Ppb NO2 Research Articles

Synthesis of NiO-In2O3 heterojunction nanospheres for highly selective and sensitive detection of ppb-level NO2

NiO-In2O3 composite nanospheres with p-n heterojunction structure were fabricated by a one-step hydrothermal method. A series of XRD, FTIR, SEM, TEM, and XPS measurements were utilized to characterize the morphology and structure of NiO-In2O3 composite nanospheres, accompanying with pure In2O3 nanospheres for comparison. The results indicated that both the diameters of pure In2O3 and NiO-In2O3 nanospheres were in the range of 400–500 nm, indicating that the introduction of Ni did not change the product morphology. The gas sensing performance showed that Ni functionalization with proper content was conducive to enhancing NO2 sensing performance compared with pure In2O3 nanospheres. The obtained NiO-In2O3 composite nanospheres showed excellent response-recovery properties to NO2 gas and high selectivity, stability, and repeatability. The highest response of 1771 was achieved for 10% NiO-In2O3 composite nanospheres to 10 ppm NO2 gas at 100 °C, and the corresponding response to 10 ppb NO2 gas was 1.2. The gas sensing mechanism of NiO-In2O3 composite nanospheres to NO2 gas was discussed based on the electron depletion theory and the formation of p-n heterojunction structure. The results show that NiO-In2O3 composite nanospheres have favorable potential application in ppb-level NO2 detection.

A transparent ZnO nanowire MEMS gas sensor prepared by an ITO micro-heater

This sturdy constructs a 3D-like heterogeneous device integrated structure using a transparent ZnO nanowire MEMS gas sensor and a blue LED. For the transparent gas sensor, ITO is used for the electrodes and the micro heater. The thermal image shows that the micro heater provides a heat source. The sensors exhibit a higher sensitivity to NO than other gases (C2H5OH, HCHO, H2S) at the optimal operating temperature of 200 ℃. For the MEMS gas sensor with blue light illumination from the bottom of the sensors, the results show that the blue light increases the carrier concentration in the ZnO nanowires. The response value to 50 ppb NO gas is increased from 48.13% to 86.17%.

Natural bamboo leaves derived sulphur-doped mesoporous heteroatom enriched carbon for high-performance supercapacitors and gas sensors

Carbon-based hybrids with three-dimensional (3D) mesoporous have received considerable attention as potential electrode materials for supercapacitors (SCs) due to their excellent electrical conductivity. However, the poor mechanical strength of the hybrid significantly affects the long-term cycling stability of SCs, which seriously hinders their practical applications. Herein, a uniform sulphur (S) doped carbon-based hybrid (CSiO2) derives from carbonized bamboo leaves, which has been controllably prepared by solvothermal treatment. The as-prepared material possesses large surface area, outstanding electrical conductivity, robust 3D structure and excellent electrochemical properties. Therefore, the as-fabricated product demonstrates superior areal capacitance of 643.2 mF cm−2 and mass capacitance of 107.9 F g−1 at 0.5 A g−1 in 3 M KOH. Furthermore, this sample also displays ultra-long cycling stability, which significantly remains 100% after 20,000 cycles and still maintains 98.1% after 30,000 cycles. Besides, the as-prepared sample reveals higher response (34.65 for 50 ppm NO2) and long-term stability (2.1% maximum fluctuation during 30 days) at room temperature. The obtained S@CSiO2 also exhibits the practical capability with an extremely low limit-of-detection of 500 ppb NO2. Thus, the as-prepared material is a potentially promising alternatives to the electrode of advanced supercapacitors and the sensing layer of gas sensors.

Reduced Graphene Oxide/Mesoporous ZnO NSs Hybrid Fibers for Flexible, Stretchable, Twisted, and Wearable NO2 E-Textile Gas Sensor.

