SO2 Gas Sensor Research Articles

Recent Advances in Electrochemical Sensors for Detecting Toxic Gases: NO₂, SO₂ and H₂S.

Toxic gases, such as NOx, SOx, H2S and other S-containing gases, cause numerous harmful effects on human health even at very low gas concentrations. Reliable detection of various gases in low concentration is mandatory in the fields such as industrial plants, environmental monitoring, air quality assurance, automotive technologies and so on. In this paper, the recent advances in electrochemical sensors for toxic gas detections were reviewed and summarized with a focus on NO2, SO2 and H2S gas sensors. The recent progress of the detection of each of these toxic gases was categorized by the highly explored sensing materials over the past few decades. The important sensing performance parameters like sensitivity/response, response and recovery times at certain gas concentration and operating temperature for different sensor materials and structures have been summarized and tabulated to provide a thorough performance comparison. A novel metric, sensitivity per ppm/response time ratio has been calculated for each sensor in order to compare the overall sensing performance on the same reference. It is found that hybrid materials-based sensors exhibit the highest average ratio for NO2 gas sensing, whereas GaN and metal-oxide based sensors possess the highest ratio for SO2 and H2S gas sensing, respectively. Recently, significant research efforts have been made exploring new sensor materials, such as graphene and its derivatives, transition metal dichalcogenides (TMDs), GaN, metal-metal oxide nanostructures, solid electrolytes and organic materials to detect the above-mentioned toxic gases. In addition, the contemporary progress in SO2 gas sensors based on zeolite and paper and H2S gas sensors based on colorimetric and metal-organic framework (MOF) structures have also been reviewed. Finally, this work reviewed the recent first principle studies on the interaction between gas molecules and novel promising materials like arsenene, borophene, blue phosphorene, GeSe monolayer and germanene. The goal is to understand the surface interaction mechanism.

High Selective SO2 Gas Sensor Based on Monolayer <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-AsSb to Detect SF6 Decompositions

The density functional theory with nonequilibrium Green’s function was adopted to explore the adsorption of SF6 decompositions (SO2, SOF2, SO2F2, H2S, and HF) on monolayer $\beta $ -AsSb as well as gas sensing response and selectivity using a simulated device. The adsorption on two side of monolayer $\beta $ -AsSb was compared. Among these five kinds of gas molecule, for both the As and Sb adsorption sites, SO2 exhibited the largest adsorption energy and electron transfer. The band gap of monolayer $\beta $ -AsSb experienced a significant decrease only when SO2 was adsorbed on the surface. All the five molecules can have chemical interactions with different degree according to density of states. The current–voltage property indicated that the monolayer $\beta $ -AsSb-based sensing device had response to all these five gases, especially at the voltage range from about 1.6 to 1.8 V. But the response to SO2 was obvious larger than other four gases for both As and Sb adsorption sites. The results suggest that monolayer $\beta $ -AsSb has high response and selectivity to SO2 which may stimulate future application for outstanding performance SO2 gas sensor in SF6-based gas insulated equipment.

Single-layer stanane as potential gas sensor for NO2, SO2, CO2 and NH3 under DFT investigation

The monolayer stanane in chair form is reported to be a novel sensor for environmentally toxic and non-toxic gas molecules for the first time. The structure, electronic and vibrational properties of all three possible conformations (chair, stirrup and boat) of stanane are studied in detail using density functional theory (DFT) based on an ab-initio technique. The interactions and charge transfer of environmentally toxic (NO2, SO2 and NH3) and non-toxic (CO2) gas molecules on the dynamically most stable hexagonal chair type hydrogenated stanene, viz. stanane has been investigated in detail. The most stable configuration, electronic properties, adsorption energies and charge transfer of these gases on stanane are systematically studied and discussed. The band gap of the pure stanane (0.52 eV) is noticed to be changed after interaction with gases. Moreover, the changes in the energy band gap and charge density is observed upon adsorption of NO2, SO2, NH3 and CO2 gases on p-type stanane based material. The results show that the selectivity of hydrogenated stanene based gas sensors is very important to enhance their sensitivity. It is found that all the gas molecules act as charge donors in which NO2 gas shows maximum adsorption on the stanane surface along with the maximum charge transfer. The nontrivial affectability and selectivity of stanane demonstrate its potential application in the field of gas sensors and superior impetuses.

