241 research outputs found
Self-assembling of TEMPO Oxidized Cellulose Nanofibrils As Affected by Protonation of Surface Carboxyls and Drying Methods
Self-assembling of cellulose nanofibrils
(CNFs) as affected by
varying extent of protonation on C6 surface carboxyls was investigated
under freeze-drying and air-drying processes. Surface carboxyls were
protonated from 10.3 to 100%, all on the same TEMPO oxidized and mechanically
blended CNFs with identical geometries and level of oxidation. Upon
freeze-drying, all CNFs assembled into amphiphilic mass. The mostly
charged CNFs assembled into the finest and most uniform fibers (Ï•
= 137 nm) that absorbed significantly more nonpolar toluene than water;
whereas the fully protonated CNFs assembled extensively into porous
and more thermally stable ultrathin filmlike structures that absorbed
water and toluene similarly. Ultrafiltration and air-drying induced
cyrstallization led to more thermally stable, semitransparent, and
hydrophilic films that showed no affinity toward nonpolar toluene.
In essence, CNFs could be tuned by varying the degree of surface carboxyl
protonation, along with drying processes, to create fibrous to film
morphologies, amphiphic to hydrophilic properties, and higher thermal
stability
Ligand-Controlled Growth of ZnSe Quantum Dots in Water during Ostwald Ripening
A strong ligand effect was observed for the aqueous-phase
growth
of ZnSe quantum dots (QDs) in the Ostwald ripening (OR) stage. The
QDs were made by injecting Se monomer at room temperature followed
by a ramp to 100 °C. The ramp produced a second, more gradual
increase in the concentrations of both Zn and Se monomers fed by the
dissolution of QDs below the critical size. The dissolution process
was followed using measurements of the mass of Zn in QDs and in the
supernatant by inductively coupled plasma optical emission spectroscopy
(ICP-OES). Despite the flux of monomers, there was little growth in
the QDs of average size based on UV–vis absorption spectra,
until the temperature reached 100 °C, when there was a period
of rapid growth followed by a period of linear growth. The linear
growth stage is the result of OR as the total mass of Zn in QDs and
in the solvent remained constant. The growth data were fit to a continuum
model for the limiting case of surface reaction control. The rate
is proportional to the equilibrium coefficient for ligand detachment
from the QD surface. The ligand 3-mercaptopropionic acid (MPA) was
the most tightly bound to the surface and produced the lowest growth
rate of (1.5–2) × 10<sup>–3</sup> nm/min in the
OR stage, whereas thiolactic acid (TLA) was the most labile and produced
the highest growth rate of 3 × 10<sup>–3</sup> nm/min.
Methyl
thioglycolate (MTG) and thioglycolic acid (TGA) produced rates in
between these values. Ligands containing electron-withdrawing groups
closer to the S atom and branching promote growth, whereas longer,
possibly bidendate, ligands retard it. Mixed ligand experiments confirmed
that growth is determined by ligand bonding strength to the QD. Photoluminescence
spectroscopy showed that the more labile the ligand, the more facile
the repair of surface defects during the exposure of the QDs to room
light
Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications
Cellulose
fibrous aerogels have been fabricated by a facile and
aqueous process that disintegrated electrospun cellulose fibers (ECFs)
and reassembled via freezing/freeze-drying with significantly improved
dry resiliency and spontaneous 89% shape recovery from ca. 70% compressive
strain. Owing to the resilient and 200–300 nm wide ECFs, the
cellulose fibrous aerogels exhibited excellent dual dry and wet resiliency
as well as improved pore accessibility. The fibrous cellular walls
interconnect the aerogel pore structure to allow extraordinary liquid
absorption capacity up to 373 g/g, accounting for 95% of the theoretical
absorption capacity. Both highly dry resilient and absorbent properties
