Mucin-Based Composites for Efficient Mercuric Biosorption

In this study, the extraordinary biosorption of mucin, a natural glycoprotein with selectivity towards metals in physiological processes, is leveraged to remove heavy metals from wastewater. The authors assess the performance of dissolved mucin for Hg²⁺ adsorption through studies of kinetics, capacity, and selectivity. The results show that mucin can adsorb more than 124 mg g⁻¹ Hg²⁺ while exhibiting ultra-fast kinetics, with an equilibrium reached in a few seconds. The adsorption levels are optimized in pHs higher than 4 and remain almost unchanged in the presence of background ions. X-ray photoelectron spectroscopy and Fourier transform infrared analyses indicated that the sorption mechanism is dominated by electrostatic interactions and mercuric complexation with mucin's active sites, whereas the undesirable removal via mercuric reduction does not occur. To use mucin in a practical and green fashion for metal adsorption, mucin-based solid structures, including films, beads, and nanofibers (NFs), are fabricated and assessed. Of these structures, the NFs show the best performance, with an uptake over 109 mg g⁻¹ and a high structural stability over multiple adsorption and regeneration cycles. The findings point to the potential use of mucin as a future green alternative for metal biosorption for environmental applications.