Faculté des sciences

Molecular Insight into Photocatalytic Reactions by TiO2 Investigated by ATR-IR Spectroscopy

Dolamic, Igor ; Bürgi, Thomas (Dir.) ; Stoeckli-Evans, Helen (Codir.) ; Kiwi-Minsker, L. (Codir.) ; Hug, S. J. (Codir.)

Thèse de doctorat : Université de Neuchâtel, 2008 ; 2018.

Today mankind faces several environmental pollution problems which are a result of our fossil fuels dependence. Water pollution, global warming, air pollution are just several tasks that rapt scientists today. The importance of the previous problems constrained people to find and use other sources of energy. The sun is one of the alternative energy sources that can be used. Continuously our... Plus

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    Summary
    Today mankind faces several environmental pollution problems which are a result of our fossil fuels dependence. Water pollution, global warming, air pollution are just several tasks that rapt scientists today. The importance of the previous problems constrained people to find and use other sources of energy. The sun is one of the alternative energy sources that can be used. Continuously our planet is provided by a huge sun light energy of about 4.3x1020J per hour, which roughly corresponds to the energy consumed on the Earth in one year (4.1x1020J).

    So far solar energy was consumed for different purposes, from more primitive, drying cloths and foodstuff to very complex such as photovoltaic cell and photocatalysis. One of the materials which find huge application in solar energy conversion is titanium dioxide. TiO2 was successfully applied as material in many fields and was extensively studied during the last three decades after A. Fujishima and K. Hondas discovery of photocatalytic activity of TiO2.

    In the last years photocatalytic reactions on TiO2 nanoparticles have attracted much interest due to their application in solar energy conversion i.e. water splitting and environmental cleaning or decomposition of organic pollutants in gaseous effluents and wastewater. Despite the importance of photocatalysis, not too much molecular level information is available today on the processes occurring at the respective solid –liquid interfaces.

    However, the reactions that take place at solid-liquid and gas-solid interface are of crucial importance for a better understanding these systems. A lot of studies have been carried out in the last years but most of them are based on analysis of stable reaction intermediates in the liquid or gas phase. Very few scientific insights were based on direct information of the reactions that take place at the interfaces.

    Fourier-transform infrared spectroscopy (FT-IR) applied in the attenuated total reflection (ATR-IR) mode is a promising method to probe solid-liquid interfaces in order to give molecular insight of the reactions occurring. In combination with modulation excitation (ME) spectroscopy the signal to noise ratio can be improved and separation of overlapping bands is possible.

    In the first part of this thesis (Chapters 3 and 4) adsorption, photocatalytic decompositions and reaction routs of dicarboxylic acids were investigated using ATR-IR spectroscopy in combination with ME spectroscopy. For the first time dissolved CO2 as the final product was detected in situ. Also other reaction products like oxalate, carbonate and carboxylate were detected on the TiO2 surface and were reported in this thesis.

    Chapter 5 deals with adsorption of monolayer protected gold nanoparticles (MPNs) on TiO2 and their behavior upon UV illumination. ATR-IR spectroscopy in combination with UV-visible spectroscopy and transmission electron microscopy (TEM) gives detailed information on the fate of adsorbed gold MPNs on TiO2 upon UV illumination. Furthermore, the combination of both in situ techniques reveals the importance of mass transport through the porous films prepared on internal reflection elements (IRE).

    In the Chapters 6 and 7 adsorption and photocatalytic degradation of several amino acids over TiO2 and Au- TiO2 thin films was investigated. Also the preparation and tailoring of Au- TiO2 catalyst was reported. Using ATR-IR combined with MES the main intermediate species could be detected on the catalytic surfaces in situ. For the first time CN- species were reported during photocatalytic mineralization of amino acids over TiO2 and Au- TiO2. The CN- promotes leaching of the gold. These findings are relevant for the application of photocatalysis by TiO2-based materials for the cleaning of drinking water.