Gas-sensing Characteristics Research Articles

Effects of Al doping on structural, optical, morphological, and low-concentration CO2 gas sensing properties of ZnO nanoparticles synthesized by sol-gel method

Abstract This work examines the morphological, structural, optical, and gas-sensing characteristics of ZnO thin films doped with Al that were created by the sol-gel spin coating technique. The thin films, doped with varying aluminum concentrations (0%, 2%, and 5%), were characterized using XRD, UV-visible spectroscopy, and FE-SEM to assess their crystallinity, band gap, and surface morphology. XRD analysis confirmed the incorporation of Al into the ZnO lattice without forming secondary phases, while UV-visible spectroscopy revealed an increase in transmittance and band gap with higher Al doping. FE-SEM images showed a transition from agglomerated grains to smoother surfaces with increased Al content. Gas sensing performance was evaluated using low-concentration CO2 as the target gas. The results demonstrated that Al doping significantly enhances the CO2 sensing response, with the 5% Al-doped ZnO exhibiting the optimal sensitivity due to increased carrier concentration and improved surface interaction. These findings suggest that Al-doped ZnO thin films are promising candidates for efficient CO2 gas sensors, combining enhanced structural and optical properties with superior gas sensing capabilities.

CO2 detection using In and Ti doped SnO2 nanostructures: Comparative analysis of gas sensing properties

This research explores the gas-sensing characteristics of undoped SnO2, as well as indium (In:SnO2) and titanium (Ti:SnO2) doped SnO2 nanostructures, which were synthesized using a homogeneous precipitation technique. Structural analyses indicate the presence of a tetragonal rutile phase with a preferred orientation along the (110) plane, with both doped samples showing shifts towards higher angles. Raman spectroscopy confirms the vibrational modes associated with SnO2 in both the pure and In: SnO2 samples, while the Ti: SnO2 sample reveals vibrational modes corresponding to both SnO2 and TiO2. Fourier-transform infrared (FTIR) spectroscopy indicates shifts in the O-Sn-O and Sn-O bonds in the doped samples, suggesting the effects of doping. X-ray photoelectron spectroscopy (XPS) results imply a combination of SnO and SnO2 phases in the undoped SnO2, while In: SnO2 samples display In-O bonding and the presence of metallic indium, and Ti: SnO2 shows Ti-O bonding. Scanning electron microscopy (SEM) images show agglomerated particles in the pure and In-doped samples, whereas the Ti-doped samples exhibit a flake-like structure. Transmission electron microscopy (TEM) analysis verifies the integration of dopants into the SnO2 crystal lattice, with average crystallite sizes measured at 44.46 nm for undoped, 34.06 nm for In: SnO2, and 42.63 nm for Ti: SnO2. Gas-sensing experiments for CO2 detection reveal that In: SnO2 demonstrates the most significant sensing response. These results underscore the impact of doping on the structural, morphological, and gas-sensing attributes of SnO2 nanostructures, offering important insights for the advancement of efficient carbon dioxide sensors.

Fluorinated polyaniline-based sensors with enhanced NH3 sensitivity

Poly(2-fluoroaniline) films were prepared by electrochemical oxidation of 2-fluoroaniline in perchloric acid solutions. These films had a characteristic globular structure, but low thickness and conductivity. For these reasons, alternative polymer films were prepared from electrolytic solutions with different aniline:2-fluoroaniline ratios. The physicochemical properties of these polymer films strongly evolved with the ratio since they were thicker and more conductive when the proportion of aniline increased while their morphology also varied significantly. The electrodeposited polymer films were then used as sensitive layers of gas sensors for ammonia detection. The addition of 2-fluoroaniline improved the performance characteristics of gas sensors for the detection of ammonia at room temperature and the poly(aniline/2-fluoroaniline)-based sensors responded to ammonia gas with good repeatability, good sensitivity (0.44 %/ppb), a very low detection limit (4 ppb), and a low dependence on humidity variations.

