Low Concentrations Of NO Research Articles

Traffic-related NO2 affects expression of Cupressus sempervirens L. pollen allergens.

Traffic pollution has been recognized as directly worsening respiratory symptoms of allergic subjects, although whether urban air pollutants can also directly increase the allergenic potential of pollen has not yet been definitely proven. Therefore, the hypothesis that intra-urban air NO2 variation influences allergens expression in Cupressus sempervirens (Cs) L. pollen was tested. Mature microsporophylls were cut from Cs trees of similar age and height (14-17 m) present in three different sites of Florence (Italy) and processed in the laboratory. Cs pollen allergens amount was determined by a semi-quantitative analysis of electrophoretically separated pollen extracts fractions. NO2 air concentrations were recorded by air monitoring stations located at a distance not exceeding 50 m from each pollen collection site, and the relative annual mean values were acquired by a publicly available database (Tuscan Regional Agency for Environment Protection). Expression of three major Cs pollen allergens was non-linearly correlated with mean annual NO2 concentrations. Expression peak of all major allergens considered was reached at NO2 air concentration (67μg/m3), far below the value at risk for direct effect on the respiratory health (European Union Directive 2008/50/EC). The findings suggest that intra-urban NO2 variations do affect the expression of Cs pollen major allergens, and an apparent low risk NO2 concentration should be regarded as indirectly harmful for increasing the allergenic potential of pollen.

Sub-ppb-Level Detection of Nitrogen Dioxide Based on High-Quality Black Phosphorus.

The development of gas sensors based on two-dimensional (2D) layered materials has received lots of focus attributing to their excellent gas sensitivity. Here, a black phosphorus (BP) gas sensor device is fabricated based on high-quality few-layered BP microribbons using a facile route. Although BP is well known to oxidize in ambient conditions, energy dispersive spectroscopy (EDS) mapping manifests that the few-layered BP microribbons undergo slight oxidation and contamination during the grinding process. It is interesting that the surface and side of BP microribbons have nanoscale thin films and step-like nanoscale thin films, respectively, owing to the in-plane slip of the few-layered BP microribbons in the process of grinding, which are different from the conventional BP bulk crystals. The layered BP microribbon gas sensor demonstrated a high response to low-concentration NO2 and a very low limit of detection (LOD) of 0.4 ppb of NO2 under N2 and air conditions, which is the lowest LOD for NO2 detection reported so far. The mechanisms for excellently sensitive detection of NO2 for the BP microribbons have been investigated by first-principles calculations combined with experiment results, revealing that the sensitization mechanisms of the BP microribbon sensor are abundant nanoscale thin films, an optimum bandgap range with optimal carrier concentration, a hierarchical homojunction structure, and strong adsorption energy to NO2. In addition, the BP microribbon sensor demonstrated high selectivity to NO2, a low LOD under a high relative humidity, and good repeatability. The reported results of the BP sensor may provide great promise for improving the performance of other 2D material-based gas sensors and may expand sensing applications.

Construction of organic-inorganic “chelate” adsorption sites on metal oxide semiconductor for room temperature NO2 sensing

Metal oxide semiconductors (MOS) have been extensively studied for gas sensing due to their excellent chemical stability and adjustable electronic properties. However, there is still a lack of ingenious design strategies to achieve customizable gas detection in complex environments. Herein, a novel and scalable strategy of constructing organic-inorganic “chelate” adsorption sites is proposed to promote the affinity of MOS sensing materials to target molecules. Specifically, 3-aminopropyltriethoxysilane (APTES)-functionalized reduced graphene oxide (rGO) was decorated on In2O3 tubes (AG/Inx), and its NO2 sensing performance was studied. As a result, the optimal AG/Inx shows boosted room-temperature NO2 response, and its response to 1 ppm NO2 is 4.8 times that of In2O3. More attractively, the optimal AG/Inx exhibits good selectivity, as well as outstanding detection ability (Rg/Ra = 1.6) for low concentration NO2 (20 ppb). Experimental results suggest that APTES-rGO not only acts as the electron acceptor to accelerate charge transfer, but also enhances NO2 adsorption. Further theoretical calculations reveal that NO2 is simultaneously adsorbed at rGO and APTES via a flexible “chelate” mechanism. The multidentate adsorption configuration remarkably strengthens the NO2-host interaction, which is conducive to improving sensing performance. This work may inspire the material design of a new generation high-performance gas sensors.

