Selective Gas Detection Research Articles

Facile formation of nanoporous reduced graphene oxide via epoxy-based negative photoresist laser irradiation for highly sensitive and selective gas detection

This study aims to advance gas sensor technology, particularly focusing on chemiresistive gas sensors known for their simplicity and cost-effectiveness. SU-8, an epoxy-based negative photoresist characterized by the presence of eight epoxy groups, is employed as a precursor to laser-induced graphene. Under CO2 laser irradiation, SU-8 rapidly dissociates, forming a porous graphite-like surface and transforming into reduced graphene oxide (rGO). This rGO exhibits exceptional sensitivity, detecting 20 ppb of NO2 at room temperature (25℃), representing a significant achievement for singular materials. Furthermore, the study demonstrates the scalability of rGO not only as a sensing material but also as a framework through a straightforward deposition process. The deposition of SnO2 on rGO shows remarkable selectivity and sensitivity toward NO2 gas, achieving an ultra-low limit of detection of 26.2 ppt. Subsequent Pd deposition enhances the gas sensor's selectivity for hydrogen gas, highlighting its scalability as a framework for diverse gas sensors beyond NO2. In summary, this study showcases the capability of carbonized SU-8 to detect low-concentration NO2 using a singular material. It underscores the material's potential as a versatile framework for gas sensors, demonstrating its adaptability across various gas sensing applications.

Employing the pyroelectric effect in LiTaO3 thin film for infrared detection of complex gases

Abstract In this paper, the lithium tantalite ( LiTaO 3 ) thin film has been employed as the highly sensitive element for infrared detection of compound (refrigerant) gases such as 1,1,1,2-Tetrafluoroethane ( C 2 H 2 F 4 ) and 1,1,1,2,3,3,3-Heptafluoropropane ( C 3 F 7 H ). The LiTaO 3 thin film was subjected to the mid-infrared light from output transmission spectra of C 2 H 2 F 4 as well as C 3 F 7 H molecules used as sources. The technology for preparation of LiTaO 3 thin film as well as detector design and manufacturing are presented. Particular attention was paid to production of conductive electrodes, including a very thin semitransparent Au layer evaporated on the top surface of LiTaO 3 pyroelectric material. Important characteristics of the LiTaO 3 based pyroelectric system are briefly discussed. Additionally, the design, construction, and performance of the gas chamber operating as a channel for gas sensor testing is briefly described. The pyroelectric open-circuit voltage generated in LiTaO 3 was boosted with a signal processing circuit for selective high-sensitivity detection of compound gases at room temperature. The infrared (IR) filters such as titanium dioxide ( TiO 2 ) and zinc oxide ZnO having narrow bandwidth and working at a normal incidence were integrated into a compact and portable pyroelectric micro-sensor before the LiTaO 3 pyroelectric element in the same package for cleaning background in a broad IR spectrum of both refrigerant gases. The performance, stability, and accuracy of fabricated LiTaO 3 -based IR gas sensors operating on the pyroelectric open-circuit voltage were tested and improved. IR gas sensors designed and prepared in this study can be utilized for non-contact, sensitive, and selective detection of highly hazardous and explosive gases.

Ni-doped (MoO3/MoS2) heterostructure chemiresistive sensor for dual selective detection of NH3 and NOx at room temperature

The transition metal dichalcogenide heterostructures are emerging as promising candidates for room-temperature gas sensors. This work presents a Ni-doped (MoO3/MoS2) heterostructure, synthesized via hydrothermal methods with varying Ni concentrations, for the dual selective detection of NH3 and NOx gases. The electronic sensitization of Ni improves the sensitivity of heterostructure. The heterostructure was characterized by using X-ray diffractometer, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), with Ni incorporation confirmed by X-ray photoelectron spectroscopy (XPS). The 10 % Ni-doped MoO3/MoS2 heterostructure showed high sensitivity, achieving responses of 15 % and 18.3 % towards 10 ppm NH3 and NOx, respectively, with detection limits of 0.13 ppm and 0.11 ppm. Furthermore, the sensor demonstrated outstanding cyclic stability, device-to-device reproducibility, and long-term stability, with a retained response of 98.1 % and 98.5 % towards NH3 and NOx, respectively. These findings highlight the potential of Ni-doped (MoO3/MoS2) heterostructures for dual gas sensing applications at room temperature.

