scholarly journals On tuning architectonics of nanoscaled assemblies of Zn-Ga-Al -based oxides obtained from layered double hydroxides precursors

2019 ◽  
Author(s):  
Corina E Ignat ◽  
Gabriela Carja ◽  
Laura E Romila ◽  
Doina Lutic
Keyword(s):  
Electron Microscopy ◽  
Layered Double Hydroxides ◽  
Photoelectron Spectroscopy ◽  
Mixed Oxides ◽  
Thermal Transformation ◽  
Thermal Analyses ◽  
Advanced Materials ◽  
X Ray ◽  
Calcination Temperatures ◽  
Double Hydroxides

Nanoscaled self-assemblies with engineered architectonics are important for obtaining advanced materials with specific applications in nanotechnology. We investigated here the morphology features at the nanoscale of the assemblies of the mixed oxides obtained through the thermal transformation of Zn2+Me3+ (Me=Al/Ga) layered double hydroxides (LDHs), as their “as-synthesized” form or after they were reconstructed in the aqueous solution of Ga2(SO4)3. The characteristics of ZnMe LDHs and the derived assemblies of mixed oxides were assessed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM/EDX), N2 adsorption at −196°C and thermal analyses (TG/DTG/DSC). The results revealed the formation nanoscaled assemblies of ZnO/ZnAl2O4/ZnGa2O4 and ZnO/Ga2O3/ZnGa2O4 starting from ZnMe(Me=Al/Ga) as precursors. Results point out that both the composition of the LDHs and the calcination temperatures can be used as parameters for tuning the nanomorphology features of the studied mixed oxides.

scholarly journals Designing Magnetic Layered Double Hydroxides and Two-Dimensional Magnetic Nano-Nets of Cobalt Ferrite through a Novel Approach

2018 ◽  
Vol 8 (11) ◽  
pp. 2099 ◽  
Author(s):  
Osama Saber ◽  
Abdullah Aljaafari ◽  
Sarah Asiri ◽  
Khalid Batoo
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Layered Double Hydroxides ◽  
Cobalt Ferrite ◽  
High Coercivity ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Double Hydroxides

The present study has a dual aim of supporting magnetic nanoparticles over the nanolayers of LDHs and designing two-dimensional magnetic nano-nets of cobalt ferrite. In this trend, nanoparticles of CoFe2O4 were prepared and supported by Co-Fe LDH through urea hydrolysis. The nanolayered structures of Co-Fe LDH were confirmed by X-ray diffraction, energy-dispersive X-ray spectrometry, FT-IR spectra, thermal analyses, and transmission electron microscopy. In addition, they indicated that 13.2% CoFe2O4 were supported over Co-Fe LDH. Transformation of the nanolayered structures of Co-Fe LDH to nano-nets was achieved by the catalytic effect of the supported CoFe2O4 nanoparticles through solvent thermal technique. X-ray diffraction patterns and transmission electron microscopy images confirmed the transformation of the supported Co-Fe LDH to nano-nets of cobalt ferrite. In order to indicate the effect of the LDH for designing the nano-nets, nanoparticles of cobalt ferrite were prepared by the same technique without LDH. The magnetic behavior of the nano-nets and the supported Co-Fe LDH were measured and compared with the nanoparticles through vibrating sample magnetometer technique. The magnetic parameters indicated that the prepared nano-nets have ferromagnetic behavior and high coercivity. However, the prepared nanoparticles revealed a superparamagnetic state and low coercivity. The experimental results concluded that the incorporation of nanoparticles with nanowires into nano-net structures has been found to be an efficient way to improve their magnetic properties and prevent their agglomerations. Finally, layered double hydroxides are an important source for constructing magnetic nanolayered structures and nano-nets.

scholarly journals Facet-Dependent Reactivity of Fe2O3/CeO2 Nanocomposites: Effect of Ceria Morphology on CO Oxidation

