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1
Sotelo-Vazquez, C. "Modification of titania films by chemical vapour deposition for enhanced photocatalysis". Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1553144/.
Testo completoAbstract (sommario):
Titanium dioxide (TiO2) is the leading material for self-cleaning applications due to its intrinsic properties, such as chemical inertness, mechanical robustness, high photocatalytic activity and durability to extend photocatalytic cycling. However, its relatively wide bandgap limits its outdoor applications. There has been a strenuous effort to try and improve the photocatalytic efficiency of TiO2, in particular by modifying its electronic structure to enhance its function under solar illumination. The most commonly studied approaches for achieving this have been to incorporate anionic and/or cationic species into the TiO2 structure and the design of TiO2-based heterojunction systems. The addition of nitrogen, phosphorus and sulfur species into the matrix of TiO2 was investigated. Films were grown using atmospheric-pressure chemical vapour deposition (APCVD). The nitrogen-doped system has been investigated most prominently to enhance and extend the photocatalytic response of TiO2 materials into the visible region of the electromagnetic spectrum. Nitrogen can either replace oxygen sites (Ns, substitutional doping) or sit within the TiO2 structure (Ni, interstitial doping) and form N-O groups with lattice oxygen. Interestingly, these NOx groups, as well as NHx surface species present similar binding energies, ca. 400 eV, hindering the identification of the nitrogen species and their role in the photocatalytic response of the material. Various synthesis conditions were experimented using different nitrogen precursors (tert-butylamine, benzylamine and ammonia), which were used to establish a correlation between surface and bulk nitrogen species and the photocatalytic behaviour of the N-TiO2 films. A loss of the Ni environment (as observed by X-ray photoelectron spectroscopy), as well as a decrease in photoactivity over time was observed, suggesting a direct participation of the nitrogen species in photocatalytic iv processes. In addition to traditional CVD methods, a pulse precursor approach was used for the first time, to the best of our knowledge, to synthesise stratified N-doped TiO2 thin films, by adding nitrogen into specific regions of the N-TiO2 film. Physical and functional comparison of stratified and non-stratified N-TiO2 films with similar structural and morphological features allowed us to evaluate the benefits of this synthetic approach, which not only resulted in an increase in the photocatalytic efficiency of the stratified N-TiO2 films but also did not affect the overall crystallinity of the films. The addition of phosphorus and sulfur was investigated as the most promising alternative to the use of nitrogen doping, as both could be added to the lattice of TiO2 either as cations or anions. Through functional testing, it was found that both dopant species were beneficial from a photocatalytic point of view. Interestingly, the use of APCVD techniques to deposit P-TiO2 thin films resulted in the addition for the first time, to the best of our knowledge, of P3- species, as well as P5+, to the TiO2 structure with the relative proportion being determined by the synthesis conditions. Through Hall effect probe, photocatalytic testing and transient absorption spectroscopy (TAS) analyses, it was found that the incorporation of P3- species was detrimental from an electrical conduction and photocatalytic point of view; however, the presence of solely P5+ species resulted in P-TiO2 films with enhanced self-cleaning and TCO properties. These results provide important insights on the influence of dopant nature and its location within a semiconductor’s structure. Heterojunction semiconductor materials are used in a wide range of applications including catalysis, electronic devices, sensors and solar-to-chemical energy conversion. These materials benefit from effective electron transfer processes, electron tunnelling, surface passivation and other synergistic effects to enhance their performance beyond the individual components. By using CVD methods, two different v heterojunction systems, rutile/ anatase TiO2 and WO3/TiO2, were grown. The interposition of an amorphous TiO2-based interlayer allowed direct vapour deposition of anatase on a rutile substrate, which is otherwise hindered by templating. The subsequent crystallisation of the amorphous interlayer after annealing, allowed us to investigate the impact of an efficient interface between the two rutile-anatase phases in the photodegradation of an organic model pollutant, stearic acid. Clear evidence on the synergy between the two polymorphs and more importantly, on the charge flow across the interface, which is against much conventional understanding, was evaluated through the photoreduction of silver particles. This charge flow involves electron transfer from rutile to anatase. Likewise, a conformal coating of WO3 nanorods with TiO2 was performed using APCVD techniques. The resulting WO3/TiO2 heterojunction films showed an electron transfer phenomenon, where electrons moved from WO3 into TiO2, against widely reported observation. State-of-the-art hybrid density functional theory (DFT) and hard X-ray photoelectron spectroscopy (HAXPES) were employed to elucidate the electronic interaction at the heterojunction of the WO3 and TiO2 crystalline phases. This vectorial charge separation reduces electron-hole recombination and most likely extends the lifetime and relative population of photogenerated charges. These results provide important insights on the influence of vectorial charge separation in heterojunctions. These phenomena had a dramatic impact on the photocatalytic efficiency of the heterojunction films, which are among the very highest ever reported by a thin film.
2
Liao, Xiaohong. "The synthesis of nano titania particles using a DC transferred arc plasma reactor". Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104690.
Testo completoAbstract (sommario):
The effect of quench conditions on the properties of titanium dioxide produced using atransferred arc process was studied. Rutile phase TiO2 in the form of micron sized powder wasdecomposed and vaporized in a continuous feed DC transferred arc system. The hot gas streamexiting the reactor contained a mixture of the decomposition products of titania includingtitanium suboxides (TiO, Ti2O3), argon (Ar), and oxygen (O2). Rapid quenching of this gasstream with dry air resulted in the production of a titania aerosol. Collection of the product tookplace in the filtration system. The quench conditions studied included pre-quenchtemperature, T1, quench rate, Rq, residence time, tau , and operating power, Ptorch . Thecharacterization of particles includes phase identification, phase content calculation, sizedistribution analysis, elemental composition analysis, and morphology examination.The range of quench conditions studied were as follows, 1300 < T1 < 1700K, 8000 < Rq < 18000K/s, 50 < tau < 80ms, 7.6 < Ptorch < 12.0kW. In general, high quench rate producedsmall size and high surface area products. Residence time had no obvious effect on product sizeand crystal phase formation. Low operating power produced a high anatase fraction product. Inall cases, spherical particles of a polymorphous mixture of anatase and rutile with no evidence ofsintering were produced. Particle size ranged from less than 10 to 300nm. A representativesample has the mode of 22.3nm, median of 28.1nm and geometric standard deviation of 1.6nm.L'effet des conditions de trempe sur les propriétés du dioxyde de titane produit par unprocédé à arc transféré a été étudié. Des poudres de TiO2 de la phase rutile et de taillemicrométrique ont été alimentées en continu dans un arc à courant continu (CC), décomposées etvaporisées. Le flux de gaz chauds sortant du réacteur contenait un mélange de produits dedécomposition : notamment de l'oxyde de titane (TiO), du Ti2O3, de l'argon (Ar) et de l'oxygène(O2). Une trempe rapide de cet écoulement de gaz avec de l'air sec a abouti à la production d'unaérosol d'oxyde de titane qui fût ensuite récupéré avec l'aide d'un système de filtration. Lesconditions opératoires étudiées comprenaient la température initiale avant la trempe, T1 , lavitesse de trempe, Rq , le temps de résidence, tau , et la puissance de l'arc, Ptorch . La phase, lateneur de la phase, la distribution de taille, la composition élémentaire ainsi que la morphologiedes poudres produites ont été obtenus.La gamme de conditions de trempe étudiées était la suivante : 1300 < T1 < 1700 K, 8000 < Rq < 18000 K/s, 50 < tau < 80 ms, 7.6 < Ptorch < 12.0 kW. En général, les taux de trempe élevés ontgénéré des poudres de petite taille et surface spécifique élevée. Le temps de résidence n'a euaucun effet évident sur la taille des poucres ainsi que sur la formation de la phase cristalline. Unefaible puissance d'opération de la torche mène à la formation de poudres ayant une forteproportion de la phase anatase. Dans tous les cas, des poudres sphériques constituées d'unmélange polymorphe d'anatase et de rutile, sans apparence de frittage, ont été produites. La taillecharactéristique des poudres varie de 10 à 300 nm. Un échantillon représentatif a montré unmode de 22.3 nm, une médiane de 28.1 nm et une écart type géométrique de 1.6 nm.
3
Yoshikawa, Naruo. "The chemical and photochemical reactivity of modified and unmodified high area titania surfaces". Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343010.
Testo completo
4
Kang, Chin-Shuo. "CONTROL OF TITANIUM DIOXIDE NANOFIBER CRYSTALLINITY, PARTICLE SIZE AND MORPHOLOGY". University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron161960479044817.
