ABSTRACT This study investigated the influence of temperature and humidity on the decomposition efficiency of benzene vapor in a packed-bed UV/TiO2 photocatalytical reactor. The packed-bed annular photocatalytical reactor illuminated by a 15-watt ultraviolet lamp was originally designed for this particular study. Pyrex glass beads coated with Degussa P-25 TiO2 (80 % anatase) were packed in the photocatalytical reactor. The operating parameters investigated in this study included reaction temperature (100-260¢J), water vapor concentration (0-1.58¡Ñ104 mg/m3), retention time (3.1-10.3 sec), and inlet benzene concentration (239-478 mg/m3). Experimental results indicated that the decomposition efficiency of benzene increased with reaction temperature whish was lower than 180¢J, for oxygen content of 21 %, water vapor concentration of 4.69¡Ñ103- 1.58¡Ñ104 mg/m3, and reaction temperature lower then 180¢J. However, the decomposition efficiency of benzene could not be further increased for reaction temperature higher than 180¢J. In addition, the decomposition efficiency of benzene increased with water vapor concentration which was lower than 1.16¡Ñ104 mg/m3. For water vapor concentration higher than 1.16¡Ñ104 mg/m3, the decomposition of benzene could not be further enhanced significantly. In this study, up to 100% of benzene decomposition could be achieved at water vapor concentration of 1.58¡Ñ104 mg/m3 and reaction temperature of 180¢J. Moreover, the decomposition efficiency of benzene increased from 57 to 100% as retention time increased from 3.1 to 10.3 seconds, while decreased from 100 to 65% as benzene concentration increased from 239 to 478 mg/m3. Modified Langmiur-Hinshewood kinetic model was applied to simulate the photocatalytic decomposition of benzene in the annular packed-bed photocatalytic reactor. The simulation of experimental results was successfully developed to describe the reaction rate of benzene for various reaction temperatures (160-260¢J) during the UV/TiO2 photocatalytical reaction process. Furthermore, reaction rate constant (KLH) and adsorption equilibrium constant (Kc and Kw) were functions of reaction temperature, where can the described by the Arrihenius Law. The rate controlling steps were either photocatalytic reaction on the surface adsorption of reaction products from the surface photocatalysts.

The purpose of this study is using titanium dioxide (TiO2) as gate oxide on thin film transistor (TFT) and discussed with their physical, chemical and electrical properties. Amorphous silicon (a-Si) and polycrystalline silicon (poly-Si) are used as substrates. The metal-organic chemical vapor deposition (MOCVD) and the liquid phase deposition (LPD) are used as the TiO2 growth methods. About the LPD growth method, ammonium hexafluoro-titanate ((NH4)2TiF6) and hexafluorotitanic acid (H2TiF6) are used as Ti sources. We are interested in two parts: (1) the growth mechanisms, physics properties, chemical properties and electrical properties of MOS structure; (2) the fabrication processes and electrical properties of devices. In the first part, we discuss the thin films characteristics on a-Si and poly-Si substrates. For the MOCVD growth method, the MOCVD-TiO2 film tends to form the poly structure. Poly structure has a higher dielectric constant, however, higher traps and dangling bonds also exist at the grain boundaries. Thus, poly structure of TiO2 film has a higher leakage current. For the LPD growth method, the film tends to form the amorphous structure. Amorphous structure has lower leakage current but also has lower dielectric constant. The film that grown from the (NH)2TiF6 source is called LPD-TiO2 film. The film that grown from the (NH)2TiF6 source is called LPD-TixSi(1-x)Oy film. Both films are incorporated with OH and F ions during the growth, the OH and F ions can be outgassed during the low temperature annealing process. In addition, appropriate F ions in the film can passivate the traps and dangling bonds. The low temperature treatments in N2 or O2 ambient and post-metallization annealing (PMA) are adopted to improve the film characteristics. On the other hand, the substrate is not a prefect structure (not a single structure). Thus the film may be influenced by substrate during the annealing treatment. In the second part, the electrical properties of TFT devices were discussed under the coplanar structure. There are several differences of the operation principle in TFT and MOSFET. A-Si and poly-Si are the un-doped substrates with many traps in the bulk. The channel should be occurred through the full depletion mode. The full depletion region is the substrate that under the gate electrode. Thus, the key point is kept the suitable thickness. Too thick, the channel can not appear. Too thin, the substrate may be over-etched. For ion implantation, due to the thinner active layer, the ion implantation energy should be lowed. In addition, the activation temperature and activation time should be adjusted suitable. We have fabricated the TFT devices with the MOCVD-TiO2 as gate oxide on poly-Si substrate. From the I-V characteristics, the Kink effect can be observed. However, the Ion/Ioff ratio is still low. We must further study how to increase the Ion/Ioff ratio.

