Integration of homogeneous and heterogeneous advanced oxidation processes: Confined iron dancing with cyclodextrin polymer.

A novel catalyst which integrates heterogeneous and homogenous Fenton reactions is designed and fabricated by encapsulating 2,5-dihydroxy-1,4-benzoquinone (2,5-DBQ) in ECDP-Fe3O4, a composite of Fe3O4 nanoparticles immobilized on a β-cyclodextrin polymer (ECDP) with ethylene diamine tetraacetic acid (EDTA) as cross-linking agent. The 2,5-DBQ@ECDP-Fe3O4 has superior catalytic performance for 4-nitrophenol and 2,4-dichlorophenol degradation compared with control systems. Mechanism study revealed that although the initial active site is Fe3O4 loaded on ECDP, the actually catalyst is the iron ions released from Fe3O4 but confined within the composite. EDTA in β-cyclodextrin polymer can improve both the solubility and adsorption capacity to H2O2 of Fe3O4. The quinone molecules 2,5-DBQ in the β-cyclodextrin cavity can accelerate Fe3+/Fe2+ cycle adjacent to the cavity, thus in favor of the decomposition of H2O2 into OH as main reactive oxidizing species. The current catalyst integrates the advantages of homogeneous and heterogeneous advanced oxidation processes and is promising in practical applications.