Excellent Gas-sensing Performance Research Articles

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.

Enhanced n-butanol sensitivity and selectivity of Sb-doped ZnO–Co3O4 nanoparticles synthesized by solvothermal method

Sb-doped ZnO–Co 3 O 4 nanoparticles with excellent gas-sensing performance for n -butanol were synthesized by a simple one-step solvothermal route and annealing process. Microstructure, morphology, and element valence states were characterized by X-ray diffraction, field scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Sensing performance of Sb-doped ZnO–Co 3 O 4 composite nanoparticles for various volatile organic components was comprehensively investigated. Results show that nanocomposites exhibit high selectivity and sensitivity to n -butanol when doped with Sb at a level of 8%. Specifically, the selectivity of 8% Sb-doped ZnO–Co 3 O 4 sensor to 100 ppm n -butanol reached a response of 61.129 at optimal operating temperature of 200 °C, which is significantly higher than that of ZnO–Co 3 O 4 composite materials prepared without Sb doping. Improved sensing performance of Sb-doped ZnO–Co 3 O 4 was attributed to electronic and chemical sensitization effects of Sb as well as the formation of shallow donor complex defects.

Room-Temperature High-Performance Ammonia Gas Sensing Based on Molybdenum Trioxide Nanobelts Thin-Film

Ammonia, a kind of ubiquitous gas with poisonous, colorless and a strong pungent odor, is widely applied in fields of chemistry, architecture, food refrigeration, and so on. Excessive ammonia gas (NH3) in the atmosphere may promote the formation of haze, further bringing about environmental pollution. Besides, for humans, NH3 with high concentration can damage many organs such as eyes, skin and respiratory organs, causing tears, sore throat, and even pulmonary edema and death. Therefore, sensitive and rapid detection of the leakage or emission of low-concentration NH3 is of great significance in the fields of human health diagnosis, home air safety, and gas environment monitoring. To achieve this goal, in this work, molybdenum trioxide (MoO3) nanobelts were successfully synthesized by utilizing an in-situ facile one-step hydrothermal method with the help of concentrated hydrochloric acid, and then as-synthesized MoO3 nanobelts were sprayed onto interdigital electrodes substrates to construct thin-film chemiresistive sensors. The sensitive material was characterized by multiple characterization techniques such as XRD, SEM, TEM, BET and Raman, and its gas-sensing performance was systematically investigated. At optimum operation temperature (room temperature, 25±2 ℃), the sensor based on MoO3 nanobelts exhibited a high gas sensitivity response of ~17% towards NH3 with a concentration of 5 ppm, accompanied by a fast response speed of ~60 s and full recovery. It was one of the best cases of NH3 sensors based on MoO3 nanomaterials, taking into account the operation temperature and gas response. In addition, the sensor displayed a good selectivity to NH3 over other potential interfering gases including CO, CO2, H2S and SO2, as well as good humidity resistance. Besides, MoO3 sensor possessed a fine limit of detection of 25 ppb by calculating the ratio of triple mean square error of the background signal to the sensor’s sensitivity. These excellent gas-sensing performance to NH3 was attributed to the porosity of MoO3 nanoribbons, and the interspaces between nanobelts that facilitate gas accessibility and interaction between gas molecules and nanomaterials. More important, these results showed that the as-prepared MoO3 sensor had great potential for efficient and real-time monitoring of low-concentration NH3 emissions at room temperature, which also provided a feasible alternative for low-power NH3-sensitive sensors based on metal oxide semiconductor nanomaterials.

Ppb-Level Butanone Sensor Based on ZnO-TiO2-rGO Nanocomposites

In this paper, ZnO-TiO2-rGO nanocomposites were successfully synthesized by the hydrothermal method. The morphology and structure of the synthesized nanomaterials were characterized by SEM, XRD, HRTEM, and XPS. Butanone is a typical ketone product. The vapors are extremely harmful once exposed, triggering skin irritation in mild cases and affecting our breathing in severe cases. In this paper, the gas-sensing properties of TiO2, ZnO, ZnO-TiO2, and ZnO-TiO2-rGO nanomaterials to butanone vapor were studied. The optimum operating temperature of the ZnO-TiO2-rGO sensor is 145 °C, which is substantially lower than the other three sensors. The selectivity for butanone vapor is greatly improved, and the response is 5.6 times higher than that of other organic gases. The lower detection limit to butanone can reach 63 ppb. Therefore, the ZnO-TiO2-rGO sensor demonstrates excellent gas-sensing performance to butanone. Meanwhile, the gas-sensing mechanism of the ZnO-TiO2-rGO sensor to butanone vapor was also analyzed.

