Calcination Of Precursor Research Articles

Thermal degradation of BaAl2Si2O8:Eu2+ phosphor excited by near ultraviolet light

Eu2+doped BaAl2Si2O8 phosphor was synthesized by one-step calcination of precursors that were prepared by chemical co-precipitation. The thermal degradation properties of BaAl2Si2O8:Eu2+ were investigated by photoluminescence, lifetime and chromaticity coordinate measurements. BaAl2Si2O8:Eu2+ is efficiently excited by incident light of 250–400 nm, which matches the emission of near ultraviolet LED chips well. BaAl2Si2O8:Eu2+ exhibits broad blue emission at 470 nm because of the 4f65d1-4f7 (8S7/2) transition of Eu2+ ions, and the emission band shows an unusual blue shift with bandwidth broadening and emission intensity decreasing as the annealing temperature is increased. The luminescence decay and CIE chromaticity coordinates of BaAl2Si2O8:Eu2+ were determined to investigate its application in white LEDs.

A new simple synthesis and characterization of Sm-doped ceria and its homogeneous precursor [Ce0.80Sm0.20(Ac)3(Gly)

Abstract A new method for the synthesis of Ce 0.80 Sm 0.20 O 1.90 is presented. A drying of a solution of ethylene glycol and stoichiometric amounts of the acetates Ce(C 2 H 3 O 2 ) 3 · x H 2 O and Sm(C 2 H 3 O 2 ) 3 · x H 2 O resulted in a highly crystalline product of [Ce 0.80 Sm 0.20 (C 2 H 3 O 2 ) 3 (C 2 H 6 O 2 )] n , a new chained polymeric coordination compound. With the calcination of this precursor at 900 °C and sintering at 1150 °C, pure Ce 0.80 Sm 0.20 O 1.90 , was obtained with the desired homogeneity and density. This paper reports elemental (CHN and ICP-MS) and single crystal X-ray structure analyses of the precursor [Ce 0.80 Sm 0.20 (C 2 H 3 O 2 ) 3 (C 2 H 6 O 2 )] n . Its thermal decomposition to Ce 0.80 Sm 0.20 O 1.90 has been studied via HT-XRD and TG–DTA analysis. The structure and composition of Ce 0.80 Sm 0.20 O 1.90 was also confirmed by powder XRD (Rietveld refinement).

Dielectric properties of Bismuth Titanate densified by Spark Plasma Sintering and Pressureless Sintering

Bismuth Titanate powder Bi4Ti3O12 of 175nm mean particle size has been synthesized through chemical precipitation and calcination of chemical precursors at 700°C. Ceramic pellets were sintered by conventional Pressureless Sintering (PLS) and Spark Plasma Sintering (SPS) techniques. SPS is shown to be effective in inhibiting grain growth and allowing the formation of a homogeneous microstructure. The optimum SPS temperature is 800°C in less than 5min. PLS specimens seem to be more sensible to temperature rise and sintering time, undergoing grain grow and plates-like morphology. This fact leads formation of a given crystallographic texture. Dielectric properties of SPS specimens are found dependent of the electric signal frequency and less sensitive to sintering temperature than PLS counterparts.

GISAXS/GIXRD View of ZnO Films with Hierarchical Structural Elements

ZnO films constituted of porous sheet-like structures, formed by calcination of precursor, were examined using scanning electron microscopy and simultaneous small-angle scattering and diffraction of the synchrotron-sourced X-rays, under the grazing-incidence conditions. The presented analysis enabled insight into the complexity of the film morphology, which revealed substrate sensitivity on the microscopic and nanoscopic length scales. The average size and spatial arrangement of nanoparticles, single-crystal domains, and the average size and features of nanopores in sheet-like structures were determined for films deposited on glass, polycrystalline ZnO layer, and silicon.

Preparation and activity of Cu/Zn/Al/Zr catalysts via hydrotalcite-containing precursors for methanol synthesis from CO2 hydrogenation

A series of Cu/Zn/Al/Zr catalysts were synthesized by calcination of hydrotalcite-containing precursors with different Cu2+/Zn2+ atomic ratios (n). Two other catalysts (n = 2) were also prepared via phase-pure hydrotalcite-like and conventional rosasite precursors for comparison. XRD and UV-Vis-NIR DRS characterizations demonstrate that most Cu2+ of hydrotalcite-containing materials did not enter the layer structure. The Cu dispersion of the catalysts decreases with the increase of Cu content, while both the exposed Cu surface area and the Cu+ and Cu0 content on the reduced surface reach a maximum when n is 2. The catalytic performance for the methanol synthesis from CO2 hydrogenation was also tested. The catalytic activity and selectivity of the catalysts (n = 0.5–4) via hydrotalcite-containing precursors rise first and then decrease with increasing Cu2+/Zn2+ ratios, and the optimum performance is obtained over the catalyst with Cu2+/Zn2+ = 2. Moreover, the Cu/Zn/Al/Zr catalyst (n = 2) via hydrotalcite-containing precursor exhibits the best catalytic performance, which is mainly due to the maximum content of active species compared with another two catalysts derived from different precursors.

