Amyloid Fibril Templated MOF Aerogels for Water Purification

Design and fabrication of versatile adsorbents for universal water purification following green chemistry principles remain challenging. Here, it is shown that amyloid fibrils from protein waste can be used as a functional scaffold for metal organic framework (MOF) biomimetic mineralization. The resulting amyloid fibrils/ZIF-8 hybrid aerogels can effectively remove nine different heavy metal ions from water due to their hierarchical porous structure. Importantly, amyloid fibrils/ZIF-8 hybrid aerogels can efficiently remove Hg2+ and Pb2+ from water over five consecutive adsorption-regeneration cycles. Furthermore, a dual removal pathway of adsorption and catalytic degradation is observed in the synthetic dyes, indicating that the aerogel preserves its porous nature and maintains the integrity of versatile functional ligands within ZIF-8. Finally, it is shown that these hybrid aerogels can also perform successfully in oil-water separation. Considering the facile synthesis procedure, high removal efficiency, affordable cost, and regeneration possibilities, the amyloid fibrils/ZIF-8 hybrid aerogel stands as an ideal candidate for addressing open challenges in wastewater treatment and water purification.

The mechanical properties of aerogels were evaluated using a Z010 (Zwick) through compressive strain-stress curves measurements at a maximum strain of 10%, 30%, 40%, and 70%, respectively.

Adsorption experiments for heavy metals
The maximum adsorption capacity (qm) of the hybrid aerogel for each heavy metal ion was calculated with the initial and final concentrations of the metal ions as determined in solution using atomic absorption spectroscopy (AAS) in solution. The initial concentration of each heavy metal ion was 10 mM. The qm (mg/g) was calculated using equation S1 V m in which C0 and Ce (mg/L) are defined as the initial and final concentrations of the heavy metal ions, respectively, V (L) is the volume of the heavy metal ion solution, and m (g) represents the weight of the hybrid aerogel used in this study.
For the isothermic adsorption study, 5 mg of aerogel was utilized, and the concentration of Hg 2+ solution was varied from 0.1 to 4000 ppm. For all aforementioned experiments, the samples were left with a magnetic stirrer for 24 h. A single binding metal−ligand pair with a single average binding constant was presumed in this approach. For the data simulation of the binding isotherms, equation S2 was used [4]

Dye removal experiments
The maximum dye removal capacity was determined using 1000 ppm of each prepared dye.
UV-vis spectrometer was used to measure the concentration of each dye before and after treatment with hybrid aerogel. The maximum dye removal capacity was obtained through the same equation (S1) as that for heavy metals.
To evaluate the reusability of hybrid aerogel, crystal violet and malachite green solutions (5 mL, 10 ppm) were employed as model compounds. Their concentrations before and after adsorption by 5 mg hybrid aerogel were measured for 3 consecutive cycles. The regeneration of aerogel was achieved by soaking in methanol anhydrous for 12 h. To understand the influence of pH value, the removal efficiency for crystal violet have been measured with a pH range of 3.5-7.5.
The non-photocatalytic activity of hybrid aerogel was measured by reducing acid fuchsin under dark conditions at room temperature. Typically, 40 mg of aerogel was placed into 10 mL of acid fuchsin solution with a concentration of 25 ppm. The acid fuchsin solution was replaced periodically to evaluate the continuous removal performance of the catalyst. To explore photocatalytic efficacy, 40 mg of aerogel was immersed in 10 mL of 25 ppm aqueous solution of methylene blue. After 30 min in the dark, the solution was irradiated by using a COB LED lamp (Prolinx GmbH) at 300 W. The lamp was located at a distance of 100 cm above the top surface of the methylene blue solution. The absorbance of the solution was recorded at specific time intervals [5] .

Oils/Organics sorption Experiments
The surface wettability of the hybrid aerogels was quantified by measuring the contact angle of a water droplet placed on a cylinder surface of the aerogel. For organic solvent sorption, droplets of n-hexane (stained with Sudan III) were put on the surface of the water, and 20 mg of aerogel was then gently contacted the organic and subsequently finish the sorption.
The sorption weight gain (%) of hybrid aerogel was measured through a series of sorption experiments toward oily compounds, including acetone, chloroform, isopropanol, t-butanol, cyclohexane, heptane, toluene, hexadecane, peanut oil, and olive oil. In brief, the aerogels were soaked into oils/organics for 20 seconds until reaching sorption equilibrium and then taken out without liquid drip and weighed immediately [6] . The weight gain (Wg) after sorption of the aerogel was calculated by equation S4, where mc (g) and m0 (g) were the weight of the hybrid aerogel after and before sorption, respectively. The regeneration of aerogel refers to the complete evaporation of organics was performed at hood under room temperature. The reusability tests of the hybrid aerogel for oils/organics sorption were repetitions of the same sorption procedure as described above, and calculated after each sorption-evaporation cycle and calculated through a previously described protocol [7] .