Toxic Gas Monitoring Research Articles

Network of artificial olfactory receptors for spatiotemporal monitoring of toxic gas.

Excessive human exposure to toxic gases can lead to chronic lung and cardiovascular diseases. Thus, precise in situ monitoring of toxic gases in the atmosphere is crucial. Here, we present an artificial olfactory system for spatiotemporal recognition of NO2 gas flow by integrating a network of chemical receptors with a near-sensor computing. The artificial olfactory receptor features nano-islands of metal-based catalysts that cover the graphene surface on the heterostructure of an AlGaN/GaN two-dimensional electron gas (2DEG) channel. Catalytically dissociated NO2 molecules bind to graphene, thereby modulating the conductivity of the 2DEG channel. For the energy/resource-efficient gas flow monitoring, trust-region Bayesian optimization algorithm allocates many sensors optimally in a complex space. Integrated artificial neural networks on a compact microprocessor with a network of sensors provide in situ gas flow predictions. This system enhances protective measures against toxic environments through spatiotemporal monitoring of toxic gases.

A Novel Mechanism Based on Oxygen Vacancies to Describe Isobutylene and Ammonia Sensing of p-Type Cr2O3 and Ti-Doped Cr2O3 Thin Films

Gas sensors based on metal oxide semiconductors (MOS) have been widely used for the detection and monitoring of flammable and toxic gases. In this paper, p-type Cr2O3 and Ti-doped Cr2O3 (CTO) thin films were synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method. Detailed analysis of the thin films deposited, including structural information, their elemental composition, oxidation state, and morphology, was investigated using XRD, Raman analysis, SEM, and XPS. All the gas sensors based on pristine Cr2O3 and CTO exhibited a reversible response and good sensitivity to isobutylene (C4H8) and ammonia (NH3) gases. Doping Ti into the Cr2O3 lattice improves the response of the CTO-based sensors to C4H8 and NH3. We describe a novel mechanism for the gas sensitivity of p-type metal oxides based on variations in the oxygen vacancy concentration.

Wool powder assisted colorimetric sensing yarn with high sensitivity for NH3 monitoring

Colorimetric sensors have applications in gas monitoring due to their simple and quick detection through visible color changes. However, it remains challenging to prepare colorimetric sensors with high sensitivity. Herein, this work fabricated a biomass-based colorimetric sensing yarn with high sensitivity using anthocyanins as the colorimetric dye and wool powder as an effective ammonia (NH3) adsorbent. The sensitivity of the prepared yarns was evaluated for detection limit and response time. Surprisingly, the addition of 3% wool powder greatly improved the sensitivity of the prepared yarns, with a reduction of both detection limit and responsive time from 100 ppm to 20 ppm, and 2 min to 20 s, respectively when exposed in 150 ppm NH3. The prepared yarns also showed good selectivity and reusability. An example of the practical use of colorimetric yarns was presented. This work provides a facile strategy for fabricating wearable devices for toxic gas monitoring with visual output.

Enhancing biphenylene sensitivity for BF3 detection via nitrogen doping: A DFT study

The detection and monitoring of toxic gases are critical components of environmental protection. Boron trifluoride (BF3), in particular, poses a significant threat to both the environment and human health due to its destructive properties. To address this challenge, the development of highly reactive and sensitive sensors for detecting and trapping BF3 is essential. This study explores the potential of pristine biphenylene (BP), boron-doped BP (B-BP), and nitrogen-doped BP (N-BP) as gas sensors for BF3 detection using density functional theory (DFT) calculations at the M062X/6–31 g(d,p) level of theory. We found that nitrogen doping significantly enhances the reactivity of BP toward BF3 originating from strong chemisorption with an adsorption energy of −9.38 kcal/mol. This is accompanied by a notable 19.96 % change in the electronic energy gap, making N-BP an exceptionally sensitive material for gas detection. The results will be supported by natural bond orbital analysis, providing a detailed electronic analysis of the sensing capabilities of N-BP. Our results suggest that n-type doping can be an effective strategy to enhance both the reactivity and sensitivity of carbon-based monolayers for detecting boron trifluoride.

