Sensitive Gas Detection Research Articles

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.

Functionalized Mo[formula omitted]BX[formula omitted] (X = H, OH, O) MBenes as a promising sensor, capturer and storage material for environmentally toxic gases: A case study of 1T and 2H phase

MBenes analogous to MXenes, exfoliated from the bulk MAB phase (M = transition metal, A = IIIA and IVA group, and B = boron) have appeared as promising two dimensional (2D) materials due to their intriguing properties. Here, we report the 2D 1T-2H-phase of Mo2B with their functionalized derivatives Mo2BX2 (X= H, OH, O) and investigate their structural, electronic, and adsorption behavior of toxic gases using the first-principles calculations. This study finds that pristine and functionalized MBenes have dynamic and thermal stability and possess metallic nature in both phases. Based on adsorption behavior and comparison with other 2D materials, we find that pristine MBenes are a desirable adsorbent for NO2, SO2, and CO2 capture. In contrast, the moderate adsorption energies for functionalized MBenes-NH3 systems reveal good sensitivity for NH3 gas detection in both phases. In particular, 2H-Mo2BH2 has higher CT (−0.11e) and appropriate adsorption energy (−0.30 eV), leads a shorter recovery time. Further, DOS calculations reveal that the electrical conducting behavior of MBenes makes them suitable for NH3 detection with a short recovery time. Our results would provide the first insight into the surface-functionalized effect on the structural and electronic properties of the MBenes, and shed light on the application of MBenes for the sensing and catalyst of typical toxic and greenhouse gases, respectively.

An Indium–Gallium–Zinc–Oxide Layer Decorated With Gold Nanoparticles for Ultrahigh Sensitive Formaldehyde Gas Detection

An interesting formaldehyde (HCHO) gas sensor is fabricated using a sputtered indium–gallium–zinc–oxide (IGZO) layer decorated with gold (Au) nanoparticles (NPs). Based on the use of Au NPs, the efficiently increased surface area to volume ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{A}$ </tex-math></inline-formula> /V) ratio and catalytic reactivity cause the effective enhancement of HCHO gas sensing performance. Experimentally, under 20 ppm HCHO gas, an ultrahigh sensing response of 6855 with a response (recovery) time of 30 s (13 s) is obtained for the fabricated Au NP/IGZO sensor at 225 °C. A lower detectable content of 200 ppb HCHO/air gas at 225 °C is achieved. Furthermore, an improved GM(1, 1) model is used to enhance the prediction ability and meliorate data transmission efficiency within the acceptable reduction error range. This algorithm uses preprocessing to find the starting point of a sensing response and evaluate the influence of noise. This algorithm can efficiently improve the transmission efficiency without increasing the computational complexity. The studied device also displays the advantages of a simple structure, cost-effective production, and suitable application in the internet of things (IoT).

Highly sensitive self-powered ammonia gas detection enabled by a rationally designed PANI/commercial cellulosic paper based triboelectric nanogenerator

The schematic diagram of a PANI/cellulosic paper based eco-friendly triboelectric nanogenerator for self-powered ammonia sensing.

Adsorption of NH3 on Monolayer SiC Doped with Noble Metals: A First-Principles Study

We investigates the effect of noble metals (Ag, Au, and Pt) doped SiC for the adsorption behavior of NH3 gas by using the first-principles method. The influence of NH3 gas and noble metals upon the electronic characteristics of SiC structures are explored. In comparison to the pristine structure, the doped SiC structures reveal significant changes in electronic characteristics, and the adsorption capacity is greatly improved due to incorporation of noble metals. Thus, the sensitivity is enhanced in contrast to the pristine structure. Our results show that the Pt-doped SiC might be a useful candidate for developing sensitive NH3 gas detectors.

First‐principles Study of SO2 and NO Gas Sensors Based on SnTe Monolayer

AbstractThe structural and electronic properties of SnTe monolayer after the adsorption of gas molecules (CH4, CO2, NH3, CO, H2S, NO, SO2, NO2 and Cl2) were investigated by first‐principles calculations based on density functional theory (DFT). The results showed that SO2, NO, NO2 and Cl2 were chemisorbed on SnTe monolayer with strong adsorption energies. In addition, because of the high sensitivity of the adsorption of SO2 and NO gases on SnTe monolayer, the bandgap of the developed system changed significantly, with a reduction of 22.88 % and 71.65 %, respectively. The results indicate that SnTe monolayer has highly sensitive SO2 and NO gas detection capability, especially for NO. And it can act as a disposable gas sensor or metal‐free catalyst for the detection and catalysis of pollution gases, such as NO2 and Cl2.

