Óxido de silício obtido a partir de fibras de coco modificado com óxido de ferro: aplicação em fotodegradação do corante amarelo de tartrazina

Abstract

The present work used green coconut fibers to produce silica. This silica was modified with iron nanoparticles to be applied as photocatalysts in the degradation reaction of the tartrazine yellow dye used as a model dye. The obtained material was characterized by infrared, where it was possible to observe the decrease of the organic peaks, which suggest the mineralization of the sample, while the calcination brought the intensification of the peak related to Si-O-Si. XRD demonstrated the transition of SiO2 from its amorphous form to the quartz structure, through the analyses of Scanning Microscopy and Energy Dispersive System - SEM-EDS it was possible to observe the transformation of the structure of these fibers, in addition to the chemical composition before and after the treatment/calcination, indicating good mineralization. The Np- Fe3O4/SiO2 system was obtained from the synthesis of magnetic nanoparticles by means of the co-precipitation method in the presence of silica. From the X-ray Diffraction - XRD results, it was possible to identify the characteristic peaks of magnetite in the crystal fields of 220, 311, 400, 511 and 440. Evidence of the synthesis of nanoparticles was also obtained by spectrophotometry in the UV-Vis region, when a curve with no peaks and an elevation of the baseline were obtained, parameters that confirm the presence of manometric particles. The morphological analysis through Scanning Microscopy - SEM suggests a spherical shape in addition to a polydispersity, it is possible to notice that the iron was coupled to the silica surface, results that are evidenced by Energy Dispersion Spectroscopy - EDS. An approximate particle size of 10 nm is estimated. Through the results of thermal analysis by TG/DTG, the results showed that the chemical treatment with NaOH changed the degradation temperature of the fibers and that the thermal stability of the treated fibers increased when compared to the in natura fibers and that the calcined fiber has a greater resistance when subjected to different temperatures. Finally, the dye photodegradation tests performed showed significant results in the presence of H2O2, which intensified the production of hydroxyl radicals capable of degrading the azo dye molecules. Regarding the use of Np- Fe3O4/SiO2 and SiO2, in the presence of H2O2 the efficiency in the degradation of the tartrazine yellow dye was 100%.