Optical fiber sensors based on nanostructured materials for environmental applications

La contaminación ambiental es la presencia de agentes físicos, químicos o biológicos presentes en el agua, suelo y aire; siendo perjudiciales para la salud de las personas, así como para la vida vegetal y animal. Las actividades económicas son esenciales para el desarrollo de la sociedad, sin embargo, muchas de estas actividades son una fuente de contaminación constante. Por ejemplo, la fuga de fluidos y gases en plantas industriales afectan negativamente a la salud e higiene para la elaboración de alimentos, bebidas, aditivos y materias primas causando un impacto ambiental y económico negativo en la industria. La búsqueda continua de métodos para el desarrollo de sistemas de medición es una característica de la evolución tecnológica de la humanidad. Las fibras ópticas presentan varias ventajas para ser empleadas en sistemas sensores; tales ventajas son: inmunidad a la interferencia electromagnética, dimensiones reducidas, ligeras, bajas pérdidas, fácil multiplexación y resistencias a la corrosión, entre otras. En general, podemos encontrar una amplia gama de aplicaciones en la industria para el desarrollo de sensores en fibra óptica. Sin embargo, en esta tesis se han seleccionado tres aplicaciones industriales de interés relevante: detección de gas amoniaco a bajas concentraciones, detección de adulteración en bebidas alcohólicas y detección de adulteración de combustibles. Se caracterizan los parámetros de los sensores desarrollados tales como la sensitividad, reversibilidad, reproducibilidad y precisión para la medición de cada tipo de sensor. Los resultados obtenidos en esta tesis serán útiles en el estudio de nuevos materiales aplicables a sensores ópticos, permitiendo la apertura a nuevas vías de investigación en el campo de los sensores en fibra óptica para aplicaciones industriales.Environmental pollution is the presence of physical, chemical or biological agents in water, soil and air which are harmful to our health, safety and welfare of the people as well as plant and animal life. Economic activities are essential to the development of society; however, many of these activities are a constant source of contamination. For example, leakage of fluids and gases in industrial plants adversely affect the health and hygiene for food processing, beverages, additives and raw materials causing serious environmental and economic impact on the general industry. The continual search for methods for developing measurement systems is a feature in the technological evolution of humankind. Optical fibers exhibit several advantages such as being immune to electromagnetic interferences, reduced dimensions, lightweight, low losses, easy multiplexation and resistant to corrosion for the development of optical fibers sensors. However, we selected three applications were the principle of operation of our sensor provides an advantage over other reported sensors: gaseous ammonia detection for low concentrations, adulteration of alcoholic beverages detection and combustibles quality control. The overall objective of this research is to design, fabricate, deploy and verify the correct operation of optical fiber structures for the identification of interesting liquid and gaseous environmental pollutants. The sensors parameters such as its sensitivity, reversibility, reproducibility and accuracy of measurement for each type of sensor are also characterized. These results obtained from this thesis would be a useful work in the study of new materials applicable to optical sensors, while opening new avenues of research in the field of optical fiber sensors for industrial applications.La realización de esta tesis ha sido posible gracias al apoyo recibido por parte del Consejo Nacional de Ciencia y Tecnología (CONACYT) bajo el contrato CB-2010/157866 y CB-2010/156529, así como de la Comisión Interministerial de Ciencia y Tecnología a través de la financiación de los proyectos CICYT fondos FEDER TEC2010-17805.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

Luminescence Sensors Applied to Water Analysis of Organic Pollutants—An Update

The development of chemical sensors for environmental analysis based on fluorescence, phosphorescence and chemiluminescence signals continues to be a dynamic topic within the sensor field. This review covers the fundamentals of this type of sensors, and an update on recent works devoted to quantifying organic pollutants in environmental waters, focusing on advances since about 2005. Among the wide variety of these contaminants, special attention has been paid polycyclic aromatic hydrocarbons, pesticides, explosives and emerging organic pollutants. The potential of coupling optical sensors with multivariate calibration methods in order to improve the selectivity is also discussed

Development of a generic multi-analyte optical sensor platform for fluorescence-based sensing

