WEB Can we save the oceans with the use of a simple powder? A top-down journey on titanium dioxide
The impact of TiO2 as a fundamental material for new technologies is still nowadays worldwide recognized. This semiconductor proved to be able of major photocatalytical activity within visible light irradiation, which turns out to be a powerful tool for water splitting or environmental cleaning [Migani, Lan]. Moreover, TiO2 powders with negligible rate of impurities can be synthesized at very affordable prices. Also optimal reaction rates at basic pH conditions have been reported for several adsorbates [Dai, Zhu, Gao], showing an environmental dependence. This motivates more complex simulations of small organic pollutants taking into account surface defect states, aqueous environment with varying pH conditions as well as the presence of different pollutants at different concentrations.
In the present contribution I will be focusing on some extensive studies regarding the interaction of nine worldwide abundant aqueous contaminants with this metal oxide surface. Our journey starts from a large amorphous system investigated via classical Force Fields (FF) methods [Derr]. As a next step, we are exploring the competition between different pollutants through Density Functional Tight Binding (DFTB) approach, which we complete with findings about their adsorption on several small rutile surfaces on the Density Functional Theory (DFT) level. Independently from the class of applications, all contaminants show thermodynamically stable geometries with hydroxyl and carboxylic groups towards the surface on pristine and reconstructed surfaces of rutile. As a highlight, I will show how one of the most discussed herbicides of our time, Glyphosate, strictly forms two bidentated Ti-O complexes at the surface, promoting a very strong adsorption.
In general, the understanding of the adsorption of such pollutants on TiO2 under environmental conditions is as interesting as challenging due to the high complexity of the interface systems. This gives raise to several insights on the way through further optimization of waste water cleaning treatments.