JP4863290B2 - Method for producing carbon nanosheet composite, 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, particularly for the removal of trace amounts of organic pollutants. The present invention relates to a method for producing a suitable carbon nanosheet composite 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.

  For example, in Patent Document 1, as an endocrine disrupting substance-containing water treatment method, an adsorbent composed of a hydrophobic porous material such as zeolite, or an adsorbent carrying an oxidation catalyst thereon is used, or further, Irradiation and ozone aeration are used together, but even in this case, it can be applied only to organic substances with a concentration range of at least 100 ppb to 10 ppm, and adsorbent preparation (requirement of pore size, surface bonding of hydrophobic groups, etc.) ) And the loading of the oxidizing agent are complicated and disadvantageous from the viewpoint of economy.

On the other hand, the present inventors dispersed graphite oxide obtained by oxidizing graphite in an alkali, or expanded the layer with long-chain organic ions in advance, followed by hard crosslinking such as metal or metalloid oxide. It has been reported that a carbon-containing porous composite with a high surface area can be synthesized by introducing an agent (see Patent Documents 2 and 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).
JP 2000-254666 A JP 2003-192316 A JP 2004-217450 A JP 2006-272266 A

  The present invention has been made in view of the circumstances as described above, and provides a treatment agent for removing organic environmental pollutants, which is more efficient and whose preparation means is not complicated. It is intended to do. Another object of the present invention is to provide a method capable of completely removing trace amounts of organic environmental pollutants.

  As a result of further investigation on the layered product of the graphite oxide in which the titanium oxide is inserted between the layers in the process of advancing research to achieve the above-mentioned object, the present inventors have described in Patent Document 4 described above. Without being subjected to a pre-expansion treatment with a long-chain organic amine, a long-chain surfactant, a long-chain alcohol or the like, the graphite oxide layer was simply peeled off by stirring in a basic solution. The inventors have also found that titanium oxide can be introduced by using a sheet-like graphite oxide. Moreover, the crystallinity of the titanium oxide introduced into the said sheet-like graphite oxide is improved by using the transparent sol obtained by hydrolyzing an organic titanium compound beforehand in acidic aqueous solution as a raw material of the titanium oxide to introduce | transduce. 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 can be photodegraded after being adsorbed and concentrated.

The present invention has been completed based on these findings, and is as follows.
(1) An organic titanium compound was previously hydrolyzed in an acidic aqueous solution to produce transparent titania, and the obtained transparent sol was obtained by peeling the layered graphite oxide by stirring in a basic aqueous solution. A method for producing a titanium oxide-introduced carbon nanosheet composite comprising mixing and stirring with a dispersion of sheet-like graphite oxide and then firing the mixture.
(2) The method for producing a titanium oxide-introduced carbon nanosheet composite according to (1), wherein the firing is performed in a vacuum atmosphere.
(3) The method for producing a titanium oxide-introduced carbon nanosheet composite according to (1) or (2), wherein the titanium oxide contains anatase microcrystals as a main component.
(4) Organic pollutant removal treatment characterized by comprising a carbon nanosheet composite obtained by any one of the above methods (1) to (3) and capable of incorporating organic pollutants between the layers. Agent.
(5) A method for removing an organic pollutant, comprising using the carbon nanosheet composite obtained by any one of the methods (1) to (3) to incorporate an organic pollutant between the layers.

  The carbon nanosheet composite produced by the method of the present invention adsorbs and concentrates organic pollutants present at low concentrations by incorporating organic pollutants between the layers, making them completely harmless under energy-saving conditions In particular, it is possible to cope with the removal treatment of extremely low concentration organic pollutants of about several to several tens of ppb.

The layered body of graphite oxide used as a base material in the present invention is prepared by, for example, immersing graphite in a mixed solution of concentrated sulfuric acid and nitric acid, adding potassium chlorate to react, or mixing concentrated sulfuric acid and sodium nitrate. It is prepared by dipping in a liquid, adding potassium permanganate and 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. The oxygen atoms and hydrogen atoms are bonded to these changed carbon atoms and oxygen atoms can be introduced between the layers. The interlayer distance of the graphite oxide layered product thus produced is usually about 0.6 to 1.1 nm.

