Azaindole grafted titanium dioxide for the photodegradation of pharmaceuticals under solar irradiation.

The application of metal-free organic molecules grafted titanium dioxide (TiO) as photocatalysts for the degradation of pharmaceuticals under solar light has been scarcely studied. Herein, a novel photocatalyst was synthesized anchoring a bipolar electron-donor and -acceptor molecule based on azaindole derivative (AZA4) onto TiO aiming to improve the photoactivity under simulated solar irradiation. The TiO-azaindole (TiO-AZA4) was fully characterized, confirming that AZA4 was successfully grafted onto TiO and improving the light absorption. The grafted TiO was applied in the photodegradation of acetaminophen in water, showing a significantly better photocatalytic performance compared to that of pure TiO under both solar and visible irradiations. AZA4 grafting leads to the TiO band gap narrowing and favors the charge separation, thus improving the TiO photoactivity. The photocatalytic performance of TiO-AZA4 was evaluated using different conditions such as photocatalyst dose or initial pH of the solution, and the radical species involved in the process were investigated. The high activity of TiO-AZA4 was confirmed in the photodegradation of a mixture of pharmaceuticals, namely acetaminophen, ibuprofen, and antipyrine, further demonstrating its stability and catalytic performance in a novel continuous flow test under simulated solar irradiation, thus finding a new strategy to design solar-light driven photocatalysts for the degradation of pollutants in water.