A DFT and EPR study on the effect of N-F co-doping of TiO2

A DFT and EPR study on the effect of N-F co-doping of TiO2

C. Di Valentin,¹ E. Finazzi, G. Pacchioni,

Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53, 20125, Milano, Italy

A. Selloni

Department of Chemistry, Princeton University, Princeton N.J. 08540, USA

S. Livraghi, A. M. Czoska, M.C. Paganini, E. Giamello,

Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I - 10125 Torino, Italy

1 Electronic address: cristiana.divalentin@mater.unimib.it

Figure S1: Spin density plot for the triplet spin configuration of Ns-Fs/TiO2 as obtained with the PBE calculation.

Figure S2: N,F-codoped TiO2 EPR spectra recorded at RT. a) N/F=1, b) N/F=10, c) N/F=100.

Comparison of the intensities of Nb• species is better performed on room temperature recorded spectra (Fig.S2) to avoid interference with the signals of molecular NO trapped in TiO2 as impurity (and not involved in visible light absorption) whose intensity randomly varies for the various samples. The NO signal in fact vanishes at room temperature as the species, weakly adsorbed on the inner cavities of the material, in such conditions desorbs and is no longer visible in EPR (ref.11 c and e of the manuscript).

Fig S2 clearly shows, as reported in the text, that the intensity of Nb• increases with increasing the N/F ratio i.e. with decreasing the nitrogen concentration in the material. In spectrum S2a the Nb•

species is barely visible and shows up only at lower temperature following the behaviour expected for paramagnetic species.