Atomic-level insights into sensing performance of toxic gases on the InSe monolayer decorated with Pd and Pt under humid environment

The timely detection and monitoring of toxic gases are crucial for preserving the ecological environment and preventing their adverse effects on human health. In this study, we investigate the adsorption characteristics and sensitivity performance of Pd- and Pt-decorated InSe monolayers, referred to as Pd-InSe and Pt-InSe, towards five toxic gases (CO, NO, NH3, H2S, and SO2) using first-principle calculations. The results show that the doping of Pd and Pt atoms significantly improves the conductivity, adsorption capabilities, and sensing properties of InSe monolayer to these toxic gases. Both Pd-InSe and Pt-InSe monolayers exhibit chemical adsorption of CO, NO, NH3, and H2S, with adsorption energies ranging from –0.56 eV to –1.04 eV, leading to noticeable changes in the bandgap (8.84 % ∼ 31.03 %). Furthermore, the CO/Pd-InSe and H2S/Pt-InSe systems demonstrate excellent sensitivity, with high sensing response values of 1.54×104 and 66.20, respectively, and their sensitivity remains unaffected under humid environments. Importantly, Pt-InSe exhibits a fast recovery time of 0.05 s at 298 K, making it highly promising for the recyclable detection of H2S at room temperature. In contrast, Pd-InSe can be utilized as a reusable gas sensor for CO at 448 K with a good recovery time of 0.5 s. This work can provides theoretical guidance for the design and fabrication of InSe-based gas sensors for the detection of toxic gases.

Real-Time Monitoring of Toxic Gases using Artificial Neural Networks with SnO2-based Thick Film Gas Sensors

The present study aims to develop an advanced system for real-time identification and measurement of harmful gases using Pd-doped SnO2-based thick film gas sensors integrated with Artificial Neural Networks. These sensors, renowned for their exceptional sensitivity and selectivity, undergo testing in a meticulously controlled gas chamber environment. Here, gas concentrations, temperature, and humidity are meticulously controlled. The gas chamber setup allows for mixing gases like carbon monoxide, nitrogen dioxide, and sulfur dioxide with nitrogen gas to achieve desired concentrations ranging from to . Temperature is kept at and relative humidity is maintained between to . The sensitivity analysis of the sensor demonstrates its adeptness in detecting low concentrations of target gases, with sensitivity increasing as gas concentrations rise, also the selectivity assessments highlight their ability to accurately differentiate between target gases and common interferents, ensuring precise detection even in complex gas mixtures. Response time testing indicates rapid detection capabilities, crucial and useful for emergencies. The Artificial Neural Network model, trained via the backpropagation algorithm, demonstrates remarkable accuracy, precision, recall, and F1 scores in predicting gas concentrations. The findings indicate that this integrated system offers a reliable and efficient solution for toxic gas detection, with potential applications in industrial safety and environmental monitoring.

First principles study of transition metal (TM = Sc, Ti, V, Cr, Mn) doped penta-BAs5 monolayer for adsorption of CO, NH3, NO, SO2

In this paper, the adsorption capacity of intrinsic penta-BAs5 monolayer on CO, NH3, NO, SO2 and the effect of transition metal doping on gas sensing characteristics are systematically studied by first-principles calculations. Adsorption energy, recovery time, band structure, charge transfer and density of states (DOS) are investigated. The electronic properties and sensing mechanisms under different adsorption systems are expounded. The results showed that the intrinsic penta-BAs5 monolayer had the strongest adsorption capacity for NO and weak sensitivity to CO, NH3 and SO2, which shown strong gas selectivity. Moreover, the recovery time of NO at 380 k was 3.93 s, which was more inclined to be desorption at high temperature. In addition, Sc and Ti doping could selectively improve the adsorption capacity of the intrinsic penta-BAs5 monolayer. The charge transfer of SO2-Sc-BAs5 and CO-Ti-BAs5 were increased by 6.78 and 10.33 times compared with those before doping. The band structure and DOS show that Ti atom and CO have orbital hybridization, which improved the interaction between gases and penta-BAs5. Therefore, intrinsic penta-BAs5, Sc-BAs5 and Ti-BAs5 are suitable for gas sensing and toxic gas monitoring, and have broad application prospects.

