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Long-Term Oxidation Susceptibility in Ambient Air of the Semiconductor Kesterite Cu 2ZnSnS 4 Nanopowders Made by Mechanochemical Synthesis Method. MATERIALS (BASEL, SWITZERLAND) 2023; 16:6160. [PMID: 37763438 PMCID: PMC10533042 DOI: 10.3390/ma16186160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2023] [Revised: 09/02/2023] [Accepted: 09/05/2023] [Indexed: 09/29/2023]
Abstract
The often overlooked and annoying aspects of the propensity of no-oxygen semiconductor kesterite, Cu2ZnSnS4, to oxidation during manipulation and storage in ambient air prompted the study on the prolonged exposure of kesterite nanopowders to air. Three precursor systems were used to make a large pool of the cubic and tetragonal polytypes of kesterite via a convenient mechanochemical synthesis route. The systems included the starting mixtures of (i) constituent elements (2Cu + Zn + Sn + 4S), (ii) selected metal sulfides and sulfur (Cu2S + ZnS + SnS + S), and (iii) in situ made copper alloys (from the high-energy ball milling of the metals 2Cu + Zn + Sn) and sulfur. All raw products were shown to be cubic kesterite nanopowders with defunct semiconductor properties. These nanopowders were converted to the tetragonal kesterite semiconductor by annealing at 500 °C under argon. All materials were exposed to the ambient air for 1, 3, and 6 months and were suitably analyzed after each of the stages. The characterization methods included powder XRD, FT-IR/UV-Vis/Raman/NMR spectroscopies, SEM, the determination of BET/BJH specific surface area and helium density (dHe), and direct oxygen and hydrogen-content analyses. The results confirmed the progressive, relatively fast, and pronounced oxidation of all kesterite nanopowders towards, mainly, hydrated copper(II) and zinc(II) sulfates, and tin(IV) oxide. The time-related oxidation changes were reflected in the lowering of the energy band gap Eg of the remaining tetragonal kesterite component.
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Synthetic Opals or Versatile Nanotools-A One-Step Synthesis of Uniform Spherical Silica Particles. Int J Mol Sci 2023; 24:13693. [PMID: 37761996 PMCID: PMC10530679 DOI: 10.3390/ijms241813693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 08/25/2023] [Accepted: 09/01/2023] [Indexed: 09/29/2023] Open
Abstract
Synthetic opals, a composition of homogeneous silica spheres in the mesoscale size range, have attracted the attention of scientists due to their favorable chemical and physical properties. Their chemical inertness and stability, biocompatibility, homogeneity, elevated specific surface area, and ease of functionalization of their surfaces make them a versatile nanotool. In the present study, the Stöber process was used to investigate the effect of parameters, such as reagent concentration and synthesis temperature, on the resulting silica particle size and structure. The optimal conditions for successfully obtaining homogeneous particles in the mesoscale range with high reproducibility were investigated. Several synthesis procedures and their dependence on the reaction temperature were presented to allow the selection of the assumed diameter of silica spheres. The numerous samples obtained were examined for size, homogeneity, structure, and specific surface area. On the basis of specific surface area measurements and nuclear magnetic resonance studies, the internal hierarchical structure of the spherical silica was confirmed as consisting of a solid core and layers of secondary spheres covered by a solid shell. Structural studies (X-ray Spectroscopy, X-ray Absorption Near-Edge Structure, and nuclear magnetic resonance), together with infrared vibrational spectroscopy, showed no dependence of the structure of the obtained mesospheres on the concentration of reagents and the size of the obtained particles.
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Spectroscopic studies on phosphate-modified silicon oxycarbide-based amorphous materials. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 291:122341. [PMID: 36634493 DOI: 10.1016/j.saa.2023.122341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 12/31/2022] [Accepted: 01/06/2023] [Indexed: 06/17/2023]
Abstract
Vibrational spectroscopy is the most effective, efficient and informative method of structural analysis of amorphous materials with silica matrix and, therefore, an indispensable tool for examining silicon oxycarbide-based amorphous materials (SiOC). The subject of this work is a description of the modification process of SiOC glasses with phosphate ions based on the structural examination including mainly Infrared and Raman Spectroscopy. They were obtained as polymer-derived ceramics based on ladder-like silsesquioxanes synthesised via the sol-gel method. With the high phosphate's volatility, it was decided to introduce the co-doping ions to create [AlPO4] and [BPO4] stable structural units. As a result, several samples from the SiPOC, SiPAlOC and SiPBOC systems were obtained with various quantities of the modifiers. All samples underwent a detailed structural evaluation of both polymer precursors and ceramics after high-temperature treatment with Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS-NMR). Obtained results proved the efficient preparation of desired materials that exhibit structural parameters similar to the unmodified one. They were X-ray-amorphous with no phase separation and crystallisation. Spectroscopic measurements confirmed the presence of the crucial Si-C bond and how modifying ions are incorporated into the SiOC network. It was also possible to characterise the turbostratic free carbon phase. The modification was aimed to improve the bioperformance of the materials in the context of their future application as bioactive coatings on metallic implants.