Efficient Electron Transfer by Plasmonic Silver in SrTiO3 for Low-Concentration Photocatalytic NO Oxidation.

Photocatalysis presents a feasible option to control low-concentration NO emissions from industrial burning facilities, and increasing excitons in quantity and improving surface activity are the crucial issues to be solved. Plasmonic silver with the orientation of the (111) plane is uniformly distributed on the Ti-O termination of the SrTiO3 (STO) (100) plane (major). The NO conversion rate has a sixfold increment compared to pristine STO. Meanwhile, the toxic NO2 had a significant decline in the absence of water. This high performance could be attributed to the unique property of the localized surface plasmonic resonance of silver particles, which increases the optical response range of the catalyst. Meanwhile, the formation of a Schottky junction could promote the charge separation and enhance the lifetime of excitons via the electron transfer from silver particles to STO. More importantly, the Ag-O bond of the heterojunction increases the charge density of adjacent Ti, preferring to bond with the antibonding orbital electron of adsorbed molecules, which offers a favorable channel for the NO adsorption and activation of reactive oxidation species.

Room temperature NO2 gas sensor based on stain-etched porous silicon: Towards a low-cost gas sensor integrated on silicon

In this work, we investigate the use of a new low-cost gas sensor based on porous silicon to detect low concentration of NO2 at room temperature. In this work, we focused on the gas sensing properties of two different types of porous silicon (PS) prepared by a simple chemical method namely nano-porous silicon (nano-PS) and macro-porous silicon (macro-PS). The prepared sensors are characterized by different pores size, thicknesses and porosity. Electronic properties of the synthesized structures were studied by measuring the effective minority carrier lifetime using a µPCD lifetime tester. Structural properties and morphology of PS samples were also presented using Fourier transforms infrared (FTIR) spectroscopy and scanning electron microscope (SEM). The gas sensing properties of nano-PS and macro-PS were performed at room temperature for NO2 gas. Macro-PS and nano-PS sensors exhibit different behaviors attributed to the difference in their morphologies. The tested sensors exhibit considerable sensitivity at room temperature to low concentration of NO2 (4 ppm) during response time up to 45 s.

Photo-oxidation and kinetics of gaseous elemental mercury using CeO2/TiO2{001} and {101} photocatalysts in the atmosphere of multiple air pollutants

In this study, the photo-oxidation and kinetics of elemental mercury (Hg0) with self-prepared TiO2 and CeO2/TiO2 at 100–200 ℃ were explored. The surface properties of the photocatalysts were characterized before conducting the Hg0 photo-oxidation experiments. Both field emission scanning electron microscopy and high-resolution transmission electron microscopy showed that the grain size of TiO2 {101} was smaller than TiO2 {001}. XPS spectral showed that cerium (Ce) valence shifting between CeO2 and Ce2O3 generated strong oxidant O2-. Chemisorbed oxygen (Oα) was found to be more active than lattice oxygen (Oβ). Doping CeO2 to anatase-TiO2 effectively enhanced the photo-oxidation of Hg0. Higher Hg0 photo-oxidation efficiency and better thermal stability were observed in CeO2/TiO2{001} than CeO2/TiO2{101}. The photo-oxidation efficiency of Hg0 decreased with reaction temperature. In N2+Hg0+NO, low NO concentration (< 100 ppm) suppressed and high NO concentration (>300 ppm) enhanced the oxidation of Hg0. In N2+Hg0+SO2, SO2 competed with Hg0 for active sites on the surface of photocatalysts and suppressed the photo-oxidation of Hg0 since sulfate and sulfite as reaction products were observed on the surface of photocatalysts. Both facets could not prevent from being poisoned, however, CeO2/TiO2{001} could decelerate sulfur poisoning. On simulation by LH kinetic model, the reaction rate constant increased and the equilibrium constant decreased with reaction temperature, indicating that the photo-oxidation of Hg0 was dominated by physical adsorption.

