A critical review of microplastics and nanoplastics in wastewater: Insights into adsorbent-based remediation strategies.

This review aims to provide a comprehensive overview of the current state of research on the removal of microplastics (MPs) and nanoplastics (NPs), with a focus on adsorption-based solutions. The presence of plastic particles in the environment is a growing concern due to their widespread distribution across aquatic, terrestrial, and atmospheric systems. To address this environmental issue, researchers have explored various removal technologies, including coagulation, sand filtration, membrane filtration, and adsorption. A bibliometric analysis of 7641 keywords from 771 publications reveals that adsorption is the most widely studied removal technique. Thus, this has led to a deeper exploration of various adsorbents and their mechanisms, including their interactions with plastic particles and how they can be optimised for higher removal performance. The main adsorption mechanisms involve electrostatic interactions, hydrogen bonding, π-π interactions, and hydrophobic effects. Chemisorption is the primary interaction in the adsorption process, while physisorption is affected by the size and surface properties of plastic particles. A trend analysis indicates that carbon-based and metal-based adsorbents dominate the research landscape, with higher publication rates compared to biopolymer-based adsorbents. However, from an environmental perspective, biopolymer-based adsorbents are preferable due to their biodegradability, low toxicity, and renewable nature. This review discusses the mechanisms of these adsorbents, evaluates the limitations of current removal technologies, and outlines future research directions aimed at developing advanced and sustainable adsorbents to address the growing challenge of plastic pollution.