ORCID Profile
0000-0002-4380-9403
Current Organisation
Nanyang Technological University
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Publisher: MDPI AG
Date: 25-12-2022
DOI: 10.3390/MOLECULES28010174
Abstract: Perovskite-related materials show very promising properties in many fields. Pb-free perovskites are particularly interesting, because of the toxicity of Pb. In this study, hybrid double perovskite MA2KBiCl6 (MA = methylammonium cation) was found to have interesting variable temperature behaviours. Both variable temperature single crystal X-ray diffraction, synchrotron powder diffraction, and Raman spectroscopy were conducted to reveal a rhombohedral to cubic phase transition at around 330 K and an order to disorder transition for inorganic cage below 210 K.
Publisher: Mineralogical Society of America
Date: 2005
Publisher: American Chemical Society (ACS)
Date: 21-12-2007
DOI: 10.1021/ES071124F
Abstract: A new heterogeneous Fenton-like system, consisting of supported Au catalysts and hydrogen peroxide, was proved to be effective in removing low level organic compounds (ca. 100 ppm) such as phenol, ethanol, formaldehyde, and acetone in aqueous solution. Among all gold catalysts the Au/ hydroxyapatite (Au/HAp) exhibits the highest activity, and even better than the conventional iron ions exchanged zeolite (Fe/ ZSM-5) catalyst. In particular, unlike the limited operational pH range (pH: 2 approximately 5) for the other heterogeneous Fenton catalysts such as Fe/ZSM-5, Au/HAp shows higher stability even in strong acid solution (pH approximately 2), due to almost no leaching of active metal from supports into solution. It can be potentially applied in treating the industrial wastewaters with strong acidity and purifying drinking water. In addition, in the case of complete oxidation of phenol, a plausible route was suggested for deep understanding of this process.
Publisher: Elsevier BV
Date: 08-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TA03331D
Abstract: Trends in the Young's Modulus and Hardness for the hybrid perovskites CH 3 NH 3 PbX 3 (X = I, Br and Cl) are assessed in relation to the underlying chemical bonding.
Publisher: AIP Publishing
Date: 08-07-2003
DOI: 10.1063/1.1591070
Abstract: In this work, we report the discovery of a vortex pinning source: semicrystalline defect wells in self-aligned nanostructured MgB2. It is demonstrated that these aperiodic regions trap numerous crystal defects migrating along nanodomain boundaries during self-alignment and act as intense vortex pinning centers that significantly enhance the high-field performance of MgB2. This suggests that the density of trapped defects in the wells is much greater than that found in other vortex pinning sources.
Publisher: Wiley
Date: 28-09-2009
Publisher: American Chemical Society (ACS)
Date: 29-09-2004
DOI: 10.1021/JP047902X
Publisher: Elsevier BV
Date: 10-2007
Publisher: Wiley
Date: 07-02-2016
DOI: 10.1111/JACE.14146
Publisher: Springer Science and Business Media LLC
Date: 27-09-2005
Publisher: MDPI AG
Date: 04-06-2019
DOI: 10.3390/MA12111814
Abstract: Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 ≤ x ≤ 0.8) was prepared by solid-state and wet chemical processing to explore the impact of the synthesis route and mode of crystal chemical incorporation of copper on the antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) strains. Apatites prepared by solid-state reaction showed unit cell volume dilation from 527.17 Å3 for copper-free HA to 533.31 Å3 for material of the putative composition Ca10(PO4)6[Cu0.8(OH)0.4O0.8] consistent with Cu+ insertion into the [001] hydroxyapatite channel. This was less pronounced (528.30 Å3 to 529.3 Å3) in the corresponding wet chemical synthesised products, suggesting less complete Cu tunnel incorporation and partial tenancy of Cu in place of calcium. X-ray absorption spectroscopy suggests fast quenching is necessary to prevent oxidation of Cu+ to Cu2+. Raman spectroscopy revealed an absorption band at 630 cm−1 characteristic of symmetric O-Cu+-O units tenanted in the apatite channel while solid-state 31P magic-angle-spinning nuclear magnetic resonance (MAS NMR) supported a vacancy-Cu+ substitution model within the apatite channel. The copper doping strategy increases antibacterial efficiency by 25% to 55% compared to undoped HA, with the finer particle sizes and greater specific surface areas of the wet chemical material demonstrating superior efficacy.
Publisher: American Chemical Society (ACS)
Date: 04-12-2020
Publisher: Wiley
Date: 14-07-2010
Publisher: Springer Science and Business Media LLC
Date: 05-02-2018
DOI: 10.1557/ADV.2018.154
Publisher: IOP Publishing
Date: 14-08-2004
Publisher: The Royal Society
Date: 08-12-1986
Abstract: High-resolution transmission electron microscopy and selected-area electron diffraction show that all phases of the general formula [Ba x Cs y [(Al, Ti) 3+ 2 x + y Ti 4+ 8-2 x - y ] O 16 , 1.08 ≼ x + y ≼ 1.51 have the hollandite-type substructure. These hollandites display commensurate and incommensurate superlattices owing to the ordered insertion of large cations (Ba 2+ , Cs + ) into the (2, 2) tunnel interstices of the octahedral (Al, Ti) O 6 framework. Multiplicity ( m ) of a supercell is defined as d supercell ided by d 002 for the subcell. Ordering may be one-dimensional, in which case the cation sequences between (2, 2) channels are independent, three-dimensional with lateral correlation between tunnels, or a combination of both. One-dimensional superstructures yield commensurate multiplicities of 4 in all phases except an aluminous caesium hollandite where m = 6. Three-dimensional superstructures are both incommensurate and commensurate, with 4.5 0 ≼ m ≼ 6.5 9 . Multiplicities correlate directly with caesium content per formula unit, establishing a maximum in caesiumrich hollandites. Among barium ( y = 0) and caesium endmembers, ( x = 0) multiplicities increase modestly with increasing Al 3+ : (Al + Ti) 3+ content. Superstructure dimensionality is largely determined by the nature and proportions of the trivalent species, rather than the tunnel cations one-dimensional order is commonplace in hollandites rich in trivalent titanium but rare in aluminous hollandites. High-resolution electron microscopy supports the interpretation of incommensurate superstructures as fine-scale intergrowths of commensurate microdomains with m = 4, 5, 6 or 7. For aluminous hollandites, rare ex les of structural modifications involving tunnels of different cross-sectional dimensions may be found, i. e. T(2, n ), 1 ≼ n ≼ 3 intergrowths. As all specimens are sensitive to the electron beam, prolonged irradiation at high electron fluxes can initiate the transformation of single-crystal hollandite to single-crystal rutile. A mechanism for this transformation is proposed, whereby the hollandite crystals initially adjust their multiplicity to six. Growth fronts on {101} holl subsequently propagate through the crystals consuming hollandite and leaving rutile: the structure of the interface between the phases is believed to contain components of rutile possessing antiphase boundaries. In this reconstructive transformation, [100] of the newly formed rutile invariably lies almost parallel to [110] of the original hollandite. Less severe electron irradiation or argon ion beam milling causes crystals to twin polysynthetically. The superlattice properties of [Ba x Cs y [(Ti, Al) 3+ 2 x + y Ti 4+ 8-2 x - y ] O 16 hollandites are integrated with those of other hollandites to identify and evaluate the factors responsible for the stoichiometries and preferred superstructures of hollandites in general. These factors include electrostatic repulsion between large cations in the same tunnel, interaction between cations in neighbouring tunnels, the shielding capacity of the octahedral framework, and kinetic effects.
Publisher: International Union of Crystallography (IUCr)
Date: 11-11-2008
DOI: 10.1107/S0021889808032718
Abstract: The local environment of titanium in nanocrystalline sol-gel synthesized titania, cobaltiferous titania and silica–titania core–shell photocatalysts was investigated using X-ray absorption spectroscopy (XAS). Anatase reconstructively transforms to rutile via a persistent amorphous phase that is retained, in part, up to 1273 K. In nanotitania, temperature-dependent trends in Ti order correlation observed by XAS parallel the development of amorphous content extracted from powder X-ray diffraction patterns, such that amorphicity shows a transient maximum at ∼873 K with the onset of rutile crystallization. Cobaltiferous and core–shell materials behaved similarly, but with anatase retained to 973 and 1273 K, respectively. In the former, cobalt redox reactions may stabilize anatase to higher temperatures by ready charge-balancing during the loss of hydroxyl and the formation of oxygen vacancies. In the core–shell architecture, higher Ti coordination and interatomic distance variance in the first- and second-nearest-neighbour shells are maintained to 1273 K by interaction of a substantially aperiodic TiO 6 network with the glassy silica substrate, which inhibits crystallization of rutile from the amorphous intermediate. Comparisons are also drawn with the commercial P25 catalyst. The overall transformation mechanism can be summarized as gel → non-stoichiometric anatase → amorphous titania → rutile. Smaller anatase crystals and a higher average Ti—Ti coordination environment in the core–shell structure may enhance photocatalytic activity directly, by creating larger specific surface areas and hosting reactive defects, or indirectly, by inhibiting exciton annihilation in aperiodic titania and delaying the crystallization of less photoactive rutile.
Publisher: JMIR Publications Inc.
Date: 21-10-2020
DOI: 10.2196/18916
Abstract: Respiratory disease is the third most common cause of death in New Zealand, with Pacific people living in New Zealand bearing the greatest burden of this type of disease. Although some epidemiological outcomes are known, we lack the specifics required to formulate targeted and effective public health interventions. The Pacific Islands Families (PIF) birth cohort study is a study that provides a unique source of data to assess lung function and current respiratory health among participants entering early adulthood and to examine associations with early life events during critical periods of growth. This paper aims to provide an overview of the design, methods, and scope of the Respiratory Health of Pacific Youth Study, which uses the overall PIF study cohort aged 18-19 years. From 2000-2019, the PIF study has followed, from birth, the growth, and the development of 1398 Pacific children born in Auckland, New Zealand. Participants were nested within the overall PIF study (at ages 18-19 years) from June 2018, and assessments were undertaken until mid-November 2019. The assessments included respiratory and general medical histories, a general physical examination, assessment of lung function (forced expiratory volume and forced vital capacity), self-completed questionnaires (St George’s Respiratory Questionnaire, European Quality of Life 5 Dimensions-3 Level, Epworth Sleepiness Scale for Children and Adolescents, and Leicester Cough Questionnaire), blood tests (eosinophils, Immunoglobulin E, Immunoglobulin G, Immunoglobulin A, Immunoglobulin M, and C-reactive protein), and chest x-rays. Noninferential analyses will be carried out on dimensionally reduced risk and protective factors and confounders. Data collection began in June 2018 and ended in November 2019, with a total of 466 participants recruited for submission of the paper. Collection and collation of chest x-ray data is still underway, and data analysis and expected results will be published by November 2020. This is the first longitudinal observational study to address the burden of respiratory disease among Pacific youth by determining factors in early life that impose long-term detriments in lung function and are associated with the presence of respiratory illness. Identifying risk factors and the magnitude of their effects will help in adopting preventative measures, establishing whether any avoidable risks can be modified by later resilient behaviors, and provide baseline measurements for the development of respiratory disease in later adult life. The study results can be translated into practice guidelines and inform health strategies with immediate national and international impact. DERR1-10.2196/18916
Publisher: American Chemical Society (ACS)
Date: 14-06-2007
DOI: 10.1021/JP0726384
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B906639J
Abstract: The crystal chemistry of the cuprate apatites A(I)(4)A(II)(6)(PO(4))(6)Cu(x)O(y)(H)(z) (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily alent (Cu(2+)) but in the calcium and strontium analogues co-exists with minor Cu(3+). This is in contrast with a previous work where Cu(1+) and Cu(2+) were reported.
