JP2019218218A - Processing method of carbon nanomaterial - Google Patents

Abstract

To provide a method for decomposing a carbon nanomaterial by an oxidation treatment.SOLUTION: A processing method of a carbon nanomaterial includes treating of a mixture containing the carbon nanomaterial and water with an aqueous solution of hypochlorous acid or an aqueous solution of hypochlorite. The carbon nanomaterial can be selected from carbon nanotube, graphene, carbon nanohorn, and fullerene. Alternatively, the carbon nanomaterial may contain at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.SELECTED DRAWING: Figure 2

Description

One embodiment of the present invention relates to a method for treating a carbon material. For example, one of the embodiments of the present invention relates to a method for treating a carbon nanomaterial having a basic skeleton of sp ² carbon such as carbon nanotube, graphene, carbon nanohorn, and fullerene.

Carbon nanomaterials such as carbon nanotubes (hereinafter, also referred to as CNTs), graphene, carbon nanohorns, fullerenes, and the like are compounds substantially composed of only sp ² carbon atoms. These carbon nanomaterials have excellent chemical stability, mechanical properties, Shows heat resistance and electrical properties. For this reason, the application of carbon nanomaterials as industrial materials is being actively studied, and about several hundred tons of carbon nanomaterials per year have been produced on an industrial scale.

  These materials do not naturally exist in nature, but are artificially synthesized using an arc discharge method, a laser ablation method, a chemical vapor synthesis method, or the like. However, in recent years, such artificially synthesized carbon nanomaterials have also been biodegraded by some biologically-derived enzymes, horseradish peroxidase (HRP) and human neutrophil enzymes (MPO: Myeloperoxidase). (See Non-Patent Documents 1 to 3). Non-Patent Document 4 reports that carbon nanomaterials such as graphene oxide whose hydrophilicity is improved by oxidation are decomposed by hypochlorite.

Allen, B.S. L. (Allen, BL), 7 others, "Biodegradation of Single-Walled Carbon Nanotubes through Enzymatic Catalysis", Nano Letter (Nano Letter 200), United States, (8) Year, Volume 8, p3899-3903 Kagan, V. E. FIG. (Kagan, VE), and 20 others, "Carbon nanotubes degraded by neutrophil myeloperoxidase are less likely to induce lung inflammation (Carbon nanotubules degraded by neurophililoxidase lesson technology, radiation technology) (Nature Nanotechnology), (UK), 2010, p1-6. Jean, M. (Zhang, M.), et al., “Biodegradation of carbon nanohorns in macrophage cell”, Nanoscale, (UK), 2015, Vol. 7, p2834-2840 Leon, M. (Leon, N.), et al., "Hypochlorite degrades two-dimensional graphene oxide sheets faster than oxidized one-dimensional carbon nanotubes or nanohorns." Oxidized carbon nanotubes and nanohorns ", Nature Partner Journal 2D Materials and Applications, (UK), 2017, Vol. 39, p1-9.

  An object of one embodiment of the present invention is to provide a method for decomposing a carbon nanomaterial such as a carbon nanotube. For example, one of the embodiments of the present invention is a method for treating a carbon nanomaterial using an inexpensive and low-environmental oxidizing agent to convert it into an environmentally harmless compound, and a wastewater treatment method using the same. Is one of the issues.

  One embodiment of the present invention is a method for processing a carbon nanomaterial. This treatment method includes treating a mixture containing the carbon nanomaterial and water with an aqueous solution of hypochlorous acid or an aqueous solution of hypochlorite.

  The carbon nanomaterial can be selected from carbon nanotube, graphene, carbon nanohorn, and fullerene. The carbon nanomaterial may include at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.

  The mixture may further include a surfactant. The above treatment can be performed in a temperature range of 0 ° C. or more and 60 ° C. or less. The hypochlorite can be selected from hypochlorites of elements selected from Group 1 metals and Group 2 elements, and for example, sodium hypochlorite can be used.

  According to one embodiment of the present invention, a carbon nanomaterial can be oxidatively decomposed into a compound having a small environmental load by a simple and inexpensive method under a mild condition. For this reason, the waste liquid containing the carbon nanomaterial can be treated quickly and inexpensively, and the environmental pollution caused by the carbon nanomaterial can be effectively prevented.

