37 research outputs found
Quinone Reduction in Ionic Liquids for Electrochemical CO<sub>2</sub> Separation
We
report the redox activity of quinone materials, in the presence
of ionic liquids, with the ability to bind reversibly to CO<sub>2</sub>. 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 CO<sub>2</sub>,
this transformation occurs at much lower potentials than in a CO<sub>2</sub>-inert environment. In the absence of CO<sub>2</sub>, 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
CO<sub>2</sub> occurs. In particular, the 1,4-napthoquinone and 1-ethyl-3-methylimidazolium
tricyanomethanide, [emim]Â[tcm], system reported here shows a higher
quinone solubility (0.6 and 1.9 mol·L<sup>–1</sup> 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]Â[tcm] explains the measured solubility of quinone.
The achieved high quinone solubility enables effective CO<sub>2</sub> separation from the dilute gas mixture that is contact with the
cathode by overcoming back-diffusive transport of CO<sub>2</sub> from
the anodic side
Capture and Electrochemical Reduction of CO<sub>2</sub> 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)Âethyl
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
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
Ultra-Wide-Range Electrochemical Sensing Using Continuous Electrospun Carbon Nanofibers with High Densities of States
Carbon-based sensors for wide-range
electrochemical detection of
redox-active chemical and biological molecules were fabricated by
the electrospinning of polyacrylonitrile fibers directly onto a polyacrylonitrile-coated
substrate followed by carbonization at 1200 °C. The resulting
electrospun carbon nanofibers (ECNFs) were firmly attached to the
substrate with good mesh integrity and had high densities of electronic
states (DOS), which was achieved without need for further modifications
or the use of any additives. The mass of ECNFs deposited, and thus
the electroactive surface area (ESA) of the sensor, was adjusted by
varying the electrospinning deposition time, thereby enabling the
systematic manipulation of the dynamic range of the sensor. A standard
redox probe (FeÂ(CN)<sub>6</sub><sup>3–/4–</sup>) was
used to demonstrate that the ECNF sensor exhibits strong electrocatalytic
activity without current saturation at high analyte concentrations.
Dopamine was used as a model analyte to evaluate the sensor performance;
we find that the ECNF device exhibits a dynamic range ∼10<sup>5</sup> greater than that of many existing carbon-based sensors.
The ECNF sensors exhibited excellent sensitivity, selectivity, stability,
and reproducibility for dopamine detection