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The effect of microstructure on corrosion resistance and anodising behaviour of a 3rd generation lithium-containing aluminium alloy, AA 2099-T8, has been studied. Microstructural characterisation of the alloy has shown elongated grains with high angle grain boundaries and approximately equiaxed subgrains with low angle grain boundaries. Two types of constituent particles of high and reduced contents of copper were found, which are present individually or in the form of multiphase particles. The alloy also contains rod-like Al-Cu-Mn-Li and spherical (Al3Zr) dispersoids, and fine age hardening precipitates of T1 (Al2CuLi), (Al3Li) and (Al2Cu).Immersion testing in a chloride-containing solution revealed two types of localised corrosion sites: one was initiated from intermetallics and quickly became passivated; the other lasted for the course of testing, with extensive boundary attack. The latter has been correlated to grains and subgrains with relatively high stored energy.Alkaline etching removed intermetallics from alloy surface; generated a copper-enriched layer in the alloy matrix immediately beneath the residual alumina film; and gradually developed a surface nanotexture. The surface nanotexture has been correlated to the formation of copper-rich nanoparticles within the copper-enriched layer.Anodising the alloy in tartaric-sulphuric acid disclosed that copper in the alloy matrix could be occluded in the anodic film material as copper-rich nanoparticles or be oxidized and incorporated into the film material as copper ions, depending on the anodising voltage. In the latter case, the process was accompanied by oxygen gas generation within the film material, forming anodic films with lateral porosity. Intermetallics of different compositions behaved differently during anodising, leading to modification of the morphology and composition of anodic films. Concerning the effect of alkaline etching on anodising behaviour of the alloy, the removal of intermetallics increased anodising efficiency; the pre-developed copper-enriched layer advanced the establishment of the steady-state film/alloy interface. Variation of copper-enriched layer structure is revealed by the detection of copper-rich nanoparticles in the copper-enriched layer. The copper-rich nanoparticles have structures consistent with either θ", θ' or θ phases. Machining damage can be detected not only by chromic acid anodising (CAA) but also by tartaric-sulphuric acid anodising (TSAA). Neither CAA nor TSAA can be used for detecting shallow corrosion pits.

Malignant bone tumours often require a patient to make the choice between limb salvage surgery and complete amputation. The Ti-6Al-4V alloy is the material of choice for implantable orthopaedic devices as it provides a favourable combination of biocompatibility, corrosion resistance and mechanical properties. The only drawback of titanium is that, owing to its bio-inertness, living tissue struggles to attach, creating an opportunity for bacterial adhesion. The “race for the surface” is the term given for the competition between living tissue and bacteria to colonise the implant surface. If bacterial adhesion occurs at a higher rate than tissue adhesion, the chance of infection rises significantly. It has been shown that there is an opportunity to give tissue adhesion the edge by slowing down the initial colonisation of the implant surface by free-swimming bacteria. Silver has a relatively low toxicity level of 28 mg/kg in the body. Current research has focussed mainly on reducing bio-inertness and improving the antimicrobial properties of titanium via the incorporation of silver. In general, the studies conducted on antibacterial surfaces are limited to testing the final sample directly in contact with bacteria, with no attempt to measure silver release rate profiles. The research in this dissertation aimed to investigate methodologies for the incorporation of silver into a modified surface of Ti-6Al-4V in order to facilitate an antimicrobial effect for use in orthopaedic implants. The methodologies investigated were: anodic oxidation of Ti-6Al-4V, followed by silver ion exchange; Ag-doped TiO2 fused to the surface of Ti-6Al-4V via anodic oxidation; and Ag ion implantation into anodically oxidised and polished Ti-6Al-4V. The generated surfaces and sub-surfaces were characterised microstructurally via SEM, FIB, TEM and AFM and chemically by RBS, XRD, AAS and EDS. Ag+ release rate investigations were conducted with the use of ICP-MS. This study was limited to the use of two anodising electrolytes (i.e. 0.5M H2SO4 and 2.1M H3PO4) and altering the AgNO3 