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

Abstract 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.