Adsorption of SO2 molecules on Fe-doped carbon nanotubes: the first principles study

In this paper, the first-principles method has been employed to study the adsorption behavior of SO2 molecules on pristine carbon nanotubes (CNTs) and Fe-doped CNTs with or without the existence of vacancy defects. Through the analysis of geometric structure, adsorption energy, charge transfer, and electron density, our calculation illustrates that the adsorption of SO2 molecules is only a weak physical adsorption on both pristine CNTs and vacancy-defected CNTs. After doping with Fe, however, a much stable chemical adsorption is formed between SO2 and CNTs, where the adsorption distance decreases by a maximum of 44.8%, and the adsorption energy and charge transfer increase by a maximum of 1513.3% and 373.9%, respectively. Calculations of front orbit and density of states reveal that Fe-doping narrows the band gap and increases the electrical conductivity of the CNTs. The density of states of Fe-doped CNTs and SO2 molecules are clearly reinforced at the Fermi level, implicating that there is stronger coupling between Fe atoms and SO2 molecules and this enhances the adsorption of SO2 molecules on these CNTs. The study provides useful guidance on how to improve the interactions between air pollutant SO2 molecules and CNTs and illustrates that Fe-doped CNTs could be potentially applied as a next-generation SO2 gas sensor and collector.

A hybrid YSZ/SnO2/MEMS SO2 gas sensor.

This study uses a solid YSZ electrolyte film in a SnO2 MEMS SO2 gas sensor of the semiconductor type to enhance the redox reaction. The YSZ film is prepared by RF sputtering. XRD analysis shows the presence of the (111), (200), (220) and (311) peaks that denote the crystallization planes of YSZ. The experimental results show that the SnO2 MEMS SO2 gas sensor with a YSZ film has a better sensor response than a pure SnO2 MEMS SO2 gas sensor or a YSZ MEMS SO2 gas sensor when the SO2 concentration and the sensor's temperature sensors are 250 ppb and 400 °C, respectively. The YSZ/SnO2 sensor's measured responses are around 6%, 45%, 20% and 16% when the sensor is respectively operated at 250 °C, 300 °C, 350 °C, and 400 °C.

Gas molecule adsorption on twisted nanographene C96H36 derivative: A theoretical study

Abstracts Twisted C96H36, a newly synthesized nanographene, may have distinct properties from those of planar graphene. The adsorption behaviors of H2, CO, NO, NH3, SO2, and HCHO on the surface of C96H36 derivative, which was labelled as C96, were systematically investigated by computational methods. The adsorption behaviors of 1–20 formaldehyde molecules on C96 were calculated to reveal potential uses of C96. The results indicate that these molecules could be physically absorbed on the surface of C96 with absorption energies in the range 0.5–5.5 kcal mol−1. The calculated HOMO-LUMO energy gap also showed that C96 could act as a potential gas sensor for O2 and SO2. When one formaldehyde molecule is absorbed, it prefers to locate at the edge of the distorted moiety of C96. A second formaldehyde also prefers to be absorbed at another edge position of the distorted moiety of C96. The results show that the absorption energies for the third to twelfth formaldehyde molecules are concentrated at 5 kcal mol−1, which indicates that more formaldehyde molecules could be absorbed onto C96, but a limit of 20 formaldehyde molecules was calculated.

Monolayer Sc2CO2: A Promising Candidate as a SO2 Gas Sensor or Capturer

Toxic gaseous SO2 adsorption on O-terminated M2CO2 (M = Sc, Hf, Zr, and Ti) monolayers has been studied by means of first-principle calculations. It is demonstrated that monolayer Sc2CO2 is most preferred for the SO2 molecule with suitable adsorption strength and apparent charge transfer. Moreover, the electronic conductivity of Sc2CO2 displays a sharp increase after the adsorption of SO2. In particular, the adsorption strength of SO2 on Sc2CO2 can be further enhanced or weakened by applying tensile strains or controlling external electronic fields, which is greatly desirable to realize the capture or reversible release of toxic SO2 gas. These distinctive features endow the Sc2CO2 monolayer with high selectivity and sensitivity as a potential candidate for SO2 gas sensor, as well as efficient control for gaseous SO2 capture.

