Supercritical Synthesis Research Articles

Improved performance of SrFe12O19 bulk magnets through bottom-up nanostructuring.

The influence of synthesis and compaction parameters is investigated with regards to formation of high performance SrFe12O19 bulk magnets. The produced magnets consist of highly aligned, single-magnetic domain nanoplatelets of SrFe12O19. The relationship between the magnetic performance of the samples and their structural features is established through systematic characterization by Vibrating Sample Magnetometry (VSM) and Rietveld refinement of powder X-ray diffraction data (PXRD). The analysis is supported by complementary techniques including Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and X-ray pole figure measurements. SrFe12O19 hexagonal nanoplatelets with various sizes are synthesized by a supercritical hydrothermal flow method. The crystallite sizes are tuned by varying the Fe/Sr ratio in the precursor solution. Compaction of SrFe12O19 nanoplatelets into bulk magnets is performed by Spark Plasma Sintering (SPS). Rietveld refinement of the pressed pellets and texture analysis of pole figure measurements reveal that SPS pressing produces a high degree of alignment of the nanoplatelets, achieved without applying any magnetic field prior or during compaction. The highly aligned nanocrystallites combined with crystal growth during SPS give rise to an enormous enhancement of the magnetic properties compared to the as-synthesized powders, leading to high performance bulk magnets with energy products of 26 kJ m(-3).

Supercritical synthesis of a magnetite-reduced graphene oxide hybrid with enhanced adsorption properties toward cobalt & strontium ions

The current study presents a supercritical synthesis of magnetite-reduced graphene oxide (M-RGO) in methanol media, in which Fe3O4 nanoparticles are simultaneously formed, surface modified and decorated on the surface of the reduced graphene oxide.

Local Distortions in Nanostructured Ferroelectric Ceramics through Strain Tuning

Ferroelectric materials are highly sensitive to grain size reduction because strain and ferroelectric polarization have a direct connection. Using 15 nm (Ba,Sr)TiO3 particles obtained by advanced supercritical synthesis and their densification by high‐pressure spark plasma sintering under air, reproducible and dense nanostructured ceramics are achieved. Taking advantage of the high pressure (up to 600 MPa) applied during the sintering step, the internal stress generated at the grain scale can be monitored to compensate for the particle surface stress due to size effect. Both the local dynamics observed by Raman scattering and the overall dielectric behavior consistently indicate a recovery of the ferroelectric properties as the sintering pressure is increased. This unique behavior shows that low‐temperature and high‐pressure processing enables designing nanostructured functional ceramics exhibiting original properties.

Supercritical Synthesis and Characterization of Graphene–PbS Quantum Dots Composite with Enhanced Photovoltaic Properties

Lead sulfide quantum dots (PbS QDs) were decorated onto a graphene surface in a semi-core–shell structure using supercritical ethanol. The temperature of ethanol played significant role in controlling size and agglomeration of QDs as well as the extent of reduction of graphene. Average size of the QDs was estimated by transmission electron microscopy to be around 3.96 nm and by quantum models to be about 4.34 nm. PbS QDs prepared at 330 °C were of high purity, and the yield was 99%. Instrumental and chemical analyses demonstrated formation of a strong bond between PbS QDs and graphene, through a Pb–O–C bridge. UV and photoluminescence measurements along with theoretical considerations revealed that integration of PbS QDs with graphene results in efficient separation of the electron–hole, thus enhancing photo → electric energy conversion. This outcome was further evidenced by comparison of performance of PbS/G in a solar cell, with the performance of pristine PbS QDs.

Supercritical synthesis of poly (2-dimethylaminoethyl methacrylate)/ferrite nanocomposites for real-time monitoring of protein release.

