Studies on State and Structure of Noble Metals in Electrocatalyst Made by Coprecipitation Method

The electrocatalysts of Pt/C, PtRu/C and Ru/C were prepared by the impregnation method. The facet characterization, the dispersion and the particle size for the catalysts were determined by means of X ray diffraction and transmission electron microscopy. X ray photoelectron spectroscopy was also used to analyze the state and the valency of the noble metals. The results show that the particle size was in nanometer range and the binary metals have come into being an alloy. The platinum in the catalysts existed in zero valency. The valency of the ruthenium on the surface is different from that in the body, while the ruthenium on the surface existed in oxide form. PtRu/C and Pt/C are of good activity to the electrooxidation of hydrogen except Ru/C. PtRu/C is more tolerant of CO than Pt/C, and CO is only adsorbed on Pt.

Enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_(2) mixed oxides prepared by sulfate-aided coprecipitation method

Ceria-zirconia based mixed oxides(CZs)have been applied in three-way catalysts(TWCs)for their high surface area and oxygen storage capacity(OSC).In this work,enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_(2)mixed oxides was realized via a facile and scalable approach,namely,sulfateaided coprecipitation method was labelled as CZ-S.Sulfate ion(SO_(4)^(2-))was added into raw solution in the form of sulfuric acid and acted as coordination agent.The control sample was prepared by conventional coprecipitation method without sulfuric acid added and labelled as CZ.The promotion effect of sulfate ion was analyzed systematically by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),N_(2)adsorption-desorption,Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),OSC and hydrogen temperatureprogrammed reduction(H_(2)-TPR)analysis.XRD and high resolution TEM results reveal that CZ-S have homogeneous distributions of elements.TEM and SEM images show that fresh samples of CZ-S have narrower distributions of grain sizes and larger pore sizes than those of CZ.Through cross analysis of structure and morphology of CZ and CZ-S,we find that the introduction of sulfate ions results in uniform distributions of elements,narrows distributions of grain sizes,and enables the formation of secondary loose packing of sub-particles,which lead to enhanced thermal stability of the samples of CZ-S upon aging process at high temperature.After aging treatment at 1100℃for 10 h,aged samples of CZ-S present larger specific surface areas and pore volumes than the aged sample prepared by conventional coprecipitation method without sulfate ions added.Furthermore,the aged sample of CZ-S2(SO_(4)^(2-)/Zr=1)possesses the highest specific surface area of 21.9 m2/g and the biggest pore volume of 0.035 mL/g among all aged samples.

Controlled Preparation of Monodisperse CoFe_2O_4 Nanoparticles by a Facile Method

CoFe2O4 nanoparticles （NPs） were synthesized by coprecipitation method using FeCl3·6H2O and CoCl2·6H2O as precursors.The synthesized conditions were optimized,such as added means of precipitator,quantity of precipitator,the mol ratio of Fe 3＋ to Co2＋,reaction temperature and pH value.The synthesized material was characterized by XRD,TEM,FTIR,EDS,Raman and its magnetic properties were studied by VSM.The experimental results confirm that the sample is cubic spinel structure CoFe2O4 with a narrow size distribution and a good dispersion feature.CoFe2O4 NPs with well-controlled shape and size was obtained at 70℃.The magnetic properties indicate superparamagnetic behavior and good saturated magnetization.

Synthesis and Tribological Properties of Copper-alumina Nanocomposites Prepared by Coprecipitation Technique

The objective of this work is to study the synthesis of copper-alumina nanocomposites using the coprecipitation process and hot-pressing method, and investigate their mechanical properties. The effects of calcination temperature on the average size of composite particles and chemical composition after calcination were also analyzed. The sintering parameters including sintering temperature, hot pressure and packing time were optimized to fabricate the alumina nanoparticles reinforced copper matrix composites（CMCs）. The density, microhardness and tribological properties of the CMCs reinforced with 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt% of alumina nanoparticles were investigated correspondingly. The results showed that the optimum preparation parameters for the CMCs were 900 ℃ of hot pressing temperature, 27.5 MPa of hot pressure and 2 hrs of packing time. The CMC reinforced with 2 wt% of alumina nanoparticles had the lowest wear rate, with the relative wear resistance of 3.13.

