Nitrogen-containing Precursor Research Articles

Spectroscopic Analyses of Carbon Alloy Catalysts Derived from Hyper-Branched Polymer as a New Nitrogen-Containing Precursor

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Nitrogen-doped graphene nanosheet-supported non-precious iron nitride nanoparticles as an efficient electrocatalyst for oxygen reduction

Nitrogen-doped graphene-supported carbon-containing iron nitride (FeCN/NG) was synthesized by the chemical impregnation of iron and nitrogen-containing precursors in the presence of ammonia under thermal treatment. The resultant graphene-based material acted as an electrode with a much higher electrocatalytic activity in the catalysis via a 4-electron pathway in fuel cells. The results of X-ray diffraction, scanning electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy indicated that graphite oxide was successfully reduced to nitrogen-doped graphene. X-Ray absorption spectroscopy further confirmed that carbon was incorporated into iron nitride, demonstrating that Fe–N–C catalytic active sites may be responsible for the oxygen reduction reaction. To the best of our knowledge, this is the first report of the combination of N-doped graphene with non-precious metal for oxygen reduction in fuel cells, and may open up a new possibility for preparing graphene-based nanoassemblies for intensive applications.

Properties of Nitrogen-Functionalized Ordered Mesoporous Carbon Prepared Using Polypyrrole Precursor

Nitrogen-doped ordered mesoporous carbon was synthesized using SBA-15 as the template and polypyrrole as the nitrogen-containing carbon precursor. Transmission electron microscopy and Brunauer, Emmett, and Teller adsorption revealed a honeycomb-like ordered mesoporous structure with an average pore diameter of 3.3 nm with a narrow distribution. X-ray photoelectron spectroscopy showed that pyridinic and quaternary nitrogen functionalities were the dominant nitrogen surface functional groups. A high percentage of nitrogen was retained in the carbon surface . The prepared nitrogen-functionalized support had a specific double layer capacitance of 182.5 F/g. Also, its intrinsic oxygen reduction activity was better than that of Vulcan XC-72R. Accelerated degradation test showed that nitrogen-functionalized carbon was highly resistant to electrochemical corrosion.

What’s in the Pool? A Comprehensive Identification of Disinfection By-products and Assessment of Mutagenicity of Chlorinated and Brominated Swimming Pool Water

BackgroundSwimming pool disinfectants and disinfection by-products (DBPs) have been linked to human health effects, including asthma and bladder cancer, but no studies have provided a comprehensive identification of DBPs in the water and related that to mutagenicity.ObjectivesWe performed a comprehensive identification of DBPs and disinfectant species in waters from public swimming pools in Barcelona, Catalonia, Spain, that disinfect with either chlorine or bromine and we determined the mutagenicity of the waters to compare with the analytical results.MethodsWe used gas chromatography/mass spectrometry (GC/MS) to measure trihalomethanes in water, GC with electron capture detection for air, low- and high-resolution GC/MS to comprehensively identify DBPs, photometry to measure disinfectant species (free chlorine, monochloroamine, dichloramine, and trichloramine) in the waters, and an ion chromatography method to measure trichloramine in air. We assessed mutagenicity with the Salmonella mutagenicity assay.ResultsWe identified > 100 DBPs, including many nitrogen-containing DBPs that were likely formed from nitrogen-containing precursors from human inputs, such as urine, sweat, and skin cells. Many DBPs were new and have not been reported previously in either swimming pool or drinking waters. Bromoform levels were greater in brominated than in chlorinated pool waters, but we also identified many brominated DBPs in the chlorinated waters. The pool waters were mutagenic at levels similar to that of drinking water (~ 1,200 revertants/L-equivalents in strain TA100–S9 mix).ConclusionsThis study identified many new DBPs not identified previously in swimming pool or drinking water and found that swimming pool waters are as mutagenic as typical drinking waters.

