Photo Fenton and Fenton-Like Systems

PHOTO FENTON AND FENTON-LIKE SYSTEMS

When Fe3+ ions are added to the H2O2/UV process, the process is commonly called Photo-Fenton-type oxidation. At pH 3, the Fe (OH)2+ complex is formed because of the acidic environment:


Fe3+ + H2O ---->Fe (OH)2+ + H+


Fe (OH)2+ < -----Fe3+ + OH–


When exposed to UV irradiation, the complex is further subjected to decomposition and will produce .OH and Fe2+ ions:


Fe (OH)2+ ----> Fe2+ + .OH (In the presence of UV)

It is apparent that the photo-Fenton-type reaction relies heavily on the UV irradiation to initiate the generation of OH radical. If desired, organic pollutants can be mineralized completely with UV/visible irradiation. A number of herbicides and pesticides can be totally mineralized by the hν-Fe(III)/H2O2 process, and the mineralization of chlorophenol as well.


The increased efficiency of Fenton/Fenton -like reagents with UV/visible irradiation is attributed to:


– Photo-reduction of ferric ion: irradiation of ferric ion (and/or ferric hydroxide) produces ferrous ion according to reaction. The ferrous ion produced reacts with hydrogen peroxide generating a second hydroxyl radical and ferric ion, and the cycle continues;


– Efficient use of light quanta: the absorption spectrum of hydrogen peroxide does not extend beyond 300 nm and has a low extinction coefficient beyond 250 nm. On the other hand, the absorption spectrum of ferric ion (and/or hydroxyl ferric ions) extends to the near-UV/visible region and has a relatively large extinction coefficient, thus enabling photo-oxidation and mineralization even by visible