Gas Sensor Applications Research Articles

Synergistic effects of Mg doping on TiO2 for improved toxic gas sensing performance at room temperature

The gas sensing characteristics of magnesium (Mg)-doped titanium dioxide (TiO2) films were investigated using a spray pyrolysis method. TiO2 Thin films with varying Mg doping concentrations (0, 2.5, and 5 weight percentages) were deposited and tested for their gas detection ability to organic compounds such as ethanol, butanol, toluene, xylene, and formaldehyde at room temperature. Results disclosed that introducing Mg into TiO2 enhanced the gas sensing characteristics, particularly for formaldehyde. Mg-doped TiO2 film improved the change in electrical resistance during gas adsorption, leading to an increased response in formaldehyde detection. Additionally, XRD revealed the crystal structure, while Raman spectroscopy provided insights into molecular vibrational modes of the fabricated films. FESEM allowed for high-resolution imaging of surface morphology, and atomic force microscope assessed surface roughness and other properties of the as deposited samples. UV-Vis spectroscopy was utilized to examine the optical characteristics. The collective results strongly indicated that the introduction of Mg significantly improved the gas-sensing capabilities of TiO2 films, making them highly promising for various gas-sensing applications.

Enhancements of Structural and Optical Properties of MgO: SnO2 Nanostructure Films

This study investigates the structural and optical properties of MgO:SnO2 nanoparticles using the Chemical precipitation method, The thin films were deposited by the spin coating technique on glass substrates. X-ray diffraction analysis proved the crystalline structure of prepared thin films, with the peaks corresponding to the (110), (101), (200), (211), and (220) planes, with the tetragonal SnO2 crystal structure, Fourier transforms infrared (FTIR), and scanning electron microscope (SEM) used to characterize the functional groups, shape, and dimensions of synthesized metal oxide nanoparticles. The optical properties of the films were studied by UV-Vis spectroscopy, and the bandgap energy was estimated to be in the range of (3.9 - 3.4 eV). The refractive index and extinction coefficient of the films were also determined, and the results indicated that the films had good transparency in the visible region, The study concludes that MgO:SnO2 thin films obtained by spin coating technique have potential applications in optoelectronics and gas sensors.

Adsorption behavior of Janus MoSiGeN4 monolayer for gas-sensing application with high sensitivity and reuse

Two-dimensional (2D) Janus materials have raised considerable attention from the scientific community because of their asymmetric structure and distinctive physical characteristics. Here, we theoretically study the surface gas adsorption effects on the monolayer MoSiGeN4 (MSGN) due to its high carrier mobility and tunable electronic properties. The results show that the built-in electric field in MSGN results in lower adsorption energies on the Si-side than that on the Ge-side. Additionally, the Si-side of MSGN exhibits higher sensitivity to NO2 detection, and the recovery time and conductivity of NO2 adsorption on MSGN are found to be 1.92 × 10−9 s and 138 k/(S × m−1), respectively. Particularly, the Si-side MSGN-based sensors have higher sensitivity for gas detection. This finding provides possibilities for gas sensors with selectivity and sensitivity based 2D Janus monolayers.

Synthesis, study and characterization of spinel CoFe2O4 for the ethanol gas-sensing applications

Synthesis, study and characterization of spinel CoFe2O4 for the ethanol gas-sensing applications

The Effect of Annealing Temperature on Iron-Doped Tungsten Oxide Structure and Photosensitive Gas Sensor Applications