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The effect of functionalized hydroxyapatite on the crystallization process, morphology and thermomechanical properties of polyoxymethylene composites. EXPRESS POLYM LETT 2023. [DOI: 10.3144/expresspolymlett.2023.20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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The Effect of Fluorides (BaF 2, MgF 2, AlF 3) on Structural and Luminescent Properties of Er 3+-Doped Gallo-Germanate Glass. MATERIALS (BASEL, SWITZERLAND) 2022; 15:5230. [PMID: 35955165 PMCID: PMC9369573 DOI: 10.3390/ma15155230] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 07/22/2022] [Accepted: 07/23/2022] [Indexed: 01/05/2023]
Abstract
The effect of BaF2, MgF2, and AlF3 on the structural and luminescent properties of gallo-germanate glass (BGG) doped with erbium ions was investigated. A detailed analysis of infrared and Raman spectra shows that the local environment of erbium ions in the glass was influenced mainly by [GeO]4 and [GeO]6 units. Moreover, the highest number of non-bridging oxygens was found in the network of the BGG glass modified by MgF2. The 27Al MAS NMR spectrum of BGG glass with AlF3 suggests the presence of aluminum in tetra-, penta-, and octahedral coordination geometry. Therefore, the probability of the 4I13/2→4I15/2 transition of Er3+ ions increases in the BGG + MgF2 glass system. On the other hand, the luminescence spectra showed that the fluoride modifiers lead to an enhancement in the emission of each analyzed transition when different excitation sources are employed (808 nm and 980 nm). The analysis of energy transfer mechanisms shows that the fluoride compounds promote the emission intensity in different channels. These results represent a strong base for designing glasses with unique luminescent properties.
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Rehydration Driven Acid Impregnation of Thermally Pretreated Ca-Bentonite—Evolution of the Clay Structure. MATERIALS 2022; 15:ma15062067. [PMID: 35329522 PMCID: PMC8951250 DOI: 10.3390/ma15062067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Revised: 03/03/2022] [Accepted: 03/07/2022] [Indexed: 11/25/2022]
Abstract
A new approach to acid activation of raw Ca-bentonite was explored. The method consisted in dehydration of clay by thermal pretreatment at 200 °C, followed by immediate impregnation with H2SO4 solution. The acid concentration was 1.5 × or 2.0 × cation exchange capacity (CEC) of clay. The volume of the liquid was adjusted so as to leave the material in the apparently dry state. Structural evolution of the activated solids after 1, 2, 3, and 4 weeks of storage was monitored with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), 27Al magic angle spinning nuclear magnetic resonance (MAS NMR), and chemical analysis. In the macroscopically dry solids, the rehydrated interlayer Ca2+ underwent rapid exchange with H3O+ and formed extra-framework gypsum. Acid attack on montmorillonite structure resulted in continuous removal of layer forming Mg, Al, and Fe cations, with Mg2+ being eliminated most efficiently. No significant damage to the montmorillonite lattice was observed. Al was extracted both from the tetrahedral and the octahedral sheets. Under less acidic conditions, the monohydrated H-montmorillonite changed upon storage to bi-hydrated form, as a result of clay auto-transformation. Higher concentrations of acid in the pore network of clay stabilized the H-form of montmorillonite. The data indicate that compositional transformation of acid impregnated bentonite extended beyond the one month of aging investigated in the present work.
