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

Author(s)

Nícolas Perciani de Moraes

• Document type: Master's Dissertation
• Press: Lorena.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI)
• Defense date: 2019-02-01

Examining board members

Liana Alvares Rodrigues; Emerson Sarmento Gonçalves; Sebastiao Ribeiro; Robson da Silva Rocha

• Advisor: Liana Alvares Rodrigues

Abstract

The development of ZnO/Carbon xerogel hybrid photocatalysts was studied, in order to increase the quantum efficiency of the degradation process of persistent organic pollutants. Specifically, the preparation of the ZnO-carbon xerogel hybrid was studied, being this the most significant technological innovation of this project, considering that the catalytic effect of this hybrid was not studied in the literature. The use of carbon xerogel in the preparation of the semiconductor-carbonaceous material is justified by its excellent electrical conductivity, high surface area and porosity, the latter being easily manipulated by modifications in the synthesis parameters. The choice of tannin as the precursor of the xerogel aims at reducing costs and environmental impacts, adding value to the proposed technological innovation. The influence of the pH and route of synthesis were evaluated, as well as the influence of the calcination temperature on the properties of the materials. Diffuse reflectance spectroscopy was the technique used to determine the gap energy of the samples. The morphology, elemental analysis, crystalline and chemical structure of the materials were determined by scanning electron microscopy, dispersive energy spectrometry, X-ray diffractometry, infrared and Raman spectroscopy, respectively. The charge balance on the material surface was analyzed by the point of zero charge methodology (PZC). The photocatalytic action of the material was evaluated by the decomposition of 4-chlorophenol and bisphenol A, determined by UV-Visible spectroscopy. All materials have the hexagonal crystalline structure of zinc oxide (wurtzite). The materials without tannin in their composition also present the zinc hydroxychloride monohydrate phase. The X-ray diffractograms and bandgap values obtained confirm the incorporation of the carbon in the crystalline structure of the zinc oxide. The materials produced via the alcohol route have lower values of crystallite and particle size, as well as a higher content of graphite in their composition and larger surface area, while the materials produced in aqueous solution have lower values of gap energy. All the materials presented photocatalytic activity when subjected to visible and solar radiation, and the materials with intermediate proportions between carbon xerogel and zinc oxide were superior for the photodegradation process. The materials produced via alcohol route are superior to those produced in aqueous solution, as far as the photocatalysis process is concerned. The maximum values found for the degradation of 4-chlorophenol and bisphenol A were 88% and 78%, respectively, obtained by the material XZnC 3.0 (EtOH). The calcination temperature and amount of potassium hydroxide used in the synthesis significantly influence the properties of the materials, so that the optimum conditions for the synthesis of the materials were calcination at 300 °C and 8 g of potassium hydroxide used in the synthesis. The mechanism of photocatalysis is strongly influenced by the generation of hydroxyl radicals and the materials present stability for recycling in industrial processes. (AU)

• FAPESP's process: 16/20920-5 - Heterogeneous photocatalysis applied in the degradation of organic pollutants using a hybrid zinc oxide-carbon xerogel as catalyst
• Grantee: Nicolas Perciani de Moraes
• Support Opportunities: Scholarships in Brazil - Master