KINETIC STUDIES ON UV-PHOTODEGRADATION OF SOME CHLOROPHENOLS USING TIO₂ CATALYST

ABSTRACT

A number of chlorophenols, namely 2-chlorophenol, 2,4,-dichlorophenol and 2,4,6-trichlorophenol, were decomposed in aqueous solution by using TiO₂ as photoactivated catalyst under UV radiation emitted by a 125 W medium pressure Hg lamp in an immersion well-type quartz photoreactor. The organic-bound chlorine was converted into the environmentally harmless inorganic chloride. For catalyst doses between 0.1 and 0.5 g l⁻¹ the reaction mechanisms are elucidated. The corresponding rate constants were obtained by periodically measuring the remaining chlorophenol, and converted chloride in solution. A theoretical model for the degradation pathway is proposed expressing the rate as a linear function of the concentrations of chlorophenol and catalyst. Aside from the model-calculated values, the pseudo-first order rate constants for a rough approximation of chlorophenols degradation as well as the kinetic parameters of Langmuir-Hinshelwood type decomposition are compared. The photodegradation rate of chlorophenols followed the order: Cl₃ċPh>Cl₂ċPh>ClċPh.

Keywords:

• Chlorophenols
• Photodegradation
• Photocatalytic decomposition
• UV radiation
• Titanium dioxide
• Water treatment

ACKNOWLEDGMENT

The authors wish to express their gratitude to the Third World Academy of Sciences (TWAS) for the supply of the laboratory scale photoreactor as a part of the Research Grant Programme.