37 research outputs found

    One-Pot Synthesis of Water-Swellable Mg–Al Layered Double Hydroxides and Graphene Oxide Nanocomposites for Efficient Removal of As(V) from Aqueous Solutions

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    In this Article, we report a remarkably simple and efficient method for the preparation of layered double hydroxides and graphene oxide (LDHs/GO) nanocomposites with varying GO amounts via a hydrothermal process. The graphene nature in the resulting LDHs/GO nanocomposites was confirmed by X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), N<sub>2</sub> adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). The LDHs/GO nanocomposites exhibited swelling behavior in water and forming a gel. The adsorption performance of the LDHs/GO nanocomposites was evaluated for the removal of arsenate (As­(V)) from aqueous solutions, and the results showed that the ratio of GO to LDHs in the nanocomposites significantly affected the adsorption capacity. Higher and lower amounts of GO in LDHs/GO nanocomposites showed lower adsorption capacity of As­(V). A maximum adsorption capacity of 183.11 mg/g (2.44 mmol/g) was achieved on the LDHs/GO containing 6.0% GO due to the higher Brunauer–Emmett–Teller (BET) surface area than other samples. Owing to their high uptake capability of As­(V), water-swellable LDHs/GO nanocomposites are expected to have potential applications as adsorbents for As­(V) polluted water cleanup

    Big Groundwater Data Sets Reveal Possible Rare Contamination Amid Otherwise Improved Water Quality for Some Analytes in a Region of Marcellus Shale Development

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    Eleven thousand groundwater samples collected in the 2010s in an area of Marcellus shale-gas development are analyzed to assess spatial and temporal patterns of water quality. Using a new data mining technique, we confirm previous observations that methane concentrations in groundwater tend to be naturally elevated in valleys and near faults, but we also show that methane is also more concentrated near an anticline. Data mining also highlights waters with elevated methane that are not otherwise explained by geologic features. These slightly elevated concentrations occur near 7 out of the 1,385 shale-gas wells and near some conventional gas wells in the study area. For ten analytes for which uncensored data are abundant in this 3,000 km<sup>2</sup> rural region, concentrations are unchanged or improved as compared to samples analyzed prior to 1990. Specifically, TDS, Fe, Mn, sulfate, and pH show small but statistically significant improvement, and As, Pb, Ba, Cl, and Na show no change. Evidence from this rural area could document improved groundwater quality caused by decreased acid rain (pH, sulfate) since the imposition of the Clean Air Act or decreased steel production (Fe, Mn). Such improvements have not been reported in groundwater in more developed areas of the U.S

    Anisotropic Photophysical Properties of Highly Aligned Crystalline Structures of a Bulky Substituted Poly(thiophene)

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    The photophysical properties of a phenyl-substituted poly­(thiophene), poly­(3-(2,5-dioctylphenyl)­thiophene) (PDOPT), were studied as a function of polarization and degree of orientation of the crystalline structure. Under well-chosen controlled conditions, large-sized spherulitic crystals of PDOPT were successfully prepared from the melt. From polarized optical microscopy and X-ray diffraction, the molecular orientation of PDOPT within the spherulite was determined, indicating that the fastest growth direction of the spherulite was the <i>a</i>-axis. This implied that crystallization of PDOPT was directed by the packing of the side chains rather than the backbones, which are significantly separated. As the crystalline lamellae were all radially oriented, the local absorbance strongly depended on the polarization of the incoming light. Compared to randomly oriented crystals in a quenched and thus rapidly crystallized sample, PDOPT spherulites displayed red-shifted absorption and emission spectra, combined with a reduced photoluminescence quantum yield. Even for these markedly separated polymer backbones (1.47 nm), the reduced photoluminescence suggests an enhancement of interchain interactions of highly ordered bulky substituted polythiophene induced by crystallization

    High-strength Al–5Mg<sub>2</sub>Si–2Mg–2Fe alloy with extremely high Fe content for green industrial application through additive manufacturing

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    Achieving superior mechanical properties of Al alloys with high content of Fe impurities is very challenging. Here, a feasible method was applied to accommodate high Fe content (∌2.2 wt.%) and obtain superior strength in an Al–5Mg2Si–2Mg–2Fe alloy by using additive manufacturing. Heterogeneous distribution of Fe, including a high number density of α-Al12(Fe,Mn)3Si particles distributed at the melting pool boundary and excessive Fe segregated along the cell boundaries that divided by Mg2Si eutectics, was verified as the beneficial factor for the alloy design and strength enhancement. In addition to the heterogeneous grains that contain fine cells, the interactions between dislocations and coherent Mg2Si eutectics and the α-Al12(Fe,Mn)3Si particles played an important role in improving the mechanical properties. This work represents a breakthrough in recycling high-strength Al alloys with extremely high Fe doping for green industrial application through additive manufacturing.</p