concentration (0.05 - 5.0M) and Ag implantation dosage (0.4 - 1.2x1017 ions/cm2 ), where applicable to the method. Results from the Ag ion exchanged samples showed that, microstructurally, the surface produced via anodising in 0.5M H2SO4 and 2.1M H3PO4 were different in terms of pore morphology, Ra, pore homogeneity across the surface and crystal structure. Sub-surface analysis via FIB/TEM found that the ca. 200nm thick TiO2 samples all contained silver nanoparticles (AgNPs). Samples anodised in 0.5M H2SO4 produced an anatase crystal structure, whilst those anodised in 2.1M H3PO4 produced rutile crystal structures. Silver uptake by samples anodised in 0.5M H2SO4 showed decreases in Ag absorption at high (5.0M) AgNO3 ion exchange concentrations, relative to low (0.05M) concentrations. The opposite effect was observed for samples anodised in 2.1M H3PO4. Ag+ release curves corroborated the absorption data by displaying the same trends in terms of Ag+ release post ion exchange. It was concluded that it was a combination of diffusion bottlenecking and higher reactivity of the anatase phase formed during anodising in 0.5M H2SO4 with Ag+ versus the rutile phase that led to these trends. Synthesis of TiO2 powders showed that increasing the AgNO3 concentration (0.05-5M) resulted in AgTiO2 powders with increasing Ag content. Ag-TiO2 powder was successfully fused to the surfaces via anodic oxidation in 0.5M H2SO4 and 2.1M H3PO4 at 100V. Ag-TiO2 powder fused preferentially in areas where downward pressure was present. Microstructurally, the sub-surfaces produced an anodic oxide approximately 200nm thick, to which a significantly thicker, AgNP-containing, TiO2 was attached. XRD data indicated additional Brookite (020) peaks, owing to the presence of the attached Ag-TiO2 powder on the surfaces. Ag-TiO2 powders attached via 0.5M H2SO4 showed a higher overall Ag+ release at all investigated powder concentrations (0.48 - 76.93 wt% Ag) versus those attached via 2.1M H3PO4. This was concluded to be due to the anatase phase produced by 0.5M H2SO4 having greater oxidative power, thus accelerating oxidative dissolution of the AgNPs. RBS data corroborated these trends. Relative to their Ag ion exchange counterparts, the Ag-TiO2 samples had a lower Ag+ release at 0.05M and 0.5M AgNO3 concentrations. However, at 5.0M AgNO3 the Ag-TiO2 samples had a higher Ag+ release. This was the trend irrespective of the anodising electrolyte. Both the anatase and rutile TiO2s showed a reduction in Ra post Ag ion implantation and the polished Ti6Al4V samples showed an increase in Ra. This was due to preferential erosion of areas with high free surface energy. In the case of both TiO2s these were “high points” in the oxide and for polished Ti6Al4V these were the grain boundaries. Both TiO2s were amorphised during ion implantation. All ion implanted TiO2 showed the presence of AgNPs within the first 50nm of the surface. These AgNPs increased in size as the implantation dosage was increased. Polished Ti6Al4V showed no AgNP formation but EDS mapping confirmed that the silver was also located 50nm within the surface. TiO2 Ag+ release was similar for both implantation dosages because the surfaces had been supersaturated at the low dose, thus an increase in implantation dose had no significant effect on further silver uptake. The release rates were also similar between the oxides because of amorphisation. Polished Ti6Al4V showed an increase in Ag uptake and Ag+ release when the implantation dose was increased. RBS results corroborated the observed Ag+ release results. In comparison, both the ion exchanged samples and the Ag-TiO2 fused samples showed performances in similar ranges of Ag+ release. The Ag-TiO2 samples showed a greater degree of tailorability of the Ag+ release, whereas the ion exchanged samples showed a lesser sensitivity to an increase in AgNO3 concentration. Ag ion implanted samples showed an order of magnitude lower Ag+ release relative to the other studied methods. In comparison to literature, all ion exchanged and Ag-TiO2 samples had the potential to have a 100% antimicrobial effect (AE). Ion implanted oxides had a 55-100% potential, while the polished Ti6Al4V had a 55% AE at low dose and a 100% AE at high dose. In order to achieve maximum silver ion release and the associated antimicrobial effect, the technique of Ag-TiO2 fused to the surface using the 2.1M H3PO4 and 0.5M H2SO4 electrolytes yielded the best results, with a silver ion release of 550 and 600 ppb respectively over two weeks. This technique also satisfied the research aim, in that the methodology offered a combination of tailorability of silver release and commercial scalability.

