Gas-sensing Properties Research Articles

Carbon gas sensors synthesized using acacia auriculiformis tree branches to detect methanol, ethanol, acetone vapors and ammonia gas

Metal oxides and carbon are the prime candidates of gas sensor devices. For the inaugural instance, carbonaceous particulate matter was meticulously derived from the branches of Acacia auriculiformis tree indigenous to Sri Lanka to detect vapor and gas. It is worth noting that biomass derived carbon had hitherto remain unexplored in the realm of vapor and gas detection. Carbon films were fabricated via the doctor blade method. The resistivity characteristic of these carbon samples exhibited discernible variations upon exposure to methanol, ethanol, acetone vapors, and ammonia gas. Notably, the gas-sensing properties of sample derived from the central core and the outer shell of Acacia auriculiformis tree branches were independently assessed in these vapors and gas at ambient temperature. Various analytical techniques, including X-ray diffraction (XRD), UVvisible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), were judiciously employed to scrutinize the structural attribute, optical band gap, chemical composition and surface morphology of the aforementioned carbon film samples, respectively. XRD analyses unequivocally confirmed the successful formation of carbonaceous films. FTIR spectra conspicuously delineated the presence of oxygen within the carbon films. Importantly, the optical band gap of our carbon films manifested within the range characteristic of organic carbon. Furthermore, the resistance of the carbon films demonstrated a significant reduction upon adsorption of each vapor. It is noteworthy that while gas sensitivities and response times were superior for carbon derived from the central core of the Acacia tree branches, the recovery times were notably expedited for carbon synthesized from the outer shell of these branches. The zenith of gas sensitivity, an impressive 187%, was recorded in response to 1000 ppm of methanol vapor, when employing carbon sourced from the central core of the acacia tree branches.

Effect of annealing temperature for structural, electrical, and ammonia sensing properties of pristine ZnO and ZnO/SiO2 nanoparticles

The main objective of this research was to study the electrical and gas-sensing properties of Zinc oxide (ZnO) nanoparticles. The samples were divided into two conditions in the preparation process. In the first condition, ZnO powder was annealed at temperatures of 650, 700, and 750 ๐C for 2 h, while the second condition involved mixing ZnO powder with SiO2 powder and annealing at temperatures of 650, 700 and 750 ๐C for 2 h. The characteristics of the prepared samples were studied by scanning electron microscopy (SEM) and the X-ray diffraction technique (XRD). The SEM images showed the agglomeration of the particles with micron-sized diameters. In addition, the XRD patterns of all samples exhibited the hexagonal structure of ZnO. Assessment of the electrical properties of the samples was carried out by forward bias from 0 – 15 V and reverse bias from 0 V to -15 V. The I – V characteristic curves showed diode-like rectifying behavior.The gas-sensing property of the samples was investigated by using ammonia gas, and ZnO nanoparticles annealed at 750 ºC for 2 h were found to have the highest sensitivity.

Theoretical insights into the structural, electronic and gas-sensing properties of Sc-decorated black phosphorus via strain engineering

Structural and electronic properties of Sc-decorated black phosphorus (SP) and its gas sensing for NO molecule were investigated using density functional theory with the emphasis on the response to applied strain. It found that SP transformed into indirect bandgap semiconductor, and converted into a metal characteristic under strain. SP showed strong interaction with the NO with a high adsorption energy of −2.92 eV since the orbital hybridization and extensive charge transfer, and exhibited 3.3-fold sensitivity compared to black phosphorus, suggesting that SP was a potential NO sensor. Furthermore, strain engineering provided an effective route to facilitate the desorption of NO.

Exploring the weak visible-near-infrared and NO2 detection capabilities of PbS/Sb2O5 heterostructures with DFT interpretations

