Dissertations / Theses on the topic 'Formaldehyde sensors'

Atmospheric formaldehyde (H2CO) is an intermediate product common to the degradation of many volatile organic compounds and therefore it is a central component of the tropospheric chemistry. While the global formaldehyde background is due to methane oxidation, emissions of non-methane volatile organic compounds (NMVOCs) from biogenic, biomass burning and anthropogenic continental sources result in important and localised enhancements of the H2CO concentration. Recent spaceborne nadir sensors provide an opportunity to quantify the abundance of tropospheric formaldehyde at the global scale, and thereby to improve our knowledge of NMVOC emissions. This is essential for a better understanding of the processes that control the production and the evolution of tropospheric ozone, a key actor in air quality and climate change, but also of the hydroxyl radical OH, the main cleansing agent of our troposphere. For this reason, H2CO satellite observations are increasingly used in combination with tropospheric chemistry transport models to constrain NMVOC emission inventories in so-called top-down inversion approaches. Such inverse modelling applications require well characterised satellite data products consistently retrieved over long time periods.

This work reports on global observations of formaldehyde columns retrieved from the successive solar backscatter nadir sensors GOME, SCIAMACHY and GOME-2, respectively launched in 1995, 2002 and 2006. The retrieval procedure is based on the differential optical absorption spectroscopy technique (DOAS). Formaldehyde concentrations integrated along the mean atmospheric optical path are derived from the recorded spectra in the UV region, and further converted to vertical columns by means of calculated air mass factors. These are obtained from radiative transfer simulations, accounting for cloud coverage, surface properties and best-guess H2CO profiles, the latter being derived from the IMAGES chemistry transport model. A key task of the thesis has consisted in the optimisation of the H2CO retrieval settings from multiple sensors, taking into account the instrumental specificities of each sounder. As a result of these efforts, a homogeneous dataset of formaldehyde columns covering the period from 1996 to 2010 has been created. This comes with a comprehensive error budget that treats errors related to the spectral fit of the columns as well as those associated to the air mass factor evaluation. The time series of the GOME, SCIAMACHY and GOME-2 H2CO observations is shown to be consistent and stable over time. In addition, GOME-2 brings a significant reduction of the noise on spatiotemporally averaged observations, leading to a better identification of the emission sources. Our dataset is used to study the regional formaldehyde distribution, as well as its seasonal and interannual variations, principally related to temperature changes and fire events, but also to anthropogenic activities. Moreover, building on the quality of our 15-year time series, we present the first analysis of long-term changes in the H2CO columns. Positive trends, in the range of 1.5 to 4% yr-1, are found in Asia, more particularly in Eastern China and India, and are related to the known increase of anthropogenic NMVOC emissions in these regions. Finally, our dataset has been extensively used in several studies, in particular by the BIRA-IASB modelling team to constrain NMVOC emission fluxes. The results demonstrate the high potential of satellite data as top-down constraint for biogenic and biomass burning NMVOC emission inventories, especially in Tropical ecosystems, in Southeastern Asia, and in Southeastern US.

Le formaldéhyde (H2CO) joue un rôle central dans la chimie de la troposphère en tant que produit intermédiaire commun à la dégradation chimique de la plupart des composés organiques volatils dans l’atmosphère. L’oxydation du méthane est responsable de plus de la moitié de la concentration moyenne globale du formaldéhyde. Sur les continents en revanche, les hydrocarbures non-méthaniques (NMVOCs) émis par la végétation, les feux de biomasse et les activités humaines, augmentent de façon significative et localisée la concentration de H2CO. Les récents senseurs satellitaires à visée nadir offrent la possibilité de quantifier à l’échelle globale l’abondance du formaldéhyde dans la troposphère et de ce fait, d’améliorer notre connaissance des émissions de NMVOCs. Ceci est essentiel à la compréhension des mécanismes contrôlant la production et l’évolution de l’ozone troposphérique, élément clé pour la qualité de l’air et les changements climatiques, mais aussi du composé hydroxyle OH, le principal agent nettoyant de notre troposphère. C’est pourquoi, une méthode de plus en plus répandue pour améliorer les inventaires d’émissions des NMVOCs consiste en l’utilisation d’observations satellitaires de H2CO en combinaison avec un modèle de chimie et de transport troposphérique, dans une approche appelée modélisation inverse. Ce genre d’application demande des produits satellitaires bien caractérisés et dérivés de façon cohérente sur de longues périodes de temps.