Anodisation has been studied for almost eighty years, primary in the field of corrosion science, as a simple and efficient way of producing thick protective oxide coatings on Al, Ti or Zr alloys. Anodisation is an electrochemical oxidation process which relies on the migration of ions across solid films under the action of a large electric field. From the fundamental point of view, many aspects regarding the growth of anodic films have been studied extensively. However, so far, little interest has been devoted to the mechanical aspects involved in the growth process, despite their considerable importance both from an applied as well as from a fundamental point of view. A solid understanding of internal stresses development is indeed crucial in order to guarantee the durability of anodic coatings, their structural and functional properties. In addition, the stress evolution directly reflects the motion of the ions in the film and therefore provides a unique means to investigate in situ the growth mechanisms of anodic films. In this thesis, we have studied the evolution of the internal stresses in anodic TiO2 films in situ during their growth. The stresses have been obtained from changes in the curvature of cantilevered anode samples, measured using a high-resolution multi-beam optical sensor. We demonstrate, for the first time, the capability of this type of curvature sensor for monitoring processes in liquid environments. Experimental data on the internal stresses developing in anodic TiO2 films is provided, and trends regarding the influence of the experimental conditions on the stress evolution are identified. In particular, the evolution of the internal stresses is shown to be strongly correlated with the evolution of the electrochemical variables, which directly demonstrates the interest of curvature measurements as a fundamental technique for investigating the details of the growth process of anodic oxide films. The reversible and irreversible stress contributions associated, respectively, with electrostriction and with growth-related ionic transport have been separated from one another and quantified. A novel constitutive model for the electrostriction stress has been proposed which explicitly takes into account the effect of dielectrostriction.

High strength 7xxx aluminium alloys are used extensively in the aerospace industry because the alloys offer excellent mechanical properties. Unfortunately, the alloys can suffer localised corrosion due to the presence of large intermetallic particles at the alloy surface that are aligned in the rolling direction. Laser surface melting (LSM) techniques offer the potential to reduce and/or to eliminate the intermetallic phases from the surface of the alloy without affecting the alloy matrix.The present study concerns the application of LSM using an excimer laser to enhance the corrosion resistance of AA 7075-T6 aluminium alloy. The initial stage of the project was aimed at optimising the laser conditions for production of a uniform microstructure, with the increase in the corrosion resistance of the alloy being determined by potentiodynamic polarization measurements in sodium chloride solution. Low and high laser energy densities were used with a different number of pulses per unit area to treat the alloy surface, which were achieved by changing both the laser fluence and the pulse repetition frequency. A laser fluence of 3.3 J/cm2 with 80 pulses was subsequently selected as the optimum condition to treat the surface of the alloy. The composition and microstructure of the alloy before and after LSM treatment, and following corrosion tests, were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).After the laser treatment, the surface and the cross-sections of the alloy showed a significant reduction in the number of large intermetallic particles and a relatively homogenous melted layer was generated that provided significant improvement in the resistance of the alloy against corrosion, as assessed by several corrosion test methods, including exfoliation corrosion (EXCO) tests. However, delamination of the melted layer was observed after extended testing in the EXCO solution which is possibly related to the formation of bands of fine magnesium and zinc-rich precipitates within the melted layer. Therefore, anodising in sulphuric acid was applied to the LSM alloy, in order to further increase the corrosion resistance and to protect the laser treated layer from delamination by generating a thin oxide film over the LSM layer. The results revealed that the anodic treatment increased the resistance of the alloy to exfoliation attack.

