Cobalt catalyzed carbonyl functionalization to boost the biodegradation of polyethylene by Bacillus velezensis C5

Abstract

Polyethylene plastics are widely used in daily life since known for their resistance to biodegradation, but posing a significant environmental challenge. The biodegradation of polyethylene can contribute to environmental protection and facilitate energy conservation, in comparison with physical or chemical methodologies. However, the stable and inert C–C bond structure of polyethylene limits biodegradation effectiveness, leading to a slow breakdown rate and extended life cycle. In this study, Co(acac)2 was used as a catalyst to generate free radicals that activated the interface of low-density polyethylene, resulting in the formation of oxygen-containing functional groups. Under the condition of Co(acac)2-mediated catalysis at 120 °C for 24 h, the carbonyl index of polyethylene rose from 0 to 2.99. The weight-average molecular weight of polyethylene was reduced by 8.77 % compared to the control, leading to the generation of small molecules. The density functional theory elucidated showed that the active oxygen substitution in the single electron transfer reaction was driven by the high-energy intermediate alkyl radical. The bond energy of the resulting carbonyl functional group (CO) is 76.4 % lower than that of the original C–C bond, making it more susceptible to cleavage and depolymerization. Following 90 d of biodegradation, the laccase activity showed a 25 % increase compared to the control, indicating an improved oxidase release by chemical oxidation. The weight loss of low-density polyethylene was 23.91 %, and the microbial degradation efficiency was 2.32 times higher. This strategy significantly improves the ability of microorganisms to degrade low-density polyethylene and is a novel approach to the design of pathways for the polyolefin degradation.