Micro‐Raman investigation of transition‐metal‐doped ZnO nanoparticles

We measured the Raman spectra of ZnO nanoparticles (ZnO‐NPs), as well as transition‐metal‐doped (5% Mn(II), Fe(II) or Co(II)) ZnO nanoparticles, with an average size of 9 nm. A typical Raman peak at 436 cm⁻¹ is observed in the ZnO‐NPs, whereas Zn_1−xMn_xO, Zn_1−xFe_xO and Zn_1−xCo_xO presented characteristic peaks at 661, 665 and 675 cm⁻¹, respectively. These peaks can be related to the formation of Mn₃O₄, Fe₃O₄ and Co₃O₄ species in the doped ZnO‐NPs. Moreover, these samples were analyzed at various laser powers. Here, we observed new vibrational modes (512, 571 and 528 cm⁻¹), which are specific to Mn, Fe and Co dopants, respectively, and ZnO‐NPs did not reveal any additional modes. The new peaks were interpreted either as disorder activated phonon modes or as local vibrations of Mn‐, Fe‐ and Co‐related complexes in ZnO. Copyright © 2007 John Wiley & Sons, Ltd.     

Micro‐Raman and portable Raman spectroscopic investigation of blue pigments in selected Delft plates (17–20th Century)

The blue pigment as well as other materials in a blue, white and ‘gold’ 17th century Delft dish were analysed and compared to the blue pigment(s) used in a modern blue‐and‐white Delft dish, obtained from a tourist shop in Amsterdam in 2004. The ancient Delft blue pigment was compared to a commercial Delft blue powder identified as a cobalt‐doped willemite, Zn_2−xCo_xSiO₄. The 17th century Delft pigment showed a closer correspondence to the olivine, alpha‐cobalt silicate. The pigment in the modern blue Delft dish was mainly a vanadium‐doped zircon, ZrSiO₄:V⁴⁺, with small amounts of cobalt, identified by EDX analysis. The cobalt compound could, however, not be characterised here for the modern dish. The pigment in the ‘golden’ rim was identified as pyrochlore yellow, PbSnSbO_6.5. Copyright © 2009 John Wiley & Sons, Ltd.     

EPMA mapping method for small particles of Al3Fe,Al6Fe, α‐AlFeSi and β‐AlFeSi in 1050‐H18 aluminum sheets

We developed an EPMA mapping method for small Al_aFe_bSi_c particles in 1050‐H18 aluminum sheet, which is one of the base materials coated by photoresist in advance called PS plate (pre‐sensitized printing plate). In this method, we used the ratios of relative x‐ray intensities, I_Fe/I_Al and I_Fe/I_Si instead of the mass ratios, Fe/Al and Fe/Si, of the main elements which constitute the particles and tried to determine the ratios of relative x‐ray intensities using Monte Carlo calculations. Furthermore, using this developed mapping method, we performed the mapping of small Al_aFe_bSi_c particles such as Al₃Fe (0–3%Si as impurities), Al₆Fe (0–1%Si as impurities), α‐AlFeSi(Al_8.3Fe₂Si) and β‐AlFeSi(Al_8.9Fe₂Si₂) in 1050‐H18 aluminum sheets. We found that the discrimination of these particles was achieved with this mapping method. We confirmed that this method is useful for the mapping of Al_aFe_bSi_c particles in 1050‐H18 aluminum sheets. Copyright © 2004 John Wiley & Sons, Ltd.     

Study of spin–phonon coupling in LiFe1 − xMnxPO4olivines

LiFe_{1 − x}Mn_xPO₄ olivines are promising material for improved performance of Li‐ion batteries. Spin–phonon coupling of LiFe_{1 − x}Mn_xPO₄ (x = 0, 0.3, 0.5) olivines is studied through temperature‐dependent Raman spectroscopy. Among the observed phonon modes, the external mode at ~263 cm⁻¹ is directly correlated with the motions of magnetic Fe²⁺/Mn²⁺ ions. This mode displays anomalous temperature‐dependent behavior near the Néel temperature, indicating a coupling of this mode with spin ordering. As Mn doping increases, the anomalous behavior becomes clearly weaker, indicating the spin–phonon coupling quickly decreases. Our analyses show that the quick decrease of spin–phonon coupling is due to decrease of the strength of spin–phonon coupling, but not change of spin‐ordering feature with Mn doping. Importantly, we suggest that the low electrochemical activity of LiMnPO₄ is correlated with the weak spin–phonon coupling strength, but not with the weak ferromagnetic ground state. Our work would play an important role as a guide in improving the performances of future Li‐ion batteries. Copyright © 2015 John Wiley & Sons, Ltd.     