This work describes the development of two advanced sensor platforms based on different spectroscopic techniques. The first, and the primary focus of this work, is an enhanced generic multi-analyte sensor platform for fluorescence-based sensors and the second is an absorbance-based portable sensor for the detection of nitrates in groundwater. A generic multi-analyte sensor platform can be applied to a broad range of areas such as food packaging and blood gas analysis. A multi-analyte optical sensor platform for enhanced capture of fluorescence was modelled, designed and fabricated. The sensor platform was developed using a range of microfabrication techniques. Films sensitive to oxygen, relative humidity and carbon dioxide respectively were developed for the context of indoor air-quality monitoring. Deposition methods for printing the sensor solutions onto the sensor platforms were also investigated. The sensor films and platforms were integrated into a working sensor chip with both a fluorescence intensity and phase fluorometric detection system. An absorbance-based portable sensor for the detection of nitrates in groundwater was also developed. This was based on the direct absorbance of UV-light by the nitrate ion. Other contaminants, which could be found in groundwater and interfere with the nitrate detection, such as humic acid and chlorides, were investigated and compensated for

In-situ photocatalytic remediation of organic contaminants in groundwater

This research is about the development of a photocatalytic reactor design, Honeycomb, for in-situ groundwater remediation. Photocatalysis, typically a pseudo first order advanced oxidation process, is initiated via the illumination of UVA light on the catalyst, i.e. titanium dioxide (TiO2). In the presence of oxygen, highly reactive oxidising agents are generated such as superoxide (O2-), hydroxyl (OH·-) radicals, and holes (hvb+) on the catalyst surface which can oxidise a wide range of organic compounds. The target contaminant is methyl tert butyl ether (MTBE), a popular gasoline additive in the past three decades, which gives the water an unpleasant taste and odour at 20 µg L-1, making it undrinkable. This research consists of three major parts, i.e. (i) establishing a suitable catalyst immobilisation procedure, (ii) characterisation and evaluation of reactor models and (iii) scale up studies in a sand tank. TiO2 does not attach well onto many surfaces. Therefore, the first step was to determine a suitable immobilisation procedure by preparing TiO2 films using several potential procedures and testing them under the same conditions, at small scale. The coatings were evaluated in terms of photocatalytic activity and adhesion. The photocatalytic activity of the coatings was tested using methylene blue dye (MB), which is a photocatalytic indicator. A hybrid coating, which comprises a sol gel solution enriched with Aeroxide TiO2 P25 powder, on woven fibreglass exhibited the best adhesion and photocatalytic activity among samples evaluated. Thus, it was used to produce immobilised catalyst for this research. Consequently, the immobilisation procedure was scaled up to synthesize TiO2 coatings for the potential photocatalytic reactor design. The photocatalytic activity of the coatings produced from the scaled up immobilisation procedure were reasonably comparable to that produced at small scale. Due to the UVA irradiation and mass transfer limitations, photocatalytic reactors are typically compact in order to maximise their efficiency to accommodate high flows, particularly in water and wastewater treatment. In the case of groundwater, however, the treatment area can span up to meters in width and depth. Groundwater flow is significantly lower than that of water treatment, as the reactor design does not need to be compact. Considering both factors, a photocatalytic reactor design of hexagonal cross-section (Honeycomb) was proposed, in which the structures can be arranged adjacent to each other forming a honeycomb. A model was constructed and tested in a 4 L column (cylindrical) reactor, using the MB test to characterise the reactor performance and operating conditions. This was followed by a hydraulic performance study, which encompasses single and double pass flow studies. The single pass flow study involves the photocatalytic oxidation (PCO) of MB and MTBE, while the double pass flow study was focused on the PCO of MTBE only. The double pass can simulate two serially connected reactors. Single pass flow studies found that the critical hydraulic residence time (HRT) for the PCO of MB and MTBE is approximately 1 day, achieving up to 84 % MTBE removal. Critical HRT refers to the minimum average duration for a batch of contaminant remaining in the reactor in order to maintain the potential efficiency of the reactor. Double pass studies showed the reactor can achieve up to 95 % MTBE removal in 48 hours, and that reactor performance in the field of serially connected reactors can be estimated by sequential order of single pass removal efficiency. In groundwater, there are likely to be other impurities present and the effects of groundwater constituents on the reactor efficiency were studied. The MTBE PCO rate is affected by the presence of organic compounds and dissolved ions mainly due to the competition for hydroxyl radicals and the deactivation of catalyst surface via adsorption of the more strongly adsorbed organic molecules and ions. Despite the presence of organic compounds and dissolved ions, the reactor achieved about 80 % MTBE removal in 48 hours. A double pass flow study showed that the overall efficiency of the photocatalytic reactor in the field can be estimated via sequential order of its efficiency in a single pass flow study using the actual groundwater sample in the laboratory. A sand tank was designed for the simulation of the clean up of an MTBE plume from a point source leakage using the 200 mm i.d. Honeycomb I prototype. Honeycomb I achieved up to 88.1 % MTBE removal when the contaminated groundwater flowed through (single pass) at 14.6 cm d-1. The critical HRT for Honeycomb I was also approximately 1 day, similar to that in the column reactor. The response of MTBE removal efficiency towards flow obtained in the column reactor and sand tank was generic, indicating that the reactor efficiency can be obtained via testing of the model in the column reactor. The presence of toluene, ethylbenzene and o-xylene (TEo-X) decreased the MTBE removal efficiency in both the sand tank and column reactor. The same set of catalyst and 15 W Philips Cleo UVA fluorescent lamp was operated for a total of about 582 h (24 d) out of the cumulative 1039 h (43 d) sand tank experiments, achieving an overall MTBE removal efficiency of about 76.2 %. The experiments in the column reactor and sand tank exhibited the reliability of the immobilised catalyst produced in this research. This research demonstrates the potential of Honeycomb for in-situ groundwater remediation and also proposes its fabrication and installation options in the field