In the present invention, the layered product of graphite oxide thus produced is dispersed in a basic aqueous solution to form a sheet-like graphite oxide.
Specifically, the graphite layered material is sufficiently agitated and dispersed in a basic aqueous solution, preferably by ultrasonic treatment, to separate the graphite layered material to obtain a sheet-like graphite oxide. It is.

Next, a titanium nano-particle precursor is introduced into the sheet-like graphite oxide whose layers have been peeled in this way to produce a carbon nanosheet composite composed of the sheet-like graphite oxide into which titanium oxide has been introduced. it can.
As a method for introducing the titanium oxide precursor into the sheet-like graphite oxide, an organic titanium compound is previously hydrolyzed in an acidic aqueous solution to produce a transparent titania, and the obtained transparent sol is converted into the sheet-like graphite. Mix and agitate with oxide dispersion.

The amount of the organotitanium compound in the transparent sol used is 70 times or less, preferably 30 times the number of moles of the ion-exchangeable sheet-like graphite oxide (GO) (hereinafter abbreviated as [H ⁺ ]). The sheet-like graphite oxide and the transparent sol are mechanically stirred and mixed so as to be not more than twice, more preferably 5 to 25 times.
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 30 times or less, more preferably 5 to 25 times. An oxide precursor containing the precursor may be used.

In order to form a stable carbon nanosheet composite into which titanium oxide is introduced using the sheet-like graphite oxide into which the titanium oxide precursor has been introduced in this way, the titanium oxide precursor is formed on the sheet-like graphite oxide by the above method. After being introduced, it is preferably dried at 50 to 150 ° C. and then fired in an inert atmosphere.
Firing is performed by heat treatment at a firing temperature of 500 to 1000 ° C, preferably 500 to 700 ° C for 1 to 8 hours. By the calcination treatment, a stable carbon nanosheet composite of the present invention in which titanium oxide is introduced is obtained.

  At least the organic titanium compound used in the method of the present invention is not particularly limited as long as it becomes titanium oxide by the above-described baking treatment, and preferably the one in which most of the titanium oxide becomes anatase-type titanium oxide crystals. . More specifically, for example, titania sol, esters of titanic acid and lower alcohols, for example, alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl Examples include esters with alcohols. Preferred examples of the titanium oxide precursor include tetraethoxy titanium and tetraisopropoxy titanium.

  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 sheet of sheet-like graphite oxide. 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, mesomil, Methoxychlor, Milex, Nitrophen, Toxaphene, Tributyltin, Triphenyltin, Trifluralin, Alkylphenol (C5-C9), Nonylphenol, 4-octylphenol, Bisphenol A, Di-2-ethylhexyl phthalate, Dibutylbenzyl phthalate, Phthalic acid Di-n-butyl, dicyclohexyl phthalate, diethyl phthalate, benzo (a) pyrene, 2,4-dichlorophenol, di-2-ethylhexyl adipate, benzophenone, 4-nitrotoluene, octachlorostyrene, aldicarb, Benomyl, Kipong (Chlordecone), Manzeb (Mancozeb), Mannebu, Methylam, Metribuzin, Cipermethrin, Esfenvalerate, Fenvalerate, Permethrin, Vinclozoline, Di Bed, ziram, dipentyl phthalate, dihexyl phthalate, environmental hormones such as phthalic acid dipropyl and such persistent organic pollutants such as furans and the like.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited at all by these Examples.
(Example 1: Production of sheet-like graphite oxide)
As the layered graphite oxide (GO), one produced by the method of Hummers and Offeman (W. Hummers and RE Offeman, J. Am. Chem. Soc., 80, 1339 (1958)) was used.
0.2 g of this layered graphite oxide (GO) is added to 20 mL of 0.05N NaOH aqueous solution, which is stirred for 30 minutes by sonication to peel off the layered graphite oxide, and sheet graphite oxide (GO).
The CEC of the obtained sheet-like graphite oxide (GO) was 6.74 mmol / g.
(Example 2: Production of transparent titania sol)
8.52 g of tetraisopropoxytitanium (Ti (OC ₃ H ₇ ) ₄ ) was added to a 0.36N HCl aqueous solution and reacted at 50 ° C. for 3 to 5 hours to obtain a transparent sol.

