Gas Sensor Applications Research Articles

Fast and selective isoprene gas sensor: Influence of polystyrene size and role of the au catalyst on gas sensing properties

Sacrificial methods using polystyrene (PS) templates are extensively applied in various research fields, particularly for fabricating gas sensors. The many processing advantages of these methods, such as a uniform particle size distribution, ease of manipulation, and potential for functionalization enable the fabrication of intricate nanostructures with precise control of the geometry and surface-area-to-volume ratio. Nevertheless, no previous study has investigated the fundamental correlation between the size of the PS particles used as a template and the performance of the resulting functional gas sensor. In this study, we fabricated In2O3 hollow hemispheres (HHs) with PS template sizes ranging from 200 to 3000 nm to explore the essential aspects for gas sensor applications. Notably, compared to In2O3 thin films, In2O3 HHs-based sensors prepared using a 3000 nm PS template exhibited a larger surface area, particularly when formed in a monolayer, and achieved an enhanced gas response to C2H5OH by approximately 132 times. By decorating In2O3 HHs with Au nanoparticles, the detection of C5H8 at 350 ℃ among various volatile organic compounds was significantly enhanced (increase ratio = 31.7), achieving a response of 483 and a theoretical detection limit as low as 743 parts per trillion (ppt). In addition, the highly porous structure with Au decoration achieved an extremely short response time of less than 2 s. These unprecedented results provide critical insights into conventional sensor technologies and pave the way for potential health-monitoring applications and bioelectronics.

Pure and Ce-Doped MnO2–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

Pure and Ce-Doped MnO2–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

Simulations of Infrared Reflectivity and Transmission Phonon Spectra for Undoped and Doped GeC/Si (001).

Exploring the phonon characteristics of novel group-IV binary XC (X = Si, Ge, Sn) carbides and their polymorphs has recently gained considerable scientific/technological interest as promising alternatives to Si for high-temperature, high-power, optoelectronic, gas-sensing, and photovoltaic applications. Historically, the effects of phonons on materials were considered to be a hindrance. However, modern research has confirmed that the coupling of phonons in solids initiates excitations, causing several impacts on their thermal, dielectric, and electronic properties. These studies have motivated many scientists to design low-dimensional heterostructures and investigate their lattice dynamical properties. Proper simulation/characterization of phonons in XC materials and ultrathin epilayers has been challenging. Achieving the high crystalline quality of heteroepitaxial multilayer films on different substrates with flat surfaces, intra-wafer, and wafer-to-wafer uniformity is not only inspiring but crucial for their use as functional components to boost the performance of different nano-optoelectronic devices. Despite many efforts in growing strained zinc-blende (zb) GeC/Si (001) epifilms, no IR measurements exist to monitor the effects of surface roughness on spectral interference fringes. Here, we emphasize the importance of infrared reflectivity Rω and transmission Tω spectroscopy at near normal θi = 0 and oblique θi ≠ 0 incidence (Berreman effect) for comprehending the phonon characteristics of both undoped and doped GeC/Si (001) epilayers. Methodical simulations of Rω and Tω revealing atypical fringe contrasts in ultrathin GeC/Si are linked to the conducting transition layer and/or surface roughness. This research provided strong perspectives that the Berreman effect can complement Raman scattering spectroscopy for allowing the identification of longitudinal optical ωLO phonons, transverse optical ωTO phonons, and LO-phonon-plasmon coupled ωLPP+ modes, respectively.

Reusable gasochromic gas sensor with enhanced selectivity for acidic gases via surface-engineered all-inorganic perovskite nanocrystals

The use of strong acids is crucial for the fabrication of highly integrated semiconductor devices. To effectively detect and alert against the potential hazards of acid gas leakage, considerable advancements have been made to enhance gas sensor sensitivity. However, most available gas sensors only detect cations (H+), making it challenging to precisely identify the specific types of acids present. Cesium lead halide perovskite nanocrystals, renowned for their exceptional optical properties, have emerged as promising candidates for gas-sensing applications. Nonetheless, concerns regarding reuse stability persist. In this study, surface engineering via solution-phase ligand exchange is conducted to address halide vacancies and prevent acid-induced structural degradation. The resulting surface-modified perovskites exhibit remarkable gasochromic sensitivity and selectivity towards HCl and HNO3. Furthermore, the vivid emission properties of these perovskites enable the visual detection of danger without the need for additional warning equipment. Finally, the reusability of the gas sensors is evaluated, and the perovskite-based sensors are recyclable.

