Elevated Calcination Temperatures Research Articles

SiO2 loading combined with high temperature calcination of kesterite Cu2ZnSnS4 nanocrystals towards enhanced photocatalytic H2 evolution

In this paper, highly efficient Cu2ZnSnS4 (CZTS) towards photocatalytic H2 evolution was successfully fabricated by SiO2 loading and high temperature calcination. X-ray diffraction (XRD) and Raman shifts revealed CZTS was pure phase with kesterite structure. Transmission electron microscope (TEM) and high resolution TEM showed CZTS could maintain nanoscale size and kesterite structure after being calcined. The SiO2 loading was found to be an efficient approach to avoid the aggregation of CZTS nanocrystals during high temperature calcination. As the elevated calcination temperature, the crystallinity of CZTS increased without observable size change, which suggested the no change on the specific surface area. All CZTS/SiO2 exhibited superior photocatalytic H2 evolution. Especially, the photocatalytic H2 evolution rates for per unit mass CZTS was significantly enhanced, which was mainly attributed to the good dispersion, the improved crystallinity and the less loss of specific surface area during high temperature calcination.

Nanostructured hybrid materials as precursors of mesoporous NiMo-based catalysts for the propane oxidative dehydrogenation

Nanostructured hybrid materials made of guest ions and a self-assembled copolymer were used as precursors for the preparation of NiMo-based catalysts. The hybrids were calcined in air and the recovered materials were characterized and tested in propane oxidative dehydrogenation. A 6-fold improvement of the yield to propene is obtained as compared with classically prepared catalysts. The exothermic degradation profile of the copolymer is the key point of our approach as it allows to prepare a porous β-NiMoO4, namely the phase particularly desired for its superior propene selectivity. More precisely, the polar backbone and the aliphatic side chains of the copolymer burn at different temperatures. The former ignites at moderate temperatures and initiates the early crystallization of β-NiMoO4. Occurring at higher temperature, the decomposition of the aliphatic part then induces the formation of mesopores. A β-NiMoO4 can thus be prepared at moderate temperatures whereas elevated calcination temperatures (>650 °C) are usually required. This peculiar behavior enables to prevent the texture of NiMoO4 from sintering and to maintain at high levels its mesoporosity, specific area and thus catalytic activity. At the end, the use of our tailor designed copolymer template allows reaching the remarkably high propene yields obtained.

Photovoltaic and photocatalytic performance of electrospun Zn2SnO4 hollow fibers

The phase pure hollow Zn2SnO4 and green emitting ZnO-SnO2-Zn2SnO4 composite fiber have been prepared by post calcining the as formed fiber by electrospin technique. Depending upon the calcination temperature, the as prepared fiber exhibited a striking variation in composition, microstructure, optical and photo-electrochemical properties. The composition dependent dissimilarity in photovoltaic performance and photocatalytic activity has been established in this work. A relatively enhanced open circuit voltage (Voc) of 0.76V, fill factor (FF) of 59.78%, short circuit current (Jsc) of 4.2mA/cm2 and an overall conversion efficiency (ɳ) of 1.93% have been achieved for the phase pure Zn2SnO4 porous fiber obtained at the elevated calcination temperature of 1000°C. On the contrary, a relatively reduced Voc, FF, JSC and ɳ of 0.70V, 42.54%, 3.8mA/cm2 and 1.17%, respectively, have been achieved for the 800°C calcined dense fiber consisting of a mixture of three distinct phases ZnO, SnO2 and Zn2SnO4. Unlike photovoltaic behaviour the trend in photocatalytic performance interestingly got reversed for the ZnO-SnO2-Zn2SnO4 composite fiber owing to its superior photo-induced charge separation ability followed by generation of larger amount of active hydroxyl radicals (OH.). Our results establish the composite fiber as a preferred photocatalyst in comparison to phase pure Zn2SnO4 towards the textile dyes Methylene blue and Congo red and non absorbing organic pollutants such as Phenol and Bisphenol A under UV illumination.

Processing and crystallographic structure of non-equilibrium Si-doped HfO2

Si-doped HfO2 was confirmed to exist as a non-equilibrium state. The crystallographic structures of Si-doped HfO2 were studied using high-resolution synchrotron X-ray diffraction and the Rietveld refinement method. Incorporation of Si into HfO2 and diffusion of Si out of (Hf,Si)O2 were determined as a function of calcination temperature. Higher thermal energy input at elevated calcination temperatures resulted in the formation of HfSiO4, which is the expected major secondary phase in Si-doped HfO2. The effect of SiO2 particle size (nano- and micron-sized) on the formation of Si-doped HfO2 was also determined. Nano-crystalline SiO2 was found to incorporate into HfO2 more readily.

