CH4 Gas Sensor Research Articles

High Sensitivity CH4 and CO2 Gas Sensor Using Fiber Bragg Grating Coated with Single Layer Graphene

This article outlines the development of a Fiber Bragg Grating (FBG) intended for use as a sensor for CH4 and CO2 gases. Following fabrication, the FBG was effectively treated with a layer of Graphene Material through a modified RF Sputtering process. This coating procedure involved introducing argon gas into the chamber and subjecting the FBG, securely held by two vacuum stages, to a temperature range of 27°C to 600°C by adjusting the power supplied to the cathode and anode, ranging from 0 to 125 Watts. Subsequently, the FBG was employed as a key sensing element within an experimental setup aimed at measuring gas concentrations within a confined space. The assessment involved analyzing the reflected signal of the FBG using an Optical Interrogator System, which demonstrated a shift in the Bragg wavelength of the reflected signal corresponding to varying gas concentrations. This study indicates promising outcomes for the Graphene-coated FBG as a gas sensor. The sensor’s sensitivity was evaluated based on the Bragg wavelength shift resulting from gas presence within the chamber. The Graphene-coated FBG exhibited sensitivities of 3.3 ppm for CH4 and 3.7 ppm for CO2, surpassing those reported in prior research efforts.

UV-activated CH4 gas sensor based on Pd@Ni/ZnO microspheres

Developing methane (CH4) gas sensors with low working temperatures and high response has garnered substantial interest in reliably monitoring CH4 and achieving intrinsic safety. In this work, we combined photo-activation with bimetallic doping to explore CH4-sensing performance. ZnO, Pt/ZnO, and Pt@Ni/ZnO composites with different contents of Pt@Ni were synthesized. Their morphology, structure, and optical properties were characterized using various techniques. Subsequently, their CH4 sensing performance was systematically evaluated under ultraviolet (UV) illumination. The results show that the sensor based on 3Pt@Ni/ZnO composite demonstrated superior CH4 sensing performance among all sensors under UV illumination, presenting a low working temperature of 60 °C, a high response (904.04), which is approximately 60 times higher than pure ZnO (14.97) toward 5000 ppm CH4, and good response and recovery times of 4/174 s. The improved gas-sensing mechanism of the 3Pt@Ni/ZnO sensor was discussed and ascribed to the UV illumination, the synergistic effect of the bimetallic Pt@Ni, and the hollow structure of the ZnO. This study provides a promising gas-sensing material for CH4 detection at a low temperature assisted with UV illumination.

NiO/ZnO heterojunction microspheres for methane detection at room temperature

Low working temperature CH4 gas sensors are necessary to explore to obtain intrinsic safety. In this work, NiO/ZnO microspheres were synthesized through facile hydrothermal methods and the strategy of photo-activation was used to develop room-temperature CH4 gas sensors. The characterizations of as-prepared samples were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence spectra, and electrochemical impedance spectroscopy. The results indicated that NiO/ZnO is a microsphere structure assembled with porous nanosheets. NiO/ZnO composite had good optical properties to use light energy. The methane gas-sensing performances were systematically investigated at room temperature. It shows that the prepared sensors exhibit good CH4 gas sensing performances at room temperature under UV illumination. NiO/ZnO microspheres exhibited enhanced response values. In particular, NiO/ZnO-2 sensor exhibited the highest response (8.61–5000 ppm CH4), which is 3.42 times of pure ZnO, low detection limit, good selectivity, and repeatability under UV light. The excellent gas sensing performances may be related to the UV light and the formation of heterojunction, which widens the depletion layer and increases the amount of valid carriers. This work gives a sight to explore photo-activated CH4 gas sensors.

