scholarly journals A New Synthetic Route to Organic Aerogels

1990 ◽  
Vol 180 ◽  
Author(s):  
R.W. Pekala ◽  
C.T. Alviso
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
Synthetic Route ◽  
Melamine Formaldehyde ◽  
Resorcinol Formaldehyde ◽  
Surface Areas ◽  
New Material ◽  
New Type ◽  
Organic Aerogel ◽  
Organic Aerogels

ABSTRACTThe aqueous, sol-gel polymerization of melamine with formaldehyde, followed by supercritical extraction, leads to the formation of a new type of organic aerogel. Synthetic conditions (e.g. reaction time, pH) affect the density, transparency, and microstructure of the resultant aerogels. Unlike previous organic aerogels based upon resorcinol-formaldehyde, the melamine-formaldehyde aerogels are both colorless and transparent. Low densities (0.1–0.8 g/cc), high surface areas (∼1000 m2/g), and optical clarity are only a few of the promising characteristics of this new material.

Imaging organic aerogels at the molecular level

1991 ◽  
Vol 49 ◽  
pp. 418-419
Author(s):  
G.C. Ruben ◽  
R.W. Pekala
Keyword(s):  
Pore Size ◽  
High Surface ◽  
Sol Gel ◽  
Acoustic Properties ◽  
Porous Solids ◽  
Dense Matrix ◽  
High Porosity ◽  
Microporous Material ◽  
Surface Areas ◽  
Organic Aerogels

The sol-gel polymerization of metal alkoxides or certain multifunctional organic monomers leads to 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, it is necessary to remove the the aforementioned solvent under supercritical conditions. The low density, microporous material that results from this operation is known as an aerogel. Aerogels have an ultrafine cell/pore size (< 500 Å), connected porosity, high surface areas (400-1000 m2/g), and an ultrastructure composed of interconnected colloidal-like particles or polymeric chains with characteristic dimensions of 100 Å. This ultrastructure is responsible for the unique optical, thermal, and acoustic properties of aerogels. For example, the ultrafine cell/pore size minimizes light scattering; and thus, aerogels are transparent porous solids. The high porosity of aerogels makes them excellent insulators with their thermal conductivity being approximately 100X lower than that of the fully dense matrix. Finally, the aerogel skeleton is responsible for the low sound velocities observed in these materials (i.e. 100-300 m/sec).

scholarly journals Investigating the Role of the Catalyst within Resorcinol–Formaldehyde Gel Synthesis

Gels ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 142
Author(s):  
Elisha Martin ◽  
Martin Prostredny ◽  
Ashleigh Fletcher
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
Initial Solution ◽  
Solution Ph ◽  
Gel Properties ◽  
Resorcinol Formaldehyde ◽  
Surface Areas ◽  
The Individual ◽  
The Relationship

Resorcinol–formaldehyde (RF) gels are porous materials synthesized via a sol–gel reaction and subsequently dried, producing structures with high surface areas and low densities—properties that are highly attractive for use in various applications. The RF gel reaction takes place in the presence of a catalyst, either acidic or basic in nature, the concentration of which significantly impacts final gel properties. The full extent of the catalyst’s role, however, has been subject to debate, with the general consensus within the field being that it is simply a pH-adjuster. The work presented here explores this theory, in addition to other theories postulated in the literature, through the synthesis and analysis of RF gels catalysed by mixtures of relevant compounds with varying concentrations. The relationship between catalyst concentration and initial solution pH is decoupled, and the individual roles of both the cation and the anion within the catalyst are investigated. The results presented here point towards the significance of the metal cation within the RF gel reaction, with similar structural properties observed for gels synthesized at constant Na+ concentrations, regardless of the initial solution pH. Furthermore, through the use of alternative cations and anions within catalyst compounds, the potential effects of ions on the stabilization of macromolecules in solution are explored, the results of which suggest a ‘Hofmeister-like’ series could be applicable within the catalysis of RF gel reactions.

scholarly journals Recent Trends in Covalent and Metal Organic Frameworks for Biomedical Applications

Nanomaterials ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 916 ◽  
Author(s):  
Georges Chedid ◽  
Ali Yassin
Keyword(s):  
Drug Delivery ◽  
Biomedical Applications ◽  
Materials Science ◽  
High Surface ◽  
Metal Organic Frameworks ◽  
Great Promise ◽  
Surface Areas ◽  
Metal Organic ◽  
New Type ◽  
Recent Trends

Materials science has seen a great deal of advancement and development. The discovery of new types of materials sparked the study of their properties followed by applications ranging from separation, catalysis, optoelectronics, sensing, drug delivery and biomedicine, and many other uses in different fields of science. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are a relatively new type of materials with high surface areas and permanent porosity that show great promise for such applications. The current study aims at presenting the recent work achieved in COFs and MOFs for biomedical applications, and to examine some challenges and future directions which the field may take. The paper herein surveys their synthesis, and their use as Drug Delivery Systems (DDS), in non-drug delivery therapeutics and for biosensing and diagnostics.

