JP4858988B2 - Method for producing carbon nanosheet composite without firing, and organic pollutant removal method and remover using composite obtained by the method - Google Patents

Description

  The present invention relates to a method for producing a carbon nanosheet composite, and a method and a removal agent for organic pollutants using the composite obtained by the method. In particular, the present invention relates to a carbon nanosheet composite without firing. The present invention relates to a method for producing and a method for removing trace amounts of organic pollutants using the carbon nanosheet composite.

At present, there are concerns that organic environmental pollutants such as persistent organic pollutants (POPs) and environmental hormones may remain in the environment for a long time even in trace amounts, causing harm to biological systems including humans. Removal of trace amounts of organic environmental pollutants is an important issue to be solved.
The removal treatment method of these organic environmental pollutants includes an adsorption method using an adsorbent, a plant absorption method, catalytic oxidation, ozone aeration, electrolysis, etc. or a combination of an adsorption method and a detoxification method. Although many patent applications relating to these have been seen, the concentration of the target substance is usually large, and even if it is small, it is several ppm or more.

The inventors have dispersed graphite oxide obtained by oxidizing graphite in an alkali, or previously expanded the layers with long-chain organic ions, and then added a hard crosslinking agent such as a metal or metalloid oxide. It has been reported that a carbon-containing porous composite with a high surface area can be synthesized by introduction (see Patent Documents 1 to 3). Furthermore, the present inventors mechanically uniformly mixed the graphite oxide layered body using a smaller amount of an organic metal species or an organic metalloid species, thereby efficiently and in a short time. It has also been found that organometallic species can be inserted between graphite oxide layers. The organometallic seed-inserted graphite oxide obtained by such a method maintains a regular layered structure, and as a result, the interlayer distance gradually increases as the amount of the organometallic or organic metalloid seed increases. The carbon-containing porous composite material having a surface area of 1000 m ² / g or more can be constantly synthesized by subjecting the organometallic seed-inserted graphite oxide obtained by such a method to post-treatment such as carbonization. I found it. In these methods, when an organotitanium compound is contained as an organometallic species, a layered product of graphite oxide whose layers are expanded by titanium oxide can be produced. Has been found to have photocatalytic activity despite being inserted into the graphite oxide layer (see Patent Document 4).

In the process of confirming the effectiveness as a treating agent for removing organic environmental pollutants by utilizing the photocatalytic activity of titanium oxide inserted into the graphite oxide layer, the present inventors have confirmed that the titanium oxide is interlayered. As a result of further examination of the graphite oxide layered material inserted into the film, a pre-expansion treatment with a long-chain organic amine, a long-chain surfactant, a long-chain alcohol, or the like as described in Patent Document 4 is performed. In addition, the inventors have found that titanium oxide can be introduced also by using a sheet-like graphite oxide obtained by simply peeling off a layered product of graphite oxide in a basic solution. And as a raw material of the titanium oxide to be introduced, the crystallinity of the titanium oxide introduced into the sheet-like graphite oxide is enhanced by using a transparent sol obtained by hydrolyzing an organic titanium compound in an acidic aqueous solution in advance. At the same time, the inventors have found that the main component can be anatase microcrystals with high photocatalytic activity. Furthermore, the carbon nanosheet composite formed by introducing the titanium oxide having improved crystallinity into the sheet-like graphite oxide in this way has a low concentration of organic environmental pollutants at a faster removal rate than the conventional remover. It came to discover that it was what can be photodegraded after adsorption | suction and concentration (refer patent document 5).
JP 2003-192316 A JP 2004-217450 A JP 2004-217450 A JP 2006-272266 A Japanese Patent Application No. 2007-107467

However, the method of Patent Document 5 requires sintering at a high temperature, and is not yet sufficient in terms of economy for producing a composite. Furthermore, as a result of investigations by the present inventors, it has also been found that there is a possibility of increasing the efficiency of photolysis activity by further optimizing the crystal form of titania in the composite.
The present invention has been made on the basis of the above knowledge, and is a highly efficient and simple preparation means for a treating agent for removing organic environmental pollutants using a carbon nanosheet composite. An object of the present invention is to provide a treatment agent that can be produced economically.

