CO Gas Sensor Research Articles

Improving gas sensing properties of armchair graphene nanoribbons by oxygen–hydrogen terminated edges

This work is focused on the effects of doping and neutralizing edges of armchair graphene nanoribbon (AGNR) on its gas sensing behavior. Four types of structures, pristine AGNR, boron doped AGNR, nitrogen doped AGNR and defective AGNR, when the ribbons edges are terminated by both hydrogen and oxygen atoms at the same time, are investigated in detail. First, interaction of the aforementioned structures with three gases molecules, CO, O2 and CO2, are investigated by using the density functional theory, then their applications as gas sensors are studied. An AGNR structure depending on its edge termination and type of the adsorbed gas illustrates different atomic configurations. Different atomic configurations show different physical structure, chemical behavior and electronic properties. Our results have shown that the adsorptions of the three gases molecules have stronger interaction with the defective AGNR than with the other three AGNR structures. Therefore, based on quantum analysis of energy and calculation of current flow, the defective AGNR neutralized by both H and O at edges, concurrently, shows high sensitivities to CO, O2 and CO2 gases molecules. In fact, the strong interactions between adsorbed gases molecules and AGNR cause significant changes in electronic properties of edge terminated AGNR. It is worth mentioning that the sensitivity of graphene based gas sensors could be significantly improved by introducing suitable dopants and defects. The results presented in this work indicate that the defective AGNR terminated by both hydrogen and oxygen atoms can operate as a selective CO, O2 and CO2 gas sensor.

Realization of Au-decorated WS2 nanosheets as low power-consumption and selective gas sensors

We introduced a selective and self-heated CO gas sensor based on Au-decorated WS2 nanosheets. Au nanoparticles (NPs) were decorated on WS2 NSs using UV irradiation technique at different irradiation times (1, 15 and 30 s). SiO2 grown on Si was used as substrates and the gas sensors with top electrode configuration were fabricated. Gas sensors were able to work under self-heating mode with an applied voltage of 2 V for selective CO sensing. The results of CO gas sensing demonstrated the promising effects of Au for the enhanced response and selectivity towards CO gas. Also, the low-voltage operation at room temperature resulted in low-power consumption. This study demonstrates realization of selective CO gas sensor using a facile approach along with low power consumption.

Solution-processed Au@rGO/GaN nanorods hybrid-structure for self-powered UV, visible photodetector and CO gas sensors

Although metal nanoparticles (NPs) have been widely reported, Au NPs functionalized reduced graphene oxide (rGO)/GaN nanorods (NRs) for multi-functional applications are rarely discussed. The rGO is a well known transparent electrode and has been considering an alternative electrode to ITO in the current optoelectronic community. In this work, Au NPs functionalized rGO (Au@rGO)/GaN NRs hybrid structure probed for photodetector and CO gas sensing applications. The hybrid structure was characterized by scanning electron microscopy, transmission electron microscope, current-voltage characteristics, photo conductivity, and gas sensor measurements. The Au@rGO/GaN NRs showed higher photoresponsivity (λ = 382 nm, 516 nm) compared to rGO/GaN NRs at room temperature. The rising and falling times of Au@rGO/GaN NRs are faster than that of rGO/GaN NRs. The hybrid structure Au@rGO/GaN NRs exhibited high CO gas response compared to rGO/GaN NRs at room temperature (∼38% to the 20 ppm). Au NPs played an important role in terms of electronic and chemical changes in the hybrid structure for improving both photodetectors the CO gas response. Such a multi-functional hybrid device is an interest of various room temperature applications.

