Preparation of amino acid nanoparticles at varying saturation conditions in an aerosol flow reactor

In this article, we describe the synthesis of new and ion-selective nanofiltration (NF) membranes using polyvinylidene fluoride (PVDF) nanofibers and hyperbranched polyethylenimine (PEI) as building blocks. These new nanofibrous composite (NFC) membranes consist of crosslinked hyperbranched PEI networks supported by PVDF nanofibrous scaffolds that are electrospun onto commercial PVDF microfiltration (MF) membranes. A major objective of our study was to fabricate positively charged NF membranes that can be operated at low pressure with high water flux and improved rejection for monovalent cations. To achieve this, we investigated the effects of crosslinker chemistry on membrane properties (morphology, composition, hydrophobicity, and zeta potential) and membrane performance (salt rejection and permeate flux) in aqueous solutions (2,000?mg/L) of four salts (NaCl, MgCl₂, Na₂SO₄, and MgSO₄) at pH 4, 6, and 8. We found that an NFC?CPVDF membrane with a network of PEI macromolecules crosslinked with trimesoyl chloride has a high water flux (~30?L?m^?2?h^?1) and high rejections for MgCl₂ (~88 %) and NaCl (~65 %) at pH 6 using a pressure of 7?bar. The overall results of our study suggest that PVDF nanofibers and hyperbranched PEI are promising building blocks for the fabrication of high performance NF membranes for water purification.     

Plasma surface modification of nanofiltration (NF) thin-film composite (TFC) membranes to improve anti organic fouling

Commercial nanofiltration (NF) thin-film composite (TFC) membranes were treated by low-pressure NH₃ plasma, and the effects of the plasma treatment were investigated in terms of the membrane hydrophilicity, pure water flux, salt rejection, protein adsorption, and humic acid fouling. Experimental results indicated that the membrane surface hydrophilicity was increased by the plasma treatment, and changes in the hydrophilicity as well as membrane performance including permeate flux and fouling varied with the original membrane characteristics (e.g., roughness and hydrophilicity). Water flux of plasma treated membranes was the highest with 10 min and 90 W of plasma treatment, and salt rejection was mainly affected by the intensity of the plasma power. Results of bovine serum albumin (BSA) adsorption demonstrated that the protein adsorption decreased with increasing plasma treatment time. The plasma treatment that resulted in more negatively charged surfaces could also better prevent Aldrich humic acid (AHA) attachment on the membrane surface.     

Optimization of high pressure bioactive compounds extraction from pansies (Viola × wittrockiana) by response surface methodology

Response surface methodology (RSM) was employed for the first time to optimize high pressure extraction (HPE) conditions of bioactive compounds from pansies, namely: pressure (X₁: 0–500?MPa), time (X₂: 5–15?min) and ethanol concentration (X₃: 0–100%). Consistent fittings using second-order polynomial models were obtained for flavonoids, tannins, anthocyanins, total reducing capacity (TRC) and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity. The optimum extraction conditions based on combination responses for TRC, tannins and anthocyanins were: X₁?=?384?MPa, X₂?=?15?min and X₃?=?35% (v/v) ethanol, shortening the extraction time when compared to the classic method of stirring (approx. 24?h). When the optimum extraction conditions were applied, 65.1?mg of TRC, 42.8?mg of tannins and 56.15?mg of anthocyanins/g dried flower were obtained. Thus, HPE has shown to be a promising technique to extract bioactive compounds from pansies, by reducing the extraction time and by using green solvents (ethanol and water), for application in diverse industrial fields.     

