Urea Homogeneous Precipitation Method Research Articles

Controlled synthesis of CeNbZrO solid solution with high thermal stability and application in catalytic degradation of C6H5CH3 and C6H5Cl

A series of CeNbZrO composite oxides with different (CeNb)/Zr molar ratios were prepared by urea homogeneous precipitation method and systematically characterized. The thermal stability, degradation performance and structure-activity relationship of these catalysts for eliminating C6H5CH3 and C6H5Cl mixed pollutants were evaluated. The results indicated that with the increase of ZrO2 content, the catalytic activity of CeNbxZrO increased first and then decreased. Among them, the CeNb3.3ZrO catalyst (Ce/Nb/Zr=2/1/3.3, molar ratio) exhibited the highest catalytic activity (C6H5CH3: T90%=310oC, C6H5Cl: T90%=344oC) and thermal stability. Compared with the traditional CeO2-MnO2 catalyst, the T90% of the CeNb3.3ZrO catalyst in the degradation of C6H5Cl was reduced by 100oC. CeNb3.3ZrO exhibited high specific surface area and strong oxidation ability, which enhanced the redox cycles and promoted the interactions between metal ions. In addition, the formation of Ce2Zr3O10 solid solution made its structure stable even at high temperature. Overall, the optimized CeNb3.3ZrO has broad prospects in the catalytic treatment of volatile organic compounds and some other related fields in thermal catalysis. Environmental implicationC6H5CH3 and C6H5Cl are typical VOCs with certain toxicity, which pollute air environment and cause harm to human health. In this paper, CeNbZrO composite oxides with different (CeNb)/Zr molar ratios were prepared by urea homogeneous precipitation method. It was found that the CeNb3.3ZrO catalyst had higher specific surface area and stronger oxidation ability, and promoted the complete degradation of C6H5CH3 and C6H5Cl at lower temperatures by destroying the C-C, C-H and C-Cl bonds of the reactants.

Selective hydrogenolysis of furfuryl alcohol to 1,2-pentanediol over CuMg supported on mesoporous silica: Effect of pore size and shape

Utilizing urea homogeneous precipitation method, Cu and Mg species were successfully supported on SBA-15, KIT-6, and MCM-41 respectively for furfuryl alcohol (FFA) hydrogenolysis to 1,2-pentanediol (1,2-PeD). The catalytic results showed that the yield of 1,2-PeD followed the order of CuMg/SBA-15 > CuMg/KIT-6 > CuMg/MCM-41, especially the maximum of 50.0 % over CuMg/SBA-15 surpassing that of most copper-based catalysts reported. It is found that FFA conversion dramatically increases with the raising of Cu dispersion, attributing to the high exposure of active sites. Meanwhile, the selectivity of 1,2-PeD is strongly depended on the Cu0/Cu+ ratio of catalyst and CuMg/SBA-15 with the highest value of 57.6 % is derived from the largest Cu0/Cu+ ratio. In a word, CuMg/SBA-15 shows the excellent activity along with stability owing to the synergy between large Cu0/Cu+ ratio and good Cu dispersion, providing by two-dimensional hexagonal straight channel arrangement with generous pore diameter. Innovatively, it is put forward that dual adsorption sites of both MgO and Cu species in the CuMg/SBA-15 catalyst promote the FFA ring-opening to yield 1,2-PeD based on the comparison of Cu dispersion, metal-support (M−S) interaction and the adsorption capacity for furan rings with Cu/SBA-15. This study provides a novel approach for catalyst design for this reaction, focusing on optimizing the catalytic performance by fine-tuning structure of the support.