The combination of two cost-effective processes, i.e. casting and anodising, would be an interest for the aluminium component applications. However, there are some obstacles in the application of anodising on cast Al alloys. The challenges mostly relate to the alloying elements especially Si and the surface quality. With the development of casting process, cast aluminium alloys with low Si content can be casted, and a complex geometry component with reasonably good surface finish can be achieved. This study aims to identify the influence of Si on anodising and mechanical properties of Al-Si alloys. In this study, six Al-Si alloys with three different Si level and two different Sr level were investigated. Sr acts as a modifier to change the morphology of Si particles. The directional solidification technology was used to vary the microstructure coarseness by controlling the cooling rate to study the influence of Si level, Si particle morphology and cooling rate on mechanical properties, oxide layer formation and corrosion protection performance in cast Al-Si alloys. This study has observed that Si has a significant influence on anodising. During anodising, Si particles are anodised at a lower rate than the Al phase. The presence of Si particles in eutectic phase make the oxide layer locally thinner and more defected due to the low oxide growth rate in eutectic phase. This study observed the presence of residual metallic Al phase beneath or between Si particles. Due to their presence and their geometry, Al can be shielded by Si particles and prevented from oxidation. Si particles also act as a key role in the corrosion protection of oxide layer in Al-Si alloys. The corrosion attack propagates along Si particles as well as oxide defects to the Al substrate. It is found that the morphology of Si particles has a significant influence on the oxide layer formation and corrosion protection performance of the oxide layer on cast Al-Si alloys. A substantially improvement the corrosion resistance of anodised layer on Al-Si alloys is attributed to the morphology change from interconnected flakes to disconnected Si fibres when Sr is added, with less oxide defects and better oxide distribution. The Si level governs the mechanical properties of Al-Si based alloys. An increase of Si content in Al alloys improves the mechanical properties such as ultimate tensile and yield strength as well as hardness of the materials, but decreases the ductility. However, an increase of Si level in Al alloys decreases the thickness of oxide layer, and thereby, the corrosion protection of the oxide layer is deteriorated. / Kombinationen av två kostnadseffektiva processer, gjutning och anodisering, är av intresse för tillämpning på aluminiumkomponenter. Det finns dock hinder för tillämpning av anodisering på gjutna aluminiumlegeringar. Utmaningarna relaterar till effekten av legeringselement, i synnerhet Si, och komponentens ytkvalité. Med utvecklingen av gjutprocesser kan aluminiumlegeringar med lågt Si-innehåll gjutas, och komponenter med komplex geometri med förbättrad ytkvalité kan uppnås. Denna studie syftar till att identifiera påverkan av Si på anodisering och mekaniska egenskaper hos Al-Si-baserade legeringar. I denna studie undersöktes sex Al-Si-legeringar med tre nivåer av Si och två nivåer av Sr. Tillsatser av Sr leder till modifikation av morfologin hos Si-partiklar. Med hjälp av tekniken ”riktad stelning” varierades stelningshastigheten för att studera sambanden mellan halten och morfologin av Si, mikrostrukturens grovlek och dess inverkan på mekaniska egenskaper, samt oxidskiktets bildning och korrosionsbeständighet hos gjutna Al-Si-legeringar. Denna studie visar att Si har ett betydande inflytande på anodisering r. Under anodisering, anodiseras Si-partiklar i en lägre takt än Al-fasen. Närvaron av Si-partiklar i eutektisk fas bidrar till ett lokalt förtunnat oxidskikt med fler defekter på grund av den låga oxidtillväxthastigheten i eutektisk fas. Denna studie observerade förekomsten av kvarvarande metalliska Al fasen under eller mellan Si-partiklar. På grund av Si-partiklarnas närvaro och geometri, kan Al skärmas från oxidation. Si-partiklar har även en nyckelroll i korrosionsskydd av oxidskiktet i Al-Si-legeringar. Korrosionsangreppet propagerar längs Si-partiklar samt oxiddefekter till Al-substrat. Morfologin av Si-partiklar har funnits ha en betydande inverkan på oxidskiktets bildning och korrosionsskydd hos gjutna Al-Si-legeringar. En väsentlig förbättring av korrosionsbeständigheten i anodiserat skikt hos Al-Si-legeringar tillskrivs förändring av kiselns morfologi från sammankopplade flingor till osammanhängande fibrer när Sr tillsätts, med mindre oxiddefekter och bättre fördelning av oxid. Si halten påverkar de mekaniska egenskaperna hos Al-Si-baserade legeringar. En ökning av Si innehålleti Al-legeringar förbättrar de mekaniska egenskaperna såsom brott och sträckgräns samt hårdhet hos materialen, men minskar duktiliteten. En ökning med Si halt i Al-legeringar minskar dessvärre tjockleken hos oxidskiktet, och därigenom, försämrar oxidskiktets korrosionsskydd.