Deposition of polymeric perfluored thin films in proton ionic membranes by plasma processes

In this work the surfaces of polymeric membranes based on Nafion (proton conducting material), used in proton exchange membranes fuel cells (PEMFC) had been modified by plasma deposition of perfluored polymers, in order to improve its functioning in systems of energy generation (fuel cells). The deposition increases the chemical resistance of the proton ionic polymers without losing the electrical properties. The processing of the membranes also reduces the permeability of the membranes to the alcohols (methanol and ethanol), thus preventing poisoning of the fuel cell. The processing of the membranes of Nafion was carried through in a system of plasma deposition using a mixture of CF₄ and H₂ gases. The plasma processing was made mainly to increase the chemical resistance and result in hydrophobic surfaces. The Fourier transformed infrared (FTIR) technique supplies a spectrum with information about the CF_n bond formation. Through the Rutherford back scattering (RBS) technique it was possible to verify the deposition rate of the polymeric layer. The plasma process with composition of 60% of CF₄ and 40% of H₂ presented the best deposition rate. By the spectrum analysis for the optimized configuration, it was possible to verify that the film deposition occurred with a thickness of 90 nm, and fluorine concentration was nearly 30%. Voltammetry made possible to verify that the fluorination increases the membranes chemical resistance, improving the stability of Nafion, becoming an attractive process for construction of fuel cells.     

Novel electrospun PAN�CPVC composite fibrous membranes as polymer electrolytes for polymer lithium-ion batteries

Composite fibrous membranes based on poly(acrylonitrile)(PAN)-poly(vinyl chloride)(PVC) have been prepared by electrospinning. The fibrous membranes are made up of fibers of 850- to 1,300-nm diameters. These fibers are stacked in layers to produce a fully interconnected pore structure. Polymer electrolytes were prepared by immersing the fibrous membranes in 1 M LiClO₄-PC solution for 60 min. The condition of pure PAN polymer electrolytes is jelly, which has poor mechanical performance and cannot be used. But when PVC with a good mechanical stiffener was added to PAN, the condition of composite PAN?CPVC polymer electrolytes becomes free-standing. In addition, the optimum electrochemical properties have been observed for the polymer electrolyte based on PAN?CPVC (8:2, w/w) to show ionic conductivity of 1.05?×?10^?3 S cm^?1 at 25 °C, anodic stability up to 4.9 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. The promising results showed that fibrous PEs based on PAN?CPVC (8:2, w/w) have good mechanical stability and electrochemical properties. This shows a great potential application in polymer lithium-ion batteries.     

A theoretical study on tuning band gaps of monolayer and bilayer SnS2 and SnSe2 under external stimuli

Based on density functional theory, we systematically study the mechanical and electronic properties of monolayer and bilayer SnS₂ and SnSe₂. The electronic properties of these layers can be significantly tuned by applying in-plane strains and electric fields perpendicular to the sheets. The band gaps of monolayer SnS₂ and SnSe₂ slightly increase with the in-plane tensile strains, and they start to decrease after critical strains (5% for monolayer SnS₂ and 7% for monolayer SnSe₂). The band gaps of bilayer SnS₂ and SnSe₂ have a similar tendency to the monolayers with smaller critical strains (1% for bilayer SnS₂ and 2% for bilayer SnSe₂), which enables a semiconductor-to-metal transition at 10% strain for bilayer SnSe₂. We also find that an external electric field perpendicular to bilayer SnS₂ and SnSe₂ modulates their electronic band gaps. Semiconductor-to-metal transitions are achieved at the electric fields of 0.27 V/Å for bilayer SnS₂ and 0.13 V/Å for bilayer SnSe₂.     

Stable and high conductivity ceria/bismuth oxide bilayer electrolytes for lower temperature solid oxide fuel cells

A highly conductive bismuth oxide/ceria bilayer electrolyte was developed to reduce solid oxide fuel cell (SOFC) operating temperatures. Bilayer electrolytes were fabricated by depositing a layer of Er_0.2Bi_0.8O_1.5 (ESB) of varying thickness via pulsed laser deposition and dip-coating on a Sm_0.2Ce_0.8O_1.9 (SDC) substrate. The open-circuit potential (OCP) and ionic transference number (t _i) of ESB/SDC electrolytes were tested in a fuel cell arrangement as a function of relative thickness, temperature, and with H₂/H₂O and CO/CO₂ on the anode side and air on the cathode side. These EMF measurements showed a significant increase in OCP and t _i with the bilayer structure, as compared to the cells with a single SDC electrolyte layer. Furthermore, improvement in the OCP and t _i of bilayer SOFCs was observed with increasing relative thickness of the ESB layers. Hence, the bilayer structure overcomes the limited thermodynamic stability of bismuth oxides and prevents electronic conductivity of ceria-based oxides in reducing atmosphere.     

