Nanoplastics Extraction from Water by Hydrophobic Deep Eutectic Solvents

Nanoplastics pollution, a growing environmental threat, adversely affects ecosystems and human health. The challenge in extracting and detecting nanoplastics from environmental matrices lies in their minuscule sizes, varied shapes, and low concentration. We demonstrate an efficient approach employing hydrophobic deep eutectic solvents (HDESs) for the liquid/liquid extraction of polystyrene (PS) beads (nominally sized 0.1, 0.2, 0.3, 0.5, and 1.0 μm), a stand-in for nanoplastics, from both fresh and saline water. Of ten different HDES systems evaluated, those described by 1:2 molar ratios of tetrabutylammonium bromide ([N4444]Br):decanoic acid or tetraoctylammonium bromide ([N8888]Br):decanoic acid as well as 1:1 thymol:menthol showed exceptional efficiency, achieving nearly complete removal (a mean extraction efficiency of 98.4%) of nanoplastics in a single pass across a range of nanoplastic sizes from 100 to 1000 nm. The HDES comprising 1:2 [N4444]Br:decanoic acid exhibits a high extraction capacity, effectively capturing at least 17.2 wt % of PS. Crucially, the extractive fluids comprise benign components, and the hydrophobicity of these HDESs helps to prevent water phase contamination, showcasing their potential as a sustainable solution to the nanoplastics problem.