A supercritical carbon dioxide (SCC)-assisted process was developed to synthesize protein-supported poly (2-dimethylaminoethyl methacrylate)/ferrite nanocomposites (PNCs). The process involve 2,2-azobisisobutyronitrile-initiated in situ polymerization of 2-dimethylaminoethyl methacrylate in presence of ferrite nanoparticles and bisacrylamide at 90 ± 1 °C, 1200 psi over 6 h in SCC. This was followed by subsequent loading of bovine serum albumin (BSA) as a model protein over PNCs in phosphate buffer (PBS, pH 7.4) at 1200 psi, 35 ± 1 °C over additional 2 h in SCC. The formation of PNCs was ascertained through ultraviolet-visible, Fourier transform-infrared, X-ray diffraction spectra, transmission electron, atomic force microscopy and magnetometry. The developed process extends large scale production of nanomagnetic PNCs suitable as carrier for protein release applications with optimal release properties. The release of protein from PNCs under in vitro in PBS down to nanomolar range with high temporal resolution, speed and reproducibility was quantified through square wave voltammetry.

Supercritical synthesis and in situ deposition of PbS nanocrystals with oleic acid passivation for quantum dot solar cells

Colloidal quantum dot solar cells have recently attracted significant attention due to their low-processing cost and surging photovoltaic performance. In this paper, a novel, reproducible, and simple solution-based process based on supercritical fluid toluene is presented for in situ growth and deposition PbS nanocrystals with oleic-acid passivation. A lead precursor containing sulfur was mixed with oleic acid in toluene and processed in a supercritical fluid condition at different temperatures of 140, 270 and 330 °C for 20 min. The quantum dots were deposited on a fluorine-doped tin oxide glass substrate inside the supercritical reactor. Transmission electron microscopy, X-ray diffraction, absorption and dynamic light scattering showed that the nanocrystals processed at the supercritical condition (330 °C) are fully crystalline with a narrow size distribution of ∼3 nm with an absorption wavelength of 915 nm (bandgap of 1.3 eV). Fourier transform infrared spectroscopy indicated that the PbS quantum dots are passivated by oleic acid molecules during the growth. Photovoltaic characteristics of Schottky junction solar cells showed an improvement over devices prepared by spin-coating.

Pulsed-Flow Near-Critical and Supercritical Synthesis of Carbon-Supported Platinum Nanoparticles and In Situ X-ray Diffraction Study of Their Formation and Growth

The formation and growth of carbon (C)-supported platinum (Pt) nanoparticles in a high-temperature, high-pressure ethanol solution have been studied by in situ synchrotron radiation powder X-ray diffraction (PXRD). Supercritical synthesis is shown to be an efficient way to prepare Pt nanoparticles, and the crystallite size of Pt nanoparticles is much smaller when formed with supporting C material compared with synthesis without C. On the basis of the time-resolved in situ PXRD data, a surface stress of 2.65 N/m is derived from the size dependence of the cell parameters. As proof of concept, C-supported Pt nanoparticles were subsequently synthesized in a pulsed-flow supercritical reactor, which offers complete control of the reaction temperature, pressure, and residence time. Well-dispersed Pt nanoparticles decorated on the supporting C material can be obtained by adjusting the reaction conditions, and the electrocatalytic activity of the samples is explored. A mass activity of 0.1209 A/mgPt at a potential...

Supercritical synthesis of layered elongated hexagonal titanium phosphate nanoplates

Elongated hexagonal α-titanium phosphate nanoplates with single-crystalline and controllable structures were synthesized in supercritical ethanol without any template.

Supercritical Synthesis of Ethyl Esters via Transesterification from Waste Cooking Oil Using a Co-Solvent

Biofuels became more promising alternative to the fossil fuels because of the depletion of fossil resources, renewability, environmental benefits, and energy security. Ethanolysis of waste cooking oil with hexane as co-solvent was carried out for the production of fatty acid ethyl ester (FAEE). This process reduced the severity of process parameters with high purity biodiesel yield. Process variables such as co-solvent ratio, ethanol to oil molar ratio, reaction temperature and reaction time were optimized. The maximum biodiesel yield of 88% was obtained at ethanol/oil molar ratio of 40:1, co-solvent (hexane) to oil ratio of 0.2% (v/v), reaction temperature of 300°C in 20 min of reaction time. Fatty acid ethyl ester (biodiesel) samples produced from this process were measured and evaluated using GC-MS analytical instrument. Thermo gravimetric analysis (TGA) was also performed to examine the thermal stability of waste cooking oil, ethyl esters and fuel blends. Fuel properties of ethyl esters were determined and compared with the ASTM standards for biodiesel, regular diesel and ethyl esters from different feedstock.