Assessment of titanium - tungsten iron oxide and their gas sensor application

Assessment of titanium - tungsten iron oxide and their gas sensor application

Promising CO2 gas sensor application of zinc oxide nanomaterials fabricated via HVPG technique

Highly effective gas sensors for detecting a range of hazardous and toxic gases were successfully applied in the present study using Zinc oxide (ZnO) nanomaterials. In this work, the horizontal vapor phase growth (HVPG) technique was perfectly capable of the synthesis of zinc oxide (ZnO) nanomaterials. The effect of the growth time with different dwell times was discussed by comparing the SEM-EDX analysis and photoluminescence characterization of the samples. Magnetic field (AMF) was also incorporated to determine the effect of AMF on the synthesis of ZnO nanomaterials. The results showed that the ZnO nanorods and root-like shapes are formed with more than 5 μm length and a few nm diameters. The optimum parameter showed the sensors are shiner than the less effective sensor when applied. The introduction of an external magnetic field led to a reduced energy band gap by a maximum of 15 %. The non-AMF band gap energy value is observed to be between 3.51 and 3.58 eV, while the value obtained using AMF is found to be between 2.94 and 3.22 eV. During the CO2 gas sensor test, AMF ZnO nanomaterial samples exhibited higher voltage and gradient compared to non-AMF samples.

NO sensing properties of MoS2/WSe2 heterostructure at room temperature under UV light irradiation

Transition metal dichalcogenides (TMDs) have recently sparked interest in gas-sensing applications. Generally, the kinetics of gases show minimal reactivity when the sensor is operable at room temperature (RT). Photon excitation is a potential solution for enhancing gas kinetics at RT. The present study delves gas sensing properties of MoS2/WSe2 heterostructure, emphasizing its effectiveness in detecting a broad range of NO concentration (0.1 ppm to 10 ppm) at room temperature using UV-light (266 nm & 355 nm) as a catalyst. The results reveal a remarkable 13x & 5x amplification in NO detection at 10 ppm for MoS2/WSe2 heterostructure compared to pristine WSe2 and MoS2, which were primarily tested. The highest relative sensor response of 95.4 % is reported for 10 ppm of NO gas at RT under 266 nm illumination. The sensing results revealed a substantial reduction in the limit of detection (LOD) to around 16 ppb, followed by a swift response speed of 10.31/14.38 seconds. The synergistic combination of WSe2 and MoS2 and their high specific surface area enhance NO sensitivity under UV exposure. The fabricated device holds substantial importance in environmental monitoring and healthcare, paving the way for real-time data acquisition in gas sensing.

First principle investigation on gas sensing properties of MoS2/ZnO heterojunction

MoS2/ZnO heterojunction is theoretically constructed based on density functional theory (DFT). The adsorption and electrical properties of MoS2/ZnO heterojunction after adsorbing six toxic gas molecules (CO, NO, NO2, SO2, H2S and NH3) are investigated, including adsorption energy, energy gap, density of states, charge density difference, planar-average charge density, total charge density, work function and recovery time. The results suggest that the adsorption energy of MoS2/ZnO for six gas molecules are significantly increased compared with intrinsic MoS2. Especially, the adsorption energy of the heterojunction for NO2, SO2, H2S and NH3 reach to −0.88, −0.98, −0.79 and −1.08 eV, respectively, indicating that the adsorption behavior is changed from physisorption to chemisorption. In addition, after adsorption of gas molecules (CO, NO, NO2, SO2, H2S and NH3), the energy gap of MoS2/ZnO is decreased to 0.793, 0.964, 0.834, 0.864, 0.804 and 0.770 eV, respectively, which indicates that the conductivity of MoS2/ZnO is improved. The adsorption distance (D) is also decreased after adsorption gases, especially for H2S gas molecule (0.797 Å). In addition, the work function (WF) of adsorption system is decreased and the charge transfer is increased. These results indicate that the interaction between MoS2/ZnO and gas molecules is stronger than that of intrinsic MoS2. Therefore, MoS2/ZnO has potential application for gas sensor to detect toxic gas molecules.

