Fotodegradação do corante azul de metileno aplicando catalisadores livres e suportados em fibras ocas cerâmicas

Abstract

The textile sector is considered one of the most important for the Brazilian economy, however it is one of the sectors with the most toxic effluents, which are mainly loaded with surfactants, metals, and dyes. Among these pollutants is methylene blue, a dye classified as cationic and used by the textile industry to dye silks and leathers, besides this dye is toxic to humans and may cause mutagenic and carcinogenic effects. The conventional effluent treatments are not the most suitable for treating effluents with dyes and, therefore, studies propose the application of alternative treatments, such as heterogeneous photocatalysis. The photocatalytic process is based on the formation of hydroxyl radicals that oxidize the pollutants and to do this, they require the use of an irradiation source and catalysts, the zinc oxide (ZnO) and titanium (TiO2) are the most applied, due to its good chemical stability and reasonable cost. The use of immobilized catalysts represents an improvement in the process mainly due to their ease of reuse. Thus, in this work, the potential of ZnO and TiO2 catalysts in free and immobilized forms was evaluated. As support, the use of hollow alumina fibers with asymmetric pore distribution was evaluated. Moreover, the influence of the type of light on the degradation of the methylene blue dye was verified, being evaluated the visible light and ultraviolet C (UVC). Finally, the possibility of reusing the catalysts was verified. The effect of the initial dye concentration was evaluated in photocatalytic systems and ranged from 5 to 30 mg/L. In all systems it was observed that the photocatalytic activity decreases as the dye concentration increases. The ZnO/visible light and TiO2/UVC light systems obtained a methylene blue removal index greater than 95% for all initial dye concentrations, and the treated samples presented a luminosity index of 16.85 and 12.84 and in the phytotoxicity test there was no inhibition in the germination of Lactuca sativa seeds. As for the ZnO/UVC light system, despite having 96% efficiency in removing methylene blue, there were inhibitory effects in the phytotoxicity test were observed with the treated sample, probably due to production of phenol. The TiO2/visible light photocatalytic system showed the lowest dye removal rates. Due to higher dye removal efficiency and lamp accessibility, the system with visible light and immobilized ZnO catalyst was evaluated. The system with ZnO immobilized under visible light proved to be efficient for concentrations below 15 mg/L, with removal rates greater than 80%, and the phytotoxicity test showed no inhibitory effects. The reuse of the immobilized ZnO catalyst was efficient up to the eighth cycle with removal rates greater than 80%, without the need to treat the catalyst between one cycle and another. Thus, the immobilized system proved to be efficient by applying visible light as an irradiation source, indicating that the system can be adapted to receive sunlight to activate the catalyst.