ZnO-POLYVINYL ALCOHOL HYDROGELS FOR PHOTOCATALYTIC APPLICATIONS

This work studies the immobilization of zinc oxide (ZnO) nanoparticles (NPs) in polyvinyl alcohol (PVOH) hydrogels. One of the main difficulties of heterogeneous photocatalysis is the separation of the photocatalyst at the end of the process, especially when it is a powder. Therefore, the photocatalyst immobilization in a polymeric substrate facilitates the photocatalytic procedure. Herein, ZnO NPs were prepared by the sol-gel method, in ethanolic medium1. The hydrogels were prepared by slowly adding the ZnO NPs (amount corresponding to 15% of the mass of PVOH) to an aqueous PVOH dispersion (PVOH dispersion concentration was 7.5% w/w), followed by dry casting for obtaining films. Photocatalytic studies were performed using methyl orange (MO) as a model molecule. The hydrogels were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). By means of transmission electron microscopy (TEM) it was observed that ZnO NPs are spherical shape and have an average size of 7.8±1.4 nm. XRD pattern of the hydrogels PVOH and PVOH/ZnO15 showed the characteristic crystalline patterns of PVOH and ZnO2. MO photodegradation behavior in the presence of PVOH hydrogel, after five cycles, is very similar than without the hydrogel (~10% degradation). However, MO degraded 25 to 30% with PVOHZnO15 hydrogel, which demonstrates the potentiality and the reusability (up to 5 times) of the PVOH ZnO NPs hydrogels in photocatalysis, especially in wastewater treatment.