Special Issue "Hydrothermal Synthesis of Nanoparticles"

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Synthesis, Interfaces and Nanostructures".

Deadline for manuscript submissions: 20 February 2022.

Special Issue Editors

Dr. Gimyeong Seong
E-Mail Website
Guest Editor
New Industrial Creaction Hatchery Center (NICHe), Tohoku University, Sendai, Japan
Interests: supercritical hydrothermal synthesis of metal and metal oxides; non-equilibrium material synthesis; metal substitution; organic-inorganic hybrid materials; nanocatalysts; heavy oil upgrading; lignin degradation; methane reforming; methane oxidative coupling reaction
Dr. Juan Carlos Rendón-Angeles
E-Mail Website
Guest Editor
Center for Research and Advanced Studies of the National Polytechnic Institute, Mexico City, Mexico
Interests: hydrothermal synthesis of perovskite oxide materials; hydrothermal self-assembling particle crystal growth on silicate oxides; hydrothermal microwave-assisted processing for nanoparticle synthesis

Special Issue Information

Dear Colleagues,

Hydrothermal synthesis of nanoparticles is a processing technique that has gained particular interest in material science in the last two decades. The recent developments in the preparation of nanoparticles by heterogeneous chemical solution reactions favored the production of a large number of advanced functional materials. Additionally, the particle size control enhanced by high crystallization kinetics occurring in aqueous substances provides the sufficient conditions to produce nanoparticles of various inorganic compounds. The innovation of technology triggers the challenge of optimizing the synthesis of nanostructured advanced and functional materials to overcome the requirements of the current technology. Hence, the hydrothermal synthesis (including supercritical region) of nanoparticles has emerged as a sustainable technique to produce inorganic materials on a large scale in continuous flow reactors at a relatively low cost.

Therefore, this Special Issue intends to gather state-of-the-art advances, regardless of selective contributions, in the research on the hydrothermal synthesis of nanomaterials. Original and review papers on scientific fundamentals and technological applications of the hydrothermal synthesis of nanoparticles of new nanomaterials for energy storage, catalysis engineering use, and environmental sustainability challenges are particularly welcome.

Dr. Gimyeong Seong
Dr. Juan Carlos Rendón-Angeles
Guest Editors

Manuscript Submission Information

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Keywords

  • Hydrothermal synthesis
  • Supercritical fluids
  • Reaction kinetics
  • Morphology control
  • Crystallization
  • Crystal growth
  • Heterogeneous chemical reactions
  • Catalysts
  • Nanoparticles
  • Functional materials

Published Papers (9 papers)