Testo completo
5
Stewart, Gregory D. "Numerical simulation of titania deposition in a cold-walled impinging jet type APCVD reactor". Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1178908165.
Testo completo
6
PENA, DONOVAN ALEXANDER. "DEVELOPMENT AND CHARACTERIZATION OF MIXED OXIDE CATALYSTS FOR THE SELECTIVE CATALYTIC REDUCTION OF NITRIC OXIDE FROM STATIONARY SOURCES USING AMMONIA". University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054307250.
Testo completo
7
Kafizas, A. G. "Combinatorial atmospheric pressure chemical vapour deposition for optimising the functional properties of titania thin-films". Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1334459/.
Testo completoAbstract (sommario):
Titanium dioxide (TiO2) is the leading material for self-cleaning applications due to its chemical inertness, mechanical robustness, durability to extended photocatalytic cycling, low cost and high photocatalytic activity. There has been a concerted effort to try and improve the material’s functional properties through impurity doping; altering the band structure and electronic transport properties. However, any improvements are difficult to optimise using traditional methods. Thin-film combinatorial methods have heralded the discovery of more than 20 new families of materials since their resurgence in the mid-90’s. Such methods enable a high diversity of states to be produced in a single deposition and are now being used more prominently to optimise the functional properties of existing materials. Atmospheric pressure chemical vapour deposition (APCVD) has been applied in a combinatorial fashion to deposit thin-films containing compositional gradients and is also the native method in which thin-films of TiO2 are mass-produced. Utilising combinatorial APCVD, we investigated N, Nb and W doped TiO2 thin-film systems. The Ndoped TiO2 system has been studied most prominently for improved visible light photocatalysis. Nitrogen can either substitute oxygen sites (substitutional doping - Ns) or enter within the TiO2 framework (interstitial doping - Ni), yet there is little consensus on which type of doping or dopant concentration yields the more active photocatalyst. Using the combinatorial APCVD approach, TiCl4 and ethyl acetate precursors were used to form the host TiO2 matrix with either NH3 or t-butylamine used as the N-sources. From three separate investigations we were able to produce combinatorial films with transitional composition/ phase gradients of (i) Ns/ Ni-doped to pure Ni-doped anatase TiO2 (0 ≤ Ns: Ti ≤ 8.4 %, 0.57 ≤ Ni: Ti ≤ 3.3 %), (ii) Ns-doped anatase TiO2 and rutile TiO2 phase mixtures (0 ≤ Ns: Ti ≤ 11 %, 0 ≤ anatase TiO2 ≤ 100 %, 0 ≤ rutile TiO2 ≤ 41 %) and (iii) pure pseudo-brookite Ti3-δO4N to pure Ni-doped anatase TiO2 phase mixtures. In tailoring high-throughput screening methods to these systems we were able to characterise large numbers of unique states across each combinatorial system and inter-relate their physical and functional properties. It was found that (i) pure Ni-doped anatase TiO2 is a more photocatalytically active material than Ns-doped anatase TiO2 under UVA and visible light (> 420 nm), (ii) un-doped anatase TiO2 is more photocatalytically active than Ns-doped anatase TiO2 under UVA light and (iii) pseudo-brookite Ti3-δO4N is a more active photocatalyst than Ni-doped anatase TiO2 under UVA light. The photocatalytic activity of Nb and W doped TiO2 solid solutions had not previously been investigated; however, their film resistivities for potential applications as more durable transparent conducting oxide materials had been. Using combinatorial APCVD we were able to produce NbxTi1-xO2 (0.0004 ≤ x ≤ 0.0194) and WxTi1-xO2 (0.0038 ≤ x ≤ 0.1380) anatase TiO2 thin-film solid solutions with transitional composition gradients. The Nbdoped system was formed from combining TiCl4, ethyl acetate and NbCl5 precursors. By characterising the film with our screening methods were we able to determine the strong functional inter-relationship between the material’s bandgap, photocatalytic activity and film resistivity in three dimensions; where an increased photocatalytic activity was associated with a lower bandgap energy and electrical resistance. The importance of oxygen vacancies on increasing charge carrier mobility presided over the number of charge carriers in the system (Nb-doping level). The W-doped system was formed from combining TiCl4, ethyl acetate and WCl6 precursors. Using high-throughput screening methods once more, the strong physical inter-relationship between the material’s Raman shift, unit cell volume and W-doping level were determined; where increased W-doping increasingly expanded the unit cell in the a/b axis and caused the prominent Raman active Eg vibrational mode of (144 cm-1) to shift to higher energies. Increased W-doping increasingly disrupted crystallisation, yielding less active photocatalysts. More interestingly however, increased preferred orientation in the (211) plane induced a greater degree of photo-induced surface wetting. Given the mechanism for the photo-induced wetting process in anatase TiO2 is, to our knowledge, yet to be studied, the trends highlighted the importance of the (211) plane in this process. Films synthesized by the combinatorial APCVD route, analysed in conjunction with high-throughput characterisation methods, provide a shortcut to understanding and optimising the functional properties of composition/ phase space.
8
Marszewski, Michal. "Development of highly porous crystalline titania photocatalysts". Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1476281107453411.
Testo completo
9
Hodgkinson, John L. "Atmospheric pressure glow discharge plasma enhanced chemical vapour deposition of titania and aluminium based thin films". Thesis, University of Salford, 2009. http://usir.salford.ac.uk/26717/.
Testo completoAbstract (sommario):
Atmospheric pressure glow discharge (APGD) plasma CVD was used to deposit thin films of titania at 200 °C using two different precursors. The resulting films were characterised using techniques including XPS, RBS and XRD. It was established that annealing at temperatures as low as 275 °C produced crystalline films that were photocatalytically active. When annealed at 300 °C, the photoactivity was greater than that of a commercially available "self-cleaning" titania film. The effects of the different precursors, annealing times and temperatures on the crystallinity and photoactivity are discussed. This thesis also describes first reported deposition of aluminium oxide thin films by APGD, plasma-enhanced CVD. This approach allows deposition at substantially lower substrate temperatures than normally used in atmospheric pressure based processing. The films are analysed by SEM, XPS, RBS, XRD, and optical properties. It is demonstrated that the APGD approach yields films which are essentially smooth, conformal and free from pinholes or other imperfections. Further novel work was undertaken exploring the deposition of composite metal/ metal oxide thin films using APGD CVD. The described approach employs a parallel- plate dielectric barrier configuration, and the deposition of such materials is discussed with respect to their influence on discharge conditions. Controlled and variable composition films were produced based on aluminium which showed metallic-like reflection (up to 60% visible), and were conductive (~1 O per square). The films were analysed by RBS, SEM, AFM and optical spectroscopy. This new class of APGD-CVD derived thin film material, when combined with the associated low thermal load and attractions for industrial scaling, offers significant potential for new applications. The studies resulted in three full papers, and four posters.
10
Pettit, Sandra L. "Investigation of TiO2 and InVO4-TiO2 Semiconductors for the Photocatalytic Degradation of Aqueous Organics". Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5103.
Testo completoAbstract (sommario):
Water is a vital natural resource. To develop more sustainable water systems, we must focus efforts on the removal of persistent contaminants. Aqueous organic contaminants include azo dyes, halogenated organics (e.g. pesticides), and algal and bacterial metabolites. The latter are common to surface waters and freshwater aquaculture systems and can cause taste and odor problems. Two of the principal organoleptic compounds are geosmin and 2-methylisoborneol (MIB). Traditional oxidation treatment methods, utilizing chlorine, hydrogen peroxide, and potassium permanganate, have been employed with varying levels of efficacy for removal of these and other organic contaminants. Advanced Oxidation Processes (AOPs) have greater potential for the removal of persistent contaminants than traditional methods due to their higher pollutant removal rates, their ability to degrade a variety of organic material, and their ability to completely mineralize compounds [1].
An emerging AOP technology is the use of titania based photocatalysts for water treatment. Titanium dioxide (TiO2) is an effective, inexpensive, and stable photocatalyst used for the decomposition of aqueous organics. Titania is primarily activated by the ultraviolet portion of the spectrum due to its energy band gap of 3.0-3.2 eV (depending upon crystalline structure). Photocatalytic efficiency can be enhanced or tuned through the use of semiconductor dopants and the variance of titania crystal structure (i.e. anatase to rutile ratios). Metal oxides, like indium vanadate (InVO4), may enhance reaction rates through new interfacial reaction sites and electron scavenging, transport, and storage. InVO4 has been shown to have four sub-bandgap transitions, of which three are in the visible range [2]. In this work, the synthesis of InVO4-TiO2 composite semiconductors is examined to shift photo-initiation into the visible portion of the spectrum. Parametric studies of the visible spectrum photodegradation of methyl orange, an azo dye, and 2-chlorophenol provide a basis for analysis. Methyl orange was utilized to ascertain the effect of pure and mixed phase titania in the semiconductor composites.
