Dra. Yeber-Ortiz, Maria

Arsenic (III) is a common by product of mining activity. This contaminant can have a high environmental impact because it might accumulate in the food chain and seriously affect human health. The purpose of this study is to develop a method to remove arsenic (III) using the photo catalyst TiO2-N activated by visible light. The catalyst TiO2 Degussa P-25 was doped with nitrogen in order to narrow the energy gap and to work with radiation in the visible range. A multi variable approach was used in order to optimize the removal of arsenic, varying the concentration of the catalyst and the pH, maintaining the initial concentration of As (III) in 3 mg L–1. Two optima were determined, in one of which As (III) was reduced by 96.7% at pH 2, and in the other As was reduced by 80% at pH 7. Furthermore, the toxicity of the As (III) solutions was determined using Daphnia magna before and after the photochemical treatment. Mortality in the initial concentration was 87%. After the treatment at pH 2.0, a significant reduction in toxicity was recorded, with a mortality of only 30%.

Dyes used in the textile industry have varied and complex structures are designed to resist degradation by external agents. Most are water soluble, resistant to chemical agents and not biodegradable, so they cannot be easily removed by wastewater treatment plants. Remazol Brilliant Blue R (RBBR) is one of the most important colorants in the textile industry, and it is frequently used as a starting material in the production of polymer dyes. This work studied the degradation of a textile dye by a heterogeneous photocatalysis process, using a titanium dioxide catalyst doped with nitrogen from urea, in the presence of visible light irradiation. For the optimization of the process a Box-Benhken experimental design was performed. Where, the TiO 2 was varied from 0.1 gL ⁻¹ (-1) to 1.0 gL ⁻¹ (+1), and the pH between 2.0 (-1) to 11(+1). With the optimal response it was possible to remove 86.3% of the dye (R ² = 0.987 and Q ² = 0.873, p < 0.001). The mineralization grade was determined through TOC analysis, which reached 50%, and the toxicity was evaluated with Daphnia magna nematodes, which was reduced considerably after photocatalytic treatment.