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TEM images of a WO3 nanosheets and the corresponding SAED pattern, b 2 wt% Ru–WO3 nanosheets and HRTEM images of c neat WO3 and d 2 wt% Ru–WO3
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In this paper, WO3 nanosheets were prepared by an acidification method and Ru catalyst was loaded on the surface of nanosheets through a conventional impregnation process. NH3 gas sensors based on the neat and Ru-loaded WO3 nanosheets were fabricated by the scree-printing technique and their sensing properties to NH3 were investigated. The morpholo...
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WO3 nanosheets was prepared by an acidification method and the Rh catalyst was dispersed on the surface of the nanosheets with a wet impregnation method. The morphology of pristine WO3 and Rh modified WO3 nanosheets and their responses to acetone gas were studied. According to oxygen adsorption combined with TPR results, the sensing and sensitizati...
A novel method for the detection of short pulses of gas at very low concentrations, the differential surface reduction (DSR), is presented. DSR is related to the temperature pulsed reduction (TPR) method. In a high temperature phase, e.g., at 400 °C, the surface of a metal oxide semiconductor gas sensor (MOS) is oxidized in air and then cooled abru...
Citations
... f Mechanism of pristine WO 3 and Ru-decorated WO 3 sensors. Reproduced with permission from Ref. [316]. Copyright 2018, Springer Nature. ...
... Thus, Ru NPs decoration was a valid strategy to promote the sensing behavior of the SMOs-based sensor. Qiu et al. [316] synthesized WO 3 nanosheets through an acidification method, followed by a conventional impregnation process to decorate the Ru catalyst. The response of the Ru-decorated WO 3 nanosheets gas sensor was ~ 18 towards 20 ppm NH 3 at 300 °C, which was approximately twice that of the pure WO 3 nanosheets. ...
Highly sensitive gas sensors with remarkably low detection limits are attractive for diverse practical application fields including real-time environmental monitoring, exhaled breath diagnosis, and food freshness analysis. Among various chemiresistive sensing materials, noble metal-decorated semiconducting metal oxides (SMOs) have currently aroused extensive attention by virtue of the unique electronic and catalytic properties of noble metals. This review highlights the research progress on the designs and applications of different noble metal-decorated SMOs with diverse nanostructures (e.g., nanoparticles, nanowires, nanorods, nanosheets, nanoflowers, and microspheres) for high-performance gas sensors with higher response, faster response/recovery speed, lower operating temperature, and ultra-low detection limits. The key topics include Pt, Pd, Au, other noble metals (e.g., Ag, Ru, and Rh . ), and bimetals-decorated SMOs containing ZnO, SnO 2 , WO 3 , other SMOs (e.g., In 2 O 3 , Fe 2 O 3 , and CuO), and heterostructured SMOs. In addition to conventional devices, the innovative applications like photo-assisted room temperature gas sensors and mechanically flexible smart wearable devices are also discussed. Moreover, the relevant mechanisms for the sensing performance improvement caused by noble metal decoration, including the electronic sensitization effect and the chemical sensitization effect, have also been summarized in detail. Finally, major challenges and future perspectives towards noble metal-decorated SMOs-based chemiresistive gas sensors are proposed.
... As shown in Fig. 3.1 (b), the 50Fe 50 W-MC FF sample observed changes in the structural morphology, which might be due to the higher loading of iron that collapses the MC sphere. 10Fe 90 W-MC FF shows uniform carbon spheres without aggregation, indicating the successful metal incorporation in MC support [33]. ...
... To insight the structure morphology and phase identification, we studied HR-TEM and STEMEDX elemental mapping of 10Fe 90 W-MC FF catalyst (Fig. 4). The HR-TEM images (Fig. 4a) clearly show the dspacing value of 0.29 and 0.23 nm corresponding to the Fe 3 O 4 and Fe 2 O 3 formation, and the lattice d-spacings of 0.31, 0.38, and 0.53 nm correspond to the orthorhombic WO 3 , monoclinic WO 3 , and hexagonal WO 3 , respectively [30][31][32][33][34]. The STEM-EDX elemental mapping images (Fig. 4b) clearly show that iron and tungsten are highly dispersed/ incorporated on porous carbon support without impurities. ...