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Investigating the Crystallization Process of Boron-Bearing Silicate-Phosphate Glasses by Thermal and Spectroscopic Methods. Molecules 2022; 27:molecules27030867. [PMID: 35164124 PMCID: PMC8839742 DOI: 10.3390/molecules27030867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 01/20/2022] [Accepted: 01/22/2022] [Indexed: 11/16/2022] Open
Abstract
Glasses and devitrificates from the SiO2-B2O3-P2O5-K2O-CaO-MgO system with constant contents of SiO2 and P2O5 network formers, modified by the addition of B2O3, were analyzed. All materials were synthesized by the traditional melt-quenching technique. The glass stability (GS) parameters (Krg, ∆T, KW, KH) were determined. The effect of the addition of B2O3 on the GS, liquation phenomenon, crystallization process, and the type of crystallizing phases were examined using SEM-EDS, DSC, XRD, and Raman spectroscopy imaging methods. It was observed that the addition of B2O3 increased the tendency of the glass to crystallize. Both phosphates (e.g., Ca9MgK(PO4)7, Mg3Ca3(PO4)4), and silicates (e.g., K2Mg5(Si12O30), CaMg(Si2O6), MgSiO3) crystallized in the studied system. The Raman spectrum for the orthophosphate Mg3Ca3(PO4)4 stanfieldite type was obtained. Boron ions were introduced into the structures of crystalline compounds at high crystallization temperatures. The type of crystallizing phases was found to be related to the phenomenon of liquation, and the order of their occurrence was dependent on the Gibbs free enthalpy.
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Influence of Dry Milling on Phase Transformation of Sepiolite upon Alkali Activation: Implications for Textural, Catalytic and Sorptive Properties. MATERIALS 2020; 13:ma13183936. [PMID: 32899570 PMCID: PMC7558943 DOI: 10.3390/ma13183936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 09/01/2020] [Accepted: 09/03/2020] [Indexed: 12/03/2022]
Abstract
Activation of natural sepiolite by means of grinding in a planetary mill followed by wet NaOH activation was studied for the purpose of endowing the product with enhanced basicity for potential catalytic/sorptive applications. Synthesized solids were characterized with X-ray powder diffraction (XRD), N2 adsorption/desorption, scanning electron microscopy (SEM), energy dispersive (EDX), atomic absorption (AAS), Fourier-transform infrared (FTIR) and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Surface basicity was determined by titration with benzoic acid. Grinding changed the pathway of sepiolite phase transformation upon NaOH treatment. The as-received sepiolite evolved to Na-sepiolite (loughlinite) with a micropore system blocked by nanocrystalline Mg(OH)2, while ground samples yielded magnesium silicate hydrate phase (MSH), with well-developed microporous texture. In unmilled sepiolite desilication involved preferential leaching of Si from the center of the structural ribbons, while in ground samples additional loss of Si from ribbon-ribbon corner linkages was observed. In all cases treatment with NaOH led to enhancement of surface basicity. Synthesized materials were tested as catalysts in a base-catalyzed aldol self-condensation of acetone and oxidation of cyclohexanone to ε-caprolactone, as well as CO2 sorbents. Catalytic trends depended not only on samples’ basicity, but also on texture and phase composition of the catalysts. Grinding combined with alkali activation proved a simple and effective method for boosting CO2-sorption capacity of sepiolite to the level comparable to amine-functionalized, acid-activated sepiolite sorbents.
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Tailoring selectivity in the liquid-phase isomerization of α-pinene on dealuminated ferrierite-type zeolites. Catal Today 2020. [DOI: 10.1016/j.cattod.2019.03.045] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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10
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Influence of UV aging on some rheological properties of footwear leather. POLIMERY-W 2019. [DOI: 10.14314/polimery.2019.9.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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The effect of hot liquid water treatment on the properties and catalytic activity of MWW zeolites with various layered structures. Catal Today 2018. [DOI: 10.1016/j.cattod.2017.10.