Method for recovering carbon nanomaterial in dispersion liquid

Abstract

The invention provides a method for recovering a carbon nanomaterial in a dispersion liquid, which comprises the following steps: mixing a carbon nanomaterial dispersion liquid dispersed by an ionic surfactant and an ionic material with the electrical property opposite to that of the ionic surfactant to flocculate the carbon nanomaterial to obtain a flocculated dispersion system; and carrying out solid-liquid separation, cleaning and drying on the flocculated dispersion system to obtain the carbon nanomaterial. According to the method provided by the invention, the carbon nanomaterial in the dispersion liquid is flocculated to form large particles, recovery can be realized through solid-liquid separation of a physical means, additional addition of an auxiliary reagent is not needed, the method is simple, the separation effect is good, and the problem that the carbon nanomaterial is difficult to directly realize recovery through solid-liquid separation is solved; the recovery rate of the carbon nanomaterial reaches 90% or above, and great economic benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterials and relates to a method for recovering nanomaterials, in particular to a method for recovering carbon nanomaterials in a dispersion. Background Art

[0002] Carbon nanomaterials, with their excellent mechanical, electrical and thermal properties, have shown wide application potential in composite materials, new energy batteries, hydrogen storage materials, supercapacitors, biomedicine and other fields. However, nanomaterial powders need to be evenly dispersed before use to fully exert their excellent performance, but problems also arise. Once these dispersions are discarded in the environment at will, it will not only cause environmental pollution, but also be a huge waste of carbon nanomaterials. Therefore, there is an urgent need for an efficient method for separating carbon nanomaterials from carbon nanomaterial dispersions to achieve the recovery and reuse of carbon nanomaterials and promote the sustainable use of resources.

[0003] The most direct methods for separating solid materials from liquid materials are centrifugal technology and filtration technology. Centrifugal technology uses the strong centrifugal force generated when an object rotates at high speed to cause the suspended particles placed in the rotating body to settle or float, so that some particles can be concentrated or separated from other particles. However, the uniformly dispersed carbon nanomaterials are small in size, and it is difficult for the centrifuge to completely separate the carbon nanoparticles from the liquid. There are still a lot of carbon nanomaterials remaining in the upper clear liquid, and the stably dispersed carbon nanomaterials require a long time during the centrifugation process, which consumes a lot of energy and has low efficiency. The filtration technology is to filter the dispersed liquid through filter paper or membrane filter, but the uniformly dispersed carbon nanomaterials are small in size, and filter paper or filter membrane with extremely small porosity is required for filtration. A small amount of nanomaterials will still penetrate when using 0.45μm filter paper for filtration. In addition, carbon nanomaterials are easy to block the pores on the filter paper, resulting in low filtration efficiency. Therefore, the filtration method requires frequent replacement of filter paper or membrane filter, which increases the difficulty of operation.

[0004] Therefore, based on the deficiencies of the prior art, the present invention provides a method for recovering carbon nanomaterials in a dispersion. Summary of the invention

[0005] The purpose of the present invention is to provide a method for recovering carbon nanomaterials in a dispersion liquid, so as to solve the problem that the carbon nanomaterials in the carbon nanomaterial dispersion liquid are small in size and difficult to separate, and to realize the recovery and reuse of the carbon nanomaterials.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for recovering carbon nanomaterials in a dispersion, the method comprising the following steps:

[0008] (1) mixing a carbon nanomaterial dispersion treated with an ionic surfactant and an ionic material having an electrical property opposite to that of the ionic surfactant to flocculate the carbon nanomaterial to obtain a flocculated dispersion system;

[0009] (2) The flocculated dispersion system is subjected to solid-liquid separation, washing, and drying to obtain carbon nanomaterials.

[0010] The method provided by the present invention destroys the double electron layer structure formed by the ionic surfactant in the dispersed system by adding ionic materials with opposite electrical properties into the dispersed liquid, breaks the stability of the ionic surfactant in the dispersed system, causes the nanomaterial to flocculate and form large particles, so that the carbon nanomaterial in the dispersed system can be recovered by solid-liquid separation through physical means without the need to add additional auxiliary reagents. The method is simple and has good separation effect, thus solving the problem that the carbon nanomaterial is difficult to recover directly by solid-liquid separation.

[0011] Preferably, the carbon nanomaterial in the carbon nanomaterial dispersion in step (1) includes any one of graphene, graphene oxide, carbon nanotubes, carbon black or fullerene, or a combination of at least two of them. Typical but non-limiting combinations include a combination of graphene and carbon nanotubes, a combination of carbon nanotubes and carbon black, a combination of carbon black and fullerenes, a combination of graphene, carbon nanotubes and carbon black, or a combination of carbon nanotubes, carbon black and fullerenes.

