scholarly journals Characterization of carbon cryogels synthesized by sol-gel polycondensation

2005 ◽  
Vol 70 (1) ◽  
pp. 21-31 ◽  
Author(s):  
Biljana Babic ◽  
Divna Djokic ◽  
Nedeljko Krstajic
Keyword(s):  
Specific Capacitance ◽  
Linear Dependence ◽  
Sol Gel ◽  
Nitrogen Adsorption ◽  
Inert Atmosphere ◽  
Square Root ◽  
Surface Areas ◽  
Wide Range ◽  
Scan Rate ◽  
Hclo4 Solution

Resorcinol-formaldehyde (RF) cryogels were synthesized by the sol-gel polycondensation of resorcinol (R) with formaldehyde (F) and freeze-drying was carried out with t-butanol. Carbon cryogels were obtained by pyrolyzing RF cryogels in an inert atmosphere. Characterization by nitrogen adsorption showed that the carbon cryogels were micro and mesoporous materials with high specific surface areas (SBET ? 550 m2/g). Cyclic voltammeter experiments at various scan rates (2 to 200 mV s-1) were performed to study the electrical double-layer charging of carbon cryogel electrodes in 0.5 mol dm-3 HClO4 solution. It has been demonstrated that it is possible to sub-divide the total specific capacitance into the mesoporous and the microporous specific capacitance by analyzing the linear dependence of the charge (q) on the reciprocal of the square root of the potential scan rate (?-1/2), and the linear dependence of the reciprocal charge (1/q) on the square root of the potential scan rate (?-1/2). The specific capacitance was found to be constant over a wide range of sample weight (12.5 to 50.0 _g) and a very promising specific capacitance value of 150 F/g, was found for this material operating in an acidic 0.5 mol dm-3 HClO4 solution at room temperature.

Characterization of Carbon Cryogel Synthesized by Sol-Gel Polycondensation and Freeze-Drying

2005 ◽  
Vol 494 ◽  
pp. 327-332 ◽  
Author(s):  
B. Babić ◽  
B. Kaludjerović ◽  
D. Djokić ◽  
N. Krstajić
Keyword(s):  
Specific Capacitance ◽  
Linear Dependence ◽  
Freeze Drying ◽  
High Surface ◽  
Sol Gel ◽  
Nitrogen Adsorption ◽  
Inert Atmosphere ◽  
Square Root ◽  
Scan Rate ◽  
Carbon Cryogel

Resorcinol-formaldehyde (RF) cryogels were synthesized by sol-gel polycondensation of resorcinol with formaldehyde and freeze-drying carried out with t-butanol. Carbon cryogels were obtained by pyrolyzing RF cryogels in an inert atmosphere. Characterization by nitrogen adsorption showed that carbon cryogels were micro- and mesoporous materials with high surface areas (500 m2/g< SBET <700 m2/g). Cyclic voltammetry experiments at various scan rates (2 to 200 mV s-1) were carried out to study the electrical double-layer charging of carbon cryogel electrodes in 0.5 mol dm-3 HClO4 solution. It has been demonstrated that the total specific capacitance can further be divided into mesoporous and microporous specific capacitance by analyzing the linear dependence of the specific capacitance (C) on the reciprocal of the square root of the potential scan rate ( ν -1/2), as well as linear dependence of the reciprocal specific charge (1/C) on the square root of the potential scan rate ( ν 1/2).

Low-Cost Preparation of SBA-15 Silica Molecular Sieve and High Humidity Sensing Property in a Wide Range of Relative Humidity

2016 ◽  
Vol 852 ◽  
pp. 1455-1462
Author(s):  
Jie Zhang ◽  
Yong Heng Zhu ◽  
Shi Zao Kang ◽  
Xiang Qing Li ◽  
Jia Qiang Xu
Keyword(s):  
Relative Humidity ◽  
Molecular Sieves ◽  
Low Cost ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Nitrogen Adsorption ◽  
Fast Response ◽  
Humidity Sensing ◽  
Wide Range

In this paper, different SBA-15 molecular sieves were prepared in a facile sol-gel method by using a low-cost sodium silicate as silicon source at different ripening temperature. The materials were characterized by small-angle XRD, TEM, nitrogen adsorption–desorption test. The results showed that ripening temperature can affect the pore size and mesostructure of SBA-15. High surface area SBA-15 can be obtained at low ripening temperature, and plugged mesostructure can be prepared at high temperature. The gravimetric humidity sensing property of the materials were tested based on a transducer of quartz crystal microbalance. The test results revealed that all the samples showed high response in the wide range of relative humidity. The sensors based on that prepared at 35°C show a good stability and linearity in the range of 11.3%RH to 98%RRH along with fast response (12s) and recovery time (8s), ultrahigh sensitivity and low hysteresis, implying that has a great potential for humidity detection.