Hydrogenation of furfural to 1,5-pentanediol over CuCo bimetallic catalysts

AbstractA series of CuxCo3–xAl hydrotalcite-like catalysts with different Cu/Co molar ratios were synthesized by the urea homogeneous precipitation method and used for the direct hydrogenation-hydrogenolysis of furfural to 1,5-pentanediol. The results showed that the Cu/Co molar ratio of the catalyst had a significant effect on its textural properties and catalytic performance. The catalyst exhibited excellent catalytic performance when the molar ratio of Cu/Co was 1:29 (Cu0.1Co2.9Al), and the conversion of furfural was 100% together with 51.1% yield of pentanediol among which the yield of 1,5-pentanediol was 41.1%, under the reaction condition of 140 °C, 4 MPa H2 for 6 h. Extensive characterization techniques, including temperature-programmed reduction (H2-TPR), temperature-programmed desorption (H2-TPD), X-Ray photoelectron spectroscopy (XPS) and Raman confirmed that the excellent catalytic activity of Cu0.1Co2.9Al catalyst was attributed to the highest content of Cu0 and CoOx on its surface, and a synergistic catalytic effect was present between them. Typically, Cu0 was used to adsorb and activate H2, and CoOx with much oxygen vacancies promoted the adsorption and activation of C=O groups in furfural molecules, leading to the quick conversion of furfural to furfuryl alcohol. In addition, the oxygen vacancies anchored the –OH in the intermediate furfuryl alcohol to produce a C2-terminal oblique adsorption on the catalyst surface. Then it promoted the hydrogenation of C2=C3 with the weakening and cleavage of C2–O1 bond, and enhanced the selectivity of 1,5-pentanediol.

Effect of sintering activation energy on Si3N4 composite ceramics

This study investigated the activation energy and kinetic characteristics of silicon nitride (Si3N4) composite ceramics produced using different preparation methods. The effects of the linear shrinkage, expansion ratio, and heating rate on the sintering process were analysed in detail. The obtained results reveal that the finer particle size produced using the urea homogeneous precipitation method obviously enhanced the densification rate and reduced the atomic diffusion distance. Moreover, the densification sintering process was carried out efficiently, and the largest densification rate was achieved in advance. According to the Arrhenius curve, the activation energy of the Si3N4 composite ceramics calculated using the urea homogeneous precipitation method (310.94 kJ/mol) was lower than that achieved using the mechanical ball-milling method (365.11 kJ/mol). Additionally, the flexural strength and hardness of the Si3N4 composite ceramic prepared using the urea homogeneous precipitation method were 740 ± 42 MPa and 16.20 ± 30 GPa, respectively, which is attributed to this composite ceramic's higher diffusion rate and small grain size.

Nanocomposites of CsPbBr3 perovskite quantum dots embedded in Gd2O3:Eu3+ hollow spheres for LEDs application

Gd2O3:Eu3+@CsPbBr3 quantum dots (QDs) mesoporous hollow nanocomposites with good luminescent properties and high stability were built. Among which, the hollow Gd2O3:Eu3+ spheres and CsPbBr3 QDs were prepared by urea homogeneous precipitation and hot-injection method, respectively. Finally, the Gd2O3:Eu3+@CsPbBr3 QDs shell–core compounds were constructed through mechanical stirring. The structure, morphology, stability and luminescent properties were studied by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry/thermogravity (DSC/TG), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence excitation/photoluminescence (PLE/PL) and life decay tools. Compared to the original CsPbBr3 QDs, Gd2O3:Eu3+@CsPbBr3 QDs display better photostability, thermal stability and current stability. The resulting Gd2O3:Eu3+@CsPbBr3 QDs composite exhibits good yellow emission. The Gd2O3:Eu3+@CsPbBr3 QDs mixed silicone resin was directly coated on the blue LED chip, then the w-LED device with the color coordinate of (0.31, 0.32) was successfully assembled. The Gd2O3:Eu3+@CsPbBr3 QDs compounds with excellent luminescent properties and stability are expected to be widely used in lighting and display areas.