Publisher: American Chemical Society (ACS)
Date: 23-11-2011
DOI: 10.1021/IC201673R
Abstract: Fluor-chlorellestadite solid solutions Ca(10)(SiO(4))(3)(SO(4))(3)Cl(2-x)F(x), serving as prototype crystalline matrices for the fixation of hazardous fly ash, were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The lattice parameters of the ellestadites vary linearly with composition and show the expected shrinkage of unit cell volume as fluorine (IR = 1.33 Å) displaces chlorine (IR = 1.81 Å). FTIR spectra indicate little or no OH(-) in the solid solutions. All compositions conform to P6(3)/m symmetry where F(-) is located at the 2a (0, 0, (1)/(4)) position, while Cl(-) is displaced out of the 6h Ca(2) triangle plane and occupies 4e (0, 0, z) split positions with z ranging from 0.336(3) to 0.4315(3). Si/S randomly occupy the 6h tetrahedral site. Ellestadites rich in Cl (x ≤ 1.2) show an overall deficiency in halogens (<2 atom per formula unit), particularly Cl as a result of CaCl(2) volatilization, with charge balance achieved by the creation of Ca vacancies (Ca(2+) + 2Cl(-) →□(Ca) + 2□(Cl)) leading to the formula Ca(10-y)(SiO(4))(3)(SO(4))(3)Cl(2-x-2y)F(x). For F-rich compositions the vacancies are found at Ca(2), while for Cl-rich ellestadites, vacancies are at Ca(1). It is likely the loss of CaCl(2) which leads tunnel anion vacancies promotes intertunnel positional disorder, preventing the formation of a P2(1)/b monoclinic dimorph, analogous to that reported for Ca(10)(PO(4))(6)Cl(2). Trends in structure with composition were analyzed using crystal-chemical parameters, whose systematic variations served to validate the quality of the Rietveld refinements.
Publisher: World Scientific Pub Co Pte Lt
Date: 12-2004
DOI: 10.1142/S0219581X04002619
Abstract: The properties influencing the photocatalytic activity of TiO 2 particles have been suggested to include the surface area, crystallinity, crystallite size and crystal structure. Therefore, manipulation of the microstructure of titania, especially of nanocrystalline powders, is very important in the preparative process. In this study, nanocrystalline TiO 2 powders with controlled particle size and phase composition were synthesized at low temperature ( °C) by a modified sol–gel method. The effects of gelation temperature were systematically investigated. It was found that this parameter played a critical role in determining the crystallinity of single phase anatase. With increasing gelation temperature, the crystallinity of anatase improved initially and then decreased if the temperature was raised to 80°C. These nanomaterials were characterized comprehensively by powder X-ray diffraction (including Rietveld analysis), high-resolution transmission electron microscopy, DSC/TGA thermal analysis and UV–Vis spectrometry.
Publisher: Elsevier BV
Date: 03-0010
Publisher: American Vacuum Society
Date: 03-2001
DOI: 10.1116/1.1347048
Abstract: The Ti layer deposited by ionized metal plasma deposition technique and the reacted region between Ti and Al–0.5%Cu, in Al–0.5%Cu/Ti/SiO2/Si structure, were characterized by scanning transmission electron microscopy (STEM) and Rutherford backscattering spectroscopy (RBS). The results indicate that the Ti layer with a column-like structure grew epitaxially in the close-packed [001] direction. This growth mechanism resulted in a high-density Ti layer in Al–0.5%Cu/Ti/SiO2/Si structure. This epitaxially grown Ti layer has anisotropic diffusion properties that can retard the diffusion of Al across the Ti layer in the initial stage of high temperature Al sputtering or reflow processes. But the column-like Ti crystals recrystallized during further processing, altered the [001] alignment of the crystals to cause the interdiffusion of Ti and Al. The reactions between Ti and Al took place subsequently and formed the intemetallic Al3Ti, Al5Ti2, TiAl, and Ti3Al layers from the surface inwards. As the diffusion of Al in Ti, Ti3Al, and TiAl decreased in order, the formation of Ti3Al and TiAl layers further retarded the diffusion of Al into the SiO2 layer. It can be concluded that the intermetallic layers play an important role of diffusion barrier that impede the migration of Al across the films.
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B907704A
Abstract: Apatite-like materials are of considerable interest as potential solid oxide fuel cell electrolytes, although their structural vagaries continue to attract significant discussion. Understanding these features is crucial both to explain the oxide ion conduction process and to optimise it. As the composition of putative P6(3)/m apatites with ideal formula [A(I)(4)][A(II)(6)][(BO(4))(6)][X](2) is varied the [A(I)(4)(BO(4))(6)] framework will flex to better accommodate the [A(II)(6)X(2)] tunnel component through adjustment of the A(I)O(6) metaprism twist angle (varphi). The space group theory prescribes that framework adaptation during phase changes must lead to one of the maximal non-isomorphic subgroups of P6(3)/m (P2(1), P2(1)/m, P1[combining macron]). These adaptations correlate with oxygen ion conduction, and become crucial especially when the tunnels are filled by relatively small ions and/or partially occupied, and if interstitial oxygens are located in the framework. Detecting and completely describing these lower symmetry structures can be challenging, as it is difficult to precisely control apatite stoichiometry and small departures from the hexagonal metric may be near the limits of detection. Using a combination of diffraction and spectroscopic techniques it is shown that lanthanum strontium germanate oxide electrolytes crystallise as triclinic (A), monoclinic (M) and hexagonal (H) bi-layer pseudomorphs with the composition ranges: [La(10-x)Sr(x)][(GeO(4))(5+x/2)(GeO(5))(1-x/2)][O(2)] (0 <or=x<or= 1) apatite-2A[La(10-x)Sr(x)][(GeO(4))(5+x/2)(GeO(5))(1-x/2)][O(2)] (1 <or=x<or= 2) apatite-2M[La(10-x)Sr(x)][(GeO(4))(6)][O(2)][H(delta)] (2 <or=x<or= 2.96) apatite-2M[La(10-x)Sr(x)][(GeO(4))(6)][O(2)][H(delta)] (2.96 <or=x<or= 5.32) apatite-2HFurthermore, at typical fuel cell operating temperatures apatite-2A and apatite-2M will transform to apatite-2H, with the latter showing the highest conduction. The results show that small twist angles and high symmetry enhance oxygen mobility with these properties tailored by adjusting the relative size of the framework to tunnel. This information can hence aid in the design of new materials with improved oxide ion conductivity.
Publisher: Cambridge University Press (CUP)
Date: 18-03-2019
DOI: 10.1017/S0885715619000150
Abstract: Apatite-type materials A I 4 A II 6 (BO 4 ) 6 X 2 have two unique cations sites A I and A II , which can host large mono-, di- tri- and tetra-valent cations. The average cation radii will affect the twist angle and lattice constants. However, there are few reports on the influence of B site substitutions on the twist angle and lattice parameters. It is believed that the lattice constant variation as a function of B site substitutions may not follow the same twist-angle model as proposed for A site. This work reports our results on the crystal chemistry of synthetic apatite Ca 10 (V x P 1−x O 4 ) 6 F 2 obtained through the crystal structure characterization using Rietveld refinement and high-resolution transmission electron microscopy. The quantification of vanadium hosphorus partitioning in BO 4 tetrahedra showed that equilibrium with more than 70% substitution of phosphorous by vanadium was difficult to achieve unless longer annealing (about 1 week at 900 °C) was employed. In comparison with the apatites with different ionic radii at A I and A II sites, Ca 10 (V x P 1−x O 4 ) 6 F 2 apatites with different ionic radii at B site show little twist angle variation for the whole series, which indicates that the dilation of unit cell constants is mainly because of the expansions of BO 4 tetrahedra when A site cation is fixed.
Publisher: Mineralogical Association of Canada
Date: 12-2008
Publisher: Elsevier BV
Date: 08-2012
Publisher: IOP Publishing
Date: 19-05-2002
Publisher: American Chemical Society (ACS)
Date: 25-12-2003
DOI: 10.1021/CM0348287
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C001612H
Abstract: The crystal structures of the ferric carbonate-hydroxyapatite (Fe-CHAp) and oxyapatite (Fe-OAp) pseudomorphs were investigated by powder neutron diffraction and Fourier transform infrared spectroscopy. At low iron loadings, Fe-CHAp (x = 0.1) is A-B type carbonate apatite-2H, where atmospheric CO(2) displaces tunnel hydroxyl and framework phosphate (Ca(2+) + 2PO(4)(3-) --> square(Ca) + 2CO(3)(2-) and Ca(2+) + OH(-) --> Fe(3+) + CO(3)(2-)), while Fe-CHAp (x = 0.2) is A type carbonate apatite-2M. For high iron loadings (x = 0.5), near the solubility limit, Fe(3+) incorporation includes concomitant oxidation of hydroxyl groups (Ca(2+) + OH(-) --> Fe(3+) + O(2-)). The discontinuity in the lattice metric at x approximately 0.2 together with a progressive reduction of OH(-) and CO(3)(2-), substantiates these incorporation mechanisms. The general formula of Fe-CHAp is [Ca(4-x)(F)Fe(x)][Ca(6-y)(T) square(y)][(PO(4))(6-y)(CO(3))(y)][(OH(4))(2-x)(CO(3))(x)] (0 < or = x < or = 0.2, 0 < or = y < or = 0.2) and Fe-OAp is [Ca(3.8)(F)Fe(0.2)][Ca(6-x)(T)Fe(x)][(PO(4))][O(0.2+x)(OH)(1.8-x)] (0 < x 27.(0) degrees, monoclinic and triclinic structures are preferable.
Publisher: American Chemical Society (ACS)
Date: 16-07-2018
DOI: 10.1021/ACS.INORGCHEM.8B01160
Abstract: Vanadate ellestadites Ca
Publisher: IEEE
Date: 2005
Publisher: Elsevier BV
Date: 06-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0NR00159G
Abstract: Uniform SnO(2) nanorod arrays were deposited on a 4 inch SiO(2)/Si wafer by plasma-enhanced chemical vapor deposition (PEVCD) at low deposition temperature of around 300 degrees C. The SnO(2) nanorods were connected at the roots, thus the nanorod sensors could be fabricated by a feasible way compatible with microelectronic processes. The surface of the sensors was modified by Pt nanoparticles deposited by dip coating and sputtering, respectively. The sensing properties of the Pt-modified SnO(2) nanorod sensors to CO and H(2) gases were comparatively studied. After surface modification of Pt, the sensing response to CO and H(2) gases increased dramatically. The 2 nm Pt-modified SnO(2) nanorod sensors by sputtering showed the best sensing performance. By increasing Pt thickness from 2 nm up to 20 nm, the optimal working temperature decreased by 30 degrees C while the sensing response also decreased by about 4 times. Comparing these two Pt modification approaches by dip coating and sputtering, both could achieve comparable promotion effect if the Pt thickness can be controlled around its optimal value. The deposition technique of SnO(2) nanorod arrays by PECVD has good potential for scale-up and the fabrication process of nanorod sensors possesses simplicity and good compatibility with contemporary microelectronics-based technology.