DFT study of sensing properties of defected and transition-metal doped V2CF2 towards CH4

As a new type of gas sensor, MXenes material is of great significance in indoor harmful gas detection. The geometric, electronic, and magnetic properties of CH4 adsorbed on intact, F-vacancy defected, and transition-metal (TMs: Mn, Co, Ni, Zn, Nb, Mo) doped V2CF2 have been investigated based on density functional theory. Perfect V2CF2 and F-vacancy defected substrates exhibited low charge transfer, long adsorption distance, and small adsorption energy for CH4. The adsorption mechanism was physical adsorption. After introducing Co and Ni dopants, the adsorption mechanism of CH4 changed to be chemisorption. Additionally, the asymmetric electron spin distribution between the dopant and V atom caused the substrate to change from being non-magnetic to magnetic, as shown by the electronic density of states diagrams. The hybridization between TM-3d orbitals and the p orbitals of the CH4 molecule significantly improved the adsorption stability. It is hoped that the results could provide ideas for creating new CH4 gas sensors based on MXenes.

High precision and sensitivity detection of gas measurement by laser wavelength modulation spectroscopy implementing an optical fringe noise suppression method

In this work, a novel method to suppress optical fringe noise in the tunable diode laser absorption spectroscopy is proposed and applied to the CH4 gas sensor perturbed by optical fringes for higher detection precision and sensitivity. For the 2nd harmonic(2f) signal of 20 ppm CH4 spoiled by optical fringes and random noise, by the novel method, the signal-to-noise ratio (SNR) of the 2f signal is improved about 6.5 times from 17 to 182 with an optimal averaging spectral range Δλ. A ∼1.5 times improvement in the measurement precision of CH4 is achieved compared to unprocessed raw signal. The corresponding minimum detectable concentration can be improved from 3 ppb down to 0.78 ppb. The corresponding noise equivalent absorption sensitivity (NNEA) and the noise equivalent concentration (NEC) of the system is 6.13×10−11 cm−1 W Hz−1/2 and 0.181 ppm, respectively.

ZnO/Pd Encapsulated Within a Zeolitic Imidazolate Framework-7 Shell as a Sensitive and Selective Methane Sensor

Highly sensitive and selective methane (CH4) gas detection is a critical challenge in complex practical scenarios. Herein, this work presents an excellent CH4 gas sensor based on ZnO/Pd nanorods encapsulated in a zeolitic imidazolate framework (ZIF)-7 shell. Compared with the ZnO/Pd sensor, the ZnO/Pd@ZIF-7 sensor exhibited a faster response/recovery time (2.3/8.3 s) and higher response (668.5%) toward 5000 ppm of CH4 gas at 180 °C. Furthermore, a 22-fold higher selectivity to CH4 against ethanol (C2H5OH) was observed. The improved sensitivity and selectivity of the ZnO/Pd@ZIF-7 sensor are attributed to the dual roles played by the ZIF-7 shell; first, it generates more chemisorbed oxygen on the ZnO surface while improving the catalytic activity of Pd, and it facilitates the catalytic oxidation of CH4 and ultimately improves the sensitivity. Moreover, the ZIF-7 shell has filtering effects, which significantly reduces the response of interfering gases and exhibits excellent CH4 selectivity. This paper explores the strategy of combining a dual-functional ZIF-7 shell with ZnO/Pd, proposing a gas sensor design concept that broadens the application of metal–organic framework materials for CH4 detection.

Adsorption and Gas-Sensing Properties of Agn (n = 1-4) Cluster Doped GeSe for CH4 and CO Gases in Oil-Immersed Transformer.

The adsorption mechanism of CO and CH4 on GeSe, modified with the most stable 1-4 Ag-atom clusters, is studied with the help of density functional theory. Adsorption distance, adsorption energy, total density of states (TDOS), projected density of states (PDOS), and molecular orbital theory were all used to analyze the results. CO was found to chemisorb exothermically on GeSe, independent of Ag cluster size, with Ag4-GeSe representing the optimum choice for CO gas sensors. CH4, in contrast, was found to chemisorb on Ag-GeSe and Ag2-GeSe and to physisorb on Ag3-GeSe and Ag4-GeSe. Here, Ag GeSe was found to be the optimum choice for CH4 gas sensors. Overall, our calculations suggest that GeSe modified by Ag clusters of different sizes could be used to advantage to detect CO and CH4 gas in ambient air.