Le travail présenté dans ce manuscrit porte sur l’inversion des colonnes de formaldéhyde à partir de spectres de la radiation solaire rétrodiffusée par l’atmosphère terrestre, mesurés par les senseurs GOME, SCIAMACHY et GOME-2, lancés successivement en 1995, 2002 et 2006. La méthode d’inversion est basée sur la spectroscopie d’absorption optique différentielle (DOAS). Les concentrations de formaldéhyde intégrées le long du chemin optique moyen dans l’atmosphère sont dérivées à partir des spectres mesurés, et ensuite transformées en colonnes verticales par le biais de facteurs de conversion appelés facteurs de masse d’air. Ces derniers sont calculés à l’aide d’un modèle de transfert radiatif, en tenant compte de la présence de nuages, des propriétés de la surface terrestre et la distribution verticale supposée du formaldéhyde, fournie par le modèle IMAGES. Un des objectifs principaux de la thèse a été d’optimiser les paramètres d’inversion pour H2CO, et ceci pour les trois senseurs, tout en tenant compte des spécificités de chaque instrument. Ces efforts ont conduit à la création d’un jeu de données homogène, couvrant la période de 1996 à 2010. Les colonnes sont fournies avec un bilan d’erreur complet, incluant les erreurs liées à l’inversion des concentrations dans les spectres, ainsi que celles provenant de l’évaluation des facteurs de masse d’air. La série temporelle des observations de GOME, SCIAMACHY et GOME-2 présente une bonne cohérence et stabilité sur toute la période. Nous montrons aussi que la meilleure couverture terrestre de GOME-2 entraîne une réduction significative du bruit sur les observations moyennées, permettant une meilleure identification des sources d’émission. Notre jeu de données est exploité pour étudier la distribution régionale du formaldéhyde, ainsi que ses variations saisonnières et interannuelles, principalement liées aux variations de température et aux feux de végétation, mais aussi aux activités anthropiques. De plus, en s’appuyant sur la qualité de la série temporelle de 15 ans, nous présentons la première analyse des variations à long terme des concentrations de H2CO. Des tendances positives, de l’ordre de 1.5 à 4% par an, sont observées en Asie, en particulier dans l’est de la Chine et en Inde, liées à l’augmentation des émissions anthropiques d’hydrocarbures dans ces régions. Finalement, nos données ont été largement exploitées par le groupe de modélisation de l’IASB pour faire des études de modélisation inverse des émissions de NMVOCs. Les résultats démontrent le haut potentiel des données satellitaires pour contraindre les inventaires d’émissions dues à la végétation et aux feux de biomasse, particulièrement dans les écosystèmes tropicaux, en Asie du sud-est, et dans le sud-est des Etats-Unis.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Se estudia la influencia del dopaje y de la temperatura sobre las propiedades físicas de hetero-estructuras hexagonales principalmente basadas en carbono y nitruro de boro tanto uni- y bi-dimensionales, este estudio se divide en tres partes. Por un lado, se estudia el efecto del dopaje de nitruro de boro en nanotubos de carbono armchair (6, 6) (hetero-nanotubos de nitruro de boro y carbono) sobre las propiedades del transporte cuántico de fonones y electrones, variando patrones de distribución y concentración de dopaje. Por otro lado, se estudia la forma como afecta la temperatura del sustrato sobre las propiedades del transporte térmico clásico en hetero-nanocintas de grafeno/nitruro de boro hexagonal y nitruro de boro hexagonal/grafeno, e influenciados por la asimetría estructural. Análogamente, también se estudia el efecto de la temperatura media y bias en hetero-nanocintas de grafeno/X (X=nitruro de boro hexagonal, carburo de silicio hexagonal, y grafeno hidrogenado), afectados por dos tipos de interfaces (zigzag y armchair). Por último, se estudia las propiedades electrónicas del proceso de adsorción de la molécula del Formaldehído (CH2O) sobre el sustrato de nitruro de boro hexagonal hidrogenado. Para ello, la metodología empleada en estos trabajos consistió en el uso de tres métodos computacionales; las funciones de Green fuera del equilibrio (NEGF) en combinación con el método de la teoría del funcional de la densidad basado en tight-binding (DFTB), dinámica molecular fuera del equilibrio (NEMD), y cálculos de la teoría del funcional de la densidad, respectivamente. Por un lado, los resultados respecto al efecto del dopaje sobre el transporte cuántico muestran que al aumentar la concentración del dopaje en los hetero-nanotubos de nitruro de boro y carbono armchair (6, 6), los coeficiente de transmisión fonónico y electrónico se reducen, este comportamiento ocurre a frecuencias altas y cerca de los bordes de la banda de valencia y conducción, respectivamente. Los patrones de distribución de dopaje helicoidal y horizontal permiten un transporte de fonones adecuados cuantificados en una alta conductancia de fonones a 300K. Todos los hetero-nanotubos de nitruro de boro y carbono armchair (6, 6) poseen un comportamiento semiconductor a diferencia del nanotubo de carbono armchair (6, 6) con un bandgap modulable respecto a la concentración de dopaje de nitruro de boro. Por otra parte, los resultados del efecto de la temperatura del sustrato sobre el transporte térmico clásico en las hetero-nanocintas muestran que existe una influencia que incrementa la rectificación térmica (>30 %) a temperaturas bajas (>300K) para el sustrato de Si(100), esto debido al acople fuerte tipo Van der waals entre el sustrato y la hetero-nanocinta de nitruro de boro hexagonal/grafeno. Además, la asimetría estructural tipo-T genera una rectificación térmica en sistemas puros y hetero-nanocintas de grafeno/nitruro de boro hexagonal y nitruro de boro hexagonal/grafeno, este efecto está relacionado con los cambios en el grado de localización de los modos vibracionales de frecuencias altas . Sin embargo, la resistencia térmica interfacial y la rectificación térmica se reducen con la temperatura media en las XIV hetero-nanocintas de grafeno/X, independientemente de la interface armchair o zigzag, debido a que el flujo térmico en direcciones opuestas llegan a ser similares a altas temperaturas. El efecto de la temperatura bias, en la curva J − α, determina que el fujo térmico tiene una preferencia marcada en la dirección de X al grafeno, observando el fenomeno de la resistencia térmica diferencial negativa en los sistemas de grafeno/nitruro de boro hexagonal y grafeno/grafano. Por último, la trayectoria de mínima energía, la densidad de estados total y la densidad de estados proyectada del proceso de adsorción muestran que la molécula formaldehído, CH2O, se quimisorbe sobre el sustrato de hBN hidrogenado con una energía de adsorción de 1.42eV mediante vacancias de hidrógeno en el átomo de B, donde también la distribución de densidad de espín y la transferencia de carga presentan evidencias de la existencia de una reacción en cadena de moléculas CH2O sobre el sustrato de nitruro de boro hexagonal.
Consejo Nacional de Ciencia y Tecnología (Perú). Fondo Nacional de Desarrollo Científico y Tecnológico (Fondecyt)
Tesis