Publisher: Elsevier BV
Date: 07-2009
Publisher: The Electrochemical Society
Date: 2006
DOI: 10.1149/1.2168289
Publisher: American Chemical Society (ACS)
Date: 21-08-2017
Publisher: Elsevier BV
Date: 10-1991
Publisher: Oxford University Press (OUP)
Date: 08-2008
DOI: 10.1017/S143192760808313X
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008
Publisher: American Chemical Society (ACS)
Date: 11-02-2010
DOI: 10.1021/LA904751Q
Abstract: We demonstrate a simple synthetic strategy for the fabrication of single-phase rare earth (RE) doped gadolinium oxide (Gd(2)O(3):RE where RE = terbium (Tb), ytterbium (Yb), and erbium (Er)) nanorods (NRs) as multimodal imaging probes. The NRs are ultranarrow and exhibit both emission and magnetic characteristics. The Tb-doped and Yb/Er-codoped Gd(2)O(3) NRs exhibit down- and up-conversion fluorescence respectively, and also exhibit paramagnetism. Importantly, these codoped NRs possess excellent magnetic characteristics, as shown in their longitudinal relaxation time (T1) -weighted image contrast, which is closer to that of commercial Gadovist for magnetic resonance imaging (MRI) applications. This property opens up new avenues in the development of contrast agents.
Publisher: Elsevier BV
Date: 12-2004
Publisher: American Chemical Society (ACS)
Date: 03-09-2010
DOI: 10.1021/JA1058923
Abstract: The excellent performance of hydroxyapatite, a novel non-precious metal catalyst, for formaldehyde (HCHO) combustion at room temperature is reported. Temperature-programmed surface reaction results indicated that hydroxyl groups bonded with the channel Ca(2+) may be responsible for adsorption/activation of HCHO.
Publisher: American Chemical Society (ACS)
Date: 03-07-2017
Publisher: Informa UK Limited
Date: 30-04-2010
Publisher: Trans Tech Publications, Ltd.
Date: 04-2006
DOI: 10.4028/WWW.SCIENTIFIC.NET/SSP.111.183
Abstract: Mechanochemical process was employed to prepare Fe/MgO and Fe/NaCl nanocomposites. The carbon nanostructures (nanotubes and carbon-encapsulated Fe nanoparticles) were successfully synthesized using two nanocomposites as the catalyst. Our wok revealed that the morphology of Fe nanoparticles in the Fe/MgO nanocomposites depended on the distribution and particle size of iron oxides in the precursors. The size of Fe nanoparticles greatly affected their catalytic properties and the morphologies of carbon nanotubes. The successful carbon encapsulation of Fe nanoparticles was achieved by using the mechanochemically derived Fe/NaCl catalyst.
Publisher: Elsevier BV
Date: 04-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B506799E
Publisher: Wiley
Date: 21-04-2016
Abstract: We report the pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin-orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO3 -type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase-mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction.
Publisher: The Electrochemical Society
Date: 2007
DOI: 10.1149/1.2769828
Publisher: Elsevier BV
Date: 02-2000
Publisher: American Chemical Society (ACS)
Date: 25-07-2006
DOI: 10.1021/ES0601033
Abstract: Stabilization efficiencies of spinel-based construction ceramics incorporating simulated nickel-laden waste sludge were evaluated and the leaching behavior of products investigated. To simulate the process of immobilization, nickel oxide was mixed alternatively with gamma-alumina, kaolinite, and hematite. These tailoring precursors are commonly used to prepare construction ceramics in the building industry. After sintering from 600 to 1480 degrees C at 3 h, the nickel aluminate spinel (NiAl204) and the nickel ferrite spinel (NiFe204) crystallized with the ferrite spinel formation commencing about 200-300 degrees C lower than for the aluminate spinel. All the precursors showed high nickel incorporation efficiencies when sintered at temperatures greater than 1250 degrees C. Prolonged leach tests (up to 26 days) of product phases were carried out using a pH 2.9 acetic acid solution, and the spinel products were invariably superior to nickel oxide for immobilization over longer leaching periods. The leaching behavior of NiAl2O4 was consistent with congruent dissolution without significant reprecipitation, but for NiFe2O4, ferric hydroxide precipitation was evident. The major leaching reaction of sintered kaolinite-based products was the dissolution of cristobalite rather than NiAl2O4. This study demonstrated the feasibility of transforming nickel-laden sludge into spinel phases with the use of readily available and inexpensive ceramic raw materials, and the successful reduction of metal mobility under acidic environments.
Publisher: Trans Tech Publications, Ltd.
Date: 2005
DOI: 10.4028/WWW.SCIENTIFIC.NET/JMNM.23.383
Abstract: Mechanical milling was employed to prepare the nanocomposite precursors for the catalytic growth of carbon nanostructures. For alumina substrates, our study showed that mechanical-millingderived catalyst precursors possessed high hydrogen reduction efficiency that in turn enabled the high yield of CNTs. The alloying effects presented by the mechanical milling could accelerate the substitutional reactions between the parent oxides and thus the quality of CNTs was apparently improved. In addition, by using water-soluble substrates such as NaCl, we realized large-scale formation of carbon-encapsulated metal nanoparticles (CEMNs) that can be completely separated by a simple washing process. It was found that the morphologies of as-obtained carbon nanostructures were strongly dependent on the substrate effects. By selecting different salt substrates, we can strategically change the morphologies of the as-obtained nanostructures, from CNTs to CEMNs and the intermediate state between CNTs and CEMNs, such as quasi-nanocages.
Publisher: Elsevier BV
Date: 02-2011
Publisher: International Union of Crystallography (IUCr)
Date: 17-01-2008
DOI: 10.1107/S0108768107066402
Abstract: The crystal chemistries of synthetic mimetite, Pb 10 (As 5+ O 4 ) 6 (Cl 2 − x O x /2 ), a neutral apatite, and finnemanite, Pb 10 (As 3+ O 3 ) 6 Cl 2 , a reduced apatite, were characterized using a combination of X-ray powder diffraction, neutron diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Both phases conform to hexagonal P 6 3 / m symmetry however, the temperature-driven transformation of clinomimetite to mimetite described earlier was not confirmed. The average mimetite structure is best described through the introduction of partially occupied oxygen sites. A better understanding of the mixed arsenic speciation in apatites can guide the formulation of waste form ceramics and improve models of long-term durability after landfill disposal.
Publisher: AIP Publishing
Date: 07-05-2002
DOI: 10.1063/1.1479213
Abstract: A chemical method has been developed for synthesizing boron nitride nanowires through the reaction of a mixture gas of nitrogen (N2) and ammonia (NH3) over nanoscale α-FeB particles at 1100 °C. Boron content in the product comes from the α-FeB catalyst itself. Transmission electron microscopic image indicates an abundant quantity of BN nanowires with diameter about 20 nm and length up to several tens of microns. The product has also been characterized by high-resolution electron microscopy and electron energy loss spectrometer. The perfectly straight lattice fringes with an interlayer spacing of about 0.333 nm corresponding to d0002 spacing of h-BN indicate that the BN nanowires are well crystallized. Also, a growth mechanism has been speculated.
Publisher: American Chemical Society (ACS)
Date: 03-05-2012
DOI: 10.1021/IC300585T
Abstract: Melilite-type [A(2)](2)[B(I)](2)[B(II)(2)O(7)](2) gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa](2)[Ga](2)[Ga(2)O(7)](2), grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga(2)O(7)] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P42(1)m(α, α, 0)00s(α, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) Å, c = 5.2641(3) Å, onto which modulation vectors are superimposed: q(1) = α (a* + b*), q(2) = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.
Publisher: American Chemical Society (ACS)
Date: 09-05-2007
DOI: 10.1021/JP071877O
Publisher: Elsevier BV
Date: 10-2014
Publisher: Elsevier BV
Date: 11-2014
Publisher: Japan Institute of Metals
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 07-07-2006
DOI: 10.1021/ES052324Z
Abstract: The feasibility of stabilizing nickel-laden sludge from commonly available Al-rich ceramic precursors was investigated and accomplished with high nickel incorporation efficiency. To simulate the process, nickel oxide was mixed alternatively with gamma-alumina, corundum, kaolinite, and mullite and was sintered from 800 to 1480 degrees C. The nickel aluminate spinel (NiAl2O4) was confirmed as the stabilization phase for nickel and crystallized with efficiencies greater than 90% for all precursors above 1250 degrees C and 3-h sintering. The nickel-incorporation reaction pathways with these precursors were identified, and the microstructure and spinel yield were investigated as a function of sintering temperature with fixed sintering time. This study has demonstrated a promising process for forming nickel spinel to stabilize nickel-laden sludge from a wide range of inexpensive ceramic precursors, which may provide an avenue for economically blending waste metal sludges via the building industry processes to reduce the environmental hazards of toxic metals. The correlation of product textures and nickel incorporation efficiencies through selection of different precursors also provides the option of tailoring property-specific products.
Publisher: International Union of Crystallography (IUCr)
Date: 18-03-2004
DOI: 10.1107/S0108768104001843
Abstract: The synthetic vanadinites (Pb x Ca 10− x )(VO 4 ) 6 (F 1−2 y O y □ y ) 2 , 0.57 x 9 and 0.10 y 0.47, adopt the P 6 3 / m apatite structure with 9.7835 (3) ≤ a ≤ 10.0531 (1) Å and 7.0318 (2) ≤ c ≤ 7.3033 (1) Å. The calcium endmember is monoclinic, space group P 2 1 / m , with a = 9.7370 (3), b = 9.7358 (4), c = 7.00572 (9) Å, γ = 120.002 (5)°. For mixed metal compounds ( x ≠ 0) the partitioning of calcium and lead over the A I (4 f ) and A II (6 h ) positions is nonstoichiometric, with lead preferentially favouring the larger A II site at a partitioning coefficient k Pb ( A I / A II ) ≃ 0.33 for all x 7. A miscibility gap exists for 2 x 3. Trends in crystallographic parameters can be correlated through consideration of the A I O 6 metaprism twist angle (φ) that can be used to derive ideal cell parameters from triangular anion networks.
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B403530E
Publisher: Springer Science and Business Media LLC
Date: 15-07-2011
Publisher: Mineralogical Society
Date: 04-2014
DOI: 10.1180/MINMAG.2014.078.2.07
Abstract: Lead-containing (Pb- B-X )-2 H apatites encompass a number of [ A F ] 4 [ A T ] 6 [( BO 4 ) 6 ] X 2 compounds used for waste stabilization, environmental catalysis and ion conduction, but the influence of the stereochemically active lone-pair electrons of Pb 2+ on crystal chemistry and functionality is poorly understood. This article presents a compilation of existing structural data for Pb apatites that demonstrate paired electrons of Pb 2+ at both the A F and A T results in substantial adjustments to the Pb F O 6 metaprism twist angle, φ. New structure refinements are presented for several natural varieties as a function of temperature by single-crystal X-ray diffraction (XRD) of vanadinite-2 H (ideally Pb 10 (VO 4 ) 6 C l2 ), pyromorphite-2 H (Pb 10 (PO 4 ) 6 Cl 2 ), mimetite- 2H/M (Pb 10 (As 5+ O 4 ) 6 Cl 2 ) and finnemanite-2 H (Pb 10 (As 3+ O 3 ) 6 Cl 2 ). A supercell for mimetite is confirmed using synchrotron single-crystal XRD. It is suggested the superstructure is necessary to accommodate displacement of the stereochemically active 6s 2 lone-pair electrons on the Pb 2+ that occupy a volume similar to an O 2− anion. We propose that depending on the temperature and concentration of minor substitutional ions, the mimetite superstructure is a structural adaptation common to all Pb-containing apatites and by extension apatite electrolytes, where oxide ion interstitials are found at similar positions to the lonepair electrons. It is also shown that plumbous apatite framework flexes substantially through adjustments of the Pb F O 6 metaprism twist-angles (φ) as the temperature changes. Finally, crystalchemical [100] zoning observed at submicron scales will probably impact on the treatment of diffraction data and may account for certain inconsistencies in reported structures.
