Study of nano-ZnO/Graphene-based photocatalyst to degrade Triclosan under UV and visible light

Abstract

"In recent years, a growing problem with water treatment has arisen due to the presence of endocrine-disrupting compounds (EDC), which persist in surface, waste, and drinking water. A significant example of EDC is triclosan (TCS), a bactericidal widely used in deodorant formulations, toothpaste, soaps, powders, cosmetics, textiles, plastics, polymers, fibers, and medical implant devices. Then, given the use of these products, triclosan has been directly discharged into wastewater, although it has also been detected in surface water, sludge, sediment, and drinking water. The treatment of water, by conventional methods, removes in some cases up to 90% of EDC. However, with such residual concentrations of triclosan, it is necessary to develop methods to remove even trace concentrations of these pollutants. Heterogeneous photocatalysis, which is usually carried out under ultraviolet radiation to activate the semiconductor and thereby to trigger reduction and oxidation reactions that are responsible for degrading and mineralizing organic compounds, such as triclosan. Nano ZnO is a semiconductor that has demonstrated potential photocatalytic activity to degrade EDC, but its development can be improved by using an electron transport material as graphene or graphene oxide. Modification of ZnO nanoparticles with graphene and graphene oxide (GO) was carried out, and the obtained hybrid photocatalyst was used for the photodegradation of TCS. The carbon material amount was evaluated to modify nano-ZnO catalyst using two different methods mechanical and photo-irradiation, and the resultant materials were characterized in order to determine their physicochemical and photocatalytic properties. Regarding the photocatalytic evaluation, the results of the photodegradation process for TCS showed that carbon materials act as a trap of electrons improving the performance of ZnO even at low TCS concentration (8 mg.L-1) under visible and UV radiation. The graphene base-modified photocatalysts with the highest concentration (0.5% w/w) showed the best photocatalytic performance under visible light degrading up to 47% of TCS and showed a reaction rate constant two times higher than pure ZnO in contrast with the 95% of the TCS degraded under UV light. In addition, the hybrid nano-ZnO/GO photocatalyst was immobilized in a polymer matrix (PVA hydrogel), as an alternative to support photocatalyst in real WWTPs obtaining a TCS degradation of 32% under visible radiation. This research contributes to the understanding how to enhance the efficiency of hybrid photocatalysts and the photoactive polymer material under natural light radiation (solar light) in APOs."