Changes with time in the appearance of the CNT dispersion liquid in Example 1 and Comparative Example 1. FIG. 6 shows a change with time in the absorption intensity of the CNT dispersion liquids of Example 1 and Comparative Example 1. FIG. Changes with time in appearance of the CNT dispersions of Example 2 and Comparative Example 2. 6 shows the change over time in the absorption intensity of the CNT dispersions of Example 2 and Comparative Example 2. Changes over time in the appearance of the CNT dispersions of Examples 3 and 4 and Comparative Examples 3 and 4. Changes over time in the absorption intensity of the CNT dispersions of Examples 3 and 4 and Comparative Examples 3 and 4. FIG. 3 is a transmission electron microscope (SEM) image of a CNT residue after treatment in the presence and absence of an oxidizing agent. Raman spectrum of CNT residue after treatment in the presence and absence of an oxidizing agent. The change over time of the absorption intensity of the CNT dispersions of Example 6 and Comparative Example 6. The time-dependent change in the absorption intensity of the CNT dispersions of Example 7 and Comparative Example 7. The CNT residue after an oxidation process, the SEM-EDS analysis result of a control experiment, and a carbon mapping image.

  Hereinafter, embodiments of the invention disclosed in the present application will be described. Of the other effects different from the effects brought about by the following embodiments, those which are obvious from the description of the present specification or which can be easily predicted by those skilled in the art are, according to the present invention, of course. It is understood to be brought.

  One embodiment of the present invention is a method for treating a carbon nanomaterial such as CNT, graphene, carbon nanohorn, and fullerene. This treatment method includes oxidatively decomposing the carbon nanomaterial by treating (oxidizing) the carbon nanomaterial with a solution of an oxidizing agent.

  Various materials can be used as the carbon nanomaterial. For example, when CNT is treated as a carbon nanomaterial, its structure is not limited, and either single-walled CNT or multi-walled CNT may be used. The CNTs may be capped at one end or have a structure with one or both ends open. Alternatively, a peapot in which fullerene is included in the CNT may be used. There is no restriction on the length of the CNT.

  When treating graphene as a carbon nanomaterial, independent single-layer graphene may be used, or oligographene or graphite in which a plurality of graphenes are stacked may be used. Alternatively, graphene oxide in which a part of the basic skeleton is oxidized may be used.

When treating fullerene as a carbon nanomaterial, not only _C60 and _C70 but also _C74 , _C76 , _{C78 and the} like may be used. Further, fullerene containing a metal ion such as scandium, lanthanum, or cerium may be used, or fullerene having a functional group such as an ester group in which a part of carbon is modified may be used.

  Although there is no limitation on the type of the oxidizing agent, an oxidizing agent which is available at a low cost, has a small burden on the environment, and has low toxicity is preferable. For example, hypochlorous acid, hypochlorite, ozone, hydrogen peroxide and the like can be mentioned. Above all, hypochlorous acid or hypochlorite is an oxidizing agent produced in a living body, and is particularly preferred because it has a particularly small load on the environment.

  Examples of the hypochlorite include salts of elements selected from Group 1 metals or Group 2 elements, and specifically, sodium hypochlorite, potassium hypochlorite, and lithium hypochlorite. , Magnesium hypochlorite and calcium hypochlorite. Of these, sodium hypochlorite is preferred because it is mass-produced industrially and can be obtained at low cost.

  The concentration of the oxidizing agent in the oxidizing agent solution can be appropriately selected, for example, from the range of 0.1% by weight or more and 10% by weight or less. The concentration of the oxidizing agent contained in the oxidizing agent solution and the amount of the oxidizing agent solution are appropriately adjusted so that the oxidizing agent is contained in a stoichiometric amount or more with respect to the carbon in the basic skeleton of the carbon nanomaterial to be treated. . As described below, when hypochlorous acid or hypochlorite is used as the oxidizing agent, two equivalents of the oxidizing agent react with carbon forming the basic skeleton of the carbon nanomaterial. Therefore, in this case, the concentration and amount of the oxidizing agent are adjusted such that the oxidizing agent is twice or more moles of carbon.

