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1.
This article, the second part of our review series on the use of supercritical carbon dioxide (scCO2) for synthesis of nanostructured material deals with the production techniques that involve chemical transformations. Taking
advantage of both solvent and anti-solvent tunable properties of scCO2, many nanostructured materials including supported/unsupported nanoparticles, quantum nanodots, nanofilms, nanorods, nanofoams,
and nanowires can be prepared. Furthermore, material surfaces can be functionalized using scCO2. scCO2 can also be used as a carbon source for the controlled synthesis of carbon nanotubes and fullerenes or as an oxygen source
for metal oxide nanostructures. Moreover, materials produced using scCO2 does not usually need additional purification or drying steps. Depending on surface properties, the morphology of the final
material can be adjusted by tuning the process conditions and the reactant concentrations. 相似文献
2.
V. V. Zheleznov V. Yu. Maiorov N. V. Polyakova V. E. Silant’ev T. A. Sokol’nitskaya Yu. V. Sushkov E. I. Voit 《Radiochemistry》2018,60(6):618-624
New nanostructured mesoporous materials of the composition TiO2/ZrO2/SiO2 were prepared by the template sol–gel method using a siloxane–acrylate emulsion as a template. The morphology and structure of these materials and their ability to take up U(VI) were studied. The influence of various factors (ZrO2 content, pH of solution) on the sorption properties was studied. The suggested materials allow efficient sorption of U(VI) from sulfate solutions with low U(VI) concentrations and can be used in final purification processes. 相似文献
3.
Irene G. Cano Sergi Dosta Joan Ramon Miguel Jose Maria Guilemany 《Journal of Materials Science》2007,42(22):9331-9335
Producing nanostructured materials through metastable phases is interesting in the field of ceramic materials. Metastable
phases can be obtained by the Atmospheric Plasma Spray (APS) technique which, is a well-known technique to produce coatings.
The initial powders are melted during the spraying obtaining a homogenized phase due to their solubility in the liquid state.
Afterwards, the molten droplets are quenched in a cooled medium, producing the sought metastable phases. Finally, during material
consolidation, the metastable structure evolves due to a dual structure. A suppression of the grain growth is produced as
a consequence of the immiscibility of both phases in the solid state. Due to their small grain size and uniform structure,
these nanostructured materials exhibit very interesting properties such as higher hardness and toughness. The aim of this
research has been to produce nanostructured Al2O3–TiO2 ceramic powders through APS + quenching route, starting from commercially available micron-sized powders. A complete characterization
of the obtained structures using XRD, SEM, FESEM and EDS has been carried out in the Thermal Spray Center (CPT) of the University
of Barcelona. 相似文献
4.
A new process is described for the suspension synthesis of polycrystalline Pt-γ-Al2O3-CeO2 catalytic materials and coatings, with maltose, C12H22O11, as a reductant and structure former. The process parameters have been optimized in terms of the dispersion medium composition and the way in which Pt is introduced. The coatings are highly uniform in chemical and phase composition, as evidenced by quantitative analysis, optical microscopy, and x-ray microanalysis results. Characteristically, the coatings have a highly porous structure and good adhesive properties. Catalysts prepared by the proposed process show high activity for the oxygen oxidation of CO. The process can be used to fabricate Pt-Pd-Rh catalysts on block supports for the purification of vehicle exhaust gases and industrial off-gases. It has the advantage that high-porosity multicomponent catalytic coatings can be produced on cordierite block supports in a single step. 相似文献
5.
V. V. Zyryanov N. F. Uvarov A. S. Ulikhin V. G. Kostrovskii B. B. Bokhonov V. P. Ivanov V. A. Sadykov A. T. Titov K. S. Paichadze 《Inorganic Materials》2009,45(1):90-98
The structure of the Zr0.88 Sc0.1Ce0.01Y0.01O1.955 solid solution, a candidate for the use as a solid electrolyte in fuel cells with a low temperature, has been investigated using x-ray powder diffraction and Raman spectroscopy. Single-phase ceramic materials have been produced from powders prepared by the mechanochemical synthesis from ZrO2 nanoprecursors purified of the impurities introduced during grinding of commercial zirconia. The solid solution has a rhombohedral structure at room temperature owing to the partial ordering of oxygen vacancies. The electrical conductivity of the ceramic materials sintered at temperatures below 1570 K exhibits a hysteresis due to the delay of the martensitic transition from the cubic phase to the rhombohedral phase upon cooling of the sample. The nanostructured ceramic materials are characterized by a high mechanical strength and unusually close values of the activation energies for bulk and grain-boundary electrical conduction. 相似文献
6.