Catalysts ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 371 ◽  
Author(s):  
Maria Lykaki ◽  
Sofia Stefa ◽  
Sόnia Carabineiro ◽  
Pavlos Pandis ◽  
Vassilis Stathopoulos ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Co Oxidation ◽  
Photoelectron Spectroscopy ◽  
Rational Design ◽  
Mixed Oxides ◽  
Specific Activity ◽  
Catalytic Performance ◽  
Catalytic Systems ◽  
X Ray ◽  
Full Characterization

Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe2O3/CeO2). A full characterization study involving N2 adsorption at –196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe2+ species.

scholarly journals Investigation of Thermal Behavior of Layered Double Hydroxides Intercalated with Carboxymethylcellulose Aiming Bio-Carbon Based Nanocomposites

2019 ◽  
Vol 3 (2) ◽  
pp. 55
Author(s):  
Vagner R. Magri ◽  
Alfredo Duarte ◽  
Gustavo F. Perotti ◽  
Vera R.L. Constantino
Keyword(s):  
Layered Double Hydroxides ◽  
Mixed Oxides ◽  
Degree Of Crystallinity ◽  
X Ray Diffraction ◽  
Experimental Conditions ◽  
X Ray ◽  
Vibrational Spectroscopies ◽  
Xrd Patterns ◽  
Double Hydroxides ◽  
The Degree Of Crystallinity

Carboxymethylcellulose (CMC), a polymer derived from biomass, was intercalated into layered double hydroxides (LDH) composed by M2+/Al3+ (M2Al-CMC, M = Mg or Zn) and evaluated as precursors for the preparation of biocarbon-based nanocomposites by pyrolysis. M2Al-CMC hybrids were obtained by coprecipitation and characterized by X ray diffraction (XRD), vibrational spectroscopies, chemical analysis, and thermal analysis coupled to mass spectrometry. Following, pyrolyzed materials obtained between 500–1000 °C were characterized by XRD, Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Above 600 °C, Raman spectra of all samples showed the presence of graphitic carbon, which plays a role in the degree of crystallinity of produced inorganic phases (for comparison purposes, M2Al-CO3 materials were investigated after calcination in the same experimental conditions). XRD patterns of Mg2Al-CMC pyrolyzed between 600–1000 °C showed poorly crystallized MgO and absence of spinel reflections, whereas for Zn2Al-CMC, it was observed well crystallized nanometric ZnO at 800 °C, and ZnAl2O4 and γ-Al2O3 phases at 1000 °C. Above 800 °C, the carbothermic reaction was noticed, transforming ZnO to zinc vapour. This study opens perspectives for nanocomposites preparation based on carbon and inorganic (mixed) oxides through precursors having organic-inorganic interactions at the nanoscale domain.

Synthesis of Diphenyl Carbonate by Oxidative Carbonylation of Phenol with Pd-Co/Hopcalite

2013 ◽  
Vol 750-752 ◽  
pp. 1292-1295 ◽  
Author(s):  
Hong Xia Guo ◽  
Jing De Lü ◽  
Hui Qiang Wu ◽  
Shu Juan Xiao ◽  
Jie Han
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Mixed Oxides ◽  
Physical Structure ◽  
Crystal Phase ◽  
Oxidative Carbonylation ◽  
Diphenyl Carbonate ◽  
X Ray ◽  
Scanning Electron

Hopcalite mixed oxides were used as support of the catalyst for the synthesis of diphenyl carbonate (DPC) by oxidative carbonylation of phenol .The catalyst was characterized by scanning electron microscopy (SEM), X-ray power diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that the size of the particles is well-distributed and the physical structure is favorable, which contribute to the reaction efficiently. The main crystal phase in catalyst is CuMn2O4, CoMn2O4and Pd0.5Pd3O4, and the valency of Mn and Co remains unchanged. Finally, the synthesis of DPC was carried out and it was found that the yield and selectivity could reach 43.5% and 99.6%, respectively.

scholarly journals Structural analysis of defects in layered double hydroxides and related mixed oxides