Selective Identification of Hazardous Gases Using Flexible, Room-Temperature Operable Sensor Array Based on Reduced Graphene Oxide and Metal Oxide Nanoparticles via Machine Learning.

Selective detection and monitoring of hazardous gases with similar properties are highly desirable to ensure human safety. The development of flexible and room-temperature (RT) operable chemiresistive gas sensors provides an excellent opportunity to create wearable devices for detecting hazardous gases surrounding us. However, chemiresistive gas sensors typically suffer from poor selectivity and zero-cross selectivity toward similar types of gases. Herein, a flexible, RT operable chemiresistive gas sensors array is designed, featuring reduced graphene oxide (rGO) and rGO decorated with zinc oxide (ZnO), titanium dioxide (TiO2), and tin dioxide (SnO2) nanoparticles (NPs) on a flexible polyimide (PI) substrate. The sensor array consists of four different sensing layers capable of the selective identification of various hazardous gases such as NO2, NO, and SO2 using machine learning (ML). The gas sensor array exhibits a stable response even when mechanically deformed or exposed to high humidity (up to 60%). Each gas sensor, due to the different metal oxide NPs, shows unique responses in terms of sensitivity, responsiveness, response time, and recovery time to different gases. Consequently, the sensor array generates distinct response patterns that effectively differentiate between the target gases. By leveraging these distinctive recovery patterns and employing a data fusion approach in ML, specific concentrations of target gases can be distinguished. Using ML with fused array sensing data, the training and test accuracies achieved were 98.20 and 97.70%, respectively. This innovative combination of sensor arrays and ML offers significant potential for selective gas detection in environmental monitoring and personal safety applications.

Strain and External Electric Field Engineering of S-Terminated MXene on Selective and Sensitive Detection of N-Containing Compound Gases: A Computational Study.

Gas sensors are used for monitoring hazardous gases and vapors. With the emergence of S-terminated MXene synthesis, herein, we explore the sensing ability of Ti3C2S2 toward N-containing gases, including NH3, NO, NO2, trimethylamine (TMA), and nicotine (NT), using first-principles calculations and a statistical thermodynamic model. We find that Ti3C2S2 exhibits high selectivity to TMA, NO, and NT with moderate adsorption energies of -0.610, -0.490, and -0.476 eV, respectively, minimizing environmental noise from ambient gases. The electronic structure of Ti3C2S2 subtly alters upon adsorption of TMA, NO, and NT, facilitating detectable signals in the sensing device. However, the adsorption of NO2 and NH3 is less pronounced due to weak physisorption (<0.3 eV). Employing engineering strategies including biaxial strain and an external electric field greatly enhances the selectivity and sensitivity of NO2 (NH3) detection by boosting adsorption strength up to -0.351 eV with ε = 5% (-0.370 eV with |E⃗| = 0.6 V/ Å). In addition, the moderate adsorption energies of the gases result in a suitable recovery time in the range of milliseconds, leading to high reusability of the sensing device. The estimated adsorption densities suggest potential coverage of these N-containing molecules even at low concentrations and room temperature. Computational analysis of the sensing capability of Ti3C2S2 using the nonequilibrium Green's function method indicates that it is a promising gas-sensing material. In addition, mechanical modifications, electric field adjustments, and gate voltage alterations could be used to obtain effective sensing materials for N-containing gas detection.

