High-Performance Gas Sensing Research Articles

Electrostatically Doped Junctionless Graphene Nanoribbon Tunnel Field-Effect Transistor for High-Performance Gas Sensing Applications: Leveraging Doping Gates for Multi-Gas Detection.

In this paper, a new junctionless graphene nanoribbon tunnel field-effect transistor (JLGNR TFET) is proposed as a multi-gas nanosensor. The nanosensor has been computationally assessed using a quantum simulation based on the self-consistent solutions of the mode space non-equilibrium Green's function (NEGF) formalism coupled with the Poisson's equation considering ballistic transport conditions. The proposed multi-gas nanosensor is endowed with two top gates ensuring both reservoirs' doping and multi-gas sensing. The investigations have included the IDS-VGS transfer characteristics, the gas-induced electrostatic modulations, subthreshold swing, and sensitivity. The order of change in drain current has been considered as a sensitivity metric. The underlying physics of the proposed JLGNR TFET-based multi-gas nanosensor has also been studied through the analysis of the band diagrams behavior and the energy-position-resolved current spectrum. It has been found that the gas-induced work function modulation of the source (drain) gate affects the n-type (p-type) conduction branch by modulating the band-to-band tunneling (BTBT) while the p-type (n-type) conduction branch still unaffected forming a kind of high selectivity from operating regime point of view. The high sensitivity has been recorded in subthermionic subthreshold swing (SS < 60 mV/dec) regime considering small gas-induced gate work function modulation. In addition, advanced simulations have been performed for the detection of two different types of gases separately and simultaneously, where high-performance has been recorded in terms of sensitivity, selectivity, and electrical behavior. The proposed detection approach, which is viable, innovative, simple, and efficient, can be applied using other types of junctionless tunneling field-effect transistors with emerging channel nanomaterials such as the transition metal dichalcogenides materials. The proposed JLGNRTFET-based multi-gas nanosensor is not limited to two specific gases but can also detect other gases by employing appropriate gate materials in terms of selectivity.

Hollow ZnWO4/In2O3 Nanotubes for Ultrasensitive and Rapid Trace Detection of Triethylamine

The directional modulation of metal oxide semiconductors (MOSs) can be effective in developing high-performance gas-sensing materials. Herein, we propose an efficient strategy by modifying ZnWO4 on In2O3 to achieve controllable modulation of oxygen vacancies and energy band structures in ZnWO4/In2O3 heterostructures. The sensor based on optimized ZnWO4/In2O3 exhibits significantly enhanced performance to detect triethylamine, including a lower operating temperature (100 °C), a higher responsivity (Ra/Rg = 221.2 for 100 ppm), and a lower detection limit (500 ppb). In addition, the fabricated sensor exhibits faster response and good selectivity. The improved gas-sensing performance could be attributed to the acid–base interaction between triethylamine gas and ZnWO4, the formation of heterojunctions, and the increase of oxygen vacancies to achieve a synergistic modulation of the chemical and energy band structures. It is anticipated that our current investigation could offer insights and a useful strategy for triethylamine detection.

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing.

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B. Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H2 S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.

Pore Size Modulation in Flexible Metal‐Organic Framework Enabling High Performance Gas Sensing

AbstractPore size plays a critical role in determining the performance of metal‐organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore‐size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent‐coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL‐88B. Pore‐size‐dependent gas sensitivity and selectivity were studied for the first time in the MIL‐88B samples. The optimized MIL‐88B‐20 % sample showed one of the best sensing performances among all the reported MOF‐based H2S‐sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore‐size and properties, but also may inspire the development of high‐performance gas sensing materials.

Facile Synthesis of ZnO/WO3 Nanocomposite Porous Films for High-Performance Gas Sensing of Multiple VOCs.

