One-Step Microheterogeneous Formation of Rutile@Anatase Core–Shell Nanostructured Microspheres Discovered by Precise Phase Mapping

Nanostructured core–shell microspheres with a rough rutile core and a thin anatase shell are synthesized via a one-step heterogeneous templated hydrolysis process of TiCl₄ vapor on the aerosol water–air interface. The rutile-in-anatase core–shell structure has been evidenced by different electron microscopy techniques, including electron energy-loss spectroscopy and 3D electron tomography. A new mechanism for the formation of a crystalline rutile core inside the anatase shell is proposed based on a statistical evaluation of a large number of electron microscopy data. We found that the control over the TiCl₄ vapor pressure, the ratio between TiCl₄ and H₂O aerosol, and the reaction conditions plays a crucial role in the formation of the core–shell morphology and increases the yield of nanostructured microspheres

Shedding Light on Aging of N‑Doped Titania Photocatalysts

A detailed analysis of nitrogen dopant behavior in nanostructured microspheres of the TiO₂ photocatalyst obtained by the thermally assisted reactions in aqueous sprays method has been performed for the first time using electron paramagnetic resonance, X-ray photoelectron spectroscopy, and UV–vis spectroscopy and is supported by theoretical simulation of possible defect structures. The nitrogen species were found to undergo the N^• to N^– transformation during sample storage under different conditions, with an activation energy of about 0.45 eV. Three main possible evolution pathways for the dopant state were identified and discussed. It was established that the most probable transformation consists of migration of an oxygen vacancy site to an interstitial nitrogen atom followed by the formation of a nonparamagnetic substitution nitrogen center. Possible diffusion routes of oxygen vacancy and corresponding energy barriers were estimated and found to be in agreement with experimental observations