The electronic behaviors of visible light sensitive Nb2O5/Cr2O3/carbon clusters composite materials

Nano-sized Nb₂O₅/Cr₂O₃/carbon clusters composite material has been successfully obtained by the calcination of a Nb(HC₂O₄)₅/CrCl₃/starch complex under an argon atmosphere. The compositions of the resulting composite materials were determined using ICP, elemental analysis and surface characterization by XRD and TEM. The UV–VIS and XPS spectra of the composites were also obtained. ESR spectral examinations suggest the possibility of an electron transfer in the process of Nb₂O₅ → carbon clusters → Cr₂O₃. The reduction reaction of methylene blue with the resulting composite material has also been examined.     

CO2-enhanced dehydrogenation of ethane over sonochemically synthesized Cr/clinoptilolite-ZrO2 nanocatalyst: Effects of ultrasound irradiation and ZrO2 loading on catalytic activity and stability

CO₂-enhanced oxidative dehydrogenation of ethane was investigated over sonochemically synthesized Cr/clinoptilolite-ZrO₂ nanocatalyst with the aim of assessing the effect of composite support and ultrasonic irradiation on the nanocatalyst reactivity and stability. To this aim, ZrO₂ promoted clinoptilolite supports varying in zirconia content (0, 25, 50 wt%) were synthesized by hydrothermally precipitation method and impregnated with chromium nitrate under ultrasound irradiation. The samples were characterized by XRD, FESEM, EDX, TEM, ICP, BET, FTIR, TPR-H₂ and TPD-NH₃ techniques. The characterization results indicated that ultrasound irradiation could not only reduce the formation of Cr₂O₃ and decrease submicron particle size of chromium oxide to nanometer scale, but also promote the distribution of metallic particles and strengthen the chromium-support interaction. As a result, utilizing ultrasound irradiation in the synthesis of Cr/Clinoptilolite helped to maintain a high and stable catalytic activity. These features were more prominent in the presence of zirconia. It was found that the metal oxide nanoparticles with about 4–8 nm are dispersed uniformly on the surface of composite support containing 25 wt% ZrO₂ (CLT-Z25). Moreover, the addition of ZrO₂ resulted in the formation of new strong acid sites and a significant modification in the reducibility of chromium species, which alongside homogenous and small Cr nanoparticles account for the superior catalytic performance of ZrO₂ containing samples. However, excessive loading of ZrO₂ (50 wt%) severely covered the surface of clinoptilolite, afforded the aggregations of metallic particles and thereupon, weakened the contact between clinoptilolite and ZrO₂, which together with more acid strength seriously resulted in the deactivation of catalyst. In spite of superior initial activity of ZrO₂-rich sample among the catalysts tested, ultrasonic synthesized Cr/CLT-Z25 nanocatalyst showed the best catalytic performance after 5 h-catalytic reaction.     

Synthesis and electronic behaviors of TiO2/carbon clusters/Cr2O3 composite materials

Nano-structured TiO₂/carbon clusters/Cr₂O₃ composite material has been successfully obtained by the microwave treatment of a TiO(acac)/Cr(acac)₃/epoxy resin complex. The compositions of the composite materials were determined using ICP, elemental analysis and surface characterization by SEM-EDX, TEM and XRD. ESR spectral examinations suggest the possibility of an electron transfer in the process of TiO₂ → carbon clusters → Cr₂O₃ with an oxidation site at TiO₂ particles and a reduction site at Cr₂O₃ particles. The preliminary experimental results show that the calcined materials could decompose methylene blue under visible-light irradiation.     

Fabrication and luminescent properties of Al2O3:Cr3 + microspheres via a microwave solvothermal route followed by heat treatment

AlOOH:Cr^3 + powders were synthesized via a microwave solvothermal route at 433 K for 30 min and were used as the precursor and template for the preparation of γ-Al₂O₃:Cr^3 + by thermal transformation at 773 K for 2 h in air. The obtained γ-Al₂O₃ based powders were microspheres with an average diameter about 1.9 μm. Photoluminescence (PL) spectra showed that the Al₂O₃:Cr^3 + particles presented a symmetric broad R band at 696 nm without appreciable splitting when excited at 462 nm. It is shown that the 0.04 mol% of doping concentration of Cr^3 + ions in γ-Al₂O₃:Cr^3 + is optimum. According to Dexter's theory, the critical distance between Cr^3 + ions for energy transfer was determined to be 47.54 Å. Based on the corresponding PL spectrum, full width at half maximum (FWHM) of Al₂O₃:Cr^3 + (0.04 mol%) was calculated to be 3.35 nm.     

