10 research outputs found
Forming Nanoparticle Monolayers at Liquid–Air Interfaces by Using Miscible Liquids
One standard way of forming monolayers
(MLs) of nanoparticles (NPs)
is to drop-cast a NP dispersion made using one solvent onto a second,
immiscible solvent; after this upper solvent evaporates, the NP ML
can be transferred to a solid substrate by liftoff. We show that this
previously universal use of only immiscible solvent pairs can be relaxed
and close-packed, hexagonally ordered NP monolayers can self-assemble
at liquid–air interfaces when some miscible solvent pairs are
used instead. We demonstrate this by drop-casting an iron oxide NP
dispersion in toluene on a dimethyl sulfoxide (DMSO) liquid substrate.
The NPs are energetically stable at the DMSO surface and remain there
even with solvent mixing. Excess NPs coagulate and precipitate in
the DMSO, and this limits NPs at the surface to approximately 1 ML.
The ML domains at the surface nucleate independently, which is in
contrast to ML growth at the receding edge of the drying drop, as
is common in immiscible solvent pair systems and seen here for the
toluene/diethylene glycol immiscible solvent pair system. This new
use of miscible solvent pairs can enable the formation of MLs for
a wider range of NPs
Resolving the Growth of 3D Colloidal Nanoparticle Superlattices by Real-Time Small-Angle X‑ray Scattering
The kinetics and intricate interactions governing the
growth of
3D single nanoparticle (NP) superlattices (SLs, SNSLs) and binary
NP SLs (BNSLs) in solution are understood by combining controlled
solvent evaporation and <i>in situ</i>, real-time small-angle
X-ray scattering (SAXS). For the iron oxide (magnetite) NP SLs studied
here, the larger the NP, the farther apart are the NPs when the SNSLs
begin to precipitate and the closer they are after ordering. This
is explained by a model of NP assembly using van der Waals interactions
between magnetite cores in hydrocarbons with a ∼21 zJ Hamaker
constant. When forming BNSLs of two different sized NPs, the NPs that
are in excess of that needed to achieve the final BNSL stoichiometry
are expelled during the BNSL formation, and these expelled NPs can
form SNSLs. The long-range ordering of these SNSLs and the BNSLs can
occur faster than the NP expulsion
Resolving the Growth of 3D Colloidal Nanoparticle Superlattices by Real-Time Small-Angle X‑ray Scattering
The kinetics and intricate interactions governing the
growth of
3D single nanoparticle (NP) superlattices (SLs, SNSLs) and binary
NP SLs (BNSLs) in solution are understood by combining controlled
solvent evaporation and <i>in situ</i>, real-time small-angle
X-ray scattering (SAXS). For the iron oxide (magnetite) NP SLs studied
here, the larger the NP, the farther apart are the NPs when the SNSLs
begin to precipitate and the closer they are after ordering. This
is explained by a model of NP assembly using van der Waals interactions
between magnetite cores in hydrocarbons with a ∼21 zJ Hamaker
constant. When forming BNSLs of two different sized NPs, the NPs that
are in excess of that needed to achieve the final BNSL stoichiometry
are expelled during the BNSL formation, and these expelled NPs can
form SNSLs. The long-range ordering of these SNSLs and the BNSLs can
occur faster than the NP expulsion
Resolving the Growth of 3D Colloidal Nanoparticle Superlattices by Real-Time Small-Angle X‑ray Scattering
The kinetics and intricate interactions governing the
growth of
3D single nanoparticle (NP) superlattices (SLs, SNSLs) and binary
NP SLs (BNSLs) in solution are understood by combining controlled
solvent evaporation and <i>in situ</i>, real-time small-angle
X-ray scattering (SAXS). For the iron oxide (magnetite) NP SLs studied
here, the larger the NP, the farther apart are the NPs when the SNSLs
begin to precipitate and the closer they are after ordering. This
is explained by a model of NP assembly using van der Waals interactions
between magnetite cores in hydrocarbons with a ∼21 zJ Hamaker
constant. When forming BNSLs of two different sized NPs, the NPs that
are in excess of that needed to achieve the final BNSL stoichiometry
are expelled during the BNSL formation, and these expelled NPs can
form SNSLs. The long-range ordering of these SNSLs and the BNSLs can
occur faster than the NP expulsion
Iodine Monochloride (ICl) as a Highly Efficient, Green Oxidant for the Oxidation of Alcohols to Corresponding Carbonyl Compounds
<div><p>ABSTRACT</p><p>Iodine monochloride (ICl) was discovered to be a highly efficient, green oxidant, which can oxidize aldose hemiacetals, diarylmethanols, arylalkylmethanols, anddialkylmethanols to the corresponding aldose lactones, diarylmethanones, arylalkylmethanones, and dialkylmethanones, respectively, in high yields. ICl as a green, metal-free oxidant is characterized by mild reaction condition, short reaction time, good yield, and broad scope.</p></div
Passivation of CdSe Quantum Dots by Graphene and MoS<sub>2</sub> Monolayer Encapsulation
The encapsulation of a monolayer
of CdSe quantum dots (QDs) by
one-to-three layer graphene and MoS<sub>2</sub> sheets protects the
QDs from oxidation. Photoluminescence (PL) from the QD cores shows
a much slower decrease in core diameter over time due to slower oxidation
in regions where the QDs are covered by van der Waals (vdW) layers
than in those where they are not, for chips stored both in the dark
and in the presence of light. PL mapping shows that the CdSe QDs under
the central part of the vdW sheet age slower than those near its edges,
because oxidation of the covered QDs is limited by transport of oxygen
from the edges of the vdW sheets and not transport across the vdW
layers. The transport of oxygen to the covered QDs is analyzed by
coupling the PL results and a model of QD core oxidation
Small Angle X‑ray Scattering of Iron Oxide Nanoparticle Monolayers Formed on a Liquid Surface
In situ small-angle X-ray scattering
(SAXS) is used to show that
iron oxide nanoparticles (NPs) of a range of sizes form hexagonally
ordered monolayers (MLs) on a diethylene glycol liquid surface, after
drop-casting the NPs in hexane and subsequent hexane evaporation.