of the ECF aerogel are highly advantageous for hydrocarbon/oil contamination
removal and for hydrocarbon/water separation applications. In addition,
the ECF aerogel could be carbonized into carbon aerogel in supercapacitors
for energy storage
Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications
Cellulose
fibrous aerogels have been fabricated by a facile and
aqueous process that disintegrated electrospun cellulose fibers (ECFs)
and reassembled via freezing/freeze-drying with significantly improved
dry resiliency and spontaneous 89% shape recovery from ca. 70% compressive
strain. Owing to the resilient and 200–300 nm wide ECFs, the
cellulose fibrous aerogels exhibited excellent dual dry and wet resiliency
as well as improved pore accessibility. The fibrous cellular walls
interconnect the aerogel pore structure to allow extraordinary liquid
absorption capacity up to 373 g/g, accounting for 95% of the theoretical
absorption capacity. Both highly dry resilient and absorbent properties
of the ECF aerogel are highly advantageous for hydrocarbon/oil contamination
removal and for hydrocarbon/water separation applications. In addition,
the ECF aerogel could be carbonized into carbon aerogel in supercapacitors
for energy storage
Solvent-Triggered Self-Assembly of CdTe Quantum Dots into Flat Ribbons
Diluting an aqueous colloid containing
purified CdTe quantum dots
(QD) by injecting into common organic solvents triggered self-assembly
into a variety of structures. Nanoribbons formed in methanol with
aspect ratios near 1000 containing discrete dots lacking a packing
order. The flat ribbons were 30–90 nm (8–22 QDs) wide
based on AFM and TEM, about 8–18 nm (2–5 QDs) high based
on AFM, and 0.5–10 μm long based on SEM. Passivation
of defect sites, likely by S, enhanced the photoluminescence of the
ribbons relative to the raw QDs. Multibranched clusters containing
fused dots formed in IPA as well as ribbons with pendent nodules.
The photoluminescence of the assortment was attenuated compared to
the raw QDs. Injecting into acetone not only yielded ribbons and clusters
but also dissolved the dots over a period of 20 days, forming flower-like
assemblies whose petals consisted of bundles of CdS wires. Diluting
in solvents with lower dielectric constants than water initially aggregated
the dots by reducing the electrostatic screening between the negatively
charged thioglycolic acid (TGA) ligand layers. The solubility of TGA
in the solvents determined the superstructure that formed. Extracting
the smallest portion of this layer in methanol promoted vectorial
growth into ribbons consistent with dipole–dipole attractive
and charge–charge repulsive interactions. Removing more of
the TGA layer in IPA caused the dots to fuse into webs containing
clustered ribbons and branches, and the directional nature of the
superstructure was lost. Completely deprotecting the surface in acetone
promoted photoetching and dissolved the dots. Control of the ligand
surface density by means of the solubility adds another method to
direct spontaneous self-organization of QDs
Synthesis of Cellulose Nanofibril Bound Silver Nanoprism for Surface Enhanced Raman Scattering
Silver
nanoprisms (AgNPs) were robustly synthesized using TEMPO-oxidized
cellulose nanofibrils (CNFs) as a dual capping and shape-regulating
agent for the first time. Reducing AgNO<sub>3</sub> with NaBH<sub>4</sub> in CNF suspensions produced smaller but more uniform Ag nanospheres
(AgNSs) with increasing Ag<sup>+</sup>/CNF ratios. CNF bound AgNSs
were facilely transformed to AgNPs by etching with H<sub>2</sub>O<sub>2</sub>, supporting the capping and shape-regulating capability of
CNFs. AgNPs could also be synthesized directly in a one-shot reduction
reaction with NaBH<sub>4</sub> in the presence of both CNFs and H<sub>2</sub>O<sub>2</sub>. The AgNPs transformed from CNF bound AgNSs
are similar to those synthesized directly, but more stable against
H<sub>2</sub>O<sub>2</sub>. Successful synthesis of AgNPs with 80–320