Comparative performance study of four nanofiltration membranes in the separation of mercury and chromium

In this paper, four nanofiltration membranes, viz., (1) coating of N,O-carboxymethyl chitosan (NOCC) on polyethersulfone ultrafiltration (PES UF) substrate membrane; (2) chitosan and acrylonitrile butadiene styrene (ABS) in the blend ratio of 0:100 (ABS); (3) diethylenetriamine pentaacetic acid coating via casting method on PES UF substrate membrane (DC50); and (4) NOCC and cellulose acetate (CA) polymer blend solution (0.4?wt%) coated on a glass plate (NOCC?CCA), were selected from our previous work. By using these membranes, separation behaviour of mercury and chromium ions was studied at different operating conditions from their salt solutions. From the experimental data, it is evident that ABS membrane gave highest observed solute rejection (92.88 and 88.67?% for 10?ppm feed concentration of mercury sulphate?Cwater system and chromium sulphate?Cwater system, respectively) and NOCC?CCA membrane gave highest permeate volume flux. But from the rejection as well as permeate volume flux point of view, NOCC?CPES membrane is considered to be the best choice among all the membranes.     

Neural network enhanced 3D turbo spin echo for MR intracranial vessel wall imaging

PurposeTo improve the signal-to-noise ratio (SNR) and image sharpness for whole brain isotropic 0.5 mm three-dimensional (3D) T₁ weighted (T₁w) turbo spin echo (TSE) intracranial vessel wall imaging (IVWI) at 3 T.MethodsThe variable flip angle (VFA) method enables useful optimization across scan efficiency, SNR and relaxation induced point spread function (PSF) for TSE imaging. A convolutional neural network (CNN) was developed to retrospectively enhance the acquired TSE image with PSF blurring. The previously developed VFA method to increase SNR at the expense of blur can be combined with the presented PSF correction to yield long echo train length (ETL) scan while the acquired image remains high SNR and sharp. The overall approach can enable an optimized solution for accelerated whole brain high-resolution 3D T₁w TSE IVWI. Its performance was evaluated on healthy volunteers and patients.ResultsThe PSF blurred image acquired by a long ETL scan can be enhanced by CNN to restore similar sharpness as a short ETL scan, which outperforms the traditional linear PSF enhancement approach. For accelerated whole brain IVWI on volunteers, the optimized isotropic 0.5 mm 3D T₁w TSE sequence with CNN based PSF enhancement provides sufficient flow suppression and improved image quality. Preliminary results on patients further demonstrated its improved delineation for intracranial vessel wall and plaque morphology.ConclusionThe CNN enhanced VFA TSE imaging enables an overall image quality improvement for high-resolution 3D T₁w IVWI, and may provide a better tradeoff across scan efficiency, SNR and PSF for 3D TSE acquisitions.     

Preparation and characterization of crosslinked proton conducting membranes based on chitosan and PSSA-MA copolymer

Proton conducting crosslinked complex membranes were prepared by blending of a cationic polyelectrolyte, i.e. chitosan (CS) and an anionic polyelectrolyte, i.e. poly(4-styrenesulfonic acid-co-maleic acid) (PSSA-MA). In particular, the dual function of PSSA-MA as a crosslinker and a proton conductor is described. The esterification reaction between –OH of CS and –COOH of PSSA-MA and the complex formation of NH₃⁺ of CS and SO₃^? of PSSA-MA were confirmed using FT-IR spectroscopy. The ion exchange capacity (IEC) of membranes continuously increased with PSSA-MA concentrations, resulting from the increase of ionic groups. However, the membranes exhibited the minimum values of proton conductivity and water uptake at 50–67 wt.% of PSSA-MA due to the effect of crosslinking and complex formation. In addition, a maximum of Young's modulus was achieved at 50 wt.% of PSSA-MA, as revealed by universal testing machine (UTM). Thermogravimetric analysis (TGA) showed that the thermal stability of membranes increased with increasing PSSA-MA concentrations and was the highest at 50 wt.% of PSSA-MA.     