Recent advances in ZnO nanostructure as a gas-sensing element for an acetone sensor: a short review.

Air pollution is a severe concern globally as it disturbs the health conditions of living beings and the environment because of the discharge of acetone molecules. Metal oxide semiconductor (MOS) nanomaterials are crucial for developing efficient sensors because of their outstanding chemical and physical properties, empowering the inclusive developments in gas sensor productivity. This review presents the ZnO nanostructure state of the art and notable growth, and their structural, morphological, electronic, optical, and acetone-sensing properties. The key parameters, such as response, gas detection limit, sensitivity, reproducibility, response and recovery time, selectivity, and stability of the acetone sensor, have been discussed. Furthermore, gas-sensing mechanism models based on MOS for acetone sensing are reported and discussed. Finally, future possibilities and challenges for MOS (ZnO)-based gas sensors for acetone detection have also been explored.

Macroscopic analysis and design of Si HFGFET gas sensor for sensitive gas detection

In this study, we investigate gas sensing performance of horizontal floating-gate field-effect transistor (HFGFET) gas sensors having different FET channel width and length, and the number and length of FG fingers using both technology computer-aided design (TCAD) device simulation and actual gas sensing measurement. The HFGFET gas sensors have a control-gate (CG) and a FG, which are horizontally interdigitated. An indium oxide (In2O3) film is locally deposited between the CG and FG to be used as a sensing layer. Utilizing a simplified equivalent circuit and electrical characteristics of the HFGFET gas sensors, we define a new parameter G, which represents a magnitude of gas sensitivity. The effect of channel width and length, and the number and length of FG fingers of the HFGFET gas sensors on gas sensitivity is first investigated by TCAD device simulation, and then verified by NO2 and H2S gas sensing measurement.

Preparation and mechanism of high-performance ammonia sensor based on tungsten oxide and zinc oxide composite at room temperature

Based on ZnO and WO3·H2O composite (ZW), a high performance ammonia (NH3) gas sensor was synthesized by hydrothermal method. Compared with WO3·H2O, ZW sensor has good selectivity and sensitivity for NH3 gas detection at room temperature, with fast response/recovery time of 2.4 s/1.2 s, low detection limit of 0.76 ppm, excellent endurance to humidity and good stability for a long time. With smaller size in it, ZW provides more active sites to absorb NH3 molecules. More free oxygens on surface of ZW will react with more NH3 molecules, thus to improve the sensitivity of ZW. Furthermore, the heterojunction structure of ZW compound can enhance resistance modulation at the interface between ZnO and WO3·H2O, which further improves the sensitivity of WO3·H2O for NH3 detection. This study shows the combination of ZnO can significantly improve the performance of NH3 gas sensor based on WO3·H2O at RT.

Pressure calibration- and profile fitting-free spectroscopy technology based on deep neural network for gas sensing

Laser absorption spectroscopy provides an opportunity for online, sensitive, and non-destructive gas detection. The absorption lines or bands are specific to each species; thus, they can be applied to specific recognition. Gas concentrations can be obtained by fitting the measured spectra using a pressure-dependence model. Thus, the accurate values of parameters, such as pressures, line strengths, and line-broadening coefficients, are essential. However, the gas can be identified qualitatively and quantitatively without fitted spectra by an accurate model in this paper. A deep learning assisted spectroscopy technology is proposed in this study and the concentrations are obtained free of pressure calibration- and profile fitting. Rapid CH4 analysis is demonstrated, and the feasibility of the proposed deep neural network (DNN) -based algorithm is verified by the experimental results.

Batch Nanofabrication of Suspended Single 1D Nanoheaters for Ultralow-Power Metal Oxide Semiconductor-Based Gas Sensors.

The demand for power-efficient micro-and nanodevices is increasing rapidly. In this regard, electrothermal nanowire-based heaters are promising solutions for the ultralow-power devices required in IoT applications. Herein, a method is demonstrated for producing a 1D nanoheater by selectively coating a suspended pyrolyzed carbon nanowire backbone with a thin Au resistive heater layer and utilizing it in a portable gas sensor system. This sophisticated nanostructure is developed without complex nanofabrication and nanoscale alignment processes, owing to the suspended architecture and built-in shadow mask. The suspended carbon nanowires, which are batch-fabricated using carbon-microelectromechanical systems technology, maintain their structural and functional integrity in subsequent nanopatterning processes because of their excellent mechanical robustness. The developed nanoheater is used in gas sensors via user-designable localization of the metal oxide semiconductor nanomaterials onto the central region of the nanoheater at the desired temperature. This allows the sensing site to be uniformly heated, enabling reliable and sensitive gas detection. The 1D nanoheater embedded gas sensor can be heated immediately to 250°C at a remarkably low power of 1.6mW, surpassing the performance of state-of-the-art microheater-based gas sensors. The presented technology offers facile 1D nanoheater production and promising pathways for applications in various electrothermal devices.