Synergistic effects of α-Fe2O3 nanoparticles and Fe-doping on gas-sensing performance of NiO nanowires and interface mechanism

High surface area nickel oxide nanowires (NiO NWs), Fe-doped NiO NWs and α-Fe2O3/Fe-doped NiO NWs were synthesized with nanocasting pathway, and then the morphology, microstructure and components of all samples were characterized with XRD, TEM, EDS, UV–vis spectra and nitrogen adsorption–desorption isotherms. Owing to the uniform mesoporous template, all samples with the same diameter exhibit the similar mesoporous-structures. The loaded α-Fe2O3 nanoparticles should exist in mesoporous channels between Fe-doped NiO NWs to form heterogeneous contact at the interface of n-type α-Fe2O3 nanoparticles and p-type NiO NWs. The gas-sensing results indicate that Fe-dopant and α-Fe2O3-loading both improve the gas-sensing performance of NiO NWs sensors. α-Fe2O3/Fe-doped NiO NWs sensors presented the highest response to 100 ppm ethanol gas (55.264) compared with Fe-doped NiO NWs (24.617) and NiO NWs sensors (3.189). The donor Fe-dopant increases the ground state resistance and the absorbed oxygen content in air. α-Fe2O3 nanoparticles in electron depletion region result in the increasing resistance in ethanol gas and decreasing resistance in air. In this way, α-Fe2O3/Fe-doped NiO NWs sensor presents the excellent gas-sensing performance due to the formation of heterogeneous contact at the interface.

Self-Hybrid Transition Metal Oxide Nanosheets Synthesized by a Facile Programmable and Scalable Carbonate-Template Method.

2D transition metal oxides (TMO) nanosheets have attracted considerable attention in both fundamental research and practical applications. Herein, a convenient programmable and scalable carbonate crystals templating synthesis is developed to produce high-quality self-hybrid TMO nanosheets (Si-WO3- x , Tax Oy , Mnx Oy ) and their respective polymetallic oxide hybrid nanosheets with tunable composition, low-cost and high-yield. Taking tungsten oxide nanosheets as example, silicotungstic acid precursor is in situ converted into tungsten oxide nanosheets like scales on the surface of calcium carbonate crystals through the simple soaking-drying-calcination process, and after selectively dissolving calcium carbonate by etching, the dispersive tungsten oxide nanosheets with unique self-hybrid Si-doped h-WO3 /ε-WO3 /WO2 compositions are obtained, which show excellent acetone gas-sensing performances at low temperatures. This carbonate-template method opens up the possibility to economically produce various functional TMO nanosheets with specific compositions for diverse applications.

Core-double shell ZnO@In2O3@ZnO hollow microspheres for superior ethanol gas sensing

