Mechanism of Nitrogen-Concentration Dependence on pH Value: Experimental and Theoretical Studies on Nitrogen-Doped TiO₂

Abstract

Experiments and density functional theory (DFT) calculations were combined in an attempt to investigate the origin of the differences in nitrogen concentration incorporated by N-doped TiO 2 . X-ray photoelectron spectroscopy (XPS), UV−vis diffusive reflectance spectra (UV−vis), and photodegradation experiments were conducted to set some premises for DFT calculations. Fourier transform infrared (FT-IR) spectroscopy was applied to investigate the NH x -containing species in the dried precipitate from the hydrolysis. [Ti(H 2 O) a (NH 3 ) b (OH) c Cl d ] (4− c − d ) ( a + b + c + d = 6) is defined as the Ti complex produced by the hydrolysis process, and its pH-dependent character was further determined by Gibbs energy calculations for the reaction based on those of related equations. Adsorption energies of NO on TiO 2 surfaces were calculated to study the ability of NO x to be incorporated into the TiO 2 matrix under different pH conditions. Finally, we propose three processes as being responsible for the dependence of the nitrogen concentration on the pH value.