Spatiotemporal dynamics of NO2 concentration with linear mixed models: A Bangladesh case study

There is currently a limited understanding of how climatic and anthropogenic factors affect atmospheric NO2 concentration, and how these factors are associated with air pollution over space and time. Using high-resolution TROPOMI satellite data, this study estimates both the degree of association between climatic and anthropogenic factors, and the spatiotemporal variability of NO2 concentration over Bangladesh. Several linear mixed models were developed to isolate possible factors affecting the NO2 concentration values recorded between July 2018 and June 2019). This included monthly mean maximum temperature (MMAXT), rainfall, wind speed (WS), relative humidity (RH), enhanced vegetation index (EVI), population density, and distance from industrial activities. The study revealed that the very urbanized central region of Bangladesh experienced high NO2 concentrations, particularly from September through to March. Dynamic variables such as RH, MMAXT, RAIN, and WS can positively or negatively influence NO2 depending on the time of year. Areas with a high vegetation cover, a low population density, and located some distance from industrial areas tended to have low NO2 concentrations. This study concluded that policy measures such as transboundary air quality agreements, the introduction of a month-specific green tax, decentralization, industrial relocation, and increased urban tree plantation activities could all prove valuable in reducing NO2 pollution in Bangladesh.

Visible Light Driven Ultrasensitive and Selective NO2 Detection in Tin Oxide Nanoparticles with Sulfur Doping Assisted by l‐Cysteine

AbstractIn the pandemic era, the development of high‐performance indoor air quality monitoring sensors has become more critical than ever. NO2 is one of the most toxic gases in daily life, which induces severe respiratory diseases. Thus, the real‐time monitoring of low concentrations of NO2 is highly required. Herein, a visible light‐driven ultrasensitive and selective chemoresistive NO2 sensor is presented based on sulfur‐doped SnO2 nanoparticles. Sulfur‐doped SnO2 nanoparticles are synthesized by incorporating l‐cysteine as a sulfur doping agent, which also increases the surface area. The cationic and anionic doping of sulfur induces the formation of intermediate states in the band gap, highly contributing to the substantial enhancement of gas sensing performance under visible light illumination. Extraordinary gas sensing performances such as the gas response of 418 to 5 ppm of NO2 and a detection limit of 0.9 ppt are achieved under blue light illumination. Even under red light illumination, sulfur‐doped SnO2 nanoparticles exhibit stable gas sensing. The endurance to humidity and long‐term stability of the sensor are outstanding, which amplify the capability as an indoor air quality monitoring sensor. Overall, this study suggests an innovative strategy for developing the next generation of electronic noses.

A Detection Method for Low Concentrations of SO₂ and NO

Nitric oxide (NO) and sulfur dioxide (SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) are mainly from burning fossil fuels. They are toxic gases and harmful to environment and human health. It is very important to monitor the level of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NO in flue gas. In this work, an optical SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NO measurement system was established based on differential optical absorption spectroscopy (DOAS). A cross-sensitivity band of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NO was selected, fast Fourier transform (FFT) was employed to decompose the differential optical density (DOD) characteristics of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in the mixed gas, inverse FFT (IFFT) was employed to reconstruct the DOD of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and the interference of NO on SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was overcome. The most sensitive absorption peak but strongly interfered by SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was selected to monitor NO. A method that was employed to decompose the DOD of NO was proposed, and the interference of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on NO was overcome. The full-scale error of system reached 0.7% for SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NO, respectively, and the detection limit (DL) of SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NO reached 0.36 and 0.39 ppm, respectively.

