Cold plasma-induced fragmentation and surface modification of polystyrene microplastics in aqueous systems

Cold plasma offers a reagent-free route for modifying persistent polymer particles, but fragmentation must be distinguished from chemical destruction. Here, polystyrene microplastics were examined in a recirculating air-plasma water reactor at 22–40 °C. A 1 μm fraction (1 mg L −1 ) was used for time-resolved analysis, while a 10 μm fraction (100 mg L −1 ) provided a supplementary qualitative assessment under a different polymer loading. Dynamic light scattering, turbidity, flow cytometry, electron microscopy, atomic force microscopy, and Fourier-transform infrared spectroscopy showed progressive particle-size redistribution, loss of spherical morphology, surface roughening, and moderate spectral changes consistent with surface modification. For the 1 μm suspension, the mean hydrodynamic diameter decreased from approximately 1.02 μm to 94 nm within 20 min. An empirical first-order fit described the diameter redistribution (k app approximately 0.12 min −1 ), but this parameter does not represent an intrinsic chemical degradation rate. The 10 μm particles showed slower transformation into lower-micrometre fractions; direct quantitative size comparison is limited by the different initial polymer loadings and the upper measurement range of dynamic light scattering. The results demonstrate fragmentation and surface modification rather than mineralization and support considering cold plasma as a potential pretreatment before downstream separation or further oxidation.