Effects of Textural Properties on the Response of a SnO2-Based Gas Sensor for the Detection of Chemical Warfare Agents

The sensing behavior of SnO2-based thick film gas sensors in a flow system in the presence of a very low concentration (ppb level) of chemical agent simulants such as acetonitrile, dipropylene glycol methyl ether (DPGME), dimethyl methylphosphonate (DMMP), and dichloromethane (DCM) was investigated. Commercial SnO2 [SnO2(C)] and nano-SnO2 prepared by the precipitation method [SnO2(P)] were used to prepare the SnO2 sensor in this study. In the case of DCM and acetonitrile, the SnO2(P) sensor showed higher sensor response as compared with the SnO2(C) sensors. In the case of DMMP and DPGME, however, the SnO2(C) sensor showed higher responses than those of the SnO2(P) sensors. In particular, the response of the SnO2(P) sensor increased as the calcination temperature increased from 400 °C to 800 °C. These results can be explained by the fact that the response of the SnO2-based gas sensor depends on the textural properties of tin oxide and the molecular size of the chemical agent simulant in the detection of the simulant gases (0.1–0.5 ppm)

A review of sensing technologies for gas nerve agents, through the use of agent mimics in the gas phase: future needs

The aim of the work presented in this review is to present a detailed summary of the current sensing technology available within the scientific literature for the detection of nerve agent simulants in the gas phase, focussing on the recognised sarin surrogate: dimethyl methylphonate (DMMP). The use of simulants for the development of sensing technology has been widely established for nerve agents to reduce the potential risk to personnel and to offer a realistic, simple molecule to try and test the technology. The present review compiles a comparison of different sensors and their respective sensing mechanisms. These sensing technologies are then compared to the U.S environmental protection agencies standard for concentration of Sarin at 15 ppb (known lethal dose). Only some work developed using semiconductor detectors present a reliable system able to detect DMMP with low LoD (0.05 ppb), fast response time (0.02 mins) and good recovery times (0.5 min)

Preparación y caracterización de sensores a base de óxidos metálicos y su aplicación para la detección de insecticidas organofosforados