Fast-Response and Low-Power Self-Heating Gas Sensor Using Metal/Metal Oxide/Metal (MMOM) Structured Nanowires.

With the escalating global awareness of air quality management, the need for continuous and reliable monitoring of toxic gases by using low-power operating systems has become increasingly important. One of which, semiconductor metal oxide gas sensors have received great attention due to their high/fast response and simple working mechanism. More specifically, self-heating metal oxide gas sensors, wherein direct thermal activation in the sensing material, have been sought for their low power-consuming characteristics. However, previous works have neglected to address the temperature distribution within the sensing material, resulting in inefficient gas response and prolonged response/recovery times, particularly due to the low-temperature regions. Here, we present a unique metal/metal oxide/metal (MMOM) nanowire architecture that conductively confines heat to the sensing material, achieving high uniformity in the temperature distribution. The proposed structure enables uniform thermal activation within the sensing material, allowing the sensor to efficiently react with the toxic gas. As a result, the proposed MMOM gas sensor showed significantly enhanced gas response (from 6.7 to 20.1% at 30 ppm), response time (from 195 to 17 s at 30 ppm), and limit of detection (∼1 ppm) when compared to those of conventional single-material structures upon exposure to carbon monoxide. Furthermore, the proposed work demonstrated low power consumption (2.36 mW) and high thermal durability (1500 on/off cycles), demonstrating its potential for practical applications in reliable and low-power operating gas sensor systems. These results propose a new paradigm for power-efficient and robust self-heating metal oxide gas sensors with potential implications for other fields requiring thermal engineering.

Enhanced selectivity of novel sea urchin-like h-/m-WO3 hetero nanoflowers for highly sensitive detection of ammonia by double filtration method

Real-time monitoring of toxic gases and breath markers can be performed by metal oxide semiconductor-based chemo-resistive gas sensors due to their simple structures, low cost, and faster and better recovery and response. Due to the effective electron-hole separation, tuning the development of phase junctions of the metal oxide is an efficient method for improving their gas sensing properties. In this study, two distinct hydrothermal methods were used to synthesize h-/m-WO3 hetero-nanoflowers. In the first method, L-Cysteine was used to facilitate the formation of phase junctions between h-WO3 and m-WO3 nanostructures, whereas Thiourea was used in the second. Various characterisation approaches validated the hexagonal-monoclinic phase junction development in the nanoflowers. The sensing material fabricated using Thiourea with a concentration of 0.01M performed better than other sensors. At 350°C, the selected sample displayed outstanding ammonia sensing capacity with the experimental detection limit of 1 ppm (response=3.33). The theoretical detection limit is determined to be 27 ppb. The selectivity of the sensor towards NH3 over H2S and acetone is increased by combining the devices with a double filtration setup. The effectiveness of the selected h-/m-WO3 sensor for diagnosing kidney dysfunction was evaluated by analyzing simulated breath samples.