Volatile organic compounds (VOCs) in the indoor air have adverse effects on the dwellers residing in a building or a vehicle. One of these effects is called sick building syndrome (SBS). SBS refers to situations in which the users of a building develop acute health effects and discomfort depending on the time they spend inside some buildings without having any specific illness. Furthermore, monitoring volatile organic compounds could lead to early diagnosis of specific illnesses through breath analysis. Among those VOCs formaldehyde, acetaldehyde can be listed. In this thesis, VOC detecting thin film sensors have been investigated. Such sensors have been manufactured using semiconducting metal oxides, ligand activated gold nanoparticles and Graphene/TiO2 mixtures. Advanced gas deposition unit, have been used to produce NiO thin films and Au nanoparticles. DC magnetron sputtering has been used to produce InSnO and VO2 thin film sensors. Graphene/TiO2 sensors have been manufactured using doctor-blading. While presenting the results, first, material characterization details are presented for each sensor, then, gas sensing results are presented. Morphologies, crystalline structures and chemical properties have been analyzed using scanning electron microscopy, X-ray diffraction and X-ray photo electron spectroscopy. Furthermore, more detailed analyses have been performed on NiO samples using extended X-ray absorption fine structure method and N2 adsorption measurements. Gas sensing measurements were focused on monitoring formaldehyde and acetaldehyde. However, responses ethanol and methane were measured in some cases to monitor selectivity. Graphene/TiO2 samples were used to monitor NO2 and NH3. For NiO thin film sensors and Au nano particles, fluctuation enhanced gas sensing is also presented in addition to conductometric measurements.

