Enhanced visible-light photocatalytic properties of SnO2 quantum dots by niobium modification

The incorporation of transition metal elements is an effective route to enhance the photocatalytic properties of semiconductors. Tin oxide (SnO2) has a wide band gap of 3.6 eV, which inhibits its applications as visible-light photocatalysts. In this work, niobium-modified SnO2 quantum dots (Nb-SnO2 QDs) are synthesized by a one-step hydrothermal method. The crystal structures and optical properties of the Nb-SnO2 QDs are characterized and the photocatalytic performances are evaluated by the degradation of organic contaminants under visible-light illumination. The rate constant of Nb-SnO2 QDs increases 2.34 times as that of pristine SnO2 QDs in MO degradation. The improved photocatalytic properties are ascribed to the modified band structure by the transition metal. The main active radical is determined to be O2− in the photocatalytic process. The first principle computational models are established based on the experimental characteristics of Nb-SnO2 QDs. The calculation reveals that Nb incorporation brings an impurity energy level in the band structure, which is originated from the 4d orbital electrons of Nb atoms.