The TiO2 photodegradation of geosmin and MIB has been previously demonstrated in small-scale batch slurry reactions. Slurry systems require the downstream separation of catalyst from the liquid. Laboratory trials use centrifugation or micro-filtration. Alternatively, immobilization of the photocatalyst could allow scale-up of the process. Here, titania was immobilized on glass plate substrates using an ethanol spray technique.
Finally, naturally tainted waters may contain a number of constituents in addition to the target compounds. In recirculating aquaculture systems, the water contains natural organic matter (NOM), ammonia, nitrite/ nitrate, and carbonate species. These constituents may block light penetration, block reaction sites, scavenge hydroxyl radicals, or affect the surface chemistry of the catalyst. Further, geosmin and MIB concentrations are extremely low, in the ppt range. Naturally tainted waters from MOTE Marine Laboratory Aquaculture Research Park are treated in the laboratory and in situ to demonstrate TiO2 degradation efficiency for trace concentration geosmin and MIB degradation in a complex water matrix.
11
Karslioglu, Osman. "Photocatalytic And Photoelectrochemical Water Splitting Over Ordered Titania Nanotube Arrays". Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610388/index.pdf.
Testo completoAbstract (sommario):
The objective of this study was to investigate photocatalytic water splitting over ordered TiO2 nanotube arrays. Synthesis of ordered nanotube arrays of titania, as a micron thick film on a titanium foil was accomplished by electrochemical anodization methods defined in the literature. Effect of two
types of electrolyte (aqueous and organic) on the micro-morphology was observed by scanning electron microscopy. Optimum anodization times for the TiO2 nanotube electrodes, synthesized in ethylene glycol electrolyte, were different for acidic and basic electrolytes. Optimum times were determined as 2 hours in acidic and 4 hours in basic solutions. An H-type cell was constructed using a two side anodized titanium foil aiming the photocatalytic, stoichiometric and separate evolution of H2/O2 from the splitting of water. Gas evolution was observed at a rate of approximately 1 mL/h in the anode and 0.5 mL/h in the cathode, which implied the reverse of the desired stoichiometry. As the surface was corroded in that experimental conditions, electrochemical properties of the synthesized films were investigated by cyclic voltammetry
(CV) at milder conditions. CV showed the reduction of Ti4+ to Ti3+, beginning at -0.2 V (vs. Ag/AgCl). Since the process is accompanied by proton intercalation to the oxide, non-annealed samples showed higher currents in that region. Non-annealed samples showed no photocurrent. Photocurrents obtained in this work, on the average 0.1-0.2 mA/cm2, were one order of magnitude lower than the similar studies in the literature.
12
Sheerin, Ephraim A. "Synthesis of Ethanol from High Pressure Syngas over Rhodium-Based Catalysts". University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397476742.
Testo completo
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Pickering, Jon W. "Applications of Optical Properties from Nanomaterials for Enhanced Activity of a Titania Photocatalyst under Solar Radiation". Scholar Commons, 2015. https://scholarcommons.usf.edu/etd/5760.
Testo completoAbstract (sommario):
In recent years, employing advanced oxidation processes (AOPs) as a means of wastewater remediation has emerged as a promising route towards maintaining a sustainable global water management program. The heterogeneous photocatalytic oxidation process has been of particular interest due to the prospective of utilizing solar radiation as the driving force behind the degradation of pollutants. Of the photocatalyst studied to date, TiO2 remains the most attractive material for environmental applications due to its affordability, stability, biocompatibility and high quantum yield. A key draw back however is roughly only 5% of solar radiation incident on earth can provide the energy required (3.0-3.2 eV) to generate the electron-hole pairs necessary for photo-oxidation. As a means to improve the process under solar irradiance, optical properties such as surface plasmon resonance of metallic nanoparticles and upconversion luminescence of rare earth ions have been exploited for improved light harvesting as well as the generation of more usable UV light from lower energy photons. In order to explore these phenomena and their role in the enhancement of this AOP, the photocatalytic degradation of organic dyes was studied under various conditions employing Degussa P25 TiO2 as the photocatalyst. Ag nanocubes, Ag-Pd core-shell nanoparticles and YAG:Yb+3,Er+3 served as the dopants for the various studies which resulted in enhanced degradation rates, insight into the applicability of utilizing Yb+3 as sensitizing ion under solar radiation and a novel core-shell nanoparticle synthesis.
14
Yilmaz, Emre. "Sensitization Of Sol-gel Derived Titania-silica Photocatalytic Thin Films With Ascorbic Acid". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614226/index.pdf.
Testo completoAbstract (sommario):
The photocatalytic activity of semiconductor metal oxides can be improved by the addition of sensitizer which enhances the band gap by considerable red shift of the absorption edge of semiconductor. In the present study, the effect of ascorbic acid as sensitizer on the photocatalytic activity of titania-silica binary mixtures was studied. The SiO2-TiO2 mixtures having 50wt%Ti:Si composition were prepared with sol-gel method. The surface area and porosity of the samples were modified by using various amounts of polyethylene glycol (PEG) as template. The thin films of the samples were obtained by dip coating of glass plates to colloidal solutions. The samples were characterized by methylene blue adsorption method and UV-Vis spectrophotometry. The photocatalytic activities of the samples were measured with methylene blue degradation, methyl orange degradation and direct water splitting in the presence and absence of ascorbic acid. Increase in the surface area and reaction rate with increasing PEG addition until a threshold value was observed. Highest methylene blue degradation activity was observed for 27g PEG added sol-gel derived film and surface area of this film is measured as 44m2/m2. Ascorbic acid presence shows a significant increase in the photocatalytic degradation activity of methyl orange. The sensitization effect of ascorbic acid was also compared with the effect of EDTA. It was found that the effect of ascorbic acid on the methyl orange degradation rate is significantly higher than the effect of EDTA. However, the effect of EDTA is more pronounced in water splitting reaction.
15
Frank, Marla Lea. "Novel strategies for design of high temperature titania-based gas sensors for combustion process monitoring". Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1063808231.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xviii, 279 p.; also includes graphics (some color). Includes bibliographical references (p. 256-279).
16
Lee, Seungjin. "Hydrolysis of organophosphorous esters induced by nanostructured titania-based replicas of diatom microshells". Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-05192006-110527/.
Testo completo
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Sharma, Gaytri. "Synthesis and characterization of nanostructured Tungsta/Vanadia/Titania catalysts for the oxidation of dimethyl sulfide". Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1228163508.
Testo completo
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Li, Haitao. "Synthesis of Titanium Dioxide Photocatalyst with the Aid of Supercritical Fluids". Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4912.
Testo completoAbstract (sommario):
Titanium Dioxide (TiO2) emerged as one of the most popular photocatalysts since 1970's. However, its photocatalytic activity requires UV irradiation due to its large band gap unless further functionalization or modifications are performed. Furthermore, recovery issue has always been a major drawback, if the more effective form nano particles are utilized.
The key objectives of this research were synthesizing new TiO2 based photocatalyst systems that are effective with both the UV and the visible light while utilizing novel superior environmentally friendly techniques enabling development of nano-structured photocatalysts that can be easily recovered. In this dissertation research, highly porous nano-structured TiO2/WO3/Fe3+ aerogel composite photocatalyst are prepared, characterized, and tested for model photocatalytic reactions. The photocatalyst structure is tailored to capture environmental pollutants and enable their decomposition in-situ under both UV and visible light through photodecomposition to smaller benign substances.
A novel and green method is applied to prepare unique surfactant templated aerogel photocatalysts with highly porous nano-structure, high surface area, and tailored pore size distribution. Sol-gel process followed by supercritical fluids extraction and drying allowed synthesis of highly porous composite TiO2/WO3 aerogel. The surfactant template was completely removed with the aid of a supercritical solvent mixture followed with heat treatment. Fe3+ ion was incorporated within the composite aerogel photocatalyst as dopant either at the sol-gel co-precipitation step or at a subsequent supercritical impregnation process. Supercritical drying followed with heat treatment results in titanium dioxide with the most profound anatase crystal structure. Neutral templates were used to further enhance retention and tuning of the nano-pore structure and the surface properties. The Nitrogen adsorption-desorption isotherms methods were used to follow the removal of solvents and templates as well as tracking the textural properties of the synthesized aerogel. Surfactant-templated aerogels, which show remarkable thermal stability and uniform pore size distribution, exhibit specific surface areas three times more than the highly optimized commercial nano-particles, industry standard TiO2 photocatalyst Degussa P-25, even after heat treatment.