Sub-ppb SO2 gas sensor based on NASICON and LaxSm1-xFeO3 sensing electrode

A NASICON-based mixed-potential gas sensor utilizing the perovskite-type orthoferrite LaxSm1-xFeO3 (x=0.2, 0.4, 0.5, 0.6, 0.8) sensing electrode (SE) was designed for SO2 detection. The research mainly put emphasis on the effect of different La3+ doping ratios in LaxSm1-xFeO3 on the sensing characteristics, and the highest response value (-86.5mV) to 1ppm SO2 was observed for the sensor using La0.5Sm0.5FeO3-SE. The response value of the fabricated sensor displayed segmentally linear relationship with the logarithm of SO2 concentration in the ranges of 0.005-0.2ppm and 0.2–5ppm, and the slopes were −8 and −86mV/decade, respectively. Otherwise, the low detection limit of the present sensor even could reach to 5ppb with an accurate response value (-8.4mV). Meanwhile, the sensor also showed good repeatability, long-term stability and selectivity toward other interfering gases. Furthermore, the electrochemical impendence curves indicated the reason that the sensor attached with La0.5Sm0.5FeO3-SE displayed the higher response values than the other sensors. The result indicated that differences of electrocatalytic activity was caused by diverse La3+ doping content in sensing electrode. The sensing mechanism related to the mixed potential was demonstrated by the polarization curve.

A comparative study of RGO-SnO2 and MWCNT-SnO2 nanocomposites based SO2 gas sensors

An attempt has been made in the present work to develop a hybrid nanocomposite sensor by exploiting the novel properties of Tin oxide (SnO2), MWCNTs (Carbon nanotubes) and reduced graphene oxide (RGO) for the efficient detection of SO2 gas. MWCNT-SnO2 and RGO-SnO2 hybrid nanocomposite sensors have been prepared by incorporating MWCNTs and RGO into SnO2 nanoparticle colloidal solution respectively by chemical route. Low sensing response of 1.2 is obtained for bare SnO2 sensor at 220°C towards 500ppm SO2 gas. However, enhanced sensing response of ∼22 has been observed for the RGO-SnO2 sensor compared to ∼5 obtained for MWCNT-SnO2 sensor at a lower operating temperature of 60°C towards the same concentration of SO2 gas. Modulation of space charge region at the interface of n-SnO2 and p-RGO on interaction with the target SO2 gas is responsible for the enhanced response.

SnO2 thin film sensor having NiO catalyst for detection of SO2 gas with improved response characteristics

Present work focuses on the growth of SnO2 thin films with high electrical resistivity using RF sputtering technique for fabrication of SO2 gas sensors. NiO catalyst has been incorporated over the surface of SnO2 thin film in the form of continuous layer and dotted nanoclusters to improve the response characteristics. Enhanced sensing response of about 56 has been observed for the NiO dotted cluster/SnO2 sensor at a relatively lower operating temperature of 180°C towards 500ppm SO2 gas. The contribution of both (i) modulation of depletion region at the interface of n type SnO2 film and p type NiO catalyst on interaction with the target SO2 gas and (ii) the spill over mechanism are considered to be the main reasons for the obtained enhanced response.

Fabrication of chemiresistive gas sensors based on multistep reduced graphene oxide for low parts per million monitoring of sulfur dioxide at room temperature

The proposed multistep reduction of graphene oxide includes two-step reduction process. The graphene oxide is reduced by hydrazine hydrate followed by further reduction with low energy nitrogen ion beam implantation technique. From the Raman spectra, reduction of graphene oxide samples has been estimated on the basis of Tuinstra and Koenig relation. FT-IR studies have shown the removal of oxygen functional groups such as epoxy, hydroxyl and carboxylic on reduction. Ion implantation has enhanced electrical conductivity and specific surface area of graphene oxide on reduction. Besides reduction, the second step has modified the surface morphology of the samples making them more appropriate for gas adsorption. The sample with higher implantation dose (1015ions/cm2) exhibits promising potential for room temperature chemiresistive SO2 gas sensor at ppm levels as low as 5ppm with reasonable response, selectivity and stability.

Investigation of Silver Catalytic Properties on Reduced Graphene Oxide to Enhance Gas Sensitivity and Selectivity from Mixed VOC Gases

