13 research outputs found
Differential Microscopic Mobility of Components within a Deep Eutectic Solvent
From
macroscopic measurements of deep eutectic solvents such as
glyceline (1:2 molar ratio of choline chloride to glycerol), the long-range
translational diffusion of the larger cation (choline) is known to
be slower compared to that of the smaller hydrogen bond donor (glycerol).
However, when the diffusion dynamics are analyzed on the subnanometer
length scale, we find that the displacements associated with the localized
diffusive motions are actually larger for choline. This counterintuitive
diffusive behavior can be understood as follows. The localized diffusive
motions confined in the transient cage of neighbor particles, which
precede the cage-breaking long-range diffusion jumps, are more spatially
constrained for glycerol than for choline because of the stronger
hydrogen bonds the former makes with chloride anions. The implications
of such differential localized mobility of the constituents should
be especially important for applications where deep eutectic solvents
are confined on the nanometer length scale and their long-range translational
diffusion is strongly inhibited (e.g., within microporous media)
Quantum Chemical Evaluation of Deep Eutectic Solvents for the Extractive Desulfurization of Fuel
Sulfur
compounds in fuels are converted to SO<sub><i>x</i></sub> during combustion, poisoning automotive catalytic converters
and creating serious environmental concerns (e.g., acid rain). The
efficient desulfurization of liquid fuel is thus a critical step toward
minimizing SO<sub><i>x</i></sub> emissions and their associated
environmental impact. To address this problem, governments worldwide
have passed stringent legislation regulating the maximal sulfur levels
allowable in fuels. In the petroleum refining industry, the conventional
method for removing sulfur from fuel is catalytic hydrodesulfurization
which, while highly efficient for removing mercaptans, thioethers,
and disulfides, shows limited performance in removing aromatic organosulfur
compounds exemplified by dibenzothiophene. To meet these strict environmental
targets, innovative strategies beyond hydrodesulfurization for the
deep desulfurization of fuel are sought. One key strategy entails
the oxidation of refractory organosulfur compounds in liquid fuel,
coupled with efficient liquid/liquid extraction of the oxidized sulfur
compounds using an immiscible solvent phase (i.e., oxidative desulfurization).
In this study, we employ computational chemistry to gain atomistic-level
insight into the specific interactions responsible for the extraction
of key organosulfur compounds and their oxidation products from fuel
using deep eutectic solvents (DESs). Specifically, we perform quantum
chemical calculations involving the well-studied DESs reline (1:2
choline chloride:urea) and ethaline (1:2 choline chloride:ethylene
glycol) to characterize the intermolecular interactions, charge transfer
behavior, and thermodynamics associated with their application for
organosulfur extraction. We observe that the model aromatic sulfur
compounds (ASCs) benzothiophene and dibenzothiophene interact with
choline and the hydrogen bond donor (HBD; i.e., urea or ethylene glycol)
of the DES via a plurality of weak noncovalent interactions. However,
the chloride ion is essentially noninteractive with the ASC due to
retention of the conventional hydrogen bond network existing within
the initial DES. Oxidation of the model ASCs to their respective sulfoxide
and sulfone products was shown to enhance interactions with the DES
components, particularly the HBD species due to its propensity for
forming multiple hydrogen bonds. We further demonstrate that, upon
oxidation, the ASCs exhibit significant and favorable free energies
of solvation, suggesting that oxidation will aid in the partition
of these sulfur compounds from liquid fuel to a conventional DES phase
Ionic Liquid Anion Controlled Nanoscale Gold Morphology Grown at a Liquid Interface
Two different ionic
liquids comprising the tetrabutylphosphonium
cation ([P<sub>4444</sub>]) paired with the strongly coordinating
anions 6-aminocaproate ([6-AC]) or taurinate ([tau]) were prepared
and employed in an aqueous/organic liquid bilayer system to generate
nanoscale gold by AuÂ(OH)<sub>4</sub><sup>â</sup> photoreduction.