  The inventors of the present invention have intensively studied to achieve the above-mentioned object, and require firing at a high temperature by using a solution obtained by mixing and stirring an inorganic titanium salt and citric acid. In addition, the present inventors have found that the crystal form of titania in the composite can be optimized.

The present invention has been completed based on these findings, and is as follows.
(1) Manufacture of a titanium oxide-introduced carbon nanosheet composite characterized by mixing a solution obtained by mixing and stirring an inorganic titanium salt and citric acid and a graphite oxide and then hydrothermally treating the mixture. Method.
(2) The method for producing a titanium oxide-introduced carbon nanosheet composite according to (1), wherein the graphite oxide is a layered graphite oxide.
(3) The method for producing a titanium oxide-introduced carbon nanosheet composite according to (2), wherein the mixture is refluxed before the hydrothermal treatment.
(4) Production of titanium oxide-introduced carbon nanosheet composite according to (1), wherein the graphite oxide is a graphite oxide obtained by stirring a layered graphite oxide in a basic aqueous solution. Method.
(5) The method for producing a titanium oxide-introduced carbon nanosheet composite according to (1) to (4), wherein the hydrothermal treatment is performed at 100 to 200 ° C.
(6) The method for producing a titanium oxide-introduced carbon nanosheet composite according to any one of (1) to (5), wherein the titanium oxide contains anatase microcrystals as a main component.
(7) Organic pollutant removal treatment characterized by comprising a carbon nanosheet composite obtained by any one of the above methods (1) to (6) and capable of incorporating organic pollutants between the layers. Agent.
(8) A method for removing an organic pollutant, comprising using the carbon nanosheet composite obtained by any of the above methods (1) to (6) to incorporate an organic pollutant between the layers.

  According to the method of the present invention, high temperature firing is not required, and the produced carbon nanosheet composite adsorbs organic pollutants present at a low concentration by incorporating organic pollutants between the layers. It can be concentrated and detoxified completely under energy-saving conditions, and in particular, it can cope with the removal treatment of extremely low concentration organic pollutants of about several to several tens of ppb.

  The present invention is a method for producing a carbon nanosheet composite using graphite oxide as a base material, and titanium oxide is introduced into the base material, and an inorganic titanium salt and citric acid are used in advance as a raw material constituting the titanium oxide. A solution obtained by mixing and stirring (hereinafter sometimes referred to as “TC solution”) is mixed with graphite oxide and then hydrothermally treated.

The graphite oxide (hereinafter sometimes referred to as “GO”) used in the method of the present invention may be a layered graphite oxide or a graphite oxide in a state where the layers are separated.
Layered graphite oxide is prepared by, for example, immersing graphite in a mixture of concentrated sulfuric acid and nitric acid and adding potassium chlorate to react, or by immersing in a mixture of concentrated sulfuric acid and sodium nitrate and adding potassium permanganate. It is prepared by reacting. By these treatments, at least a part of the carbon atoms of the graphite changes from the sp ² state to the sp ³ state, from a state like a carbon atom forming a so-called benzene ring to a state of a saturated aliphatic carbon atom. As a result, oxygen atoms and hydrogen atoms are bonded to these changed carbon atoms, and oxygen atoms can be introduced onto the carbon layer. The interlayer distance of the graphite oxide layered product thus produced is usually about 0.6 to 1.1 nm.

By dispersing the layered graphite oxide produced as described above in a basic aqueous solution, the layered graphite oxide is obtained.
Specifically, the graphite oxide layer can be peeled off by sufficiently stirring and dispersing the graphite oxide in a basic aqueous solution, preferably by ultrasonic treatment or the like.

  In the method of the present invention, the layered graphite oxide is mixed with a solution (TC solution) obtained by mixing and stirring the inorganic titanium salt and citric acid, or the layer is peeled off. A carbon nanosheet composite in which titanium oxide is introduced between carbon nanosheets can be produced by mixing the resulting dispersion of graphite oxide and then hydrothermally treating the resulting mixture.

