4. Degradación de fenoles en un reactor solar empleando nanopartículas de óxido de titanio dopado soportadas sobre sólidos fotónicos

Abstract

The increasing demand for drinking water in urban areas of the country, as well as deficiencies in the systems of wastewater treatment lead our society to a possible scenario where will not have the availability of the resource to adequately support its development. Among the pollutants most dangerous and difficult to remove, are some chemical compounds originate mainly in industries known as "Persistent Organic Compounds", including phenols. For this reason it has become necessary to develop new and efficient technologies, able to purify these wastes. Heterogeneous Photocatalysis is an alternative, environmentally friendly and effective for treating water with these features. However, the main limitation of this technique is the use of materials that are activated by light in the ultraviolet region of the electromagnetic spectrum. Therefore, developing solids capable of absorbing sunlight will reduce operational costs for working with large volumes of effluents. In this sense, the efforts made by different research groups (in countries with potential for solar applications) have focused on the design of synthetic routes to modify the molecular structure of these solids, which in turn could be economical and with high yields. So, this work seeks to contribute with the development of these systems, to screen the application of this technology in industrial wastewater generated in our country and achieve that aqueous discharges comply with existing legal regulations, ensuring preservation of natural water bodies. Due to the different methods typically used to modify the preferred semiconductor in Heterogeneous Photocatalysis, titanium dioxide (TiO2), the study was divided into three stages: (i) A systematic analysis was carried out on the effect (over TiO2 photoactivity) of doping with certain metal ions and also the TiO2 partial reduction under a hydrogen atmosphere; in order to obtain a novel co-doped solid with better optical properties. At this stage, the iron was the best dopant of a group of ten elements studied, and it was determined that a pre-treatment with nitric acid favors the reduction of TiO2 allowing to prepare a novel co-doped material formed by a mechanical mixture of both solids in equivalent mass ratios; (ii) Various synthetic methods for co-doped TiO2 nanoparticles preparation were evaluated for suitable incorporation into solids with potential photonic behavior based on SiO2 and carbon. In this second stage of the investigation it was found that sol-gel route using TiCl4 as a precursor, and iron incorporation by wet impregnation provides doped nanoparticles with the desired characteristics. (iii) Incorporation of co-doped TiO2 nanoparticles on SiO2 and carbon spheres allowed materials more effectives on the photodegradation of various phenols, both at laboratory and bench scale. In this regard it was suggested that a mechanism of charge transfer through grain boundaries existing in interfaces, is responsible for the improvements in TiO2 photoactivity. Likewise, the co-doped solid supported in carbon spheres introduced features that were beneficial to the process. Including easy retrieval and greater adsorption of the phenolic compounds employed as probe molecules. The use of this material in the treatment of 20L of water contaminated with a mixture of phenols allowed degradation by more than 80%, demonstrating the potential of thistechnology for wastewater treatment.