Ultrasensitive Gas Sensor Research Articles

Design of ultrasensitive gas sensor based on self-assembled Pd-SnO2/rGO porous ternary nanocomposites for ppb-level hydrogen

With the accelerating development of the hydrogen economy, more requirements are put forward for the detection capability of portable hydrogen sensors. Though the fast and accurate detection of hydrogen has been indispensable, there are still some challenges in the detection of extremely low concentrations of hydrogen. In this work, Pd-SnO2/rGO ternary nanocomposites with porous structures were synthesized by a facile template-free hydrothermal method. The effects of each element and its contents on the sensitivity and selectivity to hydrogen were systematically studied. The best hydrogen sensing property was produced by the synergistic effect of the 5.0 Pd-SnO2/rGO ternary nanocomposite, which showed a response of 32.38 toward 200 ppm hydrogen at 360 ℃. Especially, the response of 5.0 Pd-SnO2/rGO to 0.5 ppm (500 ppb) hydrogen reached 2.4, indicating the great potential in the detection of extremely low concentrations of hydrogen. The mechanism of high hydrogen sensitivity and selectivity was elaborated in combination with the analysis of band structure. All the as-prepared sensors exhibit quantitative concentration-response function relationships, favorable reversibility, and long-term stability. This work may provide a feasible strategy for the design of novel H2 sensors with high sensitivity to extremely low concentrations of hydrogen.

Ultra-sensitive gas sensor based fano resonance modes in periodic and fibonacci quasi-periodic Pt/PtS2 structures

Ultra-sensitive greenhouse gas sensors for CO2, N2O, and CH4 gases based on Fano resonance modes have been observed through periodic and quasi-periodic phononic crystal structures. We introduced a novel composite based on metal/2D transition metal dichalcogenides (TMDs), namely; platinum/platinum disulfide (Pt/PtS2) composite materials. Our gas sensors were built based on the periodic and quasi-periodic phononic crystal structures of simple Fibonacci (F(5)) and generalized Fibonacci (FC(7, 1)) quasi-periodic phononic crystal structures. The FC(7, 1) structure represented the highest sensitivity for CO2, N2O, and CH4 gases compared to periodic and F(5) phononic crystal structures. Moreover, very sharp Fano resonance modes were observed for the first time in the investigated gas sensor structures, resulting in high Fano resonance frequency, novel sensitivity, quality factor, and figure of merit values for all gases. The FC(7, 1) quasi-periodic structure introduced the best layer sequences for ultra-sensitive phononic crystal greenhouse gas sensors. The highest sensitivity was introduced by FC(7, 1) quasiperiodic structure for the CH4 with a value of 2.059 (GHz/m.s−1). Further, the temperature effect on the position of Fano resonance modes introduced by FC(7, 1) quasi-periodic PhC gas sensor towards CH4 gas has been introduced in detail. The results show the highest sensitivity at 70 °C with a value of 13.3 (GHz/°C). Moreover, the highest Q and FOM recorded towards CH4 have values of 7809 and 78.1 (m.s−1)−1 respectively at 100 °C.

Light-activated ultrasensitive NO2 gas sensor based on heterojunctions of CuO nanospheres/MoS2 nanosheets at room temperature

MoS2-based gas sensor has become an effective platform to detect NO2 gas. However, room-temperature NO2 gas sensor based on MoS2 are facing low sensitivity and poor response/recovery behaviors because of low-reacting activity between gas-sensing materials and NO2 gas at room temperature. Purposefully, a room-temperature NO2 gas sensor based on CuO/MoS2 heterojunctions with excellent sensitivity and fast response/recovery speeds is successfully realized. More attractively, the CuO/MoS2-3 sensor exhibits remarkable response (8.98) and short response/recovery time of 18.5/53.5 s to 10 ppm NO2 at room temperature under red light illumination, which is obviously better than that under dark. The improved sensitivity and fast response/recovery behaviors are attributed not only to the charge separation efficiency derived from the effect of heterojunctions, but also to the charge flow on the sensing layer in the context of NO2/MoS2/CuO interaction under red light illumination. In addition, the fabricated sensor has low detection limit (50 ppb), excellent reversibility and high selectivity to NO2 against other gases. After 40 days, the CuO/MoS2-3 sensor still maintains a relatively stable response with the fast response time (<18.5 s) under red light illumination, ensuring a long-term and fast detection to NO2 in practical applications.

