Gas Sensors Research Articles

MOF-derived SnO2 nanoparticles for realization of ultrasensitive and highly selective NO2 gas sensing

Herein, SnO2 nanoparticles (NPs) were synthesized from a Sn-metal organic framework (MOF) through a hydrothermal synthesis approach for NO2 sensing studies. The expected phase, morphology and composition of the SnO2 NPs were demonstrated via different characterizations. The individual sizes of SnO2 NPs were ∼20–30 nm, and they had a high surface area (185.31 m2/g). The sensing properties were measured at various temperatures towards NO2 gas. It showed very high responses of 240.60 and 3984.98–10 and 100 ppm NO2, respectively, at 200°C. Also, it still displayed a high response of 47.11–100 ppm NO2 gas at 25°C. Enhanced response of MOF-derived SnO2 NPs gas sensor was owing to the high surface area of the SnO2 NPs, the presence of oxygen vacancies, formation of plenty of SnO2-SnO2 homojunctions and the creation of SnO/SnO2 heterojunctions. The synthesis method employed in this study led to the preparation of high surface area SnO2 NPs that can be used for preparing other metal oxides for the development of sensors.

Biaxial strain modulation of NO2 adsorption on χ3 borophene: A first-principles study

Based on first-principles calculations, the effects of applying biaxial strain to χ3 borophene and the adsorption behavior of NO2 molecule on the surface of χ3 borophene under strain are investigated. Firstly, the pristine borophene exhibits a metallic electronic structure and the thermodynamic stability of χ3 borophene is demonstrated by molecular dynamics simulations. Different adsorption sites and orientations are selected on the χ3 surface, and the optimal adsorption is found to be the S2 conformation, which has an adsorption energy of −1.589 eV. The applied biaxial strain significantly alters the electron density distribution of the χ3 borophene surface, which is predicted to be able to achieve a modification of the adsorption properties for NO2. Finally, we investigate the NO2 adsorption behavior of χ3 borophene surfaces under 1% to 5% biaxial tensile and compressive strains. Biaxial strain is found to enhance the NO2 adsorption capacity of the χ3 borophene surface, and χ3 at 3% biaxial tensile strain has the highest adsorption energy. Therefore, these results show that χ3 borophene can be a candidate material for gas sensors and theoretically guide researchers to develop more effective sensor materials for gas sensing.

Design and construction of bio carbon derived Bi2Fe4O9 nanocomposites sensor for clad modified optical fiber sensors for detection of ethanol gas

Bio carbon (BC) derived Bi2Fe4O9 hybrid sensor was fabricated via sonochemical approach. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption-desorption were used to determine the structural, morphological and porosity characteristics, respectively. The materials' gas-sensing properties were evaluated using a clad-modified optical fiber sensor. The orthorhombic structure with Pbam space group of Bi2Fe4O9 confirmed by the relative diffraction pattern. All sharp intense diffracted patterns might be indexed based on the standard value ((JCPDS card No. 74-1098). Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images illustrate those granular sheets with aggregated spherical shaped morphology of BC and Bi2Fe4O9, respectively. The pristine Bi2Fe4O9 exhibits Raman modes at 378 cm−1 and 617 cm−1, which is ascribed to the orthorhombic structure. The orthorhombic structure was already confirmed from XRD results. BFOG5 sample shows high SSA (107.5 m2/g) and pore size (38.4 nm), which is nearly 2.2 times greater than that of pristine Bi2Fe4O9 (54.3 m2/g and 23.4 nm). Fiber optic sensor was fabricated and tested for ethanol gas with various gas concentrations (0–500 ppm). The sensitivity (defined as slope of fitted line) enhanced from 14.69 (count/%) for bare Bi2Fe4O9 to 33.94 (count/%) for Bi2Fe4O9/BC (BFOG5). The response and recovery time was 25 s and 20 s for Bi2Fe4O9/BC (BFOG5) sensor, which is higher than that of bare Bi2Fe4O9 (42 s and 33 s). Our findings pave the way for a unique hybrid Bi2Fe4O9/BC composite to be used in a highly sensitive C2H5OH gas sensor system at RT.

