JP3697513B2 - Manganate nanosheet ultrathin film and method for producing the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an ultrathin film in which manganate nanosheets and organic polymers are alternately accumulated, an manganate nanosheet ultrathin film obtained by removing the polymer, and a method for producing each of these ultrathin films.
In particular, the present invention relates to an ultrathin manganate nanosheet that is expected as an electrode material using solid-state redox properties and a method for producing the same.
[0002]
[Prior art and problems of the invention]
In recent years, transition metal oxides have attracted attention as part of creating new functions. In particular, active proposals and reports regarding the thin film technology have been sent to various academic societies and publications.
Manganese oxide thin film is one of them and is no exception. A wide range of reports have been made on the direction of research, from the very basic to the proposal of specific utilization technologies. In addition, such research trends are reflected in the patent literature, and in various fields, inventions relating to manganese oxide thinning technology have been actively made.
The film forming technique is manufactured by a sol-gel method, electrodeposition, a CVD method, or the like.
[0003]
However, in the conventional method, it is difficult to control the film thickness in the nanometer range in the sol-gel method and the electrolytic oxidation method, and the CVD method has to be based on an extremely expensive apparatus, and has advantages and disadvantages. In the future, it is expected that extremely precise control of the film thickness will be required as advanced use of manganese oxide thin films progresses. In consideration of the above circumstances, the present invention intends to provide a manganate nanosheet ultrathin film capable of controlling the film thickness at an ultrafine film thickness level by a method completely different from the conventional method and a method for producing the same. It is.
[0004]
[Means for Solving the Problems]
Therefore, as a result of earnest research, we obtained manganic acid nanosheets by subjecting layered manganese oxides to specific chemical treatment as described later, and obtained manganic acid nanosheets and separately prepared organic polycations from the liquid phase. It is systematically adsorbed to the substrate material with a thickness in the sub-nm to nm range, and it is possible to form a film by repeating this, and by adjusting and selecting the number of times of adsorption, a very fine film thickness can be controlled. It was found that it is possible to provide an ultra-thin film formed by layer-by-layer while controlling the composition and structure of the film at a nano level and a method for producing the same. The present invention has been made based on this finding.
[0005]
That is, the present invention is intended to provide an ultrathin film of a manganate nanosheet and a method for producing the same by alternately adsorbing the manganate nanosheet and the organic polycation to the substrate, respectively, which has been difficult to achieve. It is an object of the present invention to provide a new ultra-thin film that can easily achieve thickness control at a sub-nm and a method for manufacturing the same, and configurations taken for this purpose are described in (1) to (7) below. Street.
[0006]
(1) An ultrathin film comprising a manganate nanosheet and a polymer, wherein manganate nanosheets (two-dimensional crystallites) obtained by peeling off layered manganese oxide microcrystals and a polymer are alternately laminated.
(2) The ultrathin film comprising the manganate nanosheet and the polymer as described in (1) above, wherein the two-dimensional crystallite comprises a manganate nanosheet represented by MnO ₂ .
(3) By repeating the operation of alternately immersing the substrate in the colloidal solution in which the manganic acid nanosheet is suspended and the cationic polymer solution, the nanosheet and the polymer are adsorbed on the substrate, respectively, and the both components are sub-nm to nm. A method for producing an ultrathin film comprising a manganic acid nanosheet and a polymer, wherein a multilayer film that repeats alternately at a level interval is accumulated.
(4) A two-dimensional crystallite (manganate nanosheet) obtained by peeling off layered manganese oxide microcrystals and a polymer are alternately laminated, and then the polymer is removed to obtain an ultrathin manganate nanosheet. Manganate nanosheet ultra-thin film.
(5) The ultrathin manganate nanosheet according to (4), wherein the two-dimensional crystallite is composed of a manganate nanosheet represented by MnO ₂ .
(6) By repeating the operation of alternately immersing the substrate in the colloidal solution in which the manganic acid nanosheet is suspended and the cationic polymer solution, the nanosheet and the polymer are adsorbed on the substrate, respectively, and the two components are sub-nm to nm. A method for producing an ultra-manganese nanosheet ultrathin film, comprising laminating alternately repeating films at level intervals and then removing the polymer to obtain an ultrathin manganate nanosheet.
(7) The method for producing an ultrathin manganese oxide film as described in (6) above, wherein the means for removing the polymer is performed by heating and is removed by decomposition.
[0007]
The manganic acid nanosheet, which is a direct raw material to be laminated on the substrate, is obtained by exfoliating up to one host layer by applying a special chemical treatment to the manganese oxide having a layered structure. Manganese oxide-based nanomaterials with morphological and structural features that are not found in conventional manganese oxides, such as a molecular thickness of 1 nm or less and high two-dimensional anisotropy. (Patent pending).
[0008]
Here, the manganese oxide having a layered structure used as a starting material in the present invention is a composition formula A _X MnO ₂ (A is one or two or more alkalis selected from Li, Na, K, Rb, or Cs). It is a group of compounds given by metals, x ≦ 1). The layered manganese oxide (K _0.45 MnO ₂ ) used in the present invention was synthesized and used by an original method developed by the present inventors as described in Examples described later. Regarding the layered manganese oxide, C.I. Delmas, C.I. By Fouassier et al. Under the title “Les Phases K _X MnO ₂ (x <1)”. anorg. allg. Chem. vol. 420, p. 184-192 (1976).
