Application of TiO2 Nanotubes Gas Sensors in Online Monitoring of SF6 Insulated Equipment

Titanium dioxide nanotube arrays (TNTAs) are a typical three-dimensional nanomaterial. TNTA has rich chemical and physical properties and low manufacturing costs. Thus, TNTA has broad application prospects. In recent years, research has shown that because of its large specific surface area and nanosize effect, the TNTAs have an enormous potential for development compared with other nanostructure forms in fields such as light catalysis, sensor, and solar batteries. TNTAs have become the hotspot of international nanometer material research. The tiny gas sensor made from TNTA has several advantages, such as fast response, high sensitivity, and small size. Several scholars in this field have achieved significant progress. As a sensitive material, TNTA is used to test O2, NO2, H2, ethanol, and other gases. In this chapter, three SF6 decomposed gases, namely SO2, SOF2 and SO2F2, are chosen as probe gases because they are the main by-products in the decomposition of SF6 under PD. Then, the adsorption behaviors of these gases on different anatase (101) surfaces including intrinsic, Pt-doped and Au-doped, are studied using the first principles density functional theory (DFT) calculations. The simulation results can be used as supplement for gas-sensing experiments of TNTA gas sensors. This work is expected to add insights into the fundamental understanding of interactions between gases and TNTA surfaces for better sensor design

Comparative Study of Materials to SF6 Decomposition Components

In order to judge the inside insulation fault of SF6 insulated equipment, the gas-sensing properties to a series of characteristic SF6 decomposition components, SOF2, SO2F2, SO2, H2S, CF4, HF, and SF6, have been studied. In this study, a comparative study of these gas-sensing materials has been made in theoretical and experimental fields to find the optimal gas-sensing material, and put forward the effective approaches to improve the gas-sensing properties of materials

Nanostructured Metal Oxide Semiconductors towards Greenhouse Gas Detection

Climate change and global warming are two huge current threats due to continuous anthropogenic emissions of greenhouse gases (GHGs) in the Earth’s atmosphere. Accurate measurements and reliable quantifications of GHG emissions in air are thus of primary importance to the study of climate change and for taking mitigation actions. Therefore, the detection of GHGs should be the first step when trying to reduce their concentration in the environment. Throughout recent decades, nanostructured metal oxide semiconductors have been found to be reliable and accurate for the detection of many different toxic gases in air. Thus, the aim of this article is to present a comprehensive review of the development of various metal oxide semiconductors, as well as to discuss their strong and weak points for GHG detection

Experimental Analysis of Modified CNTs-Based Gas Sensor

As a significant equipment in power system, the operation condition of transformers directly determines the safety of power system. Therefore, it has been an indispensable measure to detect and analyze the dissolved gases in transformers, aiming to estimate the early potential faults in oil‐insulated transformers. In this chapter, the adsorption processes between modified carbon nanotubes (CNTs) (CNTs‐OH, Ni‐CNTs) and dissolved gases in transformers oil including C2H2, C2H4, C2H6, CH4, CO, and H2 have been simulated based on the first principle theory. Meanwhile, the density of states (DOS), adsorption energy, charge transfer amount, and adsorption distance of adsorption process between CNTs and dissolved gases were calculated. Moreover, two kinds of sensors, mixed acid‐modified CNTs and NiCl2‐modified CNTs, are prepared to conduct the dissolved gases response experiment. Then, the gas response mechanisms were investigated. Finally, the results between response experiment and theoretical calculation were compared, reflecting a good coherence with each other. The CNTs gas sensors possess a relatively high sensitivity and fine linearity, and could be employed in dissolved gas analysis equipment in transformer

