Carbon Dots-TiO2 Nanocomposites for the Enhanced Visible-Light Driven Photodegradation of Methylene Blue

Herein, the conjugation of carbon dots (CDs) with TiO2 nanoparticles is reported to prepare a photocatalytic nanocomposite for an enhanced visible-light-driven photodegradation of methylene blue (MB). CDs are prepared from citric acid (CA) and ethylenediamine (EDA) via hydrothermal treatment. Using MB as a model pollutant, it is observed that, under visible-light irradiation, the nanocomposite presents an increment of the catalytic performance of 367% when compared to bare TiO2. This is achieved because the addition of CDs leads to increased visible-light absorption and hinders the recombination of photogenerated charge carriers. Thus, CDs are capable of bridging some of the limitations posed by TiO2. Tests using reactive species scavengers indicate that the main active species involved in the photodegradation by the nanocomposites are superoxide radicals followed by hydroxyl radicals, which differs from bare TiO2. Lastly, a life cycle assessment (LCA) study shows that, when accounting for performance, the nanocomposites have lower relative environmental impacts than bare TiO2. In addition, the safety of the produced CDs is shown by in vitro assays. In summary, due to conjugation with CDs, a relevant increment in the catalytic performance of TiO2 is achieved; providing an important step toward the sustainable rational design of active visible-light-driven photocatalysts.

Automated summary

In this study, the conjugation of carbon dots (CDs) with TiO2 nanoparticles was reported to prepare a photocatalytic nanocomposite for enhanced visible-light-driven photodegradation. The addition of CDs led to an increase in visible-light absorption and hindered the recombination of photogenerated charge carriers, resulting in a significant improvement in the catalytic performance of TiO2. The nanocomposites exhibited a different active species profile compared to bare TiO2, with superoxide radicals and hydroxyl radicals being the main active species. Additionally, a life cycle assessment showed that the nanocomposites had lower relative environmental impacts and the safety of the produced CDs was confirmed by in vitro assays. This study provides an important step towards the sustainable rational design of active visible-light-driven photocatalysts.