Multi-physical quantities sensing based on the nematic liquid crystal Janus metastructure in theory

Breaking through the idea limitation of traditional single-scale and single-function sensors, a multi-scale and multi-function Janus metastructure (JMS) is proposed in this article, which is constructed by the specific methods to break its parity. Using the change of transmission spectrum, JMS can realize multi-physical quantities detection with different sensing performances, when electromagnetic waves propagate on positive and negative scales respectively. For selective gas detection, JMS can conveniently detect 0–3.5 % methane concentrations with sensitivity (S) of 22.932 THz/RIU and 0–3 % hydrogen concentrations with S of 43.494 THz/RIU, avoiding the problem of complex and dangerous external operation conditions required for previous gas sensors. Based on the electro-optical effect of nematic liquid crystal, JMS can realize wide-range electric field direction (EFD) sensing of 10°–80° and 100°–170° by taking the advantages of multi-scale detection, which is wider than existing 0°–90° EFD sensors. Because nematic liquid crystal is thermotropic, JMS can also achieve accurate temperature detection of 283.15–318.15 K. Finally, through comparison, it is proved that JMS proposed has the potential of multi-scenario applications, and meets the urgent demand for excellent performance sensors in the fields of dangerous gas transportation, atmospheric EFD detection and industrial manufacturing temperature control.

A Comparative Review of Graphene and MXene-Based Composites towards Gas Sensing.

Graphene and MXenes have emerged as promising materials for gas sensing applications due to their unique properties and superior performance. This review focuses on the fabrication techniques, applications, and sensing mechanisms of graphene and MXene-based composites in gas sensing. Gas sensors are crucial in various fields, including healthcare, environmental monitoring, and industrial safety, for detecting and monitoring gases such as hydrogen sulfide (H2S), nitrogen dioxide (NO2), and ammonia (NH3). Conventional metal oxides like tin oxide (SnO2) and zinc oxide (ZnO) have been widely used, but graphene and MXenes offer enhanced sensitivity, selectivity, and response times. Graphene-based sensors can detect low concentrations of gases like H2S and NH3, while functionalization can improve their gas-specific selectivity. MXenes, a new class of two-dimensional materials, exhibit high electrical conductivity and tunable surface chemistry, making them suitable for selective and sensitive detection of various gases, including VOCs and humidity. Other materials, such as metal-organic frameworks (MOFs) and conducting polymers, have also shown potential in gas sensing applications, which may be doped into graphene and MXene layers to improve the sensitivity of the sensors.

Enhancing detection of thermal runaway gases: Exploiting doping and vacancy effects in GeS quantum dots

This study investigates chemical modifications on Germanium Sulfide (GeS) quantum dots (QDs) for selective detection of thermal runaway gases (TRGs). We examine how doping with oxygen, phosphorus, silicon, and introducing sulfur vacancies at edge and surface regions affect the structural, electronic, and optical properties of GeS-QDs and their derivatives. Our findings reveal significant changes in bond parameters, formation energy, electronic band gap, and light absorption behavior. Oxygen doping enhances stability, while other dopants and sulfur vacancies increase reactivity towards TRGs (H2, CO, CH4, C2H4). All materials show favorable adsorption for these gases, with C2H4 displaying the strongest binding affinity. Adsorption minimally affects core electronic structure (HOMO) but shifts surface electronic states (LUMO). Sulfur vacancies reduce the energy gap, enhancing conductivity and facilitating TRGs detection. These results suggest that GeS-QDs can be effectively tuned for selective TRG detection by manipulating their chemical composition and surface characteristics.

Metal-enhanced carbon-nitrogen material for selective detection of hazardous gases: Insights from interface electronic states

In this study, utilizing density functional theory, the C3N1 monolayer modified by Ir, Pd, Pt, and Rh atoms (Ir/Pd/Pt/Rh-C2N1) was chosen for selective adsorption of C2H2 amidst multiple gases (H2O, C2H2, and C4H10O2). According to the results of cohesive energy and ab initio molecular dynamics simulations, it is indicated that precious metal atoms can be stably anchored on the monolayer while enhancing the conductivity of the material The analysis of the electrostatic potential and work function determined the highly active sites and electron release capacity. In addition, the adsorption energy and distance disclosed the gas-solid interface structure of multiple gases on the Ir/Pd/Pt/Rh-C2N1 monolayer. Importantly, C2H2 exhibits strong responses to p-type semiconductor Pt-C2N1 and n-type semiconductor Ir-C2N1, respectively. Crystal Orbital Hamilton Population reveals the difference in adsorption energy due to modifications involving four precious metals. Interestingly, for the first time, the density of states calculation reveals that under the coexistence of multiple gases, the Pt/Ir-C2N1 monolayer effectively eliminates the interference of other gases and has a unique response only to C2H2. In real situations, with the basis of Gibbs free energy and Einstein's law of diffusion, it was determined that Pt-C2N1 and Ir-C2N1 showed excellent hydrophobicity, a wider temperature range, and a low diffusion activation energy barrier. In summary, Pt-C2N1 and Ir-C2N1 detect C2H2 without interference, maintaining fundamental principles, responsiveness, stability, and versatility unaffected by external factors.

