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1.3 PHYSICAL SCIENCES
Titanium dioxide (TiO2) suspensions have widely been used as photocatalysts, either alone or in a doped form to degrade organic compounds and kill bacteria. Because of its relatively large band gap, UV light has been the most efficient radiation used to allow this catalysis to occur. TiO2 has also been immobilised on electrodes in order to separate the ‘reduction’ and ‘oxidation’ reactions. Typical systems involve the oxidation of a ‘fuel’ at a TiO2 coated anode and the reduction of oxygen at a separate cathode, where the passage of current can be monitored, and this work utilises such a system. In this work, there are two systems described. TiO2 coatings have been prepared on carbon ink based electrodes as anodes, while the cathodes were ink electrodes loaded with cobalt (II) phthalocyanine (CoPc). These electrodes are characterised and used in a fuel cell configuration with formic acid as a substrate in a one compartment cell. In this case the light source was modelled on visible radiation using either a 60 W tungsten lamp or a Q Sun system. The second system involves the use of TiO2 coated electrodes with air electrodes as cathodes in either one or two compartment set ups, using many water soluble organic compounds as fuels. Such a system can be used to degrade many organics such as benzaldehyde, 1,2- dihydroxybenzene (CAT) potassium hydrogen phthalate, 2-propanol, phthalic acid (HHP), 4-chlorophenol, and ascorbic acid to mention but a few. The rate of degradation depends on the light source used, amount of lumens from the light source reaching the catalytically coated surface, passivation, chemical nature and stability of the organic compound, pH and cell configuration. With daylight as the source, at room temperature the photoelectrocatalyic (pec) cell connected for 11 days brought about an 88 % degradation of CAT, 4 times more than a similar surface confined photocatalytic (pc) cell could offer. Another pec cell also produced over 4 times more degradation than its equivalent pc cell; this time eliminating 90 % of the initial amount of the common vitamin ascorbic acid, using visible light and within 3 hours. There was over 3 times as much HHP degraded in a one compartment pec cell using UV light and an air cathode rather than for a similar surface confined pc cell, with half of the concentration of the aromatic chemical eliminated within 3 hours. A qualitative model was developed for the cyclic voltammetric behaviour of formic acid, where a reversible system was transformed into a steady state system, depending on Langmuir Hinshelwood parameters; k’ and K.In separate work square wave voltammetry was applied to microelectrodes to obtain a peaked current response. Parameters such as pulse height, frequency and step height were varied and a simple model was applied.
Enright, Patrick. (2008). Enhanced absorption metal oxides for photocatalytic applications. Dublin Institute of Technology. doi:10.21427/D79P4D.