Volatile organic compounds (VOCs) that easily evaporate at room temperature have caused detrimental to respiratory, allergic, and/or immune effects in humans. Increased awareness of toxicity on these VOC gases has led many studies to focus on direct measurement of these harmful VOCs with high sensitivity at lower operating temperature. Gas sensors based on surface chemical reaction of semiconducting metal oxides are readily available commercially. To improve gas sensing performance with lowered operating temperature and high sensitivity, adequate catalysts are commonly used. However, there is still limit to lower sensing temperature of metal oxides to room temperature. It has been reported that graphene oxide (GO), a graphene sheet linked to oxygen functional groups, has potential to realize room temperature operation. Additional advantage of the GO includes large scale and low cost production for commercial application. In this study, GO thin films were deposited by drop coating and thermally reduced under Ar to eliminate the functional groups from GO films. The electrical properties of GO transformed from an insulator to semiconductor support GO to easily be activated for sensing gases. To enhance selective gas sensing at room temperature, many types of noble metals such as Pt and Au can be considered as an activators or sensitizers. We investigated GO with silver catalyst with relatively low cost. The formation of Ag island clusters driven by deposition conditions and their VOC gas sensing was characterized to find optimal condition of catalysts. The morphologies of silver catalyst decoated GO film were analyzed with SEM, TEM, and XRD, and the quantity of the silver catalyst was measured by EDS. Gas sensing response to VOCs was measured at room temperature to extract characteristic feature. In order to determine selective detection of specific VOC gas, 2 types and 5 types of mixed gases such as formaldehyde, benzene, styrene, toluene, and xylene were used. Detailed discussion on and the mechanism of silver catalytic effect on GO will be given. AcknowledgementThis research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy, a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology, and Auburn University IGP.References Vlachos, D. S., C. A. Papadopoulos, and J. N. Avaritsiotis. "On the electronic interaction between additives and semiconducting oxide gas sensors." Applied physics letters 69.5 (1996): 650-652.Tyagi, Punit, et al. "Metal Oxide Catalyst assisted SnO2 thin film based SO2 gas sensor." Sensors and Actuators B: Chemical (2015).Ahn, Hosang, et al. "Volatile gas sensing properties of phase and composition gradient SnOx thin films by combinatorial sputter deposition." ECS Solid State Letters 2.1 (2013): P11-P13.Li, Yongjie, et al. "Catalytic performance of Pt nanoparticles on reduced graphene oxide for methanol electro-oxidation." Carbon 48.4 (2010): 1124-1130.Wang, Jianwei, et al. "Dielectrophoretic assembly of Pt nanoparticle-reduced graphene oxide nanohybrid for highly-sensitive multiple gas sensor." Sensors and Actuators B: Chemical 220 (2015): 755-761.Park, Hyejin, et al. "Transition of gas sensing behavior in non-reduced graphene oxides with thermal annealing." Materials Letters 136 (2014): 164-167.

Adsorption of SO2 molecule on doped (8, 0) boron nitride nanotube: A first-principles study

Adsorptions of SO2 on Al-, Ca-, Co-, Cu-, Ge-, Ni-, and Si-doped (8, 0) boron nitride nanotube (BNNT) have been studied using first-principles approach based on density functional theory in order to exploit their potential applications as SO2 gas sensors. The electronic properties of the BNNT-molecule adsorption adducts are strongly dependent on the dopants. The most stable adsorption geometries, adsorption energies, charge transfers, and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of (8, 0) BNNT based chemical gas sensors for SO2 can be drastically improved by introducing appropriate dopant. Si is found to be the best choice among all the dopants.

Metal oxide catalyst assisted SnO2 thin film based SO2 gas sensor

Sulfur dioxide (SO2) is one of the most toxic and hazardous gas having adverse effect on the health and environment. In the present report, an attempt is made to fabricate SO2 gas sensor using SnO2 thin film integrated with various metal oxide catalyst (PdO, CuO, NiO, MgO, V2O5) in the form of 10nm thin dotted clusters of 600μm diameter. The structural, optical and surface morphological properties of the SnO2 thin film have been studied. The bare SnO2 thin film sensor exhibits the sensing response of about 1.3 at 220°C whereas, NiO/SnO2 sensor shows the enhanced sensing response (∼56) towards 500ppm SO2 gas at a relatively low operating temperature (180°C). A correlation has been established between the observed sensing response and the properties of the sensing film. Selectivity of the NiO/SnO2 sensor was tested towards different interfering gases and found to be highly selective for SO2 gas.

A new potentiometric SO₂ sensor based on Li₃PO₄ electrolyte film and its response characteristics.

A potentiometric SO2 gas sensor based on Li3PO4 solid electrolyte has been developed using Au as the reference electrode and Li2SO4/V2O5 as the sensing electrode. The Li3PO4 film was deposited on Al2O3 substrate by resistance heating evaporation. Two Au films with designed patterns were formed on the Li3PO4 film by micro-fabrication technologies. The sensing electrode covers one electrode partly using thick-film technology. The electromotive force values between the sensing electrode and the reference electrode were measured and various characteristics were studied including sensitivity, response characteristics, and stability and selectivity. According to the results, we conclude that an optimal working temperature of the SO2 sensor is 500 °C, the measurement range is 0-100 ppm, the sensitivity is about 32.47 mV/dec, the response and the recovery time is about 5 min and 10 min, respectively. And the stability and the selectivity of the sensor are good, making it have potential in SO2 measurement of living environment.

