ESTUDO DA DEGRADAÇÃO DE TRICLOSAN VIA FOTOCATÁLISE HETEROGÊNEA UTILIZANDO SEMICONDUTOR LIVRE E IMOBILIZADO

Abstract

Triclosan is a compound with bactericidal effect that is frequently used in personal hygiene products. Recently, it has been found in surface water and wastewater even after conventional treatment. In the search for efficient alternative methods of degradation, are studied among them Oxidative Advanced Processes (AOPs), which are based on hydroxyl radical generation (HO), which is a strong oxidizing agent. The objective of this work was to study the degradation of triclosan using Heterogeneous Photocatalysis (HP), characterized by the use of a free and immobilized photocatalyst. In this work titanium dioxide (TiO2) and zinc oxide (ZnO) were used as photocatalysts. An analytical routine was established using High Performance Liquid Chromatography (HPLC) followed by partial validation. The determination of the TCS in aqueous solution was performed in the linear range of 0.1 to 10.0 mg L-1, with R2 = 0.999, limit of detection (LOD) 0.3 mg L-1 and limit of quantification (LOQ) 1. 0 mg L-1. The characterization of the catalysts allowed to identify for the TiO2 the anatase phase, with a bandgap of 3.22 eV. The immobilization of this catalyst in calcium alginate does not cause great damage to its activity, since the characterization of the spheres demonstrated that in fact the TiO2 was present in them, in an amount of 0,267 ± 0,058 mg per sphere, according to FEG images, had a rough surface. Complementing the characterization, the images by EDS also showed that the catalyst was evenly distributed throughout the surface. In the studies with ZnO as catalyst, we identified the wurtzite phase, with bandgap of 3.14 eV. In the same way as previously, the immobilization does not cause damage to its catalytic activity, as well as the morphology of its spheres are being very close to TiO2 and also with surface distribution in all the analyzed areas (0.267 ± 0.058 mg ZnO per sphere). Also, a factorial design of experiments was carried out, where the best conditions found for both catalysts were pH 10 and 30 mg L-1. The kinetics of degradation demonstrated that the photolysis followed a first-order reaction whereas for the others the order followed was of pseudo-first order. The half-life times between free and immobilized studies did not show large variations, but TiO2 was slightly higher than ZnO. As good results with artificial radiation were achieved, studies with solar radiation were performed. The photolysis continued with a first order of reaction (t1/2 = 16.98 min) while the FH with immobilized TiO2 continued to follow a pseudo-first order (t1/2 = 22.88 min). The ZnO changed to second order (T1/2 = 11.72 min), demonstrating good efficiency using a renewable source of radiation. In the mineralization studies, TOC analysis were used to monitor the total organic matter removal of the samples. In these studies TiO2 presented a great advantage in relation to photolysis, because with about 18h of reaction, the photocatalysis was able to mineralize amounts greater than 90% while the photolysis was only about 40%. This difference was not so great for ZnO, because with this time there was a gain of approximately 10%, but it also showed superiority. These differences are easily observed using the half-life times, where for the photolysis the mineralization followed a first-order reaction with t1/ 2 = 1565 min, while the TiO2 and ZnO followed a second-order reaction with t1/2 = 76.14 min and t1/2 = 1354 min respectively.