Development of modified TiO2 nanotubes for electrochemical treatment of endocrine disruptors: Bisphenol A and n-propylparaben.

Abstract

With the advent of the industrial revolution in the XVIII century began the greatest technological and scientific development ever seen. All this progress, however, contributes to increase environmental pollution, especially the contamination of water bodies. Currently, among the pollutants found in industrial environment, bisphenol A compounds and n-propyl require attention because they are widely used in the industry of plastics and cosmetics, and have high solubility in water. However, these molecules can adversely interact with the system. These compounds, also known as endocrine disruptors - ED, are a class of substances that cause adverse effects to the endocrine system. The effects include a range of reproductive problems, changes in hormone levels, immune functions and several types of cancer. In this context, many physical and chemical treatments have been proposed to remove these compounds in an aqueous medium. Conventional methods employed, such as adsorption, reverse osmosis and ultrafiltration do not destroy those compounds but merely transfer pollutant from one phase to the other. Thus, alternative methods based on heterogeneous photocatalysis has been shown as an alternative to the existing effluent treatment. In these methods the reactions are triggered using a semiconductor activated by irradiation of sunlight or artificial light which catalyzes reactions. Considering the semiconductors, TiO2 nanotubes have attracted great attention because of their precise structures, controlled walls and pores, improving absorption of radiation. However, the major limitation to their use is the low absorption of visible light (less than 5%), which precludes the use of natural light as a power source for treating pollutants. Accordingly, the addition of dopant materials in TiO2 nanotubes have been used as a strategy for increasing photocatalytic efficiency. Metals can confer differences in bandgap energy level by changing the photoactivity of TiO2 and also the absorption band of radiation. As main effect, photoactivity is increased, which improves the degradation of organic pollutants. Considering these aspects, this project proposes the development of TiO2 nanotubes modified, using the methodology of electrochemical anodization. To evaluate photoactivity increases different doping metals as tungsten, vanadium and manganese are going to be used. This project intends to perform the degradation of endocrine disruptors n-propyl and bisphenol-A through photoelectrocatalysis, obtaining the maximum mineralization and invalidation of biological activity. The degradation processes efficiency will be evaluated by the decay of concentration, formation of inorganic ions, reduction of the total organic carbon content and ecotoxicity. In addition, this project wants to identify possible intermediates formed during the degradation, aiming to establish degradation mechanisms for each of the endocrine disruptors.