Photocatalytic Hydrogen Production using a Mesoporous TiO2 Doped with Pt: Semiconductor Synthesis, Oxidation-Reduction Network and Quantum Efficiencies.

The present PhD dissertation establishes that hydrogen can be produced using mesoporous TiO2 as a photocatalyst, doped with platinum atoms (Pt), in a slurry medium, under near-UV irradiation and with ethanol as a sacrificial reagent (scavenger). These mesoporous TiO2 photocatalysts were prepared using a sol-gel method. The mesoporous Pt-TiO2 photocatalyst displayed a reduced 2.34 eV band gap compared to the bare TiO2 (3.20 eV). Photocatalytic hydrogen production experiments were performed in a Photo-CREC Water II Reactor (PCW-II Reactor). This novel unit provides both radial and axial symmetrical irradiation profiles. Furthermore, macroscopic energy balances developed in this unit, showed a maximum 96% light absorption efficiency. Runs in the PCW-II Reactor showed that hydrogen molecules were formed through the coupling of H• radicals under oxygen-free conditions. The use of 2.00 v/v% ethanol as a sacrificial reagent enabled the production of significant amounts of hydrogen with the simultaneous formation of hydrogen peroxide, methane, ethane, acetaldehyde and carbon dioxide by-products. It was confirmed that the extent of hydrogen generation in the presence of ethanol is a function of the pH level and Pt loading on the mesoporous TiO2 photocatalyst. Additionally, it was established that the reaction networks leading to hydrogen production, using the various photocatalysts, shared common reactivity features. For example, it was shown that under an inert gas atmosphere, ethanol consumption takes place sub-stoichiometrically. This points towards the simultaneous formation and consumption of ethanol. Regarding the consumption of the ethanol scavenger, experimental observations were supported by an “in series-parallel” reaction network. With respect to energy efficiencies, it was observed that the maximum 22.6 % Quantum Yields found for hydrogen generation indicates a very good degree of photon utilization (45.2%). Thus, this PhD dissertation contributes to the development of novel semiconductors for hydrogen production via water dissociation. It is demonstrated that when using the synthesized mesoporous semiconductors with added Pt, in a Photo-CREC-Water II Reactor unit, encouraging Quantum Yields are achieved

Hybrid rendering of exploded views for medical image atlas visualization

Medical image atlases contain much information about human anatomy, but learning the shapes of anatomical regions and making sense of the overall structure defined in the atlas can be problematic. Atlases may contain hundreds of regions with complex shapes which can be tightly packed together. This makes visualisation difficult since the shapes can fit together in complex ways and visually obscure each other. In this work, we describe a technique which enables interactive exploration of medical image atlases that permits the hierarchical structure of the atlas and the content of an underlying medical image to be investigated simultaneously. Our method enables a user to create visualizations of the atlas similar to the exploded views used in technical illustrations to show the structure of mechanical assemblies. These views are constrained by the geometry of the atlas and the hierarchical structure to reduce the complexity of user interaction. We also enable the user to explode the atlas meshes themselves. The atlas meshes are registered with a medical image which is displayed on the cut surfaces of the meshes using raycasting. Results from the AAL human brain atlas are presented and discussed

Photocatalytic hydrogen production using mesoporous TiO2 doped with Pt

A series of mesoporous TiO2 (meso-TiO2) were synthesized using the sol-gel technique. A Pluronic F127 triblock-copolymer, a structure-directing agent, was incorporated as a soft template into the sol-gel. In addition, and during a separate synthesis, the sol-gel was doped with a Pt precursor. Semiconductors were prepared with 1.00 wt.%, 2.50 wt.%, 5.00 wt.% Pt nominal loadings, respectively. They were calcined at 500 ◦C and 550 ◦C following synthesis. Morphological and structural properties were studied by: a) X-ray diffraction, b) UV–vis spectrophotometry, c) N2 adsorption-desorption (BET, BJH), and d) X-ray photoelectron spectroscopy (XPS). Optical band gap values for meso-TiO2 and Pt-meso-TiO2 were cal- culated by Kubelka-Munk (K-M) function coupled with Tauc plot methodology. It was observed that the prepared semiconductors displayed pore sizes in the 10–40 nm range with bimodal distributions. Their photocatalytic activity forhydrogenproductionvia water splitting was established ina Photo-CRECWater- II reactor under near-UV light irradiation. The aqueous solution contained 2% v/v ethanol, employed as a renewable organic scavenger. The prepared semiconductors showed that the mesoporous 2.50 wt.% Pt-TiO2 has the highest photoactivity for hydrogen generation. This suggests the important role played by the loading of platinum as a TiO2 dopant, reducing the optical band gap, increasing electron storage and diminishing, as a result, electron-hole recombination. The measured Quantum Yield (QY), obtained using a rigorous approach, was established for the mesoporous 2.50 wt.% Pt-TiO2 at a promising level of 22.6%

Diseño de adsorbentes para la eliminación de compuestos nitrogenados modelo representativos de cargas a diesel

