Construction of upconversion nitrogen doped graphene quantum dots modified BiVO₄ photocatalyst with enhanced visible-light photocatalytic activity

A direct and facile “bottom-up’’ approach was carried out to prepare nitrogen doped graphene quantum dots (NGQDs) under hydrothermal conditions. The as-synthesized NGQDs exhibited an excellent excitation-independent upconversion and downconversion photoluminescent (PL) behavior. And further, the NGQDs/BiVO₄ composite photocatalysts were also fabricated to investigate enhanced visible-light photocatalytic performance. The addition of NGQDs in the NGQDs/BiVO₄ could improve the photocatalytic performance, and the results indicated 5.0 wt% NGQDs/BiVO₄ composites showed the optimal photocatalytic performance. The quenching of effects of different scavengers demonstrated that superoxide radical played a major role in MB degradation. A possible mechanism that NGQDs could enhance the photocatalytic performance of NGQDs/BiVO₄ composites had been also proposed. It was estimated that the photocatalytic performance of the NGQDs/BiVO₄ composites for the degradation of MB under visible light could be primarily ascribed to upconversion PL character of NGQDs and the efficient separation of photogenerated electrons and holes.