Ultrasensitive gas sensor based on Pd/SnS2/SnO2 nanocomposites for rapid detection of H2

With the emergence of hydrogen economy worldwide and the increase of safety problems caused by the highly flammable and explosive characteristics of hydrogen (H2), it is urgent to develop the portable sensors that can sensitively and quickly detect H2 leaks. In this work, the H2 sensing characteristics of Pd/SnS2/SnO2 nanocomposites synthesized via hydrothermal route as well as impregnation route were systematically investigated for the first time. The influence of different SnS2 and Pd loading on the H2 sensing performances of SnO2 nanoparticles was revealed by varying the addition levels of thiourea and palladium chloride. The H2 sensing experimental results demonstrated that SnS2 and Pd modification can greatly enhance the sensing capabilities of SnO2, where 1.0 at% Pd/SnS2/SnO2 sensor exhibited high response (95) and rapid response/recovery time (1/9 s) to 500 ppm H2 at 300 ℃, thus outperforming the current reported sensing performances of SnO2-based H2 sensors. The superior sensing characteristics of Pd/SnS2/SnO2 were attributed to the simultaneous synergistic effect of the three components. This study will supply a rational strategy for designing high sensitive and rapid response H2 sensors.

NO2 sensors based on crystalline MoSe2 porous nanowall thin films with vertically aligned molecular layers prepared by sputtering

This work reports room temperature operable ultrasensitive NO2 gas sensors fabricated from vertically aligned crystalline MoSe2 porous nanowall thin films prepared by a facile and scalable DC sputtering technique at room temperature without any post-annealing and selenization treatment. The microstructural and compositional studies were carried out using XRD, Raman, FESEM, HRTEM, EDS and XPS to identify the quality and properties of the deposited MoSe2 thin films and to realize the underlying gas sensing mechanism. The NO2 gas sensing performance of vertically aligned MoSe2 porous nanowall thin film sensors was recorded over a wide range of NO2 gas concentrations (0.1–50 ppm) at room temperature (30 °C). The fabricated sensing device based on grown MoSe2 thin film exhibits excellent sensing characteristics (relative sensor response = –78.3% and response/ recovery time ~ 20 s/ 174 s for 10 ppm NO2 gas) along with high selectivity, real-time response, rapid on-off switching and adequate stability at room temperature. The observed substantial enhancement in sensing performance is attributed to the superior charge transfer process as a consequence of augmented adsorption of gas molecules mediated by the higher surface-to-volume ratio of the unique nanostructure, i.e., edge-enriched crystalline MoSe2 nanowalls along with the 3D porous surface structure in addition to the significant catalytic activity of MoSe2. Thus, this uniquely developed highly nanocrystalline sputtered MoSe2 porous nanowall thin films with vertically aligned molecular layers deposited at room temperature is cost-effective and highly desirable for developing low-powered high-performance gas sensors.

Porous reduced graphene oxide for ultrasensitive detection of nitrogen dioxide

The defect engineering in graphene plays a significant role for the application of gas sensors. In this work, we proposed an efficient method to prepare ultrasensitive gas sensors based on the porous reduced graphene oxide (PRGO). Photo-Fenton etching was carried out on GO nanosheets in a controlled manner to enrich their vacancy defects. The resulting porous graphene oxide (PGO) was then drop-coated on interdigital electrodes and hydrothermal reduced at 180 °C. Controllable reduction was achieved by varying the water amount. The gas sensor based on PRGO-5 min-6 h exhibited superior sensing and selective performance toward nitrogen dioxide (NO2), with an exceptional high sensitivity up to 12 ppm−1. The theoretical limit of detection is down to 0.66 ppb. The excellent performance could be mainly attributed to the typical vacancy defects of PRGO. Some residue carboxylic groups on the edges could also facilitate the adsorption of polar molecules. The process has a great potential for scalable fabrication of high-performance NO2 gas sensors.