The Contribution of Meteorological Parameters and the COVID-19 Partial Lockdown on Air Quality in Rio de Janeiro, Brazil

This study evaluated the pollutant levels (NO2, SO2, CO, and O3), air quality index (AQI) and the influence of meteorological variables and coronavirus disease (COVID-19) pandemic on the air quality in Rio de Janeiro. The data set used comprises periods before (March-April, 2019) and during pandemic (March-April, 2020). According to the AQI results, on most days, the air quality was ranked as “good”. Brazilian air quality standards for SO2, O3, and NO2 were not exceeded in any of the monitoring stations during partial lockdown, while CO exceeded in all periods in one site due to industrial emission. Comparing both periods, descriptive statistics for the meteorological parameters presented no differences, which suggests similar conditions. However, when evaluated week by week in 2020, weather conditions presented some differences that probably affected pollutant concentrations. The correlations between O3 and NO2 and some meteorological parameters indicate that variations in both favored ozone formation, since it is a photochemical process favored by temperature and solar radiation and that, in Rio de Janeiro, low NO2 concentrations lead to increased O3. The improvements on air quality during the partial lockdown may be attributed mainly to a reduction on emission sources rather than weather conditions.

Promotion of angiogenesis toward transplanted ovaries using nitric oxide releasing nanoparticles in fibrin hydrogel

Transplantation of ovary is one method of facilitating fertility preservation to increase the quality of life of cancer survivors. Immediately after transplantation, ovaries are under ischemic conditions owing to a lack of vascular anastomosis between the graft and host tissues. The transplanted ovaries can suffer damage because of lack of oxygen and nutrients, resulting in necrosis and dysfunction. In the technique proposed in this paper, the ovary is encapsulated with nitric oxide-releasing nanoparticles (NO-NPs) in fibrin hydrogels, which form a carrying matrix to prevent ischemic damage and accelerate angiogenesis. The low concentration of NO released from mPEG-PLGA nanoparticles elicits blood vessel formation, which allows transplanted ovaries in the subcutis to recover from the ischemic period. In experiments with mice, the NO-NPs/fibrin hydrogel improved the total number and quality of ovarian follicles after transplantation. The intra-ovarian vascular density was 4.78 folds higher for the NO-NPs/fibrin hydrogel groups compared to that for the nontreated groups. Finally, in vitro fertilization revealed a successful blastocyst formation rate for NO-NPs/fibrin hydrogel coated ovaries. Thus, NO-NPs/fibrin hydrogels can provide an appropriate milieu to promote angiogenesis and be considered as adjuvant surgery materials for fertility preservation.

High-efficiency adsorption of elemental mercury from flue gas by K-intercalated 1T&2H MoS2

Alkali metal K is widely present in the earth's crust (the seventh abundant element), which can improve the activity and stability of the adsorbent. This study explored a simple calcination method, using the intercalation of K ions, successfully partially transformed commercial molybdenum disulfide (2H-MoS2) into 1T-MoS2, and used it for the adsorption of Hg0 in the flue gas. The experimental results showed that when the K ratio was 2:1(MK-3), the removal rate of Hg0 can reach 90.5 in a wide temperature range. Compared with 2H-MoS2, the mercury removal efficiency of MK-3 was increased by about 40%. After long-term and cycles experiments, the mercury removal efficiency of the MK-3 remained largely unchanged. In the simulated flue gas experiment, HCl could promote the mercury removal efficiency of sample MK-3, SO2 had no obvious effect on the mercury removal efficiency of sample MK-3, while SO2 and low concentration NO have no obvious effect on the mercury removal efficiency of the sample. It was found that during the intercalation of K ions, the interlayer spacing of MK-3 increased, and holes and cracks appeared on the base surface, which made it possible for Hg0 to enter the MoS2 interlayer and adsorb, thereby expanded the adsorption space of Hg0. DFT simulations showed that 1T-MoS2 significantly improves the surface activity of the adsorbent, thereby enhancing the stability of the sample to adsorb Hg0. Therefore, K intercalated in MoS2 can provide a promising method to capture Hg0 in coal-fired flue gas.