Smell cancer by machine learning-assisted peptide/MXene bioelectronic array

Non-invasive detection of tumors is of utmost importance to save lives. Nonetheless, identifying tumors through gas analysis is a challenging task. In this work, biosensors with remarkable gas-sensing characteristics were developed using a self-assembly method consisting of peptides and MXene. Based on these biosensors, a mimetic biosensor array (MBA) was fabricated and integrated into a real-time testing platform (RTP). In addition, machine learning (ML) algorithms were introduced to improve the RTP's detection and identification capabilities of exhaled gas signals. The synthesized biosensor, with the ability to specifically bind to targeted gas molecules, demonstrated higher performance than the pristine MXene, with a response up to 150% greater. Besides, the MBA successfully detected 15 odor molecules affiliated with five categories of alcohols, ketones, aldehydes, esters, and acids by pattern recognition algorithms. Furthermore, with the ML assistance, the RTP detected the breath odor samples from volunteers of four categories, including healthy populations, patients of lung cancer, upper digestive tract cancer, and lower digestive tract cancer, with accuracies of 100%, 94.1%, 90%, and 95.2%, respectively. In summary, we have developed a cost-effective and precise model for non-invasive tumor diagnosis. Furthermore, this prototype also offers a versatile solution for diagnosing other diseases like nephropathy, diabetes, etc.

Synthesis and structural characteristics of AgxSn1–xO2 nanocomposites and their sensing performance toward methane, hydrogen, and carbon monoxide

The physical features and potential applications of metal oxide semiconductor nanomaterials can be influenced by doping, heat treatment, and applied synthesis techniques. Herein, a simple hydrothermal method was used to synthesize AgxSn1–xO2 nanocomposites (x=0, 0.05, 0.2, 0.4, 0.5, and 1). The crystal structure, surface morphology, chemical bonding, surface area, and oxidation states are investigated. FTIR, XRD, HR-TEM, SEM, and XPS techniques were used to characterize the AgxSn1–xO2 nanocomposites, while the electrical resistivity measurement was conducted to assess their gas-sensing characteristics. The findings demonstrate that Ag atoms are evenly distributed inside the tetragonal SnO2 lattice up to x=0.4, meanwhile, a further increase in x leads to the growth of a cubic Ag2O phase alongside the SnO2 phase. The crystallite size of the SnO2 phase was increased as the Ag concentration increased, whereas reduced for the Ag2O phase. The pure SnO2 phase exhibits spherical nanoparticles, whereas the AgxSn1–xO2 nanocomposites (x > 0) have a morphology of nanosheets and nanoplates. The average BET surface area was improved to 358 m2/g by increasing the Ag content up to x=0.2. The XPS confirms the presence of various oxides such as Sn 3d, O 1 s, and Ag 3d. The AgxSn1–xO2 nanocomposites were employed as electrical sensors to detect CH4, H2, and CO gases at an operating temperature range of 200–400 °C. The Ag0.2Sn0.8O2 nanocomposites show the best response/recovery time towards CH4 at 200 °C. The AgxSn1–xO2 composite exhibits a good response towards CH4 compared to H2, and CO gases.

Enhanced Gas Sensing Characteristics of a Polythiophene Gas Sensor Blended with UiO‐66 via Ligand Functionalization

AbstractConjugated polymers exhibit significant potential for use in gas sensors owing to their flexibility and straightforward preparation. However, the performance of organic gas sensors based on such materials is currently suboptimal owing to their poor charge‐transport properties and limited selectivity. To address this limitation, a novel strategy that involves blending a chemically modified metal–organic framework (MOF) material, UiO‐66, with a conjugated polymer is developed. The MOF porous material is chemically modified with polar nitrogen‐containing functional groups (amino and nitro groups) to create gas molecule adsorption sites. To evaluate the impact of these modifications on the sensing performance, experiments that combined the sensing performance with a density functional theory simulation are conducted. The findings reveal that gas sensors fabricated using an amine‐functionalized MOF blended with conjugated polymers exhibit significantly higher sensitivity than home polymer devices, the sensing performance of the UiO‐66‐NH2/P3HT blend film improved by a factor of two with a sensitivity of ≈2%/ppm and an LOD of 0.001 ppt. Additionally, these devices exhibit exclusive NO2‐sensing performance for other gases such as CO2 and SO2.

