Mucin‐Based Composites for Efficient Mercuric Biosorption

Abstract

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.

Selective metal recovery by mucin: turning gold from wastewater into a peroxymonosulfate-activated catalyst

“…When isolated in solution, Au exhibited the highest adsorption out of the metals due to its strong affinity to mucin as a trivalent large cation. Also, as was demonstrated in our previous research regarding mercury–mucin interactions, 23 there could be several binding sites in mucin that can bind soft acids such as Au, including carboxylate, sulfate, and amide. Al also exhibited large adsorption as a trivalent hydrolytic cation that can bind electrostatically to carboxylate groups.…”

“…The transparent red hue is the typical color of suspended Au NPs in a solution, contributing to the visible-light adsorption due to the surface plasmon resonance of the particles. 23,51,52 The Au adsorption isotherm (Fig. 2B) suggests a maximum Au capacity of 750 mg g −1 on mucin.…”

“…This elevated performance of mucin in the NF architecture has also been demonstrated in mercuric adsorption, in which higher rates of mercury ions were adsorbed to the mucin-impregnated NF than to dissolved mucin. 23 The XRD spectrum of the Au NPs in the NF is shown in Fig. 4C.…”

“…25 Mucin has been previously demonstrated as an efficient and selective biosorbent for mercury ions (rather than other cations like calcium and sodium), which is not surprising, as this sort of selective sorption is one of mucin's natural roles in the natural mucus layer. 23 These mucin characteristics were studied in different living organisms, such as fish, snails, and the human body. 32,33 Importantly, mucin has also been shown to participate in a bio-assisted synthesis of metal ion-derived NPs within the mucin structure (particularly, with gold, palladium, and silver).…”

“…Our previous studies indicate that mucin glycoprotein can be used as a biomaterial for wastewater remediation. [22][23][24] Mucin is a large extracellular glycoprotein and the building block of biological mucus, a semi-permeable viscous mesh 25 with a primary role of protecting organs by blocking harmful environmental particle molecules and pathogens. 26,27 Mucin can be extracted from various living sources, including mammals (e.g., pig or bovine) and non-mammals (e.g., snails, worms, or jellyfish), 28,29 and is commonly produced as a byproduct in the meat industry.…”