Mo-Doped LaFeO3 Gas Sensors with Enhanced Sensing Performance for Triethylamine Gas.

Triethylamine is a common volatile organic compound (VOC) that plays an important role in areas such as organic solvents, chemical industries, dyestuffs, and leather treatments. However, exposure to triethylamine atmosphere can pose a serious threat to human health. In this study, gas-sensing semiconductor materials of LaFeO3 nano materials with different Mo-doping ratios were synthesized by the sol-gel method. The crystal structures, micro morphologies, and surface states of the prepared samples were characterized by XRD, SEM, and XPS, respectively. The gas-sensing tests showed that the Mo doping enhanced the gas-sensing performance of LaFeO3. Especially, the 4% Mo-doped LaFeO3 exhibited the highest response towards triethylamine (TEA) gas, a value approximately 11 times greater than that of pure LaFeO3. Meantime, the 4% Mo-doped LaFeO3 sensor showed a remarkably robust linear correlation between the response and the concentration (R2 = 0.99736). In addition, the selectivity, stability, response/recovery time, and moisture-proof properties were evaluated. Finally, the gas-sensing mechanism is discussed. This study provides an idea for exploring a new type of efficient and low-cost metal-doped LaFeO3 sensor to monitor the concentration of triethylamine gas for the purpose of safeguarding human health and safety.

Effect of Au nanoparticles on mitigating the negative impacts of humidity on ZnO gas sensors to detect triethylamine at room temperature

The impact of humidity on the efficiency of gas sensors has become highlighted in the realm of gas detection. Due to the complex relationship between humidity and gas sensor performance, the development of gas sensors has recently focused on minimizing humidity-related interference. This research aims to address humidity-related challenges in zinc oxide (ZnO) gas sensors designed to detect triethylamine. The ZnO nanostructures (NSs) were synthesized using thermal decomposition methods at varying temperatures (380 °C, 480 °C, and 580 °C) and annealing times (3 h, 7 h, 12 h, and 21 h). X-ray diffraction (XRD) confirmed the formation of a wurtzite hexagonal close-packed structure in ZnO NSs. Scanning electron microscopy (SEM) images provided insights into the morphologies of ZnO NSs at different annealing temperatures, while energy dispersive spectroscopy (EDS) demonstrated the elemental distribution. Subsequently, gold (Au) nanoparticles were uniformly sputtered onto ZnO sensors with thickness variations (0.1 nm, 0.6 nm, 1 nm, 5 nm, and 10 nm). XPS was employed to analyse the elemental composition and oxygen vacancies of the synthesized sensing materials. The effectiveness of 0.6 nm-thick Au nanoparticles in mitigating humidity effects was observed in ZnO sensors synthesized at 380 °C. The results indicated that ZnO sensors coated with 0.6 nm-thick Au nanoparticles exhibited highly stable responses to ethanol and triethylamine at different humidity levels from 50 % to 90 %. Notably, these sensors demonstrated promising selectivity towards triethylamine (with a response of 17.57) compared to various gas targets at room temperature. The sensor exhibited rapid response and recovery times of 9.8 s and 4.4 s, respectively, toward triethylamine with excellent stability in variable humid environments. The sensor maintained a consistent response over 24 days, demonstrating good stability at high humidity.

Toward rationally designing high-performance perovskite sensing material: Role of dielectric constant and crystal symmetry

P-type oxide semiconductor gas sensors have gained increasing attention for their distinctive catalytic activity, high oxygen adsorption, and high humidity resistance. However, the low gas response of p-type sensors restricts their utilization, prompting numerous attempts to overcome this limitation. In this study, we have successfully engineered a promising p-type gas sensor by increasing the dielectric constant and optimizing crystal symmetry, departing from conventional approaches such as reducing particle size, constructing complex heterojunctions, and decorating with noble metals. The as-prepared multiferroic Bi0.92Dy0.8FeO3 gas sensor exhibits a well-defined gas response to acetone, demonstrating ultralow detection limits, distinctive selectivity, high humidity resistance, and long-term stability. Through comparisons of crystal symmetry, morphology, specific surface area, atomic chemical environment, dielectric properties, and sensing properties among a series of Dy3+ doped BiFeO3 solid solutions, we attribute this extraordinary sensing performance of Bi0.92Dy0.8FeO3 to its higher dielectric constant and unique domain-wall structure arising from its non-centrosymmetric crystal structure. This work provides additional perspective for preparing high-performance gas sensors.