Adsorption Kinetics of NO2 Gas on Pt/Cr-TiO2/Pt-Based Sensors

Metal oxides are excellent candidates for the detection of various gases; however, the issues such as the limited operating temperature and selectivity are the most important ones requiring the comprehensive understanding of gas adsorption kinetics on the sensing layer surfaces. To this context, the present study focuses mainly on the fabrication of a Pt/Cr-TiO2/Pt type sensor structure that is highly suitable in reducing the operating temperature (from 400 to 200 °C), extending the lower limit NO2 gas concentration (below 10 ppm) with fast response (37 s) and recovery (24 s) times. This illustrates that the sensor performance is not only solely dependent on the nature of sensing material, but also, it is significantly enhanced by using such a new kind of electrode geometry. Moreover, Cr doping into TiO2 culminates in altering the sensor response from n- to p-type and thus contributes to sensor performance enhancement by detecting low NO2 concentrations selectively at reduced operating temperatures. In addition, the NO2 surface adsorption kinetics are studied by fitting the obtained sensor response curves with Elovich, inter-particle diffusion, and pseudo first-order and pseudo second-order adsorption models. It is found that a pseudo first-order reaction model describes the best NO2 adsorption kinetics toward 7–170 ppm NO2 gas at 200 °C. Finally, the sensing mechanism is discussed on the basis of the obtained results.

Boosted photocatalytic NO removal performance by S-scheme hierarchical composites WO3/Bi4O5Br2 prepared through a facile ball-milling protocol

• Composites WO 3 /Bi 4 O 5 Br 2 were constructed via a facile ball-milling protocol. • The structure-effect relationship was successfully established. • These binary composites showed enhanced photocatalytic NO removal efficiencies. • A plausible S-scheme model was speculated in photocatalysis mechanism. It is crucial to develop an efficient system of high photocatalytic capability over NO removal and simultaneous avoidance of toxic NO 2 formation. In this study a serious of hierarchical composites WO 3 /Bi 4 O 5 Br 2 (WB) were successfully fabricated by a facile ball-milling protocol and systematically characterized by various analytical techniques. Both expected ingredients were realized and coexisted in composites to generate heterojunction structures by microstructural analyses. Under visible light irradiation, these samples were exposed to photocatalytic removal of NO measurements, where aforementioned binary hierarchical WB composites showed reinforced NO removal efficiency with the high selectivity for NO 3 – /NO 2 – species in comparison to bare WO 3 and Bi 4 O 5 Br 2 , mainly associating to the efficient migration and spatial segregation of charge carries through heterojunction domains with suitable phase composition instead of the slightly varied visible light absorption and specific surface area. In addition, a possible photocatalysis mechanism was deduced in a S-scheme model by active species determination and band structures estimation of these robust catalysts. This investigation shed light on the facile fabrication of hierarchical composites via the ball-milling treatment with enhanced photocatalytic removal of low concentration NO in ppb level under visible light.

Simulation of the effects of microplastics on the microbial community structure and nitrogen cycle of paddy soil