Öz
 Bu çalışmada, demirin tungsten oksit yapısına katkılanması ve ardından 550oC'de tavlanması ile kristal yapı ve gaz sensör tepkisindeki değişimler incelenecektir. Absorpsiyon-dalga boyu ölçümleri sonucunda yapının hesaplanan bant aralığının 3,08-3,15 eV arasında olduğu görüldü. İnce filmlerin doğrudan optik bant aralığı enerjisi (Eg), Tauc denklemi kullanılarak hesaplanmıştır. Bant aralığındaki elektronik konfigürasyondaki değişiklik sonucunda 0,7 eV'lik bir artış gösterdi. İnce filmin ısıl işlemi sonucunda absorpsiyon miktarı ve absorpsiyon dalga boyu değişmiştir. Böylece yarı iletkenin optik bant aralığında bir genişleme meydana gelir. Püskürtme tekniği ile büyütülen WO3:Fe filmlerin X-ışını kırınım deseni yapının amorf olduğunu göstermektedir ancak havada 550 derecede tavlama sonrasında kaliteli bir polikristal yapı oluştuğu görülmektedir ki bu da SEM görüntülerinde bu sonucu desteklemektedir. WO3: Fe'nin XRD modellerinin tüm belirgin tepe noktaları, yedi belirgin tepe noktası (24o, 34o, 42o, 37.38o, 49o, 55o, 61o) sunan tungsten oksitin kübik yapısına endekslenebilir. Daha sonra, RF-DC co-sputter tekniği ile büyütülen demir katkılı tungsten oksit (WO3:Fe) yapılarının yapısal, optik ve topografik özellikleri taramalı elektron mikroskobu (SEM), atomik kuvvet mikroskobu (AFM), X- ışın kırınımı (XRD) ve UV-VIS foto spektroskopi teknikleri. RF-DC co-sputtering ile büyütülen demir katkılı tungsten oksit (WO3:Fe) metal oksit yapısının hidrojen gazına tepkisi 1000 ppm akış değerlerinde, 300 oC sıcaklıkta beyaz ışık ve karanlıkta ölçülmüştür. Tüm ölçümler aynı döngüde 300 s, 180 s ve 120 s olarak alındı. İncelenen ince filmlerin karanlıkta gaz sensörü uygulamasına uygun olduğu, beyaz ışık altında ise uygun olmadığı görülmüştür.

ZnO Intercalated PVA-PEDOT:PSS Composite Nanofiber for Detection of Ammonia Gases

Keywords: Ammonia, Electrospinning, and Zinc OxideThe matter of air pollution has dramatically risen the worldwide concern on detecting of hazardous gases present in the atmosphere because they are highly detrimental to human health [4,5]. Additionally, the detection and monitoring of such harmful gases is necessary for process control in the industry as well as the general safety of the environment. Zinc oxide (ZnO) is an n-type semiconductor with a wide direct bandgap width (3.37 eV), high excitation binding energy (60meV), high electron mobility, thermal stability, and excellent electrical properties [1]. Other promising materials for gas-sensing applications encompass single elements, silicon and tellurium-based materials and organic semiconductors. The sensing materials that are of intense research interest are conducting polymers such as polyaniline (PANI), polypyrrole (PPy) and poly(3,4-thylenedioxythiophene) (PEDOT) used in the fabrication of polymer-based gas sensors [2]. Its capability to work at low operating temperatures while maintaining high sensitivity leads to the synergistic effect when in combination with metal oxides to produce high-performance gas sensors. They are very appealing in terms of energy saving as they do not need an additional source of heat, consequently reducing the operating cost, simplifying the fabrication process, and extending the lifespan of the device [3]. In this work, ZnO intercalated PVA-PEDOT:PSS composite nanofiber as a sensing layer was prepared by electrospinning method. This material was characterized both morphologically and structurally by X-ray diffraction analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy and thermogravimetric analysis. The results from TEM and SEM show well distribution of ZnO particles in the polymer matrix. The gas measurement results reveal that the fabricated ZnO loaded PVA-PEDOT:PSS composite sensor exhibits excellent gas response (63%) to ammonia gas in 100 ppm gas concentration at 120 °C. Acknowledgment This research was supported by the research grant 021220CRP0122 “Development of highly sensitive MOS based nano-film gas sensors” from Nazarbayev University. References S. Bhati, M. Hojamberdiev, and M. Kumar, “Enhanced sensing performance of ZnO nanostructures-based gas sensors: A Review,” Energy Reports, vol. 6, pp. 46–62, 2020.Yan, Y. et al. (2020) “Conducting polymer-inorganic nanocomposite-based Gas Sensors: A Review,” Science and Technology of Advanced Materials, 21(1), pp. 768–786.Zhang, J. et al. (2015) “Nanostructured materials for room-temperature gas sensors,” Advanced Materials, 28(5), pp. 795–831.C. Eze, E. Schaffner, E. Fischer, T. Schikowski, M. Adam, M. Imboden, M. Tsai, D. Carballo, A. von Eckardstein, N. Künzli, C. Schindler, and N. Probst-Hensch, “Long-term air pollution exposure and diabetes in a population-based Swiss cohort,” Environment International, vol. 70, pp. 95–105, 2014.C. Shim, J. Han, D. K. Henze, M. W. Shephard, L. Zhu, N. Moon, S. K. Kharol, E. Dammers, and K. Cady-Pereira, “Impact of NH3 emissions on particulate matter pollution in South Korea: A case study of the seoul metropolitan area,” Atmosphere, vol. 13, no. 8, p. 1227, 2022. Figure 1