Doctor of Philosophy

dissertationCurrently, all over the world, a lot of money is being pumped into the healthcare domain to facilitate development of rapid, point-of-care disease diagnostic platforms, which are relatively cheap with enhanced ease-of-use capabilities that can be deployed in low-resource settings which have higher prevalence of disease infected cases. Volatile organic compounds (VOCs) represent one class of biomarkers that has been less explored but possesses immense potential from a disease diagnostic standpoint. Tuberculosis (TB) has been a cause of significant health concern affecting a large population of people in Africa and Asia and recently, researchers have identified four specific TB VOCs from the breath of infected patients, through GC-MS analysis techniques. Rapid, accurate diagnosis is critical for timely initiation of treatment and, ultimately, control of the disease. Lack of access to appropriate diagnostic tools is caused, in part, by shortcomings as currently available diagnostics are often ill-adapted to resource-limited settings or specific patient needs, or may be priced out of reach. Although many countries still rely on basic tools such as smear microscopy, new diagnostics are changing the TB diagnostics landscape. Some groups have previously attempted to develop breath-based TB detection techniques utilizing evanescent wave technology and colorimetry-based pattern detection techniques, but no sensors exist for detection of the four methyl ester-based VOCs. In the research presented in this dissertation, we have attempted to develop a low-cost, metal functionalized titania nanotubular array-based sensor platform for electrochemical detection of the four major TB volatile organic biomarkers (VOBs). TiO2 or titania nanotubes is an easy-to-synthesize, robust, wide bandgap (~3.2 eV) semiconductor material with excellent vectorial charge transport properties. In addition, the nanotubular morphology presents a large surface-area-to-volume ratio with sufficient metal bound active sites which facilitates efficient binding with the VOBs of interest. Titania nanotubes with an optimized morphology and stoichiometry and functionalized with cobalt through the incipient wetting impregnation, and an in-situ lattice functionalization method for electrochemical detection of the four TB VOBs and their subsequent integration into a sensor hardware, has been investigated. The potential light assisted, plasmonic-based sensing capabilities of gold nanoparticle functionalized TiO2 nanotubes have been illustrated as well. In the end, a similar but slightly tweaked sensing platform has been tested for the detection of nonpulmonary colorectal cancer as well, extending the detection capabilities of the fabricated sensor substrate and leaving room for further research for screening of other life-threatening diseases. Improved access to better TB screening and diagnostics may present potential opportunities that may include efforts to accelerate market entry and/or scale-up of the innovative sensing platform that addresses unmet needs

Silica and Silicon Based Nanostructures

Silica and silicon-based nanostructures are now well-understood materials for which the technologies are mature. The most obvious applications, such as electronic devices, have been widely explored over the last two decades. The aim of this Special Issue is to bring together the state of the art in the field and to enable the emergence of new ideas and concepts for silicon and silica-based nanostructures

Design of Polymeric Sensing Materials for Volatile Organic Compounds: Optimized Material Selection for Ethanol with Mechanistic Explanations

