Catalytic combustion of volatile aromatic compounds over CuO-CeO<Subscript>2</Subscript> catalyst

Ce_1?x Cu _x O₂ oxide solid solution catalysts with different Ce/Cu mole ratios were synthesized by the one-pot complex method. The prepared Ce_1?x Cu _x O₂ catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H₂ temperature-programmed reduction (H₂-TPR). Their catalytic properties were also investigated by catalytic combustion of phenyl volatile organic compounds (PVOCs: benzene, toluene, xylene, and ethylbenzene) in air. XRD analysis confirmed that the CuO species can fully dissolve into the CeO₂ lattice to form CeCu oxide solid solutions. XPS and H²-TPR results indicated that the prepared Ce_1?x Cu _x O₂ catalysts contain abundant reactive oxygen species and superior reducibility. Furthermore, the physicochemical properties of the prepared Ce_1?x Cu _x O₂ catalysts are affected by the Ce/Cu mole ratio. The CeCu₃ catalyst with Ce/Cu mole ratio of 3.0 contains abundant reactive oxygen species and exhibits superior catalytic combustion activity of PVOCs. Moreover, the ignitability of PVOCs is also affected by the respective physicochemical properties. The catalytic combustion conversions of ethylbenzene, xylene, toluene, and benzene are 99%, 98.9%, 94.3%, and 62.8% at 205, 220, 225, and 225 °C, respectively.     

Thermal behavior of layered perovskite-like compounds in the Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>-BiFeO<Subscript>3</Subscript> system

The thermal properties of compounds of the general formula Bi _{m + 1} Fe _{m ? 3} Ti₃O_{3m + 3}, which are layered perovskite-like phases of the Aurivillius type, are investigated as a function of their composition. It is demonstrated that the temperature of decomposition of the Bi _{m + 1} Fe _{m ? 3} Ti₃O_{3m + 3} compounds decreases with an increase in the thickness of perovskite-like layers alternating in the structure and that the composition dependence of the temperature of the structural transition observed in these compounds exhibits a more complex behavior. The linear thermal expansion coefficients of all the compounds under investigation are found to be virtually independent of the composition.     

SHS of Y<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>-based mineral-like ceramics: Influence of green density

Explored was the influence of compacting pressure (P) and green density (ρ) on the properties of Zr-doped mineral-like pyrochlore ceramics Y₂(Ti_{1 – x} Zr _x )₂O₇ (x ≤ 0.3) prepared by SHS method. The optimal ρ values that provide minimal porosity and maximal mechanical strength of synthesized ceramics were found. An increase in ρ was found to decrease combustion temperature and increase pyrochlore lattice parameter a. Green density was also found to affect phase composition of the SHS-produced ceramics under study.     

Raman spectra and surface structure of CaO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass leached in potassium hydroxide solutions

It is difficult to research on the surface structure of amorphous phase in fly ash during leaching reaction due to crystalline phase and complex structure. In the present work, in order to reveal the effects of leaching reaction on the surface structure of amorphous phase in fly ash, the modelling CaO-Fe₂O₃-Al₂O₃-SiO₂ glass was prepared by the traditional melting methods. The leaching reaction of CaO-Fe₂O₃-Al₂O₃-SiO₂ glass with 7.5 M KOH was investigated by spectroscopy, spectrophotometer and wet chemical method. The results show that the content of Q ¹, Q ², Q ³ and Q ⁴ of glass without corrosion was 4.21, 9.51, 23.03 and 52.55%, respectively, which shows that the network polymerization of glass is compact. The leaching reaction of glass can be described by the following equation: dS/dt = k/(r + S ₀). Leaching in KOH for various times induces the content of Q ⁴ and Q ¹ to be decreased, and Q ² and Q ³ increased, resulted in the depolymerization of network and the surface glass dissolved in alkaline solution to form a gel phase. In stage one of leaching reaction, the rate of iron ion leached from glass surface was slow, which resulted in the small slope of straight-line relationship of leaching curve. In the following stage, the leaching rate of iron ion increased with the prolongation of time.     