The synthesized catalysts were characterized by using SEM, FIB, EDS, XRD, XPS and porosimetry prior to post photocatalytic activity evaluation through a model photocatalytic reaction. The band gaps of the catalysts were also determined by using diffuse reflectance spectroscopy.
The model reaction employed Methylene Blue (MB) photo-oxidation under UV and visible light. Resulting aerogel TiO2/WO3/Fe3+ photocatalyst exhibited comparable photocatalytic capability to Degussa P25 under UV light exposure and offered much superior photocatalytic capability under visible light exposure.
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Zhou, Ming. "Novel photocatalytic TiO2-based porous membranes prepared by plasma-enhanced chemical vapor deposition (PECVD) for organic pollutant degradation in water". Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS090/document.
Testo completoAbstract (sommario):
Le dépôt chimique en phase vapeur assisté par plasma est appliqué pour préparer des couches minces amorphes de TiO2 à basse température. Un recuit à 300 °C pendant un temps minimum de 4,5 h permet de former la phase cristalline anatase. Les principales caractéristiques de ces couches minces comme leur structure cristalline, leur microstructure, leur largeur de bande interdite et leur hydrophilie de surface, sont déterminées. Leurs performances fonctionnelles comme photocatalyseurs sont d'abord examinées selon le test breveté par Pilkington, consistant à éliminer sous irradiation UV de l'acide stéarique préalablement adsorbé sur les couches de TiO2 ici déposées sur des plaquettes de silicium. Des membranes M100 (couche continue de TiO2) et M800 (couche de TiO2 couvrant les grains de support) sont préparées sur les couches de surface macroporeuses de supports poreux en alumine, de tailles moyennes de pores respectives, 100 nm et 800 nm. Ces membranes sont testées en condition "statique", avec la diffusion d'un soluté organique dilué dans l'eau. Pour le bleu de méthylène, on montre que la quantité de composé détruit par unité de surface de membrane et par unité de temps est égale à 2 × 10-8 mol m-2 s-1 pour la membrane M100 et 1 × 10-8 mol m-2 s- 1 pour la membrane M800. Ces membranes sont également testées dans des conditions "dynamiques", à savoir en procédé baromembranaire, avec deux configurations différentes (couche photocatalytique du côté de l'alimentation ou du côté du perméat) et trois composés organiques différents (bleu de méthylène, acide orange 7 et phénol). La modélisation du procédé (adsorption et réaction photocatalytique) est finalement réalisée à partir des données expérimentales disponiblesPlasma-enhanced chemical vapor deposition is applied to prepare amorphous TiO2 thin films at low temperature. Post-annealing at 300 °C for minimal staying time 4.5 h is required to form crystalline anatase phase. Characteristics of the TiO2 thin films including crystalline structure, microstructure, band gap and surface hydrophilicity, are determined. Functional performance of these anatase thin films as photocatalysts is first examined with patented Pilkington assessment by removing, under UV irradiation, stearic acid initially adsorbed on TiO2 layers here deposited on silicon wafers. Membranes M100 (TiO2 continuous layer) and M800 (TiO2-skin on support grain) are prepared on the macroporous top layer of porous alumina supports with an average pore size of 100 nm and 800 nm, respectively. These membranes are tested in “static” condition under the effect of diffusion of an organic solute in water. For Methylene Blue it is shown that the quantity of destroyed compound per unit of membrane surface area and per unit of time is equal to 2×10−8 mol m-2 s-1 for M100 and 1×10−8 mol m-2 s-1 for M800. These membranes are also tested in “dynamic” conditions, i.e. pressure-driven membrane processes, with two different configurations (photocatalytic layer on the feed side or on the permeate side) and three different organics (Methylene Blue, Acid Orange 7 and phenol). Process modelling (adsorption and photocatalysis reaction) is finally carried out from the available experimental outputs
20
Miller, Duane D. "In Situ Infrared Spectroscopy Study of Gold Oxidation Catalysis". University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1152205534.
Testo completo
21
Kumar, Prateek. "Heat Capacity and Oxidation Kinetic Studies of Fe-Ti Composite Metal Oxide (ITCMO) using Simultaneous Differential Scanning Calorimetry and Thermogravimetric Analysis". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1502723527531035.
Testo completo
22
Liu, Chang. "The spectroscopic and structural characterization of chlorine modification of MoOx catalysts supported over silica/titania mixed oxides for the oxidative dehydrogenation of ethane and propane". Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1095645498.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xiv, 157 p.; also includes graphics. Includes bibliographical references (p. 145-153).
23
Vernon, Jonathan P. "Morphology-preserving chemical conversion of bioorganic and inorganic templates". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/47521.
Testo completoAbstract (sommario):
The generation of nanostructured assemblies with complex (three-dimensional, 3D) self-assembled morphologies and with complex (multicomponent) tailorable inorganic compositions is of considerable technological and scientific interest. This research demonstrates self-assembled 3D organic templates of biogenic origin can be converted into replicas comprised of numerous other functional nanocrystalline inorganic materials. Nature provides a spectacular variety of biologically-assembled 3D organic structures with intricate, hierarchical (macro-to-micro-to-nanoscale) morphologies. Morphology-preserving chemical conversion of such readily available, structurally complex templates will provide a framework for chemical conversion of synthetic organic templates and, potentially, production of organic/inorganic composites. Four research thrusts are detailed in this dissertation. First, chemical conversion of a nanostructured bioorganic template into a multicomponent oxide compound (tetragonal BaTiO₃ via layer-by-layer surface sol-gel coating and subsequent morphology-preserving microwave hydrothermal processing was demonstrated. Second, photoluminescence was imparted to bioorganic template structures through morphology-preserving chemical conversion to exhibit both the dramatic change in properties such processing can provide, and the potential utility of chemically transformed templates in anti-counterfeiting / authentication applications. Third, the reaction mechanism(s) for morphology-preserving microwave hydrothermal conversion of TiO₂ to BaTiO₃, were studied with the aid of Au inert markers on single crystal rutile TiO₂. Finally, constructive coating techniques (SSG) and moderate temperature (< 500C) heat treatments were utilized to modify and replicate structural color and were coupled with deconstructive focused ion beam microsurgery to prepare samples for microscale structure/property interrogation. Specifically, the effects of coating thickness and coating composition on reflection spectra of structurally colored templates were examined. Also, the effects of the replacement of natural material with higher index of refraction inorganic materials on optical properties were studied. The three processing research thrusts constituting chapters 1, 2 and 4 take advantage of moderate temperature processing to ensure nanocrystalline materials, either for shape preservation or to prevent scattering in optical applications. The research thrust presented in chapter 3 examines hydrothermal conversion of TiO₂ to BaTiO₃, not only to identify the reaction mechanism(s) involved in hydrothermal conversion under morphology-preserving conditions, but also to introduce inert marker experiments to the field of microwave hydrothermal processing.
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Torres, Heredia Victor Elias. "Silver nanostructures: chemical synthesis of colloids and composites nanoparticles, plamon resonance properties and silver nanoparticles monolayer films prepared by spin-coating". Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/52807.
Testo completoAbstract (sommario):
El presente trabajo tiene como objetivo desarrollar en solución acuosa y a tem-peratura ambiente, rutas de síntesis química coloidal de nanopartículas de plata y nano-partículas compuestas estables. Se obtienen nanopartículas de plata reproducibles, con un control morfológico de tamaño y forma durante el proceso de síntesis. Llevamos a cabo el estudio de las propiedades ópticas (espectros de absorción de las resonancias de plasmones superficiales (SPR)) que caracterizan a una determinada forma y tamaño. El análisis incluye estructuras nanométricas de plata de diferentes tamaños, en ambientes diversos y formas diferentes, como esferas, prolates, y prismas de diferente sección transversal, etc
Se ha demostrado que la síntesis química produce coloides de nanopartículas de plata esféricas y anisotrópicas estables. La morfología y estabilidad de las nanopartícu-las coloidales son estudiadas mediante técnicas de espectroscopia y microscopía elec-trónica. El rol y concentración necesaria de cada uno de los reactivos para producir co-loides estables mediante síntesis química son determinadas. Se ha demostrado que, con-trariamente a las opiniones actualmente expresadas en la literatura, es posible controlar el tamaño de las nanopartículas de plata y obtener coloides de nanopartículas de plata esféricas y anisotrópicas estables por largo tiempo, utilizando una ruta de síntesis quí-mica sencilla y una baja concentración de reactivos estabilizadores (PVP).