    Integration of a Superparamagnetic Scaffold and Magnetic Field To Enhance the Wound-Healing Phenotype of Fibroblasts

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    Most of the existing scaffolds for guiding tissue regeneration do not provide direct mechanical stimulation to the cells grown on them. In this work, we used nanofibrous superparamagnetic scaffolds with applied magnetic fields to build a “dynamic” scaffold platform and investigated the modulating effects of this platform on the phenotypes of fibroblasts. The results of enzyme-linked immunosorbent and transwell assays indicated that fibroblasts cultivated in this platform secreted significantly higher type I collagen, vascular endothelial growth factor A, and transforming growth factor-ÎČ1 and did so in a time-dependent manner. At the same time, they produced fewer pro-inflammatory cytokines, including interleukin-1ÎČ and monocyte chemoattractant protein-1; this, in turn, accelerated the osteogenesis of preosteoblasts with the help of increased basic fibroblast growth factor as well as balanced extracellular matrix components. Mechanistic studies revealed that the platform modulated the phenotypic polarization of fibroblasts through the activation of components of integrin, focal adhesion kinase, and extracellular signal-regulated kinase signaling pathways and the inhibition of the activation of Toll-like receptor-4 and nuclear factor ÎșB. Overall, the platform promoted the wound-healing phenotype of fibroblasts, which would be of great benefit to the scaffold-guided tissue regeneration

    Copper-Ion-Assisted Growth of Gold Nanorods in Seed-Mediated Growth: Significant Narrowing of Size Distribution via Tailoring Reactivity of Seeds

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    In the well-developed seed-mediated growth of gold nanorods (GNRs), adding the proper amount of Cu<sup>2+</sup> ions in the growth solution leads to significant narrowing in the size distribution of the resultant GNRs, especially for those with shorter aspect ratios (corresponding longitudinal surface plasmon resonance (LSPR) peaks shorter than 750 nm). Cu<sup>2+</sup> ions were found to be able to catalyze the oxidative etching of gold seeds by oxygen, thus mediating subsequent growth kinetics of the GNRs. At proper Cu<sup>2+</sup> concentrations, the size distribution of the original seeds is greatly narrowed via oxidative etching. The etched seeds are highly reactive and grow quickly into desired GNRs with significantly improved size distribution. A similar mechanism can be employed to tune the end cap of the GNRs. Except for copper ions, no observable catalytic effect is observed from other cations presumably due to their lower affinity to oxygen. Considering the widespread use of seed-mediated growth in the morphology-controlled synthesis of noble metal nanostructures, the tailoring in seed reactivity we presented herein could be extended to other systems

    Handedness of Twisted Lamella in Banded Spherulite of Chiral Polylactides and Their Blends

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    Banded spherulite resulting from lamellar twisting due to the imbalanced stresses at opposite fold surfaces can be formed by isothermal crystallization of chiral polylactide and its blends with poly­(ethylene glycol) (PEG). Using a polarized light microscope, the handedness of the twisted lamella in banded spherulite is determined. With the same growth axis along the radial direction as evidenced by wide-angle X-ray diffraction (WAXD) for isothermally crystallized samples at different temperatures, the twisted lamellae of chiral polylactides (poly­(l-lactide) (PLLA) and poly­(d-lactide) (PDLA)) display opposite handedness. The split-type Cotton effect on the CO stretching motion of vibrational circular dichroism (VCD) spectra helps determine the helix handedness (i.e., conformational chirality). The results indicate that the conformational chirality can be defined by the molecular chirality through intramolecular chiral interactions. Moreover, the preferred sense of the lamellar twist in the banded spherulite corresponds to the twisting direction identified by the C–O–C vibration motion of VCD spectra, reflecting the role of intermolecular chiral interactions in the packing of polylactide helices. Similar results are obtained in the blends of chiral polylactides and poly­(ethylene glycol) (PEG, a polymer compatible with polylactide), indicating that the impact of chirality is intrinsic irrespective of the specific crystallization conditions. In contrast to the chiral polylactides, the spectrum of the crystalline stereocomplex that associates PLLA and PDLA shows VCD silence. The spectroscopic results are in line with the morphological observations. No banded spherulites are observed in the stereocomplex crystallites due to the symmetric packing of mirror L- and D-chain conformations in the fold surfaces and the crystallites core
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