Photocatalysis for Reductive Transformation of Nitrate and Chromate in Drinking Water

abstract: Contamination of drinking water supplies from oxo-anion pollutants necessitates treatment prior to potable use. This dissertation aims to inform and improve light delivery (emission spectra, radiant intensity, reactor configuration) in order to enhance the photocatalytic reduction of hexavalent chromium (Cr(VI)) and nitrate, two common oxo-anions in drinking water, and photocatalytic oxidation of two model organic pollutants (methylene blue, (MB) and para-chlorobenzoic acid (pCBA)). By varying the photon fluence dose, two metrics (contaminant quantum yield (Φ), and electrical energy per order (EEO)) were used to assess photocatalytic reactor performance. A detailed literature review and experimental results demonstrated how different irradiance sources with variable intensity and emission spectra synergistically enhanced contaminant removal by a coupled photolytic/photocatalytic reaction mechanism. Cr(VI) was photocatalytically reduced on TiO2 and formed Cr(OH)3(s) in a large-scale slurry reactor, but Cr(III) was then photolyzed and reformed Cr(VI). UV light also led to photo-aggregation of TiO2 which improved its recovery by the ceramic membrane within the reactor. For nitrate reduction, light source emission spectra and fluence dose delineate the preferred pathways as intermediates were reduced via wavelength-dependent mechanisms. HONO was identified as a key nitrate reduction intermediate, which was reduced photocatalytically (UV wavelengths) and/or readily photolyzed at 365nm, to yield nitrogen gases. Photocatalytic nitrate reduction efficiency was higher for discrete wavelength irradiation than polychromatic irradiation. Light delivery through aqueous media to the catalyst surface limits efficiency of slurry-based photocatalysts because absorption and scattering of light in nanomaterial slurries decreases effective photon transmittance and minimizes photolytic reactions. The use of optical fibers coupled to light emitting diodes (OF-LED) with immobilized catalyst demonstrated higher performance compared to slurry systems. OF-LED increased Φ for MB degradation by increasing direct photon delivery to the photocatalyst. Design of OF-LED reactors using bundled optical fibers demonstrated photocatalytic pCBA removal with high Φ and reduced EEO due to increased surface area and catalytic sites compared to single OF/LED couples. This work advances light delivery as well as the suspension and attachment of nanoparticles in photocatalytic water treatment for selective transformation of oxo-anions and organic compounds to innocuous species.Dissertation/ThesisDoctoral Dissertation Civil, Environmental and Sustainable Engineering 201

