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Development of ZnO/Bi2O3/Carbon xerogel ternary composites as photocatalysts for the degradation of persistent organic pollutants

Grant number: 18/16360-0
Support type:Scholarships in Brazil - Doctorate
Effective date (Start): March 01, 2019
Effective date (End): February 28, 2022
Field of knowledge:Engineering - Materials and Metallurgical Engineering
Principal Investigator:Liana Alvares Rodrigues
Grantee:Nicolas Perciani de Moraes
Home Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil

Abstract

This project will generate scientific knowledge to increase the competitive edge, technological base of EEL/USP in the material area. It is intended to explore the development of ternary composites based on zinc oxide, bismuth oxide and carbon xerogel, sensitive to visible light radiation, for application in photocatalytic processes using sunlight. For this, the preparation of the ZnO/Bi2O3/Carbon xerogel composite will be studied, since the coupling of semiconductors by type II or Z-scheme heterojunctions is beneficial to the photocatalytic process. In these types of heterojunctions, the potential of the conduction and valence bands of the semiconductors are different, promoting the transfer of photogenerated charges between them, increasing the recombination time and, consequently, the photocatalytic activity of the material. The use of carbon xerogel in the preparation of the semiconductor-carbonaceous material, besides producing a composite with greater sensitivity to visible light, is justified by its excellent electrical conductivity, high surface area and porosity. Variations in the process parameters, such as the synthesis route (in aqueous or alcoholic media, using acid or basic catalyst), ratio between semiconductor/carbonaceous matrix, modification of the carbonaceous precursor and variation in the calcination temperature, to obtain composites with different morphological characteristics, dispersion of the inorganic phase in the organic phase, 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/xerogel ratio of carbon, it will be possible to estimate the optimum value in which the material presents greater photocatalytic activity under visible light radiation. The study of the type of solvent used in the synthesis of the composites is fundamental, as this directly affects the morphological uniformity, the reaction rate and the shrinkage of the material during the curing and calcination step, parameters that interfere in the adsorption and photodegradation step of the photocatalytic process. The determination of the optimum 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 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 presence of xerogel on the crystallization temperature of the oxides. The photocatalytic action of the material will be evaluated by the decomposition of 4-chlorophenol and bisphenol A, highly toxic organic pollutants with low biodegradability. The band gap energy of the samples will be determined using diffuse reflectance spectroscopy. The crystallographic phase, morphology, elemental analysis, analysis of metal content, and porosity of the samples will be examined by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), Raman spectroscopy, infrared spectroscopy and nitrogen adsorption-desorption isotherms, respectively. Differential Scanning Calorimetry (DSC) will be used to measure enthalpy changes due to changes in the physical and chemical properties of the samples. Thermogravimetry (TGA) will be used to evaluate the thermal stability of the materials. (AU)

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