  Examples of the solvent used in the oxidation treatment of the carbon nanomaterial include water and carboxylic acid. However, water is preferable because it is inexpensive, odorless, and has no burden on the environment. Examples of the carboxylic acid include formic acid and acetic acid. Further, a plurality of solvents may be used. For example, when water is the main solvent, alcohol solvents such as methanol, ethanol, and propanol; ketone solvents such as acetone and methyl ethyl ketone; amide solvents such as N, N-dimethylformamide and N, N-dimethylacetamide; Aromatic hydrocarbon solvents such as xylene, non-aromatic solvents such as hexane and cyclohexane, heteroaromatic solvents such as pyridine and thiophene, halogen solvents such as methylene chloride and chloroform, ethyl acetate and methyl acetate And a sulfur-containing solvent such as dimethyl sulfoxide.

  The temperature of the oxidation treatment is not limited, and is appropriately selected from the range of 0 ° C. or more and 50 ° C. or less. For example, the oxidation treatment can be performed at 37 ° C., whereby a high treatment speed can be obtained and the decomposition of the oxidizing agent can be suppressed. The oxidation treatment may be performed at room temperature (15 ° C. or more and 25 ° C. or less) without heating or cooling.

  The oxidation treatment may be performed in the presence of a surfactant. The carbon nanomaterial is difficult to disperse in a solvent depending on the structure or the substituent to be introduced, but disperses relatively easily in a solvent such as water in the presence of a surfactant. Therefore, by performing the treatment in the presence of the surfactant, the decomposition rate of the carbon nanomaterial can be increased. The surfactant can be selected from monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkyl benzene sulfonates, monoalkyl phosphates, tetraalkyl ammonium salts, and the like. Alternatively, an ionic liquid such as a pyridinium salt or an imidazolium salt that exists as a liquid at normal temperature may be used as the surfactant.

Since the basic skeleton of the carbon nanomaterial is composed of only sp ² carbon, this oxidation treatment includes a reaction represented by the following scheme. More specifically, when hypochlorous acid, a hypochlorite of a Group 1 metal, and a hypochlorite of a Group 2 element are used as an oxidizing agent, the following scheme (1) is used, respectively. The reaction represented by (3) is included.
Here, n is the number of moles of carbon constituting the basic skeleton of the carbon nanomaterial, and M is a Group 1 metal or a Group 2 element.

  As understood from the above scheme, in the oxidation treatment of the present embodiment, carbon dioxide and metal chloride or hydrochloric acid are generated by oxidative decomposition of the carbon nanomaterial. Since these compounds can be easily treated by a general exhaust device, a neutralization device, and a waste liquid treatment device, it is understood that the oxidation treatment of the present embodiment has a small load on the environment. Particularly, since hypochlorous acid and hypochlorite are available at low cost, by applying this embodiment, the carbon nanomaterial can be easily, inexpensively, and processed without imposing a burden on the environment. A method is provided for:

  When synthesizing and manufacturing a carbon nanomaterial, or when processing or subjecting it to a reaction, the carbon nanomaterial may be contained in a by-product waste liquid. Although there is relatively little information on the toxicity of carbon nanomaterials, some carbon nanomaterials are suspected of being carcinogenic, so it is important to ensure that the carbon nanomaterials in the waste liquid are treated. Conventionally, the treatment of carbon nanomaterials in a waste liquid has been performed by filtering the waste liquid and then incinerating the residue. For this reason, the production cost and utilization cost of the carbon nanomaterial increase due to the cost and time for filtration. This causes the incompletely treated waste liquid to be dumped or leaked.

