Search Results (112)

Metal oxide semiconductor (MOX) sensors are emerging as a groundbreaking technology due to their remarkable features: high sensitivity, rapid response time, low cost, and potential for miniaturization. Their ability to detect volatile organic compounds (VOCs) in real time makes them ideal tools for applications across various fields, including environmental monitoring, medicine, and the food industry. This paper explores the evolution and growing utilization of MOX sensors, with a particular focus on atmospheric pollution monitoring, non-invasive disease diagnostics through the analysis of volatile compounds emitted by the human body, and food quality assessment. The crucial role of MOX sensors in monitoring the freshness of food and water, detecting chemical and biological contamination, and identifying food fraud is specifically examined. The rapid advancement of this technology offers new opportunities to improve quality of life, food safety, and public health, positioning MOX sensors as a key tool to address future challenges in these vital sectors. Full article

This study presents a comprehensive uncertainty and sensitivity analysis of the effective neutron multiplication factor ($k_{\mathrm{eff}}$) in a large-scale sodium-cooled fast reactor (SFR) modeled after the European Sodium Fast Reactor. Utilizing the Serpent Monte Carlo code and the ENDF/B-VII.1 cross-section library, this research investigates the impact of cross-section perturbations in key isotopes (²³⁵U, ²³⁸U, and ²³⁹Pu for both mixed oxide (MOX) and metal fuels. Particular focus is placed on the capture, fission, and inelastic scattering reactions, as well as the effects of fuel temperature on reactivity through Doppler broadening. The findings reveal that reactivity in MOX fuel is highly sensitive to the fission cross sections of fissile isotopes (²³⁹Pu and ²³⁸U, while capture and inelastic scattering reactions in fertile isotopes such as ²³⁸U play a significant role in reducing reactivity, enhancing neutron economy. Additionally, this study highlights that metal fuel configurations generally achieve a higher ($k_{\mathrm{eff}}$) compared to MOX, attributed to their higher fissile atom density and favorable thermal properties. These results underscore the importance of accurate nuclear data libraries to minimize uncertainties in criticality evaluations, and they provide a foundation for optimizing fuel compositions and refining reactor control strategies. The insights gained from this analysis can contribute to the development of safer and more efficient next-generation SFR designs, ultimately improving operational margins and reactor performance. Full article

The quantification of methane concentrations in air is essential for the quantification of methane emissions, which in turn is necessary to determine absolute emissions and the efficacy of emission mitigation strategies. These are essential if countries are to meet climate goals. Large-scale deployment of methane analyzers across millions of emission sites is prohibitively expensive, and lower-cost instrumentation has been recently developed as an alternative. Currently, it is unclear how cheaper instrumentation will affect measurement resolution or accuracy. To test this, the Wireless Autonomous Transportable Methane Emission Reporting System (WATCH₄ERS) has been developed, comprising four commercially available sensing technologies: metal oxide (MOx,), Non-dispersion Infrared (NDIR), integrated infrared (INIR), and tunable diode laser absorption spectrometer (TDLAS). WATCHERS is the accumulated knowledge of several long-term methane measurement projects at Colorado State University’s Methane Emission Technology Evaluation Center (METEC), and this study describes the integration of these sensors into a single unit and reports initial instrument response to calibration procedures and controlled release experiments. Specifically, this paper aims to describe the development of the WATCH₄ERS unit, report initial sensor responses, and describe future research goals. Meanwhile, future work will use data gathered by multiple WATCH₄ERS units to 1. better understand the cost–benefit balance of methane sensors, and 2. identify how decreasing instrumentation costs could increase deployment coverage and therefore inform large-scale methane monitoring strategies. Both calibration and response experiments indicate the INIR has little practical use for measuring methane concentrations less than 500 ppm. The MOx sensor is shown to have a logarithmic response to methane concentration change between background and 600 ppm but it is strongly suggested that passively sampling MOx sensors cannot respond fast enough to report concentrations that change in a sub-minute time frame. The NDIR sensor reported a linear change to methane concentration between background and 600 ppm, although there was a noticeable lag in reporting changing concentration, especially at higher values, and individual peaks could be observed throughout the experiment even when the plumes were released 5 s apart. The TDLAS sensor reported all changes in concentration but remains prohibitively expensive. Our findings suggest that each sensor technology could be optimized by either operational design or deployment location to quantify methane emissions. The WATCH₄ERS units will be deployed in real-world environments to investigate the utility of each in the future. Full article

