Porous silica-carbon composites and a method of producing the same

Abstract

Porous silica-carbon composites are obtained by mixing fine particulate carbon dispersed in water by a surfactant, alkali metal silicate aqueous solution, and mineral acid so as to produce co-dispersion in which silica hydrosol, produced by reaction of the alkali metal silicate and the mineral acid, and the fine particulate carbon are uniformly dispersed, and gelling silica hydrosol, contained in the co-dispersion, and making the co-dispersion into porous bodies. The porous silica-carbon composites are prepared so as to have specific surface area from 20 to 1000 m.sup.2/g, pore volume from 0.3 to 2.0 ml/g, and average pore diameter from 2 to 100 nm.

Claims

1. A method of producing porous silica-carbon composites, the method comprising: mixing fine particulate carbon dispersed in water by a surfactant, alkali metal silicate aqueous solution, and mineral acid so as to produce a co-dispersion in which silica hydrosol, produced by reaction of the alkali metal silicate and the mineral acid, and the fine particulate carbon are uniformly dispersed; and gelling the silica hydrosol, contained in the co-dispersion, and making the co-dispersion into porous bodies having specific surface area from 20 to 1000 m.sup.2/g, pore volume from 0.3 to 2.0 ml/g, and average pore diameter from 2 to 100 nm, wherein a carbon content of the porous silica-carbon composites is from 1 to 50%, wherein the porous silica carbon composite comprise fine particulate carbon dispersed inside a silica gel.

2. The method of producing porous silica-carbon composites according to claim 1 further comprising, subsequently to the step of making the co-dispersion into porous bodies, a step of calcining the porous bodies so as to remove the surfactant.

3. The method of producing porous silica-carbon composites according to claim 2, wherein the calcining is conducted within a range of temperature condition from 200 to 500° C. and calcining duration from 0.5 to 2 hours.

4. The method of producing porous silica-carbon composites according to claim 1, wherein the step of producing the co-dispersion is conducted such that the fine particulate carbon is added and mixed with one of the alkali metal silicate aqueous solution and the mineral acid, and subsequently added and mixed with the other one of the alkali metal silicate aqueous solution and the mineral acid.

5. The method of producing porous silica-carbon composites according to claim 1, wherein the step of producing the co-dispersion is conducted such that the alkali metal silicate aqueous solution and the mineral acid are mixed so as to obtain silica hydrosol, and the fine particulate carbon is subsequently added and mixed with the silica hydrosol.

Description

MODE FOR CARRYING OUT THE INVENTION

(1) The following describes embodiments of the present invention by way of example.

Embodiment 1

(2) 1.7 g of a non-ionic surfactant (product name: DISPARLON AQ-380, manufactured by Kusumoto Chemicals, Ltd.) and 10 g of carbon black (product name: VALCAN XC-72, manufactured by Cabot Corporation) were added to 35.5 g of deionized water and well agitated so as to obtain carbon-black dispersion solution.

(3) 12 g of dilute sulfuric acid (6 mol/L) and 78 g of sodium silicate with silica concentration 25% were mixed, and 100 g of silica sol was obtained, to which the above-described carbon-black dispersion solution was added and further well agitated.

(4) When the entire mixture became solid gel (hydrogel), the hydrogel was broken down approximately to a size of 1 cm.sup.3 and subjected to 5 times of batch cleaning with 1 L of deionized water.

(5) To the cleaned hydrogel, 1 L of deionized water was added, and the pH value was adjusted to 10 with aqueous ammonia. Heating was subsequently conducted at 85° C. for 8 hours. After solid-liquid separation took place, drying was conducted at 180° C. for 10 hours. In the present embodiment, calcining was additionally conducted at 350° C. for 2 hours in order to remove the surfactant. As a result, 26.8 g of porous silica-carbon composites was obtained. It is to be noted that calcining may be conducted if necessary, and whether or not to conduct calcining may be arbitrary determined.

(6) Values for the physical property of the sintered product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 530 m.sup.2/g, pore volume 0.58 ml/g, average pore diameter 4.3 nm, and carbon content by percentage 29.8% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

Embodiment 2

(7) A similar procedure was conducted as in Embodiment 1, except that 1.2 g of an anionic surfactant (product name: OROTAN SN, manufactured by The Dow Chemical Company) was used alternatively to the non-ionic surfactant. As a result, 26.8 g of porous silica-carbon composites was obtained.

(8) Values for the physical property of the sintered product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 327 m.sup.2/g, pore volume 0.90 ml/g, average pore diameter 11.0 nm, and carbon content by percentage 32.3% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

Embodiment 3

(9) A similar procedure was conducted as in Embodiment 1, except that 62 g of commercially available carbon-black dispersion solution (product name: LIONPASTE W-311N, manufactured by LION Corporation). As a result, 24.2 g of porous silica-carbon composites was obtained.

(10) Values for the physical property of the sintered product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 412 m.sup.2/g, pore volume 1.11 ml/g, average pore diameter 10.8 nm, and carbon content by percentage 23.8% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

Embodiment 4

(11) 1.7 g of a non-ionic surfactant (product name: DISPARLON AQ-380, manufacture by Kusumoto Chemicals Ltd.) and 8 g of carbon black (product name: VALCAN XC-72, manufactured by Cabot Corporation) were added to 64 g of deionized water and agitated. To this mixture, 80 g of sodium silicate No. 3 was added and well agitated so as to obtain a carbon-black dispersion solution.

