Morphology control of TiO2-based nanomaterials for sustainable energy and environmental applications

It is unquestionable that one of the most important challenges of our society is the development of new energy strategies to tackle global warming and the exhaustion of fossil fuels generation. In this sense, it is of vital importance the production of less contaminating energy with positive effects on the reduction of greenhouse gas emissions. The conversion of solar energy into chemical energy in the form of so-called "solar fuels" as hydrogen is one of the main strategies today to solve the energy problem we face in the near future. Nanotechnology is a key area that can help solving this issue. In fact, by using the tools offered by nanotechnology, it is possible to obtain photocatalytic nanomaterials that offer solutions to these problems. The main aim of this thesis was to design new photocatalysts based on TiO2 with improved harvesting of visible light, which covers 43% of sunlight. The main focus of this PhD thesis was the evaluation of the effect of different transitions metals on the absorption properties of TiO2 samples with controlled morphology (nanosheets with reactive (001) exposed facets) on the photocatalytic activity in H2 production from biomasses and in degradation of polluting dyes. In the case of the TiO2 semiconductors, it was paid particular attention to bi-dimensional nanocrystals to decrease the e-/h+ recombination rate and in the synergistic effect of the combination of two polymorphs (anatase/brookite). Basically the research activity carried out can be summarized as follows: synthesis of novel nanomaterials, including the preparation of metal-doped TiO2 nanocrystal with controlled morphology; evaluation of photocatalytic activity under realistic conditions (bio-alcohols photo-reforming and degradation of organic compounds in self-cleaning materials) and the effect of the metal transitions in both activity and selectivity; sub-nanometric characterization of selected photocatalysts by mean of Advanced Electron Microscopy Techniques. Throughout the duration of this experimental work, was handled many advanced characterization techniques to obtain a deeper understanding of the nature of the samples and get to explain their behaviour in different photocatalytic experiments. Several techniques such as textural characterization, band-gap measures using UV-diffuse reflectance spectroscopy, XPS, ICP, XRF have been used for obtaining trial data which have been used to obtain results. Particular attention has been devoted to the characterization of the materials by electron microscopy.