Nebulized spray pyrolysis deposited CdO thin films for liquefied petroleum gas and ethanol gas sensor

High quality cadmium oxide (CdO) thin films were prepared through an inexpensive and simple nebulized Spray Pyrolysis (neb-SP) technique. The transparent conducting CdO thin films deposited at different substrate temperatures (TS) for the ethanol and liquefied petroleum gas (LPG) sensor application. XRD, SEM, UV–vis Spectroscopy and Hall Effect were done to study the structural, morphological, optical and electrical properties respectively. Polycrystalline nature thin films shows (1 1 1) cubic structure as the prominent peak. Surface morphology studies reveal that the grain size and roughness of the films are increased with increase in the substrate temperature. The average transmittance of the yellowish transparent CdO thin films is about 57%, thus the films are transparent in the visible region. The optical band gap (Eg) value of the CdO films increased from 2.16 to 2.28 eV with increase in the TS from 225 °C to 300 °C. The minimum value of electrical resistivity of the films is 1.40 × 10−3 Ωcm obtained at 275 °C. The neb-SP deposited CdO thin film (275 °C) shows maximum response to the ethanol and LPG gas sensitivity of 31.87% and 16.4% respectively at operating temperature of 573 K. Thus the results authenticate that the CdO thin films deposited low substrate temperature with high quality can be achieved via neb-SP technique compared to other wet chemical or physical method.

Charge-Transfer Complexes: Fundamentals and Advances in Catalysis, Sensing, and Optoelectronic Applications.

Supramolecular assemblies, formed through electronic charge transfer between two or more entities, represent a rich class of compounds dubbed as charge-transfer complexes (CTCs). Their distinctive formation pathway, rooted in charge-transfer processes at the interface of CTC-forming components, results in the delocalization of electronic charge along molecular stacks, rendering CTCs intrinsic molecular conductors. Since the discovery of CTCs, intensive research has explored their unique properties including magnetism, conductivity, and superconductivity. Their more recently recognized semiconducting functionality has inspired recent developments in applications requiring organic semiconductors. In this context, CTCs offer a tuneable energy gap, unique charge-transport properties, tailorable physicochemical interactions, photoresponsiveness, and the potential for scalable manufacturing. Here, an updated viewpoint on CTCs is provided, presenting them as emerging organic semiconductors. To this end, their electronic and chemical properties alongside their synthesis methods are reviewed. The unique properties of CTCs that benefit various related applications in the realms of organic optoelectronics, catalysts, and gas sensors are discussed. Insights for future developments and existing limitations are described.

Monitoring of meat quality and change-point detection by a sensor array and profiling of bacterial communities

BackgroundReal-time monitoring of food consumer quality remains challenging due to diverse bio-chemical processes taking place in the food matrices, and hence it requires accurate analytical methods. Thresholds to determine spoiled food are often difficult to set. The existing analytical methods are too complicated for rapid in situ screening of foodstuff. ResultsWe have studied the dynamics of meat spoilage by electronic nose (e-nose) for digitizing the smell associated with volatile spoilage markers of meat, comparing the results with changes in the microbiome composition of the spoiling meat samples. We apply the time series analysis to follow dynamic changes in the gas profile extracted from the e-nose responses and to identify the change-point window of the meat state. The obtained e-nose features correlate with changes in the microbiome composition such as increase in the proportion of Brochothrix and Pseudomonas spp. and disappearance of Mycoplasma spp., and with representative gas sensors towards hydrogen, ammonia, and alcohol vapors with R2 values of 0.98, 0.93, and 0.91, respectively. Integration of e-nose and computer vision into a single analytical panel improved the meat state identification accuracy up to 0.85, allowing for more reliable meat state assessment. SignificanceAccurate identification of the change-point in the meat state achieved by digitalizing volatile spoilage markers from the e-nose unit holds promises for application of smart miniaturized devices in food industry.