Carbon nanowall-based gas sensors for carbon dioxide gas detection

Carbon nanowalls (CNWs) have attracted significant attention for gas sensing applications due to their exceptional material properties such as large specific surface area, electric conductivity, nano- and/or micro-porous structure, and high charge carrier mobility. In this work, CNW films were synthesized and used to fabricate gas sensors for carbon dioxide (CO2) gas sensing. The CNW films were synthesized using an inductively-coupled plasma (ICP) plasma-enhanced chemical vapor deposition (PECVD) method and their structural and morphological properties were characterized using Raman spectroscopy and electron microscopy. The obtained CNW films were used to fabricate gas sensors employing interdigitated gold (Au) microelectrodes. The gas sensors were fabricated using both direct synthesis of CNW films on interdigitated Au microelectrodes on quartz and also transferring presynthesized CNW films onto interdigitated Au microelectrodes on glass. The CO2 gas-sensing properties of fabricated devices were investigated for different concentrations of CO2 gas and temperature-ranges. The sensitivities of fabricated devices were found to have a linear dependence on the concentration of CO2 gas and increase with temperature. It was revealed that devices, in which CNW films have a maze-like structure, perform better compared to the ones that have a petal-like structure. A sensitivity value of 1.18% was obtained at 500 ppm CO2 concentration and 100 °C device temperature. The CNW-based gas sensors have the potential for the development of easy-to-manufacture and efficient gas sensors for toxic gas monitoring.

Facile preparation of Au-loaded mesoporous In2O3 nanoparticles with improved ethanol sensing performance.

The in situ monitoring of toxic volatile organic compound gases using metal oxide-based gas sensors is still challenging. Herein, mesoporous In2O3 nanoparticles, assembled using smaller nanoparticles, were synthesized via a facile solvothermal method and used to load Au nanoparticles to prepare mesoporous Au/In2O3 for ethanol detection. The obtained In2O3 and Au/In2O3 were meticulously analysed by XRD, SEM, BET, TEM and XPS techniques. It was revealed that Au nanoparticles were uniformly distributed on mesoporous In2O3 nanoparticles. Notably, the obtained mesoporous 1% Au/In2O3 is highly sensitive to ethanol gas at an optimal working temperature of 180 °C, showing a response of 55 to 50 ppm of ethanol, which is considerably higher compared to that of In2O3 nanoparticles. The significantly enhanced sensitivity results from the electronic and chemical sensitization effects of Au nanoparticles. Moreover, the mesoporous Au/In2O3 nanoparticles also showed eminent selectivity, short response/recovery time, low detection limit, good linear relationship, superb repeatability, and wonderful long-term stability, suggesting that Au/In2O3 nanoparticles have great potential application for in situ monitoring of ethanol gas.

Synthesize of Ni0.75Zn0.25Fe2O4 Spinel Oxide as a Working Electrode for Formaldehyde Electrochemical Gas Sensors

Gas sensor with yttrium stabilized zirconia film in electrochemistry have been rapidly applied in the monitoring of toxic and harmful gases, and nickel spinel ferrite (NFO) is one of the most studied working electrodes. However, the sensing performance to formaldehyde (HCHO) is quiet poor. In this work, the sol-gel method was used to prepare Zn-doped NFO (Ni0.75Zn0.25Fe2O4) oxide, and the Zn-doped NFO was applied as the working electrode of the electrochemical gas sensor of HCHO. The phase structure, micromorphology, and surface area of the prepared Ni0.75Zn0.25Fe2O4 oxide were evaluated for the working electrode. The results showed that when the operating temperature reached 480 °C, the sensor with Ni0.75Zn0.25Fe2O4 as the working electrode achieved high response value of −17 mV to 5 ppm HCHO, and the response/recovery time was 28/20 s. The polarization curve was further performed to validate the mechanism of the observed sensing behavior. Meanwhile, the response signal of the fabricated sensor increased logarithmically with the log (HCHO) in the investigated range of 1–5 ppm, and the corresponding sensitivity reached −29.08 mV/decade.

Metal-modified C3N1 monolayer sensors for battery instability monitoring

High-performance sensors achieved highly selective monitoring of toxic gases produced after the battery becomes unstable.