(Example 3: Production of carbon nanosheet composite)
The dispersion of sheet-like graphite oxide (GO) obtained in Example 1 and the transparent titania sol obtained in Example 2 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 and vacuum-dried, and then baked at 250 ° C., 350 ° C., 450 ° C., 550 ° C., and 650 ° C. in a vacuum to form a carbon nanosheet composite (hereinafter “Ti-1.44”). -GO-22.3-T ", where T is the calcination temperature (° C) and 1.44 is the molar ratio of HCl to tetraisopropoxide).

(Comparative Example 1: Production of a composite comprising a layered body of graphite oxide)
On the other hand, as a comparative example, 0.2 g of the above-mentioned layered graphite oxide (GO) was not directly dispersed in the alkaline solution, but was simply mixed directly with the transparent titania sol obtained by the same method as in Example 2. In the same manner as in Example 3, the composite of layered graphite oxide and titanium oxide (hereinafter referred to as “Ti-1.44-GO-22.3-T-nd”. Here, “1. .44 "and" T "are the same as described above, and nd means that they were directly mixed without dispersion. What was obtained in this way was not like Example 3 in which titania particles were intercalated between carbon nanosheet layers, but titania was supported only on the outer surface layer. This is called a supported composite.
Further, after evaporating water from the clear titania sol solution without mixing with GO, vacuum firing was performed at 350 ° C. and 550 ° C., respectively, and single titania powders (hereinafter referred to as “TiO ₂ -350” and “TiO ₂ -550 respectively”). Is obtained.).

FIG. 1 shows the X-ray diffraction pattern of the composite obtained in Example 3. In the figure, an X-ray diffraction pattern of a sample that was not fired was shown as a comparative example.
From FIG. 1, the A (101) diffraction peak derived from the (101) plane of anatase increases with an increase in the firing temperature, and thus anatase crystals begin to grow gradually. However, when the temperature exceeds 550 ° C., rutile. It was found that crystals (R (110) peak) began to form.

Example 4
In Example 3, the baking temperature was set to 550 ° C., and the amount of the transparent titania sol used was 22.3 times the molar number of Ti with respect to [H ⁺ ] of GO, and tetraisopropoxy used in the clear sol synthesis. The carbon nanosheet composite was prepared in the same manner as in Example 3 except that the molar ratio of HCl to hydrogen (hereinafter referred to as x) was changed to 0.36, 0.72, 1.08, 1.44, and 4. (Hereinafter referred to as “Ti-x-GO-22.3-550”).
FIG. 2 shows the X-ray diffraction pattern of the composite obtained in this example.
FIG. 2 indicates that a high x value of x = 4 does not significantly affect the anatase crystal size and promotes the growth of rutile crystals.

(Example 5)
The carbon nanosheet composite obtained in Example 4 and the support composite (Ti-1.44-GO-22.3-T-nd) obtained in Comparative Example 1 and single titania particles (TiO ₂ − 350, TiO ₂ -550), the TiO ₂ content (wt%) from thermogravimetric analysis, the anatase crystal size (LA ₍₁₀₁₎ / nm, where LA ₍₁₀₁₎ = 0 from X-ray diffractometry. .9λ / βcos θ; where λ = 0.15418 nm (CuKα ray wavelength), β = half-value width of diffraction peak of A (101), θ = diffraction angle) and weight ratio of anatase crystal in titania crystal (AF / wt %, _{where, AF = 100 × I A (} 101) / (I A (101) + 1.265I R (110)); _{Note, I A (101), I} R (110) are respectively A (101) , R (110) diffraction peak Strength) from BET analysis for nitrogen adsorption isotherm, BET specific surface area (S _BET / m ² g ⁻¹ ), and BJH analysis for nitrogen adsorption isotherm from mesopore volume (V _meso / mlg ⁻¹ ), mesopore size (D _meso / nm) was determined respectively.

From Table 1, (1) the titania content of the Ti-x-GO-22.3-550 sample is almost the same regardless of the value of x, (2) the carbon nanosheet obtained by dispersing and peeling GO The titania content of the composite is greater than the titania content of the supported composite (comparative example) obtained with undispersed GO, (3) when x = 0.72, the specific surface area is the largest ( 4) The mesopore size is around 4 nm regardless of the value of x. (5) The anatase crystal size of the Ti-x-GO-22.3-550 sample does not change greatly as x increases. It can be seen that the content of crystals gradually decreases, and (6) the specific surface area and mesopore capacity of the composite are larger than that of titania alone.
From these results, it can be said that the carbon nanosheet composite has superior characteristics to the support composite and the single titania powder in terms of overall properties such as porosity, titania content, crystal size / component, and the like.

