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Sankarampadi Aravamudhan Elementary aspects of the photo catalytic process with materials like TiO2 in decontaminating polluted water.
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Sankarampadi Aravamudhan Elementary aspects of the photo catalytic process with materials like TiO2 in decontaminating polluted water. To degrade the small organic molecular pollutants by photochemical degradation and complete mineralization to reduce the compound to elementary compounds like H2O, CO2, and H2 Exploring mechanistic aspects by using QM computational chemistry with a view on the design considerations of water purifying plants. Practical aspects to compare with trends discernible by theoretical studies NCCT 2017- PRAGATI Kakinada SA
THE IMPORTANCE OF DIFFUSION PHENOMENON HAS BEEN POINTED OUT IN THE PREVIOUS SLIDES NCCT 2017- PRAGATI Kakinada SA
Even for those who are well versed with techniques in Computational Quantum Chemistry, these critical aspects of taking care of the diffusion phenomenon in the medium while subjecting bulk solution (model) could be off the track features to account for during routine geometry-optimiziation algorithms. A few illustrative situations are explained in the following slide-features as the main contents of this presentation NCCT 2017- PRAGATI Kakinada SA
The typical organic small molecules considered are (aromatic/ heterocyclic) ring compounds. Mainly oxygen containing rings are illustrated, so that as the illustration proceeds subtle aspects of the differences in the conditions, when C-H bonds, C-C bonds and C-O bonds break to result in fragmented small molecules, becomes reasonably evident. Importantly, the initial breaking condition of the starting structure and proceeding for further break down of the fragments as well to finally yield CO2, H2O and H2 so that the result is reckoned as complete degradation or mineralization of the compound NCCT 2017- PRAGATI Kakinada SA
Initially the reactive radical species have to be generated and be available in the medium; then, as the diffusion process inherent in the medium results in bringing the molecules/radicals together to enable appropriate reaction step. NCCT 2017- PRAGATI Kakinada SA
Water diffusion and acquiring electron from surface not depicted Electron-acquired water molecules are negatively charged and diffuse into themedium; availble for further consequences (Water, oxygen, hydrogen peroxide) Molecules in the medium hn e- e- TiO2 surface h+ h+ NCCT 2017- PRAGATI Kakinada SA
Even when the molecules are well packed, the iteration process would minimize the energy only to a few iterations, afterwards, since the independent molecules are stable units they get a mutual disposition as if each of them is a hard sphere only with a repulsion rather than attraction. It is important to note the reactive radicals to be efficient, the stable molecules must have appropriate reactive canters for radicals to influence the molecules. Illustration in next slide. Geometry optimization from the guessed structutre to stable fomration of molecules by group of atoms Distributionsn of stanle molecules subjected to the same geometry optimization by QM method.. Even if initially energy decreases it may not get to a minimum The results reported in this presentation are obtained with PM3 semi empirical, method mostly
With this type of molecule, initial degradation could come about without much difficulty by the use of oxygen molecules (in the system above 4 negatively charged oxygen molecules) can be seen. These type of molecules can be present in water as pollutants. After the initial degradation, proceeding towards complete mineralization requires adding oxidizing agents like Oxygen and hydrogen peroxide, as the oxidation-reduction process are in progress. Adjusting the relative concentration for efficient mineralization. Organic Molecule is 1,4 dioxin
A few images gathered as intermediate stages before final convergence are illustrated for explaining the observable trends Chloro-benzene; (6-momembered ring) 1,4 Dioxin; (6-memebered ring) Furan; (5-membered ring) NCCT 2017- PRAGATI Kakinada SA
Chloro-benzene NCCT 2017- PRAGATI Kakinada SA
Note the ring opening by breaking a C- C bond NCCT 2017- PRAGATI Kakinada SA
1,4-Dioxin NCCT 2017- PRAGATI Kakinada SA
Furan NCCT 2017- PRAGATI Kakinada SA
Thank you NCCT 2017- PRAGATI Kakinada SA
