SnO2 Sensor Research Articles

Study of the response behavior of a CdS-SnO2 thick film for high selectivity towards propanol gas.

Gas monitoring devices are in demand for a rapidly growing range of applications. Metal oxide-based gas sensors have been extensively used for the detection of toxic pollutant gases, combustible gases, and hydrocarbon vapors. The sensitivity for a low concentration and observed response and the recovery times of the reported gas sensors are not satisfactory, and it needs further detailed studies. In the present work, undoped SnO2 and cadmium sulfide (CdS)-doped SnO2 thick films were fabricated using the screen-printing method to study their sensing behavior towards tested organic vapors such as acetone, propanol, and ethanol. The sensing properties of fabricated sensors were investigated for the test gases, i.e. acetone, propanol, and ethanol, at an elevated temperature of 473 K. It was observed that the 2 wt% CdS-doped SnO2 sensor showed a maximum response (78%) and was highly selective (44.6%) to propanol over acetone and ethanol. The results showed that the diminution of the SnO2 crystallite size with the CdS content leads to an improvement in the response of the SnO2 sensor for the tested gases. The microstructural properties are also correlated to the sensing behavior. The measurement showed that the CdS-SnO2 thick film sensor is highly sensitive. At the same time, it is more selective to propanol than the other test gases, ethanol and acetone.

Enhanced acetone gas-sensing characteristics of Pd-NiO nanorods/SnO2 nanowires sensors.

Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas, but it can cause dangerous effects on human health. Thus, the fabrication of highly sensitive and selective sensors for recognition of acetone is incredibly important. Here, we prepared the SnO2/Pd-NiO (SPN) nanowires-based gas sensor for the detection of acetone, in which, the amount of Pd nanoparticles were varied to enhance the performance of the devices. We demonstrated that the acetone gas sensing performance of the SPN device was significantly enhanced, showing increases of 3.72 and 6.53 folds compared to pristine SnO2 and NiO sensors, respectively. The Pd-NiO 0.01% wt Pd SPN sensor (SPN-1) exhibited an excellent response (Ra/Rg = 14.88) toward 500 ppm acetone gas. The SPN-1 sensor also showed a fast gas response time of 11/150 seconds with 500 ppm Acetone at 450 °C, while the recovery time was 468/526 seconds. Additionally, the sensor showed good selectivity toward acetone over other reducing gases, such as NH3, CH4, and VOCs. With those results, the SPN-1 sensor shows superiority compared to sensors based on pure materials.

Embedding Pd into SnO2 drastically enhances gas sensing.

Combustion aerosol processes can uniquely embed noble metals into semiconducting particles. Here, monocrystalline SnO2 particles embedded with Pd and/or PdOx were made by flame spray pyrolysis (FSP) of appropriate precursors through microexplosions by droplet-to-particle conversion as the crystal size was proportional to the cube root of precursor solution concentration, C. These particles were air-annealed and leached with nitric acid for removal of metallic Pd from their surface. The SnO2 crystal size varied from 11 to 24 nm and was in close agreement with the primary particle size determined by nitrogen adsorption. The embedded fraction of Pd ranged from about 30 to 80% of the nominal Pd-content. This was achieved by judiciously varying the C, Pd content and the ratio of precursor solution to dispersion oxygen flowrates during FSP. The response of sensors made by doctor blading films of such particles to 1 ppm of acetone and CO was evaluated at 350 °C and 50% relative humidity. Embedding Pd/PdOx into SnO2 significantly increased the sensor response: 2-6 times over that of pure or conventionally-made Pd-containing SnO2 sensors at low nominal Pd-contents (0.2 mol%). For higher ones (i.e. 1 mol% Pd), the sensor response was enhanced by up to two orders of magnitude. This is attributed to Pd atoms in the SnO2 lattice near the particle surface and/or Pd/PdOx clusters acting as nanoelectrodes into SnO2 films and altering their transducing properties as shown by high resolution electron microscopy, XPS and baseline resistance measurements of pure and Pd-embedded SnO2 sensing films.

