Estudo das propriedades estruturais, superficiais e fotocatalíticas de SnO2, CuO e heterojunções SnO2/CuO

Abstract

In recent years, scientific interest in the synthesis of p-n-type heterojunctions for photocatalytic applications has grown, and a good candidate for photocatalyst is SnO2 because it is stable, non-toxic, and has low production cost. However, tin (IV) oxide, when used individually in photocatalytic reactions, presents high rates of internal recombination, preventing the continuation of the reaction. SnO2 when combined with oxides with lower bandgap energy tend to form semiconductor heterojunctions, which have the ability to narrow the tin oxide bandgap and decrease internal recombinations. The literature has reported the preparation of SnO2/CuO heterojunctions with potential activation by visible light. The objective of this work was to insert Cu2+ ions into the SnO2 structure, creating p-n heterojunctions and to monitor the crystalline, electronic, surface and photocatalytic properties of the materials. The heterojunctions were obtained by the coprecipitation method with 5, 15 and 25% of Cu2+ and characterized by several techniques in order to know their physicochemical characteristics. The XRD revealed that the insertion of copper in the SnO2 structure changes the crystallinity of the sample, since, when increasing the content of Cu2+ cations by 5, 15 and 25%, a decrease in the crystallite size to 9.23, 7, is detected. 45 and 7.13, respectively. The decrease in crystallinity promotes the increase in structural defects that is correlated with the increase in surface area determined by the N2 physisorption analysis by the B.E.T. It was verified, through diffuse reflectance spectroscopy, that the insertion of Cu2+ to SnO2 creates additional energy levels in the bandgap in the heterojunctions, since it was noticed the emergence of a new absorption band at 750 nm, accompanied by a shift to the region red of the spectrum, the estimated bandgap values decrease with increasing copper content reaching 2.3; 2.0 and 1.5 eV for the heterojunctions SnO2/CuO 5%, SnO2/CuO 15%, SnO2/CuO 25%, respectively. Scanning electron microscopy results revealed that pure SnO2 has an irregular rocky morphology, while pure CuO has an agglomerated surface in spherical shapes. surface morphology, because as the Cu content increased in the heterojunctions, the surface of the materials acquired an agglomerated surface, similar to pure CuO. The photocatalysts synthesized in this work were applied in the photodegradation of methylene blue as a cationic dye and eosin Y as an anionic dye, the most efficient material in the degradation of methylene blue was pure SnO2 which obtained 65, 55% of photodegradation using natural and simulated sunlight, respectively. Then the heterojunction SnO2/CuO 5% obtained reaction efficiency in the photodegradation of methylene blue of 56 and 53% using natural and simulated sunlight. Reaction tests with eosin Y showed the same profile where pure SnO2 and SnO2/CuO 5% materials were more efficient, reaching 77 and 69% of photodegradation using simulated sunlight.