Potential for multi-application advancements from doping zirconium (Zr) for improved optical, electrical, and resistive memory properties of zinc oxide (ZnO) thin films

Transition metal-doped Zinc oxide (ZnO) thin films with an optimal wide band gap and semiconducting nature find numerous applications in optoelectronic devices, gas sensors, spintronic devices, and electronics. In this study, Zirconium (Zr) doped ZnO thin films were deposited on ITO (Indium Tin oxide) coated glass substrate using RF-magnetron sputtering. Optical and electrical properties were examined for their potential use in resistive random-access memory (RRAM) applications. X-ray Diffraction (XRD), UV–vis spectroscopy, x-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) were used to investigate structural, optical, and compositional properties and roughness respectively. The results demonstrate that the films possess crystalline properties. Additionally, an augmentation in Zr concentration correlates with an elevation in the optical band gap, ascending from 3.226 eV to 3.26 eV, accompanied by an increase in Urbach energy from 0.0826 eV to 0.1234 eV. The film with the highest Zr content among all the films demonstrated the best electrical performance for resistive memory applications. Incorporating Zr as a dopant shows enhancement in the electrical performance and such ZnO films with optimum concertation of Zr can potentially be used in RRAM. ZnO being a versatile host material, its doping with Zr may extend its applications in catalysis, gas sensing, energy storage, and biomedical engineering. ZnO thin films employ zirconium (Zr) as a dopant, which is a novel way to improve the material’s characteristics. Although ZnO has been thoroughly researched, adding Zr presents a novel technique to enhance optical, electrical, and resistive memory characteristics all at once that has not been fully investigated.

DFT Study on the Janus ZrSSe Monolayer for Its Potential Application in NO Gas Sensing.

The growth of industry has resulted in increased global air pollution, necessitating the urgent development of highly sensitive gas detectors. In this work, the adsorption of the Janus ZrSSe monolayer for CO, CO2, NH3, NO, NO2, and O2 was studied by first-principles calculations. First, the stability of the ZrSSe monolayer is confirmed through calculations of cohesive energy and AIMD simulations. Furthermore, the calculations indicate that the Se layer exhibits higher selectivity and sensitivity toward gas molecules compared to the S layer. Specifically, among the gases adsorbed on the Se layer, NO has the shortest adsorption distance (1.804 Å), the lowest adsorption energy (-0.424 eV), and the greatest electron transfer (0.098 e). Additionally, density of states analysis reveals that adsorption of NO, NO2, and O2 on the Janus ZrSSe monolayer can induce a transition from a nonmagnetic to a magnetic state. The adsorption of NO not only alters the magnetic state but also induces a transition from a semiconductor to metal, which is highly advantageous for gas sensing applications. There results suggest that the Janus ZrSSe monolayer has the potential to serve as a highly sensitive detector for NO gas.

Investigating the adsorption performance of agricultural greenhouses hazardous gases on Rh doped HfX2 (X=S, Se) monolayers through DFT for potential gas sensor applications

This study uses density functional theory to study the adsorption performance of agricultural greenhouses hazardous gases on Rh doped HfX2 (X=S, Se) monolayers. After multiple geometric optimizations, the most stable adsorption configuration was found. The results indicate that the adsorption energy of Rh doped HfX2 monolayers is very stable for adsorbing small molecule gases. The change in the total density of states of the adsorption system reveals the transfer and recombination of electrons during the adsorption process, and the partial density of states helps to understand the interactions between bonding atoms. Molecular orbital analysis shows that LUMO is mainly concentrated near Hf atoms, while HOMO is mainly concentrated near X atoms, Rh atom, and gases. By calculating the work function, the interaction strength and electron transfer mechanism between the adsorbent and the metal surface are revealed. In addition, the recovery time indicates that HfX2 and Rh-HfSe2 are excellent adsorbents for these four gases at room temperature, but when HfS2 operates at 473 K, it will be an efficient and excellent gas sensor for the four gases. Thus, Rh-HfS2 can be a feasible resistance sensing material for Cl2 and SO2. This DFT results provide a theoretical basis for potential gas sensor applications of Rh doped HfX2 (X=S, Se) monolayers, leading to the design and development of more efficient greenhouse gas identification sensor devices.

Synthesis, characterization, and gas-sensing application of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles

Fabrication of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles, with x = 0.00, 0.01, 0.02, 0.04, 0.06, and 0.08, has been carried out using a wet chemical co-precipitation method. The effect of the rare earth Nd3+ doping on the prepared ferrites was structurally investigated using x-ray diffraction (XRD) along with Rietveld refinement. The results indicate great crystallinity in the FCC Fd3m spinel structure of Cd0.5Zn0.5NdxFe2–xO4 nanoparticles. The lattice parameter increases with the increase of doping concentration from 8.5378 until 8.5432 Å and the crystallite size obtained using Debye-Sherrer, Williamson–Hall, Size-strain plot (SSP), and Halder-Wagner (H-W) methods, decreases until the solubility limit of the materials is at x = 0.04. By using transmission electron microscopy (TEM), the morphological analysis reveals the spherical shape of the samples with minor agglomeration with the aid of using a Polyvinylpyrrolidone (PVP) capping agent. The grain size ranges from 14.37 to 15.24 nm. Raman spectroscopy verifies the incorporation of Nd3+ in the octahedral sites and the decrease in particle size. The elemental composition was verified using x-ray photoelectron spectroscopy (XPS). The magnetic properties were studied using a vibrating sample magnetometer (VSM) and it shows superparamagnetic behavior with a decrease in the saturation magnetization from 2.207 to 1.918 emu g−1 and an increase in coercivity from 7.194 to 14.397 G. The prepared materials were tested as liquefied petroleum gas (LPG) sensors by studying their sensitivity, selectivity, optimum working temperature, response, and recovery times. Nd3+ doping shows a great increase in LPG sensing sensitivity 4 to 20 times than the pure samples. The doping concentration also decreases the response and recovery times.

Architectures of MoS2/SnO2 nanoflowers for NO2 gas detection

In this research, a two-step hydrothermal technique is used to fabricate a NO2 gas sensor based on MoS2 nanoflowers with SnO2 nanoparticles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were used to determine the morphologies, nanostructures, and compositions of the materials. The nanocomposites consisting of MoS2/SnO2 demonstrated a remarkable sensing response (38.6) towards 100 ppm of NO2. Moreover, the nanocomposites showed a rapid response and recovery time (42/147 S) when exposed to 100 ppm at temperature (250 °C). The MoS2/SnO2 nanocomposites demonstrated exceptional selectivity to NO2 against CO, NH3, and H2S, as well as demonstrated good repeatability. The significant gas detection characteristics could potentially be controlled by the distinctive structures of thin layers assembled into flower-like formations of two-dimensional MoS2. The multi-joint nanostructures promote the process of transferring the electrical charge of the carrier and the response to MoS2/SnO2 and NO2. The fabricated sensors are considered as potential candidates for the commercial in the nitrogen dioxide gas-sensing applications.

Self-Assembled Ti3C2TX MXene Thin Films for High-Performance Ammonia Sensors

MXenes have emerged as a fascinating material for RT gas-sensing applications due to their outstanding properties. This work reports the design and fabrication of a high-performance ammonia sensor based on MXenes material. To improve its sensing performance, a MXenes nanosheets thin film with a thickness of ≈ 10 nm was prepared using a scalable self-assembled method. Specifically, we employed the controlled and enhanced interfacial self-assembled method to fabricate a continuous and conductive MXene ultra-thin film. The morphology and the structure of the produced MXene materials and their films were characterized by combining multi-characterization tools. Altoghether, these highlight the uniform and continuous deposition of the MXene nanosheets film on the glass substrate. The electrical characterization indicates a sheet resistance value of 4.82 × 105 Ω/sq. The fabricated devices present good RT sensing performances for NH3 detection, ranging from 1 to 20 ppm. This demonstrates the outstanding sensitivity of MXene with a value of 1.92 % for the lowest concentration (1 ppm), a fast response (179 s) and a recovery time of (612 s), which is related to the high quality of the ultra-thin MXene sensiting layer. Moreover, the sensors demonstrate high degree of stability and excellent reproducibility, make them suitable candidate for practical applications like environmental monitoring.

Electrohydrodynamic-Jet-Printed SnO2-TiO2-Composite-Based Microelectromechanical Systems Sensor with Enhanced Ethanol Detection.

Ethanol sensors have found extensive applications across various industries, including the chemical, environmental, transportation, and healthcare sectors. With increasing demands for enhanced performance and reduced energy consumption, there is a growing need for developing new ethanol sensors. Micro-electromechanical system (MEMS) devices offer promising prospects in gas sensor applications due to their compact size, low power requirements, and seamless integration capabilities. In this study, SnO2-TiO2 nanocomposites with varying molar ratios of SnO2 and TiO2 were synthesized via ball milling and then printed on MEMS chips for ethanol sensing using electrohydrodynamic (EHD) printing. The study indicates that the two metal oxides dispersed evenly, resulting in a well-formed gas-sensitive film. The SnO2-TiO2 composite exhibits the best performance at a molar ratio of 1:1, with a response value of 25.6 to 50 ppm ethanol at 288 °C. This value is 7.2 times and 1.8 times higher than that of single SnO2 and TiO2 gas sensors, respectively. The enhanced gas sensitivity can be attributed to the increased surface reactive oxygen species and optimized material resistance resulting from the chemical and electronic effects of the composite.

