Electrical conductivity of titanium pyrophosphate between 100 and 400 °C: effect of sintering temperature and phosphorus content

The synthesis of titanium pyrophosphate is carried out, and the material is sintered at different temperatures between 370 and 970 °C. Yttrium is added during the synthesis to act as acceptor dopant, but it is mainly present in the material in secondary phases. The conductivity is studied systematically as a function of sintering temperature, pH₂O, pO₂, and temperature (100–400 °C). Loss of phosphorus upon sintering above 580–600 °C is confirmed by energy dispersive spectroscopy and combined thermogravimetry and mass spectrometry. The conductivity decreases with increasing sintering temperature and decreasing phosphorus content. The highest conductivity is 5.3?×?10^?4 S cm^?1 at 140 °C in wet air (pH₂O?=?0.22 atm) after sintering at 370 °C. The conductivity is higher in wet atmospheres than in dry atmospheres. The proton conduction mechanism is discussed, and the conductivity is attributed to an amorphous secondary phase at the grain boundaries, associated with the presence of excess phosphorus in the samples. A contribution to the conductivity by point defects in the bulk may explain the conductivity trend in dry air and the difference in conductivity between oxidizing and reducing atmospheres at 300–390 °C. Slow loss of phosphorus by evaporation over time and changes in the distribution of the amorphous phase during testing are suggested as causes of conductivity degradation above 220 °C.     

Thermal decomposition study of HAuCl4·3H2O and AgNO3 as precursors for plasmonic metal nanoparticles

Thermal decomposition of HAuCl₄·3H₂O and AgNO₃, as precursors for Au and Ag nanoparticles, respectively, was monitored by coupled TG–DTA with TG/EGA–FTIR and EGA–MS techniques in a flowing 80 %Ar + 20 %O₂ and Ar atmospheres in the temperature range of 30–600 °C. The intermediate and final products of thermal decomposition were analysed by ex situ XRD and FTIR techniques. The thermal degradation of HAuCl₄·3H₂O starts immediately after melting at 75 °C and takes place in three steps in the temperature range of 75–320 °C with total mass loss of 49.4 and 49.7 % in artificial air and Ar atmospheres, respectively. EGA by MS and FTIR revealed a simultaneous release of H₂O and HCl in the temperature range of 75–235 °C. EGA by MS revealed a release of Cl₂ at around 225 °C and in the interval of 250–320 °C. According to the XRD analysis, the main solid product in the end of the first decomposition step at 190 °C is AuCl₃; in the end of the second decomposition step at 240 °C is AuCl and the final product at 320 °C is Au. The thermal decomposition of AgNO₃ takes place in a single step in the temperature range of 360–515 °C with a total mass loss of 39.0 and 37.8 % in flowing artificial air and Ar atmospheres, respectively. According to EGA–MS and EGA–FTIR the main evolved gases are NO₂, NO and O₂. The final product of the thermal decomposition at 600 °C is Ag irrespective of the atmosphere.     

Temperature dependence of DC electrical conductivity of kaolin

The samples from kaolin Sedlec were investigated by the help of DTA, TG, and temperature dependences of DC conductivity using Pt wire electrodes and linear heating up to 1,050 °C. After drying, the samples contained ~1.5 mass% of the physically bound water. DTA and TG reflected generally known facts about a release of the physically bound water, dehydroxylation, and metakaolinite → Si–Al spinel transformation. The results of electrical measurements showed the electric current passed over the maximum at 60 °C. The self-ionization of water results in the process H₂O → H⁺ + OH^? in the water layers on the crystal surfaces; consequently, OH^? and H⁺ are the main charge carriers in the low-temperature region. The water molecules simultaneously evaporate from the sample which decreases the number of the charge carriers. When the physically bound water evaporates, the current is carried mostly by K⁺ and Na⁺ ions. During dehydroxylation, the hydroxyls OH^? split into H⁺ and O^2?. The ions H⁺ jump to the neighboring OH^? groups creating the water molecules. The ions O^2?remain bounded to the newly created metakaolinite lattice. Therefore, mobile protons contribute to the electric current. At the same time, this contribution gradually decreases because of the escape of H₂O from the sample. The sharp current peak and DTA peak at 970 °C imply relatively fast metakaolinite → Si–Al spinel transformation. This DC current peak results from the shift of Al³⁺ and O^2? ions into new positions.     