Zinc oxide nanoclusters and their potential application as CH4 and CO2 gas sensors: Insight from DFT and TD-DFT.

We have investigated the adsorption of CH4 and CO2 gases on zinc oxide nanoclusters (ZnO NCs) using density functional theory (DFT). It was found that the CH4 tends to be physically adsorbed on the surface of all the ZnO NCs with adsorption energy in the range -11 to -14 kcal/mol. Even though, the CO2 is favorably chemisorbed on the Zn12 O12 and Zn15 O15 NCs, with adsorption energy about -38 kcal/mol at B3LYP/6-311G(d,p) level of theory. When the CH4 and CO2 gases are adsorbed on the ZnO NCs, their electrical conductivities are decreased, and thus the studied ZnO NCs do not generate an electrical signal in the presence of CH4 and CO2 gases. Interestingly, both pure and gas adsorbed Zn22 O22 NC exhibited more favorable electronic and reactive properties than other NCs. Comparison of the structural, electronic, and optical data predicted by DFT/B3LYP and TD-DFT/CAM-B3LYP calculations with those experimentally obtained show good agreement.

Ba-Modified ZnO Nanorods Loaded with Palladium for Highly Sensitive and Rapid Detection of Methane at Low Temperatures

Exploring novel sensing materials to rapidly identify CH4 at low temperatures is crucial for various practical applications. Herein, a novel ZnO-xBa/Pd with Ba of cocatalyst loading from 0 to 2.0 wt% was facilely prepared using a two-step impregnation method to improve the sensitivity of the CH4 gas sensor. The microstructure, chemical states of the elements, and surface properties of ZnO-Ba/Pd were characterized, and the gas-sensitive performance of ZnO-Ba/Pd sensors was investigated. Compared to methane sensors based on other inorganic and organic material sensors, the sensor based on ZnO-1.0Ba/Pd exhibited a faster response/recovery time (1.4 s/8.3 s) and higher response (368.2%) for 5000 ppm CH4 at a lower temperature (170 °C). Moreover, the ZnO-1.0Ba/Pd sensor exhibited full reversibility and long-term stability, as well as excellent selectivity at 170 °C. The excellent performance of the ZnO-Ba/Pd sensor was attributed to the electron donation by Ba, which increases the electron density around Pd, thus enhancing the catalytic activity of Pd and promoting oxygen adsorption on the ZnO surface. The present work provides a method for the rational design and synthesis of sensitive materials in practical CH4 detection.

Fabrication of TiO2 nanofibers based sensors for enhanced CH4 performance induced by notable surface area and acid treatment

We report on the notable surface area and gas sensing properties of TiO2 nanofibers synthesized following a microwave assisted hydrothermal method followed by washing with various concentrations of Hydrochloric acid (HCl) and distilled water (DW). The sample washed with DW only had narrow nanofibers in diameter. Structural analyses showed that the TiO2 nanofibers were made of 55% of the anatase phase, while the 45% was associated to the rutile phase. Moreover, at higher HCl concentration, an increased crystallite size and nanofibers diameter were observed from the X-ray diffraction and scanning electron microscopy analyses, respectively. A remarkable increase in surface area of 1375.238 m2/g was observed with a change in morphology from nanoparticles to nanofibers (i.e. the sample washed with 1.0 M HCl). The gas sensing properties, such as response, sensitivity and selectivity were tested towards CH4, NH3, CO and NO2 gases at different operating temperatures. The TiO2 nanofibers washed with 1.0 M HCl presented higher selectivity and sensitivity (0.62 ppm−1) towards CH4 gas at 23 °C. This was attributed to the exceptionally high surface area and crystallinity provided by the one dimensional nanofibers. The improved sensitivity and selectivity at room temperature for the 1.0 M HCl treated sample suggested that it could be applied as a low-power consumption CH4 gas sensor. The gas sensing mechanism is also discussed in detail.