Target effects on electrical properties and laser induced voltages of La_(0.72)Ca_(0.28)MnO_3 thin films prepared by pulsed laser deposition

La0.72Ca0.28MnO3 thin films were deposited on untilted and 15° tilted LaAlO_3 （100） single crystalline substrates by pulsed laser deposition. The polycrystalline targets used in the deposition process were synthesized by sol-gel and coprecipitation methods, respectively. The structure, electrical transport properties and surface morphology of the targets and films were studied. It is found that, compared with coprecipitation method, the sol-gel target has more homogeneous components and larger density and grain size, thus the higher insulator-metal transition temperature and larger temperature coefficient of resistivity. The thin film prepared by sol-gel target has a uniform grain size and higher quality. The metal-insulator transition temperature is higher and the laser induced voltage signal is larger. Preparing the target by sol-gel method can largely improve the properties of corresponding thin films in pulsed laser deposition process.

A new candidate as the cathode material for intermediate and low temperature SOFCs

In order to develop the new cathode materials suitable for intermediate and low temperature solid oxide fuel cells (IT/LTSOFCs), LaNi1-xFexO3 (x=0.4-0.8) (LNF) materials were synthesized using coprecipitation method. Their structures and morphologies were investigated by XRD and SEM, and their electronic conductivities at different temperatures were measured by dc four terminal method. Fuel cells were fabricated to evaluate the electrochemical properties of the LNF materials as cathodes at different temperatures. The performance of 450-497 mW·cm-2 was obtained in the temperature region of 580-650 ℃ for the LaNi0.2Fe0.8O3 cathode, and of 209-227 mW·cm-2 at 400-500 ℃ for the LaNi0.4Fe0.6O3. The excellent fuel cell performances indicate that the LNF materials are good cathodes for IT/LTSOFCs.

Matrix Induced Synthesis of Eu^(3+) Doped Zn_3(PO_4)_2 and LaPO_4 Phosphors by in-Situ Composing Hybrid Precursors

Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ and LaPO_4∶Eu 3+ were synthesized by in-situ co-precipitation method. X-ray diffraction and scanning electronic micrograph were used to characterize the resultant samples, whose particle size are in the range of micrometer. The emission spectra of Zn_3(PO_4)_2∶Eu 3+ (λ_ ex=245 nm) and LaPO_4∶Eu 3+ (λ_ ex=390 nm) shows that the emission for Eu 3+ in Zn_3(PO_4)_2 is dominated by the 5D_0→7F_1 (592 nm) magnetic-dipole transition,While the dominant emission for Eu 3+ in LaPO_4 is the typical hypersensitive transition 5D_0→7F_2 (618 nm).

Synthesis and Characterization of CoFe_2O_4 Nanoparticles

CoFe2O4 nanoparticles that were synthesized by coprecipitation method were heat-treated at different temperature , and analyzed by XRD and TEM. The particle size and magnetic properties of CoFe2O4 nanoparticles also was tested. The results showed that the average sizes became large as the heat-treated temperature increased, the saturation magnetization and remanent magnetization increased with the heat-treated temperature too.

Synthesis of Magnetic Manganese Ferrite

MnFe2O4 polycrystalline powders were prepared by the chemical coprecipitation method. When the reaction temperature is above 80 ℃, through depositing and washing, the MnFe2O4 can be obtained directly without calcining. However, when it is below 80 ℃, we have to calcine the precursor in order to obtain MnFe2O4, which does not result in pure spinal structure but a mixture of MnFe2O4 and α-Fe2O3. The powders＇ magnetic property was characterized with a Vibrating Sample Magnetometer. The phase structure, crystal size and lattice constant were presented by an X-ray diffractometer. In addition, the morphology of the powder was observed with a scan electron microscope and a transmission electron microscope.