La presente tesis se centra en realizar la síntesis y caracterización de óxidos metálicos dopados con metales de transición para mejorar su sensibilidad para detectar vapores de dos pesticidas organofosforados, Clorpirifós y Malatión. Los óxidos estudiados son el óxido de zinc (ZnO) dopado con Zr, ZnO dopado con Ag, y el óxido de estaño (SnO2) dopado con Pt y Zr. La síntesis del ZnO se realiza mediante la aplicación de dos metodologías de síntesis hidrotermal: (a) Precipitación asistida por microondas y (b) precipitación en autoclave; mientras que el dopaje del ZnO se realiza agregando los precursores de los dopantes (AgNO3 y ZrOCl2) a la mezcla de reacción. El SnO2 dopado con Zr y Pt se obtiene a partir del óxido de estaño comercial (Merck) y se lleva a cabo en dos etapas: 1) Dopaje del SnO2 con Zr por mezcla mecánica y 2) dopaje de SnO2 con Pt por reducción de este con SnSO4. La caracterización de estos materiales se realiza mediante análisis por DRX, FTIR, UV, SEM-EDS, TEM y sorción de N2. Además, se realiza la cuantificación de la concentración de pesticidas en las muestras comerciales que se aplican en los ensayos de sensado mediante HPLC. Se obtienen las señales de respuesta con mayor estabilidad para largos tiempos de sensado con los sensores de óxido de zinc dopado con Zr por síntesis en autoclave (AT-Zr-ZnO). Su caracterización por XRD revela que el dopaje es sustitucional y no se identifican fases adicionales. Se lleva a cabo un estudio de las condiciones óptimas de temperatura (entre 210°C y 220°C), concentración del dopante en el óxido de zinc y el óxido de estaño. La temperatura tiene un efecto positivo en la sensibilidad de todos los sensores ensayados. A la temperatura de ensayo de 220°C se logra maximizar la sensibilidad de los mejores sensores (AT-Zr-2.0-ZnO y Pt-0.13-ZrO2-0.15-SnO2) por el Malatión. En el caso del sensado del Clorpirifós, se obtienen mejores resultados con el sensor Pt-0.13-ZrO2-0.15-SnO2, cuya señal se favorece a 210°C. Además, la sensibilidad del Pt-0.13-ZrO2-0.15-SnO2 respecto al AT-Zr-2.0-ZnO a 220°C es mayor para el Clorpirifós, pero menor para el Malatión. El método de tratamiento estadístico PCA permite la evaluación de las señales de muestras con diferentes concentraciones de pesticidas. Los mejores PCA, obtenidos con los datos de las mediciones utilizando los sensores más sensibles, muestran una varianza total explicada mayor al 90% y una mejor diferenciación entre muestras de aire contaminado con pesticidas y muestras de aire sin contaminación.This thesis focuses on the synthesis and characterization of metal oxides doped with transition metals to improve their sensitivity to detect vapors of two organophosphorus pesticides, Chlorpyrifos and Malathion. The oxides studied are Zr doped zinc oxide (ZnO), Ag doped ZnO, and tin oxide (SnO2) doped with Pt and Zr. The synthesis of ZnO is carried out through the application of two hydrothermal synthesis methodologies: (a) Microwave assisted precipitation and (b) autoclave precipitation; while ZnO doping is conducted by adding the dopant precursor (AgNO3 or ZrOCl2) to the reaction mixture. SnO2 doped with Zr and Pt is prepared from commercial tin oxide (Merck). The doping process was carried out in two stages: 1) Zr doped SnO2 is obtained by mechanical mixing and 2) Pt doped SnO2 is prepared by reduction with SnSO4. The characterization of these materials is carried out by employing DRX, FTIR, UV, SEM-EDS, TEM and sorption of N2 analysis. In addition, the quantification of pesticide concentration in commercial samples, that are used in the sensing essays, is performed with HPLC. Response signals are obtained with greater stability for long sensing times with zinc oxide sensors doped with Zr by autoclave synthesis (AT-Zr-ZnO). Its characterization by XRD reveals that doping is substitutional and no additional phases are identified. A study of the optimum temperature conditions (between 210°C and 220°C), concentration of the dopant in zinc oxide and tin oxide is carried out. The temperature has a positive effect on the sensitivity of all the sensors tested. At the test temperature of 220°C, the sensitivity of the best sensors (AT-Zr-2.0-ZnO and Pt-0.13-ZrO2-0.15-SnO2) for Malathion can be maximized. In the case of Chlorpyrifos, better results are obtained for the Pt-0.13-ZrO2-0.15-SnO2 sensor, whose signal is favored at 210°C. In addition, the sensitivity of Pt-0.13-ZrO2-0.15-SnO2 with respect to AT-Zr-2.0-ZnO at 220°C is higher for Chlorpyrifos, but lower for Malathion. The statistical treatment method PCA allows the evaluation of the signals of samples with different concentrations of pesticides. The best PCA, obtained with the data of the measurements using the most sensitive sensors, show a total explained variance greater than 90% and a better differentiation between air samples contaminated with pesticides and air samples without contamination.Tesi

Design, fabrication and characterization of a gas preconcentrator based on thermal programmed adsorption/desorption for gas phase microdetection systems