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Pillaring of layered zeolite precursors with ferrierite topology leading to unusual molecular sieves on the micro/mesoporous border. Dalton Trans 2018; 47:3029-3037. [PMID: 29485158 DOI: 10.1039/c7dt03718j] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Layered zeolite materials with FER layer topology can produce various condensed and expanded structures including zeolite frameworks, FER and CDO, their interlayer expanded forms (IEZ), and organic-intercalated and pillared derivatives. This work concerns pillaring of the surfactant-swollen derivative with a gallery height of ca. 2.5 nm between layers by treatment with tetraethylorthosilicate (TEOS) at room and elevated temperatures. The materials obtained at 100 °C and higher showed unusual properties including 2 nm pores on the micro/mesoporous border and disordered layer packing indicated by the absence of distinct low angle interlayer peaks at d-spacing >3 nm (∼3° 2θ Cu Kα radiation) in the X-ray diffraction pattern (XRD). TEOS treatment at room temperature produced a pillared molecular sieve with the expected mesoporous characteristics, namely a pore size of around 3 nm and a high intensity low angle (001) peak at 2.3° 2θ, and a d-spacing of 3.8 nm, in the XRD. The characterization aiming to elucidate the nature of the obtained unusual products included gas adsorption isotherms, aberration corrected (Cs-corrected) Scanning Transmission Electron Microscopy (STEM) studies and 29Si solid state NMR. BET surface area values decreased with the temperature of TEOS treatment from approximately 1200 m2 g-1 to ∼900 and 600 m2 g-1, at room temperature, 100 °C, and 120 °C, respectively. The 29Si solid state NMR revealed the presence of both Q3 ((SiO)3SiOX, X = H or minus charge) and Q4 ((SiO)4Si) centers giving separated signals up to the pillaring step. After pillaring at 100 °C and calcination, the nominal intensity ratios Q4 : Q3 were 2.17 and 2.61 but the signals were merged into one broad peak indicating the structural heterogeneity of Si-O coordination. The microscopy showed the presence of FER layers in the samples but the overall structure and composition were not well-defined. The observed unusual disorganization and possible partial degradation of layers during pillaring may result from the combination of high temperature, alkalinity (surfactant hydroxide) and siliceous composition of the layers. The obtained pillared products are of interest for the preparation of larger pore catalysts and sorbents or controlled drug delivery.
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Non-porous and porous materials prepared by cross-linking of polyhydromethylsiloxane with silazane compounds. Eur Polym J 2018. [DOI: 10.1016/j.eurpolymj.2017.12.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Boron‐Doped Polygonal Carbon Nano‐Onions: Synthesis and Applications in Electrochemical Energy Storage. Chemistry 2017; 23:7132-7141. [DOI: 10.1002/chem.201700914] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Indexed: 11/10/2022]
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Alteration of the structure and surface composition of crystalline-amorphous porous clay heterostructures upon iron doping from metal-organic source. SURF INTERFACE ANAL 2016. [DOI: 10.1002/sia.6011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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20
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Ammonolytical conversion of microcrystalline gallium antimonide GaSb to nanocrystalline gallium nitride GaN: thermodynamics vs. topochemistry. RSC Adv 2015. [DOI: 10.1039/c5ra16868f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Reaction of microcrystalline powders of gallium antimonide GaSb with ammonia afforded in one step high yields of nanocrystalline powders of the semiconductor gallium nitride GaN. The product was made as a mixture of the cubic and hexagonal polytypes.
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Improving the accuracy of PGSE DTI experiments using the spatial distribution of b matrix. Magn Reson Imaging 2014; 33:286-95. [PMID: 25460327 DOI: 10.1016/j.mri.2014.10.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 10/21/2014] [Indexed: 11/17/2022]
Abstract
A novel method for improving the accuracy of diffusion tensor imaging (DTI) is proposed. It takes into account the b matrix spatial variations, which can be easily determined using a simple anisotropic diffusion phantom. In opposite to standard numerical procedure of the b matrix calculation that requires the exact knowledge of amplitudes, shapes and time dependencies of diffusion gradients, the new method, which we call BSD-DTI (B-matrix spatial distribution in DTI), relies on direct measurements of its space-dependent components. The proposed technique was demonstrated on the Bruker Biospec 94/20USR system, using the spin echo diffusion sequence to image an isotropic water phantom and an anisotropic capillary phantom. The accuracy of the diffusion tensor determination was improved by an overall factor of about 8 for the isotropic water phantom.