(Example 6)
Carbon nanosheet composite obtained in Example 4 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 body (Ti-x-GO-22.3-550) was added, and the change over time in the MO concentration under dark and light irradiation conditions was measured.
The results are shown in FIG. In the figure, the “dark state” is a state in which light is completely cut, and is a state in which only the adsorption action of the sample on the MO works. On the other hand, the “light irradiation state” 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 the photodecomposing action is active. In the figure, ◯ is x = 0.36, □ is x = 0.72, ▲ is x = 1.08, ● is x = 1.44, and ◆ is x = 4. Each case is shown.

FIG. 3 shows that the MO concentration after 24 hours in the dark state is reduced by 50% or less in all the carbon nanosheet composites, and it can be seen that these composites have an excellent adsorption effect on MO. On the other hand, under the light irradiation conditions, the MO concentration continued to decrease with time, and in the composite synthesized with x <1.08, the MO concentration became close to zero in another 2 days.
From the above, it can be said that the carbon nanosheet composite has not only an adsorption concentration action but also a photodegradation activity, and it is possible to efficiently remove low-concentration organic pollutants by the cooperative action of both.

(Comparative Example 2)
Under the same method and conditions as in Example 6, the removal effect on MO of the supported composite and single titania powder was examined. FIG. 4 compares the time-dependent changes in the MO concentration in the dark state and the light irradiation state of these samples with those of the carbon nanosheet composite in Example 6. In the figure, ▽ is a supported composite (Ti-1.44-GO-22.3-T-nd), △ is a single titania powder (TiO ₂ -350), and ◇ is a single titania powder ( TiO ₂ -550), respectively.
FIG. 4 shows that the composite state of the carbon nanosheet composite is superior to the supported composite, and that the carbon nanosheet composite has good porosity with respect to a single titania powder, and the affinity of the carbon nanosheet to organic matter. Therefore, it can be seen that the carbon nanosheet composite is very excellent in adsorptivity to MO. Therefore, considering the removal effect in the light irradiation state and the adsorption concentration effect in the dark state, in the case of the carbon nanosheet composite, the removal rate for the low concentration MO is larger than that of the support composite and the single titania powder. It can be said that it has improved.

  The present invention provides a sheet-like graphite oxide in which titanium dioxide mainly composed of anatase crystals, which is useful as a photocatalyst, is introduced, and an organic pollutant removing agent having excellent adsorption concentration characteristics and strong photocatalytic activity. In addition, since the active sites of the photocatalyst are present on the sheet-like graphite oxide sheet, 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 X-ray-diffraction pattern of the composite_body | complex obtained in Example 3. The figure which shows the X-ray-diffraction pattern of the composite_body | complex obtained in Example 4. The figure which shows the removal effect with respect to MO of the carbon nanosheet composite of this invention Comparison diagram of removal effect on MO of carbon nanosheet composite of the present invention, supported composite and single titania powder

Claims (5)

  A sheet-like graphite obtained by preliminarily hydrolyzing an organic titanium compound in an acidic aqueous solution to produce transparent titania, and exfoliating the obtained transparent sol by stirring the layered graphite oxide in a basic aqueous solution. A method for producing a titanium oxide-introduced carbon nanosheet composite comprising mixing and stirring with an oxide dispersion, followed by firing.   The method for producing a titanium oxide-introduced carbon nanosheet composite according to claim 1, wherein the firing is performed in a vacuum atmosphere.   The said titanium oxide has an anatase microcrystal as a main component, The manufacturing method of the titanium oxide introduction | transduction carbon nanosheet composite_body | complex of Claim 1 or 2 characterized by the above-mentioned.   An organic contaminant removal treatment agent comprising the carbon nanosheet composite obtained by the method according to any one of claims 1 to 3, wherein an organic contaminant 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 claim 1 to take in an organic pollutant between the layers.

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