Solid-solid interface formation in TiO2 nanoparticle networks.

Aiming at a comparison of microstructure and paramagnetic properties of mesoporous TiO2 nanoparticle networks, we subjected entirely different TiO2-x precursor structures to vacuum annealing. The transformation of an amorphous TiO2-x, gel obtained by sol-gel processing of an ethylene glycol-modified titanium precursor-into a network of interconnected anatase nanocrystals was explored by means of X-ray diffraction, nitrogen sorption, and electron microscopy. Crystalline junctions between the particles emerge from temperature treatment. This process of particle network formation is different from that related to the vapor phase grown anatase nanocrystals where particle-particle interface formation is induced by contact with water. It was found that, after annealing up to 873 K and controlled sample purification in oxygen atmosphere, both types of samples exhibit high concentrations of particle-particle interfaces and comparable properties in terms of surface area, porosity, and microstructure. With electron paramagnetic resonance (EPR) we observed on nonstoichiometric TiO2-x networks an identical type of subsurface defect which is related to the presence of solid-solid interfaces.