Recording ion channels across soy-extracted lecithin bilayer generated by water-soluble quantum dots

We report on the quantum dot (QD)-induced ion channels across a soya-derived lecithin bilayer supported on a laser drilled of ~100 μm aperture of cellulose acetate substrate that separates two electrolytic chambers. Adequate current bursts were observed when the bilayer was subjected to a gating voltage. The voltage-dependent current fluctuation, across the bilayer, was attributed to the insertion of ~20?nm sized water-soluble CdSe QDs, forming nanopores due to their spontaneous aggregation. Apart from a closed state, the first observable conductance levels were found as 6.3 and 11?nS, as for the respective biasing voltages of ?10 and ?20?mV. The highest observable conductance states, at corresponding voltages were ~14.3 and 21.1?nS. Considering two simplified models, we predict that the non-spherical pores (d_nspore) can be a better approximation over spherical nanopores (d_spore) for exhibiting a definite conductance level. At times, even d_nspore?≤?4d_spore and that the non-spherical nanopores were associated with a smaller No. of QDs than the case for spherical nanopores, for a definite conductance state. It seems like the current events are partly stochastic, possibly due to thermal effects on the aggregated QDs that would form nanopores. The dwell time of the states was predicted in the range of 384–411?μs. The ion channel mechanism in natural phospholipid bilayers over artificial ones will provide a closer account to understand ion transport mechanism in live cells and signaling activity including labelling with fluorescent QDs.     

Study on performance of a novel P(VDF-HFP)/SiO2 composite polymer electrolyte using urea as pore-forming agent

Novel poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))-based composite polymer electrolyte (CPE) membranes doped with different contents of nano-SiO₂ using urea as a pore-forming agent were prepared by phase inversion method, and the desired CPEs were obtained by being immersed into 1.0 M LiPF₆-EC/DMC/EMC electrolytes for 0.5 h. The physicochemical properties of the CPEs were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). The results show that the CPEs doped with 10 % nano-SiO₂ exhibit the best performance, in which the SEM images of the as-prepared polymer membranes present homogeneous surface and abundant micropores; the uptake ratio is up to 107.4 %; EIS and LSV analysis also show that the ionic conductivity at room temperature and electrochemical stability window of the modified membrane can reach 3.652 mS cm^?1 and 5.0 V, respectively; the interfacial resistance R _i is 380 Ω cm^?2 in the first day,then increases rapidly to a stable value about 500 Ω cm^?2 in a 5-day storage at room temperature. The Li/As-fabricated CPEs/LiCoO₂ cell also shows excellent charge-discharge performance, which suggests that it can be a potential electrolyte for the lithium-ion battery.     

The improvement of moisture resistance and thermal stability of Ca3SiO4Cl2:Eu phosphor coated with SiO2

Green-emitting phosphors Ca₃SiO₄Cl₂:Eu²⁺ were prepared by the high temperature solid-state method. Sol-gel process was adopted to encapsulate the as-prepared phosphors with tetraethylorthosilicate (TEOS) as silicon coating reagent. Fluorescence spectrometer, scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) patterns were employed to characterize the emission spectra, the surface morphologies and the phase structures, respectively. The chemical stability testing was operated by the method of soaking the phosphors in deionized water and roasting them at different temperatures. The results indicated that the surfaces of the green phosphors were evenly coated by SiO₂ and the phase structure of the coated phosphors remained the same as the uncoated samples. The luminance centre of Eu²⁺ did not shift after surface treatment and the luminance intensity of coated phosphors was lower than that of the uncoated samples. The results demonstrated that the water-resistance stability of the coated phosphor was improved to some degree because the pH value and the luminance intensity variation were both smaller than the uncoated phosphor after steeping within the same time. Moreover, the thermal stability of coated phosphors was enhanced obviously compared to the original samples based on the temperature dependent emission spectra measurement.     