The formation of the ordered NP ML is followed in real time by SAXS
when using a heptane solvent. During drying, the NPs remain in the
hexane or heptane layer, and an ordered structure is not formed then.
After drying, the NPs are farther apart than expected from only van
der Waals attraction between the NP cores and Brownian motion considerations,
which suggests the importance of ligand attraction in binding the
NPs
Evolution and Size Distribution of Solid CO<sub>2</sub> Particles in Supercritical CO<sub>2</sub> Releases
CO<sub>2</sub> transportation safety is important for the successful
implementation of carbon capture and storage (CCS) projects. The formation
of solid CO<sub>2</sub> is a unique phenomenon in high-pressure CO<sub>2</sub> release. The evolution and size distribution of dry ice particles
have a significant impact on assessment of the consequences of accidental
release of supercritical CO<sub>2</sub> from a pipeline. The motivation
is to investigate the particle behavior and size distribution and
understand how the impact factors affect them. An experiment with
various measurement methods was developed to carry out controllable
CO<sub>2</sub> release from a high-pressure vessel. The macroparameters
such as jet configuration, temperature, and velocity were recorded.
Meanwhile, motion of the microparticles was also analyzed. In addition,
the effects of initial pressure and temperature on the particle size
distribution were investigated. The results showed that the agglomeration
influenced the size distribution at different positions of the jet
Crystallographic Habit Tuning of Li<sub>2</sub>MnSiO<sub>4</sub> Nanoplates for High-Capacity Lithium Battery Cathodes
Li<sub>2</sub>MnSiO<sub>4</sub> has attracted significant attention as a
cathode material for lithium ion batteries because of its high theoretical
capacity (330 mA h g<sup>–1</sup> with two Li<sup>+</sup> ions
per formula unit), low cost, and environmentally friendly nature.
However, its intrinsically poor Li diffusion, low electronic conductivity,
and structural instability preclude its use in practical applications.
Herein, elongated hexagonal prism-shaped Li<sub>2</sub>MnSiO<sub>4</sub> nanoplates with preferentially exposed {001} and {210} facets have
been successfully synthesized via a solvothermal method. Density functional
theory calculations and experimental characterization reveal that
the formation mechanism involves the decomposition of solid precursors
to nanosheets, self-assembly into nanoplates, and Ostwald ripening.
Hydroxyl-containing solvents such as ethylene glycol and diethylene
glycol play a crucial role as capping agents in tuning the preferential
growth. Li<sub>2</sub>MnSiO<sub>4</sub>@C nanoplates demonstrate a
near theoretical discharge capacity of 326.7 mA h g<sup>–1</sup> at 0.05 C (1 C = 160 mA h g<sup>–1</sup>), superior rate
capability, and good cycling stability. The enhanced electrochemical
performance is ascribed to the electrochemically active {001} and
{210} exposed facets, which provide short and fast Li<sup>+</sup> diffusion
pathways along the [001] and [100] axes, a conformal carbon nanocoating,
and a nanoscaled platelike structure, which offers a large electrode/electrolyte
contact interface for Li<sup>+</sup> extraction/insertion processes
Understanding the Improved Kinetics and Cyclability of a Li<sub>2</sub>MnSiO<sub>4</sub> Cathode with Calcium Substitution
Limited
practical capacity and poor cyclability caused by sluggish
kinetics and structural instability are essential aspects that constrain
the potential application of Li<sub>2</sub>MnSiO<sub>4</sub> cathode
materials. Herein, Li<sub>2</sub>Mn<sub>1–<i>x</i></sub>Ca<sub><i>x</i></sub>SiO<sub>4</sub>/C nanoplates
are synthesized using a diethylene-glycol-assisted solvothermal method,
targeting to circumvent its drawbacks. Compared with the pristine
material, the Ca-substituted material exhibits enhanced electrochemical
kinetics and improved cycle life performance. In combination with
experimental studies and first-principles calculations, we reveal
that Ca incorporation enhances electronic conductivity and the Li-ion
diffusion coefficient of the Ca-substituted material, and it improves
the structural stability by reducing the lattice distortion. It also
shrinks the crystal size and alleviates structure collapse to enhance
cycling performance. It is demonstrated that Ca can alleviate the
two detrimental factors and shed lights on the further searching for
suitable dopants