Nanoporous membranes with electrochemically switchable, chemically stabilized ionic selectivity

Abstract

Nanopore size, shape, and surface charge all play important roles in regulating ionic transport through nanoporous membranes. The ability to control these parameters in situ provides a means to create ion transport systems tunable in real time. Here, we present a new strategy to address this challenge, utilizing three unique electrochemically switchable chemistries to manipulate the terminal functional group and control the resulting surface charge throughout ensembles of gold plated nanopores in ion-tracked polycarbonate membranes 3 cm(2) in area. We demonstrate the diazonium mediated surface functionalization with (1) nitrophenyl chemistry, (2) quinone chemistry, and (3) previously unreported trimethyl lock chemistry. Unlike other works, these chemistries are chemically stabilized, eliminating the need for a continuously applied gate voltage to maintain a given state and retain ionic selectivity. The effect of surface functionalization and nanopore geometry on selective ion transport through these functionalized membranes is characterized in aqueous solutions of sodium chloride at pH = 5.7. The nitrophenyl surface allows for ionic selectivity to be irreversibly switched in situ from cation-selective to anion-selective upon reduction to an aminophenyl surface. The quinone-terminated surface enables reversible changes between no ionic selectivity and a slight cationic selectivity. Alternatively, the trimethyl lock allows ionic selectivity to be reversibly switched by up to a factor of 8, approaching ideal selectivity, as a carboxylic acid group is electrochemically revealed or hidden. By varying the pore shape from cylindrical to conical, it is demonstrated that a controllable directionality can be imparted to the ionic selectivity. Combining control of nanopore geometry with stable, switchable chemistries facilitates superior control of molecular transport across the membrane, enabling tunable ion transport systems.

Polyelectrolyte layer-by-layer deposition on nanoporous supports for ion selective membranes

“…The slope of the lines can be used to calculate the ion transference capability, or transference numbers. The membrane voltage, V m , for a 1 : 1 monovalent salt can be described by a modied version of the Nernst equation shown in eqn (1), 1,9 V m ¼ 0:…”

“…2,3 Many groups have successfully leveraged a variety of responsive chemistries to alter the surface charge, and resulting ion transport, through a nanoporous membrane. [4][5][6][7][8][9] Moreover, different ion transport behavior can be achieved through control of the nanopore shape. For example, cones can give rise to different degrees of ion rectifying behaviors normally absent in simple cylindrical nanopores, an important factor for overall control of ion transport in the membranes.…”

Amplified Charge Transfer for Anionic Redox Probes through Oriented Mesoporous Silica Thin Films

“…Transport phenomena involving small molecules/ions or macromolecules within nanopores have been largely studied by using nanoporous membranes, [1][2][3][4][5][6] mainly because of their great interest for applications in separation, [7] sensinga nd biosensing, [8][9][10] or medicald evices. [11] Compared with the widely used organic functional polymer membranes, [12] inorganic nanoporous materials (such as zeolites, [13] porous silicon, [14] anodized alumina, [15,16] mesoporous silica and related organicinorganic hybrids, [16][17][18] or someo thers [19] )o ffer the advantage of better control of the nanostructure and easier surface modification.…”

In situ electro-organic synthesis of hydroquinone using anisole on MWCNT/Nafion modified electrode surface and its heterogeneous electrocatalytic reduction of toxic Cr(vi) species

“…57 Furthermore, an electro-Fenton-based hydroxylation of benzene to catechol and hydroquinone in acidic solution was also observed. 27 Meanwhile in the literature, homogeneous condition-based oxidation of aryl methoxy and heteroatomcontaining aromatic units to respective aryl hydroxy derivatives at high oxidation potential, >1 V vs. Ag/AgCl 63,64 were reported. In this work, we believed that the {HOO-Fe n+ /O(CH 3 )-Ph, n ¼ 0-2} complex is formed with the aid of p-p interaction between benzene-ring of PhOCH 3 and sp 2 carbon of MWCNT, similar to the mechanism proposed by Hamilton and Friedman, 4 helped in the overall heterogeneous-molecular transfer reaction (Scheme 1).…”