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Research

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Article
Preparation of Silicon Hydroxyapatite Nanopowders under Microwave-Assisted Hydrothermal Method
Nanomaterials 2021, 11(6), 1548; https://doi.org/10.3390/nano11061548 - 11 Jun 2021
Viewed by 337
Abstract
The synthesis of partially substituted silicon hydroxyapatite (Si-HAp) nanopowders was systematically investigated via the microwave-assisted hydrothermal process. The experiments were conducted at 150 °C for 1 h using TMAS (C4H13NO5Si2) as a Si4+ precursor. [...] Read more.
The synthesis of partially substituted silicon hydroxyapatite (Si-HAp) nanopowders was systematically investigated via the microwave-assisted hydrothermal process. The experiments were conducted at 150 °C for 1 h using TMAS (C4H13NO5Si2) as a Si4+ precursor. To improve the Si4+ uptake in the hexagonal structure, the Si precursor was supplied above the stoichiometric molar ratio (0.2 M). The concentration of the TMAS aqueous solutions used varied between 0.3 and 1.8 M, corresponding to saturation levels of 1.5–9.0-fold. Rietveld refinement analyses indicated that Si incorporation occurred in the HAp lattice by replacing phosphate groups (PO43−) with the silicate (SiO4) group. FT-IR and XPS analyses also confirmed the gradual uptake of SiO4 units in the HAp, as the saturation of Si4+ reached 1.8 M. TEM observations confirmed that Si-HAp agglomerates had a high crystallinity and are constituted by tiny rod-shaped particles with single-crystal habit. Furthermore, a reduction in the particle growth process took place by increasing the Si4+ excess content up to 1.8 M, and the excess of Si4+ triggered the fine rod-shaped particles self-assembly to form agglomerates. The agglomerate size that occurred with intermediate (0.99 mol%) and large (12.16 mol%) Si contents varied between 233.1 and 315.1 nm, respectively. The excess of Si in the hydrothermal medium might trigger the formation of the Si-HAp agglomerates prepared under fast kinetic reaction conditions assisted by the microwave heating. Consequently, the use of microwave heating-assisted hydrothermal conditions has delivered high processing efficiency to crystallize Si-HAp with a broad content of Si4+. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
Hydrothermal Synthesis of Iridium-Substituted NaTaO3 Perovskites
Nanomaterials 2021, 11(6), 1537; https://doi.org/10.3390/nano11061537 - 10 Jun 2021
Viewed by 397
Abstract
Iridium-containing NaTaO3 is produced using a one-step hydrothermal crystallisation from Ta2O5 and IrCl3 in an aqueous solution of 10 M NaOH in 40 vol% H2O2 heated at 240 °C. Although a nominal replacement of 50% [...] Read more.
Iridium-containing NaTaO3 is produced using a one-step hydrothermal crystallisation from Ta2O5 and IrCl3 in an aqueous solution of 10 M NaOH in 40 vol% H2O2 heated at 240 °C. Although a nominal replacement of 50% of Ta by Ir was attempted, the amount of Ir included in the perovskite oxide was only up to 15 mol%. The materials are formed as crystalline powders comprising cube-shaped crystallites around 100 nm in edge length, as seen by scanning transmission electron microscopy. Energy dispersive X-ray mapping shows an even dispersion of Ir through the crystallites. Profile fitting of powder X-ray diffraction (XRD) shows expanded unit cell volumes (orthorhombic space group Pbnm) compared to the parent NaTaO3, while XANES spectroscopy at the Ir LIII-edge reveals that the highest Ir-content materials contain Ir4+. The inclusion of Ir4+ into the perovskite by replacement of Ta5+ implies the presence of charge-balancing defects and upon heat treatment the iridium is extruded from the perovskite at around 600 °C in air, with the presence of metallic iridium seen by in situ powder XRD. The highest Ir-content material was loaded with Pt and examined for photocatalytic evolution of H2 from aqueous methanol. Compared to the parent NaTaO3, the Ir-substituted material shows a more than ten-fold enhancement of hydrogen yield with a significant proportion ascribed to visible light absorption. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
Fabrication of Liquid Scintillators Loaded with 6-Phenylhexanoic Acid-Modified ZrO2 Nanoparticles for Observation of Neutrinoless Double Beta Decay
Nanomaterials 2021, 11(5), 1124; https://doi.org/10.3390/nano11051124 - 27 Apr 2021
Viewed by 418
Abstract
The observation of neutrinoless double beta decay is an important issue in nuclear and particle physics. The development of organic liquid scintillators with high transparency and a high concentration of the target isotope would be very useful for neutrinoless double beta decay experiments. [...] Read more.
The observation of neutrinoless double beta decay is an important issue in nuclear and particle physics. The development of organic liquid scintillators with high transparency and a high concentration of the target isotope would be very useful for neutrinoless double beta decay experiments. Therefore, we propose a liquid scintillator loaded with metal oxide nanoparticles containing the target isotope. In this work, 6-phenylhexanoic acid-modified ZrO2 nanoparticles, which contain 96Zr as the target isotope, were synthesized under sub/supercritical hydrothermal conditions. The effects of the synthesis temperature on the formation and surface modification of the nanoparticles were investigated. Performing the synthesis at 250 and 300 °C resulted in the formation of nanoparticles with smaller particle sizes and higher surface modification densities than those prepared at 350 and 400 °C. The highest modification density (3.1 ± 0.2 molecules/nm2) and Zr concentration of (0.33 ± 0.04 wt.%) were obtained at 300 °C. The surface-modified ZrO2 nanoparticles were dispersed in a toluene-based liquid scintillator. The liquid scintillator was transparent to the scintillation wavelength, and a clear scintillation peak was confirmed by X-ray-induced radioluminescence spectroscopy. In conclusion, 6-phenylhexanoic acid-modified ZrO2 nanoparticles synthesized at 300 °C are suitable for loading in liquid scintillators. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
Direct Observation Techniques Using Scanning Electron Microscope for Hydrothermally Synthesized Nanocrystals and Nanoclusters
Nanomaterials 2021, 11(4), 908; https://doi.org/10.3390/nano11040908 - 02 Apr 2021
Viewed by 415
Abstract
Metal oxide nanocrystals have garnered significant attention owing to their unique properties, including luminescence, ferroelectricity, and catalytic activity. Among the various synthetic methods, hydrothermal synthesis is a promising method for synthesizing metal oxide nanocrystals and nanoclusters. Because the shape and surface structure of [...] Read more.