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.

Highly conjugated three-dimensional van der Waals heterostructure-based nanocomposite films for ultrahigh-responsive TEA gas sensors at room temperature

Ultrasensitive gas sensors have been successfully fabricated with the high-quality COFs@SnO2@CNS heterostructures and exhibit an excellent TEA sensing performance at room temperature.

Metastable Antimony‐Doped SnO2 Quantum Wires for Ultrasensitive Gas Sensors

AbstractDoping is fundamental to controlling the properties of bulk semiconductors. Although the antimony (SbV)‐doping strategy is widely employed in the design of practical tin oxide (SnO2) semiconductor gas sensors for higher signal‐to‐noise ratio, challenges remain to dope semiconductor nanocrystals since the diffusion of impurity atoms may be far from realized at the synthesis temperatures used. Herein, a metastable Sb‐doping strategy is proposed to overcome the serious receptor‐versus‐transducer mismatch in SnO2 quantum wires (QWs). The solvothermal synthesis of colloidal SbIII‐doped SnO2 QWs has been conducted at 180 °C, whereby the antimony amount is varied to optimize the structural and morphological properties for higher surface activity and electrical conductivity. A unique n‐type doping mechanism arising from the stable presence of SbIII on SnO2 (101) facets via SnII‐O‐SbIII is demonstrated. Further, the use of sensitive (down to 4 ppb, the lowest detection limit ever reported), fast (response and recovery time of 43 s and 96 s toward 10 ppm of H2S) gas sensors for H2S detection at near room temperature (40 °C) is showcased. The metastable Sb‐doping strategy may pave the way to ultrasensitive gas sensor possessing low power consumption and excellent integration compatibility to satisfy the increasing demand for ubiquitous and reliable gas detection.

Ultrasensitive gas sensor based on nanocube In2O3-CNH composite at low operating temperature

A facile solvothermal route prepared In2O3/CNH nanocomposites with different CNH concentrations. All nanocomposites' structural and morphological properties were investigated by XRD, FESEM, TEM, XPS, and BET. The H2S sensing performance of the sensors based on them was tested, operated between 40 °C and 300 °C. The results showed that the optimal composition is In2O3/CNH (2 wt%) with a sensor signal to 2 ppm H2S, at an operating temperature of 70 °C, of almost 3000. The sensors demonstrated excellent selectivity, low impact of humidity and good reproducibility and stability. The superior sensor performance is related to the p-n junction formation between the CNH and In2O3, which determines the increase of the surface band bending and the sensor response. The gas sensing mechanism is thoroughly discussed, and the In2O3/CNH nanocomposite sensor can be considered an ideal candidate for high-performance detection of H2S with low-power consumption.

Ultrasensitive acetone gas sensor can distinguish the diabetic state of people and its high performance analysis by first-principles calculation

Detecting the acetone in human exhaled breath sensitively and selectively plays an important role in the noninvasive diagnosis of diabetes. However, obtaining a reliable response to ppb level acetone in exhaled breath directly is still a big challenge. Here, an ultrasensitive acetone gas sensor based on p-Rh2O3-n-ZnO porous heterostructure has been fabricated. The detection limit of the sensor reaches to 50 ppb. The sensor exhibits well repeatability, selectivity and linear response. A good linear relationship between the response and ambient relative humidity is observed. Without removing the water vapor of the exhaled gas, it can distinguish the acetone concentration of the diabetic patients from that of healthy people, implying that the sensor could be used in the diagnosis of diabetes. The synergistic effect of p-Rh2O3-n-ZnO porous heterostructure makes the sensor own ultrasensitive detecting ability towards acetone. Theoretical models have been built by first-principles calculation to reveal the possible reasons for its ultrasensitivity. It should be pointed out that the much lower adsorption energy (− 1.03 eV) of the acetone molecule on Rh2O3 may be the chief cause of the lower detection limit of the sensor.