Enhanced Morphological Properties of Macroporous Silicon with the Incorporation of Au-Ag Bimetallic Nanoparticles for Improved CO2 Gas Sensing

In this work, the effects of incorporating bare macroporous silicon (macro-Psi) layer with bimetallic nanoparticles Au-Ag on the performance Psi CO2 gas sensor synthesized by a laser-assisted etching (LAE) process were investigated. Well-controlled and simple immersion process of bare macro-Psi layer in the 10−3 M of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) individually and in the mixing solution with ratio 1:1 was employed to synthesize monometallic AuNPs/macro-Psi, AgNPs/macro-Psi, and bimetallic Au-AgNPs/macro-Psi hybrid structures of CO2 gas sensors. Morphological properties of bare macro-Psi layer, monometallic, and bimetallic hybrid structures were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray analysis (EDS). Electrical characteristics (I–V)of the sensor were measured primary in a vacuum case and with CO2 at 0.2, 0.5, 1, and 1.5 mbar gas pressures. The result showed a significant enhancement in sensitivity and temporal response of the bimetallic hybrid structures compared with that of monometallic and bare macro-Psi layer and an enhanced performance of the sensors due to the high value of integrated specific surface area of the bimetallic nanoparticles and the resulting Schottky barrier height.

Early Detection for Li-Ion Batteries Thermal Runaway Based on Gas Sensing

Thermal Runaway of Li-ion batteries is a major safety risk, and the propagation of fire from one cell to the neighboring cells is a huge challenge. Furthermore, the risk of damage to loose cells in the waste and recycling stream can result in catastrophic fires leading to property damage and injury. During storage and transport, batteries from collection centers awaiting recycling are typically housed in metal 55 gallon (0.208 m3) drums. Several accidents resulting in thermal runaway have occurred, without being observed from the outside until gas pressure caused the vessel to rupture. Early and robust detection for thermal runaway events could enable protection and mitigation to reduce the risks. Previous studies have used voltage or current to detect possible thermal runaway events, assuming the cells are assembled into a pack where electrical and thermal measurements are feasible. However, in this case, without any battery management system that measures the current, voltage, and temperature of the individual cells, the only information we can get is from a few sensors at the lid of the drum. To address the challenges of storage and transport, a Li-ion battery thermal runaway early detection method based on gas sensing is developed. To compare the performance of several detection methods, a 0.208 m3 cylindrical storage drum filled with fully charged 18650 cells, is simulated in COMSOL. In the simulation, an 18650 NMC cell, located in the center of the drum, as shown in Fig. 1, triggers a hard internal short circuit and leads to thermal runaway. A single cell thermal runaway can heat neighboring cells and triggers new thermal runaway events, thus causing a chain reaction of more and more thermal runaway cells [1]. A nine-cell system, with three cells in parallel and three cells in series, is simulated. Each battery is spaced 2 mm from each other, and the free space is assumed to be filled with air. The results for temperature evolution of each cell during thermal runaway propagation is shown in Fig. 2. As seen from the figure, the second cell triggers thermal runaway after 710 seconds. The remaining cells quickly enter the thermal runaway state after the second cell. The detection of thermal runaway must be made before this time if corrective action is to be applied. So, this time is used as the benchmark of thermal runaway detection in this study, defined as propagation critical time. To detect possible thermal runaway, temperature sensors are located on the surface of the drum as shown in Fig. 1. From the simulation result, at 710 seconds, the maximum surface temperature change on the drum surface is less than 0.001 °C. In this simulation, conventional surface temperature sensing approach (e.g., Infrared Imaging) cannot detect the thermal runaway event before the propagation critical time of 710s when the second cell starts a thermal runaway event. Extending the model of [2] inside a drum full of 18650 cells, the detection of a single thermal runaway event by CO2 gas sensors is investigated. Li-ion battery vents significant amount of gas during thermal runaway, and due to SEI decomposition reaction at the early stage of thermal runaway [3], CO2 is generated and vented from battery to the drum space. This gas sensing approach then monitors the concentrations of CO2 inside the drum, and cell venting during thermal runaway can be detected when the concentrations of CO2 are high. The CO2 sensor is located at the center of the drum top surface in Fig .1, and the detection threshold of CO2 concentrations for a thermal runaway event is set to be 2000 ppm. Fig. 3 shows the evolution of CO2 concentrations with time. The initial gas venting speed will accelerate the CO2 species transport process, and CO2 propagates to most of the drum space in a short period. The detection can be made at 85 seconds, which is ahead of the propagation critical time 710 seconds. This study shows the faster response of gas sensing comparing to drum surface temperature sensing in a cylindrical drum. With the use of gas sensing approach in large battery storage facilities, the speed of thermal runaway event detection can be improved and precede the propagation of thermal runaway to additional cells. Reference [1] Kim, G-H.; Pesaran, A.; Smith, K. No. NREL/PR-540-43186. National Renewable Energy Lab.(NREL), Golden, CO (United States), 2008. [2] Cai, T.; Stefanopoulou, A.; Siegel, J. In Dynamic Systems and Control Conference, ASME: 2018. [3] Feng, X.; Ouyang, M.; Liu, X.; Lu, L.; Xia, Y.; He, X. Energy Storage Materials 2018, 10, 246-267. Figure 1