Publisher: International Union of Crystallography (IUCr)
Date: 17-07-2007
DOI: 10.1107/S0108768107024317
Abstract: Oxygen conduction at low temperatures in apatites make these materials potentially useful as electrolytes in solid-oxide fuel cells, but our understanding of the defect structures enabling ion migration is incomplete. While conduction along [001] channels is dominant, considerable inter-tunnel mobility has been recognized. Using neutron powder diffraction of stoichiometric `La 10 (GeO 4 ) 6 O 3 ', it has been shown that this compound is more correctly described as an La 10 (GeO 4 ) 5 (GeO 5 )O 2 apatite, in which high concentrations of interstitial oxygen reside within the channel walls. It is suggested that these framework interstitial O atoms provide a reservoir of ions that can migrate into the conducting channels of apatite, via a mechanism of inter-tunnel oxygen diffusion that transiently converts GeO 4 tetrahedra to GeO 5 distorted trigonal bipyramids. This structural modification is consistent with known crystal chemistry and may occur generally in oxide apatites.
Publisher: American Society of Mechanical Engineers
Date: 26-06-2016
Abstract: Generation III/III+ nuclear reactors operate with working fluid under subcritical conditions (Tc = 647K, pc = 22.115MPa). The efficiency, limited by the ratio of source and sink temperatures, is restricted by operating below the critical temperature. The supercritical water reactors (SCWRs) are able to rise efficiency limit while operating at the supercritical conditions. The amount of energy carried by working fluid is higher leading to potential efficiency improvement of nearly 30% above current nuclear stations. Therefore, rendering nuclear energy as one of the most efficient decarbonized electrical energy sources with efficiency of 45% and capacity factor of ca. 90%. Typical capacity factors of competing wind turbines and solar PV cells reaches 45% and 15% while the efficiencies 50% and 45%, respectively. In a subcritical reactor a uniform heat flux is generated due to relatively constant fuel moderation. However, due to a change of density during transition from sub- to supercritical conditions, the fuel moderation is uneven along the fuel rod and results in a non-uniform heat generation. The literature on SCWR neutronics suggests higher heat generation at the fuel channel entrance. In this paper we simulated for the first time such non-uniform heat flux generated in a SCWR, we analyze the impacts of such flux on the working medium flow and suggest ways to mitigate negative impacts of non-uniform heat flux. The study was conducted with use of Computational Fluid Dynamics (CFD) software. Obtained results show that the shape of heat flux curve along the channel highly influences the wall temperature distribution along the fuel channel. The differences in maximum wall temperatures can be up to 200K for different curve’s shape. Moreover, the maximum wall temperature is always higher than in default case i.e. when uniform heat flux is applied. It is possible to control the wall temperature distribution by adjusting the shape of heat flux along the axis. Such adjustment can be made by using different enrichment levels along the fuel rod axis, unfortunately any change in power distribution caused rapid temperature increase at the upstream location.
Publisher: Wiley
Date: 24-05-2011
Publisher: International Union of Crystallography (IUCr)
Date: 22-01-2010
DOI: 10.1107/S0108768109053981
Abstract: Certain complex structures are logically regarded as intergrowths of chemically or topologically discrete modules. When the proportions of these components vary systematically a polysomatic series is created, whose construction provides a basis for understanding defects, symmetry alternation and trends in physical properties. Here, we describe the polysomatic family A 5 N B 3 N O 9 N + 6 X N δ (2 ≤ N ≤ ∞) that is built by condensing N apatite modules ( A 5 B 3 O 18 X δ ) in configurations to create B n O 3 n + 1 (1 ≤ n ≤ ∞) tetrahedral chains. Hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] typifies a widely studied polysome where N = 2 and the tetrahedra are isolated in A 10 ( B O 4 ) 6 X 2 compounds, but N = 3 A 15 ( B 2 O 7 ) 3 ( B O 4 ) 3 X 3 (ganomalite) and N = 4 A 20 ( B 2 O 7 ) 6 X 4 (nasonite) are also known, with the X site untenanted or partially occupied as required for charge balance. The apatite modules, while topologically identical, are often compositionally or symmetrically distinct, and an infinite number of polysomes is feasible, generally with the restriction being that an A : B = 5:3 cation ratio be maintained. The end-members are the N = 2 polysome with all tetrahedra separated, and N = ∞, in which the hypothetical compound A 5 B 3 O 9 X contains infinite, corner-connected tetrahedral strings. The principal characteristics of a polysome are summarized using the nomenclature apatite -( A B X )- NS , where A / B / X are the most abundant species in these sites, N is the number of modules in the crystallographic repeat, and S is the symmetry symbol (usually H , T , M or A ). This article examines the state-of-the-art in polysomatic apatite synthesis and crystallochemical design. It also presents X-ray and neutron powder diffraction investigations for several polysome chemical series and examines the prevalence of stacking disorder by electron microscopy. These insights into the structure-building principles of apatite polysomes will guide their development as functional materials.
Publisher: Wiley
Date: 20-06-2012
Publisher: JMIR Publications Inc.
Date: 26-03-2020
Abstract: espiratory disease is the third most common cause of death in New Zealand, with Pacific people living in New Zealand bearing the greatest burden of this type of disease. Although some epidemiological outcomes are known, we lack the specifics required to formulate targeted and effective public health interventions. The Pacific Islands Families (PIF) birth cohort study is a study that provides a unique source of data to assess lung function and current respiratory health among participants entering early adulthood and to examine associations with early life events during critical periods of growth. his paper aims to provide an overview of the design, methods, and scope of the i Respiratory Health of Pacific Youth Study /i , which uses the overall PIF study cohort aged 18-19 years. rom 2000-2019, the PIF study has followed, from birth, the growth, and the development of 1398 Pacific children born in Auckland, New Zealand. Participants were nested within the overall PIF study (at ages 18-19 years) from June 2018, and assessments were undertaken until mid-November 2019. The assessments included respiratory and general medical histories, a general physical examination, assessment of lung function (forced expiratory volume and forced vital capacity), self-completed questionnaires (St George’s Respiratory Questionnaire, European Quality of Life 5 Dimensions-3 Level, Epworth Sleepiness Scale for Children and Adolescents, and Leicester Cough Questionnaire), blood tests (eosinophils, Immunoglobulin E, Immunoglobulin G, Immunoglobulin A, Immunoglobulin M, and C-reactive protein), and chest x-rays. Noninferential analyses will be carried out on dimensionally reduced risk and protective factors and confounders. ata collection began in June 2018 and ended in November 2019, with a total of 466 participants recruited for submission of the paper. Collection and collation of chest x-ray data is still underway, and data analysis and expected results will be published by November 2020. his is the first longitudinal observational study to address the burden of respiratory disease among Pacific youth by determining factors in early life that impose long-term detriments in lung function and are associated with the presence of respiratory illness. Identifying risk factors and the magnitude of their effects will help in adopting preventative measures, establishing whether any avoidable risks can be modified by later resilient behaviors, and provide baseline measurements for the development of respiratory disease in later adult life. The study results can be translated into practice guidelines and inform health strategies with immediate national and international impact. ERR1-10.2196/18916
Publisher: AIP Publishing
Date: 04-12-2006
DOI: 10.1063/1.2402227
Abstract: The authors previously reported an unusual phenomenon of strain relaxation accompanied by a reduction in threading dislocation density (TDD) on a Si0.77Ge0.23 layer grown on top of alternating layers of Si0.77Ge0.23∕Si0.76Ge0.23C0.01 [Appl. Phys. Lett. 88, 041915 (2006)]. In this letter, the mechanism by which SiGeC domains, formed during annealing at 1000°C, assist in TDD annihilation process is further investigated. A g∙b analysis of transmission electron microscope images showed the formation of pure edge dislocations from the reaction of two 60° misfit dislocations, which glide and/or slip with the assistance of the localized interfacial strain of the SiGeC domains. TDD reduction in this structure is thus due to the annihilation of threading dislocation arms during misfit dislocation combination.
Publisher: Trans Tech Publications, Ltd.
Date: 2005
DOI: 10.4028/WWW.SCIENTIFIC.NET/JMNM.23.367
Abstract: Nanohybrid thin films consisting of nanocrystalline TiO2 particles in poly(methyl methacrylate)(PMMA) were successfully synthesized by in-situ sol-gel and polymerization assisted by spin coating. Using titanium isoproproxide (Ti-iP), methyl methacrylate (MMA) and 3-(trimethoxysily)propyl methacrylate (MSMA) as the starting materials, nanohybrids containing up to 60% Ti-iP in PMMA were realized. The resulting nanohybrid thin films coated on quartz substrates are optically transparent and demonstrate nonlinear optical behaviour, where their nonlinear absorption increases with the loading of Ti-iP in PMMA, as confirmed by Z-scan measurements. Using pump-probe technique, these thin films are shown to exhibit an ultrafast relaxation time of ~1.5 picosecond.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4TA05132G
Abstract: Melilite, a tetrahedral-layered structure, shows strong anisotropic oxygen ion conduction at intermediate temperatures, which can be controlled by increasing the number of interstitial oxygen and reducing the size of interlayer cations.
Publisher: IOP Publishing
Date: 27-06-2006
Publisher: International Union of Crystallography (IUCr)
Date: 18-03-2004
DOI: 10.1107/S0108768104001831
Abstract: The synthetic vanadinites (Pb x Ca 10− x )(VO 4 ) 6 F 2δ , 1 x 9, adopt a P 6 3 / m apatite structure with 9.7590 (1) ≤ a ≤ 10.1179 (1) Å and 7.0434 (3) ≤ c ≤ 7.4021 (1) Å. The partitioning of calcium and lead over the A I (4 f ) and A II (6 h ) positions is nonstoichiometric with lead preferentially entering the larger A II site. High-resolution electron microscopy showed that s les annealed for 10 h at 1073 K are in disequilibrium with calcium- and lead-rich microdomains co-existing at unit-cell scales. For (Pb 5 Ca 5 )(VO 4 ) 6 F 2δ , sintering in excess of 2 weeks is required for the metals to order macroscopically. As annealing progresses, c / a , the partitioning coefficient k Pb ( A I / A II ) and the A I O 6 metaprism twist angle (φ) adjust cooperatively to enlarge the apatite channel, and thereby accommodate higher lead content. These results demonstrate that φ is a sensitive measure of disequilibrium and a useful device for monitoring changes in apatite topology as a function of composition.