(12) While 110 g of 1.25 mol/L dilute sulfuric acid was vigorously agitated, the carbon-black dispersion solution was gradually added so as to produce silica sol. The obtained silica sol was poured into an airtight container, heated at 80° C. for 3 hours, and hydrogel was obtained. The subsequent procedure was conducted in the same manner as in Embodiment 1, and 30.4 g of porous silica-carbon composites was obtained.

(13) Values for the physical property of the sintered product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 348 m.sup.2/g, pore volume 0.96 ml/g, average pore diameter 11.0 nm, and carbon content by percentage 24.9% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

Embodiment 5

(14) Although calcining was conducted at 350° C. for 2 hours in Embodiment 1, this calcining step was omitted and the other part of the procedure was conducted in the same manner as in Embodiment 1. As result, 28.4 g of porous silica-carbon composites was obtained.

(15) Values for the physical property of the non-fired product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 521 m.sup.2/g, pore volume 0.57 ml/g, average pore diameter 4.4 nm, and carbon content by percentage 31.2% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

Embodiment 6

(16) Although calcining was conducted at 350° C. for 2 hours in Embodiment 1, this calcining condition was changed so as to conduct the calcining step at 500° C. for hours, and the other part of the procedure was conducted in the same manner as in Embodiment 1. As a result, 19.5 g of porous silica-carbon composites was obtained.

(17) Values for the physical property of the sintered product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 492 m.sup.2/g, pore volume 0.56 ml/g, average pore diameter 4.6 nm, and carbon content by percentage 9.8% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

Embodiment 7

(18) 0.2 g of a non-ionic surfactant (product name: DISPARLON AQ-380, manufactured by Kusumoto Chemicals, Ltd.) and 1.0 g of carbon black (product name: VALCAN XC-72, manufactured by Cabot Corporation) were added to 35.5 g of deionized water and well agitated so as to obtain carbon-black dispersion solution. A similar procedure was conducted as in Embodiment 1, except that this carbon-black dispersion solution was used. As a result, 20.5 g of porous silica-carbon composites was obtained.

(19) Values for the physical property of the sintered product, obtained by nitrogen adsorption measurement, were as follows: specific surface area 273 m.sup.2/g, pore volume 1.13 ml/g, average pore diameter 16.4 nm, and carbon content by percentage 3.9% (measured by an elemental analyzer “Vario EL III” [manufactured by Elementar Analysensysteme GmbH]).

(20) [Conductive Property Evaluation]

(21) 0.1 g of PTFE powder (3 μm) was added, as a binder, to 0.9 g of each test powder obtained from Embodiment 1 to Embodiment 7, and mixed well with an agate mortar. Subsequently, a small amount of deionized water was added to each mixture and further mixed well.

(22) Each of the mixture was compressed and molded at 1100 kg/cm.sup.3 by a tablet molding dice having 10 mm in diameter, and then sufficiently dried on a hotplate set to 120° C. so as to obtain samples, each having 1.0 mm in thickness and 10.0 mm in diameter, for electrically-conductive property evaluation. The electrically-conductive property was evaluated by conductive property (S/cm) according to the four-point probe method by using a resistivity meter Loresta-GP (manufactured by Mitsubishi Chemical Analytech, Ltd.).

(23) Measurement results are shown in Table 1 presented below.

(24) TABLE-US-00001 TABLE 1 SPECIFIC CARBON ELECTRICAL SURFACE AREA PORE VOLUME CONTENT BY CONDUCTIVITY (m.sup.2/g) (ml/g) PERCENTAGE (%) (S/cm) EMBODIMENT 1 530 0.58 29.8 3.30 × 10.sup.−1 EMBODIMENT 2 327 0.90 32.3 2.76 × 10.sup.−1 EMBODIMENT 3 412 1.11 23.8 1.51 × 10.sup.−1 EMBODIMENT 4 348 0.96 24.9 2.13 × 10.sup.−1 EMBODIMENT 5 521 0.57 31.2 1.84 × 10.sup.−1 EMBODIMENT 6 492 0.56 9.8 2.99 × 10.sup.−2 EMBODIMENT 7 273 1.13 3.9 2.68 × 10.sup.−4

(25) As is clear from Table 1 shown above, the porous silica-carbon composites according to Embodiment 1 to Embodiment 7 exhibit high specific surface area, large pore volume, and high electrically-conductive properties.

(26) [Modifications]

(27) Although the above has described embodiments of the present invention, the present invention is not limited to one specific embodiment described above and may be carried out in various ways.

(28) The above-described embodiments have presented some examples wherein a non-ionic surfactant, an anionic surfactant, and commercially available carbon-black dispersion solution containing a surfactant are respectively used. However, the surfactant is not limited to these examples. Some other types of surfactant, for example, a cation surfactant or an ampholytic surfactant, may be alternatively used as long as the surfactant enables to disperse carbon, such as carbon black, which is hydrophobic and in the form of fine particulate, in water.

(29) Moreover, the above-described embodiments have presented some examples wherein calcining is conducted at specific calcining temperatures and for specific calcining duration. The calcining temperature and calcining duration, however, may be arbitrarily adjusted. It is to be noted that, since calcining at extremely high temperature for a long duration may negatively affect the physical property of end products (particularly the porosity), calcining temperature and duration are preferably selected within a range in which such negative influence is not created. The range that the inventors have confirmed by experiment is, for example, calcining temperature from 200 to 500° C. and calcining duration from 0.5 to 2 hours. In a case wherein calcining was conducted within this range, end products had good physical properties.

(30) It goes without saying that, in a case wherein a surfactant contained in end products does not cause problems, determination whether or not to include a calcining step can be arbitrarily made, and that the calcining step may be omitted as in the above-described Embodiment 5, for example.