Hongfei Lin Takashi Fujii Reisuke Takisawa Toru Takahashi Toshiyuki Hashida 《Journal of Materials Science》2008,43(7):2307-2315
The hydrothermal autoclave experiments were conducted to simulate the interactions in the scCO2/water/rock minerals (quartz, biotite and granite) reaction systems using a Hastelloy C reaction cell at 100 °C. The dissolution
characteristics of rock minerals and their surface texture alternation after hydrothermal treatment were examined by ICP-AES
and SEM/EDX investigation, respectively. The results suggested that the hydrolysis of plagioclase phase should be mainly responsible
for the elements dissolved from the Iidate granite samples. The dissolution was encouraged by the introduction of CO2 in the water/granite system, and generated an unknown aluminosilicate. No distinct chemical alternations occurred in the
water-free scCO2/granite system, which indicated that rock minerals should be chemically stable in the water-free scCO2 fluids under the current mild experimental conditions. Both the highest concentration of Ca existing in the scCO2/vapor/granite system and the SEM observation results of calcite deposit, suggested that a meaningful CO2 minerals trapping process should be potential in the CO2-rich field during a short physicochemical interaction period. 相似文献
7.
K. Sadecka M. H. Berger K. Orlinski I. Jozwik D. A. Pawlak 《Journal of Materials Science》2017,52(10):5503-5510
The development of novel manufacturing techniques of nano-/micromaterials, especially metallodielectric materials, has enabled dynamic development of such fields as nanoplasmonics. However, the fabrication methods are still mostly based on time-consuming and costly top-down techniques limited to two-dimensional materials. Recently, directional solidification has been proposed and utilized for manufacturing of volumetric nanoplasmonic materials using the example of a Bi2O3–Ag eutectic-based nanocomposite. Here, we explain the evolution of silver in this composite, from the crystal growth through the post-growth annealing processes. Investigation with tunneling electron microscopy shows that silver initially enters the composite as an amorphous AgBiO3 phase, which is formed as a wetting layer between the grains of Bi2O3 primary phase. The post-growth annealing leads to decomposition of the amorphous phase into Bi2O3 nanocrystals and intergranular Ag nanoparticles, providing the tunable localized surface plasmon resonance at yellow light wavelengths. 相似文献
8.
D. Bochenek P. Niemiec M. Adamczyk I. Szafraniak-Wiza 《Journal of Materials Science》2018,53(19):13501-13512
Modern electronics expect functional materials that are eco-friendly and are obtained with lower energy consumption technological processes. The multiferroic lead-free BaFe1/2Nb1/2O3 (BFN) ceramic powder has been prepared by mechanochemical synthesis from simple oxides at room temperature. The development of the synthesis has been monitored by XRD and SEM investigations, after different milling periods. The obtained powders contain large agglomerates built by crystals with an estimated size about 12–20 nm depending on the period of milling. From this powder, the multiferroic BFN ceramic samples have been prepared by uniaxial pressing and subsequent sintering pressureless method. The morphology of the BFN ceramic samples strongly depends on high-energy milling duration. The properties of the ceramic samples have been investigated by dielectric spectroscopy, in broad temperature and frequency ranges. The high-energy milling of the powders has strongly affected the dielectric permittivity and dielectric loss of the BaFe1/2Nb1/2O3 ceramic samples. The usage of the mechanochemical synthesis to obtain the multiferroic lead-free BFN materials reduces the required thermal treatment and simultaneously improves the parameters of the BFN ceramics. 相似文献
9.
