Photo-assisted degradation of anionic and cationic dyes over iron(III)-loaded resin in the presence of hydrogen peroxide

Ferric species were immobilized on different types of ionic exchange resins, and used as a heterogeneous catalyst for degradation of cationic and anionic dye pollutants under visible light (λ > 450 nm) irradiation in the presence of H2O2. It was found that for the photodegradation of cationic dyes, malachite green and methylene blue, the immobilized catalyst on a strongly or weakly cationic resin was much more effective than the catalyst supported on an anionic resin, whereas an opposite order in the catalyst activity was observed for the photodegradation of anionic dyes, phloxine and X3B. This significant difference was mainly attributed to the dye adsorption, which enhanced the electron transfer from the excited dye to the immobilized ferric species. All the catalysts were stable upon visible light irradiation, and less than 3.2 μM of dissolved Fe species was detectable in the filtrate solution. When the ferric species was loaded on an amphoteric exchange resin, the immobilized catalyst was effective to the photodegradation of both cationic and anionic dyes. The anionic dyes were notably adsorbed on such the catalyst, but the catalyst exhibited weak affinity toward cationic dyes. Due to the inner salt effect, some dissolved ferric species was released from the solid, and consequently made some contribution to the overall dye degradation via both the Fenton reaction and the photosensitization pathway. Although the amphoteric resin-supported catalyst was stable to the visible light, it was corroded to a certain level upon UV irradiation. It was found that such photodissolution was greatly depressed in the presence of H2O2.