A POM-based copper-coordination polymer crystal material for phenolic compound degradation by immobilizing horseradish peroxidase

Abstract

A new polyoxometalate (POM)-based organic–inorganic hybrid Cu-coordination polymer, namely {((Cu(bipy))₂(μ-PhPO₃)₂Cu(bipy))₂H(PCuW₁₁O₃₉)·3H₂O}_n (denoted as compound 1, bipy = 2,2′-bipyridine, PhPO₃ = phenylphosphonate), was self-assembled hydrothermally. Single-crystal X-ray diffraction (SC-XRD) analysis shows that two unique types of 1D chains are present in compound 1, i.e. Cu(II)-organophosphine and organonitrogen complex cation ([((Cu(bipy))₂(μ-PhPO₃)₂Cu(bipy))₂]⁴⁺) chains and Cu-monosubstituted Keggin-type polyoxoanion ([PCuW₁₁O₃₉]⁵⁻) chains, forming a hetero-POM. Crystalline compound 1 as a new enzyme immobilization support exhibited a high horseradish peroxidase (HRP) loading capacity (268 mg g⁻¹). The powder X-ray diffraction (PXRD), FTIR, zeta potential, confocal laser scanning microscopy (CLSM) and circular dichroism (CD) results show that HRP is only immobilized on the surface of compound 1 through simple physical adsorption without a secondary structure change. This POM-immobilized enzyme (HRP/1) was first used for degradation of pollutants in wastewater, and it showed a high degradation efficiency and TOC removal efficiency for phenol, 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) within 30 min reaction time. Moreover, HRP/1 exhibited better operational and storage stabilities and reusability compared with free HRP. This work suggests that POMs can be used as new supports for enzyme immobilization and POM-immobilized enzymes may be used as a new kind of biocatalyst for degradation of phenolic pollutants.