(Invited) Solid State Electrochemical Gas Sensors: Fundamentals, Materials and Applications

Solid-state electrochemical gas sensor (SSEGS) typically functions on the principles based on galvanic cells i.e. the output signals (e.g., V, I etc.) provides the information on the gas of interest. Monitoring oxygen in automobiles is a good example of solid-state potentiometric gas sensors, where the potential difference (V) helps translate to determine air-to-fuel ratio.1 The generation of potential could be measured in three different configurations:2 (i) directly measuring mobile species (type I), (ii) indirectly measuring immobile components (type II), and (iii) analyzing other species by employing auxiliary solid-phases (type III). Fast Na+ and Li+ ion conducting Na-β”-alumina, NASICON-type and Li6BaLa2Ta2O12 garnet have been continuously investigated as potentiometric sensor.3,4 Although all these types cover wide range of gaseous concentration, the technique struggles on providing high resolution results at lower gas concentrations. On the other hand, amperometric (I) gas sensors are known to operate over a narrow range of gas concentrations with higher resolutions. However, both solid-state potentiometric and amperometric gas sensors face the challenges of not being able to accurately detect the industrially important gases (e.g., CO2, SOx, H2S, CH4) due to the cross-sensitivities and stability issues, particularly at high temperatures. In other words, these challenges demand new materials with better selectivity, sensitivity and stability under aggressive environments (e.g., high temperature, toxic gases). Unlike potentiometric and amperometric sensors, resistive-type (R) sensors cover large number of materials including ion, electron and mixed conducting semiconductor-based materials (e.g., SnO2, TiO2, CuO). The research on resistive-type sensors has been further extended to various p- and n-type semiconductor-based perovskites owing to their remarkable stability at elevated temperatures as well as excellent structural flexibility to accommodate desired dopants.5 Thus, this emphasizes the importance of fundamental research and improvements on materials’ characteristic properties to overcome the persisting challenges with SSEGS. Here, we attempt to discuss the transition from fast-ion conducting ceramics to semiconductor-based mixed conductors highlighting the necessity of SSEGSs for current industrial applications. References Wagner, C., Über den Mechanismus der elektrischen Stromleitung im Nernststift, Naturwissenschaften 1943, 31, 265-268.Weppner, W., Solid-state electrochemical gas sensors, Sens. Actuators 1987, 12, 107-119.Möbius, H.-H., Galvanic solid electrolyte cells for the measurement of CO2 concentrations, J. Solid State Electrochem. 2004, 8, 94-109.Zhu, Y.; Thangadurai, V.; Weppner, W., Garnet-like solid state electrolyte Li6BaLa2Ta2O12 based potentiometric CO2 gas sensor, Sens. Actuators, B 2013, 176, 284-289.Mulmi, S.; Thangadurai, V., Preparation, Structure and CO2 Sensor Studies of BaCa33Nb0.67−xFexO3−δ, J. Electrochem. Soc. 2013, 160, B95-B101.