Publisher: Elsevier BV
Date: 07-2011
Publisher: American Chemical Society (ACS)
Date: 25-03-2016
DOI: 10.1021/JACS.5B13409
Abstract: Rare earth silicate apatites are one-dimensional channel structures that show potential as electrolytes for solid oxide fuel cells (SOFC) due to their high ionic conductivity at intermediate temperatures (500-700 °C). This advantageous property can be attributed to the presence of both interstitial oxygen and cation vacancies, that create diffusion paths which computational studies suggest are less tortuous and have lower activation energies for migration than in stoichiometric compounds. In this work, neutron diffraction of Nd(28+x)/3AlxSi6-xO26 (0 ≤ x ≤ 1.5) single crystals identified the locations of oxygen interstitials, and allowed the deduction of a dual-path conduction mechanism that is a natural extension of the single-path sinusoidal channel trajectory arrived at through computation. This discovery provides the most thorough understanding of the O(2-) transport mechanism along the channels to date, clarifies the mode of interchannel motion, and presents a complete picture of O(2-) percolation through apatite. Previously reported crystallographic and conductivity measurements are re-examined in the light of these new findings.
Publisher: Wiley
Date: 27-11-2017
Abstract: High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (<10 nm) perovskite nanoplates, are retained and these exhibit simultaneous photoluminescence emission enhancing (a 15-fold enhancement in the photoluminescence) and carrier lifetime shortening (from ≈18.3 ± 0.8 to ≈7.6 ± 0.5 ns) after releasing of pressure from 11 GPa. This pressure-induced comminution of hybrid perovskite NCs and a subsequent amorphization-recrystallization treatment offer the possibilities of engineering the advanced hybrid perovskites with specific properties.
Publisher: Elsevier BV
Date: 05-2017
Publisher: IOP Publishing
Date: 15-02-2007
Publisher: Springer Science and Business Media LLC
Date: 09-2008
Abstract: The photocatalytic degradation of methylene blue (MB) over a porous titania-hydroxyapatite (HAp) composite under ultraviolet radiation was studied. The catalyst was prepared by coating porous HAp with a titanium butoxide [Ti(OBu) 4 ] sol at titania loadings of 17–49 wt%. Quantitative powder x-ray diffraction showed higher proportions of anatase as the calcination temperature increased from 500 to 800 °C due to crystallization of an amorphous precursor. The transformation of anatase to rutile was delayed until 900 °C, demonstrating the high thermal stability of the composite. Decomposition of HAp to α- and β- tricalcium phosphates takes place at 900 °C and is accompanied by the formation of perovskite at 1000 °C. A systematic study of the influence of calcination temperature and titania:HAp ratios demonstrated that for the optimal material, a surface area of 100 m 2 g −1 was obtained at a titania loading of 49 wt% and calcination temperature of 600 °C. A highly dispersed suspension of finely ground titania-HAp enhanced the photodegradation of MB, allowed a high percentage recovery of catalyst, and was shown to be recyclable.
Publisher: Elsevier BV
Date: 08-2015
Publisher: Springer Science and Business Media LLC
Date: 03-2008
DOI: 10.1007/BF03215622
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3TA10518K
Publisher: Elsevier BV
Date: 04-2004
Publisher: Elsevier BV
Date: 07-2013
Publisher: Elsevier BV
Date: 05-2002
Publisher: Springer Science and Business Media LLC
Date: 24-08-2023
DOI: 10.1007/S40820-023-01169-4
Abstract: Electrocatalytic synthesis under mild conditions has become increasingly important as one of the practical alternatives for industrial applications, especially for the green ammonia (NH 3 ) industry. A properly engineered electrocatalyst plays a vital role in the realization of superior catalytic performance. Among various types of promising nanomaterials, metal–organic frameworks (MOFs) are competitive candidates for developing efficient electrocatalytic NH 3 synthesis from simple nitrogen-containing molecules or ions, such as N 2 and NO 3 − . In this review, recent advances in the development of electrocatalysts derived from MOFs for the electrosynthesis of NH 3 are collected, categorized, and discussed, including their application in the N 2 reduction reaction (NRR) and the NO 3 − reduction reaction (NO 3 RR). Firstly, the fundamental principles are illustrated, such as plausible mechanisms of NH 3 generation from N 2 and NO 3 − , the apparatus of corresponding electrocatalysis, parameters for evaluation of reaction efficiency, and detection methods of yielding NH 3 . Then, the electrocatalysts for NRR processes are discussed in detail, including pristine MOFs, MOF-hybrids, MOF-derived N-doped porous carbons, single atomic catalysts from pyrolysis of MOFs, and other MOF-related materials. Subsequently, MOF-related NO 3 RR processes are also listed and discussed. Finally, the existing challenges and prospects for the rational design and fabrication of electrocatalysts from MOFs for electrochemical NH 3 synthesis are presented, such as the evolution of investigation methods with artificial intelligence, innovation in synthetic methods of MOF-related catalysts, advancement of characterization techniques, and extended electrocatalytic reactions. "Image missing"
Publisher: Wiley
Date: 28-04-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0TC02038A
Abstract: Novel Cs-containing triple cation perovskite nanocrystals produce high-performance LEDs as a result of improved surface passivation and environmental stability.
Publisher: Mineralogical Society of America
Date: 24-09-2012
DOI: 10.2138/AM.2012.4069
Publisher: American Chemical Society (ACS)
Date: 28-11-2007
DOI: 10.1021/IC700863G
Abstract: ZnO nanocrystals, nanorods, and tablets were prepared at 110, 140, and 180 degrees C in a water-ethanol system. Nanorods (~2 x 40 nm) arranged in serpentine morphologies formed by the oriented coalescence of anhedral ZnO nanocrystals (~3.5 nm diameter), while tabular ZnO grew by [1210] textural attachment of the nanorods. The development of these crystal habits is believed to proceed via a dissolution and growth mechanism mediated by a transient amorphous phase. Materials synthesized at intermediate temperatures (125 and 160 degrees C) possessed microstructures containing mixed crystal forms in the expected orientation relationship. Photoluminescent spectra of the nanocrystals and nanorods showed blue shifts of 0.16 and 0.13 eV with respect to the bulk ZnO band gap (3.26 eV) due to quantum confinement, with the narrow emission peaks typical of particles possessing uniform size and shape. The larger tablets displayed a less energetic emission (3.10 eV) ascribed to exciton-exciton collisions.
Publisher: Elsevier BV
Date: 09-2018
Publisher: International Union of Crystallography (IUCr)
Date: 08-09-2009
DOI: 10.1107/S0021889809031021
Abstract: The performance of photocatalytic titania powders is regulated, in part, by nonstoichiometry and the proportions of the crystalline and amorphous components. These variables can be quantitatively established by Rietveld analysis of diffraction data when internal standards are used to fix absolutely the crystallochemical parameters during quantitative phase analysis and to correct for mass absorption. Here, fixed-wavelength neutron and multiple-wavelength X-ray powder diffraction are used to assess phase development in alkoxide-derived titania gel as a function of temperature. In this manner, it is shown that the amorphous gel is progressively replaced by anatase for temperatures ≤ 773 K, and that during the reconstructive transition to rutile (773–873 K) aperiodicity increases as anatase is broken down to clusters of TiO 6 octahedra, with a fraction (∼10 wt%) of this short-range order persisting to 1273 K. Microabsorption correlates with X-ray energy, leading to systematic aberrations in the Rietveld scale factors connected to microstructural evolution which accompanies phase development during heat treatment. These changes are consistent with encapsulation of anatase and rutile by ubiquitous non-diffracting materials. The appearance of significant quantities of an intervening disordered phase during the dimorph transformation is supportive of recent kinetic models however, its impact on catalytic activity remains to be determined.
Publisher: American Chemical Society (ACS)
Date: 25-01-2016
DOI: 10.1021/JACS.5B11373
Abstract: CeNbO4.25 is reported to exhibit fast oxygen ion diffusion at moderate temperatures, making this the prototype of a new class of ion conductor with applications in a range of energy generation and storage devices. To date, the mechanism by which this ion transport is achieved has remained obscure, in part due to the long-range commensurately modulated structural motif. Here we show that CeNbO4.25 forms with a unit cell ∼12 times larger than the stoichiometric tetragonal parent phase of CeNbO4 as a result of the helical ordering of Ce(3+) and Ce(4+) ions along z. Interstitial oxygen ion incorporation leads to a cooperative displacement of the surrounding oxygen species, creating interlayer "NbO6" connectivity by extending the oxygen coordination number to 7 and 8. Molecular dynamic simulations suggest that fast ion migration occurs predominantly within the xz plane. It is concluded that the oxide ion diffuses anisotropically, with the major migration mechanism being intralayer however, when obstructed, oxygen can readily move to an adjacent layer along y via alternate lower energy barrier pathways.
Publisher: American Chemical Society (ACS)
Date: 02-05-2014
DOI: 10.1021/IC402370E
Abstract: Apatite-type oxides ([A(I)4][A(II)6][(BO4)6]O2), particularly those of the rare-earth silicate and germanate systems, are among the more promising materials being considered as alternative solid oxide fuel cell electrolytes. Nonstoichiometric lanthanum silicate and germanate apatites display pure ionic conductivities exceeding those of yttria-stabilized zirconia at moderate temperatures (500-700 °C). In this study, mixed Si/Ge-based apatites were prepared by hydrothermal synthesis under mild conditions rather than the conventional solid-state method at high temperatures. Single-phase and highly crystalline nanosized apatite powders were obtained with the morphology changing across the series from spheres for the Si-based end member to hexagonal rods for the Ge-based end member. Powder X-ray and neutron analysis found all of these apatites to be hexagonal (P63/m). Quantitative X-ray microanalysis established the partial (<15 at%) substitution of La(3+) by Na(+) (introduced from the NaOH hydrothermal reagent), which showed a slight preference to enter the A(I) 4f framework position over the A(II) 6h tunnel site. Moreover, retention of hydroxide (OH(-)) was confirmed by IR spectroscopy and thermogravimetric analysis, and these apatites are best described as oxyhydroxyapatites. To prepare dense pellets for conductivity measurements, both conventional heat treatment and spark plasma sintering methods were compared, with the peculiar features of hydrothermally synthesized apatites and the influence of sodium on the ionic conductivity considered.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0DT00690D
Abstract: High oxygen content apatite germanates, La(10)Ge(6-x)W(x)O(27+x), have been prepared by doping on the Ge site with W. In addition to increasing the oxygen content, this doping strategy is shown to result in stabilisation of the hexagonal lattice, and yield high conductivities. Structural studies of La(10)Ge(5.5)W(0.5)O(27.5) show that the interstitial oxygen sites are associated to a different degree with the Ge/WO(4) tetrahedra, leading to five coordinate Ge/W and significant disorder for the oxygen sites associated with these units. Raman spectroscopy studies suggest that in the case of the WO(5) units, the interstitial oxygen is more tightly bonded and therefore not as mobile as in the case of the GeO(5) units, thus not contributing significantly to the conduction process.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-07-2019
Abstract: Tunable PL emission of 2D halide perovskites occurs when pressure-induced anisotropic deformation modifies quantum confinement.
