Controllable electrostatic self-assembly of sub-3 nm graphene quantum dots incorporated into mesoporous Bi2MoO6 frameworks: efficient physical and chemical simultaneous co-catalysis for photocatalytic oxidation

Abstract

Over the past few years, the direct assembly of co-catalyst/modification materials into mesoporous photocatalysts has been considered a great challenge. Additionally, for photooxidation, the simultaneous achievement of fast charge separation, broad spectrum photocatalytic activity and higher carrier utilization efficiency (generating more active oxidizing groups) is quite necessary but has never been studied. To this end, for the first time, using sub-3 nm GQDs as co-catalyst, we have successfully achieved uniform modification for a mesoporous photocatalyst (mesoporous Bi₂MoO₆) using a novel electrostatic self-assembly method. The sub-3 nm GQDs, which were prepared from graphene nanosheets by a modified chemical oxide method, exhibit many unique physical and chemical properties, such as small size, electronic capture, up-conversion, and in particular, peroxidase-like activity. After the GQDs were modified, the resulting mesoporous hybrid photocatalyst (GQDs–BM) exhibited excellent charge separation efficiency and broad spectrum photocatalytic activity from UV to NIR light. More importantly, we found that a certain amount of H₂O₂ was produced through a photoreduction effect during the photocatalytic process. Unfavorably, for bare Bi₂MoO₆, the continuously-accumulating H₂O₂ could not efficiently convert into ·OH by a one-photoelectron reduction, which results in the indirect waste of photo-excited electrons. However, the chemical co-catalysis of GQDs could make this process (H₂O₂ → ·OH) more quick and efficient and moreover, did not need any additional photoelectrons, which means the effective enhancement of the utilization efficiency of photo-excited electrons (generating more ·OH). Additionally, for the as-prepared GQDs–BM, a sharp increase in photo-degradation activity for different target pollutants, such as BPA, MB, TC, CIP and phenol further confirmed that the simultaneous physical and chemical co-catalysis of GQDs can efficiently enhance the photocatalytic activity of mesoporous Bi₂MoO₆.