Recubrimientos de nanopartículas esféricas de plata estabilizadas con polivinilpirroli-dona (PVP) sobre substratos de vidrio óptico son preparados mediante el proceso de spin-coating y un posterior tratamiento térmico.
Diferentes morfologías tipo core-shell de Ag@SiO2 son preparados mediante un método químico simple y rápido, sin necesidad de adicionar reactivos de acoplamiento o modificadores superficiales de la sílice. Proponemos mecanismos de reacción para la preparación de diferentes nano-estructuras tipo core-shell de plata-sílice. Las nanopartí-culas compuestas de sílice-plata muestran unas propiedades de absorción de resonancia plasmónica muy evidentes. El trabajo de éste capítulo ha sido realizado en colaboración con Juan C. Flores, quien desarrolló la ruta de síntesis como parte de sus estudios de doctorado.
Por último, una modificación del método sol-gel es empleada para la prepara-ción de nanopartículas de TiO2, y partículas compuestas de Ag@TiO2, SiO2@TiO2-Ag y SiO2@Ag@TiO2. Diferentes morfologías tipo core-shell son preparadas mediante un método químico simple y rápido sobre un substrato óxido, sin necesidad de adicionar agentes de acoplamiento o modificaciones superficiales. Las evidentes propiedades de absorción plasmónica de las nanopartículas de plata mostradas por las partículas com-puestas han demostrado la presencia de plata metálica sobre la titania, sin la posterior oxidación de la capa de plata por el contacto directo con la titania (TiO2). Esta evidencia es confirmada por la técnica de microscopía electrónica de alta resolución. Las propie-dades de absorción plasmónica de las partículas compuestas hacen a estos materiales muy prometedores para aplicaciones foto-catalíticas.The present work aims to develop chemical synthesis routes of stable colloidal silver nanoparticles and composites nanoparticles in aqueous solution at room tempera-ture. We obtain reproducible morphological control of silver nanoparticles size and shape during synthesis solely by solution chemistry and carry out the study of the opti-cal properties (surface plasmon resonances (RPS) absorption spectra) which character-ize a specific shape and size. The analysis includes silver nanosized bodies of different size, in diverse environments and of various shapes, as spheres, prolates, and prisms of different transversal section, etc. Synthetic wet chemistry routes yielding stable colloids of spherical and aniso-tropic silver nanoparticles are demonstrated, and the morphology and stability of the colloidal nanoparticles studied extensively through spectroscopy and electron micros-copy techniques. The role of each reagent and the concentrations required to obtain sta-ble colloid via these wet chemical routes is determined. It was shown that, contrary to commonly expressed opinions in the literature, it is possible to control the particle size of silver nanoparticles and obtain long-term sable colloids of both spherical and aniso-tropic silver nanoparticles using simple chemical routes and low concentration of stabi-lizing agent (PVP). Films of polyvinylpyrrolidone (PVP) stabilized spherical silver nanoparticles are also prepared, by using spin coating on standard optical glass plates and subsequent thermal processing. Different core-shell type morphologies of Ag@SiO2 are also produced using a simple and rapid chemical method, without using added coupling agents or surface modifications of silica. We propose reaction mechanisms for the formation of the dif-ferent silica-silver core-shell nanostructures. The silica-silver composite nanoparticle display clear plasmonic resonance absorption properties. This chapter work has been done in collaboration with PhD student Juan C. Flores who developed the synthesis route as part of his doctoral studies. Finally, a sol-gel chemistry approach was used to fabricate nanoparticles in the systems TiO2, Ag@TiO2, Ag@TiO2-SiO2 and TiO2@Ag@SiO2. Different core-shell morphologies are produced using a simple and rapid chemical method. without using added coupling agents or surface modifications of the oxide substrate. Clear silver na-noparticle plasmonic absorption properties shown by the composite nanoparticles demonstrate the formation of metallic Ag, without the oxidation of Ag nanoshell in di-rect contact with TiO2, evidence confirmed also by high resolution electron microscopy. The plasmonic absorption properties of the composites nanoparticles make them a promising material for photocatalytic applications.
25
Drews, Aaron M. "Control of Thermal Expansion Coefficient of a Metal Powder Composite via Ceramic Nanofiber Reinforcement". University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1248114951.
Testo completo
26
Klettlinger, Jennifer Lindsey Suder. "Fischer-Tropsch Cobalt Catalyst Improvements with the Presence of TiO2, La2O3, and ZrO2 on an Alumina Support". University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1333981467.
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27
Nagpure, Suraj R. "SYNTHESIS OF TITANIA THIN FILMS WITH CONTROLLED MESOPORE ORIENTATION: NANOSTRUCTURE FOR ENERGY CONVERSION AND STORAGE". UKnowledge, 2016. http://uknowledge.uky.edu/cme_etds/67.
Testo completoAbstract (sommario):
This dissertation addresses the synthesis mechanism of mesoporous titania thin films with 2D Hexagonal Close Packed (HCP) cylindrical nanopores by an evaporation-induced self-assembly (EISA) method with Pluronic surfactants P123 and F127 as structure directing agents, and their applications in photovoltaics and lithium ion batteries. To provide orthogonal alignment of the pores, surface modification of substrates with crosslinked surfactant has been used to provide a chemically neutral surface. GISAXS studies show not only that aging at 4°C facilitates ordered mesostructure development, but also that aging at this temperature helps to provide orthogonal orientation of the cylindrical micelles which assemble into an ordered mesophase directly by a disorder-order transition. These films provide pores with 8-9 nm diameter, which is precisely the structure expected to provide short carrier diffusion length and high hole conductivity required for efficient bulk heterojunction solar cells. In addition, anatase titania is a n-type semiconductor with a band gap of +3.2 eV. Therefore, titania readily absorbs UV light with a wavelength below 387 nm. Because of this, these titania films can be used as window layers with a p-type semiconductor incorporated into the pores and at the top surface of the device to synthesize a photovoltaic cell. The pores provide opportunities to increase the surface area for contact between the two semiconductors, to align a p-type semiconductor at the junction, and to induce quantum confinement effects.
These titania films with hexagonal phase are infiltrated with a hole conducting polymer, poly(3-hexylthiophene) (P3HT), in order to create a p-n junctions for organic-inorganic hybrid solar cells, by spin coating followed by thermal annealing. This assembly is hypothesized to give better photovoltaic performance compared to disordered or bicontinuous cubic nanopore arrangements; confinement in cylindrical nanopores is expected to provide isolated, regioregular “wires” of conjugated polymers with tunable optoelectronic properties, such as improved hole conductivity over that in bicontinuous cubic structure. The kinetics of infiltration into the pores show that maximum infiltration occurs within less than one hour in these films, and give materials with improved photovoltaic performance relative to planar TiO2/P3HT assemblies. These oriented mesoporous titania films are also used to develop an inorganic solar cell by depositing CdTe at the top using the Close Spaced Sublimation (CSS) technique. A power conversion efficiency of 5.53% is measured for heterostructures built using mesoporous titania films, which is significantly enhanced relative to planar TiO2/CdTe devices and prior reports in the literature. These mesoporous titania films have a great potential in inorganic solar cell development and can potentially replace CdS window layers which are conventionally used in inorganic CdS-CdTe solar cells. The last part of the dissertation addresses layer-by-layer synthesis to increase the thickness of mesoporous titania films with vertically oriented 2D-HCP nanopores, and their use in lithium ion batteries as negative electrodes because of advantages such as good cycling stability, small volume expansion (~3%) during intercalation/extraction and high discharge voltage plateau. The high surface area and small wall thickness of these titania films provide excellent lithium ion insertion and reduced Li-ion diffusion length, resulting in stable capacities as high as 200-250 mAh/g over 200 cycles.
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Coutinho, Cecil A. "Multi-functional composite materials for catalysis and chemical mechanical planarization". [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002980.
Testo completo
29
Pappas, Dimitrios. "Synthesis and Characterization of Novel Titanium Oxide Nanotubes - Applications as Catalyst Support for the Selective Catalytic Reduction of Nitrogen Oxides". University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397233960.