Preparation and Luminescent Properties of Series of Strontium Metaborate Light-emitting Materials

The SrB2O4•4H2O and SrB2O4•4H2O∶Eu light-emitting materials have been synthesized by liquid coprecipitation method, and SrB2O4 and SrB2O4∶Eu have been synthesized by calcination precursor method. All the as-prepared products were characterized by the XRD, EDS and SEM, respectively. Their luminescent properties were investigated by fluorescence spectroscopy, and the influences of reaction time and the doping concentration of Eu on the emission intensities have also been investigated. The results show that the matrixes of SrB2O4•4H2O and SrB2O4 have stronger luminescence in the UV region, and SrB2O4•4H2O∶Eu and SrB2O4∶Eu samples have the strongest emission peaks near 613 nm. By adjusting the reaction time and increasing the amount of doping, the quenching effect of structural water on the luminescence can be overcome, which improves the luminescence of SrB2O4•4H2O∶Eu with higher redorange ratio. It shows that SrB2O4•4H2O is a new good hydrated borate matrix for light-emitting materials.

Synthesis of Titania Nanotubes and its Application on Oxalic Acid Removal from Aquatic Environment

Titania nanotubes were synthesized after the protonation and calcination of titanate precursors prepared at different hydrothermal temperatures. Calcination of the titanate precursors at various temperature, governs the TiO2nanotubes formation. It was observed that sample prepared at 130°C and calcination at 500°C forms only anatase, but at 800°C, both anatase and rutile formed. The as-prepared titania nanotubes were used as photocatalyst in order to degrade organic contaminant, oxalic acid from aqueous solution by UV irradiation. 78 % oxalic acid was removed from the aqueous media at the nanotubes dose of 2 g L-1, in 120 min.

Intercalation of paracetamol into the hydrotalcite-like host

Hydrotalcite-like compounds are often used as host structures for intercalation of various anionic species. The product intercalated with the nonionic, water-soluble pharmaceuticals paracetamol, N-(4-hydroxyphenyl)acetamide, was prepared by rehydration of the Mg–Al mixed oxide obtained by calcination of hydrotalcite-like precursor at 500 °C. The successful intercalation of paracetamol molecules into the interlayer space was confirmed by powder X-ray diffraction and infrared spectroscopy measurements. Molecular simulations showed that the phenolic hydroxyl groups of paracetamol interact with hydroxide sheets of the host via the hydroxyl groups of the positively charged sites of Al-containing octahedra; the interlayer water molecules are located mostly near the hydroxide sheets. The arrangement of paracetamol molecules in the interlayer is rather disordered and interactions between neighboring molecules cause their tilting towards the hydroxide sheets. Dissolution tests in various media showed slower release of paracetamol intercalated in the hydrotalcite-like host in comparison with tablets containing the powdered pharmaceuticals.

Ethanol steam reforming over Ni/ZnAl 2O 4-CeO 2. Influence of calcination atmosphere and nature of catalytic precursor

The hydrogen production from ethanol steam reforming has been studied over Ni/ZnAl 2O 4-CeO 2 catalysts. The influence of calcination atmosphere and nature of catalytic precursor was analyzed. The impregnation of Ni was carried out from two different nickel salts: nitrate (Nt) and acetate (Ac). The catalysts were obtained from the precursor calcination under reductive and oxidative atmospheres. The catalysts obtained from nitrate salt impregnation were the most carbon resistance measured as mmolC/mol reacted C 2H 5OH, and those obtained under a reductive atmosphere were the most stable, as evidenced by smaller activity losses. The Ni(Nt)/ZnAl 2O 4-CeO 2 obtained under reductive atmosphere was the most active (steady state ethanol conversion = 88%) and stable (activity loss = 14%) under mild reforming conditions (7.8% C 2H 5OH inlet concentration, H 2O:C 2H 5OH molar ratio = 4.9, reaction temperature = 650 °C and W / F = 49 g min mol C 2 H 5 OH − 1 ). The hydrogen selectivity was 49% and the main C-containing products were CO 2, CO and C 2H 4O.

