Photo-assisted oxidation of chlorophenols in aqueous solutions using hydrogen peroxide and titanium dioxide.

In the present work, the efficiency of phenol and chlorophenol degradation under irradiation using hydrogen peroxide as oxidant and titanium dioxide powder as photo-catalyst was investigated. In the absence of titanium oxide, increased concentrations of hydrogen peroxide resulted in higher conversions. Generally, phenol was the most readily oxidized compound, whereas in excess of hydrogen peroxide, the more chlorine atoms were present in the ring, the less degradable the chlorophenol was, in terms of initial rate of oxidation. In the case of 4-chlorophenol, the catalytic photo-oxidation efficiency with hydrogen peroxide and titanium oxide was dependent on the catalyst concentration exhibiting a maximum at 0.025-0.05 g L(-1) titanium oxide. The combined use of titanium oxide and hydrogen peroxide resulted in higher degree of oxidation compared to results obtained when using hydrogen peroxide. Finally, the presence of Fe(III) proved to be beneficial for the photo-catalytic oxidation only in the presence of hydrogen peroxide.