Sintering of cold die-pressed compacts and hot pressing have been used in order to produce high efficiency, thermoelectric
ε-Zn4Sb3 bulk specimens. Single-phase Zn4Sb3 was successfully produced by sintering of cold die-pressed compacts using mixed elemental powders, and subsequent hot pressing
produced single-phase, bulk specimens without microcracks. Phase transformations in this alloy system during synthesis were
investigated using DSC, XRD and SEM. Thermoelectric properties as a function of temperature were investigated from room temperature
to 600 K and compared with results of other studies. Transport properties at room temperature were evaluated. Thermoelectric
properties of single phase Zn4Sb3 materials produced by the sintering of cold die-pressed compacts and hot pressing are comparable to the published data for
alternate processing routes. Synthesis by sintering of cold die-pressed compacts and hot pressing offers a potential processing
route to produce bulk Zn4Sb3. 相似文献
10.
Hongliang Zhu Naiyan Wang Lina Wang Kuihong Yao Xiaofei Shen 《Inorganic Materials》2005,41(6):609-612
Single-crystalline indium oxide (In2O3) nanocubes were successfully prepared via dehydration of indium hydroxide (In(OH)3) nanocubes synthesized by a hydrothermal method. In situ x-ray diffraction patterns of the phase transition were obtained. Transmission electron microscopy indicated that the morphology of the In2O3 nanocrystallites was the same as that of their precursors, In(OH)3 nanocrystallites. The reported method, the dehydration of In(OH)3 nanocrystallites prepared by a hydrothermal method, shows a simple and effective synthesis route for In2O3 nanostructured materials.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 702–705.Original English Text Copyright © 2005 by Hongliang Zhu, Naiyan Wang, Lina Wang, Kuihong Yao, Xiaofei Shen.This article was submitted by the authors in English. 相似文献
11.
E. N. Ubushaeva E. V. Likhushina K. G. Abdulvakhidov M. A. Vitchenko B. K. Abdulvakhidov V. B. Shirokov N. V. Lyanguzov Yu. I. Yuzyuk E. M. Kaidashev I. V. Mardasova 《Technical Physics Letters》2011,37(10):952-955
Relaxor ferroelectric lead scandium niobate Pb2ScNbO6 (PSN) ceramics was obtained by solidstate synthesis and a modified ceramic technology, whereby the sintering stage was preceded
by room-temperature compression and shear straining of the synthesized PSN powder in Bridgman anvils. It is established that
this mechanical activation leads to the development of dynamic recrystallization processes in PSN grains, which significantly
influence the physical properties of the final ferroelectric ceramic material. 相似文献
12.
Molybdenum disulfide (MoS2), as a representative of two-dimensional layered materials, has been extensively investigated due to their unique structure and interesting electronic and optical properties. However, the controllable synthesis of monolayer and pyramidal MoS2 nanostructures needs improvement, and their growth mechanism requires more investigations. Here, uniform MoS2 nanostructures from monolayer flakes, few-layer pyramids to multilayer blocks were successfully fabricated by a catalyst-assisted thermal-evaporation-based chemical vapor deposition method via simply adjusting the carrier Ar gas flow rate. After the comprehensive characterization on the obtained materials, their nucleation and growth mechanisms were proposed with specifically highlighting the influence of the carrier gas flow rate, which might also be of help to understand the synthesis processes of other two-dimensional semiconducting transition metal dichalcogenides by similar method. 相似文献
13.
By using LiCO3 and MnO2, a rheological-phase-assisted microwave synthesis method has been applied in the fast preparation of spinel LiMn2O4 in order to reduce the cost of cathode materials. Comparing with the pristine LiMn2O4 obtained by the traditional solid-state reaction method, the structure and surface morphology of the samples synthesized
by the rheological-phase-assisted microwave synthesis method have been investigated. The powders were used as positive materials
for lithium-ion battery, whose charge/discharge properties and cycle performance have been examined in detail. As a result,
the powders prepared by the rheologicalphase-assisted microwave synthesis method at 750°C are pure spinel LiMn2O4 with regular shapes and uniform distribution, which exhibit higher capacity and much better reversibility than the sample
prepared by the traditional solid-state reaction.