Effects of Gd element and SiC particles on microstructures of Cf/Mg composites

In present work, Cf/Mg-8Gd and SiC+Cf/Mg-8Gd composites were fabricated by squeeze infiltration method. Gd₂O₃ coating layers were found on the surface of the carbon fibers in these two kinds of the composites, while GdC₂ precipitations were found in the hybrid reinforced composite only. Owing to this phenomenon, the coating layer in SiC+Cf/Mg-8Gd composite (88 nm) was much thinner than the one without the SiC particles (160 nm). The Gd₂O₃ coating layer formed on the surface of carbon fibers can improve the wettability between carbon fibers and magnesium alloy.     

Sonocatalytic degradation of organic dyes and comparison of catalytic activities of CeO2/TiO2, SnO2/TiO2 and ZrO2/TiO2 composites under ultrasonic irradiation

The CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites were prepared by dispersing various nano-sized oxides (CeO₂, SnO₂, ZrO₂ and TiO₂) with ultrasound and mixing TiO₂ with CeO₂, SnO₂ and ZrO₂, respectively, in boiling water in a molar ratio of 4:1, followed by calcining temperature 500 °C for 60 min. Then a series of sonocatalytic degradation experiments were carried out under ultrasonic irradiation in the presence of CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites and nano-sized TiO₂ powder. Also, the influences of heat-treatment temperature and heat-treatment time on the sonocatalytic activities of CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites, and of irradiation time and solution acidity on the sonocatalytic degradation of Acid Red B were investigated by UV–vis spectra. It was found that the sonocatalytic degradation of Acid Red B shows significant variation in rate and ratio that decreases in order: CeO₂/TiO₂ > SnO₂/TiO₂ > TiO₂ > ZrO₂/TiO₂ > SnO₂ > CeO₂ > ZrO₂, and the corresponding ratios of Acid Red B in aqueous solution are 91.32%, 67.41%, 65.26%, 41.67%, 28.34%, 26.75% and 23.33%, respectively. And that the degradation ratio is only 16.67% under onefold ultrasonic irradiation. Because of the good degradation efficiency, this method may be an advisable choice for the treatment of non- or low-transparent wastewaters in the future.     

Synthesis and characterization of ZrO2/MnO2/carbon clusters nanocomposite materials

Nano-sized ZrO₂/MnO₂/carbon clusters composite materials has been successfully obtained by the calcination of a Zr(acac)₄/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere. The compositions of the resulting composite materials were determined using inductively coupled plasma (ICP) spectroscopy, elemental analysis and surface characterization by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM). The ultraviolet–visible (UV–VIS), X-ray photoelectron spectra (XPS) and electron spin resonance (ESR) spectra of the composites were also measured. ESR spectral examinations suggest the possibility of an electron transfer in the process of MnO₂ → carbon clusters → ZrO₂. The visible light-responsive oxidation–reduction ability of the calcined material was also investigated.     

On the rate constants of OH + HO2 and HO2 + HO2: A comprehensive study of H2O2 thermal decomposition using multi-species laser absorption

Hydrogen peroxide (H₂O₂) and hydroperoxy (HO₂) reactions present in the H₂O₂ thermal decomposition system are important in combustion kinetics. H₂O₂ thermal decomposition has been studied behind reflected shock waves using H₂O and OH diagnostics in previous studies (Hong et al. (2009) [9] and Hong et al. (2010) [6,8]) to determine the rate constants of two major reactions: H₂O₂ + M → 2OH + M (k₁) and OH + H₂O₂ → H₂O + HO₂ (k₂). With the addition of a third diagnostic for HO₂ at 227 nm, the H₂O₂ thermal decomposition system can be comprehensively characterized for the first time. Specifically, the rate constants of two remaining major reactions in the system, OH + HO₂ → H₂O + O₂ (k₃) and HO₂ + HO₂ → H₂O₂ + O₂ (k₄) can be determined with high-fidelity.No strong temperature dependency was found between 1072 and 1283 K for the rate constant of OH + HO₂ → H₂O + O₂, which can be expressed by the combination of two Arrhenius forms: k₃ = 7.0 × 10¹² exp(550/T) + 4.5 × 10¹⁴ exp(?5500/T) [cm³ mol^?1 s^?1]. The rate constants of reaction HO₂ + HO₂ → H₂O₂ + O₂ determined agree very well with those reported by Kappel et al. (2002) [5]; the recommendation therefore remains unchanged: k₄ = 1.0 × 10¹⁴ exp(?5556/T) + 1.9 × 10¹¹⁺exp(709/T) [cm³ mol^?1 s^?1]. All the tests were performed near 1.7 atm.     

