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Rapid activation of microplastics by microwave heating in an aqueous phase: A novel approach for enhanced plastic recycling
Summary
Microwave heating was used to rapidly activate microplastics by partial oxidation, enhancing their subsequent degradation in catalytic wet peroxide oxidation (CWPO) processes. Graphite particles and hydrogen peroxide during microwave treatment boosted MP reactivity, with aliphatic plastics activating more effectively than aromatic ones.
• Transforming MPs into partially oxidized materials enhances their reactivity. • Graphite particles create hot spots on MPs surface by MW radiation. • Incorporation of H 2 O 2 during MW treatment boosts MP oxidation. • Aliphatic plastics activate more effectively than aromatic plastics. • MW treatment improves MP conversion and solubilized TOC in CWPO process. Microplastics (MPs) are persistent environmental pollutants that demand innovative recycling strategies. This study introduces a novel method for rapid MP activation using microwave (MW) heating in aqueous phase. The activation process has been elucidated by detailed characterization of both the MPs and the aqueous matrix. Also, the effect of operating conditions, such as MP particle size, graphite and H 2 O 2 doses, temperature and reaction time on the physical and chemical properties of the MPs and the solubilized total organic carbon (TOC) has been studied. The results indicate that the activated MPs exhibit a rougher texture, surface holes, reduced particle size, higher oxygen content, and increased thermal instability. Furthermore, oxidized short-chain organic acids, including acetic, oxalic, and formic acids, are detected in the aqueous phase. The degree of activation achieved, measured by a parameter defined as A, accounts for weight loss and decomposition temperature changes in the activated MPs. Aliphatic plastics (LDPE, PP) show higher activation levels (A up to 40 %) compared to aromatic plastics (PS, PET, PC), with the activation order being: LDPE > PP > PS ∼ PC > PET. LDPE and PP can be effectively activated at 120 °C within 10 min using a MP:H 2 O 2 mass ratio of 1:1. In contrast, PS, PC, and PET require higher temperatures (200 °C), longer reaction times (180 min) or a greater H 2 O 2 dose (MP:H 2 O 2 mass ratio of 1:5). Activation efficacy is mainly influenced by the reaction time and H 2 O 2 dose. The activated MPs improve recyclability through the CWPO process, achieving up to 15 times higher MP conversion and increased solubilized TOC compared to non-activated MPs, all while consuming less H 2 O 2 and requiring shorter reaction times. This study demonstrates that MW activation has the potential to facilitate large-scale MP chemical recycling.
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