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•A comprehensive review of resistive-based gas sensors for detection of H2S gas is presented.•Gas sensing capability of binary, ternary and quaternary compounds are ...discussed.•Different sensing mechanisms involved in H2S detection are discussed.
Gas sensors play an undeniable role in most fields of technology in the modern world; they are broadly used for public safety, pollution monitoring, quality control, breath analysis, smart homes and automobiles, and so on. Due to their low cost, high sensitivity, compact size, online detection, ease of use, portability, and low power consumption, metal oxide (MO) gas sensors have exceptional potential for detection of more than 150 gases. This paper reviews the current state-of-the-art H2S conductometric MO gas sensors. In the first part, the H2S sensing mechanism for MOs is presented in detail. In the next part, the H2S sensing characteristics of the different MOs are presented, focusing on strategies such as metal doping, heterojunction composites, and different morphologies that are applied to enhance their sensing characteristics. In general, CuO, ZnO, and SnO2 show the highest sensitivity to H2S; therefore, most of this review is dedicated to these oxides. In the last part, some unusual and emerging MOs for H2S sensing are presented.
•We reported CO gas sensing properties of 2D WS2 decorated with Au nanoparticles.•We revealed the promising effects of Au for the enhanced response and selectivity towards CO gas.•Low-voltage ...operation of the fabricated gas sensors resulted in low-power consumption.
We introduced a selective and self-heated CO gas sensor based on Au-decorated WS2 nanosheets. Au nanoparticles (NPs) were decorated on WS2 NSs using UV irradiation technique at different irradiation times (1, 15 and 30 s). SiO2 grown on Si was used as substrates and the gas sensors with top electrode configuration were fabricated. Gas sensors were able to work under self-heating mode with an applied voltage of 2 V for selective CO sensing. The results of CO gas sensing demonstrated the promising effects of Au for the enhanced response and selectivity towards CO gas. Also, the low-voltage operation at room temperature resulted in low-power consumption. This study demonstrates realization of selective CO gas sensor using a facile approach along with low power consumption.
•Pd-functionalization enhanced hydrogen sensing capability of ZnO nanowires (NWs).•Pd-functionalized ZnO NWs exhibited a bell-shaped dependence on temperature.•Pd-functionalized ZnO NWs gas sensor ...showed a high selectivity to hydrogen gas.•Superior hydrogen sensing was related to Pd nanoparticles, metallization effect of ZnO, and partial conversion of Pd to PdHx.
The detection of hydrogen (H2) gas is of importance owing to its increasing use in the modern society to achieve a cleaner life environment. In this study, bare and palladium (Pd)-functionalized ZnO nanowires (NWs) were synthesized for H2 gas sensing. The ZnO NWs were fabricated by a vapor–liquid–solid technique and Pd functionalization was performed using an ultraviolet irradiation technique. Enhanced H2 gas response of the ZnO NWs was observed after Pd functionalization. Additionally, the Pd-functionalized ZnO NW gas sensor exhibited high selectivity to H2 gas. The superior hydrogen gas sensing of the Pd-functionalized ZnO NW sensor was related mainly to the sensitization of the Pd nanoparticles, metallization effect of ZnO at the sensing temperature (350 °C), and partial PdHx formation. This study demonstrates the effectiveness of the Pd functionalization on the ZnO NWs for the realization of practical hydrogen gas sensors.
Hydrogen has captured a lot of attention in recent years because its abundance, cleanness and one of the most promising sources of green energy. However, hydrogen has an explosive nature. ...Accordingly, detection of hydrogen leaks is important from a safety point of view. In this review paper, we use numerous examples to explain how Pd-decoration on the surfaces of nanomaterials can lead to enhancements in response and selectivity toward hydrogen gas. First, we describe the importance of hydrogen detection, then the properties of Pd and PdHx are reviewed, and metallic Pd hydrogen gas sensors are discussed. Finally, we comprehensively review different semiconducting gas sensors decorated with Pd with more emphasis on the sensing mechanism. This review paper provides a simple yet informative background for researchers working in this hot field.
