Citrate Complex Precursors Research Articles

Ultrasonic assisted enhanced catalytic effect of perovskite to promote depolymerization of lignin

The search for renewable energy sources to replace fossil fuel has made lignin a promising carbon-containing resource. In this paper, LaNiO3 perovskite catalyst supported by mesoporous carrier with specific pore structure was prepared by the pore filling of MCM-41 with citrate complex precursors of nickel and lanthanum. Then the catalysts applied to maize straw lignin depolymerization. The results of low-angle XRD, N2 adsorption-desorption, IR spectroscopy and SEM confirmed that the catalyst has been successfully manufactured. Based on the yield of phenolic monomer, low molecular weight lignin derived bio-oil and high molecular weight lignin derived bio-oil as standard, the catalyst showed best catalytic effect when the reaction temperature was 250 °C, the reaction time was 6 h, the ratio of lignin to catalyst mass was 5: 1 and with ultrasonic assist. The yield of phenolic monomer was 11.46 wt% and that of bio-oil was 68.0 wt%. In general, this method is an excellent embodiment of the principle of Lignin-first as well as an excellent strategy for the production of value-added phenolics and high-quality bio-oils from lignin. It plays an important role in promoting the high value utilization of lignin in the future.

A self-encapsulated porous Sb–C nanocomposite anode with excellent Na-ion storage performance

In this study, a self-encapsulated Sb-C nanocomposite as an anode material for sodium-ion batteries (SIBs) was successfully synthesised using an SbCl3-citrate complex precursor, followed by a drying and calcination process under an inert N2 atmosphere. When the molar ratio of SbCl3 to citric acid was varied from 1 : 1 to 1 : 4, the Sb-C nanocomposite with a molar ratio of 1 : 3 (Sb-C3) exhibited the highest specific surface area (265.97 m2 g-1) and pore volume (0.158 cm3 g-1). Furthermore, the Sb-C3 electrode showed a high reversible capacity of 559 mA h g-1 at a rate of C/10 and maintained a high reversible capacity of 430 mA h g-1 even after 195 cycles at a rate of 1C. The Sb-C3 electrode exhibited an excellent rate capability of 603, 445, and 357 mA h g-1 at the rates of C/20, 5C, and 10C, respectively. Furthermore, a full cell composed of an Sb-C3 anode and a Na3V2(PO4)3 cathode exhibited good specific capacity and cyclability, making the Sb-C composite a promising anode material for high-performance SIBs.

White luminescence of Ho3+/Tm3+/Yb3+-codoped CaWO4 synthesized via citrate complex route assisted by microwave irradiation

The nanocrystalline Ho3+/Tm3+/Yb3+ co-doped CaWO4 upconversion (UC) phosphors were successfully synthesized by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperature ranging from 300 to 700 °C for 3 h. Crystallization of the Ho3+/Tm3+/Yb3+ co-doped CaWO4 was detected at 400 °C, and entirely completed at 600 °C. The Ho3+/Tm3+/Yb3+ co-doped CaWO4 heat-treated at 600 °C showed primarily spherical and homogeneous morphology. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaWO4 shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 and 651 nm respectively from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaWO4 in the Commission International De'eclairage (CIE) chromaticity diagram could be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. The UC luminescent properties on Tm3+ and Ho3+ concentrations and related mechanism based on laser pump power were discussed in detail.

A comparison study on methane dry reforming with carbon dioxide over LaNiO3 perovskite catalysts supported on mesoporous SBA-15, MCM-41 and silica carrier

The supported LaNiO3 perovskite catalysts on mesoporous carrier (LaNiO3/SBA-15, LaNiO3/MCM-41 and LaNiO3/SiO2) with different pore structures have been synthesized via filling the pores of mesoporous silica with citrate complex precursors of nickel and lanthanum, with further treatments. The catalysts were characterized by means of N2 physisorption, XRD, HRTEM+EDX, TPR, temperature-programmed hydrogenation (TPH) and TGA techniques, and their catalytic performances were measured in methane dry reforming with carbon dioxide to hydrogen and synthesis gas (syngas). The results of low-angle XRD, N2 physisorption and TEM analysis showed that LaNiO3 perovskite was formed inside the channels of mesoporous supports, and the introduction of LaNiO3 perovskite did not destroy the mesoporous structure of support. The pore structure had a substantial influence on the catalytic performance. LaNiO3/MCM-41 exhibited the higher initial catalytic activity, owing to the higher Ni dispersion, while LaNiO3/SBA-15 was superior to LaNiO3/MCM-41 in the long-term stability, which could be due to the stable silica matrix restricted the agglomeration of nickel species. The hexagonal mesopores of LaNiO3/SBA-15 were still kept intact after reaction, while the mesoporous structure in LaNiO3/MCM-41 was collapsed during the reaction, which resulted in metal particles aggregation to certain extent. For comparison, the carbon deposition was responsible for the remarkable decrease of catalytic activity over LaNiO3/SiO2 sample, evidenced by TGA and TPH results.

