Low Concentrations Of Nitrogen Dioxide Research Articles

Solution-Processed Functionalized Graphene Film Prepared by Vacuum Filtration for Flexible NO2 Sensors.

Large-scale production of graphene nanosheets (GNSs) has led to the availability of solution-processable GNSs on the commercial scale. The controlled vacuum filtration method is a scalable process for the preparation of wafer-scale films of GNSs, which can be used for gas sensing applications. Here, we demonstrate the use of this deposition method to produce functional gas sensors, using a chemiresistor structure from GNS solution-based techniques. The GNS suspension was prepared by liquid-phase exfoliation (LPE) and transferred to a polyvinylidene fluoride (PVDF) membrane. The effect of non-covalent functionalization with Co-porphyrin and Fe-phthalocyanines on the sensor properties was studied. The pristine and functionalized GNS films were characterized using different techniques such as Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and electrical characterizations. The morphological and spectroscopic analyses both confirm that the molecules (Co-porphyrin and Fe-phthalocyanine) were successfully adsorbed onto the GNSs surface through π-π interactions. The chemiresistive sensor response of functionalized GNSs toward the low concentrations of nitrogen dioxide (NO2) (0.5-2 ppm) was studied and compared with those of the film of pristine GNSs. The tests on the sensing performance clearly showed sensitivity to a low concentration of NO2 (5 ppm). Furthermore, the chemical modification of GNSs significantly improves NO2 sensing performance compared to the pristine GNSs. The sensor response can be modulated by the type of adsorbed molecules. Indeed, Co-Por exhibited negative responsiveness (the response of Co-Por-GNS sensors and pristine GNS devices was 13.1% and 15.6%, respectively, after exposure to 0.5 ppm of NO2). Meanwhile, Fe-Phc-GNSs induced the opposite behavior resulting in an increase in the sensor response (the sensitivity was 8.3% and 7.8% of Fe-Phc-GNSs and pristine GNSs, respectively, at 0.5 ppm NO2 gas).

Selective sensing performance of UV-activated ZnO nanowires decorated with Ir and Rh nanoparticles

Single-crystal zinc oxide (ZnO) nanowires (NWs) were synthesized through self-assembly hydrothermal reaction and decorated with oxidative and reductive catalytic active sites to tailor their gas sensing selectivity. The sensing performances of the developed materials were investigated under ultraviolet-light emitting diode (UV-LED) irradiation against low concentrations of nitrogen dioxide (NO2) and ammonia (NH3) gases, as oxidizing and reducing gas representatives, respectively. The growth of NWs towards the hexagonal c-axis was demonstrated, where presence of Rh3d and Ir4f active sites on the surface of ZnO NWs was observed. The sensing performance of the surface modified ZnO NWs was enhanced significantly, compared with that of the pristine ZnO NWs. The Rh-decorated ZnO NWs sensor exhibited superior performance in the detection of NO2, while the Ir sites promoted the oxidative reaction in the presence of NH3, attributed to the Fermi level of the metal-decorated films under UV irradiation.

Room-Temperature NO2 Gas Sensors Based on Granulated Carbon Nanofiber Material

Room-temperature gas sensors based on granulated carbon nanofiber material were investigated for the detection of NO2. The granulated material consisting of intertwined carbon nanofibers was synthesized by the decomposition of CH4 over the Ni/Al2O3 catalyst in a vibro-fluidized bed reactor. Carbon material was investigated using transmission electron microscopy, Raman spectroscopy, low-temperature nitrogen adsorption, and X-ray photoelectron spectroscopy. Investigation of the gas sensors towards NO2 at room temperature (25 ± 2 °C) was carried out in a dynamic flow-through setup in the range from 1 to 500 ppm. A comparison of the sensitivity gas sensor to NH3 and CH4 was also given. The sensor based on non-treated carbon nanofiber material showed the response ΔR/R0 of 5.1 % to 10 ppm of NO2. It was found that the sensor response to NO2 decreased when increasing the relative humidity. The effect of the relative humidity was more pronounced for low concentrations of nitrogen dioxide and decreases with a further increase in them.