Preparation and Characterization of RF/SiO2 Hybrid Aerogel by Sol-Gel Method

2006 ◽  
Vol 11-12 ◽  
pp. 619-622 ◽  
Author(s):  
Xiao Hong Chen ◽  
Shuang Xi Yang ◽  
Huai He Song
Keyword(s):  
Raw Materials ◽  
Sol Gel ◽  
Nitrogen Adsorption ◽  
Ethanol Solution ◽  
Raw Material ◽  
Step Method ◽  
Wide Range ◽  
Hybrid Aerogels ◽  
Adsorption Desorption ◽  
Hybrid Aerogel

A novel organic and inorganic hybrid aerogel of RF/SiO2 is synthesized by one-step method of sol-gel polycondensation reaction using resorcinol-formaldehyde and tetramethoxysilane (TMOS) in ethanol solution, followed by supercritical drying with petroleum ether. The influence of the ratio of raw material on the structure and properties of samples was studied by high resolution electron microscope (HREM), nitrogen adsorption-desorption and infrared ray technology (IR). The results showed that the network structures of RF/SiO2 hybrid aerogels were constituted by an intercross framework of RF and SiO2. The hybrid aerogels can be tuned in bulk density from 0.098 g/cm3 to 0.062 g/cm3 according to the ratio of raw materials. The data of nitrogen adsorption-desorption showed that BET specific surface area was changed from 254 cm2/g to 545 cm2/g, and the pore size of aerogels was in the wide range of 2-10 nm. The investigation of IR spectrum analysis exhibited that there were no chemical bonds formed between SiO2 and RF aerogel.

scholarly journals Comparison of Mercury Intrusion and Nitrogen Adsorption Measurements for the Characterization of Certain Natural Raw Materials Deposits

2010 ◽  
Vol 7 (1) ◽  
pp. 621-630
Author(s):  
Baghdad Science Journal
Keyword(s):  
Pore Size ◽  
Gas Adsorption ◽  
Raw Materials ◽  
Mercury Porosimetry ◽  
Construction Materials ◽  
Nitrogen Adsorption ◽  
Distribution Data ◽  
Active Components ◽  
Surface Areas ◽  
Wide Range

The porosity of materials is important in many applications, products and processes, such as electrochemical devices (electrodes, separator, active components in batteries), porous thin film, ceramics, soils, construction materials, ..etc. This can be characterized in many different methods, and the most important methods for industrial purposes are the N2 gas adsorption and mercury porosimetry. In the present paper, both of these techniques have been used to characterize some of Iraqi natural raw materials deposits. These are Glass Sand, Standard Sand, Flint Clay and Bentonite. Data from both analyses on the different types of natural raw materials deposits are critically examined and discussed. The results of specific surface areas showed considerable difference between the two sets of data on the same material. This indicates that the material have an external surface which can not be measure by mercury porosimeter. Also pore size distribution data obtained from N2 adsorption measurements shows a wide range of the smallest pore size. This result suggests that materials have micropores using IUPAC definitions of pore size.

Low-Temperature Synthetic Route for Boron Carbide Powder from Boric Acid-Citric Acid Gel Precursor

2007 ◽  
Vol 555 ◽  
pp. 255-260 ◽  
Author(s):  
Dj. Kosanović ◽  
Lj. Milovanović ◽  
S. Milovanović ◽  
A. Šaponjić
Keyword(s):  
Citric Acid ◽  
Boron Carbide ◽  
Boric Acid ◽  
Structural Information ◽  
Sol Gel ◽  
Nitrogen Adsorption ◽  
Carbide Powder ◽  
Composite Powders ◽  
Surface Areas ◽  
Acid Gel

Boron carbide powder was synthesized by sol-gel polycondensation of boric acid with citric acid. The starting materials of Serbian origin were dissolved in water and mixed homogeneously until a precomposite gel was formed, which was converted into cryogels after freeze-drying. Pyrolysing and subsequent heat treatment of these cryogels resulted in boron carbide materials. Characterization by nitrogen adsorption showed that the precomposite cryogels and the composite powders were micro and mesoporous materials with large surface areas. Materials have been analyzed by means of X-ray diffraction and scanning electron microscopy. The Rietveld refinement was employed to get the structural information of the synthesized powder. The results show that the obtained carbide powder is composed of nearly equiaxed particles of narrow size distribution.

scholarly journals Enhanced Photocatalytic Activity of Hierarchical Macro-Mesoporous Anatase byZrO2Incorporation