Due to the high electron mobility compared with Si, much attention has been focused on III-V compound semiconductors (gallium arsenide (GaAs) and indium phosphide (InP)) high-speed devices. The high-k material TiO2 not only has high dielectric constant (k = 35-100) but has well lattice match with GaAs and InP substrate. Therefore, titanium oxide (TiO2) was chosen to be the gate oxide in this study. The major problem of III-V compound semiconductors is known to have poor native oxide on it and leading to the Fermi level pinning at the interface of oxide and semiconductor. The C-V stretch-out phenomenon can be observed and the leakage current is high. The higher dielectric constant of poly-crystalline TiO2 film grown on GaAs can be obtained by metal organic chemical vapor deposition (MOCVD). But the high leakage current also occurred due to the grain boundary and defects in the poly-crystalline TiO2 film. The surface passivation of GaAs with (NH4)2Sx treatment (S-GaAs) could prevent it from oxidizing after cleaning and improve the interface properties of MOSFET. The fluorine from liquid phase deposited SiO2 solution can passivate the grain boundary of poly-crystalline MOCVD-TiO2 film and interface state. The high dielectric constant and low leakage current of fluorine passivated MOCVD-TiO2/S-GaAs can be obtained. The leakage current densities are 3.41 x 10-7 A/cm2 and 1.13 x 10-6A/cm2 at ¡Ó1.5 MV/cm, respectively. The Dit is 4.6 x 1011 cm-2eV-1 at the midgap. The dielectric constant can reach 71. In addition, the post-metallization annealing (PMA) is another efficiency way to improve the MOCVD-TiO2 quality. The mechanism of PMA process is from the reaction between the aluminum contact and hydroxyl groups existed on TiO2 film surface. Then the active hydrogen is produced to diffuse through the oxide and passivate the oxide traps. For PMA (350oC)-MOCVD-TiO2 on S-GaAs MOS structure, the leakage current densities can reach 2.5 x 10-7 and 5 x 10-7 A/cm2 at ¡Ó1.5 MV/cm, respectively. The dielectric constant and the Dit are 66 and 5.96 x 1011 cm-2eV-1, respectively. In order to avoid the leakage current from grain boundary of poly-crystalline TiO2, and liquid phase deposited TiO2 (LPD-TiO2) at low temperature can preserve the function of sulfur passivation. Therefore, the amorphous LPD-TiO2 was deposited on S-GaAs. The leakage current densities are 1.04 x 10-7 and 1.91 x 10-7 A/cm2 at ¡Ó0.5 MV/cm, respectively. The Dit is 3.2 x 1011 cm-2eV-1 and the dielectric constant is 48. The LPD-TiO2 film was deposited on (NH4)2Sx treated InP (S-InP), and the 4 x 100 £gm2 enhancement mode N channel InP MOSFET with LPD-TiO2 as gate oxide was fabricated, which showed the good characteristic. The normalized maximum gm is 43 mS/mm at VG = 1.3 V for VDS fixed at 1 V. The maximum calculated £gFE of 348 cm2/V¡Es at VDS = 1 V is obtained.

In this work, we study the technique of Titanium Dioxide(TiO2) work electrode of the dye sensitized solar cells. The research contained four parts. (I)Fabrication of porous TiO2 with sol-gel method. (II)Compare the efficiency between dense layer non-dense layer. (III)Study the characteristics of nanometer photocatalyzer layer with silver atom on porous layer. (IV)Replace the commercial dye with the novel Discotic Liquid Crystal(DLC) material which we synthesized. We compared different TiO2 particle size, and discovered the efficiency of 20nm particle which made Degussa reached 3.31%. After joining dense layer, the efficiency can be up to 3.75%. Finally, we sprayed a silver atom layer, the device efficiency increase to 4.13%. Because of the cost of the commercial dye, we replace the dye with DLC which were synthesized by ourselves. The efficiency is up to 0.46%. We offer a feasible direction in low cost and high-efficiency at present.

The high magnetoresistance is one of the most important properties that led the colossal magnetoresistance (CMR) materials been kept attention, however, because of the low phase transition temperature (Tp) and Curie temperature (TC) limits the application of the materials. The Tp could be influenced by many factors, as for the R1-xAxMnO3(R=rare earth element, A=alkaline metal, 0¡Õx¡Õ1) CMR materials, the selections of elements on R, A, and the ratio of x would make the difference. Besides these factors, when the film was grown on a substrate, the strain effect initiated at the substrate/film interface plays an essential role on the change of Tp and other physic properties. In other hand, the Sr element, existed in the SrTiO3(100) substrate, may also diffuse into the thin films during growth and alter the composition of the film and change its physic properties. In this thesis, we mainly focused on the modifying of the surface of substrates to prevent the diffusion problems. A wet chemical method was applied to modify the top layer of substrates such that the surface layer of the substrate is consisted of Ti-O layer only. By varying the high temperature annealing and etching processes, an optima processing condition was established.

