Selective Molecularly Mediated Pseudocapacitive Separation of Ionic Species in Solution

We report the development of a dual-electrode pseudocapacitive separation technology (PSST) to capture quantitatively, remotely, and in a reversible manner value-added carboxylate salts of environmental and industrial significance. The nanostructured pseudocapacitive cell exhibits elegant molecular selectivity toward ionic species: upon electrochemical oxidation, a poly­(vinylferrocene) (PVF)-based anodic electrode shows high selectivity toward carboxylates based on their basicity and hydrophobicity. Simultaneously, on the other side of the electrochemical cell, a poly­(anthraquinone) (PAQ)-based cathodic electrode undergoes electrochemical reduction and captures the counterions of these carboxylates. The separation and regeneration capability of the electrochemical cell was evaluated through the variations in concentration of the carboxylates in polar organic solvents (often used in electrocatalytic processes) upon electrochemical charging and neutralization of the polymeric cargo of the electrodes, respectively. The strong separation efficiency of the system was indicated by its ability to capture an individual carboxylate (acetate, formate, or benzoate) selectively over other competing ions present in solution in significant excess, with an electrosorption capacity in the range of 122–157 mg anions/g_cell (polymer and CNT components on the anodic and cathodic side of the cell). The ion sorption capacity of the cell was high even after five adsorption/desorption cycles (18 000 s of continuous operation). In addition, the cell exhibited molecular selectivity even between two carboxylates (e.g., between benzoate and acetate or formate) which differ only in terms of basicity and hydrophobicity. We anticipate that this strategy can be employed as a versatile platform for selective ion separations. In particular, the functionalization of electrochemical cells with the proper polymers would enable the remote and economically viable electro-mediated separation of the desired ionic species in a quantitative and reversible manner

Functional Networks of Organic and Coordination Polymers: Catalysis of Fructose Conversion

The creation of functional porous nanoscale networks with enhanced reactive group accessibility provides rich promise for novel designs of composite materials. We present a straightforward strategy for the preparation of porous polymer/MOF hybrids via polymerization of organic monomers and cross-linkers impregnated within the pores of the MOFs followed by functionalization of the resulting composite. A poly­(maleimide-<i>co</i>-dibinylbenzene) network was synthesized in the presence of MOF MIL-101­(Cr), resulting in stable hybrid composites, which were then brominated to give porous hybrids of cross-linked poly­(<i>N</i>-bromomaleimide), a polymeric analogue of N-bromosuccinimide, interconnected with crystalline nanoparticles of the MOF. Due to the large porosity and surface area, the active bromine (halamine) groups in the polymer network enabled high activity of the composites in heterogeneous catalysis of conversion of d-fructose into 5-hydroxymethylfurfural

Quinone Reduction in Ionic Liquids for Electrochemical CO₂ Separation

We report the redox activity of quinone materials, in the presence of ionic liquids, with the ability to bind reversibly to CO₂. The reduction potential at which 1,4-naphthoquinone transforms to the quinone dianion depends on the strength of the hydrogen-bonding characteristics of the ionic liquid solvent; under CO₂, this transformation occurs at much lower potentials than in a CO₂-inert environment. In the absence of CO₂, two consecutive reduction steps are required to form first the radical anion and then the dianion, but with the quinones considered here, a single two-electron wave reduction with simultaneous binding of CO₂ occurs. In particular, the 1,4-napthoquinone and 1-ethyl-3-methylimidazolium tricyanomethanide, [emim]­[tcm], system reported here shows a higher quinone solubility (0.6 and 1.9 mol·L^–1 at 22 and 60 °C, respectively) compared to other ionic liquids and most common solvents. The high polarity determined through the Kamlet–Taft parameters for [emim]­[tcm] explains the measured solubility of quinone. The achieved high quinone solubility enables effective CO₂ separation from the dilute gas mixture that is contact with the cathode by overcoming back-diffusive transport of CO₂ from the anodic side

Electroactive Behavior of Adjustable Vinylferrocene Copolymers in Electrolyte Media

