Keratin-derived bio-adsorbents for water remediation: Current and future trends

Keratin-derived bio-adsorbents have become a highly effective solution for water remediation applications, owing to their sustainable and environmentally friendly properties. Keratin, which is naturally abundant, exhibits unique physicochemical properties and is environmentally benign. It can be extracted from many biomass sources such as feathers, hooves, wool, and hair, and is characterized by a fibrous protein structure rich in functional groups such as disulfide, amino, and carboxyl groups. These attributes enable the effective binding of metal ions and organic pollutants simultaneously from the polluted water. The review highlights recent progress in keratin-based bio-adsorbents adsorbing both metal cations and oxyanions such as Pb 2+ , Ni 2+ , Co 2+ , Zn 2+ , Cr 3+ /CrO₄ 2− , Cd 2+ , AsO₃ 3− /AsO₄ 3− , and SeO₃ 2− /SeO₄ 2− , alongside organic pollutants like methylene blue, reactive blue 19, crystal violet, methyl orange, and phenolic compounds for sustainable water purification. The review also examines chemical modifications and composite materials that enhance keratin's adsorption capacity, selectivity, and regeneration potential. Additionally, it identifies significant research gaps, such as limited scalability and challenges in regeneration and reuse. Ion exchange, complexation, electrostatic interactions, and hydrogen bonding are identified as crucial mechanisms in the adsorption processes of keratin-based materials. Future research should focus on developing innovative keratin composites, employing environmentally friendly processing methods, creating mechanistic models, and conducting large-scale testing to bridge laboratory findings with industrial applications. • Keratin is a renewable biopolymer for sustainable water remediation. • Functionalized keratin adsorbs metals up to 695 mg/g and removes >90 % of dyes. • Modified keratin can retain>80 % efficiency after 5–7 reuse cycles. • Adsorption occurs via ion exchange, coordination, and redox. • Challenges remain in scalability, selective adsorption, and effective regeneration.