scholarly journals Anisotropic Magnetism in Gradient Porous Carbon Composite Aerogels

2021 ◽  
Vol 7 (1) ◽  
pp. 22
Author(s):  
Jochen Bahner ◽  
Nicolas Hug ◽  
Sebastian Polarz
Keyword(s):  
Porous Carbon ◽  
High Surface ◽  
Sol Gel ◽  
Functional Materials ◽  
Material Design ◽  
Carbon Composite ◽  
Functionally Graded ◽  
Carbon Aerogels ◽  
Pore Sizes ◽  
Composite Aerogels

Porosity is of high importance for functional materials, as it allows for high surface areas and the accessibility of materials. While the fundamental interplay between different pore sizes and functionalities is quite well understood, few studies on gradually changing properties in a material exist. To date, only a few examples of such materials have been synthesized successfully. Herein, we present a facile method for synthesizing macroscopic carbon aerogels with locally changing pore sizes and functionalities. We used ultracentrifugation to fractionate differently functionalized and sized polystyrene nanoparticles. The assembly into gradient templates was conducted in a resorcinol–formaldehyde (RF) sol, which acted as a liquid phase and carbon precursor. We show that the modification of nanoparticles and a sol–gel precursor is a powerful tool for introducing dopants (sulfur and phosphorous) and metal nanoparticles (e.g., Ni) into gradient porous carbons formed during the carbonization of the RF sol. Understanding the underlying interactions between particles and precursors will lead to a plethora of possibilities in the material design of complex functionally graded materials. We showed this by exchanging parts of the template with magnetite–polystyrene composites as templating nanoparticles. This led to the incorporation of magnetite nanoparticles in the formed gradient porous carbon aerogels. Finally, gradually increasing concentrations of magnetite were obtained, ultimately leading to macroscopic carbon aerogels with locally changing magnetic properties, while the graded porosity was maintained.

Performance Study and Structure Control of Carbon Aerogel

2013 ◽  
Vol 706-708 ◽  
pp. 897-900 ◽  
Author(s):  
Rui He ◽  
Xuan Liu ◽  
Zhen Fa Liu ◽  
Li Hui Zhang
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
Supercritical Drying ◽  
Carbon Aerogel ◽  
Preparation Condition ◽  
Carbon Aerogels ◽  
Performance Study ◽  
Structure Control ◽  
Sol Gel Process ◽  
Nanopore Structure

In this research the fabrication of carbon aerogel is reported. nanopore carbon aerogels were prepared via a sol-gel process with resorcinol and formaldehyde (RF) aerogels,which were cost-effectively manufacture form Rf wet gels by an ambient drying technique instead of conventional supercritical drying. The key of the work is to fabricate carbon aerogels with controllable nanopore structure, which means sharp pore size distribution and extremely high surface area.The influence of preparation condition of carbon aerogels was studied by scanning electron microscope and Micropore Physisorption Analyzer. The BET surface of the carbon aerogels are from 749m2/g to 1156m2/g .The size of the carbon nanoparticles are in the range of 20nm~40nm. The micro-pore volume and bore diameter can be controlled by gelation conditions such as RF mass fraction.

scholarly journals Electrochemical Behavior of Carbon Aerogels Derived From Different Precursors

1995 ◽  
Vol 393 ◽  
Author(s):  
R.W. Pekala ◽  
C.T. Alviso ◽  
J.K. Nielsen ◽  
T.D. Tran ◽  
G.A.M. Reynolds ◽  
...  
Keyword(s):  
Cell Structure ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Supercritical Drying ◽  
Inert Atmosphere ◽  
Solid Matrix ◽  
Carbon Aerogels ◽  
Energy Storage Devices ◽  
Electrochemical Double Layer

ABSTRACTThe ability to tailor the structure and properties of porous carbons has led to their increased use as electrodes in energy storage devices. Our research focuses on the synthesis and characterization of carbon aerogels for use in electrochemical double layer capacitors. Carbon aerogels are formed from the sol-gel polymerization of (1) resorcinol-formaldehyde or (2) phenolic-furfural, followed by supercritical drying from carbon dioxide, and subsequent pyrolysis in an inert atmosphere. These materials can be produced as monoliths, composites, thin films, powders, or microspheres. In all cases, the aerogels have an open-cell structure with an ultrafine pore size (<100 nm), high surface area (400-1100 m2/g), and a solid matrix composed of interconnected particles, fibers, or platelets with characteristic dimensions of 10 nm. This paper examines the effects of the carbon precursor and processing conditions on electrochemical performance in aqueous and organic electrolytes.

