N-doped carbon quantum dots-Bi4O5Br2 composites: A case of van der Waals heterojunctions for efficient photocatalytic removal of NO under visible light irradiation.

The construction of van der Waals (VDW) heterojunctions has been deemed as an effective manner to boost photocatalytic performance since the presence of weak VDW force instead of strong chemical bonds ensures structural flexibility with diminished stress and defects caused by lattice mismatch. For such, a series of VDW heterojunctions were fabricated by decorating 2D Bi4O5Br2 with 0D N-CQDs and comprehensively characterized. Accordingly, the successful establishment of 0D-2D N-CQDs-Bi4O5Br2 (CD-BOB) VDW heterojunction composites was confirmed. These VDW heterojunctions were employed for photocatalytic removal of NO at part per billion (ppb) level and showed enhanced photocatalytic outcome compared with BOB under visible light, mainly attributing to structural merits of 0D-2D morphologies integration, promoted transfer and separation of charge carriers, boosted adsorption and activation of O2 and H2O as well as reactants NO confirmed by density functional theory (DFT) calculations, and strengthened generation of abundant of reactive species. The best candidate 5 % CD-BOB achieved a maximum removal efficiency of 51 %, which was 1.89 times higher than that of BOB alone. Besides, the robust sample was able to efficiently inhibit the formation of toxic NO2. Moreover, a preliminary photocatalysis mechanism was eventually proposed based on the analytical and experimental results. This study offers valuable insights into constructing 0D-2D VDW heterojunction composites for efficiently photocatalytically removing NO under visible light illumination.