[0012] Preferably, the ionic surfactant in step (1) comprises an anionic surfactant.

[0013] Preferably, the anionic surfactant includes any one of sulfonates, sulfates, carboxylates, phosphates, amino acid salts, phenolates, enolates, ketosulfonamides or coordinated anion salts, or a combination of at least two thereof.

[0014] Preferably, the anionic surfactant includes any one of dodecyl sulfonic acid, sodium dodecylbenzene sulfonate, lignin sulfonate, sodium cellulose or sodium fatty alcohol polyoxyethylene ether sulfate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of dodecyl sulfonic acid and lignin sulfonate, a combination of sodium dodecylbenzene sulfonate and sodium cellulose, a combination of sodium cellulose and sodium fatty alcohol polyoxyethylene ether sulfate, a combination of sodium dodecylbenzene sulfonate, lignin sulfonate and sodium cellulose, or a combination of lignin sulfonate, sodium cellulose and sodium fatty alcohol polyoxyethylene ether sulfate.

[0015] Preferably, the ionic material in step (1) comprises a cationic surfactant.

[0016] Preferably, the cationic surfactant comprises any one or a combination of at least two of an amine salt type cationic surfactant, a chlorinated type cationic surfactant or a bromide type cationic surfactant.

[0017] Preferably, the cationic surfactant includes any one of cetyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, cetyltrimethylammonium chloride or didodecyldimethylammonium chloride, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of cetyltrimethylammonium bromide and dodecyldimethylbenzylammonium chloride, a combination of dodecyldimethylbenzylammonium chloride and cetyltrimethylammonium chloride, a combination of cetyltrimethylammonium chloride and didodecyldimethylammonium chloride, a combination of cetyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride and cetyltrimethylammonium chloride, or a combination of dodecyldimethylbenzylammonium chloride, cetyltrimethylammonium chloride and didodecyldimethylammonium chloride.

[0018] Preferably, the molar ratio of the ions in the ionic surfactant of step (1) to the ions with opposite charge in the ionic material is 1:(0.5-1.5), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, preferably 1:(0.8-1.3), and more preferably 1:(0.9-1.1).

[0019] Preferably, in the flocculated dispersion system of step (1), the particle size of the carbon nanomaterial particles is not less than 200 μm, for example, it can be 200 μm, 225 μm, 250 μm, 275 μm, 300 μm, 400 μm or 500 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Preferably, the solid-liquid separation method in step (2) comprises centrifugation and / or filtration.

[0021] Preferably, the centrifugal rotation speed is 50-10000r / min, for example, it can be 50r / min, 100r / min, 300r / min, 500r / min, 800r / min, 1000r / min, 2000r / min, 3000r / min, 4000r / min, 5000r / min, 8000r / min or 10000r / min, preferably 100-5000r / min, and more preferably 100-1000r / min.

[0022] Preferably, the centrifugation time is 1-10 min, for example, it can be 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, preferably 2-8 min, and more preferably 3-5 min.

[0023] Preferably, the mesh number of the filtration is not less than 80 mesh, for example, it can be 80 mesh, 100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, 350 mesh, 400 mesh or 500 mesh, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably a filter material of 200-400 mesh.

[0024] Preferably, the cleaning method comprises: adding deionized water to the solid obtained by solid-liquid separation, and then performing centrifugation and / or suction filtration.

[0025] Preferably, the cleaning is repeated 2-6 times, for example, 2 times, 3 times, 4 times, 5 times or 6 times, preferably 3-4 times.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The method provided by the present invention flocculates the carbon nanomaterial in the dispersion to form large particles, which can be recovered by solid-liquid separation through physical means without the need to add additional auxiliary reagents. The method is simple and has good separation effect, which solves the problem that carbon nanomaterials are difficult to recover directly through solid-liquid separation. The recovery rate of carbon nanomaterials reaches more than 90%, which has great economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a rendering of the operating process of the method for recovering carbon nanomaterials in a dispersion provided in Example 1. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0030] Example 1

[0031] This embodiment provides a Figure 1 A method for recovering carbon nanomaterials from a dispersion shown.

[0032] In this embodiment, carbon nanotubes and anionic surfactant sodium dodecylbenzene sulfonate are added to water for dispersion to obtain a carbon nanotube dispersion. In the carbon nanotube dispersion, the concentration of carbon nanotubes is 20 g / L, and the mass ratio of the anionic surfactant to the carbon nanotubes is 0.5:1.