The sensor is a device that converts a form of energy concerning which the information is sought, called the measurand, to a form (electrical) in which it can be usefully processed or interpreted. Sensors rely on physical or chemical phenomena and materials where those phenomena appear to be useful. Those phenomena may concern the material itself or its geometry. Hence, the major innovations in sensors come from new materials, new fabrication techniques or both. Normally, thin film sensors are realized by depositing a sensing film on a suitable substrate. There could be many combination of metals and insulating materials being deposited depending upon the application or sensing requirements. In general, sensors for various applications are fabricated using a variety of liquid phase technologies (also called as wet methods) and gas phase technologies (also called as dry methods) of deposition. Hence sensor fabrication technology requires various combination of processing technologies and newer materials. In the present work, an attempt is made to design and fabricate a thin film based pressure sensor using a combination of wet and dry deposition techniques. The diaphragm, used for sensing the pressure is coated with a hard anodic coating (Al2O3) using a wet technology, viz. pulse hard anodizing technique, for electrical insulation requirement. The piezo-resistive strain sensing films were deposited onto this coating by dry method, namely, DC Magnetron sputtering technique.. Chapter 01 gives a brief overview of sensors, their classification, principles of sensing,characteristics, materials used in the fabrication of sensors like conductors and insulators, the components of a sensor. Chapter 02 gives brief information about various techniques of depositions viz., liquid phase technologies (wet methods) and vapour phase technologies (dry methods) used to fabricate the sensors. Also, information regarding the coating property evaluation and coating characterization techniques is included. The chapter 03 presents a detailed account of work carried out to obtain an electrically insulating layer by the development of pulse hard anodizing process for aluminum alloy diaphragm, necessary process optimization and testing. The details related to the development, fabrication and testing of thin film based pressure sensors using aluminum alloy diaphragm with hard anodic coating are presented in Chapter 04. The thin film strain gauges were deposited using DC magnetron sputtering technique. The information about mask design, deposition process parameters, calibration etc is also included. Chapter 05 provides summary of the work carried out and conclusions. The scope of carrying out further work is also outlined.

Galvanic anode technology has in recent years come to the fore as a cost-effective method of successfully mitigating the corrosion of reinforcing steel in concrete structures. Developments in the field of cathodic protection have included the introduction of a novel Hybrid anode system, which uses the same sacrificial anode to pass a short-term impressed current before being connected to the steel directly to provide a long-term galvanic current. Galvanic and hybrid technologies are often seen as less powerful solutions in the treatment of reinforcement corrosion, and the test methodologies which determine the efficacy of cathodic protection systems favour impressed current technologies. The work completed has investigated the application of traditional and novel corrosion assessment techniques to laboratory samples to assess the protection offered by the hybrid treatment methodology in both treatment phases. In addition, the response of both galvanic and hybrid anodes to environmental conditions has been recorded and assessed before being discussed in the context of steel protection criteria. Finally, an investigation is presented into the on-site deterioration of commercially pure titanium feeder wire installed as part of the hybrid anode system and potential solutions to the problem have been documented. The research undertaken found that the hybrid anode system is capable of protecting steel in challenging, aggressive environments. This was confirmed by steel corrosion rate and indicative steel potential measurements. The responsive behaviour investigation showed that the current output of galvanic and hybrid anodes responds rapidly to changes in the corrosion risk posed to the steel and that this has a direct effect on anode system lifetimes. An assessment of the polarisation-based protection criteria applied to steel in concrete has found that the standard inhibits the use of responsive behaviour, and that revisions which consider the present risk of steel corrosion by considering the corrosion current resulting from the relative aggressivity of the concrete environment would be more valid in their application. A cathodic protection system based on the concepts of pit re-alkalisation and pH maintenance can fully utilise galvanic anode responsive behaviour. It was discovered that the deterioration of commercially pure titanium feeder wire seen on site installations was due to anodising in the presence of chloride media which had the potential to lead to pitting corrosion. The pitting risk varied depending on the duration of the treatment and proximity to the installed anode. An anodically grown oxide delayed the onset of corrosion in aqueous KBr solution, but did not significantly increase the pitting potential.

