Materials

545 KiB

Open AccessArticle

Investigation of Iron Oxide Morphology in a Cyclic Redox Water Splitting Process for Hydrogen Generation

by Michael M. Bobek, Richard C. Stehle and David W. Hahn

Materials 2012, 5(10), 2003-2014; https://doi.org/10.3390/ma5102003 - 23 Oct 2012

Cited by 5 | Viewed by 6260

A solar fuels generation research program is focused on hydrogen production by means of reactive metal water splitting in a cyclic iron-based redox process. Iron-based oxides are explored as an intermediary reactive material to dissociate water molecules at significantly reduced thermal energies. With [...] Read more.

A solar fuels generation research program is focused on hydrogen production by means of reactive metal water splitting in a cyclic iron-based redox process. Iron-based oxides are explored as an intermediary reactive material to dissociate water molecules at significantly reduced thermal energies. With a goal of studying the resulting oxide chemistry and morphology, chemical assistance via CO is used to complete the redox cycle. In order to exploit the unique characteristics of highly reactive materials at the solar reactor scale, a monolithic laboratory scale reactor has been designed to explore the redox cycle at temperatures ranging from 675 to 875 K. Using high resolution scanning electron microscope (SEM) and electron dispersive X-ray spectroscopy (EDS), the oxide morphology and the oxide state are quantified, including spatial distributions. These images show the change of the oxide layers directly after oxidation and after reduction. The findings show a significant non-stoichiometric O/Fe gradient in the atomic ratio following oxidation, which is consistent with a previous kinetics model, and a relatively constant, non-stoichiometric O/Fe atomic ratio following reduction. Full article

(This article belongs to the Special Issue Advanced Materials for Water-Splitting)

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1149 KiB

Open AccessArticle

Solvent Composition is Critical for Carbodiimide Cross-Linking of Hyaluronic Acid as an Ophthalmic Biomaterial

by Jui-Yang Lai

Materials 2012, 5(10), 1986-2002; https://doi.org/10.3390/ma5101986 - 23 Oct 2012

Cited by 25 | Viewed by 6436

Abstract

Hyaluronic acid (HA) is one of the most important ophthalmic biomaterials, while also being used for tissue engineering and drug delivery. Although chemical cross-linking is an effective way to improve the material performance, it may as a consequence be detrimental to the living [...] Read more.

Hyaluronic acid (HA) is one of the most important ophthalmic biomaterials, while also being used for tissue engineering and drug delivery. Although chemical cross-linking is an effective way to improve the material performance, it may as a consequence be detrimental to the living cells/tissues. Given that the cross-linking efficiency is mediated by the solvent composition during the chemical modification, this study aims to explore the stability and biocompatibility of carbodiimide cross-linked HA in relation to material processing conditions by varying the acetone/water volume ratio (from 70:30 to 95:5) at a constant 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) concentration of 100 mM. Our results indicated that after the EDC treatment in the presence of an acetone/water mixture (85:15, v/v), the HA hydrogel membranes have the lowest equilibrium water content, the highest stress at break and the greatest resistance to hyaluronidase digestion. Live/Dead assays and pro-inflammatory cytokine expression analyses showed that the cross-linked HA hydrogel membranes, irrespective of the solvent composition, are compatible with human RPE cell lines without causing toxicity and inflammation. However, it should be noted that the test samples prepared by the cross-linking in the presence of acetone/water mixtures containing 70, 75, and 95 vol % of acetone slightly inhibit the metabolic activity of viable ARPE-19 cultures, probably due to the alteration in the ionic interaction between the medium nutrients and polysaccharide biomaterials. In summary, the water content, mechanical strength and RPE cell proliferative capacity strongly depends on the solvent composition for carbodiimide cross-linking of HA materials. Full article

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529 KiB

Open AccessArticle

Development and Characterization of Amorphous Thermoplastic Matrix Graphene Nanocomposites

by Antonio Greco, Alessia Timo and Alfonso Maffezzoli

Materials 2012, 5(10), 1972-1985; https://doi.org/10.3390/ma5101972 - 22 Oct 2012

Cited by 20 | Viewed by 6196

Abstract

The aim of the present work is the development of amorphous thermoplastic matrix nanocomposites based on graphite nanoparticles. Different types of graphite were used, including unmodified graphite, graphene nanoplatelets and graphite intercalation compounds. Graphite intercalation compounds were subjected to thermal treatment to attain [...] Read more.