Highly sensitive and selective room-temperature nitrogen dioxide sensors based on porous graphene

Development of high-performance nitrogen dioxide sensors is extremely important not only for industrial applications but also for environmental monitoring and health protection. For practical applications, gas sensors with high sensitivity for low concentrations of nitrogen dioxide are desired. Here, a simple process to fabricate high-performance gas sensors based on porous reduced graphene oxide (PRGO) through a simple drop-casting technique is presented. The PRGO used as active sensing material is prepared through a scalable solution etching approach. This sensor exhibited a high sensitivity in the sub-0.5 ppm range with good selectivity and reversibility, as well as a low experimental detection limit of 20 ppb, which is much lower than the threshold exposure limit proposed by the National Ambient Air Quality Standard (53 ppb). Furthermore, it can be performed at room temperature without UV/IR light illumination or thermal assistance. This superior performance could be attributed to the high adsorption site density due to the edge sites of porous graphene. The relationship between the sensing performance and the microstructure or chemical composition of porous graphene were systematically investigated. This work paves the way for a facile tailoring of the sensor behavior as a function of graphene micromorphology.

NITROGEN DIOXIDE SEMICONDUCTOR SENSORS BASED ON In2O3–Ga2O3–WO3 COMPOSITION

The properties of oxide gas sensitive compositions In2O3–Ga2O3–WO3 prepared by sol-gel method, with tungsten oxide 5 % wt., gallium oxide 4 % wt., have been investigated. Tungsten oxide addition was established to lead to significant increase in nitrogen dioxide sensitivity. The composition structural features were studied by X-ray diffraction analysis and Raman spectroscopy. It was found that thermal treatment of mixed sols In2O3, Ga2O3, WO3 leads to the formation of hete- rogeneous two-phase material containing (In, Ga)2O3 solid solution and monoclinic WO3 phases. According to X-ray diffraction data, the growth in size of WO3 and In2O3 grains during heat treatment in the mixed In2O3–WO3 composition decelerates as compared to individual oxides. It is assumed that significant increase in the sensitivity to low concentrations of nitrogen dioxide of the composition containing WO3 additive, as compared to the initial one, may be due to the presence of multiply charged adsorption centers (W4+, W5+, W6+), as well as due to the complication (according to EPR) of the defect structure of the double In2O3–WO3 and a triple In2O3–Ga2O3–WO3 composition as compared to the initial oxides. Single-electrode semiconductor nitrogen dioxide sensors with a low threshold of detection (<< 1 ppm) and low power consumption are fabrica- ted. The response of gas sensors based on the In2O3–Ga2O3 (4 % wt.)–WO3 (5 % wt.) composition to gas mixtures containing 10 ppm of NO2 in air has a pronounced maximum at powers of 80–90 mW.

A Study on the Impact of Poly(3-hexylthiophene) Chain Length and Other Applied Side-Chains on the NO₂ Sensing Properties of Conducting Graft Copolymers.

The detection and concentration measurements of low concentrations of nitrogen dioxide (NO2) are important because of its negative effects on human health and its application in many fields of industry and safety systems. In our approach, conducting graft copolymers based on the poly(3-hexylthiophene) (P3HT) conducting polymer and other side-chains, polyethylene glycol (PEG) and dodec-1-en, grafted on a poly(methylhydrosiloxane) backbone, were investigated. The grafts containing PEG (PEGSil) and dodec-1-en (DodecSil) in two variants, namely, fractions with shorter (hexane fraction -H) and longer (chloroform fraction -CH) side-chains of P3HT, were tested as receptor structures in NO2 gas sensors. Their responses to NO2, within the concentration range of 1–20 ppm, were investigated in an nitrogen atmosphere at different operating temperatures—room temperature (RT) = 25 °C, 50 °C, and 100 °C. The results indicated that both of the copolymers with PEG side-chains had higher responses to NO2 than the materials with dodec-1-en side-chains. Furthermore, the results indicated that, in both cases, H fractions were more sensitive than CH fractions. The highest response to 1 ppm of NO2, from the investigated graft copolymers, had PEGSil H, which indicated a response of 1330% at RT and 1980% at 100 °C. The calculated lower-limit of the detection of this material is lower than 300 ppb of NO2 at 100 °C. This research indicated that graft copolymers of P3HT had great potential for low temperature NO2 sensing, and that the proper choice of other side-chains in graft copolymers can improve their gas sensing properties.

