Presence Of NO Research Articles

Effect of nitrite and nitrate on sulfate reducing ammonium oxidation

The effects of nitrite and nitrate on the integration of ammonium oxidization and sulfate reduction were investigated in a self-designed reactor with an effective volume of 5 L. An experimental study indicated that the ammonium oxidization and sulfate reduction efficiencies were increased in the presence of nitrite and nitrate. Studies showed that a decreasing proportion of N/S in the presence of NO2 - at 30 mg·L-1 would lead to high removal efficiencies of NH4 +-N and SO4 2--S of up to 78.13% and 46.72%, respectively. On the other hand, NO3 - was produced at approximately 26.89 mg·L-1. Proteobacteria, Chloroflexi, Bacteroidetes, Chlorobi, Acidobacteria, Planctomycetes and Nitrospirae were detected in the anaerobic cycle growth reactor. Proteobacteria was identified as the dominant functional bacteria removing nitrogen in the reactor. The nitritation reaction could promote the sulfate-reducing ammonium oxidation (SRAO) process. NH4 + was converted to NO2 and other intermediates, for which the electron acceptor was SO4 2-. These results showed that nitrogen was converted by the nitrification process, the denitrification process, and the traditional anammox process simultaneously with the SRAO process. The sulfur-based autotrophic denitration and denitrification in the reactor were caused by the influent nitrite and nitrate.

Synergistic Reaction of SO2 with NO2 in Presence of H2O and NH3: A Potential Source of Sulfate Aerosol.

Effect of H2O and NH3 on the synergistic oxidation reaction of SO2 and NO2 is investigated by theoretical calculation using the molecule system SO2-2NO2-nH2O (n = 0, 1, 2, 3) and SO2-2NO2-nH2O-mNH3 (n = 0, 1, 2; m = 1, 2). Calculated results show that SO2 is oxidized to SO3 by N2O4 intermediate. The additional H2O in the systems can reduce the energy barrier of oxidation step. The increasing number of H2O molecules in the systems enhances the effect and promotes the production of HONO. When the proportion of H2O to NH3 is 1:1, with NH3 included in the system, the energy barrier is lower than two pure H2O molecules in the oxidation step. The present study indicates that the H2O and NH3 have thermodynamic effects on promoting the oxidation reaction of SO2 and NO2, and NH3 has a more significant role in stabilizing product complexes. In these hydrolysis reactions, nethermost barrier energy (0.29 kcal/mol) can be found in the system SO2-2NO2-H2O. It is obvious that the production of HONO is energetically favorable. A new reaction mechanism about SO2 oxidation in the atmosphere is proposed, which can provide guidance for the further study of aerosol surface reactions.

Experimental Study on SO2-to-SO3 Conversion Over Fe-Modified Mn/ZSM-5 Catalysts During the Catalytic Reduction of NOx

Mn–Fe/ZSM-5 catalysts with different Fe loading amounts were prepared using wet impregnation and the effects of these catalysts on SO3 formation during the catalytic reduction of NOx were assessed. Variations in the catalysts’ physicochemical properties with different Fe contents were also investigated using BET, XRD, SEM–EDS, FT-IR, H2-TPR and XPS techniques. The 9Mn9Fe catalyst gave the highest SO2-to-SO3 and NOx conversions, and adding Fe also improved the catalyst’s SO2 resistance. The presence of NO2 caused the formation of nitrate ions on the catalyst surface during fast SCR. These nitrate ions re-oxidized the active sites more rapidly than O2 at low temperatures, thereby promoting the redox reaction. BET, XRD and SEM–EDS showed that optimal Fe loading amount reduced MnOx crystallinity while improving surface dispersion. Adding excessive Fe caused the active compositions to accumulate on the catalyst surface. FT-IR, H2-TPR and XPS demonstrated that optimal Fe loading amount increased the quantity of Mn4+=O bonds while raising the concentrations of Mn4+ ions and lattice oxygen, thus enhancing SO2-to-SO3-conversion. Therefore, although suitable amounts of Fe and NO2 promoted NOx conversion, these species also significantly increased SO2-to-SO3 conversion.

Carbon Materials Inhibit Formation of Nitrated Aromatic Products in Treatment of Phenolic Compounds by Thermal Activation of Peroxydisulfate in the Presence of Nitrite.