The redox-active properties of a series of ferrocene-containing vinyl polymers were investigated in aqueous and organic media. Each metallopolymer contained vinylferrocene (VFc) and a non-redox-active species (X), and was combined with carbon nanotubes (CNT) to generate P(VFcn-co-X1–n)–CNT composites for heterogeneous electrochemical analysis. Tunable pseudocapacitances spanning ca. 0.03–280 F/g VFc in aqueous solution were achieved by varying the copolymer composition, with P(VFc0.11-co-HEMA0.89) producing standardized values at ca. 160–180 F/g VFc even for differently hydrated anions. Additionally, the polymer-bound ferrocene/ferrocenium redox potential was seen to depend prominently on its electrolyte anion’s Gibbs free energy of hydration. Although the hydrophilic chloride anion negatively influenced the electrochemical stability of the VFc units when in their PVFc homopolymer, copolymerizing them with 2-hydroxyethyl methacrylate (HEMA) and introducing perchlorate anions ameliorated their overall capacity retention by 64% and 38%, respectively. Lastly, the electrodes’ responses in aprotic and protic solvents were examined for correlations with numerous solvent polarity metrics and solubility measures, with a notable observation being the stability and pseudocapacitive increase of the styrene (St)-containing P(VFc0.27-co-St0.73)–CNT from 5 to ca. 190 F/g VFc when in methanol instead of water. This study can help provide insight regarding material design considerations for redox moiety implementation in electrochemical applications

Capture and Electrochemical Reduction of CO₂ Using Molten Alkali Metal Borates

Molten alkali metal borates are a class of molten salts that have recently shown promise as high-temperature sorbents for capture of CO2 and other acid gases. Thermal swing systems based on molten borates have demonstrated CO2 capture capacities greater than those of amines, enabling efficient recovery of high-temperature heat in flue gas without practical concerns commonly associated with solid sorbents at these temperatures. In this work, we exploited generation of carbonates upon CO2 capture by borates to enable their use as electrolytic media for carbon nanotube (CNT) synthesis by CO2 splitting. Here, we report the conditions necessary to synthesize valuable multiwalled CNTs by CO2 capture and conversion as a sustainable alternative to conventional carbon-intensive CNT synthesis techniques. Effects of cathode materials and operating conditions are quantified in sodium lithium borate, achieving significantly higher CO2 uptake capacities than alkali metal carbonate salts for conversion of CO2 into CNTs in the 550–650 °C range

Light-Regulated Supramolecular Engineering of Polymeric Nanocapsules

This article describes the light-driven supramolecular engineering of water-dispersible nanocapsules (NCPs). The novelty of the method lies in the utilization of an appropriate phototrigger to stimulate spherical polymer brushes, consisting of dual-responsive 2-(dimethylamino)­ethyl methacrylate (DMAEMA) and light-sensitive spiropyran (SP) moieties, for the development or disruption of the NCPs in a controlled manner. The fabrication of the nanocarriers is based on the formation of H-type π–π interactions between merocyanine (MC) isomers within the sterically crowded environment of the polymer brushes upon UV irradiation, which enables the SP-to-MC isomerization of the photosensitive species. After HF etching of the inorganic core, dual-responsive polymeric vesicles whose walls’ robustness is provided by the MC–MC cross-link points are formed. Disruption of the vesicles can be achieved remotely by applying a harmless trigger such as visible-light irradiation. The hydrophilic nature of the DMAEMA comonomer facilitates the engineering of the vesicles in environmentally benign aqueous media and enables the controlled alteration of the NCPs size upon variation of the solution pH. The inherent ability of the NCPs to fluoresce in water opens new possibilities for the development of addressable nanoscale capsules for biomedical applications

Polyvinylferrocene for Noncovalent Dispersion and Redox-Controlled Precipitation of Carbon Nanotubes in Nonaqueous Media

