Influence of the Sol-Gel pH Process and Compact Film on the Efficiency of TiO2-Based Dye-Sensitized Solar Cells

The influence of pH during hydrolysis of titanium(IV) isopropoxide on the morphological and electronic properties of TiO2 nanoparticles prepared by the sol-gel method is investigated and correlated to the photoelectrochemical parameters of dye-sensitized solar cells (DSCs) based on TiO2 films. Nanoparticles prepared under acid pH exhibit smaller particle size and higher surface area, which result in higher dye loadings and better short-circuit current densities than DSCs based on alkaline TiO2-processed films. On the other hand, the product of charge collection and separation quantum yields in films with TiO2 obtained by alkaline hydrolysis is c. a. 27% higher than for the acid TiO2 films. The combination of acid and alkaline TiO2 nanoparticles as mesoporous layer in DSCs results in a synergic effect with overall efficiencies up to 6.3%, which is better than the results found for devices employing one of the nanoparticles separately. These distinct nanoparticles can be also combined by using the layer-by-layer technique (LbL) to prepare compact TiO2 films applied before the mesoporous layer. DSCs employing photoanodes with 30 TiO2 bilayers have shown efficiencies up to 12% higher than the nontreated photoanode ones. These results can be conveniently used to develop optimized synthetic procedures of TiO2 nanoparticles for several dye-sensitized solar cell applications.

Photoconduction action spectra of regio-regular poly(3-hexylthiopene):TiO2 diodes

The development of polymer-based photovoltaic devices brings the promise of low-cost and lightweight solar energy conversion systems. This technology requires new materials and device architectures with enhanced efficiency and lifetime, which depends on the understanding of charge-transport mechanisms. Organic films combined with electronegative nanoparticles may form systems with efficient dissociation of the photogenerated excitons, thus increasing the number of carriers to be collected by the electrodes. In this paper we investigate the steady-state photoconductive action spectra of devices formed by a bilayer of regio-regular poly(3-hexylthiophene) (RRP3HT) and TiO2 sandwiched between ITO and aluminum electrodes (ITO/TiO2:RRP3HT/Al). Photocurrents were measured for distinct bias voltages with illumination from either side of the device. Heterojunction structures were prepared by spin coating a RRP3HT film on an already deposited TiO2 layer on ITO. Symbatic and antibatic curves were obtained and a model for photocurrent action spectra was able to fit the symbatic responses. The quantum yield increased with the electric field, indicating that exciton dissociation is a field-assisted process as in an Onsager mechanism. Furthermore, the quantum yield was significantly higher when illumination was carried out through the ITO electrode onto which the TiO2 layer was deposited, as the highly electronegative TiO2 nanoparticles were efficient in exciton dissociation.

Impact of experimental Nano-HAP pastes on bovine enamel and dentin submitted to a pH cycling model

This in vitro study evaluated the preventive potential of experimental pastes containing 10% and 20% hydroxyapatite nanoparticles (Nano-HAP), with or without fluoride, on dental demineralization. Bovine enamel (n=15) and root dentin (n=15) specimens were divided into 9 groups according to their surface hardness: control (without treatment), 20 Nanop paste (20% HAP), 20 Nanop paste plus (20% HAP + 0.2% NaF), 10 Nanop paste (10% HAP), 10 Nanop paste plus (10% HAP + 0.2% NaF), placebo paste (without fluoride and HAP), fluoride paste (0.2% NaF), MI paste (CPP-ACP, casein phosphopeptide-amorphous calcium phosphate), and MI paste plus (CPP-ACP + 0.2% NaF). Both MI pastes were included as commercial control products containing calcium phosphate. The specimens were treated with the pastes twice a day (1 min), before and after demineralization. The specimens were subjected to a pH-cycling model (demineralization–6-8 h/ remineralization-16-18 h a day) for 7 days. The dental subsurface demineralization was analyzed using cross-sectional hardness (kgf/mm 2 , depth 10-220 µm). Data were tested using repeated-measures two-way ANOVA and Bonferroni's test (p<0.05). The only treatment able to reduce the loss of enamel and dentin subsurface hardness was fluoride paste (0.2% NaF), which differed significantly from the control at 30- and 50-µm depth (p<0.0001). The other treatments were not different from each other or compared with the control. The experimental Nanop pastes, regardless of the addition of fluoride, were unable to reduce dental demineralization in vitro.

