Heterogeneous photocatalysis applied in the degradation of organic pollutants using a hybrid zinc oxide-carbon xerogel as catalyst

Abstract

This project will generate scientific knowledge to increase the competitive edge, technological base of EEL/USP in the material area. We intend to explore the development of zinc-based semiconductors sensitive to visible light radiation, for application in photocatalytic processes employing sunlight. In order to achieve that, the preparation of the ZnO-xerogel carbon composite will be studied, as the sensitivity of the pure zinc oxide to visible light is low. The use of carbon xerogel in the preparation of the semiconductor-carbonaceous materials is justified by its excellent electrical conductivity, high surface area and porosity. The composite will also present greater sensitivity to visible light. The choice of tannin as the precursor of xerogel is aimed at reducing costs and environmental impacts, as well as adding value to the proposed technological innovation. Variations in the process parameters, such as synthesis path (aqueous or alcoholic), carbon/semiconductor ratio, pH and calcination temperature will be employed to obtain carbon gels with different dispersion of the inorganic phase in the organic phase, as well as different morphological characteristics, adsorption capacity and photocatalytic efficiency. By modifying the reaction pH, the type of particles (polymeric or colloidal) constituting the carbon gel will be controlled. With the study of the semiconductor/ carbon xerogel ratio it will be possible to estimate the optimum value in which the material presents ita greatest photocatalytic activity under visible light radiation. A higher ratio will lead the material to exhibit behavior similar to that of pure ZnO, presenting little sensitivity in visible radiation, whereas in lower ratio values the material does not present appreciable photocatalytic activity. The study of the type of solvent used in the synthesis of the composites is fundamental, as it directly affects the morphological uniformity, the reaction rate and the shrinkage of the material during the curing and calcination steps, parameters which interfere in the adsorption and photodegradation steps of the photocatalytic process. The determination of the optimal calcination temperature is important for the evaluation of the synergistic effect between adsorption capacity and photocatalytic activity of the prepared materials, resulting in a material with a greater sensitivity to visible light radiation for application in photocatalytic processes employing sunlight. In addition, the study of the calcination temperature will allow the evaluation of the effect of the xerogel presence at the crystallization temperature of the ZnO.The photocatalytic action of the material will be evaluated by the decomposition of 4-chlorophenol and bisphenol A, both highly toxic organic pollutants with low biodegradability. The band gap energy of the samples, the quantity of adsorbed molecules on their surfaces, and the effect of metal ion doping and metal deposition on the photocatalytic properties of the samples will be determined using diffuse reflectance spectroscopy. The materials will be characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, Raman spectroscopy, infrared spectroscopy and nitrogen adsorption-desorption isotherms, differential scanning calorimetry and Thermogravimetry (TGA) (AU)