Persulfate activation towards organic decomposition and Cr(VI)reduction achieved by a novel CQDs-TiO_2−x/rGO nanocomposite

In this work, a novel carbon quantum dots and Ti³⁺ co-modified TiO₂-graphene nanocomposite (CQDs-TiO_2−x/rGO)was successfully fabricated via a facile, relatively cheap and environmentally friendly process. The light absorption edge of CQDs-TiO_2−x/rGO was significantly extended to 481.93 nm due to the formation of Ti³⁺ impurities and Ti[sbnd]O[sbnd]C bonds and the excellent photon conversion function of CQDs. The presence of CQDs and rGO with an excellent conductivity provide dual channels for the transfer of electrons, leading to the rapid transportation and effective separation of charge carriers. To enhance the mineralization of organics in the water treatment, persulfate (PS)was introduced to the developed the CQDs-TiO_2−x/rGO-Vis reaction system. Due to the excellent photocatalytic performance of the CQDs-TiO_2−x/rGO nanocomposite, PS was efficiently activated by CQDs-TiO_2−x/rGO to produce a large number of sulfate radicals and hydroxyl radicals under visible-light irradiation. As a result, 10 mg/L bisphenol A (BPA)and phenol were completely degraded and the mineralization efficiency was improved to 82% and 76% by CQDs-TiO_2−x/rGO (0.5 g/L)in the presence of PS (2 mM)in only 5 and 20 min, respectively. Additionally, the excellent performance of CQDs-TiO_2−x/rGO was also exhibited by the efficient reduction of Cr(VI)under visible-light irradiation. The findings of the present study highlight the great potential of CQDs-TiO_2−x/rGO for environmental remediations.