Recent studies have reported that toxic nitrated aromatic products are generated during treatment of phenolic compounds by thermally activated peroxydisulfate (thermal/PDS) in the presence of nitrite (NO2-). This work explored the potential of carbon materials on controlling the formation of nitrated aromatic products using phenol as a model compound. In the presence of selected carbon materials including diverse carbon nanotubes (CNT) and powdered activated carbon (PAC), the transformation kinetics of phenol was significantly enhanced, primarily attributed to nonradical activation of PDS by carbon materials. Nitrophenols (NPs) including 2-NP and 4-NP were formed in phenol oxidation by the thermal/PDS/NO2- process, due to the reaction of phenol with reactive nitrogen species generated from NO2- oxidation. The addition of carbon materials obviously inhibited NPs formation under various experimental conditions. The bonding of nitro groups on the CNT surface was clearly confirmed by means of various characterizations, probably resulting from the competitive reaction of reactive nitrogen species with CNT vs phenol. The controlling effect of carbon materials was also verified in the cases of other phenolic compounds. Therefore, the addition of carbon materials may be a promising approach to control the formation of undesirable nitrated byproducts by the thermal/PDS process in the presence of NO2-.

Characterization of the gas effluent in the treatment of nitrogen containing pollutants in water by Fenton process

This work evidences for the first time the production of CO and NOx during the removal of nitrogen containing pollutants in water by Fenton Process, the most popular method for Advanced Oxidation Processes. Four representative nitrogen containing pollutants were selected, viz. aniline, 4-nitrophenol, pyridine and monoethanolamine. The gas effluent accumulated after 3 h of reaction at 90 °C and 3 bar was analysed. In all cases, the carbon and nitrogen mass balance was assessed. Also, an on-line off-gas analysis system was set up to monitor the off-gas variation of CO and CO2 from the beginning of the reaction.CO2 was the major component of the gas effluent. It was progressively produced upon oxidation. In contrast, CO was detected in fairly lower amounts and it was immediately produced after H2O2 injection, due to the rupture and opening of the aromatic ring. The CO formation was more favorable upon degradation of aromatic than aliphatic compounds, or when the nitrogen was in the aromatic ring, as in the case of pyridine. The nitrogen functional groups were majorly transformed into NH4+ and NO3−, while NOx was detected in low amounts (<1 mg/m3) and favoured in presence of NO2 group.These results highlight the importance of monitoring the gas phase generated in the treatment of high-loaded wastewater by AOPs in order to guarantee the environmental sustainability of the processes.

Experimental analysis of development of compulsive behavioural disorders due to intravenous fentanyl self-administration

Organophosphate triesters (OPEs) have caused great concern as a class of emerging environmental contaminants due to their widespread use and their toxicity to organisms. However, the phototransformation behavior of OPE is still not fully understood, which is important for understanding their environmental fate. In the present study, the photodegradation of tricresyl phosphate (TCP), one of the most widely detected OPEs in aqueous environments, was investigated including the direct photolysis and in the presence of several natural water factors, NO2−, Fe3+ and humic acid. The degradation process followed the pseudo-first-order kinetics, with rate constant increasing slightly with increasing initial TCP concentration. The presence of NO2− and Fe3+ was observed to promote the photochemical loss of TCP, while humic acid played a negative role on TCP transformation. Electron spin resonance (EPR) analysis showed that carbon-centered radical was produced in the photolysis process of TCP, and hydroxyl radical contributed to the promotion of rate constant for Fe3+ and NO2−. Four photolysis products were tentatively identified by HPLC-LTQ-Orbitrap MS analysis, and the possible degradation pathways of TCP were proposed. These findings provide a meaningful reference for the fate and transformation of OPEs in natural water.

