Emprego de óxidos semicondutores para tratamento de águas contaminadas por corante através de fotocatálise heterogênea

Abstract

Heterogeneous photocatalysis is an Advanced Oxidative Process, considered as a promising technique for treatment of water contaminated with dyes. In this process a source of sunlight or artificial UV radiation is applied to a semiconductor that is photoactived, interacts with water and produces highly oxidative species, such as hydroxyl radical, responsible for degradation of contaminant, reaching the full mineralization. Titanium dioxide (TiO2) photocatalyst is the most widely studied and applied due to its characteristics, such as low energy bandgap (3.2 eV). The niobium pentoxide (Nb2O5) is a compound with the potential for employment in photocatalysis due to its properties, such as bandgap energy of 3.1 to 4.0 eV, similar to that of TiO2. In this paper the synthesis of a mixed photocatalyst of TiO2 and Nb2O5, was obtained by impregnation of Nb2O5 in TiO2 P25 Degussa and a photocatalyst based in Nb2O5 prepared by C calcining the niobic acid at 500°. These photocatalysts, as well as TiO2 P25 Degussa, were characterized by XRD, FTIR and SEM and used in photocatalytic tests where pH and photocatalyst concentration were optimized. The applied radiation was provided by a high pressure mercury lamp of 125 W (no bulb shield), inserted into the solution via a glass bulb (UVA). The substance used to be degraded was the commercial textile dye Corasol Orange 2GL 250 (20 mg l-1), and monitoring the discoloration was done through measurements of spectral area reduction by UV-vis spectroscopy (190 to 800 nm). With the XRD analysis it was observed the presence of rutile and anatase structures in TiO2 and hexagonal crystalline structure in Nb2O5, which were also observed in the TiO2/Nb2O5. With the SEM analysis, it was found that the structures of Nb2O5 and TiO2/Nb2O5 are more compact than that of TiO2 and in the analysis by FTIR was possible to observe the stretching and deformation bands of photocatalysts. The photocatalyst that showed the best photocatalytic performance was TiO2 P25 Degussa (pH 6 and concentration of 600 mg.L-1), with a spectral area reduction of 96,0% within 30 minutes of reaction. Following, the mixed photocatalyst TiO2/Nb2O5 (pH 4 and concentration of 600 mg.L-1), with area reduction of 46,0% and Nb2O5 calcined at 500°C (pH 4 and concentration of 600 mg.L-1) with area reduction of 43,0%, both after 90 minutes of reaction. According to adsorption and photolysis tests performed, these parameters had little influence on the photocatalytic performance of photocatalysts TiO2/Nb2O5 and Nb2O5, wherein, for the TiO2, the photolysis contributed more clearly.