Computational modeling of the properties of TiO2 nanoparticles

In this study we discuss the electronic, structural, and optical properties of titanium dioxide nanoparticles, and also the properties of Ni(II) diimine dithiolato complexes as dyes in dye-sensitized TiO2 based solar cells. The abovementioned properties have been modeled by using computational codes based on the density functional theory. The results achieved show slight evidence on the structure-dependent band gap broadening, and clear blue-shifts in absorption spectra and refractive index functions of ultra-small TiO2 particles. It is also shown that these properties are strongly dependent on the shape of the nanoparticles. Regarding the Ni(II) diimine dithiolato complexes as dyes in dye-sensitized TiO2 based solar cells, it is shown that based on the experimental electrochemical investigation and DFT studies all studied diimine derivatives could serve as potential candidates for the light harvesting, but the e ciencies of the dyes studied are not very promising.

The Combined treatment of UV Light and Titanium Dioxide (TiO2) in Grease Filtration Technique

The aim of this thesis was to identify the best grease removal technique with the application of low power of UV light to TiO2 coated grease filters. The treatment with various power series of ozone generating and ozone free lamps to normal grease filters and TiO2 coated grease filters were examined and the obtained results are compared to each other in this paper. The effect of ozone reaction was observed and compared with the effect of TiO2. The experiments were solely based on the photo oxidation and photo catalytic oxidation reactions. TiO2 is a green catalyst used in the photocatalytic reaction. Sunflower oil was used for grease production and tetracholoroethylene as a solvent. Grease samples were collected from the ventilation duct connected to the cooking hood system. Sample extraction was done in ultrasonic bath with the principle of sonication. The sample analysis was done by FTIR machine. The result determining the concentration of grease was the quantification of saturated C-H bonds in the chosen peak group of the spectrum. A very low power of UVC light functions perfectly with the Titanium dioxide. The experimental results have shown the combined treatment of titanium dioxide and UV light is an effective method in grease removal process. The photocatalytic reaction with titanium dioxide is better than photo oxidation reaction with ozone treatment. Photocatalytic reaction is environmentally friendly, energy efficient and economical.

Pulsed electric field assisted sol-gel preparation of TiO2 particles and their photocatalytic properties

The objective of this thesis was to study the effect of pulsed electric field on the preparation of TiO2 nanoparticles via sol-gel method. The literature part deals with properties of different TiO2 crystal forms, principles of photocatalysis, sol-gel method and pulsed electric field processing. It was expected that the pulsed electric field would have an influence on crystallite size, specific surface area, polymorphism and photocatalytic activity of produced particles. TiO2 samples were prepared by using different frequencies and treatment times of pulsed electric field. The properties of produced TiO2 particles were examined X-ray diffraction (XRD), Raman spectroscopy and BET surface area analysis. The photocatalytic activities of produced TiO2 particles were determined by using them as photocatalysts for the degradation of formic acid under UVA-light. The photocatalytic activities of samples produced with sol-gel method were also compared with the commercial TiO2 powder Aeroxide® (Evonic Degussa GmbH). Pulsed electric field did not have an effect on the morphology of particles. Results from XRD and Raman analysis showed that all produced TiO2 samples were pure anatase. However, pulsed electric field did have an effect on crystallite size, specific surface area and photocatalytic activity of TiO2 particles. Generally, the crystallite sizes were smaller, specific surface areas larger and initial formic acid degradation rates higher for samples that were produced by applying the pulsed electric field. The higher photocatalytic activities were attributed to larger surface areas and smaller crystallite sizes. Though, with all of the TiO2 samples produced by the sol-gel method the initial formic acid degradation rates were significantly slower than with the commercial TiO2 powder.

Photocatalysis Studies under Visible Light Irradiation with TiO2 Obtained by Pulsed Electric Field Assisted Sol-Gel Method

The objective of this thesis was to study the effect of pulsed electric field on the preparation of TiO2 nanoparticles via sol-gel method under the visible light irradiation. The literature part introduces properties of different TiO2 crystal forms and principle of photocatalysis. It was expected that pulsed electric field would have an influence on degradation for oxalic acid and formic acid. TiO2 samples were prepared by using three frequencies (50Hz, 294Hz, and 963Hz) and two treatment times (12 minutes and 24 minutes) of pulsed electric field. The photocatalytic activities of TiO2 samples produced with sol-gel method were also compared with the TiO2 particles made by previous study and with the commercial TiO2 powder Aeroxide® (Evonic Degussa GmbH) at the same condition. Results show that pulsed electric field does have an effect on degradation for oxalic acid and formic acid. Generally, higher photocatalytic activities for oxalic acid and formic acid were obtained with lower frequency and longer treatment time of pulsed electric field.

