Utilização de uma bentonita tratada termicamente como catalisador foto-Fenton para a degradação de corantes em soluções aquosas

Abstract

The presence of toxic organic and inorganic compounds in surface waters is one of the major environmental pollution problems. The textile industries generate a large amount of effluents containing organic dyes, such as Rhodamine B and Methylene Blue. These present toxicity, mutagenic and carcinogenic properties, as well as low biodegradability. Thus, they significantly compromise the equilibrium of the aquatic ecosystem and public health, with the need for pretreatment of effluents. Thus, the main objective of this work was the discoloration and degradation by heterogeneous photo-Fenton reaction of the dyes Rhodamine B and Methylene Blue from aqueous solutions using as an catalyst an thermally treated bentonite at 200ºC. The catalyst was characterized by XRD, adsorption and desorption isotherm of N2, pore size distribution, surface area, volume and pore size, FTIR and SEM-EDS. The evaluation of the photocatalytic activity of the material using Rhodamine B as contaminant was examined under constant conditions of pH and mass of the catalyst. Iron leaching was evaluated by atomic absorption spectroscopy. To evaluate the effects of pH variation and catalyst mass on the Methylene Blue dye discoloration rate, the RCCD experimental design was performed (22). The experimental temperature was the ambient for both works. It was verified that the bentonite has a mesoporous structure, surface area corresponding to 99.18m2.g-1 and pore size of 5.55nm. For the conditions studied, the results showed a significant discoloration and degradation of the dyes. For 30, 65 and 100mg.L-1 of the Rhodamine B dye the discoloration reached, respectively, 94%, 67% and 56% and the partial degradation was proved through LC-MS, both in 300 minutes of reaction. The catalyst showed to be a highly stable material, since the iron final concentration in the solution was 1.71mg.L-1. Through RCCD 22, it was possible to optimize the operational conditions. The optimal point was at pH = 2.4 and m = 0.02g, achieving a decolorization efficiency of the methylene blue dye equivalent to 93.9%, in the time of 180 minutes of photo-Fenton reaction, for an initial concentration of 50mg.L-1. For these same conditions, its degradation occurred partially, because the presence of the dye in the solution was reduced and occurred its transformation into intermediate products. Thus, the treated bentonite can be considered a promising catalyst in the heterogeneous photo-Fenton reaction for the discoloration and degradation of organic dyes in aqueous solution.