The amount of titanium oxide introduced is not more than 70 times, preferably 5 to 30 times, the number of moles of ion exchangeable graphite oxide (GO) (hereinafter abbreviated as [H ⁺ ]). Next, the TC solution and the graphite oxide are mixed.
Here, [H ⁺ ] of GO is the GO cation exchange capacity (mmol / g) per weight unit (abbreviated as Cation Exchange Capacity, CEC) multiplied by the weight of GO. GO CEC can be determined by treating GO with sodium hydroxide to exchange for sodium ions and then titrating with an acid such as hydrochloric acid.
The value of [H ⁺ ] of GO varies depending on the graphite used, the oxidation method, and the like. For example, when the CEC of GO manufactured in the examples described later is 6.74 mmol / g, When used, the [H ⁺ ] is 6.74 moles, and the number of moles of titanium oxide relative to this is 70 times or less, preferably 5 to 30 times. become.

  In the present invention, when the above-mentioned layered graphite oxide is used as the graphite oxide, it is preferably mixed with the TC solution and then refluxed, and this reflux is performed at room temperature to 180 ° C., preferably 50 to 110. It is carried out at a temperature of 30 minutes to 6 hours, preferably 30 minutes to 3 hours.

In order to form a stable carbon nanosheet composite in which titanium oxide is introduced using a mixture of a TC solution and graphite oxide, it is necessary to subject the mixture to a hydrothermal treatment.
The hydrothermal treatment is performed by treating at a temperature of 100 to 200 ° C, preferably 120 to 150 ° C for 1 to 10 hours. By the hydrothermal treatment, a stable carbon nanosheet composite of the present invention into which titanium oxide has been introduced can be obtained without firing.
Specifically, the mixture of the layered graphite oxide and the TC solution is preferably subjected to hydrothermal treatment after refluxing the mixture (referred to as “synthesis method 1”), or the layered graphite oxide in the basic solution. The carbon sheet composite of the present invention can be obtained by mixing the TC solution with the graphite oxide dispersion obtained by dispersing in (3) and then subjecting it to hydrothermal treatment (synthesis method 2).

The inorganic titanium salt used in the method of the present invention is not particularly limited as long as it becomes titanium oxide by the above-mentioned hydrothermal treatment, and preferably, most of the titanium oxide becomes anatase-type titanium oxide crystals. More specifically, for example, titanium chloride, titanium sulfate, titanium acetate and the like can be mentioned, and particularly preferable inorganic titanium salt includes titanium tetrachloride (TiCl ₄ ).

Since the pores are formed in the carbon nanosheet composite of the present invention, an object to be treated such as an organic pollutant treated by a photocatalyst is easily adsorbed, and is better adsorbed and decomposed in contact with titanium oxide. It is considered a thing.
Furthermore, the present invention provides the use of the above-described carbon nanosheet composite of the present invention as an organic contaminant removing agent. The carbon nanosheet composite of the present invention is characterized in that titanium oxide having photocatalytic activity is present on a nanosized sheet-like carbon sheet. The removal agent of the present invention not only has a large specific surface area, but also has a large pore diameter by expanding the interlayer, has excellent adsorption ability, and adsorbs organic substances to contact the internal titanium oxide. Therefore, it is considered that excellent resolution is exhibited.

  Examples of trace organic contaminants removed by the removal treatment agent of the present invention include dioxins, polychlorinated biphenyls (PCB), polybrominated biphenyls (PBB), hexachlorobenzene (HCB), and pentachlorophenol. (PCP), 2,4,5-trichlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, amitrole, atrazine, alachlor, simazine (CAT), hexachlorocyclohexane, ethyl parathion, carbaryl (NAC), chlordane, oxychlordane, trans-nonachlor, 1,2-dibromo-3-chloropropane, DDT, DDE, DDD, Kelsen, aldrin, endrin, dieldrin, endosulfan (benzoepin), heptachlor, heptachlorepoxide, malathion, mesomi , Methoxychlor, Milex, nitrophene, toxaphene, tributyltin, triphenyltin, trifluralin, alkylphenol (C5-C9), nonylphenol, 4-octylphenol, bisphenol A, di-2-ethylhexyl phthalate, dibutylbenzyl phthalate, phthalate Di-n-butyl acid, dicyclohexyl phthalate, diethyl phthalate, benzo (a) pyrene, 2,4-dichlorophenol, di-2-ethylhexyl adipate, benzophenone, 4-nitrotoluene, octachlorostyrene, aldicarb , Benomyl, Kypon (Chlordecone), Manzeb (Mancozeb), Mannebu, Methylam, Metribuzin, Cipermethrin, Esfenvalerate, Fenvalerate, Permethrin, Vinclozoline, Examples include environmental hormones such as dineb, diram, dipentyl phthalate, dihexyl phthalate, dipropyl phthalate, and residual organic pollutants such as furans.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited at all by these Examples.
In each of Examples and Comparative Examples, the layered graphite oxide (GO) is obtained by the method of Hummers and Offeman (W. Hummers and RE Offeman, J. Am. Chem. Soc., 80, 1339 (1958)). The manufactured one was used. The CEC of this layered graphite oxide was 6.74 mmol / g.