Synthesis of multielement ferrites and their silica composites

Ferrites of composition M0.2Co0.4Zn0.4Fe2O4 with M = Cu2+, Mn2+ and Ni2+ were prepared by citrate complex method. Later, their composites with silica have also been obtained by a simple route. The citrate complex precursors of multielement ferrites were characterized by FTIR spectroscopy and thermal analysis, been found a similar behavior for the three systems. The thermal treatment (at 400, 600 and 800 °C) of precursors gives, as result, the spinel type cubic ferrite pure when the ions substituted were copper and nickel; when manganese was used an hematite phase was obtained as contaminant at 800 °C. The presence of all ions involved and the particle size was corroborated by EDX analysis and measured from a TEM micrograph, respectively. The magnetic parameters related to magnetic properties, magnetization and coercivity, were different depending of the chemical composition of the ferrite and the thermal treatment temperature, as it was expected. At room temperature, the values obtained were near to those reported for Co-ferrite in bulk. The synthesis route of the composites M0.2Co0.4Zn0.4Fe2O4-SiO2, proposed in this work, gives as result magnetic nanoparticles in an amorphous silica matrix. Their magnetic properties were depending on weight percentage of the magnetic phase in the composite.

Controllable synthesis of spinel nano-ZnMn2O4via a single source precursor route and its high capacity retention as anode material for lithium ion batteries

Agglomerated pure spinel ZnMn2O4 nanoparticles with flake-shaped structure have been synthesized viacalcination of an agglomerated Zn–Mn citrate complex precursor, which was prepared with high yield by a convenient, environmentally benign and low temperature route. The composition, morphology and thermal decomposition of the Zn–Mn citrate complex were studied by C&H elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The resulting ZnMn2O4 nanoparticles obtained from the precursor calcination at 700 °C were systematically characterized by XRD, FTIR, N2Adsorption/Desorption, SEM, TEM, HRTEM and selected area electron diffraction (SAED). The results show that the ZnMn2O4 material was agglomerated to form a porous texture in pure phase. The electrochemical properties of the agglomerated ZnMn2O4 material were investigated to determine its reversible capacity, rate and cycling performance as the anode material for lithium ion batteries (LIBs). This ZnMn2O4 material exhibited promising capacity retention of over 200 cycles at varying discharge rates. The electrode also exhibited attractive rate capabilities yielding capacity of 330 mAh g−1 after more than 35 cycles at 600 mA g−1.The ameliorated electrochemical performance can be ascribed to the high crystallinity and porous texture of the ZnMn2O4 material which provided short diffusion paths for lithium ions. Ex situXRD analysis of the electrodes after discharging and charging to the selected voltage was conducted and the possible lithium insertion mechanisms are discussed. This study suggests that the ZnMn2O4 material synthesized via the single source precursor route is a promising anode material for LIBs.

Controllable Synthesis of Pure-Phase Rare-Earth Orthoferrites Hollow Spheres with a Porous Shell and Their Catalytic Performance for the CO + NO Reaction

Pure perovskite LnFeO3 (Ln = La, Pr−Tb) hollow spheres with porous shell and solid spheres (Ln = Dy−Yb, Y) have been successfully synthesized via calcination of a Ln-Fe citrate complex precursor, which was prepared via a convenient and effective hydrothermal method. The reaction parameters to obtain the Ln-Fe citrate complex with Ln/Fe = 1:1 can be calculated using a diagram of reaction species distribution in the solution. The calculated value was coincident well with the experimental one. The composition and the thermal decomposition processes of the Ln-Fe citrate complex were investigated carefully, using elemental analysis, inductively coupled plasma analysis (ICP), energy-dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The formation mechanism of the Ln-Fe citrate complex hollow spheres was proposed as an acidic digestion ripening process. Furthermore, all 13 pure-phase LnFeO3 microspheres had an excellent ca...

Preparation and Electric Property of Lead-Free KNbO3 Piezoceramics Derived from Citrate Complex Precursor

The synthesis of well-crystalline KNbO 3 nanopowder has been carried out by using citrate complex precursor method. By using this powder as raw materials, dense KNbO 3 ceramics (RD = 98.9%) was successfully prepared, and showed excellent ferroelectric and piezoelectric properties. The effect of starting K/Nb mixture ratio in aqueous precursor solution on the crystallinity and electric properties of derived KNbO 3 ceramics was studied. It was found that an appropriate superfluous addition of the K-souce (K/Nb = 1.05) was required to synthesis excellent KNbO 3 ceramics, because of the existence of residual K+ ions in the aqueous solution without being involved in the formation of the chelating complex.