Study of Ethanol Gas Sensing Characteristics of An Al-Doped SnO₂ Thin Film Decorated With Gold Nanoparticles

Study of Ethanol Gas Sensing Characteristics of An Al-Doped SnO₂ Thin Film Decorated With Gold Nanoparticles

Influence of a Magnetic Field on the Structure, Morphology and Gas Sensing Characteristics of ZnO: Al Thin Films Prepared by Pulsed Laser Ablation

In this work, aluminium-doped zinc oxide (AZO) nanostructure at 0.3 wt% and 0.5 wt% Al was synthesized using the pulse-laser ablation technique in liquid(PLAL) using pulsed Nd: YAG laser of a fundamental wavelength of (1064 nm). The process was done in the absence and presence of an external magnetic field. The deposited AZO nanostructures by drop-casting on etched-Si wafers were examined by different techniques. The XRD test illustrates enhancing the crystallinity of the prepared thin films by applying an external magnetic field. The FESEM images displayed the change of nanostructure to nano-sheets of high surface area after using a 77.2 mT permanent magnet placed behind the target during the ablation process. The gas sensor based on the AZO nanostructures has higher sensitivity against NO2 than H2S. Increasing the Al ratio from 0.3 wt% to 0.5 wt% changed the properties of the prepared samples to have small porosity and small surface area, which negatively affected the properties of the sensor

Sensitivity-Enhanced, Room-Temperature Detection of NH3 with Alkalized Ti3C2Tx MXene.

A layered Ti3C2Tx MXene structure was prepared by etching MAX-phase Ti3AlC2 with hydro-fluoric acid (HF), followed by alkalization in sodium hydroxide (NaOH) solutions of varying concentrations and for varying durations. Compared to sensors utilizing unalkalized Ti3C2Tx, those employing alkalized Ti3C2Tx MXene exhibited enhanced sensitivity for NH3 detection at room temperature and a relative humidity of 40%. Both the concentration of NaOH and duration of alkalization significantly influenced sensor performance. Among the tested conditions, Ti3C2Tx MXene alkalized with a 5 M NaOH solution for 12 h exhibited optimal performance, with high response values of 100.3% and a rapid response/recovery time of 73 s and 38 s, respectively. The improved sensitivity of NH3 detection can be attributed to the heightened NH3 adsorption capability of oxygen-rich terminals obtained through the alkalization treatment. This is consistent with the observed increase in the ratio of oxygen to fluorine atoms on the surface terminations of the alkalization-treated Ti3C2Tx. These findings suggest that the gas-sensing characteristics of Ti3C2Tx MXene can be finely tuned and optimized through a carefully tailored alkalization process, offering a viable approach to realizing high-performance Ti3C2Tx MXene gas sensors, particularly for NH3 sensing applications.

Design of an economic, portable, compact, and indigenous instrument setup for measuring sensing characteristics of thin film gas sensors.

Thin film gas sensor characterization is very demanding for various applications because of technical design trade-offs in commercially available gas sensors. For gas sensing characterization, a suitable gas-testing experimental setup is very much needed in this context. Various factors in the experimental setup can affect a thin film gas sensor's response beyond gas exposure. These factors include the test chamber's volume, relative humidity, uniform operating temperature, uniform pressure, uniform gas density, uniform gas distribution, uniform gas concentration in the gas chamber, and uniform relative gas flow velocity over the surface of the sensor. All these environmental parameters, not being so predictive in nature, induce an inherent design trade-off in the experimental setup design. Although all the commercially available gas testing experimental setups are equally good considering the dedicated purpose for which they are made. However, all of them are for generic applications but not for specific applications because of their inherent trade-offs in their usability features. Those trade-offs always provide an opportunity to introduce a new setup with its own unique advantages. Hence, in this article, we have presented a portable, compact, indigenous gas sensing experimental setup for studying the performance of gas sensors. We have characterized and tested the setup using a ZnO based thin film gas sensor when exposed to CO2 gas at concentrations ranging from 1445 to 4631 ppm. The proposed gas sensing setup's compact size offers unique advantages, including portability and compatibility for uniform environmental conditions.

