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.

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 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.

scholarly journals New Trends in Bio-Based Aerogels

Pharmaceutics ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 449 ◽  
Author(s):  
Loredana Elena Nita ◽  
Alina Ghilan ◽  
Alina Gabriela Rusu ◽  
Iordana Neamtu ◽  
Aurica P. Chiriac
Keyword(s):  
Biomedical Applications ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Acoustic Properties ◽  
High Porosity ◽  
Natural Polymers ◽  
Flame Resistance ◽  
Strength Limit ◽  
Properties Of Materials

(1) Background: The fascinating properties of currently synthesized aerogels associated with the flexible approach of sol-gel chemistry play an important role in the emergence of special biomedical applications. Although it is increasingly known and mentioned, the potential of aerogels in the medical field is not sufficiently explored. Interest in aerogels has increased greatly in recent decades due to their special properties, such as high surface area, excellent thermal and acoustic properties, low density and thermal conductivity, high porosity, flame resistance and humidity, and low refractive index and dielectric constant. On the other hand, high manufacturing costs and poor mechanical strength limit the growth of the market. (2) Results: In this paper, we analyze more than 180 articles from recent literature studies focused on the dynamics of aerogels research to summarize the technologies used in manufacturing and the properties of materials based on natural polymers from renewable sources. Biomedical applications of these bio-based materials are also introduced. (3) Conclusions: Due to their complementary functionalities (bioactivity, biocompatibility, biodegradability, and unique chemistry), bio-based materials provide a vast capability for utilization in the field of interdisciplinary and multidisciplinary scientific research.

Synthesis of a Low-Density Copper Oxide Monolithic Aerogel Using Inorganic Salt Precursor

2011 ◽  
Vol 217-218 ◽  
pp. 1165-1169
Author(s):  
Yu Tie Bi ◽  
Hong Bo Ren ◽  
Lin Zhang
Keyword(s):  
Electron Microscopy ◽  
Copper Oxide ◽  
Inorganic Salt ◽  
Copper Chloride ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Low Density ◽  
High Porosity ◽  
Different Temperatures

Copper oxide monolithic aerogel was prepared by sol–gel method using inorganic salt as precursor, ethanol as the solvent, and propylene oxide as the gelation agent. Calcination of the as-prepared aerogels at different temperatures induced a phase change which resulted in the formation of a mesoporous copper oxide aerogels. Field emission scanning electron microscopy (FESEM), Highresolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller(BET) methods were used to characterize the as-prepared aerogels. The combined results indicated that the as-prepared CuO aerogel has high porosity, high surface area, and low density. The X-ray diffraction (XRD) patterns show that the as-prepared CuO aerogel is highly crystalline and is identified to be predominantly copper chloride hydroxide, Cu2Cl(OH)3。

Nitrogen functionalized hierarchical microporous/mesoporous carbon with a high surface area and controllable nitrogen content for enhanced lead(ii) adsorption

RSC Advances ◽  
2016 ◽  
Vol 6 (95) ◽  
pp. 92186-92196 ◽  
Author(s):  
Kunquan Li ◽  
Jinfan Cao ◽  
Hua Li ◽  
Jiamin Liu ◽  
Mingzhou Lu ◽  
...  
Keyword(s):  
Mesoporous Carbon ◽  
Phenol Formaldehyde ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Phenol Formaldehyde Resin ◽  
Formaldehyde Resin ◽  
Mesoporous Carbons ◽  
Lead Adsorption ◽  
Nitrogen Doped

Nitrogen-doped hierarchical microporous/mesoporous carbons (NHMCs) were conveniently fabricated for enhanced lead adsorption through a sol–gel method and NaOH-assisted activation with a soluble melamine–phenol–formaldehyde resin as a precursor.

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

Synthesis and structural characteristics of high surface area TiO2 aerogels by ultrasonic-assisted sol–gel method

2018 ◽  
Vol 29 (7) ◽  
pp. 075702 ◽  
Author(s):  
Feng Qingge ◽  
Cai Huidong ◽  
Lin Haiying ◽  
Qin Siying ◽  
Liu Zheng ◽  
...  
Keyword(s):  
Surface Area ◽  
Structural Characteristics ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Gel Method ◽  
Sol Gel Method ◽  
Ultrasonic Assisted

Texture Evaluation of Sol-Gel Derived Mesoporous Bioactive Glass

2013 ◽  
Vol 284-287 ◽  
pp. 230-234
Author(s):  
Yu Jen Chou ◽  
Chi Jen Shih ◽  
Shao Ju Shih
Keyword(s):  
Surface Area ◽  
Calcination Temperature ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Nitrogen Adsorption ◽  
Bioactive Glasses ◽  
Transmission Electron ◽  
Sol Gel Process ◽  
Adsorption Desorption

Recent years mesoporous bioactive glasses (MBGs) have become important biomaterials because of their high surface area and the superior bioactivity. Various studies have reported that when MBGs implanted in a human body, hydroxyl apatite layers, constituting the main inorganic components of human bones, will form on the MBG surfaces to increase the bioactivity. Therefore, MBGs have been widely applied in the fields of tissue regeneration and drug delivery. The sol-gel process has replaced the conventional glasses process for MBG synthesis because of the advantages of low contamination, chemical flexibility and lower calcination temperature. In the sol-gel process, several types of surfactants were mixed with MBG precursor solutions to generate micelle structures. Afterwards, these micelles decompose to form porous structures after calcination. Although calcination is significant for contamination, crystalline and surface area in MBG, to the best of the authors’ knowledge, only few systematic studies related to calcination were reported. This study correlated the calcination parameters and the microstructure of MBGs. Microstructure evaluation was characterized by transmission electron microscopy and nitrogen adsorption/desorption. The experimental results show that the surface area and the pore size of MBGs decreased with the increasing of the calcination temperature, and decreased dramatically at 800°C due to the formation of crystalline phases.

Highly stable metal-organic framework UiO-66-NH2 for high-performance triboelectric nanogenerators

2021 ◽  
Author(s):  
Yong-Mei Wang ◽  
Xinxin Zhang ◽  
Dingyi Yang ◽  
Liting Wu ◽  
Jiaojiao Zhang ◽  
...  
Keyword(s):  
High Performance ◽  
Metal Organic Framework ◽  
High Surface ◽  
High Surface Area ◽  
Triboelectric Nanogenerator ◽  
High Porosity ◽  
Chemically Modified ◽  
Metal Organic ◽  
Triboelectric Nanogenerators ◽  
Organic Framework

Abstract The high porosity, controllable size, high surface area, and chemical versatility of a metal-organic framework (MOF) enable it a good material for a triboelectric nanogenerator (TENG), and some MOFs have been incorporated in the fabrication of TENGs. However, the understanding of effects of MOFs on the energy conversion of a TENG is still lacking, which inhibits the improvement of the performance of MOF-based TENGs. Here, UiO-66-NH2 MOFs were found to significantly increase the power of a TENG and the mechanism was carefully examined. The electron-withdrawing ability of Zr-based UiO-66-family MOFs was enhanced by designing the amino functionalized 1,4-terephthalic acid (1,4-BDC) as ligand. The chemically modified UiO-66-NH2 was found to increase the surface roughness and surface potential of a composite film with MOFs embedded in polydimethylsiloxane (PDMS) matrix. Thus the total charges due to the contact electrification increased significantly. The composite-based TENG was found to be very durable and its output voltage and current were 4 times and 60 times higher than that of a PDMS-based TENG. This work revealed an effective strategy to design MOFs with excellent electron-withdrawing abilities for high-performance TENGs.

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