Tailor-made mesoporous SiO2/Au thin film with a substitutable interface for highly sensitive and selective room-temperature gas detection of VOCs

Trace amounts of volatile organic compounds (VOCs) were detected in Au chip interfaces modified with mesoporous SiO2 nanomaterials by using a surface plasmon resonance (SPR) technique. With Kretchmann-configuration SPR, it was possible to detect interactive and specific signal changes between a SiO2/Au gas-sensor surface and acetone, formaldehyde, and methane gases at room temperature. A dielectric spacing layer on Au was expanded and SPR signals were amplified by the mesoporous SiO2 nanoparticles with a large surface area and surface properties that were easily modified with specific ligands and became highly sensitive to, and selective for, the target gas molecules. A phosphonitrilic chloride trimer (PNCT), a universal self-assembled monolayer (SAM), and post-treatment for simple substitutions of ligands equipped the surfaces of SiO2 nanoparticles with targeted receptors, which resulted in the sensitive and selective detection of acetone to CH3-, formaldehyde to NH2-, and methane to Cl-functional groups. The chips modified with each functional group had a response time of about 2 s for concentrations of each gas that ranged from 0.2 to 3.0 ppm. The sensors modified with the functional groups showed limit of detection (LOD) values of 0.3, 0.6, and 0.5 ppm, respectively, which exceeded the Occupational Safety and Health Administration (OSHA) regulations, and limit of quantification (LOQ) values of 0.9, 1.8, and 1.6 ppm. Relative humidity of 45 ∼ 84 % under ambient air had negligible influence on the baseline signals in this SPR gas-sensing system. These sensors have the potential to monitor VOCs in both environmental and indoor settings.

Chirp modulation improves accuracy and capacity in photoacoustic spectroscopy

Method reduces temperature sensitivity for better trace gas detection

Origin of the High Selectivity of the Pt-Rh Thin-Film H2 Gas Sensor Studied by Operando Ambient-Pressure X-ray Photoelectron Spectroscopy at Working Conditions.

The Pt-Rh thin-film sensors exhibit excellent sensitivity and selectivity for H2 gas detection. Here, we studied the mechanism of highly selective detection of H2 by the Pt-Rh thin-film sensors with ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) measurements at working conditions, which were paralleled with electric resistivity measurements. The elemental composition and chemical state of surface Pt and Rh drastically change depending on the background gas environments, which directly link to the sensor response. It is revealed that surface segregated Pt atoms accelerate dissociative adsorption of H2, resulting in a reduction of the sensor surface and then a decrease of electric resistivity of the film, whereas a thin oxidized Rh layer blocks dissociation of the other reducing agent, that is, NH3. This is supported from the adsorption energetics obtained by the density functional theory (DFT) calculations.

Recycled Bifunctional Heterostructure Material: g-GaN/SnS for Photocatalytic Decomposition of Water and Efficient Detection of NO2.

Recently, the energy crisis and environmental pollution problems have become increasingly severe. There is an urgent need to develop a class of multifunctional materials that can both produce clean energy and detect harmful gases. Herein, we propose a g-GaN/SnS heterostructure and explored its dual-optimal performance in photocatalytic hydrogen production and gas detection. Our results demonstrated that the g-GaN/SnS heterostructure has a suitable type II band alignment and excellent absorption in the visible range, which both indicate its potential application in photocatalysis. Furthermore, when the g-GaN/SnS heterostructure acted as a gas detection material, it was consistently susceptible to NO2 gas molecules, according to charge transfer. Additionally, it has a very suitable material recovery time (∼0.5 h) when used for NO2 detection, illustrating the recyclability of the material. Interestingly, the applied electric field of -0.4 V/Å can greatly increase the absorption coefficient in the visible range to 150% of the original. Also, the applied electric field of 0.6 V/Å can substantially enhance the gas detection sensitivity by 27% compared to the case without the electric field. Thus, the g-GaN/SnS heterostructure we proposed not only has the advantage of being bifunctional but also has the potential to be recycled.

Sensitive mid-infrared photothermal gas detection enhanced by self-heterodyne harmonic amplification of a mode-locked fiber laser probe

In this work, a method of photothermal spectroscopic signal extraction is presented. The refractive index modulation readout is realized in a purely frequency detection-based approach, by demodulating the beatnotes of a mode-locked fiber laser operating at 1.56 µm. A unique and non-complex self-heterodyne harmonic amplification technique is employed, yielding an increase in the limit of detection by a factor of 22. The sensor's performance was evaluated by detecting nitric oxide at 5.26 µm, confirming the feasibility of separating the pump and probe sections of the device. The sensor reached a detection limit of 9.6 parts-per-billion by volume for an integration time of 136 s, with only a 20 cm-long laser-gas molecules interaction path length.