The aim of the present work is the development of amorphous thermoplastic matrix nanocomposites based on graphite nanoparticles. Different types of graphite were used, including unmodified graphite, graphene nanoplatelets and graphite intercalation compounds. Graphite intercalation compounds were subjected to thermal treatment to attain exfoliation of the nanofiller. The exfoliation process was studied by means of thermal analysis. The nanofillers and nanocomposites were characterized by means of X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analysis. The nanocomposites were further characterized by means of mechanical and dielectric analysis. The flammability of the nanocomposites was also analyzed. Results obtained indicate that addition of the nanofiller allows improving the proprieties of the amorphous thermoplastic matrix. The effect of the degree of dispersion of the nanofiller is particularly relevant for the dielectric properties of the nanocomposites, whereas no direct correlation between degree of dispersion and mechanical properties can be observed. Full article

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362 KiB

Open AccessReview

Recent Advances in the Photorefraction of Doped Lithium Niobate Crystals

by Yongfa Kong, Shiguo Liu and Jingjun Xu

Materials 2012, 5(10), 1954-1971; https://doi.org/10.3390/ma5101954 - 22 Oct 2012

Cited by 79 | Viewed by 8397

Abstract

The recent advances in the photorefraction of doped lithium niobate crystals are reviewed. Materials have always been the main obstacle for commercial applications of photorefractive holographic storage. Though iron-doped LiNbO₃ is the mainstay of holographic data storage efforts, several shortcomings, especially the [...] Read more.

The recent advances in the photorefraction of doped lithium niobate crystals are reviewed. Materials have always been the main obstacle for commercial applications of photorefractive holographic storage. Though iron-doped LiNbO₃ is the mainstay of holographic data storage efforts, several shortcomings, especially the low response speed, impede it from becoming a commercial recording medium. This paper reviews the photorefractive characteristics of different dopants, especially tetravalent ions, doped and co-doped LiNbO₃ crystals, including Hf, Zr and Sn monodoped LiNbO₃, Hf and Fe, Zr and Fe doubly doped LiNbO₃, Zr, Fe and Mn, Zr, Cu and Ce triply doped LiNbO₃, Ru doped LiNbO₃, and V and Mo monodoped LiNbO₃. Among them, Zr, Fe and Mn triply doped LiNbO₃ shows excellent nonvolatile holographic storage properties, and V and Mo monodoped LiNbO₃ has fast response and multi-wavelength storage characteristics. Full article

(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)

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873 KiB

Open AccessArticle

Guidelines for the Bandgap Combinations and Absorption Windows for Organic Tandem and Triple-Junction Solar Cells

by Ben Minnaert and Peter Veelaert

Materials 2012, 5(10), 1933-1953; https://doi.org/10.3390/ma5101933 - 22 Oct 2012

Cited by 32 | Viewed by 7391

Abstract

Organic solar cells have narrow absorption windows, compared to the absorption band of inorganic semiconductors. A possible way to capture a wider band of the solar spectrum—and thus increasing the power conversion efficiency—is using more solar cells with different bandgaps in a row, [...] Read more.

Organic solar cells have narrow absorption windows, compared to the absorption band of inorganic semiconductors. A possible way to capture a wider band of the solar spectrum—and thus increasing the power conversion efficiency—is using more solar cells with different bandgaps in a row, i.e., a multi-junction solar cell. We calculate the ideal material characteristics (bandgap combinations and absorption windows) for an organic tandem and triple-junction solar cell, as well as their acceptable range. In this way, we give guidelines to organic material designers. Full article

(This article belongs to the Special Issue Photovoltaic Materials 2012)

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139 KiB

Open AccessArticle

Lateral Dynamics in Polymer-Supported Membranes

by Shigeyuki Komura, Sanoop Ramachandran and Kazuhiko Seki

Materials 2012, 5(10), 1923-1932; https://doi.org/10.3390/ma5101923 - 19 Oct 2012

Cited by 7 | Viewed by 5669

Abstract

We investigate the lateral dynamics in a purely viscous lipid membrane which is supported by a thin polymer sheet (polymer-supported membrane). The generalized frequency-dependent mobility tensor of the polymer-supported membrane is obtained by taking into account the viscoelasticity of the polymer sheet. Due [...] Read more.

