Feather keratin-based hybrid adsorbents: Reproducibility and efficacy in metal removal from synthetic wastewater

Abstract

This study investigates the reproducibility of two effective keratin-based biopolymers (KBPs), modified through specific chemical processes, and their subsequent combination for the simultaneous removal of multiple metals from synthetic wastewater. The KBPs modified with an ionic liquid and propylamine are designated as KBP-IV and KBP-V, respectively. Under simulated industrial conditions, both KBP-IV and KBP-V exhibited high adsorption capacities, effectively removing oxyanions (e.g., V⁵⁺, Cr⁶⁺, As³⁺) and divalent cations (e.g., Ni²⁺, Co²⁺, Cd²⁺), respectively. The surface characteristics of the triplicate modifications of each KBP-IV or KBP-V in this study demonstrated consistent thermal properties, crystallinity, and functional groups. These results confirm the reproducibility of these materials, as reflected in the consistent metal adsorption outcomes across the various modifications. A hybrid adsorbent (KBP-IX) was produced by combining KBP-IV and KBP-V in a 1:1 ratio to evaluate their combined effectiveness in multi-metal removal. KBP-IX adsorbed all divalent cations and oxyanions, with better divalent cation removal than KBP-V but lower oxyanion removal than KBP-IV. Isotherm studies were performed using several two and three-parametric nonlinear isotherm models for the adsorption of V⁵⁺ and Cr⁶⁺ on KBP-IX. Cr⁶⁺ adsorption was aligned more closely with the Redlich-Peterson isotherm model (χ² = 1.94E-5, R² = 0.9986), which incorporates elements of both the Langmuir (monolayer) and Freundlich (multilayer) models, while V⁵⁺ was better represented by the Langmuir (monolayer) isotherm model (χ² = 1.75E-4, R² = 0.9838). The findings of this work underscore the promising potential of these KBPs for valorization and their reproducibility in effectively removing divalent cations and oxyanions from synthetic industrial wastewater.