Testo completo
30
Watson, Rick Bruce. "The physical, chemical, and structural characteristics of MoOx catalysts supported over the binary oxide of Silica/Titania and relationships to their behavior in the oxidative dehydrogenation of Propane and Ethane /". The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu14864018952095.
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31
Zibin, Hai. "Modification of Titania with Gold-Copper Bimetallic Nanoparticles and Preparation of Copper-Based Photocatalysts : Application in Water Treatment". Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00926757.
Testo completoAbstract (sommario):
Photocatalysis is recently extensively studied because it implies a variety of potential industrial applications ranging from the hydrogen generation of water splitting to the treatment of waste water. Among all the semiconductors, TiO2 has attracted the most attention. But the rate of the electron-hole recombinations is very important and TiO2 is active only under UV light. Various methods are developed to enhance the photoactivity of TiO2. Other semiconductors like copper oxides and copper sulfides also attracted attention due to their lower band-gaps which allow applications in solar photocatalysis. In this work, different kinds of photocatalysts were developed and studied: surface modified TiO2 with metal nanoparticles and copper sulfides and oxides. The nanostructures were characterized by different techniques: HRTEM, SEM, XRD, XPS, HAADF-SEM, and TRMC. Their photocatalytic activity was studied for degradation of model pollutants: phenol, rhodamine B and methyl orange. Different chemical and radiolytic methods have been investigated to modify the surface of TiO2 by mono- and bimetallic (Au, Cu and Au-Cu) nanoparticles in the aim to improve its photocatalytic activity. The best results in term of photocatalytic activity have been obtained with reduction of THPC (tetrakis (hydroxymethyl) phosphonium chloride) and with radiolytic reduction after deposition with urea. Titania surface modification with Au, Cu and bimetallic Au-Cu NPs enables the increase of the photocatalytic activity under UV light. We have found that very small amounts of metal (0.5% wt.) can activate titania for photocatalytic applications, thus the costs of photocatalyst preparation are relatively low. Radiolytic syntheses of non-TiO2 photocatalysts including Cu2O and CuS nanostructures with different morphologies have been developed. The photocatalytic activity of the synthesized photocatalysts has been studied. Truncated octahedral Cu2O exhibit an excellent photocatalytic activity under visible illumination. CuS nanotubes (NTs) exhibit both a high ability to adsorb dyes and a photocatalytic activity under visible light.
32
Das, Saikat. "FUNDAMENTAL STUDIES OF SURFACTANT TEMPLATED METAL OXIDE MATERIALS SYNTHESIS AND TRANSFORMATION FOR ADSORPTION AND ENERGY APPLICATIONS". UKnowledge, 2015. http://uknowledge.uky.edu/cme_etds/48.
Testo completoAbstract (sommario):
This work addresses fundamental aspects of designing templates and curing conditions for the synthesis of mesoporous metal oxide thin films. The first section addresses selection of cationic-carbohydrate surfactant mixtures to synthesize templated silica thin films for selective adsorption of simple carbohydrates based on molecular imprinting. Nuclear magnetic resonance and fluorescence spectroscopy results suggest a novel structure for mixtures of alkyl glucopyranosides or xylopyranosides with cationic (trimethylammonium) surfactants. Despite thermodynamically favorable mixing, the carbohydrate headgroups in the mixed micelle adopt an inverted configuration with their headgroups in the micelle core, and therefore are inaccessible for molecular imprinting. This orientation occurs even when the alkyl tail length of the carbohydrate surfactant is greater than that of the cationic surfactant, but this limitation can be overcome by introducing a triazole linker to the carbohydrate surfactant. The next section addresses the effects of aging conditions on the structural and chemical evolution of surfactant templated silica thin films. The third section describes the synthesis of carbohydrate/cationic surfactant imprinted silica thin films with orthogonally oriented cylindrical pores by modifying the glass surface with a random copolymer. The last part of the dissertation addresses the effect of pore orientation on the transformation mechanism of block copolymer templated titania thin films during high temperature curing. Mesoporous titania thin films can be used for photochemical and solar cell applications, but doing so requires addressing the tradeoff between loss of mesostructural order and growth of crystallinity during thermal treatment. By using advanced x-ray scattering techniques it has been shown that the titania films with vertically oriented pores can better withstand the anisotropic stress that develops during thermal treatment compare to titania films with mixed pore orientation. For instance, films with parallel or mixed pores can only be heated at 400 °C for a brief time (~10 min) without loss of order, while orthogonally oriented films can be heated at 550 °C or greater for extended time periods (on the order of hours) without significant loss of long-range mesopore structure. Detailed kinetic modeling was applied to enable the comparison of activation energy for mesostructure loss in films as a function of pore orientation and thickness.
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Inturi, Siva Nagi Reddy. "Nano-Catalyst Synthesized by Flame Spray Pyrolysis (FSP) for Visible Light Photocatalysis". University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511884949728835.
Testo completo
34
Awaluddin, Amir. "Fundamental studies of chemical vapour deposition processes : Far-IR synchrotron studies of the adsorption of tim oxide precursors on tin oxide and direct liquid injection CVD growth of titania thin films on silicon". Thesis, University of Salford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272929.
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35
Woods, Matthew P. "Activity and Selectivity in Oxidation Catalysis". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228175906.
Testo completo
36
Wang, Junwei. "Chemical doping of metal oxide nanomaterials and characterization of their physical-chemical properties". Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1333829935.
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37
Kandasamy, Ispran S. "Metalorganic chemical vapour deposited titanium dioxide thin films". Thesis, Brunel University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235909.
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38
Jacobsen, S. M. "Chemical, catalytic and spectroscopic properties of titanium (II)". Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381356.
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39
Johnson, Saccha Ellen. "Atmospheric pressure chemical vapour deposition of titanium nitride from titanium tetrachloride and ammonia". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242208.
Testo completo
40
Bastien, Samuel. "Selective chemical stripping of titanium aluminum nitride coating from titanium substrate using hydrogen peroxide and potassium oxalate". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110474.
Testo completoAbstract (sommario):
Titanium Aluminum Nitride (TiAlN) is an important industrial coating that improves hardness and corrosion resistance. The objective of the present work is to develop chemical methods which selectively remove TiAlN coatings deposited on Titanium substrates. The selected stripping solution consists of hydrogen perox¬ide (H2O2) and potassium oxalate (K2C2O4). Coupons of Ti-6-4 coated with a notional 10 micron thick coating of TiAlN were exposed to a stripping solution at varying temperature and compositions. Overall, it was found that increasing the temperature of reaction or the concentration of reactants led to an increase in stripping rate of the coating and substrate. The selectivity also increased with an increase in tempera¬ture or potassium oxalate concentration, but decreased with an increase in hydrogen peroxide concentration. The highest stripping rate that was obtained for the coating was of 39 µm/hr at a tempe¬rature of 75oC, a concentration of hydrogen peroxide of 5.9 mol/L and a potassium oxalate concentra¬tion of 0.226 mol/L. At the same conditions, uncoated samples were found to be stripped at a rate of 6.6 µm/hr. The best selectivity that was obtained was of 6.8, at a potassium oxalate concentra¬tion of 0.226 mol/L, a hydrogen peroxide concentration of 4.4 mol/L and a 75oC temperature. It was also found that the ratio of Ti:Al in the coating had a major effect on its chemical resistance to H2O2 and K2C2O4 mixtures.Titanium Aluminum Nitride (TiAlN) est un revêtement industriel important puisqu'il améliore la dureté et la résistance à la corrosion. L'objectif de ce travail est de développer des techniques chimiques qui enlèvent de façon sé¬lective des revêtements de TiAlN déposés sur des substrats de Titane. La solution chimique sélection¬née consiste de peroxyde d'hydrogène (H2O2) et d'oxalate de potassium (K2C2O4). Des échantillons de Ti-6-4 couverts d'une couche de TiAlN d'une épaisseur notionnelle de 10 micromètres ont été exposés à plusieurs solutions chimiques avec des températures et concentrations variées. De façon générale, nous avons trouvé que si on augmentait la température de la réaction ou la concentration des réactants, cela faisait augmenter les vitesses de dégradation du revêtement et du substrat. La sélectivité augmentait aussi avec une hausse de la température ou de la concentration d'oxalate de potassium, mais diminuait avec une hausse de la concentration de peroxyde d'hydrogène. La plus haute vitesse de dissolution du revêtement qui a été obtenue était de 39 µm/hr à une température de 75oC, une concentration de peroxyde d'hydrogène de 5.9 mol/L et une concentration d'oxalate de potassium de 0.226 mol/L. À des conditions similaires, le substrat se dissolvait à une vitesse de 6.6 µm/hr. La meilleure sélectivité obtenue était de 6.8, à une concentration d'oxalate de potassium de 0.226 mol/L, une concentration de peroxyde d'hydrogène de 4.4 mol/L et une température de 75oC. Nous avons aussi trouvé que le ratio de Ti:Al dans le revêtement a un impact majeur sur sa résistance chimique aux solutions de H2O2 et de K2C2O4.