We investigate the lateral dynamics in a purely viscous lipid membrane which is supported by a thin polymer sheet (polymer-supported membrane). The generalized frequency-dependent mobility tensor of the polymer-supported membrane is obtained by taking into account the viscoelasticity of the polymer sheet. Due to its viscoelasticity, the cross-correlation functions of two particles embedded in the membrane exhibit an anomalous diffusion. A useful relation for two-point microrheology connecting the cross-correlation function and the modulus of the polymer sheet is provided. Full article

(This article belongs to the Special Issue Supported Lipid Membranes)

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370 KiB

Open AccessArticle

Monitoring Wood Degradation during Weathering by Cellulose Crystallinity

by Francesca Lionetto, Roberta Del Sole, Donato Cannoletta, Giuseppe Vasapollo and Alfonso Maffezzoli

Materials 2012, 5(10), 1910-1922; https://doi.org/10.3390/ma5101910 - 19 Oct 2012

Cited by 253 | Viewed by 11697

Abstract

The degree of crystallinity of cellulose was used for assessing the degradation level of coated and uncoated samples of pine wood after weathering. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy measured the changes in the surface crystallinity of cellulose resulting from [...] Read more.

The degree of crystallinity of cellulose was used for assessing the degradation level of coated and uncoated samples of pine wood after weathering. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy measured the changes in the surface crystallinity of cellulose resulting from weathering, both natural and artificial. Both techniques revealed an increase in the crystallinity index (CI) of cellulose when wood was subjected to weathering. An increase in the size of crystallites was also observed by XRD measurements. These results were related to the reduction of the amorphous fractions of wood, and, consequently, to the enrichment of the relative crystalline content. Thanks to FT-IR analysis, the degradation of hemicellulose was observed for uncoated samples after exposure to artificial weathering. The effect of weathering was less evident on coated samples because of the protective action of the coating. A good correlation between the crystallinity indexes obtained from FT-IR and XRD was found. The experimental results proved that the proposed method may be a very useful tool for a rapid and accurate estimation of the degradation level of wood exposed to weathering. This methodology can find application in the field of conservation and restoration of wooden objects or in the industry of wood coatings. Full article

(This article belongs to the Special Issue Advances in Cellulosic Materials)

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1282 KiB

Open AccessReview

Controlling Morphological Parameters of Anodized Titania Nanotubes for Optimized Solar Energy Applications

by Andrew Haring, Amanda Morris and Michael Hu

Materials 2012, 5(10), 1890-1909; https://doi.org/10.3390/ma5101890 - 19 Oct 2012

Cited by 60 | Viewed by 8104

Abstract

Anodized TiO₂ nanotubes have received much attention for their use in solar energy applications including water oxidation cells and hybrid solar cells [dye-sensitized solar cells (DSSCs) and bulk heterojuntion solar cells (BHJs)]. High surface area allows for increased dye-adsorption and photon absorption. [...] Read more.

Anodized TiO₂ nanotubes have received much attention for their use in solar energy applications including water oxidation cells and hybrid solar cells [dye-sensitized solar cells (DSSCs) and bulk heterojuntion solar cells (BHJs)]. High surface area allows for increased dye-adsorption and photon absorption. Titania nanotubes grown by anodization of titanium in fluoride-containing electrolytes are aligned perpendicular to the substrate surface, reducing the electron diffusion path to the external circuit in solar cells. The nanotube morphology can be optimized for the various applications by adjusting the anodization parameters but the optimum crystallinity of the nanotube arrays remains to be realized. In addition to morphology and crystallinity, the method of device fabrication significantly affects photon and electron dynamics and its energy conversion efficiency. This paper provides the state-of-the-art knowledge to achieve experimental tailoring of morphological parameters including nanotube diameter, length, wall thickness, array surface smoothness, and annealing of nanotube arrays. Full article

(This article belongs to the Special Issue Advanced Materials for Water-Splitting)

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777 KiB

Open AccessArticle

In Vivo Toxicity of Intravenously Administered Silica and Silicon Nanoparticles

by Sergey Ivanov, Sergey Zhuravsky, Galina Yukina, Vladimir Tomson, Dmitry Korolev and Michael Galagudza

Materials 2012, 5(10), 1873-1889; https://doi.org/10.3390/ma5101873 - 16 Oct 2012

Cited by 63 | Viewed by 8499

Abstract

Both silicon and silica nanoparticles (SiNPs and SiO₂NPs, respectively) are currently considered to be promising carriers for targeted drug delivery. However, the available data on their in vivo toxicity are limited. The present study was aimed at investigation of SiNP and [...] Read more.