Low‐temperature Synthesis of Peony‐like Spinel Li4Ti5O12 as a High‐performance Anode Material for Lithium Ion Batteries

AbstractPeony‐like spinel Li4Ti5O12 was synthesized via calcination of precursor at the temperature of 400°C, and the precursor was prepared through a hydrothermal process in which the reaction of hydrous titanium oxide with lithium hydroxide was conducted at 180°C. The as‐prepared product was investigated by SEM, TEM and XRD, respectively. As anode material for lithium ion battery, the Li4Ti5O12 obtained was also characterized by galvanostatic tests and cyclic voltammetry measurements. It is found that the peony‐like Li4Ti5O12 exhibited high rate capability of 119.7 mAh·g−1 at 10 C and good capacity retention of 113.8 mAh·g−1 after 100 cycles at 5 C, and these results indicate the peony‐like Li4Ti5O12 has promising applications for lithium ion batteries with high performance.

Synthesis of MoVTeNb Oxide Catalysts with Tunable Particle Dimensions

AbstractReliable procedures for the controlled synthesis of phase‐pure MoVTeNb mixed oxides with M1 structure (ICSD 55097) and tunable crystal dimensions were developed to study the structure sensitivity of the selective oxidation of propane to acrylic acid. A series of powdered M1 catalysts was successfully prepared on a gram scale by using a hydrothermal‐based route, purification of biphasic M1‐M2 (M2 phase – ICSD 55098) oxide systems, and an innovative approach utilizing a superheated water vapor treatment of calcined precursors. The influence of the preparation technique on the particle morphology and the size is discussed. Detailed experimental studies highlight that the as‐derived catalytic materials were indeed phase‐pure and compositionally uniform MoVTeNb oxide M1 powders, composed of single‐crystalline and structural defect‐free crystals grown along the c axis. The morphologically different catalysts were studied in the selective oxidation of propane to acrylic acid, revealing that active sites appear on the entire M1 surface and illustrating the high sensitivity of catalyst performance on the catalyst synthesis method.

Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions

An industrially applicable cobalt-based catalyst was optimized for the production of multiwalled carbon nanotubes (CNTs) from ethene in a hot-wall reactor. A series of highly active Co–Mn–Al–Mg spinel-type oxides with systematically varied Co:Mn ratios was synthesized by precipitation and calcined at different temperatures. The addition of Mn drastically enhanced the catalytic activity of the Co nanoparticles resulting in an extraordinarily high CNT yield of up to 249 g CNT/g cat. All quaternary catalysts possessed an excellent selectivity towards the growth of CNTs. The detailed characterization of the obtained CNTs by electron microscopy, Raman spectroscopy and thermogravimetry demonstrated that a higher Mn content results in a narrower CNT diameter distribution, while the morphology of the CNTs and their oxidation resistance remains rather similar. The temperature-programmed reduction of the calcined precursors as well as in situ X-ray absorption spectroscopy investigations during the growth revealed that the remarkable promoting effect of the Mn is due to the presence of monovalent Mn(II) oxide in the working catalyst, which enhances the catalytic activity of the metallic Co nanoparticles by strong metal-oxide interactions. The observed correlations between the added Mn promotor and the catalytic performance are of high relevance for the production of CNTs on an industrial scale.

Solvothermal synthesis of ceria nanoparticles with large surface areas

Ceria nanoparticles were obtained by the calcination of precursors synthesised via the solvothermal reaction of cerium acetate. The CeO 2 samples obtained by the thermal decomposition of Ce(C 7H 15COO) 3· xH 2O synthesised by solvothermal reaction in 1,4-butanediol in the presence of octanoic acid had an extremely large surface area of 180 m 2/g. The Ru catalyst supported on this CeO 2 sample showed a high catalytic activity for benzyl alcohol oxidation.

Effect of heat treatment on particle growth and magnetic properties of electrospun Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers

Sr0.8La0.2Zn0.2Fe11.8O19/poly(vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol–gel assisted electrospinning. Subsequently, the M-type ferrite Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers with diameters about 120 nm were obtained by calcination of these precursors at different heat treatment conditions. The precursor and resultant Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. With the calcination temperature increased up to 1,000 °C for 2 h or the holding time prolonged to 12 h at 900 °C, the Sr0.8La0.2Zn0.2Fe11.8O19 particles gradually grow into a hexagonal elongated plate-like morphology due to the dimensional control along the nanofiber length. These elongated plate-like particles will be linked one by one to form the nanofiber with a necklace-like morphology. The magnetic properties of the Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers are closely related to grain sizes, impurities and defects in the ferrite, which are influenced by the calcination temperature, holding time and heating rate. After calcined at 900 °C for 12 h with a heating rate of 3 °C/min, the optimized magnetic properties are achieved with the specific saturation magnetization 75.0 A m2 kg−1 and coercivity 426.3 kA m−1 for the Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers.