CoMnMgAl Hydrotalcite-like Compounds and their Complex Oxides: Facile Synthesis and FCC SO_x Removal

The X-CoMnMgAl hydrotalcite-like precursors(X-LDHs) were first synthesized by the coprecipitation method using Cl-, CO32-, NO3- and SO42- as the corresponding guest anions, which were further used to prepare X-CoMnMgAl complex oxides(X-LDOs) through calcination. The structure and the surface morphology of the as-prepared samples were characterized by FT–IR, XRD, N2 adsorption-desorption and SEM. These as-prepared X-LDOs could act as sulfur-transfer catalysts for desulfurization. The activity of SOx adsorption and regeneration was evaluated via a self-assembled fixed-bed reactor simulating the conditions found in the fluid catalytic cracking units. These four types of sulfur-transfer catalysts with the same phase but different structure displayed the following order of desulfurization efficiency: CO3-LDO >Cl-LDO >NO3-LDO > SO4-LDO.

A Cost-Effective Co-precipitation Method for Synthesizing Indium Tin Oxide Nanoparticles without Chlorine Contamination

Indium tin oxide （ITO） nanoparticles with crystallite size of 12.6 nm and specific surface area of 45.7 m 2 ·g-1 were synthesized by co-precipitation method.The indium solution was obtained by dissolving metal indium in HNO3.The tin solution was obtained by dissolving metal tin in HNO3 and followed by stabilizing with citric acid.The free of chlorine ions in the synthesis process brought several advantages：shortening the synthesis time,decreasing the particle agglomeration,decreasing the chlorine content in the ITO nanoparticles and improving the particle sinterability.This is the first time to report the synthesis of ITO nanoparticles free from chlorine contamination without using the expensive metal alkoxides as starting materials.

Zn_(0.5)Co_(0.5)Mn_(0.5)Fe_(0.5)Al_(0.5)Mg_(0.5)O_(4) high-entropy oxide with high capacity and ultra-long life for Li-ion battery anodes

Owing to the robust Li-ion storage properties induced by entropy stabilization effect,transition metal(TM)-based high-entropy oxides(HEOs)are promising electrode materials for highperformance Li-ion batteries(LIBs).In this study,a six-component Zn_(0.5)Co_(0.5)Mn_(0.5)Fe_(0.5)Al_(0.5)Mg_(0.5)O_(4) spinel-structured HEO(denoted as 6M-HEO,where M=Zn,Co,Mn,Fe,Al,and Mg)was synthesized using a facile coprecipitation method.When used as an anode of the LIBs,its stable high-entropy nanostructures exhibit high specific capacity(290 mAh·g^(−1) at a current density of 2 A·g^(−1)),ultra-long cycling stability(maintained 81%of the initial capacity after 5000 cycles),and outstanding rate performance.Such excellent performance can be attributed to two factors.Firstly,its high-entropy structure can reduce the stress caused by intercalation and avoid volume expansion of the HEO nanostructures.As a result,the cyclic stability was significantly enhanced.Secondly,owing to the unique element selection in this study,four active elements(Zn,Co,Mn,and Fe)were incorporated in inactive MgO and Al2O3 matrice after the first discharge process,which would allow such high-entropy materials to withstand the rapid shuttle of Li ions.

Novel seed-assisted synthesis of indium tin oxide submicro-cubes and their resistivity

Indium tin oxide films,an important n-type semiconductor oxide,show great prospects in optoelectronic device applications.Consequently,as a key raw material of targets for sputtering films,it is important to prepare low-resistivity indium tin oxide powders.Herein,low-resistivity indium tin oxide submicro-cubes are synthesized by a seed-assisted coprecipitation method.The effects of seed content,In^(3+)concentration,aging time,reaction temperature and calcination temperature on resistivity were investigated by single factor and orthogonal experiments.To ensure reliability and reproducibility of data,each experiment was repeated three times and resistivity of each sample was measured three times to obtain average value.The results indicated that optimal sample was matched with cubic phase In_(2)O_(3).The single-crystal indium tin oxide particles exhibited a regular cubic shape with a size of nearly 500 nm and low resistivity of 0.814Ω·cm.Compared with particles prepared by the conventional coprecipitation method,indium tin oxide submicro-cubes showed good dispersion.The presence of seed particles provided nucleation sites with lower energy barriers and promoted formation of submicro-cubes.The face-to-face contact among particles and good dispersion contributed to electron transfer,resulting in lower resistivity.The seed-assisted synthesis provides a novel way to prepare low-resistivity indium tin oxide submicro-cubes.