Humidity is a well-known interference factor in metal oxide (MOX) gas sensors, significantly impacting their performance in various applications such as environmental monitoring and medical diagnostics. This study investigates the effects of adsorbed water on MOX conductivity using two different materials: pure tin oxide (SnO₂) and a tin–titanium–niobium oxide mixture (SnTiNb)_xO₂ (STN). The results reveal that (SnTiNb)_xO₂ sensors exhibit reduced sensitivity to humidity compared to pure tin oxide, rendering them more suitable for applications where humidity presence is critical. We aimed to shed light on a still controversial debate over the mechanisms involved in the water surface interactions for the aforementioned materials also by exploring theoretical studies in the literature. Experimental analysis involves varying temperatures (100 to 800 °C) to understand the kinetics of surface reactions. Additionally, a brief high-temperature heating method is demonstrated to effectively remove adsorbed humidity from sensor surfaces. The study employs Arrhenius-like plots for graphical interpretation, providing insights into various water adsorption/desorption phenomena. Overall, this research contributes to a deeper understanding of the role of humidity in MOX gas sensor mechanisms and offers practical insights for sensor design and optimization. Full article

Incorporating insect meals into poultry diets has emerged as a sustainable alternative to conventional feed sources, offering nutritional, welfare benefits, and environmental advantages. This study aims to monitor and compare volatile compounds emitted from raw poultry carcasses and subsequently from cooked chicken pieces from animals fed with different diets, including the utilization of insect-based feed ingredients. Alongside the use of traditional analytical techniques, like solid-phase microextraction combined with gas chromatography-mass spectrometry (SPME-GC-MS), to explore the changes in VOC emissions, we investigate the potential of S3+ technology. This small device, which uses an array of six metal oxide semiconductor gas sensors (MOXs), can differentiate poultry products based on their volatile profiles. By testing MOX sensors in this context, we can develop a portable, cheap, rapid, non-invasive, and non-destructive method for assessing food quality and safety. Indeed, understanding changes in volatile compounds is crucial to assessing control measures in poultry production along the entire supply chain, from the field to the fork. Linear discriminant analysis (LDA) was applied using MOX sensor readings as predictor variables and different gas classes as target variables, successfully discriminating the various samples based on their total volatile profiles. By optimizing feed composition and monitoring volatile compounds, poultry producers can enhance both the sustainability and safety of poultry production systems, contributing to a more efficient and environmentally friendly poultry industry. Full article

Crystal violet (CV) is an organic chloride salt and a triphenylmethane dye commonly used in the textile processing industry, also being used as a disinfectant and a biomedical stain. Although CV is widely used, it is carcinogenic to humans and is retained by industrial-produced effluent for an extended period. The different types of metal oxide (MO_x) have impressive photocatalytic properties, allowing them to be utilized for pollutant degradation. The role of the photocatalyst is to facilitate oxidation and reduction processes by trapping light energy. In this study, we investigated different types of metal oxides, such as titanium dioxide (TiO₂), zinc oxide (ZnO), zirconium dioxide (ZrO₂), iron (III) oxide (Fe₂O₃), copper (II) oxide (CuO), copper (I) oxide (Cu₂O), and niobium pentoxide (Nb₂O₅) for the CV decomposition reaction at ambient conditions. For characterization, BET and Raman spectroscopy were applied, providing findings showing that the surface area of the anatase TiO₂ and ZnO were 5 m²/g and 12.1 m²/g, respectively. The activity tests over TiO₂ and ZnO catalysts revealed that up to ~98% of the dye could be decomposed under UV irradiation in <2 h. The decomposition of CV is directly influenced by various factors, such as the types of MO_x, the band gap–water splitting relationship, and the recombination rate of electron holes. Full article

Metal-oxide (MOx) thin-film transistors (TFTs) require complex circuit structures to cope with their depletion mode characteristics, making them applicable only to large-area active matrix (AM) displays despite their low manufacturing cost and decent performance. In this paper, we report a simple MOx 10T-2C scan driver circuit that overcomes the depletion mode characteristics using a series-connected two transistor (STT) configuration and clock signals with two kinds of low-voltage levels. The proposed circuit has a wide operating range of TFT characteristics, i.e., −2.8 V ≤ V_TH ≤ +3.0 V. Through the measurement results of the manufactured sample, it was confirmed that the performance and area of our circuit are suitable for high-resolution mobile displays. Full article

