In situ Fe3O4 nanoparticles coating of polymers for separating hazardous PVC from microplastic mixtures

Poly(vinyl chloride) (PVC) poses great challenges to the recycling of plastic wastes since it highly deteriorates the properties of other plastics and induces the formation of hazardous chlorinated dioxins and furans. For the first time, we developed a novel hydrophilization method of polymers, the in situ magnetite (Fe 3 O 4 ) nanoparticles (NPs) coating, to facilitate the flotation separation of PVC from microplastic mixtures. A homogeneous Fe 3 O 4 NPs layer was selectively fabricated on the surface of non-PVC microplastics via a facile in situ coprecipitation method. This obviously decreased the contact angle of non-PVC microplastics by approximately 30° due to the plenty of hydroxyl groups on the surface of Fe 3 O 4 NPs. However, the fabrication was not observed on the surface of PVC due to the weak interaction between Fe 3+ /Fe 2+ and the surface of PVC. In this regard, the application of in situ Fe 3 O 4 NPs coating in the flotation separation of PVC was systematically optimized using Box-Behnken design of response surface methodology. Quadratic models were generated to predict the floatability of microplastics, ascertain the effect of independent and interacted parameters, and numerically optimize the separation efficiency. Under optimum conditions, the Removal r a t e $\mathit{Removal}rate$ , Purity $\mathit{Purity}$ , and Recovery $\mathit{Recovery}$ of PVC were 100.0%, 99.6%, and 100.0%, respectively. This study provides novel insights into the surface hydrophilization of polymers and shows promising prospects for facilitating the recycling of plastic wastes.