Publisher: American Chemical Society (ACS)
Date: 21-06-2003
DOI: 10.1021/JA035096M
Abstract: High-quality Zn(x)Cd(1-x)Se nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals. With increasing Zn content, a composition-tunable emission across most of the visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. The photoluminescence (PL) properties for the obtained Zn(x)Cd(1-x)Se nanocrystals (PL efficiency of 70-85%, fwhm = 22-30 nm) are comparable to those for the best reported CdSe-based QDs. In particular, they also have good PL properties in the blue spectral range. Moreover, the alloy nanocrystals can retain their high luminescence (PL efficiency of over 40%) when dispersed in aqueous solutions and maintain a symmetric peak shape and spectral position under rigorous experimental conditions. A rapid alloying process was observed at a temperature higher than "alloying point". The mechanism of the high luminescence efficiency and stability of Zn(x)Cd(1-x)Se nanocrystals is explored.
Publisher: Elsevier
Date: 2005
Publisher: American Chemical Society (ACS)
Date: 24-08-2012
DOI: 10.1021/JP304187V
Publisher: Elsevier BV
Date: 12-2011
Publisher: Springer Science and Business Media LLC
Date: 03-2008
DOI: 10.1007/BF03215620
Publisher: Wiley
Date: 07-08-2018
Abstract: The reversible, ultrafast, and multistimuli responsive phase transition of vanadium dioxide (VO
Publisher: American Chemical Society (ACS)
Date: 05-10-2009
DOI: 10.1021/JP906923Z
Publisher: AIP Publishing
Date: 26-09-2011
DOI: 10.1063/1.3644958
Abstract: Nanoscale phase separation was investigated in epitaxial strained BiFeO3 thin films on LaAlO3 single crystal substrate. In biaxial strained thin films, nanoscale mixtures of the tetragonal-like and rhombohedral-like phases occur with a film thickness above 35 nm. For 10-30 nm ultrathin ones, tetragonal-like single phase is confirmed using synchrotron x-ray and the atomic force microscopy studies. However, nanoscale phase separations are still observed in quasi-uniaxial transmission electron microscopy foil specimens for those ultrathin films, indicating the phase separation emerges in a much smaller thickness in uniaxial constraint films than that in biaxial ones.
Publisher: Elsevier BV
Date: 11-2011
Publisher: Elsevier BV
Date: 07-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2003
DOI: 10.1039/B211976E
Publisher: American Chemical Society (ACS)
Date: 14-07-2009
DOI: 10.1021/LA9007262
Abstract: A deposition-precipitation (DP) process was used to prepare silica-titania core-shell pebbles decorated with nanocrystalline gold suitable for low-temperature catalytic oxidation of carbon monoxide (CO). The microstructure, phase content, crystallography, and catalytic activity were correlated with the pH (3-8), aging time (15, 30, 60 min), and heat treatment employed for gold crystallization (200-400 degrees C). A homogeneous metal distribution, high gold loading (3.7-4.4 wt %), and superior interfacial adhesion between gold and titania were obtained when the support pebbles were prepared at 600 degrees C, a temperature lower than that required for the anatase-to-rutile transformation. Nucleation and growth of {111} faceted gold was favored at mid-pH (6.4-8), while smaller crystals (<7.5 nm) were obtained at short aging times (<or=60 min) and low growth temperatures (<or=300 degrees C). Catalytic activity was optimized by homogeneously dispersing gold nanocrystals (3 nm) using pH 6.4 and an aging time of 30 min. These robust materials may offer superior activity and lifetimes when deployed in fluidized bed catalytic cracking units.
Publisher: AIP Publishing
Date: 26-03-2002
DOI: 10.1063/1.1465107
Abstract: Three mechanisms for the formation of Cu diffusion channels in the Ta layer of a Cu/Ta/SiO2/Si structure are proposed. First, it is suggested that stacking faults formed during the recovery process induce localized regions of high internal energy in the Ta layer, from which Cu channels originate. Second, chemical reaction occurs at 800 °C and forms Ta4CuO11 across the Cu/Ta interface in Cu and Ta layers, which opens up channels for Cu diffusion. Third, triple junctions at the grain boundary of the Cu and Cu/Ta interface provide sites for the initiation of channel formation at 800 °C. At 950 °C, these channels in the diffusion barrier are absent, but Ta was oxidized into disordered Ta2O5 that may contain pathways for Cu diffusion.
Publisher: American Chemical Society (ACS)
Date: 11-02-2015
DOI: 10.1021/CM504009D
Publisher: American Chemical Society (ACS)
Date: 14-10-2019
Publisher: Elsevier BV
Date: 2005
Publisher: Wiley
Date: 02-08-2013
DOI: 10.1111/JACE.12489
Publisher: Elsevier BV
Date: 08-2006
DOI: 10.1016/J.JENVMAN.2005.08.026
Abstract: The geographical limitations of Singapore, its restricted natural resources and voluminous municipal and industrial waste streams, make environmental management a major challenge for the island state. In an attempt to find ways to reduce importation of raw materials and the waste sent to landfill, light weight aggregates were produced from marine clay and a CaF(2)-rich semiconductor industry sludge. Aggregates were produced in a bench-scale rotary kiln with three clay/sludge loadings (90/10, 70/30 and 50/50%). All three mixtures showed good bloating behavior during firing and the ceramic pellets (1-1.5cm diameter) had densities well below that required for light-weight aggregates. In the initial tests, the pore sizes of the aggregates were in general too large resulting in high water absorption. Comparisons between the composition of the two waste products and the aggregates showed a significant loss of fluorine (40-60%) during processing a problem which may require flue gas treatment. Leach testing showed that the formed aggregates would not pose a human or environmental hazard in terms of fluorine mobilization.
Publisher: Oxford University Press (OUP)
Date: 08-2002
Publisher: Elsevier BV
Date: 10-2011
Publisher: American Chemical Society (ACS)
Date: 10-08-2005
DOI: 10.1021/CM0505042
Publisher: Elsevier BV
Date: 03-2012
Publisher: Wiley
Date: 08-12-2004
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3RA42246A
Publisher: American Chemical Society (ACS)
Date: 18-10-2006
DOI: 10.1021/ES060972S
Abstract: The capability of three dimensionally ordered macroporous (3DOM) hydroxyapatite, Ca10(PO4)6(OH)2 (HAp), to capture cadmium and lead ions from their respective salt solutions was studied as a function of temperature. Synthesis of 3DOM material was achieved by colloidal crystal templating of polystyrene spheres (1 microm diameter) using calcium nitrate (Ca(NO3)2) and orthophosphoric acid (H3PO4) as precursors. The macroporous product consisted primarily of HAp (>80% depending on the sintering temperature) together with amorphous calcium phosphate. The sorption ability of 3DOM material to Cd/Pb ion was benchmarked against HAp powder prepared via the same route without the template. On the basis of quantitative X-ray diffraction (XRD) and analytical transmission electron microscopy(ATEM) 3DOM HAp demonstrated a higher uptake of cadmium, viz. x = 0.71 in Ca10-xCdx(PO4)6(OH)2 than nonporous HAp (x = 0.42). The incorporation of Cd was homogeneous in the 3DOM HAp crystals (as compared to the powder) leading to a decrease in lattice parameters as Cd2+ has a smaller ionic radius compared to Ca2+. A preference for Cd to enter the Ca" tunnel site of HAp was consistent with this being the readily exchangeable site. The lead-bearing solution acted to collapse the macropores through the rapid crystallization of pyromorphite (Pb10(P04)6(OH)2) via a dissolution-precipitation mechanism, possibly promoted by the amorphous component, that overwhelmed HAp ion exchange. The rapid crystallochemical incorporation of Cd and fixation of Pb by 3DOM HAp demonstrates the potential of thin-walled porous structures for the treatment of contaminated waters.
Publisher: American Geophysical Union (AGU)
Date: 20-12-2011
DOI: 10.1029/2011JC007171
Publisher: Trans Tech Publications Ltd.
Date: 15-04-2006
Publisher: Elsevier BV
Date: 04-1989
Publisher: Elsevier BV
Date: 11-2010
Publisher: American Chemical Society (ACS)
Date: 05-1991
DOI: 10.1021/JO00011A060
Publisher: Elsevier BV
Date: 07-2008
Publisher: Wiley
Date: 27-09-2007
Publisher: American Meteorological Society
Date: 06-2011
DOI: 10.1175/1520-0477-92.6.S1
Abstract: Several large-scale climate patterns influenced climate conditions and weather patterns across the globe during 2010. The transition from a warm El Niño phase at the beginning of the year to a cool La Niña phase by July contributed to many notable events, ranging from record wetness across much of Australia to historically low Eastern Pacific basin and near-record high North Atlantic basin hurricane activity. The remaining five main hurricane basins experienced below- to well-below-normal tropical cyclone activity. The negative phase of the Arctic Oscillation was a major driver of Northern Hemisphere temperature patterns during 2009/10 winter and again in late 2010. It contributed to record snowfall and unusually low temperatures over much of northern Eurasia and parts of the United States, while bringing above-normal temperatures to the high northern latitudes. The February Arctic Oscillation Index value was the most negative since records began in 1950. The 2010 average global land and ocean surface temperature was among the two warmest years on record. The Arctic continued to warm at about twice the rate of lower latitudes. The eastern and tropical Pacific Ocean cooled about 1°C from 2009 to 2010, reflecting the transition from the 2009/10 El Niño to the 2010/11 La Niña. Ocean heat fluxes contributed to warm sea surface temperature anomalies in the North Atlantic and the tropical Indian and western Pacific Oceans. Global integrals of upper ocean heat content for the past several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the ocean in the Earth's energy budget. Deep and abyssal waters of Antarctic origin have also trended warmer on average since the early 1990s. Lower tropospheric temperatures typically lag ENSO surface fluctuations by two to four months, thus the 2010 temperature was dominated by the warm phase El Niño conditions that occurred during the latter half of 2009 and early 2010 and was second warmest on record. The stratosphere continued to be anomalously cool. Annual global precipitation over land areas was about five percent above normal. Precipitation over the ocean was drier than normal after a wet year in 2009. Overall, saltier (higher evaporation) regions of the ocean surface continue to be anomalously salty, and fresher (higher precipitation) regions continue to be anomalously fresh. This salinity pattern, which has held since at least 2004, suggests an increase in the hydrological cycle. Sea ice conditions in the Arctic were significantly different than those in the Antarctic during the year. The annual minimum ice extent in the Arctic—reached in September—was the third lowest on record since 1979. In the Antarctic, zonally averaged sea ice extent reached an all-time record maximum from mid-June through late August and again from mid-November through early December. Corresponding record positive Southern Hemisphere Annular Mode Indices influenced the Antarctic sea ice extents. Greenland glaciers lost more mass than any other year in the decade-long record. The Greenland Ice Sheet lost a record amount of mass, as the melt rate was the highest since at least 1958, and the area and duration of the melting was greater than any year since at least 1978. High summer air temperatures and a longer melt season also caused a continued increase in the rate of ice mass loss from small glaciers and ice caps in the Canadian Arctic. Coastal sites in Alaska show continuous permafrost warming and sites in Alaska, Canada, and Russia indicate more significant warming in relatively cold permafrost than in warm permafrost in the same geographical area. With regional differences, permafrost temperatures are now up to 2°C warmer than they were 20 to 30 years ago. Preliminary data indicate there is a high probability that 2010 will be the 20th consecutive year that alpine glaciers have lost mass. Atmospheric greenhouse gas concentrations continued to rise and ozone depleting substances continued to decrease. Carbon dioxide increased by 2.60 ppm in 2010, a rate above both the 2009 and the 1980–2010 average rates. The global ocean carbon dioxide uptake for the 2009 transition period from La Niña to El Niño conditions, the most recent period for which analyzed data are available, is estimated to be similar to the long-term average. The 2010 Antarctic ozone hole was among the lowest 20% compared with other years since 1990, a result of warmer-than-average temperatures in the Antarctic stratosphere during austral winter between mid-July and early September.