[ES] La presente Tesis Doctoral se centra en la síntesis de nanoestructuras híbridas de TiO2/ZnO para su utilización como fotoelectrocatalizadores durante la producción de hidrógeno a partir de la rotura de la molécula de agua mediante fotoelectrocatálisis y la degradación fotoelectrocatalítica de pesticidas. La principal ventaja de las nanoestructuras híbridas de TiO2/ZnO frente a otros fotocatalizadores basados en materiales semiconductores radica en su capacidad para formar heterouniones en las que se intercalan las bandas de valencia y conducción de ambos semiconductores. Este fenómeno produce una disminución del ancho de banda del fotoelectrocatalizador y de los procesos de recombinación de los pares electrón-hueco fotogenerados y un aumento del rango de absorción de la luz, lo que mejora sus propiedades como fotoelectrocatalizadores. Las nanoestructuras híbridas de TiO2/ZnO obtenidas en la presente Tesis Doctoral se sintetizaron mediante electrodeposición de ZnO sobre nanoesponjas de TiO2. Las nanoesponjas de TiO2 se formaron mediante anodizado electroquímico de titanio en condiciones hidrodinámicas y, posteriormente, se electrodepositó ZnO sobre la superficie de las nanoesponjas de TiO2 modificando la concentración de precursor (Zn(NO3)2 0.5-60 mM), la temperatura (25-75 °C) y el tiempo (15-60 min). Además, se estudió la influencia de electrodepositar ZnO sobre nanoesponjas de TiO2 amorfo o nanoesponjas de TiO2 cristalino, observándose una mejora significativa de la actividad fotoelectrocatalítica de las nanoestructuras híbridas de TiO2/ZnO electrodepositadas sobre nanoesponjas de TiO2 cristalino. Las nanoestructuras híbridas de TiO2/ZnO sintetizadas tuvieron morfología en forma de nanoesponjas, nanobarras hexagonales, nanobarras sin definir y nanoláminas, estudiando la influencia de la concentración de Zn(NO3)2, temperatura y tiempo durante el proceso de electrodeposición de ZnO sobre su comportamiento como fotoelectrocatalizadores. Las nanoestructuras híbridas de TiO2/ZnO sintetizadas se caracterizaron mediante Microscopía Electrónica de Barrido de Emisión de Campo (FE-SEM), Espectroscopía de Energía Dispersiva de Rayos X (EDX), Microscopía Electrónica de Transmisión (TEM), Microscopía de Fuerza Atómica (AFM), Difracción de Rayos X (DRX), Espectroscopía UV-Visible y mediciones de la banda prohibida. Además, se caracterizaron fotoelectroquímicamente mediante ensayos de rotura de la molécula de agua mediante fotoelectrocatálisis y estabilidad frente a la fotocorrosión y electroquímicamente mediante Espectroscopía de Impedancia Fotoelectroquímica (PEIS) y ensayos de Mott-Schottky. Los resultados evidenciaron que las nanoestructuras híbridas de TiO2/ZnO electrodepositadas sobre TiO2 cristalino a 75 °C durante 15 minutos con una concentración de Zn(NO3)2 de 30 mM fueron las más favorables para llevar a cabo aplicaciones fotoelectroquímicas debido a que ofrecieron buena estabilidad frente a la fotocorrosión, elevada respuesta fotoelectroquímica (177 % superior a la de las nanoesponjas de TiO2), baja resistencia a la transferencia de carga y elevada densidad de portadores de carga, en comparación con las nanoesponjas de TiO2. Por último, las nanoestructuras híbridas de TiO2/ZnO óptimas se emplearon como fotoelectrocatalizadores en aplicaciones energéticas y medioambientales. Por un lado, se evaluó la producción teórica de hidrógeno que se obtendría al utilizar las nanoestructuras híbridas de TiO2/ZnO sintetizadas en la presente Tesis Doctoral como fotoánodos durante el proceso de rotura de la molécula de agua mediante fotoelectrocatálisis. Por otro lado, se evaluó la utilización de las nanoestructuras híbridas de TiO2/ZnO óptimas en la degradación fotoelectrocatalítica de pesticidas (Imazalil) en agua, obteniéndose un porcentaje de degradación del 99.6 % llevando a cabo la degradación fotoelectrocatalítica de 10 ppm de Imazalil en Na2SO4 0.1 M durante 24 horas aplicando un potencial de 0.6 V (Ag/AgCl(KCl 3M)). / [CA] La present tesi doctoral se centra en la síntesi de nanoestructures híbrides de TiO2/ZnO per a utilitzar-les com a fotoelectrocatalitzadors durant la producció