Metal (Au, Ag, Pt) Doping Effects on the Gas-Sensing Mechanism and Characteristics of Two-Dimensional WS2: A First-Principle

Metal (Au, Ag, Pt) Doping Effects on the Gas-Sensing Mechanism and Characteristics of Two-Dimensional WS₂: A First-Principle

The Influence of 2-Methoxyethanol as Capping Agent on WO3-Based Carbon Monoxide Gas Sensor Characteristics

Carbon monoxide (CO) gas detection using a modified WO3-based sensor is being developed. The solvent for solvothermal use, a combination of 2-Propanol and 2-Methoxyethanol, was employed as a capping agent before graphene was used as a component of nanocomposites. Following the creation of the powder, it is combined with ethyl glycol and applied to an alumina substrate using the Doctor Blade process.By X-ray diffraction research, it was discovered that the solvent combinations of 2-Propanol and 2-Methoxyethanol formed monoclinic WO3 in the amounts of 40-0 and 30-10, respectively, while the solvent combinations of 20-20 are thought to have produced W18O49 and 10-30, WO2.9, respectively. According to the SEM examination, the WO3 generated was first present as nanowires and nanorods before being calcined at 500 degrees Celsius, and it then appeared as nanoparticles. The sensor may work at a low temperature of 150°C, and the best sensitivity is found when the sensor is used at a temperature of 250°C, according to the CO gas test findings.

Synthesis of Bitter gourd-shaped Cu-doped ZnO nanostructures and their investigation for the detection of NO2 gas at low concentrations

Nitrogen dioxide (NO2) exposure can have several adverse health impacts on people, especially the respiratory system. Low selectivity, a lack of long-term stability, and structural and morphological optimization are some challenges associated with using ZnO for NO2 gas sensing. Therefore, we intended copper (Cu) doping in ZnO to alter its shape and gas-sensing characteristics. This study explores the synthesis, properties, and gas-sensing capabilities of bitter gourd-shaped Cu-doped zinc oxide (ZnO) nanostructures for the detection of nitrogen dioxide (NO2). A facile hydrothermal synthesis method was employed to synthesize bitter gourd-shaped Cu-doped ZnO nanostructures and comprehensively characterized by several techniques. Comprehensive characterizations of our produced Cu-doped ZnO nanomaterial demonstrated by X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), and different energy spectrum. The material was annealed at 400 °C in a controlled dry air environment to improve its suitability for gas sensor applications. A series of temperature-ranging experiments were conducted to get gas-sensing readings from 25 °C to 300 °C. The resulting sensor, founded upon the distinctive morphology of Cu-doped ZnO structures reminiscent of the intricate shape of bitter gourd, unveiled good selectivity with a pronounced affinity for detecting NO2 gas. Notably, the zenith of its performance was attained at an operating temperature of 200 °C, where its selectivity and sensitivity were most pronounced. Even at a low concentration of 1 ppm, the sensors displayed a maximum response of 3.7, highlighting their high sensitivity. The sensors demonstrated excellent reproducibility, selectivity, and a low detection limit. These findings position bitter gourd-shaped Cu-doped ZnO nanostructures as promising candidates for NO2 sensing applications across diverse environments.

Humidity-tolerant and highly sensitive gas sensor for hydrogen sulfide based on WO3 nanocubes modified with CeO2.

The influence of ambient humidity on the gas-sensing characteristics of metal oxide semiconductors has been one of the greatest obstacles for gas-sensing applications. In this paper, the pure WO3 and CeO2-modified WO3 nanocubes were prepared by a simple hydrothermal method, and their gas-sensing characteristics in dry and humid atmospheres were investigated. The results show that CeO2/WO3 demonstrated excellent gas-sensing properties toward H2S with high sensitivity and high selectivity at 115 °C. Noteworthy, the humidity independence of the CeO2/WO3 increased compared to the WO3. The response retentions over the whole humidity range of the CeO2/WO3-6 and CeO2/WO3-15 sensors were 70.3, and 76%, respectively, which were much higher than the WO3 sensor (17.9%). The gas-sensing mechanism of CeO2-modified WO3 is discussed based on the gas sensitivity properties. The obtained results provide a promising route to enhance the anti-humidity properties of metal oxide semiconductor gas sensors.

Low-Power Consumption IGZO Memristor-Based Gas Sensor Embedded in an Internet of Things Monitoring System for Isopropanol Alcohol Gas.