Example 1 Synthesis Method 1 Using Layered Graphite Oxide
Citric acid, titanium tetrachloride, and water were mixed and stirred so that the concentrations of citric acid and titanium tetrachloride were 0.384 N and 0.493 N, respectively, to obtain a TC solution.
100 mg of layered graphite was mixed with 28 ml of the obtained TC solution, stirred at room temperature for 3 hours, and then refluxed at 90 ° C. for 80 minutes to obtain a mixture of the TC solution and graphite oxide.
The mixture was then washed several times with water and then dispersed in 10 ml of deionized water, and the dispersion was hydrothermally treated at 150 ° C. for 2 hours.
Then, it was left in the air for a whole day and night and further vacuum-dried for a whole day and night to obtain a carbon nanosheet composite (hereinafter referred to as “GOnd-TC-90R80-150HT2”).

(Example 2: Synthesis method 1 using layered graphite oxide)
A carbon nanosheet composite (hereinafter referred to as “GOnd-TC-110R80-150HT2”) was obtained in the same manner as in Example 1, except that the reflux temperature in Example 1 was changed to 110 ° C.

(Example 3: Synthesis method 2 using a dispersion of graphite oxide)
Citric acid, titanium tetrachloride and water were mixed and stirred so that the concentrations of citric acid and titanium tetrachloride were 0.6 N and 0.77 N, respectively, to obtain a TC solution.
On the other hand, 100 mg of layered graphite oxide (GO) was added to 10 ml of 0.05N NaOH aqueous solution, which was stirred by ultrasonic treatment for 30 minutes to peel off the layered graphite oxide, and a dispersion of graphite oxide Got.
18 ml of the TC solution and the dispersion of the graphite oxide were mixed and stirred at room temperature for 3 hours.
The obtained mixed liquid was subjected to hydrothermal treatment at 150 ° C. for 2 hours.
Then, it centrifuges, the obtained solid substance is washed with deionized water and ethanol, and vacuum-dried for one day and night, and a carbon nanosheet composite (hereinafter referred to as “GO-TC-150HT2”). Obtained.

(Comparative Example 1: Example 1 of Japanese Patent Application No. 2007-107467)
Tetraisopropoxytitanium (Ti (OC ₃ H ₇ ) ₄ ) 11.36 g was added to a 0.36N HCl aqueous solution and reacted at 50 ° C. for 3 to 5 hours to obtain a transparent sol. The molar ratio of HCl to tetraisopropoxide in the obtained sol was 1.08.
The obtained transparent titania sol and the above dispersion of graphite oxide (GO) were mixed and stirred at 50 ° C. for 3 hours.
The amount of the transparent titania sol used was 22.3 times the mole of Ti and [H ⁺ ] of GO.
Next, the obtained product was washed with water, vacuum-dried, fired at 550 ° C. in vacuum, and described as a carbon nanosheet composite (hereinafter referred to as “Ti-1.08-GO-22.3-550”). )

(Comparative Example 2)
In Example 3, a single titanium oxide (hereinafter referred to as “TC-150HT2”) was obtained in the same manner as in Example 3 except that the graphite oxide dispersion was not used.

Examples 1 to 3, each of Comparative Examples 1 and 2, and commercially available titanium oxide ST-01, TiO ₂ content from thermal gravimetric analysis (wt%), anatase crystal size from X-ray diffraction method _{(L A (101)} / nm, where LA ₍₁₀₁₎ = 0.9λ / βcos θ; where λ = 0.15418 nm (CuKα ray wavelength), β = the half width of the diffraction peak at A (101), θ = diffraction Angle) from the BET analysis for the nitrogen adsorption isotherm to the BET specific surface area (S _BET / m ² g ⁻¹ ) and the BJH analysis for the nitrogen adsorption isotherm from the mesopore volume (V _meso / mlg ⁻¹ ), mesopore size (D _meso / Nm). The obtained results are shown in Table 1.

