TiO2 (B) nanotubes with ultrathin shell for highly efficient photocatalytic fixation of nitrogen

•TiO2 nanotubes were fabricated for photofixation of nitrogen.•The nanotubes possess submicrometer-sized cavitary and ultrathin shell.•It exhibits a NH3 yield of 106.6 μmolg−1 h−1 under solar irradiation.•The cavity promotes the light harvesting by multiple light scattering.•Abundant defects on ultrathin shell benefit the carrier separation.