[0033] The recovery method comprises the following steps:

[0034] (1) adding a cationic surfactant cetyltrimethylammonium bromide to the carbon nanotube dispersion, wherein the molar ratio of the cation of the cationic surfactant to the anion of the anionic surfactant is 1:1, and gently shaking the mixture to make it uniform and then letting it stand for 10 minutes until the dispersion flocculates, thereby obtaining a flocculated dispersion system;

[0035] (2) Filter the obtained dispersion system on a 300-mesh filter cloth to obtain a carbon nanotube flocculation liquid, add deionized water to the carbon nanotube flocculation liquid, let it stand for 2-3 minutes, and then filter it again. Repeat this cycle of cleaning for 4 times to obtain a carbon nanotube flocculation liquid, which is then dried to obtain carbon nanotubes.

[0036] Example 2

[0037] This embodiment provides a method for recovering carbon nanomaterials in a dispersion.

[0038] In this embodiment, carbon nanotubes and anionic surfactant sodium cellulose are added to water for dispersion to obtain a carbon nanotube dispersion. In the carbon nanotube dispersion, the concentration of carbon nanotubes is 20 g / L, and the mass ratio of the anionic surfactant to the carbon nanotubes is 0.1:1.

[0039] The recovery method comprises the following steps:

[0040] (1) adding a cationic surfactant dodecyldimethylbenzyl ammonium chloride to the carbon nanotube dispersion, wherein the molar ratio of the cation of the cationic surfactant to the anion of the anionic surfactant is 1:1, and the dispersion is gently shaken and allowed to stand for 10 minutes until flocculation occurs, thereby obtaining a flocculated dispersion system;

[0041] (2) Filter the obtained dispersion system on a 300-mesh filter cloth to obtain a carbon nanotube flocculation liquid, add deionized water to the carbon nanotube flocculation liquid, let it stand for 2-3 minutes, and then filter it again. Repeat this cycle of cleaning for 4 times to obtain a carbon nanotube flocculation liquid, which is then dried to obtain carbon nanotubes.

[0042] Example 3

[0043] This embodiment provides a method for recovering carbon nanomaterials in a dispersion.

[0044] In this embodiment, carbon nanotubes and anionic surfactant sodium polyoxyethylene fatty alcohol ether sulfate are added to water for dispersion to obtain a carbon nanotube dispersion. In the carbon nanotube dispersion, the concentration of carbon nanotubes is 20 g / L, and the mass ratio of the anionic surfactant to the carbon nanotubes is 2:1.

[0045] The recovery method comprises the following steps:

[0046] (1) adding a cationic surfactant, didodecyl dimethyl ammonium chloride, to the carbon nanotube dispersion, wherein the molar ratio of the cation of the cationic surfactant to the anion of the anionic surfactant is 1:1, and the dispersion is gently shaken and allowed to stand for 10 minutes, and flocculation occurs in the dispersion to obtain a flocculated dispersion system;

[0047] (2) Filter the obtained dispersion system on a 300-mesh filter cloth to obtain a carbon nanotube flocculation liquid, add deionized water to the carbon nanotube flocculation liquid, let it stand for 2-3 minutes, and then filter it again. Repeat this cycle of cleaning for 4 times to obtain a carbon nanotube flocculation liquid, which is then dried to obtain carbon nanotubes.

[0048] Example 4

[0049] This embodiment provides a method for recovering carbon nanomaterials in a dispersion. Compared with Example 1, an equimolar amount of the cationic surfactant is replaced by ammonium chloride, and the rest is the same as Example 1.

[0050] Example 5

[0051] This embodiment provides a method for recovering carbon nanomaterials in a dispersion. Compared with Example 1, the molar ratio of the cations of the cationic surfactant to the anions of the anionic surface active agent is controlled to be 0.5:1, and the rest is the same as Example 1.

[0052] Example 6

[0053] This embodiment provides a method for recovering carbon nanomaterials in a dispersion. Compared with Example 1, the molar ratio of the cations of the cationic surfactant to the anions of the anionic surface activity is controlled to be 1.5:1, and the rest is the same as Example 1.

[0054] Example 7

[0055] This embodiment provides a method for recovering carbon nanomaterials in a dispersion. Compared with Embodiment 1, the number of cleaning times is 2, and the rest is the same as Embodiment 1.

[0056] Comparative Example 1

[0057] This comparative example provides a method for recovering carbon nanomaterials in a dispersion. Compared with Example 1, no cationic surfactant is added, and a 0.45 μm filter membrane is used during filtration. The rest is the same as Example 1.