Graphitic g-C3N4-WO3Composite: Synthesis and Photocatalytic Properties

Graphitic g-<TEX>$C_3N_4-WO_3$</TEX> composite was synthesized simply by decomposing melamine in the presence of <TEX>$WO_3$</TEX> at <TEX>$500^{\circ}C$</TEX>. The obtained material was characterized by XRD, SEM, IR and XPS. The results showed that the as-prepared composite exhibits orthorhombic <TEX>$WO_3$</TEX> phase coated by g-<TEX>$C_3N_4$</TEX> and the g-<TEX>$C_3N_4$</TEX> decomposed completely with N-doped <TEX>$WO_3$</TEX> remaining at elevated calcination temperatures. The photocatalytic activity of the composite was evaluated by the photodegradation of methylene blue under visible light. An enhancement in photocatalytic activity for the graphitic g-<TEX>$C_3N_4-WO_3$</TEX> composite compared to the conventional nitrogen-doped <TEX>$WO_3$</TEX> was observed, which can be attributed to the presence of g-<TEX>$C_3N_4$</TEX> in the material.

Synergistic antibacterial activity of TiO2 co-doped with zinc and yttrium

In this study, a sol–gel method was successfully developed to synthesize zinc and/or yttrium doped titania powders. The as-prepared materials were characterized by X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance spectroscopy (DRS) and X-ray photoluminescence (PL) spectroscopy. It was found that the phase structures of as-prepared materials were transformed from anatase TiO2 to rutile TiO2 by elevated calcination temperatures, accompanied with Zn3TiO8, ZnTiO3 and Y2Ti2O7 phases appearance. Photocatalytic antibacterial experimental study implied that zinc and yttrium co-doped titania exhibited better performance than zinc or yttrium doped alone under visible light irradiation. The enhanced photocatalytic effect was ascribed to co-doping of Zn and Y in TiO2.

β-MnO2 sacrificial template synthesis of Li1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery cathodes

Lithium-rich manganese-based oxide Li1.2Ni0.13Co0.13Mn0.54O2 nanorods and polyhedrons have been successfully prepared using precursor β-MnO2 nanorods as sacrificial templates at a calcination temperature of 750, 800, 850 or 900 °C. X-ray diffraction (XRD) and scanning electron microscope (SEM) measurements show that the elevated calcination temperatures help to improve the layered structure and average particle size of the target products. Rod-like Li1.2Ni0.13Co0.13Mn0.54O2 can be obtained at low calcination temperatures (i.e., 750 and 800 °C), which becomes polyhedral at 850 or 900 °C. As lithium ion battery cathodes, the Li1.2Ni0.13Co0.13Mn0.54O2 obtained at 850 °C shows the highest discharge capacity of 239.2 mA h g−1 at 20 mA g−1, and a stable discharge capacity of 92.8 mA h g−1 at 1000 mA g−1. The good electrochemical performances of the 850 °C sample should be attributed to the better crystal structure and/or the more appropriate particle size compared with those of other samples.

Improvement of luminescence properties of Ca0.8Zn0.2TiO3:Pr3+ prepared by hydrothermal method

Abstract

Effect of Zr/Ce molar ratio on the structure of powders and Zr1−x Ce x O2 coatings on quartz fiber reinforced polyimide matrix composites via sol–gel process

In this investigation, Zr1−xCexO2 coatings were fabricated on quartz fiber reinforced polyimide matrix composites via sol–gel process at 400 °C. The phase evolution, structural and morphological characteristic of specimens were investigated by differential scanning calorimetric, Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy. The significant phase evolution of final powders with the decreasing Zr/Ce molar ratio could be observed as follows: tetragonal (t′) → cubic + tetragonal (t′) → tetragonal (t″). BET specific surface areas of powders exhibited a decreased tendency with the increasing calcination temperature as well as the decreasing Zr/Ce molar ratio. The average crystallite size and the mean particle size increased with the elevated calcination temperature, while the particle size also increased with the increase in Ce content. The progressive addition of Ce could promote the sintering process and the densification of coating. Morphologies of coatings changed with the variation of the Zr/Ce molar ratio. The results indicate that Zr0.75Ce0.25O2 coating with the Zr/Ce molar ratio of 3 is a stable uniform coating with excellent adhesion.

