High-concentration N-doped La2Ti2O7 nanocrystals: Effects of nano-structuration and doping sites on enhancing the photocatalytic activity

A series of N-doped La2Ti2O7 nanocrystal for photocatalytic NOx oxidation are successfully prepared by a two-steps process including hydrothermal reaction and heat treatment under NH3 flow. The effects of different nitrogen doping amounts on the structure, optical property and photocatalytic activity of the obtained N-doped La2Ti2O7 are investigated. The photocatalytic activity and stability of the N-doped La2Ti2O7 samples are evaluated through photocatalytic oxidation of NOx under UV and visible light irradiation. The nanosheet morphology of N-doped La2Ti2O7 is originated from La2Ti2O7 precursor synthesized by hydrothermal reaction. The addition of triethanolamine (TEA) in the hydrothermal reaction largely affects the morphology of La2Ti2O7 to form nanocrystal. The light absorption of La2Ti2O7 nanocrystal is cut off at 338 nm, while the N-doped La2Ti2O7 nanocrystals exhibit the extended light absorption up to 560 nm. It is found that the N doping into La2Ti2O7 enhances absorption in the visible light region to exhibit higher activity for photocatalytic oxidation of NO gas. The optimized N-doped La2Ti2O7 nanocrystal with 4.79 at% of nitrogen dopant possesses the best photocatalytic NOx oxidation activity under both ultraviolet and visible light irradiation compared with N-doped La2Ti2O7 samples obtained by hydrothermal reaction without TEA or flux synthesis of La2Ti2O7 and the subsequent treatment with NH3. The enhancement of photocatalytic activity should originate from simultaneous achievement of large specific surface area and strong visible light absorption due to the large amount of nitrogen dopants.