Metal oxides prepared through the nanocasting approach-mechanistic study, surface interactions and applications in separation

Mesoporous metal oxides are nowadays widely used in various technological applications, for instance in catalysis, biomolecular separations and drug delivery. A popular technique used to synthesize mesoporous metal oxides is the nanocasting process. Mesoporous metal oxide replicas are obtained from the impregnation of a porous template with a metal oxide precursor followed by thermal treatment and removal of the template by etching in NaOH or HF solutions. In a similar manner to the traditional casting wherein the product inherits the features of the mold, the metal oxide replicas are supposed to have an inverse structure of the starting porous template. This is however not the case, as broken or deformed particles and other structural defects have all been experienced during nanocasting experiments. Although the nanocasting technique is widely used, not all the processing steps are well understood. Questions over the fidelity of replication and morphology control are yet to be adequately answered. This work therefore attempts to answer some of these questions by elucidating the nanocasting process, pin pointing the crucial steps involved and how to harness this knowledge in making wholesome replicas which are a true replication of the starting templates. The rich surface chemistry of mesoporous metal oxides is an important reason why they are widely used in applications such as catalysis, biomolecular separation, etc. At times the surface is modified or functionalized with organic species for stability or for a particular application. In this work, nanocast metal oxides (TiO2, ZrO2 and SnO2) and SiO2 were modified with amino-containing molecules using four different approaches, namely (a) covalent bonding of 3-aminopropyltriethoxysilane (APTES), (b) adsorption of 2-aminoethyl dihydrogen phosphate (AEDP), (c) surface polymerization of aziridine and (d) adsorption of poly(ethylenimine) (PEI) through electrostatic interactions. Afterwards, the hydrolytic stability of each functionalization was investigated at pH 2 and 10 by zeta potential measurements. The modifications were successful except for the AEDP approach which was unable to produce efficient amino-modification on any of the metal oxides used. The APTES, aziridine and PEI amino-modifications were fairly stable at pH 10 for all the metal oxides tested while only AZ and PEI modified-SnO2 were stable at pH 2 after 40 h. Furthermore, the functionalized metal oxides (SiO2, Mn2O3, ZrO2 and SnO2) were packed into columns for capillary liquid chromatography (CLC) and capillary electrochromatography (CEC). Among the functionalized metal oxides, aziridinefunctionalized SiO2, (SiO2-AZ) showed good chemical stability, and was the most useful packing material in both CLC and CEC. Lastly, nanocast metal oxides were synthesized for phosphopeptide enrichment which is a technique used to enrich phosphorylated proteins in biological samples prior to mass spectrometry analysis. By using the nanocasting technique to prepare the metal oxides, the surface area was controlled within a range of 42-75 m2/g thereby enabling an objective comparison of the metal oxides. The binding characteristics of these metal oxides were compared by using samples with different levels of complexity such as synthetic peptides and cell lysates. The results show that nanocast TiO2, ZrO2, Fe2O3 and In2O3 have comparable binding characteristics. Furthermore, In2O3 which is a novel material in phosphopeptide enrichment applications performed comparably with standard TiO2 which is the benchmark for such phosphopeptide enrichment procedures. The performance of the metal oxides was explained by ranking the metal oxides according to their isoelectric points and acidity. Overall, the clarification of the nanocasting process provided in this work will aid the synthesis of metal oxides with true fidelity of replication. Also, the different applications of the metal oxides based on their surface interactions and binding characteristics show the versatility of metal oxide materials. Some of these results can form the basis from which further applications and protocols can be developed.

Síntesis y caracterización de oxidos ceramicos en el sistema SrO-Li2O-TiO2

Tesis (Maestría en Ciencias con Especialidad en Química Analítica) UANL

Estudio de nuevos compuestos en el sistema Cs2O-TiO2-SiO2

Tesis (Maestría en Ciencias con Especialidad en Ingeniería Cerámica) UANL

Envejecimiento artificial para el BAO-TIO2, utilizado como elemento dieléctrico en un capacitor

Tesis ( Maestro en Ciencias de la Ingeniería Mecánica, con Especialidad en Térmica y Fluidos) UANL, 2002

Síntesis de nanoestructuras bidimensionales de oro y plata depositadas sobre TiO2 por rocío pirolítico asistido por ultrasonido.

Tesis (Doctorado en Química de los Materiales) UANL, 2011.

Influence de la taille de départ, de l’état d’agglomération et de la dose de nanoparticules de dioxyde de titane (TiO2) inhalées sur la réponse pulmonaire chez le rat