  It should be noted that graphene oxide is obtained by partially oxidizing (pre-treating) graphene, one of the carbon nanomaterials, with a strong oxidizing agent such as permanganic acid, permanganate, sulfuric acid, nitric acid, or a mixed acid. Is reported to be decomposed in an aqueous solution of hypochlorous acid (see Non-Patent Document 4). However, as experimentally shown in Examples, in the treatment method of this embodiment, such oxidative The point is that the carbon nanomaterial can be completely decomposed under mild conditions using an inexpensive oxidizing agent without performing treatment. Therefore, the treatment method of the present embodiment does not require the use of an oxidizing agent containing a heavy metal, and does not involve a neutralization treatment of a high-concentration acid waste liquid such as a mixed acid. Further, in this treatment method, a filtration step is not essential, and no harmful substances to the environment are produced as by-products. Furthermore, it is possible to quickly decompose the carbon nanomaterial even in the presence of a surfactant. When a carbon nanomaterial is dispersed in a solvent such as water, a surfactant is frequently used. Therefore, there is a high possibility that the surfactant is mixed in a waste liquid containing the carbon nanomaterial. Considering these facts, the treatment method according to the present embodiment is a simple and effective treatment method for the waste liquid containing the carbon nanomaterial, and by applying this, prevents the leakage of the carbon nanomaterial to the environment, It is possible to promote the production, development and use of carbon nanomaterials while ensuring safety.

  Hereinafter, an example according to the above embodiment will be described.

1. Example 1
In this embodiment, an oxidation treatment of single-walled CNT in water with sodium hypochlorite will be described.

  A CNT dispersion was prepared by adding 1 mL of a mixture (0.1 mg / mL) of single-walled CNT and water and 4 mL of an aqueous solution (50 mg / mL) of sodium hypochlorite pentahydrate (manufactured by Wako Co., Ltd.) to a glass bottle. At 37 ° C. As Comparative Example 1, 1 mL of a mixture (0.1 mg / mL) of single-walled CNT and water and 4 mL of pure water were added to a glass bottle to prepare a CNT dispersion, which was allowed to stand under the same conditions. The single-walled CNT used was a super-growth CNT having a length of about 1 mm, and was synthesized by supplying an ethylene gas containing a trace amount of water while heating in the presence of an iron catalyst.

  FIG. 1 shows the change over time in the appearance of the CNT dispersion. FIG. 1 shows photographs of the appearance at 0 hour, 24 hours, 48 hours, and 96 hours after the start of the processing in order from the left. In each of the appearance photographs, the right side is Example 1, and the left side is Comparative Example 1. is there. As shown in FIG. 1, the CNT dispersion liquid at the start of the oxidation treatment is colored black and is opaque due to the CNT, but it is confirmed that the coloring disappears quickly in Example 1 after the start of the oxidation treatment. Was. In contrast, in Comparative Example 1, the coloring of the CNT dispersion did not disappear, and the initial coloring was maintained even after 96 hours.

  FIG. 2 shows the change over time in the absorption of the CNT dispersion at 700 nm. As shown in FIG. 2, the absorption of the CNT dispersion of Example 1 rapidly decreased about 1 hour after the start of the oxidation treatment, and almost no absorption was observed after about 30 hours. On the other hand, it can be seen that the intensity of the absorption of the CNT dispersion of Comparative Example 1 hardly changed even after 96 hours.

  The above results suggest that the single-walled CNT is rapidly decomposed by the treatment method of the present embodiment.

2. Example 2
In this embodiment, an oxidation treatment of multilayer CNTs in water with sodium hypochlorite will be described.

  1 mL of a mixture (0.1 mg / mL) containing multilayer CNTs (manufactured by Nanocyl, NC7000) and water and 4 mL of an aqueous solution (50 mg / mL) of sodium hypochlorite pentahydrate (manufactured by Wako) are added to a glass bottle. To prepare a CNT dispersion, which was allowed to stand at 37 ° C. As Comparative Example 2, 1 mL of a mixture (0.1 mg / mL) containing multilayered CNTs and water and 4 mL of pure water were added to a glass bottle to prepare a CNT dispersion, which was allowed to stand under the same conditions.

  FIG. 3 shows the change over time in the appearance of the CNT dispersion. As in FIG. 1, FIG. 3 shows photographs of the appearance at 0, 24, 48, and 96 hours after the start of processing in order from the left, and in each of the photographs, Example 2 is on the right side and Comparative Example is on the left side. 2. As in Example 1, the CNT dispersion at the start of the oxidation treatment was colored black due to the multilayer CNTs, but it was confirmed in Example 2 that the coloring disappeared quickly after the oxidation treatment was started. On the other hand, in Comparative Example 2, the coloring of the CNT dispersion liquid did not disappear, and the initial coloring was maintained even after 96 hours.