A General Nonhydrolytic Sol‐Gel Route to Oxides

1994 ◽  
Vol 346 ◽  
Author(s):  
Sylvie Acosta ◽  
Pascal Arnal ◽  
Robert J.P. Corriu ◽  
Dominique Leclercq ◽  
P. Hubert Mutin ◽  
...  
Keyword(s):  
Nucleophilic Substitution ◽  
High Surface ◽  
Sol Gel ◽  
Metal Center ◽  
Binary Oxides ◽  
Surface Areas ◽  
Sol Gel Process ◽  
Silica Alumina ◽  
The One ◽  
Oxygen Donors

ABSTRACTA nonhydrolytic sol‐gel route based on the condensation between chlorides and oxygen donors such as ethers and alkoxides is presented. Four examples, silica, alumina, titania and binary oxides in the Al/Si system show that this is a general route. The mechanism of this condensation is completely different from the one of classical sol‐gel process, since it implies nucleophilic substitution at the carbon center instead of the metal center. As a consequence, the differences in reactivity between different metals are reduced. In addition, the structure of the precursors may be retained in the gel. Thus, the nonhydrolytic sol‐gel process is very efficient for the preparation of homogeneous bicomponent oxides. Futhermore, nonhydrated gels are formed, which allowed us to prepare amorphous aluminas with high surface areas.

Preparation and Characterization of Phloroglucinol-Resorcinol-Formaldehyde Carbon Aerogels

2013 ◽  
Vol 423-426 ◽  
pp. 523-527
Author(s):  
Xuan Liu ◽  
Zhen Fa Liu ◽  
Hao Lin Fu ◽  
Rui He ◽  
Li Hui Zhang
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Sol Gel ◽  
High Specific Surface Area ◽  
Carbon Aerogels ◽  
Resorcinol Formaldehyde ◽  
Sol Gel Process ◽  
Solvent Replacement ◽  
Organic Aerogels

Phloroglucinol-resorcinol-formaldehyde organic aerogels (PRF) were prepared using phloroglucinol, resorcinol and formaldehyde in a sol-gel process, solvent replacement and drying at room temperature. The phloroglucinol-resorcinol-formaldehyde carbon aerogels (CPRF) were prepared by charring the PRF at high temperature under the aegis of helium flow. The microstructure of CPRF was characterized by infrared spectroscopy, specific surface area analyzer and scanning electron microscopy. The results showed that the CPRF had continuous network structure and high specific surface area.

Pyrolysis of Organosilicon Gels to Silicon Carbide

1986 ◽  
Vol 73 ◽  
Author(s):  
Joseph R. Fox ◽  
Douglas A. White ◽  
Susan M. Oleff ◽  
Robert D. Boyer ◽  
Phyllis A. Budinger
Keyword(s):  
Silicon Carbide ◽  
Surface Area ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Carbon Chain ◽  
Carbon Chain Length ◽  
Pyrolysis Products ◽  
Surface Areas ◽  
Physical Measurements

AbstractSol-gel precursors to silicon carbide have been prepared using trifunctional chloro and alkoxysilanes which contain both the silicon and carbon necessary for SiC formation. Crosslinked gels having the ideal formula [RSiO1 5].]n have been synthesized by a hydrolysis/condensation scheme for a series of saturated and unsaturated R groups. The starting gels have been characterized by a variety of elemental analysis, spectroscopic and physical measurements including IR. XRD. TGA.. surface area and pore volume. A particularly powerful method for characterizing these gels is the combination of 13C and 29 Si solid state NMR which can provide information about the degree of crosslinking as well as residual hydroxy/alkoxy content.The controlled pyrolysis of these gels has been used to prepare silicon carbide-containing ceramic products with surface areas in excess of 600m2/gm. The pyrolysis products are best described as a partially crystalline, partially amorphous mixture of β-SiC, silica and carbon. The effect of carbon chain length and the degree of unsaturation in the R group on the composition and surface area of the product has been determined. The origin of the high surface area of the pyrolysis products has been identified and its implications on potential uses of these materials is discussed.

Aryl-Bridged Polysilsesquioxanes - New Microporous Materials.