Certain biomarkers in exhaled breath are indicators of diseases in the human body. The non-invasive detection of such biomarkers in human breath increases the demand for simple and cost-effective gas sensors to replace state-of-the-art gas chromatography (GC) machines. The use of metal oxide (MOX) gas sensors based on thin-film structures solves the current limitations of breath detectors. However, the response at high humidity levels, i.e., in the case of exhaled human breath, significantly decreases the sensitivity of MOX sensors, making it difficult to detect small traces of biomarkers. We have introduced, in previous work, the concept of a hybrid gas sensor, in which thin-film-based MOX gas sensors are combined with an ultra-thin (20–30 nm) polymer top layer deposited by solvent-free initiated chemical vapor deposition (iCVD). The hydrophobic top layer enables sensor measurement in high-humidity conditions as well as the precise tuning of selectivity and sensitivity. In this paper, we present a way to increase the hydrogen (H₂) sensitivity of hybrid sensors through chemical modification of the polymer top layer. A poly(1,3,5,7-tetramethyl-tetravinylcyclotetrasiloxane) (PV4D4) thin film, already applied in one of our previous studies, is transformed into a silsesquioxane-containing top layer by a simple heating step. The transformation results in a significant increase in the gas response for H₂ ~709% at an operating temperature of 350 °C, which we investigate based on the underlying sensing mechanism. These results reveal new pathways in the biomedical application field for the analysis of exhaled breath, where H₂ indicates gastrointestinal diseases. Full article

Two-dimensional Layered Amorphous Metal Oxide Sensors (LAMOS) represent a new class of 2D amorphous oxide (a-MOx) interfaces with unveiled properties in gas sensing applications. Herein, we report the humidity and gas sensing response of p- and n-type chemoresistive few-layered (2D) amorphous a-SnO₂, a-In₂O₃, and a-Cr₂O₃, discussing their reaction mechanisms using DFT modelling and electrical tests. LAMOS interfaces can be easily prepared by controlled oxidation in air of a large class of exfoliated 2D TMDs, MCs, and TMTH (Transition Metal Dichalcogenides, Chalcogenides, and Trihalides) like WS₂, MoS₂, SnSe₂, In₂Se₃, NiCl₂, and CrCl₃, yielding 2D amorphous a-MOx interfaces. LAMOS platforms preserving all the surface-to-volume advantages of their 2D precursors show excellent gas sensing properties representing a new class of material for gas sensing applications. Full article

This research paper presents a case study on the application of Metal Oxide Semiconductor (MOX)-based VOC/TVOC sensors for indoor air quality (IAQ) monitoring. This study focuses on the ease of use and the practical benefits of these sensors, drawing insights from measurements conducted in a university laboratory setting. The investigation showcases the straightforward integration of MOX-based sensors into existing IAQ monitoring systems, highlighting their user-friendly features and the ability to provide precise and real-time information on volatile organic compound concentrations. Emphasizing ease of installation, minimal maintenance, and immediate data accessibility, this paper demonstrates the practicality of incorporating MOX-based sensors for efficient IAQ management. The findings contribute to the broader understanding of MOX sensor capabilities, providing valuable insights for those seeking straightforward and effective solutions for indoor air quality monitoring. This case study outlines the feasibility and benefits of utilizing MOX-based sensors in various environments, offering a promising avenue for the widespread adoption of user-friendly technologies in IAQ management. Full article

Chemiresistive gas sensors based on metal oxide (MOX) semiconductors are attractive devices used to detect gaseous compounds in many applications. In fluid power systems, they could be exploited to monitor the odor changes of the hydraulic fluid that occur with aging. In this work, an extensive investigation has been performed for many kinds of hydraulic fluids aged in different conditions with the aim to develop a portable device to be installed in every system for performing predictive maintenance increasing system efficiency, reliability, and sustainability. Full article

Gas sensors based on metal oxide (MOX) semiconductors doped with oxygen vacancies (VO) have many advantages over stoichiometric MOX, such as higher surface reactivity and lower operating temperature. However, preparing reduced MOX is challenging, and the impact of different VO types and concentration on sensing performance is still unclear. In this work, we developed a tailored reducing thermal treatment for creating controlled VO in MOX. The effect of the length and temperature of the treatment was investigated using several characterization methods. Finally, measurements were performed to evaluate the impact of VO type and concentration on reduced MOX sensing performance. Full article