One Pot Synthesis and Characterizations of Nanosize Lithium Metal Silicates and Lithium Metal Flurophosphates for Lithium Ion Battery Applications

Recently, orthosilicates and flurophosphates have been investigating for the cathode applications in lithium ion battery. Orthoslicate materials are built of abundant elements such as Si, Fe and Mn, which makes them cheap cathode materials for large scale high capacity batteries that can operate at higher temperatures1,2. Fluorophosphates have been considered as potential lithium insertion/ extraction cathodes3,4. Both, silicates and fluorophosphates have the ability of delivering two lithium ion discharge capacity (290-333 mAhg-1). Herein, we present a supercritical fluid process to synthesize Li2MSiO4 and Li2MPO4F (M= Fe, Mn and Co) nanoparticles ranging from 5-50 nm and their electrode properties have been investigated. These cathode materials are synthesized via supercritical fluid process by controlling the size and shape. The supercritical synthesis was carried out at 300-450 oC for 5 min-30 min of reaction time using mixed solution of water, ethanol, EG as solvents and ascorbic acid, oleic acid and oleylamine as surfactants. The as-synthesized Li2MSiO4 and Li2MPO4F (M= Fe, Mn and Co) nanoparticles were characterized by XRD, TEM, TG-DTA and FTIR analysis. Further, the electrochemical property of Li2MSiO4 and Li2MPO4F (M= Fe, Mn and Co) cathode materials have been investigated by galvanostatic charge-discharge method. Fig. 1 shows the TEM images of Li2FeSiO4 and Li2FePO4F nanoparticles synthesized by supercritical method at 300-450 oC for 5-30 min. The particles exhibited 5-50 nm in diameter with sphere like morphology. The different kind of morphology with variable size can be synthesized at supercritical conditions. The flower like morphology, rod like morphology and ultrafine particles were successfully synthesized and their electrochemical property was investigated. The charge-discharge curve of carbon coated Li2FeSiO4 and Li2FePO4F nanoparticles showed 180 mAhg-1 and 150 mAhg-1, respectively at 0.05C as shown in fig 1.References 1) A. Nyten, et al. Electrochem.Commun., 2005, 7, 156.2) Y.X. Li, et al. J. Power Sources. 2007, 174, 528. 3) R. Dominko,.et al, J. Electrochem. Commun., 2006, 8, 217. 4) B.L. Ellis, et al. Nature Mater., 2007, 6, 749.Fig.1 TEM image and charge discharge profile of Li2FeSiO4 and Li2FePO4F cathode nanomaterials

LiCoPO4 and Li2CoSiO4 Nanoparticles Synthesis by Supercritical Fluid Process for Lithium Ion Battery Application

