Photocatalytic degradation of organic molecules by poly (vinyl alcohol)/zinc oxide hydrogels

Zinc oxide (ZnO) nanoparticles (NPs) were immobilized in polyvinyl alcohol (PVOH) hydrogels with the aim of preparing photocatalytic gels. Spherical ZnO NPs were obtained using the sol-gel method with an average diameter of 7.3 ± 1.1 nm. Hydrogels were prepared with different proportions of ZnO (5, 15 and 30 wt%) using the dry casting method and subsequently characterized by ray diffraction X (DRX) and thermogravimetric analysis (TG). In the images obtained by scanning electron microscopy (SEM) it was observed the presence of ZnO NPs uniformly distributed in the polymeric matrix. As a proof-of-concept, photocatalytic activity of hydrogels, using a mercury vapor lamp, was first studied using methyl orange dye (MO). From this study, it was concluded that the hydrogels promoted between 35 and 40% dye degradation and the hydrogels could be reused for at least five consecutive photocatalysis cycles. Next, bisphenol-A (BPA), an important endocrine disruptor found in drinking water, was used as the interest analyte. It was found that the initial BPA concentration is the most significant parameter in the photocatalytic process. Mass spectrometry was employed to identify the degradation products of BPA. Eleven by-products were identified among them nine of these by-products exhibit lower toxicity compared to BPA. It was concluded that ZnO NPs was successfully immobilized in PVOH matrix to obtain shape-controlled photocatalytic hydrogels that can be applied in photodegradation processes.