Meric Yilmaz Salman, Türker Salman, Mustafa Ersin Pekdemir
The simultaneous capture of micro and nanoplastics is governed by particle size dependent transport and interfacial interactions that cannot be fully understood from single component experiments. Here, the competitive adsorption of 1 µm polystyrene microplastics (PS MPs) and 100 nm polystyrene nanoplastics (PS NPs) was investigated in single and binary component systems at the interface of a magnetically recoverable Fe3O4@MIL-100(Fe)/CNT hybrid (mFMC). In the single component system, PS MPs reached approximately 95% removal within 60 min, whereas PS NPs approached equilibrium more gradually. In the binary system, the presence of PS NPs markedly reduced the early stage adsorption rate of PS MPs, indicating size dependent competition at the heterogeneous mFMC-water interface. At pH 7, removal efficiencies reached 93.0% for PS MPs and 92.5% for PS NPs within 360 min. Zeta potential measurements and classical DLVO calculations provided a consistent framework for interpreting the pH dependent adsorption behavior. Interaction energy profiles under acidic and neutral conditions were consistent with high removal, whereas the energy barriers observed under alkaline conditions agreed with the decline in particle attachment. Raman spectral changes together with BET and SEM observations further supported surface coverage and possible contributions from hydrophobic and π-π interactions at CNT rich interfacial regions. The hybrid maintained removal efficiencies of at least 90% in tap water, textile wastewater and urban wastewater treatment plant effluent. After five adsorption-desorption cycles, removal remained at 90.2% for PS MPs and 88.0% for PS NPs. These findings establish a mechanistic link between particle size, competitive interfacial access and pH dependent interaction energies, providing a basis for the simultaneous removal of mixed size plastic contaminants from complex water matrices.