Graphene quantum dots/NiTi layered double hydroxide heterojunction as a highly efficient De-NOx photocatalyst with long persistent post-illumination action

Persistent photocatalysis is an attractive process to broaden the spectrum of environmental applications. Herein, blue luminescent graphene quantum dots (GQD) are incorporated into NiTi-based layered double hydroxide nanosheets (NiTi-LDH) by a facile impregnation method. The enhanced performance of GQD/NiTi-LDH leads to excellent NO photo-removal activity (61 %) and insignificant NO2 release (< 0.6 %), beating the standard TiO2 P25 (48 % and 14.2 %, respectively). Interestingly, after the end of light irradiation period, GQD/NiTi-LDH maintained a NO removal efficiency higher than 20 % for up to 75 min regardless of the previous irradiation time. This De-NOx post-photocatalytic process is the most effective reported at present. The dark/light mechanism is explained by the electron storage capacity of NiTi-LDH under light excitation, which is assisted by the electron migration from GQD to NiTi-LDH. Once the light is shut off, electrons are released and take part in the superoxide radical generation.