41
Yamin, Yas. "Elaboration de photocatalyseurs à base de nanotubes de TiO2 modifiés par WO3 et ZnO : applications à l'élimination de méthyléthylcétone et de l'H2S sous illumination UV-A et solaire". Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00869959.
Testo completoAbstract (sommario):
Il est couramment admis que le niveau de pollution dans l'environnement intérieur pouvait dépasser le niveau de pollution extérieur. C'est la raison pour laquelle la qualité de l'air intérieur est devenue une préoccupation sociétale importante en raison de la durée croissante que nous passons dans ces environnements. Les procédés d'oxydation avancée (POA), parmi lesquels l'oxydation photocatalytique, sont des techniques pertinentes pour la purification de l'air. En photocatalyse, les nanotubes de titane montrent un intérêt tout particulier en raison de leurs propriétés intrinsèques spécifiques de par leurstructure tubulaire. Ce matériau unidimensionnel engendre un rapport surface/volume important qui donne accès à une surface spécifique et à des capacités d'adsorption importantes, mais aussi à des propriétés de transport électronique accrues. Deux molécules modèles gazeuses ont été retenues, la méthyléthylcétone (MEC) et le sulfure de dihydrogène (H2S). Ces molécules diffèrent de par leur composition chimique (présence ou non d'hétéroatomes) et leurs propriétés physico-chimiques et reflètent différentes catégories de pollutions chimiques et olfactives. Afin d'améliorer les performances photocatalytiques des nanotubes, de TiO2 synthétisés par méthode hydrothermale, que ce soit sous illumination UV-A ou solaire, des modifications avec un autre semi-conducteur WO3 ou ZnO ont été entreprises. Les mêmes modifications ont également été réalisées sur le photocatalyseur commercial TiO2 P25 (Evonik). Une des finalités de ce travail est la corrélation des conditions de synthèse de ces matériaux avec leurs caractéristiques physico-chimiques et avec leurs propriétés photocatalytiques vis-àvis de l'élimination des deux polluants étudiés. Une approche mécanistique a également été menée.
42
Zhang, Jian. "Orthogonal chemical functionalization of titanium tungsten (TiW) based surfaces". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC030.
Testo completoAbstract (sommario):
Avec le développement de nouveaux dispositifs apparait le besoin d’être capable de contrôler la chimique de surfaces de substrats multi-échelle et multi-matériaux. Plusieurs techniques font appel à de la chimie localisée via différentes technologies. Une approche consiste à exploiter les différences de réactivités chimiques entre les différents matériaux du substrat et différents groupements chimiques de manière à fonctionnaliser sélectivement chaque matériaux pour former des couches minces organiques de type « Self Assembled Monolayer »: Ce principe proposée par Pr. G. M. Whitesides est appelé chimie orthogonale. Dans le cadre de cette thèse, le but ultime était de réaliser la fonctionnalisation chimique orthogonale de substrats dont la surface était composée de SiO2/Au/TiW La première étape de ce travail a été de déterminer pour la première fois la fonction chimique la plus adaptée pour la fonctionnalisation de TiW. Pour se faire nous avons comparé la chimie des silanes, des acides phosphoniques et des catéchols. Après caractérisations (XPS, ToF-SIMS, IR) des différentes couches, la voie des acides phosphoniques semblait être celle donnant lieu à la couche la plus stable. Ensuite nous avons étudié l’orthogonalité sur de substrats bi-matériaux (SiO2/TiW ou Au/TiW), et enfin sur substrat dont la surface était constituée de Au/SiO2/TiWThe development of nanotechnologies makes it possible to manufacture the micro or nanometric-sized patterns with various materials (dielectrics, metals, semiconductors). These heterogeneous surfaces are commonly used in the electronics industry for the production of nanoelectronic structures and components: transistors, memories or sensors. The concept of orthogonal chemical functionalization was first proposed by George M. Whitesides to modify the surfaces composed of different materials at the macroscopic scale. In this context, this PhD work aimed at exploring the orthogonal chemical functionalization approach on a predefined patterned titanium tungsten (TiW) surface by lithography producing. Pattern materials (Au, SiO2) are chosen to have different chemical properties, which can be functionalized with completely independent reactions. To achieve this aim, we have studied three different chemical groups for the formation of organolayers (silane, catechol, phosphonic acid) on TiW for the first time. The three layers were characterized (XPS, IR, ToF-SIMS) and the stability of the formed organolayers was also addressed. Then we developed and ascertained the orthogonal chemical functionalization of patterned Au/TiW and Au/SiO2/TiW surfaces. It proposes a novel strategy for the orthogonal functionalization on a triple-material patterned surface. In addition, the capture of nanoparticles by electrostatic interaction at specific location on Au/TiW patterned substrate was successfully implemented to prove the interest of such method for colloids trapping
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Thomas, T. "Chemical vapour deposition of titanium and vanadium arsenide thin films". Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1310479/.
Testo completoAbstract (sommario):
This thesis describes the chemical vapour deposition (CVD) of titanium and vanadium arsenide thin films. The compounds [TiCl4(AsPh3)], [TiCl4(AsPh3)2], [TiCl4(Ph2AsCH2AsPh2)], [TiCl4(tBuAsH2)n] have been synthesised from the reaction of TiCl4 with the corresponding arsine, and they have been investigated as potential single-source precursors to TiAs. Additionally, [TiCl3(NMe2)(μ-NMe2)2AsCl] has been synthesised from the reaction of TiCl4 and As(NMe2)3, and although was thought not to be a suitable single-source precursor to TiAs due to its lack of preformed Ti-As bonds, its use a potential single-source precursor to TiN has been investigated. All synthesised compounds have been characterised using NMR, mass spectrometry and elemental analysis, and decompositional profiles studied by thermogravimetric analysis (TGA). Aerosol assisted (AA) and low pressure (LP)CVD have been used to investigate the use of the compounds as single-source precursors, with deposited films analysed by X-ray powder diffraction, wavelength dispersive X-ray (WDX) analysis and scanning electron microscopy (SEM). Thin films of TiAs have been deposited via the dual-source atmospheric pressure (AP)CVD reactions of tBuAsH2 with both TiCl4 and [Ti(NMe2)4]. This arsenic precursor has also been investigated within the deposition of VAs films via dual-source routes with its reaction with VCl4 and VOCl3. All deposited films have been characterised using X-ray powder diffraction, WDX, X-ray photoelectron spectroscopy (XPS), Raman microscopy, and SEM, with properties such as adherence, hardness, water contact angles and reflectivity measured.
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Price, Timothy Simon. "Cold gas dynamic spraying of titanium coatings". Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/12491/.