Volatile organic compounds (VOCs) in indoor environments have typical features of multiple components, high concentration, and long duration. The development of gas sensors with high sensitivity to multiple VOCs is of great significance to protect human health. Herein, we proposed a sensitive ZnO/WO3 composite chemi-resistive sensor facilely fabricated via a sacrificial template approach. Based on the transferable properties of self-assembled monolayer colloidal crystal (MCC) templates, two-dimensional honeycomb-like ordered porous ZnO/WO3 sensing matrixes were constructed in situ on commercial ceramic tube substrates with curved and rough surfaces. The nanocomposite thin films are about 250 nm in thickness with large-scale structural consistency and integrity, which facilitates characteristic responses with highly sensitivity and reliability. Furthermore, the nanocomposite sensor shows simultaneous responses to multiple VOCs that commonly exist in daily life with an obvious suppression sensing for traditional flammable gases. Particularly, a detection limit of 0.1 ppm with a second-level response/recovery time can be achieved, which is beneficial for real-time air quality assessments. We proposed a heterojunction-induced sensing enhancement mechanism for the ZnO/WO3 nanocomposite film in which the formation of abundant heterojunctions between ZnO and WO3 NPs significantly increases the thickness of the electron depletion layer in the bulk film and improves the formation of active oxygen species on the surface, which is conducive to enhanced responses for reducing VOC gases. This work not only provides a simple approach for the fabrication of high-performance gas sensors but also opens an achievable avenue for air quality assessment based on VOC concentration detection.

Graphene and g-C3N4-Based Gas Sensors

The efficient monitoring of the environment is currently gaining a continuous growing interest in view of finding solutions for the global pollution issues and their associated climate change. In this sense, two-dimensional (2D) materials appear as one of highly attractive routes for the development of efficient sensing devices due, in particular, to the interesting blend of their superlative properties. For instance, graphene (Gr) and graphitic carbon nitride g-C3N4 (g-CN) have specifically attracted great attention in several domains of sensing applications owing to their excellent electronic and physical-chemical properties. Despite the high potential they offer in the development and fabrication of high-performance gas-sensing devices, an exhaustive comparison between Gr and g-CN is not well established yet regarding their electronic properties and their sensing performances such as sensitivity and selectivity. Hence, this work aims at providing a state-of-the-art overview of the latest experimental advances in the fabrication, characterization, development, and implementation of these 2D materials in gas-sensing applications. Then, the reported results are compared to our numerical simulations using density functional theory carried out on the interactions of Gr and g-CN with some selected hazardous gases’ molecules such as NO2, CO2, and HF. Our findings conform with the superior performances of the g-CN regarding HF detection, while both g-CN and Gr show comparable detection performances for the remaining considered gases. This allows suggesting an outlook regarding the future use of these 2D materials as high-performance gas sensors.

Three-Dimensional Ceo2@Carbon-Quantum-Dots Scaffold Modified with AU Nanoparticles on Flexible Substrates for High Performance Gas Sensing at Room Temperature

Three-Dimensional Ceo2@Carbon-Quantum-Dots Scaffold Modified with AU Nanoparticles on Flexible Substrates for High Performance Gas Sensing at Room Temperature

Evaluating the Fitness of Combinations of Adsorbents for Quantitative Gas Sensor Arrays.

Robust, high-performance gas-sensing technology has applications in industrial process monitoring and control, air quality monitoring, food quality assessment, medical diagnosis, and security threat detection. Nanoporous materials (NPMs) could be utilized as recognition elements in a gas sensor because they selectively adsorb gas. Imitating mammalian olfaction, sensor arrays of NPMs use measurements of the adsorbed mass of gas in a set of distinct NPMs to infer the gas composition. Modular and adjustable NPMs, such as metal-organic frameworks (MOFs), offer a vast material space to sample for combinations to comprise a sensor array that produces a response pattern rich with information about the gas composition. Herein, we frame quantitative gas sensing, using arrays of NPMs, as an inverse problem, which equips us with a method to evaluate the fitness of a proposed combination of NPMs in a sensor array. While the (routine) forward problem is to use an adsorption model to predict the mass of gas adsorbed in each NPM when immersed in a gas mixture of a given composition, the inverse problem is to predict the gas composition from the observed masses of adsorbed gas in the NPMs of the array. The fitness of a given combination of NPMs for gas sensing is then determined by the conditioning of its inverse problem: the prediction of the gas composition provided by a fit (unfit) combination of NPMs is insensitive (sensitive) to inevitable errors in the measurements of the mass of gas adsorbed in the NPMs. For illustration, we use experimentally measured adsorption data to analyze the conditioning of the inverse problem associated with a (IRMOF-1 and HKUST-1) CH4/CO2 sensor array.