Publisher: Elsevier BV
Date: 05-2010
Publisher: Elsevier BV
Date: 03-2004
Publisher: Springer Science and Business Media LLC
Date: 03-03-2010
Publisher: Elsevier BV
Date: 03-2005
Publisher: Elsevier BV
Date: 05-2006
Publisher: Elsevier BV
Date: 11-2010
Publisher: Elsevier BV
Date: 08-2003
Publisher: Elsevier BV
Date: 08-2011
Publisher: Elsevier BV
Date: 2013
Publisher: AIP Publishing
Date: 23-01-2006
DOI: 10.1063/1.2165283
Abstract: We report an observation of strain relaxation in lattice-mismatched heteroepitaxial Si1−xGex layers, accompanied by a reduction in threading dislocation density (TDD). This occurs on a Si0.77Ge0.23 layer grown on top of alternating layers of Si0.77Ge0.23∕Si0.76Ge0.23C0.01. The present scheme allows us to grow a high-quality 85% relaxed Si0.77Ge0.23 layer with a TDD of ∼104∕cm2. The high-resolution transmission electron microscope results showed the presence of Si1−x−yGexCy domains (with x⩽0.23 and y⩽0.01) after annealing at 1000°C. We infer that the formation of these domains assist the low TDD relaxation by releasing the epitaxial misfit strain as localized discrete strain and by blocking the propagation of misfit dislocations.
Publisher: Elsevier BV
Date: 04-2009
Publisher: Elsevier BV
Date: 05-2007
Publisher: Elsevier BV
Date: 10-2010
Publisher: Elsevier BV
Date: 09-2005
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TA01125F
Abstract: This article describes a variable temperature solid-state NMR and single crystal X-ray/neutron diffraction study of the hybrid perovskites (CH 3 NH 3 )PbX 3 (X = I, Br and Cl).
Publisher: IOP Publishing
Date: 27-04-2004
Publisher: Elsevier BV
Date: 03-2019
Publisher: American Chemical Society (ACS)
Date: 26-05-2007
DOI: 10.1021/JP072934G
Publisher: Elsevier BV
Date: 12-2008
Publisher: Elsevier BV
Date: 04-2001
Publisher: Springer Science and Business Media LLC
Date: 12-07-2017
Publisher: American Chemical Society (ACS)
Date: 28-09-2018
DOI: 10.1021/JACS.8B09316
Abstract: The pressure-induced structural evolution of formamidinium-based perovskite FAPbI
Publisher: American Chemical Society (ACS)
Date: 04-10-2007
DOI: 10.1021/LA702230H
Abstract: Highly dispersed gold nanocrystals decorating silica spheres were prepared from HAuCl4 and NaOH via a deposition-precipitation (DP) process, in which the isoelectric point (IEP) of the substrate was adjusted during sphere synthesis by interaction of the surface with ammonia molecules. Through the systematic variation of pH (4-8), reaction temperature (65-96 degrees C), and time (10-30 min), a superior product with small (2-5 nm), homogeneously distributed gold crystals was obtained at pH 7 and a reaction temperature of 96 degrees C. These materials will offer enhanced performance as catalysts and contrast enhancers in biomedical imaging.
Publisher: American Meteorological Society
Date: 07-2010
Publisher: Elsevier BV
Date: 02-2021
Publisher: American Chemical Society (ACS)
Date: 23-10-2017
Publisher: The Chemical Society of Japan
Date: 05-08-2019
DOI: 10.1246/CL.190266
Publisher: Elsevier BV
Date: 02-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B810947H
Publisher: American Chemical Society (ACS)
Date: 14-10-2010
DOI: 10.1021/AM1004865
Abstract: Truncated nanocubes of barium titanate (BT) were synthesized using a rapid, facile microwave-assisted hydrothermal route. Stoichiometric composition of pellets of nanocube BT powders was prepared by two-stage microwave process. Characterization by powder XRD, Rietveld refinement, SEM, TEM, and dielectric and polarization measurements was performed. X-ray diffraction revealed a polymorphic transformation from cubic Pm3̅m to tetragonal P4mm after 15 min of microwave irradiation, arising from titanium displacement along the c-axis. Secondary electron images were examined for nanocube BT synthesis and annealed at different timings. Transmission electron microscopy showed a narrow particle size distribution with an average size of 70 ± 9 nm. The remanence and saturation polarization were 15.5 ± 1.6 and 19.3 ± 1.2 μC/cm(2), respectively. A charge storage density of 925 ± 47 nF/cm(2) was obtained Pt/BT/Pt multilayer ceramic capacitor stack had an average leakage current density of 5.78 ± 0.46 × 10(-8) A/cm(2) at ±2 V. The significance of this study shows an inexpensive and facile processing platform for synthesis of high-k dielectric for charge storage applications.
Publisher: American Chemical Society (ACS)
Date: 12-11-2015
Publisher: Schweizerbart
Date: 13-04-2010
Publisher: Elsevier BV
Date: 26-08-2010
Publisher: IOP Publishing
Date: 10-01-2006
Publisher: Springer Science and Business Media LLC
Date: 21-10-2010
Publisher: American Chemical Society (ACS)
Date: 14-11-2008
DOI: 10.1021/IC801491T
Abstract: Ferric hydroxyapatites (Fe-HAp) and oxyapatites (Fe-OAp) of nominal composition [Ca(10-x)Fe(x)(3+)][(PO(4))(6)][(OH)(2-x)O(x)] (0 < or = x Fe(3+) + CO(3)(2-)), while at higher loadings, "interstitial" oxygen is tenanted in the framework (2Ca(2+) + (vac) --> 2Fe(3+) + O(2+)). Although Fe(3+) is smaller than Ca(2+), the unit cell dilates as iron enters apatite, providing evidence of oxygen injection that converts PO(4) tetrahedra to PO(5) trigonal bipyramids, leading to the crystal chemical formula [Ca(10-x)Fe(x)][(PO(4))(6-x/2)(PO(5))(x/2)][(OH)(2-y)O(2y)] (x Fe(2+) aliovalent replacement does not require oxygen penetration and the cell volume contracts with iron loading. All of the materials were paramagnetic, but at low iron concentrations, a transition arising from crystallographic modification or a change in spin ordering is observed at 90 K. The excipient behavior of Fe-OAp was superior to that of HAp and may be linked to the crystalline component or mediated by a ubiquitous nondiffracting amorphous phase. Fe-HAp and Fe-OAp are not intrinsically suitable magnetic agents for drug delivery but may be useful in reactive cements that promote osteoblast proliferation.
Publisher: Informa UK Limited
Date: 21-01-2011
Publisher: Wiley
Date: 05-2005
Publisher: AIP Publishing
Date: 12-2010
DOI: 10.1063/1.3514005
Abstract: A micromechanism of thermosonic gold wire bonding was elaborated by examining its interfacial characteristics as a result of the bonding process, including the fragmentation of the native aluminum oxide layer on Al pads, and formation of initial intermetallic compounds (IMCs). It is found that the existence of an approximately 5 nm thick native oxide layer on original Al pads has a significant effect on the bonding, and the nucleation of IMCs during the bonding process must overcome this relatively inert thin film. Bonding strength was fundamentally determined by the degree of fragmentation of the oxide films, through which the formation of IMCs can be initiated due to the direct contact of the metal surfaces to be bonded. The extent of fracture the oxide layer was strongly influenced by the level of ultrasonic power, as at its high level alumina fragmentation becomes pervasive resulting in contiguous alloy interfaces and robust bonds. The IMCs formed at the interfaces were identified as Al4Al and AuAl2 with a thickness of 150–300 nm. The formation mechanism of such IMCs was explained by the effective heat of formation theory.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C1JM13752B
Publisher: Wiley
Date: 10-2002
Publisher: IOP Publishing
Date: 04-04-2007
Publisher: American Chemical Society (ACS)
Date: 29-03-2013
DOI: 10.1021/CM4000685
Publisher: SPIE
Date: 21-12-2007
DOI: 10.1117/12.759383
Publisher: American Chemical Society (ACS)
Date: 15-11-2019
Publisher: American Chemical Society (ACS)
Date: 20-08-2014
DOI: 10.1021/IC501558R
Abstract: A single-crystal structure determination of Nd8Sr2Si6O26 apatite, a prototype intermediate-temperature electrolyte for solid oxide fuel cells grown by the floating-zone method, was completed using the combination of Laue neutron diffraction and Raman spectroscopy. While neutron diffraction was in good agreement with P6₃/m symmetry, the possibility of P6₃ could not be convincingly excluded. This ambiguity was removed by the collection of orientation-dependent Raman spectra that could only be consistent with P6₃/m. The composition of Nd8Sr2Si6O26 was independently verified by powder X-ray diffraction in combination with electron probe microanalysis, with the latter confirming a homogeneous distribution of Sr and the absence of chemical zonation commonly observed in apatites. This comprehensive crystallochemical description of Nd8Sr2Si6O26 provides a baseline to quantify the efficacy of cation vacancies, oxygen superstoichiometry, and symmetry modification for promoting oxygen-ion mobility.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4DT02088J
Abstract: Ellestadites are silicate–sulphate apatite matrices for the immobilization of toxic metal waste. Phosphate-rich chlorellestadite, Ca 10 [(SiO 4 ) x (PO 4 ) 6−2x (SO 4 ) x ]Cl 2 (0 ≤ x ≤ 1) show promise as ceramic waste forms for hazardous fly ashes rich in sulphur and chlorine.
Publisher: International Union of Crystallography (IUCr)
Date: 28-01-2003
DOI: 10.1107/S0108768102019894
Abstract: The crystal structures of the [ A (1) 2 ][ A (2) 3 ]( B O 4 ) 3 X apatites and the related compounds [ A (1) 2 ][ A (2) 3 ]( B O 5 ) 3 X and [ A (1) 2 ][ A (2) 3 ]( B O 3 ) 3 X are collated and reviewed. The structural aristotype for this family is Mn 5 Si 3 ( D 8 8 type, P 6 3 / mcm symmetry), whose cation array approximates that of all derivatives and from which related structures arise through the systematic insertion of anions into tetrahedral, triangular or linear interstices. The construction of a hierarchy of space-groups leads to three apatite families whose high-symmetry members are P 6 3 / m , Cmcm and P 6 3 cm . Alternatively, systematic crystallographic changes in apatite solid-solution series may be practically described as deviations from regular anion nets, with particular focus on the O(1)— A (1)—O(2) twist angle φ projected on (001) of the A (1)O 6 metaprism. For apatites that contain the same A cation, it is shown that φ decreases linearly as a function of increasing average ionic radius of the formula unit. Large deviations from this simple relationship may indicate departures from P 6 3 / m symmetry or cation ordering. The inclusion of A (1)O 6 metaprisms in structure drawings is useful for comparing apatites and condensed-apatites such as Sr 5 (BO 3 ) 3 Br. The most common symmetry for the 74 chemically distinct [ A (1) 2 ][ A (2) 3 ]( B O 4 ) 3 X apatites that were surveyed was P 6 3 / m (57%), with progressively more complex chemistries adopting P 6 3 (21%), P \\bar 3 (9%), P \\bar 6 (4.3%), P 2 1 / m (4.3%) and P 2 1 (4.3%). In chemically complex apatites, charge balance is usually maintained through charge-coupled cation substitutions, or through appropriate mixing of monovalent and alent X anions or X -site vacancies. More rarely, charge compensation is achieved through insertion/removal of oxygen to produce B O 5 square pyramidal units (as in ReO 5 ) or B O 3 triangular coordination (as in AsO 3 ). Polysomatism arises through the ordered filling of [001] B O 4 tetrahedral strings to generate the apatite–nasonite family of structures.
