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

Abstract

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.