Metal oxide nanocrystals have garnered significant attention owing to their unique properties, including luminescence, ferroelectricity, and catalytic activity. Among the various synthetic methods, hydrothermal synthesis is a promising method for synthesizing metal oxide nanocrystals and nanoclusters. Because the shape and surface structure of the nanocrystals largely affect their properties, their analytical methods should be developed. Further, the arrangement of nanocrystals should be studied because the properties of nanoclusters largely depend on the arrangement of the primary nanocrystals. However, the analysis of nanocrystals and nanoclusters remains difficult because of their sizes. Conventionally, transmission electron microscopy (TEM) is widely used to study materials in nanoscale. However, TEM images are obtained as the projection of three-dimensional structures, and it is difficult to observe the surface structures and the arrangement of nanocrystals using TEM. On the other hand, scanning electron microscopy (SEM) relies on the signals from the surface of the samples. Therefore, SEM can visualize the surface structures of samples. Previously, the spatial resolution of SEM was not enough to observe nanoparticles and nanomaterials with sizes of between 10 and 50 nm. However, recent developments, including the low-landing electron-energy method, improved the spatial resolution of SEM, which allows us to observe fine details of the nanocluster surface directory. Additionally, improved detectors allow us to visualize the elemental mapping of materials even at low voltage with high solid angle. Further, the use of a liquid sample holder even enabled the observation of nanocrystals in water. In this paper, we discuss the development of SEM and related observation technologies through the observation of hydrothermally prepared nanocrystals and nanoclusters. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
The Role of the Surface Acid–Base Nature of Nanocrystalline Hydroxyapatite Catalysts in the 1,6-Hexanediol Conversion
Nanomaterials 2021, 11(3), 659; https://doi.org/10.3390/nano11030659 - 08 Mar 2021
Viewed by 392
Abstract
Hydroxyapatite is known to have excellent catalytic properties for ethanol conversion and lactic acid conversion, and their properties are influenced by the elemental composition, such as Ca/P ratio and sodium content. However, few reports have been examined for the surface acid–base nature of [...] Read more.
Hydroxyapatite is known to have excellent catalytic properties for ethanol conversion and lactic acid conversion, and their properties are influenced by the elemental composition, such as Ca/P ratio and sodium content. However, few reports have been examined for the surface acid–base nature of hydroxyapatites containing sodium ions. We prepared nanocrystalline hydroxyapatite (Ca-HAP) catalysts with various Ca/P ratios and sodium contents by the hydrothermal method. The adsorption and desorption experiments using NH3 and CO2 molecules and the catalytic reactions for 2-propenol conversion revealed that the surface acid–base natures changed continuously with the bulk Ca/P ratios. Furthermore, the new catalytic properties of hydroxyapatite were exhibited for 1,6-hexanediol conversion. The non-stoichiometric Ca-HAP(1.54) catalyst with sodium ions of 2.3 wt% and a Ca/P molar ratio of 1.54 gave a high 5-hexen-1-ol yield of 68%. In contrast, the Ca-HAP(1.72) catalyst, with a Ca/P molar ratio of 1.72, gave a high cyclopentanemethanol yield of 42%. Both yields were the highest ever reported in the relevant literature. It was shown that hydroxyapatite also has excellent catalytic properties for alkanediol conversion because the surface acid–base properties can be continuously controlled by the elemental compositions, such as bulk Ca/P ratios and sodium contents. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
Hydrothermal Synthesis of Various Shape-Controlled Europium Hydroxides
Nanomaterials 2021, 11(2), 529; https://doi.org/10.3390/nano11020529 - 19 Feb 2021
Viewed by 469
Abstract
Eu(OH)3 with various shape-controlled morphologies and size, such as plate, rod, tube, prism and nanoparticles was successfully synthesized through simple hydrothermal reactions. The products were characterized by XRD (X-Ray Powder Diffraction), FE-SEM (Field Emission- Scanning Electron Microscopy) and TG (Thermogravimetry). The influence [...] Read more.
Eu(OH)3 with various shape-controlled morphologies and size, such as plate, rod, tube, prism and nanoparticles was successfully synthesized through simple hydrothermal reactions. The products were characterized by XRD (X-Ray Powder Diffraction), FE-SEM (Field Emission- Scanning Electron Microscopy) and TG (Thermogravimetry). The influence of the initial pH value of the starting solution and reaction temperature on the crystalline phase and morphology of the hydrothermal products was investigated. A possible formation process to control morphologies and size of europium products by changing the hydrothermal temperature and initial pH value of the starting solution was proposed. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
One-Pot Hydrothermal Synthesis of Victoria Green (Ca3Cr2Si3O12) Nanoparticles in Alkaline Fluids and Its Colour Hue Characterisation
Nanomaterials 2021, 11(2), 521; https://doi.org/10.3390/nano11020521 - 18 Feb 2021
Viewed by 583
Abstract
One-pot hydrothermal preparation of Ca3Cr2Si3O12 uvarovite nanoparticles under alkaline conditions was investigated for the first time. The experimental parameters selected for the study considered the concentration of the KOH solvent solution (0.01 to 5.0 M), the [...] Read more.
One-pot hydrothermal preparation of Ca3Cr2Si3O12 uvarovite nanoparticles under alkaline conditions was investigated for the first time. The experimental parameters selected for the study considered the concentration of the KOH solvent solution (0.01 to 5.0 M), the agitation of the autoclave (50 rpm), and the nominal content of Si4+ (2.2–3.0 mole). Fine uvarovite particles were synthesised at 200 °C after a 3 h interval in a highly concentrated 5.0 M KOH solution. The crystallisation of single-phase Ca3Cr2Si3O12 particles proceeded free of by-products via a one-pot process involving a single-step reaction. KOH solutions below 2.5 M and water hindered the crystallisation of the Ca3Cr2Si3O12 particles. The hydrothermal treatments carried out with stirring (50 rpm) and non-stirring triggered the crystallisation of irregular anhedral particles with average sizes of 8.05 and 12.25 nm, respectively. These particles spontaneously assembled into popcorn-shaped agglomerates with sizes varying from 66 to 156 nm. All the powders prepared by the present method exhibited CIE-L*a*b* values that correspond to the Victoria green colour spectral space and have a high near infrared reflectance property. The particle size and structural crystallinity are factors affecting the Victoria pigment optical properties, such as CIE-L*a*b* values, green tonality, and near-infrared reflectance. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Article
Large-Scale Synthesis Route of TiO2 Nanomaterials with Controlled Morphologies Using Hydrothermal Method and TiO2 Aggregates as Precursor
Nanomaterials 2021, 11(2), 365; https://doi.org/10.3390/nano11020365 - 01 Feb 2021
Viewed by 583
Abstract
TiO2 of controlled morphologies have been successfully prepared hydrothermally using TiO2 aggregates of different sizes. Different techniques were used to characterize the prepared TiO2 powder such as XRD, XPS, FEGSEM, EDS, and HRTEM. It was illustrated that the prepared TiO [...] Read more.
TiO2 of controlled morphologies have been successfully prepared hydrothermally using TiO2 aggregates of different sizes. Different techniques were used to characterize the prepared TiO2 powder such as XRD, XPS, FEGSEM, EDS, and HRTEM. It was illustrated that the prepared TiO2 powders are of high crystallinity with different morphologies such as nanobelt, nanourchin, and nanotube depending on the synthesis conditions of temperature, time, and additives. The mechanism behind the formation of prepared morphologies is proposed involving nanosheet intermediate formation. Furthermore, it was found that the nanoparticle properties were governed by those of TiO2 nanoparticles aggregate used as a precursor. For example, the size of prepared nanobelts was proven to be influenced by the aggregates size used as a precursor for the synthesis. Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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Review