2019 ◽  
Vol 62 (1-2) ◽  
pp. 39-54
Author(s):  
N.N. Leont’eva ◽  
V.A. Drozdov ◽  
O.B. Belskaya ◽  
S.V. Cherepanova
Keyword(s):  
Layered Double Hydroxides ◽  
Mixed Oxides ◽  
Simulation Method ◽  
X Ray Diffraction ◽  
Structural Mechanism ◽  
X Ray ◽  
Physicochemical Methods ◽  
The Difference ◽  
Double Hydroxides

This article provides an overview of the results of studying the defects in the structure of MgAl and NiAl layered double hydroxides and their thermal decomposition products up to 1000 °C, obtained over the last 10 years in the laboratory of analytical and physicochemical methods of research at the Institute of Hydrocarbons Processing of the SB RAS. The presented results were performed using the X-ray diffraction pattern simulation method for onedimensional (1D) disordered crystals. Changes in the type of structure defects are found depending on the calcination temperature, including in situ X-ray diffraction. A structural mechanism for the formation of a dehydrated phase at T=200 °C is proposed. New models of MgAl and NiAl oxide structures are presented. The structures of the phases included in the products of hydration of oxides are established. The difference in the behavior of oxides during hydration is explained.

scholarly journals Thermal Evolution of Natural Layered Double Hydroxides: Insight from Quintinite, Hydrotalcite, Stichtite, and Iowaite as Reference Samples for CO3- and Cl-Members of the Hydrotalcite Supergroup

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 961
Author(s):  
Elena S. Zhitova ◽  
H. Chris Greenwell ◽  
Mariya G. Krzhizhanovskaya ◽  
David C. Apperley ◽  
Igor V. Pekov ◽  
...  
Keyword(s):  
High Temperature ◽  
Amorphous Phase ◽  
Layered Double Hydroxides ◽  
Thermal Evolution ◽  
Thermal Transformation ◽  
Thermal Analyses ◽  
Nuclear Magnetic Resonance Analysis ◽  
Spinel Type ◽  
Temperature Range ◽  
Double Hydroxides

In Situ high-temperature powder X-ray diffraction experiments were undertaken for the coarse crystalline natural layered double hydroxides (LDHs) quintinite, hydrotalcite, stichtite, and iowaite in the temperature range 25–1000 °C, with thermal analyses of these minerals and their annealed forms carried out in parallel. In the temperature range from 25 °C to 170–210 °C quintinite, hydrotalcite, and stichtite (carbonate members of the LDH family) demonstrated contraction of the basal d00n-value of 0.1–0.3 Å, followed by a sharp contraction of 1.0–1.1 Å at T > 170–210 °C. The high-temperature modified states were stable up to 380–420 °C, before decomposing to an amorphous phase. Iowaite (chloride member of the family) was stable up to 320 °C and transformed to an amorphous phase at higher temperature. Iowaite experiences continuous contraction of the d00n-value of up to 0.5 Å in the temperature range 25–200 °C, reaching a plateau at a temperature range of 200–320 °C. Assessing the reversibility of thermal transformation shows complete reconstruction of the crystal structure of the hydrotalcite and iowaite heated to 300 °C. Solid-state nuclear magnetic resonance analysis shows that some Al changes coordination from 6- to 4-fold, synchronously with quintinite transformation to the amorphous phase. All phases transform to periclase and a spinel-type compound upon further heating. Thermal analysis of samples annealed at 125 °C shows that carbonate members do not have a tendency to form dehydrated phases, whereas for iowaite, a dehydrated phase having 0.9 apfu lesser water content as in the initial sample has been obtained. Thermal evolution of LDHs is found to depend on the nature of the interaction of interlayer species and water molecules to H atoms of the metal-hydroxide layer.