Both silicon and silica nanoparticles (SiNPs and SiO₂NPs, respectively) are currently considered to be promising carriers for targeted drug delivery. However, the available data on their in vivo toxicity are limited. The present study was aimed at investigation of SiNP and SiO₂NP (mean diameter 10 and 13 nm, respectively) toxicity using both morphological and functional criteria. Hematological and biochemical parameters were assessed in Sprague-Dawley rats 5, 21 and 60 days after administration of NPs. Inner ear function was determined using otoacoustic emission testing at 21 and 60 days after infusion of NPs. Furthermore, the histological structure of liver, spleen and kidney samples was analyzed. Intravenous infusion of SiNPs or SiO₂NPs (7 mg/kg) was not associated with significant changes in hemodynamic parameters. Hearing function remained unchanged over the entire observation period. Both inter- and intragroup changes in blood counts and biochemical markers were non-significant. Histological findings included the appearance of foreign body-type granulomas in the liver and spleen as well as microgranulation in the liver after administration of NPs. The number of granulomas was significantly lower after administration of SiNPs compared with SiO₂NPs. In conclusion, both tested types of NPs are relatively biocompatible nanomaterials, at least when considering acute toxicity. Full article

(This article belongs to the Special Issue Nanotoxicology)

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736 KiB

Open AccessArticle

Theory-Guided Materials Design of Multi-Phase Ti-Nb Alloys with Bone-Matching Elastic Properties

by Martin Friák, William Art Counts, Duancheng Ma, Benedikt Sander, David Holec, Dierk Raabe and Jörg Neugebauer

Materials 2012, 5(10), 1853-1872; https://doi.org/10.3390/ma5101853 - 15 Oct 2012

Cited by 76 | Viewed by 8300

Abstract

We present a scale-bridging approach for modeling the integral elasticresponse of polycrystalline composite that is based on a multi-disciplinary combination of(i) parameter-free first-principles calculations of thermodynamic phase stability andsingle-crystal elastic stiffness; and (ii) homogenization schemes developed forpolycrystalline aggregates and composites. The modeling is [...] Read more.

We present a scale-bridging approach for modeling the integral elasticresponse of polycrystalline composite that is based on a multi-disciplinary combination of(i) parameter-free first-principles calculations of thermodynamic phase stability andsingle-crystal elastic stiffness; and (ii) homogenization schemes developed forpolycrystalline aggregates and composites. The modeling is used as a theory-guidedbottom-up materials design strategy and applied to Ti-Nb alloys as promising candidatesfor biomedical implant applications. The theoretical results (i) show an excellent agreementwith experimental data and (ii) reveal a decisive influence of the multi-phase character ofthe polycrystalline composites on their integral elastic properties. The study shows thatthe results based on the density functional theory calculations at the atomistic level canbe directly used for predictions at the macroscopic scale, effectively scale-jumping severalorders of magnitude without using any empirical parameters. Full article

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921 KiB

Open AccessArticle

Preparation of Poly-(Methyl vinyl ether-co-maleic Anhydride) Nanoparticles by Solution-Enhanced Dispersion by Supercritical CO₂

by Ai-Zheng Chen, Guang-Ya Wang, Shi-Bin Wang, Jian-Gang Feng, Yuan-Gang Liu and Yong-Qiang Kang

Materials 2012, 5(10), 1841-1852; https://doi.org/10.3390/ma5101841 - 10 Oct 2012

Cited by 10 | Viewed by 8269

Abstract

The supercritical CO₂-based technologies have been widely used in the formation of drug and/or polymer particles for biomedical applications. In this study, nanoparticles of poly-(methyl vinyl ether-co-maleic anhydride) (PVM/MA) were successfully fabricated by a process of solution-enhanced dispersion by supercritical CO [...] Read more.