Thermal decomposition-assisted, aspect ratio controlled ZnO nanorods towards highly selective H2 gas detection

ZnO nanostructures with various aspect ratios have been synthesized for H2 gas detection applications. The thermal-decomposition method was employed at different annealing temperatures (350, 450, and 550 °C) and its impact on various shapes/sizes of ZnO nanostructures is demonstrated. Thermal decomposition performed at 350 °C exhibited a maximum (∼6.25) aspect ratio among them. Its capability of H2 sensing was also observed to be maximum by realizing ∼483% of sensor response at 180 °C under H2 gas concentration of 80 ppm. The sensor response is ∼3 times (∼177%) and ∼9 times (∼53%) higher at ZnO nanostructure synthesized at 350 °C than at 450 °C, and 550 °C, respectively. The higher sensor response has been attributed to the increased availability of active surface area for adsorption/desorption of gas molecules. ZnO@350 nanostructure showed significantly higher selectivity towards H2 gas than other target chemical inputs. We have also studied H2-induced metallization on the surface of ZnO nanostructures which plays an important role for improving the selectivity and sensor response. This study provides insight into the role of aspect-ratio-controlled shape/sized ZnO in improving H2 gas sensing.

Selective and reversible carbon mono oxide gas detection using silver doped octahedral molecular sieves (OMS-2) nanorods

In this work a potable, resistive sensor is fabricated for the selective detection of CO gas using nanorods of Ag doped octahedral molecular sieves-2 (Ag-OMS-2). During exposure to carbon monoxide (CO) gas at room temperature, resistance of Ag-OMS-2 film was dropped from 557 kΩ to 352 kΩ in just 18 sec. However, exposed sample regained its initial resistance value in 25 sec when CO gas source was removed. Both sensing and recovery processes were carried out at room temperature. The sensor film showed excellent reproducibility during several cycles of CO gas exposure. Swift activation of oxygen molecules for the oxidation of CO by the silver present in the tunnel of manganese oxide network is supposed to be responsible for sensing activity of Ag-OMS-2 towards carbon monoxide gas.

Integrated Photonic Sensors for the Detection of Toxic Gasses—A Review

Gas sensing is crucial for detecting hazardous gasses in industrial environments, ensuring safety and preventing accidents. Additionally, it plays a vital role in environmental monitoring and control, helping to mitigate pollution and protect public health. Integrated photonic gas sensors are important due to their high sensitivity, rapid response time, and compact size, enabling precise recognition of gas concentrations in real-time. These sensors leverage photonic technologies, such as waveguides and resonators, to enhance performance over traditional gas sensors. Advancements in materials and fabrication techniques could further improve their efficiency, making them invaluable for environmental monitoring, industrial safety, and healthcare diagnostics. In this review, we delved into photonic gas sensors that operate based on the principles of evanescent field absorption (EFA) and wavelength interrogation methods. These advanced sensing mechanisms allow for highly sensitive and selective gas detection, leveraging the interplay of light with gas molecules to produce precise measurements.

Gas sensor array based on carbon-based thin-film transistor for selective detection of indoor harmful gases

Gas sensor array based on carbon-based thin-film transistor for selective detection of indoor harmful gases

Aminated reduced graphene oxide-carbon nanotube composite gas sensors for ammonia recognition

