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 NO_x 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 NO_x 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 NO_x 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.