E-textiles are gaining growing popularity recently due to low cost, light weight, and conformable compatibility with clothes in wearable and portable smart electronics. Here, an easy-handing, low cost, and scalable fabricating strategy is reported to fabricate conductive, highly flexible, and mechanically stretchable/twisted fiber gas sensor with great wearability and knittability. The proposed gas sensor is built using commercially available cotton/elastic threads as flexible/stretchable templates and reduced graphene oxide/mesoporous zinc oxide nanosheets as sensing layers to form conducting fibers. The as-prepared fiber demonstrates sensitive sensing response, excellent long-term stability (84 days), low theoretical detection limit (43.5 ppb NO2), great mechanical deformation tolerance (3000 bending cycles, 1000 twisting cycles and 65% strain strength), and washing durability in room-temperature gas detection. More significantly, scalable wearable characteristics including repairability, reliability, stability, and practicability have been efficiently improved, which are achieved by knotting the fractured fibers, incorporating multiple sensors in series/parallel and weaving multisensor array networks integrated into clothes. The good sensing properties, superior flexibility, and scalable applications of wearable fibers may provide a broad window for widespread monitoring of numerous human activities in personal mobile electronics and human-machine interactions.

Room Temperature Detection of NO2 at ppb Level and Full Recovery by Effective Modulation of the Barrier Height for Titanium Oxide/Graphene Schottky Heterojunctions

AbstractSimultaneous achievement of high response, high sensitivity, low detection limit, and full recovery at room temperature (RT) is quite challenging for gas sensors. Herein, ultrathin titanium oxide/graphene Schottky heterojunction sensors (SHS) are fabricated with varying junction areas. Increasing junction area favors the sensing performance. A change of 11.822 meV in Schottky barrier height (SBH) is induced by 3 ppm NO2 exposure, accompanied by a change of −36.54% in current, ≈18 and 36 times that for bare titanium oxide and graphene sensors at RT, respectively. A high sensitivity of 10.430% ppm−1, low detection limit of 28 ppb, and complete recovery for 100 ppb NO2 are simultaneously achieved at RT. 100 ppm NH3 can be detected with full recovery as well. The superior performance of SHS is predominantly attributed to the effective modulation of SBH (exponential change in current) by gas adsorption and the charge transfer to interfaces enhanced by the presence of ultrathin continuous oxide layers. The sensing mechanism can be understood via energy band diagrams. This study proposes an idea of designing SHS with ultrathin n‐metal oxides and p‐graphene to simultaneously achieve high sensitivity, low detection limit, and full recovery for NO2 and other gases at RT.

Hierarchical Self‐Assembly of Tetrakis(1‐pyrenyl)porphyrins into Microscopic Petals and Flowers with Ultrasensitive Room‐Temperature NO2 Sensing in a Broad Humidity Range

AbstractA metal free meso‐tetrakis(1‐pyrenyl)porphyrin H2T[(Pyr)4]P (1) and its cobalt congener CoT[(Pyr)4]P (2) are firstly fabricated into the hierarchical nanopetals and micro‐ball‐flowers, respectively, by a simple solution‐based method. Unexpectedly highly sensitive, stable, selective and reproducible responses to 50–400 ppb NO2 gas are obtained at room temperature for the aggregates of both 1 and 2, within 2 min dynamic exposure period at a broad relative humidity (RH) range of 0%‐75%. In particular, the micro‐ball‐flowers of 2 achieve a sensitivity of 91.4 and 214% ppm−1 at 45% RH and 75% RH, respectively, demonstrating the potentials as chemical sensors operating in real‐world atmospheres. Furthermore, the sensitivity of 1 and 2 remains almost unchanged under 0%–75% RH after 6 months. The present work represents one of the best results among organic‐based ppb‐level NO2 sensors operating under a broad RH range in terms of sensitivity and stability to humidity variations at room temperature.

