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

The application of metal-free organic molecules grafted titanium dioxide (TiO2) 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 TiO2 aiming to improve the photoactivity under simulated solar irradiation. The TiO2-azaindole (TiO2-AZA4) was fully characterized, confirming that AZA4 was successfully grafted onto TiO2 and improving the light absorption. The grafted TiO2 was applied in the photodegradation of acetaminophen in water, showing a significantly better photocatalytic performance compared to that of pure TiO2 under both solar and visible irradiations. AZA4 grafting leads to the TiO2 band gap narrowing and favors the charge separation, thus improving the TiO2 photoactivity. The photocatalytic performance of TiO2-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 TiO2-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.

Effect of Activating Agent on the Properties of TiO2/Activated Carbon Heterostructures for Solar Photocatalytic Degradation of Acetaminophen.

Several activated carbons (ACs) were prepared by chemical activation of lignin with different activating agents (FeCl3, ZnCl2, H3PO4 and KOH) and used for synthesizing TiO2/activated carbon heterostructures. These heterostructures were obtained by the combination of the activated carbons with a titania precursor using a solvothermal treatment. The synthesized materials were fully characterized (Wavelength-dispersive X-ray fluorescence (WDXRF), X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption-desorption, Fourier transform infrared (FTIR) and UV-visible diffuse reflectance spectra (UV-Vis DRS) and further used in the photodegradation of a target pharmaceutical compound (acetaminophen). All heterostructures were composed of anatase phase regardless of the activated carbon used, while the porous texture and surface chemistry depended on the chemical compound used to activate the lignin. Among all heterostructures studied, that obtained by FeCl3-activation yielded complete conversion of acetaminophen after 6 h of reaction under solar-simulated irradiation, also showing high conversion after successive cycles. Although the reaction rate was lower than the observed with bare TiO2, the heterostructure showed higher settling velocity, thus being considerably easier to recover from the reaction medium.