Monodisperse colloidal spheres for (Y,Eu)2O3 red-emitting phosphors: establishment of processing window and size-dependent luminescence behavior

The urea-based homogeneous precipitation method was introduced in the preparation of monodisperse colloidal spheres for (Y0.95Eu0.05)2O3 red-emitting phosphors, and the processing window was defined. Particle size and shape are significantly affected by the ion concentration and the urea/RE3+ molar ratio R (RE3+=Y3++Eu3+). A low ion concentration is beneficial in forming monodisperse spheres and extending their formation domain. Increasing R results in a gradual change in the composition of spherical particles from the core-shell Eu(OH)CO3@Y(OH)CO3 structure to a homogeneous solid solution, thereby significantly lowering the calcination temperature at which precursors convert to oxides. Upon UV excitation into the charge-transfer band at 254 nm, the uniform phosphor spheres of (Y0.95Eu0.05)2O3 exhibit typical red emissions at 613 nm; the emission is stronger from larger particles mainly because of their smaller surface area. Both the luminescence intensity and quantum efficiency of the oxide phosphors increase with elevated calcination temperatures. The spherical shape and excellent dispersion of the precursor particles (∼450 nm in diameter) have been well retained after calcination at 1000 ○C for 4 h, and the resultant oxide phosphors exhibit external and internal quantum efficiencies of 50 and 82%, respectively.

Pore structure and surface acidity evaluation of Fe-PILCs

Fe-PILCs via different conditions using smectites from Hancili (Turkey) and Wyoming (USA) were synthesised. Presaturation had little effects on the basal spacing values while it had important effects on thermal stabilities of the products. Products having basal spacing (d_{001}) around 1.30 nm and surface area up to 160 m^2 g^{-1} were obtained. The thermal behaviour, X-ray diffraction (XRD) patterns, and nitrogen adsorption/desorption experiments confirmed that thermally stable and micro-mesoporous products were obtained although at elevated calcination temperature. Delaminated sample with basal spacing value of 2.79 nm was obtained. Surface acidity of clay was enhanced by pillaring. Chemically sorbed pyridine Fourier transform infrared spectroscopy (FTIR) bands were preserved at elevated desorption temperatures.

Doping and grain size effects in nanocrystalline ZrO2–Sc2O3system with complex phase transitions: XRD and Raman studies

Weakly-agglomerated nanocrystalline (ZrO2)1−x(Sc2O3)x (x = 0.02–0.16) powders with high surface area (106–186 m2 g−1) and uniform particle size (5.7–9.5 nm) were synthesized by a two-step hydrothermal process in the presence of urea, and their complex phase evolution upon calcinations over 400–1400 °C were studied by a combined utilization of X-ray diffraction, in situ high temperature X-ray diffraction, near infrared Fourier transform Raman and ultraviolet Raman spectroscopies. It was discovered that the growth of the grains comprised two stages, and the apparent activation energies, Ea1 (<800 °C) and Ea2 (>800 °C), are in the range of 5.5–12 kJ mol−1 and 80–140 kJ mol−1, respectively. The crystallite size, microstrain, surface area and growth activation energy of the samples showed a strong dependence on the Sc3+ doping concentration. The nanocrystalline (ZrO2)1−x(Sc2O3)x samples underwent complex phase transitions upon calcination from 800 to 1000 °C. Tetragonal and cubic phases have been preserved when the samples calcined below 800 °C as a result of crystallite size and doping effects. At elevated calcination temperature of 1000 °C, the compositions at x = 0.04, 0.10 and 0.14 seemed to be in the metastable phase boundaries of m + t, t + β (Sc2Zr7O17) and β + γ (Sc2Zr5O13), respectively. As calcined at 1400 °C, the grain size was in the micrometre regime, and t → m, c → t″, c → β and c → γ phase transitions occurred on the cooling stage for x ≤ 0.04, x = 0.08, 0.10 ≤ x ≤ 0.12 and x ≥ 0.14, respectively, resulting in the existence of m, t, t″, β and γ phases in turn at room temperature. Moreover, it was found that the tetragonal phase has been enriched at the surface region for the as-calcined (ZrO2)0.94(Sc2O3)0.06 and (ZrO2)0.92(Sc2O3)0.08 samples.