•Promising effects of Pd on the response enhancement to hydrogen gas are discussed.•Different sensing mechanisms related to the presence of Pd are discussed.•Different materials in combination with Pd as hydrogen gas sensors are discussed.
•We investigated the hydrogen sensing of Pd-loaded ZnO nanofibers in regard to the effect of e-beam irradiation.•We optimized the sensing condition in terms of amount of Pd loading and e-beam ...irradiation dose.•The optimized sensor irradiated with 150 kGy had the high response (Ra/Rg) of 74.7 under 100 ppb of H2.
We evaluated the hydrogen gas-sensing characteristics of Pd-loaded (0.1, 0.3, 0.6, and 1 wt%) ZnO nanofibers prepared by a facile electrospinning technique and the effect of different electron beam (e-beam) doses (50, 100, and 150 kGy) on sensing performance. The sensor loaded with 0.6 wt% Pd had the highest response to hydrogen among the Pd-loaded sensors. The sensor irradiated with 150 kGy had the high response (Ra/Rg) of 74.7–100 ppb of H2 at 350 °C. Metallization effects in ZnO, the formation of structural defects due to e-beam irradiation, the catalytic activity of Pd, and the presence of ZnO–Pd heterojunctions were the main factors yielding high sensitivity towards H2. The strategy of combining e-beam irradiation and Pd loading to enhance H2 sensing can be applied to realize reliable gas sensors and the widespread use of hydrogen as a green energy alternative to fossil fuels.
Schematic of sensing mechanisms in Pd-decorated CuO nanowires
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•We fabricated pristine and Pd-functionalized CuO nanowires (NWs) for H2S gas sensing.•Gas-sensing response towards H2S ...was enhanced by the Pd functionalization, at 25–100 °C.•Self-heating tests showed that the Pd-functionalized sensors exhibited a selective response to H2S gas at 5 V.•Enhancement of sensing was attributable to CuO/Pd heterostructures and catalytic effects of both CuS and Pd.
In this study, we fabricated pristine and Pd-functionalized CuO nanowires (NWs) for H2S gas sensing. The CuO NWs were synthesized using a vapor–liquid–solid method and the Pd functionalization was achieved by ultraviolet irradiation of a Pd precursor solution in the presence of the CuO NWs. The characterization results confirmed the formation of pristine and Pd-functionalized CuO NWs with favorable compositions and morphologies. The gas-sensing response of the NWs towards H2S was enhanced by the Pd functionalization, at 25–100 °C. Moreover, self-heating tests showed that the Pd-functionalized gas sensors exhibited a selective response to H2S gas when a low voltage (5 V) was applied. The superior performance of the Pd-functionalized gas sensor was attributable to not only the catalytic effects of both CuS and Pd but also the CuO/Pd heterostructures. The results demonstrate that the fabricated H2S sensors are energy-efficient and could be used in various electronic devices.
•For gas sensing studies, we synthesized Sb-implanted SnO2 NWs at different doses.•Sensor response was enhanced by Sb-implantation, where the lowest dose showed the best performance.•Involved ...mechanisms are explained by doping-induced change of electron concentration and generation of surface defects.
We describe gas sensing improvements of SnO2 nanowire (NW) gas sensors by Sb-ion implantation. SnO2 NWs were grown through a vapor-liquid-solid growth technique and Sb-ion implantation was performed by an ion implanter at different doses of 2 × 1013, 2 × 1014, and 2 × 1015 ion/cm2. The morphology and chemical compositions were confirmed by different characterization techniques. Gas sensing results demonstrated the gas sensing improvement by Sb-implantation, where the lowest dose gas sensor showed the best performance towards tested gases. However, high doses led to a reduced sensing response. We suggested the related sensing mechanism based not only on change of electron concentration by substituting Sn4+ ions to Sb+5 ions, but also on generation of surface defects. This study can open new possibilities to use ion-implantation as promising way to enhance the sensing capability of different gas sensors.
