Enhancement the photocatalytic activity of TiO2 characterisation of ascorbic acid modified TiO2 and modelling the photocatalytic degradation reaction of hydroquinone

TiO2 is the photocatalyst used extensively in the photocatalytic degradation reactions oforganic pollutants. However, the photocatalytic activity has been found to be too low for themost of the aromatic compounds, due to the low surface coverage of TiO2 particles.Therefore, in recent years, attention has been directed towards surface modification of TiO2.Surface modifiers increase the photocatalytic activity of TiO2 by inhibiting electron-holerecombination process and by exploring the wavelength response range.In this study, with the intention of determining the effects of surface modificaton, the kineticsof the photocatalytic degradation of hydroquinone has been investigated experimentally, byusing ascorbic acid (AA) modified TiO2. Hydroquinone has been chosen as the modelcompound, since dihydroxybenzenes are toxic intermediate products of the photocatalyticdegradation reactions of phenolic compounds which constitute an important class of waterand air contaminants. The reactions have been carried out in a constant temperature batch-type photoreactor using pure and surface modified TiO2 P25 Degussa as the photocatalyst.The effects of the catalyst loading, initial concentration of hydroquinone and surfacemodification on the degradation rate have been determined. Surface modified catalyst hasbeen characterized by using structural methods and thermal analyses such as FTIR, XRD,SEM and DTA-TG.In the theoretical part, in order to investigate the effect of surface modification by ascorbicacid on the electronic structure of anatase and to find models suitable for determining theelectronic properties of TiO2, a cluster model Ti9O18 cut from the anatase bulk structure hasbeen modeled. Calculations have been carried out using Density Functional Theory DFT atB3LYP/LANL2DZ level. The formation process of the complex and its effect on theelectronic structure of TiO2 have been examined. The optimized geometries, the frontier-orbital energies, energy gaps, Mulliken charge distributions of the atoms on the surface havebeen determined. Finally, the product distribution for the photocatalytic degradation ofhydroquinone has been determined by means of quantum chemical methods and theTransition State Theory calculations for all the possible reaction paths.Keywords: Hydroquinone, surface modification, ascorbic acid, photocatalytic degradation,titanium dioxide.