Synthesis and properties of BaCe1−xYxO3−δ–BaWO4 composite protonic conductors

Barium cerate doped by trivalent rare earth metal ions is a potentially huge component of materials for electrochemical industry due to its high protonic conductivity. However, the poor chemical stability especially in the presence of CO₂, SO₂ or H₂O, resulting in decreasing the mechanical durability of obtained materials, limits their possible applications. The new approach towards stable ceramic protonic conductors with high electrical conductivity is presented. Thermal stability of yttrium doped (10 mol%) of BaCeO₃ was enhanced by forming the composite material BaCe_0.9Y_0.1O₃–BaWO₄ (10 mol% of BaWO₄). The synthesis was performed by solid-state reaction method. The detailed study of thermal decomposition of starting powders mixture was performed using thermogravimetry and differential thermal analysis (TG/DTA) techniques combined with Evolved Gas Analysis (EGA—mass spectrometry). Structure, phase composition and microstructure together with thermal stability of sintered materials were determined. The exposition tests were performed to characterise the stability of composites in carbon dioxide and water vapour-rich atmospheres. The samples were exposed to atmosphere containing CO₂/H₂O (7 % of CO₂ in air, 100 % RH) at temperature of 25 °C for 300 h. Thermal analysis supplied with mass spectrometry was applied to analyse the materials after the test. The results of this experiment showed better chemical resistance of composite material—BaCe_0.9Y_0.1O₃ with 10 mol% of BaWO₄ compared to single phase material.     

Synthesis and visible light photocatalytic activity of Ag spot-coated TiO2–60 wt% SrO composite powders

Nano-sized TiO₂–60 wt% SrO composite powders were synthesized from titanium isopropoxide and Sr(OH)₂·8H₂O by use of a sol–gel method. Ag spot-coated TiO₂–60 wt% SrO composite powders containing 3, 5, or 7 wt% Ag were synthesized by hydrothermal-assisted attachment, by use of Ag hydrosol in a high-pressure bomb at 250 °C and 450 psi. Nano-sized Ag particles approximately 5–25 nm in diameter adhered to the TiO₂–60 wt% SrO₂ composite powders. The photocatalytic activity of Ag spot-coated TiO₂–SrO powders in the degradation of phenol showed that all were highly active when irradiated with UV light. TiO₂–60 wt% SrO composite powder spot-coated with 5 wt% Ag was more photocatalytically active under visible light than TiO₂–SrO composite powder.     

Synthesis,characterization and thermal stability of new dumbbell-shaped isobutyl-substituted POSSs linked by aromatic bridges

Five new dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages R₇(SiO_1.5)₈ (with R = isobutyl), linked to various aromatic bridges (Ar, Ar–Ar, Ar–O–Ar, Ar–S–Ar and Ar–SO₂–Ar, where Ar = p-C₆H₄) were prepared through a literature method opportunely modified by us to make easier preparation and increase yield, which was higher than 70 % in all cases. The obtained products were the expected ones, as supported by the results of elemental analysis and ¹H NMR spectra. Their resistance to the thermal degradation in both flowing nitrogen and static air atmosphere was checked by degrading samples at 10 °C min^?1 and determining temperatures at 5 % mass loss (T _5%) and residues at 700 °C. The T _5% values in air were lower than the corresponding ones in nitrogen, but the trend among the various POSSs investigated was the same in both used atmospheres, with the most high value for the compound having the Ar–O–Ar aromatic bridge. The residues at 700 °C in air of the compounds having not hetero-atoms (O or S) in the aromatic bridge were higher than those in nitrogen, whilst no substantial difference was observed for the other ones.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1–20 ng/g) by wet chemistry is challenging. Combustion–trapping techniques have been shown to be an appropriate alternative [1]. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O₂ stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H₂O, CO₂, SO₂, etc. The O₂ carrier gas, including combustion products and elemental Hg, is then purged into a 40 % (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO₃/1HCl (v/v), 25 mL/min O₂ flow rate, and a dynamic temperature ramp rate (15 °C/min for 25–150 and 600–900 °C; 2.5 °C/min for 150–600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81–102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80–120 %. This protocol has the advantages of a short sample processing time (～3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.     

Study of crystallization process of soda lead silicate glasses by thermal and spectroscopic methods

The crystallization process of some glasses in the ternary Na₂O–SiO₂–PbO system with good chemical stability that can be used for waste inertization was studied using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and scanning electron microscopy. The parent glasses were characterized by XRD and FT-IR, and their vitreous state was determined. DTA measurements evidenced glass transition (T _g) and crystallization temperatures (T _c). The thermal treatments were conducted at vitreous transition temperature (400 °C) and at highest effect of crystallization (650 °C). XRD evidenced the lead and sodium silicate crystalline phases in samples treated at 650 °C for 12 h. Micrometer crystallites dispersed in the glass matrices have affected the transparence of glasses and made them opaque after treatment at 650 °C. The influence of oxide quantities in compositions on the crystallization tendency was revealed. A PbO higher content than that of SiO₂ as well as lower Na₂O content decreased the tendency of crystallization.     

Phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia

The phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia (4Y-PSZ) precursor powders have been investigated using the coprecipitation route, using zirconium oxide chloride octahydrate (ZrOCl₂·8H₂O) and yttrium nitrate (Y(NO₃)₃·6H₂O) as the initial materials. Differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), and high resolution TEM (HRTEM) were utilized to characterize the behavior of phase transformation and crystalline growth of the 4Y-PSZ precursor powders after calcined. Tetragonal ZrO₂ crystallization occurred at about 718.2 K. The activation energy of tetragonal ZrO₂ crystallization was 227.0 ± 17.4 kJ/mol, obtained by a non-isothermal method. The growth morphology parameter (n) and growth mechanism index were close to 2.0, showing that tetragonal ZrO₂ had a plate-like morphology. The crystalline size of tetragonal ZrO₂ increased from 7.9 to 27.6 nm when the calcination temperature was increased from 973 to 1,273 K. The activation energies of tetragonal ZrO₂ growth were 14.97 ± 0.33 and 84.46 ± 6.65 kJ/mol when precursor powders after calcined from 723–973 and 973–1,273 K, respectively.     

Solvothermal synthesis and structural characterization of a novel erbium(III)-carboxylate polymeric complex

A novel erbium(III)-carboxylate polymeric complex [{Er(H₂btec)_2/4(btec)_3/6(H₂O)}·2H₂O] _n , simplified as ECPC, (H₄btec=1,2,4,5-benzenetetracarboxylic acid) was synthesized under solvothermal conditions (H₂O/acetic acid). ECPC obtained was characterized by differential thermal analysis/thermogravimetry (DTA/TG), single-crystal X-ray diffraction, elemental analysis and FT-IR analysis techniques. The result of single-crystal X-ray diffraction analysis shows that the ECPC crystallizes in monoclinic symmetry, and the space group P2(1)/n, a=10.6933(15) Å, b=7.1243(10) Å, c=17.092(2) Å, α=γ=90°, β=97.109(2)°, V=1292.1(3) Å³, Z=4, R ₁=0.0286, wR ₂=0.0686. ECPC demonstrates a 3-D supramolecular framework containing nine-coordinate erbium centers and channels. The uncoordinated water molecules occupy the channels in ECPC. The results of TG/DTA, IR and elemental analysis performed also give positive information of the proposed crystal structure.     

Dopant depends on morphological and electrochemical characteristics of LiMn 2– X Mo X O4 cathode nanoparticles

For the first time, solid solutions of LiMn_2–X Mo _X O₄ nanoparticles were synthesized by combustion method at 700 °C in air. The synthesized LiMn_2–X Mo _X O₄ (X?=?0.0–0.2) nanoparticles were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy (FT-IR), Field emission-scanning electron microscopy, and Particle size analysis. The unit-cell constant is increasing from 8.237 to 8.293 Å with the increase of Mo, the presence of Mo at X?≤?0.05 in LiMn_2–X Mo _X O₄ nanoparticles retained the spinel structure (Fd-3m), whereas on increasing the Mo (X?≥?0.05 %), the ordering of Li⁺ ions in both octahedral and tetrahedral cationic position leads to the lowering of symmetry (P4₁32). On increasing the Mo content, prominent peak splitting and broadening are observed at 600–500 and 830 cm^?1 for Li–Mn–O and Mo–O respectively in the FT-IR spectra. The TG/DTA spectrum reveals that the convenient formation of Li mangano-molybdate is at 700 °C. The voltammograms of all the samples show two redox peaks centered around 4 V except for the sample with higher Mo doping (X?=?0.2). The sample with X?=?0.03 shows higher redox peak current values. A marginal increase of 146 Ω R _ct value was found for the LiMn_1.97Mo_0.03O₄ nanomaterial after 10th cycle which is rather high for the rest of the materials. A discharge capacity retention of 88 % at 50th cycle is observed for X?=?0.03 sample, while the other samples exhibit drastically reduced capacity. The LiMn_1.97Mo_0.03O₄ nanoparticle can able to deliver higher and constant discharge capacity, and it may be a good alternative for the existing cathode materials.     