High response methane sensor based on Au-modified hierarchical porous nanosheets-assembled ZnO microspheres

Detecting methane (CH4) gas is very important owing to its widely use as a fossil fuel with an explosive hazard in modern society. In this study, a CH4 gas sensor was prepared, which is based on hierarchical porous nanosheets-assembled Au/ZnO microspheres with diameters of 10–12 μm. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the textural properties and morphology of the nanocomposites. In addition, the gas sensing properties of the sensors basedon pure ZnO and Au/ZnO nanomaterials were systematically investigated. By modifier Au nanoparticles, the characteristics of ZnO based sensor for CH4 detection were significantly enhanced. Especially, the Au/ZnO based sensor with an Au content of 1.0 at.% exhibited the best sensing performances (4.16) of 100 ppm CH4 at 250 °C. Furthermore the sensor also exhibited a good linear relation (10–2000 ppm CH4 concentration), excellent repeatability, satisfactory stability and a low detection limit of detection (1.83 ppm). The possible enhanced sensing mechanism could be attributed to the synergism between the unique hierarchical porous nanosheets-assembled microspheres structure and the sensitizing actions utilized by the Au nanoparticles.

Nitrogen-doped Diamond Nanowire Gas Sensor for the Detection of Methane

Diamond-based sensors have shown great potential in the past few years due to their unique physicochemical properties. We report on the development of high-performance nitrogen-doped ultrananocrystalline diamond (UNCD) nanowire-based methane (CH4) gas sensors, taking advantage of a large surface-to-volume ratio and a small active area offered by the 1D nanowire geometry. The morphologic surface and crystalline structures of UNCD are also characterized by using scanning electron microscopy (SEM) and Raman scattering, respectively. By using synthesized nanowire arrays combined with 4-pin electrical electrodes, prototypic highly sensitive CH4 gas sensors have been designed, fabricated and tested. Various parameters including the sensitivity, response and recovery times, and thermal effect on the performance of the gas sensor have also been investigated in order to quantitate the sensing ability. Enhanced by the small grain size and porosity of the nanowire structure, fabricated nanowire UNCD sensors demonstrated a high sensitivity to CH4 gas at room temperature down to 2 ppm, as well as fast response and recovery times which are almost 10 times faster than that of regular nanodiamond thin film based sensors.

Construction of novel Pd–SnO2 composite nanoporous structure as a high-response sensor for methane gas

The reasonable design of the semiconducting metal oxides modified by noble metal element compositing and the ingenious construct of the particular microstructure have been proved to be an effective method to promote the gas sensing capability of chemiresistor-type sensors. Herein, Pd–SnO2 composite nanoporous structure is fabricated by a controllable and low-power hydrothermal method. A novel weak acid glucose-assisted growth method is proposed to promote the formation of nanoporous structure. Under weak acidic environment, the complete hydrolysis of precursor (SnCl4·5H2O), leading to nanocrystallines hard to grow and create a large number of small nanoparticles with an average crystallite size of ∼10 nm, which assemble to form interstitial holes between nanoparticles. The experimental results reveal that the Pd–SnO2 composite nanoporous structure exhibits prominent methane (CH4) gas sensing performances as compared with pure SnO2 nanoparticles. Especially, 2.5 mol% Pd–SnO2 composite nanoporous structure based on sensor shows an ultra-fast response of 17.60 at 3000 ppm within 3 s to reach a stable-state and fast recovers within 5 s at an operating temperature of 340 °C, it has barely been reported that the sensor based on CH4 gas presented such excellent performances. And more importantly, the sensor based on 2.5 mol% Pd–SnO2 composite nanoporous structure also possesses high repeatability and long-term stability. These results are due to the fact that the unique nanoporous structures of composite and the chemical sensitization and electronic sensitization of Pd, which provide an effective strategy to achieve eminent gas-sensing performances of CH4 gas sensors.