The text was submitted by the authors in English. 相似文献
14.
The synthesis of rutile (TiO2) nanostructured materials at low temperature from TiCl4 aqueous solution was described. TiO2 coatings on polystyrene (PS) particles were prepared by layer-by-layer assembly technique. The samples were characterized
by DTA-TG, SEM, XPS, TEM and XRD techniques. The experimental results showed that pure rutile-TiO2 coatings with nanocrystal structure were synthesized at 100 °C. On the surface of PS particles, sphere-type TiO2 coatings exhibited uniform shape and a narrow size distribution. The amount of TO2 (wt%) and shell thickness of particles increased with the adding of coating layers. Hollow TiO2 spheres were obtained by calcination at 450 °C. TiO2/PS with 2 coating layers showed higher degradation rate. The photocatalytic activity of hollow TiO2 spheres was higher than that of TiO2/PS. 相似文献
15.
Xiuxiu Zhao Danhui Wang Nana Yuan Yue Zheng Lin Li Zhishan Bo Jianjun Zhou Hong Huo 《Journal of Materials Science》2017,52(5):2484-2494
In this study, we successfully developed a novel method to create [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoscale aggregates using supercritical carbon dioxide (scCO2) annealing and fabricated bulk heterojunction (BHJ) solar cells with the nanoscale PCBM to improve device performance. PCBM forms nanoscale aggregates with a size of approximately 70 nm after scCO2 annealing at 11 MPa and 50 °C for 60 min. However, PCBM remains amorphous after thermal annealing (TA) at 150 °C for 5 min. The morphology, structure, and crystallinity of poly(3-hexylthiophene) (P3HT) in the scCO2-treated P3HT film are nearly the same as those in the TA-treated P3HT film. In the P3HT/PCBM blend, the formation of PCBM nanoscale aggregates by scCO2 treatment decreases the disturbance for P3HT crystallization and improves diffusion and regular packing of P3HT molecular chains. This increases the crystallinity of P3HT so that it becomes higher than that in the TA-treated blend film. The nanoscale aggregates of PCBM and the higher crystallinity of P3HT give the scCO2-treated P3HT/PCBM BHJ solar cells a maximum power conversion efficiency (PCE) of 2.74%, which is much higher than that of the as-cast device (PCE is 1.70%) and a little higher than the highest PCE (2.64%) of thermally annealed devices. These results indicate that scCO2 is an effective, mild, and environmental method to modulate the nanoscale aggregates of PCBM and to improve the PCE of BHJ solar cells. However, the size of the PCBM aggregates is a little larger than the most suitable size of the exciton diffusion length, leading to limited improvement of the PCE. 相似文献
16.
N. N. Vinogradova B. I. Galagan L. N. Dmitruk L. V. Moiseeva V. V. Osiko E. E. Sviridova M. N. Brekhovskikh V. A. Fedorov 《Inorganic Materials》2005,41(6):654-657
Processes are described for the synthesis and melt growth of rare-earth-doped K2LaCl5, K2BaCl4, and K2SrCl4, using rare-earth oxides as starting materials. The solubility of rare-earth activators in Bridgman-grown crystals are determined, and the spectroscopic properties of K2LaCl5〈Nd〉 crystals are investigated.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 748–752.Original Russian Text Copyright © 2005 by Vinogradova, Galagan, Dmitruk, Moiseeva, Osiko, Sviridova, Brekhovskikh, Fedorov. 相似文献
17.
S. M. Badalyan M. N. Rumyantseva S. A. Nikolaev A. V. Marikutsa V. V. Smirnov A. S. Alikhanian A. M. Gaskov 《Inorganic Materials》2010,46(3):232-236
Nanocrystalline tin dioxide has been synthesized, and its surface has been modified with Au and NiO. Their distributions in
the nanocrystalline tin dioxide have been examined by X-ray diffraction and transmission electron microscopy. The NO2 sensing properties of the materials have been studied in the range 100–1000 ppb. Both gold and nickel enhance the NO2 response of SnO2. Codoping with Au and NiO markedly enhances its sensing response and, in addition, lowers the peak response temperature.
