Detection Of Gas Molecules Research Articles

High selectivity humidity sensors of functionalized graphite oxide with more epoxy groups

With large amounts of functional groups, graphene oxide (GO) is a promising sensing material for detecting gas molecules. Due to the different binding abilities between different oxygen-containing functional groups and target gas molecules, the selective response of the target gas can be realized through the regulation of functional groups in the GO structure. Herein, a new kind of GO with abundant epoxy groups was prepared by adding water as the activator in the low-temperature stage. The structure, spectral characteristics, and humidity sensitivity were systematically investigated by the XRD, FT-IR, XPS and sensitivity curves. The results showed that epoxy groups in GO structures could be effectively controlled with the addition of activator. Besides, the GO with more epoxy groups exhibited excellent selective sensitivity for humidity. At a 32.8% RH environment, the sensitivity of this kind of GO could reach 40.1%, and the response and recovery curves almost kept the same during five response and recovery cycles.

Highly sensitive toxic gas molecule sensor based on defect-induced silicene

The performance of a silicene-based nanosensor for toxic gas molecules detection is investigated using DFT calculations in terms of sensing configurations, adsorption energies, charge transfer, band gap modulations and density of states. While silicene provides acceptable sensing capability for NO and NO2 molecules, its sensing features should be improved for other toxic gases. The vacancy defect in silicene is considered due to enhancing the adsorption parameters which cause the absorption energies increments more than 3 times for NO, NO2 and CO molecules and 10 times for HCN. Furthermore, non-zero DOS values around Fermi level are obtained during sensing based on defected silicene which introduce the vacancy defected silicene as a highly sensitive sensor for toxic gas molecules.

Effect of Cation Substitution on the Gas-Sensing Performances of Ternary Spinel MCo2O4 (M = Mn, Ni, and Zn) Multishelled Hollow Twin Spheres.

Advanced sensing materials are in high demand for sensitive, real-time, and continuous detection of gas molecules for gas sensors, which have been becoming an effective tool for environmental monitoring and disease diagnosis. Cobalt-containing spinel oxides are promising sensing materials for the gas-sensing reaction owing to their element abundance and remarkable activity. Structural and component properties can be modulated to optimize the sensing performances by substituting Co with other transition metals. Herein, a systematic study of spinel MCo2O4 oxides (M = Mn, Ni, and Zn) toward gas sensing is presented. Results show that ZnCo2O4 materials with a multishelled hollow twin-sphere structure obtained excellent sensing performances to formaldehyde and acetone at different temperatures. The replacement of Co with Zn in the lattice improves the oxygen-chemisorbing ability, which allows new opportunities to synthesize and design highly sensitive chemical sensors.

Adsorption of toxic gas molecules on pristine and transition metal doped hexagonal GaN monolayer: A first-principles study

Using the first-principles calculations based on density functional theory (DFT-D2 method), we systematically study the structural, energetic, electronic and magnetic properties of toxic gas molecules (H2S, NH3 and SO2) adsorbed on pristine and transition metal (TM) atom (Fe, Mn) doped GaN monolayer (GaN-ML). The results show that the H2S and NH3 are physisorbed on pristine GaN-ML with small adsorption energy, charge transfer, and long adsorption distance. While chemical adsorption character of SO2 on GaN-ML can be obtained, which means that the pristine GaN-ML is sensitive to SO2. We find that the adsorption ability of pristine GaN-ML can be improved by introducing TM dopants. TM (Fe, Mn) doping can increase adsorption energy and charge transfer of the adsorbed systems, except for SO2 adsorbed Fe doped GaN-ML. The enhancing interaction between adsorbed molecules and the TM doped GaN-ML can dramatically induce electrical conductivity changes. Therefore, the TM doped GaN-ML is more suitable for gas molecules detection compared with the pristine GaN-ML. These present properties of gas molecules adsorbed on the pristine and TM doped GaN-ML will help to guide scientists to develop better two-dimensional GaN-based gas sensors in the future.

A carrier velocity model for electrical detection of gas molecules.