Inside Cover: Sustainable Synthesis of Balsalazide and Sulfasalazine Based on Diazotization with Low Concentrations of Nitrogen Dioxide in Air (Chem. Eur. J. 17/2017)

Inside Cover: Sustainable Synthesis of Balsalazide and Sulfasalazine Based on Diazotization with Low Concentrations of Nitrogen Dioxide in Air (Chem. Eur. J. 17/2017)

Sustainable Synthesis of Balsalazide and Sulfasalazine Based on Diazotization with Low Concentrations of Nitrogen Dioxide in Air.

Low concentrations of nitrogen dioxide, which arises as a side product from a range of industrial processes, can effectively be recycled through the diazotization of anilines. The studies reported herein now demonstrate that the removal of nitrogen dioxide from gas streams is even more effective when hydrophilic anilines are used as starting materials. The diazonium salts, which are obtained in this way in up to quantitative yields, can directly be employed in azo coupling reactions, thus opening up an attractive route to the industrially important group of azo compounds.

Ultrasensitive, real-time trace gas detection using a high-power, multimode diode laser and cavity ringdown spectroscopy.

We present a simplified cavity ringdown (CRD) trace gas detection technique that is insensitive to vibration, and capable of extremely sensitive, real-time absorption measurements. A high-power, multimode Fabry-Perot (FP) diode laser with a broad wavelength range (Δλlaser∼0.6 nm) is used to excite a large number of cavity modes, thereby reducing the detector's susceptibility to vibration and making it well suited for field deployment. When detecting molecular species with broad absorption features (Δλabsorption≫Δλlaser), the laser's broad linewidth removes the need for precision wavelength stabilization. The laser's power and broad linewidth allow the use of on-axis cavity alignment, improving the signal-to-noise ratio while maintaining its vibration insensitivity. The use of an FP diode laser has the added advantages of being inexpensive, compact, and insensitive to vibration. The technique was demonstrated using a 1.1W (λ=400 nm) diode laser to measure low concentrations of nitrogen dioxide (NO2) in zero air. A sensitivity of 38 parts in 1012 (ppt) was achieved using an integration time of 128ms; for single-shot detection, 530ppt sensitivity was demonstrated with a measurement time of 60μs, which opens the door to sensitive measurements with extremely high temporal resolution; to the best of our knowledge, these are the highest speed measurements of NO2 concentration using CRD spectroscopy. The reduced susceptibility to vibration was demonstrated by introducing small vibrations into the apparatus and observing that there was no measurable effect on the sensitivity of detection.

A Novel NO<SUB>2</SUB> Sensor Based on TiO<SUB>2</SUB> Nanotubes Array with <I>In-Situ</I> Au Decoration

Au decorated TiO2 nanotubes array was successfully fabricated on a Ti-Au alloy via an electrochemical anodization process. The crystal phase and microstructure of the TiO2 nanotubes array were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. Au particles were well distributed among TiO2 nanotubes and acted as the catalyst. It was found that the sensor based on Ti-Au alloy anodization can be a promising sensor which was highly sensitive to low concentrations of nitrogen dioxide (NO2), and response at room temperature. The sensitivity of Au-decorated TiO2 nanotubes sensor was 36.11 to 8 ppm NO2 at room temperature. Meanwhile, the resistance signal of Au-decorated TiO2 sensor changes quickly within 80 s upon exposure to 8 ppm NO2 at 35 degrees C, the undecorated TiO2 however takes much more time (>110 s) to respond and the resistance signal remains unstable.

Ozone exposure and its influence on the worsening of childhood asthma

It is well documented that high levels of many airborne pollutants can adversely affect many systems of the human body. The aim of this study was to evaluate the specific impact of ozone (O(3)) on the worsening of childhood asthma, comparing children living at regions with high and low O(3) concentrations (reference site) without the confounding effects of other pollutants. Pollutant concentrations were monitored and data concerning asthma prevalence were collected through a questionnaire. The studied population consisted of 478 children aged 6-13 years old enrolled in four schools of the municipalities where monitoring was performed. Remote sites were identified with very low concentrations of nitrogen dioxide and volatile organic compounds and high concentrations of O(3). The prevalence of wheeze for lifetime period and in the past year was 15.9% and 6.3%, respectively. Asthmatic children were identified when dyspnoea and wheezing were simultaneously mentioned in the absence of upper respiratory infections; according to that, the lifetime prevalence of asthmatic symptoms at the remote sites was 7.1%. The comparison with other previous studies was difficult because the criteria for analysis are not conveniently established. The prevalence of childhood asthmatic symptoms was about 4% higher at the high O(3) site than at the low O(3) site.