Synthesis and electrical transport properties of Lu2+xTi2−xO7−x/2 oxide-ion conductors

The Lu_2+xTi_2−xO_7−x/2 (x = 0; 0.052; 0.096; 0.286; 0.44; 0.63; 33.3–49 mol% Lu₂O₃) nanoceramics with partly disordered pyrochlore-type structure are prepared by sintering freeze-dried powders obtained by a co-precipitation technique with 1600 °C annealing. Similar to pyrochlore-like compositions in the zirconate system, some of the new titanates are good oxide-ion conductors in air. The new solid-state electrolytes have oxide-ion conductivity in the interval of 1.0 × 10^− 3 – 2.5 × 10^− 3 S/cm at 740 °C in air. This value of conductivity is comparable with that of ZrO₂/Y₂O₃ ceramics. The conductivity of Lu_2+xTi_2−xO_7−x/2 depends on the chemical composition. The highest ionic conductivity is exhibited by nearly stoichiometric Lu_2+xTi_2−xO_7−x/2 (x = 0.096; 35.5 mol% Lu₂O₃) material containing ∼ 4.8 at.% Lu_Ti anti-site defects.     

Preparation of proton conductive composites with CsHSO4/CsH2PO4 and phosphosilicate gel

New composite materials were prepared using cesium hydrogen sulfate (CsHSO₄) or cesium dihydrogen phosphate (CsH₂PO₄) and phosphosilicate gel (P₂O₅–SiO₂ gel). In X-ray diffraction patterns of these composites, diffraction peaks due to Cs₂H₅(SO₄)₂(PO₄) and CsH₅(PO₄)₂ were observed for CsHSO₄–(P₂O₅–SiO₂ gel) composites and CsH₂PO₄–(P₂O₅–SiO₂ gel) composites, respectively. These composites showed high conductivities in the order of 10^− 3 S cm^− 1 at 150 °C due to melting of Cs₂H₅(SO₄)₂(PO₄) or CsH₅(PO₄)₂ in the composites. In the cooling process, the CsHSO₄–(P₂O₅–SiO₂ gel) composites kept relatively high conductivity to 110 °C where solidification of Cs₂H₅(SO₄)₂(PO₄) occurs, whereas CsH₂PO₄–(P₂O₅–SiO₂ gel) composites showed relatively high conductivity continuously to ambient temperature.     

Preparation and luminescence of (SBA-15)–Eu2O3 composite materials

In this study, (SBA-15)–Eu₂O₃ host-guest composites have been prepared with SBA-15 mesoporous sieve as host and Eu₂O₃ as guest via the solid-phase ultrasonic method and liquid-phase medium ultrasonic method. The host–guest composite materials showed the properties of luminescence. Four excitation peaks appeared in the excitation spectra of the samples. The excitation peaks are located at 397, 415, 466, 537 nm; 392, 408, 464, 532 nm and 393, 406, 465, 533 nm for the nano-Eu₂O₃, the liquid-phase medium ultrasonic method (LPMUM) and the solid-phase ultrasonic method (SPUM) samples, respectively. SBA-15 has the well-ordered hexagonal arrays of mesopores, which makes centrosymmetry of Eu³⁺ higher in the prepared (SBA-15)–Eu₂O₃ samples. The intensity of ⁵D₀→⁷F₁ transition strengthens, and the intensity of ⁵D₀→⁷F₂ transition weakens.     

Characterization of doped La0.7A0.3Cr0.5Mn0.5O3 − δ (A = Ca,Sr, Ba) electrodes for solid oxide fuel cells

Doped lanthanum manganese chromite based perovskite, La_0.7A_0.3Cr_0.5Mn_0.5O_3 ? δ (LACM, A = Ca, Sr, Ba), on yttria-stabilized zirconia (YSZ) electrolyte is investigated as potential electrode materials for solid oxide fuel cells (SOFCs). The electrical conductivity and electrochemical activity of LACM depend on the A-site dopant. The best electrochemical activity is obtained on the La_0.7Ca_0.3Cr_0.5Mn_0.5O_3 ? δ/YSZ (LCCM/YSZ) composite electrodes. The conductivity of LCCM is 29.9 S cm^? 1 at 800 °C in air, and the electrode polarization resistance (R_E) of the LCCM/YSZ composite cathode for the O₂ reduction reaction is 0.5 Ω cm² at 900 °C. The effect of Gd-doped ceria (GDC) impregnation on the LCCM cathode polarization resistances is also studied. GDC impregnation significantly enhances the electrochemical activity of the LCCM cathode. In the case of the 6.02 mg cm^? 2 GDC-impregnated LCCM cathode, R_E is 0.4 Ω cm² at 800 °C, ~ 60 times smaller than 24.4 Ω cm² measured on a LCCM cathode without the GDC impregnation. Finally the electrochemical activities of the doped lanthanum manganese chromites for the H₂ oxidation reaction are also investigated.     

