A holistic review of hydrogel applications in the adsorptive removal of aqueous pollutants: Recent progress, challenges, and perspectives

Due to the unique physical and chemical characteristics of hydrogels, such as hydrophilicity, swellability, and modifiability, there is increasing research interest in the development and application of novel hydrogels in water and wastewater treatment. Hydrogels have exhibited superior performance in the adsorptive removal of a wide range of aqueous pollutants including heavy metals, nutrients, and toxic dyes. However, there remain certain challenges which need to be addressed in order to evolve hydrogel based treatment systems from the lab-scale to practical applications. This review provides a coverage of the latest developments in the application of hydrogels for the adsorptive removal of aqueous pollutants. A holistic overview of different steps involved in the hydrogel based treatment systems is provided, and the influencing factors and mechanisms of pollutants removal are reviewed. Major challenges pertaining to adsorption kinetics, operational pH range, interference, and hydrogel recovery are examined. Important considerations such as stability and reusability of hydrogels and resource recovery are also discussed, for economic and sustainability concerns.