Latent fingerprint detection with luminescent Y2O3:Eu3+ nanoparticles

Abstract In this study, a facile urea homogeneous precipitation method was used to prepare luminescent Y2O3:Eu3+ nanoparticles (NPs). The morphology, structure and optical properties of prepared nanoparticles were characterized using a scanning electron microscope (SEM), X-ray diffraction (XRD) and photoluminescence (PL). Under the constant 254 nm UV light illumination, the prepared Y2O3:Eu3+ NPs exhibited strong red emission with the highest peak centered at 612 nm. The prepared nanoparticles were further utilized as the optical contrast material for latent fingerprint detection on different surfaces

Synthesis and characterization of radio and thermoluminescence properties of Sm doped Gd2O3, Gd2O2S and Gd2O2SO4 nanocrystalline phosphors

In this study, nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm phosphors were successfully synthesized through the urea homogeneous precipitation method. Nanocrystalline Gd2O2S:Sm phosphors with two different concentrations of sulfur were prepared. In the first procedure, the weight of sulfur was five times more than Gd2O3 weight (was called sample Gd2O2S:Sm(1)) and in the second procedure, it was equal (was called sample Gd2O2S:Sm(2)). The nanocrystalline powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, radioluminescence and thermoluminescence. The XRD and FT-IR results confirmed that nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders had the cubic, hexagonal and orthorhombic structure in preparation temperatures of 620 °C and 900 °C. The SEM images showed that nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders had a semi-spherical shape with a uniform mean size of about 30 nm in diameter and confirmed the XRD results. The presence of all elements was confirmed in the synthesized samples using EDX spectroscopy. The results showed that the weight percent of sulfur during the preparation of Gd2O2S had an effect on the size, morphology and the luminescence intensity of nanocrystalline Gd2O2S powder. Under X-ray irradiation (40 kV and 40 mA), the emission spectra of nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm phosphors were studied. The results showed the orange-red emission peaks which were observed at 605 nm were the strongest emission peak for all nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders. This peak was corresponded to the 4G5/2-7H7/2 energy transition of Sm3+ ion. The TL response of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm after irradiation with different X-ray time exposure exhibited a peak shifting towards the lower temperatures. The glow curve deconvolution method was used to calculate trapping parameters and the obtained results were investigated in detail.

Vertically/parallelly orientated growth of NiCo2O4 nanosheet onto surface of hierarchically N-doped porous carbon for improved supercapacitor

ABSTRACTHere, hierarchically N-doped porous carbon (HPNC) with very high surface area was prepared by a facile one-pot pyrolysis of ethylenediaminetetraacetic acid tripotassium salt dihydrate used as the carbon/nitrogen source and pore activating agent. The NiCo2O4 nanosheets were vertically grown onto the surface of HPNC (V-NiCo2O4/HPNC) via a urea homogeneous precipitation method by a microwave heating. Whereas the parallelly orientated NiCo2O4/HPNC (P-NiCo2O4/HPNC) was fabricated by a usual water-bath heating. The loading content of V-NiCo2O4/HPNC was higher than that of the P-NiCo2O4/HPNC, thus resulting in the larger specific capacitance. V-NiCo2O4/HPNC exhibited the high specific capacity (434.8 F g-1 at 1.0 A g-1), good rate performance, cycle stability (capacitance retention of 103% at 5 A g-1 after 1000 cycles) and lower resistance, owing to the synergistic advantages of HPNC and vertically orientated NiCo2O4 nanosheets, which provided high electrical conductivity, and effective electrolyte ions and electrons transport path.

Hydrogenation Performance of Acetophenone to 1-Phenylethanol on Highly Active Nano Cu/SiO2 Catalyst