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Review
Behavior of Silicon Carbide Materials under Dry to Hydrothermal Conditions
Nanomaterials 2021, 11(5), 1351; https://doi.org/10.3390/nano11051351 - 20 May 2021
Viewed by 428
Abstract
Silicon carbide materials are excellent candidates for high-performance applications due to their outstanding thermomechanical properties and their strong corrosion resistance. SiC materials can be processed in various forms, from nanomaterials to continuous fibers. Common applications of SiC materials include the aerospace and nuclear [...] Read more.
Silicon carbide materials are excellent candidates for high-performance applications due to their outstanding thermomechanical properties and their strong corrosion resistance. SiC materials can be processed in various forms, from nanomaterials to continuous fibers. Common applications of SiC materials include the aerospace and nuclear fields, where the material is used in severely oxidative environments. Therefore, it is important to understand the kinetics of SiC oxidation and the parameters influencing them. The first part of this review focuses on the oxidation of SiC in dry air according to the Deal and Grove model showing that the oxidation behavior of SiC depends on the temperature and the time of oxidation. The oxidation rate can also be accelerated with the presence of H2O in the system due to its diffusion through the oxide scales. Therefore, wet oxidation is studied in the second part. The third part details the effect of hydrothermal media on the SiC materials that has been explained by different models, namely Yoshimura (1986), Hirayama (1989) and Allongue (1992). The last part of this review focuses on the hydrothermal corrosion of SiC materials from an application point of view and determine whether it is beneficial (manufacturing of materials) or detrimental (use of SiC in latest nuclear reactors). Full article
(This article belongs to the Special Issue Hydrothermal Synthesis of Nanoparticles)
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