N, S co-doped carbon quantum dots/TiO2 composite for visible-light-driven photocatalytic reduction of Cr (VI)

A novel carbon quantum dots (CQDs) sensitized TiO2 (N, S-CQDs/TiO2) composite was prepared and used as a visible-light-active photocatalyst for the reduction of Cr (VI), one of the most toxic heavy metal ions. Experi-mental results from the batch reaction process indicated that the composite was able to completely reduce Cr (VI) to Cr (III) at pH 2.0 after 3 h ' exposure to visible light with the initial Cr (VI) concentration being 20.0 mg/L and a catalyst dosage of 1.0 g/L. It was also found that lower pH and lower initial concentration of Cr (VI) led to high reduction efficiency. Compare with pure TiO2, a four-fold increase in reduction efficiency of Cr (VI) was achieved by the N, S-CQDs/TiO2 composite under the same reaction conditions. The prepared composite also demon-strated good reusability and stable photocatalytic performance in real water samples. Results from this study confirm that sensitization of TiO2 with CQDs is efficient in broadening the light absorption range of TiO2, expanding its application in visible-light-driven photocatalysis.