Performance of activated carbons in consecutive phenol photooxidation cycles

The long term performance of semiconductor-free activated carbons showing photochemical activity was explored by monitoring the photodegradation of phenol from aqueous solution along 20 h of illumination in consecutive photocatalytic cycles. The efficiency of the process was evaluated in terms of phenol conversion, mineralization degree and evaluation of degradation intermediates upon cycling. Data showed a strong dependence of the photooxidation efficiency on the hydrophobic/hydrophilic nature of the carbons. The outstanding role of dissolved oxygen as a promoter of phenol photodegradation through the formation of O-radicals upon illumination of the carbons was also demonstrated. The excess of oxygen not only improved phenol conversion and mineralization, but delayed the clogging of the carbon's porosity upon cycling. This is important since a fraction of the photooxidation reaction also takes place inside the porous network of the carbon materials. Overall, the performance of the activated carbons, especially in conditions of excess of oxygen, is comparable to that of commercial titania.