Vibrational spectroscopy study of hydrothermally produced scorodite (FeAsO4·2H2O), ferric arsenate sub‐hydrate (FAsH; FeAsO4·0.75H2O) and basic ferric arsenate sulfate (BFAS; Fe[(AsO4)1−x(SO4)x(OH)x]·wH2O)

Three crystalline ferric arsenate phases: (1) scorodite; FeAsO₄·2H₂O, (2) ferric arsenate sub‐hydrate (FAsH; FeAsO₄·0.75H₂O) and (3) basic ferric arsenate sulfate (BFAS; Fe[(AsO₄)_1−x(SO₄)_x(OH)_x]·wH₂O) synthesized by hydrothermal precipitation (175–225 °C) from Fe(III)‐AsO₄³⁻–SO₄²⁻ solutions have been investigated via Raman and infrared spectroscopies. The spectroscopic nature of these high‐temperature Fe(III)‐ AsO₄³⁻–SO₄²⁻ phases has not been extensively studied despite their importance to the hydrometallurgical industrial processing of precious metal (Au and Cu) arsenic sulfidic ores. It was found that scorodite, FAsH and BFAS all gave rise to very distinct arsenate, sulfate and hydroxyl vibrations. In scorodite and FAsH, the distribution of the internal arsenate modes was found to be distinct, with the factor effect being more predominant in the crystal system. For the crystallographically unknown BFAS phase, vibrational spectroscopy was used to monitor the arsenate ↔ sulfate solid solution behavior that occurs in this phase where the molecular symmetry of arsenate and sulfate in the crystal structure is reduced from an ideal T_d to a distorted T_d or C₂/C_2v symmetry. With the new collected vibrational data of the pure phases, the use of attenuated total reflectance infrared (ATR‐IR) spectroscopy was finally extended to investigate the nature of the arsenate in an industrial residue generated by pressure oxidation of a gold ore, where it was found that the arsenate was present in the form of BFAS. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoelectrochemical properties of texture‐controlled nanostructured α‐Fe2O3 thin films prepared by AACVD

Nanostructured α‐Fe₂O₃ thin film electrodes were deposited by aerosol‐assisted chemical vapour deposition (AACVD) for photoelectrochemical (PEC) water splitting on conducting glass substrates using 0.1 M methanolic solution of Fe(acac)₃. The XRD analysis confirmed that the films are highly crystalline α‐Fe₂O₃ and free from other iron oxide phases. The highly reproducible electrodes have an optical bandgap of ～2.15 eV and exhibit anodic photocurrent. The current–voltage characterization of the electrodes reveals that the photocurrent density strongly depended on the film morphology and deposition temperature. Scanning electron microscopy (SEM) analysis showed a change in the surface morphology with the change in deposition temperature. The films deposited at 450 °C have nanoporous structures which provide a maximum electrode/electrolyte interface. The maximum photocurrent density of 455 µA/cm² was achieved at 0.25 V vs. Ag/AgCl/3M KCl (～1.23 V vs. RHE) and the incident photon to electron conversion efficiency (IPCE) was 23.6% at 350 nm for the electrode deposited at 450 °C. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Lithium solvation and diffusion in the 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

The Raman spectra of (1 − x)(BMITFSI), xLiTFSI ionic liquids, where 1‐butyl‐3‐methylimidazolium cation (BMI⁺) and bis(trifluoromethane‐sulfonyl)imide anion (TFSI⁻) are analyzed for LiTFSI mole fractions x < 0.4. As expected from previous studies on similar TFSI‐based systems, most lithium ions are shown to be coordinated within [Li(TFSI)₂]⁻ anionic clusters. The variation of the self‐diffusion coefficients of the ¹H, ¹⁹F, and ⁷Li nuclei, measured by pulsed‐gradient spin‐echo NMR (PGSE‐NMR) as a function of x, can be rationalized in terms of the weighted contribution of BMI⁺ cations, TFSI⁻ ‘free’ anions, and [Li(TFSI)₂]⁻ anionic clusters. This implies a negative transference number for lithium. Copyright © 2008 John Wiley & Sons, Ltd.     