Generally, as the concentration of ionic liquid in the organic phase
was increased, the resulting quasi-spherical gold nanoparticles were
smaller in size and presented less aggregation, leading to marked
increases in the catalytic efficiency for 4-nitrophenol reduction
using borohydride. The diffusion of the ionic liquids across the liquid/liquid
interface was also investigated, revealing partition coefficients
of 6.0 and 7.6 for [P<sub>4444</sub>]Â[6-AC] and [P<sub>4444</sub>]Â[tau],
respectively. Control studies elucidated that biphasic interfacial
reduction was necessary to achieve stable nanoparticles possessing
high catalytic activity. When the ionic liquid anion was instead replaced
by the weakly coordinating bisÂ(trifluoroÂmethylÂsulfonyl)Âimide
([Tf<sub>2</sub>N]), photoreduction of AuÂ(OH)<sub>4</sub><sup>â</sup> led to holey, wavy gold nanowires instead of spherical nanoparticles,
indicating the dramatic morphological control exerted by the coordination
strength of the ionic liquid anion. This strategy is straightforward
and simple and opens up a number of intriguing avenues for controllably
preparing plasmonic colloids for a range of applications from catalysis
to optical sensing
Polyol Synthesis of Magnetite Nanocrystals in a Thermostable Ionic Liquid
We
report on the development of a facile, one-pot synthesis of single-crystalline
magnetite (Fe<sub>3</sub>O<sub>4</sub>) nanoparticles (NPs) based
on the thermal decomposition of the nontoxic iron precursor ironÂ(III)Âacetylacetonate
within the ionic liquid trihexyltetradecylphosphonium bisÂ(trifluoromethylsulfonyl)Âimide
([P<sub>6,6,6,14</sub>]Â[Tf<sub>2</sub>N]) using 1,2-hexadecanediol
as a polyol reducing agent in an âiono-polyolâ process.
In this expedient approach, the [P<sub>6,6,6,14</sub>]Â[Tf<sub>2</sub>N] acts both as a low-volatility, thermostable solvent and
as the colloid-stabilizing agent, eliminating the requirement for
additional surface-capping agents. Performing the synthesis at 300
or 350 °C yielded quasi-spherical, monodispersed Fe<sub>3</sub>O<sub>4</sub> NPs with a mean size of 14 nm. Evidence from thermogravimetry,
X-ray fluorescence, and infrared analysis is consistent with nanocrystal
coverage by a partial bilayer of [P<sub>6,6,6,14</sub>]Â[Tf<sub>2</sub>N], accounting for the excellent dispersibility of the Fe<sub>3</sub>O<sub>4</sub> NPs in solvents such as hexane, toluene, and methylene chloride.
Time-dependent thermogravimetric analysis reveals that [P<sub>6,6,6,14</sub>]Â[Tf<sub>2</sub>N] is transiently stable at 300 °C for 30 min
(sufficient for nanocrystal formation) but rapidly degrades at 350
°C or higher. By employing a reaction temperature of 300 °C,
the [P<sub>6,6,6,14</sub>]Â[Tf<sub>2</sub>N] can be recycled and reused
multiple times for the subsequent preparation of Fe<sub>3</sub>O<sub>4</sub> NPs with no ill effects in terms of particle size, uniformity,
or agglomeration. Finally, we demonstrate that the Fe<sub>3</sub>O<sub>4</sub> NPs can be dispersed into [P<sub>6,6,6,14</sub>]Â[Tf<sub>2</sub>N] as a solventless carrier fluid to produce an âiono-ferrofluidâ
responsive to an external magnetic field
Structure and spectroscopy of uranyl and thorium complexes with substituted phosphine oxide ligands
Phosphine oxide ligands are important in the chemistry of the nuclear fuel cycle. We have synthesized and characterized a series of phosphine oxide ligands with polycyclic aromatic hydrocarbon (PAH) groups to enhance the spectroscopic features of uranyl, UO_2^(2+), and to make detection more efficient. Complexation of OPPh_2R, Râ=âC_(10)H_7 (naphthyl); C_(14)H_9 (phenanthrenyl); C_(14)H_9 (anthracenyl); and C_(16)H_9 (pyrenyl), to UO_2(NO_3)_2 afforded the eight-coordinate complexes, UO_2(NO_3)_2(OPPh_2R)_2. An eleven-coordinate complex, Th(NO_3)_4[OPPh_2(C_(14)H_9)]_3, C_(14)H_9 = phenanthrenyl, was structurally characterized, and was found to be the first thorium compound isolated with three phosphine oxide ligands bound. The phosphine oxide ligands were not fluorescent but the anthracenyl-substituted ligand showed broad, red-shifted emission at approximately 50ânm relative to typical anthracene, making this ligand set a possibility for use in detection. The synthesis and spectroscopy of the uranyl and thorium complexes are presented
Characterization of a Novel Ionic Liquid Monopropellant for Multi-Mode Propulsion
A deep eutectic 1:2 molar ratio mixture of choline-nitrate and glycerol [Cho][NO3] - glycerol is investigated as a fuel component in a binary mixture propellant for multi-mode micropropulsion. Specifically, binary mixtures of the novel ionic liquid fuel with hydroxyl-ammonium nitrate (HAN) and ammonium nitrate (AN) are considered and compared against our previously investigated propellant [Emim][EtSO4]-HAN. Chemical rocket performance simulations predict this new propellant to have higher performance (280 vs. 250 sec specific impulse) at lower combustion temperature (1300 vs. 1900K), relaxing catalyst melting temperature requirements and making it a promising alternative. Qualitative experimental investigation of synthesized propellants on a hot plate in atmosphere indicate the AN mixtures are significantly