Chitosan/hydroxyapatite/Fe3O4 magnetic composite for metal-complex dye AY220 removal: Recyclable metal-promoted Fenton-like degradation

• A new heterogeneous Fenton catalyst chitosan/hydroxyapatite/Fe3O4 (CS/HA/Fe3O4) magnetic composite was prepared.
• CS/HA/Fe3O4 was efficiently (95.0%) used for AY220 removal.
• CS/HA/Fe3O4 can efficiently adsorb Co2 + released from AY220 degradation and thus avoid a secondary pollution.
• With Co2 + adsorbed on the surface of CS/HA/Fe3O4, its degradation efficiency of AY220 dramatically increased.

Cross-linked Chitosan (CS) loaded with iron species has been widely used as heterogeneous Fenton catalysts for organic contaminant removal. In comparison with raw-CS based Fenton catalysts, it exhibited an improved degradation efficiency due to the stabilization of cross-linking agents. With cross-linking, however, most reactive sites of CS were occupied by cross-linking agents, making its capability decreased sharply for adsorbing the released metal ions from metal-complex dye degradation. In this work, in order to efficiently adsorb the released metal ions from metal-complex dyes and avoid a secondary pollution, a new CS-based heterogeneous Fenton catalyst (Chitosan/Hydroxyapatite/Fe3O4 magnetic composite) was developed for AY220 (a model of metal-complex dyes) removal. Hydroxyapatite (HA), a well-known biocompatible material with strong ability for metal ion adsorption, was introduced to combine with CS for Fe3O4 loading. The total removal efficiency of AY220 by the magnetic composite can reach as high as 95.0%, and the degradation efficiency of AY220 was greatly enhanced compared with a raw-CS based catalyst and bare Fe3O4. Meanwhile, the composite can efficiently adsorb Co2 + released from AY220 degradation, which can further promote the degradation of AY220. After five recyclable runs of the composite, the degradation efficiency of AY220 increased from 25.1% to 45.6%, demonstrating its potential usefulness in recyclable degradation of metal-complex dyes.