Complete degradation of polystyrene microplastics through non-thermal plasma-assisted catalytic oxidation

Abstract

In this study, a two-stage system, involving plasma degradation coupled with plasma-assisted catalytic oxidation, was developed for the degradation of polystyrene microplastics (PS-MPs) at low temperatures. The dielectric barrier discharge (DBD) plasma contributed reactive oxygen species (ROS) for the degradation of PS-MPs, and the plasma-assisted Hopcalite catalyst selectively facilitated the final oxidation of by-products to CO₂. Within 60 min, the conversion rate of PS-MPs to CO₂, α(CO₂), reached an impressive 98.4%, indicating nearly complete and harmless degradation. It was found that relying solely on the thermal activation induced by plasma heating was insufficient for achieving complete conversion, emphasizing the multifaceted synergy of plasma-catalysis. Subsequently, the cycling experiments revealed that the assistance of plasma enhanced the deactivation resistance and stability of the catalyst. When dealing with PS-MPs at a concentration of 5 wt.%, the plasma-assisted Hopcalite still exhibited 93.2% α(CO_x) and 99.5% relative CO₂ content after 10 cycles. Additionally, characterization of the plasma-modified Hopcalite using various techniques suggested an enhancement in surface-adsorbed oxygen species. On the other hand, the packed catalyst improved the uniformity of the discharge plasma, while micro-discharges within the pores could further facilitate the oxidation reaction. This work provides new insights into the comprehensive treatment of MP pollution.