Aplicação de catalisadores de Nb2O5 como materiais alternativos para redução de cromo (VI) por fotocatálise heterogênea

Abstract

The study aimed to use the Niobium Pentoxide (Nb2O5) catalyst in the photocatalytic process to reduce Chromium (VI). Cr (VI) is highly toxic and is often found in industrial effluents, mainly from tanneries. A comparison was made between Nb2O5 and TiO2, a catalyst widely used in photocatalytic reactions. The results indicated that Nb2O5 has a 20% reduction in Cr (VI) compared to TiO2. Tests were also carried out with Nb2O5 before and after calcination at 500ºC, showing that the heat treatment did not favor the catalytic activity. The parameters were: pH, radiation intensity, initial Cr (VI) concentration, amount of catalyst and catalyst reuse. The results showed that the optimum conditions of the process are: acidic pH (pH = 2), radiation intensity of 250 W, initial concentration of Cr (VI) of 10 mg L­1 and catalyst concentration of 1.5 g L­1. For the reuse test, the reduction of Cr (VI) was maintained at approximately 90% for all cycles when calcined Nb2O5 was used, while for the non­calcined catalyst the reduction was approximately 21% during the four tests. This behavior is possibly due to the greater adsorption capacity of the non­calcined material. The techniques used for the characterization of the photocatalytic material were: X­ray diffraction, specific surface area (B.E.T method), photoacoustic spectroscopy, Scanning Electron Microscopy (SEM) and X­ray Dispersive Energy Spectrometry (EDS). The study proved that the Nb2O5 catalyst is promising to be applied in tests in an industrial process to reduce Cr (VI).