Formaldehyde is one of the main gases that contribute to poor indoor air quality since it is so widely used in the manufacturing of goods. Over time, formaldehyde leaches out of various materials and reduces the quality of air. Formaldehyde, even at very low concentrations, can cause respiratory problems and a general feeling of unwellness. The World Health Organization (WHO) states that formaldehyde exposure should not exceed 0.08 ppm over a 30 minute period. Therefore, formaldehyde sensors are needed to ensure optimal indoor air quality. Polyaniline (PANI), as well as PANI doped with NiO or NiO and Al2O3, were tested to determine their suitability as sensing materials for formaldehyde. It was found that at higher concentrations of formaldehyde (above 1 ppm), PANI doped with 5% NiO and 15% Al2O3 was the most suitable sensing material with respect to both sensitivity and selectivity. At lower concentrations (below 1 ppm), however, PANI doped with 5% NiO and 15% Al2O3 did not detect formaldehyde. PANI doped with 15% NiO only was a much better option since it was able to detect the highest concentration of formaldehyde at very low concentrations (0.09 ppm) and still have moderate selectivity. A special test system was designed that could test single or multiple gases at various concentrations. Ethanol, acetaldehyde and benzene were chosen as interferents for formaldehyde and nitrogen was used to dilute the gases to achieve lower concentrations. A specialized gas chromatograph (GC) was used to determine the amount of gas or analyte that interacted with the sensing material being tested. Replicate polymer samples of varying dopant concentrations were tested with different gases at different concentrations and statistically analyzed. Both sensitivity and selectivity towards formaldehyde was taken into consideration. Among all tests conducted with single and multiple gases, it was concluded that PANI doped with 5% NiO and 15% Al2O3 was the best sensing material at high concentrations of formaldehyde (above 1 ppm), whereas PANI doped with 15% NiO was the best sensing material at low concentrations (below 1 ppm).

碩士
大葉大學
機械工程研究所碩士班
94
ABSTRACT A novel micro formaldehyde gas sensor with a sputtered NiO thin film integrated with a micro hotplate was fabricated. A microfabricated formaldehyde gas sensor is developed which uses a silica substrate with Pt micro heaters as the micro hotplate and a thin-film NiO layer as a conductivity-sensitive material. The substrate is deposited with NiO thin film as sensing elements, Pt resistors as heaters, and as interdigitated electrodes for resistance measurement. As voltages were applied to Pt heaters, temperature of micro hotplates increased. Thus, at 300oC, when formaldehyde was present in the atmosphere, it was adsorbed and as a result the electrical conductivity of NiO films was increased. The measured resistance between the interdigitated electrodes was changed. The formaldehyde gas sensor was integrated with a Pt resistor as a micro heater for the enhancement of sensitivity. A high selectivity to acetone, methanol and ethanol was alson shown in the study.

碩士
國立屏東科技大學
材料工程所
95
Abstract Student ID：M9440007 Title of Thesis：The Gas Sensing Properties of Formaldehyde Gas Sensor Total Pages：67 Name of Institute：National Ping-Tung University of Science & Technology Name of Department：Department of Materials Engineering Date of Graduation：2007.07 Degree Conferred：Master Name of Student：Yan-Ting Wu Adviser：Lung-Ming Fu, Chia-Yen Lee The Contents of Abstract in this Thesis: The purpose of this study is to design and develop semiconductor-type Formaldehyde Gas Sensor by MEMS. This sensor is suitable not only for industrial process monitoring, but also for the detection of formaldehyde concentrations in buildings in order to act as the safeguard of the human’s health condition. In the present study, the glass substrate is used as a base, then upon this base, a sensing layer, a heating device and IDEs are integrated. The integrated micro-hotplates in the proposed design provide an instantaneous and precise temperature control capability. The current experimental results show that applied voltage of 5.2W yields a constant temperature of 300 ◦C. The range of formaldehyde detected of 40 to 8600 ppb that the time response of the gas sensor developed in the present study. The average time constant of the proposed formaldehyde gas sensor is determined to be 70s for formaldehyde concentrations in the range 0–3 ppm at a micro-hotplate temperature of 300 ◦C. The recovery time of the proposed formaldehyde gas sensor is determined to be 80s that sensitivity of 0.47kΩ/ppb at 300℃and a detection limit below 800ppb. The purpose of this study is to obtain the better sensitivity and the minimal monitoring concentration. The result of this experiment presented the difference of resistance of sensing layer is proportion to the concentration of formaldehyde. Keywords: formaldehyde, micro hotplate, NiO thin film, co-sputter