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Production of laser-polarized 3He gas via metastability exchange optical pumping for magnetic resonance imaging. BIO-ALGORITHMS AND MED-SYSTEMS 2014. [DOI: 10.1515/bams-2014-0004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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23
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High acidity unilamellar zeolite MCM-56 and its pillared and delaminated derivatives. Dalton Trans 2014; 43:10501-11. [DOI: 10.1039/c4dt00130c] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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SiOC glasses produced from silsesquioxanes by the aerosol-assisted vapor synthesis method. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2013; 112:440-445. [PMID: 23746385 DOI: 10.1016/j.saa.2013.05.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 04/27/2013] [Accepted: 05/02/2013] [Indexed: 06/02/2023]
Abstract
In this paper, we describe a new method based on aerosol-assisted vapor synthesis for making glass materials by pyrolysis of readily available silsesquioxanes CH3Si(OCH3)3 and CH3Si(OC2H5)3. Combined powder X-ray diffraction (XRD) and spectroscopic studies in the far infrared region (FIR) showed that under applied conditions the method yielded amorphous materials. Subsequent structural studies with the application of the (29)Si and (13)C MAS NMR, Raman, and middle infrared (MIR) techniques led to the conclusion that the pyrolysis of the silsesquioxane precursors resulted in glass materials with a structure of amorphous silica v-SiO2. In the case of certain glasses prepared from CH3Si(OCH3)3, they were also shown to possess in the structure some Si-C bonds (black glasses), whereas those originated from CH3Si(OC2H5)3 were composites that in addition to the silica glass phase contained domains of free/unbound carbon.
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A study on the melting and crystallization of polyoxymethylene-copolymer/hydroxyapatite nanocomposites. POLYM ADVAN TECHNOL 2012. [DOI: 10.1002/pat.3086] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Immobilization of a cationic ruthenium(II) complex containing the hemilabile phosphaallyl ligand in hexagonal mesoporous silica (HMS) and application of this material as hydrogenation catalyst. J Organomet Chem 2008. [DOI: 10.1016/j.jorganchem.2007.11.032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Oxidation of cyclooctane over Mn(TMPyP) porphyrin-exchanged Al,Si-mesoporous molecular sieves of MCM-41 and SBA-15 type. Catal Today 2006. [DOI: 10.1016/j.cattod.2006.02.015] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Deuteron NMR spectra of ammonium ion isotopomers at low temperatures. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2005; 28:142-59. [PMID: 16081254 DOI: 10.1016/j.ssnmr.2005.07.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Revised: 07/06/2005] [Accepted: 07/08/2005] [Indexed: 05/03/2023]
Abstract
Partially deuterated ammonium compounds contain ammonium ion isotopomers with relative abundances given by the binomial distribution of protons and deuterons. All isotopomers with deuterons contribute characteristic deuteron NMR spectra at 5K. Experimental NMR spectra were separated and respective contributions of isotopomers were determined. The derived contributions agree with expected values for a given deuteration in the case of ammonium hexafluorophosphate. In ammonium hexachlorotellurate both NH2D2+ and about 50% of NH3D+ ions are rigid, while the remaining NH3D+ perform limited jumps. NHD3+ and ND4+ ions undergo tunnelling rotation, NH3D+ ions perform either jumps about C2 axis or limited jumps, but some stay rigid in ammonium hexachlorostannate. NH2D2+, NHD 3+ and ND4+ undergo rotational tunnelling. In the case of ammonium perchlorate, the NH3D+ ions perform either jumps about C3 axis or limited jumps whilst some remain rigid. Very low values of activation energies were derived for all spectral components from the temperature dependence of their spectra, up to about 20K, which indicates an incoherent tunnelling nature of the observed dynamic processes. The diverse mobility of NH3D+ ions appears to be the most interesting and new feature.
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Missing first points and phase artifact mutually entangled in FT NMR data--noniterative solution. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2005; 173:140-152. [PMID: 15705522 DOI: 10.1016/j.jmr.2004.11.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Revised: 07/21/2004] [Indexed: 05/24/2023]
Abstract
Even moderate distortion at the beginning of the NMR signal contributes significantly to the baseline in the reciprocal domain, when the FID-type experiment is considered. If constant phase artifact is also involved, the net problem cannot be resolved accurately, according to its constituents considered in separation. This issue is particularly severe for powder patterns in solids, featuring complex broadband spectra, which substantially mask the baseline behavior. The complete correction procedure should intrinsically deal with both artifacts, due to the mutual dependency. The aim of this work is to indicate the possibility for the exact treatment of baseline and constant phase artifacts together, providing precise measure whether the correction is successful. We have found the analytical, noniterative solution for this coupled problem in the closed form. In this paper, we introduce the correction efficiency concept in order to have the measure for the correction reliability of the resulting spectrum. Relevant efficiency parameter eta is the subject for quantitative analysis resulting in certain constraints for the measurement. We have determined exemplar trends for this parameter as a function of experimental variables such as signal-to-noise ratio and missing points number. The method is model-free and drawn from the origin of the baseline artifact; therefore has potential to work for a broad range of applications.