Effects of Al incorporation on structural and humidity-sensing properties of SnO2 sensor

Effects of Al incorporation on structural and humidity-sensing properties of SnO2 sensor

Detection of Triacetone Triperoxide in air combining SnO2 sensor e-nose enhanced with a kinetic model

In the domain of high-temperature semiconductor arrays for electronic noses (e-noses), Metal Oxide Sensors (MOS) have a pivotal role despite their non-linear response to chemical vapors. A prevalent approach to enhance the identification algorithm's performance involves implementing mathematical models during the MOS signal processing. However, certain models rely solely on mathematical goodness-of-fit, overlooking crucial features that render practical e-nose applications ineffective. This paper introduces a theoretical model for the qualitative analysis of MOS signals, focusing on two primary diffusion processes: analyte migration to the sensor's surface and the subsequent dispersion of some of these molecules within the MOS bulk. Additionally, this work discusses a model validation using an ad-hoc e-nose, built with SnO2 gas sensors, and six organic chemicals, detailing main data processing steps. Finally, disclosed results showcase a high success rate for Triacetone Triperoxide (TATP) identification, one of the most significant threats among homemade explosives (HME). The presented conclusions underscore the enhanced efficacy of the proposed signal model for e-nose vapors identification and its practical utility in strengthening pre-emptive HME identification to enhance public safety.

Effect of kinetic properties of zeolites on the gas-sensing performance of zeolite-covered SnO2 sensors

ABSTRACT Zeolite additional layers coating on metal oxide surfaces to improve the selectivity and response values of the sensors are effective and widely used. The specific adsorption and diffusion of gas molecules in the zeolite are recognised to play an important role in gas sensing improvement. In this work, the adsorption and diffusion behaviours of formaldehyde and acetone in H-Y and H-A zeolites were calculated by Monte Carlo and molecular dynamics simulations. The loading of acetone is greater than formaldehyde in these two kinds of zeolites under the same temperature and pressure, and the water load is lower. The simulation results show that the effects of the nature of the guest molecule and steric hindrance of the diffusing molecule on diffusivity are significant. The diffusivity in H-A zeolite decreases by several orders of magnitude than that in H-Y zeolite However, in H-A zeolite, the internal diffusion dominates, and only the smaller diameter formaldehyde can diffuse between the pores, which is beneficial to improving the sensing properties of formaldehyde. In addition, in the competition diffusion with water molecules, formaldehyde dominates than acetone. The H-Y/SnO2 and H-A/SnO2 sensors were prepared to verify the reliability of the molecular simulations. Research highlights The adsorption and diffusion behaviour of formaldehyde and acetone in H-Y and H-A zeolites were investigated using molecular simulation. Molecular diameter mainly influences the kinetic behaviour. The sensitisation mechanism of H-Y/SnO2 sensor to acetone and H-A/SnO2 sensor to formaldehyde was proved. Focuses on the relationship between gas-sensing the performance of zeolite-covered SnO2 sensors and the adsorption.

Room temperature solid electrolyte ozone sensor based on Ag-doped SnO2

In this paper, SnO2 was synthesized using MOFs as a sacrificial template, and Ag-doped SnO2 composite was synthesized by reducing AgNO3 with NaBH4, and O3 sensors were prepared using sodium superionic conductor (NASICON) as a solid electrolyte. At room temperature, the gas-sensitive experimental tests showed that the response of the sensor with 3 wt% Ag-SnO2 to 180–420 ppb O3 increased by about 57% and the sensitivity increased by 9.9% compared to the pure SnO2 sensor. The repeatability and stability of the 3 wt% Ag-SnO2 sensor were tested at 240 ppb O3, and the results showed that the repeatability of the sensor varied between − 2% and 2%, and the stability varied between − 4% and 4%. Therefore, the solid electrolyte sensor prepared by the excellent Ag-doped SnO2 composite material has a good application prospect in the detection of low-concentration O3.