Nanocasted Synthesis of Mesoporous LaCoO3 Perovskite with Extremely High Surface Area and Excellent Activity in Methane Combustion

Ordered mesoporous LaCoO3 perovskite with high surface area was synthesized via nanocasting strategy by using ordered mesoporous cubic (Ia3d) vinyl silica as the template. The sample, prepared by filling mesopores in silica template with a La−Co citrate complex precursor followed by calcination and silica removal, was characterized by XRD, TEM, and nitrogen sorption techniques, and its catalytic activity was tested for complete methane oxidation. The wide-angle XRD pattern showed LaCoO3 perovskite was formed and no La-oxide/Co-oxide phases were detected in the obtained material. This LaCoO3 perovskite displayed a high BET surface area of 96.7 m2 g−1 from nitrogen sorption analysis and a three-dimensional ordered mesostructure from TEM images, as well as a small-angle XRD pattern. Moreover, this material showed much higher activity in the complete methane oxidation than the conventional bulk LaCoO3 perovskite. The light-off temperature (T10) and the half-conversion temperature (T50) were at 335 and 470 °C,...

Microwave-Assisted Synthesis of MWO<sub>4</sub> and MMoO<sub>4</sub> (M = Ca, Ni) Nano-Powders Using Citrate Complex Precursor

Nano-sized MWO4 and MMoO4 (M = Ca, Ni) powders, which have scheelite and wolframite type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heattreated at temperatures from 300 to 600 °C for 3 h. Crystallization of the MWO4 and MMoO4 precursors was detected at 400 °C and completed at a temperature of 500 °C. Most of the MWO4 and MMoO4 powders heat-treated between 300 and 600 °C showed primarily spherical and homogeneous morphology. The average crystallite sizes of MWO4 (M = Ca, Ni) were between 22 and 39 nm, and those for MMoO4 (M = Ca, Ni) were between 19 and 35 nm respectively, showing an ordinary tendency to grow with temperature.

Synthesis of nanocrystalline MMoO4 (M = Ni, Zn) phosphors via a citrate complex route assisted by microwave irradiation and their photoluminescence

Nanocrystalline MMoO4 (M=Ni, Zn) phosphors, which have wolframite-type structure, were successfully synthesized at low temperatures via a modified citrate complex route assisted by microwave irradiation. The citrate complex precursors were heat-treated from 300 to 600 °C for 3 h. Crystallization of the MMoO4 (M=Ni, Zn) nanocrystallites were detected at 500 °C, and entirely completed at a temperature of 600 °C. The nanoparticles presented primarily dispersed and homogeneous morphology with particle size of 20–40 nm. The nanocrystalline MMoO4 (M=Ni, Zn) phosphors prepared at 600 °C exhibited broad luminescence in green and blue wavelength region, respectively.

Microwave-assisted synthesis of BaMoO 4 nanocrystallites by a citrate complex method and their anisotropic aggregation

BaMoO 4 powders, which have scheelite-type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 500 °C for 3 h. Crystallization of the BaMoO 4 powders were detected at 350 °C and completed at a temperature of 400 °C. TEM image of the BaMoO 4 product heat-treated at 400 °C revealed spindle-rods-like and flake-like morphology at 500 °C. The anisotropic aggregation habit of BaMoO 4 lead to two-dimensionally aggregated powder morphology, which was attributed to the high chemical potentials of the intrinsic structure of BaMoO 4.

Microwave-assisted synthesis of PbWO 4 nano-powders via a citrate complex precursor and its photoluminescence

Nanocrystalline lead tungstate (PbWO 4) powders, which have scheelite-type structure, were successfully synthesized at low temperatures using a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 600 °C for 3 h. Crystallization of the PbWO 4 precursor was detected at 400 °C, and completed at 500 °C. Nanocrystalline PbWO 4 powders heat-treated between 400 and 600 °C primarily showed spherical and disperse morphology. The average crystallite sizes of PbWO 4 were between 17 and 28 nm at temperatures between 400 and 600 °C, showing a tendency to increase with the temperature. The PbWO 4 powders prepared at 600 °C showed the strongest photoluminescent intensity, which was ascribed to the higher crystallinity and homogeneous particle morphology.