In this work, highly active nano Cu/SiO2 catalysts with various copper content were prepared by urea homogeneous precipitation method. The catalysts were characterized by N2 adsorption, XRD, H2-TPR, XPS and TEM. It was found that the nano Cu/SiO2 catalyst displayed excellent catalytic performance for the selective hydrogenation of acetophenone (AP) to 1-phenylethanol (PhE) when copper content was 25 wt%. The Cu/SiO2 catalyst had well dispersed copper species, small particle size, high BET surface area (ca. 540 m2/g) and abundant pore structure. The influence of different reaction conditions on the hydrogenation process were also discussed. AP conversion and the PhE selectivity reached 99.8% and 99.08%, respectively, under the optimal reaction conditions (Temperature: 353 K; Pressure: 2.0 MPa, LHSV: 1.0 h−1 and the molar ratio of H2/AP:15). Besides, the above catalyst maintained a high catalytic performance in the duration of 500 h operation. The synergistic effect between Cu+ and Cu0 improved the activity and stability of Cu/SiO2 catalyst. The research indicated that the catalyst had a wide industrial prospect. The Cu/SiO2 catalyst showed a good performance for AP hydrogenation. The reduced Cu/SiO2 catalyst contains both Cu+ and Cu0 consistent with XPS. Cu+ sties stabilize the methoxy and acyl species and Cu0 facilitates the decomposition of H2. Phenyl in AP and Cu had electrostatic repulsion, which was favorable for desorption of PhE.

Improved photovoltaic performance of monocrystalline silicon solar cell through luminescent down‐converting Gd2O2S:Tb3+ phosphor

AbstractThis work reports on efforts to enhance the photovoltaic performance of standard p‐type monocrystalline silicon solar cell (mono‐Si) through the application of ultraviolet spectral down‐converting phosphors. Terbium‐doped gadolinium oxysulfide phosphor and undoped‐gadolinium oxysulfide precursor powders were prepared by a controlled hydrothermal decomposition of a urea homogeneous precipitation method. The resulting rare‐earth element hydroxycarbonate precursor powders were then converted to the oxysulfide by annealing at 900°C in a sulfur atmosphere. The as‐prepared phosphors were encapsulated in ethylene vinyl acetate co‐polymer resin and applied on the textured surface of solar cell using rotary screen printing. Comparative results from X‐ray powder diffraction, field emission scanning electron microscopy, scanning transmission electron microscopy, and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. We also compared the optical reflectance and external quantum efficiency response of the cells with and without a luminescent phosphor layer. The results obtained on the terbium‐doped gadolinium oxysulfide phosphor show clearly that the down‐conversion effect induced by the terbium dopant play a crucial role in enhancing the photovoltaic cells' performance. Under an empirical one‐sun illumination, the modified cells showed an optimum enhancement of 3.6% (from 16.43% to 17.02%) in conversion efficiency relative to bare cells. In the concentration range of 1 to 2.5 mg/mL, EVA/Gd2O2S (blank) composites also improve electrical efficiency, but not as much as EVA/Gd2O2S:Tb3+ composites.

Full spectrum core-shell phosphors under ultraviolet excitation.

Ce/MgY4Si3O13:Ce-Y2O3:Eu core-shell structure was designed and accomplished via a urea homogeneous precipitation method. The as prepared phosphors can emit photons with a broad range of wavelengths from 340 nm to 700 nm under excitation light of 330 nm. The internal quantum efficiency can reach up to 68%.

Effect of temperature and pre-sintering on phase transformation, texture and mechanical properties of silicon nitride ceramics

Silicon nitride composite ceramics with excellent mechanical properties were prepared by hot pressing. The effects of temperature on the sintering process, β-Si3N4 phase transformation ratio (β%) and mechanical properties were investigated. By calculating the diffraction intensity (I), the β-Si3N4 phase transformation ratios of the three samples considered in this study were 57.2% (pre-sintered samples, PSN), 63.5% (urea homogeneous precipitation method, USN) and 66.6% (mechanical milling method, MSN) at 1550 °C, respectively. These results showed that the Si3N4 composites coated by using Y-Al precursor (USN) have a lower ratio of the phase transformation from α to β. Meanwhile, from the analysis of SEM images of the etched surface, the grain sizes were 0.47 µm (PSN), 0.39 µm (USN), and 0.43 µm (MSN) at 1650 °C, respectively. Compared to the other samples, the USN sample offered superior sintering behaviour and mechanical properties. The optimal flexural strength, hardness and fracture toughness of the Si3N4 composites coated by using the Y-Al precursor were 911 ± 69 MPa, 16.23 ± 0.24 GPa and 4.9 ± 0.35 MPa/m2 at 1650 °C, respectively.

