Mechanochemical-assisted reduction of human hair for efficient and selective removal of aqueous Hg(II) to the ppb level.

[Display omitted] • Mechanical activation increased the –SH density of human hair in the reduction. • The modified human hair (MTHH) showed > 99 % removal with 476.7 mg/g Hg(II) uptake capacity. • MTHH with a high selectivity for the Hg(II) capture could promote the biosafety of aquatic plant in the medium of Hg(II). • This work exemplified a low-cost strategy of waste control by waste for the Hg(II) capture. The hydrophobic cuticle seal and the low affinity of disulfide bonds inhibit the performance of human hair (HH), a renewable keratin waste with high sulfur content, toward the remediation of aqueous Hg(II). Herein, the mechanical activation (MA) was used to crack the cuticle seal and expose the disulfide bonds for the reduction by ammonium thioglycolate, preparing a modified HH (MTHH) with high density of thiol groups. With a high distribution coefficient (2.6 × 106 mL/g), such MTHH revealed an uptake capacity over 470 mg/g, capable of decreasing the Hg(II) concentration from 1.0 mg/L to well below 2 μg/L in the real-world samples. Moreover, MTHH with the added benefits of high selectivity and low cost could significantly reduce the phytotoxicity of Hg(II) toward aquatic crops. MTHH diminished the mercury intake of water spinaches from 24.64 to about 0.06 mg/kg when cultivating in the water with a Hg(II) concentration of 4.0 mg/L. Density functional theory (DFT) calculations and characterizations such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) demonstrated that the bonding of Hg(II) to thiol groups was responsible for the Hg(II)-selective and efficient capture. This work exemplifies a sustainable, inexpensive and user-friendly platform of keratin waste for the efficient decontamination of aqueous Hg(II). [ABSTRACT FROM AUTHOR]