The supercritical CO₂-based technologies have been widely used in the formation of drug and/or polymer particles for biomedical applications. In this study, nanoparticles of poly-(methyl vinyl ether-co-maleic anhydride) (PVM/MA) were successfully fabricated by a process of solution-enhanced dispersion by supercritical CO₂ (SEDS). A 2³ factorial experiment was designed to investigate and identify the significance of the processing parameters (concentration, flow and solvent/nonsolvent) for the surface morphology, particle size, and particle size distribution of the products. The effect of the concentration of PVM/MA was found to be dominant in the results regarding particle size. Decreasing the initial solution concentration of PVM/MA decreased the particle size significantly. After optimization, the resulting PVM/MA nanoparticles exhibited a good spherical shape, a smooth surface, and a narrow particle size distribution. Fourier transform infrared spectroscopy (FTIR) spectra demonstrated that the chemical composition of PVM/MA was not altered during the SEDS process and that the SEDS process was therefore a typical physical process. The absolute value of zeta potential of the obtained PVM/MA nanoparticles was larger than 40 mV, indicating the samples’ stability in aqueous suspension. Analysis of thermogravimetry-differential scanning calorimetry (TG-DSC) revealed that the effect of the SEDS process on the thermostability of PVM/MA was negligible. The results of gas chromatography (GC) analysis confirmed that the SEDS process could efficiently remove the organic residue. Full article

(This article belongs to the Special Issue Advances in Nanoscale Biomaterials)

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624 KiB

Open AccessArticle

Commercial Coffee Wastes as Materials for Adsorption of Heavy Metals from Aqueous Solutions

by George Z. Kyzas

Materials 2012, 5(10), 1826-1840; https://doi.org/10.3390/ma5101826 - 10 Oct 2012

Cited by 129 | Viewed by 15893

Abstract

This work aims to study the removal of Cu(II) and Cr(VI) from aqueous solutions with commercial coffee wastes. Materials with no further treatment such as coffee residues from café may act as adsorbents for the removal of Cu(II) and Cr(VI). Equilibrium data were [...] Read more.

This work aims to study the removal of Cu(II) and Cr(VI) from aqueous solutions with commercial coffee wastes. Materials with no further treatment such as coffee residues from café may act as adsorbents for the removal of Cu(II) and Cr(VI). Equilibrium data were successfully fitted to the Langmuir, Freundlich and Langmuir-Freundlich model (L-F). The maximum adsorption capacity of the coffee residues can reach 70 mg/g for the removal of Cu(II) and 45 mg/g for Cr(VI). The kinetic data were fitted to pseudo-first, -second and -third order equations. The equilibrium was achieved in 120 min. Also, the effect of pH on adsorption and desorption was studied, as well as the influence of agitation rate. Ten cycles of adsorption-desorption were carried out revealing the strong reuse potential of these low-cost adsorbents; the latter was confirmed from a brief economic approach. Full article

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642 KiB

Open AccessArticle

The Effect of a Small Amount of Water on the Structure and Electrochemical Properties of Solid-State Synthesized Polyaniline

by Weiwei Shao, Ruxangul Jamal, Feng Xu, Aminam Ubul and Tursun Abdiryim

Materials 2012, 5(10), 1811-1825; https://doi.org/10.3390/ma5101811 - 10 Oct 2012

Cited by 147 | Viewed by 7649

Abstract

A series of polyaniline (PANI) salts were synthesized with the presence of a small amount of water varying from 0 to 1 mL at the beginning of solid-state polymerization. The structure and morphology of the samples were characterized by fourier transform infrared (FTIR) [...] Read more.

A series of polyaniline (PANI) salts were synthesized with the presence of a small amount of water varying from 0 to 1 mL at the beginning of solid-state polymerization. The structure and morphology of the samples were characterized by fourier transform infrared (FTIR) spectra, ultraviolet-visible (UV-Vis) absorption spectra, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical performances of the products were investigated by galvanostatic charge-discharge, cyclic voltammetry, cycling stability and electrochemical impedance spectroscopy (EIS). The results showed that the amounts of water can affect the oxidation degree, conjugate level and crystallinity of PANI salts. All PANI salts showed spherical morphology with the diameter of about 60 nm as shown by TEM. The electrochemical tests showed the highest specific capacitance value 593.3 F.g−1 in 1 M H2SO4 for PANI prepared with the addition of 0.5 mL of water at the beginning of solid-state polymerization. Full article