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Preparation and surface properties of low-density gels synthesized using prepolymerized silica precursors. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:10389-10393. [PMID: 15544364 DOI: 10.1021/la0400656] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Properties of silica xerogels and aerogels synthesized using a number of prepolymerized silica precursors were probed by 29Si magic-angle spinning (MAS) NMR spectroscopy, the small-angle X-ray scattering (SAXS) method, the nitrogen adsorption method, and transmission electron microscopy (TEM) to show that xerogels with attractive textural properties can easily be prepared using this type of precursors and the conventional one-step, base procedure. Pore sizes and overall pore volumes in these materials can be notably larger than those in the corresponding materials synthesized using tetraethoxysilane. This positive effect stems from the stronger structure of the polymeric network due to a higher degree of silica condensation on one side and a larger thickness of polymeric chains on the other. The thorough investigations of the fine silica structure demonstrate, however, that the relationship between the microstructure of the silica precursor and the micro- and macrostructures of dry gels is complex and the use of more condensed precursors favors, but does not necessarily ensure, more porous dry materials, under the same reaction conditions. Ethyl silicate 40 may be recommended as a low-cost precursor suitable for applications in this situation.
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Deuteron NMR study of ammonium ion mobility near the order–disorder phase transition in (ND4)2PbCl6. Chem Phys Lett 2003. [DOI: 10.1016/s0009-2614(02)01692-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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ND4+ and NH3D+ dynamics in ammonium persulphate. II. Transition from low-to-high-temperature regime. J Chem Phys 2002. [DOI: 10.1063/1.1518024] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Location of the H atoms in ammonium persulphate by deuteron NMR. Verification by X-ray diffraction. ACTA CRYSTALLOGRAPHICA SECTION B: STRUCTURAL SCIENCE 2002; 58:760-9. [PMID: 12324688 DOI: 10.1107/s0108768102011199] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2002] [Accepted: 06/24/2002] [Indexed: 11/10/2022]
Abstract
It is demonstrated that H atoms can be located by the spectroscopic method of deuteron NMR. The requirement is that the 'heavy-atom' positions are known from diffraction studies. The technique allows an accuracy of the order of 0.01 A. The compound studied is ammonium persulphate (APS), (NH(4))(2)S(2)O(8). APS crystallizes in space group P2(1)/n with lattice parameters a = 6.1340 (2), b = 7.9324 (3), c = 7.7541 (3) A and beta = 94.966 (1) degrees at T = 118 K. In perdeuterated crystals of APS, only one of the deuterons of every ND(4)(+) ion becomes localized at low temperatures. Therefore, most of this work uses samples with 9% deuteration. In such crystals, most of the ammonium ions containing deuterons come in the form of NDH(3)(+) ions. At T < 25 K, the single deuteron of these ions becomes localized in one of four equilibrium sites. The deuteron site occupancies differ from each other and are measured at 17 K. The deuterons are located in three steps. (i) The deuteron quadrupole-coupling (QC) tensors are measured at 17 K. Their unique principal directions are identified, as is well justified, with the N-D bond directions. (ii) The fine structure of a deuteron NMR line is analyzed in terms of the magnetic dipole-dipole interactions between all nuclei in an NDH(3)(+) ion to obtain the N-D and D-H internuclear distances. (iii) An empirical relation between deuteron QC constants and D.O distances in N-D.O hydrogen bonds is exploited to assign the N-D bond vectors to the appropriate N atom of which there are four in the unit cell. The results are highly relevant for an understanding of the complex tunnelling and stochastic reorientation dynamics of the ammonium ions in APS. They are verified by a complementary X-ray diffraction study.
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Deuteron NMR study of the diverse mobility of the ammonium ions in the ordered phase of (ND4)2PtCl4. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2002; 22:373-393. [PMID: 12469821 DOI: 10.1006/snmr.2002.0076] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A detailed description of the diverse mobility of the ND4+ ions in the low-temperature ordered phase of (ND4)2PtCl4 is developed on the basis of single-crystal deuteron NMR spectra and site-selective T1 measurements. The ordered phase of (ND4)2PtCl4 consists of two kinds of domains in which the orientation of the ND4+ tetrahedra differs by a 90 degrees rotation about an axis which otherwise is a two-fold symmetry axis of the tetrahedra. Inside the domains, the ND4+ ions do not reorient at low temperatures. The domains are separated by domain walls which contain, according to the deuteron NMR spectra, about 10% of all ND4+ ions. These ions are highly mobile even at 10 K. On rising the temperature, the thickness of the domain walls increases, that is, the ions in more and more layers become mobile. Moreover, we provide evidence for fluctuations of the locations of the domain walls. The central resonance of the domain-wall ions shows a complicated structure below 36 K. On the basis of a tunnelling hypothesis we make an attempt to account for this structure. There are indications that the tunnelling process is incoherent.