  FIG. 4 shows the change over time in the absorption of the CNT dispersion at 700 nm. As shown in FIG. 4, the absorption of the CNT dispersion of Example 2 gradually decreased after the start of the oxidation treatment, and almost no absorption was observed after about 80 hours. On the other hand, it was confirmed that the absorption of the CNT dispersion of Comparative Example 2 hardly changed.

3. Examples 3 and 4
In this embodiment, an example in which CNT is oxidized using a commercially available aqueous solution of hypochlorous acid will be described.

  A CNT dispersion was prepared by adding 1 mL of a mixture (0.1 mg / mL) of single-walled CNT (super-growth CNT) and water and 4 mL of a 500 ppm aqueous solution of hypochlorous acid (manufactured by Sekijin) to a glass bottle (Example) 3). Similarly, 1 mL of a mixture (0.1 mg / mL) of water and 0.1 mL of a mixed solution of multilayer CNT (NC7000, manufactured by Nanocyl) and 4 mL of a 500 ppm aqueous solution of hypochlorous acid (manufactured by Sekijin) were added to a glass bottle, and the CNT dispersion was added. Prepared (Example 4). These CNT dispersions were allowed to stand at 37 ° C. As Comparative Examples 3 and 4, CNT dispersions were prepared by adding 1 mL of the above-described single-walled CNTs or a mixture (0.1 mg / mL) of water and 0.1 mL of pure water to a glass bottle, and allowed to stand under the same conditions. did.

  FIGS. 5A and 5B show changes over time in the appearance of the dispersion. FIG. 5A shows the results of the example using the single-layer CNT (Example 3, Comparative Example 3), and FIG. 5B shows the results of the example using the multilayer CNT (Example 3, Comparative Example 4). It is. FIGS. 5 (A) and 5 (B) show photographs of the appearance at 0 hour, 24 hours, 48 hours, and 96 hours after the start of processing in order from the left. In each appearance photograph, the right side is Example 3 or 4, and the left side is Comparative Example 3 or 4. As is clear from FIGS. 5 (A) and 5 (B), in both cases of the single-walled CNT and the multi-walled CNT, the CNT dispersion at the start of the oxidation treatment is blackened due to the CNT. After starting the oxidation treatment, in Examples 3 and 4, it was confirmed that the coloring of the CNT dispersion liquid gradually disappeared. In contrast, in Comparative Examples 3 and 4, the coloring of the dispersion did not disappear, and the initial coloring was maintained even after 96 hours.

  FIG. 6A shows the time-dependent change in the absorption at 700 nm of the CNT dispersions of Example 3 and Comparative Example 3, and FIG. 6B shows the time-dependent change of the absorption at 700 nm of the CNT dispersions of Example 4 and Comparative Example 4. Is shown. FIG. 6A shows that in the case of single-walled CNT, the absorption of the CNT dispersion liquid is reduced to half in about 10 to 15 hours after the start of the oxidation treatment. On the other hand, in the case of the multilayer CNT, although the decrease in absorption was slightly slow, it was found that the absorption intensity was reduced by half in about 70 to 80 hours. The decrease in absorption is slower than in Examples 1 and 2, which is considered to be due to the low concentration of the oxidizing agent. On the other hand, in Comparative Examples 3 and 4, it was confirmed that the absorption intensity did not change at all (FIGS. 6A and 6B).

4. Example 5
The morphology of the CNT residue 24 hours after the start of the oxidation treatment was observed by SEM, and the Raman spectrum was measured. A sample for SEM observation was produced by the following method. First, the treated CNT dispersion was filtered using an ultrafiltration filter (fraction molecular weight: 10,000), and the obtained CNT residue was dispersed in water (0.2 mL). This dispersion was dropped on a copper grid and dried overnight at room temperature to obtain a sample. Using a transmission electron microscope 002B HRTEM manufactured by Topcon as an SEM, an SEM image was obtained at an acceleration voltage of 120 keV and an acceleration current of 36 μA.

  FIGS. 7A and 7B show SEM images of CNT residues obtained after treating single-walled CNTs for 24 hours in the absence and presence of an oxidizing agent (sodium hypochlorite). . On the other hand, FIG. 7 (C) and FIG. 7 (D) are SEM images of CNT residues obtained after treating multilayer CNTs for 24 hours in the absence and presence of an oxidizing agent.

