Unveiling the Environmental Characteristics of Sub-1000-nm Nanoplastics: A Comprehensive Review of the Preparation Methods for Nanoplastic Model Samples

Nanoplastics (NPs, < 1 μm) are ubiquitous in the environment and pose potentially more severe ecological and health risks than microplastics (MPs, 1 μm-5 mm). Nearly almost research concerning NPs was limited to few types of nanospheres especially polystyrene (PS) due to the lack of environmentally relevant NP model samples. Preparation of diverse NP samples acts as a formidable barrier to deeply reveal environmental contamination of NPs. We highlighted this current research dilemma and critical scarcity of NP models based on remarkable difference in the aspect of morphology, structure, behavior, and toxicity between NPs and MPs. For the first time, we provide a comprehensive summary of preparation methods for pristine and functionalized NP model samples including the top-down synthesis of irregular heterogeneity and bottom-up synthesis of spherical homogeneity, mainly involving physical fragmentation, emulsion polymerization, and nanoprecipitation. This review aims to facilitate in preparation of NPs with various polymer types, general applicability in different laboratories, and suitability in large-scale production, which will be crucial to understanding their environmental prevalence, behaviors, and pollution control.