Luminescence response of ZnO nanowires to gas adsorption

Zinc oxide nanowires were synthesized by means of evaporation–condensation technique and their green photoluminescence emission at room temperature was studied during exposure to nitrogen dioxide, ethanol and humidity. A reversible modification of static photoluminescence efficiency was obtained upon exposure to low concentrations of nitrogen dioxide. The optical sensor was able to detect NO 2 values as low as 0.1 ppm in dry air, that is the attention level for outdoor detection. Time-resolved photoluminescence measurements in presence of NO 2 showed small modification of recombination rates and lifetimes due to introduction of quencher gas. The results support a surface static quenching model, according to which the gas molecules suppress a fraction of radiative transitions instead of merely reducing their probabilities.

Contribution of Ozone Precursors on Ozone Concentrations at Urban and Remote Areas

ISEE-316 Objective: The aim of this work was to analyze the contribution of nitrogen dioxide and volatile organic compounds for the ozone concentrations at urban and remote areas. For that, the concentrations of ozone and of its precursors at remote areas were assessed and compared with those observed at an urban area influenced by traffic. Material and Methods: The study was based on data measured at 1 urban site influenced by traffic, PO, and 6 remote sites, BG1, BG2, BG3, BG4, and BG5 and LO. Measurements were performed using passive samplers (to test their performance, the sampling tubes were co-located with continuous monitors at sites PO and LO). Two sampling periods were conducted during the summer of 2006: (i) A—13 days and (ii) B—26 days. The pollutants measured were ozone, nitrogen dioxide, total and some volatile organic compounds, namely, benzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, m/p-xylene, o-xylene, and toluene. Results: The results showed a satisfactory reproducibility and precision was of the measurements with passive samplers. The lowest concentrations of ozone observed at PO site were 51.0 and 40.9 mg·m−3, respectively, for A and B periods. Of all remote sites analyzed, BG4 was the one with the highest concentrations of ozone for both periods (97.9 and 122.0 mg·m−3, respectively). Nitrogen dioxide concentrations were between 12 and 20 times higher at urban site than at remote sites and volatile organic compound concentrations were between 2 and 8 times higher, due to the influence of traffic emissions. Conclusions: The quicker removal of nitrogen oxides from distant sources compared with that of volatile organic compounds, coupled with the absence of anthropogenic sources at remote areas, leads to very low concentrations of nitrogen dioxide. Such low concentrations were responsible for the high concentrations of ozone at the remote areas.

Control of semiconducting oxide gas-sensor microstructure by application of an electric field during aerosol-assisted chemical vapour deposition

Tungsten oxide thin films were deposited on gas sensor substrates from the aerosol assisted chemical vapour deposition of [W(OPh)6] in toluene at 600 °C. It was found that application of an electric field during deposition encouraged thicker film growth. The morphology of the tungsten oxide film could be altered by using stronger electric fields and by use of both direct and alternating currents. In particular the use of alternating currents produced aligned fibrous growth between the electrode gaps of the sensor substrate. This morphology produced a tungsten oxide gas sensor that was particularly sensitive to low concentrations of nitrogen dioxide.

Asthma in exercising children exposed to ozone: a cohort study

Little is known about the effect of exposure to air pollution during exercise or time spent outdoors on the development of asthma. We investigated the relation between newly-diagnosed asthma and team sports in a cohort of children exposed to different concentrations and mixtures of air pollutants. 3535 children with no history of asthma were recruited from schools in 12 communities in southern California and were followed up for up to 5 years. 265 children reported a new diagnosis of asthma during follow-up. We assessed risk of asthma in children playing team sports at study entry in six communities with high daytime ozone concentrations, six with lower concentrations, and in communities with high or low concentrations of nitrogen dioxide, particulate matter, and inorganic-acid vapour. In communities with high ozone concentrations, the relative risk of developing asthma in children playing three or more sports was 3.3 (95% CI 1.9-5.8), compared with children playing no sports. Sports had no effect in areas of low ozone concentration (0.8, 0.4-1.6). Time spent outside was associated with a higher incidence of asthma in areas of high ozone (1.4, 1.0-2.1), but not in areas of low ozone. Exposure to pollutants other than ozone did not alter the effect of team sports. Incidence of new diagnoses of asthma is associated with heavy exercise in communities with high concentrations of ozone, thus, air pollution and outdoor exercise could contribute to the development of asthma in children.