2H-SnS2 assembled with petaloid 1T@2H-MoS2 nanosheet heterostructures for room temperature NO2 gas sensing.

In this study, we explored the gas-sensing capabilities of MoS2 petaloid nanosheets in the metallic 1T phase with the commonly investigated semiconducting 2H phase. By synthesizing SnS2 nanoparticles and MoS2 petaloid nanosheets through a hydrothermal method, we achieve notable sensing performance for NO2 gas at room temperature (27 °C). This investigation represents a novel study, and to the best of our knowledge no, prior similar investigations have been reported in the literature for 1T@2HMoS2/SnS2 heterostructures for room temperature NO2 gas sensing. The formed heterostructure between SnS2 nanoparticles and petaloid MoS2 nanosheets exhibits synergistic effects, offering highly active sites for NO2 gas adsorption, consequently enhancing sensor response. Our sensor demonstrated a remarkable sensing response (R a/R g = 7.49) towards 1 ppm of NO2, rapid response time of 54 s, baseline recovery in 345 s, good selectivity and long-term stability, underscoring its potential for practical gas-sensing applications.

Understanding the NaxMnO2 System: A Thermodynamics and XPS Approach.

The NaxMnO2 system is an important class of materials with potential applications in rechargeable batteries, supercapacitors, catalysts, and gas sensors. This work reports the synthesis of NaxMnO2 (x = 0.39, 0.44, 0.48, 0.66, and 0.70) compounds and their characterization by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy (IS) techniques. The compounds in this series exhibit a significant variation in their structures with the extent of Na-content. The change in the nature of bonding with increasing Na content was investigated, and its effect on material stability as well as electrotransport properties was investigated. A detailed thermodynamic evaluation of these materials was carried out employing calorimetric techniques, and the data were correlated with changes in the chemical environment around the Na ion. This analysis is crucial for predicting the thermodynamic stability of NaxMnO2 compounds under different environments for their applications in Na-ion batteries.

Synthesis, characterization and sensing applications of TiO2 doped MOF composites for selective detection of ammonia at room temperature

Herein, we have developed a highly sensitive chemiresistive TiO2 doped metal–organic framework(MOF) composite-based sensor for ammonia detection at room temperature. Two novel Ti-MOFs@TiO2 composites are developed employing terephthalic acid and 2-amino terephthalic acid as organic linkers with Titanium tetra isopropoxide (TTIP) as a metal source by solvothermal technique. The morphology and crystallinity of synthesized compounds were characterized by using Field-emission scanning electron microscopy (FE-SEM) with EDX analysis, X-ray diffraction (PXRD), XPS and Brunauer–Emmett–Teller (BET) analysis techniques. MIL-125@TiO2 sensors exhibited a more specific surface area (374.74 m2 g−1) than the other three compounds. For gas-sensing applications, all composite materials were exposed to different gas vapours like ammonia, formaldehyde, acetic acid, ethyl alcohol, acetone, xylene, toluene and benzene at room temperature. The sensing results indicate that the sensors exhibit excellent response at low concentrations of ammonia, formaldehyde and acetic acid gases (1 ppm level). The enhanced sensor response was attributed to MIL-125@TiO2 (85 response at 50 ppm) and NH2-MIL-125@TiO2 (71 response at 50 ppm) towards ammonia gas and shows a better selectivity, sensitivity and repeatability to ammonia gas. All the materials exhibited less response times (between 8 and 45 sec) and more recovery times (between 13 and 125 sec).

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.

Synthesis, Characterisation, and Applications of TiO and Other Black Titania Nanostructures Species (Review)

Black titania, a conductive ceramic material class, has garnered significant interest due to its unique optical and electrochemical properties. However, synthesising and properly characterising these structures pose a considerable challenge. This diverse material family comprises various titanium oxide phases, many of them non-stoichiometric. The term “black TiO2” was first introduced in 2011 by Xiaobo Chen, but Arne Magneli’s groundbreaking discovery and in-depth investigation of black titania in 1957 laid the foundation for our understanding of this material. The non-stoichiometric black titanium oxides were then called the Magneli phases. Since then, the science of black titania has advanced, leading to numerous applications in photocatalysis, electrocatalysis, supercapacitor electrodes, batteries, gas sensors, fuel cells, and microwave absorption. Yet, the literature is rife with conflicting reports, primarily due to the inadequate analysis of black titania materials. This review aims to provide an overview of black titania nanostructures synthesis and the proper characterisation of the most common and applicable black titania phases.