• ZnO@In 2 O 3 @ZnO hollow microspheres have been prepared. • The heterojunctions were created at the interface of In 2 O 3 and both inner and outer ZnO. • The sensor exhibits enhanced gas-sensing properties toward ethanol. • The sensing mechanism is appropriately speculated. Core-double shell-structured ZnO@In 2 O 3 @ZnO microspheres consisting of ZnO hollow microspheres, an In 2 O 3 interlayer, and a ZnO outer layer were synthesized by decorating In 2 O 3 and ZnO on the surface of ZnO hollow microspheres. The ZnO hollow microspheres with a size of 1.4 μm provided a good matrix for the adhesion of In 2 O 3 and ZnO. Both In 2 O 3 and the ZnO shells have a loose microstructure, which provided numerous gas diffusion channels and active sites for gas diffusion and gas sensing reaction. The surface defects and electronic structure of ZnO and ZnO@In 2 O 3 @ZnO were examined by photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS). The gas sensing properties of the ZnO hollow microspheres, ZnO@In 2 O 3 core-shell microspheres, and ZnO@In 2 O 3 @ZnO core-double shell microspheres were compared using ethanol as the target gas. The response of ZnO@In 2 O 3 @ZnO toward 100 ppm ethanol was 453.2 at the optimum operating temperature of 200 °C, which was 2 and 30 times higher than that of ZnO@In 2 O 3 and ZnO. Even at a concentration of 1 ppm, the response of ZnO@In 2 O 3 @ZnO reached 53.2, indicating its excellent gas-sensing performance at low concentrations. The superior gas sensing properties of ZnO@In 2 O 3 @ZnO were attributed to its high specific surface area, abundant surface defects, and radial electronic modulation mechanism.

Shape-controlled and stable hollow frame structures of SnO and their highly sensitive NO2 gas sensing

• Novel and stable SnO hollow frames could be synthesized, including convex corner quadrilateral-, square- and octagonal-frames. • These obtained hollow frame SnO microstructures show excellent gas-sensing performances. • The detection limit of the sensor is 5 ppb at 200 °C. • The response/recovery time of the sensor is less than 60 s. In this work, tin monoxide (SnO) is synthesized successfully using a simple solvothermal method. SnCl 2 as a stannous source in the presence of oleylamine (OLA), by changing the amount of NH 3 ∙H 2 O, we prepare a series of SnO microstructures with novel and unique hollow frame morphologies, such as convex corner quadrilateral-, square- and octagonal-like structures. Meanwhile, these hollow structures are attributed to Ostwald Ripening process and the joint action of OH − and NH 4 + . In addition, these obtained hollow frame-like SnO nanostructures show excellent gas-sensing performances, including low detection limits, short response/recovery time, selectivity to NO 2 and good reproducibility. The minimum detection limit (MDL) of the sensor devices is 5 ppb at 200 °C. In addition, at a wide NO 2 concentrations detection range (e.g. 5 ppb–10 ppm), both the response and recovery time are within 60 s. The NO 2 gas sensor device still remains excellent performance after being stored over 3 months. All these advantages demonstrate a promising means of using frame-like and hollow SnO microstructures for NO 2 gas sensors application.

Synthesis of the ZnFe2O4/ZnSnO3 nanocomposite and enhanced gas sensing performance to acetone

Acetone is an important biomarker for the diagnosis of diabetes. In this work, the ZnFe2O4/ZnSnO3 nanocomposite was first prepared via a facile two-step hydrothermal method, and then obtained by the subsequent calcination process. The structure, morphology, and composition of the nanocomposite were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunner Emmet Teller (BET), scanning electron microscope (SEM), Transmission Electron Microscopy (TEM) and Fourier transform infrared spectrophotometer (DR-FTIR) techniques, and the gas-sensing performance of the composites were investigated comprehensively. The ZnFe2O4/ZnSnO3 nanocomposite is consisted by the ZnSnO3 cubic and the urchin-like ZnFe2O4. The as-prepared ZnFe2O4/ZnSnO3-0.25 gas sensor shows excellent gas-sensing performance toward acetone, including fast response-recovery time (9 s/16 s to 30 ppm acetone), long-term stability and good humidity resistance at 200°C. The improved gas sensing performance of ZnFe2O4/ZnSnO3-0.25 nanocomposite could be due to its large specific surface area, oxygen vacancy and n-n heterojunction.