Surface-modified zeolite-filled chitosan membranes for pervaporation dehydration of ethanol

Surface-modified zeolite-filled chitosan (CS) membranes were prepared by incorporating 3-mercaptopropyltrimethoxysilane (MPTMS)-modified H-ZSM-5 zeolite into chitosan for pervaporation dehydration of aqueous ethanol solution. The physicochemical characterization by XPS, FT-IR, XRD, DMA and SEM showed that -SO₃H group was readily grafted on the surface of H-ZSM-5 with the mediation of MPTMS and hydrogen peroxide, and the accompanying ion-ion interaction between -SO₃H group on surface-modified H-ZSM-5 and -NH₃⁺ group on chitosan substantially eliminated the nonselective voids at the chitosan-H-ZSM-5 interface of the filled membranes. The experimental results also revealed that H-ZSM-5 exhibited desirable size-selective and preferential adsorption effects for aqueous ethanol solution. As a result, modified H-ZSM-5 filled membranes showed higher swelling degree and permeation flux, and improved selectivity for aqueous ethanol solution. In comparison between chitosan control membrane (permeation flux 54.18 g/(m² h) and separation factor 158.02 for 90 wt.% aqueous ethanol solution at 80 °C), the modified H-ZSM-5 filled membrane with 8 wt.% filling content exhibited a remarkably improved pervaporation performance with permeation flux 278.54 g/(m² h) and separation factor 274.46 under the identical experimental condition.     

Orientation dependence of the electrocaloric effect of ferroelectric bilayer thin films

An analytical thermodynamic theory is applied to investigate the electrocaloric effect of ferroelectric BaTiO₃/SrTiO₃ bilayer thin films with different orientations at room temperature. Theoretical analysis indicates that the strong electrostatic coupling between the layers results in the suppression of ferroelectricity at a critical relative thickness which occurs approximately at 50%, 23%, and 12% of SrTiO₃ fraction in the (001), (110), and (111) bilayer thin films, respectively. The ferroelectric bilayer thin films are respected to have the largest electrocaloric effect at this critical relative thickness. Moreover, the electrocaloric effect strongly depends on the orientation and the (110) oriented bilayer thin films have the largest electrocaloric effect. Consequently, control of the orientation and the relative thickness of SrTiO₃ layer can be used to adjust the electrocaloric effect of ferroelectric bilayer thin films, which may provide the potential for practical application in refrigeration devices.     

EMI shielding effectiveness of graphene decorated with graphene quantum dots and silver nanoparticles reinforced PVDF nanocomposites

Graphene decorated with graphene quantum dots (G-D-GQDs) have been successfully synthesized using solvothermal cutting of graphene oxide. The incorporation of G-D-GQDs in polyvinyledene fluoride (PVDF) matrix shows the total EMI shielding effectiveness (SE_T) of 31 dB at 8 GHz. The main mechanism of high EMI shielding effectiveness is reflection and absorption of EM radiation. The high absorption of EM radiation is due to tunneling of electrons from GQDs. Further, decoration of G-D-GQDs with conducting Ag nanoparticles (G-D-GQDsAg) enhances the SE_T value to 43 dB at 8 GHz of PVDF/G-D-GQDsAg nanocomposite, due to increase in electrical conductivity of PVDF/G-D-GQDsAg nanocomposite and enhanced dispersion of G-D-GQDsAg in PVDF matrix. The incorporation of G-D-GQDs and G-D-GQDsAg in PVDF matrix also increases the thermal stability and crystallinity of PVDF. The increase in thermal stability and crystallinity are more for PVDF/G-D-GQDsAg nanocomposite as compare to PVDF/G-D-GQDs nanocomposite, due to better dispersion of G-D-GQDsAg in PVDF matrix. Thus, PVDF/G-D-GQDsAg nanocomposite having high SE_T value can shield 99.9% of electromagnetic radiation in X-band range, which make it suitable for EMI shielding application for consumer electronic equipment’s.     