Testo completoAbstract (sommario):
Cold gas dynamic spraying, CGDS, is a relatively new technique used to deposit materials onto the surface of a substrate. It differs to the majority of other thermal spray techniques as the substrate and particles are not exposed to high temperatures during the spraying process. This makes CGDS particularly advantageous for spraying materials such as titanium which react at high temperature. The aim of this project was to investigate the potential use of titanium coatings by CGDS as a surface treatment for medical prostheses. Titanium powder was deposited onto Ti6A14V substrate using helium gas at room temperature. Titanium coatings were also produced by a competing spray technique, shrouded arc spraying, to allow for a comparison of the two techniques to be made. Mechanical properties of the titanium coatings were measured and the influence of subsequent heat treating on the mechanical properties was also investigated. The coatings were characterised by investigating properties such as their bond strength, residual stress and stiffness, as well as the influence of the cold spray titanium coating on the fatigue life of a sprayed substrate. Scanning electron microscopy and optical microscopy techniques were also used to characterise the deposits. To further develop and optimise the CGDS process aluminium and copper coatings were also deposited and their mechanical properties compared to that of the titanium deposits. Additionally particle image velocimetry, PIV, was used to improve general understanding of the cold spray process and the effect that spray parameters have on the particle impact velocity. In the case of fatigue endurance limit and despite a compressive residual stress state measured in the titanium CGDS coatings, a 15% reduction in fatigue endurance limit was observed following the application of a CGDS titanium coating to the as received substrate, but no significant reduction was observed on its application to the grit blasted substrate. By four point bend testing it was observed that the ratio of the modulus of the titanium deposit to that of the corresponding bulk material (the modulus ratio) was 0.17, significantly below unity. For copper and aluminium, also deposited by cold spray, a modulus ratio of 0.41 and 0.16 was observed. The volume fraction and aspect ratio of porosity in each deposit was measured by SEM. However, an Eshelby equivalent homogeneous inclusion model supplied with these data was not able to predict the low modulus ratios observed. Instead, imperfect inter-particle bonding within the deposit (akin to through-thickness cracks) is the source of the low modulus ratios, with the tenacious oxide on the titanium and aluminium powder particles being more effective at preventing oxide disruption and formation of metallurgical bonds between particles upon impact, hence the lower modulus ratio for these material types. A method was developed to visually show the imperfect inter-particle bonding expected to be found within the CGDS deposits. Although porosity levels are low within cold spray deposits, individual particles are found to not be well bonded to each other which results in low coating moduli. By increasing the primary gas pressure in the cold spray process an increase in the degree of inter-particle bond formation occurred. Heat treating of the titanium coating at 1150 °C was found to improve the bond strength of the coating but drastically reduced the fatigue endurance limit. The same heat treatment temperature was found to increase the modulus ratio of the coating to 0.36 and this is attributed to a greater level of inter-particle bonding within the titanium coating occurring by diffusion bonding. However a reduction in the fatigue endurance limit was observed. This is most likely due to phase changes of the Ti6A14V substrate, the stress relaxation nature of heat treating and oxygen embrittlement occurring, despite an argon furnace used. Diagnostic tools such as particle velocity measurements are also used to gain a further general understanding of the CGDS process. Particle velocity measurements were made for titanium and copper powders using helium and nitrogen gas and a range of spray parameters. Particles of less than 9 pm in diameter were found to have the slowest particle velocities for both the copper and titanium powders. For the titanium powder up to a 200 m s-1 variation was found between the smallest and largest sized particles. This knowledge may be used in the future to optimise the size distribution of a powder feedstock prior to being used for cold spray deposition. Overall the titanium powder produced the highest particle velocities compared to the copper powder due to its lower density and therefore being easier to accelerate by the gas flow. A particle model was used to predict particle velocities. Generally the model predicted higher particle velocities then the maximum measured particle velocities and this is due to the model not taking into consideration of particles interacting with one another, the external walls of the nozzle, or the external atmosphere. These factors would all lead to particle deceleration. In comparison to titanium coatings produced by the shrouded arc process, the titanium CGDS coatings performed admirably. The shrouded arc coatings had a considerably lower fatigue endurance limit, due to tensile residual stresses within the coating, forming as particles cool on impact. However, the shrouded arc coatings showed a higher modulus ratio of approximately 1/3, which is comparable to coatings produced by other thermal spray methods.
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Rymer, Dawn Lee. "The atmospheric chemical vapor deposition of titanium nitride on polyimide substrates". Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1179952065.
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Nowotny, Maria Materials Science & Engineering Faculty of Science UNSW. "Defect disorder, semiconducting properties and chemical diffusion of titanium dioxide single crystal". Awarded by:University of New South Wales. School of Materials Science and Engineering, 2006. http://handle.unsw.edu.au/1959.4/27223.
Testo completoAbstract (sommario):
Semiconducting properties and related defect disorder for well defined TiO2 single crystal were studies. Semiconducting properties have been determined using simultaneous measurements of two independent electrical properties, including electrical conductivity, ??, and thermoelectric power, S, at elevated temperatures (1073-1323 K) in the gas phase of controlled oxygen activity (10-10 Pa < p(O2) < 75 kPa). Measurements of s and S were conducted (i) in the gas/solid equilibrium and (ii) during equilibration. Oxygen vacancies have been identified as the predominant defects in TiO2 over a wide range of p(O2). Individual conductivity components related to electrons, electron holes and ions, were determined from the obtained ?? data. The effect of p(O2) on these individual components was considered in the form of a diagram. This work led to the discovery of the formation and diffusion of Ti vacancies. However, the obtained diffusion data indicate that, in the temperature ranges commonly used in studies of semiconducting properties (1000-1400K), the Ti vacancies concentration is quenched and may thus be assumed constant. In addition it was shown that Ti vacancies in appreciable concentrations form only during prolonged oxidation. It was determined that the discrepancies in the reported n-p transition point are related to the concentration and spectrum of impurities as well as the concentration of Ti vacancies. It has been shown that the n-p transition point in high-purity TiO2 is determined by the Ti vacancy concentration. A well defined chemical diffusion coefficient, Dchem, was determined using kinetic data obtained during equilibration. A complex relationship between p(O2) and Dchem was observed. These data showed a good agreement between the obtained diffusion data and defect disorder. Examination of the determined equilibration kinetics, led to the discovery of two kinetic regimes, the result of the transport of defects at different mobilities. The determined data are considered well defined due to the following reasons: 1. The studied specimen was of exceptionally high purity and free of grain boundaries (single crystal) 2. The specimen was studied in the gas phase of controlled and well defined oxygen activity which was continuously monitored. 3. Whenever the experimental data were measured in equilibrium, the gas/solid equilibrium has been verified experimentally. 4. A good agreement between the two, self-confirmatory, electrical properties, including ?? and S has been determined simultaneously and independently. The defect disorder model derived in the present work may be used for tailoring controlled semiconducting properties through the selection of annealing conditions involving the temperature and oxygen activity.
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Buchholz, Tuisko M. "Photocatalytic oxidation of glymes in an aqueous suspension of titanium dioxide". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83853.
Testo completoAbstract (sommario):
Lower members of the glyme family CH3-(-O-CH2-CH2-)n O-CH3 are refractory to the usual biological and physicochemical treatments, do not get retained on biofilters and are hardly sorbed to activated sludge or carbon. An alternate form of elimination is hence to be devised. TiO 2 particles have been utilized in the photocatalytic degradation of organic compounds often found in contaminated waste streams. When they are exposed to UV light, an electron is excited from the TiO2 valence band into the conduction band. The photogenerated electron vacancy ("hole") can initiate the oxidation of the organic, while the photogenerated electron must be removed from the particle by transfer to a suitable electron acceptor (scavenger).The photocatalytic oxidation of triglyme in an aqueous suspension of TiO2 has been studied, proving the concept to be feasible. Characterization of the light distribution in the reactor has been carried out and related to the influence of catalyst load. The rate of the reaction was considerably enhanced by introducing Cu2+ as co-catalyst and by controlling the pH, with the existence of an optimum co-catalyst concentration ([triglyme]/[Cu 2+] = 2) and an optimum pH at 3.5. The influence of both parameters is explained and the pathway of the interfacial charge-transfer reaction is proven to be of the Fenton type (indirect oxidation through activation of water) and not of the Photo-Kolbe type (direct attack of the holes).
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Te, Alino. "Improvement in Toughness of Castings through Chemical Surface Modification". Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/1271.
Testo completoAbstract (sommario):
Alloys with good toughness and elevated temperature properties like A201 are expensive and can be more difficult to process. This results in the use of heavier but less expensive alternatives in many applications where toughness is of concern, such as steels. Common alloys such as A356 and E357 are relatively cheap and easy to work with. However, these alloys have considerably lower toughness than premium alloys. This research aims to investigate surface modification treatments that could yield better toughness at a low cost in a common aluminum alloy. The process must show significant improvement in said properties, be cost effective, and easily adaptable in a common foundry. Diffusion of coating material into the substrate was investigated with a variety of coating metals. The diffusion process was facilitated in the solutionizing step for the given substrate aluminum in order to strengthen the sub-surface region of the parts. This research aims to provide a platform for further research into the practical effects of the coating and tempering on impact and toughness properties. These samples were characterized by optical and scanning electron microscopy, EDS, impact testing, and tensile testing.
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Martin, Holly Joy. "The chemical and mechanical effects of binding chitosan to implant quality titanium". Diss., Mississippi State : Mississippi State University, 2006. http://library.msstate.edu/etd/show.asp?etd=etd-09112006-150127.
Testo completo
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巌, 偉琪. "Bonding of chemically treated titanium implants to bone". Kyoto University, 1997. http://hdl.handle.net/2433/202215.
Testo completo