In Examples 1-3 and Comparative Example 1 at a ratio of 2 L solution / 1 g sample in 50 ppm methyl orange (hereinafter referred to as “MO”) solution at an initial concentration (described as C ₀ ) at 30 ° C. The obtained carbon nanosheet composite and the titanium oxide obtained in Comparative Example 2 were added, and changes over time in the MO concentration under dark and light irradiation conditions were measured.
The result is shown in FIG. In the figure, □ indicates Example 1, ● indicates Example 2, ▲ indicates Example 3, ◯ indicates Comparative Example 1, and △ indicates Comparative Example 2. “Dark” means that the light is completely This is a dark state that is cut into two, and only the adsorption action of the sample on the MO works. On the other hand, “UV” is a state in which light is irradiated with a 6 × 15 W germicidal lamp after adsorption and equilibration for 24 hours in a dark state, and only a photodecomposing action works.

Table 1 shows the results of calculating the photolysis initial rate constant (k ₀ ) of zero-order methylene orange (MO) by the following method for the examples, comparative examples, and commercially available products.
A measurement point within 6 hours is approximated by a straight line from the relationship of C / C _{0 to} t in the light irradiation state, and k ₀ is calculated from the intercept (b) by the following equation.
k ₀ = b × C ₀ × V _L / W
Here, C ₀ is the initial concentration (50 ppm, ppm≈mg / L), V _L is the solution volume (0.02 _L ), and W is the catalyst weight (10 mg).

From Table 1 and FIG. 1, the composite obtained by the present invention has an extremely high ability to adsorb organic matter as compared with single TiO ₂ (Comparative Example 2), and the photocatalytic resolution is greatly improved as compared with that of Comparative Example 1. I understand that. And, the maximum photodegradation rate constant is more than 3 times larger than that of commercial products.
From the above, the carbon nanosheet composite produced by the method of the present invention has not only an adsorption and concentration action, but also a high photodegradation activity. It can be said that it can be removed.

  The present invention provides a graphite oxide in which titanium dioxide mainly composed of anatase crystals useful as a photocatalyst is introduced, and an organic pollutant removing agent having excellent adsorption concentration characteristics and strong photocatalytic activity, Moreover, since the active site of the photocatalyst exists on the graphite oxide, it can be selectively removed against low-concentration organic pollutants. Therefore, it can be expected that the present invention is used for the production of ultra-clean water from which organic pollutants suitable for surface treatment water such as fresh vegetables and drinking water are highly removed.

The figure which shows the MO density | concentration change of a dark state and a light irradiation state of an Example and a comparative example.

Claims (8)

  A method for producing a titanium oxide-introduced carbon nanosheet composite comprising mixing a solution obtained by mixing and stirring an inorganic titanium salt and citric acid and a graphite oxide, followed by hydrothermal treatment.   The method for producing a titanium oxide-introduced carbon nanosheet composite according to claim 1, wherein the graphite oxide is a layered graphite oxide.   3. The method for producing a titanium oxide-introduced carbon nanosheet composite according to claim 2, wherein the mixture is refluxed before the hydrothermal treatment.   The method for producing a titanium oxide-introduced carbon nanosheet composite according to claim 1, wherein the graphite oxide is a graphite oxide obtained by stirring a layered graphite oxide in a basic aqueous solution.   The method for producing a titanium oxide-introduced carbon nanosheet composite according to any one of claims 1 to 4, wherein the hydrothermal treatment is performed at 100 to 200 ° C.   The said titanium oxide has an anatase microcrystal as a main component, The manufacturing method of the titanium oxide introduction | transduction carbon nanosheet composite of any one of Claims 1-5 characterized by the above-mentioned.   A processing agent for removing organic pollutants, comprising a carbon nanosheet composite obtained by the method according to any one of claims 1 to 6, wherein organic pollutants can be taken in between the layers.   A method for removing an organic pollutant, comprising using the carbon nanosheet composite obtained by the method according to any one of claims 1 to 6 to take in an organic pollutant between the layers.

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