En esta investigación se llevó a cabo el diseño de adsorbentes para la remoción selectiva de compuestos nitrogenados presentes en las cargas diesel. Con base en una revisión bibliográfica se decidió partir de mallas moleculares mesoporosas tipo MCM-41, puesto que poseen altas áreas superficiales y diámetros de poro promedio adecuados para la adsorción de moléculas nitrogenadas presentes en el diesel. Asimismo con ayuda de una posible sustitución de átomos de silicio presentes en la estructura de la MCM-41 por algún otro elemento como cobre o aluminio, se puede dar lugar a modificaciones en las propiedades de la superficie del material, como la acidez. Estas propiedades son relevantes para este caso de estudio dado el carácter básico y no básico de las moléculas nitrogenadas, así como las altas densidades electrónicas que poseen dichos compuestos. Se prepararon tres series de materiales como posibles candidatos; adsorbentes con cobre, Cu-MCM-41(Si/Cu = 25, 50, 100 y 300) y materiales con aluminio, Al-MCM-41(Si/Al = 10, 25, 50, 100, ∞) sintetizados por el método de coprecipitación. La tercer serie consistió en impregnación de níquel, molibdeno y wolframio sobre la MCM-41 con una carga nominal de 10 œen peso. Cabe señalar que la hipótesis para la síntesis de ésta última serie fue la posible interacción de dichos metales de transición con las moléculas nitrogenadas. Los adsorbentes principalmente se caracterizaron por Fisisorción de Nitrógeno, Difracción de Rayos X (DRX), Espectroscopía de Rayos Infrarrojos por Transformada de Fourier (IR-TF), 27Al y 29Si Resonancia Magnética Nuclear Giro de Ángulo Mágico (RMN-GAM), Microscopía Electrónica de Transmisión con Alta Resolución (MET-AR), Termodesorción Programada de Piridina (TDP-Py) y Espectroscopía Ultravioleta Visible (Uv-Vis). Los sólidos sintetizados fueron evaluados en adsorción de moléculas nitrogenadas modelo como: quinolina (C9H7N ), indol (C9H8N ) y carbazol (C12H9N ), a temperatura ambiente disueltas en mezclas modelo diesel de hexadecano-tolueno (C16H34 −C6H5CH3) en un sistema por lotes. El rendimiento de los adsorbentes se comparó con un material comercial, Selexsorb-CDX (γ-alúmina-zeolita) y con alúmina (Al2O3) de referencia sintetizada previamente en el grupo de trabajo. La evaluación consistió en la medición para capacidad de adsorción sobre cada compuesto nitrogenado y el estudio dinámico de adsorción, para estimar los parámetros cinéticos característicos a través de un modelo matemático desarrollado en esta investigación. Finalmente de acuerdo a los datos obtenidos explícita o implícitamente por medio de las técnicas de caracterización previamente mencionadas se obtuvieron correlaciones entre propiedades físico-químicas y capacidad de adsorción para los materiales evaluados

Improving Object Composition Visualization via Exploded Views

Manipulating internal parts of a 3D model can be a time consuming and tedious task. On one hand, letting a user to define the position of each part can depend on the type of the object and the expertise of using modeling tools. On the other hand, using transparent visualization or cut techniques can mislead the spatial relation position between different parts of a model. An approach that attempts to mitigate previous issues is an exploded view. In this work, we introduce an improvement to the current state of exploded views by adding two features: an algorithm to automatically position the camera to show an optimal exploded view for a selected target on a variety of models, and a qualitative user study to obtain features\u27 feedback of our algorithm used by 3D software users. Our work is based on two key elements: a low-level data structure using bounding boxes (BB) and an optimization that minimizes an energy function dependent on two search spaces in parallel. Using BBs allows us to generalize the type of exploded views to any geometrical model while maintaining interactive frame-rates in our application. Simulated annealing, along with two heuristics, is used to solve the optimization. For a selected part, the optimization heuristics help to guide the direction of explosion and to move the part\u27s neighborhood in a recursive manner if necessary. We decide to call the neighbor\u27s movement megamove. Our technique is applied to a variety of models, such as furniture, anatomical datasets, and vehicles. We also test our application with users with knowledge of 3D software using a questionnaire. The user study aids our analysis of the likelihood for our exploded views to be an improvement for 3D software user expectations

Hydrogen Production via Water Dissociation Using Pt–TiO2 Photocatalysts: An Oxidation–Reduction Network

Several TiO2 based semiconductors with different Pt loadings are prepared using incipient impregnation, wet impregnation and the sol-gel method. These photocatalysts are evaluated in the Photo-CREC-Water II Photoreactor for hydrogen production via water dissociation, using an organic renewable scavenger (ethanol). Results obtained show the influence of the photocatalyst preparation in the production of hydrogen and in the observed quantum yields. Furthermore, it is established that the reaction networks leading to hydrogen production, using various photocatalysts, share common features. This analysis is developed by both identifying and quantifying different chemical species and their changes with irradiation time. Key species in this oxidation–reduction network are hydrogen, hydrogen peroxide, ethanol, methane, ethane, acetaldehyde and carbon dioxide. On this basis, it is shown that under an inert gas atmosphere, ethanol consumption is sub-stoichiometric. This points towards simultaneous ethanol consumption and the formation of the ethanol scavenger

EPR and CV studies cast further light on the origin of the enhanced hydrogen production through glycerol photoreforming on CuO:TiO2 physical mixtures

Embargado hasta 31/08/2023Different CuO nanoparticles were synthesized and tested in CuO:TiO2 physical mixtures for hydrogen production through glycerol photoreforming. CuO alone was inactive whereas its presence in CuO:TiO2 mixtures significantly improved the photoactivity of TiO2, with smaller CuO nanoparticles leading to higher hydrogen productions. Results obtained through combination of EPR and CV studies suggested the existence of a Cu(II)-Cu0 catalytic cycle. Thus, electrons promoted to the conduction band of titania could be used for CuO reduction to Cu which in turn would enable hydrogen production regenerating Cu2+ for a new catalytic cycle. All in all, a hydrogen production of 88 mmol·g−1 was obtained after 5 h on a CuO:TiO2 (10% w/w) physical mixture which is comparable to that achieved in a previous study under identical reaction conditions on 1.5%Pt/TiO2