Avaliação da atividade fotocatalítica de heterojunções de óxidos SnO2/MoO3 e TiO2/SnO2: aplicação na degradação do azul de metileno e em conversão de sorbitol

Abstract

heterojunctions with different contents of Mo, and system II (TiO2, SnO2, and heterojunctions with different contents of Sn. The photocatalysts were synthesized and characterized by several techniques in order to determine their surface, electronic and structural properties. The photocatalytic activity was evaluated in the photodegradation of the methylene blue textile dye and in the photocatalytic conversion of sorbitol into products of industrial interest. through FTIR-pyridine analysis that MoO3 showed an acidity higher than SnO2, and as the Mo content in the heterojunctions increased, the acidity also increased. With the use of SnO2, SnO2/MoO3 (5%), SnO2/MoO3 (25%), SnO2/MoO3 (50%) and MoO3, photocatalytic efficiency values were observed for the photodegradation of methylene blue of 31.9, 31.0, 49.0, 82.1 and 98.7 %, and in the photocataly conversion the sorbitol optics, the photocalytic efficiency values of 12.3, 7.4, 13.9, 17.1, 14.6% were observed, respectively. In terms of selectivity, heterojunctions with a higher Mo content, were directed towards the formation of tartronic, gluconic and oxalic acids. For system II of photocatalysts, the increase in the Sn content caused a segregation of the particles, as observed by means of SEM micrographs, and this resulted in a decrease in the surface area, and for this set of photocatalysts, the surface area was a determining factor in the assessment of photocatalytic activity. The values for photocatalytic efficiency in the degradation of methylene blue were 63.6, 78.6, 87.5, 65.1 and 45.2%, respectively. For TiO2, even though there was a lower efficiency rate in relation to SnO2, there was a total n-demethylation, which was confirmed by the presence of by-products, different from SnO2, where total n-demethylation was not confirmed. Thus, it can be inferred that the larger surface area was more favorable for the chromophore cleavage mechanism and n-demethylation. This was also confirmed in heterojunctions, when there was the lowest Sn content and the largest surface area, there was greater identification of intermediates and the chromophore cleavage was more accentuated. Regarding the photocatalytic conversion of sorbitol, TiO2, SnO2, TiO2/SnO2 (5%), TiO2/SnO2 (25%) and TiO2/SnO2 (50%), showed 56.8, 15.3, 17.6, 9.5 and 10.8%. In terms of selectivity, the products observed for system II of photocatalysts were gluconic acid, arabinose, glyceraldehyde, glycoaldehyde, glycolic acid and lactic acid. The selectivity was altered according to the increase in the Sn content. In general, it is worth mentioning that there are no reports in the literature using pure photocatalysts and heterojunctions of the type investigated in the present study for conversion of sorbitol, showing the feasibility of the present investigation.