Excellent Gas-sensing Performance Research Articles

Selective adsorption and sensing mechanism of ZnFe2O4 (111) surface towards toxic gases:A first-principles study

ZnFe2O4 possesses an excellent gas-sensing performance, but its sensing mechanism towards different toxic gas molecules requires further exploration. In this study, the competitive adsorption and sensing properties of several toxic gases (NO2, NO, SO2, CO, H2S, and NH3) on the ZnFe2O4 (111) surface were investigated using density functional theory (DFT) calculations. The adsorption energy, charge transfer (QT), occupation function, adsorption free energy, charge density difference (CDD), and density of states (DOS) were compared. The results reveal that the ZnFe2O4 (111) surface exhibits obvious adsorption for NH3, H2S, NO2, and H2O, besides the selectivity of NH3 molecule is highest. Strong chemical interactions exist between these harmful gas molecules and the ZnFe2O4 (111) surface. This study offers valuable theoretical insights into the selective adsorption and sensing mechanism, contributing to the development of high-performance gas sensors to detect toxic gases.

Hierarchically porous ZnO derived from zeolitic imidazolate frameworks for high-sensitive MEMS NO2 sensor

Three-dimensional (3D) porous metal oxide nanomaterials with controllable morphology and well-defined pore size have attracted extensive attention in the field of gas sensing. Herein, hierarchically porous ZnO-450 was obtained simply by annealing Zeolitic Imidazolate Frameworks (ZIF-90) microcrystals at an optimal temperature of 450 °C, and the effect of annealing temperature on the formation of porous nanostructure was discussed. Then the as-obtained ZnO-450 was employed as sensing materials to construct a Micro-Electro-Mechanical System (MEMS) gas sensor for detecting NO2. The MEMS sensor based on ZnO-450 displays the excellent gas-sensing performances at a lower working temperature (190 °C), such as high response value (242.18% @ 10 ppm), fast response/recovery time (9/26 s) and ultralow limit of detection (35 ppb). The ZnO-450 sensor shows better sensing performance for NO2 detection than ZnO-based composites materials or commercial ZnO nanoparticles (NPs), which are attributed to its unique hierarchically structures with high porosity and larger surface area. This ZIFs driven strategy can be expected to pave a new pathway for the design of high-performance NO2 sensors.

Pt and black phosphorus co-modified flower-like WS2 composites for fast NO2 gas detection at low temperature.

Incomplete recovery, baseline drift, and a long response time have been impeding the practical applications of transition metal dichalcogenide (TMD)-based gas sensors. Here, we report WS2 sensors with significantly improved gas recovery, rapid response, and negligible baseline drift by the incorporation of black phosphorus (BP) as well as the decoration of Pt to detect NO2 for the first time. Compared to bare WS2, the BP-WS2 sensors show higher sensitivity, better repeatability, and more excellent selectivity towards NO2 at the optimal operating temperature of 50 °C. Furthermore, the optimized 30%BP-WS2/Pt sensors exhibit a continuous enhancement in the recovery level and sensitivity with negligible baseline drift. The 30%BP-WS2/Pt sensor also exhibits a shorter response time of 28 s than 49.5 s for its counterpart WS2 sensor towards 32 ppm NO2. The enhanced sensing properties are primarily due to the combined effects of more adsorption sites provided by BP, the spill-over effect of Pt catalysis, and the WS2/BP heterostructure. Therefore, the Pt-decorated 30%BP-WS2 sensor exhibits prominent gas-sensing properties of high gas sensitivity, a low detection limit of 100 ppb, good selectivity, and fast response. Our strategy provides a new route for designing and optimizing TMD-based gas sensors with excellent gas-sensing performance.

