The adsorption and degradation of rhodamine B during the formation of Fe3O4 nanoparticles by air oxidation of Fe(OH)(2) under visible-light irradiation were investigated. The results showed that RhB could be adsorbed on a green rust II (GR II) intermediate and on the Fe3O4 product surfaces during Fe3O4 formation and be degraded via heterogeneous and homogeneous photo-Fenton-like reactions. Fe2+ and H2O2 coexisted in the reaction system, and Fe2+ or H2O2 both promoted the adsorption and degradation of RhB. As the reaction proceeded, the increase in acidity enhanced the efficiency of the photo-Fenton-like reactions, which led to an increase in RhB degradation. The adsorbed RhB underwent desorption because of the transformation of GR II and growth of Fe3O4. A possible mechanism was suggested for the comprehensive effect of RhB degradation during the reactions. (C) 2014 Elsevier B.V. All rights reserved.