In recent years, transition metal polyanionic compounds such as phosphates and silicates are considered as promising positive electrode materials for lithium-ion batteries. These members of the lithium metal polyanion family have been a major focus of research for reasons of high safety, low cost and low environmental impact. Among, metal phosphate cathode material, LiCoPO4 electrode materials have received considerable attention for the application in lithium secondary batteries due to its high stability, non toxicity, good charge/discharge capabilities and cheap cost. Recently, polyanion-containing frameworks are of great research interest in the area of lithium ion batteries, because, these materials can reversibly insert/extract two lithium ions per formula unit would help to increase the capacity and energy density. Regarding this, silicates with the general formula Li2MSiO4 (M=Mn, Fe and Co) have been considered as potential lithium insertion/ extraction cathodes. Among silicates, Li2CoSiO4 is an attractive cathode due to its high operating voltage. In this work, we have used supercritical fluid process for the synthesis of LiCoPO4 and Li2CoSiO4 nanoparticles and are investigated for lithium ion battery applications. LiCoPO4 and Li2CoSiO4 nanoparticles were synthesized from LiOH.H2O/Lithum acetyl acetonate, CoCl3.6H2O/C4H6CoO4.4H2O and H3PO4/TEOS in molar ratio of 1:1:1 for LiCoPO4 and 4:1:1 for Li2CoSiO4 nanoparticles via supercritical fluid process. Cheap solvents such as water, ethanol and water-ethanol mixed solvents were used to prepare precursor solutions and reducing agents were also used in the synthesis. Supercritical synthesis was carried out at 400-450oC for about 5-10 min of reaction time. Then, the products were washed thoroughly in water and ethanol followed by vacuum dry for overnight. The as-synthesized LiCoPO4 and Li2CoSiO4 nanoparticles showed 20-150 nm in diameter, which was analysed by transmission electron microscopy (TEM). Further, LiCoPO4 and Li2CoSiO4 nanoparticles were systematically characterized using powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS) and charge-discharge measurements. The discharge capacities of 80-110 mAhg-1 for LiCoPO4 nanoparticles and 40-110 mAhg-1 for Li2CoSiO4 nanoparticles were observed. The electrochemical property was measured by galvanostatic discharge method using 1M LiPF6 mixed in EC:DEC as electrolyte. The electrode was prepared using 10 wt% PTFE as binder. The weight ratio of active material:AB:PTFE are 80:10:10.

Supercritical synthesis in combination with a spray process for 3D porous microsphere lithium iron phosphate

Supercritical synthesis in combination with a spray process for 3D porous microspheres of lithium iron phosphate.

Supercritical Synthesis of Poly (2-Dimethylaminoethyl Methacrylate)/Ferrite Nanocomposites and Online Electrochemical Monitoring of Protein Release

A supercritical carbon dioxide (SCC) assisted process was developed to synthesize protein supported poly (2-dimethylaminoethyl methacrylate)/ferrite nanocomposites (PNCs). The process involve 2,2-azobisisobutyronitrile initiated insitu polymerization of 2-dimethylaminoethyl methacrylate in presence of ferrite nanoparticles and bisacrylamide at 90±1 oC, 1200 psi over 6 hr in SCC. This was followed by subsequent loading of bovine serum albumin (BSA) as a model protein over PNCs in phosphate buffer (PBS, pH 7.4) at 1200 psi, 35±1⁰C over additional 2 hr in SCC. The formation of PNCs was ascertained through Ultra violet-visible, Fourier transform-infrared, X-ray diffraction spectra, transmission electron, atomic force microscopy and magnetometry. The developed process extends large scale production of nanomagnetic PNCs suitable as carrier for protein release applications with optimal release properties. The release of protein from PNCs under in vitro in PBS down to nanomolar range with high temporal resolution, speed and reproducibility was quantified through square wave voltammetry.

Pulsed supercritical synthesis of anatase TiO2 nanoparticles in a water–isopropanol mixture studied by in situ powder X-ray diffraction

A new step in supercritical nanoparticle synthesis, the pulsed supercritical synthesis reactor, is investigated in situ using synchrotron powder X-ray diffraction (PXRD) to understand the formation of nanoparticles in real time. This eliminates the common problem of transferring information gained during in situ studies to subsequent laboratory reactor conditions. As a proof of principle, anatase titania nanoparticles were synthesized in a 50/50 mixture of water and isopropanol near and above the critical point of water (P = 250 bar, T = 300, 350, 400, 450, 500 and 550 °C). The evolution of the reaction product was followed by sequentially recording PXRD patterns with a time resolution of less than two seconds. The crystallite size of titania is found to depend on both temperature and residence time, and increasing either parameter leads to larger crystallites. A simple adjustment of either temperature or residence time provides a direct method for gram scale production of anatase nanoparticles of average crystallite sizes between 7 and 35 nm, thus giving the option of synthesizing tailor-made nanoparticles. Modeling of the in situ growth curves using an Avrami growth model gave an activation energy of 66(19) kJ mol(-1) for the initial crystallization. The in situ PXRD data also provide direct information about the size dependent macrostrain in the nanoparticles and with decreasing crystallite size the unit cell contracts, especially along the c-direction. This agrees well with previous ex situ results obtained for hydrothermal synthesis of titania nanoparticles.