Investigating of transition state on the Pd–Au decorated ZnO nanoparticle layers for gas sensor application

In this work, the mechanism of the transition state of electron transfer reaction on the surface of the ZnO nanoparticles-based gas sensor has been investigated. The deposited ZnO nanoparticles thick films on glass slides had been synthesized by the current heating method and modified its surface by coating novel metals of gold and palladium with a sputtering technique with different sputtering times of 45–180 s. Field emission electron microscopy (FE-SEM), x-ray diffraction spectroscopy (XRD), and energy dispersive spectroscopy (EDS) were used for the characterization of ZnO nanoparticle thick films. After that, the reflectance spectra of films were investigated using Near-IR spectroscopy in the range of 900–2500 nm to study the surface absorption efficiency. The decrease in reflectance spectra was observed for conditions over 90 s of sputtering time. The particle size distribution and zeta potential of ZnO nanoparticles were analyzed using the dynamic light scattering technique for the calculation of particle size and the electrical charge potential. The results showed that the size particle distribution ranged from 155 to 245 nm and the more extensive range of 360–1100 nm. The optimized zeta potential of −14.44 mV was exhibited at the sputtering time of 45 s. Finally, the gas sensing mechanism in terms of surface charge density was proposed and used to explain the sensitivity enhancement of both resistive and capacitive gas sensors.

Metal-organic framework based sensing materials for the application of gas sensors

Metal-organic framework based sensing materials for the application of gas sensors

Adsorption of gas molecules on monolayer As/Sb lateral heterostructures investigated by first principles

Gas detection is already crucial for addressing an increasingly polluted environment. Due to its great advantages in terms of high carrier mobility, large specific surface area, and quick reaction, two-dimensional heterojunctions are widely used in high-performance gas sensor applications. In this study, two different types of LHSs (lateral heterostructures) based on As/Sb were built along armchair (AC) and zigzag (ZZ) interfaces, and the adsorption of gas molecules (NO2, NO, and NH3) on them was examined using first-principles calculations. The findings showed that NO2 molecules are chemically adsorbed on As/Sb LHSs, whereas NH3 molecules are physically adsorbed on As/Sb LHSs, NO molecules are physically at the AC interface, and chemically adsorbed at the ZZ interface.

Surface Modulation of Co3O4 Yolk-Shell Spheres with Tungsten Doping for Superior Acetone Sensitivity.

This study introduces a promising technique to enhance the sensitivity of p-type semiconductors in gas-sensing applications. By utilizing a glycerate-templated synthesis approach, a unique hierarchical W-doped Co3O4 yolk-shell sphere (YSS)-based sensor was developed, exhibiting exceptional sensitivity toward acetone gas. The synthesized YSSs feature a yolk-shell structure with a diameter of approximately 500 nm and a large surface area of 117.46 m2/g, which allows for efficient gas interaction and high sensitivity toward acetone gas. Furthermore, the incorporation of tungsten (W), a non-noble metal, as a dopant significantly enhances the surface activity of Co3O4, leading to a remarkably high response of 16.5 toward 5 ppm acetone, which is substantially higher than that of the pure Co3O4 YSS (2.9). The W-doped Co3O4 YSS also exhibits excellent selectivity to other interfering gases and the ability to detect ultralow concentrations of acetone as low as 10 ppb. The proposed non-noble metal doping strategy presents a practical solution for enhancing the sensitivity and selectivity of p-type semiconductor-based gas sensors. This approach holds great potential for practical gas-sensing applications due to their affordability and abundance, making them a cost-effective and versatile alternative to noble metal-catalyzed sensors.