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738 KiB

Open AccessArticle

Physical and Chemical Properties of Sintering Red Mud and Bayer Red Mud and the Implications for Beneficial Utilization

by Ping Wang and Dong-Yan Liu

Materials 2012, 5(10), 1800-1810; https://doi.org/10.3390/ma5101800 - 9 Oct 2012

Cited by 145 | Viewed by 10232

Abstract

Performances of two common types of red mud, Bayer red mud and Sintering red mud, were investigated in this research. Their compositions, mechanical properties and microstructure characterization were measured through XRD, TG and SEM analysis. Their shear strength, particle size, density and hydraulic [...] Read more.

Performances of two common types of red mud, Bayer red mud and Sintering red mud, were investigated in this research. Their compositions, mechanical properties and microstructure characterization were measured through XRD, TG and SEM analysis. Their shear strength, particle size, density and hydraulic characteristics also had been performed. Huge differences between the basic mineral types of these two kinds of red mud also can be found. The comparison of compositions shows that CaCO₃ content in Sintering red mud is higher, Bayer red mud has more hazardous elements such as As, Pb and Hg and both have a high concentration of radioactivity. The micro particle of Bayer red mud is finer and more disperse, but the Sintering red mud has higher shear strength. Combining the TG and hydraulic characteristics analysis, it can be shown that Bayer red mud has higher value of water content and Sintering red mud has higher hydraulic conductivity. The paper then illustrates that Sintering red mud can become the main filling material of supporting structure of red mud stocking yard. Bayer red mud has a high reuse value and also can be used as a mixing material of masonry mortar. Full article

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530 KiB

Open AccessArticle

Polyamine-Promoted Growth of One-Dimensional Nanostructure-Based Silica and Its Feature in Catalyst Design

by Xin-Ling Liu, Pei-Xin Zhu, Yan-Feng Gao and Ren-Hua Jin

Materials 2012, 5(10), 1787-1799; https://doi.org/10.3390/ma5101787 - 1 Oct 2012

Cited by 6 | Viewed by 5766

Abstract

Crystalline linear polyethyleneimine (LPEI) is a fascinating polymer that can be used as a catalyst, template and scaffold in order to direct the formation of silica with controllable compositions and spatial structures under mild conditions. Considering the crystallization and assembly of LPEI is [...] Read more.

Crystalline linear polyethyleneimine (LPEI) is a fascinating polymer that can be used as a catalyst, template and scaffold in order to direct the formation of silica with controllable compositions and spatial structures under mild conditions. Considering the crystallization and assembly of LPEI is temperature-dependent, we adopted different accelerated cooling processes of a hot aqueous solution of LPEI in order to modulate the LPEI crystalline aggregates. We then used them in the hydrolytic condensation of alkoxysilane. A series of silica with nanofibrils, nanotubes and nanowire-based structures were achieved simply by the LPEI aggregates which were pre-formed in defined cooling processes. These specific one-dimensional nanoscale structures assembled into microscale fibers-, sheet- and platelet-like coalescences. Furthermore, the deposition kinetics was also researched by the combination of other characterizations (e.g., pH measurement, ²⁹Si MAS NMR). As a preliminary application, the hybrids of LPEI@SiO₂ were used not only as an agent for reducing PtCl₄²⁻ into Pt but also as host for loading Pt nanoparticles. The Pt-loaded silica showed good catalytic properties in the reduction of Rhodamine B by dimethylaminoborane (DMAB). Full article

(This article belongs to the Special Issue Advances in Bio-inspired Materials)

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428 KiB

Open AccessArticle

Pressure Dependence of ¹⁵N Chemical Shifts in Model Peptides Ac-Gly-Gly-X-Ala-NH₂

by Joerg Koehler, Markus Beck Erlach, Edson Crusca, Werner Kremer, Claudia E. Munte and Hans Robert Kalbitzer

Materials 2012, 5(10), 1774-1786; https://doi.org/10.3390/ma5101774 - 27 Sep 2012

Cited by 29 | Viewed by 7145

Abstract

High pressure NMR spectroscopy has developed into an important tool for studying conformational equilibria of proteins in solution. We have studied the amide proton and nitrogen chemical shifts of the 20 canonical amino acids X in the random-coil model peptide Ac-Gly-Gly-X-Ala-NH₂, [...] Read more.