Conformational analysis of 4,4‐dimethyl‐1‐(trifluoromethylsulfonyl)‐1,4‐azasilinane and 2,2,6,6‐tetramethyl‐4‐(trifluoromethylsulfonyl)‐1,4,2,6‐oxazadisilinane

4,4‐Dimethyl‐1‐(trifluoromethylsulfonyl)‐1,4‐azasilinane 1 and 2,2,6,6‐tetramethyl‐4‐(trifluoromethylsulfonyl)‐1,4,2,6‐oxazadisilinane 2 were studied by variable temperature dynamic ¹H, ¹³C, ¹⁹F NMR spectroscopy and theoretical calculations at the DFT (density functional theory) and MP2 (Møller‐Plesset 2) levels of theory. Both kinetic (barriers to ring inversion) and thermodynamic data (frozen conformational equilibria) could be obtained for the two compounds. The computations revealed two minima on the potential energy surface for molecules 1 and 2 corresponding to the rotamers with the CF₃SO₂ group directed ‘inward’ and ‘outward’ the ring, the latter being 0.2–0.4 kcal/mol (for 1 ) and 1.1 kcal/mol (for 2 ) more stable than the former. The vibrational calculations at the DFT and MP2 levels of theory give the values of the free energy difference ΔG^o for the ‘inward’ ‘outward’ equilibrium consistent with those determined from the experimentally measured ratio of the rotamers. The structure of crystalline compound 2 was ascertained by X‐ray diffraction analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Self‐association in {2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]‐thienyl}alkanols: an NMR,IR, and single‐crystal X‐ray study

syn‐2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. Single‐crystal X‐ray diffraction study of the 3,4‐ethylenedioxythiophene (EDOT) derivative shows that it exists as a centrosymmetric head‐to‐tail, syn dimer in the solid state. The IR spectra of the solids display only a broad OH absorption around 3300 cm^?1, corresponding to a hydrogen‐bonded species. ¹H Nuclear Overhauser Effect Spectroscopy (NOESY) NMR experiments in benzene reveal interactions between the tert‐butyl groups and the H2 and H6 protons of the pyridyl group. Two approaches have been used to determine association constants of the EDOT derivative by NMR titration, based on the concentration dependence of (i) the syn/anti ratio and (ii) the OH proton shift of the syn rotamer. Reasonably concordant results are obtained from 298 to 323 K (3.6 and 3.9 M^?1, respectively, at 298 K). Similar values are obtained from the syn OH proton shift variation for the 3,4‐methylenedioxythiophene (MDOT) derivative. Concentration‐dependent variation of the anti OH proton shift in the latter suggests that the anti isomer associates in the form of an open, singly hydrogen‐bonded dimer, with a much smaller association constant than the syn rotamer. Self‐association constants for 3‐pyridyl‐EDOT‐alkanols with smaller substituents vary by a factor of 4 from (i‐Pr)₂ up to (CD₃)₂, while the hetero‐association constants for the same compounds with pyridine vary slightly less. Copyright © 2007 John Wiley & Sons, Ltd.     

Facile Synthesis of Gd(OH)3‐Doped Fe3O4 Nanoparticles for Dual‐Mode T1‐ and T2‐Weighted Magnetic Resonance Imaging Applications

The facile hydrothermal synthesis of polyethyleneimine (PEI)‐coated iron oxide (Fe₃O₄) nanoparticles (NPs) doped with Gd(OH)₃ (Fe₃O₄‐Gd(OH)₃‐PEI NPs) for dual mode T₁‐ and T₂‐weighted magnetic resonance (MR) imaging applications is reported. In this approach, Fe₃O₄‐Gd(OH)₃‐PEI NPs are synthesized via a hydrothermal method in the presence of branched PEI and Gd(III) ions. The PEI coating onto the particle surfaces enables further modification of poly(ethylene glycol) (PEG) in order to render the particles with good water dispersibility and improved biocompatibility. The formed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs have a Gd/Fe molar ratio of 0.25:1 and a mean particle size of 14.4 nm and display a relatively high r₂ (151.37 × 10^?3m ^?1 s^?1) and r₁ (5.63 × 10^?3m ^?1 s^?1) relaxivity, affording their uses as a unique contrast agent for T₁‐ and T₂‐weighted MR imaging of rat livers after mesenteric vein injection of the particles and the mouse liver after intravenous injection of the particles, respectively. The developed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs may hold great promise to be used as a contrast agent for dual mode T₁‐ and T₂‐weighted self‐confirmation MR imaging of different biological systems.     

