Correlation of exfoliation performance with interlayer cations of montmorillonite in the preparation of two-dimensional nanosheets

Montmorillonite (MMT) can be exfoliated into nanosheets used in a wide range of applications as two-dimensional (2D) material. The exfoliated MMT nanosheets with high diameter–thickness ratio appear to show superior properties in preparation of nanocomposites and other functional materials. In this work, the correlation of exfoliation performance with interlayer cations of MMT in the preparation of 2D nanosheets was investigated. The thickness and lateral diameter of MMT nanosheets were quantitatively measured by atomic force microscopy (AFM) technique. AFM results showed the exfoliated K-MMT had larger lateral diameter and thinner thickness than the exfoliated Ca-MMT under the same exfoliation conditions. Molecular simulation was applied to investigate the interlayer-binding energy (IBE), population analysis and density of states. K-MMT structures tend to have higher in-plane chemical bond intensity than Ca-MMT because of the impact of antibonding. The IBE of K-MMT was higher than that of Ca-MMT after the sorption of water molecules into the neighboring monolayers, indicating that thinner naonosheets tend to be easier obtained from Ca-MMT than K-MMT in liquid exfoliation. These findings might be helpful for the preparation and application of 2D MMTNS through controlling interlayer cation species and the exfoliation properties of MMT.     

Effect of chain composition on the mechanical response of structural gel: A molecular dynamics simulation

Polymer gels, defined either from the structural point of view (structural gel) or by their mechanical properties (mechanical gel), are ubiquitous in our daily life. In our previous work (J. Phys. Chem. B, 2011, 115, 11345), we reported that, the mechanical gel formed by strong solvophobic ABA block copolymers with fixed chain compositions shows a strong mechanical response, which meant the formed gel had a high modulus. In this work, we focus on the effect of chain composition on the relationship between structural gel and mechanical gel, where the chain length of block copolymer is lower than its entanglement chain length for simplicity. Our results show that the chain composition has a great effect on the mechanical response of the ABA copolymer solutions with a strong solvophobicity. On the other hand, for the structural gel formed by weak solvophobic block polymers, we do not find any strong mechanical responses even we change the chain composition in a wide range. Moreover, we find three typical gelation processes, companied with three kinds of different mechanical responses. These results may provide us an effective method to control the mechanical property of a polymer gel as expected.     

Effects of deep eutectic solvents on H2SO4-catalyzed alkylation: Combining experiment and molecular dynamics simulation

To enhance the catalytic performance of H₂SO₄-catalyzed alkylation, various catalytic additives have drawn considerable attentions. Herein, the effects of deep eutectic solvent (DES) additives on catalytic performance and the interfacial properties of H₂SO₄ alkylation were systematically investigated using experimental methods and molecular dynamics (MD) simulation. Experimental results indicate that DESs with the optimal concentration about 1.0 wt% can efficiently improve C₈ selectivity and research octane number of alkylate, especially at low temperature, but contribute less to the lifetime of H₂SO₄. MD results reveal that the phenyl molecules of DESs additives play a major role in enhancing interfacial properties of H₂SO₄ alkylation, including enlargement of interfacial thickness, promotion of isobutane relative solubility and diffusion to butene, which is probably the main reason for the better quality of alkylate. This work gives a good guideline for the design of novel DESs for H₂SO₄ alkylation.     

Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts

A series of SAPO-34 molecular sieves with different SiO₂/Al₂O₃ ratios have been synthesized for the methanol-to-olefin (MTO) reaction. Their physico-chemical properties are characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N₂ adsorption-desorption. The results are compared with those of the commercial HZSM-5, which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO₂/Al₂O₃ ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO₂/Al₂O₃ ratio of 0.4 exhibits the highest BET surface area. FT-IR spectra indicate that HZSM-5 has both Br?nsted and Lewis acid sites and Br?nsted acid sites are stronger, whereas SAPO-34 samples are dominated only by Lewis acid sites. When the SiO₂/Al₂O₃ ratio increases, propylene and butylenes become the predominant product of the MTO reaction over HZSM-5. In contrast, the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene. According to the product distribution, the reaction mechanism over HZSM-5 catalysts is proposed.     