There are many applications in which sensing and monitoring volatile organic compounds (VOCs) and other gas analytes are important. This thesis focusses on finding suitable sensing materials for ethanol to reduce the instances of people driving while intoxicated. To find suitable sensing materials, many constraints must be taken into consideration. For example, a sensing material and sensor must have the appropriate sensitivity and selectivity required. The goal is to create a sensing material or multiple materials capable of detecting ethanol that is emitted from the skin (transdermally). This requires highly sensitive sensing materials and sensors capable of detecting ethanol close to 5 ppm. This limit of 5 ppm was confirmed by measuring transdermal ethanol. In addition, to avoid false positives, the sensor must be able to selectively identify ethanol (i.e. respond preferentially to ethanol). To achieve this goal, polymeric sensing materials were used because of their ability to be tailored towards a target analyte. Multiple polymeric sensing materials were designed, synthesized, and evaluated as a sensing material for ethanol. Both the sensitivity and selectivity of the sensing materials were evaluated using a specially designed experimental test set-up that included a highly sensitive gas chromatograph (GC) capable of detecting down to the ppb range. In total, over thirty potential sensing materials were evaluated for ethanol. These sensing materials, which include polyaniline (PANI) and two of its derivatives, poly (o-anisidine) (PoANI) and poly (2,5-dimethyl aniline) (P25DMA), doped with various concentrations of five different metal oxide nanoparticles (Al2O3, CuO, NiO, TiO2, and ZnO), were synthesized and evaluated for sensitivity and selectivity to ethanol. In addition, specialized siloxane-based polymers and other polymers such as poly (methyl methacrylate) (PMMA) and polypyrrole (PPy) were evaluated. From these thirty plus sensing materials, P25DMA doped with TiO2, NiO, and Al2O3, along with PPy, had the best sensitivity towards ethanol. Most of the materials tested, with the exception of the CuO doped P25DMA, P25DMA doped with 20% ZnO, poly (ethylene imine) (PEI), and the siloxane-based sensing materials, were able to sorb, and therefore detect, 5 ppm of ethanol. Therefore, the sensitivity requirement of 5 ppm was satisfied. In terms of selectivity, P25DMA doped with 5% Al2O3 and P25DMA doped with 10% TiO2 had the best selectivity towards ethanol with respect to five typical interferent gases (acetaldehyde, acetone, benzene, formaldehyde, and methanol). Some of the most promising polymeric sensing materials were then deposited onto two different kinds of sensors: a capacitive radio frequency identification (RFID) sensor and a mass-based microcantilever microelectromechanical systems (MEMS) sensor. These sensors were evaluated for sensitivity, selectivity, and response and recovery times. It was found that P25DMA doped with 20% NiO had a detection limit of 3 ppm on the RFID sensor, whereas P25DMA had a detection limit of 5 ppm on the MEMS sensor. It should be noted that not all sensing materials work well on all sensors. To improve the selectivity of a sensor, a sensor array or electronic nose can be used. These use a pattern-recognition algorithm to separate the responses for different gas analytes. A proof-of-principle study was done using principal component analysis that was capable of distinguishing between six different VOCs using five different polymeric sensing materials. In addition, a three sensor array was evaluated on the RFID platform. Using PCA as the filtering algorithm, four gas analytes (ethanol, methanol, acetone, and benzene) were able to be identified. These four analytes could also be identified even when in gas mixtures of twos and threes and when all four gas analytes were present. After this wide experimentation, and based on the knowledge gained from the sorption responses between various VOCs and polymers, along with what has been reported in the literature, various sensing mechanisms were proposed. These sensing mechanisms explain why certain VOCs sorb more preferentially onto certain polymers. Therefore, identifying the dominant sensing mechanisms for a target analyte can improve sensing material selection. Based on these sensing mechanisms, potential sensing materials can be chosen for a target analyte. By including other constraints from the specific application target and sensor, this list of potential sensing materials can be further narrowed. From here, these sensing materials can be evaluated for sensitivity and selectivity, before the most promising ones are deposited onto sensors for further testing. This has led to prescriptions that can be followed when designing a new sensing material for a target application. These prescriptions take into consideration the chemical nature of the target analyte (and thus, the dominant mechanisms by which it is likely to interact), any constraints of the target application (including operational temperature and type of sensor), and the chemical nature of the common interferents present with the target analyte. These prescriptions allow one to narrow down a list of hundreds or thousands of potential sensing materials to a manageable few, which can then be evaluated

Simulation and Modeling of Nanomaterials

This Special Issue focuses on computational detailed studies (simulation, modeling, and calculations) of the structures, main properties, and peculiarities of the various nanomaterials (nanocrystals, nanoparticles, nanolayers, nanofibers, nanotubes, etc.) based on various elements, including organic and biological components, such as amino acids and peptides. For many practical applications in nanoelectronics., such materials as ferroelectrics and ferromagnetics, having switching parameters (polarization, magnetization), are highly requested, and simulation of dynamics and kinetics of their switching are a very important task. An important task for these studies is computer modeling and computational research of the properties on the various composites of the other nanostructures with polymeric ferroelectrics and with different graphene-like 2-dimensional structures. A wide range of contemporary computational methods and software are used in all these studies

