Amphoteric Soy Protein-Rich Fibers for Rapid and Selective Adsorption and Desorption of Ionic Dyes

Abstract

Uniquely amphoteric soy protein (SP)-rich ultra-fine fibers (231 nm average diameter) have been facilely electrospun from aq. colloids and rendered water-insoluble by heating (150 °C, 12 h) to be highly stable over 14 d (pH 7) as well as under extremely acidic to basic (pH 0−10, 2 d) or at boil (2 h) conditions. The SP-rich fibrous membranes are easily tuned to be charged either negatively by deprotonation above or positively by protonation below the 4.5 PI of SPs. This pH-responsive amphoterism has been demonstrated for rapid adsorption of either cationic or anionic dyes, selective adsorption of either dye from their mixtures, and repetitive adsorption/desorption to recover and reuse both dyes and membranes. Chemisorption and heterogeneous adsorption of ionic dyes was confirmed by close fitting to the pseudo-second-order kinetic model (R 2 = 0.9977−0.9999) and Freundlich adsorption isotherm (R 2 = 0.9879). This is the first report of water-resilient and pH-robust ultrafine fibrous membranes fabricated from aqueous colloids of neat globular SPs, the major byproducts of under-utilized edible oil and biodiesel. The natural polyampholyte origin, amphoterism, and green processing make these fibrous materials unique and versatile for many potential applications involving both anionic and cationic species.

Turning Food Protein Waste into Sustainable Technologies

“…583 Similarly, amphoteric soy protein-rich fibrous membranes were prepared by coelectrospinning of soy protein and PVA and used for rapid and selective adsorption of cationic and anionic dyes from water. 591 Furthermore, the soy isolate hollow microsphere exhibited an acceptable removal efficiency for Zn, Cr, Cd, Cu, Pb, and Ni. 592 In other related works, soy protein isolate was incorporated and chemically immobilized in the deacetylated konjac glucomannan matrix to form adsorbents for purifying water from methylene blue 593 and copper.…”

“…Similarly, amphoteric soy protein-rich fibrous membranes were prepared by coelectrospinning of soy protein and PVA and used for rapid and selective adsorption of cationic and anionic dyes from water . Furthermore, the soy isolate hollow microsphere exhibited an acceptable removal efficiency for Zn, Cr, Cd, Cu, Pb, and Ni .…”

pH-Responsive Electrospun Nanofibers and Their Applications

“…[196] Another example of nanofiber membranes for the adsorption of cationic and anionic dyes was generated by using the amphoteric soy protein, which exhibits both negative charges at basic pH and positive charges at acidic pH with an isoelectric point at pH 4.5. [197] High mechanical stability could be achieved through fiber cross-linking by temperature-annealing via exposing the e-spun fibers to heat at 150 C. The stabilized membrane was then stable upon exposure to extreme acid and basic pH and resisted to water boiling conditions. The pH-responsiveness was demonstrated by adsorption of model dyes with repetitive adsorption/desorption cycles for the recovery and reuse of both anionic and cationic dyes.…”

Tunable surface wettability and pH-responsive 2D structures from amphiphilic and amphoteric protein microfibrils

“…SP colloids have been electrospun into ultra-ne (231 nm wide) bers to exhibit excellent amphoteric characteristics to rapidly and selectively adsorb/ desorb both cationic and anionic dyes. 9 As b-sheet secondary protein structures represent the most stable form as shown in spider silk proteins, 10 increasing such b structures may help to improve properties such as solubility and mechanically strength. Indeed, amphiphilic SP microbrils (SPMFs) were robustly generated by ice-templating colloidal SPs to selfassembled laminated brous products and then selectively disassembling in polar liquids.…”