Enhanced molecular oxygen activation of Ni2+-doped BiO2-x nanosheets under UV, visible and near-infrared irradiation: Mechanism and DFT study

Abstract

Although molecular oxygen activation plays a significant role in photocatalytic process for pollutants removal, it is still challenging to activate molecular oxygen into superoxide radical (O2−) by photocatalysts under near-infrared (NIR) light irradiation. Herein, we successfully synthesized Ni2+-doped BiO2-x nanosheets, which could efficiently achieve the molecular oxygen activation into O2− under ultraviolet (UV), visible and NIR irradiation. Meanwhile, we found the doping Ni2+ facilitated the formation of BiO2-x nanosheets. More importantly, the contribution of doping Ni2+ on full spectrum molecular oxygen activation over Ni2+-doped BiO2-x was further confirmed by experiments and density functional theory (DFT) study. The introduction of Ni2+ into BiO2-x structure resulted in the formation of a new doping energy level band between the valence band (VB) and conduction band (CB) of Ni2+-doped BiO2-x, which contributed to the faster separation of carriers and highly efficient full spectrum driven molecular oxygen activation under UV, visible and NIR irradiation, especially with the irradiation of NIR light as compared to BiO2-x. In addition, the doping Ni2+ promoted the optical absorption property of BiO2-x with narrowing band gap and the up-shift position of VB and CB. As expected, the Ni2+-doped BiO2-x nanosheets exhibited enhanced photocatalytic activity for rhodamine B (RhB) degradation under UV, visible and NIR irradiation than pure BiO2-x nanosheets. The photocatalyst still revealed high photocatalytic activity even after five cycles. Finally, a possible photocatalytic mechanism of the degradation processes by Ni2+-doped BiO2-x was proposed. This work not only confirmed Ni2+ doping could promote the formation of BiO2-x nanosheets and enhance their full spectrum driven molecular oxygen activation ability, but also presented an in-depth understanding on the mechanism of full spectrum driven molecular oxygen activation.