Low-power-consumption gas sensors are crucial for diverse applications, including environmental monitoring and portable Internet of Things (IoT) systems. However, the desorption and adsorption characteristics of conventional metal oxide-based gas sensors require supplementary equipment, such as heaters, which is not optimal for low-power IoT monitoring systems. Memristor-based sensors (gasistors) have been investigated as innovative gas sensors owing to their advantages, including high response, low power consumption, and room-temperature (RT) operation. Based on IGZO, the proposed isopropanol alcohol (IPA) gas sensor demonstrates a detection speed of 105 s and a high response of 55.15 for 50 ppm of IPA gas at RT. Moreover, rapid recovery to the initial state was achievable in 50 μs using pulsed voltage and without gas purging. Finally, a low-power circuit module was integrated for wireless signal transmission and processing to ensure IoT compatibility. The stability of sensing results from gasistors based on IGZO has been demonstrated, even when integrated into IoT systems. This enables energy-efficient gas analysis and real-time monitoring at ~0.34 mW, supporting recovery via pulse bias. This research offers practical insights into IoT gas detection, presenting a wireless sensing system for sensitive, low-powered sensors.

Comparative study on gas-sensing properties of amorphous MoS2 nanoparticles and crystalline MoS2 nanoflowers

High-performance gas sensors for the field of gas sensing have drawn a lot of attention to molybdenum sulfide materials, but there is little research on the influence of crystallization state of MoS2 on gas sensitivity performance. In this study, amorphous MoS2 and crystalline MoS2 were prepared by the hydrothermal method. Then, the gas-sensing characteristics of the as-synthesized amorphous MoS2 and crystalline MoS2 toward NO2 gas were thoroughly investigated and compared. According to the results, with an excellent response value of 1.99 toward 5 ppm NO2 at room temperature, the crystalline MoS2 gas sensor outperformed the amorphous one, while that of the amorphous MoS2 under the same condition was 1.25. However, Four times faster recovery periods were observed in the amorphous MoS2 sample compared to the crystalline MoS2 sample. At the same time, the recovery level of amorphous MoS2 is high and can be fully restored. We discovered that the primary cause of the strong recovery performance of amorphous MoS2 is the presence of localized states that facilitate the easy transition of electrons from the conduction band to the valence band, allowing for effective recombination with the holes. Additionally, the surface of the material absorbs a significant amount of oxygen, which will occupy more of the NO2 adsorption site and hasten the desorption of NO2. This work may aid in the development of gas sensors based on amorphous molybdenum sulfide.

Remarkable surface area engineering of nanosheet-assembled hierarchical p-n Ag-loaded NiO-CeO2 heterostructure for superior ethanol sensing performance

The creation of ultra-high surface areas of heterostructures based on p-n NiO-CeO2 hierarchical nanospheres and nanosheet-assembled Ag-loaded p-n NiO-CeO2 is reported, employing a straightforward hydrolysis method. A porous NiO-CeO2 heterostructure was produced by an improved 24 h urea synthesis reaction time, while the addition of Ag nanoparticles reduced the grain size and produced a remarkable surface area of 472 m2 g−1 with a significant number of adsorption sites. For the 1.0 wt% Ag-loaded p-n NiO-CeO2 heterostructure, the optical band decreased from 3.01 to 2.37 eV. Photoluminescence experiments revealed larger surface defects for the 1.0 wt% Ag-loaded NiO-CeO2 heterostructure provided additional evidence for the reduced band. Therefore, compared to its counterparts, the 1.0 wt% Ag-loaded NiO-CeO2 demonstrated superior ethanol sensing, an excellent sensitivity of 0.81 ppm−1, and an ultra-low limit of detection of 1.23 ppb, towards ethanol vapor at 100 °C. The sensing mechanism illustrated that the greater gas-sensing characteristics were associated with the catalytic effect and electronic sensitization of AgO and the engineering of nanosheet-assembled hierarchical heterostructures with an extraordinary specific surface area providing sufficient active sites for the adsorption of ethanol gas, highly porous structures, and an interlayer gap, which accelerated the ethanol diffusion, leading to enhanced sensitivity and response speed of the sensor. Therefore, this study provided a simplistic approach to engineering the nanosheet-assembled hierarchical 1.0 wt% Ag/NiO-CeO2 microspheres with enhanced ethanol sensing performance.