Fabrication of ZnO-SnO2 heterojunction inverse opal photonic balls for chemiresistive acetone sensing

The development of metal oxide semiconductor-based chemiresistive gas sensors with ultra-fast response/recovery for toxic and flammable gases is of great importance, but still challenging. Here, ZnO-SnO2 heterojunction three-dimensional (3D) inverse opal photonic crystal balls (IOPBs) were fabricated based on rapid and liquid waste-free spray drying. The spherical three-dimensional (3D) ordered macroporous skeleton can provide more active sites and faster gas diffusion channels. Furthermore, the n-n heterojunction established by ZnO and SnO2 is favorable for electron transport. The response (Ra/Rg) of IOPBs to 50 ppm acetone reaches 40.3 at an optimal operating temperature of 260 °C when the Zn/Sn atomic ratio is 1:4, which is 5 times higher than that of the pure SnO2 sensor. Response/recovery time also reduces from 23/47 s for pure SnO2 to 6/10 s. In addition, the IOPBs gas sensors also exhibit good selectivity and excellent long-term stability. This work provides a straightforward and versatile synthetic route for the preparation of 3D IOPBs to explore novel gas sensors with ultra-fast response speed.

Synergistic effects of bimetallic Pd-Au(alloy)/SnO2 nanocomposites for low temperature and selective hydrogen gas sensors

In view of the explosive nature of hydrogen gas, the demand for detection is increasing. Although Pd-based chemiresistive sensors are gaining much attention in hydrogen detection, it is easily oxidized at high temperatures, leading to the deterioration of sensing performance. To address this issue, we synthesized bimetallic Pd-Au alloy nanoparticles (NPs) and mixed them with SnO2 powder for improving the hydrogen sensing performance. The response of the bimetallic Pd-Au(alloy)/SnO2 nanocomposites (NCs) sensor toward 100 ppm hydrogen was 72.78 which is 7 times higher than that of the pure SnO2 sensor at a relatively lower working temperature of 150°C. Furthermore, when compared to other interfering gases, the sensor revealed high selectivity for hydrogen gas. The enhanced hydrogen sensing performance was attributed to the synergistic effect arising from the formation of a heterojunction interface between Pd-Au alloy and SnO2 NPs and the decomposition and absorption of hydrogen molecules by Pd-Au alloy NPs.

Significantly improved triethylamine sensing performance and mechanism of tin oxide by doping Pd: Experimental and DFT studies

Reducing the working temperature and increasing sensitivity and selectivity has always been a research hotspot in the field of MOS based gas sensors. In this work, improved triethylamine (TEA) sensing performance and mechanism of SnO2 by doping Pd have been investigated. SnO2 nanoparticles and Pd-SnO2 with different doping amounts of Pd (0%, 0.1%, 0.3%, 0.5%, and 0.7%) were successfully prepared by the hydrothermal method. The size of SnO2 nanoparticles is very uniform (∼15 nm). The SnO2 sensor exhibited the highest sensitivity to ethanol at 290 °C. After Pd doping, Pd/SnO2 sensors not only reduced the optimum working temperature but transformed selectivity from ethanol to TEA. In the Pd-SnO2 system, the 0.5Pd-SnO2 sensor exhibited high sensitivity (61), fast response-recovery properties (16 s/6 s) to 50 ppm TEA, lower detection limits (0.1 ppm), good repeatability, and higher selectivity. Furthermore, based on density functional theory calculations, the improved TEA sensing performance of 0.5Pd-SnO2 sensors can be attributed to the improved surface activity of SnO2 by Pd doping and the catalytic activation of O2 and TEA by Pd.