Flower-shaped ZnO nanomaterials for low-temperature operations in NOX gas sensors

In this study, we synthesized nanostructured zinc oxide (ZnO) by using various concentrations (0–0.05 M) of cetyltrimethylammonium bromide (CTAB) as a surfactant to optimize its morphology for gas sensor applications. The optimization process was used to elucidate the morphology effects (rod-shaped and flower-shaped morphologies). The morphologies were investigated through scanning electron microscopy, in which the assembly of nanorods leading to a spherical microstructure with a CTAB concentration of 0.005 M was observed. Brunauer–Emmett–Teller isotherm measurements revealed a surface area of 7.928 g/m2 for the flower-like morphology, which was relatively higher than those of other CTAB-assisted morphologies. Such morphological features were expected to contribute toward high-performance gas-sensing. The effect of morphology variation on the resistance of ZnO microstructures was used for gas measurements. Among the varied morphologies, a sample with a spherical flower-shaped morphology exhibited a very high response at low temperatures (~29 at 25 °C) toward NOX gas (0.75 ppm) and a high selectivity toward NOx among ammonia (NH3), toluene (C6H5CH3), carbon monoxide (CO), acetone (CH3COCH3), and ethanol (C2H5OH). Raman and photoluminescence spectroscopy analyses unraveled the presence of a high density of oxygen vacancies in the sample, thereby suggesting a close link between the defective nature of the sample and the high response of the flower-like ZnO at low temperatures.

Functional Film Coated Optical Micro/Nanofibers for High-Performance Gas Sensing

One of the challenges for optical micro/nanofiber (MNF) gas sensors is reliably measuring small volumes of samples with low detection limit and fast response. Herein, we introduce a concept of utilizing functional film coated optical MNFs for gas sensing. As a proof-of-concept, when crystal violet (CV) doped Nafion film was used for humidity sensing, the sensor exhibited nearly linear response to humidity in the range of 30%–100% relative humidity (RH), with a response time of ~150 ms and a resolution of 0.3% RH. Also, highly sensitive ammonia sensing was demonstrated by using bromothymol blue (BTB) doped polyvinyl alcohol (PVA) film, achieving a detection limit down to 30 ppb. This concept enhances the sensors’ stability by enclosing the MNF completely with polydimethylsiloxane (PDMS) microflow cell and functional film rather than suspending MNFs in a conventional large volume flow chamber. The higher sensitivity and lower detection limit are attributed to the gas-induced color changes in the pH indicator doped polymer film which improve evanescent absorption significantly. The shorter response time is due to the drastically reduced diffusional pathlength of gas by the thin layer of polymer film. Compared with the delicate surface coating technique, its simple fabrication procedure and low production cost boost the development fiber-optic sensing technology. We anticipate that the study is a starting point for practical applications of the MNF sensors.

Fabrication and Characterization of Hexagonal Tungsten Oxide Nanopowders for High Performance Gas Sensing Application

Fabrication and Characterization of Hexagonal Tungsten Oxide Nanopowders for High Performance Gas Sensing Application

Ordered Mesoporous Tin Oxide Semiconductors with Large Pores and Crystallized Walls for High-Performance Gas Sensing.

Owing to their distinct chemical and physical properties, mesoporous metal oxide semiconductors have shown great application potential in catalysis, electrochemistry, energy conversion, and energy storage. In this study, mesoporous crystalline SnO2 materials have been synthesized through an evaporation-induced co-assembly (EICA) method using poly(ethylene oxide)-b-polystyrene diblock copolymers as the template, tin chlorides as the tin sources, and tetrahydrofuran as the solvent. By controlling conditions of the co-assembly process and employing a carbon-supported thermal treatment strategy, highly ordered mesoporous SnO2 materials with a hexagonal mesostructure (space group P63/mmc) and crystalline pore walls can be obtained. The mesoporous SnO2 is employed for fabricating gas sensor nanodevices which exhibit an excellent sensing performance toward H2S with high sensitivity (170, 50 ppm) and superior stability, owing to its high surface area (98 m2/g), well-connected mesopores of ca. 18.0 nm, and high density of active sites in the crystalline pore walls. The chemical mechanism study reveals that both SO2 and SnS2 are generated during the gas sensing process on the SnO2-based sensors.

High-Performance Gas Sensing of CO: Comparative Tests for Semiconducting (SnO2-Based) and for Amperometric Gas Sensors

A comparison of the stability and sensitivity for two different sensor types (semiconductor SnO(2) devices, amperometric electrochemical sensors) has been performed. Sensitivities and drifts in the signal and in the background for various concentrations of CO have been studied for thick-film SnO(2) sensors (Pt and Pd doped) for a period in excess of 8 months. Similar performance data have been recorded for commercial amperometric sensors for a period in excess of 4 years. The two different sensor types investigated here were also compared to the well-known commercial Figaro TGS 822 sensor at similar concentrations. An objective approach for comparing different types of sensors has been developed using the "analytical sensitivity".