Bismuth tungstate nanosheets sensors based on Temkin adsorption model for triethylamine detection

Nanostructured Bi2WO6 and Bi2W2O9 were synthesized using a hydrothermal method. The crystal structure, morphology, and specific surface area were analyzed via X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The characterization results show that Bi2WO6 has a higher specific surface area and a larger pore size than Bi2W2O9, which promote oxygen adsorption and surface reactions. Gas-sensitive tests show that both sensors have a lower detection limit of 2.5 ppm as well as short response and recovery times for detecting triethylamine (TEA). They also have excellent cycling and long-term stability at 180 °C and exhibit excellent gas-sensing performance. The Bi2WO6 sensor has a higher response and sensitivity, as well as better selectivity, than the Bi2W2O9 sensor, which is related to the uniformly layered structure of the former material. We have analyzed the mechanism that enables these sensors to detect TEA and have used the Temkin adsorption model to explain the linear relationship. We find that this model provides an excellent theoretical foundation for fitting the working curve of these semiconductor sensors.

Preparation and Gas-Sensing Properties of Two-Dimensional Molybdenum Disulfide/One-Dimensional Copper Phthalocyanine Heterojunction

Although 2D MoS2 alone shows excellent gas-sensing performance, it is prone to stacking when used as the sensitive layer, resulting in insufficient contact with the target gas and lower sensitivity. To solve this, a 2D-MoS2/1D-CuPc heterojunction was prepared with different weight ratios of MoS2 nanosheets to CuPc micro-nanowires, and its room-temperature gas-sensing properties were studied. The response of the 2D-MoS2/1D-CuPc heterojunction to a target gas was related to the weight ratio of MoS2 to CuPc. When the weight ratio of MoS2 to CuPc was 20:7 (7-CM), the gas sensitivity of MoS2/CuPc composites was the best. Compared with the pure MoS2 sensor, the responses of 7-CM to 1000 ppm formaldehyde (CH2O), acetone (C3H6O), ethanol (C2H6O), and 98% RH increased by 122.7, 734.6, 1639.8, and 440.5, respectively. The response of the heterojunction toward C2H6O was twice that of C3H6O and 13 times that of CH2O. In addition, the response time of all sensors was less than 60 s, and the recovery time was less than 10 s. These results provide an experimental reference for the development of high-performance MoS2-based gas sensors.

Creating oxygen vacancies on porous tungsten oxide nanospheres via one-step muffle calcination for ultra-fast detection of ppb-level hydrogen sulfide sensors

Exploring the relationship between tungsten oxides with a controlled amount of oxygen vacancies and their gas-sensing properties with respect to hydrogen sulfide is interesting for developing excellent comprehensive gas-sensing performance materials with fast and accurate response. In this work, the WO3 nanoparticles with oxygen defective structure were synthesized by a straightforward one-step muffle calcining method. The WO3 nanoparticles prepared at the calcination temperature of 600 ℃ (Ov-WO3-600) display the high response value (2777) and ultra-fast response time (2 s) to 5 ppm hydrogen sulfide (H2S) at 100 ℃. Moreover, it also exhibits low practical detection limit (100 ppb), long-term stability, as well as remarkable admirable selectivity. The gas sensing mechanism can be explained by the fact that oxygen vacancies, as donor energy levels provide more electrons, increase the carrier mobility and narrow the band gap. This makes it easier for oxygen to capture electrons to form more adsorbed oxygen, which improves the gas sensing performance of WO3-based sensors. Hence, our study can offer guidance for the construction of fast and accurate sensing materials based on WO3.

Mesoporous Co3O4/In2O3 nanocomposites for formaldehyde gas sensors: Synthesis from ZIF-67 and gas-sensing behavior

Mesoporous In2O3 nanowires (NWs) were synthesized with nanocasting method, and then Co3O4/In2O3 nanocomposites were prepared through calcining ZIF-67. All results indicate that Co3O4 nanoparticles greatly affect the microstructures and gas-sensing properties of Co3O4/In2O3 sensors. The response to 10 ppm (formaldehyde) HCHO gas exhibits a significant improvement though the loading of Co3O4. The response values soar from 26.16 for In2O3 NWs to 92.94 for 6%Co3O4/In2O3 and up to maximum 113.6 for 8% Co3O4/In2O3, then decreases to 25.76 for 10% Co3O4/In2O3. 8% Co3O4/In2O3 sensor possesses the excellent HCHO gas-sensing performance with the highest response (113.6) and shortest response time of 20 s. The working temperature of Co3O4/In2O3 sensors is 30 °C lower than that of In2O3 sensor due to Co3O4 catalysis. P-n heterojunctions between p-type Co3O4 and n-type In2O3 affect the interfacial carrier distribution, improving the gas-sensing behavior of Co3O4/In2O3 sensors. Furthermore, oxygen vacancies also play a important role to improve the gas-sensing performance of Co3O4/In2O3 sensors.

