Cross effects between water matrix and catechol on the photo-Fenton process: Minimizing the inhibition of inorganic anions and implications on photon absorption

Photo-Fenton process is ruled by complexation of Fe(III); in particular, some inorganic ions inactivate Fe(III) by forming inactive complexes, while some organic ligands, such as catechol (CAT) are able to enhance the performance of the process. The cross effect of both, inorganic anions (F − , Cl − , Br − and BO 3 3− , present in seawater, and PO 4 3− commonly found in agricultural effluents) and CAT has been investigated. For this purpose, a mixture of six pollutants has been used as target. Among anions present in seawater, F − and Br − showed the strongest inhibitory effect at a concentration of 17 mM, which could only be partly removed by the presence of CAT. The nature of the inhibitory effect is different; while F − inactivates Fe(III) by forming complexes that prevent Fe(II) regeneration, Br − acts as scavenger for ·OH. When working at more realistic concentration, inhibition was significantly eliminated, but for Br − , in line with CAT being efficient at avoiding Fe(III) inactivation but not to prevent ·OH scavenging. Experiments with real seawater have demonstrated the efficiency of CAT, despite CAT/Fe ratios above 3 are required. For phosphates, experimental design methodology was used the determine the effect of pH, CAT/Fe and phosphate/Fe. CAT/Fe > 3 where required and the interference was stronger at higher phosphate/Fe ratio. Finally, it has ben shown that efficiency of Fe-CAT system is ruled by the volumetric rate of photon absorption (VRPA) but also by the ability of Fe(CAT) complex, to give an internal electron transfer between CAT and Fe.