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-Fe 3 O 4 , a composite of Fe 3 O 4 nanoparticles immobilized on a β-cyclodextrin polymer (ECDP) with ethylene diamine tetraacetic acid (EDTA) as cross-linking agent. The 2,5-DBQ@ECDP-Fe 3 O 4 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 Fe 3 O 4 loaded on ECDP, the actually catalyst is the iron ions released from Fe 3 O 4 but confined within the composite. EDTA in β-cyclodextrin polymer can improve both the solubility and adsorption capacity to H 2 O 2 of Fe 3 O 4 . The quinone molecules 2,5-DBQ in the β-cyclodextrin cavity can accelerate Fe 3+ /Fe 2+ cycle adjacent to the cavity, thus in favor of the decomposition of H 2 O 2 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.