Investigation on CH4 sensing characteristics of hierarchical V2O5 nanoflowers operated at relatively low temperature using chemiresistive approach

Methane (CH4) gas, the second most potent greenhouse gas share a substantial role in contributing to the global warming and it is a necessary pre-requisite to detect the release of CH4 into the environment at its early stage to combat climate change. In that front, this work is focussed to develop an effective CH4 gas sensor using vanadium pentoxide (V2O5) thin films that works at an operating temperature of ∼100 °C. To understand the effect of sputtering power towards the structural characteristics of V2O5 films, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) analysis were performed from which the orthorhombic polycrystalline structure of V2O5 thin films was confirmed with varied texture co-efficient. Further, the surface elemental studies using X-ray photoelectron spectroscopy (XPS) confirmed the prominence of V+5 oxidation state from the binding energy of V2p3/2 and O1s peak. The effect of sputtering power on the growth of different nanostructures were observed using field-emission scanning electron microscopy (FE-SEM). The critical role of adsorption and desorption kinetics of the deposited nanostructures were explained through first order kinetics based on Elovich model and the phase stability of different nanostructures were evaluated using Raman spectral analysis. This work achieved the sensor response of about ∼8% towards CH4 at an operating temperature of 100 °C towards 50 ppm concentration.

RETRACTED: Atomic layer deposition of Rh nanoparticles on WO3 thin film for CH4 gas sensing with enhanced detection characteristics

Abstract CH4 gas sensor was fabricated by depositing WO3 film (200 nm) on a ceramic substrate through E-beam evaporation, followed by depositing Rh nanoparticles on WO3 through Atomic Layer Deposition (ALD). The amount of Rh nanoparticles was regulated by ALD cycles. The TEM characterization showed that Rh nanoparticles were homogeneously distributed on WO3 thin film, and the XPS investigation indicated the interactions between Rh nanoparticles and WO3 thin film. The gas-sensing performance testing showed that, when the Rh ALD deposition cycle is 20, the sample showed the highest selectivity, which is increased by~110% compared with pure WO3, which could be attributed to the surface catalytic effect contributed by Rh nanoparticles, while over high concentration of Rh could be harmful to the gas sensing performance, which blocks the active sites on the surface of WO3 thin film. The sensing stability of WO3/Rh composite (with ALD cycle of 20) was further investigated by exposing the sensor in CH4 gas environment for one week.

Co-Evaporated CuO-Doped In2O3 1D-Nanostructure for Reversible CH4 Detection at Low Temperatures: Structural Phase Change and Properties

In order to improve the sensitivity and to reduce the working temperature of the CH4 gas sensor, a novel 1D nanostructure of CuO-doped In2O3 was synthesized by the co-evaporation of Cu and In granules. The samples were prepared with changing the weight ratio between Cu and In. Morphology, structure, and gas sensing properties of the prepared films were characterized. The planned operating temperatures for the fabricated sensors are 50–200 °C, where the ability to detect CH4 at low temperatures is rarely reported. For low Cu content, the fabricated sensors based on CuO-doped In2O3 showed very good sensing performance at low operating temperatures. The detection of CH4 at these low temperatures exhibits the potential of the present sensors compared to the reported in the literature. The fabricated sensors showed also good reversibility toward the CH4 gas. However, the sensor fabricated of CuO-mixed In2O3 with a ratio of 1:1 did not show any response toward CH4. In other words, the mixed-phase of p- and n-type of CuO and In2O3 materials with a ratio of 1:1 is not recommended for fabricating sensors for reducing gas, such as CH4. The gas sensing mechanism was described in terms of the incorporation of Cu in the In2O3 matrix and the formation of CuO and In2O3 phases.

Highly selective and sensitive CH4 gas sensors based on flame-spray-made Cr-doped SnO2 particulate films

In this research, flame-spray-made 0–2 wt% Cr-doped SnO2 nanoparticles were synthesized and methodically studied for specific detection of methane (CH4) for the first time. From characterizations using X-ray diffraction, X-ray photoelectron spectroscopy, scanning/transmission electron microscopy and nitrogen adsorption, Cr was found to form substitutional solid solution in 5–20 nm nanoparticles with tetragonal SnO2 structure. In addition, grain and particle sizes decreased while surface area increases considerably with increasing Cr content. The sensing films prepared by spin coating technique were evaluated towards various flammable and toxic gases in dry air at 200–400 °C. Gas–sensing data evidently showed that the SnO2layer with the optimum Cr-doping level of 0.5 wt% offered a remarkable response of ˜1268 with a decent response time of ˜3.9 s to 1 vol% CH4at the optimum working temperature of 350 °C. In addition, the optimal Cr-doped SnO2sensor gave high CH4 selectivity against H2, C2H2, NO2, NO, N2O, CO, NH3, SO2, C2H5OH, C3H6O and H2O. Therefore, the flame-spray-made Cr-doped SnO2material is an attractive choice for selective and sensitive detection of CH4.

