Cr (VI) reduction by photocatalyic process: Nb₂O₅ an alternative catalyst

In this study, Nb₂O₅ catalyst was applied in the photocatalytic process for the Chromium reduction. Cr (VI) is a compound classified as highly toxic and often found in industrial tannery effluents. The techniques used for the photocatalytic material characterization were: X-ray diffraction, Specific surface area (B.E.T method), photo-acoustic spectroscopy, Scanning Electron Microscopy (SEM) and X-ray Dispersive Energy Spectrometry (EDS). A comparison between Nb₂O₅ and TiO₂ (widely used in photocatalytic reactions) indicated that Nb₂O₅ has 20% more Cr (VI) reduction than TiO₂. Tests carried out with Nb₂O₅ calcined at 500 °C and with non-calcined Nb₂O₅ showed that the heat treatment did not favor the reaction. Parameters such as pH, radiation intensity, initial concentration of Cr (VI) and amount of catalyst were studied. The results indicated that the acid (pH 2), emitted radiation intensity (250 W), initial concentration Cr (VI) at 10 mg L^-1 and 1.5 g L^-1 Nb₂O₅ non-calcined are the process optimal conditions. In addition, the reuse tests for Nb₂O₅ in consecutive cycles four, were realized. Photostability was maintained at approximately 90% for all cycles when Nb₂O₅ calcined was used. On the other hand, when using Nb₂O₅ non-calcined reduced by 21% during the four tests. This behavior is possibly due to the greater adsorption capacity of the non-calcined material. Making the Nb₂O₅ catalyst attractive for considering larger scale tests.