Nanomaterial-based sensors with high sensitivity, fast response and recovery time, large detection range, and high chemical stability are in immense demand for the detection of hazardous gas molecules. Graphene nanoribbons (GNRs) which have exceptional electrical, physical, and chemical properties can fulfil all of these requirements. The detection of gas molecules using gas sensors, particularly in medical diagnostics and safety applications, is receiving particularly high demand. GNRs exhibit remarkable changes in their electrical characteristics when exposed to different gases through molecular adsorption. In this paper, the adsorption effects of the target gas molecules (CO and NO) on the electrical properties of the armchair graphene nanoribbon (AGNR)-based sensor are analytically modelled. Thus, the energy dispersion relation of AGNR is developed considering the molecular adsorption effect using a tight binding (TB) method. The carrier velocity is calculated based on the density of states (DOS) and carrier concentration (n) to obtain I–V characteristics and to monitor its variation in the presence of the gas molecules. Furthermore, the I–V characteristics and energy band structure of the AGNR sensor are simulated using first principle calculations to investigate the gas adsorption effects on these properties. To ensure the accuracy of the proposed model, the I–V characteristics of the AGNR sensor that are simulated based both on the proposed model and first principles calculations are compared, and an acceptable agreement is achieved.

Design Guidelines for High Sensitivity ZnO Nanowire Gas Sensors With Schottky Contact

Zinc oxide nanowire (ZnO NW) gas sensor with single Schottky contact is capable of sensitive detection of gas molecules. In this paper, we investigate the effect of design factors, such as NW defect density, diameter, and length, on the gas sensitivity using the 3-D numerical simulation. The sensor with lower defect density or smaller NW diameter exhibits improved gas sensitivity, while length does not have an impact when not considering the external environment, such as background gases and binding probability. Lower defect density causes low electron density within the NW in air environment, and the change in electron density due to gas adsorption is intensified, thus improving gas sensitivity. As the NW diameter decreases, the change in the electrical conductivity due to gas molecules is greatly increased due to an increase in the ratio of the depletion area to the entire NW area. In contrast, the NW length does not impact the gas sensitivity because the change in the electron density due to the gas molecule adsorption is independent of the length. These results are helpful to understand the sensing mechanism and provide design guidelines to maximize the sensitivity.

Atomistic mechanism for graphene based gaseous sensor working

Graphene based gaseous sensor has been shown experimentally to have high potential for detecting gas molecules by measuring the conductance change as induced by the adsorbed molecules on graphene. Currently, there is no atomistic based theoretical model that is able to adequately explain the working of the sensor. Based on a single-atom statistical model, the kinetics of adsorption and desorption of gas molecules on graphene was investigated in the present work, and an atomistic mechanism for the functioning of the sensor is proposed which relies on the change of the conductance when the adsorbed molecules diffuse into the defective sites. This mechanism is in agreement with previous experimental measurements and indicates some possible ways to increase the sensitivity and response speed of the sensor.

Individual Gas Molecules Detection Using Zinc Oxide–Graphene Hybrid Nanosensor: A DFT Study

Surface modification is a reliable method to enhance the sensing properties of pristine graphene by increasing active sites on its surface. Herein, we investigate the interactions of the gas molecules such as NH3, NO, NO2, H2O, and H2S with a zinc oxide (ZnO)–graphene hybrid nanostructure. Using first-principles density functional theory (DFT), the effects of gas adsorption on the electronic and transport properties of the sensor are examined. The computations show that the sensitivity of the pristine graphene to the above gas molecules is considerably improved after hybridization with zinc oxide. The sensor shows low sensitivity to the NH3 and H2O because of the hydrogen-bonding interactions between the gas molecules and the sensor. Owing to observable alterations in the conductance, large charge transfer, and high adsorption energy; the sensor possesses extraordinary potential for NO and NO2 detection. Interestingly, the H2S gas is totally dissociated through the adsorption process, and a large number of electrons are transferred from the molecule to the sensor, resulting in a substantial change in the conductance of the sensor. As a result, the ZnO–graphene nanosensor might be an auspicious catalyst for H2S dissociation. Our findings open new doors for environment and energy research applications at the nanoscale.

