Biodegradation of carbon materials by environmental peroxidases depends on the type of allotropic form

Abstract

Carbon nanomaterials, possessing unique properties and advantages, exhibit broad application prospects. However, their potential risks to life and the environment have constrained their development. Investigating various degradation strategies can mitigate their adverse effects and expand their applications, particularly within the fields of life and materials sciences. Peroxidases are widely utilized for degradation due to their capability to catalyse the breakdown of various organic compounds. In this study, three peroxidases, namely horseradish peroxidase (HRP), Pichia pastoris-expressed Eucodis® peroxidase (EP 13), and manganese peroxidase (MnP), were selected to investigate their effects on the enzymatic biodegradation of different allotropic forms of carbon materials, including graphene and single-wall carbon nanotubes (SWCNT). The obvious increase of defects and decomposition of the structures were demonstrated for graphene by Raman spectroscopy and transmission electron microscope (TEM) after the treatment with these peroxidases. No degradation was instead observed in the enzyme-treated pristine SWCNT. The differences of degradation in two carbon nanomaterials are supposed to result from their distinct physicochemical properties. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) evidenced that a number of oxygen-containing functional groups are present in graphene, likely providing the catalytic sites for the peroxidase action thus facilitating its degradation, as previously demonstrated using other types of oxidative conditions