Analysis of photoluminescence background of Raman spectra of carbon nanotips grown by plasma-enhanced chemical vapor deposition

Carbon nanotips with different structures were synthesized by plasma-enhanced hot filament chemical vapor deposition and plasma-enhanced chemical vapor deposition using different deposition conditions, and they were investigated by scanning electron microscopy and Raman spectroscopy. The results indicate that the photoluminescence background of the Raman spectra is different for different carbon nanotips. Additionally, the Raman spectra of the carbon nanotips synthesized using nitrogen-containing gas precursors show a peak located at about 2120 cm−1 besides the common D and G peaks. The observed difference in the photoluminescence background is related to the growth mechanisms, structural properties, and surface morphology of a-C:H and a-C:H:N nanotips, in particular, the sizes of the emissive tips.

Synthesis and characterization of nitrogen-doped carbon xerogels

Carbon xerogels were prepared from a nitrogen-containing polymer precursor, using melamine and urea as nitrogen sources incorporated into the polymer matrix using the sol–gel process. To investigate the effects of nitrogen on the texture, morphology and surface chemistry, the carbon xerogels were characterized by nitrogen adsorption, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and acid–base titrations. The results showed that nitrogen was incorporated onto the surface as pyridine, pyrrolic/pyridine, quaternary nitrogen, and pyridine-N-oxide. From the deconvolution of the XPS spectra, the pyrrolic/pyridine and quaternary nitrogen functionalities were found to dominate in the samples prepared from urea. All samples showed increased basicity after nitrogen incorporation.

Nitrogen-modified carbon-based catalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells

Nitrogen-modified carbon-based catalysts for oxygen reduction were synthesized by modifying carbon black with nitrogen-containing organic precursors. The electrocatalytic properties of catalysts were studied as a function of surface pre-treatments, nitrogen and oxygen concentrations, and heat-treatment temperatures. On the optimum catalyst, the onset potential for oxygen reduction is approximately 0.76 V (NHE) and the amount of hydrogen peroxide produced at 0.5 V (NHE) is approximately 3% under our experimental conditions. The characterization studies indicated that pyridinic and graphitic (quaternary) nitrogens may act as active sites of catalysts for oxygen reduction reaction. In particular, pyridinic nitrogen, which possesses one lone pair of electrons in addition to the one electron donated to the conjugated π bond, facilitates the reductive oxygen adsorption.

Development of Nitrogen-Modified Carbon-Based Catalysts for Oxygen Reduction in PEM Fuel Cells

Carbon-based catalysts for oxygen reduction reaction (ORR) were synthesized by modifying the carbon surface with nitrogen-containing precursors. The electrocatalytic properties were studied as a function of surface treatment, nitrogen and oxygen concentrations, and heattreatment temperature. The catalysts showed an onset potential for ORR close to 0.83 V and the amount of H2O2 generated was about 1 % at 0.5 V under our experimental conditions. The current transient in fuel cell at 0.4 V exhibited an initial increase of current density to approximately 0.12 A cm-2 and then a steady-state current profile for up to 200 h. The characterizations indicated that pyridinic and graphitic nitrogen acts as catalytic sites for ORR.

A pyrolytic study of the speciation and isotopic composition of nitrogen in carboniferous shales of the North German Basin

Thick layers of Palaeozoic shales are considered the potential sources of N 2 in natural gas reservoirs of the North German Basin. The nitrogen geochemistry of shale samples from five wells in northern Germany has been investigated using elemental analysis, stable isotope mass spectrometry and open system non-isothermal pyrolysis (temperature programmed pyrolysis). A combination of pyrolysis and on-line isotopic analysis of the liberated N 2 was used to identify variations in the isotopic composition of nitrogen-containing precursor species in the shales. Proportions of organic and inorganic nitrogen were assessed via pyrolysis of bulk samples and the corresponding demineralized kerogen concentrates. Total nitrogen content of the samples ranged between 640 ppm and 2350 ppm (0.64 and 2.35 mg N/g rock). Pyrograms of Namurian A and B shales indicated a clear facies trend from marine sediments to paralic and terrestrial facies. The isotopic composition of the liberated N 2 varied with temperature. The isotope trends imply the presence of several distinct precursor species with different isotope signatures.