In-situ growth of mesoporous In2O3 nanorod arrays on a porous ceramic substrate for ppb-level NO2 detection at room temperature

Mesoporous In2O3 nanorod arrays were synthesized directly on a porous ceramic substrate via a one-step hydrothermal method. The morphology and structure of the obtained In2O3 nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results revealed that In2O3 nanorod arrays with cubic phase were densely distributed on the porous ceramic substrate, showing the diameter of 120–200 nm and length of 0.5–1 μm. Especially, the nanorod was assembled by aggregated In2O3 nanoparticles with the diameters of 10–30 nm, and its large specific surface ensured the highly gas sensing performance for ppb-level NO2 detection. The response value of the mesoporous In2O3 nanorod arrays to 800 ppb NO2 was 14.9 at room temperature of 25 °C with a short response time of 14 s, and the ultraviolet light was loaded in the recovery process to shorten the recovery time to about 32 s. The growth and gas sensing mechanisms of the mesoporous In2O3 nanorod arrays were discussed. It demonstrates that this work provides a low-cost route for the fabrication of room-temperature NO2 gas sensor with high performance through in-situ growth of the sensing materials on a porous ceramic substrate.

Short-term associations between daily mortality and ambient particulate matter, nitrogen dioxide, and the air quality index in a Middle Eastern megacity

There is limited evidence for short-term association between mortality and ambient air pollution in the Middle East and no study has evaluated exposure windows of about a month prior to death. We investigated all-cause non-accidental daily mortality and its association with fine particulate matter (PM2.5), nitrogen dioxide (NO2), and the Air Quality Index (AQI) from March 2011 through March 2014 in the megacity of Tehran, Iran. Generalized additive quasi-Poisson models were used within a distributed lag linear modeling framework to estimate the cumulative effects of PM2.5, NO2, and the AQI up to a lag of 45 days. We further conducted multi-pollutant models and also stratified the analyses by sex, age group, and season. The relative risk (95% confidence interval (CI)) for all seasons, both sexes and all ages at lag 0 for PM2.5, NO2, and AQI were 1.004 (1.001, 1.007), 1.003 (0.999, 1.007), and 1.004 (1.001, 1.007), respectively, per inter-quartile range (IQR) increment (18.8 μg/m3 for PM2.5, 12.6 ppb for NO2, and 31.5 for AQI). In multi-pollutant models, the PM2.5 associations were almost independent from NO2. However, the RRs for NO2 were slightly attenuated after adjustment for PM2.5 but they were still largely independent from PM2.5. The cumulative relative risks (95% CI) per IQR increment reached maximum during the cooler months, including: 1.13 (1.06, 1.20) for PM2.5 at lag 0–31 (for females, all ages); 1.17 (1.10, 1.25) for NO2 at lag 0–45 (for males, all ages); and 1.13 (1.07, 1.20) for the AQI at lag 0–30 (for females, all ages). Generally, the RRs were slightly larger for NO2 than PM2.5 and AQI. We found somewhat larger RRs in females, age group >65 years of age, and in cooler months. In summary, positive associations were found in most models. This is the first study to report short-term associations between all-cause non-accidental mortality and ambient PM2.5 and NO2 in Iran.

Nitrogen dioxide sensing based on multiple-morphology cuprous oxide mixed structures anchored on reduced graphene oxide nanosheets at room temperature

Sensitive detection of trace nitrogen dioxide (NO2) gas at room temperature is of urgent necessity in the fields of healthcare and environment monitoring. To achieve this goal, we report on a porous composite film featuring reduced graphene oxide (rGO) nanosheets as the template platform of nanostructured cuprous oxide (Cu2O) nanowires and nanoparticles via a hydrothermal method. The sensor performance was investigated in terms of sensing response, optimal operation temperature, repeatability, long-term stability, selectivity and humidity effect on NO2 sensing. The sensor response achieved 0.66 towards 50 ppb NO2 gas with a full recovery at room temperature (25 °C ± 2 °C), which was among the best cases of Cu2O-related NO2 detection concerning sensor response and operation temperature. Moreover, a modest repeatability, stability, selectivity as well as a negligible humidity effect on NO2 sensing were exhibited. A mass of interspaces existing within nanostructured composites as well as the synergistic effect between rGO and Cu2O materials endowed the sensing layer with favorable gas accessibility and sufficient gas–solid interaction. Simultaneously, highly conductive rGO nanosheets facilitated an effective electron transfer and collection. In brief, the as-prepared rGO/Cu2O sensors showed a competitive room temperature detection capability for ppb-level NO2 gas, providing a vast potential in the future applications such as the real-time monitoring of ultralow emission.

