Photocatalytic destruction of halogenated organic compounds in water with a new photocatalysts.

摘要

In this research, a newly developed high surface area semiconductor porous material was synthesized from potassium titanium niobium mixed oxide (KTiNbO5) to be used as a photo catalyst in the presence of UV light to degrade halogenated organic compounds in water. The goal of the project was to investigate the catalytic activity of the material for its effectiveness in the degradation of the halogenated organic compounds, and it is the first investigation of this new photocatalyst with halogenated compounds. Model compounds dichloromethane, 1-chlorobutane, chlorobenzene, and trifluoroacetic acid in aqueous solutions were tested with the photocatalyst under ultraviolet light irradiation, using a batch photolysis reactor system. An improved process for preparing the photocatalysts was developed, which is more effective, faster, and less wasteful for rinsing the catalysts with a solvent exchange done in five hours instead of the original 6 days. The porous material was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption surface area analysis (BET), inductively coupled plasma optical emission spectroscopy, and X-ray fluorescence spectrometry. The project also involved researching a practical way to follow the reaction progress using the product concentrations of Cl- and F- in solution. Photo degradation kinetics was followed via titration, ion selective electrodes, ion chromatography, and total organic carbon analysis. In a mixture of the three chlorinated compounds, about 84% of the chlorine present in the compounds was released as chloride ions after 8.0 hours of irradiation with the catalyst. This was concomitant with a decrease in the pH of the solution. Loss of samples via vaporization and escape into the air was responsible for incomplete photolyzation. Several attempts to create a catalyst system using a flow-through reactive catalyst bed were not successful, and therefore a batch process was used. The photocatalytic activity of the new porous material towards halogenated organic compounds in stirred water reactors is demonstrated to be a promising alternative to TiO2 nano powders. The new catalyst had much better sedimentation characteristics than TiO2 nano powders and it can be filtered easily, qualities that TiO2 nano powders do not have.