ZnO/ZrO2 nanocomposite: Sonosynthesis,characterization and its application for wastewater treatment

ZnO/ZrO₂ nanocomposites with different ZnO: ZrO₂ molar ratios (2:1, 1:1, and 1:2)were prepared by sol gel approach under ultrasonic irradiation. For preparation of the nano-composites, the ZnO gel was directly incorporated into the ZrO₂ gel at different molar ratios. The reaction mixture was stirred continuously for two days and then it was ultrasonoicated for 30 min. The filtrated composite gel was washed, and then calcinated at 300 °C in furnace for 3 h. X-ray powder diffraction patterns exhibited well-formed crystal structures and pure crystalline phases in the synthesized nanoparticles (NPs). The FT-IR analyses indicated that the positions of peaks related to Zn-O and Zr-O absorption bands did not change in nano-composites. In addition, FESEM images indicated uniform spherical morphology of the NPs. The highest photo-degradation performance of Congo red (as a model water pollutant) was obtained by 1:2molar ratio of ZrO₂: ZnO in the nano-composite. The particle size and band gap were considered as important factors on nano-catalysts performance. Furthermore, the effects of ultrasonic irradiation, pH, and the concentration of pollutant in solution were investigated on photocatalytic performance of optimum nanocomposite.     

Ionic conductance of composite electrolytes based on network polymer with ceramic powder

Effects of ceramic fillers (α-Al₂O₃, γ-Al₂O₃ and BaTiO₃) have been investigated on the ionic conductance of polymeric complexes consisting of poly(ethylene oxide)-modified poly(methacrylate) (PEO-PMA) and lithium bis(trifluoromethylsulfonyl)imide, Li(CF₃SO₂)₂N, and ceramic powder. The addition of ceramic powder increased the ionic conductivity over an ambient temperature range. Conductivity of 4.9 × 10^− 5 S cm^− 1 at 333 K (60 °C) was obtained for the composite containing 15 wt.% α-Al₂O₃ prepared by photo-polymerization. The optimum content of Al₂O₃ was different among the methods of polymerization. The highest conductivity was obtained for the composite containing 5 wt.% of α-, or γ-Al₂O₃ prepared by thermal polymerization. The addition of the ceramic filler scarcely influenced the thermal properties of the polymer matrix. XRD and NMR experiments showed that the ionic mobility could be enhanced in the composites by addition of α-Al₂O₃. The addition of small amounts of ferroelectric BaTiO₃ also increased the ionic conductivity of the polymeric complex, but its extent was smaller than the case of the Al₂O₃ addition.     

Li4Ti5O12/Ag composite as electrode materials for lithium-ion battery

The Li₄Ti₅O₁₂/Ag composites were prepared by thermal decomposition of AgNO₃ added to Li₄Ti₅O₁₂ powders. The influence of the Ag contents and the mixing media on the particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂/Ag composites were investigated. The highest discharge capacity of the Li₄Ti₅O₁₂/Ag composite reached at the 5 wt.% of Ag content. Compared with alcohol medium, distilled water as mixing medium presented the Li₄Ti₅O₁₂/Ag composite with higher specific capacity and better cycling performance, leading to a reversible capacity after 50 cycles of 184.2 mAh/g with a capacity degradation of 3.31% compared to the second cycle at 2 C rate.     

Solid state reduction of chromium (VI) pollution for Al2O3–Cr metal ceramics application

Reduction of chromium (VI) from Na₂CrO₄ through aluminothermic reaction and fabrication of metal-ceramic materials from the reduction products have been investigated in this study. Na₂CrO₄ could be successfully reduced into micrometer-sized Cr particles in a flowing Ar atmosphere in presence of Al powder. The conversion ratio of Na₂CrO₄ to metallic Cr attained 96.16% efficiency. Al₂O₃–Cr metal-ceramic with different Cr content (5 wt%, 10 wt%, 15 wt%, 20 wt%) were further prepared from the reduction product Al₂O₃–Cr composite powder, and aluminum oxide nanopowder via pressure-less sintering. The phase composition, microstructure and mechanical properties of metal-ceramic composites were characterized to ensure the potential of the Al₂O₃–Cr composite powder to form ceramic materials. The highest relative density and bending strength can reach 93.4% and 205 MP, respectively. The results indicated that aluminothermic reduction of chromium (VI) for metal-ceramics application is a potential approach to remove chromium (VI) pollutant from the environment.     