Utilizing Hydrazine and Hydrogen as Reducing Agents to Control the Nanoscale Surface Morphology of the Palladium Thin Films

A key challenge facing fabrication of nanomaterials is the ability to precisely control the surface morphology of the nanostructures through exploitation of process parameters. In this study, palladium thin films with carefully controlled surface morphologies are obtained through the careful choice of the reducing agent used during the pre‐plating activation step in the three‐step autocatalytic electroless plating consisting of 1) surface functionalization; 2) surface activation; and 3) deposition of the film onto alumina substrates. It is important to note that the reducing agents that influenced the surface morphology of the palladium thin films are employed in the pre‐plating activation step instead of the widely utilized electroless deposition step. It is revealed in the high‐resolution scanning electron microscope results that the hydrogen reducing agent yields a dense film with 3D spheroidal morphologies with an average cluster size of ≈415 nm while the hydrazine reducing agent produces a very smooth uniform surface morphology consisting of extremely small grains. The obtained results can be exploited in controlling and tailoring the surface‐dependent properties of the palladium thin film for applications in gas sensors, detectors, or palladium‐based membranes.

Progress and Insights on Graphene and MXene‐based Emerging 2‐Dimensional Conductive Nanomaterials for Fabrication of Flexible Gas Sensors

AbstractOwing to the unique properties such as pristine interfaces, ultra‐thin and uniform thickness, 2D nanomaterials have attracted the attention from many researchers. Particularly, rGO and MXene 2D nanomaterials have received intense research interest in the application of gas sensors due to their high electrical conductivity. The coating of these 2D nanomaterials onto plastic, paper or textile substrate formed flexible, stretchable and portable gas sensors as an alternative to the conventional rigid gas sensors. To date, numerous research works on flexible gas sensors using either graphene or MXene have been published. However, the reported data is scattered and varied by multiple factors. In this short review, we revisit the advances in the current application of 2D conductive nanomaterials (mainly rGO and MXene) and their nanocomposites with metal oxides on flexible gas sensors. We focus on recent developments regarding the working mechanism, advantages, disadvantages, and performances (including gas response, selectivity, response time, and recovery time) of each type of gas sensor. Finally, this short review sheds light on future directions and prospects in the field of flexible gas sensors using 2D nanomaterials.

Multifunctional hexagonal-shaped zinc vanadate nanostructures for lithium-ion battery and NH3 gas sensor applications

Vanadium-based metal oxides are used in different fields like gas sensors, supercapacitors, and lithium (Li)-ion batteries due to their availability, layered structure, and facile synthesis. Herein, we report a temperature-effective strategy to synthesize hexagonal-shaped zinc vanadate (Zn2VO4 (ZVO)) nanostructures (NSs) via a facile hydrothermal method without any further doping of an element or carbon additive. The synthesized ZVO NSs provide large surface area, low energy band gap, and fast Li+ diffusion. When compared with the ZVO-120 (synthesized at 120 °C) and ZVO-160 samples, the ZVO-140 sample shows a lower energy band gap value of 2.57 eV with higher surface area (37 m2 g−1) and porous nature. As an anode material for Li-ion batteries, the ZVO-140 demonstrates superior rate capability (126 mA h g−1 at 1.5 A g−1) and excellent cycling performance (576 mA h g−1 after 100 cycles at 0.05 A g−1 and 327 mA h g−1 after 2000 cycles at 1 A g−1) as well as good Li+ diffusion coefficient (2.61 × 10−8 cm2 s−1). Due to these synergistic benefits, ZVO NSs are used for NH3 gas sensing application. The ZVO-140 sample exhibits excellent sensitivity (47.3%) at 190 °C with fast response/recovery time (136 s/128 s) and reliable stability towards NH3 gas (100 ppm) at 190 °C, when compared with counterparts (ZVO-120 and ZVO-160). This preparation strategy may initiate the design of advanced ZVO-based materials for multifunctional applications.

