Catalisadores de nióbio promovidos com Ag para fotorredução de cromo VI

Abstract

This undergraduate thesis investigated the effectiveness of niobium catalysts promoted with Ag for the reduction of chromium VI. Chromium is a transition metal found in several forms, with Cr(III) and Cr(VI) being the most relevant from a biological point of view. In industry, chromium is used in various processes. For example, in metallurgy, it is used in metal alloys to give these materials greater strength, with stainless steel being a notable example. In addition, the element also acts as a pigment and is present in the leather industry (tanneries), where it is applied to increase the material's resistance. However, it is important to emphasize that its use in this area has a significant environmental cost, since it is a strong pollutant. Due to its toxicity, chromium (VI) has several significant negative effects on human health, potentially causing a variety of conditions in individuals, in addition to being harmful to the environment when traces of it contaminate soils and cause a chain reaction in groundwater and other living organisms. Because it is still widely used in industry for a wide variety of purposes, this heavy metal is a source of concern and actions aimed at reducing or eliminating these industrial wastes. Studies on how to remove chromium from solutions are a promising area of study, as it is a field with increasingly more possibilities, with techniques not so widely adopted, but with great potential for waste treatment. In this context, the use of photocatalysis is a viable alternative, as it is possible to reduce chromium with radiation and a suitable catalyst. This work focused on using different conditions and catalysts to achieve the best possible results. These included the pH of the solution (2, 4.8, and 7), testing different catalyst calcination temperatures (300, 500, and 700°C), adding silver as a catalyst promoter, concentration, additive addition, and whether there is interference when air is injected. From this, results were obtained to find the best combination for reduction, using the best catalyst among those tested: titanium dioxide, niobium pentoxide, and calcined niobium pentoxide.