En aquesta tesi, proposem la fabricació y la caracterització d’un microconcentrador de gasos, per ser acoblat amb un microsistema de detecció, per millorar el seu límit de detecció davant els gasos tòxics. Aquest estudi s’aplica especialment al benzè, que es un compost d’alta cancerigenitat. El preconcentrador proposat esta basat en estructura plana, que, es una opció de fabricació més simple y permet una millor aïllament tèrmic amb el resta d’unitats del microsistema, qu’els estructures 3D proposats a la literatura. No obstant, els factors de concentració obtinguts amb l’estructura plana queden generalment més baixos, per causa de la menor quantitat de material absorbent que pot acollir. En aquesta tesis, es va superar aquest problema mitjançant l’utilització del carboní actiu, un adsorbent d’alta capacitat d’adsorció, així com l’optimització de les condicions de funcionament del dispositiu. Finalment, acoblant el microconcentrador amb un micro-cromatògraf, vam aconseguir una detecció sensible y selectiva del benzè en barreja amb altres volàtils a l’aire.The present thesis focuses on the fabrication and characterization of a gas microconcentrator for to be coupled with a detection microsystem, in order to lower its detection limit towards toxic gases and vapours in contaminated areas. This study was more especially applied to the preconcentration of benzene, a cancerigenic compound at low ppb level. A preconcentrator based on a planar structure was proposed regarding its simpler fabrication, better thermal insulation and lower power consumption, compared to the 3D structures proposed conventionally in literature. In order to obtain higher concentration factors with such structure, its small size was compensated by using a high adsorption capacity adsorbent such as activated carbon as well as the optimization of the preconcentration conditions of the device. Finally, the microconcentrator was validated as injection unit when coupled with a microchromatographic system, where a sensitive and selective analysis of benzene in mixture with other VOCs was achieved

Fluorescence Spectroscopy in Structural Studies of Plant Cell Walls

Plant cell walls represent the most abundant, renewable and biodegradable composite on Earth. Its highly complex structure consists mainly of three organic compounds: cellulose, hemicelluloses, and lignin. Cell walls have wide applications in different industries, especially for biofuels and biomaterials. Fluorescence spectroscopy is the method allowing investigation of cell wall structure thought monitoring of lignin autoflorescence and thus interactions of lignin with the other cell wall constituents. Deconvolution of fluorescence spectra reveals the number and location of spectral component peaks by calculation of the approximation of the probability density (APD) of component positions. A characteristic of complex CW fluorescence is that the emission spectrum contains multiple log–normal components originating from different fluorophores, shorter wavelengths corresponding to phenolic structures and longer wavelengths to conjugated structures in lignin. Fluorescence spectroscopy has been used for fast screening of the cell wall properties from plants of different origin (hardwood, softwood and herbaceous plant), that may be important for selection of plants for possible applications. Fluorescence spectroscopy may be applicable in the investigation of the effect of stress on the cell wall. Lignin fluorescence emission spectra, peak intensities and shifts in the positions of the long-wavelength spectral components may be indicators of changes in cell wall structure during the stress. There is an increasing application of quantum dots (QDs) in plant science, as fluorescent markers. The isolated cell wall is an appropriate object for study of the interactions with nanoparticles. The results of different physico-chemical techniques including fluorescence spectroscopy combined with spectral deconvolution, show that in the cell walls, CdSe QDs predominantly bind to cellulose, via OH groups, and to lignin, via the conjugated C=C/C–C chains. Variability of bond types in lignin is related to the involvement of this polymer in plant response to various types of stress, by introducing local structural modifications in the cell wall. Different lignin model compounds have been used in order to reveal spectroscopic properties of lignin. Lignin model polymers were synthesized from three monomers, coniferyl alcohol, ferulic acid and p-coumaric acid mixed in various ratios, simulating lignin synthesis in the real cell walls. Further, by using fluorescence spectroscopy and appropriate mathematical methods, it is possible to get deeper insight into the structural characteristics of the molecule. Future investigations will be based on synthetic cell walls and on variation in a portion of all three main components: cellulose, hemicelluloses and lignin, also having in mind results of fine structural modifications in lignin model compounds

Technology 2001: The Second National Technology Transfer Conference and Exposition, volume 1

Papers from the technical sessions of the Technology 2001 Conference and Exposition are presented. The technical sessions featured discussions of advanced manufacturing, artificial intelligence, biotechnology, computer graphics and simulation, communications, data and information management, electronics, electro-optics, environmental technology, life sciences, materials science, medical advances, robotics, software engineering, and test and measurement

