Preparation of Microplastics and Nanoplastics for Environmental Research

Reproducible, convenient, and high-yield methods for the preparation of microplastics and nanoplastics (MNPs) are crucial for advancing the detection, degradation, and environmental and toxicological studies of these emerging contaminants. While commercial MNPs are commonly used, they suffer from limitations such as restricted polymer diversity, uniform spherical morphology, inadequate representation of environmental aging and weathering characteristics, and high costs. Conversely, environmentally collected MNPs, which hold significant relevance, often exhibit poor reproducibility, require extensive characterization, and are produced in low quantities. As a result, laboratory-based preparation of MNPs has gained traction. This review article examines various methods for MNP preparation, categorizing them into top-down and bottom-up approaches. Top-down methods involve the physical fragmentation of bulk plastics through mechanical processes such as grinding, cutting, milling, abrasion, or cryogenic treatment, resulting in particles that better mimic the irregular morphologies found in environmental plastics. In contrast, bottom-up methods encompass polymerization, precipitation, and self-assembly processes to produce MNPs with well-defined sizes, shapes, and surface chemistries. We discuss the advantages, limitations, and applicability of each method in detail, with a particular emphasis on the surface properties of the resulting MNPs. This comprehensive review offers critical guidance for selecting appropriate preparation methods tailored to specific experimental designs and conditions.