Insights into the adsorption of CH2BrF on anatase TiO2(101) surface through DFT modelling

Bromofluoromethane (CH2BrF), considered a potential candidate to replace CFCs in many applications, generates serious problems about its effect on the ozone layer degradation and human effects. The adsorption of the compound on TiO2 is a key step for its decomposition through heterogeneous photocatalysis. Here, we investigated the energetics involved in the adsorption of CH2BrF on the anatase TiO2 (1 0 1) surface through detailed DFT analysis. Based on previous experimental results, the adsorbate-substrate geometry was modelled by simulating the acid-base interaction between the Br atom and the surface Ti ion and an H-bond between the CH2 group and the surface O ion. The adsorption was investigated at different surface coverages and periodicities in order to quantify and rationalise the lateral effects between co-adsorbed molecules and to estimate the interaction, distortion and binding energies in the limit of an isolated adsorbed molecule, i.e. in the limit of low coverage. The obtained constants indicate a strong repulsion due to the Br-Br interaction and a moderate attraction arising from the Br-H interaction. Then, at a given surface coverage, the most stable configuration involves the adsorption of the molecule through maximisation of the Br-Br distance and minimization of the Br-H distance. The lateral effects differ from those observed for chlorofluoromethane since the effects due to the Br-Br repulsion are stronger than those arising from the Cl-Cl repulsion. This behaviour suggests that the lateral effects cannot be generalised for a particular class of compounds, like as CH2XF, and a rigorous analysis should be always done in order to better rationalise the experimental data, to predict the most stable configuration under given experimental surface coverages and to provide the data for successive Monte Carlo simulations. © 2013 Elsevier B.V. All rights reserved.

Bromofluoromethane (CH2BrF), considered a potential candidate to replace CFCs in many applications, generates serious problems about its effect on the ozone layer degradation and human effects. The adsorption of the compound on TiO2 is a key step for its decomposition through heterogeneous photocatalysis. Here, we investigated the energetics involved in the adsorption of CH2BrF on the anatase TiO2 (101) surface through detailed DFT analysis. Based on previous experimental results, the adsorbate-substrate geometry was modelled by simulating the acid-base interaction between the Br atom and the surface Ti ion and an H-bond between the CH2 group and the surface O ion. The adsorption was investigated at different surface coverages and periodicities in order to quantify and rationalise the lateral effects between co-adsorbed molecules and to estimate the interaction, distortion and binding energies in the limit of an isolated adsorbed molecule, i.e. in the limit of low coverage. The obtained constants indicate a strong repulsion due to the Br-Br interaction and a moderate attraction arising from the Br-H interaction. Then, at a given surface coverage, the most stable configuration involves the adsorption of the molecule through maximisation of the Br-Br distance and minimization of the Br-H distance. The lateral effects differ from those observed for chlorofluoromethane since the effects due to the Br-Br repulsion are stronger than those arising from the Cl-Cl repulsion. This behaviour suggests that the lateral effects cannot be generalised for a particular class of compounds, like as CH2XF, and a rigorous analysis should be always done in order to better rationalise the experimental data, to predict the most stable configuration under given experimental surface coverages and to provide the data for successive Monte Carlo simulations.