Highly Sensitive and Selective MEMS Gas Sensor Based on WO3/Al2O3/Graphite for 2-Chloroethyl Ethyl Sulfide (2-CEES) Detection

The detection and monitoring of toxic and harmful gases play a vital role in environmental protection, human health, and industrial and agricultural production. However, it is still challenging to develop gas sensors for the detection of toxic and harmful gases with high sensitivity, good recovery and excellent selectivity. In this study, WO3/Al2O3/graphite composite materials were used for an MEMS 2-CEES gas sensor (dichlorodiethyl sulfide simulation), and the corresponding sensing properties were explored. The experimental results show that when the working temperature is 340 °C, the response of the sensor to 2-CEES gas with a concentration of 5.70 ppm is 69%, the response time is 5 s and the recovery time is 42 s. The sensor also has the advantages of long-term stability and high selectivity. Furthermore, the MEMS gas sensor array based on WO3/Al2O3/graphite composite materials has been achieved and also exhibits excellent sensing performance. Overall, this study provides a strategy for realizing high-performance dichlorodiethyl sulfide gas sensors.

ZnO Nanostructure Based Gas Sensors: Critical Review Based on their Synthesis and Morphology Towards Various Oxidizing and Reducing Gases

Abstract: Nanotechnology has enabled sensors to detect and sense a very small amount of chemical vapors. Sensors play a major role in our daily life. The use of sensors has made human life easy. One such type of sensor is the Gas sensor made up of Semiconducting metal oxides. These sensors have their own unique features which help in the easy monitoring of toxic gases. Out of all the metal oxide present, the gas sensors made up of ZnO nanostructures are mostly used in the gas sensing industry. ZnO has become a research hotspot of gas-sensing material because of the variation in resistance observed on the surface. These resistance changes are observed due to the adsorption & desorption of gases. In this review, we will be discussing the ZnO nanostructures, their preparation and their applications in the sensing of various toxic and flammable gases.

Suppress ambient temperature interference strategy based on SnO2 gas semiconductor sensor using dynamic temperature modulation mode and principal component analysis algorithm

Semiconductor gas sensors have been widely used in environmental monitoring, toxic gas monitoring, respiratory marker monitoring and other fields due to their low price and high sensitivity etc. An easily overlooked parameter, ambient temperature, is a major factor affecting the accuracy of the sensor. In this paper, a new idea to suppress ambient temperature interference is proposed. Dynamic temperature modulation method is used to extend the dimension of output information, so that both ambient temperature and target gas concentration can be expressed simultaneously. The ambient temperature component is separated by coordinate transformation and component elimination. The data inverse transformation is carried out to achieve the purpose of suppressing the ambient temperature interference. Compared with the performance optimization of gas-sensing materials and additional temperature sensors, the first advantage of this method is to reduce the complexity and power consumption of sensor devices. In addition, the use of PCA algorithm also reduces the complexity of the recognition algorithm. At the same time, more intuitive data reduces the cost of parameter optimization.

Physical properties of thermal annealing induced In2O3 thin films for sensing layer applications

Detection and monitoring of flammable, toxic and explosive gases are crucial, where active research on nanostructured metal oxide materials and thin films is enthusiastically performed to explore new paths for improving the characteristic parameters of sensors. The higher stability and appropriate electrical properties along with wide band gap of In2O3 material make it suitable for active layer to gas sensors where properties of In2O3 films could be engineered by post treatments. The present work demonstrates an influence of thermal annealing on structural, optical, topographical, morphological, elemental and electrical properties of In2O3 films for gas sensor applications. The In2O3 films of thickness 500 nm are grown onto soda lime glass and conducting ITO substrates employing physical vapor deposition based thermal evaporation technique followed by thermal annealing at 200 °C, 300 °C and 400 °C for one hour in air atmosphere. The XRD analysis indicated phase transformation from metastable rhombohedral to stable cubic phase where crystallite size corresponding to associated preferred (110) and (222) peaks is tuned in range of 32–51 nm with annealing. Optical analysis unveiled higher transmittance in ultraviolet and visible regions whereas absorbance of films is fluctuated with thermal annealing. All the In2O3 films indicated the Ohmic nature where the resistivity is detected to be enhanced with annealing. EDS patterns confirmed deposition of the films. The SEM analysis showed nanospheres like grain morphology and such well connected nanospheric features offer large surface area and stimulate adsorption of gas effectively. Hence structural, optical, electrical and morphological properties of gas sensitive In2O3 layers are greatly stimulated by thermal annealing.

