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

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.