Microwave-assisted synthesis of barium molybdate by a citrate complex method and oriented aggregation

BaMoO 4 powders, which have scheelite type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 500 °C for 3 h. Crystallization of the BaMoO 4 powders were detected at 350 °C, and completed at a temperature of 400 °C. TEM image of the BaMoO 4 product obtained above 400 °C revealed spindle-rods-like or flake-like morphology. The anisotropic growth habit of BaMoO 4 leads to the oriented aggregation, which is attributed to the high chemical potentials of the intrinsic structure of BaMoO 4. The BaMoO 4 powder prepared at 500 °C showed the strongest photoluminescent intensity.

Microwave-assisted synthesis of nanocrystalline MWO 4 (M: Ca, Ni) via water-based citrate complex precursor

Nano-sized MWO 4 (M: Ca, Ni) powders, which have scheelite and wolframite type structure, were successfully synthesized at low temperatures by a modified citrate complex method assisted by microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 500 °C for 3 h. Crystallization of the CaWO 4 and NiWO 4 nano-sized powders were detected at 300 and 350 °C, respectively, and completed at a temperature of 400 °C. Most of the CaWO 4 and NiWO 4 powders heat-treated between 350 and 450 °C showed primarily spherical and homogeneous morphology. The average crystallite sizes of CaWO 4 and NiWO 4 were between 12 and 35 nm and between 14 and 29 nm, respectively, showing an ordinary tendency to grow with temperature.

Nanocrystalline LaCoO 3 perovskite particles confined in SBA-15 silica as a new efficient catalyst for hydrocarbon oxidation

Highly crystalline LaCoO 3 perovskite particles were prepared by a novel microwave-assisted process with a La–Co citrate complex precursor in the host pores of mesoporous SBA-15 silica. The resulting material exhibited considerably higher catalytic activity in the complete methane oxidation than a LaCoO 3/SBA-15 sample prepared by a conventional method with a bulk LaCoO 3 perovskite. This suggests that a higher density of lattice defects achieved on the high-surface-area LaCoO 3 nanocrystals synthesized by microwave processing is essential for the superior performance of the catalyst.

Microwave-assisted synthesis of CaMoO 4 nano-powders by a citrate complex method and its photoluminescence property

Nano-sized CaMoO 4 powders, which have scheelite type structure, were successfully synthesized at low temperatures by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 700 °C for 3 h. Crystallizations of the CaMoO 4 nano-sized powders were detected at 400 °C, and entirely completed at a temperature of 500 °C. Almost nano-powders of CaMoO 4 heat-treated between 400 and 600 °C showed primarily spherical and homogeneous morphology. The average crystalline sizes of CaMoO 4 were 12–27 nm at temperatures of 400–700 °C, showing an ordinary tendency to increase with the temperatures. The CaMoO 4 powders prepared at 600 °C showed the strongest photoluminescence intensity.

Low-temperature synthesis of β-BiNbO4 powder by citrate sol–gel method

β-BiNbO4 powder with nanometer sized (≈65 nm) particles was prepared by citrate sol–gel technique. Using Bi-citrate and Nb-citrate as the starting precursors, the crystalline phase of β-BiNbO4 could be obtained by thermal decomposition of citrate complex precursors at a low temperature (600 °C). Infrared spectrum, thermogravimetry–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) technique and transmission electron microscopy (TEM) were used to characterize the citrate precursors and the calcined powders.

Preparation and Microstructure Evolution of Both Freestanding and Supported TiO2 Thin Films

Thin films of TiO2 were fabricated by spin-coating silicon wafers and cover glass with a titanium citrate complex precursor. The grain growth and phase development of both freestanding and supported films were studied using a combination of atomic force microscopy, x-ray diffraction, and transmission electron microscopy. Freestanding films prepared at 400 °C possess only the anatase phase, while supported films treated under the same conditions formed a small amount of the rutile phase. After heat treatment at various temperatures, results indicated that porosity was introduced into the films when the grain size grew close to the film thickness. Grain growth studies show that the grain size of the freestanding film underwent a drastic increase during the transformation from anatase to rutile. The grain size of the supported films did not show an abrupt change upon heat treatment. The grain size of the freestanding films treated at 900 °C was approximately three times larger than that of the supported films.

Spray pyrolytic deposition of barium hexaferrite thin films for magnetic recording applications

Barium hexaferrite films with particles in the 50–80 nm size range have been prepared by a simple spray pyrolytic method starting from a citrate complex precursor. High nucleation rates during thermal decomposition of citrate precursor along with low growth rates ensure the formation of nanoparticles. The particles have a predominantly perpendicular easy-axis orientation and a perpendicular coercivity of 5000 Oe. The angular-dependent coercivity measurements show a nearly monotonic angular dependence indicating weaker grain interaction and low media noise in these films, an extremely useful property for application in high-density recording media.