Photocatalytic oxidation of phenol using titanium dioxide thin films prepared by electrophoretic deposition (EPD)

Abstract

In this study, electrophoretic deposition (EPD) technique was used to deposit Ti02 thin film on a conducting glass substrate for use in water purification from organic contaminants. The deposition parameters such as the suspension liquid, suspension pH, dispersant concentration, sintering temperature, powder concentration and deposition voltage and time were optimized in order to obtain a good quality thin film in terms of homogeneity, adherence to the substrate and the extent of microcracking upon drying. Ethanol was better than propanol, water or toluene in obtaining a stable suspension. A pH of 3 gave the best suspension in terms of stability of the suspension and the speed of coating. Ti02 loading concentration was fixed at 4 wt %. The concentration of iodine which acted as the dispersant was fixed at O.3wt% with respect to Ti02 concentration. An applied voltage of 25 volts was optimum for electrophoretic deposition of Ti02 on glass substrate, while time was varied accordingly depending on the required thickness. These optimum parameters gave a good quality film in terms of adherence to the substrate, homogeneity of the film and the extent of microcracking upon drying. The photocatalytic decomposition of phenol in water was monitored by using quantitative analysis of phenol by bromination method. The results showed that the photocatalytic activity increased with film thickness up to 95 11m,above which, the activity decreased. This was attributed to poor absorption of light by the Ti02 due to light shielding effect of Ti02 particles at the bottom of the film by the particles at the top. Increase in sintering temperature was accompanied by reduced photocatalytic activity. An increase in sintering temperature reduced the surface area of the Ti02 particles. Since the photocatalytic activity process occurs at the Ti02 surface, the decrease in surface' area contributed to less particles of the contaminant being attached to the surface since there were fewer sites for adsorption of the contaminant particles. i Films with a higher fraction of anatase structure of Ti02 exhibited a higher photocatalytic activity. Sintering temperature was fixed at 573 K which was just enough to make the Ti02 particles attach to the substrate firmly. At this temperature, the photocatalytic activity was highest and the Ti02 particles adhered well to the substrate. The time needed for the decomposition of phenol was longer if the initial concentration of the contaminants in water was higher. The trend was probably due to the formation of intermediate compounds during the decomposition. Increase in temperature of the phenol solution resulted in increased photocatalytic activity. The increase in photocatalytic activity was attributed to increased solubility of oxygep in the solution at elevated temperatures. There was no decomposition of - phenol without UV illumination while an increase in UV flux intensity increased the photocatalytic activity which was attributed to an increase in photogeneration of OH radicals.