigenetic regulation of genes by affecting the function of histone and DNA modifying enzymes, thus affecting phenotypic changes within the cellular environment. In the following chapter, we provide a broad overview of how oxidative stress induced by ROS/RNS can affect epigenetics, and using lung disease as our model we link the connection between these processes.

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.

Dynamics of nitrogen and suspended solids removal in experimental stormwater biofilters under intermittent wetting and drying

This research study comprehensively analyses the dynamics of nitrogen and suspended solids removal in stormwater biofilters. The study focuses on pollutant removal during an event with time, rather than the conventional event-mean analysis. Antecedent dry days (number of days in between rainfall) during which biofilters remain dry and the inflow concentration of pollutants were two other important variables analysed in this study. The research outcome highlights the significance of dry-phase processes and the process of stabilization on filter performance and sets a paradigm shift from the current approach towards an innovative way of performance analysis of biofilters.

H2 purification by functionalized graphdiyne – role of nitrogen doping

A nitrogen modified graphdiyne is investigated concerning its performance for hydrogen purification from CH4 and CO by density functional theory with dispersion correction and transition state theory. After nitrogen doping, the porous N-graphdiyne nano-mesh shows a reduced H2 diffusion barrier and increased CH4/CO diffusion barriers, hence leading to an enhanced hydrogen purification capability.

The repertoire of nitrogen assimilation in Rhodococcus: Catalysis, pathways and relevance in biotechnology and bioremediation

The Rhodococcus genus exhibits diverse enzymatic activity that can be exploited in the conversion of natural and anthropogenic nitrogenous compounds. This catalytic response provides a selective advantage in terms of available nutrients while also serving to remove otherwise harmful xenobiotics. This review provides a critical assessment of the literature on bioconversion of organo-nitrogen compounds with a consideration of applications in bioremediation and commercial biotechnology. By examining the major nitro-organic compounds (amino acids, amines, nitriles, amides and nitroaromatics) in turn, the considerable repertoire of Rhodococcus spp. is established. The available published enzyme reaction data is coupled with genomic characterisation to provide a molecular basis for Rhodococcus enzyme activity with an assessment of the cellular properties that aid substrate accessibility and ensure stability. The metabolic gene clusters associated with the observed reaction pathways are identified and future directions in enzyme optimisation and metabolic engineering are assessed. © 2014 Society of Chemical Industry.

Removal characteristics of ammonium nitrogen from wastewater by modified Ca-bentonites

A modified inorganic bentonite (Na/Al) based on purified Ca-bentonite was prepared through exchanging Al and Na ions in the interlayer space of Ca-bentonite. The structural properties of purified and modified bentonites were characterized by XRD and SEM analysis. Batch experiments were performed for the adsorption of ammonium nitrogen and different experimental conditions were studied in order to investigate the optimum adsorption conditions. Comparative experiments were also carried out for natural Ca-bentonite (RB), unmodified purified bentonite (PB) and modified purified bentonite (MB). Through the thermodynamic analysis, the ammonium nitrogen adsorption process can be spontaneous, the standard heat was −41.46kJmol −1 , and the adsorption process based on ion exchange adsorption. The ammonium nitrogen adsorption capacity of MB (46.904mg/g) was improved compared to raw bentonite (RB) (26.631mg/g), which was among the highest values of ammonium nitrogen adsorption compared with other adsorbents according to the literatures. The described process provides a potential pathway for the removal of ammonium nitrogen at low concentrations encountered in most natural waters.