Pyrochlore cerium stannate (Ce2Sn2O7) for highly sensitive NO2 gas sensing at room temperature

Gas sensing at low temperatures remains a notable challenge at present. Owing to their strong catalytic activity, oxygen defects, and unique size, pyrochlore-based oxides have attracted considerable attention for preparing conductometric gas sensors that are effective at low temperatures. In this study, we prepared a pyrochlore-Ce2Sn2O7 structure using a facile hydrothermal method. The structure, morphology, and surface valance states of the prepared sample were analyzed. Additionally, we investigated the gas-sensing properties, such as the selectivity, response, response and recovery time, repeatability, stability, limit of detection, and influence of relative humidity on the sensing performance for NO2 gas molecules at room temperature (30 ± 2 ℃). The Ce2Sn2O7 exhibited outstanding selectivity for NO2 gas molecules compared with the interfering gas molecules such as N2O, CO, CO2, SO2, NH3,NO and H2S at room temperature (30 ± 2 ℃.). Moreover, the response and recovery time values were 4 s and 52.5 s, respectively, and an outstanding response of 125% was achieved toward 50 ppm NO2 gas molecules. The Ce2Sn2O7 sensor device exhibited excellent repeatability and stability over 90 days. The excellent gas-sensing performance was attributable to the high specific surface area, presence of oxygen vacancies, and surface-adsorbed oxygen molecules.

Room-temperature methane sensors based on ZnO with different exposed facets: A combined experimental and first-principle study

Methane is a flammable and explosive gas, which is difficult to detect at room temperature. In this work, the photo-activation route was explored to realize the monitoring of methane at room temperature, and the strategy of surface morphology engineering was used to boost excellent methane gas-sensing performance. Three types of ZnO structures: rods, plates, and spheres with exposed (001) and (100) crystal facets in different ratios, were obtained using solvothermal methods. Such characteristics of samples were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption analyzer. The gas-sensing performances of sensors based on as-prepared materials were tested under UV light and in the dark. The results indicate that sensors exhibit excellent gas-sensing performances toward methane under UV light at room temperature. ZnO spheres showed a much better response of 20.577 toward 5000 ppm methane and a faster response time of 6 s compared to ZnO plates and rods. The enhanced gas sensing properties were ascribed to high-energy exposed facets and unique hollow structures. In addition, density functional theory (DFT) was investigated to support the effect of crystal facets

Ag-nanoparticles-anchored mesoporous In2O3 nanowires for ultrahigh sensitive formaldehyde gas sensors

As the core component of gas sensors, the sensing mediums with excellent gas-sensing performance are strongly required. Herein, Ag nanoparticles were implanted into mesoporous indium oxide nanowires (In2O3 NWs) to form Ag-loaded In2O3 NW. All results indicated that Ag nanoparticles are well-dispersed in mesopores of In2O3 NWs and significantly affect specific surface area and interface oxygen vacancies. Moreover, Ag-loading tremendously improves the formaldehyde (HCHO) gas-sensing performance of Ag-loaded In2O3 sensors. Owing to Ag catalysis, the operating temperature decreases from 210 ℃ for In2O3 sensor to 150 ℃ for Ag-loaded In2O3 sensor. Ag0.025-In2O3 sensor exhibits the highest response (877.3) to 10 ppm HCHO for more oxygen vacancies and Ag spillover effect, which is about 33 times of In2O3 sensor. The formation of Schottky heterojunctions at the interface between Ag and In2O3 leads to the electron transition from In2O3 to Ag, which increases the resistance in air and HCHO gas for Ag-loaded In2O3 sensors.

