Estudo ab initio da adsorção de organofosforados em TiO2 e Ti(1-x)ZrxO2

Abstract

The study of degradation of organophosphorous is critical both in the environmental area as in chemical defense. Has been described in the literature studies on degradation of organophosphorous related to agriculture. One of the study considers the use of light in a degradation of the organophosphorous pesticide used in agriculture: the parathion. The process called heterogeneous photocatalysis involves the activation of a semiconductor (usually TiO 2) by sunlight or artificial. The absorption of photons with energy higher than the energy band gap results in the promotion of an electron from the valence band to conduction band with concomitant generation of a hole (hole) in the valence band. These holes show sufficiently positive potential, capable of forming hydroxyl radicals from water molecules adsorbed on the semiconductor surface, which can subsequently oxidize organic contaminants. The aim of this study was to determine the influence of the substitution of titanium by zirconium in TiO2 adsorption of organophosphorous, which is one of the stages of degradation of these compounds. For this we determine the structures, vibrational and electronic properties of organophosphorous adsorbed on TiO2 (101) anatase and Ti(1-x)ZrxO2. The compounds adsorbed are: parathion, sarin and VX. The idea was to propose a technique well described experimentally for the degradation of parathion for possible detoxification of organophosphorous used as chemical weapons, in this case, Sarin and VX. Was done to study the adsorption of organophosphorous in titania replaced with zirconium in the ratio Ti(1-x)ZrxO2, taking into account that changes in the structure of the catalyst increase the photocatalytic activity. Calculations verify the contribution of the adsorption energy step and comparing the structure of the pure catalyst was possible to obtain improvement in this step. We obtained energies of physisorption and chemisorption at different possible positions. The type of adsorption was confirmed with studies of in electronic difference charge. Was also obtained to vibrational frequency study. From the results it was concluded that the adsorption is processed more effectively in cases where the catalyst was used with zirconium, with adsorption energy of -25.71 kcal / mol for p-VX adsorbed. Titania in pure energy of adsorption, p-VX was -18.14 kcal / mol. The difference in electronic charge density also confirmed the results.