Mixed conductivity and electrocatalytic performance of SrFeO3-δ–SrAl2O4 composite membranes

Oxygen-ionic and electronic transport in dense (SrFe)_1−x(SrAl₂)_xO_z composites, consisting of strontium-deficient Sr(Fe,Al)O_3-δ and SrAl₂O₄ phases, is determined by the properties of perovskite-like solid solution. Increasing the content of SrAl₂O₄, with a total conductivity as low as 5 × 10^− 7 −  10^− 5 S × cm^− 1 at 973–1273 K in air, results in the gradual decrease of the partial conductivities, but also enables the suppression of thermal expansion. Compared to single-phase SrFe_1−xAl_xO_3-δ, (SrFe)_1−x(SrAl₂)_xO_z composites exhibit enhanced thermomechanical properties, while the oxygen permeability of these materials has similar values. The composite membranes exhibit stable performance under air/(H₂–H₂O–N₂) and air/(CH₄–He) gradients at 973–1173 K. The oxidation of dry methane by oxygen permeating through (SrFe)_0.7(SrAl₂)_0.3O_z results in dominant total oxidation, suggesting the necessity to incorporate a reforming catalyst into the ceramic reactors for natural gas conversion.     

Synthesis of TiO2 nanoparticles and spectroscopic upconversion luminescence of Nd3+-doped TiO2–SiO2 composite glass

Nd³⁺-doped TiO₂–SiO₂ composites were prepared by sol–gel method. Optical properties such as radiative life-time (τ), stimulated emission cross-section (σ_p) and branching ratio (β) were calculated using Judd–Ofelt theory. Violet to blue upconversion emissions at 380 nm (⁴D_3/2→⁴I_11/2), 399 nm (²P_3/2→⁴I_11/2), 420 nm (²D_5/2→⁴I_9/2) and 452 nm (²P_3/2→⁴I_13/2) were obtained under 578 nm xenon-lamp excitation. The choice of 578 nm is justified by the absorption spectra of the same samples, which shows a strong absorption peak at 578 nm. This 578 nm excitation pump produces upconversion in Nd³⁺ by a sequential two-photon absorption process.     

Preparation of poly(2-ethyl aniline)/kaolinite composite materials and investigation of their properties

Conductive poly(2-ethyl aniline) (PEAn)/kaolinite composite was prepared by chemical polymerization in aqueous HCl medium in the presence of kaolinite particles by using potassium chromate (K₂CrO₄) as oxidant. Effects of polymerization conditions, such as concentrations of oxidant and 2-ethyl aniline, polymerization time and temperature on PEAn content and conductivity of composite, were investigated. The prepared composite material, having the highest PEAn content and conductivity, was obtained in the polymerization carried out at 20 °C for 2 h with 0.2 M K₂CrO₄ and 0.2 M EAn. It was observed that the micro-hardness of prepared composites increased with the increase in the PEAn contents of composites. The highest micro-hardness value of 7.92 kg mm⁻² was reached at 24.6% PEAn content. Characterization of composites was carried out by FTIR spectroscopy, XRD, TGA and SEM techniques.     

Mesopore size dependence of the ionic diffusivity in alumina based composite lithium ionic conductors

Ordered-mesoporous Al₂O₃ was synthesized by a sol–gel method using neutral copolymer surfactants as structure-directing agents. The pore size was controlled over the 3–15 nm range by the use of various surfactants. Composites composed of the synthesized mesoporous Al₂O₃ and a lithium ion conductor (LiI) were prepared. The maximum dc electrical conductivity, 2.6 × 10^− 4 S cm^− 1 at 298 K, was observed for 50 LiI·50 Al₂O₃ composite with 4.2 nm average mesopore size, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which conductivity increased with decreasing pore size, except for samples with a pore size of 2.8 nm. The lithium ion diffusion coefficient determined by the ⁷Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) showed excellent agreement with the measured conductivity calculated by the Nernst-Einstein equation. On the other hand, lithium migration activation energies obtained by quasielastic neutron scattering (QENS) and ⁷Li NMR spin-lattice relaxation time (T₁) were considerably smaller than those obtained from electrical conductivity and PFG-NMR. This could be explained by the ion migration mechanism in heterogeneous composites and a possible enhancement of conductivity in mesoscopically confined spaces.