Tailoring the properties of polyamide thin film membrane with layered double hydroxide nanoclay for enhancement in water separation

This current paper presented a new candidate and potentially to improve the current membrane materials in water filtration process. With that, the primary materials used in this research study is layered double hydroxides (LDH) nanoclay which can be obtained from earth minerals and self-synthesized from inorganic salts were discussed thoroughly to help a better understanding of these materials. However, the current technologies of water separation were still lagging behind and ineffective especially in removal of divalent metal ions and multivalent salts. Infeasibility of reverse osmosis membrane make it not a viable option for divalent salts filtration. With that, nanofiltration (NF) membrane offered as an alternative to substitute available method. In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating layered double hydroxides (LDH) nanoclay. The LDH nanoclay with different loading ratio of 0, 0.05, 0.1, 0.15 and 0.2 were impregnated into polyamide layer on top of polysulfone substrates. The fabricated TFN were characterized in terms of physicochemical properties (SEM and FTIR) and membrane hydrophilicity (contact angle). After the addition of LDH, the morphological structures of TFN membranes were changed and the surface hydrophilicity was enhanced significantly. FESEM images displayed a typical ridge and valley morphology with nodule-like structures. As the LDH loading was increased, the contact angle decreased from 34.56° to 15.76° showing the surface hydrophilicity of membrane is improved. The separation performance of membrane was evaluated in terms of salt rejection ability by cross flow filtration system. The best performance NF membrane was found to be TFN 0.05 with high water flux and MgCl₂ rejection with values of 24.18 L/m².h and 91% respectively. This study has experimentally validated the potential of LDH materials in membrane process for improvement in water separation process.     

Interfacial spin interactions of ferromagnetic and antiferromagnetic manganite bilayers

A pulsed laser deposition technique was used to grow ferromagnetic La_0.7Sr_0.3MnO₃ (LSMO) films on antiferromagnetic La_0.33Ca_0.67MnO₃ (LCMO) and Pr_0.7Ca_0.3MnO₃ (PCMO) films in bilayer forms. The LSMO film on the PCMO layer had a more elongated out-of-plane lattice than that on the LCMO layer. The former had a lower ferromagnetic transition temperature (320 K) than the latter (350 K). The enhanced low-temperature magnetoresistance of the LSMO/PCMO bilayer suggests that the spin frustration is stronger at this bilayer than in the LSMO/LCMO bilayer. These differences indicate that strain state and defect concentration play important roles in governing interfacial spin interactions.     

Single-longitudinal mode, monolithic, green solid-state laser

We present the practical realization of a monolithic single-frequency diode pumped Nd:YVO₄/YVO₄/KTP microchip laser with birefringent filter operating at 532?nm. Theoretical analysis of the single-mode operation of such a laser configuration is presented. Experimental results are in good agreement with theoretical analysis. The laser operated with output power up to 90?mW at 532?nm. The total optical efficiency (808?nm to 532?nm) was 9.5%. Power stability was at the level of ±0.75% and the long-term frequency stability was approximately 3×10^?8. The beam has a Gaussian profile and the M2 parameter was below 1.2.     

Energy of the interaction between membrane lipid domains calculated from splay and tilt deformations

Specific domains, called rafts, are formed in cell membranes. Similar lipid domains can be formed in model membranes as a result of phase separation with raft size may remaining small (～10–100 nm) for a long time. The characteristic lifetime of a nanoraft ensemble strongly depends on the nature of mutual raft interactions. The interaction energy between the boundaries of two rafts has been calculated under the assumption that the thickness of the raft bilayer is greater than that of the surrounding membrane, and elastic deformations appear in order to smooth the thickness mismatch at the boundary. When rafts approach each other, deformations from their boundaries overlap, making interaction energy profile sophisticated. It has been shown that raft merger occurs in two stages: rafts first merge in one monolayer of the lipid bilayer and then in another monolayer. Each merger stage requires overcoming of an energy barrier of about 0.08–0.12 k _BT per 1 nm of boundary length. These results allow us to explain the stability of the ensemble of finite sized rafts.