The mechanism of the nitrate (platinum) electrode in molten alkali nitrates

The mechanism for the nitrate electrode, (Pt)NO₂, O₂/NO^?₃, is shown to be: NO^?₂ = NO₂ + e; NO₂ = NO + $\text{1}\text{2}$O₂; NO^?₃ + NO = NO^?₂ + NO₂; with the overall reaction: NO^?₃ = NO₂ + $\text{1}\text{2}$O₂ + e.     

Contribution of (NO3 −)surf Reduction to the Overall Mechanism of H2-Promoted n-C6H14-DeNOx Over Ag/Al2O3

Transient response experiments indicated that H₂-promoted n-C₆H₁₄-SCR over Ag/Al₂O₃ has a significant contribution from the pathway proceeding through the formation of surface nitrate complexes (NO₃ ^?)_surf followed by their reduction. The rate of (NO₃ ^?)_surf reduction by 300 ppm C₆H₁₄ in the presence of 1,000 ppm H₂ is virtually identical to the rate of steady-state H₂-promoted n-C₆H₁₄-SCR, while surface nitrate species reveal their inertness with respect to 300 ppm n-C₆H₁₄ only. Transient response experiments and temperature programmed desorption indicate that (NO₃ ^?)_surf is readily transformed by NO or H₂ to the reactive (NO₂ ^?)_surf complexes. The latter are further reduced by n-hexane in the presence of H₂.     

Removal of toxic nitrate ions from drinking water using conducting polymer/MWCNTs nanocomposites

New application of conducting polymers as stable nanocomposites for nitrate ion exchange materials in water and wastewater treatment and for environmental protection is introduced in this work. The nanocomposites of multi-walled carbon nanotubes (MWCNTs) with different polymers such as: polyaniline (PANI), polypyrrole (PPY), poly(1,8-diaminonaphthalene) [P(1,8-DAN)] and poly(2-vinylpyridine) (P2VP) were synthesized with different dopants as effective and reusable nanocomposites for nitrate removal from drinking water. Nitrate anions at toxic concentrations were removed from water using ion exchange mechanism without any toxic byproducts. The obtained results demonstrate that effective ion exchange occurs between NO₃ ^? and Cl^?. There are some protonated heteroatoms in polymer chains that are bonded with anions of dopants and their counter ions in nanocomposites. These dopant anions on the =NH⁺– groups of polymers can be exchanged with NO₃ ^? in water. Adsorption of NO₃ ^? on polymer/MWCNTs nanocomposites showed dependency to some parameters. Different experimental parameters such as pH and temperature of the sample, polymers dopant, and the ratio of polymer to MWCNTs in nanocomposites affect the amount of nitrate removal. The highest removal efficiency was achieved at 1.20 g L^?1 of PANI/MWCNTs (3:1) nanocomposite, pH = 6.5 and ambient temperature. After five successive cycles of nitrate removal, this parameter was still up to 70 % compared to the first run (up to 80 %).     

Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor

BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH₃COO^?/NO₃^? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH₃COO^?/NO₃^? (0.85, 0.72 and 0.62) with a constant S^2?/NO₃^? molar ratio of 0.13 were evaluated. At a CH₃COO^?/NO₃^? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N₂ yield (g N₂ g^?1 NO₃^?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g^?1 CH₃COO^?‐C consumed. Sulfide was partially oxidized to S⁰, and 71% of the S^2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH₃COO^?/NO₃^? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N₂ and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S⁰, with a yield of 0.92 g SO₄^2?‐S g^?1 S^2? consumed. CONCLUSIONS: The CH₃COO^?/NO₃^? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S⁰ or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO₂, S⁰ and N₂ as the major end products. Copyright © 2008 Society of Chemical Industry     

Effects of airborne contaminant exposure on the physical properties and filtration performance of activated, impregnated carbon

The effects of airborne contaminant exposure in humid air on the physical properties and filtration capabilities of a copper/zinc/molybdenum impregnated carbon were investigated. The impregnated carbon was exposed individually to CO₂, NH₃ and NO₂ in humid air, then evaluated for changes in metal speciation, metal distribution, porosity and water-uptake. The exposed impregnated carbon was further evaluated for changes in its ability to remove SO₂ and cyclohexane from air streams. Exposure to CO₂ did not impact the physical properties of the impregnated carbon, with changes in filtration performance were not evident. NH₃ exposure resulted in the formation of metal amine complexes, which led to a migration of impregnants from within the pores of the carbon granule to the external surface. NH₃ exposure increased SO₂ filtration while decreasing cyclohexane filtration. The decrease in cyclohexane filtration was attributed to an increase in water uptake and a decrease in porosity. NO₂ exposure significantly decreased the porosity of the carbon substrate while increasing the amount of surface oxygen. The increased surface oxygen greatly increased water uptake. NO₂ exposure greatly reduced the SO₂ breakthrough time and the ability of the material to remove cyclohexane.     

Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico‐chemical and biological technique for the removal of NO_x from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO₃^?, NO₂^?, NO via N₂O to N₂ in this unusual medium. This was done in batch experiments at 30 °C with 25 mmol dm^?3 FeEDTA solutions (pH 7.2 ± 0.2). Also Ca²⁺ (2 and 10 mmol dm^?3) and Mg²⁺ (2 mmol dm^?3) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl‐complex Fe(II)EDTA–NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 °C than NO reduction at 30 °C. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron‐mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. Copyright © 2004 Society of Chemical Industry     

EXAFS Study on Structural Change of Charcoal-supported Ruthenium Catalysts during Lignin Gasification in Supercritical Water

Lignin gasification in supercritical water over charcoal supported ruthenium trivalent salts was studied using a batch reactor at 673 K. Ruthenium (III) nitrosyl nitrate on charcoal (Ru(NO)(NO₃)₃/C) was more active than ruthenium (III) chloride on charcoal (RuCl₃/C) for the gasification reaction. EXAFS analysis revealed that ruthenium metal particles were formed in both RuCl₃/C and Ru(NO)(NO₃)₃/C catalysts during the lignin gasification and that the size of ruthenium metal in Ru(NO)(NO₃)₃/C was smaller than that in RuCl₃/C. It was concluded that well-dispersed ruthenium metal particles were active for the lignin gasification in supercritical water.     

Author Index to Volume 38

X-ray photoelectron spectroscopy (XPS) is a powerful technique for determining the surface chemical composition of atmospheric particles. In this article, we employed XPS to study atmospheric particles collected from Guangzhou city in typical sites and seasons. The results showed that the weight percentage of carbon, oxygen, nitrogen, and sulfur were about 70.5–87.1%, and these species dominated the surface structure of the particles independent of the collection site and season. Inorganic elements including Si, Na, Ca, Cl, Fe, K, Al, and Cu were also found on the particle surfaces. The high-resolution XPS spectra revealed: (1) High aromatic and aliphatic C-H, and other oxidized carbons were found on the surface of particles. (2) The nitrogen species were characterized by pyridinic, pyrrolic/amide, quaternary type nitrogen functionalities, and nitrate groups, indicating that inorganic and organic N species are both important components of N-containing particles. (3) Sulfate and sulfone groups were also present on the surface and were important components. The oxidized groups of C, N, and S were higher in winter samples, consistent with the monsoon weather of Guangzhou in winter, which is favorable for the formation of oxidized species. A comparison between total and surface analyses showed that the surface of particles was relatively high in organic carbon, NO₃ ^?, and SO₄ ^2?, and the interior of particles was higher in NH₄ ⁺. These results provide information on the formation of aerosols, e.g., NH₄ ⁺ may act as a very important nucleus and organic carbon, NO₃ ^?, and SO₄ ^2? coat the nuclei during particle growth.     

Rate of ammonia oxidation in a synthetic saline wastewater by a nitrifying mixed‐culture