InAs/InP core/shell nanowire gas sensor: Effects of InP shell on sensitivity and long-term stability

Long-term stability is an issue for semiconductor gas sensors, because the sensing material normally needs to be exposed to ambient air (oxygen and water molecules). InAs nanowires (NWs) feature good gas sensing properties at room temperature, but the NWs can be oxidized in air. In this paper, the gas sensing properties of InAs/InP core/shell NWs were investigated for the first time. It was demonstrated that the InP shell thicker than 3.3 nm can effectively retard the oxidation of InAs NWs in air for about 6 years. Moreover, the sensitivity can also be improved by introducing an InP shell. In comparison with the bare InAs NWs, ~1000 fold improvement on detection limit (i.e., 0.8 ppb NO2 at room temperature) was realized with an InP shell thicker than 3.3 nm. Related sensing mechanism is discussed.

Effects of policy-driven hypothetical air pollutant interventions on childhood asthma incidence in southern California

Childhood asthma is a major public health concern and has significant adverse impacts on the lives of the children and their families, and on society. There is an emerging link between air pollution, which is ubiquitous in our environment, particularly in urban centers, and incident childhood asthma. Here, using data from 3 successive cohorts recruited from the same 9 communities in southern California over a span of 20 y (1993 to 2014), we estimated asthma incidence using G-computation under hypothetical air pollution exposure scenarios targeting nitrogen dioxide (NO2) and particulate matter <2.5 μm (PM2.5) in separate interventions. We reported comparisons of asthma incidence under each hypothetical air pollution intervention with incidence under the observed natural course of exposure; results that may be more tangible for policymakers compared with risk ratios. Model results indicated that childhood asthma incidence rates would have been statistically significantly higher had the observed reduction in ambient NO2 in southern California not occurred in the 1990s and early 2000s, and asthma incidence rates would have been significantly lower had NO2 been lower than what it was observed to be. For example, compliance with a hypothetical standard of 20 ppb NO2 was estimated to result in 20% lower childhood asthma incidence (95% CI, -27% to -11%) compared with the exposure that actually occurred. The findings for hypothetical PM2.5 interventions, although statistically significant, were smaller in magnitude compared with results for the hypothetical NO2 interventions. Our results suggest a large potential public health benefit of air pollutant reduction in reduced incidence of childhood asthma.

Three-Dimensional-Structured Boron- and Nitrogen-Doped Graphene Hydrogel Enabling High-Sensitivity NO2 Detection at Room Temperature.

Heteroatom-doping has been proved as an effective method to modulate the electronic, physical, and chemical properties of graphene (Gr). Developing a new strategy of heteroatom-doping for high-performance gas sensing is a pivotal issue. Here, we demonstrate novel Gr-based gas sensors through three-dimensional (3D)-structured B-/N-doping nanomaterials for high-performance NO2 sensing. The 3D porous B- and N-doped reduced graphene oxide hydrogels (RGOH) are synthesized via one-step hydrothermal self-assembly and employed as transducing materials to fabricate room-temperature high-performance chemiresistors. The systematic characterizations of the as-synthesized B- and N-RGOH clearly show the uniform doping of the B and N heteroatoms and the formation of B and N components with C/O. In comparison with the pristine RGOH counterpart, the 3D B- and N-RGOH sensors exhibit 38.9 and 18.0 times enhanced responses toward 800 ppb NO2, respectively, suggesting the remarkable doping effect of the heteroatoms in improving the sensitivity. Significantly, B- and N-RGOH display the exceptionally low limit of detection of 9 and 14 ppb NO2, respectively, which are much lower than the threshold limit recommended by the U.S. Environmental Protection Agency. In addition, the developed NO2 sensors show good linearity, reversibility, fast recovery, and impressive selectivity. This work opens up a new avenue to fabricate room-temperature and high-performance NO2 sensors by incorporating B and N heteroatoms into 3D RGOH via a convenient hydrothermal self-assembly approach.