Raman investigations of Zn1−xCoxO nanocrystals: role of starting precursors on vibrational properties

The Raman spectra of sol–gel derived Co‐doped ZnO nanoparticles (NPs) in the spectral range 100–1500 cm⁻¹ were investigated. In the sol–gel method, three different series of Co‐doped ZnO particles, i.e. Zn_1−xCo_xO (x = 0.05, 0.10, 0.15, and 0.20), were obtained using three different starting precursors, viz. cobalt chloride hexahydrate, cobalt acetate tetrahydrate, and cobalt nitrate hexahydrate, respectively. It has been observed that cobalt acetate is a better precursor in comparison to cobalt chloride and cobalt nitrate to obtain single‐phase Co‐doped ZnO NPs. As for cobalt acetate‐derived NPs, no hidden secondary phase of Co₃O₄ was observed for the lower (x = 0.05) Co concentration. The Fröhlich interaction associated with the longitudinal modes was found to be destroyed with increasing Co concentration due to structural disorder and defects induced by the dopant. In addition to ZnO and Co₃O₄ vibrational modes, a few additional modes near 550 and 715 cm⁻¹ were also observed in all cases, which could be attributed to the modes due to Co doping in ZnO. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectra of apatites: La10−x Si6−y (Al,Fe)y O26±δ

Raman spectra of eight polycrystalline apatites of the general formula La_10−xSi_6−yM′_yO_{26 ± δ} with M′ = Al or Fe were obtained at 300 K. Raman spectra of La₁₀Si₄Fe₂O₂₆ and La_9.83Si_4.5Al_1.5O₂₆ were investigated in the range 80–1000 K and 80–623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO₄ tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm⁻¹ when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al‐ and Fe‐substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm⁻¹ for La₁₀Si₄Fe₂O₂₆ is replaced by a strong band at 868 cm⁻¹, suggesting that SiO₄ tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so‐called two‐mode behavior. The occurrence of FeO stretching vibrations 150 cm⁻¹ lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe⁴⁺ species. Copyright © 2006 John Wiley & Sons, Ltd.     

Magnetic and Elastic Vibrations in Manganese–Zinc Spinel Crystals as the Functions of Anisotropy Constant

The amplitudes of magnetic and elastic vibrations for Mn_0.61Zn_0.35Fe_2.04O₄ spinel crystalline slab are calculated by solving the equations describing the magnetic and elastic dynamics. The anisotropy constants, magnetization, second-order elastic constants and magnetoelastic coupling constants for a studied crystal are expressed as the functions of temperature. The magnetization vector and elastic shear components are found as the functions of the first magnetic anisotropy constant at different values of an external constant magnetic field greater than a saturation field. The procession patterns for normally and tangentially magnetized slabs are displayed for two values of the first anisotropy constant. High absolute values of the first anisotropy constant are shown to refer to reorientation of the magnetization vector.     

Raman and ab initio study of the conformational isomerism in the 1‐ethyl‐3‐methyl‐imidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

The calculated and experimental Raman spectra of the (EMI⁺)TFSI⁻ ionic liquid, where EMI⁺ is the 1‐ethyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI⁺ and TFSI⁻ conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non‐planar (np) EMI⁺ conformers are identified using the reference (EMI⁺)Br⁻ salt. The anion conformer of C₂ symmetry is confirmed to be more stable than the cis (C₁) one by 4.5 ± 0.2 kJ mol⁻¹. At room temperature, the population of trans (C₂) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C₂ anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C₁ anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.     

Multifunctional Plasmonic Co‐Doped Fe2O3@polydopamine‐Au for Adsorption,Photocatalysis, and SERS‐based Sensing

A new type of multifunctional plasmonic nanoparticles, cobalt‐doped Fe₂O₃@polydopamine‐Au (Co‐Fe₂O₃@PDA‐Au), is fabricated via coating PDA through self‐polymerization onto Co‐Fe₂O₃ and further loading gold nanoparticles by in situ reduction onto the surface of PDA shell. Benefiting from the universal adhesive ability of PDA and negative zeta potetntial of the composite, the Co‐Fe₂O₃@PDA‐Au shows strong adsorptivity for cationic dyes. The presence of gold nanoparticle with the diameter of 15 nm in the Co‐Fe₂O₃@PDA‐Au system promotes surface‐enhanced Raman scattering (SERS) activity with an impressive detection limit of 1 × 10^?6 m . Thanks to the synergistic effect of the light harvesting of PDA, the surface plasmon resonance of Au, and the electron conductibility of PDA and Au, the Co‐Fe₂O₃@PDA‐Au exhibits an enhanced photocatalytic activity comparing with unmodified Co‐Fe₂O₃. All the above‐mentioned functions enable Co‐Fe₂O₃@PDA‐Au to be a multifunctional material system for various applications toward environmental pollutants.     

Crystallization of Fe75Zr25 metallic glass: a two‐step process involving metastable bcc‐Fe and polymorphic transformation

The crystallization process of mechanically alloyed Fe₇₅Zr₂₅ metallic glasses is investigated by means of both thermo‐magnetization and in situ neutron powder thermo‐diffraction experiments in the temperature range 300–1073 K. It was found that the crystallization takes place in a two‐step process, involving firstly the appearance of metastable Fe and Fe₂Zr crystalline phases between 880 K and 980 K, and a subsequent polymorphic transformation into Fe₃Zr above 980 K. These findings explain the anomalous magnetization vs. temperature behaviour on heating–cooling cycles.