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In my research, I use sucrose to modify TiO2 nanoparticles to study the influence of sucrose modification in the performance of dye-sensitized solar cell. Two types of TiO2 are used in the experiments, one is P-25 (80% anatase, Degussa, Germany) and the other is ST-21 (100% anatase, Ishihara Sangyo, Japan). The results shows that the solar cells with TiO2 photoanode sintered in N2 has better conversion efficiency than that sintered in air. On the other hand, the TiO2 with 0.08 g/mL sucrose modification and sintered in N2 has the best conversion efficiency than the others with different sucrose concentration modifications and the highest conversion efficiency reaches 5.55 %. The performance of P-25 with 0.08 g/mL sucrose made solar cell is 10.9% higher than that without sucrose modification TiO2 photoanode made solar cell and the performance of ST-21 with 0.08 g/mL sucrose made solar cell is 5.4% higher than that without sucrose modification.

Κατά την διάρκεια αυτής της πτυχιακής εργασίας παρασκευάστηκαν δυο δείγματα νανοσύνθετων υλικών TiO2/αλλοϋσίτη, με διαφορετικές αναλογίες (60:40, 50:50) όπου μελετήθηκαν πειραματικά οι ιδιότητες τους, με σκοπό να χρησιμοποιηθούν σε επόμενο στάδιο στη φωτοκαταλυτική αποδόμηση αέριων ρύπων (π.χ. NOx) και οργανικών πτητικών ενώσεων (VOCs). Η μορφή του φωτοκαταλύτη (TiO2) που συντέθηκε ήταν ο ανατάσης. Στα τροποποιημένα πλέον δείγματα του αλλοϋσίτη, εφαρμόστηκαν διάφορες τεχνικές για τον χαρακτηρισμό των ιδιοτήτων τους, όπως: Περιθλασιμετρία Ακτίνων X, Υπέρυθρη Φασματοσκοπία Μετασχηματισμού κατά Fourier, Ηλεκτρονική Μικροσκοπία Σάρωσης και Προσδιορισμός Μεγέθους και Κατανομής Πόρων καθώς και Ειδικής Επιφάνειας. Ο φωτοκαταλύτης διασπείρεται σχετικά ομοιογενώς στις εξωτερικές επιφάνειες του αλλουσίτη, δίνοντας πολύ ενθαρρυντικά αποτελέσματα για την φωτοκαταλυτική του δράση που θα μελετηθεί σε επόμενο στάδιο. Τα νανοσύνθετα που παρασκευάστηκαν, εμφανίζουν τη δημιουργία μεσοπορώδους δομής με πόρους μεγέθους περίπου στα 5,8nm. Τα τροποποιημένα αργιλικά ορυκτά παρουσιάζουν ιδιότητες αντίστοιχες άλλων νανοσύνθετων TiO2-αλλουσίτη αποτελεσματικών για την καταπολέμηση των αέριων ανόργανων ρύπων (NOx) και των οργανικών πτητικών ενώσεων (VOCs). / During this thesis prepared two samples nanocomposite materials TiO2 / halloysite, with different ratios (60:40, 50:50) where experimentally studied their properties, to be used at a later stage in the photocatalytic degradation of gaseous pollutants (p. x. NOx) and volatile organic compounds (VOCs).

No description available.

abstract: Over the past years, an interest has arisen in resolving two major issues: increased carbon dioxide (CO2) emissions and depleting energy resources. A convenient solution would be a process that could simultaneously use CO2 while producing energy. The photocatalytic reduction of CO2 to fuels over the photocatalyst titanium dioxide (TiO2) is such a process. However, this process is presently inefficient and unsuitable for industrial applications. A step toward making this process more effective is to alter TiO2 based photocatalysts to improve their activity. The interactions of CO2 with oxygen-deficient and unmodified (210) surfaces of brookite TiO2 were studied using first-principle calculations on cluster systems. Charge and spin density analyses were implemented to determine if charge transfer to the CO2 molecule occurred and whether this charge transfer was comparable to that seen with the oxygen-deficient and unmodified anatase TiO2 (101) surfaces. Although the unmodified brookite (210) surface provided energetically similar CO2 interactions as compared to the unmodified anatase (101) surface, the unmodified brookite surface had negligible charge transfer to the CO2 molecule. This result suggests that unmodified brookite is not a suitable catalyst for the reduction of CO2. However, the results also suggest that modification of the brookite surface through the creation of oxygen vacancies may lead to enhancements in CO2 reduction. The computational results were supported with laboratory data for CO2 interaction with perfect brookite and oxygen-deficient brookite. The laboratory data, generated using diffuse reflectance Fourier transform infrared spectroscopy, confirms the presence of CO2- on only the oxygen-deficient brookite. Additional computational work was performed on I-doped anatase (101) and I-doped brookite (210) surface clusters. Adsorption energies and charge and spin density analyses were performed and the results compared. While charge and spin density analyses showed minute charge transfer to CO2, the calculated adsorption energies demonstrated an increased affinity for CO2adsorption onto the I-doped brookite surface. Gathering the results from all calculations, the computational work on oxygen-deficient, I-doped, and unmodified anatase and brookite surface structures suggest that brookite TiO2 is a potential photocatalysts for CO2 photoreduction. / Dissertation/Thesis / M.S. Chemical Engineering 2012