Analytical modeling of phosphorene-based NO2 gas sensor

Phosphorene is a new two-dimensional material that has great potentials in Nano electronic application, so it has attracted more researchers’ attention nowadays. Indeed, phosphorene is an interesting material in gas sensing, due to its high surface-to-volume ratio and its carrier mobility. Many studies have been reported on phosphorene gas sensing, but there is not enough study on analytical modeling of phosphorene gas sensing properties. In this research, by adopting data from experimental NO2-based gas sensor, an analytical model of the phosphorene gas sensing behavior is presented. Then, the experimental results of NO2 gas sensing are compared with the proposed model and acceptable agreement is reported. This new model is adapted to predict phosphorene gas sensing performance in higher NO2 gas concentrations, which demonstrates, linear relation is established in higher concentrations same as lower ppb NO2 gas concentration. So, we have predicted the result of NO2 gas sensing for higher concentration based on experimental sensing.

Near Room Temperature Light-Activated WS2-Decorated rGO as NO2 Gas Sensor.

The NO2 response in the range of 200 ppb to 1 ppm of a chemoresistive WS2-decorated rGO sensor has been investigated at operating temperatures of 25 °C and 50 °C in dry and humid air (40% RH) under dark and Purple Blue (PB) light conditions (λ = 430 nm). Few-layers WS2, exfoliated by ball milling and sonication technique, with average dimensions of 200 nm, have been mixed with rGO flakes (average dimension 700 nm) to yield WS2-decorated rGO, deposited on Si3N4 substrates, provided with platinum (30 μm gap distance) finger-type electrodes. TEM analysis showed the formation of homogeneous and well-dispersed WS2 flakes distributed over a thin, continuous and uniform underlying layer of interconnected rGO flakes. XPS and STEM revealed a partial oxidation of WS2 flakes leading to the formation of 18% amorphous WO3 over the WS2 flakes. PB-light irradiation and mild heating of the sensor at 50 °C substantially enhanced the baseline recovery yielding improved adsorption/desorption rates, with detection limit of 400 ppb NO2 and reproducible gas responses. Cross sensitivity tests with humid air interfering vapor highlighted a negligible influence of water vapor on the NO2 response. A charge carrier mechanism between WS2 and rGO is proposed and discussed to explain the overall NO2 and H2O response of the WS2–rGO hybrids.

Ambient air pollution and pulmonary vascular volume on computed tomography: the MESA Air Pollution and Lung cohort studies.

Air pollution alters small pulmonary vessels in animal models. We hypothesised that long-term ambient air pollution exposure would be associated with differences in pulmonary vascular volumes in a population-based study. The Multi-Ethnic Study of Atherosclerosis recruited adults in six US cities. Personalised long-term exposures to ambient black carbon, nitrogen dioxide (NO2), oxides of nitrogen (NO x ), particulate matter with a 50% cut-off aerodynamic diameter of <2.5 μm (PM2.5) and ozone were estimated using spatiotemporal models. In 2010-2012, total pulmonary vascular volume was measured as the volume of detectable pulmonary arteries and veins, including vessel walls and luminal blood volume, on noncontrast chest computed tomography (TPVVCT). Peripheral TPVVCT was limited to the peripheral 2 cm to isolate smaller vessels. Linear regression adjusted for demographics, anthropometrics, smoking, second-hand smoke, renal function and scanner manufacturer. The mean±sd age of the 3023 participants was 69.3±9.3 years; 46% were never-smokers. Mean exposures were 0.80 μg·m-3 black carbon, 14.6 ppb NO2 and 11.0 μg·m-3 ambient PM2.5. Mean±sd peripheral TPVVCT was 79.2±18.2 cm3 and TPVVCT was 129.3±35.1 cm3. Greater black carbon exposure was associated with a larger peripheral TPVVCT, including after adjustment for city (mean difference 0.41 (95% CI 0.03-0.79) cm3 per interquartile range; p=0.036). Associations for peripheral TPVVCT with NO2 were similar but nonsignificant after city adjustment, while those for PM2.5 were of similar magnitude but nonsignificant after full adjustment. There were no associations for NO x or ozone, or between any pollutant and TPVVCT. Long-term black carbon exposure was associated with a larger peripheral TPVVCT, suggesting diesel exhaust may contribute to remodelling of small pulmonary vessels in the general population.