Theoretical investigation of the sensing mechanism of the pure graphene and AL,B,N,P doped mono-vacancy graphene-based methane

The interaction of CH4 gas molecule on pure graphene and Al, B, N, P doped mono-vacancy graphene by using the density functional theory (DFT) to explore their potential applications as gas sensors. The results demonstrate that the system of Al doped mono-vacancy graphene is the most stable, and Al-doped mono-vacancy graphene performs the largest adsorption energies upon CH4 with the most appreciable effects on the electronic structures. In addition, the adsorption of CH4 can largely enhance the conductivity of these graphene. In summary, we believe that the Al-doped mono-vacancy graphene could be a promising candidate material for the CH4 gas sensors.

A dispersion-corrected DFT insight into the structural, electronic and CH4 adsorption properties of small tin-oxide clusters

The main goal of this paper is to investigate the structural and electronic properties of small tin-oxide clusters, SnxOy (x = 2–6), before and after methane (CH4) physisorption. To this end, we employ the dispersion-corrected density functional theory (DFT-D2). At first, we demonstrate the relative binding stability of SnxOy clusters with a fixed number of tin atoms via analysis of their binding energy per atom and second-order energy differences. Our results show that the highest relative stability occurs at y = 2, y = 3, y = 4, y = 6 and y = 8 for Sn2Oy, Sn3Oy, Sn4Oy, Sn5Oy and Sn6Oy clusters, respectively. Furthermore, with the cluster size increasing, the ring-shape to cube-like structural crossover is occurred. The higher average coordination and total number of bonds in cube-like clusters make their interatomic bonds weaker and longer. On the other hand, the cube-like clusters, in comparison with ring-shape ones, possess higher chemical potential and lower chemical hardness that lead to their more chemical reactivity. We then proceed to study the CH4 adsorption properties of the resulted most stable clusters. The lowest-energy structures of CH4-adsorbed clusters have been found by comparing the adsorption energy of different configurations. It is found that Van der Waals interactions lead to exothermic physisorption of CH4 on each tin-oxide cluster with the adsorption energy ranging from −101 to −191 meV. In addition, upon CH4 adsorption on SnxOy clusters, the energy gap is decreased which shows an enhancement in the conductivity of the clusters. As a result, the CH4 physisorption ability of these small studied tin-oxide clusters provides their application feasibility as the low-temperature CH4 gas sensors.

Synthesis and characterization of hybrid nanocomposites as highly-efficient conducting CH4 gas sensor

Functionalized (MWCNTs-COOH), non-functionalized multiwalled carbon nanotubes (MWCNTs) and polyaniline (PANI) based conducting nanocomposites (PANI/polymer/MWCNTs and PANI/polymer/MWCNTs-COOH) have been prepared in polymer matrix. The prepared nanocomposites were characterized via FTIR, TGA, Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was observed that the prepared conducting nanocomposites show excellent sensing performances toward CH4 at room temperature and both the response and recovery time were recorded at around 5s, respectively, at the room. The PANI/polymer/MWCNTs based detector had quicker/shorter response time (<1s), as well as higher sensitivity (3.1%) than that of the PANI/polymer/MWCNTs-COOH based detector. This was attributed to nonconductive -COOH that results in a poor sensitivity of PANI/polymer/MWCNTs-COOH-based prototype. The PANI/polymer/MWCNTs-COOH nanocomposites show almost 10 time higher sensitivity at higher temperature (60°C) than that at room temperature.