TiO2 functionalized AlGaN/GaN HEMT gas sensor based on capacitance change strategy under room temperature

A fast response and high-selectivity TiO2@Polymine (PEI) modified AlGaN/GaN high electron mobility transistor (HEMT) gas sensor is proposed and fabricated. It can be used to detect formaldehyde (HCHO) under room temperature (RT, about 25 °C). The working mechanism of this sensor is to affect the channel current by changing the cap capacitance of HEMT. The capacitance of amino-functionalized TiO2 as photocatalyst changes with the adsorb and degrade process under UV irradiation (365 nm, 2 mW). Compared with volatile organic compounds (VOCs), it has exhibited excellent gas-sensing performance for HCHO vapour. The detection limit of HCHO is 5 ppm and the signal sensitivity is 312 nA/ppm at RT. Due to the low operating voltage and small sensor size, it is expected to be simple and portable.

One-step preparation of flexible citric acid-doped polyaniline gas sensor for ppb-level ammonia detection at room temperature

In this work, a citric acid-doped polyaniline/polyvinylidene fluoride (CPP) flexible ammonia sensor was prepared by in situ oxidative chemical polymerization on a flexible porous polyvinylidene fluoride membrane. The CPP sensor exhibited excellent performance at room temperature (217% response for 1 ppm NH3), low detection limit (LOD) reaches 3 ppb, and rapid response and recovery times (30 s /195 s for 1 ppm NH3, respectively). Furthermore, the sensor shows outstanding flexibility and excellent stability. After 10,000 bending cycles, the CPP sensor still produces over 99% stable response. The response reached 95% of its initial value after more than 60 days of storage. The CPP sensor exhibits excellent gas-sensing performance for ammonia gas, mainly attributed to the increase in active sites induced by citric acid doping and the synergistic effect of the porous substrate. The above results demonstrated that the CPP flexible film sensor is a high-performance candidate for enhanced ammonia gas sensing properties at room temperature.

Graphitic carbon-doped SnO2 nanosheets-wrapped tubes for chemiresitive ppb-level nitric oxide sensors operated near room temperature

The development of low-temperature metal oxide-based sensors with high sensing response towards harmful ppb-level gases remains challenging. Based on the idea of biological structure imitation, we choose wooden hydrangea petals as biotemplate and carbon source to controllably replicate graphitic carbon-doped SnO2 material (GC/SnO2-6) by simply calcining the salt solution-soaked precursor at 600 °C. Its morphology is tube bundle wrapped by corrugated sheets that formed by cross-linkage of nanoparticles. The internal surface of tube wall is decorated with nanoaggregates. The fabricated GC/SnO2-6 sensor exhibits response value of 256.3 towards 1 ppm NO at 50 ℃, which is 9.9 times higher than that (S = 26.0) of pure SnO2-7 material obtained by calcining at 700 ℃ in air. Meanwhile, this sensor also has short recovery time (42 s), low actual detection limit (50 ppb), satisfactory moisture resistance and long-term stability. Such excellent comprehensive gas-sensing performance is attributed to the homogeneous mesopore and large specific surface area of its biomorphic structure, as well as the synergism of graphitic carbon doping and abundant oxygen vacancies. In addition, the enhanced sensing mechanism is also explored in detail.

In-situ construction of carbon-doped ZnO hollow spheres for highly efficient dimethylamine detection