Biomass-derived porous ZnO hierarchical microtubules for conductometric detection of n-butanol vapor

Rapidly conductometric detection of widely used n-butanol vapor has been really desirable owing to its inflammable and explosive hazards. To this end, porous ZnO hierarchical microtubules were simply prepared by a zinc nitrate impregnation and air calcination method using waste rose stem as bio-template, and the effects of different calcination temperatures on the microstructure and gas-sensing performance were also investigated. The ZnO-500 hierarchical structure after calcining at 500 °C is formed by the cross-linkage of small-sized nanoparticles, and has multistage porous distribution and microtubule arrays that facilitate rapid diffusion of n-butanol vapor. The ZnO-500 sensor exhibits short response time (Tres = 2 s), high response (S = 143.0) and low detection limit (10 ppb) to 50 ppm n-butanol vapor at an operating temperature of 252 °C. These gas-sensing indexes are obviously better than those of reported ZnO-based n-butanol sensors. Such excellent gas-sensing performance is mainly derived from the synergism of inherent characteristics of porous ZnO hierarchical microtubules, surface adsorbed oxygen and bio-template imprinting. Therefore, porous ZnO-500 microtubules can be utilized as a candidate sensing material for the detection of trace n-butanol vapor. Moreover, the gas-sensing mechanism is discussed in detail.

Two-Dimensional Nanomaterials for Wearable Breath Sensors

There has been considerable effort to develop wearable electronics from life-supporting devices for solders to fashion accessories such as smartwatches. The research of gas sensor has also attempted to adapt wearables with the power of nanotechnology. On the wearable platform, miniature gas sensors will provide real-time information about the atmosphere to protect each personnel from possible hazardous chemical attacks. In addition, wearable gas sensor can be facilitated to monitor human’s breath as medical applications. [1] One of the important factors to develop wearable gas sensors is to operate at room temperature with excellent sensing performance. Recently, two-dimensional (2D) nanostructured materials have been highlighted as new sensing materials due to their working ability at low temperatures. Unlike conventional metal oxides, 2D materials such as graphene are able to work at room temperature with comparable gas response to NO2 gas. However, insufficient sensing performance, such as sluggish recovery and low gas response, need to be developed. [2] As one attempt to enhance performance, 2D material was hybridized with metal oxide. By incorporating two nanostructured materials, synergistic effect, which comes from benefits of each material, can improve sensing performance. [3] Another novel innovation is the introduction of newly discovered 2D materials. 2D transition metal carbides and/or carbonitrides (called MXenes) are a new family of 2D materials. The vast diversity in a combination of constituent elements and ordered structure in MXenes offers future possibilities to find out a new generation of sensing materials with their superior performance. [4, 5]In this study, different types of 2D nanostructured materials and their hybrids were investigated for the breath analysis of various volatile compounds. Graphene oxide (GO) was incorporated with TiO2 nanoparticles, and the composite was photo-reduced under UV irradiation. Room temperature gas sensing was carried out against various VOC gases, and sensing performance was evaluated by comparing with pure GO. With the tailored hetero-junction at the interfaces of GO and TiO2, the composite can identify ethanol, methanol, and acetone, and its gas response was enhanced. In addition, we introduced new 2D nanostructured materials, MXenes including Ti3C2Tx and V2CTx. 2D V2CTx gas sensors showed excellent gas-sensing performance in terms of high response toward non-polar gases. Compared to the sensing properties of Ti3C2Tx MXene, 2D V2CTx sensor showed higher selectivity and long-term stability. The comparative results suggest that the modification of ordered structure and constituent elements of MXenes play a pivot role in the interaction between analyte and MXenes leading to an extensive change designed to detect individual compounds. [5, 6]References[1] Patel, S., Park, H., Bonato, P., Chan, L., & Rodgers, M. (2012). A review of wearable sensors and systems with application in rehabilitation. Journal of Neuroengineering and Rehabilitation, 9(1), 21.[2] Choi, S. J., & Kim, I. D. (2018). Recent Developments in 2D Nanomaterials for Chemiresistive-Type Gas Sensors. Electronic Materials Letters, 1-40.[3] Meng, F. L., Guo, Z., & Huang, X. J. (2015). Graphene-based hybrids for chemiresistive gas sensors. TrAC Trends in Analytical Chemistry, 68, 37-47.[4] Yu, X. F., Li, Y. C., Cheng, J. B., Liu, Z. B., Li, Q. Z., Li, W. Z., ... & Xiao, B. (2015). Monolayer Ti2CO2: a promising candidate for NH3 sensor or capturer with high sensitivity and selectivity. ACS Applied Materials & Interfaces, 7(24), 13707-13713.[5] Lee, E., VahidMohammadi, A., Prorok, B. C., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2017). Room Temperature Gas Sensing of Two-Dimensional Titanium Carbide (MXene). ACS Applied Materials & Interfaces, 9(42), 37184-37190.[6] Lee, E., VahidMohammadi, A., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2019). Two-Dimensional Vanadium Carbide MXene for Gas Sensors with Ultrahigh Sensitivity Toward Nonpolar Gases. ACS Sensors, 4, 1603-1611.

