A novel catalyst which integrates heterogeneous and homogenous Fenton reactions (oxidation of contaminants by hydroxyl radical produced by hydrogen peroxide and iron, Equation 1) is designed and fabricated by encapsulating 2,5-dihydroxy-1,4-benzoquinone (2,5-DBQ) in EDTA-crosslinked cyclodextrin polymer (ECDP-Fe3O4), a composite of Fe3O4 nanoparticles immobilized on an insoluble 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 (2,4-DCP) degradation compared with control systems.
Degradation efficiency of 2,4-dichlorophenol using Fe3O4 (1.1 g/L) or 2,5-DBQ@ECDP-Fe3O4 (2.0 g/L) catalyst, H2O2 (50 mM), and 2,4-DCP (20 g/L), pH 3
Mechanism study revealed that although the initial active site is Fe3O4 loaded on ECDP, the actual 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.
Fengxia Chen, Daojian Tang, Ya Wang, Tuo Li, Jiahai Ma: Integration of homogeneous and heterogeneous advanced oxidation processes: Confined iron dancing with cyclodextrin polymer. Chemosphere 250 (2020) 126226