Investigation of mass transfer on single droplets for the reactive extraction of zinc with D2EHPA

Investigations of mass transfer behavior with the standard test system of the European Federation of Chemical Engineering (EFCE) for the reactive extraction zinc + D2EHPA (di(2‐ethylhexyl) phosphoric acid) were carried out. Experiments were performed with single droplets in a mass transfer cell on lab‐scale. In the experiments, contact time for the mass transfer between droplets and continuous phase, concentrations of zinc, D2EHPA and sulfuric acid, diameter of droplets and hole‐diameter of sieve trays were varied. These experimental results show a systematic investigation of single droplet mass transfer behavior for the standard test system of the EFCE for the reactive extraction of zinc with D2EHPA. In the mass transfer model reported here, all transient effects are considered with an instability parameter, which was determined through experiments in a mass transfer cell. The simulation results with obtained instability parameters are in a good agreement with the experimental results. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Adsorptive separation of copper,nickel, lead,zinc and cadmium from aqueous solution using MWCNTs impregnated with D2EHPA and prior to their determination by FAAS: Kinetic and equilibrium studies

Trace metal ions in aqueous samples may be separated and preconcentrated by solid phase extraction (SPE) prior to their determination by flame atomic absorption spectrometry (FAAS). The trace amounts of heavy metals can form complex with D2EHPA – MWCNTs. The quantitative adsorption was at pH 5.0 with a flow rate of 2 mL^?1. The adsorbed metal ions can be eluted with 2.0 mol L^?1 HNO₃. The highest enrichment factor was 25. The thermodynamic parameter (ΔG) revealed that the adsorption was spontaneous. The procedure was applied to the determination of copper, nickel, lead, zinc and cadmium in laboratory water, well water and electroplating wastewater samples.     

Effect of High-Dose Vitamin D3 Intake on Ambulation, Muscular Pain and Bone Mineral Density in a Woman with Multiple Sclerosis: A 10-Year Longitudinal Case Report

Mounting evidence correlate vitamin D3 (cholecalciferol) supplementation or higher serum levels of vitamin D (25(OH)D) with a lower risk of developing multiple sclerosis (MS), reduced relapse rate, slower progression or fewer new brain lesions. We present here the case of a woman who was diagnosed with MS in 1990. From 1980 to 2000, her ability to walk decreased from ~20 to 1 km per day. Since January 2001, a vitamin D3 supplement was ingested daily. The starting dose was 20 mcg (800 IU)/day and escalated to 100 mcg (4000 IU)/day in September 2004 and then to 150 mcg (6000 IU)/day in December 2005. Vitamin D3 intake reduced muscular pain and improved ambulation from 1 (February 2000) to 14 km/day (February 2008). Vitamin D intake over 10 years caused no adverse effects: no hypercalcaemia, nephrolithiasis or hypercalciuria were observed. Bowel problems in MS may need to be addressed as they can cause malabsorption including calcium, which may increase serum PTH and 1,25(OH)2D levels, as well as bone loss. We suggest that periodic assessment of vitamin D3, calcium and magnesium intake, bowel problems and the measurement of serum 25(OH)D, PTH, Ca levels, UCa/Cr and bone health become part of the integral management of persons with MS.     

Water structure in poly(2-hydroxyethyl methacrylate): Effect of molecular weight of poly(2-hydroxyethyl methacrylate) on its property related to water

Low molecular weight poly(2-hydroxyethyl methacrylate) (polyHEMA) with a number average molecular weight (Mn) <22,600, were prepared by atom transfer radical polymerization. The molecular weight and end groups of the polyHEMA were varied, and the water content equilibrium moisture sorption and water structure were analyzed using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). Higher water content was observed for polyHEMA with Mn < 10,000. DSC revealed that the amounts of nonfreezing water are affected neither by the molecular weight nor by the end groups of the polyHEMA. On the other hand, the amount of freezing water was affected by both the molecular weight and end groups of polyHEMA, especially for polyHEMA with Mn < 20,000. The XRD-DSC measurements showed that water in polyHEMA form hexagonal ice and that the direction of crystal growth is dependent on the molecular weight. These findings indicate that the molecular weight of polyHEMA plays a significant role in the water structure in polyHEMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012