Pure ZnO and carbon-doped ZnO hollow spheres were successfully synthesized by a hydrothermal-calcination process. The doping content of carbon in ZnO was controlled by different calcination temperatures at 500 ℃ and 600 ℃ (named as ZnO-500 and ZnO-600). Systematic material characterization indicates that mesoporous ZnO hollow spheres are featured in abundant defects induced by in-situ carbon doping. Used as gas sensing materials, the response of ZnO-600 towards 200 ppm dimethylamine (83.6) is 28.6 times and 2.5 times higher than that of Pure ZnO (2.9) and ZnO-500 (32.8) at the optimum operating temperature of 240 ℃. Remarkably, the response of ZnO-600 toward 1 ppm dimethylamine is as high as 7.2, and simultaneously the limit of detection is as low as 108 ppb. In addition, ZnO-600 hollow spheres hold excellent gas-sensing performance in response-recovery speed, selectivity, repeatability, long-term stability, and water resistance towards dimethylamine. The boosted dimethylamine sensing performance of ZnO-600 is mainly attributed to synergistic effects of the unique mesoporous microstructure and rich defects induced by in-situ carbon doping. This work provides a promising material for dimethylamine detection, the properties of which can be improved for practical applications in the future. Furthermore, this contribution gives new insights into nonmetal-doped metal oxide nanostructures for high-performance gas sensors via surface defect control.

Enhanced visible light-excited ZnSnO3 for room temperature ppm-level CO2 detection

• ZnSnO 3 was synthesized by a one-step facile hydrothermal method. • ZnSnO 3 coatings exhibited excellent responses to CO 2 at room temperature. • ZnSnO 3 based sensors showed good repeatability and long-term stability. • Enhancing mechanism of sensing properties was attributed to oxygen vacancies. Aimed at the bottleneck problem in conventional gas sensors that the effective detection of CO 2 gas can only be accomplished at concentrations above thousands of ppm and higher operating temperature, in this work, microstructured ZnSnO 3 equipped with rambutan-like hexahedral features with the hollow interior was successfully synthesized through a facile one-step hydrothermal method. Visible light was utilized as an excitation source to further enhance the sensing property. The investigation elaborated that at optimum hydrothermal time of 16 h, ZnSnO 3 showed a high gas response (~4.65), repeatability, and long-term stability towards 400 ppm CO 2 at room temperature. The response under purple light was 3.5 times higher than that under dark conditions, resulting from photoelectrons' generation. Furthermore, ZnSnO 3 sensor had excellent selectivity to 50 ppm CO 2 . The large specific surface area and abundant oxygen vacancies of ZnSnO 3 contribute to the excellent gas-sensing performance, which addresses the dilemma that it is difficult to break through the energy barrier through surface interaction to impact the band structure and carrier concentration because CO 2 is a non-polar molecule formed by polar bonds. Therefore, ZnSnO 3 is a promising material for the development of devices utilized in medical respiratory detection, agricultural crop growth detection and other fields.

Humidity-Tolerant Chemiresistive Gas Sensors Based on Hydrophobic CeO2/SnO2 Heterostructure Films

The accelerated evolution of the Internet of Things has brought new challenges to the gas sensors, which are required to work persistently under harsh conditions, like high humidity. However, currently, it is quite challenging to solve the hindrance of the trade-off between gas-sensing performance and anti-humidity ability of the chemiresistive gas sensors. Herein, hydrophobic inorganic CeO2/SnO2 heterostructure films were prepared by depositing the CeO2 layers with a thickness of a few nanometers onto the SnO2 film via a magnetron sputtering method. The sensors based on the CeO2/SnO2 heterostructure films demonstrated excellent gas-sensing performance toward trimethylamine (TEA) with high response, wide detection range (0.04-500 ppm), low record detection limit (0.04 ppm), ideal reproducibility, and long-term stability, while concurrently possessing promising anti-humidity ability. A portable, wireless TEA-sensing system containing the CeO2/SnO2 sensor was constructed to realize the real-time monitoring of trace concentration of the volatiles released from a fish. This work provides a novel strategy to prepare advanced chemiresistive gas sensors for humidity-independent detection of harmful gases and vapors and will accelerate their commercialization process in the field of food safety and public health.

