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Insights into the adsorption of CH2BrF on anatase TiO2(101) surface through DFT modelling
No full textBromofluoromethane (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
Vinyl halides adsorbed on TiO2: study of the adsorbate - substrate interaction by IR spectroscopy and quantum -mechanical calculations
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Adsorption of CH2CHF on the anatase (101) surface: a quantum-mechanical study
No full textThe adsorption of CH2CHF on the anatase (101) surface has been studied by a periodic approach using
hybrid-exchange density functional theory. The simulation was performed on the basis of a recently proposed
experimental model for vinyl fluoride and chloride describing the adsorption of CH2CHX through the halogen
atom rather than the CdC double bond according to the infrared spectra. The adsorption has been investigated
using different surface coverages and periodicities, and the energetics have been considered in terms of
interaction, distortion, and binding energies. A simple model of nearest and next-nearest neighbors has been
adopted to obtain the energies in the limit of an isolated adsorbed molecule and to quantify the lateral effects.
The adsorbate-substrate interaction for the anatase surface resulted weaker than that for the rutile (110) one.
The vibrational frequencies of the adsorbed molecule have been computed and found in agreement with the
experimental ones thus supporting previous infrared interpretations
A systematic study of the influence of the slab thickness on the Lewis acidity of the rutile (110) surface: a quantum mechanical simulation of CO adsorption
No full textA systematic study of the effect of the slab thickness on the Lewis acidity of the rutile (110) surface has
been performed by simulating the adsorption of carbon monoxide. The attention has been focused on the
molecule–surface distance, the binding and interaction energies and the adsorbed CO stretching frequency.
The study shows that converging data, being in good agreement with the experimental ones,
are achieved by adopting at least a 12-atomic layers slab and that the use of the possible thinnest slab
does not lead to reliable results
DFT calculations of carbon monoxide adsorbed on anatase TiO2 (101) and (001)surfaces: correlation between the binding energy and the CO stretching frequency
No full textThe adsorption of carbon monoxide (CO) on anatase (101) and (001) surfaces was simulated using periodic density
functional theory calculations. The surface Lewis acidity was evaluated by computing the binding energy and the adsorbed
CO stretching frequency at surface coverages equal to 1 and 0.25 monolayer (ML). The obtained results, in agreement with
the experimental data, indicate that the Ti cation of the (101) surface is more electrophilic than that of the (001) surface,
corresponding to a larger surface Lewis acidity. A nearly linear correlation between the calculated binding energy and the CO stretching frequency was found for the first time at the computational level. The effects of slab relaxation on the two surfaces were also investigated and an opposite behaviour was found for the two parameters
A quantum-mechanical study of CO adsorbed on TiO2: a comparison of the Lewis acidity of the rutile (110) and the anatase (101) surfaces
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