Carbon Aerogels and Xerogels

1992 ◽  
Vol 270 ◽  
Author(s):  
Richard W. Pekala ◽  
Cynthia T. Alviso
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Particle Morphology ◽  
Inert Atmosphere ◽  
Vitreous Carbon ◽  
Carbon Aerogels ◽  
Structure Property ◽  
Microporous Material ◽  
Sol Gel Transition

ABSTRACTThe aqueous polycondensation of resorcinol with formaldehyde proceeds through a sol-gel transition and results in the formation of highly crosslinked, transparent gels. If the solvent is simply evaporated from the pores of these gels, large capillary forces are exerted and a collapsed structure known as a xerogel is formed. In order to preserve the gel skeleton and minimize shrinkage, the aforementioned solvent or its substitute must be removed under supercritical conditions. The microporous material that results from this operation is known as an aerogel. Because resorcinol-formaldehyde aerogels and xerogels consist of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths. The resultant porous materials are black in color and no longer transparent, yet they retain the ultrafine cell size (< 50 nm), high surface area (600-800 m2 /g), and the interconnected particle morphology of their organic precursors. The thermal, acoustic, mechanical, and electrical properties of carbon aerogels/xerogels primarily depend upon polymerization conditions and pyrolysis temperature. In this paper, the chemistry-structure-property relationships of these unique materials will be discussed in detail.

scholarly journals Structural Evolution in Carbon Aerogels as a function of Precursor Material and Pyrolysis Temperature

1996 ◽  
Vol 431 ◽  
Author(s):  
J. Gross ◽  
C. T. Alviso ◽  
R. W. Pekala
Keyword(s):  
Pyrolysis Temperature ◽  
Phenol Formaldehyde ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Structural Evolution ◽  
Vitreous Carbon ◽  
Carbon Aerogels ◽  
High Porosity ◽  
Precursor Material

AbstractSeveral organic reactions that proceed through a sol-gel transition have been identified at LLNL. The most-studied reaction involves the aqueous polycondensation of resorcinol (1,3- dihydroxybenzene) with formaldehyde. Recently, we have shown that phenol can be added to this polymerization as a comonomer. The resultant crosslinked gels are supercritically dried from carbon dioxide (Tc=31°C, Pc = 7.4 MPa) to give resorcinol-phenol-formaldehyde (RPF) aerogels. Because RPF aerogels are composed of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths (CRPF). The resultant aerogels are black in color and no longer transparent, yet they retain the high porosity (40–98 %), ultrafine cell/pore size (< 50 nm), high surface area (600–800 m2/g), and interconnected particle (˜10 nm) morphology of their organic precursors. In this study, we examine the acoustic and mechanical properties of these materials as a function of precursor material and pyrolysis temperature. It is shown that the elastic moduli of RPF and CRPF is higher than that of pure RF / CRF aerogels at a given density. Upon pyrolysis RPF aerogels tend to shrink to a larger extent.

scholarly journals The carbonization of aromatic molecules with three-dimensional structures affords carbon materials with controlled pore sizes at the Ångstrom-level

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Tomoki Ogoshi ◽  
Yuma Sakatsume ◽  
Katsuto Onishi ◽  
Rui Tang ◽  
Kazuma Takahashi ◽  
...  
Keyword(s):  
Porous Carbon ◽  
Carbon Materials ◽  
Carbon Sources ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Thermal Polymerization ◽  
Sodium Ion Battery ◽  
Pore Sizes ◽  
Aromatic Molecules ◽  
Template Methods

AbstractCarbon materials with controlled pore sizes at the nanometer level have been obtained by template methods, chemical vapor desorption, and extraction of metals from carbides. However, to produce porous carbons with controlled pore sizes at the Ångstrom-level, syntheses that are simple, versatile, and reproducible are desired. Here, we report a synthetic method to prepare porous carbon materials with pore sizes that can be precisely controlled at the Ångstrom-level. Heating first induces thermal polymerization of selected three-dimensional aromatic molecules as the carbon sources, further heating results in extremely high carbonization yields (>86%). The porous carbon obtained from a tetrabiphenylmethane structure has a larger pore size (4.40 Å) than those from a spirobifluorene (4.07 Å) or a tetraphenylmethane precursor (4.05 Å). The porous carbon obtained from tetraphenylmethane is applied as an anode material for sodium-ion battery.

