Effect of UV irradiation on ZnO NPs-polystirene nanocomposites investigated by means of Infrared Spectroscopy

Full text: Among the semiconductor nanoparticles (NPs), zinc oxide has received much attention due to its properties, such as, its high photocatalytic and antimicrobial activities, and protection against ultraviolet (UV) radiation [1]. In view of this, ZnO NPs were synthesized via sol-gel in alcoholic medium, in order to combine them with polystyrene (PS) in chloroform. Were obtained homogeneous nanocomposites films, presenting visible transparency and good fluorescence emitters under UV excitation. Given the ZnO photocatalytic and UV-blocker properties, PS and ZnO NPs-PS nanocomposites were UV-irradiated for almost 40 days. UV radiation induces the formation of radicals, which cause a set of events, such as, the build up of conjugated bond sequences in the polymer, which is the main reason of yellowing effect [2]. Photodegradation was investigated by infrared spectroscopy. Main changes were observed, after UV light exposure, comparing pure PS and the nanocomposite between 1600-1750 cm-1 and a band enlargement was noticed at 1700 cm-1, only for pure PS, indicating the beginning of formation of bands of the carbonyl group, which is related with the visual yellowish aspect of the film. Furthermore, dynamic light scattering and scanning electronic microscopy showed that the ZnO NPs presented mean diameters ≥ 10 nm. By X-ray diffraction it was confirmed the hexagonal structure (wurtzite) of ZnO NPs. As a main conclusion the presence of ZnO NPs in the PS matrix had improved the photostability, by slowing the yellowing. Such kind of nanocomposites can be applied to the development of transparent with UV protection materials with additional fluorescence, which can be used for the development of sensors and for tracking molecular events that happen during the photodegradation. (author)