The Effects of pH Values on Functional Mechanisms of Nitrite Anions for Q235 Carbon Steels in 0.01 mol L-1 NaNO2-HCl Solutions

For Q235 carbon steels in 0.01 mol L-1 NaNO2-HCl solutions with different pH values, the effects of pH values on the functional mechanisms of nitrite anions (NO2-) were studied. In the pH 1 and pH 2 solutions, the Q235 steels showed the electrochemical behavior of activation, and uniform corrosion (UC) was the main corrosion type on the Q235 surface. The presence of NO2- did not affect the electrochemical behavior and the corrosion type but only accelerated the anodic reaction of Fe oxidation. In the pH 3 and pH 4 solutions, the Q235 steels presented the electrochemical behavior of activation-passivation transition, and intergranular corrosion (IGC) occurred on the Q235 surface. The cathodic reaction of NO2- reduction resulted in the transition of electrochemical behavior from activation to passivation and the change of corrosion type from UC to IGC. In the pH 5 and pH 6 solutions, the Q235 steels exhibited the electrochemical behavior of self passivation-pitting, and pitting corrosion (PC) was present on the Q235 surface. The strong oxidability of NO2- played a critical role in the formation of γ-Fe2O3 passive film on the Q235 surface under the combined action of Fe2+ and NO2-.

Photo-electrochemical properties of p-type AgCoO2 prepared by low temperature method

AgCoO2 prepared by co-precipitation at low temperature (~ 80 °C) is characterized by physical and photo-electrochemical techniques. The X-ray diffraction shows broad peaks with a particle size of ~ 20 nm and a specific surface area of ∼ 28 m2 g−1. The forbidden band (1.33 eV) is due to Ag+: d → d transition, further transition at 4.50 eV is assigned to the charge transfer. The transport properties, measured up to 650 K, indicate intrinsic conductivity: σ = σo exp{− 0.24 eV/kT (Ω-cm)−1}, supporting a phonon assisted conduction mechanism. An exchange current density of 1.27 mA cm−2 in Na2SO4 (0.1 M) solution is consistent with the electrochemical stability up to 0.8 VSCE. The capacitance measurement (C−2 - E) indicates p type conduction, with a flat band potential (Efb) of 0.26 VSCE and a holes density (NA) of 7.38 × 1019 cm−3 due to the oxygen insertion in the layered lattice. The electrochemical impedance spectroscopy (EIS) data, recorded in the range (1 mHz - Hz), reveals a predominant bulk contribution with a low depletion angle of 3° and a pseudo capacitive behavior. As application, AgCoO2 is tested for the hydrogen production upon visible illumination owing to the potential of its conduction band (−0.83 VSCE), less cathodic than that of H2O/H2 (~ −0.5 VSCE). H2 evolution rate of 79 µmol g−1 min−1 is determined at neutral pH with a quantum yield of 1.92% in presence of NO2- as hole scavenger; no Ag deposition was observed after photocatalysis.

Sulfate radical-induced incorporation of NO2 group into chlorophenols

Sulfate radical ( $${\text{SO}}_{4}^{ \cdot - }$$ )-based advanced oxidation processes (SR-AOPs) are promising in situ chemical oxidation technologies that received increasing interest recently. The application of SR-AOPs for decontamination may, however, generate unexpected toxic by-products. This contribution reports that $${\text{SO}}_{4}^{ \cdot - }$$ can incorporate nitrite (NO2−) nitrogen into chlorophenols, resulting in the formation of chloronitrophenols which pose greater environmental concerns. Nitrogen dioxide radical ( $${\text{NO}}_{2}^{ \cdot }$$ ) and phenoxy radical are important precursors responsible for the formation of chloronitrophenols. High concentrations of NO2− inhibited the transformation of chlorophenol but promoted the formation of chloronitrophenol. This study underscores a need for caution in the application of SR-AOPs in the presence of NO2−, because chloronitrophenols can be more genotoxic and mutagenic than chlorophenols.

NOx-Hydrocarbon Kinetics Model Validation Using Measurements of H2O in Shock-Heated CH4/C2H6 Mixtures With NO2 as Oxidant

