Multi-approach Electron Paramagnetic Resonance Investigations of UV-Photoinduced Ti3+ in Titanium Oxide-Based Gels

EPR investigations of the photoreduction of Ti4+ into Ti3+ under UV irradiation were carried out on three titanium-based materials for which the initial concentration of Ti4+ was defined in the ternary phase diagram (TiOCl2, H2O, DMF). The kinetics of this photoreduction was monitored at 200 K and related to the initial concentration of Ti4+ in the solution. This study was complemented by a multi-approach EPR method (pulsed electron paramagnetic resonance (EPR), pulsed electron nuclear double resonance, and hyperfine sublevel correlation spectroscopy (HYSCORE)) with the aim of probing the proton environment of the Ti3+ ions. Indeed, many species such as H2O, OH-, HCOO- are located in the immediate vicinity of Ti3+. Although we found that a distribution of g tensors was involved, for simplicity, two types of g tensor were used to describe the main features of the EPR signal related to the paramagnetic ions. Additionally, we have evidenced that two kinds of protons are identified next to Ti3+ species, with specific distances determined from the hyperfine coupling parameters obtained by the HYSCORE method.