Pd nanoparticles decorated SnO2 ultrathin nanosheets for highly sensitive H2 sensor: Experimental and theoretical studies

This study is attempted to improve the hydrogen sensing performance of SnO2 based sensors by simultaneously employing two strategies of morphology control and noble metal loading. Therefore, SnO2 ultrathin nanosheets with thickness not exceeding 3.5 nm were successfully synthesized by a hydrothermal method and then different content of Pd nanoparticles were uniformly loaded onto SnO2 surface by in situ reduction with ascorbic acid. The gas sensing properties demonstrated that the introduction of Pd not only altered the selectivity of the SnO2 sensor from ethanol to hydrogen, but also significantly improved the gas sensitivity and reduced the working temperature. And the optimal 1.0%Pd/SnO2 sensor owned the highest sensitivity (75), fastest response-recovery property (21 s/13 s) to 20 ppm of hydrogen at 220 °C, and the actual detection limit is as low as 0.1 ppm. Furthermore, 1.0%Pd/SnO2 sensor exhibited excellent repeatability, reproducibility and acceptable anti-interference of humidity. The DFT studies suggest that the physisorption of the hydrogen molecules on the surface of SnO2, but chemisorption on the surface of Pd/SnO2. The improved H2 sensing performance of Pd/SnO2 sensor attributes its ultrathin thickness of SnO2 and catalytic dissociation of Pd to O2 and H2.

Gas detection strategy to suppress flow rate interference baesd on semiconductor sensor dynamic temperature modulation measurement

Semiconductor gas sensors are widely used in industry, commerce and other fields. Flow rate has great influence on its response, but there was no breakthrough research progress at present. Usually, the interference is overcome by suppressing the expression of flow rate information at the output of the sensor. In this paper, a new research idea is put forward, which uses the ability of expanding output information of dynamic temperature modulation method to express the influence of flow rate on sensor. A typical case of butanone detection by SnO2 sensor was taken as the main experiment. By analyzing the microcosmic characteristic difference between flow rate and concentration in dynamic response, the change rule of dynamic response with flow rate change can be grasped, thus eliminating its interference to qualitative analysis. On the basis of dynamic temperature modulation, PCA and LDA are used to reduce the dimension of data, and the distribution law of two-dimensional score figure is obtained about the change of concentration and flow rate. In addition, the method is validated by using ethyl ether and toluene, and the same experimental phenomena are obtained. The results show that it is not only feasible but also has certain universality to use dynamic temperature modulation method to suppress the influence of flow rate on quantitative analysis.

The stability of SnO2 and In2O3 gas sensors to water under temperature modulation mode

Temperature modulation technology has been extensively used in metal oxide semiconductor (MOS) gas sensors, especially based on micro-hotplate sensor structure. The technique not only enhances the selectivity but also increases the sensor’s sensitivity by allowing it to exhibit a highly active surface due to the effect of oxygen accumulation. However, when the MOS sensor is in a state of high surface activity, the corresponding hydroxide formation may occur when exposed to water, negatively affecting the gas sensing performance and stability of the sensor. This study focuses on the stability of SnO2 and In2O3 gas sensors during storage process after temperature modulation test. The results indicate that SnO2 exhibits good stability, while In2O3 stability is poor. The mechanism responsible for deactivation was discussed with infrared spectroscopy results. The formation of In(OH)3 was confirmed by high resolution transmission electron microscope, which further confirmed the above conclusion. These findings suggest that after temperature modulation, the gas sensitive materials stored in an atmospheric environment (20 ℃, 40%−60%RH) would generate hydroxides. When temperature modulation was repeated at (100–400 ℃), Sn(OH)4 decompose into SnO2, thus maintaining stability. In contrast, the decomposition temperature of In(OH)3 is higher. At 400 ℃, it will not decompose into In2O3 in a short time, which would lead to poor stability.

Enhanced toluene gas-sensing properties of MEMS sensor based on Pt-loaded SnO2 nanoparticles

Rapid detection of low concentration toluene is highly desirable in environment monitoring, industrial processes, medical diagnosis, etc. In this study, we prepared Pt-loaded SnO2 monodispersed nanoparticles through hydrothermal method and assembled a sensor based on micro-electro-mechanical system (MEMS) to detect toluene. Compared with the pure SnO2, the 2.92 wt% Pt-loaded SnO2 sensor exhibits a 2.75 times higher gas sensitivity to toluene at about 330 °C. Meanwhile, the 2.92 wt% Pt-loaded SnO2 sensor also has a stable and good response to 100 ppb of toluene. Its theoretical detection limit is calculated as low as 12.6 ppb. Also, the sensor has a short response time of ∼10 s to different gas concentrations, as well as the excellent dynamic response—recovery characteristics, selectivity, and stability. The improved performance of Pt-loaded SnO2 sensor can be explained by the increase of oxygen vacancies and chemisorbed oxygen species. The electronic and chemical sensitization of Pt to SnO2-based sensor, together with small size and fast gas diffusion of the MEMS design ensured fast response and ultra-low toluene detection. This provides new ideas and decent prospect for developing miniaturized, low-power-consumption, and portable application of gas sensing devices.

