Degradação de corantes têxteis ácidos e reativos por fotocatálise heterogênea, usando TiO2 como fotocatalisador

Abstract

The textile industry has the characteristic of generating huge amounts of residues, mainly the ones from yarns and fabrics dyeing operations. Conventional treatments of textile wastewaters are inefficient for degrading the majority of the dyes. Heterogeneous photocatalysis has been arising as a promising alternative for treating this kind of pollutants. In this work, the photocatalytic degradation of two simulated aqueous solutions: effluent I, composed of three acid dyes (Blue 74, Red 51, and Yellow 3), and effluent II, composed of three reactive dyes (Black 5, Red 239, and Yellow 17) was studied. Some dyeing auxiliary chemicals were also added to both effluents. Besides photocatalysis, photolysis and adsorption experiments were also performed. Preliminary tests were performed in order to optimize pH and catalyst (TiO2) dosage. Color removals by the photocatalytic process were estimated from UV-Vis spectroscopy: 96% after 240 min for effluent I and 97% after 30 min for effluent II. The mineralization degree of effluent I was low (37%) and that of effluent II negligible. For the bath containing acid dyes, toxicity experiments using lettuce seeds (Lactuca sativa) were performed. The estimated initial EC50 was 19.28 %, being toxicity completely removed after 63 min of the photocatalytic process. Photolysis did not present the same efficiency of photocatalysis, showing the importance of the catalyst in the degradation process. For both effluents, the adsorption process was not significant. The photocatalytic degradation of all studied dyes followed a pseudo-first order kinetic model