Lithium purification from aqueous solutions using bioinspired redox‐active melanin membranes

Abstract

The separation of lithium from magnesium ions in salt brines is an important step in producing raw lithium for prospective use in electrochemical storage systems. Liquid–liquid extraction of Mg2+ ions from Li+ ions is challenging because of comparable thermodynamic behavior in aqueous solutions. Removing Mg2+ ions from brines using consumable ion‐exchange membranes is also a challenging prospect due to poor chemical selectivity and compromised sustainability. Here, we propose the use of redox‐active catechols in the form of melanin pigments for selective removal of Mg2+ ions from aqueous solutions. Synthetic melanin films are oxidatively polymerized on stainless steel meshes from aqueous solutions of dopamine precursors to create electrochemically functionalized polydopamine membranes. The binding selectivity of redox‐active catechol‐bearing polydopamine melanin for Mg2+ ions in aqueous solutions was measured as a function of electrochemical cycling. The binding kinetics of Mg2+ ions to polydopamine pigments was measured. Mg2+ ions binding selectivity to polydopamine in mixed aqueous solutions containing both Li+ and Mg2+ ions were also measured. Additionally, the equilibrium binding concentrations of Mg2+ ions to polydopamine were achieved very rapidly (<1 min). Redox‐active polydopamine membranes therefore show promise as functional materials for the separation of Mg2+ and Li+ ions in aqueous solutions. © 2016 Society of Chemical Industry

Polymeric peptide pigments with sequence-encoded properties

“…DFY ox 2D sheets exhibited the highest specific charge storage capacity, followed by DYF ox (Fig. 4, D and E), which is attributed to an increase in the concentration of redox-active tyrosine-based derivatives (2,29) and is confirmed by cyclic voltammetry (CV) ( fig. S18).…”

Calcium-Mediated Control of Polydopamine Film Oxidation and Iron Chelation

“…Catechol-bearing PDA exhibits robust surface adhesion [ 2 , 3 ], metal chelation [ 4 ], and electrooxidative control over redox states [ 5 ]. These unique properties have prompted PDA’s exploration for numerous applications [ 6 , 7 ] in antifouling surfaces [ 8 , 9 ], biointerfaces [ 10 , 11 ], and high surface-area aqueous metal sorption devices [ 12 , 13 , 14 ].…”

“…A comprehensive understanding of structure-processing-property relationships in PDA could accelerate the implementation of this material in many technologies. Devices incorporating PDA, such as bio-interface coatings [ 10 , 11 ] and ion-exchange coatings [ 12 , 14 ], are most commonly applied in aqueous solutions of metal salts (e.g., body fluid and environmental waters). However, there is little knowledge regarding the temporal evolution of PDA properties in response to solutions of group I and II cations which are known to influence cohesive forces [ 26 ] and redox kinetics [ 27 ] in other catecholic materials.…”

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

“…Nevertheless, promising results have been obtained with synthetic melanin-like polymers, e.g., polydopamine. [10,103] L-dopa [43,55] Natural (Sepia, [48,56] bovine eye [41] ) 5,6-Dihydroxyindole (DHI)-melanin (QI) [57] Mg 2+ Natural (Sepia [58] ) Natural (bovine eye, [41,45] Sepia, [48,56,59] squid [60] ), dopa-melanin [45] Ca 2+ Natural (bovine eye, [41,45] Sepia, [48,56,59,61] squid [60] ), dopa-melanin [45] Fe 3+ Natural (Sepia, [56,59,62] human hair, [63] black rabbit hair [64] ), neuromelanin, [65][66][67] dopa, [68][69][70] catechols, [71] polydopamine, [72][73][74] DHI-melanin, [63] melanin from cys-dopamine, [75] diethylaminedopamine-melanin [74] Neuromelanin, [76] dopa-melanin, [74] natural (Sepia), [74] diethylamine-dopaminemelanin [74] Natural (Sepia), …”

“…[58,79] Polydopamine, a synthetic melanin analog, has been used to selectively extract and separate metal cations from aqueous solutions, leveraging on the different binding affinities of the pigments toward different cations. [67,100,101] Films of polydopamine can reduce Ag + cations into Ag nanoparticles, which impart antibacterial properties to the same films. [83] Self-assembled molecular networks of indole-2-carboxylic acid (I2CA, i.e., melanin's monomer DHICA lacking the two hydroxyl phenolic groups) have been investigated on Au (111) surfaces: I2CA showed, both in ultrahigh vacuum and at liquid/solid interfaces, hydrogen-bonded assemblies from molecular dimers, [102] the next step being the same study with DHI and DHICA.…”