Composites based on carbon nanomaterials exhibit many advantageous properties for gas sensing, such as high and fast response, room-temperature operation, and tailoring sensitivity by energy level engineering. However, only the first attempts to employ such chemosensors for gas-sensing applications have been made. In this work, an on-chip multisensor array of carboxylated carbon nanotubes (CNT), aminated reduced graphene oxide (rGO-Am), and CNT/rGO-Am nanocomposite was fabricated using a simple and low-cost spray deposition method. The CNT/rGO-Am sensor demonstrated a fast and high response to NH3 in dry air at low (25 ppm) and high (400 ppm) concentrations of 70 and 115 %, respectively. The response to NH3 in humid air increased and reached 160 % at 400 ppm. The chemosensor exhibited high sensitivity and selectivity toward ammonia with a low detection limit estimated to be below 0.2 ppb. Linear discriminant analysis of the sensor responses to different concentrations of NH3, dry and humid air revealed better discrimination when CNT/rGO-Am composites were used in combination with CNT and rGO-Am sensors in an array. This study demonstrates that composite sensors with junctions between carbon nanomaterials have great potential for practical applications in fast and selective gas detection at room temperature and different humidity.

On-Chip Annealing Using Embedded Micro-Heater for Highly Sensitive and Selective Gas Detection.

The demand for gas sensing systems that enable fast and precise gas recognition is growing rapidly. However, substantial challenges arise from the complex fabrication process of sensor arrays, time-consuming data transmission to an external processor, and high energy consumption in multi-stage data processing. In this study, a gas sensing system using on-chip annealing for fast and power-efficient gas detection is proposed. By utilizing a micro-heater embedded in the gas sensor, the sensing material of adjacent sensors in the same substrate can be easily varied without further fabrication steps. The response to oxidizing gas is constrained in metal oxide (MOX) sensing material with small grain sizes, as the depletion width of grain cannot extend beyond the grain size during the gas reaction. On the other hand, the response to reducing gases and humidity, which decrease the depletion width, is less affected by grain sizes. A readout circuit integrating a differential amplifier and dual FET-type gas sensors effectively emphasizes the response to oxidizing gases by canceling the response to reducing gases and humidity. The selective on-chip annealing method is applicable to various MOX sensing materials, demonstrating its potential for application in commercial fields due to its simplicity and expandability.

Ultra-highly sensitive dual gases detection based on photoacoustic spectroscopy by exploiting a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser.

Photoacoustic spectroscopy (PAS) as a highly sensitive and selective trace gas detection technique has extremely broad application in many fields. However, the laser sources currently used in PAS limit the sensing performance. Compared to diode laser and quantum cascade laser, the solid-state laser has the merits of high optical power, excellent beam quality, and wide tuning range. Here we present a long-wave, high-power, wide-tunable, single-longitudinal-mode solid-state laser used as light source in a PAS sensor for trace gas detection. The self-built solid-state laser had an emission wavelength of ~2 μm with Tm:YAP crystal as the gain material, with an excellent wavelength and optical power stability as well as a high beam quality. The wide wavelength tuning range of 9.44 nm covers the absorption spectra of water and ammonia, with a maximum optical power of ~130 mW, allowing dual gas detection with a single laser source. The solid-state laser was used as light source in three different photoacoustic detection techniques: standard PAS with microphone, and external- and intra-cavity quartz-enhanced photoacoustic spectroscopy (QEPAS), proving that solid-state laser is an attractive excitation source in photoacoustic spectroscopy.

Discriminative analysis of volatile organic compounds using machine-learning assisted Au loaded ZnO and TiO2-based thin film sensors

Noble metal-based particulate catalysts have traditionally been loaded or decorated onto the semiconductor metal oxide (SMO) surfaces to enhance the performance of gas sensors. Fabricating SMO-based sensors for selective detection of particular gases with high sensitivity remains a challenge. This study aims to enhance the efficacy of pure SMO and their heterostructure with gold (Au) decoration, along with an attempt to address the cross-sensitivity towards other gases through machine learning-assisted discriminative analysis. The sensitivity of sputtered ZnO thin films towards different VOCs such as acetone, ethanol, methanol, and toluene was improved by loading particulate Au. The highest sensitivity of 25 and low response time of ∼6 s and ∼4 s were achieved towards 10 ppm of ethanol and toluene, respectively. Further, Au-loaded ZnTiO3-TiO2 (ZTO) layered heterostructure was also adopted to achieve selectivity towards toluene. ZTO thin film sensor was highly sensitive towards 10 ppm of toluene, with a sensitivity of 49 and a response time of ∼6 s. Loading Au on ZnO thin film increases sensitivity towards multiple VOCs, whereas Au on ZTO heterostructure improves the selectivity towards toluene. To overcome the problem arising due to the cross-sensitivity, the idea of operating multiple sensors with different Au loading is proposed. The discriminative property of different sensors as an array, towards VOCs was analysed in detail using machine learning algorithms such as principal component analysis (PCA), linear discriminant analysis (LDA), logistic regression (LR), and artificial neural networks (ANN). The multilayer perceptron model implemented to discriminate multiple VOCs worked at a discrimination accuracy of 100 %.