A novel porous silicon sensor for detection of sub-ppm NO 2 concentrations

We developed a new technique for the deposition of free-standing porous silicon (PS) on alumina substrate with interdigital contacts (Italian Patent ENEA-INFM), thus removing the silicon substrate, that is inactive in gas detection and is much more conductive than PS. The dc and ac electrical measurements in a controlled atmosphere were performed to test the sensor response towards NO 2 (0.1–10 ppm), O 3 (200 ppb), CO (1000 ppm), benzene (20 ppm), organic vapours and humidity. The device was able to detect very low concentrations of nitrogen dioxide (100 ppb) with no interference from ozone, benzene, CO and organic vapours. Indeed humidity interferes with nitrogen dioxide detection and must be kept under control. Since PS showed great response to NO 2 at room temperature (RT), no heating of the sensor is required.

Release of aldehydes from rat alveolar macrophages exposed in vitro to low concentrations of nitrogen dioxide

This study demonstrated that aldehydes are released into the extracellular medium when alveolar macrophages (AM) are exposed to nitrogen dioxide (NO 2) at concentrations that impair cell function but do not cause cell death. Butanal, glycolaldehyde, 4-hydroxynonenal, pentanal, pentenal, and hexanal were found. Dinitrophenylhydrazine (DNP) derivitization, thin layer chromatography, high performance liquid chromatography, and gas chromatography-mass spectrometry were used to identify the products. Some of the aldehydes have potential toxicity and may be responsible, in part, for altered AM function observed following NO 2 exposure.

Alterations in the ontogeny of rat pup ultrasonic vocalization produced by prenatal exposure to nitrogen dioxide.

Wistar female rats were exposed to low concentrations of nitrogen dioxide, NO2 (1.5 and 3 ppm) from day 0 to day 20 of pregnancy. The results show that prenatal exposure to this oxidant gas produced significant changes in the duration pattern of ultrasonic vocalizations emitted by male pups removed from their nest. In particular, a significant decrease in the length of ultrasonic calls was found in both 10- and 15-day-old rats exposed to NO2 (3 ppm) during gestation. These alterations were found at dose levels which did not significantly affect reproduction parameters, body weight gain and motor activity development. These findings suggest that gestational exposure to NO2, at concentrations below those associated with overt signs of toxicity, induces in rat offspring subtle behavioral changes characterized by altered ontogeny of ultrasonic emission.

The reaction of low levels of nitrogen dioxide with methyl linoleate in the presence and absence of oxygen

The reaction of methyl linoleate with low levels of nitrogen dioxide in a carrier gas, such as helium or air, at nitrogen dioxide concentrations ranging from 2 to 228 ppm was studied and the products formed were monitored. In both aerobic and anaerobic conditions, low concentrations of nitrogen dioxide reacted with methyl linoleate predominantly to form allylic products. When a 1:1 mixture of methyl palmitate/methyl linoleate was layered over an aqueous buffer and a nitrogen dioxide stream was passed from underneath, so that the stream passed through the aqueous layer before contacting the organic layer, allylic products again predominated. In the absence of air, the allylic products consisted of allylic nitro and nitrite, derivatives of linoleate, whereas in the presence of air, allylic hydroperoxides were the principal products. The findings suggest that fatty acids with doubly allylic hydrogen atoms react preferentially by a hydrogen atom abstraction reaction rather than by the addition of nitrogen dioxide to a double bond.

Automatic colorimetric detector for traces of nitrogen dioxide in air

A reliable and easy-to-operate detector has been developed for determining low concentrations of nitrogen dioxide in air. In the detector, the air sample is bubbled through a volume of 40 cm3 of Saltzman reagent, and the transmittance of light (550 nm) by the reagent is continuously measured by a built-in photometer. The output of the detector is a dc voltage proportional to the transmittance. The reagent is replaced every 12 h. The detection limit is about 1×10−10 by volume for 1-h measuring periods. After abrupt changes in the NO2 level, the rise and fall times of the readings (from 10% to 90% of the change) are about 5 min. A microcomputer can be used to control the system and to determine the nitrogen-dioxide concentrations automatically.