d'hidrogen a partir del trencament de la molècula d'aigua mitjançant fotoelectrocatàlisi i la degradació fotoelectrocatalítica de pesticides. El principal avantatge de les nanoestructures híbrides de TiO2/ZnO enfront d'altres fotocatalitzadors basats en materials semiconductors radica en la seua capacitat per a formar heterojuncions en les quals s'intercalen les bandes de valència i conducció de tots dos semiconductors. Aquest fenomen produeix una disminució de l'ample de banda del fotoelectrocatalitzador i dels processos de recombinació dels parells electró-forat fotogenerats, i un augment del rang d'absorció de la llum, la qual cosa millora les seues propietats com a fotoelectrocatalitzadors. Les nanoestructures híbrides de TiO2/ZnO es van sintetitzar mitjançant electrodeposició de ZnO sobre nanosponges de TiO2. Les nanosponges de TiO2 es van formar mitjançant anodització electroquímica de titani en condicions hidrodinàmiques i, posteriorment, es va electrodepositar ZnO sobre la superfície de les nanosponges de TiO2 modificant la concentració del precursor (Zn(NO3)2 0.5-60 mm), la temperatura (25-75 °C) i el temps d'electrodeposició (15-60 min). A més, es va estudiar la influència d'electrodepositar ZnO sobre nanosponges de TiO2 amorf o nanosponges de TiO2 cristal·lí, i es va observar una millora significativa de l'activitat fotoelectrocatalítica de les nanoestructures híbrides de TiO2/ZnO en dur a terme el procés d'electrodeposició de ZnO sobre nanosponges de TiO2 cristal·lí. Les nanoestructures híbrides de TiO2/ZnO sintetitzades van tindre morfologia en forma de nanosponges, nanobarres hexagonals, nanobarres sense definir i nanolàmines, i es va estudiar la influència de la concentració de Zn(NO3)2, la temperatura i el temps durant el procés d'electrodeposició de ZnO sobre el seu comportament com a fotoelectrocatalitzadors. Les nanoestructures híbrides de TiO2/ZnO es van caracteritzar mitjançant microscòpia electrònica d'escombratge d'emissió de camp, espectroscòpia de raigs X per dispersió d'energia, microscòpia electrònica de transmissió, microscòpia de força atòmica, difracció de raigs X, espectroscòpia UV visible i mesuraments de la banda prohibida. D'altra banda, es van caracteritzar fotoelectroquímicament mitjançant assajos de trencament de la molècula d'aigua mitjançant fotoelectrocatàlisi i estabilitat enfront de la fotocorrosió, i electroquímicament mitjançant espectroscòpia d'impedància fotoelectroquímica i assajos de Mott-Schottky. Els resultats van evidenciar que les nanoestructures híbrides de TiO2/ZnO electrodepositades sobre TiO2 cristal·lí a 75°C durant 15 minuts amb una concentració de Zn(NO3)2 de 30 mm van ser les més favorables per a dur a terme aplicacions fotoelectroquímiques, pel fet que van oferir bona estabilitat enfront de la fotocorrosió, elevada resposta fotoelectroquímica (un 177 % superior a la de les nanosponges de TiO2), baixa resistència a la transferència de càrrega i elevada densitat de portadors de càrrega, en comparació amb les nanosponges de TiO2. Finalment, les nanoestructures híbrides de TiO2/ZnO òptimes es van emprar com a fotoelectrocatalitzadors en aplicacions energètiques i mediambientals. D'una banda, es va avaluar la producció teòrica d'hidrogen que s'obtindria en utilitzar les nanoestructures híbrides de TiO2/ZnO sintetitzades en la present tesi doctoral com a fotoànodes durant el procés de trencament de la molècula d'aigua mitjançant fotoelectrocatàlisi. D'altra banda, es va avaluar la utilització de les nanoestructures híbrides de TiO2/ZnO òptimes en la degradació fotoelectrocatalítica de pesticides (Imazalil) en aigua, i es va obtenir un percentatge de degradació del 99.6% duent a terme la degradació fotoelectrocatalítica de 10 ppm d'Imazalil en Na2SO4 0.1 M durant 24 h aplicant un potencial de 0.6 V (Ag/AgCl(KCl 3M)). / [EN] This Doctoral Thesis focuses on synthesizing TiO2/ZnO hybrid nanostructures to be used as photoelectrocatalysts in energy and environmental applications, particularly hydrogen production from water splitting by photoelectrocatalysis and photoelectrocatalytic degradation of pesticides. The main advantage of