UV illumination-enhanced ultrasensitive ammonia gas sensor based on (001)TiO2/MXene heterostructure for food spoilage detection

Ammonia has been used as an important marker to indicate the extent of food spoilage. However, current gas sensors for ammonia suffer from either insufficient sensitivity and selectivity or unsatisfactory levels of automation, impeding their practical application for on-site and real-time monitoring of food quality. To overcome these limitations, we propose here the design of a sensing material by in-situ growing (001)TiO2 onto a two-dimensional transition-metal carbide (Ti3C2Tx, MXene). In this design, TiO2 with a highly active (001) crystal plane provides efficient photogeneration under UV irradiation, while Ti3C2Tx can store holes through Schottky junction formed at the interface with TiO2, which greatly promotes the separation of electron-hole pairs, thereby enhancing ammonia sensing performance. By further introducing UV light for electron excitation, the (001)TiO2/Ti3C2Tx based sensor shows 34 times higher sensitivity for ammonia (30 ppm) than that of Ti3C2Tx. The density functional theory further revealed that the (001) plane of TiO2 and Ti3C2Tx composite configuration exhibited the highest adsorption affinity towards ammonia. Finally, an integrated circuit alarm system including near-field communication and a micro-controller system was designed to detect the decay process of fresh pork, fish, and shrimp. We believe such a sensing technology holds great promise in food quality monitoring.

Porous α-Fe2O3 gas sensor with instantaneous attenuated response toward triethylamine and its reaction kinetics

To achieve highly selective and rapid detection of triethylamine (TEA) at a relatively low temperature remains challenging. In this work, we report an ultrasensitive TEA gas sensor with a specific response based on the porous α-Fe2O3 hollow sphere array, which shell is composed of fusiform particles. At a low operating temperature (160 °C), the sensor shows high response (75.8) toward 10 ppm TEA with a short response time (2 s) and can detect TEA as low as 50 ppb. More importantly, an obvious attenuation characteristic is observed during TEA detection. This distinctive response toward TEA gas is repeatable when the operating temperature is over a threshold (>120 °C). Moreover, the instantaneous attenuated response is found to be independent of the gas concentration and humidity but much related to specific gases, demonstrating its potential to be used as a characteristic signal to achieve highly selective detection of TEA molecules. Furthermore, based on density functional theory (DFT) calculations, the attenuated response can be ascribed to a special surface dynamic reaction process involving the thermal decomposition of TEA molecules and the formation of nitrogen oxides, which is verified by the quasi in-situ X-ray photoelectron spectroscopy analysis. This work will provide a new idea for developing highly selective and sensitive sensors.

Ultrasensitive formaldehyde gas sensor based on Au-loaded ZnO nanorod arrays at low temperature

Au-loaded ZnO were successfully prepared by means of seed-assisted solvothermal methods. The vertically ordered nanorod arrays are uniformly grown on the Al2O3 substrate. The sensing properties of ZnO and Au-loaded ZnO sensors toward HCHO were investigated. Remarkably, the sensor based on 4 wt%Au-loaded ZnO nanorod arrays exhibits high response, short response and recover times, excellent selectivity, as well as low HCHO detection limit at 70 °C. After the incorporation of Au nanoparticle, the detection limit decreases from 10 ppm to 0.25 ppm, and the response increases more than 20 times under 100 ppm HCHO at 70 °C. Moreover, the mechanism of HCHO sensing with Au-loaded ZnO was explored by the calculations obtained from the first-principle studies.

