Visible-light photocatalytic reduction of Cr(VI) via carbon quantum dots-decorated TiO2 nanocomposites

Abstract

Carbon quantum dots (CQDs) having sizes of 5–10nm have been prepared facilely by a hydrothermal method and incorporated with TiO2 nanoparticles to produce CQDs-decorated TiO2 (C/TiO2) nanocomposites with various dosages of CQDs. Under visible-light irradiation, the photocatalytic activities of Cr(VI) reduction via C/TiO2 nanocomposites have been monitored and found to depend highly on the dosage of CQDs. In particular, the photocatalytic rate constant (0.0449min−1) of C/TiO2 nanocomposites with 3wt% CQDs is 8.6 times higher than that of pure TiO2 nanoparticles. When CQDs are excited by visible light, photo-generated electrons transfer from CQDs into the conduction band of TiO2 on the time scale of 1500ps. Transferred electrons are subsequently captured by Cr(VI) ions, reducing Cr(VI) into Cr(III). Thus, π-conjugated CQDs act as sensitizers to provide visible-light response to the TiO2 nanoparticles of C/TiO2 dyade structures, leading to the highly efficient photocatalytic reduction of Cr(VI). Our as-prepared C/TiO2 nanocomposites are applicable in an inexpensive way to treat wastewater by utilizing solar energy without employing electron donors.