Energy distribution of the (100)Si/HfO2 interface states

The energy distributions of interface states were determined in (100)Si/HfO2 using capacitance–voltage measurements on structures with the periphery of the metal electrode switched to inversion by controlled application of corona discharge. Together with independently applied ac conductance spectroscopy they reveal a strong impact of the HfO2 deposition technique on the interface trap density. This includes the enhancement of the Si-dangling bond defect (Pb0 centers) density and a contribution of insulator-related traps in samples deposited using a nitrogen-containing precursor.

First principles prediction of the gas-phase precursors for AlN sublimation growth.

Using a new, parameter-free first principles strategy for modeling sublimation growth, we show that while Al and N2 dominate gas concentrations in AlN sublimation growth chambers under typical growth conditions, N2 is undersaturated with respect to the crystal and therefore cannot be a growth precursor. Instead, our calculations predict that the nitrogen-containing precursors are Al(n)N (n=2,3,4), in stark contrast to assumptions used in all previous modeling studies of this system.

Characterization and fate of N-nitrosodimethylamine precursors in municipal wastewater treatment plants.

The potent carcinogen, N-nitrosodimethylamine (NDMA), is produced during disinfection of municipal wastewater effluent from the reaction of monochloramine and organic nitrogen-containing precursors. To delineate the sources and fate of NDMA precursors during municipal wastewater treatment, NDMA formation was measured after extended chloramination of both model precursors and samples from conventional and advanced wastewater treatment plants. Of the model precursors, only dimethylamine, tertiary amines with dimethylamine functional groups, and dimethylamides formed significant NDMA concentrations upon chloramination. In samples from municipal wastewater treatment plants, dissolved NDMA precursors always were present in primary and secondary effluents. Biological treatment effectively removed the known NDMA precursor dimethylamine, lowering its concentration to levels that could not produce significant quantities of NDMA upon chlorine disinfection. However, biological treatment was less effective at removing other dissolved NDMA precursors, even after extended biological treatment. Significant concentrations of particle-associated NDMA precursors only were detected in secondary effluent at treatment plants that recycled water from sludge thickening operations in which dimethylamine-based synthetic polymers were used. Effective strategies for the prevention of NDMA formation during wastewater chlorination include ammonia removal by nitrification to preclude chloramine formation during chlorine disinfection, elimination of dimethylamine-based polymers, and use of filtration and reverse osmosis to remove particle-associated precursors and dissolved precursors, respectively.

Interface state energy distribution in (1 0 0)Si/HfO 2

Energy distributions of interface states in (1 0 0)Si/HfO 2 entities were determined using capacitance–voltage measurements on structures with the periphery of the metal electrode switched to inversion by controlled application of corona discharge. This method was applied in combination with ac conductance spectroscopy to assess (1 0 0)Si/HfO 2 interface traps. The significant impact of the HfO 2 deposition process on the interface trap density is revealed. The latter includes both the enhancement of the Si-dangling bond defect (P b0 centers) density and an additional contribution of insulator-related traps in samples deposited from a nitrogen-containing precursor.

Growth of Hafnium Dioxide Thin Films by Liquid‐Injection MOCVD Using Alkylamide and Hydroxylamide Precursors

AbstractThin films of HfO2 have been deposited by liquid‐injection metal–organic (MO)CVD using two nitrogen‐containing precursors [Hf(NMe2)4] and [Hf(ONEt2)4]. The [Hf(NMe2)4] precursor deposits oxide at lower growth temperatures and over a wider temperature range than [Hf(ONEt2)4]. Varying levels of residual carbon and nitrogen were detected in the films grown from each precursor. Analysis by X‐ray diffraction (XRD) indicates that films grown from both precursors exist predominantly in the thermodynamically stable monoclinic phase. Scanning electron microscopy (SEM) shows that the morphology of the HfO2 films from each precursor is markedly different, with films deposited from [Hf(NMe2)4] having a well‐defined columnar crystalline structure, whereas films grown from [Hf(ONEt2)4] are smoother with little evidence of columnar structure. Full crystal structure data for [Hf(NMe2)4] are given, and the dielectric properties of [Al/HfO2/n‐Si(100)] MOS capacitors, fabricated using each precursor, are also reported.