Electronic Noses: From Gas-Sensitive Components and Practical Applications to Data Processing.

Artificial olfaction, also known as an electronic nose, is a gas identification device that replicates the human olfactory organ. This system integrates sensor arrays to detect gases, data acquisition for signal processing, and data analysis for precise identification, enabling it to assess gases both qualitatively and quantitatively in complex settings. This article provides a brief overview of the research progress in electronic nose technology, which is divided into three main elements, focusing on gas-sensitive materials, electronic nose applications, and data analysis methods. Furthermore, the review explores both traditional MOS materials and the newer porous materials like MOFs for gas sensors, summarizing the applications of electronic noses across diverse fields including disease diagnosis, environmental monitoring, food safety, and agricultural production. Additionally, it covers electronic nose pattern recognition and signal drift suppression algorithms. Ultimately, the summary identifies challenges faced by current systems and offers innovative solutions for future advancements. Overall, this endeavor forges a solid foundation and establishes a conceptual framework for ongoing research in the field.

Magnetoelastic resonators improve humidity sensing capabilities, wirelessly

Ushering in a new generation of remote gas sensors.

Evolution of transition metal dichalcogenide film properties during chemical vapor deposition: from monolayer islands to nanowalls

Unique properties possessed by transition metal dichalcogenides (TMDs) attract much attention in terms of investigation of their formation and dependence of their characteristics on the production process parameters. Here, we investigate the formation of TMD films during chemical vapor deposition (CVD) in a mixture of thermally activated gaseous H2S and vaporized transition metals. Our observations of changes in morphology, Raman spectra, and photoluminescence (PL) properties in combination with in situ measurements of the electrical conductivity of the deposits formed at various precursor concentrations and CVD durations are evidence of existence of particular stages in the TMD material formation. Gradual transformation of PL spectra from trion to exciton type is detected for different stages of the material formation. The obtained results and proposed methods provide tailoring of TMD film characteristics necessary for particular applications like photodetectors, photocatalysts, and gas sensors.

Effect of Ce doping on MoO3 thin films for room temperature ammonia sensing application

In this work, we report the fabrication and gas sensing application of undoped, and Ce doped (1, 2, 3, 4, 5 wt%) MoO3 thin films via simple, effective, and low-cost nebulizer spray pyrolysis method. The crystal structure of the prepared thin films was found to be monoclinic by the prominent peaks observed at (001), (002) planes and the primary peak intensities increases from undoped to 3% Ce doped MoO3 thin film. The morphology of the samples was studied by FESEM, and the films have nanofibrous network embedded with nanorods spread over the surface of the nanofibers. The optical properties were characterised by the UV–vis spectroscopy and observed that the film’s energy band gap declines from 3.28 to 3.04 eV due to the Ce dopant which alters the energy levels of the conduction and valence bands of the host by oxygen defects. The defects were analysed by the PL spectroscopy, and it proved that the PL emission peaks arose due to the oxygen deficiencies. The 3% Ce doped MoO3 produced higher PL emission intensity indicated that the higher oxygen defects sites are the cause. The gas sensing responses were measured for the pristine and 1, 2, 3, 4 and 5 wt% Ce doped MoO3 gas sensors increase from 6.48 × 102 to 1.67 × 104 and found to be higher for the 3% Ce doped sensor to detect ammonia gas. The significant gas sensing property such as rise time and fall time were observed to be least for the 3% Ce doped MoO3 thin film was 54 and 5 s. This study revealed that 3% Ce doped MoO3 thin film could be an efficient prominent ammonia gas sensor at room temperature in future.