  From FIG. 7A, a fibril-like morphology was observed in the CNT residue obtained in the absence of the oxidizing agent, and it was clearly confirmed that the structure of the single-walled CNT remained. On the other hand, in the CNT residue obtained in the presence of the oxidizing agent, it can be seen that the structure of the single-walled CNT is destroyed, and the morphology changes to an amorphous morphology (FIG. 7B). A similar tendency was confirmed even when multilayer CNTs were used. Although a clear fibril structure was confirmed in the CNT residue obtained in the absence of an oxidizing agent (FIG. 7 (C)), it was obtained in the presence of an oxidizing agent. It can be seen that the structure of the obtained CNT residue is significantly changed (FIG. 7D).

  FIG. 8A shows a Raman spectrum of a CNT residue when single-walled CNTs are used, and FIG. 8B shows a Raman spectrum (excitation wavelength: 532 nm) of a CNT residue when multilayered CNTs are used. As a sample for Raman spectrum measurement, the treated CNT dispersion is filtered using an ultrafiltration filter (fraction molecular weight: 10,000), and the residue is dispersed in water (0.2 mL). It was prepared by dropping on a plate and drying overnight at room temperature. For the measurement, a microscopic laser Raman spectrometer LabRam HR Evolution manufactured by Horiba, Ltd. was used. 8A and 8B, the solid line is a spectrum of the CNT residue obtained by treating in the presence of the oxidizing agent, and the dotted line is a spectrum of the CNT residue obtained by treating in the absence of the oxidizing agent. is there. As shown in these figures, it was confirmed that the Raman D band peak intensity increased after treating CNT in the presence of an oxidizing agent. The D band peak of the Raman spectrum of CNT is a peak indicating that CNT exists in an amorphous state or that CNT has a defect. Therefore, these results suggest that the structure of CNT is destroyed by the oxidizing agent and many defects are generated.

5. Examples 6 and 7
In this embodiment, an example in which CNT is treated in the presence of a surfactant will be described. A CNT dispersion (0.1 mg / mL) was prepared in the same manner as in Example 1 and Comparative Example 1, and 10 mg of a surfactant was added to 10 mL of the CNT dispersion. As surfactants, sodium dodecylbenzenesulfonate (BSA) and polyethylene glycol (PEG) were used. The former treatment using a surfactant is Example 6 and Comparative Example 6, and the latter treatment using a surfactant is Example 7 and Comparative Example 7. As in Comparative Example 1, Comparative Examples 6 and 7 are treatments in the absence of an oxidizing agent.

  FIG. 9 shows the change over time in the absorption of the CNT dispersion of Example 6 and Comparative Example 6 at 700 nm, and FIG. 10 shows the change over time of the absorption of the CNT dispersion of Example 7 and Comparative Example 7 at 700 nm. From these figures, it was found that the absorption of the CNT dispersion rapidly decreased after the start of the oxidation treatment, and the absorption almost disappeared after about 20 hours. On the other hand, in Comparative Example 6 and Comparative Example 7, in which no oxidizing agent was present, it was confirmed that the absorption of the CNT dispersion did not change. From this, it can be concluded that the presence of the surfactant does not affect the CNT oxidation treatment.

6. Example 8
Example 1 In this example, the result of considering the final product after the oxidation treatment, which is one of the embodiments of the present invention, will be described.

After oxidizing the single-walled CNT or the multi-walled CNT with an oxidizing agent (sodium hypochlorite) for 120 hours, the transparent CNT dispersion was heated at 75 ° C. for 1 hour to decompose sodium hypochlorite. Thereafter, when a 0.05 M aqueous solution of calcium chloride (0.5 mL) was added to 0.5 mL of the dispersion, cloudiness was immediately observed. This suggests that carbonate ions (CO ₃ ^2- ) are present in the dispersion after the oxidation treatment.