Bioethanol, which is currently produced commercially from a growing variety of renewable biomass and waste sources, is an appealing feedstock for the production of fuels and chemicals. The literature clearly shows that bioethanol is a versatile building block to be used in biorefineries. The ethanol conversion using several catalysts with acidic, basic, and redox characteristics results in a diverse assortment of high-value bioproducts. High-acidity tungsten zirconia-based catalysts are stated to compete with traditional zeolitic catalysts and can be employed in the dehydration of ethanol to ethylene, but for a low reaction temperature acetic acid is formed, which causes corrosion issues. WO₃-ZrO₂ (W/Zr = 1, atomic) catalysts modified with MoO₃ were prepared by a sol-gel-like procedure and tested in a gas phase ethanol conversion in the presence of air. The citrate derived xerogels were annealed at 853 K for 12 h, allowing low surface area (<10 m²/g) materials with a Mo-W mixed-oxide-rich surface over tetragonal nanostructured zirconia. Catalysts with MoO3-loading produced mainly acetaldehyde, instead of ethylene, as a result of the high reducibility of Mo⁶⁺ when compared to W⁶⁺. During the reaction, the Mo⁶⁺ becomes partially reduced, but Mo⁶⁺/Mo⁵⁺ species are still active for methanol conversion with increased ethylene selectivity due to the high acidity of tetrahedral MO_X species formed during the reaction. Adding water to ethanol, to simulate bioethanol, only leads to a slight inhibition in ethanol conversion over the MoO₃/(WO₃-ZrO₂) catalysts. The results show that molybdenum oxide deposited on tungstated zirconia catalyst is active, with low sensitivity to water, for the valorization of bioethanol into high-value chemicals, such as ethylene and acetaldehyde, and whose selectivity can be tuned by changing the amount of MoO₃ that is loaded. The MoO₃/(WO₃-ZrO₂) catalysts prepared show catalytic behavior similar to that of noble metal-based catalysts reported in the literature for the dehydrogenation of bioethanol in high-value chemicals. Full article

Two-dimensional (2D) vertical van der Waals heterostructures (vdWHs) show great potential across various applications. However, synthesizing large-scale structures poses challenges owing to the intricate growth parameters, forming unexpected hybrid film structures. Thus, precision in synthesis and thorough structural analysis are essential aspects. In this study, we successfully synthesized large-scale structured 2D transition metal dichalcogenides (TMDs) via chemical vapor deposition using metal oxide (WO₃ and MoO₃) thin films and a diluted H₂S precursor, individual MoS₂, WS₂ films and various MoS₂/WS₂ hybrid films (Type I: Mo_xW_1−xS₂ alloy; Type II: MoS₂/WS₂ vdWH; Type III: MoS₂ dots/WS₂). Structural analyses, including optical microscopy, Raman spectroscopy, transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy, and cross-sectional imaging revealed that the A_1g and E_2g modes of WS₂ and MoS₂ were sensitive to structural variations, enabling hybrid structure differentiation. Type II showed minimal changes in the MoS_2′s A_1g mode, while Types I and III exhibited a ~2.8 cm⁻¹ blue shift. Furthermore, the A_1g mode of WS₂ in Type I displayed a 1.4 cm⁻¹ red shift. These variations agreed with the TEM-observed microstructural features, demonstrating strain effects on the MoS₂–WS₂ interfaces. Our study provides insights into the structural features of diverse hybrid TMD materials, facilitating their differentiation through Raman spectroscopy. Full article

This study examines nickel catalysts on two different supports—magnesium oxide (MgO) and modified MgO (with 10 wt.% MOx; M = Ti, Zr, Al)—for their effectiveness in the dry reforming of methane. The reactions were conducted at 700 °C in a tubular microreactor. The study compares the best-performing catalyst with a reference catalyst (5Ni/MgO) by conducting dry reforming of methane at different reaction temperatures. The catalysts are evaluated using surface area, porosity, X-ray diffraction, infrared spectroscopy, transmission electron microscope, thermogravimeter, and temperature-programmed techniques. The 5Ni/MgO + ZrO₂ catalyst demonstrates inferior catalytic activity due to insufficient active sites. On the other hand, the 5Ni/MgO + TiO₂ catalyst shows limited catalytic excellence due to excessive coke deposits, which are six times higher than other catalysts. The 5Ni/MgO and 5Ni/MgO + Al₂O₃ catalysts have the richest basic and acidic profiles, respectively. The 5Ni/MgO + Al₂O₃ catalyst is superior to other catalysts due to its stronger metal–support interaction on the expanded surface and the efficient diffusion of carbon on its less crystalline surface. At 700 °C, this catalyst achieves 73% CH₄ conversion, and at 800 °C, it reaches 83% conversion. This study emphasizes the crucial role of the reaction temperature in reducing carbon deposition and enhancing the efficiency of the reforming process. Full article