N-Nitrosodimethylamine (NDMA) as a Drinking Water Contaminant: A Review

N-Nitrosodimethylamine (NDMA) is a member of a family of extremely potent carcinogens, the N-nitrosamines. Until recently, concerns about NDMA mainly focused on the presence of NDMA in food, consumer products, and polluted air. However, current concern focuses on NDMA as a drinking water contaminant resulting from reactions occurring during chlorination or via direct industrial contamination. Because of the relatively high concentrations of NDMA formed during wastewater chlorination, the intentional and unintentional reuse of municipal wastewater is a particularly important area of concern. Although ultraviolet (UV) treatment can effectively remove NDMA, there is considerable interest in the development of less expensive alternative treatment technologies. These alternative technologies include approaches for removing organic nitrogen-containing NDMA precursors prior to chlorination and the use of sunlight photolysis, and in situ bioremediation to remove NDMA and its precursors.

Quantitative Model Studies on the Efficiency of Precursors in the Formation of Cooling-Active 1-Pyrrolidinyl-2-cyclopenten-1-ones and Bitter-Tasting Cyclopenta-[b]azepin-8(1H)-ones

The yields of the cooling-active compounds 3-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one (1) and 5-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one (2) as well as the bitter tastants 7-methyl-2,3,6,7-tetrahydrocyclopenta-[b]azepin-8(1H)-one (3) and 7-methyl-2,3,4,5,6,7-hexahydrocyclopenta-[b]azepin-8(1H)-one (4) obtained by heating mixtures of possible Maillard-type precursors in model systems varying in temperature, pH value, or water content were determined quantitatively. The results showed that hexose-derived cyclotene is the common precursor for all four tastants and that the formation of each individual tastant is strongly determined by the structure of the nitrogen-containing precursor, e.g., reaction of cyclotene with pyrrolidine formed by thermal decarboxylation of L-proline produced the cooling compounds 1 and 2 only, whereas in the presence of 1-pyrroline formed upon Strecker reactions of L-proline, the bitter tasting azepinone 3 was produced exclusively. In contrast, the structure of the secondary amino acid L-proline enabled the formation of compound 4, whereas the pyrrolidine and 1-pyrroline, respectively, do not generate this tastant. In addition, a nonvolatile, tasteless intermediate, (S)-3-methyl-2-[(2'-carboxy)-1-pyrrolidinyl]-2-cyclopenten-1-one (5), was isolated from the cyclotene/L-proline reaction mixture and could be confirmed as an efficient precursor for the cooling compound 1. The data, obtained by these studies, are the scientific basis to tailor the desired overall flavor of foods by means of a more controlled Maillard-type technology.

Repression of GCN4 mRNA Translation by Nitrogen Starvation in Saccharomyces cerevisiae

Saccharomyces cerevisiae activates a regulatory network called "general control" that provides the cell with sufficient amounts of protein precursors during amino acid starvation. We investigated how starvation for nitrogen affects the general control regulatory system, because amino acid biosynthesis is part of nitrogen metabolism. Amino acid limitation results in the synthesis of the central transcription factor Gcn4p, which binds to specific DNA-binding motif sequences called Gcn4-protein-responsive elements (GCREs) that are present in the promoter regions of its target genes. Nitrogen starvation increases GCN4 transcription but efficiently represses expression of both a synthetic GCRE6::lacZ reporter gene and the natural amino acid biosynthetic gene ARO4. Repression of Gcn4p-regulated transcription by nitrogen starvation is independent of the ammonium sensing systems that include Mep2p and Gpa2p or Ure2p and Gln3p but depends on the four upstream open reading frames in the GCN4 mRNA leader sequence. Efficient translation of GCN4 mRNA is completely blocked by nitrogen starvation, even when cells are simultaneously starved for amino acids and eukaryotic initiation factor-2 alpha is fully phosphorylated by Gcn2p. Our data suggest that nitrogen starvation regulates translation of GCN4 by a novel mechanism that involves the four upstream open reading frames but that still acts independently of eukaryotic initiation factor-2 alpha phosphorylation by Gcn2p.