Multiplexed Gas Sensor: Fabrication Strategies, Recent Progress, and Challenges.

Due to miscellaneous toxic gases in the vicinity, there is a burgeoning need for advancement in the existing gas sensing technology not only for the survival of mankind but also for the industries based in various fields such as beverage, forestry, health care, environmental monitoring, agriculture, and military security. A gas sensor must be highly selective toward a specific gas in order to avoid incorrect signals while responding to nontarget gases. This may lead to complex scenarios depicting sensor defects, such as low selectivity and cross-sensitivity. Therefore, a multiplex gas sensor is required to address the problems of cross selectivity by combining different gas sensors, signal processing, and pattern recognition techniques along with the currently employed gas sensing technologies. The different sensing materials used in these sensor arrays will produce a unique response signal for developing a set of identifiers as the input that can be used to recognize a specific gas by its "fingerprint". This review provides a comprehensive review of chemiresistive-based multiplex gas sensors, including various fabrication strategies from expensive to low-cost techniques, advances in sensing materials, and a gist of various pattern recognition techniques used for both rigid and flexible gas sensor applications. Finally, the review assesses the current state-of-the-art in multiplex gas sensor technology and discusses various challenges for future research in this direction.

Temperature-dependent electrical resistivity of tungsten oxide thin films

Tungsten oxide (WO3) thin films have been previously investigated for various applications. Optoelectronic and electrochromic applications require detailed knowledge of the electrical properties of such films, whereas gas-sensing applications require understanding the electrical resistivity and its variation with temperature. In numerous studies on the electrical properties of WO3 thin films, the results were widely scattered and critically dependent on deposition and resistivity measurement conditions. This paper presents a systematic investigation of the electrical resistivity of WO3 thin films and its variation with temperature. WO3 thin films were deposited on heated substrates using thermal evaporation both in vacuum and under an oxygen atmosphere. Subsequently, the films were annealed in air or in vacuum. The structural, chemical, optical, and room-temperature electrical properties were measured. The temperature-dependent electrical resistivity was measured at 300–700 K in air or in vacuum. The activation energies for electrical conduction were derived from these measurements and were used to investigate the mechanisms responsible for electrical conduction.

Use of Concave Sapphire Substrate to Synthesize ZnO Nanorod Arrays and Application of a Cu-decorated ZnO Nanorod Array Gas Sensor

Use of Concave Sapphire Substrate to Synthesize ZnO Nanorod Arrays and Application of a Cu-decorated ZnO Nanorod Array Gas Sensor

Influence of vacancy defects on 2D BeN4 monolayer for NH3 adsorption: a density functional theory investigation

Two-dimensional materials have attracted a great deal of interest in developing nanodevices for gas-sensing applications over the years. The 2D BeN4 monolayer, a recently synthesized single-layered Dirac semimetal, has the potential to function as a gas sensor. This study analyzes the NH3 sensing capacity of the pristine and vacancy-induced BeN4 monolayers using first-principles density functional theory (DFT) calculations. As per the results, the NH3 molecule is physisorbed on the pristine BeN4 via weak Van der Waals interaction with a poor adsorption energy of −0.41 eV and negligible charge transfer. Introducing Be vacancy in BeN4 increased the NH3 adsorption energy to −0.83 eV due to the improved charge transfer (0.044 e) from the defective monolayer to the NH3 molecule. The structural stability, sufficient recovery time (74 s) at room temperature, and superior work function sensitivity promise the potential application of defective BeN4 as an NH3 sensor. This research will be a theoretical groundwork for creating innovative BeN4-based NH3 gas sensors.

Ocimum sanctum Leaf Extract-Assisted Green Synthesis of Pd-Doped CuO Nanoparticles for Highly Sensitive and Selective NO2 Gas Sensors.