High selectivity in NO2 gas sensing applications using polythiophene-MnO2 composite thin films

Many harmful gasses are released during the burning of fossil fuels. Thus, it is essential to create gas sensors with high efficiency and low power consumption. The easy chemical bath deposition approach was used to produce the MnO2-incorporated polythiophene (PTh/MnO2) composite thin film, and its potential application in NO2 gas sensing at the operating temperature was comprehensively examined. The physicochemical properties were examined using FT-IR, FE-SEM, EDAX, AFM, and other instruments. The effects of adding MnO2 on the physicochemical and NO2-sensing properties were studied. Out of all the oxidizing and reducing gases, the PTh/MnO2 composite sensor showed the highest NO2 selectivity when tested at operating temperature (NH3, Cl2, H2S, NO2, and methane). Every PTh/MnO2 composite thin film demonstrated improved NO2 sensing capabilities, with a maximum sensitivity of 95.67 percent for 100 parts per million of gas and a response of 20.93 percent for 0.5 parts per million of gas. Furthermore, they all reacted remarkably well to decreased NO2 gas concentrations.

MXene Supported Surface Plasmon Polaritons for Optical Microfiber Ammonia Sensing.

The properties of surface plasmons are notoriously dependent on the supporting materials system. However, new capabilities cannot be obtained until the technique of surface plasmon enabled by advanced two-dimensional materials is well understood. Herein, we present the experimental demonstration of surface plasmon polaritons (SPPs) supported by single-layered MXene flakes (Ti3C2Tx) coating on an optical microfiber and its application as an ammonia gas sensor. Enabled by its high controllability of chemical composition, unique atomistically thin layered structure, and metallic-level conductivity, MXene is capable of supporting not only plasmon resonances across a wide range of wavelengths but also a selective sensing mechanism through frequency modulation. Theoretical modeling and optics experiments reveal that, upon adsorbing ammonia molecules, the free electron motion at the interface between the SiO2 microfiber and the MXene coating is modulated (i.e., the modulation of the SPPs under applied light), thus inducing a variation in the evanescent field. Consequently, a wavelength shift is produced, effectively realizing a selective and highly sensitive ammonia sensor with a 100 ppm detection limit. The MXene supported SPPs open a promising path for the application of advanced optical techniques toward gas and chemical analysis.

Spontaneously decorated palladium nanoparticles on redox active covalent organic framework for chemiresistive hydrogen gas sensing

A rapid hydrogen (H2) sensor operating at room temperature is fabricated using covalent organic framework (COF), namely Pyromellitic dianhydride and tris(4-aminophenyl)amine (PMDA-TAPA), PT COF that has a unique ability to spontaneously reduce Pd2+ into Pd0 nanoparticles without the aid of external reducing agents. The presence of surface redox sites in COF enable the rapid formation of Pd nanoparticles on COF surface under ambient conditions. The generated material, hitherto named as Pd@amicPT portrayed remarkable H2 sensing characteristics with a rare combination of high response % (67.3 ± 1) and rapid response/recovery times (5.3/3.5 s, respectively) for 1 % H2 under ambient conditions. Our results demonstrated appreciable reproducibility, repeatability, and long term stability of sensor that remained unaffected by relative humidity and a high selectivity towards H2. Further, sensor performance is found to be superior when compared to many Pd loaded 2D material based chemiresistive H2 gas sensors.

Ab Initio Study of the Graphyne-like γ-SiC Nanoflake for Toxic Gas-Sensing Applications.

This study focuses on the geometrical, electronic, and optical properties of the γ-graphyne-like novel γ-SiC nanoflake of the γ-silicon carbide (SiC) monolayer using density functional theory calculations. γ-SiC was revealed to be a stable semiconducting nanoflake confirmed by a negative cohesive energy, real vibrational frequencies, and a 1.749 eV energy gap. The adsorption of COCl2, HCN, PH3, AsH3, CNCl, and C2N2 toxic gases on the γ-SiC nanoflake is also studied, which revealed an attractive gas-nanoflake interaction with the adsorption energy ranging from -0.21 to -0.38 eV. The adsorption results in a significant charge transfer between gas-adsorbent complexes. A significant variation in the energy gap and electrical conductivity was observed due to gas adsorption. γ-SiC showed maximum sensitivity at room temperature for CNCl gas. The entire process of adsorption is exothermic and thermodynamically stable. γ-SiC showed a high absorption coefficient over 104 orders with a significant variation in the absorption peak intensity and blue peak shifting. According to the quantum theory and reduced density gradient analysis, all of the gases are physisorbed on the γ-SiC nanoflake due to van der Waals interactions. The obtained results signify the usability of γ-SiC as a potential toxic gas sensor.