Estudio de la degradación de m-cresol, ácido ftálico y 2,4-diclorofenol mediante fotocatálisis heterogénea: síntesis y caracterización de fotocatalizadores basados en TiO2

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Photocatalytic degradation of phenolic compounds with new TiO2 catalysts

[EN] New TiO2 catalysts have been synthesised by means of a sol–gel method in which aggregates have been selected before thermal treatment. Sieving and calcination temperature have been proved to be key factors in obtaining catalysts with greater photoactivity than that of Degussa P-25. These new catalysts have been characterized by means of transmission electron microscopy (TEM), BET surface area, diffuse reflectance spectroscopy (DRS), UV–vis spectroscopy, Fourier transformed infrared (FTIR) and X-ray diffraction (XRD). The different parameters studied were compared to those obtained from two commercial catalysts (Degussa P-25 and Hombikat-UV100). The photocatalytic efficiency of the new catalysts was evaluated by the degradation of various phenolic compounds using UV light (maximum around 365 nm, 9mW). The catalyst sieved and calcinated at 1023 K, ECT-1023t, showed phenol degradation rates 2.7 times higher than those of Degussa P-25. Also in the degradation of different phenolic compounds, this catalyst showed a higher activity than that of the commercial one. The high photoactivity of this new catalyst has been attributed to the different distribution of surface defects (determined from FTIR studies) and its increased capacity to yield H2O2

Síntesis y caracterización de fotocatalizadores basados en TiO2 : estudios de la degradación de los herbicidas ácido 2,4-Diclorofenoxiacético y bentazona mediante fotocatálisis heterogénea a escala de laboratorio y planta piloto solar

Programa de doctorado: Ingeniería ambiental y desalinización

Síntesis de fotocatalizadores basados en TiO2 para la eliminación de contaminantes en fase acuosa y gaseosa

Tutor: Javier Araña Mesa. Programa de doctorado: Ingenierías Química, Mecánica y de Fabricación

Photocatalytic hydrogen production by water splitting over Au-TiO2 commercial and home-made photocatalysts

[ES]Póster presentado en 3rd European Conference on Environmental Applications of Advanced Oxidation Processes.

El contenido del póster corresponde a parte del trabajo de tesis doctoral de la Dra. Cristina Rodríguez López.

Processi di deposizione di blocking layers di TiO2 per Dye - Sensitized Solar Cells (DSSC)

Le Dye – Sensitized Solar Cells (DSSC) sono attualmente considerate tra le alternative più promettenti al fotovoltaico tradizionale. I ridotti costi di produzione e l’elevata versatilità di utilizzo rappresentano i punti di forza di questi dispositivi innovativi. Ad oggi la ricerca è concentrata prevalentemente sull’incremento delle prestazioni delle DSSC, ottenibile solamente attraverso un miglioramento delle funzioni dei singoli componenti e dell’interazione sinergica tra questi. Tra i componenti, ha recentemente assunto particolare interesse il blocking layer (BL), costituito generalmente da un film sottile di TiO2 depositato sulla superficie dell’anodo (FTO) e in grado di ottimizzare i fenomeni all’interfaccia FTO/TiO2/elettrolita. Nel corso di questo lavoro di tesi si è rivolta l’attenzione prevalentemente sulle caratteristiche del BLs (ad esempio proprietà morfologico – strutturali) cercando di mettere in correlazione il processo di deposizione con le caratteristiche finali del film ottenuto. A questo scopo è stato ottimizzato un processo di deposizione dei film via spin coating, a partire da soluzioni acquosa o alcolica di precursore (TiCl4). I film ottenuti sono stati confrontati con quelli depositati tramite un processo di dip coating riportato in letteratura. I BLs sono stati quindi caratterizzati tramite microscopia (SEM – AFM), spettrofotometria (UV.- Vis) e misure elettrochimiche (CV – EIS). I risultati ottenuti hanno messo in evidenza come i rivestimenti ottenuti da soluzione acquosa di precursore, indipendentemente dalla tecnica di deposizione utilizzata (spin coating o dip coating) diano origine a film disomogenei e scarsamente riproducibili, pertanto non idonei per l’applicazione nelle DSSC. Viceversa, i BLs ottenuti via spin coating dalla soluzione alcolica di TiCl4 sono risultati riproducibili, omogenei, e uniformemente distribuiti sulla superficie di FTO. Infine, l’analisi EIS ha in particolare evidenziato un effettivo aumento della resistenza al trasferimento di carica tra elettrodo FTO ed elettrolita in presenza di questi BLs, fenomeno generalmente associato ad un efficace blocking effect.