Electroluminescence enhancement in mid-infrared InAsSb resonant cavity light emitting diodes for CO2 detection

In this work, we demonstrated a mid-infrared resonant cavity light emitting diode (RCLED) operating near 4.2 μm at room temperature, grown lattice-matched on a GaSb substrate by molecular beam epitaxy, suitable for CO2 gas detection. The device consists of a 1λ-thick microcavity containing an InAs0.90Sb0.1 active region sandwiched between two high contrast, lattice–matched AlAs0.08Sb0.92/GaSb distributed Bragg reflector (DBR) mirrors. The electroluminescence emission spectra of the RCLED were recorded over the temperature range from 20 to 300 K and compared with a reference LED without DBR mirrors. The RCLED exhibits a strong emission enhancement due to resonant cavity effects. At room temperature, the peak emission and the integrated peak emission were found to be increased by a factor of ∼70 and ∼11, respectively, while the total integrated emission enhancement was ∼×33. This is the highest resonant cavity enhancement ever reported for a mid-infrared LED operating at this wavelength. Furthermore, the RCLED also exhibits a superior temperature stability of ∼0.35 nm/K and a significantly narrower (10×) spectral linewidth. High spectral brightness and temperature stable emission entirely within the fundamental absorption band are attractive characteristics for the development of next generation CO2 gas sensor instrumentation.

Role of oxygen vacancies in vanadium oxide and oxygen functional groups in graphene oxide for room temperature CO2 gas sensors

The greenhouse effect is involving global heating and climate change within the world. Carbon dioxide (CO2) is one of the major gas at the origin of this effect, but also the byproduct of human activity. Therefore, monitoring the indoor/outdoor CO2 emission by gas sensors is one of the priorities for environmental preservation. In this paper, the sensing performance of CO2 towards two different O-rich films have been studied; graphene oxide (GO) and vanadium dioxide (VO2). The preparation of GO film has been carried out by spray pyrolysis on fluorine tin oxide (FTO) prepared by the modified Hummers method. While the VO2 film has been sol-gel spin-coated on a glass substrate. Both films have been characterized using XRD, SEM and electrical properties. The CO2 gas sensing mechanism and the role of oxygen vacancies in VO2 are addressing. The oxygen functional groups in GO play a main role in the CO2 gas the sensitivity level and response time. Their gas sensing performances have been investigated based on measuring the response vs recovery time, dynamic response curve analysis and sensitivity. In order to better understand the sensing mechanism, characterization has been done with different gas concentrations. Both GO and VO2 based CO2-sensors are acted as an n-type sensor. Sensing behavior of GO at RT has explained to be mainly mediated by the oxygen functional groups and a wide range of active sites. In the other hand, VO2 contains oxygen vacancies and more defect sites which play a main role in the RT sensing activity and low recovery time.

Optimization of RF sputtering process parameters on electrical resistivity, deposition rate and sensitivity of Al-doped ZnO thin films grown on Si substrate using grey-Taguchi technique

Increasing environmental pollution globally demands gas sensors for monitoring urban air quality, fire and exhaust from automobiles. The need for high performance gas sensors requires a good control over sensing material structure. This paper studies the suitability of Al-doped ZnO thin films for development of CO gas sensors. Deposition of Al-doped ZnO thin films on Si substrates by the radio frequency sputtering technique was carried out to study the influence of process parameters. The process parameters selected for the analysis were power, deposition time, substrate temperature and working pressure. An orthogonal array L16 ( $$4^{4}$$ ), signal-to-noise ratio and analysis of variance (ANOVA) were performed to optimize the electrical resistivity, deposition rate and sensitivity of the thin films using the Taguchi method. Grey relational grade (GRG) was performed to obtain multiple-performance characteristics of the thin films by optimizing the process parameters. GRG analyses identified the process parameters: power 150 W, deposition time 35 min, substrate temperature $$25^{\circ }\mathrm{C}$$ and working pressure 1.5 Pa showed optimal multiple-performance characteristics. ANOVA analyses indicate that power and substrate temperature show significant effect compared with other parameters. Thin films at the annealing temperature ( $$450^{\circ }\mathrm{C}$$ ) showed a decrease in electrical resistivity and an increase in sensitivity. At the sensor operating temperature of $$150^{\circ }\mathrm{C}$$ , Al-doped thin films exhibited the lowest resistivity $$3.76 \times 10^{-3}\,\Omega $$ -cm and the highest sensitivity of 59%. The optimal multiple-performance characteristic of thin film sample identified is found suitable for CO gas-sensing applications.