Most of the kinetic studies on nitrification have been performed in diluted salts medium. In this work, the ammonia oxidation rate (AOR) was determined by respirometry at different ammonia (0.01 and 33.5 mg N‐NH₃ L^?1), nitrite (0–450 mg N‐NO₂^? L^?1) and nitrate (0 and 275 mg N‐NO₃^? L^?1) concentrations in a saline medium at 30 °C and pH 7.5. Sodium azide was used to uncouple the ammonia and nitrite oxidation, so as to measure independently the AOR. It was determined that ammonia causes substrate inhibition and that nitrite and nitrate exhibit product inhibition upon the AOR. The effects of ammonia, nitrite and nitrate were represented by the Andrews equation (maximal ammonia oxidation rate, r_AOMAX, = 43.2 [mg N‐NH₃ (g VSS_AO h)^?1]; half saturation constant, K_SAO, = 0.11 mg N‐NH₃ L^?1; inhibition constant K_IAO, = 7.65 mg N‐NH₃ L^?1), by the non‐competitive inhibition model (inhibition constant, K_INI, = 176 mg N‐NO₂^? L^?1) and by the partially competitive inhibition model (inhibition constant, K_INA, = 3.3 mg N‐NO₃^? L^?1; α factor = 0.24), respectively. The r_AOMAX value is smaller, and the K_SAO value larger, than the values reported in diluted salts medium; the K_IAO value is comparable to those reported. Process simulations with the kinetic model in batch nitrifying reactors showed that the inhibitory effects of nitrite and nitrate are significant for initial ammonia concentrations larger than 100 mg N‐NH₄⁺ L^?1. Copyright © 2005 Society of Chemical Industry     

Reaction mechanisms of lithium garnet pellets in ambient air: The effect of humidity and CO2

Li₇La₃Zr₂O₁₂ (LLZO) has been reported to react in humid air to form Li₂CO₃ on the surface, which decreases ionic conductivity. To study the reaction mechanism, 0.5‐mol Ta‐doped LLZO (0.5Ta–LLZO) pellets are exposed in dry (humidity ~5%) and humid air (humidity ~80%) for 6 weeks, respectively. After exposure in humid air, the formation of Li₂CO₃ on the pellet surface is confirmed experimentally and the room‐temperature ionic conductivity is found to drop from 6.45×10^?4 S cm^?1 to 3.61×10^?4 S cm^?1. Whereas for the 0.5Ta–LLZO samples exposed in dry air, the amount of formed Li₂CO₃ is much less and the ionic conductivity barely decreases. To further clarify the reaction mechanism of 0.5Ta–LLZO pellets with moisture, we decouple the reactions between 0.5Ta–LLZO with water and CO₂ by immersing 0.5Ta–LLZO pellets in deionized water for 1 week and then exposing them to ambient air for another week. After immersion in deionized water, Li⁺/H⁺ exchange occurs and LiOH H₂O forms on the surface, which is a necessary intermediate step for the Li₂CO₃ formation. Based on these observations, a reaction model is proposed and discussed.     

Effect of supplying a carbon extracting solution on denitrification in horizontal subsurface flow constructed wetlands

Denitrification strongly depends on the availability of carbon source in constructed wetlands (CWs). In this study, several relevant carbon source extracting solutions made from hydrolyzate of selected wetland litters were added to CWs for nitrogen removal enhancement. The feasibility of supplying a carbon extracting solution to improve potential denitrification rate in horizontal subsurface flow constructed wetland was deeply investigated. Combinations of different hydraulic retention time (HRT, especially for 2-day and 4-day) with different influent COD/N ratios were designed to prove the enhancement on denitrification by carbon source supplement. In addition, specific denitrification rate (SDNR) was calculated for the comparison of the nitrogen removal at different COD/N ratios. The sequential operation results on total nitrogen (TN) and nitrate (NO ₃ ^? -N) removal efficiencies were obtained in CW system with an influent COD/N ratio of 4.0. The accumulation of nitrite (NO ₂ ^? -N) was found to be closely related to the removal of NO ₃ ^? -N. Meanwhile, no obvious accumulation of NO ₂ ^? -N was found when the removal of NO ₃ ^? -N was relatively high.     

SiC Foams Decorated with SnO2 Nanostructures for Room Temperature Gas Sensing

Cell walls of the commercial silicon carbide (SiC)‐based foams were decorated by one‐dimensional tin dioxide (SnO₂) nanostructures. Thermal evaporation of SnO₂ powder with the assistance of a Au catalyst in inert atmosphere caused the formation of SnO₂ nanobelts on the pore surfaces. The room temperature (RT) ammonia (NH₃) and nitrogen dioxide (NO₂) gas sensing behaviors were investigated systematically in both dry and humid air atmosphere with/without UV activation. The results were compared to those for bare SnO₂ and SiC. It was shown that SiC/SnO₂ composite was efficient to detect low concentration of NH₃ (10–50 ppm) and NO₂ (1–5 ppm) under humid air and UV activation at RT.     

Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

XPS investigation of the reaction of carbon with NO, O2, N2 and H2O plasmas

The interaction of graphite with plasmas of pure gases (O₂, N₂ or H₂O), air or mixtures of gases containing NO has been studied by XPS “in situ” analysis. Depending on the type of plasma, different species of nitrogen, oxygen and carbon have been detected on the surface of graphite. The nitrogen containing species have been attributed to pyridinic, pyrrol, quartenary and oxidized groups adsorbed on the surface. The evolution with the treatment time of the relative intensity of the different nitrogen bands for Ar + NO, N₂ + NO, air or N₂ plasmas has served to propose a model accounting for the reactions of graphite with plasmas of NO containing gases. The model explains why carbon materials (in the form of graphite, soot particles, etc.) can be very effective for the removal of the NO present in exhaust combustion gases excited by a plasma. The analysis of the C1s and O1s photoemission peaks reveals the formation of C/O adsorbed species up to a maximum concentration on the surface of around 10% atomic oxygen. A general evolution is the progressive formation of C/O species where the carbon is sp³ hybridized. This tendency is enhanced when graphite is treated with the plasma of water.     

NO Reduction by CH4in the Presence of O2over Pd-H-ZSM-5

An investigation of the interaction of NO and NO₂with Pd-H-ZSM-5, as well as the reduction of NO by CH₄, has been conducted using mass spectrometry andin situinfrared spectroscopy. Prior to reaction most of the Pd in Pd-H-ZSM-5 (Pd/Al=0.048) is present as Pd²⁺cations. NO reduction by CH₄in the absence of O₂results in the progressive reduction of Pd²⁺cations above 610 K and the formation of small Pd particles. Reduction of Pd²⁺cations is significantly suppressed when O₂is added to the feed of NO and CH₄.In situinfrared spectroscopy reveals the presence of NO⁺and NO as the principal adsorbed species. NO⁺is present as a charge-compensating cation (e.g., Z⁻NO⁺) and is believed to be formed via the reaction 2 Z⁻H⁺+2 NO+1/2 O₂=2 Z⁻NO⁺+H₂O. NO⁺does not react with CH₄at temperatures up to 773 K. Adsorbed NO reacts with CH₄above 650 K and CN species are observed as intermediates. The latter species react with both NO, O₂, and presumably NO₂. Based on the accumulated data, a mechanism is proposed to explain the reduction of NO by CH₄both in the presence and absence of O₂.     

High-Resolution Mobility and Mass Spectrometry of Negative Ions Produced in a 241Am Aerosol Charger

This work concentrates on the simultaneous mobility and mass measurement of negative ions generated by the ionizing radiation in a ²⁴¹Am aerosol charger in N₂ (5.0), a 1:1-mixture of N₂ and synthetic air, pure synthetic air (5.0), and filtered laboratory air at ～30% relative humidity. Therefore, a high-resolution mobility analyzer (UDMA) and an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF) were operated in series. Experiments with N₂ as carrier gas showed a dominating signal at an electrical mobility of 2.09 cm²/Vs with 90% of the ions being nitrate based. The ion composition was altered after a baking-out to a spectrum with three strong mobility-peaks at Z₁ = 2.34 cm²/Vs, Z₂ = 1.42 cm²/Vs, Z₃ = 1.08 cm²/Vs and a higher diversity of ions in the corresponding mass spectra. The carrier gas was gradually changed from N₂ (5.0) to a 1:1-mixture of N₂ with synthetic air and pure synthetic air (5.0), having only a minor effect on the overall pattern of the ion spectrum. Using room air leads to a domination of the nitrate based ions. The mobility-dependent transmission efficiency of the UDMA was modeled using an empirical, laminar diffusion deposition model. The data were further compared to an empirical mass-mobility relationship to evaluate the fragmentation of the ion clusters in the inlet of the mass spectrometer. This study suggests that the nitrate ion, NO₃ ^?, is found to be the dominant ion species produced in an aerosol charger, and that it may be mostly responsible for the charging of aerosol particles in negative polarity.