The need for photosensors and gas sensors arises from their pivotal roles in various technological applications, ensuring enhanced efficiency, safety, and functionality in diverse fields. In this paper, interlinked PbS/Sb2O5 thin film has been synthesized by a magnetron sputtering method. We control the temperature to form the nanocomposite by using their different nucleation temperature during the sulfonation process. A nanostructured PbS/Sb2O5 with cross-linked morphology was synthesized by using this fast and efficient method. This method has also been used to grow a uniform thin film of nanocomposite. The photo-sensing and gas-sensing properties related to the PbS/Sb2O5 compared with those of other nanomaterials have also been investigated. The experimental and theoretical calculations reveal that the PbS/Sb2O5 exhibits extraordinarily superior photo-sensing and gas-sensing properties in terms of providing a pathway for electron transport to the electrode. The attractive highly sensitive photo and gas sensing properties of PbS/Sb2O5 make them applicable for many different kinds of applications. The responsivity and detectivity of PbS/Sb2O5 are 0.28 S/mWcm−2 and 1.68 × 1011 Jones respectively. The sensor response towards NO2 gas was found to be 0.98 at 10 ppb with an limit of detection (LOD) of 0.083 ppb. The PbS/Sb2O5 exhibits high selectivity towards the NO2 gas. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to analyze the geometries, electronic structure, and electronic absorption spectra of a light sensor fabricated by PbS/Sb2O5. The results are very analogous to the experimental results. Both photosensors and gas sensors are indispensable tools that contribute significantly to the evolution of technology and the improvement of various aspects of modern life.

Designed Synthesized Step-Scheme Heterojunction of Bi2WO6 Nanosheet Supported on CuBi2O4 Nanorod with Remarkable Photo-assisted Gas Sensing for N-butyl alcohol

Photo-assisted gas sensors for n-butyl alcohol detection have attracted considerable attention due to their great potential in safety production and human health. However, the sensitivity, selectivity and stability should be further improved for practical application. Herein, Bi2WO6 nanosheet supported on CuBi2O4 nanorod sensor was realized by the two-step hydrothermal method, and it exhibited excellent sensitivity and stability for n-butyl alcohol detection under blue LED light illumination at the operating work temperature of 110oC with gas concentration from 0.5 to 800 ppm. Meanwhile, the gas concentration of n-butyl alcohol obtained from the sensor was comparable to that of GC analysis. Furthermore, the sensor showed lower responses to other 25 kinds of common organic gases including alcohols, aldehydes, benzenes and ketones compared with that of n-butyl alcohol. More attractively, the Bi2WO6/CuBi2O4 sensor maintained its stable photo-assisted sensing activity over 3 months. The excellent gas-sensing property was caused by light illumination and formation of Bi2WO6/CuBi2O4 heterojunction, leading to abundant active electrons and superoxide radicals. The S-scheme mode of charge transfer at the Bi2WO6/CuBi2O4 heterojunction was revealed by the in-situ XPS and in-situ ESR analyses. The results gained herein may be useful for rational design of S-scheme heterojunction in photo-assisted gas sensor for n-butyl alcohol analysis.

CO gas-sensing properties and DFT investigation of pure and Co-modified MoO3 nanostructures: effect of solvent composition, deposition time, and cobalt concentration

CO gas-sensing properties and DFT investigation of pure and Co-modified MoO3 nanostructures: effect of solvent composition, deposition time, and cobalt concentration

In-situ constructing Se/SnO2/SnS2/SnSe2/SnSe nanocomposites for rapid detection and highly-sensitive H2S gas sensor

The bare SnS2 usually exhibits many undesirable gas-sensing performances such as low selectivity, slow response/recovery, and poor stability in the application field of gas sensors. Heterojunction and morphology engineering are crucial for achieving high-performance SnS2-based gas sensors. Here, we firstly fabricated SnS2 nanoflowers, and subsequently on the SnS2 nanoflowers’ microstructure in-situ constructed Se/SnO2/SnS2/SnSe2/SnSe nanocomposites by two-step solvothermal methods. In contrast to the pure SnS2 and SnSe2 samples, the Se/SnSe2/SnS2-based composites display a remarkable improvement in the H2S sensing properties. The phase composition, microstructure, and gas-sensing properties of the composites are well modulated by varying the S/Se ratio. The test results reveal that the S/Se-0.2 (SnS2/SnSe2 ratio = 1:5) sensor exhibits a high gas response of Ra/Rg = 11.07 and a fast response and recovery of 6 s/148 s toward 200 ppm H2S at 200 °C. More importantly, the S/Se-0.2 sensor shows remarkable selectivity, good reproducibility, and excellent long-term stability to H2S with a low detection limit of 250 ppb. The sensing mechanism is also investigated based on XRD, XPS, and SEM analysis. The strengthened gas sensitivity for the S/Se-0.2 sensor is the synergistic effects of the microstructure, defects, and multiple heterojunctions. Our work paves a new road for the design and optimization of SnS2-based gas sensors.