The observed effect of NO2 concentration in dry air on the sensing response of the SnO2〈Au, NiO〉 nanocomposite can be understood in terms of the sequence of processes that take place on the SnO2 surface upon nitrogen dioxide adsorption in the presence of chemisorbed oxygen. 相似文献
18.
Nanocrystalline semiconducting materials are attracting much attention due to their potential applications in solar energy
conversion, nonlinear optics, and heterogeneous photocatalysis. In the present investigation, we have synthesized nanostructured
TiO2 photocatalysts, which have been used in the photocatalytic degradation of phenol (one of the most common water pollutants).
These catalysts have been prepared through sol-gel technique using titanium tetra-isopropoxide as a raw material for synthesis.
Characterization techniques such as XRD, SEM and TEM have been employed for structural/microstructural investigations. XRD
results show that the as synthesized TiO2 nanopowder exhibit anatase phase, TiO2. The average sizes of the TiO2 nanopowders are ∼ 5–10 nm. The optical properties of the samples were investigated through UV-visible and fluorescence techniques.
It has been observed that absorption edge corresponds to ∼ 410 nm (bandgap, ∼ 3.02 eV). The emission peak in the fluorescence
spectrum at ∼ 418 nm corresponds to the bandgap energy of ∼ 2.97 eV. Concentration of phenol (initial concentration, ∼ 100
ppm) with illumination time was monitored by measuring the absorbance of pure and illuminated phenol through UV-visible spectrophotometer.
Salient feature of this study relates to the fact that the present sol-gel synthesized TiO2 nanopowders have been found to be better photocatalysts for phenol degradation than the presently employed commercial TiO2 (P-25, Degussa) photocatalyst. Thus, whereas phenol concentration, with the presently synthesized TiO2 nanopowders, the concentration of phenol decreases up to ∼ 32% but for commercial TiO2 nanopowder (P-25, Degussa), it decreased only up to ∼ 25%. The improved surface area is considered as an important factor
for the aforesaid decrease in phenol concentration. 相似文献
19.
A. G. Belous O. V. Ovchar A. V. Kramarenko Bostjan Jancar Jana Bezjak Danilo Suvorov 《Inorganic Materials》2010,46(5):529-533
Polycrystalline nonstoichiometric Ba(Co1/3Nb2/3)O3 (BCN) materials have been synthesized and investigated. Deviations from stoichiometry have been shown to lead to the formation
of crystalline Ba6CoNb9O30 (barium deficiency) and Ba8CoNb6O24 (cobalt deficiency). The effect of phase composition on the microwave dielectric properties of BCN has been studied. The
results demonstrate that the dielectric properties of BCN-based materials can be tuned by varying cobalt content. The materials
obtained are high-Q microwave dielectrics with temperature-stable properties. 相似文献
20.
We have grown single crystals of barium dihydrogen phosphate and studied its thermal transformations during heating to 500°C and its electrotransport properties. Ba(H2PO4)2 (Pccn) has been shown to undergo no phase transitions up to its dehydration temperature. The thermal decomposition of Ba(H2PO4)2, accompanied by dehydration, involves two steps, with maximum rates at ~265 and 370°C, and results in the formation of barium dihydrogen pyrophosphate and barium metaphosphate, respectively. The total enthalpy of the endothermic dehydration events is–244.6 J/g. Using impedance spectroscopy, we have studied in detail the proton conductivity of polycrystalline and single-crystal Ba(H2PO4)2 samples in a controlled atmosphere. Adsorbed water has been shown to have a significant effect on the proton conductivity of Ba(H2PO4)2 up to 130°C. The proton conductivity of the Ba(H2PO4)2 single crystals has been shown to be anisotropic. The conductivity anisotropy correlates with specific structural features of the salt. Higher conductivity values, 3 × 10–9 to 2 × 10–7 S/cm in the range 60–160°C, have been observed in the [100] crystallographic direction, exceeding the conductivity along [010] by an order of magnitude. The activation energy for proton conduction is 0.80 eV. 相似文献