Helmet-Mounted Real-Time Toxic Gas Monitoring and Prevention System for Workers in Confined Places.

Occupational health and safety hazards associated with confined places are mainly caused by exposure to toxic gases and oxygen deficiency. Lack of awareness, inappropriate monitoring, and improper evacuation methods can lead to worker fatalities. Although previous studies have attempted to develop systems to solve this issue, limited research is available on their application in confined places. In this study, a real-time helmet-mounted system was developed to monitor major toxic gases (methane (CH4), hydrogen sulfide (H2S), ammonia (NH3), and carbon monoxide (CO)), oxygen, temperature, and humidity. Workers outside and inside confined spaces receive alerts every second to immediately initiate the rescue operation in the event of a hazard. The test results of a confined environment (wastewater treatment unit) highlighted that concentrations of CH4 and H2S were predominant (13 ppm). Compared to normal atmosphere, CH4 concentration was 122- and 130-fold higher in the landfill and digestion tanks, respectively, while H2S was 36- and 19-fold higher in the primary and secondary clarifiers, respectively. The oxygen content (18.2%) and humidity (33%) were below the minimum required limits. This study will benefit future research to target appropriate toxic gas monitoring and alert workers by studying the existing issues and associated factors in confined places.

A Ratiometric Fluorescent Nanoprobe for Ultrafast Detection of Formaldehyde in Wood and Food Samples

AbstractFluorescent sensing of formaldehyde (FA) in the environment is of great significance for human health. However, the development of ratiometric fluorescent probes for ultrasensitive FA detection is challenging due to the lack of suitable strategies. In this study, we demonstrate that ratiometric FA nanoprobes can be facile constructed by integrating two simultaneously excitable fluorophores into a polymer matrix. Using this strategy, we developed a ratiometric fluorescent nanoprobe (Nano‐FAP‐1) for the highly sensitive detection of FA in environmental samples by incorporating a 4‐hydrazino‐1,8‐naphthalimide derivative (Na‐FA) as the receptor and 7‐diethylaminocoumarin‐3‐carboxyl ethyl acetate (Cou‐1) as the reference into a Pluronic F‐127 matrix. The probe achieved a highly sensitive and selective response to low concentrations of FA, with a response time of fewer than 5 s and a detection limit of 0.407 μM. It is worth noting that the probe can be used for the determination of FA in wood and food samples, demonstrating its potential application in the field of toxic gas monitoring and environmental protection.

On-chip monitoring of toxic gases: capture and label-free SERS detection with plasmonic mesoporous sorbents.

The detection of the spread of toxic gas molecules in the air at low concentration in the field requires a robust miniaturized system combined with an analytical technique that is portable and able to detect and identify the molecules, as is the case with surface enhanced Raman scattering (SERS). This work aims to address capability gaps faced by first responders in real-time detection, identification and monitoring of neurotoxic gases by developing robust, reliable and reusable SERS microfluidic chips. Thus, the key performance attributes of a portable SERS detection system that must be addressed in detail are its limit of detection, response time and reusability. To this purpose, we integrate a 3D plasmonic architecture based on closely packed mesoporous silica (MCM48) nanospheres decorated with Au nanoparticle arrays, denoted as MCM48@Au, into a Si microfluidic chip designed and used for preconcentration and label-free detection of gases at a trace concentration level. The SERS performance of the plasmonic platform is thoroughly analyzed using DMMP as a model neurotoxic simulant over a 1 cm2 SERS active area and over a range of concentrations from 100 ppbV to 2.5 ppmV. The preconcentration-based SERS signal amplification by the mesoporous silica moieties is evaluated against dense silica counterparts, denoted as Stöber@Au. To assess the potential for applications in the field, the microfluidic SERS chip has been interrogated with a portable Raman spectrometer, evaluated with temporal and spatial resolution and subjected to several gas detection/regeneration cycles. The reusable SERS chip shows exceptional performance for the label-free monitoring of 2.5 ppmV gaseous DMMP.