Nanoclustered Pd decorated nanocrystalline Zn doped SnO2 for ppb NO2 detection at low temperature

Nanoclustered Pd (2 mol%) was used to decorate Zn doped SnO2 (10 mol% Zn) in order to increase its sensing performances. Zn doped SnO2 built from nanoparticles was prepared by a hydrothermal method using a non-ionic surfactant - Brij52 and Tripropylamine (TPA) as co-templates. The presence of well-dispersed Zn2+ ions in the SnO2 matrix leads to a nonstoichiometric surface. Pd was deposited by subsequent wet impregnation using hydrazine as reducing agent. The as obtained powders were deposited as thick layers onto commercial substrates, in order to obtain the sensitive structures. The coexistence of a mixture of valence states (Pd0, Pd2+ and Pd4+) was highlighted on the surface of the as prepared layers. Several aspects have been followed regarding the Zn and Pd dispersion into the SnO2 matrix: the large scale and low scale morphology (SEM and TEM/HRTEM) in relation with the synthesis route, the obtained crystallographic phases (XRD, SAED) and the way in which the Zn2+ ions are inserted into the SnO2 structure (XRD, XPS, EPR), the spatial distribution of the added chemical elements, Zn and Pd (SEM, STEM, EDS). All these morphological and structural aspects, as well as the Pd surface chemistry, have been correlated with the sensing properties of the nanostructured materials under controlled gas atmosphere. Through this study, we could harvest the specific role of the aforementioned loadings towards selective detection of low NO2 concentrations, between 350 ppb to 5 ppm, at low operating temperature of 100 °C, for infield conditions.

A Room Temperature Gas Sensor Based on Sulfonated SWCNTs for the Detection of NO and NO₂.

The electrical response of sulfonated single-walled carbon nanotubes (SWCNTs) to NO and NO2, for gas sensing applications, at room temperature, is reported in this work. A specific configuration based on SWCNT deposition between double pair configuration gold electrodes, supported on a substrate, was considered for the sensing device; employed characterization technique where FTIR and SEM. The experimental results showed a p-type response of the sulfonated SWCNTs, with decrease in resistance, under exposure to NO gas (40–200 ppb) and NO2 (40–200 ppb). Also, the sensor responses to successive exposures at NO2 800 ppb together with investigation of long term stability, at 485 ppb for NO, are reported. The reaction mechanism in case of NO and NO2 detection with sulfonated SWCNTs is presented.

Strategy for Fabricating Wafer-Scale Platinum Disulfide.