Microplastics (MPs) are ubiquitous in farmland soils. However, few studies have evaluated their effects on the microbial community structure and nitrogen cycle of farmland soils. Here, 0.3% and 1% (mass percentage) of polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polylactic acid (PLA) MPs were added to paddy soil to evaluate their impact on the paddy soil microenvironment. The alpha index of the PLA MP treatment was significantly different from that of the control group (p-value < 0.05). In contrast, the indices of the PET and PVC MP treatments were not different from the control (p-value > 0.05). Among the MP treatments, the alpha index of the PLA MP group was significantly different from the PET and PVC MP groups (p-value < 0.05). PCoA analysis also indicated that there were differences between PLA and other MP groups, and different MP concentrations and exposure times had a great impact on microbial composition. The three MPs affected NH4+ metabolism by changing the abundance of a NH2OH-forming gene (amoA) and an organic nitrogen-forming gene (gdh), as well as the abundances of Thiobacillus, Bradyrhizobium, Anaeromyxobacter, Geobacter, and Desulfobacca. Further, the MPs affected NO3− metabolism by regulating the abundance of the nirS and nirK genes and the abundance of Nitrospirae. In contrast, NO2− metabolism was not significantly affected by the MPs due to the low concentration of NO2−, which was attributed to the high abundance of nirS and nirK in the sample. Taken together, our findings indicated that MP addition may have an inhibitory effect on the nitrogen cycle in paddy soils and that the effect of degradable MPs may be greater than that of their non-degradable counterparts. Given the increasing severity of worldwide MP contamination, additional studies are required to assess their impact on global ecosystems and biogeochemical cycles.

Atmospheric Autoxidation of Organophosphate Esters.

Organophosphate esters (OPEs), widely used as flame retardants and plasticizers, have frequently been identified in the atmosphere. However, their atmospheric fate and toxicity associated with atmospheric transformations are unclear. Here, we performed quantum chemical calculations and computational toxicology to investigate the reaction mechanism of peroxy radicals of OPEs (OPEs-RO2•), key intermediates in determining the atmospheric chemistry of OPEs, and the toxicity of the reaction products. TMP-RO2• (R1) and TCPP-RO2• (R2) derived from trimethyl phosphate and tris(2-chloroisopropyl) phosphate, respectively, are selected as model systems. The results indicate that R1 and R2 can follow an H-shift-driven autoxidation mechanism under low NO concentration ([NO]) conditions, clarifying that RO2• from esters can follow an autoxidation mechanism. The unexpected autoxidation mechanism can be attributed to the distinct role of the ─(O)3P(═O) phosphate-ester group in facilitating the H-shift of OPEs-RO2• from commonly encountered ─OC(═O)─ and ─ONO2 ester groups in the atmosphere. Under high [NO] conditions, NO can mediate the autoxidation mechanism to form organonitrates and alkoxy radical-related products. The products from the autoxidation mechanism have low volatility and aquatic toxicity compared to their corresponding parent compounds. The proposed autoxidation mechanism advances our current understanding of the atmospheric RO2• chemistry and the environmental risk of OPEs.

Highly Sensitive, Selective, Flexible and Scalable Room-Temperature NO2 Gas Sensor Based on Hollow SnO2/ZnO Nanofibers.

Semiconducting metal oxides can detect low concentrations of NO2 and other toxic gases, which have been widely investigated in the field of gas sensors. However, most studies on the gas sensing properties of these materials are carried out at high temperatures. In this work, Hollow SnO2 nanofibers were successfully synthesized by electrospinning and calcination, followed by surface modification using ZnO to improve the sensitivity of the SnO2 nanofibers sensor to NO2 gas. The gas sensing behavior of SnO2/ZnO sensors was then investigated at room temperature (~20 °C). The results showed that SnO2/ZnO nanocomposites exhibited high sensitivity and selectivity to 0.5 ppm of NO2 gas with a response value of 336%, which was much higher than that of pure SnO2 (13%). In addition to the increase in the specific surface area of SnO2/ZnO-3 compared with pure SnO2, it also had a positive impact on the detection sensitivity. This increase was attributed to the heterojunction effect and the selective NO2 physisorption sensing mechanism of SnO2/ZnO nanocomposites. In addition, patterned electrodes of silver paste were printed on different flexible substrates, such as paper, polyethylene terephthalate and polydimethylsiloxane using a facile screen-printing process. Silver electrodes were integrated with SnO2/ZnO into a flexible wearable sensor array, which could detect 0.1 ppm NO2 gas after 10,000 bending cycles. The findings of this study therefore open a general approach for the fabrication of flexible devices for gas detection applications.