[0058] In the examples and comparative examples, the recovery rate of the obtained carbon nanomaterials and the purity of the recovered carbon nanomaterials are listed in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] As can be seen from Table 1, the recovery rate of carbon nanomaterials and the purity of recovered carbon nanomaterials are related to the content of dispersant in the dispersion system, the ratio of anionic dispersants to ionic materials with opposite charges of ionic surfactants, and have relatively little effect on the recovery rate, but have a relatively large effect on the purity of the recovered carbon nanomaterials. Compared with Example 1, in Example 3, when the content of dispersant in the dispersion system is large, the purity of the recovered carbon nanomaterials is reduced; in Example 4, ionic compounds are used to provide charged ions, and the recovery rate and purity are significantly reduced; in Examples 5-6, when the ion molar ratio in the system is adjusted, the recovered purity is reduced, and when the ratio of anionic dispersants to ionic materials with opposite charges of ionic surfactants is close, the recovered carbon nanomaterial purity is relatively high; in Examples 1 and 7, the more times of washing, the higher the purity of the recovered carbon nanomaterials. In Comparative Example 1, the direct filtration method is used for recovery, which increases the difficulty and time of operation, and the efficiency is very low, which is not conducive to practical application.

[0063] In summary, the method provided by the present invention flocculates the carbon nanomaterials in the dispersion to form large particles, which can be recovered by solid-liquid separation through physical means without the need to add additional auxiliary reagents. The method is simple and has good separation effect, which solves the problem that carbon nanomaterials are difficult to recover directly through solid-liquid separation. The recovery rate of carbon nanomaterials reaches more than 90%, which has great economic benefits.

[0064] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering carbon nanomaterials in a dispersion, characterized in that: The recovery method comprises the following steps: (1) mixing a carbon nanomaterial dispersion treated with an ionic surfactant and an ionic material having an electrical property opposite to that of the ionic surfactant to flocculate the carbon nanomaterial to obtain a flocculated dispersion system; (2) The flocculated dispersion system is subjected to solid-liquid separation, washing, and drying to obtain carbon nanomaterials.

2. The recycling method according to claim 1, characterized in that: The carbon nanomaterial in the carbon nanomaterial dispersion in step (1) includes any one of graphene, graphene oxide, carbon nanotubes, carbon black or fullerene, or a combination of at least two of them.

3. The recovery method according to claim 1 or 2, characterized in that: The ionic surfactant in step (1) includes anionic surfactant.

4. The recycling method according to claim 3, characterized in that: The anionic surfactant includes any one or a combination of at least two of sulfonates, sulfates, carboxylates, phosphates, amino acid salts, phenolates, enolates, ketosulfonamides or coordinated anion salts; Preferably, the anionic surfactant includes any one of dodecyl sulfonic acid, sodium dodecylbenzene sulfonate, lignin sulfonate, sodium cellulose or sodium fatty alcohol polyoxyethylene ether sulfate, or a combination of at least two thereof.

5. The recycling method according to any one of claims 1 to 4, characterized in that: The ionic material in step (1) includes a cationic surfactant.

6. The recycling method according to claim 5, characterized in that: The cationic surfactant includes any one of an amine salt type cationic surfactant, a chlorinated type cationic surfactant or a bromide type cationic surfactant, or a combination of at least two thereof; Preferably, the cationic surfactant includes any one of cetyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, cetyltrimethylammonium chloride or didodecyldimethylammonium chloride, or a combination of at least two thereof.

7. The recycling method according to any one of claims 1 to 6, characterized in that: The molar ratio of the ions in the ionic surfactant to the ions with opposite electrical properties in the ionic material in step (1) is 1:(0.5-1.5), preferably 1:(0.8-1.3), and more preferably 1:(0.9-1.1); Preferably, in the flocculated dispersion system of step (1), the particle size of the carbon nanomaterial particles is not less than 200 μm.

8. The recycling method according to any one of claims 1 to 7, characterized in that: The solid-liquid separation method in step (2) includes centrifugation and / or filtration.

9. The recycling method according to claim 8, characterized in that: The centrifugal speed is 50-10000 r / min, preferably 100-5000 r / min, and more preferably 100-1000 r / min; Preferably, the centrifugation time is 1-10 min, preferably 2-8 min, and more preferably 3-5 min; Preferably, the mesh number of the filtration is not less than 80 meshes, preferably 200-400 meshes.

10. The recycling method according to any one of claims 1 to 9, characterized in that: The cleaning method comprises: adding deionized water to the solid obtained by solid-liquid separation, and then centrifuging and / or filtering; Preferably, the cleaning is repeated 2-6 times, preferably 3-4 times.

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