Photocatalytic evaluation of heterojunctions semiconductor/ZnO/carbon xerogel in the photodegradation of 4-chlorophenol in both fluidized bed and batch reactors

Abstract

This project will explore the development of semiconductor/carbon xerogel/ZnO hybrid photocatalysts, aiming at the enhancement of the quantum efficiency of the degradation of organic pollutants. This will be the greatest technological innovation of this project, as the catalytic properties of this hybrid have not been studied in literature. The ZnO possesses high photocatalytic efficiency, reaction rate and superficial reactivity. However, its visible light absorption is limited e the recombination rate is low. Thus, in order to improve the ZnO photocatalytic efficiency the semiconductor visible light excitation and the recombination time must be improved. An efficient way to improve its photoactivity is the coupling of ZnO with another semiconductor by type II heterojunctions or Z-scheme. In these types of heterojunctions, the potential of the conduction and valence bands of the semiconductors are different, promoting the transfer of the photogenerated charges among them, which increases the recombination time and, consequently, the photocatalytic activity of the material. In this project, the semiconductor coupled with ZnO must have BC lower than ZnO, thus ZnS and g-C3N4 are the selected materials. Furthermore, the low superficial area problem can be solved by coupling the (g-C3N4 or ZnS)/ ZnO with carbon xerogel, as this material presents excellent electrical conductivity, high surface area and porosity, the last being easily manipulated by modifications in the synthesis parameters. The choice of the tannin molecule as the xerogel precursor is based at reducing costs and environmental impacts, as well as adding value to the proposed technological innovation. The band gap energy of the samples will be determined using diffuse reflectance spectroscopy. The crystallographic phase, morphology and elemental analysis will be evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The hybrid photocatalytic action will be evaluated through the decomposition of 4-chlorophenol in a batch reactor and in a fluidized bed reactor. (AU)