Estrutura, morfologia e propriedades fotocatalíticas da argila Palygorskita modificada com nanocristais de α-Ag2WO4

Abstract

In this dissertation, we report the obtaining of an alternative and low cost photocatalyst for the degradation of the cationic-type organic dye of Rhodamine B (RhB) using Palygorskite (PAL) clay and α-Ag2WO4 nanocrystals (α-AWO nanocrystals). PAL clay was collected, purified with hydrogen peroxide and heat treated at 500 ºC for 2 h, designated as (PAL-500), while α-AWO nanocrystals were synthesized by the controlled precipitation method with citric acid as a chelating agent for form silver citrate, thereby reducing the nucleation rate and decreasing the average crystal size. The PAL-500 clay was modified with 30% nanocrystals of α-AWO, deseginated as (PAL-500 clay/30% α-AWO nanocrystals) were obtained through the ultrasound impregnation method. Their structures were analyzed by X-ray diffraction patterns (XRD), Raman Spectroscopy and Fourier Transform Infrared Spectroscopy (FT-IR), while the elemental chemical composition, morphology and optical behavior were investigated by X-ray fluorescence (XRF), field-emission scanning electron microscopy (FE-SEM) and diffuse reflectance spectroscopy in ultraviolet-visible (UV-Vis). XRD patterns indicate that PAL-500 clay exhibits a monoclinic (majority) structure, α-AWO nanocrystals have an orthorhombic structure, while PAL-500/30% α-AWO nanocrystals exhibit both phases. The Raman and FT-IR spectra show the presence of active vibrational modes referring to the identified monoclinic and orthorhombic structures. XRF data confirm the presence of metals (Mg, Al, Si, Mn, Fe, Ag and W) of compounds related to PAL-500 clay, α-AWO nanocrystals and PAL-500 clay/30% αAWO nanocrystals. The (FE-SEM) images show the presence of several fibers in the form of needles for PAL-500 clays, the AWO nanocrystals showed the various agglomerates in the form of rods, while the PAL-500 clay/30% α-AWO nanocrystals showed the presence of nanocrystals in the form of rods distributed on the surface of the fibers. When the UV-Vis spectra showed an optical energy range for PAL-500 clay, α-AWO nanocrystals, and PAL-500clay/30% α-AWO nanocrystals of 2.26, 3.17 and 2.46 eV, respectively. The catalytic tests for the PAL-500clay/30% α-AWO nanocrystals showed significant results, showing a photocatalytic performance of 79% degradation of RhB dye in 100 min under UV-C light and kinetic value about 16 times higher, when compared to PAL-500 clay.