Plasmonics and its Applications

Plasmonics is a rapidly developing field that combines fundamental research and applications ranging from areas such as physics to engineering, chemistry, biology, medicine, food sciences, and the environmental sciences. Plasmonics appeared in the 1950s with the discovery of surface plasmon polaritons. Plasmonics then went through a novel propulsion in the mid-1970s, when surface-enhanced Raman scattering was discovered. Nevertheless, it is in this last decade that a very significant explosion of plasmonics and its applications has occurred. Thus, this book provides a snapshot of the current advances in these various areas of plasmonics and its applications, such as engineering, sensing, surface-enhanced fluorescence, catalysis, and photovoltaic devices

A Microfluidic Reactor for Time and Spatially Resolved in situ Spectroscopic Studies on Nanoparticles During Synthesis

Der weitaus überwiegende Teil der Produktionsprozesse in der chemischen Industrie läuft in Gegenwart von Katalysatoren ab, die Geschwindigkeiten und Selektivität der beteiligten Reaktionen erheblich beeinflussen. Neben ihrer großen Bedeutung für Produktionseffi-zienz und ökonomischen Profit spielen Katalysatoren eine entscheidende Rolle beim Übergang zu einer umweltfreundlicheren, nachhaltigeren Wirtschaft, indem sie z. B. die Freisetzung gesundheits- und umweltschädlicher Nebenprodukte vermindern, die Umwandlung giftiger Substanzen in weniger gefährliche Verbindungen vorantreiben (z.B. in der Abgaskatalyse) oder die Speicherung elektrischer Energie aus erneuerbaren Quellen in Form von chemischer Energie ermöglichen. Nanopartikel und deren Präparation spielen in vielen heterogen-katalysierten Prozessen eine Schlüsselrolle. Ein großer Anteil der Atome in diesen Systemen befindet sich an Grenzflächen oder auf Oberflächen, entsprechend hoch ist das Oberflächen-Volumen-Verhältnis. Aufgrund der großen Oberflächen und ausgeprägten Grenzflächen (z.B. Nanopartikel/Support) befinden sich diese Strukturen nicht im Gleichgewichtszustand und gelten als thermodynamisch instabil. Ihre Eigenschaften unterscheiden sich signifikant von denen der Bulkmaterialien. Nanopartikel zeigen einzigartige chemische, physikalische, magnetische und elektronische Eigenschaften, die im Bereich der Materialforschung neue Perspektiven eröffnen und zu bemerkenswerten Fortschritten beim Design von Funktionsmaterialien für diverse Anwendungen beitragen, neben Katalyse z. B. auch in der chemischen Sensorik. In diesem Zusammenhang ist ein tiefgreifendes Verständnis der für Keimbildung und Wachstum monodisperser Nanopartikel maßgeblichen Kinetik und Reaktionsmechanismen von entscheidender Bedeutung für eine Optimierung von Morphologie und Struktur und maßgeschneiderte Eigenschaften. Moderne Charakteri-sierungsmethoden, insbesondere spektroskopische Techniken, leisten dazu entscheidende Beiträge. Für die im Rahmen dieser Dissertation durchgeführten experimentellen Studien wurde eine Mikrofluidik-Apparatur aufgebaut, die speziell auf kolloidale Synthese nanostrukturierter Materialien bei pulsationsfreier Dosierung von Reaktanden und hohen Durchflussraten in kontinuierlicher turbulenter Strömung (Reynolds-Zahl von etwa 2400) ausgelegt ist. Drei in den Mikrofluidik-Chip