PtS2 is a newly developed group 10 2D layered material with high carrier mobility, wide band gap tunability, strongly bound excitons, symmetrical metallic and magnetic edge states, and ambient stability, making it attractive in nanoelectronic, optoelectronic, and spintronic fields. To the aim of application, a large-scale synthesis is necessary. For transition-metal dichalcogenide (TMD) compounds, a thermally assisted conversion method has been widely used to fabricate wafer-scale thin films. However, PtS2 cannot be easily synthesized using the method, as the tetragonal PtS phase is more stable. Here, we use a specified quartz part to locally increase the vapor pressure of sulfur in a chemical vapor deposition furnace and successfully extend this method for the synthesis of PtS2 thin films in a scalable and controllable manner. Moreover, the PtS and PtS2 phases can be interchangeably converted through a proposed strategy. Field-effect transistor characterization and photocurrent measurements suggest that PtS2 is an ambipolar semiconductor with a narrow band gap. Moreover, PtS2 also shows excellent gas-sensing performance with a detection limit of ∼0.4 ppb for NO2. Our work presents a relatively simple way of synthesizing PtS2 thin films and demonstrates their promise for high-performance ultrasensitive gas sensing, broadband optoelectronics, and nanoelectronics in a scalable manner. Furthermore, the proposed strategy is applicable for making other PtX2 compounds and TMDs which are compatible with modern silicon technologies.

Low-level NO gas sensing properties of $$\hbox {Zn}_{1-x}\hbox {Sn}_{x}\hbox {O}$$ Zn 1 - x Sn x O nanostructure sensors under UV light irradiation at room temperature

\(\hbox {Zn}_{1-x}\hbox {Sn}_{x}\hbox {O}\) (\(x=0\), 0.05, 0.10, 0.15, 0.20) nanostructures have been grown through the successive ionic layer adsorption and reaction method. The structural, morphological and compositional properties of the nanostructures have been characterized through X-ray diffraction, scanning electron microscope and energy dispersive X-ray analysis, respectively. The NO gas sensing properties of sensors to 20 ppb have been systematically investigated in the dark and under UV light irradiation. A \(\hbox {Zn}_{0.90}\hbox {Sn}_{0.10}\hbox {O}\) sensor has exhibited the highest response for 20 ppb NO gas compared with other sensors. The sensor response has increased from 1.9 to 43% depending on the UV light irradiation for the \(\hbox {Zn}_{0.90}\hbox {Sn}_{0.10}\hbox {O}\) sensor. \(\hbox {Zn}_{0.90}\hbox {Sn}_{0.10}\hbox {O}\) nanostructure can be used as a suitable gas sensor material for detection of low concentration levels of NO gas.

Study on highly selective sensing behavior of ppb-level oxidizing gas sensors based on Zn2SnO4 nanoparticles immobilized on reduced graphene oxide under humidity conditions

Highly selective oxidizing gas sensors are of great importance for environmental pollution monitoring. In this work, a hybrid material containing Zn2SnO4 nanoparticles (NPs) and immobilized reduced graphene oxide (Zn2SnO4-RGO) was developed as a high performance gas sensing material for the detection of ppb-levels of oxidizing gases (NO2 and O3). The structural, morphological and compositional properties of the Zn2SnO4-RGO hybrids were systematically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which demonstrated the successful anchoring of Zn2SnO4 NPs on RGO nanosheets. The obtained Zn2SnO4-RGO hybrids exhibited outstanding sensing performance for detecting oxidizing gases (NO2 and O3) with very low cross sensitivities to reducing gases, such as C2H5OH, CH3COCH3 and CO. The Zn2SnO4-RGO based sensors exhibited high response values of up to 3.50 for 500 ppb NO2, which is higher than that for detection of 500 ppb O3 (1.78) at 30 °C under 50% relative humidity (RH). Moreover, the NO2 sensing performances of Zn2SnO4-RGO-based sensors were investigated under various RH. In all cases, the sensors based on RGO and Zn2SnO4-RGO hybrids presented p-type behavior. The sensors based on Zn2SnO4-RGO hybrids also exhibited high response values of up to 3.62 for 1 ppm NO2 at 50 °C in 80% RH, which is much higher than that of pure RGO (1.31). The excellent sensing performances are mainly ascribed to the synergetic effect of Zn2SnO4 NPs and RGO. Furthermore, the surface reaction between Zn2SnO4-RGO hybrids and NO2 can be concluded from Operando diffuse reflectance infrared Fourier transformed spectroscopy (Operando DRIFT).