碩士
國立中興大學
化學系所
102
In this study, we developed diverse electrochemical sensors based on electrodeposited various catalytic metal nanoparticles on a screen-printed edge band carbon ultramicroelectrode (SPUME) with Nafion as the solid polymer electrolyte. Uniform and well-dispersed metal-nanoparticles are well deposited on the SPUME without either protective or capped agents due to the edge diffusion effect at the SPUME. First part of this study was the development of portable gaseous formaldehyde amperometric sensor using the NPtRu-SPUME. The role of Ru was to protect the Pt from the poison of absorption of carbon monoxide. This developed gas sensing method for determination of formaldehyde showed a wide linear range from 25.4 ppb to 3.68 ppm, a very low detection limit of 1.42 ppb (S/N = 3) and excellent selectivity. Second, glycerol sensor based on the gaseous formaldehyde sensor has developed. The concentration of glycerol was determined indirectly by reacting glycerol with periodate to produce formaldehyde and formic acid. We used NAu-PtRu-SPUME here to dramatically enhance the sensitivity of glycerol determination. The developed method was successfully applied to identify the purity of glycerol in biodiesel. Overall, the glycerol sensor was found to be extremely highly sensitive and selective. Finally, we used lipase to indirectly quantified triglyceride concentration by glycerol sensing method.

碩士
靜宜大學
應用化學系
101
This study is the use of precious metal aurum and titanium dioxide (TiO2) composite material formed as a formaldehyde gas sensors, for which surface characteristics and sensor response to be discussed . This study is based on the precious metal aurum and titanium dioxide (TiO2) material as a gas sensor , because it is very easy to make and has good environmental stability and high sensitivity . This study was conducted using impregnation method with different proportions of aurum titania mixed, boiled to dryness , after milling for 24 hours to complete the sensing material preparation to X-ray diffraction (XRD) , specific surface area measuring instrument (BET) , Transmission Electron Microscopy (TEM) , analysis of composite material surface characteristics. Sensor materials based on titanium dioxide, at room temperature, to detect formaldehyde 10 ppm, the sensor response is 6.1, reaction time (T90) 164 seconds, the response time (Tr90) 275 seconds, the study showed, with a doping 1% Au/TiO2 have the best material for the gas sensor sensing signals at room temperature, formaldehyde gas 10 ppm, up 20.6 sensing signal T90 was 66 s, Tr90 to 250 s, the sensing signal increased about three times more, the T90 and Tr90 also significantly reduced the precious metal aurum and titanium dioxide (TiO2) doped as composites formaldehyde gas sensors quite worth exploring.

碩士
國立臺灣大學
工程科學及海洋工程學研究所
103
In bottom layer of Internet of Things(M2M) , there would be a lot of sensors to detect our environment in several applications such as smart home and air monitoring . Air pollution influences human health and can cause a number of diseases.The one of major air pollutiants is volatile organic compounds (VOCs) especially in BTEX and formaldehyde can cause cancer to human beings .Therefore, developing a low cost,low power consumption and reliable gas sensor is very important for sensing technology. In this work ,we demonstrated graphene material blended with Poly(methyl methacrylate,PMMA,M=15,000) composite inks deposited between gold electrode by spin coating method .The deposited graphene composite films with different mixture concentration are sensing materials for VOCs chemiresister gas sensors in room temperature.The sensor response to several VOCs gas including methanol ,ethanol , acetone , benzene ,toluene , o-xylene, formaldehyde and water vapor are investigated. The sensors selectivity ,repeatability and stability,duration are also examined .The graphene material are prepared and selectively blended with PMMA both in dispersant Tetrahydrofuran(THF) to become conductive self-assembly composite materials . We also tested the difference of sensing VOCs characteristics between spin coated pure graphene films and graphene /PMMA composite films. The optional concentration of graphene composite spin coated films show good sensor response to formaldehyde vapor with resistance change about 0.5%~30% after exposing to each vapor concentration(about 10ppm~600ppm) in room temperature .We finally use instruments such as FTIR,SEM,XRD and Raman to analysis materials .We also infer the possible sensing mechanism between the graphene-PMMA composites and the formaldehyde.

