Nanoscale investigation of photoinduced hydrophilicity variations in anatase and rutile nanopowders.

The photoactive properties of TiO2 are employed to develop surfaces with self-cleaning capabilities. Clearly, the fine-tuning of such surfaces for different applications relies on a holistic understanding of the different aspects that induce the self-cleaning behavior. Among those, the mechanisms responsible for the photoinduced surface alteration in the TiO2 allotropes are still not completely understood. In this study, TiO2 polymorphs nanopowders are investigated by combining the high spatial resolution observables of recently developed atomic force microscopy (AFM) based force spectroscopy techniques with diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Phase maps under irradiated and nonirradiated conditions for anatase and rutile suggest the existence of two distinct behaviors that are further discerned by energy analysis of amplitude and phase vs distance curves. Independently, surface analysis of anatase and rutile by means of DRIFTS spectroscopy reveals a readily distinguishable coexistence of dissociated water and molecular water on the two phases, confirming the stronger photoactivity of anatase. The peculiarity of the surface interaction under UV exposure is further investigated by reconstructing the force profiles between the oscillating AFM tip and the TiO2 phases with the attempt of gaining a better understanding of the mechanisms that cause the different hydrophilic properties in the TiO2 allotropes.

Anodic titanium oxide as immobilized photocatalyst in UV or visible light devices.

Titanium anodizing can be a powerful technique to generate photoactive oxides, strongly adherent to the metallic substrate, and to modify their chemical composition by inducing doping effects. This work investigates the photocatalytic behavior of differently obtained anodic TiO(2) films under UV and visible light irradiation, so as to define the best treatment for wastewaters purifiers. Anodizing was performed in H(3)PO(4) and H(2)SO(4) mixtures or in fluoride containing electrolytes. Morphology, elemental composition and crystal structure of the anodic films were characterized by XDR, GDOES and SEM. When amorphous oxides were obtained, an annealing treatment was used to promote the formation of anatase crystals. Annealing was also performed in nitrogen atmosphere to induce nitrogen doping. The photocatalytic efficiency of anatase-enriched TiO(2) was investigated in rhodamine B photodegradation. Doping was induced not only by annealing but also directly by anodizing, and generated photoactivity in both the UV and Vis components of light.