Construction of ultra-fast hydrogen sensor for dissolved gas detection in oil-immersed transformers based on titanium dioxide quantum dots modified tin dioxide nanosheets

Hydrogen (H2) is a typical product dissolved in transformer oil and a typical fault diagnosis gas for oil-immersed transformer equipment. The large concentration range and fast detection of H2 gas sensors have certain engineering significance. In this paper, TiO2 quantum dots (QDs) with particle size of about 5 nm were prepared by solvothermal reaction, and SnO2 nanosheets modified by TiO2 QDs was successfully prepared. The gas sensing performance of TiO2-SnO2 to H2 was systematically explored. The optimal operating temperature of the sensors is 400 °C. At the optimal operating temperature of 400 °C, the TiO2 (1 %)-SnO2 sensor demonstrated the most excellent gas sensing performance to H2, such as the short response and recovery time (2 s and 5 s to 200 ppm H2), excellent stability, outstanding selectivity and large detection range of 4.8–5000 ppm. The first-principles calculations were carried out and the gas sensing mechanism was further elaborated, which show that the improvement of the TiO2(1 %)-SnO2 is mainly ascribed to the sensitization and homojunction effect of TiO2 QDs. The TiO2 (1 %)-SnO2 gas sensor is expected to provide a choice for the dissolved gas analysis (DGA) method in transformer oil analysis.

Large-lateral-area SnO2 nanosheets with a loose structure for high-performance acetone sensor at the ppt level

Gas sensors with high sensitivity and high selectivity are required in practical applications to distinguish between target molecules in the detection of volatile organic compounds, real-time security alerts, and clinical diagnostics. Semiconducting tin oxide (SnO2) is highly regarded as a gas-sensing material due to its exceptional responsiveness to changes in gaseous environments and outstanding chemical stability. Herein, we successfully synthesized a large-lateral-area SnO2 nanosheet with a loose structure as a gas sensing material by a one-step facile aqueous solution process without a surfactant or template. The SnO2 sensor exhibited a remarkable sensitivity (Ra/Rg = 1.33) at 40 ppt for acetone, with a theoretical limit of detection of 1.37 ppt, which is the lowest among metal oxide semiconductor-based gas sensors. The anti-interference ability of acetone was higher than those of pristine SnO2 and commercial sensors. These sensors also demonstrated perfect reproducibility and long-term stability of 100 days. The ultrasensitive response of the SnO2 nanosheets toward acetone was attributed to the specific loose large lateral area structure, small grain size, and metastable (101) crystal facets. Considering these advantages, SnO2 nanosheets with larger lateral area sensors have great potential for the detection and monitoring of acetone.

A catalytic filter based on Pt-CeO2 for selective methane detection with SnO2 sensors

A microfilter structure is proposed to modulate the transient process and reaction characteristics of gas diffusion to improve the selectivity. The sensor structure is divided into a sensitive part with sensing films and microfilter, which is composed of a porous ceramic carrier and catalytic film. This structure can avoid the problems of element diffusion and low adhesion caused by the poor contact between the sensitive film and the filter film. The catalytic combustion of interfering gases is verified. Results indicate that the sensitive and selective response of the microfilter sensor to CH4 are obviously improved. The microfilter could catalyze CO and ethanol into CO2 and H2O, and activate CH4 during the diffusion process, thus improving the activity of CH4. At the same time, sensors with a new structure exhibit stability, and high adaptability to the environment. Finally, with the help of the power-law response and in-situ catalytic characterization, the sensing mechanism is explained that sensors conform to the power-law response. That is the adsorption and reaction of oxygen on the surface are the basic mechanisms of the CH4 sensing response.