Crystal structure of Pb<Subscript>6</Subscript>O[(Si<Subscript>6</Subscript>Al<Subscript>2</Subscript>)O<Subscript>20</Subscript>]

The crystal structure of Pb₆O[(Si₆Al₂)O₂₀)] is investigated using X-ray diffraction. The compound has tetragonal symmetry, space group I4/mmm, a = 11.7162(10) Å, c = 8.0435(12) Å, and V = 1104.13(2) ų. The structure is refined to R ₁ = 0.036 for 562 unique reflections with [F ₀] ≥ 4σF. The structure contains two symmetrically independent positions of the Pb²⁺ cations coordinated by five O atoms (Pb²⁺-O^2? = 2.34–2.68 Å). The TO₄ tetrahedra (T = Si, Al) form tubular [(Si₆Al₂)O₂₀] chains extended along the c axis. The O₄ oxygen atom is not bonded to the Si and Al atoms and is octahedrally coordinated by six Pb atoms with the formation of an oxo-centered OPb₆ octahedron. The assumption is made that, in some of lead silicate and aluminosilicate glasses, a number of oxygen atoms are located outside the tetrahedral structure and represent segregation centers of the Pb²⁺ cations due to the formation of oxo-centered complexes.     

Synthesis and crystal structure of a new oxohalide CdPb<Subscript>2</Subscript>O<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

A new compound, CdPb₂O₂Cl₂, is synthesized by the method of solid-phase reactions. The compound has monoclinic symmetry, space group C2/m, a = 12.392(8) Å, b = 3.8040(14) Å, c = 7.658(5) Å, β = 122.64(5)°, and V = 304.0(3) ų. The structure contains one symmetrically independent position of the Pb²⁺ cation coordinated by three O^2? anions (Pb²⁺-O^2? = 2.29–2.34 Å) and five Cl^? anions (Pb²⁺-Cl^? = 3.35–3.57 Å). The Cd²⁺ cation has a symmetric coordination with the formation of two bonds Cd-O = 2.15 Å and four bonds Cd-Cl = 2.73 Å. The oxygen atom is tetrahedrally coordinated by three Pb²⁺ cations and one Cd²⁺ cation, which leads to the formation of oxo-centered heterometallic OPb₃Cd tetrahedra. The tetrahedra are linked together into chains through common Pb atoms and into layered complexes due to sharing of the equatorial Cd atoms. The chlorine atoms are located above the cavities of the oxo-centered layer.     

Synthesis and Thermoelectric Properties of Ceramics Based on Bi<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Co<Subscript>1.7</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Oxide

Layered ceramics based on bismuth–calcium cobaltite with varied cobalt oxide contents is synthesized by the solid-phase method, the ceramics phase composition is determined, and the microstructure, thermal expansion, electroconductivity, and thermal electromotive force are investigated. The formation of just one compound, ternary oxide composed of Bi₂Ca₂Co_1.7O _y , is established within the quasi-binary Bi₂Ca₂O₅–CoO _z system. The effect of the cobalt oxide content on the Bi₂Ca₂Co _x O _y ceramics’ microstructure and physicochemical properties is analyzed. The single-phased ceramic sample Bi₂Ca₂Co_1.7O _y demonstrated the highest power factor value among all the investigated samples—26.0 μW/(m K²) at a temperature of 300 K. This sample showed the lowest value of the thermal linear expansion coefficient of 9.72 × 10^–6 K^–1.     

Transport properties of solid electrolytes based on <Emphasis Type="Italic">Me</Emphasis>Sm<Subscript>2</Subscript>S<Subscript>4</Subscript>

The solid-solution regions in the MeSm₂S₄-MeS and MeSm₂S₄-Sm₂S₃ (Me = Ca, Ba) systems are revealed. The average ion, cation, and anion transport number of the synthesized solid electrolytes xSm₂S₃[Ca(Ba)S] · (100 ? x)Ca(Ba)Sm₂S₄ (x = 1?10 mol %) are determined by the electromotive force (emf) method with the use of concentration cells with and without transfer. In the phases under investigation, the ion transfer in the temperature range 673–723 K is provided by sulfide ions (\(t_{S^2 } \) = 1.00±0.02). The diffusion coefficients of S^2? ions in the solid electrolytes are determined by potentiostatic chronoamperometry. A vacancy mechanism of defect formation is proposed. It is demonstrated that the transport characteristics of the solid electrolytes based on the CaSm₂S₄ compound are worse than those of the solid electrolytes based on the BaSm₂S₄ compound.     

