Chapter 6 - Photocatalytic ozonation

Abstract

Vanadium oxide, supported on zinc oxide (ZnO), was prepared and used as a catalyst to enforce terephthalic acid (TA) elimination, using photocatalytic ozonation based on light emission diodes (UV-ALEDs). The catalyst characterization indicated that vanadium oxide was not incorporated into the pores of zinc oxide, due to the formation of thinner flakes. The synthesized catalyst exhibited high stability, because no significant changes between fresh and used catalyst were confirmed by the XPS results. All variants of ozonation (conventional, catalytic, and photocatalytic) removed the terephthalic acid completely during 60 min; however, its reaction rate constant was higher in the catalytic and photocatalytic ozonation (22% and 25%, respectively). The ozone decomposition study indicated that terephthalic acid was degraded by the combined action of molecular ozone and hydroxyl radicals. The latter oxidant species play an important role in promoting the byproduct elimination generated during the ozonation of TA. The distribution of UV-ALEDs was evaluated in two configurations (central and external irradiation), which resulted in significant differences. These differences were confirmed by the reaction rates of the byproducts accumulation and their decomposition. Even when the energy supplied in both cases remained constant (4Wm−2), the interaction between photons and active sites in the catalyst was twice higher, when the UV-ALEDs were on the peripheral of the reactor. All these results show that VxOy/ZnO is a potential catalyst for photocatalytic ozonation using a portion of the visible electromagnetic spectrum.