Making sense out of sulfated tin dioxide mesostructures

An in-depth investigation into the synthesis, characterization and sensor response of mesoporous SnO2 materials formed utilizing tin(IV) chloride, sodium dodecylsulfonate, and urea is described. The structures have been stabilized towards calcination by increasing the condensation of the tin oxide network utilizing urea as a slow-release base. PXRD, FT-Raman, N2 gas adsorption, thermal gravimetric analysis, and pyrolysis mass spectroscopy were used to monitor the two-step surfactant decomposition in which a sulfated tin oxide surface is formed followed by removal of the sulfate groups at elevated calcination temperatures. In situ a.c. impedance measurements of the materials in dry air and 2000 ppm carbon monoxide showed that the sensitivity of these materials towards carbon monoxide was inhibited by the presence of sulfate groups on the surface, whereas after the sulfate groups were removed the materials became much more sensitive towards carbon monoxide. These materials could find promising applications as gas-selective chemical sensors, super-acid catalysts, and anode materials for lithium battery applications.

Phase transformation and grain growth of doped nanosized titania

The influence of altervalent cation doping of TiO 2 on its phase transition and grain growth has been investigated. It is shown that dopants like Fe 3+, Si 4+, V 5+, Ru 3+ and Ni 2+ affect the phase transition temperature of the titania host, and that significant variation is observed for silicon doping. Iron titanium oxide and nickel titanium oxide phases were found in the iron-doped and nickel-doped system, respectively, at elevated calcination temperatures, while other doped systems only show the modifications of anatase and rutile at the observed range of calcination temperature and dopant content. Compared with the pure TiO 2, grain growth is arrested for the iron-doped and silicon-doped systems, and this tendency is especially distinct in the silicon-doped system.

Surface Ni 2+ diffusion in sol—gel-derived tetragonal and monoclinic ZrO 2 matrices

Tetragonal and monoclinic ZrO 2 gel matrices have been synthesized from the zirconium n-propoxide-acetylacetone-water-isopropanol system. Surface Ni 2+ ion diffusion in these sol—gel-derived tetragonal and monoclinic zirconia matrices have been studied with Fourier transform infrared spectroscopy, differential thermal analysis and X-ray photoelectron spectroscopy (XPS). It is found that the Ni 2+ metal ion diffuses into the ZrO 2 continuously over the temperature range of 400–600°C for both tetragonal and monoclinic ZrO 2 matrices, and later forms a thermodynamically stable Ni 2+/ZrO 2 solid solution at the elevated calcination temperatures. Higher Ni 2+ surface contents in tetragonal ZrO 2 are measured by XPS, indicating a larger specific surface area for tetragonal gel matrix. In addition to the +2 oxidation state, +3 for Ni is also detected in Ni/ZrO 2 systems. The atomic ratio of Ni 2+/Ni 3+ varies and peaks at 700°C in the tetragonal ZrO 2. However, in the monoclinic case, the ratio remains constant throughout the course of experiments. Diffusion thermodynamic quantities are investigated and the diffusion activation energy determined for Ni 2+ ion in ZrO 2 matrices is 0.40 eV. The oxidation states of surface metals (Ni and Zr) and crystallinity of the system during the phase transformation are also addressed.

Interaction of Ni(II,III) and Sol-Gel Derived ZrO2 in Ni/ZrO2 Catalyst System

ABSTRACTNiO/ZrO2 catalyst has a selectivity for producing higher hydrocarbons, whereas NiO on classical supports gives rise to methanation of CO + H2 mixture. In this study, tetragonal and monoclinic ZrO2 gel carriers have been synthesized using sol-gel method. The interaction of nickel ions with a sol-gel derived catalyst support has been investigated using FTIR, DTA, and XPS. It is found that the nickel ions diffuses into the ZrO2 continuously over 400 to 600°C for both tetragonal and monoclinic ZrO2, and forms a thermodynamically stable Ni/ZrO2 solid solution at elevated calcination temperatures. Higher nickel surface contents are observed in tetragonal ZrO2. In addition to Ni2+, Ni3+ ions are also detected in Ni/ZrO2 system. Cation ratio of Ni2+/Ni3+ peaks at 700°C in the tetragonal ZrO2. In the monoclinic case, the ratio remains constant at different elevated temperatures. The diffusion activation energy for Ni(II,III) on both tetragonal and monoclinic in ZrO2 is 0.40 eV.

