Geração de hidrogênio concomitante à degradação do glifosato por fotoeletrocatálise e fotocatálise

Abstract

The increasingly apparent demand for energy, the increase in atmospheric pollution and the needs for renewable fuels have led to an increase in research and development of technologies aimed at generating clean and renewable energy. In front of this scenario, hydrogen is an attractive possibility. The photoelectrocatalysis or photocatalysis technique has been widely used in the degradation and treatment of pollutants. However, using of this technique aiming at the production of hydrogen gas in parallel with decontamination is still little studied. For the application of these techniques, there are nanoparticles. The study of production and characterization of nanostructured materials has been one of the most attractive topics among research related to materials science, due to the possibilities of improving the various properties that nanostructured materials can have in comparison to materials obtained by conventional processes. This work developed and evaluated a photocatalytic and photoelectrocatalytic system to produce hydrogen gas using nanostructured semiconductors. Simultaneously, the degradation of glyphosate, an herbicide that has been commonly found in surface waters of several countries, was evaluated. Artificial light was used for conversion into hydrogen gas through the cleavage of water, by absorption of photons by semiconductor materials. For this, a reactor with a capacity of 250 mL and a quartz window for lighting was used. Irradiation occurred in photoanodes formed by semiconductor films deposited on conductive glass containing fluorine-doped tin oxide (FTO). The FTO coating was carried out with the following nanomaterials and order of deposition: WOx/Fe3O4, Fe3O4/WOx, Fe3O4/TiO2, TiO2/Fe3O4, WOx/TiO2, TiO2/WOx. A 99.9% pure platinum (Pt) plate was used as the counter electrode, in addition to a mercury vapor lamp as the irradiation source. The results showed the heterojunction involving WOX/TiO2 presented greater photoactivity, both in the photoelectrocatalysis and in the photocatalysis, resulting in an efficiency of conversion of solar energy into hydrogen of approximately 0.0468% and 0.0179%, respectively. Significant values, if compared to isolated semiconductors. There was an increase in the electrical conductivity of the solution after the glyphosate herbicide degradation tests. The solution, when the TiO2/Fe3O4 film was used, had its conductivity increased from 20,721 μS.cm-1 to 24,135 μS.cm-1 , indicating that the Fe3O4 nanoparticles caused an improvement in the absorbance in the visible light region, and consequently, they produced more free radicals, which degraded glyphosate generating, among some ions, phosphate. In photoelectrocatalysis it was possible to obtain more than 5% of phosphate ions, comparing the initial availability with what remained in the solution after 120 minutes. In terms of generated hydrogen, it was possible to obtain 51.7 µmol and 20.31 µmol, in photoelectrocatalysis and photocatalysis, respectively, using WOx/TiO2 film, demonstrating that the application of an external potential makes the water photolysis process more efficient.