Zn^(2+) substituted superparamagnetic MgFe_(2)O_(4) spinel-ferrites:Investigations on structural and spin-interactions

Nano-magnetic ferrites with composition Mg_(1-x)Zn_(x)Fe_(2)O_(4)(x=0.3,0.4,0.5,0.6,and 0.7)have been prepared by coprecipitation method.X-ray diffraction(XRD)studies showed that the lattice parameter was found to increase from 8.402 to 8.424A with Zn^(2+) ion content from 0.3 to 0.7.Fourier transform infrared(FTIR)spectra revealed two prominent peaks corresponding to tetrahedral and octahedral at around 560 and 430 cm^(-1) respectively that confirmed the spinel phase of the samples.Transmission electron microscopy(TEM)images showed that the particle size was noted to increase from 18 to 24 nm with an increase in Zn content from x=0.3 to 0.7.The magnetic properties were studied by vibrating sample magnetometer(VSM)and electron paramagnetic resonance(EPR)which ascertained the superparamagnetic behavior of the samples and contribution of superexchange interactions.The maximum magnetization was found to vary from 23.80 to 32.78 emu/g that increased till x=0.5 and decreased thereafter.Further,X-ray photoelectron spectroscopy(XPS)was employed to investigate the chemical composition and substantiate their oxidation states.

Structural,thermomagnetic,and dielectric properties of Mn0.5Zn0.5GdxFe2-xO4(x=0,0.025,0.050,0.075,and 0.1)

In this paper,effect of Gd^3+was investigated on structural,magnetic,and dielectric properties of Mn0.5Zn0.5GdxFe2–xO4(x=0,0.025,0.050,0.075,and 0.1)nanoparticles prepared by facile coprecipitation method.X-ray diffraction(XRD)studies confirmed the single cubic spinel phase for all the samples and showed that lattice parameter(aexp)was found to increase from 8.414 to 8.446Åwith the substitution of Gd3+ions due to their larger ionic radii than the replaced Fe3+ions.Shape and size of developed nanoparticles were studied using transmission electron microscopy(TEM)and found that particle size decreased from 31.06 to 21.12 nm for x=0–0.1.Magnetic properties showed that maximum magnetization decreased from 39.21 to 23.59 emu/g,and Curie temperature decreased from 192 to 176℃with increase in x from 0 to 0.1 due to weakening of superexchange interaction.Dielectric parameters like dielectric constant(e¢ande¢),dielectric loss(tanδ),AC conductivity(σac),and impedance(Z¢and Z¢)as a function of frequency and composition were analyzed and discussed.It was found thate¢,e¢,σac,and tanδvalues decreased with Gd substitution,which has been explained based on Maxwell–Wagner theory and hopping mechanism of electrons between Fe3+and Fe2+ions at octahedral sites.Nyquist plots for all the developed compositions showed single semi-circular arc which indicate the dominant effect of grain boundaries.

Continuous synthesis of extremely small-sized iron oxide nanoparticles used for T_(1)-weighted magnetic resonance imaging via a fluidic reactor