Nanocomposites SnO₂/SiO₂ for CO Gas Sensors: Microstructure and Reactivity in the Interaction with the Gas Phase.

Nanocomposites SnO2/SiO2 with a silicon content of [Si]/([Sn] + [Si]) = 3/86 mol.% were obtained by the hydrothermal method. The composition and microstructure of the samples were characterized by EDX, XRD, HRTEM and single-point Brunauer-Emmet-Teller (BET) methods. The surface sites were investigated using thermal analysis, FTIR and XPS. It is shown that the insertion of silicon dioxide up to the value of [Si]/([Sn] + [Si]) = 19 mol.% stabilizes the growth of SnO2 nanoparticles during high-temperature annealing, which makes it possible to obtain sensor materials operating stably at different temperature conditions. The sensor properties of SnO2 and SnO2/SiO2 nanocomposites were studied by in situ conductivity measurements in the presence of 10–200 ppm CO in dry and humid air in the temperature range of 150–400 °C. It was found that SnO2/SiO2 nanocomposites are more sensitive to CO in humid air as compared to pure SnO2, and the sample with silicon content [Si]/([Sn] + [Si]) = 13 mol.% is resistant to changes in relative air humidity (RH = 4%–65%) in the whole temperature range, which makes it a promising sensor material for detecting CO in real conditions. The results are discussed in terms of the changes in the composition of surface-active groups, which alters the reactivity of the obtained materials.

CO2 gas sensor based on macro porous silicon modified with trimetallic nanoparticles

Two kinds of modified macro porous silicon (maPsi) layer with trimetallic nanoparticles surface alloying and core–shell forms CO2 gas sensors were fabricated and tested successfully. Trimetallic Au–Ag–Pd nanoparticles were prepared by an ion reduction process of different metallic salts on maPsi layer by a simple immersion process. As-formed maPsi layer was fabricated by a laser assisted etching (LAE) process with laser power density illumination, current density and etching time of about: 25 mW/cm2, 20 mA/cm2 and 20 min, respectively. Immersion process with different immersion times were carried out at a fixed concentration 1 mM of HAuCl4, AgNO3 and PdCl2 to synthesize Au–Ag–PdNPs/maPsi hybrid structures. Trimetallic core–shell nanoparticles form was prepared at (6, 8) min immersion times, while for surface alloying nanoparticles form was prepared at (2, 4) min immersion times in a mixed solution with a fixed ratio 1:1:1 at room temperature. The structural aspects of the as-formed maPsi layer and trimetallic Au–Ag–Pd nanoparticles were demonstrated by field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS). The electrical properties of the modified maPsi layers with trimetallic nanoparticles with and without CO2 gas sensor were found at room temperature. A specific enhancement in gas sensitivity for trimetallic surface alloying nanoparticles form compared with that of the core–shell nanoparticles form was obtained due to the higher specific area to volume ratio.

Batch-fabricated CO gas sensor in large-area (8-inch) with sub-10 mW power operation

Gas sensors that can operate with sub-10 mW power consumption are in great demand in application where mobile devices are used to detect harmful gases in real time. Such low power gas sensors can be realized by employing miniaturized and air-suspended microheater platforms; however, a productive and reliable fabrication method should be developed for their practical use. Here, we present a batch-fabrication method based on a surface micro-machining process to uniformly and reliably produce the sub-10 mW power oerating gas sensors on an 8-inch wafer area. The fabricated gas sensors showed a reproducible and sensitive response to various concentrations of carbon monoxide gas (as low as 1 ppm) with 5.0 mW power operation, which is among the lowest power achieved for semiconducting metal-oxide gas sensors. In addition, the devices showed low sample-to-sample variation and high reliability in a long-term stability test, verifying their potential for practical use in mobile gas sensing applications.

