Size-Dependent Photocatalytic Activity of Colloidal Silicon Quantum Dot

Photocatalytic activity of water-dispersible all-inorganic Si quantum dots (QDs) with heavily B and P codoped shells was studied by monitoring bleaching of Rhodamine B (RhB) in a mixture aqueous solution of Si QDs and RhB under light irradiation. The size of Si QDs was changed from 2.8 to 9.0 nm. A strong size dependence was observed in the dissociation rate of RhB. The observed size dependence of the rate could be well explained by the Marcus theory, which considers charge transfer from the LUMO of Si QDs to that of RhB. Quenching of the photoluminescence (PL) and the shortening of the PL lifetime of Si QDs due to the electron transfer to RhB were also observed. From these two approaches, we demonstrated that the quantum size effect plays a crucial role for the enhanced photocatalytic activity of Si QDs.