Green hydrogel as sustainable adsorbents: Bridging biopolymer & environmental remediation

To limit increasing amounts of water pollution and to further the Circular Bioeconomy paradigm, there is a need for the development of sustainable and cost-effective adsorbents. Currently, there is much research being conducted on the use of biopolymers-based GHs in treating wastewater, however, most of the literature is focused on their materials properties so that little insight is provided into how the structure of hydrogels relates to their adsorption characteristics, reuse potential and practicality in real-life situations. Therefore, this review provides a critical overview of green hydrogels based on renewable resources and the waste generated during their production, using a structure-property-performance format. This paper will discuss the influence of polymer chemistry, functional group distribution, crosslinking techniques and network architecture on the adsorption capacity, selectivity, mechanical stability and regeneration potential of GHs. The assessment of the removal of the major classes of pollutants has been systematically evaluated in terms of the dominant adsorption mechanisms that could occur. Additionally, the green synthesis approaches are critically analyzed for their sustainability, durability, and scalability. Furthermore, the key limitations have been identified to highlight the gaps between laboratory studies and practical application. By bringing together a comparative analysis of different approaches, the mechanistic basis for adsorption, and application-based challenges, this review provides design principles and directions for future work to rationally develop next-generation, green hydrogel adsorbents for sustainable wastewater remediation.