scholarly journals Elucidation of the Crystal Growth Characteristics of SnO2 Nanoaggregates Formed by Sequential Low-Temperature Sol-Gel Reaction and Freeze Drying

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1738
Author(s):  
Saeid Vafaei ◽  
Alexander Wolosz ◽  
Catlin Ethridge ◽  
Udo Schnupf ◽  
Nagisa Hattori ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Low Temperature ◽  
Photoelectron Spectroscopy ◽  
High Performance ◽  
Freeze Drying ◽  
Sno2 Nanoparticles ◽  
Sol Gel ◽  
Functional Materials ◽  
Cost Effective ◽  
High Concentration

SnO2 nanoparticles are regarded as attractive, functional materials because of their versatile applications. SnO2 nanoaggregates with single-nanometer-scale lumpy surfaces provide opportunities to enhance hetero-material interfacial areas, leading to the performance improvement of materials and devices. For the first time, we demonstrate that SnO2 nanoaggregates with oxygen vacancies can be produced by a simple, low-temperature sol-gel approach combined with freeze-drying. We characterize the initiation of the low-temperature crystal growth of the obtained SnO2 nanoaggregates using high-resolution transmission electron microscopy (HRTEM). The results indicate that Sn (II) hydroxide precursors are converted into submicrometer-scale nanoaggregates consisting of uniform SnO2 spherical nanocrystals (2~5 nm in size). As the sol-gel reaction time increases, further crystallization is observed through the neighboring particles in a confined part of the aggregates, while the specific surface areas of the SnO2 samples increase concomitantly. In addition, X-ray photoelectron spectroscopy (XPS) measurements suggest that Sn (II) ions exist in the SnO2 samples when the reactions are stopped after a short time or when a relatively high concentration of Sn (II) is involved in the corresponding sol-gel reactions. Understanding this low-temperature growth of 3D SnO2 will provide new avenues for developing and producing high-performance, photofunctional nanomaterials via a cost-effective and scalable method.

High-Surface-Area Alumina-Silica Nanocatalysts Prepared by a Hybrid Sol-Gel Route Using a Boehmite Precursor

2010 ◽  
Vol 93 (12) ◽  
pp. 4047-4052 ◽  
Author(s):  
Padmaja Parameswaran Nampi ◽  
Padmanabhan Moothetty ◽  
Wilfried Wunderlich ◽  
Frank John Berry ◽  
Michael Mortimer ◽  
...  
Keyword(s):  
Surface Area ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area

Super Hybrid Materials

2011 ◽  
Vol 700 ◽  
pp. 145-149 ◽  
Author(s):  
Tadafumi Adschiri ◽  
S. Takami ◽  
K. Minami ◽  
T. Yamagata ◽  
K. Miyata ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Refractive Index ◽  
Supercritical Water ◽  
Metal Salt ◽  
High Surface ◽  
Functional Materials ◽  
High Refractive Index ◽  
High Thermal Conductivity ◽  
Base Catalysts ◽  
Supercritical Hydrothermal Synthesis

Various composite materials have been developed, but in many cases problems arise due to the combined materials such as fabrication becoming difficult because of the significant increase in viscosity, and transparency of the polymer is sacrificed. These issues can be overcome by controlling the nanointerface; however, this is considered as a difficult task since nanoparticles (NPs) easily aggregate in polymer matrices because of their high surface energy. Organic functionalization of inorganic NPs is required to increase affinity between NPs and polymers. For fabricating multi-functional materials, we proposed a new method to synthesize organic modified NPs by using supercritical water. Because organic molecules and metal salt aqueous solutions are miscible in supercritical water and water molecules serve as acid/base catalysts for the reactions, hybrid organic/inorganic NPs can be synthesized under the supercritical condition. The hybrid NPs show high affinity for the organic solvent and the polymer matrix, which leads to the fabrication of these super hybrid NPs. How to release the heat from the devices is the bottle neck of developing the future power devices, and thus nanohybrid materials of polymer and ceramics are required to achieve both high thermal conductivity and easy thin film flexible fabrication, namely trade-off functions. Surface modification of the BN particles via supercritical hydrothermal synthesis improves the affinity between BN and the polymers. This increases the BN loading ratio in the polymers, thus resulting in high thermal conductivity. Transparent dispersion of high refractive index NPs, such as TiO2 and ZrO2, in the polymers is required to fabricate optical materials. By adjusting the affinity between NPs and the polymers, we could fabricate super hybrid nanomaterials, which have flexiblility and high refractive index and transparency.

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