Syntheses of Mg–Al–NO3 layered double hydroxides with high crystallinity in the presence of amines

2016 ◽  
Vol 94 (1) ◽  
pp. 66-71 ◽  
Author(s):  
Kamellia Nejati ◽  
Azam Mokhtari ◽  
Fatemeh Khodam ◽  
Zolfaghar Rezvani
Keyword(s):  
Electron Microscopy ◽  
Layered Double Hydroxides ◽  
Homogeneous Solution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Analysis Techniques ◽  
Structure And Morphology ◽  
Different Types ◽  
Double Hydroxides ◽  
Scanning Electron

In the present work, layered double hydroxides of Mg–Al were synthesized with nitrate interlayer anions in the presence of different types of amines such as ethylenediamine, dimethylamine, and trimethylamine, without a N2 atmosphere, from a homogeneous solution using the coprecipitation method. The concentration of the different types of amines and pH of the solution were adjusted to produce high-purity and -crystallinity samples. The structure and morphology of layered double hydroxides were characterized and investigated by powder X-ray Diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and thermogravimetric analysis techniques. The analyses showed that with increasing amine concentration, both crystallinity and purity of the samples increase at pH 10.5.

Characterization of Chromate-Intercalated Layered Double Hydroxides

2006 ◽  
Vol 514-516 ◽  
pp. 1541-1545 ◽  
Author(s):  
Margarita del Arco ◽  
Daniel Carriazo ◽  
Cristina Martín ◽  
Amalia M. Pérez Grueso ◽  
Vicente Rives
Keyword(s):  
Layered Double Hydroxides ◽  
Thermal Analyses ◽  
Basal Spacing ◽  
X Ray Diffraction ◽  
N2 Adsorption ◽  
Exchange Method ◽  
X Ray ◽  
Ft Ir ◽  
Double Hydroxides

PXRD (powder x-ray diffraction), FT-IR (Fourier Transform infrared), N2 adsorption at - 196 °C and TG/DTA (thermogravimetric and differential thermal analyses) techniques have been used for characterisation of MgAl- and ZnAl-CrO4 LDHs, which had been prepared by the ion exchange method from the corresponding chloride LDH (layered double hydroxides) precursors. The results indicates that the oxometalate intercalation in both systems produces interlayer microporosity and a basal spacing of 8.7 Å; This gallery height decreases when the samples are calcined in the temperature range 100-300 °C, due to a grafting process. A larger thermal stability is detected for MgAl-CrO4 sample than for the zinc-containing one.

scholarly journals Hydrogen Production from Aqueous Methanol Solutions Using Ti–Zr Mixed Oxides as Photocatalysts under UV Irradiation

Catalysts ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 938 ◽  
Author(s):  
Pérez-Larios ◽  
Rico ◽  
Anaya-Esparza ◽  
Vargas ◽  
González-Silva ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Mixed Oxides ◽  
Sol Gel ◽  
High Resolution Electron Microscopy ◽  
Aqueous Methanol ◽  
Experimental Conditions ◽  
X Ray ◽  
Methanol Solutions ◽  
Aqueous Methanol Solutions

The synthesis and characterisation of Ti–Zr mixed oxides containing 1 to 10 wt.% of Zr is herein reported. In addition, the samples were tested as photocatalysts in the generation of hydrogen from aqueous methanol solutions. The solids were prepared by sol-gel and then characterised by X-ray diffraction, high resolution electron microscopy, X-ray photoelectron spectroscopy, physisorption of nitrogen, scanning electron microscopy, UV-vis and Raman spectroscopies. The results show the presence of anatase as a predominant structure and the oxides present larger specific surface areas than that of pure titania. A maximum value of 168 m2/g was determined for the sample with 5 wt.% of zirconium. The calculated band gap energies varied from 3.05 to 3.15 eV. It was observed that the greater the zirconium content in the solid, the higher the generation rate of hydrogen when testing the Ti–Zr solids as photocatalysts. Under our experimental conditions, the best catalyst, Ti–Zr oxide with 10 wt. % Zr, showed a production rate of 2100 μmol of H2/h which was about tenfold higher than that observed for pure titania.

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