Application of flame-formed carbon nanoparticle films for ethanol sensing

Carbon nanoparticles (CNPs) have received considerable attention due to their exceptional qualities and adaptability. Their unique physical and chemical characteristics make them extremely intriguing as materials for numerous high-potential applications, such as electronics and gas sensing. This study focused on producing carbon-based nanomaterial devices by deposition of flame-formed carbon nanoparticles on a suitable substrate and investigating their gas-sensing properties. CNPs were produced in a fuel-rich laminar premixed ethylene/air flame and the collected CNP film was morphologically and electrically characterized. The electrical conductivity of the film was investigated as a function of ethanol concentration and amount of deposited material. Notably, CNP films exhibited high sensitivity to ambient ethanol gas concentrations, and rapid recovery times at room temperature, and showed a sensitivity increasing with the amount of deposited material and the surface complexity. Our findings demonstrate the high potential of combustion-generated CNPs as building materials for low-cost and portable ethanol sensors.

Preparation and morphology controlling of Co3O4 nanostructures and their gas-sensing properties

Preparation and morphology controlling of Co3O4 nanostructures and their gas-sensing properties

Operating temperature and ruthenium doping influence on the charge carriers type transition in the ɑ-Fe2O3 sensors upon liquefied petroleum gases detection

Metal oxide-based sensors have been extensively used for environmental monitoring, health, and safety. This work focuses on synthesizing ɑ-Fe2O3 and doping it with Ruthenium (Ru) to study its gas-sensing properties over flammable and hazardous gases. An anomalous behavior was observed during the Liquefied Petroleum Gas (LPG). This Ru-doped ɑ-Fe2O3 showed a charge carrier switching transition from n- to p-type conductivity due to Ru doping and the sensor’s operating temperature. The switching behavior on the Ru-doped samples happened between 3,000 and 4,000 ppm of the LPG concentrations. However, the Ru doping content did not seem to be affecting this transition except to alter the LPG response. The sensors’ operating temperature did alter the switching transition from n- to p-type conductivity. The temperatures varied from 175 to 225 °C. Metal Oxide Semiconductor (MOS) based on α -Fe2O3 nanoparticle doped with ruthenium (Ru- α-Fe2O3) was more selective towards LPG with a gas response of 24.41.

Annealing-induced enhancement of TiO2-ZnO nanocomposites for high-performance room-temperature air pollutant detection in fiber optic sensors

Fiber optic sensors, promising for their compactness and remote sensing abilities, are explored in this study as a platform for detecting volatile organic compounds (VOCs) using nanocrystalline metal oxide composites like TiO2-doped ZnO. Hydrothermally synthesized (S1 sample)and annealed composites (500 °C (S2 sample) and 1200 °C (S3 sample) annealing) were investigated for their gas-sensing properties towards inorganic gas like ammonia and VOCs like acetone, and isopropyl alcohol. Remarkably, annealing at 1200 °C yielded S3 sample with higher response (7.5 %) towards ammonia at room temperature for 500 ppm concentration. This superior performance is attributed to increased surface area, narrowed bandgap, and faster response/recovery times (18/15 s) compared to other samples. The proposed sensing mechanism involves the adsorption and desorption of oxygen molecules on the sensor surface, altering refractive index and light scattering, ultimately modulating the transmitted light intensity. X-ray diffraction, SEM imaging, and UV–Vis absorption techniques confirmed the structure and morphology of the nanocomposites.

Gas-sensing properties of p-type of nitrogen-doped ZnO nanorods prepared by deep cryogenic treatment

This study developed p-type nitrogen-doped zinc oxide nanorods (NZO NRs) using a chemical bath deposition and deep cryogenic treatment. These NRs were employed to create the device structure of metal-oxide-metal (MSM) and p-n junction for a volatile organic compound gas sensor. Deep cryogenic treatment is the process of immersing ZnO NRs in liquid nitrogen to achieve NZO NRs. SEM results show that the morphology of NZO changes from hexagonal to nib shapes. XRD and TEM results demonstrate that the peak of (002) shifts, and lattice dislocation was observed in NZO specimen. XPS and EDS analysis proved that the N atoms were successfully doped into ZnO. Optical analysis showed the lower band gap and a broader absorption region of NZO NRs. The doping mechanism of NZO is deduced as polar molecules distributed on the high-surface area of ZnO NRs, with iron playing a catalytic role. The MSM structure of the p-type NZO gas sensor, exhibiting high response, lifetime and selectivity, was verified at room temperature. The gas sensor with a p-n junction structure exhibits a faster response time to ethanol.