One method frequently used to reduce NOx emissions is exhaust gas recirculation, where a portion of the exhaust gases, including NOx, is reintroduced into the combustion chamber. While a significant amount of research has been performed to understand the important fuel/NOx chemistry, more work is still necessary to improve the current understanding on this chemistry and to refine detailed kinetics models. To validate models beyond global kinetics data, such as ignition delay time or flame speed, the formation of H2O was recorded using a laser absorption diagnostic during the oxidation of a mixture representing a simplistic natural gas (90% CH4/10% C2H6 (mol)). This mixture was studied at a fuel lean condition (equivalence ratio = 0.5) and at atmospheric pressure. Unlike in conventional fuel-air experiments, NO2 was used as the oxidant to better elucidate the important, fundamental chemical kinetics by exaggerating the interaction between NOx and hydrocarbon-based species. Results showed a peculiar water formation profile, compared to a former study performed in similar conditions with O2 as oxidant. In the presence of NO2, the formation of water occurs almost immediately before it reaches more or less rapidly (depending on the temperature) a plateau. Modern, detailed kinetics models predict the data with fair to good accuracy overall, while the GRI 3.0 mechanism is proven inadequate for reproducing CH4/C2H6 and NO2 interactions.

Catalytic partial oxidation of CH4 to syn gas (H2/CO) in presence of N2O over periclase type SiO2@Ni(Mg,Al)O catalyst synthesized by non aqueous route

Periclase type Ni/Mg/Al mixed-metal oxide prepared from sol-gel derived SiO2@Ni-Mg-Al Layered Double Hydroxides (LDH) nanocomposite at SiO2:LDH ratios 0:1 and 1:1 was used as a catalyst for catalytic partial oxidation (CPO) of CH4 in presence of N2O as well as oxygen. The catalysts were characterized by XRD, BET surface area, H2-TPR and XPS analysis. The presence of SiO2 dispersant influenced the catalytic property. The nascent oxygen formed by the decomposition of N2O does not re-oxidize Ni0 like molecular oxygen which act as the active species and leads to partial oxidation of CH4. SiO2@Ni-Mg-Al (1:1) catalyst showed about 99.99% H2 and 99.8% CO yield between the temperature range of 200-500 °C.

A Gas Sensor Based on a Single SnO Micro-Disk

In this study, individual nanofabricated SnO micro-disks, previously shown to exhibit exceptional sensitivity to NOx, are investigated to further our understanding of gas sensing mechanisms. The SnO disks presenting different areas and thickness were isolated and electrically connected to metallic electrodes aided by a Dual Beam Microscope (SEM/FIB). While single micro-disk devices were found to exhibit short response and recovery times and low power consumption, large interconnected arrays of micro-disks exhibit much higher sensitivity and selectivity. The source of these differences is discussed based on the gas/solid interaction and transport mechanisms, which showed that thickness plays a major role during the gas sensing of single-devices. The calculated Debye length of the SnO disk in presence of NO2 is reported for the first time.

A simple yet sensitive colorimetric nitrite ions assay based on diazotization with p‑Aminobenzoic and coupling with phloroglucinol in acidic medium.

Immoderate intake of nitrite (NO2-) is deleterious human health and may result in causing dangerous diseases. In this study, nitrite detection system was successfully fabricated based on a unique diazo-coupling reaction of p‑Aminobenzoic acid (PABA) and phloroglucinol (1, 3, 5‑trihydroxybenzene). Upon the presence of NO2- in an acid medium, p‑Aminobenzoic acid could not only form diazonium ion easily but also couple with p‑Aminobenzoic acid, and results forming yellow water-soluble azo dye that shows maximum absorption at 434 nm. Under the further accurate determination condition, such as acid concentration, amount of reagents and time required, the naked-eye detection of NO2- showed excellent selectivity in compared with some anions. Especially, diazotization and coupling reaction proposed here is very fast and control of pH and temperature are unnecessary. Moreover, the color is stable for several days and Beer's law is obeyed over a wide range. Reliable detection can be made in the range of 0.05 to 1 p.p.m. of nitrite ion. Detection limit was calculated to be 0.024 p.p.m. (0.52 μ M) by UV-visible spectroscopy and 0.05 p.p.m. (1.09 μ M) by naked-eye. By using an electrochemical method, IR, SEM, and 1HNMR, the sensing mechanism can be easily verified. More importantly the proposed method was successfully applied for the determination of nitrite in a real water sample.