... The O 1 s spectrum (Fig. 6c) shows three major peaks positioned at 530.2 eV, 531.3 eV, and 532.5 eV, corresponding to the lattice oxygen and hydroxyl group. The C 1 s spectrum (Fig. 6d) shows three peaks at 286.1 eV, 286.7 eV, and 289.1 eV, indicating C -O, C-OH, and C--O, respectively [33]. XPS spectra clearly show that the oxidation state of W 6+ is more predominant than W 5+ and the maximum intensity of W 6+ is due to the WO 3 attached with lattice oxygen which is matched with O 1 s spectra [32,33]. ...
We have prepared iron and tungsten oxides incorporated mesoporous carbon (MC) catalysts using a simple hydrothermal methodology with different carbon sources, and the catalytic performance was investigated for cyclohexanone oxidation. An adequate amount of metal oxide loading has displayed a key role in the selective catalyst for adipic acid (AA) synthesis. The MC catalyst has shown its prime activity under the influence of redox properties of W⁵⁺/W⁶⁺ and Fe²⁺/Fe³⁺ as promoters. The 10%Fe 90%W-MC fructose as a carbon source catalyst has provided its best selectivity of 87% for AA at 120 °C.
... The humidity sensor (SHT31-ARP, Sensirion, Switzerland) was used to calibrate the humidity so that it remains constant. A Keithley multimeter (Keithley 2000, USA) was used to collect all measured sensor data [16]. The sensor response was defined as S ¼ jV1 À V2j, where V 1 and V 2 were the equilibrium response values of the catalytic sensor in the target gas and air, respectively [17]. ...
In this study, a catalytic-type combustible gas sensor was fabricated by the screen-printing method. Pt supported catalysts (Pt-HZSM5) were prepared by a wet impregnation method using HZSM5 zeolite as support. It was found that Pt-HZSM5 catalysts have a highly catalytic activity to H2 and CO at low temperatures and a selectively and fully combustible was observed at only 150 °C. A good dispersion state of Pt nanoparticles on HZSM5 zeolite particles was beneficial for the catalytic oxidization of CO and H2. However, a high loading amounts lead to a poor dispersion state and a weak catalytic activity. The thick film sensor based on Pt-HZSM5 catalyst was found to be highly sensitive to combustible gas with a good linearity up to 2% and a limitation of detection (LOD) around 50 ppm. Due to the low operation temperature, a highly selectivity was obtained for CO and H2 and no cross-sensitivity to interfering gases such as CH4 and VOCs. It was indicated that the present developed catalytic-type gas sensors could be used for the leakage detection and monitor for H2 and CO with a low power consumption and a good selectivity.
... It is observed that NH 3 response was also relatively poor, merely 3.2 with 20 ppm of NH 3 at 300 °C. Comparing with conventional n-type MOS sensors such as WO 3 [41][42][43], it is concluded that the responses of Cr 2 WO 6 sensors to typical inorganic gases were relatively poor. When exposed to ethanol of 5 ppm, the response could reach to 5.4 at 300 °C, which is lower with the same concentration to acetone. ...
In the present work, gas sensors based on Cr2WO6 nanoparticles were fabricated by a screen-printing technique, and the sensing properties were characterized with acetone and other typical reducing gases under both dry and humid air backgrounds. Interestingly, it was found that Cr2WO6 sensors showed a p-type conduction characteristic with a highly sensitive response to acetone vapor in a relatively low concentration. In the presence of humidity, resistances of Cr2WO6 sensors were significantly increased; nevertheless, sensor responses were obviously inhibited. In addition, the basic sensing mechanism of Cr2WO6 sensor was also investigated based on oxygen adsorption behavior and catalytic properties of Cr2WO6 surface. According to experimental results, it is proposed that the resistive responses of Cr2WO6 sensor to reducing gases were highly oxygen-dependent, indicating that the surface oxygen adsorption and reaction also played the basic role in the sensing process as that observed in typical n-type MOS sensors. Additionally, sensors also suffered from a high cross-sensitivity to water vapor due to the competition of chemisorption of water and oxygen on the surface of Cr2WO6.