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The dynamics of ND4+ and NH3D+ groups in ammonium persulphate studied by deuteron nuclear magnetic resonance. I. Tunneling and stochastic reorientations at low temperatures. J Chem Phys 2002. [DOI: 10.1063/1.1476698] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Iterative lineshape analysis of quadrupolar echo spectra of a damped CD(3) quantum rotor: preliminary evidence of a novel mechanism of stochastic spin exchange. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2001; 148:277-288. [PMID: 11237633 DOI: 10.1006/jmre.2000.2252] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
It is demonstrated that the wealth of information about damped quantum rotation of CD(3) groups, contained in quadrupolar echo spectra, can be fully explored in a broad temperature range using a method of iterative analysis of the spectral lineshapes. The recently reported lineshape equation which, apart from the quantum tunneling and the dissipative Alexander--Binsch terms, contains an additional dissipative term having no classical analog is shown to be capable of describing even subtle details of the spectra of a crystal of acetylsalicylic acid--CD(3) oriented specifically in the magnetic field. Preliminary evidence of the occurrence of this novel dissipative mechanism in the system studied is reported. The results obtained seem to suggest that there is no "classical limit" in the dissipative behavior of this system.
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Abstract
One- (1-D) and two-dimensional (2-D) carbon-13 NMR exchange measurements in powder samples of isotopically normal durene under magic angle spinning (MAS) are reported. The experiments include rotor synchronized 2-D exchange (RS2DE), 1-D magnetization transfer (MT) and time reverse ODESSA (tr-ODESSA). The latter two experiments were performed as a function of several external parameters, including proton decoupling field during mixing time, sample spinning rate and partly, of temperature. The effects of these parameters on the spin exchange induced by spin diffusion and by chemical, or physical exchange, is discussed. Spin exchange between all types of carbons in the durene molecules occurs on the time scale of seconds. From the dependence of the spin exchange rate on the external parameters it is concluded that the process is dominated by spin diffusion. On the basis of these results an upper limit of 10(-16) cm2 s(-1) can be set for the self-diffusion constant in crystalline durene.
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The synergetic effect of cobalt and indium in ferrierite catalysts for selective catalytic reduction of nitric oxide with methane. Chem Commun (Camb) 1998. [DOI: 10.1039/a808314b] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Anisotropy of the proton T1 and the low-field relaxation in NH4 ClO4 below 20K. SOLID STATE NUCLEAR MAGNETIC RESONANCE 1996; 7:105-119. [PMID: 8986023 DOI: 10.1016/s0926-2040(96)01247-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The spin-lattice relaxation of protons in NH4ClO4 at low temperatures has been studied theoretically and experimentally. The NH4 librational tunneling determines the spin-librational wavefunctions, which are derived first. The dominant transition rates related to the magnetic dipolar interaction between the NH4 protons are then obtained. They reproduce well the angular dependence of the proton relaxation time. When all the transition rates are taken into account, both the temperature and frequency dependence of the relaxation rate agree with our experimental data for a powder sample. Reasons for the non-exponential relaxation are discussed. Apart from the angular dependence of the relaxation rate, they include the tunnel frequency distribution, the coupling to the tunnel reservoir and the effect of deuterons in their natural concentration.
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Novel “ship-in-the-bottle” type catalyst: evidence for encapsulation of 12-tungstophosphoric acid in the supercage of synthetic faujasite. Catal Letters 1996. [DOI: 10.1007/bf00813725] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Coherent isotropic averaging in zero‐field nuclear magnetic resonance. I. General theory and icosahedral sequences. J Chem Phys 1995. [DOI: 10.1063/1.469584] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Coherent isotropic averaging in zero‐field nuclear magnetic resonance. II. Cubic sequences and time‐reversal of spin couplings. J Chem Phys 1995. [DOI: 10.1063/1.469585] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Theoretical aspects of higher‐order truncations in solid‐state nuclear magnetic resonance. J Chem Phys 1992. [DOI: 10.1063/1.463321] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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