Ultrasensitive NO2 Gas Sensors Based on Layered α‐MoO3 Nanoribbons

AbstractThe detection and monitoring of nitrogen dioxide (NO2) plays a vital role in the environmental, healthcare, farming, and industrial sectors. However, the development of NO2 gas sensors with simultaneously high sensitivity, reversibility, low detection limit, and excellent selectivity remains challenging. In this work, an ultrasensitive NO2 gas sensor with superb selectivity and reversibility is demonstrated based on α‐phase molybdenum trioxide (α‐MoO3). Nanoribbons of α‐MoO3 are synthesized via vapor phase transport (VPT) and systematically characterized using a combination of advanced characterization probes. At an optimal operating temperature of 125 °C, the α‐MoO3‐based sensor shows a very high sensitivity toward NO2 with a detection limit as low as 24 ppb, while also exhibiting excellent selectivity and reversibility. Such impressive performance originates from the layered nature of the α‐MoO3 nanoribbons as well as the hierarchical assembly of the nanoribbons as the sensing layer. The study demonstrates a facile sensing platform based on α‐MoO3 for ultrasensitive and selective NO2 gas sensing.

(Invited) Self-Assembling Organic Semiconductors for Chemical Sensing

Self-assembling monolayers of organic semiconductors are promising for monolayer organic field-effect transistors (OFETs) and various devices based on them, in particular low power consumption integrated circuits and ultrasensitive gas sensors [1]. Recently we have developed highly stable organosilicon derivatives of organic semiconductor benzothieno[3,2-b][1]benzothiophene (BTBT) capable to self-assembly into a monolayer semiconducting film by Langmuir–Blodgett, Langmuir–Schaefer (LS) or spin-coating methods [2,3]. These monolayer films were used for preparation of OFET devices, which demonstrated excellent electrical performance with a hole mobility up to 7 × 10−2 cm2 V−1 s−1, a threshold voltage around 0 V and an on–off ratio of 105 as well as long-term stability of half-year storage under ambient conditions. They were successfully utilized for multiparamertic real time detection of NH3 and H2S in dry air [4]. Modified by additional metal-containing porphyrin receptor layer, two-layer OFETs were investigated as ultrasensitive gas sensors for NH3 and H2S real-time detection in the humid air [5]. Introduction of the receptor layers on top of the LS semiconducting monolayer provides the device sensitivity enhancement as well as allows tuning the sensor selectivity. They demonstrated the improvement of both the limit of detection (down to ca. 60−70 ppb) and sensitivity in the air with relative humidity up to 60 %. Impressive combination of the sensor high sensitivity and reproducibility with fast response and full recovery after finishing the analyte exposure enables utilizing the fabricated two-layer OFETs as chemo-sensors in real gas analyzing systems environmental pollutions control. This work was supported by the Russian Science Foundation (grant 19-73-30028).

Ultrasensitive NO2 gas sensor with insignificant NH3-interference based on a few-layered mesoporous graphene

• A novel sub-ppm NO 2 gas sensor based on a few-layered mesoporous graphene (FLMG). • Few-layered mesoporous graphene is optimized at 100 min by a high-energy ball milling. • The room-temperature sensor exhibited high sensitivity, low cost and simple fabrication. • FLMG-based sensor shows an insignificant NH 3 and humidity interference. Few-layered mesoporous graphene (FLMG) is employed as a sensing material to develop an innovative and high-sensitivity room temperature NO 2 sensor through a simple manufacturing process. For this purpose, sensing material is optimized at 100 min by a high-energy milling process where natural graphite is used as a precursor: it is an inexpensive, sustainable and suitable active material. The large number of defects created and the enhanced degree of mesoporosity produced during the milling process determine the physical principles of operation of the designed device. NO 2 gas sensing tests reveal an improved and selective performance with a change in resistance of ∼16 % at 0.5 ppm under ultraviolet photo-activation, establishing a detection limit around ∼25 ppb. Interestingly, the response of the developed sensor to humidity is independent in the measured range (0–33 % relative humidity at 25 °C) and the dependency to the presence of NH 3 is rather poor as well (∼1.5 % at 50 ppm).