Paramagnetic Gd-Doped Zirconia Nanoparticles for Potential T1-Weighted MRI Imaging

In this paper, Gd-doped zirconia (ZrO[Formula: see text] nanoparticles were prepared using a facile urea homogeneous precipitation method. The morphology, structural properties and magnetic properties of Gd-doped zirconia nanoparticles (NPs) have been analyzed by field emission transmission electron microscopy (FETEM), X-ray diffraction (XRD) and magnetic properties measurement system (MPMS), respectively. Toxicity analysis suggested that prepared Gd-doped ZrO2 NPs have good biocompatibility. The contrast enhancement ability of prepared Gd-doped ZrO2 NPs was tested by a 1.5T small animal MRI scanner. Obvious image brightening confirmed that prepared Gd-doped ZrO2 NPs can be potentially used for T1-weighted MRI imaging.

Facile synthesis of tube-shaped Mn-Ni-Ti solid solution and preferable Langmuir-Hinshelwood mechanism for selective catalytic reduction of NOx by NH3

We present a tube-shaped Mn-Ni-Ti solid solution for the selective catalytic reduction of NOx with NH3 (NH3-SCR) through a facile self-templated urea-homogeneous precipitation method, which leads to the fine dispersion of the MnOx and NiOx active species in the TiO2 lattice. The ratio of Mn/Ni/Ti is an important factor to affect the crystallinity of Mn-Ni-Ti solid sulotion, and the catalyst with a Mn/Ni/Ti ratio of 2/3/5 (Mn2-Ni3) exhibits the significant structure distortion. The abundant surface defects induce more generation of Mn4+ species, surface adsorbed oxygen and Lewis acid sites, and acclerate the adsorption and activation of NO molecules. The appropriate Mn/Ni ratio inhibits the competitive adsorption of NH3 with NO, and facilitates the Langmuir-Hinshelwood (L-H) mechanism to form N2, which acts as a much more rapid pathway in comparison to the parallel one following Eley-Rideal (E-R) mechanism. The readily occurence of L-H mechanism significantly improves the SCR performance of catalyst.

Theoretical analysis on quenching mechanisms for Lu2O3: Eu3+ nanospheres

Lu2O3 nanospheres with various concentrations of Eu3+ are synthesized via urea homogeneous precipitation method. The influence of the Eu3+ doping concentration on the structural, optical properties was systemically studied. The emission spectra of Lu2O3: Eu3+ nanospheres consist of a group of sharp lines from blue to red light originating from 5D1, 0→7FJ transitions of Eu3+. The photoluminescence intensities and decay times varies with the increasing Eu3+ concentrations, which are attributed to the energy transfer among the Eu3+ ions. The fluorescent quenching is mainly due to the D–D interaction by using the Van Uitert’s model and Dexter’s model. The Lu2O3: Eu3+ phosphor exhibits good thermal characteristics. The emission intensity of Lu2O3: Eu3+ phosphor only decreases 8% with the increasing of temperature from 303 to 403 K. The temperature quenching behavior of Lu2O3: Eu3+ is attributed to the crossover process via the charge transfer band with high activation energy of 0.264 eV. Moreover, the Judd–Ofelt parameters $$\Omega_{\lambda}$$ (λ = 2, 4, 6) of Eu3+ in Lu2O3 phosphor were also calculated.

Preparation and Optical Properties of Y2O3:Tb3+ Nanoballs.

Y2O3:Tb3+ nanoballs were synthesized via the urea homogeneous precipitation method (UPM). The resulting Y2O3:Tb3+ phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy, ultraviolet-visible (UV-vis) absorption spectra, and general photoluminescence spectra. The particle sizes estimated using X-ray diffractometry and scanning electron microcopy were about 50-200 nm. The emission intensity of the Y2O3:Tb3+ was low when the doping concentra- tions of Tb3+ were higher. The optimum concentration of Tb3+ for synthesis of Y2O3:Tb3+ nanocrystals is 1%.