Facile synthesis of N-doped carbon sheets-ZnO hybrids for NO2 sensing at ppb level

Constructing heterostructure and N-doping are two effective methods to improve gas sensing performance. Herein, a facile novel solution calcination strategy has been proposed to synthesize N-doped carbon sheets-zinc oxide (NC-ZnO) hybrids for low concentration NO2 detection. The formation of NC is accompanied by generation of ZnO particles on its surface to construct heterostructure. Intriguingly, NO3- acts as an expanding agent and N source in the calcination process, wherein the N elements are directly doped into carbon sheets. As expected, the prepared heterostructural NC-ZnO-63 hybrids exhibit 74.9 times enhancement of response as well as high sensitivity (~ 265.8–20 ppm NO2), excellent repeatability and selectivity compared with pure ZnO. Importantly, the measured detection limit of the NC-ZnO-63 sensor to NO2 is about 100 ppb (~ 0.3) and the calculated detection limit is 2.65 ppb. Furthermore, the influences of humidity on testing NO2 gas have been researched systematically which would provide guidance for practical use of similar sensors. In this work, ZnO and derived carbon are low-cost, eco-friendly, and the synthesis strategy presented here is simple and repeatable, which provides new idea for mass fabricating other-type metal oxides-NC hybrids for various applications.

Synergistic Effects of a Combination of Vacuum Ultraviolet–Induced Oxidation and Wet Absorption Process on Removal of Nitric Oxide at Room Temperature

Removal of low concentration NO in enclosed space by a new combined process incorporating vacuum ultraviolet (VUV)-induced oxidation and wet absorption process at room temperature was studied. Effects of NO initial concentration, gas flow rate, and humidity on NO conversion in the VUV irradiation process were first investigated. Subsequently, the absorption aqueous solutions were optimized, and the Na2S2O3 inhibitor was used in the wet absorption process in order to absorb the generated NO2. The results demonstrated that NO conversion was increased with the decreasing initial concentration and gas flow rate, and moreover, humidity had a promoting effect on NO oxidation because of the generation of hydroxyl radicals (·OH) under VUV irradiation. Na2SO3 solution was favorable for the absorption of NO2, and the NOx conversion can reach 85% at the initial stage, while it was decreased to 25% after 20 min absorption for the rapid free radical chain reaction nature between Na2SO3 and NOx. In addition, the Na2S2O3 inhibitor was chosen to suspend the presented rapid reaction, the removal efficiency of NOx was increased with the augment of the Na2S2O3 concentration, and it can be stabilized at 85% even after 4 h reaction with the Na2S2O3 concentration of 1.5%.

Carbon-dots conductometric sensor for high performance gas sensing

In this paper the first example of using C-dots (CDs) as sensing nanomaterial for monitoring low concentrations of NO2 in ambient air is reported. In the logic to support a green circular economy, CDs were prepared from a natural low cost precursor consisting in olive solid waste (OSW) by a simple pyrolysis process combined with chemical oxidation. Characterization data showed the formation of spherical CDs with dimensions in the narrow size range from 0.5 to 5 nm and charged with functional groups (COO- (carboxylate), C-O-C (epoxide) and C-OH (hydroxyl) imprinting excellent water colloidal dispersion. The nanomaterial was used to fabricate and test a conductometric gas sensor (CDs-sensor) that was found to exhibit excellent performances in terms of high and selective response to sub-ppm concentration of NO2 at low temperature (150 °C), low limit of detection (LOD) of 50 ppb, good reproducibility and stability over use and aging. To the best of our knowledge, this is the first example reported in the literature of CDs high performances gas sensing material. Results here presented pave the way for a new class of a carbon nanomaterial for gas sensing to be applied in the field of environmental monitoring.