Copyright 2014 American Association for Aerosol Research     

Versuche zur trennung der anionen nitrat,nitrit, hyponitrit und nitrohydroxylaminat am anionenaustauscher wofatit SBW

The separation of NO₃^?, NO₂^?, N₂O₂^2? and N₂O₃^2? has been studied by elutionchromatography on the strong basic anion-exchange resin Wofatit SBW. The solutions proper for elution-chromatography have been chosen on basis of measured anion-affinities. Quantitative separations were obtained with the mixtures of N₂O₂^2?, NO₂^? and NO₃^? as well as of N₂O₃^2?, NO₂^? and NO₃^? with a solution of Na₂SO₄. Both separation methods can be applied to prepare solutions of hyponitrite and nitrohydroxylaminate which are free of nitrate and nitrite.     

Investigation of NO Adsorption and NO/O2 Co-adsorption on NOx-Storage-Components by DRIFT-Spectroscopy

NO adsorption and NO/O₂ co-adsorption on CeO₂ at different temperatures was studied by DRIFT-Spectroscopy. The results indicate that this oxide plays an important role in storing NO _x . FTIR studies show that NO adsorption is dominated by the formation of nitrite species. Furthermore, cis- and trans hyponitrite species are detected. Co-adsorption of NO/O₂ leads to the formation of nitrates. The experimental data show that the formation of nitrates is a consecutive reaction: adsorption of NO to form nitrite species (NO₂ ^–), followed by an oxidation to form nitrate species (NO₃ ^–).     

Dominant Mechanisms that Shape the Airborne Particle Size and Composition Distribution in Central California

The size and composition of ambient airborne particulate matter is reported for winter conditions at five locations in (or near) the San Joaquin Valley in central California. Two distinct types of airborne particles were identified based on diurnal patterns and size distribution similarity: hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. Daytime PM₁₀ concentrations for sulfate/ammonium/nitrate particles were measured to be 10.1 μ g m^?3, 28.3 μ g m^?3, and 52.8 μ g m^?3 at Sacramento, Modesto and Bakersfield, California, respectively. Nighttime concentrations were 10–30% lower, suggesting that these particles are dominated by secondary production. Simulation of the data with a box model suggests that these particles were formed by the condensation of ammonia and nitric acid onto background or primary sulfate particles. These hygroscopic particles had a mass distribution peak in the accumulation mode (0.56–1.0 μ m) at all times. Daytime PM₁₀ carbon particle concentrations were measured to be 9.5 μ g m^?3, 15.1 μ g m^?3, and 16.2 μ g m^?3 at Sacramento, Modesto, and Bakersfield, respectively. Corresponding nighttime concentrations were 200–300% higher, suggesting that these particles are dominated by primary emissions. The peak in the carbon particle mass distribution varied between 0.2–1.0 μ m. Carbon particles emitted directly from combustion sources typically have a mass distribution peak diameter between 0.1–0.32 μ m. Box model calculations suggest that the formation of secondary organic aerosol is negligible under cool winter conditions, and that the observed shift in the carbon particle mass distribution results from coagulation in the heavily polluted concentrations experienced during the current study. The analysis suggests that carbon particles and sulfate/ammonium/nitrate particles exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode.     

Nitrate removal from water by quaternized pine bark using choline based ionic liquid analogue

BACKGROUND: The objective of this study was to quaternize pine bark (PB) wood residues using green chemistry and to use the quaternized PB to remove nitrate (NO₃^?) from water. The quaternization process was achieved by reacting the wood residues with an ionic liquid analogue comprised of a choline chloride derivative and urea. Batch adsorption tests were used to delineate the NO₃^? uptake by the modified pine bark (MPB). Fourier Transform Infrared Spectroscopy (FTIR) analysis and Zeta potential measurements were used to characterize the changes at the surface of the PB due to quaternization and NO₃^? uptake. RESULTS: The MPB has a maximum NO₃^? uptake capacity of 2.91 mmol g^?1. The NO₃^? uptake kinetics indicated that diffusion through the boundary layer of the MPB was the rate limiting step. The Langmuir adsorption model provided a better fit for the uptake data than the Freundlich model, indicating monolayer adsorption. The uptake process was found dependent on concentration, pH and ionic strength, and was also spontaneous and exothermic. The desorption–regeneration experimental results indicated a 95% efficiency after five consecutive regeneration cycles. CONCLUSIONS: The quaternization technique was found very effective for developing effective and green anion exchange resins to remove NO₃^? from water. © 2012 Society of Chemical Industry