Magnetic properties of iron-boron-oxide and iron-phosphor-oxide glasses prepared by sol-gel method

The magnetic properties of powders made from dried gel were measured as a function of calcination temperature up to 600 degrees C. The magnetic moment of iron oxide was enhanced by adding a small amount of boron. A maximum moment of 49.5 emu/g, which is about a 20% increase over that of nondoped Fe-O powders, was obtained at the mol. ratio of B/(Fe+B)=0.2. Doping with phosphorus, on the contrary, diminishes the magnetic moment. In both cases, the magnetic moment is considered to originate from fine maghemite particles dispersed in a glass network. The addition of such glass-forming elements as boron and phosphorus suppresses the growth of iron-oxide particles as well as the crystallographic transition from maghemite to hematite at elevated calcination temperature. The suppression is more pronounced for phosphorus than for boron. In addition, Fe B-O thin films were prepared by spin-coating an Fe-B-O gel solution on glass substrates. A large magnetization exceeding 3 kG was obtained after the gel was dried at 200 degrees C in air and subsequently annealed at 400 degrees C in a vacuum. It is found that a key factor in the realization of films with large magnetization is to dry the coated gel at low temperature. X-ray diffraction of the films shows a hollow pattern, indicating that they consist of very fine maghemite particles. >

Raman spectroscopy of chromium oxide supported on Al 2O 3, TiO 2 and SiO 2: a comparative study

The interaction of chromium oxide with Al 2O 3, TiO 2 and SiO 2 supports is investigated with Raman spectroscopy. The influence of the nature of the oxide support, calcination temperature and chromium oxide loading upon the molecular state of the supported chromium oxide is determined. The Raman studies reveal that the oxide supports stabilize the chromium oxide as Cr(VI) in tetrahedral coordination at moderate chromium oxide coverages. The surface chromium oxide is present as monomers and dimers on alumina, monomers and possibly dimers on titania, and monomers and polymers (dimers, trimers and tetramers) on silica. On the alumina support, the ratio of dimers/monomers increases with the chromium oxide coverage. On the silica support, the ratios of trimers/dimers and tetramers/dimers also increase with chromium oxide coverage. The surface chromium(VI) oxide species on titania, however, are not stable to elevated calcination temperatures and appear to be converted to a lower chromium oxide oxidation state. The silica support stabilizes the surface chromium(VI) oxide state at elevated calcination temperatures, but the surface chromium oxide polymers are not stable and convert to isolated surface chromium(VI) oxide monomers. Most of these differences are thought to be related to the differing surface-hydroxyl chemistries of Al 2O 3, TiO 2 and SiO 2 supports.

The interaction of V 2O 5 with Ti0 2(anatase): Catalyst evolution with calcination temperature and O-xylene oxidation

The interaction of V 2O 5 with the surface of TiO 2(anatase) was studied over the temperature range 110–750 °C. The V 2O 5 TiO 2 (anatase) system was characterized with laser Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, X-ray diffraction, thermal gravimetric analysis, BET, and catalytic performance for o-xylene oxidation to phthalic anhydride. The state of V 2O 5 TiO 2 (anatase) possessing high loadings of vanadia is strongly dependent on calcination temperature. In the presence of vanadia the TiO 2(anatase) support exhibits a simultaneous loss in surface area and structural transformation to rutile at elevated calcination temperatures. The morphology of the supported vanadia phase also depends on calcination temperature. At low calcination temperatures, 110–200 °C, the vanadia exists as vanadyl oxalate, the starting vanadia salt. At intermediate calcination temperatures, 350–575 °C, vanadia is present as a complete monolayer of surface vanadia species coordinated to the titania support and V 2O 5 crystallites. At calcination temperature of 575 °C and above, the supported vanadia phase reacts with the TiO 2(anatase) support to yield V x Ti 1 − x O 2(rutile). These structural changes have a pronounced effect on the catalytic performance of V 2O 5 TiO 2 (anatase) catalysts for the oxidation of o-xylene. The optimum catalytic performance is observed for prolonged calcination at intermediate temperatures, 350–575 °C, where a complete monolayer of surface vanadia exists on the TiO 2(anatase) support. The complete monolayer of surface vanadia and crystalline vanadia phases remain intact during the o-xylene oxidation reaction and become partially reduced by the reaction environment.