(Invited) Suspended Graphene-Based Sensor for Real-Time and Highly Sensitive Monitoring of VOCs

Volatile organic compounds (VOCs) are emitted from solids or liquids with high vapor pressure and are often combustible and toxic, so on site real-time monitoring is vital. Currently photoionization detectors (PIDs) are used for VOC monitoring. PID devices are bulky and expensive to make and operated at high voltage to operate. As such there is a need for more portable and less expensive methods for detecting VOCs. We developed a novel gas sensor for (VOCs) detection. This technology utilizes suspended graphene membranes to provide real-time, ultrasensitive VOC detection. A freestanding graphene film suspended over an array of cavities or trench can offers increased surface area (twice over) and gives a direct method of sensing when VOCs adsorbed at the surface of graphene. Our sensor requires low voltages to operate, immediate response, high sensitivity and a larger theoretical range of detection than photoionization detectors sensors and it is a non-specific as PIDs. In this work, we shall present a 3 mm X 3 mm square chip, fabricated using conventional photolithography, containing an array of two terminal devices. Each individual device consists of a monolayer graphene sheet suspended over multiple cavities and clamped by two metal contacts. Suspended graphene, as opposed to substrate-based graphene, significantly reduces the surface charge hindrances and allows for ultrasensitive detection of gas molecules. The fabricated graphene chip has been successfully tested for toluene vapors. Currently, testing is underway to functionalize graphene for selective detection of different gases.

Adsorption of the Gas Molecules NH3, NO, NO2, and CO on Borophene

Two-dimensional materials can be utilized to detect gas molecules in low concentration due to their high surface-to-volume ratios. In this respect, we investigate in the present work recently fabricated borophene, two-dimensional B, which has buckled and line-defective phases. Both are systematically studied for four gas molecules: NH3, NO, NO2, and CO. In each case, the adsorption energy is found to be high and borophene develops distinct wrinkles. Our results provide a thorough understanding of the interaction between borophene and the gas molecules. An excellent performance of borophene as gas sensor is demonstrated by simulating the material’s transport characteristics by means of the nonequilibrium Green’s function method.

Detection of gas molecules on single Mn adatom adsorbed graphyne: a DFT-D study

As one of the prominent applications in intelligent systems, gas sensing technology has attracted great interest in both industry and academia. In the current study, the pristine graphyne (GY) without and with a single Mn atom is investigated to detect the gas molecules (CO, CH4, CO2, NH3, NO and O2). The pristine GY is promising to detect O2 molecules because of its chemical adsorption on GY with large electron transfer. The great stability of the Mn/GY is found, and the Mn atom prefers to anchor at the alkyne ring as a single atom. Upon single Mn atom anchoring, the sensitivity and selectivity of GY based gas sensors is significantly improved for various molecules, except CH4. The recovery time of the Mn/GY after detecting the gas molecules may help to appraise the detection efficiency for the Mn/GY. The current study will help to understand the mechanism of detecting the gas molecules, and extend the potentially fascinating applications of GY-based materials.

Computational investigation of gas detection and selectivity on TiS3 nanoflakes supported by experimental evidence.

Titanium trisulfide (TiS3), a transition metal chalcogenide, bears the potential to replace silicon, when taking the form of nanoflakes, due to its favorable band gap and optical response. In this paper, we investigate the response of TiS3 nanoflakes to gas detection through a careful quantum computational approach and a few succinct measurements. The computations are benchmarked and compared with a relevant experiment at each step, where their results/conclusions are discussed. The most stable surface of TiS3 particles is determined as (001), in agreement with the literature. The adsorption of 5 gas molecules is characterized through formulating and estimating their adsorption intensity values, rather than using singled-out values of binding energies. This formulation, which is rooted in a statistical view of the gas adsorption process, distinguishes H2 and CH4 molecules from H2O and O2 explicitly and unambiguously through comparing their adsorption profiles. The difference in the adsorption intensities thus predicts and elucidates the difference in the sensing behaviour of TiS3 particles. This work suggests that the computationally obtained profile for the adsorption spectrum of gas molecules serves as a tool/criterion to predict the selectivity of their detection by TiS3.

First-principles study of gas adsorption on γ-graphyne

Inspired by recent successes in the development of graphene-based gas sensors capable of single gas molecule detection, we investigate the adsorption of gas molecules (NO, NO2, NH3, CO, SO2 and H2S) on γ-graphyne which has an energy gap of 0.49 eV via first-principle calculations. The results show that the adsorption of NO (or NO2) at an adsorption density of above 2% (or 4%) can change the graphyne from semiconductor to semimetal or metal, while the other molecules have little effect on the energy gap, suggesting that γ-graphyne can be used as sensitive sensor for selectively detecting NO2 or NO molecules.