Mechanisms of NO2 Detection in Hybrid Structures Containing Reduced Graphene Oxide: A Review.

The sensitive detection of harmful gases, in particular nitrogen dioxide, is very important for our health and environment protection. Therefore, many papers on sensor materials used for NO2 detection have been published in recent years. Materials based on graphene and reduced graphene oxide deserve special attention, as they exhibit excellent sensor properties compared to the other materials. In this paper, we present the most recent advances in rGO hybrid materials developed for NO2 detection. We discuss their properties and, in particular, the mechanism of their interaction with NO2. We also present current problems occuring in this field.

Palladium doped tungsten oxide nanoparticle nanocomposite for sensitive detection of CO2 and LPG gases

According to the results from paleoclimate data, long-term variations in climate change were affected by the concentration levels of carbon dioxide (CO2), besides the liquid petroleum gases (LPG) as a gas product of petroleum during the refining treatment. Herein, CO2 and LPG sensing device was fabricated by hydrothermally treated WO3 nanoparticles achieving significant responses of 89% and 82% towards CO2 and LPG gases. The synthesis approach was enhanced by incorporating palladium (Pd) with a doping level. The Physico-chemical properties of Pd-doped WO3 specimens with different contents from Pd (0.3, 0.6, 0.9, and 1.2wt.%) were evaluated using various tools such as XRD, FESEM, HRTEM, EDX, TGA, FTIR, Raman spectroscopy, and UV–Vis spectrophotometry. At WO3/(0.9wt.%) Pd, the device demonstrated a tremendous high response rate against the CO2 to be 164%. While the sensitivity of LPG recorded a higher response of 125% with WO3/(0.6wt.%) Pd nanocomposite. The resistance of the two platinum electrode sensors for different gases at different temperatures is used to measure and figure out how the sensors work electrically when exposed to other gases. This research proposes a method for enhancing the sensing performance of nanomaterials based on metal oxides.

Assembly of 2D-MoS2 with graphene layer for highly sensitive and selective gas detection at room temperature

Two-dimensional (2D) graphene has been regarded as a promising gas sensing material operated in room temperature. However, practical use of pure graphene as a gas sensor still faces problems owing to its insufficient sensitivity, selectivity and stability. In the present study, 2D-molybdenum disulfide (2D-MoS2) were successfully assembled with graphene oxide (GO) with the assistance of poly (diallyl dimethylammonium chloride) (PDDA). The intercalation of PDDA and stacking of 2D-MoS2 significantly expand the interlayer spacing of GO from 0.77 nm to 1.44 nm in the GO-PDDA-MoS2 composite. The rGO-PDDA-MoS2 sensing chip could be obtained by in-situ reduction of GO-PDDA-MoS2 pre-coated on an interdigital electrode in hydrazine vapor. The sensor exhibited excellent sensitivity, selectivity and stability for H2S and NO detection with a limit detection as low as 3 ppb and 5 ppb, respectively. The enhanced sensing performance could be ascribed to the increased gas accessibility and specific binding site resulted from the introduction of PDDA and 2D-MoS2. Furthermore, its potential application in the diagnosis of respiratory disease was demonstrated. Exhaled breath (EB) spiked with 50 ppb NO and 15 ppb H2S for simulating EB of asthma patients could be successfully discriminated from the normal EB.

Ultra-high sensitive photoacoustic gas detector based on differential multi-pass cell

We designed and manufactured a set of high-sensitivity photoacoustic (PA) gas detector based on differential multi-pass cell (DMPC) with a chamber volume of only 162 mL, which realized real-time online monitoring of CH4 in the atmosphere. The effective absorption optical path of DMPC reached 4.92 m, which enhanced the PA signal from the two dimensions of optical excitation and acoustic resonance. A 3D-printed muffler was integrated into the detector to eliminate the gas flow noise generated by the pump. A 1651 nm distributed feedback (DFB) laser was used to accomplish the measurement of CH4. The analysis results showed that the minimum detection limit (MDL) of CH4 reached 0.6 ppb with an averaging time of 500 s. In addition, the normalized noise equivalent absorption (NNEA) coefficient was 1.79 × 10−10 cm−1 W/Hz1/2. Continuous flow monitoring of CH4 in the atmosphere was carried out to confirm the reliability and feasibility of the PA system based on DMPC.