Aplicação de óxidos mistos de a-Fe2O3/Nb2O5 obtidos pelo método Pechini em reações de fotodegradação

Abstract

New catalysts with high efficiency for the degradation of organic compounds at effluents, mediated by sunlight and that are stable, has been a great challenge. In this work, mixed oxides of -Fe2O3/Nb2O5 were prepared from a Pechini method, with two different mass ratios (-Fe2O3 and Nb2O5 (60/40 and 80/20, respectively) and calcination temperatures between 500 and 800 ° C. The influence of these parameters was investigated on the materials structural, morphological, optical and photocatalytic properties. These catalysts were submitted to methylene blue (MB) degradation tests by both photocatalysis and photo-Fenton reaction. The best performing sample in these initial tests was used in the following tests to optimize the process operating conditions through a 24 experimental design with triplicate at the central point. The catalytic reaction mechanism, the limiting step, the reaction rate law and the catalyst stability were also evaluated. Crystalline nanoparticles were obtained with significant differences in their properties and in the degradation efficiency of the methylene blue dye under UV-Vis radiation. Calcination temperatures between 500 and 800 °C led to the formation of different crystalline phases, including: -Fe2O3, Nb2O5, FeNbO4 and FeNb2O6; as well as the formation of materials with multigap behavior. The sample of 60 % -Fe2O3 and 40 % of Nb2O5 and calcined at 500 ºC (0,6-Fe/Nb-1) presented the highest catalytic activity and was then used in the following tests at photo-Fenton-like reactions. According to the factorial experimental design 24 performed, the variables that presented a significant effect on the response were: AM, catalyst and H2O2 concentrations. The proposed mechanism followed an LH type kinetics with double site mechanism, with the highest colour removal percentage obtained at 85 % after 4 h of experiment, under the optimum operating conditions found. This result this result was superior to pure synthesized oxides. The catalyst was stable even after 5 consecutive cycles of reaction, unlike Nb2O5, with potential application in the treatment of environmental pollutants.