We report noncovalent dispersion of carbon nanotubes (CNTs) in organic liquids with extremely high loading (∼2 mg mL^–1) using polyvinylferrocene (PVF). In contrast to common dispersants, PVF does not contain any conjugated structures or ionic moieties. PVF is also shown to be effective in controlling nanotube dispersion and reprecipitation because it exhibits redox-switchable affinity for solvents, while maintaining stable physical attachment to CNTs during redox transformation. This switchability provides a novel approach to creating CNT-functionalized surfaces. The material systems described here offer new opportunities for applications of CNTs in nonaqueous media, such as nanotube–polymer composites and organic liquid-based optical limiters, and expand the means of tailoring nanotube dispersion behavior via external stimuli, with potential applications in switching devices. The PVF/CNT hybrid system with enhanced redox response of ferrocene may also find applications in high-performance biosensors and pseudocapacitors

Magnetic Lyogels for Uranium Recovery from Wet Phosphoric Acid

The work introduces composite magnetic materials designed to capture uranium from wet-process phosphoric acid (WPA) containing 6 M H₃PO₄, 2% H₂SO₄, sodium fluoride, and metal salts of Fe­(III) and Al­(III). The materials include poly­(vinyl chloride) (PVC) covalently modified with N,N-diethyldithiocarbamate (DEDTC) or O,O-diethyldithiophosphate (DEDTP) moieties by nucleophilic substitution of the >C–Cl bonds of PVC. To maintain the polymer processability, the maximum substitution degree was kept below 42%. The modified PVC formed stable organic gel (lyogel) materials with liquid uranium extractants such as di­(2-ethylhexyl)­phosphoric acid (DEHPA) or a liquid mixture of trialkylphosphine oxides, Cyanex 923. To impart the magnetic recoverability to the lyogels, iron nanoparticles (20–50 nm) coated by carbon for chemical stability were incorporated. The resulting magnetic lyogels contain variable contents of liquid extractants, maintain particle shape, exhibit very low leaching of the extractants, and are chemically stable in extremely corrosive acidic environments. Kinetics of uranium capture and equilibrium sorption capabilities of the magnetic lyogels have been evaluated. The lyogels are readily recovered by a magnet and recycled without any loss of the material. Efficient uranium stripping from the lyogels is enabled by 1 M aqueous ammonium carbonate. Lyogel recyclability and reuse were demonstrated in at least three cycles of the uranium loading and recovery

Schizophrenic Diblock-Copolymer-Functionalized Nanoparticles as Temperature-Responsive Pickering Emulsifiers

Stimuli-responsive pickering emulsions have received considerable attention in recent years, and the utilization of temperature as a stimulus has been of particular interest. Previous efforts have led to responsive systems that enable the formation of stable emulsions at room temperature, which can subsequently be triggered to destabilize with an increase in temperature. The development of a thermoresponsive system that exhibits the opposite response, however, i.e., one that can be triggered to form stable emulsions at elevated temperatures and subsequently be induced to phase separate at lower temperatures, has so far been lacking. Here, we describe a system that accomplishes this goal by leveraging a schizophrenic diblock copolymer that exhibits both an upper and a lower critical solution temperature. The diblock copolymer was conjugated to 20 nm silica nanoparticles, which were subsequently demonstrated to stabilize O/W emulsions at 65 °C and trigger phase separation upon cooling to 25 °C. The effects of particle concentration, electrolyte concentration, and polymer architecture were investigated, and facile control of emulsion stability was demonstrated for multiple oil types. Our approach is likely to be broadly adaptable to other schizophrenic diblock copolymers and find significant utility in applications such as enhanced oil recovery and liquid-phase heterogeneous catalysis, where stable emulsions are desired only at elevated temperatures

Kinetics of the Change in Droplet Size during Nanoemulsion Formation

The evolution of droplet size during nanoemulsion formation is critical for the rational design of nanoemulsions in areas such as drug delivery and materials synthesis. In this article, we discuss the relative importance of various time scales involved in nanoemulsion formation and propose a population balance model for droplet breakup that takes into account the droplet’s internal viscosity. The proposed model gives a qualitative agreement between average droplet size and polydispersity data for nanoemulsions prepared by high-pressure homogenization and ultrasonication. On the basis of these modeling results, we propose a correlation to obtain a parity plot for the droplet size data. We show that our model and correlation also work well with data from the existing literature. The proposed model and correlation can be used to guide future population balance studies and experimental preparation of nanoemulsions