Highly-enhanced toluene gas-sensing behavior of high-valent metal-cations doped Co3O4 nanostructures derived from ZIF-67 MOF

In this paper, the different valent metal-cations (Zn2+, In3+ and Zr4+) doped porous Co3O4 nanostructures were synthesized through the pyrolysis of ZIF-67 metal–organic framework (MOF). The influence of the different valence and doping content of metal-cations on the morphology, microstructures and gas-sensing performance of Co3O4 sensors is discussed in detail. The Zr-doped Co3O4 nanostructures present the higher specific surface area for the smaller average grain size, and the toluene gas-sensing performance of Co3O4 nanostructures is significantly improved with the high-valent Zr-doping. The high valence Zr-doping greatly improves the toluene gas-sensing properties, which Co2.717Zr0.189O4 sensor exhibits the highest response value of 94.58 to 100 ppm toluene gas (3.8-fold of Co3O4 sensor). The donor Zr-doping to p-type Co3O4 nanostructures optimizes the hole distribution and further affects Fermi level. Combining with the more oxygen adsorption from the high specific surface area, the resistance in air greatly decreases and resistance in toluene gas increases.

Improving Surface Structures of Al-Doped Zinc Oxide Thin Films to Apply in CO Gas-Sensing Property by Designing Processes Through RF Magnetron Sputtering

Improving Surface Structures of Al-Doped Zinc Oxide Thin Films to Apply in CO Gas-Sensing Property by Designing Processes Through RF Magnetron Sputtering

Ethanolamine gas sensors based on NdFeO3 modified hexagonal pyramid shaped ZnO nanocrystals

It is well known that two metal oxides can form depletion layers at the interface by constructing heterojunctions due to the different Fermi energy levels of each metal oxide, which can improve the carrier mobility and provide significant advantages for gas sensing. In this work, NdFeO3 nanoparticles were grown on ZnO with hexagonal cone structure by secondary hydrothermal method to successfully construct n-ZnO/p-NdFeO3 heterojunctions, and the crystal structures, oxygen vacancies, microstructures, optical properties, and gas-sensing properties of the ZnO/NdFeO3 composites were investigated. The ZnO/NdFeO3 sensors showed good ethanolamine (EA) The response characteristics of the ZnO/NdFeO3 sensor to ethanolamine (EA) with a concentration of 100 ppm EA at 240 °C (Rg/Ra) is about 25, which improves the response by a factor of 1.6 and 1.32 compared with that of NdFeO3 and ZnO. Meanwhile, it has excellent selectivity, good cyclic reproducibility, and durable long-term stability with response/recovery times of 19 s/49 s. The improved EA sensing performance of NdFeO3-modified ZnO, in addition to its large specific surface area due to its unique rough inhomogeneous structure, is also related to the higher concentration of oxygen vacancies at the ZnO/NdFeO3 interface after the composite. In addition, the construction of ZnO/NdFeO3 heterostructure brings more efficient carrier migration, which is favorable to the surface reaction and diffusion of EA molecules, and lowers the ZnO operating temperature, thus reducing the energy consumption. The ZnO/NdFeO3 composite sensor based on n-p heterojunction provides a valuable strategy for the detection of volatile organic compounds.

Effects of Visible Light on Gas Sensors: From Inorganic Resistors to Molecular Material-Based Heterojunctions.

In the last two decades, many research works have been focused on enhancing the properties of gas sensors by utilising external triggers like temperature and light. Most interestingly, the light-activated gas sensors show promising results, particularly using visible light as an external trigger that lowers the power consumption as well as improves the stability, sensitivity and safety of the sensors. It effectively eliminates the possible damage to sensing material caused by high operating temperature or high energy light. This review summarises the effect of visible light illumination on both chemoresistors and heterostructure gas sensors based on inorganic and organic materials and provides a clear understanding of the involved phenomena. Finally, the fascinating concept of ambipolar gas sensors is presented, which utilised visible light as an external trigger for inversion in the nature of majority charge carriers in devices. This review should offer insight into the current technologies and offer a new perspective towards future development utilising visible light in light-assisted gas sensors.