Coupled methane and nitrous oxide biotransformation in freshwater wetland sediment microcosms

Anaerobic oxidation of methane (AOM) coupled to denitrification is becoming the focus of scientific inquiry due to its potential contribution to global carbon and nitrogen cycles. AOM has been previously reported to proceed with nitrate (NO3−) or nitrite (NO2−). However, little research has been conducted on the simultaneous use of methane (CH4) and nitrous oxide (N2O). Here, coupled CH4 and N2O biotransformation in a freshwater wetland sediment was obtained in a 7-day anaerobic sediment incubation assay. The significant CO2 accumulation and decrease of CH4 emission in sediment microcosms was attributed to two mechanisms: inhibition of methanogenesis and N2O-dependent AOM. To further confirm the coupled CH4 and N2O transformation, a 13C-labelled stable isotope tracer assay after anaerobic incubation was conducted with N2O and/or CH4 amendments. The N2O-dependent AOM rate was 3.41 ± 0.13 nmol CO2 g−1 dry sediment·day−1. According to metagenomic analysis, addition of N2O stimulated AOM by increasing the activity and abundance of methanotrophic bacteria and by increasing enzymatic activities in the electron transport chain. Based on these results, we propose coupled CH4 and N2O biotransformation in the sediment microcosms for the first time, carried out by unidentified methanotroph(s) via intra‑oxygen produced in the presence of N2O. Such a process has the potential to reduce the emission of two highly potent greenhouse gases and makes a significant contribution to the link of global carbon and nitrogen cycles in anoxic environments.

Simple fabrication method of silicon/tungsten oxide nanowires heterojunction for NO2 gas sensors

Heterojunctions, formed at the interface between two different materials, have attracted much attention as a gas-sensing material. In particular, Si/tungsten oxide (WOX) heterojunctions are well known to be capable of gas detection at low temperature and to increase the sensitivity to and selectivity of NO2. However, during the fabrication process of the Si/WOX nanostructure-based sensor it is difficult to control the synthesis position of the nanostructures; hence, it is complicated or time consuming. In this work, semiconducting gas sensors based on n-type silicon/n-type suspended tungsten oxide nanowire (WOX NW) heterojunctions were fabricated by stress-induced method for WOX NW synthesis on Si MEMS structures. With this fabrication technique, the growth position of the WOX NWs can be controlled by patterning of the WOX seed film, and the NWs can be synthesized by simply heating the seed film for 20 min. In addition, all fabrication processes consist of batch-processes. Unlike conventional WOX-based sensors, the resistance of this sensor is reduced in the presence of NO2, an oxidizing gas, due to the band bending phenomenon of the Si/WOX NW heterojunction. The fabricated sensor can detect 500 ppb of NO2 and exhibits excellent selectivity to CO and toluene, which are exhaust gases, like NO2. This selectivity will be particularly useful when using sensors to detect NO2 in exhaust gases of automobiles or factories.

TRA and DRIFTS studies of the fast SCR reaction over CeO2/TiO2 catalyst at low temperatures

The CeO2/TiO2 catalyst was prepared by a deposition-precipitation method, which exhibited high low-temperature activity under the fast SCR condition. By using transient reaction analysis (TRA), the steps in the fast SCR, including NO2 adsorption and decomposition, reaction between nitrates and NO, ammonium nitrate formation and reduction by NO, were investigated. Diffuses reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments, via NO + O2 or NO + NO2 adsorption, ammonium species reaction with NOx and NO reaction with NH4NO3, were designed to identify the roles of NO, NO2 and NH3 in fast SCR. Based on L-H mechanism, the NH4NO3 formation played an important role in low-temperature SCR reaction. Compared with the behavior in standard SCR, the higher activity in the presence of NO2 was ascribed to the faster NH4NO3 formation rate and larger amounts of nitrates/nitrites. This phenomenon provided a basis for developing Ce-based catalysts as SCR catalysts for diesel exhaust aftertreatment.

Pulse Radiolysis and Computational Studies on a Pyrrolidinium Dicyanamide Ionic Liquid: Detection of the Dimer Radical Anion.