TiO2/ZnO hybrid nanostructures over other photocatalysts based on semiconductor materials is their ability to form heterojunctions in which the valence and conduction bands of both semiconductors are intercalated. This phenomenon produces a decrease in the band gap of the nanostructures, the recombination processes of the photogenerated electron-hole pairs, and an increase in the light absorption range, which improves their properties as photoelectrocatalysts. The TiO2/ZnO hybrid nanostructures formed in this Doctoral Thesis were synthesized by electrodeposition of ZnO on TiO2 nanosponges. First, TiO2 nanosponges were formed by electrochemical anodization of titanium under hydrodynamic conditions (3000 rpm) and, subsequently, ZnO was electrodeposited on the surface of the TiO2 nanosponges by modifying the precursor concentration (Zn(NO3)2 0.5 - 60 mM), the temperature (25 - 75 °C) and the electrodeposition time (15 - 60 min). In addition, the influence of performing the ZnO electrodeposition on amorphous TiO2 nanosponges (before the thermal treatment) or crystalline TiO2 nanosponges (after the thermal treatment) was studied, showing a significant improvement in the photoelectrocatalytic activity of TiO2/ZnO hybrid nanostructures by carrying out the ZnO electrodeposition process on crystalline TiO2 nanosponges. In this Doctoral Thesis, TiO2/ZnO hybrid nanostructures with morphologies of nanosponges, hexagonal nanorods, undefined nanorods, and nanosheets were synthesized by studying the influence of Zn(NO3)2 concentration, temperature and time during the ZnO electrodeposition process. In addition, the performance of TiO2/ZnO hybrid nanostructures as photoelectrocatalysts was studied. The synthesized TiO2/ZnO hybrid nanostructures were characterized morphologically, photoelectrochemically, and electrochemically. On the one hand, they were morphologically characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Diffraction X-Ray (XRD), UV-Visible Spectroscopy and band gap measurements. On the other hand, they were characterized photoelectrochemically by e water splitting and stability against photocorrosion tests and electrochemically by Photoelectrochemical Impedance Spectroscopy (PEIS) and Mott-Schottky tests. The results showed that TiO2/ZnO hybrid nanostructures electrodeposited on crystalline TiO2 at 75 °C for 15 minutes with a Zn(NO3)2 concentration of 30 mM were the most favourable for carrying out photoelectrochemical applications because they offered good stability against photocorrosion, high photoelectrochemical response (177 % higher than that of TiO2 nanosponges), low resistance to charge transfer and high density of charge carriers, compared to TiO2 nanosponges. Finally, the optimal TiO2/ZnO hybrid nanostructures were used as photoelectrocatalysts in energy and environmental applications. On the one hand, the theoretical hydrogen production obtained with the TiO2/ZnO hybrid nanostructures synthesized in this Doctoral Thesis during the water splitting tests was evaluated. On the other hand, the use of the optimal TiO2/ZnO hybrid nanostructures as photoelectrocatalysts in the photoelectrocatalytic degradation of pesticides (Imazalil) in water was evaluated, obtaining a degradation percentage of 99.6 % carrying out the photoelectrocatalytic degradation of 10 ppm of Imazalil in Na2SO4 0.1 M for 24 hours applying a potential of 0.6 VAg/AgCl (3M KCl). / Agradezco al Ministerio de Ciencia e Innovación la concesión de la subvención proporcionada por el Sistema Nacional de Garantía Juvenil (PEJ2018- 003596-A-AR), al Ministerio de Economía, Industria y Competitividad la concesión del proyecto CTQ2016-79203-R y al Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación la concesión del proyecto PID2019-105844RB- I00/MCIN/AEI/ 10.13039/501100011033, en los cuales he podido participar durante el desarrollo de la presente Tesis Doctoral. / Navarro Gázquez, PJ. (2023). Desarrollo de nuevos electrodos basados en nanoestructuras híbridas de óxidos metálicos semiconductores para aplicaciones energéticas y medioambientales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/194708