Fenton- and photo-assisted Fenton advanced oxidation processes generate reactive oxygen species from hydrogenperoxide and are candidates for the remediation of dye wastewaters. The purpose of this study was to investigate interactions of iron (III) with hydroxyazo dyes. The o-hydroxyazo dyes Acid Orange 7 (AO7; 4-[(2-hydroxynaphthalen-1-yl)azo]benzenesulfonic acid sodium salt) and Acid Orange 10 (AO10;