integrierte Zyklonmischer ermöglichen homogenes Mischen der Reaktanden in kurzer Zeit (< 2 ms bei einem Durchfluss von 2.6 L h-1) für schnelle Reduktionsprozesse, gefolgt von einem Mäanderkanal. Der Mikrofluidik-Aufbau ermög-licht darüber hinaus eine Röntgen-basierte Charakterisierung der Partikel während der Synthese und damit unmittelbaren Zugang zu Informationen bzgl. der maßgeblichen Reaktionsmechanismen und Kinetik. Im Mikrofluidikreaktor herrscht eine ideale Strömung vor, um die seit Beginn der Reaktion verstrichene Zeit mit der Position des Röntgenstrahls entlang des Mikrokanals mit hoher zeitlicher Auflösung direkt korrelieren zu können. Die Zyklonmischer im Mikrofluidik-Chip reduzieren hierbei die Totzeit, d.h. die für homogenes Mischen der Reaktanden erforderliche Zeit, auf 2 ms. Das Zusammenwirken von Mikroverfahrenstechnik und In-Situ-XAS-Messzellendesign ermöglicht so eine Untersuchung der Reaktionskinetik mit bislang nicht verfügbarer zeitlicher Auflösung. Als Fallstudie im Rahmen dieser Arbeit wurden frühe Reaktionsstadien (2 -20 ms) der Bildung von Gold-Nanopartikeln aus Au(III) in Gegenwart eines starken Reduktionsmittels (NaBH4) und einer oberflächenaktiven Komponente (PVP als Surfactant) in situ mittels Röntgenabsorptionsspektroskopie mit Synchrotronlicht bei hohem Reaktandendurchfluss im Bereich turbulenter Mischbedingungen verfolgt. Gold-, Palladium- und homogene Gold-Palladium-Legierungs-Nanopartikel mit mittleren Durchmessern von ca. 1 nm und schmalen Größenverteilungen wurden in diesem Mikroreaktor mit NaBH4 als Reduktionsmittel und Polyvinylpyrrolidone (PVP) als oberflächenaktiver Komponente (Surfactant) synthetisiert. Die Struktur dieser Nanopartikel, sowohl in Kolloidlösung als auch geträgert auf Titanoxid, wurde mittels verschiedener volumen- und oberflächenempfindlicher Charakterisierungstechniken wie UV/Vis-Spektroskopie, Elektronenmikroskopie, Energiedispersiver Röntgenspektroskopie (EDX), Röntgenabsorptionsspektroskopie (XAS), Röntgendiffraktion (XRD), Röntgen-photoelektronenspektroskopie (XPS) und Ultrahochvakuum-Fourier-Transform-Infrarot-spektrometrie (UHV-FTIR) analysiert. Die Ergebnisse dieser Untersuchungen weisen auf einen bemerkenswerten Einfluss des molaren Au:Pd-Verhältnisses auf die kristallo-graphische und elektronische Struktur der Gold-Palladium-Legierungs-Nanopartikel hin. Die Größe der Partikel nahm während der Aufbringung auf das Trägermaterial zu. Gleichwohl zeigten die hergestellten Nanomaterialien bei Aktivitätsmessungen ein hohes Potential als Katalysatoren für die CO-Oxidation und im Hinblick auf Anwendungen in der chemischen Sensorik. Der Mikrofluidikreaktor konnte auch erfolgreich für eine Cofällungsreaktion genutzt werden. Ein Vergleich von mikrofluidisch und in einem diskontinuierlichen Rührreaktor (Batch-Reaktor) synthetisierten CuO/ZnO/Al2O3–Katalysatoren zeigte, dass die im Mikrofluidikreaktor hergestellten Materialien kleinere mittlere Partikeldurchmesser, entsprechend größere spezifische Oberflächen und eine gleichmäßigere Verteilung von Cu und Zn in den Partikeln aufwiesen. Zukünftig kann der Mikrofluidikreaktor auch zur Untersuchung von Präzipitationsreaktionen mittels röntgenbasierter Methoden wie XAS, Röntgenkleinwinkelstreuung und Röntgendiffraktion genutzt werden