Metal-organic framework-derived Cr-doped hollow In2O3 nanoboxes with excellent gas-sensing performance toward ammonia

Transition metal ions doping is an effective method to improve the gas sensing performance of metal oxide semiconductors. Herein, we report the synthesis of Cr-doped In2O3 samples by calcining metal-organic frameworks (MOFs)-precursors prepared by a simple oil bath method. The experimental characterization results show that the as-prepared samples exhibit uniform hollow nanoboxes with large specific surface areas. Through comparison, the 0.5 wt% Cr-doped In2O3 sample with complete and regular morphology was selected for a series of gas-sensitive performance tests. The results show that the sensor has good detection performance for ammonia (NH3). Gas-sensing tests revealed that the sensor exhibited excellent sensing performance towards NH3 with low operating temperature (140 °C), high selectivity, good repeatability, relatively high response, low detection concentration (~ 1 ppm), and short response time (~ 1 s). The generation of lattice defects and the increased conductivity after doping are the reasons for the excellent performance of the sensor. This provides a new strategy for the research and preparation of high performance gas sensors.

Absorbent cotton derived mesoporous CeO2 hollow tubule for enhanced detection of p-xylene at low energy consumption

Ultra-sensitive detection of flammable and carcinogenic p-xylene gas at relatively low energy consumption through metal oxide-based sensors remains a great challenge due to its high stability. Herein, mesoporous CeO2 hollow microtubules with cubic fluorite structure were simply prepared by immersing absorbent cotton into cerium salt and subsequent calcination. The effect of calcination temperature on the microstructure and gas-sensing performance was also studied. The CeO2-500 hierarchical structure calcinated at 500 °C is composed of cross-linked nanoparticles with small size (12 nm), which possesses relatively large specific surface area (60.8 m2·g−1), well-distributed mesopores (15.0 nm) and abundant oxygen vacancy defects. At a relatively low operating temperature of 133 °C, CeO2-500 sensor shows a fast response to 100 ppm p-xylene (Tres = 5.4 s) and detection limit of 100 ppb, which represents the lowest value in reported CeO2-based sensors. Such excellent gas-sensing performance is highly related to the intrinsic structural properties of mesoporous CeO2-500 hollow microtubule, surface adsorbed oxygen and oxygen vacancy defects caused by Ce3+ ions.

Biomass-derived hierarchical porous ZnO microtubules for highly selective detection of ppb-level nitric oxide at low temperature

• Porous ZnO hierarchical structure was simply prepared by using hemp fiber as biotemplate. • Hemp fiber template plays a vital role in regulating microstructure and performance of ZnO-600. • The ZnO-600 sensor exhibits fast response, high sensitivity and selectivity to trace NO at 92 °C. • The detection limit of 5 ppb NO for ZnO-600 material is the lowest in reported ZnO-based sensors. Highly sensitive and selective detection of nitric oxide (NO) has recently attracted much attention due to its environmental pollution and biological role. Herein, hierarchical porous ZnO microtubules were simply and massively prepared through zinc salt immersion and air calcination using hemp fiber as biotemplate. The effect of different calcination temperature on the microstructure and gas-sensing performance was investigated. The ZnO-600 microtubules calcined at 600 °C are assembled from the cross-linking nanoparticles with good crystallinity. Especially, the multi-pores and diverse nano-channels are in favor of the quick diffusion and adsorption of target gas, enabling ZnO-600 material to present excellent gas-sensing performance towards trace NO. At low working temperature of 92 °C, the sensor fabricated by ZnO-600 microtubules to NO exhibits high response (10 ppm, S = 78.54), fast response-recovery, good selectivity as well as satisfactory stability and anti-humidity. Meanwhile, this sensor represents the lowest detection limit of 5 ppb (S = 1.22) among all reported ZnO-based sensors. Moreover, the gas-sensing mechanism for ZnO-600 material is demonstrated to be surface adsorption control model.

