REMOVAL OF CHLOROPHENOLS FROM WATER BY PHOTOCATALYTIC OXIDATION

Photocatalyst, TiO2, upon irradiation with uv light produces electrons and positive holes. The positive holes are strong oxidation agents that can oxidize organic compounds such as chlorophenol to mineral acids e.g. HCl and CO2. Factors such as pH, chlorophenol concentration, concentration of TiO2 and inorganic electrolytes that may affect the oxidation of chlorophenol were investigated. The rate of the chlorophenol oxidation follows a first order reaction with respect to the chlorophenol concentration and independent of pH. The rate increases with concentration of TiO2, reaches a maximum level at 3 g/L then decreases to a constant value upon further increase in TiO2. Increasing the degree of chlorination appears to increase the extent and the rate of oxidation. For mono-chlorophenols the extent of oxidation follows: 4-chloro > 3-chloro > 2-chloro phenol. For dichlorophenols, the order is 2,6-dichloro almost-equal-to 2,5-dichloro > 2,4-dichloro-almost-equal-to 2,3-dichlorophenol. For symmetrical chlorophenols, the oxidation increases in the order: 4-chloro > 2,5 - dichloro > 2,4,6-trichlorophenol. Pentachlorophenol is rapidly decomposed but the extent of oxidation is not complete.