The mechanism of efficient photoreduction nitrate over anatase TiO2 in simulated sunlight.

Revealing the activation mechanism of nitrate (NO3-) reduction is crucially important to design high-efficiency photocatalysts for NO3- removal. In this work, the performance of photoreduction NO3- has been thoroughly studied over different crystalline phases TiO2. Photodegradation rate of NO3- over anatase TiO2 is found to be higher than that of rutile TiO2 at simulated sunlight, which can achieve high NO3- conversion of 94% and 100% nitrogen selectivity (original concentration of 50 mg/L NO3--N) at reaction time of 4 h. With the aid of in situ Fourier Transform Infrared (FTIR) and density functional theory (DFT) calculations, the possible reaction paths of photoreduction NO3- over anatase TiO2 was verified from theory and practice sides. NO3- was adsorbed on surface Ti site to form bridging nitrate (M - O)2NO model. Then, monodentate nitrite (M-O-N-O) model was the dominant intermediate in the reduction process of NO3-. This study presents a new opinion of photoreduction NO3- reaction paths.