Complex Formation Equilibria of Unusual Seven Coordinate Fe(III) Complexes with DNA Constituents

Seven-coordinate Fe(III) complexes [Fe(dapsox)(H₂O)₂]⁺, where [dapsox = 2,6-diacetylpyridine-bis(semioxamazide)] is an equatorial pentadentate ligand with five donor atoms (2O and 3N), were studied with regard to their acid–base properties and complex formation equilibria. Stability constants of the complexes and the pK _a values of the ligands were measured by potentiometric titration. The interaction of [Fe(dapsox)(H₂O)₂]⁺ with the DNA constituents, imidazole and methylamine·HCl were investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaNO₃. The hydrolysis constants of the [Fe(dapsox)(H₂O)₂]⁺ cation (pK _a1 = 5.94 and pK _a2 = 9.04), the induced ionization of the amide bond and the formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with DNA constituents supporting the hepta-coordination mode of Fe(III). The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for interaction of [Fe(dapsox)(H₂O)₂] with uridine.     

A Computationally Efficient Approach to Applying the SAFT Equation for CO2 + H2O Phase Equilibrium Calculations

The statistical associating fluid theory equation of state (EoS) is employed in a time efficient way for the correlation and prediction of vapor–liquid equilibrium of the CO₂ + H₂O binary system for the temperature (10–100 °C) and pressure (1–600 bar) ranges suitable for simulation of CO₂ geologic sequestration. The effective number of segments and energy parameter are correlated with the reduced temperature. Simple mixing rules are applied to obtain binary interaction parameters. Assigning a fixed H₂O composition in the mixing rule makes the phase equilibrium calculations relatively fast compared to other EoS’s. The results obtained by the model used were found to be in satisfactory agreement with the literature data.     

Growth mechanism and photocatalytic properties of flower-like Bi2WO6 powders synthesized by a microwave hydrothermal method

Pure orthorhombic phase Bi₂WO₆ powders were synthesized by a microwave hydrothermal method in the absence of surfactants and templates, using Bi(NO₃)₃·5H₂O and Na₂WO₄·2H₂O as raw materials. Photocatalytic properties of the samples prepared at different reaction temperatures were also studied with Rhodamine B (RhB) solution as the target catabolite under visible light. The results indicate that flower-like Bi₂WO₆ powders can be obtained by controlling the microwave reaction temperatures in the absence of any additives. The growth of flower-like Bi₂WO₆ powders is a multistage layer assembly process, in which the flower-like Bi₂WO₆ self-assembling with the uniform size about 2 μm is synthesized at 180 °C. At the same time, the photocatalytic reaction rate constant (k) gets up to 0.04167/min and the degradation rate of RhB solution is more than 96 % after being irradiated under visible light for 70 min.     

A thermoanalysis of phase transformations and linear shrinkage kinetics of ceramics made from ultrafine plasmochemical ZrO2(Y)–Al2O3 powders

The methods of X-ray diffraction analysis, thermogravimetric analysis, differential scanning calorimetry, and dilatometry are used to study special features of the structural-phase state of the 80 mass% ZrO₂(Y)–20 mass% Al₂O₃ plasmochemical powders (PCPs) and their effects on the sintering of composite ceramics. It is revealed that the ZrO₂(Y)–Al₂O₃ powder composite represents a mechanical mixture containing crystalline tetragonal zirconium dioxide and aluminum oxide nanoparticles, the latter found in an amorphous state and partially included into the ZrO₂(Y) lattice, thus forming metastable solid solutions of variable composition. Heating of the composite powder within the temperature range 740–1,000 °C reveals an exothermal effect associated with decomposition of metastable states of aluminum oxide. This is accompanied by the formation of the corundum-phase nuclei having subcritical dimensions. They achieve the critical sizes at higher temperatures T > 1200 °C, when α-Al₂O₃ is finally crystallized. The shrinkage response of the powder compacts during non-isothermal sintering is measured in a sensitive dilatometer. It is shown that the shrinkage curve consists of several stages that closely correlate with the concurrent structural-phase transformation in the composite ZrO₂(Y)–Al₂O₃ powder mixture. The decisive contribution into shrinkage during non-isothermal sintering of composite comes from the high-temperature stages with the maximum shrinkage rate at the temperatures 1,250 and 1,550 °C. It is found out that the regime of sintering the ultrafine PCPs (T = 1,600 °C, t = 1 h) allows producing composite ceramic materials with a porosity of Q ≈ (5–7) %, microhardness H _v = 12.3 GPa, and crack resistance К _1c = (10–11) MPa m^0.5.     

Anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their color properties

Synthesis of rutile pigments is based on solid state reaction and on Hedvall effect, i.e., phase transformation from anatase to rutile. Therefore, it is important to know the thermal behavior of these compounds (the temperature of this change). The goal was to prepare rutile pigments of type Ti_1?3xCr_xNb_2xO_2+x/2 by conventional solid state method from titanium dioxide TiO₂ (AV-01, anatase), to determine an influence of composition (x = 0, 0.05, 0.10, 0.20, 0.30, 0.50) and calcination temperature (850; 900; 950; 1,000; 1,050; 1,100; 1,150 °C) on color properties of these compounds and to analyze other starting compounds of titanium (hydrated anatase paste TiO₂·nH₂O, titanyl sulfate dihydrate TiOSO₄·2H₂O (VKR 611), hydrated sodium titanium oxide paste Na₂Ti₄O₉·nH₂O) and their reaction mixtures for x = 0.05 by simultaneous TG–DTA analysis. According to the highest chroma C of color, the optimal conditions for synthesis of these pigments are concentration x = 0.05 and calcination temperature 1,050 °C and higher. It was observed that initial temperature 760–830 °C is needful for a formation of rutile structure. This temperature is the lowest for hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium.     

Preparation of CuCr<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders using two different chromium sources

CuCr₂O₄ spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr₂O₃) and (ii) ammonium dichromate ((NH₄)₂Cr₂O₇). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO₃)₂·3H₂O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr₂O₃, Cu(NO₃)₂·3H₂O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr₂O₃). In the second case (ii), (NH₄)₂Cr₂O₇, Cu(NO₃)₂·3H₂O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH₄)₂Cr₂O₇ took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr₂O_3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr₂O₄) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr₂O₄ was highlighted by XRD and FTIR analyses.     

Sol–gel synthesis,crystal structure,surface morphology,and optical properties of Eu2O3-doped La2Mo3O12 ceramic

In this paper, we report the synthesis of the La–Mo–O tartrate gel precursors with the initial composition for La₂Mo₃O₁₂ ceramic prepared from different starting materials by an aqueous sol–gel synthesis route using tartaric acid as a complexing agent. Moreover, the La–Mo–O carbonate–tartrate and nitrate–tartrate gel precursors doped with x % of Eu₂O₃ (x = 0.5, 1.0, 2.0, 4.0, and 8.0) by aqueous sol–gel synthesis method were also prepared. The thermal decomposition of both the La–Mo–O carbonate–tartrate and nitrate–tartrate gels, which is the critical stage of this preparation technique, is investigated in detail. X-ray diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy were used for the determination of crystal structure, surface morphology, and optical properties of the La–Mo–O:xEu₂O₃ samples annealed at 400, 500, 600, 700, 800, 900, and 1,000 °C temperatures, respectively. The obtained results show that the thermal decomposition of the La–Mo–O tartrate gel precursors has occurred in a separate manner. The differences that came up during the thermal treatment of La–Mo–O tartrate gels have related only with the initial composition that determined the different crystallization ways of final compounds. Besides, the dopant concentration mainly influences the size of obtained particles and agglomeration of synthesized final materials. The initial composition of the La–Mo–O gel precursors has significant influence on the formation of final crystal phases at relatively lower temperatures than was expected according to the TG–DTA measurements. Finally, the optical properties of La–Mo–O tartrate gel precursors annealed at 500 °C depend on the nature of the initial compounds, which were used during the aqueous sol–gel process.     

Synthesis, Spectral, Thermal and CO2 Absorption Studies on Birnessites Type Layered MnO6 Oxide

Birnessite type layered MnO₆ oxides with increased crystallinity were synthesized from six carbohydrates and three dihydric phenols viz., dextrose, starch, fructose, galactose, maltose, lactose, catechol, resorcinol, quinol and KMnO₄ through the formation of a sol–gel. All of the MnO₆ oxides were characterized by powder XRD. The strong signal at 2θ ~ 12° corresponding to 7.4 Å refers to the Mn–Mn distance between the adjacent layers. The interlayer volume is dispersed with K⁺ ions and H₂O molecules. The presence of interlayer K⁺ ions is indicated by a signal at 25°, corresponding to a distance of 3.5 Å. IR spectra of the oxides show signature bands at ca. 500 cm^?1 due to the stretching modes occurring for MnO₆ entity. A broad band observed at ca. 3300 cm^?1 is due to interlayer water molecules. Thermal analysis indicated three stage decomposition with the formation of MnO₂ at ca. 600 °C through the intermediate formation of Mn(OH) _n . The MnO₆ exhibited a remarkable CO₂ scrubbing ability, which has also been investigated.