First-principles study of SO2 molecule adsorption on the pristine and Mn-doped boron nitride nanotubes

To exploit the potential application of nitride nanotube (BNNT), the adsorption of sulfur dioxide (SO2) on pristine and Mn-doped BNNT was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are discussed. SO2 molecule is weakly adsorbed on the pristine BNNT. The Mn-doped BNNT show high reactivity toward SO2 regardless of the MnB site or MnN site adsorption. The larger formation energies and analysis of density of states show the SO2 molecules are chemically bonded to Mn-doped BNNT and the covalent interaction between the SO2 molecule and Mn atom can be formed. Therefore, the Mn-doped BNNT can be used as SO2 gas sensor manufacturing raw materials, and it may be a potential material for nanodevice applications.

SO2 gas sensor based on Ag-Ag2SO4-BaSO4 sensing electrode

A sulfur dioxide (SO2) gas sensor based on a novel structural sensing electrode was fabricated. The sensor consists of yttria-stabilized zirconia as the oxygen ion conductor, silver sulfate-based salts as the auxiliary phase, a silver/platinum mixed paste as the sensing electrode/catalyst, and a platinum paste as the reference electrode. Ball milling was employed to decrease the particle size of the silver sulfate-barium sulfate (Ag2SO4-BaSO4) auxiliary phase. After the Ag2SO4-BaSO4 mixture ball-milling for 20 h, the as-obtained sensor showed the highest sensitivity to SO2 gas. Furthermore, in order to optimize the sensing electrode, particles of metallic silver were mixed with silver sulfate-based salts, and the as-designed sensing electrode displayed an improved sensitivity to SO2 gas at a low temperature (400 °C).

Improving SO2 gas sensing properties of graphene by introducing dopant and defect: A first-principles study

Adsorption of sulfur dioxide (SO2) on intrinsic and modified graphene, including Stone–Wales (SW) defect, Al doping and a combination of these two, was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are thoroughly discussed. It was found that SO2 molecule is weakly adsorbed on the intrinsic and SW defected graphenes and their electronic properties were slightly changed. The Al-doped graphene and the defect–dopant combination show high reactivity toward SO2. Compared with Al-doped adsorption system, the adsorption energy for Al-doped SW defect adsorption system can be enhanced by the introduction of a SW defect. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO2 can be drastically improved by introducing dopant and defect, and the Al-doped SW graphene is more suitable for SO2 gas detection.

Synthesis of SnO<sub>2</sub> Nanostructure Thin Film and its Prospective as Gas Sensors

This report describes the preparation of gas sensors based on SnO2 semiconductor nanostructure thin films synthesized using chemical bath deposition (CBD) technique. As the rapid demand of the gas sensors based on the semiconductor materials, there have been significant efforts to improve the performance of the semiconductors sensors. SnO2, which has good electrical and mechanical properties, is one of the potential materials to be developed. In the present study, the SnO2, prepared using CBD technique with stannous cloride as precursors, has nanopattern that give much SO2 particles to access into the semiconductor surface. The resulting nanostructure SnO2 thin films have been confirmed by X Ray Diffractions (XRD), Energy Dispersive Spectroscopy (EDS) and Scanning Electronic Micrsocopy (SEM). The as fabricated SnO2 thin films sensors were then characterized as SO2 gas sensors in various concentrations for several different operating temperatures. The sensors have good sensitivity as low as 30 ppm of SO2 gas at the optimum temperature of 2000 C.

Synthesis of SnO<sub>2</sub> Nanostructure Thin Film and its Prospective as Gas Sensors

This report describes the preparation of gas sensors based on SnO2 semiconductor nanostructure thin films synthesized using chemical bath deposition (CBD) technique. As the rapid demand of the gas sensors based on the semiconductor materials, there have been significant efforts to improve the performance of the semiconductors sensors. SnO2, which has good electrical and mechanical properties, is one of the potential materials to be developed. In the present study, the SnO2, prepared using CBD technique with stannous cloride as precursors, has nanopattern that give much SO2 particles to access into the semiconductor surface. The resulting nanostructure SnO2 thin films have been confirmed by X Ray Diffractions (XRD), Energy Dispersive Spectroscopy (EDS) and Scanning Electronic Micrsocopy (SEM). The as fabricated SnO2 thin films sensors were then characterized as SO2 gas sensors in various concentrations for several different operating temperatures. The sensors have good sensitivity as low as 30 ppm of SO2 gas at the optimum temperature of 2000 C.