Publisher: American Chemical Society (ACS)
Date: 02-09-2011
DOI: 10.1021/JA206441X
Abstract: Melilite-type gallium oxides are potential intermediate temperature electrolytes for solid oxide fuel cells. Single crystals of [CaNd](2)[Ga](2)[Ga(2)O(7)](2) grown using an optical floating zone furnace have been investigated using transmission electron microscopy and powder and single-crystal X-ray diffraction. The anion array topologically conforms to a [(3.5.4.5)(2), 3.5.3.5] network that contains distorted pentagonal tunnels. The distortion is necessary to achieve space filling and accommodate structural misfit between the layers. Satisfactory bond lengths and angles are obtained through two-dimensional modulation in the tetragonal based plane, leading to five-dimensional symmetry in the superspace group P(4⁻)2(1)m(α,α,0)00s((a⁻)a,0)000, α = 0.2319(2), with modulation vectors q(1) = α(a* + b*) and q(2) = α(-a* + b*). Both displacive and occupational modulations are found. Through this mechanism, melilites are primed to accommodate mobile oxygen interstitials, suggesting a rational approach to crystallochemical tailoring that will enhance ionic diffusion and optimize electrolyte performance.
Publisher: American Chemical Society (ACS)
Date: 07-11-2002
DOI: 10.1021/JP026814E
Publisher: AIP Publishing
Date: 06-08-2007
DOI: 10.1063/1.2768904
Abstract: Fe Pt : Al 2 O 3 nanocomposite thin films have been synthesized by magnetic trapping assisted pulsed laser deposition. The annealing temperature required for phase transition from low Ku fcc-FePt to high Ku fct-FePt is lowered down from about 600°C for conventional pulsed laser deposition (PLD) to 300°C for magnetic trapping assisted PLD. For the s le annealed at 300°C with fct phase FePt nanoparticles, the average nanoparticle size is estimated to be about 8.7±2.1nm, and the magnetic properties are improved which makes it a potentially good candidate for possible applications in high density data storage.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0NR08093D
Abstract: Demonstration of Rb 2 CuX 3 (X = Br, Cl) colloidal nanocrystals under UV light with a representation of one-dimensional Rb 2 CuBr 3 crystal structure.
Publisher: Elsevier BV
Date: 03-2009
Publisher: American Chemical Society (ACS)
Date: 13-07-2010
DOI: 10.1021/JA102617R
Abstract: Low-temperature CO oxidation over a compositional series of Pd-Au nanoalloy catalysts supported on silica fume was studied. Except for the pure metals, these materials invariably showed biphasic separation into palladium- and gold-rich components. Performance was optimal for a catalyst of bulk composition Pd(4)Au(1), a mixture of Pd(90)Au(10) (72.5 at. %) and Pd(31)Au(69) (27.5 at. %), that was remarkably active at 300 K and more stable than a pure Au catalyst. For bulk materials dominated by Pd (Pd:Au = 16:1 8:1 4:1), the palladium-rich alloy fraction frequently adopted hollow sphere or annular morphology, while the gold-rich crystals were often multiply twinned. Quantitative powder X-ray diffraction (XRD) showed that under the synthesis conditions used, the Au solubility limit in Pd crystals was approximately 12 at. %, while Pd was more soluble in Au (approximately 31 at. %). This was consistent with X-ray photoelectron spectroscopy (XPS), which revealed that the surfaces of Pd-rich alloys were enriched in gold relative to the bulk composition. In situ Fourier transform infrared spectra collected during CO oxidation contained a new band at 2114 cm(-1) (attributed to linear CO-Au/Au-Pd bonds) and reduced intensity of a band at 2090 cm(-1) (arising from a linear CO-Pd bond) with escalating Au content, indicating that the Pd sites became increasingly obscured by Au. High-resolution electron micrographs (HRTEM) of the Pd-rich alloys revealed atomic scale surface defects consistent with this interpretation. These results demonstrate that gold-containing biphasic Pd nanoalloys may be highly durable alternatives for a range of catalytic reactions.
Publisher: Elsevier BV
Date: 08-2008
Publisher: American Chemical Society (ACS)
Date: 22-05-2008
DOI: 10.1021/LA703899J
Abstract: A monodispersed silica-titania core-shell photocatalyst was synthesized via a sol-gel route without the need of pH adjustment, cationic polyelectrolytes, or surfactants in a process where silica spheres were impregnated with hydrolyzed titanium tetrabutoxide, incubated at room temperature, and then condensed using an ethanol/water (1:1) solvent. Four coating cycles in a 10% v/v titania sol produced homogeneous titania shells. The quality of catalysts was assessed quantitatively using Rietveld analysis of powder X-ray diffraction patterns combined with X-ray fluorescence spectrometry. During calcination, the anatase-to-rutile transformation was delayed to 1000 degrees C, which is approximately 300 degrees C higher than usually observed. The thermal stability and surface area of titania were enhanced through the slow crystal growth of anatase. The photocatalytic activity of the core-shell photocatalysts calcined at 400-600 degrees C was found to be proportional to the thickness of titania but did not directly correlate with the surface area.
Publisher: American Chemical Society (ACS)
Date: 12-05-2007
DOI: 10.1021/ES070160B
Abstract: Accelerated photodegradation of methylene blue (MB) over three-dimensionally ordered macroporous (3DOM) titania (pore sizes: 0.5 and 1 microm) is demonstrated. The catalysts were synthesized by colloidal crystal templating against polystyrene spheres using a metal alkoxide precursor. The 3DOM titania walls which are predominantly anatase (> 98%) were decorated homogeneously with gold nanoparticles (5-7 nm) by pH-controlled precipitation of Au from HAuCl4 using sodium hydroxide. A combination of powder X-ray diffraction (XRD), analytical transmission electron microscopy (ATEM) and X-ray photoelectron spectroscopy (XPS) confirmed the deposition of Au(0) on the 3DOM titania macroporous walls. Photocatalytic activity was monitored by following the degradation of MB with activity benchmarked against commercial P25 (Degussa) and powdertitania prepared by hydrolysis of titanium ethoxide. Macroporous 3DOM titania with pore diameter 0.5 microm had the highest first-order rate constant of 0.042 min(-1) for decomposition of MB, compared to 0.025 min(-1) for P25 titania. Deposition of gold on the 3DOM titania surfaces decreased the reaction rate by covering the surface active sites.
Publisher: Elsevier BV
Date: 10-2011
Publisher: Springer Science and Business Media LLC
Date: 05-2007
Abstract: Novel magnetic cobalt ferrite nanostructures with curved surfaces (i.e., nanobowls and hollow nanospheres) in a periodic array have been fabricated by in situ reduction of a cobalt and iron salt solution mixture in the interstitial spaces of three-dimensional, close-packed, polystyrene sphere templates. The effect of the shape created by this nanostructure and magnetocrystalline anisotropy introduced by suitable annealing were used to tailor the coercivity to values relevant to high-density data-storage applications.
Publisher: American Chemical Society (ACS)
Date: 10-07-2007
DOI: 10.1021/EF070004Q
Publisher: SPIE-Intl Soc Optical Eng
Date: 2008
DOI: 10.1117/1.2976140
Abstract: The use of microfluidics for biofluid analysis offers a cheaper alternative to conventional techniques in disease diagnosis. However, traditional microfluidics design may be complicated by the need to incorporate separation elements into the system in order to facilitate specific molecular detection. Alternatively, an optical technique known as surface-enhanced Raman spectroscopy (SERS) may be used to enable identification of analyte molecules directly from a complex s le. This will not only simplify design but also reduce overall cost. The concept of SERS-based microfluidics is however not new and has been demonstrated previously by mixing SERS-active metal nanoparticles with a model s le, in situ, within the microchannel. Although the SERS reproducibility of these systems was shown to be acceptable, it is, however, not stable toward variations in the salt content of the s le, as will be shown in this study. We have proposed a microfluidics design whereby periodic SERS-active metal nanostructures are fabricated directly into the microchannel via a simple method of spin coating. Using artificial as well as human urine s les, we show that the current microfluidics is more stable toward variations in the s le's ionic strength.
Publisher: American Chemical Society (ACS)
Date: 28-03-2008
DOI: 10.1021/LA703580R
Abstract: A direct process for preparing contiguous gold shells (15-25 nm thick) over amorphous silica spheres (200 nm) is described. In this method, gold seeds are synthesized from HAuCl(4) in a dilute NaOH solution using deposition-precipitation with subsequent metallization by sodium borohydride (NaBH(4)). The ease of dispersing gold nanocrystals on spheres of bare silica and spheres after grafting with ammonia was studied as a function of pH (4-8), reaction temperature (65-96 degrees C), and time (5-30 min). Additional parameters requiring optimization included the quantity of NaBH4 and the HAuCl(4) in K(2)CO(3) solution to silica volume ratio. The evolution of gold nanocrystal growth was monitored by transmission electron microscopy, and the bathochromic shift of ultraviolet-visible absorption was correlated with shell perfection and thickness.
Publisher: Elsevier BV
Date: 2003
DOI: 10.1016/S0142-9612(02)00267-3
Abstract: A cogent understanding of the microstructure, and indeed nano-structure, of hydroxyapatite (HA) and the interface between Ti-6Al-4V and HA is crucial to its appropriateness as a biomaterials. This paper reports the analysis of plasma-sprayed HA/Ti-6Al-4V composites by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to elucidate the intricate nature of the materials following plasma spray processing and in vitro evaluation. The novel Ti-6Al-4V/HA composite coating, with approximately 48 wt% HA, had demonstrated attractive tensile adhesion strength (approximately 28 MPa) and improved Young's modulus (approximately 55 GPa). Experimental results demonstrated that amorphous calcium phosphate and fine HA grains were formed during rapid splat solidification in the as-sprayed composite coatings. Small Ti-6Al-4V grains were observed adjacent to the amorphous calcium phosphate. The coatings were further heat treated at 600 degrees C for 6 h, and significant crystallisation of the amorphous calcium phosphate phase took place. However, complete crystallisation was not achieved at this temperature, as the coatings invariably contained a small amount of amorphous calcium phosphate phase in some local regions. After immersion in simulated body fluid for 2 weeks and 10 weeks, TEM and STEM confirmed that the interfaces inside the coating maintained good microstructural integrity.
Publisher: Oxford University Press (OUP)
Date: 08-2014
Publisher: American Geophysical Union (AGU)
Date: 09-2013
DOI: 10.1002/ROG.20022
Publisher: Elsevier BV
Date: 05-2006
Location: Australia
No related grants have been discovered for Tim White.