Comparison of the enhanced gas sensing properties of tin dioxide samples doped with different catalytic transition elements

Effect of Manganese Distribution on Sensor Properties of SnO2/MnOx Nanocomposites

Nanocomposites SnO₂/MnO_x with various manganese content (up to [Mn]/[Sn] = 10 mol. %) and different manganese distribution were prepared by wet chemical technique and characterized by X-ray diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and mapping, IR and Raman spectroscopy, total reflection X-ray fluorescence, mass-spectrometry with inductive-coupled plasma (ICP-MS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy. A different distribution of manganese between the volume and the surface of the SnO₂ crystallites was revealed depending on the total Mn concentration. Furthermore, the identification of surface MnO₂ segregation was performed via Raman spectroscopy. There is a strong dependence of the sensor signal toward CO and, especially, NO) on the presence of MnO₂ surface segregation. However, manganese ions intruding the SnO₂ crystal structure were shown to not almost effect on sensor properties of the material.

Etching process enhanced H2O2 sensing performance of SnO2/Zn2SnO4 with reliable anti-humidity ability

In this work, sol-gel and chemical etching methods are adopted to synthesize zinc hydroxystannate materials. Cubic tin dioxide and zinc stannate composite materials with a definite structure are successfully prepared at varied annealing temperatures and times by using the synthesized zinc hydroxystannate as a sacrificial template. After a gas sensing test, tin dioxide and zinc stannate composite samples etched at 650 °C and annealed for 4 h exhibit a strong response and outstanding selectivity to hydrogen peroxide. Furthermore, the samples prepared under such conditions demonstrate long-term stability, and also a specified level of tolerance after the humidity stability test. Moreover, because of the simple preparation method and rapid detection of hydrogen peroxide, it is worth noting that samples prepared following the etching process at the 650 °C annealing temperature for 4 h exhibit the significant benefits of tin dioxide and zinc stannate composites. In this modern era, this research emphasizes the sample's potential for the rapid identification and detection of hydrogen peroxide.

The Key Role of Active Sites in the Development of Selective Metal Oxide Sensor Materials

Development of sensor materials based on metal oxide semiconductors (MOS) for selective gas sensors is challenging for the tasks of air quality monitoring, early fire detection, gas leaks search, breath analysis, etc. An extensive range of sensor materials has been elaborated, but no consistent guidelines can be found for choosing a material composition targeting the selective detection of specific gases. Fundamental relations between material composition and sensing behavior have not been unambiguously established. In the present review, we summarize our recent works on the research of active sites and gas sensing behavior of n-type semiconductor metal oxides with different composition (simple oxides ZnO, In₂O₃, SnO₂, WO₃; mixed-metal oxides BaSnO₃, Bi₂WO₆), and functionalized by catalytic noble metals (Ru, Pd, Au). The materials were variously characterized. The composition, metal-oxygen bonding, microstructure, active sites, sensing behavior, and interaction routes with gases (CO, NH₃, SO₂, VOC, NO₂) were examined. The key role of active sites in determining the selectivity of sensor materials is substantiated. It was shown that the metal-oxygen bond energy of the MOS correlates with the surface acidity and the concentration of surface oxygen species and oxygen vacancies, which control the adsorption and redox conversion of analyte gas molecules. The effects of cations in mixed-metal oxides on the sensitivity and selectivity of BaSnO₃ and Bi₂WO₆ to SO₂ and VOCs, respectively, are rationalized. The determining role of catalytic noble metals in oxidation of reducing analyte gases and the impact of acid sites of MOS to gas adsorption are demonstrated.

Film Growth of Tetragonal SnO2 on Glass Substrate by Dip-Coating Technique for Ethanol Sensing Applications

A thin film sensor based on tetragonal SnO2 nanoparticles was fabricated by combining the sol–gel method and a dip-coating technique on a cylindrical glass substrate. The sensing material was produced through a cycling annealing process at 400 and 600 °C, using tin chloride (IV) pentahydrate as a precursor in polyethylene glycol (PEG) solution as a surfactant. Materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), revealing tetragonal phase formation with no impurities. The sensor′s assembly was done with low-cost materials such as Cu electrodes, Cu-Ni tube pins, and glass-reinforced epoxy laminate as the base material. For signal variation, an adequate voltage divider circuit was used to detect ethanol′s presence on the surface of the sensor. The fabricated sensor response to gaseous ethanol at its operating temperature at ambient pressure is comparable to that of a commercial sensor, with the advantage of detecting ethanol at lower temperatures. The sensor response (S = Ra/Rg) to 40 ppm of ethanol at 120 °C was 7.21. A reported mathematical model was used to fit the data with good results.