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
M. L. García-Benjume ◽  
M. I. Espitia-Cabrera ◽  
M. E. Contreras-García
Keyword(s):  
Photocatalytic Activity ◽  
Sol Gel ◽  
Nitrogen Adsorption ◽  
Mesoporous Structure ◽  
Tween 20 ◽  
X Ray Diffraction ◽  
Surface Areas ◽  
Photocatalytic Effect ◽  
Different Temperatures ◽  
Adsorption Desorption

The effect of the addition of zirconia in the photocatalytic behaviour of titania is analysed. In order to increase the ways for reagent and product diffusion in the material, a sol-gel hydrothermal synthesis route using Tween-20 as a directing agent to obtain a hierarchical macro-mesoporous structure is proposed. Nanostructured macro-mesoporous TiO2/ZrO2photocatalyst with 0, 10, 20, 30, and 100% mol of ZrO2were obtained and calcined at different temperatures. The crystalline structure was analyzed by X-ray diffraction and TEM. The porosity was confirmed by SEM, TEM, and nitrogen adsorption-desorption isotherms. The worm-like mesoporous structure was confirmed by TEM. The specific surface areas obtained by Brunauer-Emmet-Teller method (BET) ranged from 125 to 180 m2/g. The Tween-20 total elimination from the structure by thermal treatment was confirmed by infrared spectroscopy and thermogravimetric analysis. Additionally, the photocatalytic effect of the zirconia addition was studied in the methylene blue (MB) degradation reaction, and the best photocatalytic activity was obtained in the sample with 10% mol of ZrO2, degrading up to 92% the MB.

Heterogeneous Interactions of Methylamines on Porous Adsorbents. Part I. The Adsorption of Monomethylamine on Silica Gels and Silica–Alumina

1972 ◽  
Vol 50 (11) ◽  
pp. 1666-1674 ◽  
Author(s):  
W. G. Cook ◽  
R. A. Ross
Keyword(s):  
Nitrogen Adsorption ◽  
Silica Gels ◽  
Heats Of Adsorption ◽  
Surface Areas ◽  
Pore Size Distributions ◽  
Wide Range ◽  
Heat Curve ◽  
Silica Alumina ◽  
Adsorption Heats ◽  
Adsorption Desorption

The adsorption of monomethylamine has been studied near its boiling point, 266 °K, on silica–alumina and on a wide range of silica gels by measurement of adsorption–desorption isotherms and isothermal calorimetric heats of adsorption. In addition, surface areas and pore-size distributions have been determined by low-temperature nitrogen adsorption. Heats of adsorption on Davison "923" silica gel varied from around 33.0 kcal/mol at θ = 0.01 to 6.2 kcal/mol at monolayer completion. Maxima were observed in this heat curve in the regions of θ = 0.15, 0.28, and 0.40. These phenomena are believed to be related to interactions among the adsorbed species in pores of diameters approaching molecular dimensions. Heats of adsorption on silica–alumina fell smoothly from 39.5 kcal/mol at θ = 0.03 to 13.0 kcal/mol at θ = 1.00. Adsorption–desorption characteristics of methylamine were also examined on a series of silica gels with widely different pore structures. The variations in the heats of adsorption with surface coverage are discussed in terms of both the nature of the adsorbed surface species and lateral interactions among the adsorbed molecules.

Low-Density Microcellular Carbon Materials

MRS Bulletin ◽  
1990 ◽  
Vol 15 (12) ◽  
pp. 37-40
Keyword(s):  
Heat Treatment ◽  
Phenol Formaldehyde ◽  
Sol Gel ◽  
Carbon Foam ◽  
Inert Atmosphere ◽  
Surface Areas ◽  
Treatment Conditions ◽  
Low Thermal Expansion ◽  
Carbon Foams ◽  
Technology Applications

The low atomic number, good chemical reistance, and low thermal expansion of carbon foams make them attractive for many specialty applications. In general, we are interested in carbon LDMMs that have a maximum cell size of 25 μm and densities less than 0.05 g/cm3. These requirements are beyond the state of the art for most commercial carbon foams; thus, the DOE National Laboratories have concentrated on producing materials that meet these demanding requirements using various phase-separation, sol-gel, and replication processes.In all cases, the final carbon foam is derived from a polymer precursor. Most polymers (e.g., polymethyl methacrylate) simply depolymerize and revert to their monomeric form when heated to high temperatures in an inert atmosphere. Cross-linked phenol-formaldehyde and polyfurfuryl alcohol are polymers that leave substantial carbon chars (greater than 50 wt%) after pyrolysis near 1000°C. Polyacrylonitrile also leaves a large carbon char (˜40 wt%)) after partial oxidation at 200°C followed by heat treatment at 1000°C. The latter char is a partially ordered graphite while the former chars are totally amorphous.The microstructure and properties of carbon LDMMs depend on synthetic procedure and heat treatment conditions. We have been able to make carbon LDMMs with cell sizes as small as 100 Å or with densities as low as 0.015 g/cm3. Furthermore, surface areas of 50–1000 m2/g have been obtained with microstructures ranging from ribbonlike webs to interconnected colloidal-like particles. The ability to control these various parameters presents new opportunities to design carbon LDMMs for high technology applications, examples of which include sensors, electrodes, and high temperature filters.

