In this study, Sb ions were implanted into p-type tungsten disulfide (WS2) nanosheets (NSs) at four different doses and carbon monoxide (CO) gas-sensing properties were investigated in the ...self-heating mode. The ratio of Sb5+ to Sb3+ was approximately 7:3, implying that Sb5+ ions were dominant and acted as donors to change the conductivity of WS2 to n-type. Implanting 2 × 1013 Sb ions/cm2 followed by annealing at 500 °C resulted in a sensor with the highest response to CO gas. Subsequently, the surface of the optimal gas sensor was decorated with Au nanoparticles (NPs), leading to its improved response to CO gas. The main parameters related to the enhanced gas performance of the optimized gas sensor were the increase in O ionosorption with generation of S vacancies, formation of Au/Sb–WS2 heterojunctions, and catalytic and spillover effects of Au NPs. The possibility of realizing a self-heated, CO-gas-sensitive sensor using decorating Sb-implanted WS2 NSs with Au was demonstrated.
•Sb-implantation changed the gas sensing behavior of WS2 from p-type to n-type.•Implanting Sb improved the gas-sensing properties by increasing O adsorption.•CO gas sensing in self-heating mode was studied under applied voltages of up to 5 V.•Au decoration further enhanced the response and selectivity to CO gas.
•Gas sensors based on pristine and Au-decorated WS2 nanoflakes were prepared on flexible substrate.•Au-decorated WS2 nanoflakes showed good selectivity to CO gas along with excellent ...flexibility.•Sensing mechanism was discussed.
A flexible and selective CO gas sensor was fabricated from Au-functionalized two-dimensional (2D) WS2 nanoflakes on polyamide substrate. Au-functionalized 2D WS2 nanoflakes gas sensors fabricated on polyamide can be operated under self-heating mode (1-5 V) with good selectivity to CO gas. Gas sensors fabricated on polyamide not only showed flexibility, but also demonstrated good stability and repeatability. In particular, even after 1000 times tilting, the optimized gas sensor could detect low concentrations of CO gas. The underlying sensing mechanism is discussed in detail. The results indicated the feasibility of realization of low-energy consumption and flexible gas sensors using Au-functionalization on 2D WS2 nanoflakes.
This paper proposes a method for improving the reducing or oxidizing gas-sensing abilities of p-type oxide nanowires (NWs) by locally modifying the hole-accumulation channel through the attachment of ...p-type nanoparticles (NPs) with different upper valence band levels. In this study, the sensing behaviors of p-CuO NWs functionalized with either p-NiO or p-Co3O4 NPs were investigated as a model materials system. The attachment of p-NiO NPs greatly improved the reducing gas-sensing performance of p-CuO NWs. In contrast, the p-Co3O4 NPs improved the oxidizing gas-sensing properties of p-CuO NWs. These results are associated with the local suppression/expansion of the hole-accumulation channel of p-CuO NWs along the radial direction due to hole flow between the NWs and NPs. The approach proposed in this study provides a guideline for fabricating sensitive chemical sensors based on p-CuO NWs.
Carbon nitrides with a high N/C atomic ratio (>2) are expected to offer superior basicity and unique electronic properties. However, the synthesis of these nanostructures is highly challenging since ...many parts of the CN frameworks in the carbon nitride should be replaced with thermodynamically less stable NN frameworks as the nitrogen content increases. Thermodynamically stable C3N7 and C3N6 with an ordered mesoporous structure are synthesized at 250 and 300 °C respectively via a pyrolysis process of 5‐amino‐1H‐tetrazole (5‐ATTZ). Polymerization of the precursor to the ordered mesoporous C3N7 and C3N6 is clearly proved by X‐ray and electron diffraction analyses. A combined analysis including diverse spectroscopy and FDMNES and density functional theory (DFT) calculations demonstrates that the NN bonds are stabilized in the form of tetrazine and/or triazole moieties in the C3N7 and C3N6. The ordered mesoporous C3N7 represents the better oxygen reduction reaction (ORR) performances (onset potential: 0.81 V vs reversible hydrogen electrode (RHE), electron transfer number: 3.9 at 0.5 V vs RHE) than graphitic carbon nitride (g‐C3N4) and the ordered mesoporous C3N6. The study on the mechanism of ORR suggests that nitrogen atoms in the tetrazine moiety of the ordered mesoporous C3N7 act as active sites for its improved ORR activity.
Thermodynamically stable C3N7 and C3N6 are discovered for the first time via stabilization of NN bonds in tetrazine and/or triazole moieties through a low‐temperature pyrolysis process of 5‐amino‐1H‐tetrazole. Triazole‐based mesoporous C3N7 exhibits better oxygen reduction reaction activity than s‐heptazine‐based carbon nitrides due to its inordinate core structure.
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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.
•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.
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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.
•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.
Gas sensors are of a great interest for applications including toxic or explosive gases detection in both in-house and industrial environments, air quality monitoring, medical diagnostics, or control ...of food/cosmetic properties. In the area of semiconductor metal oxides (SMOs)-based sensors, a lot of effort has been devoted to improve the sensing characteristics. In this work, we report on a general methodology for improving the selectivity of SMOx nanowires sensors, based on the coverage of ZnO nanowires with a thin ZIF-8 molecular sieve membrane. The optimized ZnO@ZIF-8-based nanocomposite sensor shows markedly selective response to H2 in comparison with the pristine ZnO nanowires sensor, while showing the negligible sensing response to C7H8 and C6H6. This original MOF-membrane encapsulation strategy applied to nanowires sensor architecture pave the way for other complex 3D architectures and various types of applications requiring either gas or ion selectivity, such as biosensors, photo(catalysts), and electrodes.
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