Selective gas detection using phase change material infused photonic crystal

A photonic crystal-based optical gas detector is proposed, incorporating phase change material (PCM) to modulate the sensing properties. The multi-gas detection process is designed in the range of 650 nm to 2500 nm. Ge2Sb2Te5 (GST) is employed as a phase change material with significant optical property variations. It can exist in two self-sustaining, bi-stable phases: a crystalline GST (CGST) and an amorphous GST (AGST). The dielectrics (i.e., Si, SiO2, GST, and Au) are used in various combinations, such as Au-Si, Au-Si-SiO2, Au-GST-SiO2, and GST-Au. Plane light waves are used to model the nanoporous structures over a broad wavelength range (650 nm to 2500 nm). The optical spectral response of the structures, including the reflectivity spectrum, power absorption spectrum, and electric field distribution, is investigated by varying the GST thickness, dimension, and geometry of the nanoholes. Liquid ammonia has the highest selectivity of any gas from 650 nm to 1000 nm, at about 29%, whereas carbon monoxide has the maximum sensitivity of 32%. The interchanging of layers increases the sensitivity of all the gases. With a sensitivity and selectivity of 78% and 40%, respectively, carbon monoxide exhibits the greatest values.

Graphene-based nanocomposites for gas sensors: challenges and opportunities

Abstract Exposure to toxic gases resulting from rapid industrialization poses significant health risks living organisms including human. Consequently, researchers in this modern scientific era have shown keen interest in the selective detection of these toxic gases. The development of fast, economical, selective, and highly sensitive gas sensors has become a crucial pursuit to accurately detect toxic gases and mitigate their adverse effects on the natural environment. Graphene-based nanocomposites have emerged as promising candidates for selectively detecting toxic gases due to their extensive surface area. This review paper provides a comprehensive summary of recent advancements in graphene-based gas sensors. The paper also offers an overview of various synthetic strategies for graphene and its hybrid architectures. Additionally, it delves into the detailed sensing applications of these materials. Challenges and limitations in this field have been critically evaluated and highlighted, along with potential future solutions.

Towards a Miniaturized Photoacoustic Sensor for Transcutaneous CO2 Monitoring.

A photoacoustic sensor system (PAS) intended for carbon dioxide (CO2) blood gas detection is presented. The development focuses on a photoacoustic (PA) sensor based on the so-called two-chamber principle, i.e., comprising a measuring cell and a detection chamber. The aim is the reliable continuous monitoring of transcutaneous CO2 values, which is very important, for example, in intensive care unit patient monitoring. An infrared light-emitting diode (LED) with an emission peak wavelength at 4.3 µm was used as a light source. A micro-electro-mechanical system (MEMS) microphone and the target gas CO2 are inside a hermetically sealed detection chamber for selective target gas detection. Based on conducted simulations and measurement results in a laboratory setup, a miniaturized PA CO2 sensor with an absorption path length of 2.0 mm and a diameter of 3.0 mm was developed for the investigation of cross-sensitivities, detection limit, and signal stability and was compared to a commercial infrared CO2 sensor with a similar measurement range. The achieved detection limit of the presented PA CO2 sensor during laboratory tests is 1 vol. % CO2. Compared to the commercial sensor, our PA sensor showed less influences of humidity and oxygen on the detected signal and a faster response and recovery time. Finally, the developed sensor system was fixed to the skin of a test person, and an arterialization time of 181 min could be determined.