En raison de leur petite taille, les nanoparticules (NP) (< 100 nm) peuvent coaguler très rapidement ce qui favorise leur pénétration dans l’organisme sous forme d’agglomérats. L’objectif de cette recherche est d’étudier l’influence de l’état d’agglomération de NP de dioxyde de titane (TiO2) de trois tailles de départ différentes, 5, 10-30 ou 50 nm sur la toxicité pulmonaire chez le rat mâle (F344) exposé à des aérosols de 2, 7 ou 20 mg/m3 pendant 6 heures. Dans une chambre d’inhalation, six groupes de rats (n = 6 par groupe) ont été exposés par inhalation aiguë nez-seulement à des aérosols ayant une taille primaire de 5 nm, mais produits sous forme faiblement (< 100 nm) ou fortement (> 100 nm) agglomérée à 2, 7 et 20 mg/m3. De façon similaire, quatre autres groupes de rats ont été exposés à 20 mg/m3 à des aérosols ayant une taille primaire de 10-30 et 50 nm. Les différents aérosols ont été générés par nébulisation à partir de suspensions ou par dispersion à sec. Pour chaque concentration massique, un groupe de rats témoins (n = 6 par groupe) a été exposé à de l’air comprimé dans les mêmes conditions. Les animaux ont été sacrifiés 16 heures après la fin de l’exposition et les lavages broncho-alvéolaires ont permis de doser des marqueurs d’effets inflammatoires, cytotoxiques et de stress oxydant. Des coupes histologiques de poumons ont également été analysées. L’influence de l’état d’agglomération des NP de TiO2 n’a pu être discriminée à 2 mg/m3. Aux concentrations massiques de 7 et 20 mg/m3, nos résultats montrent qu’une réponse inflammatoire aiguë est induite suite à l'exposition aux aérosols fortement agglomérés. En plus de cette réponse, l’exposition aux aérosols faiblement agglomérés à 20 mg/m3 s’est traduite par une augmentation significative de la 8-isoprostane et de la lactate déshydrogénase. À 20 mg/m3, les effets cytotoxiques étaient plus importants suite à l’exposition aux NP de 5 nm faiblement agglomérées. Ces travaux ont montré dans l'ensemble que différents mécanismes de toxicité pulmonaire peuvent être empruntés par les NP de TiO2 en fonction de la taille de départ et de l’état d’agglomération.

Modified mesoporous MCM-41 as hosts for photochromic spirobenzopyrans

The influence of the chemical composition and silylation of mesoporous MCM-41 materials on the photochromic behaviour of adsorbed spiropyran (BIPS) and 6-nitrospiropyran was studied. Upon incorporation, the spiropyrans underwent ring opening to form either zwitterionic merocyanine or its corresponding O-protonated form. In all silica MCM-41 or in the MCM-41 containing aluminium, the O-protonated merocyanine was predominantly formed. In the case of MCM-41 modified by silylation of the OH groups, a mixture of zwitterionic merocyanine and spiropyran was present. The photochromic response was studied by means of steady-state irradiation and by laser flash photolysis. Steady-state irradiation (λ > 450 nm) of the solid samples gives rise in all cases to an intensity decrease of the absorption bands corresponding to either the protonated or the unprotonated merocyanine form (reverse photochromism). In contrast, laser flash photolysis at 308 nm of spiropyrans supported on silylated MCM-41 allows observation of the photochemical ring opening of residual spiropyran to the corresponding zwitterionic form (normal photochromism).

Preparation, Characterization and Dilectric Properties of Ceramics in the BaO-Nd2O3-TiO2 System

The dielectric ceramics BaNd2Ti3Oto, BaNd2Ti4O12 and BaNd2Ti5O14 have been prepared by Conventional solid state ceramic route. The sintered ceramic samples have been characterized by X-ray diffraction and Scanning Electron Microscopy (SEM). The dielectric properties in the microwave frequency range have been measured using conventional microwave dielectric resonator methods. The BaNd2Ti1O10, BaN2Ti4O12 and BaNd2Ti5O14 have dielectric constants (Er) ~ 60, 84 and 77 respectively. They have relatively high quality factors

Microwave dielectric properties of MO -La2O3-TiO2 (M = Ca, Sr, Ba) ceramics

Single-phase polycrystalline ceramics in the MO-La2O3-Ti02 (M = Ca, Sr, Ba) system, such as cation-deficient hexagonal perovskites CaLa4Ti4O15, SrLa4Ti4O15, BaLa4Ti4O15, and Ca2La4Ti5O18 and the orthorhombic phases CaLa4Ti5O17 and CaLa8Ti9O31, were prepared through the solid-state ceramic route. The phases and structure of the ceramics were analyzed through x-ray diffraction and scanning electron microscopy. The microwave dielectric properties of the ceramics were studied using a network analyzer. The investigated ceramics show high Er in the range 42 to 54, high quality factors with Q x f in the range 16,222 to 50,215 GHz, and low Tf in the range -25 to +6 ppm3/°C. These high dielectric constant materials with high Q x f up to 50,215 GHz are suitable for applications where narrow bandwidth and extremely low insertion loss is necessary, especially at frequencies around 1.9 GHz

Sol-Gel Mesoporous Silica Aerogels and Bio Hybrids for Functional Applications

The thesis covers a systematic investigation on the synthesis of silica aerogels and microspheres with tailored porosity, at ambient conditions by varying the experimental parameters as well as using organic templates. Organically modified silica-gelatin and silica-chitosan hybrids were developed for the first time using alkylalkoxysilanes such as MTMS and VTMS. Application of novel silica-biopolymer antiwetting coatings on different substrates such as glass, leather and textile is also demonstrated in the thesis.