Adsorption and sensing properties of dissolved gases in transformer oil using Cun and Pdn (n=1–3) cluster doped WSe2 monolayers

When the transformer fails, the transformer oil will decompose and produce fault characteristic gases. Detecting dissolved gases in the oil is significant to maintaining the safety and stability of the transformers. This manuscript mainly studies six modified substrates of Cun and Pdn (n=1–3) clusters modified WSe2, and applies them to detect three target gases (CO, CH4, C2H2). By analyzing key parameters based on density functional theory, TMn clusters can effectively improve the electrical conductivity of WSe2 and improve the detection ability of target gases. The order of adsorption effects of target gases on six modified substrates is as follow: TM1-WSe2 is consistent with Cu3-WSe2 (C2H2 > CO > CH4), and TM2-WSe2 is the same with Pd3-WSe2 (CO > C2H2 > CH4). The optimal recovery time for each gas is ultimately determined and these modifications are found to be effective in distinguishing and detecting the three gases. The research results show that WSe2 can be used as a gas sensor material, which provides a theoretical basis for detecting the operating status of oil-immersed transformers.

Real time detection and identification of fish quality using low-power multimodal artificial olfaction system

Single gas quantification and mixed gas identification have been the major challenges in the field of gas detection. To address the shortcomings of chemo-resistive gas sensors, sensor arrays have been the subject of recent research. In this work, the research focused on both optimization of gas-sensing materials and further analysis of pattern recognition algorithms. Four bimetallic oxide-based gas sensors capable of operating at room temperature were first developed by introducing different modulating techniques on the sensing layer, including constructing surface oxygen defects, polymerizing conducting polymers, modifying Nano-metal, and compositing flexible substrates. The signals derived from the gas sensor array were then processed to eliminate noise and reduce dimension with the feature engineering. The gases of were qualitatively identified by support vector machine (SVM) model with an accuracy of 98.86 %. Meanwhile, a combined model of convolutional neural network and long short-term memory network (CNN-LSTM) was established to remove the interference samples and quantitatively estimate the concentration of the target gases. The combined model based on deep learning, which avoids the overfitting with local optimal solutions, effectively boosts the performance of concentration recognition with the lowest root mean square error (RMSE) of 2.3. Finally, a low-power artificial olfactory system was established by merging the multi-sensor data and applied for real-time and accurate judgment of the food freshness.

Pd Nanoclusters-Sensitized MIL-125/TiO2 Nanochannel Arrays for Sensitive and Humidity-Resistant Formaldehyde Detection at Room Temperature.

Among the various hazardous substances, formaldehyde (HCHO), produced worldwide from wood furniture, dyeing auxiliaries, or as a preservative in consumer products, is harmful to human health. In this study, a sensitive room-temperature HCHO sensor, MTiNCs/Pd, has been developed by integrating Pd nanoclusters (PdNCs) into mesoporous MIL-125(Ti)-decorated TiO2 nanochannel arrays (TiNCs). Thanks to the enrichment effect of the mesoporous structure of MIL-125 and the large surface area offered by TiNCs, the resulting gas sensor accesses significantly enhanced HCHO adsorption capacity. The sufficient energetic active defects formed on PdNCs further allow an electron-extracting effect, thus effectively separating the photogenerated electrons and holes at the interface. The resulting HCHO sensor exhibits a short response/recovery time (37 s/12 s) and excellent sensitivity with a low limit of detection (4.51 ppb) under ultraviolet (UV) irradiation. More importantly, the cyclic redox reactions of Pdδ+ in PdNCs facilitated the regeneration of O2-(ads), thus ensuring a stable and excellent gas sensing performance even under a high-humidity environment. As a proof-of-principle of this design, a wearable gas sensing band is developed for the real-time and on-site detection of HCHO in cigarette smoke, with the potential as an independent device for environmental monitoring and other smart sensing systems.