Role of surface functional groups of hydrogels in metal adsorption: From performance to mechanism

Hydrogels have been studied quite intensively in recent decades regarding whether their metal adsorption abilities may be modified or even enhanced via functionalization (i.e., functionalizing the surfaces of hydrogels with specific functional groups). Studies have found that functionalizing hydrogels can in fact give them higher adsorptive power. This enhanced adsorptive performance is articulated in this paper through critically reviewing more than 120 research articles in such terms as the various techniques of synthesizing functionalized hydrogels, the roles that specific functional groups play on adsorption performance, selectivity, reusability, as well as on adsorption mechanism. Moreover, this critical review offers insight into future designs of functionalized hydrogels with specific metal adsorption capabilities. [Display omitted] •Hydrogels and their composites applied for the metal adsorption are reviewed.•Different surface functionalizing routes of hydrogels are summarized.•Adsorption mechanisms that are linked to the surface functional groups are discussed.•Critical roles that surface functional groups of hydrogels play are evaluated.•Challenges of functionalized hydrogels in metal adsorption are discussed.