A pulse radiolysis study on pyrrolidinium cation based ionic liquids is presented herein. Time-resolved absorption spectra for 1-methyl-1-propylpyrrolidinium dicyanamide (DCA) at 500 ns after the electron pulse show broad absorption bands at wavelengths below 440 nm and at 640 nm. In pyrrolidinium bis(trifluoromethylsulfonyl)imide (NTf2) and tris(perfluoroethyl)trifluorophosphate (FAP) ILs, the transient absorption below 440 nm is much weaker. The absorption at 500 ns, which increases with wavelength from 500 nm to beyond 800 nm, was assigned to the tail of the solvated electron NIR absorption spectrum, since it disappears in the presence of N2O. In the DCA IL, the presence of a reducing species was confirmed by the formation of pyrene radical anion. The difference in the transient species in the case of the DCA IL compared to other two ILs should be due to the anion, with cations being similar. In pseudohalide ILs such as DCA, radicals are formed by direct hole trapping by the anion (X- + h+ → X•), followed by addition to the parent anion. Prediction of the UV/vis absorption spectra of the dimer radical anion by computational calculation supports the experimental results. The oxidizing efficiency of (DCA)2•- and its reduction potential ( E(DCA)2•-/(2DCA-)) have been determined.

Extracellular ATP activates eNOS and increases intracellular NO generation in Red Blood Cells.

It has been well documented that ATP activates NOS enzymes and causes increased NO production in several cell types. Although RBC known to possesses eNOS enzyme activity, it has not been investigated whether RBC eNOS could be induced by extracellular ATP. The aim of the present study is to evaluate extracellular ATP mediated eNOS activation and NO production in RBC. RBC packed were isolated from healthy volunteers and re-suspended in Hepes solution at a hematocrit of 0.01 l/l. Intracellular NO and Ca+2 levels and eNOS activation measured by flow cytometry in response to P2X receptor agonist, Bz-ATP, in the absence and presence of NOS, P2 receptors and PI3K inhibitors. P2X receptor agonist Bz-ATP found to increase intracellular NO, Ca+2 and serine 1177 phosphorylated eNOS levels and these responses have shown to be suppressed by NOS enzyme, P2 receptors and PI3K inhibitors. The results of the study clearly demonstrated extracellular ATP induced NO generation in RBC through intracellular Ca+2 and PI3K/Akt pathways. The mechanism we described here might be important at basal conditions and also in conditions with increased ATP release.

Urea-related reactions and their active sites over Cu-SAPO-34: Formation of NH3 and conversion of HNCO

Urea-SCR is an efficient method to reduce NOx emission from diesel vehicles, but the active sites of Cu-SAPO-34 for urea-related reactions have not been well identified. In the present work, a series of Cu-SAPO-34 catalysts with different copper species were prepared and tested for urea thermolysis, urea hydrolysis and urea-SCR. Temperature-programmed experiments and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) were used to determine isolated Cu2+ ions as the main active sites for these reactions. HNCO (isocyanic acid) and NH3 are formed via urea thermolysis. HNCO is less active than NH3 to interact with NO, and most of HNCO is hydrolyzed to produce NH3 in urea-SCR. In the presence of NO2, the reactivity of HNCO as a reducing agent is promoted, but both HNCO-SCR and HNCO hydrolysis would be inhibited by the deposition of NH4NO3. These findings provide a foundation for improving deNOx efficiency of Cu-SAPO-34 catalysts on diesel vehicles.

Study of the NO2 sensing mechanism of PEDOT-RGO film using in situ Raman Spectroscopy

In this work, the mechanism of the NO2 reaction with PEDOT-RGO composite film has been investigated via in situ Raman spectroscopy. Reduced graphene oxide (RGO), poly(3,4-ethylenedioxytiophene)-reduced graphene oxide (PEDOT-RGO) and poly(3,4-ethylenedioxytiophene)/ClO4− (PEDOT/ClO4−) films were fabricated using an electrodeposition method and used as resistance sensors of gaseous nitrogen dioxide. The experimental results indicate that NO2 causes overoxidation of the PEDOT polymer (PEDOT/ClO4− film) which leads to resistance increase and irreversible response. In contrast, the PEDOT-RGO response in the presence of NO2 is reversible. During short NO2 exposure, PEDOT from the PEDOT-RGO composite does not react to the gas but the presence of RGO in the PEDOT-RGO composite does not affect the overoxidation potential. It was found that the nitrogen dioxide reacts more readily to reduced graphene oxide, thus RGO “protects” the polymer against the adverse overoxidation process.