A flexible, transparent and high-performance gas sensor based on layer-materials for wearable technology

Gas sensors play a vital role among a wide range of practical applications. Recently, propelled by the development of layered materials, gas sensors have gained much progress. However, the high operation temperature has restricted their further application. Herein, via a facile pulsed laser deposition (PLD) method, we demonstrate a flexible, transparent and high-performance gas sensor made of highly-crystalline indium selenide (In2Se3) film. Under UV–vis-NIR light or even solar energy activation, the constructed gas sensors exhibit superior properties for detecting acetylene (C2H2) gas at room temperature. We attribute these properties to the photo-induced charger transfer mechanism upon C2H2 molecule adsorption. Moreover, no apparent degradation in the device properties is observed even after 100 bending cycles. In addition, we can also fabricate this device on rigid substrates, which is also capable to detect gas molecules at room temperature. These results unambiguously distinguish In2Se3 as a new candidate for future application in monitoring C2H2 gas at room temperature and open up new opportunities for developing next generation full-spectrum activated gas sensors.

Fabricating a QCM Device with the Nanostructures Using the AAO Template

Quartz Crystal Microbalance (QCM) method is one of promising approach to detect gas molecules and bio materials since it has advantages in real time measurement, high sensitivity, and portability. However, the method shows poor sensitivity to low molecular weight materials because of its measuring principle, mass change. To improve the sensitivity to the low molecular weight materials, we introduce to fabricate nano structures on the quartz crystal. As the results, the surface area derived from nano stractures to bind with analytes is greatly improved. Anodizing Aluminiun Oxide (AAO) is known as a one of attractive functional materials which has self assembled nano structure provided by anodizing highly-pure Aluminium in the acid solutions, for examples, oxalic acid and sulfuric acid. The nano structure of AAO is controllable by the anodizing condition such as voltage, anodizing time, and the acid solutions. Then, we can get the regularly arranged pores with high aspect ratio. Our nano structures on the quartz crystal were referred from the AAO nano structure. Figure 1 shows the nanowires array composed of Au. The nanowires were fabricated on a SiO2 substrate. The shape of the nanowire was evaluated by Scanning electron microscopy (SEM). Average of the height and the diameter of the nanowire was 1 μm and 70 nm, respectively. As the results, we could get the aspect ratio more than 14. In fact, large surface area was achieved on the quartz crystal. By using our process, nanowire positions would be arranged in three angles lattice. This manufacture procedure to fabricate Au nanowire arrays used electrical plating, so it enables to fabricate arbitrary nanowire arrays to suit someone’s measurement needs by changing the plating solution. To detect antigen-antibody reaction, we manufactured Au nanowires that have a high affinity with protein and the cell because of thiol linkage. Our fabricating process was written below. Ti/Au/Al (30/100/1000 nm thick, respectively) was sputtered on the SiO2 substrate by using a DC magnetron sputtering equipment. AAO was obtained by anodizing the Al thin film with Pt plate (cathode) with applied voltage of 40 V in 0.3 M oxalic acid. Then, the sample was immersed in 0.3 M phosphoric acid to expand pores size and to remove the barrier layer which was located on the AAO bottom. The sample was electrodeposited at constant current of 0.004 mA/mm2 using Au plating solutions. Finally, regularly arranged nanowires were obtained by removing AAO in 1 M phosphoric acid. By this manufacture procedure, we fabricated nanowires structure on the sensor electrode and tried to detect the antigen-antibody reaction using the QCM method which had nano structures on the quartz crystal. In the conference, we will show the result about the comparison measurement. Figure 1

Nano-structured interface of graphene and h-BN for sensing applications

The atomically-precise controlled synthesis of graphene stripes embedded in hexagonal boron nitride opens up new possibilities for the construction of nanodevices with applications in sensing. Here, we explore properties related to the electronic structure and quantum transport of a graphene nanoroad embedded in hexagonal boron nitride, using a combination of density functional theory and the non-equilibrium Green's functions method to calculate the electric conductance. We find that the graphene nanoribbon signature is preserved in the transmission spectra and that the local current is mainly confined to the graphene domain. When a properly sized nanopore is created in the graphene part of the system, the electronic current becomes restricted to a carbon chain running along the border with hexagonal boron nitride. This circumstance could allow the hypothetical nanodevice to become highly sensitive to the electronic nature of molecules passing through the nanopore, thus opening up ways to detect gas molecules, amino acids, or even DNA sequences based on a measurement of the real-time conductance modulation in the graphene nanoroad.