Synthesis and crystal structure of the low-temperature modification of Li<Subscript>12</Subscript>Zn<Subscript>4</Subscript>(P<Subscript>2</Subscript>O<Subscript>7</Subscript>)<Subscript>5</Subscript>

The crystal structure of a low-temperature modification of the Li₁₂Zn₄(P₂O₇)₅ compound has been determined by full-profile analysis from the X-ray powder diffraction data. The compound crystallizes in the monoclinic crystal system (a = 5.130(1) Å, b = 13.454(1) Å, c = 8.205(1) Å, β = 90.36(1)°, space group P2₁/n, Z = 4) and has a framework structure in which the zinc and lithium atoms statistically occupy equivalent positions.     

Crystal structure of new compound (Rb,K)<Subscript>2</Subscript>Cu<Subscript>3</Subscript>(P<Subscript>2</Subscript>O<Subscript>7</Subscript>)<Subscript>2</Subscript>

A new compound of (Rb,K)₂Cu₃(P₂O₇)₂ is obtained by high-temperature reactions from a mixture of RbNO₃, KNO₃, Cu(NO₃)₂, and (NH₄)₄P₂O₇. The crystal structure was solved by direct methods and refined to R ₁ = 0.056 for 5022 independent reflections. The compound belongs to a rhombic crystal system, P2₁2₁2₁, Z = 8, a = 9.9410(7) Å, b = 13.4754(6) Å, c = 18.6353 (3) Å, and R = 0.056. The basis of the structure is a complex copper-phosphate skeleton of the composition of [Cu₃(P₂O₇)₂]^2–, which can be regarded as consisting of two types of heteropolyhedral layers parallel to the (001) plane. The layers are alternated with each other, forming a frame, in the cavities of which the positions of alkali cations are located, statistically populated with K⁺ and Rb⁺ ions. Based on the refined populations of the positions of alkali cations, an exact chemical formula of the compound can be written as Rb_1.28K_0.72Cu₃(P₂O₇)₂. The compound is the most complex among those known to this day of the composition of A₂ ^IB₃ ^II(P₂O₇)₂ (A = Li, Na, K, Rb, or Cs; B = Ni, Cu, or Zn).     

Crystal structure and thermal expansion of ammonium pentaborate NH<Subscript>4</Subscript>B<Subscript>5</Subscript>O<Subscript>8</Subscript>

Anhydrous ammonium pentaborate NH₄B₅O₈ has been synthesized by thermal dehydration of larderellite NH₄[B₅O₇(OH)₂] · H₂O at a temperature of 290°C for 7 h. The crystal structure has been determined from the X-ray powder diffraction data: a = 7.58667(5) Å, b = 12.00354(8) Å, c = 14.71199(8) Å, R _p = 6.23, R _wp = 7.98, R _B = 12.7, R _F = 8.95, and β-KB₅O₈ structure type. The double interpenetrating framework is formed by pentaborate groups, each consisting of a boron-oxygen tetrahedron and four triangles, in which all oxygen atoms are bridging. The thermal behavior of the NH₄B₅O₈ compound has been investigated using thermal X-ray diffraction. As for other pentaborates of this type, the thermal expansion of the NH₄B₅O₈ compound is anisotropic and reaches a maximum along the a axis. The thermal expansion coefficients are as follows: α _a = 39 × 10^?6, α _b = 6 × 10^?6, α _c = 20 × 10^?6, and α _V = 65 × 10^?6 °C^?1.     

Crystallization and thermal transformations in nanocrystals of the YPO<Subscript>4</Subscript>-LuPO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

Nanocrystals of yttrium lutetium phosphates of the general formula Y_1?x Lu_xPO₄ · nH₂O are synthesized. The temperature dependence of the nanocrystal size is investigated in the range 200–1100°C. The formation of a series of continuous solid solutions belonging to the tetragonal crystal system is revealed, and the limits of their thermal stability are determined.     

