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•Creation of a novel self-heated CO gas sensor based on Au-functionalized networked SnO2-ZnO core-shell nanowires.•Increasing the applied voltage particularly enhanced the ...self-heating effect.•Power consumption at 3 and 20 V was estimated to be 11.3 nW and 8.3 μW.
We report a novel self-heated CO gas sensor based on Au-functionalized networked SnO2-ZnO core-shell nanowires. Increasing the applied voltage particularly enhanced the sensing response due to the self-heating effect within the sensor, and the sensors exhibited good performance without the need for an external heater. The power consumption at 3 and 20 V was estimated to be 11.3 nW and 8.3 μW, respectively. In a sensor with the optimal ZnO shell thickness of 80 nm, the responses for 50 ppm CO were 1.17 and 1.62 at 3 and 20 V, respectively. Also, the important role of ZnO-ZnO homojunctions in the self-heating of the sensor was demonstrated by increasing the ZnO shell thickness, which led to an increase in the sensor response. Furthermore, the optimized sensor exhibited outstanding selectivity toward CO gas. The optimized ZnO shell, the catalytic effect of Au, and the Joule effect contributed to the good, selective response toward CO gas with low power consumption. Since low power consumption is a fundamental requirement for wireless sensors and sensor arrays, this sensor with very low power consumption is a promising choice for such applications.
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•CuO functionalized SnO2-ZnO core-shell nanowires NWs were prepared and used for H2S sensing.•CuO functionalized SnO2-ZnO C-S NWs with a shell thickness of 80 nm had better sensing ...ability than thinner-shelled samples.•Sensing enhancement was due to a higher self-heating effect, SnO2-ZnO heterointerfaces, and the promising role of CuO NPs.
Future gas sensors require minimal power consumption to enable their integration into portable electronics such as smart mobile phones. We developed H2S gas sensors based on a self-heating effect using metal oxide nanowires (NWs). We fabricated bare SnO2 NWs, CuO functionalized SnO2 NWs, and a CuO functionalized SnO2-ZnO core-shell (C–S) NW sensor, and tested their sensor response towards H2S gas by applying different external voltages at room temperature. It was found that the CuO functionalized SnO2-ZnO C-S NW gas sensor had higher response to H2S gas relative to other tested sensors due to higher self-heating effect, formation of heterojunctions, phase transformation, and spillover effects of CuO nanoparticles. Without external heat, the selective H2S detection obtained in this work demonstrates the possibility of embedding low power consumption gas sensors in portable devices for detection of H2S as a biomarker for early diagnosis of diseases.
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•We investigated the sensing behaviors of ZnO-SnO2 core-shell NWs, with the shell layer being deposited by ALD.•We obtained high sensor responses at 1 ppm of 18.24, 14.94, and 16.46, ...respectively, to CO, C7H8, and C6H6 gases.•The main sensing mechanism was related to the radial modulation effect as well as the volume fraction of the shell to the total volume of core-shell nanowires.
ZnO-SnO2 core-shell nanowires (C-S NWs) with different shell thicknesses (0–120 nm) were prepared and their sensing behavior was systematically studied. ZnO-SnO2 C-S NWs were prepared using a two-step synthesis procedure, where core ZnO NWs were synthesized by a vapor-liquid-solid growth technique, and subsequently these cores were coated with SnO2 shell layers by using an advanced atomic layer deposition technique. The sensors were exposed to 10-ppm CO, C6H6, and C7H8 gases at an optimal working temperature. The shell thickness was optimized to be 40 nm, for which the sensor revealed the highest sensitivity and fastest dynamics to the above-mentioned gases. The sensing mechanism was discussed in detail and the dominant mechanism was related to the radial modulation effect as well as the volume fraction of the shell to the total volume of C-S NWs.
•Applications of core-shell nanostructures in gas sensors are discussed.•Mechanisms of gas sensing in core-shell nanostructures are discussed.•Effect of shell thickness is comprehensively discussed.
...High-performance gas sensors are needed to improve safety in daily life. Even though the gas sensing performance of new nanostructured metal oxides has improved significantly, some aspects of these novel nanomaterials have not been fully explored. Core-shell (C-S) and hollow shell nanostructures are two types of advanced materials for gas sensing applications. Their popularity is mainly due to the synergetic effects of the core and shell in C-S nanostructures, the high surface areas of both C-S and hollow nanostructures, and the possibility of tuning the shell thickness within the range of the Debye length for such nanostructures. In addition to the type of sensing material, morphology, sensing temperature, and porosity, shell thickness is one of the most important design parameters. Unfortunately, less attention has been paid to the effect of shell thickness on the gas sensing properties. Herein, we demonstrate that the thickness has an undeniable role in the gas sensing response of the resulting material. In this review, we present the first overview of this aspect of sensing materials. By referring to related works, we show how shell thickness can affect the sensing properties of both C-S and hollow nanostructures. Researchers in this field will be able to fabricate more sensitive gas sensors for real applications by better understanding the effect of shell thickness on the gas sensing properties of C-S and hollow nanostructured materials.
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•Amounts of Pt and Pd nanoparticles on SnO2 nanowires were optimized for NO2 gas sensing improvement.•The NO2 gas responses showed a bell-shaped dependency on the amount of Pt and Pd ...nanoparticles.•The approximation model can be used to find the optimum amount of the metal nanoparticles.