Optimizing Gas Sensing Properties of Fe-Loaded Indium Zinc Oxide Nanocomposite for Efficient Detection of Ammonia Gas

The current study delineates the role of gas sensing properties of Fe-IZO (Iron loaded Indium Zinc oxide) a mixed metal oxide nanocomposite. The heterostructured Fe-IZO nanocomposite (NC) was synthesized via the facile co-precipitation method. The Fe-IZO NC was characterized by various experimental techniques and the results attained allowed us to suggest the mechanism for considering the connection between morphological variations and gas-sensing characteristics of Fe-IZO NC. One of the cutting-edge circumstances now-a-days is the prime use of gas sensors for environmental applications. The NC has a good selectivity for NH3 gas that has shown good stability up to 80 d. The response time (ℸres) is 64 s, recovery time (ℸrec) is 72 s for 50 ppm (parts per million) and obtained a highest response of 87% at room temperature. The Fe-IZO NC heterostructure with efficient charge transfer can enable the subsequent reaction mechanism with NH3 gas and the adsorbed oxygen ions leading to an increased response. Consequently, the results attained in this work has shown that the synthesized heterostructured NC sensor is suitable for room temperature NH3 sensing with high performance.

Tailoring gas sensing properties of WS2 monolayer via Nb and Co embedding for highly sensitive and selective detection of HCN and H2S gases: a first principle study

We report on the adsorption performances of HCN, H2S, HF, and H2 gases on Nb and Co embedded WS2 monolayer using density functional theory calculations. The adsorption configurations, adsorption energy, charge transfer, density of state, band structure, and recovery time were studied to evaluate the possible tailoring of gas sensing properties to improve sensitivity and selectivity of the WS2 monolayer. The results show that HCN exhibits better adsorption on the Nb-embedded WS2 with an adsorption energy of −1.09 eV and charge transfer of −0.18 e, whereas H2S shows superior adsorption on the Co-embedded WS2 with an adsorption energy of −1.1 eV and charge transfer of 0.23 e. Better sensitivity and selectivity were recorded for the adsorption of the HCN and H2S on the Nb and Co-embedded WS2 monolayer respectively. At 398 K, the recovery times for the two sensing systems are 54 s and 61 s for Nb-embedded WS2 with HCN and Co-embedded WS2 with H2S respectively making them suitable for gas sensing applications. The study reveals the promising capabilities of Nb-embedded WS2 and Co-embedded WS2 in detecting HCN and H2S, respectively. In addition, it thoroughly investigates the influence of surface modifications on the characteristics of gas sensors.

Effective Reinforcement of Visible Light Photocatalytic and Gas Sensing Characteristics of Nanocrystalline TiO2: Gd-Based Nb and Mo Dopants

Efficient compositions for the selective detection of ethanol gas and the removal of organic contaminants were realized by codoping of (Gd, Nb) and (Gd, Mo) ions into TiO2. TiO2, Ti0.96Gd0.01Nb0.03O2, and Ti0.96Gd0.01Mo0.03O2 samples were prepared by a coprecipitation method. For all compositions, a crystalline anatase phase of TiO2 was detected. Compared to pure TiO2, the absorption edges of Ti0.96Gd0.01Nb0.03O2 and Ti0.96Gd0.01Mo0.03O2 samples were red-shifted, further broadening towards visible light. The morphological studies demonstrate that the grains of TiO2 were more refined after (Gd, Nb) and (Gd, Mo) codoping. The photocatalytic efficiency of the Ti0.96Gd0.01Mo0.03O2 catalyst for degrading 20 mg/L reactive yellow 145, brilliant green, and amoxicillin was 98, 95, and 93% in 90 min, respectively. The reusability experiments indicate that the Ti0.96Gd0.01Mo0.03O2 catalyst had high stability during reuse. The high photocatalytic activity of the Ti0.96Gd0.01Mo0.03O2 catalyst was correlated to the broad visible-light absorption and effective separation of electron–hole pairs by Gd3+ and Mo6+ cations. The gas sensing characteristic is reflected by the high sensitivity of the Ti0.96Gd0.01Nb0.03O2 sensor to ethanol gas in the presence of different gases at 275 °C. The obtained results indicated that the (Gd, Mo) mixture could more effectively induce the photocatalytic properties of TiO2 while (Gd, Nb) dopants were the best for reinforcing its sensing characteristics.