  The dispersion obtained after decomposing sodium hypochlorite was extracted with methylene chloride, and the extract was subjected to liquid chromatography-mass spectrometry (LC-MS). Mass spectrometry was performed using a high performance double focusing mass spectrometer Mstation JMS-700 manufactured by JEOL. As a result, almost no peak attributed to the aromatic hydrocarbon was detected, and only a small peak at m / z 131 was detected in the extract from the CNT dispersion liquid after the oxidation treatment for 24 hours. Further, this peak was not detected at all in the mass spectrum of the extract from the CNT dispersion obtained after the oxidation treatment for a longer time.

  Using an energy dispersive X-ray spectrometer (EDS) mounted on the SEM, CNT residues generated after treatment with an oxidizing agent were subjected to elemental analysis. The sample used for the analysis was prepared as follows. After treating the single-walled CNT or the multilayered CNT for 120 hours in the presence of an oxidizing agent (sodium hypochlorite), 6.5 M hydrochloric acid (100 μL) is added to the CNT dispersion which has become transparent, and the dispersion is further heated to 70 ° C. For several minutes. After confirming that hypochlorous acid is not detected using hypochlorous acid test paper (hypochlorous acid test paper WAP-ClO manufactured by Kyoritsu Riken Co., Ltd.), the pH was adjusted using sodium hydroxide aqueous solution, The obtained solution was dropped on a SiN wafer and dried to obtain a sample. For SEM observation and EDS analysis, a field emission scanning electron microscope SU8200 manufactured by Hitachi High-Technologies and an energy dispersive X-ray spectrometer 5060 FlatQUAD manufactured by Bruker were used, respectively.

  FIGS. 11A and 11B show the results of EDS analysis of CNT residues after oxidation treatment of single-walled CNT and multilayered CNT, respectively. FIG. 11 (C) corresponds to a control experiment and is a result obtained by analyzing a sample prepared from a solution of CNT-free water and sodium hypochlorite. In these figures, the left side is an EDS analysis result, and the right side is a carbon mapping image. It should be noted that, as can be seen from the comparison of the EDS analysis results, the peaks derived from carbon, oxygen, chlorine, and sodium were found in all the samples including the control experiment, although CNT was not used in the control experiment. Are the same, and the carbon mapping images have almost no difference between all of these samples. This suggests that the carbon abundance is almost the same between these samples. From the EDS analysis results, it was confirmed that the molar ratio of sodium to chlorine was approximately 1: 1.

  The above results suggest that in the oxidation treatment of the present embodiment, the carbon nanomaterial is chemically oxidized by the oxidizing agent and decomposed into carbon dioxide. That is, it can be said that the present oxidation treatment proceeds with the reaction represented by the above-described scheme as a main reaction route. Since almost no peak corresponding to an aromatic hydrocarbon was detected in LC-MS, and the carbon mapping image of the CNT residue was similar to that of the control experiment, the oxidation reaction proceeded almost quantitatively. It is suggested that the CNTs are virtually completely degraded.

  From the above examples, it is possible to quickly and quantitatively oxidatively decompose a carbon nanomaterial exemplified by CNT under mild conditions by applying the oxidation treatment which is one of the embodiments of the present invention. It was confirmed that. In addition, the oxidation treatment is not affected by the surfactant and does not give environmentally burdensome by-products. Therefore, by applying the embodiment of the present invention, it becomes possible to efficiently treat, for example, a waste liquid containing a carbon nanomaterial and detoxify the waste liquid.

Claims (8)

  A method for treating a carbon nanomaterial, comprising treating a mixture containing a carbon nanomaterial and water with an aqueous solution of hypochlorous acid or an aqueous solution of hypochlorite.   The processing method according to claim 1, wherein the carbon nanomaterial is selected from a carbon nanotube, graphene, carbon nanohorn, and fullerene.   The processing method according to claim 1, wherein the carbon nanomaterial includes at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.   The processing method according to claim 1, wherein the mixture further includes a surfactant.   The processing method according to claim 1, wherein the processing is performed in a temperature range of 0 ° C. or more and 60 ° C. or less.   The treatment method according to claim 1, wherein the hypochlorite is a hypochlorite of an element selected from a Group 1 metal and a Group 2 element.   The treatment method according to claim 6, wherein the hypochlorite is sodium hypochlorite.   A method for treating a waste liquid containing the carbon nanomaterial, comprising the treatment method according to claim 1.