Synthese, Charakterisierung und Anwendungsbeispiele neuartige poröser Kieselgel-Materialien im Nano- bis Mikrometerbereich mit sphärischer Morphologie

Abstract Im Rahmen dieser Arbeit wurden verschiedene neue Synthesewege zur Darstellung poröser Kieselgele untersucht. Als porenbildende Template wurden hierzu eine Reihe niedermolekularer und polymerer Verbindungen eingesetzt. Dabei sollten die Teilchenmorphologie und die Parameter der Porenstruktur durch die Bedingungen bei der Reaktion und nicht durch eine Nachbehandlung eingestellt werden. Hauptziel der Arbeit war es, eine Synthese zu entwickeln, bei der durch den Einsatz eines geeigneten Templats sphärische Kieselgelpartikel mit Porengrößen über 10 nm hergestellt werden können. Zusätzlich zur Materialsynthese gelang es Informationen über den Bildungsmechanismus poröser Kieselgele zu erhalten.Weiterhin wurden die Materialien als Säulenmaterial in der Chromatographie, als Adsorbens zur Probensammlung (sample tracking), als Katalysatorträgermaterial und als Marker für Biomoleküle eingesetzt.

ATRP-Synthese von Poly(N-Isopropylacrylamid)-Bürsten in wässrigem Medium und Anpassung des Nano-Plotters zur Beschichtung von Mikrocantilever-Sensoren

Das Ziel dieser Arbeit ist die Synthese von Polymerbürsten auf Silizium durch Aufbringen der Reaktionslösung mit einem Pipettiersystem. Dies ist für die Beschichtung von Microcantilever Sensoren interessant, um spezifische Fühler mit funktionellen Polymerschichten, die auf chemische oder physikalische Einflüsse reagieren, zu bauen. Bisherige Synthesemethoden werden in Lösung durchgeführt. Atom Transfer Radical Polymerization ist etabliert, um definierte Schichten von Polymerbürsten herzustellen. Die Kombination mit einer “Spot Printing”-Technik kann eine Alternative sein, um einzelne Cantilever mit einer Breite von 90 μm und einer Länge von 750 μm zu beschichten. Dafür wurde eine Chemie getestet, die mit dem Pipettiersystem Nano-Plotter der Firma Gesim umsetzbar ist. Aus einer Mischung aus Wasser und DMF wurden Poly(N-Isopropylacrylamid)-Bürsten auf Silizium mit Schichtdicken bis zu 40 nm hergestellt. Es war nötig den Nano-Plotter anzupassen, damit zum einen auf die Microcantilever Sensoren pipettiert werden kann und zum andern die Nanoliter großen Tropfen über den Reaktionszeitraum stabil sind. Auf diese Weise konnten Linien mit einer Schichtdicke von ca. 2 nm auf Siliziumwafer hergestellt werden. Die “Spot-Printing” Methode ist daher eine gute Ergänzung zur herkömmlichen Synthese.

Sviluppo di un sistema miniaturizzato per il controllo real-time di assetto di nano e microsatelliti

Microsatelliti e nanosatelliti, come ad esempio i Cubesat, sono carenti di sistemi integrati di controllo d’assetto e di manovra orbitale. Lo scopo di questa tesi è stato quello di realizzare un sistema compatibile con Cubesat di una unità, completo di attuatori magnetici e attuatori meccanici, comprendente tutti i sensori e l’elettronica necessaria per il suo funzionamento, creando un dispositivo totalmente indipendente dal veicolo su cui è installato, capace di funzionare sia autonomamente che ricevendo comandi da terra. Nella tesi sono descritte le campagne di simulazioni numeriche effettuate per validare le scelte tecnologiche effettuate, le fasi di sviluppo dell’elettronica e della meccanica, i test sui prototipi realizzati e il funzionamento del sistema finale. Una integrazione così estrema dei componenti può implicare delle interferenze tra un dispositivo e l’altro, come nel caso dei magnetotorquer e dei magnetometri. Sono stati quindi studiati e valutati gli effetti della loro interazione, verificandone l’entità e la validità del progetto. Poiché i componenti utilizzati sono tutti di basso costo e di derivazione terrestre, è stata effettuata una breve introduzione teorica agli effetti dell’ambiente spaziale sull’elettronica, per poi descrivere un sistema fault-tolerant basato su nuove teorie costruttive. Questo sistema è stato realizzato e testato, verificando così la possibilità di realizzare un controller affidabile e resistente all’ambiente spaziale per il sistema di controllo d’assetto. Sono state infine analizzate alcune possibili versioni avanzate del sistema, delineandone i principali aspetti progettuali, come ad esempio l’integrazione di GPS e l’implementazione di funzioni di determinazione d’assetto sfruttando i sensori presenti a bordo.