Nanostructured GaN and AlGaN/GaN heterostructure for catalyst-free low-temperature CO sensing

The use of expensive catalysts (e.g. platinum) and high operation temperature (>300 °C) has plagued the cost-effectiveness and thereby the commercialization of III-Nitride semiconductors based gas sensing technology. Inadequate research on the development of catalyst-free room-temperature CO sensing using GaN based structures is the critical reason behind the subjugation of this area. Therefore, in the present article, we aimed the development of GaN & AlGaN/GaN heterostructure based gas sensors for catalyst-free low-temperature CO sensing (at 100 ppm). To explore the underlying science behind such mechanism, the morphological, electronic and electrical properties of the devices were thoroughly investigated. The analysis revealed that CO sensing on GaN (and AlGaN/GaN heterostructure) is governed via the chemical nature of ambient-oxidation induced amorphous oxide layer (O2−, O2– or OH– species), which acts as donor/acceptor state at the surface. Besides, the critical device parameters like Schottky barrier height and electron accumulation associated with series resistance and leakage current (forward/reverse) displayed significant variation with temperature (27–250 °C) and perturbed the effective carrier transport/collection and ultimately the device efficiency. The study demonstrates that nanostructured surfaces can open avenues for the development of catalyst-free room temperature operating III-Nitride semiconductor based CO sensors.

Effect of p- or n-Type Semiconductor on CO Sensing Performance of Catalytic Combustion-Type CO Gas Sensor with CeO2-ZrO2-ZnO Based Catalyst

Abstract Novel catalytic combustion-type CO gas sensors were successfully devised by applying precious metal-free catalysts composed of the p- or n-type semiconducting Ln2CuO4-loaded CeO2-ZrO2-ZnO (Ln2CuO4/CZZn; Ln = La, Nd, and Sm). Complete CO oxidation using the p-type semiconducting La2CuO4/CZZn catalyst occurred at 350 °C, while the n-type semiconducting Nd2CuO4/CZZn and Sm2CuO4/CZZn catalysts completely oxidized CO gas at 220 °C and 200 °C, respectively. All the fabricated sensors exhibited quantitative detection of CO gas over 250 °C. The La2CuO4/CZZn catalyst has the smallest heat capacity, which dramatically increases the Pt coil temperature compared with the other catalysts, resulting in the highest sensor signal. However, the sensor applying Nd2CuO4/CZZn and Sm2CuO4/CZZn catalysts exhibited faster response time to CO gas than the sensor employing La2CuO4/CZZn catalyst due to their superior CO oxidation activity.

Solid-state potentiometric CO2 sensor combining Li3PO4 with MoO3-doped Li2CO3 sensing electrode

The potentiometric CO2 gas sensors based on Li3PO4 thin film using different MoO3-doped Li2CO3 as sensing electrodes were investigated. The sensing electrode materials were prepared by screen printing while the Li3PO4 electrolyte thin film by thermal evaporation. The materials’ phase composition and the microstructures were characterized by X-ray diffraction (XRD), energy-dispersive spectrum (EDS), and scanning electron microscopy (SEM). The sensors were tested at the temperature ranging from 350 °C to 500 °C with an interval of 25 °C. The results showed that all sensors have better sensing properties at higher working temperatures. Among them, the sensor attached with 10 wt% MoO3-doped Li2CO3 exhibit excellent sensing performance, and its sensitivity attains to 95.7 mV/decade and the response and recovery time are 16 s and 22 s respectively at 500 °C. Its output EMF is more stable than any other sensors annealed at 550 °C. The MoO3-doped Li2CO3 sensing electrodes can significantly improve the sensors’ properties because of the porous microstructure and catalytic characteristics during the reaction period.

Study of WO3–In2O3 nanocomposites for highly sensitive CO and NO2 gas sensors

Pure semiconductor tungsten oxide (WO3), indium oxide (In2O3) and mixed nanocomposites with different WO3 to In2O3 ratios were successfully synthesized by simple sol-gel method following calcination at 600 °C. The morphology, phase composition and features of crustal structure of the materials were studied by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transition electron microscopy and electron paramagnetic resonance spectroscopy. It was found that the nanocomposite materials are characterized by fine crystallinity of 8–38 nm, highly defective crystal cells and presence of delocalized electrons in their structures, which can significantly affect gas sensitivity. The gas sensors based on WO3–In2O3 composite structures exhibited excellent CO and NO2 detecting performance at optimal operating temperature of ∼240 °C and ∼140 °C, respectively.