Parameters of luminescence and the local structure of Eu<Superscript>3+</Superscript> centers in fluorogermanate glasses

The influence of the chemical nature of the local environment of Eu³⁺ ions on the parameters of luminescence of these centers in glasses of the (BaGeO₃)_{1 ? x ? y} (Al₂O₃) _x (0.45CaF₂ · 0.55MgF₂) _y (x = 0.25, y = 0; x = 0.17, y = 0.17; x = 0.15, y = 0.22; x = 0.07, y = 37.00; x = 0, y = 0.45) system is investigated. The oxidation state of europium atoms and the degree of homogeneity of their local environment in the glasses are determined using ¹⁵¹Eu Mössbauer spectroscopy.     

Density and microhardness of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The density d at a temperature of 25°C is measured by the hydrostatic weighing method, the Vickers microhardness H _V is determined, and the fluctuation free volume fraction f _g is calculated for glasses in the SrO-B₂O₃-SiO₂ system with a constant strontium oxide content in the range from 35 to 45 mol %. It is demonstrated that the quantities H _V and f _g decrease and the density d increases with an increase in the SrO content.     

Solution-Combustion Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as a Cathode Material for Lithium-Ion Batteries

A cathode material for lithium-ion batteries–LiNi_1/3Co_1/3Mn_1/3O₂–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g^–1 retained 95.7% of its value after 75 charge/discharge cycles at I_c = 14 mA g^–1 (0.2C rate), I_d = 70 mA g^–1 (0.5C rate).     

SHS-produced Co<Superscript>2+</Superscript>Ti<Superscript>4+</Superscript>-doped barium and strontium hexaferrites: Static and dynamic magnetic properties

Static and dynamic magnetic properties of SHS-produced BaFe_12–2x (Co _х Ti _х )O₁₉ (х = 1.0, 1.1, 1.2) and SrFe_12–2y (Co _y Ti _y )O₁₉ (0 ≤ y ≤ 1.0) hexaferrites were characterized by magnetization and FMR measurements. Dynamic properties of SrFe_12–2y (Co _y Ti _y )O₁₉ hexaferrites were rationalized in terms of not only magnetic anisotropy but also the anisotropy of magnetomechanical ratio. SHS-produced ferrites can be recommended for designing radar-absorbent coatings and other SHF devices operating in the range 20–50 GHz.     

Excitation and photoluminescence spectra of solid solutions based on lanthanum indate LaInO<Subscript>3</Subscript> of a perovskite structure doped with Nd<Superscript>3+</Superscript> and Cr<Superscript>3+</Superscript> ions

Using a solid-phase method, single-phase solid solutions of La_1–x Nd _x InO₃ (x = 0.007, 0.02, 0.05), LaIn0.99Cr0.01O3, and La_0.95Nd_0.05In_0.995Cr_0.005O₃ have been obtained and their excitation and photoluminescence (PL) spectra have been studied at room temperature. It is found that the intensity of excitation and PL bands for La_1–x Nd _x InO₃ solid solutions depends on the degree of the substitution of La³⁺ ions by Nd³⁺ ions. A solid solution with 0.02 < x < 0.05 possesses the largest intensity of the PL bands in IR wavelength range of 850–950, 1040–1100, and 1350–1370 nm. It is found that replacing 0.5% of In³⁺ ions in a solid solution of La^0.95Nd^0.05InO₃ by Cr³⁺ ions leads to a substantial increase in the intensity of all the PL bands by exciting with light of the wavelength of λ_exc = 490 nm and a decrease in the intensity of all the PL bands by an excitation with light of the wavelengths of λ_exc = 358, 532, and 585 nm.     