1990 ◽  
Vol 180 ◽  
Author(s):  
Kenneth J. Shea ◽  
Owen Webster ◽  
Douglas A. Loy
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
Refractive Indices ◽  
Surface Areas ◽  
New Family ◽  
Rigid Rod ◽  
Optical Applications ◽  
Degree Of Condensation ◽  
Gel Processing ◽  
Thermal Stability Of

ABSTRACTThe first representatives of a new family of microporous, aryl-bridged polysilsesquioxanes have been prepared by sol-gel processing of bis-1,4-(triethoxysilyl)benzene la, bis-4,4′- (triethoxysilyl)biphenyl 2a, bis-4,4′-(triethoxysilyl)terphenyl 3a, and bis-9,10-triethoxysilyl anthracene 4a. The bis(trichlorosilyl) analogs of la and 2a (lb and 2b, respectively) were also examined. The materials produced by hydrolysis and condensation of the monomers provide an opportunity to fully condense to a network with rigid-rod organic spacers interspaced at regular intervals in the silicate-like framework. The xerogels produced upon subsesquent processing of the gels have extremely high surface areas (256–1100 m2/g; BET) with porosities confined to the micropore domain (< 200 nm). Solid state (CP MAS) 13C and 29Si NMR were used to evaluate the extent of hydrolysis and degree of condensation in the xerogels. The porosity and thermal stability of the aryl bridged polysilsesquioxanes may lead to applications as chromatographic absorbents. The transparent materials may also have optical applications arising from both the gels′ high refractive indices and the covalent incorporation of ultraviolet chromophores.

Porous Solids of Boron Phosphate, Aluminum Phosphate, and Silicon Phosphate

1994 ◽  
Vol 371 ◽  
Author(s):  
K. B. Babb ◽  
D. A. Lindquist ◽  
S. S. Rooke ◽  
W. E. Young ◽  
M. G. Kleve
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Total Pore Volume ◽  
Aluminum Phosphate ◽  
Porous Solids ◽  
Gel Point ◽  
Average Pore ◽  
Average Pore Radius ◽  
Surface Areas

AbstractAnhydrous sol-gel condensation of triethyl phosphate [(CH3CH2O)3PO] with boron trichioride (BCl3), triethyl aluminum [(CH3CH2)3Al] or silicon tetrachloride [SiCI4] in organic solvents led to rigid gels. The pore fluid of the gels was removed under supercritical conditions in a pressurized vessel to form porous solids. The condensation chemistry prior to the gel point was monitored by solution 1H, 13C, 31P, and 11B NMR. The materials were then calcined at progressively higher temperatures to produce high surface area phosphates. Nitrogen gasphysisorption was used to determine the surface areas, total pore volume, and average pore radius of the products. FT-IR was used to determine functional groups in the materials. The microstructure was also examined by scanning electron microscopy.

Mesoporous Ordered Organosilicas Containing Zr and Ti Species

2010 ◽  
Vol 163 ◽  
pp. 55-58
Author(s):  
M. Zienkiewicz ◽  
Stanislaw Pikus ◽  
E. Olszewska ◽  
M. Barczak
Keyword(s):  
Photoelectron Spectroscopy ◽  
High Surface ◽  
Sol Gel ◽  
Titanium Isopropoxide ◽  
Inorganic Materials ◽  
Isomorphous Substitution ◽  
Periodic Mesoporous Organosilica ◽  
Structure Directing Agent ◽  
Surface Areas ◽  
Bridging Groups

Periodic mesoporous organosilica materials (PMOs) are the new class of porous and hybrid organic-inorganic materials. They represent exceptional and functional bridged polysilsesquioxanes prepared by sol-gel processing of monomers using triblock copolymers or ionic surfactants as the structure directing agents. By changing the monomer type, various organic functional groups may be incorporated into the framework of PMO materials. Moreover it is possible to introduce heteroatoms in the structure of mesoporous materials via isomorphous substitution of the silicon atoms. In the present study, we report the preparation and characterization of the series of zirconium, titanium and mixture of them, doped mesoporous silica. The PMOs have been synthesized by the hydrolysis and the condensation of bridged silsesquioxane precursors containing two different organic bridging groups ((R’)3Si-CH2-CH2-Si(R’)3, R’ - methoxy or ethoxy). The influence of temperature of synthesis on the structure of PMOs was examined. PMO-Zr and PMO-Zr-Ti were synthesized by employing a zirconyl chloride octahydrate (ZrOCl2•8H2O), titanium isopropoxide, NaCl, bis(trimethoxysilyl)ethane (BTME) as a silica source and triblock copolymer P123 as the structure directing agent while PMO-Ti was prepared using 1,2-bis(triethoxysilyl)ethane (BTESE), titanium isopropoxide, NaOH and cetyltrimethylammonium bromide (CTABr) as a structure directing agent. The resulting materials exhibited well-ordered two-dimensional hexagonal space group p6mm, high surface areas in the range of 700-1100 m2/g. The X-ray photoelectron spectroscopy (XPS) analysis indicated the successful incorporation of heteroatoms into hybrid PMOs and the IR spectra confirmed satisfactory removal of the surfactants.

ChemInform Abstract: Fast Sol-Gel Synthetic Route to High-Surface-Area Alumina Aerogels.

ChemInform ◽  
2010 ◽  
Vol 28 (48) ◽  
pp. no-no
Author(s):  
D. J. SUH ◽  
T.-J. PARK ◽  
J.-H. KIM ◽  
K.-L. KIM
Keyword(s):  
Surface Area ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Synthetic Route ◽  
Alumina Aerogels
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