less reactive, and are therefore not investigated further. Quantitative reactivity studies using a microreactor indicate that both 65:35% and 80:20% by mass [Cho][NO3] - glycerol to HAN propellants have a decomposition temperature 26-88% higher than [Emim][EtSO4]-HAN, depending on the catalyst material. Additionally, the decomposition rate (or self-heating rate) was 2 to 17 times slower for [Cho][NO3] - glycerol - HAN on titanium and platinum catalysts, but the 65:35% propellant decomposition rate was approximately 10 °C/s (37%) faster on rhenium. It was also observed that propellants with the novel ionic liquid fuel contain endothermic reaction steps, and therefore higher input heat flux was required to maintain a temperature rise. Overall the results indicate [Emim][EtSO4]-HAN with platinum catalyst is still most promising as a multi-mode micropropulsion propellant
Tuning Task-Specific Ionic Liquids for the Extractive Desulfurization of Liquid Fuel
Extractive
desulfurization of liquid fuel is a simple process that
requires minimum energy input and can be operated via existing liquidâliquid
extraction apparatuses. In particular, to achieve deep desulfurization,
the conventional hydrodesulfurization (HDS) process has shown limitations
in the removal of aromatic sulfur compounds. Recently, extractive
desulfurization using a new type of nonvolatile solvent, ionic liquids
(ILs), has yielded promising results. However, there is a lack of
systematic evaluation of the effect of IL structure on desulfurization
efficiency, and a lack of mechanistic understanding regarding how
ILs lead to the partition of aromatic sulfur compounds from fuel to
the IL phase. The present study examines a total of 71 ILs and two
deep eutectic solvents (DESs) with combinations representing various
cations and anions. We identify a number of ILs that yield high partition
coefficients [up to 1.85 mgÂ(S) kg (IL)<sup>â1</sup>/mgÂ(S) kg
(oil)<sup>â1</sup>] for the partition of aromatic sulfur compounds
between ILs and <i>n</i>-octane or <i>n</i>-dodecane
as surrogates for gasoline or diesel, respectively. We find that the
high sulfur partition coefficient correlates with a high dipolarity/polarizability
(Ï*) or a low solvent polarizability (SP) of ILs carrying the
same cation and different anions, but correlates with a low dipolarity/polarizability
(Ï*) for ILs carrying the same anion paired to cations bearing
different alkyl chain lengths. We further demonstrate that a four-step
extraction using ILs can achieve 99% dibenzothiophene (DBT) removal
(i.e., an initial sulfur content of 500 ppm is reduced to <5 ppm
following extraction)
Combined Small-Angle Neutron Scattering, Diffusion NMR, and Molecular Dynamics Study of a Eutectogel: Illuminating the Dynamical Behavior of Glyceline Confined in Bacterial Cellulose Gels
Bacterial Cellulose Ionogels as Chemosensory Supports
To
fully leverage the advantages of ionic liquids for many applications,
it is necessary to immobilize or encapsulate the fluids within an
inert, robust, quasi-solid-state format that does not disrupt their
many desirable, inherent features. The formation of ionogels represents
a promising approach; however, many earlier approaches suffer from
solvent/matrix incompatibility, optical opacity, embrittlement, matrix-limited
thermal stability, and/or inadequate ionic liquid loading. We offer
a solution to these limitations by demonstrating a straightforward
and effective strategy toward flexible and durable ionogels comprising
bacterial cellulose supports hosting in excess of 99% ionic liquid
by total weight. Termed bacterial cellulose ionogels (BCIGs), these
gels are prepared using a facile solvent-exchange process equally
amenable to water-miscible and water-immiscible ionic liquids. A suite
of characterization tools were used to study the preliminary (thermo)Âphysical
and structural properties of BCIGs, including no-deuterium nuclear
magnetic resonance, differential scanning calorimetry, thermogravimetric
analysis, scanning electron microscopy, and X-ray diffraction. Our
analyses reveal that the weblike structure and high crystallinity
of the host bacterial cellulose microfibrils are retained within the
BCIG. Notably, not only can BCIGs be tailored in terms of shape, thickness,
and choice of ionic liquid, they can also be designed to host virtually
any desired active, functional species, including fluorescent probes,
nanoparticles (e.g., quantum dots, carbon nanotubes), and gas-capture
reagents. In this paper, we also present results for fluorescent designer
BCIG chemosensor films responsive to ammonia or hydrogen sulfide vapors
on the basis of incorporating selective fluorogenic probes within
the ionogels. Additionally, a thermometric BCIG hosting the excimer-forming
fluorophore 1,3-bisÂ(1-pyrenyl)Âpropane was devised which exhibited
a ratiometric (two-color) fluorescence output that responded precisely
to changes in local temperature. The ionogel approach introduced here
is simple and has broad generality, offering intriguing potential
in (bio)Âanalytical sensing, catalysis, membrane separations, electrochemistry,
energy storage devices, and flexible electronics and displays