Synthesis and Characterization of Morphology-Controlled TiO2 Nanocrystals Opportunities and Challenges for their Application in Photocatalytic Materials

Morphology-controlled titania nanocrystals (NCs) are indicated as promising building blocks for the generation of new photocatalytic materials, where precise tailoring of particle size and exposed crystal surfaces enables to fulfill specific reactivity requirements. In fact, beyond the dimensions, the presence of different TiO2 facets dramatically affects its photoactivity. This has been recently connected to the peculiar electronic band structures of specific surfaces and to their ability in promoting the concentration of different photogenerated defects. The most mature methods for the synthesis of shape-controlled TiO2 utilize organic surfactants, which commonly remain anchored to the NCs surfaces, often precluding their final use in photocatalytic applications. Although several alternatives have been provided (e.g., ligand exchange), there is still an urgent need to identify approaches for controlling morphology by also granting tunable surface functionalities, easy scalable procedures, and applicability in "friendly" materials (e.g., pellet, membranes, or flexible substrates). Bearing these challenges in mind, this chapter briefly presents the basic synthesis strategies for tuning morphology and surfaces of TiO2 NCs, focusing on those that may guarantee a transfer of the NCs intrinsic features to technological applicable photocatalytic materials. A brief state of art of the microscopic and spectroscopic techniques utilized for verify and study their morphology-dependent functionalities will be described. In this context and aiming to suggest implementation of TiO2 reactivity, a special attention will be devoted to spectroscopies (mainly ESR) allowing to monitor quasi "in situ" the photocatalytic mechanism. Finally, some perspectives for the inclusion of shape-controlled TiO2 NCs in smart materials will be proposed.