Precise tailoring of multiple nanostructures based on atomic layer assembly via versatile soft-templates

Nanodevices have higher requirements for nanofabrication in tuning the size, shape and spatial arrangement of nanostructures and their assemblies in nanoscale, however, which are often beyond the reach of conventional lithography or self-assembly techniques. In view of the above, we develop atomic layer assembled nanofabrication based on soft-templates to break through the limitations of traditional rigid-templates, having very well scalability and powerful fabrication capability for multiple solid or hollow nanostructures. Versatile soft-templates can be freely patterned at the nanoscale by mature lithographic processes, along which a precisely controlled atomic layer deposition can assemble high-aspect-ratio nanostructures with a flexible tailoring of the size, shape and spatial array, and then a dry etching process removes soft scaffolds and leaves freestanding nanostructures over large-area, rigid or soft substrates. To highlight the potentials of this fabrication strategy, the high-performance optical metasurface and ultra-sensitive H2 gas sensor are demonstrated. This approach endows the conventional lithography and assembly techniques with new powerful functionalities and more scalability in nanofabrication, providing a simply promising route to generating complex multiple nanostructures, towards a broad application in modern nanodevices.

Engineering SnO2 nanorods/ethylenediamine-modified graphene heterojunctions with selective adsorption and electronic structure modulation for ultrasensitive room-temperature NO2 detection

Ever-increasing concerns over air quality and the newly emerged internet of things (IoT) for future environmental monitoring are stimulating the development of ultrasensitive room-temperature gas sensors, especially for nitrogen dioxide (NO2), one of the most harmful air pollution species released round-the-clock from power plants and vehicle exhausts. Herein, tin dioxide nanorods/ethylenediamine-modified reduced graphene oxide (SnO2/EDA-rGO) heterojunctions with selective adsorption and electronic structure modulation were engineered for highly sensitive and selective detection of NO2 at room temperature. The modified EDA groups not only enable selective adsorption to significantly enrich NO2 molecules around the interface but also realize a favorable modulation of SnO2/EDA-rGO electronic structure by increasing the Fermi level of rGO, through which the sensing performance of NO2 is synergistically enhanced. The response of the SnO2/EDA-rGO sensor toward 1 ppm NO2 reaches 282%, which exceeds the corresponding SnO2/rGO sensor by a factor of 2.8. It also exhibits a low detection limit down to 100 ppb, enhanced selectivity, and rapid response/recovery kinetics. This approach to designing a novel heterojunction with significantly enhanced chemical and electric effects may shed light on the future engineering of gas-sensing materials.

Ultrasensitive NO2 gas sensor based on Sb-doped SnO2 covered ZnO nano-heterojunction

Sb-doped SnO2 covered ZnO nano-heterojunction (Sb-doped SnO2/ZnO NHs) are prepared by using a microwave hydrothermal method. The effect about morphology and gas sensor performance of the SnO2/ZnO NHs with Sb-doping is studied in detail. The SEM indicated that the morphology of SnO2 changed from nanowires to nanosheets by Sb-doping and the growth direction of SnO2 was vertical to the plane of ZnO from the TEM. Compared with undoped SnO2/ZnO NHs, the gas sensor response became higher as the concentration of Sb-doping increased which shows the sensor performance can be enhanced by Sb-doped SnO2. The change of morphology by Sb-doping increased the number of surface active sites and defects. In addition, a certain concentration of O vacancy was induced by Sb-doping to provide more free electrons that can also be captured by NO2. The research may provide a reference for studying the effect of Sb-doped composite materials and gas sensor performance.