scholarly journals Surface Studies on Glass Powders Used in Commercial Glass-Ionomer Dental Cements

Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5279
Author(s):  
Agata Wawrzyńczak ◽  
Jacek Kłos ◽  
Izabela Nowak ◽  
Beata Czarnecka
Keyword(s):  
Thermogravimetric Analysis ◽  
Specific Surface ◽  
Inert Atmosphere ◽  
Water Binding ◽  
Surface Areas ◽  
Wide Range ◽  
Powder Mass ◽  
Commercial Glass ◽  
Textural Parameters ◽  
Glass Powders

The surface properties of three commercial ionomer glass powders, i.e., Fuji IX, Kavitan Plus and Chemadent G-J-W were studied. Samples were analyzed by X-ray fluorescence spectroscopy (XRF), and the density was determined by gas pycnometry. Morphology was studied using scanning electron microscopy (SEM) and laser diffraction (LD) technique, whereas low-temperature nitrogen sorption measurements determined textural parameters like specific surface area and pore volume. Thermal transformations in the materials studied were evaluated by thermogravimetric analysis (TGA), which was carried out in an inert atmosphere between 30 °C and 900 °C. XRF showed that Fuji IX and Kavitan Plus powders were strontium-based, whereas Chemadent G-J-W powder was calcium-based. Powders all had a wide range of particle sizes under SEM and LD measurements. Specific surface areas and pore volumes were in the range 1.42–2.73 m2/g and 0.0029 to 0.0083 cm3/g, respectively, whereas densities were in the range 2.6428–2.8362 g/cm3. Thermogravimetric analysis showed that the glass powders lost mass in a series of steps, with Fuji IX powder showing the highest number, some of which are attributed to the dehydration and decomposition of the polyacrylic acid present in this powder. Mass losses were more straightforward for the other two glasses. All three powders showed distinct losses at around 780 °C and 835 °C, suggesting that similar dehydration steps occur in all these glasses. Other steps, which differed between glass powders, are attributed to variations in states of water-binding on their surfaces.

PORE STRUCTURES AND SURFACE AREAS OF HARDENED PORTLAND CEMENT PASTES BY NITROGEN ADSORPTION

1964 ◽  
Vol 42 (2) ◽  
pp. 426-438 ◽  
Author(s):  
R. Sh. Mikhail ◽  
L. E. Copeland ◽  
Stephen Brunauer
Keyword(s):  
Portland Cement ◽  
Pore Space ◽  
Nitrogen Adsorption ◽  
Type I ◽  
Pore System ◽  
Hydraulic Radius ◽  
Cement Ratio ◽  
Surface Areas ◽  
Water To Cement Ratio ◽  
Wide Range

The investigations were performed on five hardened pastes of a type I (normal) portland cement, having initial weight ratios of water to cement of 0.35, 0.40, 0.50, 0.57, and 0.70, and hydrated for 12, 12, 12, [Formula: see text], and [Formula: see text] years, respectively. The percentage hydration ranged from 90 to 98%.Nitrogen adsorption and desorption isotherms were determined for all pastes at the boiling point of nitrogen, from low pressures to almost the saturation pressure. The BET surface areas were calculated, and the pore space accessible to nitrogen was obtained by a slight extrapolation of the isotherms. In addition, pore structure analysis was made for three of the five pastes by the method of Cranston and Inkley.The specific surface areas of the five pastes were also determined by water vapor adsorption, and the total porosity to water was measured. For every paste, the water areas and porosities were greater than the nitrogen areas and porosities.The main conclusions from the results were as follows.(1) There is a wide range of pore sizes in the pastes.(2) Nitrogen is excluded from a part of the pore system by two mechanisms; some of the pores are too narrow and others have too narrow entrances to admit nitrogen.(3) The hydraulic radius (the volume of the pore system divided by the surface area of the pore walls) for the system of small pores increases with increasing water to cement ratio.(4) The hydraulic radius of the system of large pores also increases with increasing water to cement ratio, but the increase is smaller than for the small pores.(5) The paste with water to cement ratio of 0.35 has enough pore space for complete hydration.Some practical implications of the above conclusions are discussed.

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