Fabrication and modeling of laser ablated NiO nanoparticles decorated SnO2 based formaldehyde sensor

In this study, we have reported the fabrication of p-NiO/n-SnO2 heterojunction based formaldehyde (HCHO) sensor by decorating the surface of pre-deposited SnO2 thin film with laser ablated NiO nanoparticles (NPs). In atmospheric air, NiO NPs were produced by a moving laser beam on the surface of pure (99.99%) Ni pellet to decorate sputtered deposited SnO2 thin film directly to form NiO/SnO2 p-n heterojunction. After fabrication, gas sensing properties of NiO/SnO2 sensor were investigated systemically towards HCHO and it exhibited higher response (Ra/Rg) of about 31.04 towards 50 ppm HCHO at 210 °C with good selectivity compared with pristine SnO2 sensor. Moreover, adsorption (Ka) and desorption rate constant (Kd), response time (τres), recovery time (τrec) and surface coverage (θ) of NiO/SnO2 sensor were extracted from experimental data using Langmuir gas adsorption-desorption model via curve fitting method and the models demonstrated the irreversible type of gas sensing behaviour towards HCHO. The experimental results revealed that the laser ablation method has a great potential to use as alternative chemical free surface decoration route to fabricate metal oxide heterojunction based sensors for the detection of formaldehyde or other toxic gases.

Highly selective and sensitive detection of carcinogenic benzene using a raisin bread-structured film comprising catalytic Pd-Co3O4 and gas-sensing SnO2 hollow spheres

The facile and affordable fabrication of sensors that can detect carcinogenic benzene has remained a long-standing challenge, as sophisticated nano-architectures and/or sensing films are essential to ensure benzene selectivity. Herein, we report a raisin bread-structured film fabricated by mixing two different types of oxide hollow spheres, as a novel, cost-effective platform for the highly selective and sensitive detection of benzene. The film comprises catalytic Pd-Co3O4 (i.e., raisins) and gas-sensing SnO2 hollow spheres (i.e., bread), prepared by ultrasonic spray pyrolysis. In contrast to films of pure SnO2 or Pd-Co3O4 hollow spheres, which are partially selective to reactive gases such as xylene/toluene/ethanol, raisin bread films are highly selective to less reactive benzene. Thus, an array of the SnO2, Pd-Co3O4, and raisin bread sensors enables exclusive benzene identification with principal component analysis. The superior benzene-sensing properties of raisin bread sensors are attributed to the oxidative consumption of reactive gases by the catalytic raisins, whereas less-consumed benzene sensitively reacts with the gas-sensing bread. This is supported by proton transfer reaction-quadrupole mass spectrometry analysis. This work provides a simple, rational strategy to attain gas selectivity to chemically stable benzene and is expected to trigger the development of ubiquitous portable devices to monitor airborne benzene.

Small hollow ternary composite oxide semiconductor nanomaterials for conductometric HCHO sensors

In this work, the simple solvothermal method is adopted to synthesize nanometer sized hollow ternary composites of Pd@ZnO-SnO2 by using the protective effect of PVP molecules and ZIF-8 templates. The corresponding characterization such as SEM, XRD, XPS, TEM and HRTEM are employed to confirm the nanostructures, compositions and element distributions. Unlike other composites based on SnO2, the sensing materials in this work have small sizes (∼100 nm). More importantly, compared to pure SnO2 sensor, the sensor based on ternary nanocomposites of Pd@ZnO-SnO2 provides higher response, faster response speed and better selectivity. The extraordinary sensing performance is not only dependent on the complex heterojunctions in the ternary composite oxide semiconductor nanomaterials, but is also affected by the modulate of the oxygen vacancy and chemisorbed oxygen. In addition, the catalytic effect of the noble metal Pd also leads to the pronounced sensing properties. This promising sensing nanomaterials have offered unprecedented opportunities for the prevention of HCHO hazards.