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Enhancing microplastic analysis: Hyperpolarized ¹²⁹xe NMR to probe surface morphologies and pore structures
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This study applied hyperpolarized xenon-129 NMR spectroscopy to probe the surface morphology and microstructure of microplastic particles, examining how surface roughness, cracks, and pore structures affect their environmental behavior. The technique revealed surface features relevant to particle aging, contaminant adsorption, and interactions with biological molecules that conventional imaging methods cannot characterize.
Microplastic particles (MPP) exhibit diverse behaviors influenced by their surface morphology. The drag coefficient and, thus, transport mechanisms depend on the surface area, roughness, and shape.[1] Together with cracks, they affect the interaction between the polymer and the molecules from the environment, potentially accelerating ageing through freeze-thaw cycles. Additionally, the build-up of an eco-corona depends on the surface morphology, further impacting toxicity and environmental effects. Thus, understanding MPP surface morphologies is paramount. Current adsorption measurements, while informative, only capture surface area changes over weathering periods. For example, polystyrene particles experience a surface increase from 0.5 to 2.5 m²/g and size reduction from 160 to 20 µm after 3200 h of weathering. Although highly sensitive, Atomic Force Microscopy (AFM) struggles to probe deep cracks and requires extensive measurements to quantify features in each sample. These limitations highlight the necessity for a more sensitive and comprehensive method for surface analysis. In this regard, Hyperpolarized (HP) ¹²⁹Xe Nuclear Magnetic Resonance (NMR) is a successful technique. The chemical shift is very sensitive to its confinement, making it an ideal probe to detect changes in porosity within the nanometer size range. With our home-built Polariser, we create hyperpolarised xenon gas, increasing sensitivity by five orders of magnitude and, therefore, rapidly detecting mesopores and small amounts of micropores.[2] Utilising ¹²⁹Xe NMR measurements, the development of multiscalar pore structures in PS MPPs postulated by Meides et al. is verified.[3] Referencing with samples of known pore sizes enables the relation function between pore size and chemical shift, revealing a significant increase in micropores by a factor of four in volume. Thus, HP ¹²⁹Xe NMR provides a deeper understanding of microplastic surface characteristics, improving our ability to assess their environmental impact and toxicity. [1]Kabir et al.,PolymJ,2015,47,564 [2]Stäglich et al., J.Phys.Chem.A.,2022,126,16,2578-2589. [3] Meides et al., Environ.Sci.Technol.,2021,55,7930 Also see: https://micro2024.sciencesconf.org/559663/document
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Enhancing microplastic analysis: Hyperpolarized ¹²⁹xe NMR to probe surface morphologies and pore structures
AI summary Read the abstract
Researchers applied hyperpolarized xenon-129 NMR spectroscopy to probe the surface morphology of microplastic particles, detecting surface roughness and cracks not visible by standard techniques. Surface characteristics revealed by NMR influence how microplastics interact with environmental molecules and biological surfaces.
Weathering of microplastic creates nanometre-sized surface-near cavities – A 129Xe NMR spectroscopic study
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When plastic breaks down in the environment, it doesn't just get smaller, it develops tiny hidden pockets and pores on its surface, some smaller than 1/1000th the width of a human hair. Using a specialized imaging technique, researchers discovered these microscopic nooks are too small for standard tools to detect, but they matter because they can trap and hold onto toxic chemicals and pollutants. This means weathered microplastics may be better at soaking up and carrying harmful substances than previously realized, which is important since these particles can end up in water, food, and eventually our bodies.
Weathering of microplastic creates nanometre-sized surface-near cavities – A 129Xe NMR spectroscopic study
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When plastic waste breaks down in the environment, it doesn't just crumble into smaller pieces—it also develops tiny pits and rough patches on its surface, almost like microscopic craters. Using advanced imaging and a specialized gas-based scanning technique, researchers found that these nanoscale nooks and crannies can act like sponges, potentially trapping pollutants and toxic chemicals. This matters because it means weathered microplastics may carry more hitchhiking contaminants than fresh plastic, which could affect how these particles transport harmful substances through water, soil, and eventually into our bodies.
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Researchers reviewed how synchrotron-based imaging techniques — which use powerful X-ray beams to see extremely fine details — can detect and chemically identify micro- and nanoplastics that conventional methods miss, including plastics absorbed into biological tissues. These high-resolution tools are still in early stages but show strong potential for mapping microplastic contamination at the nanoscale.
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