Effect of Li<Subscript>2</Subscript>O on the Refractive Index and Optical Band Gap of Cadmium Phosphate Glasses

A series of lithium cadmium phosphate glasses having composition (mol %) xLi₂O-(50 ? x)CdO-50P₂O₅ were prepared in a platinum crucible by the melt quenching technique. The quantity x varies in the range 0–40. The mass density and refractive index of these glasses were found in the ranges 3.95–2.89 g/cm₃ and 1.55–1.40, respectively. The optical absorbance studies were also carried out on these glasses to measure their energy gaps. The absorption spectra of these glasses were recorded in the UV-visible range. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range 2.58–3.5 eV. It was observed that the density, the refractive index, and the optical band gap energy decrease with increasing amount of lithium oxide. The band tailing, worked out from the Urbach plots, shows an increase with increasing Li₂O content and lies in the range 0.47–0.78 eV. The absorption coefficient is observed to show an exponential dependence on the photon energy.     

Effect of Cu promoter and alumina phases on Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for propane dehydrogenation

We investigated the effects of different Cu weight ratio on θ or γ-Al₂O₃ which were impregnated with platinum in terms of catalytic activity for propane dehydrogenation and physicochemical properties. 1.5 wt% Pt, 0-10 wt% Cu catalyst supported on θ-Al₂O₃ or γ-Al₂O₃ was prepared by incipient wetness co-impregnation. Enhanced Pt dispersion by increasing Cu contents in γ-Al₂O₃ supported catalyst was confirmed via XRD and XPS. Pt and CuO was separated in Pt-Cu/θ-Al₂O₃, but Pt-Cu alloy was identified after reduction treatment. Also, adding Cu in Pt/Al₂O₃ makes catalyst’s acidity lower and this property led to increased propylene yield in propane dehydrogenation. However, Pt₃Cu was not good for yield of PDH, which was confirmed in Pt-10Cu/θ-Al₂O₃ through XRD.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles coated by new functionalized tetraaza-2,3 dialdehyde micro-crystalline cellulose: synthesis,characterization, and catalytic application for degradation of Acid Yellow 17

In this study, we developed an original approach for preparing cellulose-coated magnetite nanoparticles (NPs). Two novel Schiff bases (PDA-g-DAC) and [Bz-(PDA-g-DAC)] were synthesized via condensation reactions of periodate oxidized micro-crystalline cellulose (DAC) with o-phenylene diamine (PDA) to obtain its azomethine derivative with 85% yield. Subsequently, the functionalization of (PDA-g-DAC) with benzil (Bz) yields the tetraaza macrocycle [Bz-(PDA-g-DAC)]. The physicochemical characterization of the condensation products was performed using ¹³CNMR, FTIR, ATG, DSC, and X-ray diffraction techniques. Magnetic nanomaterial-based Schiff base cellulose was successfully prepared using in situ chemical co-precipitation of coordinated ferric and ferrous ions in cellulose Schiff base matrix under optimized conditions, and then, its magnetic properties were characterized. The results demonstrated that the Fe₃O₄ NPs coated with [Bz-(PDA-g-DAC)] were homogeneously coated in the matrix under ultrasonic irradiation with the saturation magnetization of 69.50 emu g^?1. In addition, XRD line broadening analysis showed that the average particle size of the NPs was 37.3 nm. Furthermore, FTIR spectra demonstrated that [Bz-(PDA-g-DAC)] concavity was anchored to magnetite Fe₃O₄ NPs through azomethine groups. Vibrating sample magnetometry (VSM) of [Bz-(PDA-g-DAC)@Fe₃O₄] magnetic nanocomposite samples showed the typical behavior of ferromagnetism. This study provided a green and facile method to inhibit magnetic nanoparticle aggregation. Activity results revealed that the prepared [Bz-(PDA-g-DAC)@Fe₃O₄] catalyst shows the maximum activity for degradation of Acid Yellow 17 (AY17) compared to other prepared catalysts. After degradation reaction, the [Bz-(PDA-g-DAC)@Fe₃O₄] catalyst was recovered from the reaction mixture via an external magnet and used for further five consecutive cycles with excellent catalytic activity, successively, which was comparable to the fresh catalyst. The catalyst degradation efficiency and its easy separation exhibited that [Bz-(PDA-g-DAC)@Fe₃O₄] catalyst is a promising material for the removal of AY17 from aqueous solutions in green chemistry perspectives.