High-Sensitive Ammonia Sensors Based on Tin Monoxide Nanoshells

Ammonia (NH₃) is a harmful gas contaminant that is part of the nitrogen cycle in our daily lives. Therefore, highly sensitive ammonia sensors are important for environmental protection and human health. However, it is difficult to detect low concentrations of ammonia (≤50 ppm) using conventional means at room temperature. Tin monoxide (SnO), a member of IV⁻VI metal monoxides, has attracted much attention due to its low cost, environmental-friendly nature, and higher stability compared with other non-oxide ammonia sensing material like alkaline metal or polymer, which made this material an ideal alternative for ammonia sensor applications. In this work, we fabricated high-sensitive ammonia sensors based on self-assembly SnO nanoshells via a solution method and annealing under 300 °C for 1 h. The as fabricated sensors exhibited the response of 313%, 874%, 2757%, 3116%, and 3757% (∆G/G) under ammonia concentration of 5 ppm, 20 ppm, 50 ppm, 100 ppm, and 200 ppm, respectively. The structure of the nanoshells, which have curved shells that provide shelters for the core and also possess a large surface area, is able to absorb more ammonia molecules, leading to further improvements in the sensitivity. Further, the SnO nanoshells have higher oxygen vacancy densities compared with other metal oxide ammonia sensing materials, enabling it to have higher performance. Additionally, the selectivity of ammonia sensors is also outstanding. We hope this work will provide a reference for the study of similar structures and applications of IV⁻VI metal monoxides in the gas sensor field.

Ultra-sensitive and selective NH3 room temperature gas sensing induced by manganese-doped titanium dioxide nanoparticles

The study of the fabrication of ultra-high sensitive and selective room temperature ammonia (NH₃) and nitrogen dioxide (NO₂) gas sensors remains an important scientific challenge in the gas sensing field. This is motivated by their harmful impact on the human health and environment. Therefore, herein, we report for the first time on the gas sensing properties of TiO₂ nanoparticles doped with various concentrations of manganese (Mn) (1.0, 1.5, 2.0, 2.5 and 3.0mol.% presented as S1, S2, S3, S4 and S5, respectively), synthesized using hydrothermal method. Structural analyses showed that both undoped and Mn-doped TiO₂ crystallized in tetragonal phases. Optical studies revealed that the Mn doped TiO₂ nanoparticles have enhanced UV→Vis emission with a broad shoulder at 540nm, signifying induced defects by substituting Ti⁴⁺ ions with Mn²⁺. The X-ray photoelectron spectroscopy and the electron paramagnetic resonance studies revealed the presence of Ti³⁺ and singly ionized oxygen vacancies in both pure and Mn doped TiO₂ nanoparticles. Additionally, a hyperfine split due to Mn²⁺ ferromagnetic ordering was observed, confirming incorporation of Mn ions into the lattice sites. The sensitivity, selectivity, operating temperature, and response-recovery times were thoroughly evaluated according to the alteration in the materials electrical resistance in the presence of the target gases. Gas sensing studies showed that Mn²⁺ doped on the TiO₂ surface improved the NH₃ sensing performance in terms of response, sensitivity and selectivity. The S1 sensing material revealed higher sensitivity of 127.39 at 20 ppm NH₃ gas. The sensing mechanism towards NH₃ gas is also proposed.

Study of structural properties and defects of Ni-doped SnO2 nanorods as ethanol gas sensors

An ethanol gas sensor with enhanced sensor response was fabricated using Ni-doped SnO₂ nanorods, synthesized via a simple hydrothermal method. It was found that the response (R = R ₀/R _g) of a 5.0 mol% Ni-doped SnO₂ (5.0Ni:SnO₂) nanorod sensor was 1.4 × 10⁴ for 1000 ppm C₂H₅OH gas, which is about 13 times higher than that of pure SnO₂ nanorods, (1.1 × 10³) at the operating temperature of 450 °C. Moreover, for 50 ppm C₂H₅OH gas, the 5.0Ni:SnO₂ nanorod sensor still recorded a significant response reading, namely 2.0 × 10³ with a response time of 30 s and recovery time of 10 min. To investigate the effect of Ni dopant (0.5-5.0 mol%) on SnO₂ nanorods, structural characterizations were demonstrated using field emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy and an ultraviolet-visible spectrometer. XRD results confirmed that all the samples consisted of tetragonal-shaped rutile SnO₂ nanorods. It was found that the average diameter and length of the nanorods formed in 5.0Ni:SnO₂ were four times smaller (∼6 and ∼35 nm, respectively) than those of the nanorods formed in pure SnO₂ (∼25 and 150 nm). Interestingly, both samples had the same aspect ratio, ∼6. It is proposed that the high response of the 5.0Ni:SnO₂ nanorod sensor can be attributed to the particle size, which causes an increase in the thickness of the charge depletion layer, and the presence of oxygen vacancies within the matrix of SnO₂ nanorods.