Pd nanocrystal sensitization two-dimension porous TiO2 for instantaneous and high efficient H2 detection

Hydrogen (H2) molecules are easy to leak during production, storage, transportation and usage. Because of their flammability and explosive nature, quick and reliable dectection of H2 molecule is of great significance. Herein, an excellent H2 gas sensor has been realized based on Pd nanocrystal sensitized two-dimensional (2D) porous TiO2 (Pd/TiO2). The formation of 2D porous TiO2 with the removal of graphene oxide template has been monitored by an in-situ transmission electron microscope. It is found that the size of the GO template can be almost completely replicated by 2D TiO2. The Pd/TiO2 sensor exhibited an instantaneous response and a satisfactory low detection limit for H2 detection. These excellent gas-sensing performances (good selectivity, unique linearity response and high stability) can be attributed to the unique 2D porous structure and the synergistic effect between oxidized Pd and TiO2, including the unique adsorption properties of O2 or/and H2 on Pd/TiO2, the reaction between PdO and H2 gas, and the regulated depletion layer arising from p-type PdO to n-type TiO2. This work demonstrates a rational design and synthesis of highly efficient H2 sensitive materials for energy and manufacturing security.

Tunable NH4F-Assisted Synthesis of 3D Porous In2O3 Microcubes for Outstanding NO2 Gas-Sensing Performance: Fast Equilibrium at High Temperature and Resistant to Humidity at Room Temperature

NO2 gas sensors based on metal oxides under wild conditions are highly demanded yet an incomplete surface reaction and humidity interference on the gas-sensing performance limit their applications. Herein, we report three-dimensional (3D) porous In2O3 microcubes via a simple hydrothermal strategy to produce outstanding NO2 gas-sensing performance: fast equilibrium of the surface reaction at 150 °C and negligible humidity dependence on the NO2 gas sensing at room temperature. The 3D porous In2O3 microcubes with high surface areas, suitable pore sizes, rich oxygen vacancies, and high conductivity are testified. The underlying structural transformation mechanism for 3D porous In2O3 is investigated in detail. The as-made 3D porous In2O3 microcubic gas sensors present excellent gas-sensing performance to 50 ppm NO2 at 150 °C, including a high response value (2329), fast response/recovery time (10/9 s), a low detection limit (10 ppb), long-term stability (60 days), and strong selectivity. Furthermore, they exhibit relatively stable NO2 gas response under humidity variation (20-80%). The NO2 gas mechanism under the interference of water is also clarified.

Ex-situ XPS analysis of yolk-shell Sb2O3/WO3 for ultra-fast acetone resistive sensor

The preparation of fast, highly responsive and reliable gas sensing devices for the detection of acetone gas is considered to be a key challenge for the development of accurate disease diagnosis systems through exhaled respiratory gases. In the paper, yolk shell Sb2O3/WO3 is synthesized and its gas sensing performance was studied by static test system. Special, the maximum response value of 1:1 Sb2O3/WO3 yolk-shell (WO3-1 YSL) sensor to 100 ppm acetone can reach as high as 50.0 at 200 ℃. And it also exhibits excellent response/recover time (4 s/5 s), low detection limit (2 ppm) and superior selectivity towards acetone. More importantly, in mixed selective gas test, the sensor shows high selectivity towards acetone. And the mechanism is analyzed by ex-situ XPS. The excellent gas-sensing performance can be attributed to unique yolk-shell structure, which facilitates the rapid transport of charge carriers from the surface to the bulk and provides more active sites for gas adsorption and desorption; the heterojunction between of Sb2O3 and WO3, which promotes oxygen pre-adsorption on the surface and increasing the interfacial potential; the increased oxygen vacancies which allowing more chemisorbed oxygen to form.