Quercetin-mediated green synthesis of Au/TiO2 nanocomposites for the photocatalytic degradation of antibiotic ciprofloxacin

Contaminated water is one of the world's largest health and environmental problem. Emerging pollutants, such as pharmaceutics, are raising increasing concerns, as they are non-regulated toxic chemicals found in low concentrations that are very resilient to conventional water treatments. In the search for effective methods to address this problem, photocatalysis arises as a possible solution to degrade organic pollutants. TiO2 is one of the most widely used catalysts, but the reduced photoactivation under visible radiation constitutes a major drawback. The inclusion of plasmonic nanoparticles, such as gold (AuNPs), can improve the ability to absorb visible radiation from sunlight. AuNPs synthesis methods include toxic and expensive reagents. Herein, an alternative method is proposed, using the flavonoid quercetin to act as the reducing agent in the deposition of AuNPs on the surface of TiO2 (Au/TiO2). The method is optimised, and different loadings of gold are tested. The characterisation of Au/ TiO2 confirms increased absorption in the visible wavelength range with increasing concentrations of gold as well as a reduction in the energy band gap. The photocatalytic efficiency of Au/TiO2 was evaluated for the degradation of the antibiotic ciprofloxacin under UV and simulated sunlight irradiation, obtaining a maximum degradation of 86 and 95%, respectively.