Extremely small-sized iron oxide nanoparticles(ESIONPs)with sizes less than 5 nm have shown great promise as T_(1)contrast agents for magnetic resonance imaging(MRI).However,their facile and scalable production with simultaneously endowed biocompatible surface chemistry remains difficult to be realized.In this study,by using the coprecipitation method implemented in a specially designed gas/liquid mixed phase fluidic reactor,polyglucose sorbitol carboxymethyether(PSC)coated ESIONPs were continuously synthesized with controllable particle sizes ranging from 1.8 to 4 nm.Among the differently sized ESIONPs,the 3.7-nm ESIONPs exhibit the best performance as T_(1)MRI contrast agent,featuring a high r_(1) value of 4.11(mmol L^(−1))^(−1)s^(−1)and low r_(2)/r_(1) ratio of 7.90 under a clinical 3 T MR scanning,as well as the excellent T_(1)MRI contrast effect in not only water but also the cellular environment and blood vessel.Furthermore,the ESIONPs possess long-term stability and good dispersity in aqueous dispersions,making them ideal candidates as safe and effective T_(1)-weighted MRI contrast agent for real clinical use.

The green-emitting fluorescence of nano Y_2O_3:Er^(3+) under different excitations

The green-emitting fluorescent powders of nano Y2O3：Er^3＋ were fabricated by the coprecipitation method. The X-ray diffrac- tion pattern shows that as-prepared Y2O3：Er^3＋ is the cubic phase crystal with a grain size of about 30 nm. The UV-Vis spec- trum indicates Y^O3：Er^3＋ exhibits five ultraviolet visible absorption peaks at 365, 377, 489, 521 and 652 nm respectively. Meanwhile, the fluorescence spectra of Y2O3：Er^3＋ display four emission peaks at 522, 537, 550 and 562 nm at the excitation of 365,377 and 521 nm, respectively. The green-emitting fluorescent mechanism of Y2O3：Er^3＋ is proposed as well. Additionally, the temperature dependence of fluorescence properties and metal Ag fluorescence enhancement effect are investigated. Results show that increasing the annealing temperature and metal Ag doping both can enhance the fluorescence intensity. The maxi- mum enhancement is 87.5% after Ag is doped.

Synthesis and luminescent properties of Ba_(3)Y_(3.88)Gd_(0.12)O_(9):Eu^(3+) phosphors with enhanced red emission

In this work,the Gd^(3+)/Eu^(3+) activated Ba_(3)Y_(4)O_(9)(BYO)phosphors were successfully synthesized via coprecipitation method at 1400℃.The precursor composition,crystal structure stability,microscopic morphology,photoluminescence(PL)/photoluminescence excitation(PLE)spectra and fluorescence attenuation analysis of the phosphors are discussed in detail.The chemical composition of the precursor was determined by Fourier transform infrared spectroscopy(FT-IR)and thermogravimetry(TG)analysis;According to field emission-scanning electron microscopy(FE-SEM)analysis,it is found that the particle size of phosphor is uniform and the agglomeration is few.According to PL/PLE spectra analysis,Ba_(3)Y_(3.28)Eu_(0.6)Gd_(0.12)O_(9) phosphors has the strongest excitation band at 260 nm and the strongest emission band at 614 nm,and the fluorescence intensity of Ba_(3)Y_(3.28)Eu_(0.6)Gd_(0.12)O_(9) is higher than that of Ba_(3)Y^(3.4)Eu^(0.6)O_(9).The quenching concentration of Eu^(3+)in Ba_(3)Y_(3.88–4x)Eu_(4x)Gd_(0.12)O_(9) phosphors is x=0.15 and the mechanism of quenching concentration of Eu^(3+)is electric dipole-quadrupole type interactions.The lifetime value of Ba_(3)Y_(3.88–4x)Eu_(4x)Gd_(0.12)O_(9)(x=0.15)phosphors is 0.686 ms and decreases with the increase of Eu^(3+)content.In addition,the CIE chromaticity diagram of Ba_(3)Y_(3.28)Eu_(0.6)Gd_(0.12)O_(9) phosphors is(0.66,0.34).Finally,the lamp beads assembled with Ba_(3)Y_(3.28)Eu_(0.6)Gd_(0.12)O_(9) phosphors have an ideal luminous effect.Therefore,the Ba_(3)Y_(3.88–4x)Eu_(4x)Gd_(0.12)O_(9) phosphors designed in this work may hopefully meet the requirements of various lighting and optical display applications.