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•n- SnO2/p-Cu2O core-shell nanofibers were synthesized by electrospinning and ALD techniques.•Shell thickness was controlled by the number of ALD cycles.•The gas sensors with a 30 nm ...shell thickness showed the highest response to CO gas.•The pristine SnO2 gas sensor showed the highest response to NO2 gas.•The sensing mechanism with respect to the shell variations was discussed.
SnO2-Cu2O core-shell nanofibers (C-S NFs) with various shell thicknesses (15–80 nm) were fabricated for gas (CO and NO2) sensing applications. SnO2 NFs were produced by electrospinning and then coated with Cu2O by atomic layer deposition, which allows control of the shell thickness. The role of the Cu2O shell thickness on the sensing characteristics was investigated systematically. The sensor responses to both CO and NO2 gases exhibited bell-shaped curves in the range of 15–80 nm, which was related to the radial modulation of the hole-accumulation layer (HAL) in the Cu2O and blocking of the expansion of the HAL because of the existence of the n-p heterojunction. In addition, the volume fraction of the shell relative to the total volume of C-S has a direct effect on the total degree of resistance modulation. Furthermore, the effects of SnO2 surface-Cu2O heterojunctions and Cu2O grain boundaries on the sensing behavior are explained. This study revealed an important aspect of C-S nanostructures for sensing studies, which is needed to optimize the shell thickness and obtain the strongest response towards specific hazardous gases.
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•Bare, Au-, SnO2-, and Au-SnO2-decorated WS2 nanosheets were prepared for CO sensing.•Gas sensing studies were performed under self-heating mode with a low power ...consumption.•Au-SnO2-co-decorated WS2 nanosheet showed the highest response of 3.687 to 50 ppm CO gas at 4.7 V.•Optimized gas sensor revealed high flexibility under tilting, bending, and stretching conditions.•Underlying sensing mechanism is explained in detail.
In this study, WS2 nanosheets that are bare or decorated with Au, SnO2, or a combination of Au and SnO2 were realized on flexible polyamide substrates. The fabricated sensors were operated for CO gas sensing in applied-voltage-induced self-heating mode. Not only optimal applied voltage was varied for the sensing of different gases, but also that the sensors behaved uniquely in response to CO gas. In particular, the Au-SnO2-co-decorated WS2 nanosheet gas sensor under an optimized applied voltage of 4.7, displayed the highest response (Ra/Rg = 3.687–50 ppm CO gas) and the highest selectivity to CO gas among the different gas sensors investigated. Furthermore, the optimized gas sensor indicated good gas response under tilting, bending and stretching conditions. The formation of Au-WS2 Schottky junctions, SnO2-WS2 heterojunctions and the role played by Au NPs in the catalysis CO gas were the most contributed effects to the sensing. The results obtained in this study provide new avenues towards fabrication of flexible, low power gas sensors using metal chalcogenides.
•Preparation of superhydrophobic austenitic stainless steel surfaces using an etching method.•Study of effects of HF etchant and NaCl solution on the final surface properties.•The highest water ...contact angle was 168° with a sliding angle of 2°.•Excellent durability after 30 days was demonstrated.•The fabricated surfaces showed self-cleaning properties.
Stainless steels are among the most common engineering materials and are used extensively in humid areas. Therefore, it is important that these materials must be robust to humidity and corrosion. This paper reports the fabrication of superhydrophobic surfaces from austenitic stainless steel (type AISI 304) using a facile two-step chemical etching method. In the first step, the stainless steel plates were etched in a HF solution, followed by a fluorination process, where they showed a water contact angle (WCA) of 166° and a sliding angle of 5° under the optimal conditions. To further enhance the superhydrophobicity, in the second step, they were dipped in a 0.1 wt.% NaCl solution at 100 °C, where the WCA was increased to 168° and the sliding angle was decreased to ∼2°. The long-term durability of the fabricated superhydrophobic samples for 1 month storage in air and water was investigated. The potential applicability of the fabricated samples was demonstrated by the excellent superhydrophobicity after 1 month. In addition, the self-cleaning properties of the fabricated superhydrophobic surface were also demonstrated. This paper outlines a facile, low-cost and scalable chemical etching method that can be adopted easily for large-scale purposes.