The functionalization of noble metal nanoparticles (NPs) is a highly efficient method for increasing the sensing performance of metal oxide nanowire (NWs) gas sensors. Despite the well-established strategy, the level of the optimal functionalization for obtaining the maximum sensing response has rarely been reported. Herein, the surfaces of SnO2 NWs were functionalized with Pt and Pd NPs, and the gas sensing characteristics were then investigated using NO2 as an example gas. The sensing responses obtained at the optimal temperature showed a bell-shaped dependency on the proportion of surface coverage by Pd and Pt NPs. The sensing mechanism is explained and the results were also fitted to a simple theoretical model based on modulation in the conduction channel via the chemical and electronic sensitization on NWs. This study provides guidelines on the amount of metal NPs for achieving the optimal sensing responses in metal oxide NWs gas sensors.
•Novel hybrid SnO2–ZnO core–shell nanowires functionalized by Au nanoparticles.•The resulting sensor exhibited a very high response of 26.6–100ppb CO gas.•The very good selectivity of the sensor to ...CO gas.•Heterojunctions and the catalytic effect of Au greatly improved the CO sensing capability.
An extremely sensitive CO sensor based on novel hybrid SnO2–ZnO core–shell (C–S) nanowires (NWs) functionalized by Au nanoparticles (NPs) was synthesized. First, networked SnO2 NWs were successfully prepared using the vapor–liquid–solid growth method on an electrode layer with special patterns. A ZnO shell was subsequently coated on the SnO2 core using atomic layer deposition, and Au NPs were then attached onto the ZnO shell using γ-ray radiolysis. The resulting sensor exhibited a very high response of 26.6–100ppb CO gas. Furthermore, the responses to other gases such as C6H6 and C6H7 were extremely low, indicating the very good selectivity of the sensor to CO gas. Besides acting as heterojunctions, the catalytic effect of the Au NPs on CO gas greatly improved the CO sensing capability of the Au-functionalized SnO2–ZnO C–S NWs. The high sensitivity and selectivity of this sensor can open a path for prompt toxic monitoring and early detection of fatal diseases related to CO.
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•We introduced selective toluene and benzene gas sensors based on Pt- and Pd-functionalized ZnO nanowires.•Pt- and Pd-functionalized ZnO NW sensors work with the low power consumption ...of 208 and 139 μW at 5 V, respectively.•We explained the related sensing mechanisms.
Selective toluene and benzene gas sensors, based on Pt- and Pd-functionalized ZnO nanowires (NW) in self-heating mode, are presented. The thickness of the initial sputtered metal layer (5 and 10 nm) and annealing temperature (500–750 °C) were varied to optimize the formation of Pt nanoparticles (NPs), whereas the UV irradiation time was optimized to obtain isolated Pd NPs on the surface of crystalline ZnO NWs. After a series of gas sensing studies and optimization of the gas sensors under the self-heating mode, Pt- and Pd-functionalized ZnO NWs showing most sensitive responses to toluene and benzene gases, respectively, and exhibiting sufficient selectivity for these two amongst other reducing gases were obtained. At room temperature, under an applied voltage of 20 V, the maximum response of Pt-functionalized ZnO NWs (initial thickness, 5 nm; annealing temperature, 600 °C) to 50 ppm toluene is 2.86. Moreover, the maximum response of Pd-functionalized ZnO NWs (UV irradiation time, 5 s) to 50 ppm benzene is 2.20. Further, the sensing mechanisms of these sensors are explained. Chemical sensitization by Pd and Pt, as well as the generation of ZnO/Pd and ZnO/Pt heterointerfaces enhanced the sensing performance of these sensors. The selective sensing of toluene and benzene gases by Pt- and Pd-functionalized ZnO NWs, respectively, is explained in terms of the adsorption phenomena. This study opens a pathway to the fabrication of selective toluene and benzene gas sensors with low power consumption operating in the self-heating mode.
•Gas sensors based on rGO-loaded ZnO nanofibers are developed.•Functionalization effect by Au or Pd nanoparticles is investigated.•Low concentrations of reducing gases such as CO, C6H6 and C2H5OH are ...tested.•Synergistic sensing mechanisms by metal and rGO are suggested.
Noble metal-functionalized, reduced graphene oxide (rGO)-loaded metal oxides are a new class of ternary composites that combine the advantages of each component, resulting in exceptional materials. But, there are few reports on their use as gas sensors. This paper reports the gas sensing behavior of Au or Pd-functionalized rGO-loaded ZnO nanofibers (NFs) synthesized by using a combination of facile, cost-effective sol-gel and electrospinning methods. An examination of the gas sensing properties revealed that Au-functionalized NFs have a very high response to CO gas. In particular, the gas response (Ra/Rg) to 1ppm of CO was as high as 23.5, whereas Pd-functionalized NFs showed a high response to C6H6 gas (11.8 to 1ppmC6H6). The presence of rGO/ZnO heterointerfaces, the catalytic effect of Au and Pd nanoparticles (NPs), and the high surface area of NFs were the main factors that contributed to the strong response of the Au or Pd-functionalized rGO-loaded ZnO NFs sensors. These results show that the combination of noble metals, such as Au or Pd NPs, with rGO and ZnO can impart new gas sensing functionality that is potentially useful for CO or C6H6 sensing applications, respectively.
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