... The first two methods are only suitable for specific use occasions and cannot be used for vehicle exhaust monitoring. For the sensor method, especially the resistance type [8][9][10][11][12][13][14][15] and potentiometric type [16][17][18][19][20][21][22][23][24][25][26][27][28] ammonia sensors are the mainstream of research, and have received extensive attention. However, due to the shortcomings of low operating temperature, poor selectivity and long-term stability, the resistance sensor cannot be applied for exhaust. ...
The NH3 sensitivity of a potentiometric YSZ-based planar sensor utilizing ZnFe2O4 sensing electrode (SE) was tuned by sputtering Au on the SE. ZnFe2O4 was prepared by sol-gel method and calcined at 900 °C. ZnFe2O4-SE was prepared by screen printing and sintered at 1100 °C for 3 h. SEM results show that Au is uniformly distributed in the network structure of the ZnFe2O4-SE. The response characteristics of the sensor to 5–80 ppm NH3 were evaluated between 650 °C and 750 °C, and it was found that the response rate and response signal increased significantly after gold sputtering on SE. The performance improvement by gold sputtering may originate from enhanced catalytic activity of the anodic electrode reaction, which was observed by the polarization curve test. At 700 °C, the sensor exhibited the largest sensitivity with the slope of −31.3 mV/decade, and its response to 80 ppm NH3 was −42.3 mV, and it has relatively short response and recovery time of 25 s and 49 s for 80 ppm NH3, respectively. It could even displayed a considerable signal for 5 ppm NH3 at each temperature. The oxygen concentration had non-negligible influence on the NH3 response signal. It showed tiny cross sensitivities toward NOx and C3H8, but weak CO cross sensitivity. When the water vapor concentration is within 10%, the water vapor has a small influence on the response signal. The sensor also displayed slight signal drifts in weekly tests in six weeks, which showed that ZnFe2O4 had a good long-term stability.
... The change in gas concentration modifies the catalytic carrier concentration, thereby facilitating the sensing behavior 9 . Since the sensitivity was still low in the aforementioned method, the development of nanomaterials with high surface to volume ratio is indispensable, which results in high sensitivity, selectivity and stability 10,11 . The polymer-nanotubes/nanorods composites synthesized by template-based self-assembly process were used for effective sensing applications 12 . ...
Metal oxides based graphene nanocomposites were used for ammonia vapour sensing. The self-assembly process was adopted to prepare freestanding flexible pure rGO, CeO2-rGO and SnO2-rGO composite papers. The structural studies confirmed the formation of rGO composite papers. The ammonia vapor sensing was demonstrated using an impedance analyzer at different humidity levels as well as concentration. The CeO2-rGO composite paper achieved a sensitivity of 51.70 ± 1.2%, which was higher than that of pure rGO and SnO2-rGO composite paper. Both the surfaces (top and bottom) of the papers are active in efficiently sensing ammonia, which makes the present work unique. The results reveal that metal oxide/rGO papers can be effectively utilized in real time sensor application.
Ammonia (NH3) is a hazardous gas with an irritating odor that poses severe risks even in small quantities. To this end, in this article, an NH3 sensor based on FeCo2O4/WO3/reduced graphene oxide (rGO) ternary composites was designed by taking advantage of the utility of rGO for the enhancement of gas-sensitive properties of semiconductor materials at low temperatures as well as the unique physicochemical properties of spinel-type metal oxides. The synthesized products were analyzed using multiple techniques to determine their morphology and elemental composition. The results indicate successful growth of FeCo2O4/WO3 nanocomposites on rGO film, forming heterojunctions. The gas sensitivity tests show that the minimum detection concentration of the FeCo2O4/WO3/rGO gas sensor is 500 ppb, and the response value to 100 ppm NH3 is 19.8, which is about five and eight times higher than the WO3 and FeCo2O4 gas sensors, respectively. More critically, the optimal working temperature of the gas sensing element modified with rGO is 220 °C, which is reduced to varying degrees compared to both single and binary gas sensing units. On the other hand, the FeCo2O4/WO3/rGO gas sensing element has the ability to quickly detect NH3 in the low concentration ranges, such as a response/recovery time of only 2 s/1 s for 1 ppm gas. The structure of the FeCo2O4/WO3/rGO ternary composites is responsible for the enhanced performance of the gas sensing element, resembling the formation of a p-n-p heterojunction structure.