High pressure NMR spectroscopy has developed into an important tool for studying conformational equilibria of proteins in solution. We have studied the amide proton and nitrogen chemical shifts of the 20 canonical amino acids X in the random-coil model peptide Ac-Gly-Gly-X-Ala-NH₂, in a pressure range from 0.1 to 200 MPa, at a proton resonance frequency of 800 MHz. The obtained data allowed the determination of first and second order pressure coefficients with high accuracy at 283 K and pH 6.7. The mean first and second order pressure coefficients and for nitrogen are 2.91 ppm/GPa and −2.32 ppm/GPa², respectively. The corresponding values and for the amide protons are 0.52 ppm/GPa and −0.41 ppm/GPa². Residual dependent ¹J_1H15N-coupling constants are shown. Full article

(This article belongs to the Special Issue NMR in Materials Science)

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3302 KiB

Open AccessReview

Hard-X-ray Zone Plates: Recent Progress

by Syue-Ren Wu, Yeukuang Hwu and Giorgio Margaritondo

Materials 2012, 5(10), 1752-1773; https://doi.org/10.3390/ma5101752 - 27 Sep 2012

Cited by 52 | Viewed by 9144

Abstract

The technology to focus hard-X-rays (photon energy larger than 1–2 keV) has made great progress in the past three years. The progress was particularly spectacular for lenses based on the Fresnel zone plate concept. The spatial resolution notably increased by a factor of [...] Read more.

The technology to focus hard-X-rays (photon energy larger than 1–2 keV) has made great progress in the past three years. The progress was particularly spectacular for lenses based on the Fresnel zone plate concept. The spatial resolution notably increased by a factor of three, opening up entirely new domains of application, specifically in biomedical research. As we shall see, this evolution is the result of a painstaking optimization of many different aspects rather than of a single technical breakthrough. Full article

(This article belongs to the Special Issue X-ray Imaging in Materials Science)

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958 KiB

Open AccessArticle

Study of Morphological Changes in MgH₂ Destabilized LiBH₄ Systems Using Computed X-ray Microtomography

by Tabbetha Dobbins, Shathabish NaraseGowda and Leslie G. Butler

Materials 2012, 5(10), 1740-1751; https://doi.org/10.3390/ma5101740 - 26 Sep 2012

Cited by 2 | Viewed by 5815

Abstract

The objective of this study was to apply three-dimensional x-ray microtomographic imaging to understanding morphologies in the diphasic destabilized hydride system: MgH₂ and LiBH₄. Each of the single phase hydrides as well as two-phase mixtures at LiBH₄:MgH₂ [...] Read more.

The objective of this study was to apply three-dimensional x-ray microtomographic imaging to understanding morphologies in the diphasic destabilized hydride system: MgH₂ and LiBH₄. Each of the single phase hydrides as well as two-phase mixtures at LiBH₄:MgH₂ ratios of 1:3, 1:1, and 2:1 were prepared by high energy ball milling for 5 minutes (with and without 4 mol % TiCl₃ catalyst additions). Samples were imaged using computed microtomography in order to (i) establish measurement conditions leading to maximum absorption contrast between the two phases and (ii) determine interfacial volume. The optimal energy for measurement was determined to be 15 keV (having 18% transmission for the MgH₂ phase and above 90% transmission for the LiBH₄ phase). This work also focused on the determination of interfacial volume. Results showed that interfacial volume for each of the single phase systems, LiBH₄ and MgH₂, did not change much with catalysis using 4 mol % TiCl₃. However, for the mixed composite system, interphase boundary volume was always higher in the catalyzed system; increasing from 15% to 33% in the 1:3 system, from 11% to 20% in the 1:1 system, and 2% to 14% in the 2:1 system. The parameters studied are expected to govern mass transport (i.e., diffusion) and ultimately lead to microstructure-based improvements on H₂ desorption and uptake rates. Full article

(This article belongs to the Special Issue Recent Advances in Hydrogen Storage Materials)

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Materials, Volume 5, Issue 10 (October 2012) – 18 articles , Pages 1740-2014

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