In view of facile, cost-effective, and environmentally friendly synthetic methods, palladium-doped copper oxide (Pd-CuO) nanoparticles have been synthesized from Ocimum sanctum (commonly known as "Tulsi") phytoextract for gas-sensing applications. The structural, morphological, and compositional properties of Pd-doped CuO nanoparticles were studied using various techniques such as XRD, FESEM, XPS, and EDX. The characterization results confirmed the doping of Pd on CuO nanoparticles, and Pd-CuO nanostructures appear as nanoflakes in FESEM analysis. The gas-sensing response of Pd (1.12 wt %)-CuO nanoflake-based sensor was measured at 5-100 ppm concentration of different gases, NO2, H2S, NH3, and H2, at 125 °C. Gas-sensing tests reveal that the sensitivity of the sensor were 81.7 and 38.9% for 100 and 5 ppm concentrations of NO2, respectively, which was significantly greater than that of pure CuO. The response and recovery times of the sensor were 72 and 98 s for 100 ppm of NO2 gas, while they were 90 and 50 s for 5 ppm NO2. The calculated limit of detection (LOD) value of the sensor is 0.8235. This appealing LOD is suitable for real-time gas detection. The gas sensor was found to exhibit excellent selectivity toward NO2 gas and repeatability and stability in humid (80%) conditions. The Pd doping in CuO nanostructures plays a significant role in escalating the sensitivity and selectivity of CuO-based NO2 gas sensor suitable to work at low operating temperatures.

Effect of Ultraviolet Light on Mn3O4 Thin Films that are Grown Using SILAR for Room-Temperature Ozone Gas Sensors

Successive ionic layer adsorption and reaction (SILAR) is a promising technique to fabricate gas sensors at room temperature. However, the quality of the films is poor, leading to reduced surface area and increased defects within the film structure, thus decreasing the overall gas response. Inferior film quality also negatively affects the stability and reproducibility of the gas sensors over time. This study determines the effect of UV treatment on the structural, morphological, and ozone (O3) gas-sensing properties of p-type Mn3O4 thin films. As UV treatment time increases, the O3 gas-sensing characteristics increase because a porous structure with a higher surface area is formed and electrical conductivity is increased. Under a UV intensity of 20 mW cm−2, the Mn3O4 sensor exhibits gas response, response time, and recovery time of 1.62, 58, and 39 s, respectively, against 5 ppm concentration of O3 gas. Moreover, the Mn3O4 gas sensor exhibits excellent long-term stability showing around 3% variation in gas response over 60 d. This strategy allows the deposition of high-quality p-type Mn3O4 thin films using SILAR for applications in flexible gas sensors.

Synthesis and Characterization of Zn0.5Co0.5Fe2O4 Nanoparticles for Gas Sensing Applications

In this study, Zn0.5Co0.5Fe2O4 nanoparticles were synthesized by solution combustion method. The solution combustion method is a convenient, chief, environment friendly, and capable for the synthesis of high-quality nanomaterials. As prepared Zn0.5Co0.5Fe2O4 were annealed at 800 °C. The electrical, thermal, structural, magnetic, morphological and gas sensing properties of the synthesised materials has been studied in details. The spinel crystal structure was confirmed from X-ray diffraction, with average crystalline size of 37 nm. The elemental compositions in the synthesized powder were estimated using EDX spectra. The magnetic nature of the material was confirmed from vibrating sample magnetometer (VSM), conducted at room temperature with highest applied field of 15 KOe and it shows ferromagnetic behaviour. The nearly spherical particles shapes were observed from TEM and FESEM images. The fabricated thick films of the synthesised material were exposed to various gases like NH3, Cl2, H2, CO2 and LPG at different temperatures. It was observed that the gas sensing responses depends on their operating temperature. Additionally, the sensor has a quick response time and a speedy recovery time. The gas sensing results demonstrated that Zn0.5Co0.5Fe2O4 is a novel gas sensor material with good sensitivity and selectivity to LPG compared to other gases. The probable LPG gas sensing mechanism is schematically represented in this paper. This study provides, Zn0.5Co0.5Fe2O4 synthesised using low-cost solution combustion technique has a great potential in future gas sensing fields.