Continuous supercritical synthesis of high quality UV-emitting ZnO nanocrystals for optochemical applications

Download options Please wait... Article information DOI https://doi.org/10.1039/C3TC30737A Article type Paper Submitted 19 Apr 2013 Accepted 03 Jun 2013 First published 03 Jun 2013 Download Citation J. Mater. Chem. C, 2013,1, 5058-5063 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Continuous supercritical synthesis of high quality UV-emitting ZnO nanocrystals for optochemical applications E. S. Ilin, S. Marre, V. Jubera and C. Aymonier, J. Mater. Chem. C, 2013, 1, 5058 DOI: 10.1039/C3TC30737A To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Evgeniy S. Ilin Samuel Marre Véronique Jubera Cyril Aymonier

Highly controlled crystallite size and crystallinity of pure and iron-doped anatase-TiO2nanocrystals by continuous flow supercritical synthesis

Abstract

Supercritical synthesis of biodiesel.

The synthesis of biodiesel fuel from lipids (vegetable oils and animal fats) has gained in importance as a possible source of renewable non-fossil energy in an attempt to reduce our dependence on petroleum-based fuels. The catalytic processes commonly used for the production of biodiesel fuel present a series of limitations and drawbacks, among them the high energy consumption required for complex purification operations and undesirable side reactions. Supercritical fluid (SCF) technologies offer an interesting alternative to conventional processes for preparing biodiesel. This review highlights the advances, advantages, drawbacks and new tendencies involved in the use of supercritical fluids (SCFs) for biodiesel synthesis.

Ceria–zirconia mixed oxide prepared by continuous hydrothermal synthesis in supercritical water as catalyst support

A number of different synthetic methods have been applied to prepare ceria–zirconia and related mixed oxides. Continuous hydrothermal synthesis in supercritical water (supercritical synthesis) is a method to prepare metal oxide nanoparticles rapidly and continuously using supercritical water as anti-solvent. Highly crystallized nanoparticles of homogeneous complex metal oxides as well as single metal oxides could be produced easily by the supercritical synthesis. It would be valuable to compare the physicochemical properties of ceria–zirconia mixed oxides prepared by the supercritical synthesis and those by other conventional methods.The supercritical synthesis could lead to ceria–zirconia mixed oxides with higher thermal stability and better oxygen storage capacity (OSC) due to its sparsely-agglomerated morphology, while the co-precipitation resulted in densely agglomerated morphology. Rh-loaded ceria–zirconia catalysts with ceria–zirconia as support were applied for catalytic reduction of NO by CO. Rh-loaded ceria–zirconia catalyst by supercritical synthesis showed superior catalytic performances, together with better reducibility and higher thermal stability. Ceria–zirconia mixed oxide prepared by supercritical synthesis had more potential applications as catalyst support mainly due to its sparsely-agglomerated morphology and higher thermal stability, compared with those by the co-precipitation method.

ChemInform Abstract: Eu3+:Y2O3 Microspheres and Microcubes: A Supercritical Synthesis and Characterization.

AbstractThe title compound is synthesized by reaction of Y(NO3)3 and Eu(NO3)3 in mixed supercritical solvents (pH 7 adjusted with KOH, 400 °C, 40 MPa, 10 min), followed by calcination at 1000 °C (1 h).

Watching Materials Form: Real-Time X-ray Studies of Sub- and Supercritical Syntheses of LiFePO4 and LiFe1-xMnxPO4Nanoparticles

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