Highly sensitive and portable gas sensing system based on reduced graphene oxide

Graphene has been widely used in gas-sensing applications due to its large specific surface area and strong adsorption ability. Among different forms of graphene used as gas-sensing materials, reduced graphene oxide is one of the most convenient and economical materials to integrate with Si-based electronics, which is very important to graphene-based gas sensors. In addition, the stacking structure of graphene oxide flakes facilitates absorption and detection of gas molecules. Based on reduced graphene oxide, a highly sensitive and portable gas-sensing system was demonstrated here. Solution-based graphene oxide was cast on a chip like a TF memory card and then reduced thermally. A signal acquisition system was designed to monitor resistance variation as a sign of gas concentration. This miniature graphene-based gas sensor array demonstrates a new path for the use of graphene in gas-detection technologies. And the creation of a sensitive and portable graphene gas sensor also shows great potential in fields such as medicine and environmental science.

The small molecule optical probes for gases with potential medical applications

Various gas molecules exist in the life systems. According to their functions, they can be divided into: signaling gas molecules (gasotransmitters) and non-signaling gas molecules. Similar to the gasotransmitters, the non-signaling gas molecules are of great potential and can be valuable in medical applications, such as serving as specific index for disease status and treating medical conditions. Since their distributions and concentrations are closely related to the health status, selective detection and imaging of these gas molecules is very important. Electrochemistry and mass spectroscopy are traditional methods to detect such gas molecules. However, these methods need expensive instruments and complicated data processing. Recently, optical probes have been emerged as important tools in detecting gas molecules with simple operations. The current review focuses on the recent development on the optical probes for the non-signaling gas molecules.

Gas Sensing on Oxidized Bronze

We perform oxidation and phase segregation of bronze (an alloy of Cu: Sn = 95: 5) and demonstrate that the heterogeneous oxide formed is suitable for oxygen sensing. Tin oxide (SnO2) is an n-type semiconductor whereas, cupric oxide (CuO) is a p-type semiconductor. Both oxides have shown sensitivity to detecting gas molecules. Therefore, the presence of both n and p-type oxide on the same substrate can lead to a sensory platform with a wide array of gas sensing capabilities. Thermally oxidized bronze forms a CuO layer on top, underneath which exists a mixed, CuO-SnO2 layer. It is found that Sn segregates to the grain boundaries whereas Cu exists mostly on grain surfaces. This happens due to the differences in the diffusion constants of the Cu and Sn atoms. Further, the oxidation process creates a variety of nanostructures including CuO nanowires and SnO2 plates. Supporting characterization data is provided via SEM, HRTEM, Raman and x-ray diffraction. The oxidized samples are then prepared as conductometric sensors for testing various gasses. As an example, on the introduction of dry air into a vacuum chamber (maintained at 2 mTorr), the devices showed a 10% resistance change at 400 K and a 6% resistance change at 373 K. This indicates that facile thermal oxidation of low-cost alloy substrates can lead to the formation of effective, ‘on-skin’ sensors.

Broadband and tunable optical parametric generator for remote detection of gas molecules in the short and mid-infrared.

The development of a novel broadband and tunable optical parametric generator (OPG) is presented. The OPG properties are studied numerically and experimentally in order to optimize the generator's use in a broadband spectroscopic LIDAR operating in the short and mid-infrared. This paper discusses trade-offs to be made on the properties of the pump, crystal, and seeding signal in order to optimize the pulse spectral density and divergence while enabling energy scaling. A seed with a large spectral bandwidth is shown to enhance the pulse-to-pulse stability and optimize the pulse spectral density. A numerical model shows excellent agreement with output power measurements; the model predicts that a pump having a large number of longitudinal modes improves conversion efficiency and pulse stability.