     

Solvation of AgTFSI in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid investigated by vibrational spectroscopy and DFT calculations

In this paper we investigate the solvation of silver bis(trifluoromethylsulfonyl)imide salt (AgTFSI) in 1‐ethyl‐3‐methylimidazolium TFSI [EMI][TFSI] ionic liquid by combining Raman and infrared (IR) spectroscopies with density functional theory (DFT) calculations. The IR and Raman spectra were measured in the 200–4000 cm⁻¹ spectral region for AgTFSI/[EMI][TFSI] solutions with different concentrations ([AgTFSI] <0.2 mole fraction). The analysis of the spectra shows that the spectral features observed by dissolution of AgTFSI in [EMI][TFSI] solution originate from interactions between the Ag⁺ cation and the first neighboring TFSI anions to form relatively stable Ag complexes. The ‘gas phase’ interaction energy of a type [Ag(TFSI)₃]²⁻ complex was evaluated by DFT calculations and compared with other interionic interaction energy contributions. The predicted spectral signatures because of the [Ag(TFSI)₃]²⁻ complex were assessed in order to interpret the main IR and Raman spectral features observed. The formation of such complexes leads to the appearance of new interaction‐induced bands situated at 753 cm⁻¹ in Raman and at 1015 and 1371 cm⁻¹ in IR, respectively. These specific spectral signatures are associated with the ‘breathing’ mode and the S–N–S and S–O stretching modes of the TFSI anions engaged in the complex. Finally, all these findings are discussed in terms of interaction mechanisms enabling the electrodeposition characteristics of silver from AgTFSI/[EMI][TFSI] IL‐based electrolytic solutions. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural and Optical Properties of Zn1‐xMgxO Prepared by Calcination of ZnO + Mg(OH)2 after Hydro Micro Mechanical Activation

Zn_1‐xMg_xO microcrystals are produced in the 0.15 ≤ x ≤ 1 composition range by calcination of ZnO + Mg(OH)₂ after hydro micro mechanical activation according to the patent WO2018065735A1. The structural properties of the samples have revealed the cohabitation of wurtzite and rock‐salt phases for x values ranging from 0.15 up to 0.6 with a clear increase of the proportion of cubic phase with x. A single cubic phase is observed in the range 0.66 ≤ x < 1. From the purity of these samples produced at very low cost, it is expected that they will be used as precursors for growth of advanced light emitters integrated into an already existing process as they exhibit exceptionally efficient (and robust with T) light emission in the ultraviolet region.     

Surface‐enhanced Raman spectroscopy of 4‐tert‐butylpyridine on a silver electrode

We report the observation of large surface‐enhanced Raman scattering (SERS) (10⁶) for 4‐tert‐butylpyridine molecules adsorbed on a silver electrode surface in an electrochemical cell with electrode potential set at − 0.5 V. A decrease in electrode potential to − 0.3 V was accompanied by a decrease in relative intensities of the vibrational modes. However, there were no changes in vibrational wavenumbers. Comparison of both normal solution Raman and SERS spectra shows very large enhancement of the intensities of a₁, a₂, and b₂ modes at laser excitation of 488 nm. Enhancement of the non‐totally symmetric modes indicates the presence of charge transfer as a contributor to the enhancement. Copyright © 2011 John Wiley & Sons, Ltd.     

Matrix‐isolation IR spectroscopy of R‐(+)‐3‐methylcyclopentanone in para‐hydrogen crystal

High‐resolution infrared (IR) spectra of R‐(+)‐3‐methylcyclopentanone (R3MCP) in para‐hydrogen (pH₂) crystal were recorded and compared with the corresponding IR spectra of R3MCP in Argon (Ar) isolation matrix as well as the IR spectra of the neat crystalline R3MCP at low deposition temperature of 4 ± 0.05 K. Moreover, IR spectra of R3MCP, hosted in pH₂ crystal, were recorded using a high‐resolution Fourier transform IR spectrometer as a function of sample concentration and over the range 10–300 ppm. Furthermore, density functional theory calculations of simulated IR spectra for the optimized geometries of R3MCP equatorial‐methyl and axial‐methyl conformers are compared with experimental spectra for the purpose of investigating molecular conformation. Upon comparison between theoretical and experimental IR spectra, vibrational modes arising from equatorial and axial conformers have been successfully assigned and related to the individual conformer's structure. Copyright © 2015 John Wiley & Sons, Ltd.