Chapter 34 - Biocompatibility of nanocellulose: Emerging biomedical applications

Nanocellulose already proved to be a highly relevant material for biomedical applications, ensued by its outstanding mechanical properties and, more importantly, its biocompatibility. Nevertheless, despite their previous intensive research, a notable number of emerging applications are still being developed. Interestingly, this drive is not solely based on the nanocellulose features, but also heavily dependent on sustainability. The three core nanocelluloses encompass cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). All these different types of nanocellulose display highly interesting biomedical properties per se, after modification and when used in composite formulations. Novel applications that use nanocellulose includewell-known areas, namely, wound dressings, implants, indwelling medical devices, scaffolds, and novel printed scaffolds. Their cytotoxicity and biocompatibility using recent methodologies are thoroughly analyzed to reinforce their near future applicability. By analyzing the pristine core nanocellulose, none display cytotoxicity. However, CNF has the highest potential to fail long-term biocompatibility since it tends to trigger inflammation. On the other hand, neverdried BNC displays a remarkable biocompatibility. Despite this, all nanocelluloses clearly represent a flag bearer of future superior biomaterials, being elite materials in the urgent replacement of our petrochemical dependence

Sorption isotherms of volatile molecules on micro- and mesoporous nanosized siliceous materials based on acoustic wave devices.

Microporous zeolites and mesoporous periodically silicious materials offer interesting features, like porosity in general, host-guest interactions and among others, sorption phenomena. The application of addressable individual material pixels, pin-printed onto adequate pre-treated supporting surfaces for gas-sensor systems was evaluated. The contact pin-printing technique, well known in bio-science, was adopted and optimized. The successful deposition of colloidal suspensions of zeolite materials on Au-covered glass slides with chemically attached intermediate anchoring molecules was demonstrated on a 100 μm scale (chapter 3). In a collaboration with the physical department of the LMU Munich (Prof. Kotthaus) a gas sensor system, based on surface acoustic wave devices was developed. Thin layers of porous material in the sub-microgram range were applied, in order to record adsorption isotherms and to determine the released heat of adsorption of specific analyte gases. Related to very small sample amounts and short diffusion times the necessary experimental measurement time could be reduced down to several minutes (chapter 9). An existing rudimentary quartz crystal microbalance (QCM) was enhanced and an automated intelligent equilibrium system was developed. Furthermore, the system was equipped with liquid mass controllers in order to measure the sorption properties together with vaporized liquid solvents (chapter 4). The developed QCM measurement setup was applied as advanced research tool in order to investigate sorption properties of various porous samples and to obtain the thermodynamic parameter, the isosteric heat of adsorption. The incorporation of organic moieties into siliceous frameworks leads to a wide variety of adsorbate–adsorbent interactions including weak Van-der-Waals attractions as well as strong interactions such as Coulomb forces. Depending on the desired properties of such substituted highly porous matrix materials, optimized synthesis routes can be established to enhance the desired internal pore surface–affinity towards certain volatile compounds. Based on a fundamental knowledge of the host–guest system, sorption related applications may benefit from individually fine-tuned and modified sample materials. The sorption isotherms and isosteric heat of adsorption for non-modified, phenyl- Summary IIIIIIIII modified, cyano-modified, vinyl-modified and mercapto-functionalized mesoporous material for ethanol and 1-butanol sorption were determined. Additionally, nanosized zeolites, like ZSM-5, Sil-1 and zeolite beta were investigated (chapter 6). Furthermore, sorption isotherms of vaporized toluene on non-modified and phenyl-functionalized mesoporous silica samples were determined using the gravimetric QCM technique at different temperatures. The mesoporous silica was modified by in situ via co-condensation and via post-synthesis grafting approaches, respectively. All samples were thoroughly characterized by several standard techniques and additionally with toluene sorption experiments on the automated QCM setup. The different heats of adsorption of toluene on the various modified silica surfaces obtained by the sorption data made it possible to gain additional information about the degree and type of surface functionalization. It is thus demonstrated that QCM studies can be a powerful and convenient tool for efficient investigations of functionalized mesoporous silica particles that yield valuable quantitative information on molecule-surface interactions (chapter 8)