Study of PWM regulation effect using boost converter on electrolysis injection system based on Fuzzy Logic Controller

The aim of this paper is study the effect of PWM regulation on electric boost converter. The converter was used for electric driver in electrolysis injection system in order to modified the gas flow production. Electric driver will result the modified gas flow that injected into the combustion engine. The proposed scheme was expected to rose the combustion process and reduce the CO emission. The PMW regulation on this paper was developed using fuzzy logic controller that obtained feedback signal from CO gas sensor measurement. The experimental result showed that CO concentration measured about 330 PPM and its reduced until 253 PPM after the implementation of PWM variation.

Pt decorated SnO2 nanoparticles for high response CO gas sensor under the low operating temperature

Gas sensors based on noble metal/metal oxide are applied extensively, and show a relatively high response to carbon monoxide at inferior operating temperature. In this paper, a carbon monoxide sensor based on Pt decorated SnO2 nanoparticles is obtained by a hydrothermal method. Abundant characterization methods are used to analyze the structure, morphology, chemical state and specific surface area of the as-prepared compounds. The pure SnO2 sensor exhibits inferior operating temperature and low response for the detection of carbon monoxide. In contrast, the observed response of the sensor with the as-synthesized 1.5 mol% Pt decorated SnO2 is up to 610.45 at a low operating temperature of 80 °C, and the response value is about three times higher than that of SnO2 sensor. The significantly improved performance is thoroughly explained in terms of the adsorption–desorption mechanism, and the chemical sensitization and electronic sensitization of Pt.

High Response CO Sensor Based on a Polyaniline/SnO₂ Nanocomposite.

A polyaniline (PANI)/tin oxide (SnO2) composite for a CO sensor was fabricated using a composite film composed of SnO2 nanoparticles and PANI deposition in the present study. Tin oxide nanoparticles were synthesized by the sol-gel method. The SnO2 nanoparticles provided a high surface area to significantly enhance the response to the change in CO concentration at low operating temperature (<75 °C). The excellent sensor response was mainly attributed to the relatively good properties of PANI in the redox reaction during sensing, which produced a great resistance difference between the air and CO gas at low operating temperature. Therefore, the combination of n-type SnO2 nanoparticles with a high surface area and a thick film of conductive PANI is an effective strategy to design a high-performance CO gas sensor.

Synthesis of carbon nanotubes by direct liquid injection chemical vapor deposition method and its relevance for developing an ultra-sensitive room temperature based CO2 sensor

Abstract The present paper reports the synthesis and characterization of Multiwalled Carbon Nanotube (MWCNT) based thin film and its application as a CO2 gas sensor. The MWCNT was prepared by direct liquid injection chemical vapor deposition method (DLICVD) using ethanol as a precursor in the presence of argon gas atmosphere and furnace temperature at 750 °C. The thin film of MWCNT was prepared by using the spin coating technique and characterized using Scanning electron microscope (SEM), UV–Visible spectrometer, Particle size analyzer and X-ray diffractometer (XRD). The vibrational and rotational spectra were observed through Fourier Transform Infra-Red Spectroscopy (FTIR) and Raman Spectroscopy. The SEM image of the thin film exhibited the nanotubular structure grown throughout the surface. From XRD, the minimum crystallite size was found to be 14 nm. The optical energy band gap of the nanotube-based thin film was found as 3.6 eV. The synthesized CNT-based thin film was employed for the CO2 sensing at room temperature. The sensor response of the sensor was found as 2.1 and the results were found 98% reproducible. The response and recovery times were found to be 30.2 and 49.6 s, respectively. Theoretical calculations were also performed in the support of CO2 sensing through the MWCNT.