Recent innovations in the developments of biopolymer-based materials for the removal of micro- and nanoplastics: A review of performance, critical factors, practicability and knowledge gaps

Microplastics (MPs) and nanoplastics (NPs) are considerable environmental risks. Various adsorbents have been explored for their removal; however, challenges, such as generation of secondary pollutants, limited biocompatibility, poor biodegradability, and insufficient safety, have constrained their large-scale application and commercialization/marketing. Recently, biopolymers have gained significant interest for the adsorptive removal of MPs/NPs due to their biodegradability, biocompatibility and high removal efficiency (∼80-98 % for plastic particles (PPs). Therefore, this review focuses on a critical evaluation of the removal of MPs and NPs by biopolymer-based materials. These materials are categorized into four major classes: hydrogels, aerogels, sponges and functionalized fibers, and their removal efficiencies are systematically examined. Importantly, particular attention is given to key influencing factors, including the intrinsic properties of biopolymer-based materials, characteristics of PPs, solution pH, salinity, reaction time, competing ions/pollutants, stirring speed and natural organic matter. In addition, the potential of these biopolymer-based materials for removing MPs/NPs from real water samples is also highlighted. Furthermore, the regeneration, reusability, stability, biocompatibility and biodegradability of biopolymer-based materials are thoroughly discussed. Importantly, critical challenges related to scalability, economic feasibility, and end-of-life assessment are emphasized to support the transition of this technology from laboratory research to real-world application. Finally, the existing research gaps and future directions are outlined to guide the development of more effective biopolymer-based materials for mitigating PPs pollution.