Using a protrusion sapphire substrate to synthesize ZnO nanoflower arrays and application of Cu decorated ZnO nanoflower arrays as a H2 and CO gas sensor

In this study, a straightforward method is proposed to grow ZnO nanoflower arrays, which will be utilized as gas sensors for detecting H2 and CO gases. The process involves using the sol–gel method to create the ZnO thin films on a sapphire substrate with protrusion structure. These thin films are then annealed to serve as the seed layer for the subsequent growth of ZnO nanorods. For the synthesis of the ZnO nanorods, a 0.3[Formula: see text]M solution containing C6H[Formula: see text]N4 and Zn(CH3COO)[Formula: see text]O was employed as the precursor, and the hydrothermal method was used at 90∘C for a synthesis time of 60[Formula: see text]min. Due to the unique protrusion structure of the ZnO seed layer, the ZnO nanorods grew perpendicular to it, resulting in the formation of the ZnO nanoflowers. Furthermore, the ZnO seed layer’s matrix structure enables the growth of the ZnO nanoflowers in an orderly array pattern. For the further enhancement of the sensing properties of the gas sensor, a deposition method was used to decorate the Cu nanomaterials on the ZnO nanoflower arrays. The undecorated and Cu-decorated ZnO nanoflower arrays were proceeded to fabricate devices utilizing complemented by an interdigital upper electrode. Subsequently, the gas-sensing performance of both sensor types was compared concerning their ability to detect H2 and CO gases. The findings in this research conclusively indicate that sensors fabricated using the Cu-decorated ZnO nanoflower arrays exhibited a remarkable enhancement in gas-sensing properties when compared to the device using the undecorated ZnO nanoflower arrays, particularly for detecting H2 and CO gases. These results demonstrated that the Cu-decorated sensors had substantially higher response rates and faster response times during the gas-detecting processes.

Effect of ZnO thickness on gas sensing behavior of WS2-ZnO p-n heterojunction nanosheets towards reducing gases

Optimization of materials in heterojunction gas sensors is vital for achieving the highest gas-sensing performance. In this study, we synthesized pristine ZnO, pristine WS2 nanosheets (NSs), and ZnO with different thicknesses (10–50 nm) on WS2 NSs to study their gas-sensing properties. It was found that at 150°C and 300°C, the sensors with ZnO layers of 10 and 30 nm, respectively, exhibited the highest response to reducing gases. At low temperatures, the role of WS2 in gas sensing was dominant, whereas at high temperatures, ZnO played a dominant role. Therefore, the sensor with the thinnest ZnO layer demonstrated the best performance at low temperatures, while at higher temperatures, the sensor with a ZnO thickness of 30 nm exhibited optimal performance. Also, at 300°C, WS2 was oxidized to WO3. Furthermore, to decrease overall power consumption, we conducted sensing measurements under self-heating conditions on a WS2-ZnO (10 nm) p-n heterojunction NS sensor and found that the gas sensor, under a low applied voltage of 4.2 V, exhibited the highest response to reducing gases. The enhanced gas sensing of the optimized gas sensors was attributed to the formation of heterojunctions and the optimal thickness of the ZnO layer on WS2 at appropriate temperatures.

Graphene-Wrapped ZnO Nanocomposite with Enhanced Room-Temperature Photo-Activated Toluene Sensing Properties.

Graphene-wrapped ZnO nanocomposites were fabricated by a simple solvothermal technology with a one-pot route. The structure and morphology of these as-fabricated samples were systematically characterized. The adding of graphene enhanced the content of the oxygen vacancy defect of the sample. All gas-sensing performances of sensors based on as-prepared samples were thoroughly studied. Sensors displayed an ultrahigh response and exceptional selectivity at room temperature under blue light irradiation. This excellent and enhanced toluene gas-sensing property was principally attributed to the synergistic impacts of the oxygen vacancy defect and the wrapped graphene in the composite sensor. The photo-activated graphene-wrapped ZnO sensor illustrated potential application in the practical detection of low concentrations of toluene under explosive environments.

Room-temperature highly sensitive triethylamine detection by few-layer Nb2CTxMXene nanosheets.

MXene, a class of two-dimensional materials that are emerging as rising stars in the field of materials, are receiving much attention in sensing. Ti3C2TxMXene, the most maturely researched MXene, is widely used in energy, biomedical, laser, and microwave shielding applications and has also been expanded to gas sensing and wearable electronics applications. Compared with Ti3C2Tx, Nb2CTxMXene is more difficult to etch and has higher resistances at room temperature; so, few studies have been reported on their use in the sensing field. Based on the preparation of few-layer Nb2CTxMXene by intercalation, this study thoroughly examined their gas-sensing properties. The successfully prepared few-layer Nb2CTxshowed good selectivity and high sensitivity to triethylamine at room temperature, with response values up to 47.2% for 50 ppm triethylamine and short response/recovery time (22/20 s). This study opens an important path for the design of novel Nb-based MXene sensors for triethylamine gas detection.