Enhanced photoluminescence of Fe3O4@Y2O3:Eu3+ bifunctional nanoparticles by the Gd3+ co-doping

In this paper, the Gd3+ codoped bifunctional coreshell nanoparticles, Fe3O4@(Y1-xGdx)2O3:Eu3+, were synthesized through a Urea Homogeneous Preci-pitation method. The microstructure, luminescence, and magnetic properties of the codoped samples were investigated and discussed with the help of various analytic techniques including X-ray diffraction, scanning electron microscope, photo-luminescence spectra, cathodelumincence mapping and vibrating sample magnetometer. The co-doped sample (x = 0.3), emitting at 612 nm dominantly under the 254 nm excitation, exhibited the photoluminescence intensity 2.7 times higher than the undoped one (x = 0), due to the efficient energy transfer between Gd3+ and Eu3+. The Fe3O4@(Y1-xGdx)2O3:Eu3+ core–shell nanoparticles were spherical and uniform, and had a particle size of about 180 nm in diameter. They also showed a saturation magnetization of 1.09 emu/g, a coercivity of 20 Oe and a remanence of 0.01emu/g. The enhanced photoluminescence and good magnetic properties of the title core–shell nanocomposites allow them to be used in biomedical applications.

Effect of solution pH value changes on fluorescence intensity of magnetic-luminescent Fe3O4@Gd2O3:Eu3+ nanoparticles

AbstractIn this paper, bifunctional Fe3O4@Gd2O3:Eu3+ core-shell nanoparticles with both magnetic and fluorescent properties were synthesized through a urea homogeneous precipitation (UHP) method. Particular emphasis was placed on investigating the influence of the solution pH value on the photoluminescence of the core-shell nanocomposites. It showed that the samples treated at the solution of pH=3.0 had the highest luminescence due to the enhanced crystallinity and size uniformity of nanoparticles. The Fe3O4@Gd2O3:Eu3+ nanocomposites exhibited an almost spherical shape with a mean diameter of 60 nm, and had strong red emissions of Eu3+ at 612 nm as well as good magnetization with the saturation magnetization of 1.29 emu/g. It thus indicated that the core-shell nanocomposites investigated has great potential in biomedical applications.

Effect of doping concentration on particle growth and luminescence properties of monodispersed Dy3+: Y2O3

Submicron-sized Dy3+: Y2O3 particles were successfully prepared via an urea homogeneous precipitation method, followed by a calcination at 800 °C. TG-DSC, FT-IR, X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), scanning electron microscope (SEM), photoluminescence (PL), and photoluminescence excitation (PLE) spectra were used to characterize the prepared samples. The particles were spherical shape and monodispersed. More importantly, the spherical Y2O3 particles were found to have significant changes in size with varying dopant concentration of the Dy3+ ions, ranging approximately from 550 to 840 nm. The possible growth mechanism of the particles was proposed. Under 349 nm excitation, the crystalline powders exhibited blue and yellow emissions due to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively. It was further found that with proper Dy3+ doping concentration, the luminescence color hue was tuned close to the ideal white light with color coordinates of (0.33, 0.33). The submicron-sized Dy3+: Y2O3 phosphor is a promising candidate for the white light emitting diodes (WLEDs).

Magnetic-luminescent properties of Fe3O4@Gd2O3:Eu3+ coreshell nanocomposites

A simple Urea Homogeneous Precipitation (UHP) method was employed to synthesize bifunctional core-shell nanoparticles of Fe3O4@Gd2O3:Eu3+. X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectroscopy (PL) and vibrating sample magnetometer (VSM) were used to characterize the structure, morphology, luminescence and magnetic properties of the composites, respectively. Results show that the nanocomposites possess both luminescent and magnetic properties, thus the synthesized nanoparticles may find potential application in the area of biomedicine, such as drug targeting, fluorescence label and cell separation.