Effect of alkali cations on the CuZnOAl2O3 low temperature water gas-shift catalyst

Low temperature water gas-shift catalysts containing 1.0% by weight of alkali elements (Li, K, Rb and Cs) were prepared by impregnation of a ternary Cu/ZnO/Al2O3 (CZA) base catalyst. The calcined precursors were characterized by different physical and chemical techniques such as X-ray diffraction, X-ray fluorescence, N2O chemisorption, N2 adsorption at low temperature and X-ray photoelectron spectroscopy. Then these precursors were activated and tested in the low temperature water gas-shift reaction (LT-WGS). It was shown that the K-containing CZA catalyst exhibited the highest CO conversion level at reaction temperature within the range 450–530K. In addition, the alkali promoters were found to prevent methanol production at temperatures higher than 480K.

Synthesis of nanocrystalline ytterbium-doped yttria by citrate-gel combustion method and fabrication of ceramic materials

Nanosized ytterbium doped yttria powders were prepared by citrate-gel combustion techniques. As-synthesized precursor and calcined powders were characterized for their crystalline structure, particle size and morphologies. Nanocrystalline Yb 3+:Y 2O 3 powders with pure cubic yttria crystal structure were obtained by calcination of as-prepared precursors at 1100 °C for 3 h. Powders obtained were well dispersed with an average particle size of 60 nm. By using the obtained powders, nearly full dense Yb 3+:Y 2O 3 ceramics were produced by vacuum sintering at 1800 °C for 12 h. The emission spectrum of the sintered ceramics under the excitation wavelength of 905 nm illustrates that there are three fluorescence peaks locating at 976 nm, 1030 nm and 1075 nm respectively, all corresponding to the 2 F 5/2 → 2 F 7/2 transitions of ytterbium ion.

Synthesis powder precursor of LAS ceramics via pH controlled wet chemical process

A powder precursor of β-spodumene based LAS ceramics was synthesized by sol–gel process and precipitation method using Li 2CO 3, Al 2SO 4 and sol of SiO 2 in dilute solution of H 2SO 4. The wet chemical pH controlled methods used for synthesis of LAS ceramic's precursor are able to prevent the extremely low acidity of gel. These techniques provide an interesting option for preparation of LAS ceramics because the produced amount of corrosive gases during the thermal treatment (calcination) of precursor is reduced. Thermal analysis methods (simultaneous TG-DTA), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for investigation of precursor composition and properties.

Synthesis and gas sensing properties of bundle-like α-Fe 2O 3 nanorods

Bundle-like α-Fe 2O 3 nanostructures were successfully synthesized by a simple calcination of β-FeOOH precursor derived from a hydrothermal method in the presence of poly(vinyl pyrrolidone). The as-prepared products were characterized by X-ray power diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The results indicated that bundle-like nanostructures were composed of well-aligned single crystalline nanorods with the diameters of 20–30 nm and the lengths of 200–300 nm. The gas sensing properties of as-prepared products were investigated. It was found that the sensor based on α-Fe 2O 3 nanostructure exhibited high response, quick response–recovery, and good repeatability to acetone at 250 °C.

Electrochemical performance of single crystalline spinel LiMn 2O 4 nanowires in an aqueous LiNO 3 solution

Single crystalline cubic spinel LiMn 2O 4 nanowires were synthesized by hydrothermal method and the precursor calcinations. The phase structures and morphologies were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). Galvanostatic charging/discharging cycles of as-prepared LiMn 2O 4 nanowires were performed in an aqueous LiNO 3 solution. The initial discharge capacity of LiMn 2O 4 nanowires was 110 mAh g −1, and the discharge capacity was still above 100 mAh g −1 after 56 cycles at 10C-rate, and then 72 mAh g −1 was registered after 130 cycles. This is the first report of a successful use of single crystalline spinel LiMn 2O 4 nanowire as cathode material for the aqueous rechargeable lithium battery (ARLB).

Investigation of Phase Transformation and Structure Evolution of Electrospun Copper Oxide Nanofibers during Thermal Annealing

One-dimensional nanostructures, like nanofibers, nanobelts, nanotubes, nanorods have been regarded as a new class of nanomaterials that have been attracted as the most promising building blocks for verity applications in the last few years. As one type of important structures with intensive research efforts have been devoted to the production and investigation of the metal oxides. Metal oxide nanofibers have different potential to play an essential role in a series of application such as optics, nanoelectronics, catalysts, sensors, storage, optoelectonics, and full cell. Copper oxide nanostructures is a promising semiconductor material with potential applications in photochemical, electrochemical, electrochromic especially in water splitting, catalysts, and fabrication of photovoltaic devices. In this paper electrospinning method via sol-gel was used to fabricate copper oxide nanofibers. Copper oxide nanofibers with different morphology were synthesized by different calcinations temperature. In this paper, effective parameters such as voltage, concentration of precursor and different calcinations temperature were characterized by thermal gravimetric analysis, scanning electron microscopy (SEM), Transmission electron microscopy, x-ray diffraction(XRD), Fourier transform infrared spectroscopy (FTIR) and Brunauer Emmett and Teller (BET).