A study was carried out on the consequences of the -OHsurf/F- exchange occurring at the surface of TiO2 P25 when suspended in HF/F- solutions. The maximum extent of fluorination was reached at pH 3.0, resulting in the fixation on the surface of ca. 2.5 F-/nm2. The surface features of fluorinated samples under two selected conditions were investigated by IR spectroscopy, in comparison with pristine TiO2. The collected data suggested that bridged -OHsurf, likely located on regular facets, was more resistant to exchange with F-. Combined high resolution transmission electron microscopy (HRTEM), inductively coupled plasma mass spectrometry (ICP-MS) and IR measurements indicated that the fluorination performed in the adopted condition did not induce any etching of TiO2 particles, and the -OHsurf/F- exchange appeared reversible by treatment in concentrated basic solutions. Furthermore, fluorination resulted in an increase of the Lewis acid strength of surface Ti4þ sites, which, as a consequence, retained adsorbed water molecules even after outgassing at 423 K. Such an effect involved the overwhelming majority of cations exposed on regular facets
Effect of fluorination on the surface properties of titania P25 Powder: an FTIR study
Faga M G;Coluccia S;
2010
Abstract
A study was carried out on the consequences of the -OHsurf/F- exchange occurring at the surface of TiO2 P25 when suspended in HF/F- solutions. The maximum extent of fluorination was reached at pH 3.0, resulting in the fixation on the surface of ca. 2.5 F-/nm2. The surface features of fluorinated samples under two selected conditions were investigated by IR spectroscopy, in comparison with pristine TiO2. The collected data suggested that bridged -OHsurf, likely located on regular facets, was more resistant to exchange with F-. Combined high resolution transmission electron microscopy (HRTEM), inductively coupled plasma mass spectrometry (ICP-MS) and IR measurements indicated that the fluorination performed in the adopted condition did not induce any etching of TiO2 particles, and the -OHsurf/F- exchange appeared reversible by treatment in concentrated basic solutions. Furthermore, fluorination resulted in an increase of the Lewis acid strength of surface Ti4þ sites, which, as a consequence, retained adsorbed water molecules even after outgassing at 423 K. Such an effect involved the overwhelming majority of cations exposed on regular facetsI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
