235 research outputs found

    Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications

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    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

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    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

    Dual Wet and Dry Resilient Cellulose II Fibrous Aerogel for Hydrocarbon–Water Separation and Energy Storage Applications

    No full text
    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

    Ligand-Controlled Growth of ZnSe Quantum Dots in Water during Ostwald Ripening

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    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

    No full text
    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

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    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

    Synthesis of Cellulose Nanofibril Bound Silver Nanoprism for Surface Enhanced Raman Scattering

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    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

    Overexpression of miR-133 attenuated hypertrophic response.

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    <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.

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    <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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