碩士
靜宜大學
應用化學系
105
In this study, sensing material TiO2 polymeric nanospheres are prepared by hydrothermal synthesis from carbon spheres and titanium (IV) n-butoxide. For detecting formaldehyde gas, the sensing materials were characterized by X-ray Diffraction (XRD), high resolution surface area and porosimetry analyser (ASAP/BET), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive spectrometer (EDS) and elemental analyzer. It exhibited a high response to 10 ppm at room temperature, response time (T90) is 74 seconds and recovery time (Tr90) is 102 seconds. It might be used in detecting formaldehyde gas and improve quality of air in the future.

碩士
大同大學
材料工程學系(所)
94
For fabricating the excellent water-resistant humidity sensitive layer, the organic humidity sensitive monomer mixed with phenol-formaldehyde resin solution was successfully prepared by spin-coating on comb-shaped electrodes. The spin-coating sensitive layers were exposed to UV-light to induce grafting and curing reaction. Mixing with the resin solution cam improve the adhesion between the polymerized film and electrode substrate. Unfortunately, it tends to solve in water because the adhesion between the copolymerized monomer and electrode substrate is poor. When we deposit hydrophobic HMDSZ (hexamethyldisilazane) plasma film onto the comb-shaped electrodes as an interface before grafting, the plasma treatment can provide the free radicals that can bond with humidity-sensitive polymer strongly by graft reaction, therefore the device has a good water resistivity. The impedance can very by 4 order between humidity of35~95%. Temperature dependence, hystersis, response time, water durability under various environments were also investigated.

碩士
國立勤益科技大學
化工與材料工程系
102
Formaldehyde sensor plays an important role in applications of industrial process and environmental monitorning. In this thesis, Nafion®/Pt (sputtering)/Ti/glass plate, Nafion®/Pd/Pt (sputtering)/Ti/glass plate and Nafion®/Pt/Pt(sputtering)/Ti/glass plateelectrodes are prepared by the microfabricationand the hydrogen bubble template techniques, which are used as the sensing electrodes of amperometric formaldehyde gas sensor. The characteristics of the preparing electrodes, the sensing properties and the aging phenomena of amperometric formaldehyde gas sensor are also investigated. The Pd/Pt(sputtering)/Ti/glass plate and Pt/Pt(sputtering)/Ti/glass plateelectrodes are electrodeposited by applying hydrogen bubble template technique with variable current densities and charges. The maximum electrochemical active areasand roughness factors of Pd/Pt(sputtering)/Ti/glass plate and Pt/Pt(sputtering)/Ti/glass plateelectrodes are obtainedto be 106.8 cm2 and 427.2, as well as 37.29 cm2 and 149.14 with the preparing current densities and charges of 0.15 and 0.05 A cm-2, as well as 12 and 12 C, respectively. Using the home-made electrodes as the sensing electrodes, the aging of amperometric formaldehyde gas sensors is caused by (1) the poisoning the electrodes by the strong adsorption of intermediates produced in the anodic oxidation of formaldehyde, and (2) retarding the mass transfer of formaldehyde caused by paraformaldehyde formed on the surface of Nafion®film. The sensing electrodes can be reactivated by (1) applying 0.9 and 0.8 V on the poisoning Pt and Pd electrodes for 3 min to oxidize the intermediates adsorbed on the electrode surface,and (2) depolymerizing the paraformaldehyde formed on the surface of Nafion film by passing90 ℃ N2 gasfor 20 min. When 1.25μl of the 5 wt% Nafion solution is used to prepared Nafion film on the sensing electrode, the maximum specific sensitivity of Nafion®/Pt (sputtering)/Ti/glass plate electrode is obtained to be 465.39 μA ppm-1g-1 for the amperometric formaldehyde operated at 200 ml min-1 100 RH% gas with 1 - 6 ppm formaldehyde. Using the same sensing conditions for the amperometric formaldehyde gas sensor, the maximum specific sensitivities of Nafion®/Pd/Pt (sputtering)/Ti/glass plate and Nafion®/Pt/Pt(sputtering)/Ti/glass plate electrodes are obtained to be 153.24and 147.24 μA ppm-1g-1, respectively, by using 3.5μl Nafion® solution to formaing the Nafion film on the sensing electrodes.

