Solid-state processes of introducing oxygen vacancies and transference of fluorine to n-TiO2 nanoparticles by co-milling with PTFE powder were examined by diffuse reflectance spectroscopy (DRS) of UV, visual, near- and mid-IR regions, thermal analyses (TG-DTA), energy-dispersive X-ray spectroscopy (EDXS), X-ray photo-electron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. The broad absorption peak at around 8800/cm (1140nm) was attributed to the change in the electronic states, viz. electrons trapped at the oxygen vacancies (Vo) and d–d transitions of titanium ions. Incorporation of fluorine into n-TiO2 was concentrated at the near surface region and amounted to about 40at% of the total fluorine in PTFE, after co-milling for 3 h, as confirmed by the F1s XPS spectrum. The overall atomic ratio, F/Ti, determined by EDXS was 0.294. By combining these analytical results, a mechanism of the present solid state processes at the boundary between PTFE and n-TiO2 was proposed. The entire process was triggered by the partial oxidative decomposition of PTFE. This was accompanied by the abstraction of oxygen atoms from the n-TiO2 lattices. Loss of the oxygen atoms results in the formation of the diverse states of locally distorted coordination units of titania, i.e. TiO6−nVon, located at the near surface region. This leads subsequent partial ligand exchange between F and O, to incorporate fluorine preferentially to the near surface region of n-TiO2 particles, where local non-crystalline states predominate.

Introduction of Oxygen Vacancies and Fluorine into TiO2 Nanoparticles by Co-Milling with PTFE. M.Senna, V.Šepelák, J.Shi, B.Bauer, A.Feldhoff, V.Laporte, K.D.Becker: Journal of Solid State Chemistry, 2012, 187, 51–7