Development of Optical Sensors for Chemical Detection

Detection of biodiesel at low and high concentrations in diesel is highly desired in the aviation and fuel industries. Cross contamination of jet fuel with biodiesel may impact the thermal stability and freezing point which can cause deposits in the fuel system or cause the fuel to gel, leading to jet engine operability problems and possible engine flameout. A dye doped optical sensor utilizing the dye Nile Blue Chloride has been developed for quick and direct detection of biodiesel which mainly contains fatty acid methyl esters (FAME). The sensing mechanism relies on the solvatochromatic properties of the dye which undergoes a color change from blue to pink. A detection limit of 0.250 ppm (parts per million) and quantification limit of 0.750 ppm is obtained with a dynamic range from 0.5–200,000 ppm (20% v/v) FAME. This sensor is a viable alternative to compliment more sophisticated and expensive bench top techniques in current use. The detection of chloroform in aqueous and non-aqueous has direct environmental and pharmaceutical applications, due to its well documented toxicity. A sensor has been developed based on a modified Fujiwara reaction for detecting chloroform, a halogenated hydrocarbon, in the visible spectrum. 2,2’-dipyridyl and tetra-n-butyl ammonium hydroxide are the modified Fujiwara reagents encapsulated within a sensing film. Upon exposure to chloroform in non-aqueous solution, a colored product is produced within the film which can be analyzed spectroscopically yielding a detection limit of 0.830 ppm (v/v) and quantification limit of 2.77 ppm. Monitoring and detection of gas plume constituents is a useful diagnostic tool in evaluating combustion efficiency, ensuring safe testing conditions, and in quantifying greenhouse gas emissions. Rocket engine ground tests are vital to ensure the performance of the rocket engines during critical space missions. Optical sensors were developed for remote sensing applications to detect isopropyl alcohol utilizing the dye Chromoionophore IX. This sensor gave a detection limit of 9, 13, 21 ppm and quantification limits of 32, 43, and 70 ppm for methanol, ethanol, and isopropyl alcohol respectively. Also a fingerprinting method was developed utilizing several indicator dyes in order to detect kerosene vapor

The influence of sulfate in aluminum coagulation of water

Aluminum salts are the most common coagulants used in water treatment to remove contaminants. The objectives of this research was to provide an understanding of some aspects of the influence of sulfate in aluminum coagulation chemistry of natural water. Al(III) solutions were titrated with base to study the role of sulfate in the hydrolysis/precipitation of aluminum. Jar tests were conducted to treat water samples containing varying concentrations of aquatic humic substances (AHS), sulfate and pH. The kinetics and adsorption isotherms of sulfate and aquatic humic substances on aluminum precipitate were developed in adsorption experiments using aluminum precipitate adsorbents. The application of a sensor for Al(III) based on immobilized morin was investigated. Aluminum chloride and aluminum nitrate had similar hydrolysis/precipitation characteristics. Aluminum precipitation occurred at a lower formation function ratio r = (OH) \sb{b}/ (Al) \sb{t} for aluminum sulfate than for aluminum chloride or aluminum nitrate. The aluminum sulfate precipitate was presumed to be an Al-OH-SO\sb4 solid. Equilibrium calculation (ALCHEMI) predicted jurbanite for similar conditions. The addition of sulfate to aluminum chloride solutions resulted in titration curves similar to that of aluminum sulfate. Acidification of the sample prior to titration did not impact the titration curves. An aluminum speciation scheme was presented showing the predominance of monomers at low r ratios, followed by polymers, and Al(OH)\sb4\sp- at high r ratios. pH had the most influence in the coagulation of the water samples treated. The impact of sulfate and AHS additions varied depending on the pH. Turbidity and AHS removal were greater at pH4 than at pH7. Maximum removals were obtained at pH5.5. The formation function fell within the range measured in the Al(III) titration experiments. Higher aluminum precipitates were measured at pH7. The adsorption data of aquatic humic substances (AHS) on aluminum chloride and aluminum sulfate precipitates fitted the Freundlich isotherm best. More AHS adsorbed to the aluminum sulfate precipitate. Little difference existed between the AHS absorbed to either aluminum chloride or aluminum sulfate at pH5.5 and 7. AHS adsorbed to aluminum precipitates formed with AHS. Sulfate adsorption on aluminum precipitates increased with decreasing pH and fitted the Langmuir isotherm best. The competition between AHS and sulfate for the adsorption sites of the aluminum precipitates favored AHS. Inconsistent results were obtained with the sensor based on immobilized morin. Modifications to the procedure and the use of other ligands were recommended in lieu of morin