碩士
國立勤益科技大學
化工與材料工程系
106
The sensing performances of a planar amperometric formaldehyde gas sensor based on the porous Pt electrode prepared with the hydrogen bubble dynamic template (HBDT) technique, and cast with Nafion film as the solid polymer electrolyte (SPE) are investigated in this thesis. The effect of temperature, concentrations of H2SO4 and H2PtCl6, charge passed (Qpt) and current density for preparing Pt sensing electrode on the characteristics and the sensing properties of the sensing electrode is investigated by using the conventional method. The conditions for the preparation of Pt sensing electrode are optimized by using the mixture design technique. The surface morphologies and crystallographic information of as-prepared electrode materials are analyzed by the FESEM and XRD, respectively. The electrochemical properties are investigated by the cyclic voltammetry (CV) and chronoamperometry technique. Based on the investigation with the conventional experimental technique, the maximum specific sensitivity of the amperometric HCHO gas sensor is obtained to be 20.37 μA ppm-1 mg-1 due to the higher specific electrochemical surface area (SECSA) (22.89 m2 g-1) of the porous Pt sensing electrode prepared in 0.0075 M H2PtCl6 and 0.05 M H2SO4 aqueous solution at 30 oC with QPt and the current density of 6 C and 0.075 A cm-2. The experimental results reveal that the specific sensitivity of the HCHO gas sensor are mainly affected by the concentration of H2PtCl6, Qpt and temperature for preparing Pt sensing electrode, which are optimized by using the mixture design technique. The relationship between the specific sensitivity of the HCHO gas sensor (Y) and the normalized [H2PtCl6] (X1), Qpt (X2) and temperature (X3) for preparing Pt sensing electrode is obtained to be Y = 17.24 X1 + 8.35X2 + 13.30X3 + 25.63X1X3 The maximum specific sensitivity of the HCHO gas sensor was obtained to be 23.44 μA ppm-1 mg-1 for preparing the Pt sensing electrode in 0.007 M H2PtCl6 and 0.05 M H2SO4 aqueous solution with QPt and the current density of 3.0 C and 0.075 A cm-2 at 31 oC. The mass transfer resistance of the HCHO gas sensor within the gas phase can be neglected for gas flow rate greater than 450 ml min-1. When the gas flow rate is fixed at 450 ml min-1, the specific sensitivity of the amperometric HCHO gas sensor is increased from 38.05 to 43.85 A ppm-1 mg-1 by decreasing the Nafion film thickness from 2.84  0.08 to 1.18  0.10 m due to the decrease in the mass transfer resistance within the Nafion film. The diffusivity of HCHO within the Nafion film is found to be 2.33 x 10-9 cm2 s-1. The fading fraction of the specific sensitivity of Nafion®/Pt/Au/Al2O3 sensing electrode is 32.3% for 5 sensing runs due to the formation of intermediates CO(ads) and HCOOH(ads) on the Pt sensing electrode surface. The effect of 1.33 ppm acetone, 70.71 ppm benzene, and 0.039 % CO2 on the selectivity of Nafion®/Pt/Au/Al2O3 sensing electrode is slight. The selectivity of the HCHO gas sensor is affected by the presence of 35 ppm ethanol and 20% O2 due to the oxidation of ethanol and reduction of O2 on the sensing electrode. The response time (t90) and detection limits of the Nafion®/Pt/Au/Al2O3 sensing electrode are obtained to be 240-325 s and 20 ppb, respectively, which is less than the legal levels of formaldehyde in the indoor air defined by WHO (World Health Organization) (80 ppb) for 30 min exposure limit.

碩士
國立屏東科技大學
材料工程所
98
The purpose of study to apply MEMS techniques to design and manufacture a micro-column-based GC chip which have the same effect of GC capillaries and SS(Semiconductor Sensor) Chips with deposited oxide layer for detecting formaldehyde and TVOCs, which may afterward connect the GC chip. The developed platform technologies can separate mixing samplein the GC chip and detects their species and concentrations in the SS chips. This study exploits the realization of wet-etched micro columns for GC chip and SS chip. The leakage test and mixture gas separate test achieved a fruitful separate result for Ethylbenzene-Xylene mixture at 17.1 cm/s linear flow rate in GC chip column that thermal bound with Pyrex 7740 glass wafer and polar content coating. The E-beam evaporation and sputtering techniques are used to deposit inter-digitized electrodes (IDEs) and sensing layer of SS chip receptivity. It also was considered the sensing characteristics of before and after bounded cover plate.