The power of EPR techniques in revealing active sites in heterogeneous photocatalysis: The case of anion doped TiO2

Here we critically discuss the use of electron paramagnetic resonance (EPR) technique in the investigation of anion doped TiO2 based photocatalyst. Starting from a brief general overview of the potentiality of the EPR technique to investigate local properties of a given material, we used selected applications on the characterization of bare, C-, N-, B-, F-, and some anion co-doped TiO2 to highlight the power of this approach and to discuss its limitations and future challenges. In particular, we emphasize the need of other complementary techniques in addition to the EPR characterization, such as high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and computational calculations.