nm truncated edges was confirmed by light blue solution color, sharp
out-of-plane quadruple resonance peak at 334 nm and prominent in-plane
dipole resonance peaks at 762–900 nm. The [111] lattice plane
of AgNP was clearly evident by its predominant XRD peak at 38°,
confirming the unique shape-regulating ability of the nearly fully
surface carboxylated CNFs. The CNF surface bound AgNPs were easily
fabricated into freestanding CNF/AgNPs films that showed excellent
surface enhanced Raman scattering of Rhodamine 6G with analytical
enhancement factor of 5 × 10<sup>3</sup> in contrast to none
from the CNF/AgNSs film
Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications
Cellulose
fibrous aerogels have been fabricated by a facile and
aqueous process that disintegrated electrospun cellulose fibers (ECFs)
and reassembled via freezing/freeze-drying with significantly improved
dry resiliency and spontaneous 89% shape recovery from ca. 70% compressive
strain. Owing to the resilient and 200–300 nm wide ECFs, the
cellulose fibrous aerogels exhibited excellent dual dry and wet resiliency
as well as improved pore accessibility. The fibrous cellular walls
interconnect the aerogel pore structure to allow extraordinary liquid
absorption capacity up to 373 g/g, accounting for 95% of the theoretical
absorption capacity. Both highly dry resilient and absorbent properties
of the ECF aerogel are highly advantageous for hydrocarbon/oil contamination
removal and for hydrocarbon/water separation applications. In addition,
the ECF aerogel could be carbonized into carbon aerogel in supercapacitors
for energy storage
Assembling and Redispersibility of Rice Straw Nanocellulose: Effect of <i>tert</i>-Butanol
Self-assembling
of sulfuric-acid-hydrolyzed cellulose nanocrystals (CNCs, 6.4 nm wide)
and TEMPO oxidized cellulose nanofibrils (CNFs, 2.1 nm wide) from
aqueous suspensions was induced by rapid freezing (−196 °C,
10 min) and slow lyophilization (−50 °C, 0.05 mbar, 2
days). The assembled structures contain submicron (200–700
nm) wide and tens of micrometer long fibers at up to 0.1–0.5%
and 0.01–0.05%, the critical fiber-to-film transformation concentrations
for CNCs and CNFs, respectively. The assembled fiber widths were significantly
reduced to ∼40 nm, that is, by 1 order of magnitude, when 10%
of the aqueous media was replaced with <i>tert</i>-butanol.
Further increasing <i>tert</i>-butanol contents in the media
to 93/7 (CNCs) and 50/50 (CNFs) <i>tert</i>-butanol/water,
both at 0.1% nanocellulose concentration, reduced longitudinal assembling
for CNCs and lateral assembling for CNFs as well as increased critical
fiber-to-film transformation concentration for CNFs. While all assembled
structure could be redispersed in water, those from <i>tert</i>-butanol/water could also be easily redispersed in DMF aided with
brief 2 min ultrasonication. None of the assembled structures could
be redispersed in the lower dielectric constant ethanol, acetone or
chloroform
Overexpression of miR-133 attenuated hypertrophic response.
<p>(A) RT-PCR showed that the expression of lncRNA-ROR was decreased by overexpression of miR-133 in a concentration-dependent manner. Relative expression levels of mRNA (B) or protein (C) of ANP and BNP were decreased by overexpression of miR-133. NC represents negative control. * p<0.05, ** p<0.01.</p
MicroRNA 133 negatively correlated with lncRNA-ROR.
<p>(A) Relative mRNA expression levels of miR-21, miR-208, and miR-449 were increased in cultured cardiomyocytes after PE treatment. (B) Relative mRNA expression levels of miR-1, miR-133, and miR-30 were decreased in cultured cardiomyocytes after PE treatment. Plotting the expression of miR-133 (C) or miR-208 (D) against that of lncRNA-ROR in the heart of mice model of cardiac hypertrophy showed that there was no correlation between miR-208 and lncRNA-ROR, however, miR-133 negatively correlated with lncRNA-ROR. * p<0.05, ** p<0.01 compared between control and PE-treated cells.</p
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