Adsorption and degradation of water pollutants on TiO2

Abstract

Given the enormous presence of organic pollutants in aquatic environments, it is essential to study an effective way to eliminate them. Titanium dioxide (TiO2) is one of the most widely used materials for promoting photocatalytic activity. Thanks to it oxidation-reduction reactions can be generated, capable of degrading adsorbant contaminants into substances that are no longer harmful. Experimental data indicate the feasibility of this process, but do not explain the specific way in which the functional groups of pollutants interact with the surface of TiO2. Computational chemistry must therefore take note of this and support the research from an atomistic point of view. In this work, the problem is addressed through several levels of theory that allow the development of a top-down protocol. The dynamic evolution of nine water pollutants is investigated on an amorphous TiO2 surface in order to observe their main adsorption modes. Among them glyphosate (GGG), a very powerful herbicide harmful for our health, shows a force of attraction much higher than that of the other molecules. Its adsorption and possible degradation are then studied in detail on a pristine surface rutile-(110), obtaining results in line with experiments. The interaction of water with two reconstructed surfaces validated on pristine models is also investigated beforehand in a direct comparison between density functional theory (DFT) and density functional tight-binding (DFTB). Through this work we want to understand the interaction of organic molecules of different species at the interface with TiO2. We ask about the effect of complexities such as material roughness, competition between molecules of the same species, and the role that the solvent plays. Especially this last factor can in fact be decisive also during degradation processes and needs special attention.