CuO-sensitized amorphous ZnSnO3 hollow-rounded cubes for highly sensitive and selective H2S gas sensors

Hydrogen sulfide (H2S), a toxic and flammable gas, poses a substantial threat to human health and the ambient environment. Therefore, producing responsive H2S sensors that have excellent selectivity and work at low temperatures has been a goal for researchers. In this study, hollow-rounded cubes composed of copper oxide (CuO)-sensitized amorphous zinc stannate (zinc tin oxide (ZTO)) were prepared by a coprecipitation method combined with an impregnation treatment. Various characterization methods are employed to analyze the crystal phase, morphology, and composition of the synthetic materials. The results showed that the materials were composed of hollow, rounded, amorphous cubes with a 500–700 nm uniform particle size. The as-prepared materials were applied to gas sensors, and their H2S-sensing performance was systematically tested. Compared with the ZTO- and CuO-based sensors, the CuO/ZTO-based sensor exhibited excellent gas-sensing performance toward H2S, with a maximum response value of 574–10 ppm H2S and a low operating temperature of 160 °C. In addition, the sensor showed higher selectivity and a low detection limit of 200 ppb. The findings indicate that the CuO/ZTO composite is promising as an H2S-sensing material with potential applications in the field of environmental air monitoring.

Ag modified Tb-doped double-phase In2O3 for ultrasensitive hydrogen gas sensor

Herein, an Ag modified Tb-doped In2O3 nanocomposite with two coexisting crystalline phases was synthesized by hydrothermal and annealing methods. The gas-sensing performance test results revealed that the In2O3 composite with two coexisting crystalline phases improves the stability and accuracy of the sensor compared to In2O3 with only a cubic phase. Moreover, Ag modified Tb-doped In2O3 sensor not only has an excellent response to hydrogen (H2) of ppb level (4.63 for 500 ppb H2) but also greatly improves the selectivity, stability, and reliability of the H2 sensor at a low optimal operating temperature. The coexistence of the two crystal phases enhances the stability of the sensor materials and the introduction of oxygen vacancies and the spillover effect by Tb doping and Ag modification enhances the gas-sensing performance. In particular, the synergistic effect of Ag modification and Tb doping also reduces the response attenuation effect during H2 reaction process. The gas-sensing mechanism of the prepared sensor provides an effective strategy to achieve an excellent gas-sensing performance for H2 gas.

High performance of gas sensor based on Bi-doped ZnSnO3/CuO nanocomposites for acetone

Bi-doped ZnSnO 3 /CuO composite (Bi–ZnSnO 3 /CuO) was synthesized by in situ precipitation in this study. The material structure, morphology, size, specific surface area, and surface composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). Bi–ZnSnO 3 /CuO composite had a profoundly porous structure. CuO was bolstered on the surface of cubic ZnSnO 3 . The addition of Bi and CuO effectively expanded the substance of oxygen vacancies and chemisorbed oxygen of ZnSnO 3 /CuO. Gas-sensing test results appeared that Bi–ZnSnO 3 /CuO had excellent gas-sensing performances for acetone, with a 386.19 sensitivity to 100 ppm acetone under an optimal operating temperature of 375 °C and a response/recovery time of 4 s/12.5 s. The excellent improvement in the gas-sensing performances of Bi–ZnSnO 3 /CuO over those of ZnSnO 3 can be due to the rich mesoporous structure and the arrangement of a large number of oxygen defects and p-n heterojunctions. Excellent gas-sensing performances make Bi–ZnSnO 3 /CuO an ideal sensing material for acetone gas. • The highly porous structure on the surface of the Bi–ZnSnO 3 /CuO composite. • The content of oxygen vacancies (O vac ), and chemisorbed oxygen (O che ) increased greatly (Bi–ZnSnO 3 /CuO). • The operating temperature of Bi–ZnSnO 3 /CuO (375 °C) is lower than that of ZnSnO 3 (425 °C). • The sensitivity of Bi–ZnSnO 3 /CuO under 100 ppm acetone gas was 386.19, and the response/recovery time was only 4 s/12.5 s.

Room-temperature triethylamine sensing of a chemiresistive sensor based on Sm-doped SnS2/ZnS hierarchical microspheres

An Sm-doped SnS2/ZnS sensor shows excellent gas-sensing performance towards triethylamine at room temperature.