ABTS as an electron shuttle to accelerate the degradation of diclofenac with horseradish peroxidase-catalyzed hydrogen peroxide oxidation.

Horseradish peroxidase (HRP)-catalyzed hydrogen peroxide (HO) oxidation could degrade a variety of organic pollutants, but the intrinsic drawback of slow degradation rate limited its widespread application. In this study, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) was introduced into HRP/HO system as an electron shuttle to enhance diclofenac degradation under neutral pH conditions. The green-colored ABTS radical (ABTS), generated by the oxidation of ABTS with HRP-catalyzed HO oxidation, was proved to be the main reactive species for the rapid degradation of diclofenac in HRP/HO/ABTS system. There was no destruction of ABTS/ABTS in HRP/HO/ABTS system, and ABTS was verified as an ideal electron shuttle. The reaction conditions including solution pH (4.5-10.5), HRP concentration (0-8 units mL) and HO concentration (0-500 μM) would impact the formation of ABTS, and affect the degradation of diclofenac in HRP/HO/ABTS system. Moreover, compared with Fenton and hydroxylamine/Fenton systems, HRP/HO/ABTS system had better diclofenac degradation efficiency, higher HO utilization efficiency and stronger anti-interference capacity in actual waters. Overall, the present study provided a meaningful and promising way to enhance the degradation of organic pollutants in water with HRP-catalyzed HO oxidation.