Aligned CNx nanotubes by pyrolysis of ferrocene/C60 under NH3 atmosphere

Aligned CNx (x<0.1) nanotubes have been generated by pyrolyzing ferrocene/C60 mixtures at 1050 °C in an ammonia atmosphere. The structure and composition of the product were determined by high-resolution transmission electron microscopy and high spatial resolution electron energy-loss spectroscopy. The CNx tubes (15–70 nm diameter, <50 μm length) grown in large flakes (<3 mm2) consist of a reduced number of “graphitic” layers (<15 on either side) arranged in a bamboo-like structure. Areas of high nitrogen concentration were found within curved or corrugated “graphite-like” domains. The observation of a well-developed double peak in the σ* feature of the N K-edge suggests that the material has not undergone the transition to the fullerene-like phase known for nitrogenated carbons. Incorporation of nitrogen from the gas phase (NH3) into CNx nanotubes therefore leads to improved and more efficient N substitution into the network as compared to the synthesis with solid nitrogen-containing precursors reported earlier.

Catalytic Reduction of Nitrogen Oxides by Olefins in the Presence of Oxygen over Copper/Alumina: Influence of Copper Loading and Formation of Byproducts

The performance of copper/alumina in the selective catalytic reduction of NOxby olefins in excess oxygen has been studied by means of FTIR gas phase analysis. Special emphasis was devoted to the formation of harmful byproducts such as N2O, HCN, and NH3. The effect of copper loading, reaction temperature, nitrogen oxides (NO, NO2), hydrocarbons (ethene, propene), and water on activity and on the formation of byproducts has been investigated. Increasing the copper loading from 0.46 to 1.65 wt% CuO resulted in a shift of the maximum activity to lower temperatures and in slightly lower nitrogen yields. NO2was reduced more efficiently than NO with both reductants, whereas no significant difference in activity was observed when either ethene or propene was used as a reductant. Water addition suppressed catalytic activity and leveled off the influence of copper loading. Substantial amounts of N2O, HCN, and NH3were observed for copper-containing catalysts, with ethene showing a markedly lower tendency to form HCN and N2O. Addition of water to the feeds eliminated HCN formation and suppressed the production of N2O but had only a marginal effect on NH3formation. Temperature-programmed surface reaction (TPSR) andin situFTIR experiments in various atmospheres with catalysts loaded under reaction conditions with dry feeds revealed the presence of surface deposits containing precursor species for ammonia and hydrogen cyanide formation. No such species were found when catalysts were loaded with feeds containing water. Reference TPSR measurements with acetonitrile and ethyl isocyanate in oxygen- and/or water-containing atmospheres showed a temperature dependence of ammonia formation comparable to that observed for the loaded catalyst, giving evidence that nitrile as well as isocyanate intermediates formed on the catalyst surface could be the source of ammonia found in catalytic activity testing. FTIR spectroscopy revealed the presence of nitrogen-containing surface species for catalysts loaded with a dry feed containing NO and propene, while no such species were found when wet feeds were used. Upon heating in H2/N2, cyanide species were produced, whereas isocyanate surface intermediates appeared in the spectra after heating in O2/N2. The findings are in accordance with a mechanism in which a nitrogen-containing precursor, which can be a nitrile or an oxime species, reacts to surface isocyanate and/or cyanide species. Hydrolysis of these intermediates provides a pathway to NH3.

PACVD nano-crystalline BCN thin films obtained by use of an organoboron precursor

Thin films of the BCN system deposited by use of gas mixtures composed of a boron- and nitrogen-containing organic precursor, argon and hydrogen are investigated with the aid of a radiofrequency PACVD procedure. The structure and composition of these films are found to be strongly affected by the mole ratio between the organoboron precursor and hydrogen. The films obtained at high values of this ratio are amorphous: they become partially crystalline on decreasing this ratio. The deposit obtained at a relatively low value of this ratio is composed of a mixture of cubic boron nitride and boron carbide. Use of a considerable excess of hydrogen in the gas mixture is found to allow poorly crystalline and amorphous phases in the BCN system to be completely removed from the deposit.