[0009]
As a result of diligent research, the present inventors have determined that this layered manganese oxide is acid-treated and converted to hydrogen type H _{X ′} MnO ₂ .nH ₂ O (x ′ ≦ 1, 0 ≦ n ≦ 3) By shaking in an aqueous solution of an amine or the like, a colloidal solution in which the layers constituting the mother crystal, that is, the nanosheets, were separated and dispersed in water one by one was succeeded.
This nanosheet was isolated for the first time from the layered oxide and independently provided by the present inventors, and the specificity of its form, properties, etc. was as described in the following. It has been clarified that it has a completely different form, structure, and properties from the parent crystal and the conventional manganese oxide fine powder.
The thickness of the nanosheet depends on the crystal structure of the starting mother crystal, but is extremely thin, 1 nm or less. On the other hand, the lateral size is on the order of sub-μm to μm and has a very high two-dimensional anisotropy.
[0010]
Since this manganic acid nanosheet is a kind of polyanion having a negative charge, it can be alternately adsorbed in a self-assembled manner on an appropriately treated substrate surface by combining with a polymer having a positive charge. That is, it has been clarified that when a substrate having a positively charged surface is immersed in a colloidal solution in which manganate nanosheets are dispersed, the nanosheet is adsorbed on the substrate surface by electrostatic interaction.
[0011]
Then, when the surface is completely covered with the manganate nanosheet, the charge state of the substrate surface changes to negative, the accumulation of the nanosheet beyond that does not proceed due to electrostatic repulsion, and the adsorption reaction self-stops. Next, when the substrate is immersed in an organic polycation solution, the surface is covered with the polycation in the future. By repeating this self-organized adsorption reaction, manganate nanosheets and polymers are alternately accumulated layer-by-layer, and an ultra-thin film can be synthesized.
[0012]
As a result, the obtained thin film has a nanostructure in which manganate nanosheets and organic polymers are stacked in the nm range.
The actual film forming operation is according to the following procedures and procedures. First, a series of operations of (1) immersing in a manganic acid nanosheet colloid solution → (2) cleaning with pure water → (3) immersing in an organic polycation solution → (4) cleaning with pure water is a cycle. Is repeated as many times as necessary.
[0013]
As the organic polycation, poly (diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI), polyallylamine hydrochloride (PAH) and the like are suitable. The substrate can be made of various materials such as a quartz glass plate, a Si wafer, a mica plate, a graphite plate, and an alumina plate, and the size is not limited in principle.
[0014]
However, cleaning and pretreatment of the surface prior to the lamination operation is essential. The cleaning treatment is typically performed by washing with a neutral detergent, degreasing with an organic solvent, washing with concentrated sulfuric acid or the like. The pretreatment is an operation for stably starting the self-assembly reaction, and is immersed in an organic polycation solution such as PEI to adsorb the polycation and introduce a positive charge on the substrate surface.
[0015]
The growth of the multilayer ultrathin film can be monitored by measuring the ultraviolet / visible absorption spectrum for each cumulative operation. As a representative example, FIG. 1 shows ultraviolet / visible absorption spectrum data when an ultrathin film is constructed by combining a manganate nanosheet and PDDA. This data is observation data measured when the concentration of the manganic acid nanosheet colloidal solution is 0.08 g dm ⁻³ . PDDA has no meaningful absorption in this measurement wavelength region, and the observed absorption is derived from the manganate nanosheet. As the absorbance increases almost in proportion to the number of times of accumulation (FIG. 2), it can be seen that a certain amount of manganate nanosheets is accumulated on the substrate for each accumulation operation, and regular thin film growth occurs. It is proved that. FIG. 3 shows a change in the color tone of the sample thus formed, and it is confirmed that a dark brown color peculiar to manganese oxide is gradually exhibited as the cumulative number increases.
[0016]
FIG. 4 shows X-ray diffraction data of the sample in the same film forming process. As the accumulation proceeds, a broad diffraction peak appears in the vicinity of 2θ = 10 °, and its intensity gradually increases (FIG. 4). This peak can be considered to reflect the repetition period of the manganic acid nanosheet and PDDA, which again confirms that the multilayer ultrathin film is regularly grown. The interplanar spacing is around 0.80 nm, which confirms that the nanostructure has a sub-nm range.
[0017]
The cumulative amount of manganate nanosheets on the multilayer ultrathin film can be controlled over a wide range by changing the concentration, pH, immersion time, etc. of the nanosheet colloid solution among the process parameters of the adsorption cycle. As an example, FIG. 5 shows the relationship between the cumulative number of times when the manganate nanosheet colloid solution is formed using a manganate nanosheet colloid solution having a concentration of 0.01 g dm ⁻³ and the ultraviolet / visible absorption spectrum. Yes. It is possible to suppress the cumulative amount of manganate nanosheets by using a solution with a clearly low concentration. Even in such a case, a regular growth of a layer-by-layer multilayer film is possible.
[0018]
The organic polymer can be removed by heating from the organic / inorganic composite ultrathin film in which the manganic acid nanosheets and polymer thus prepared are accumulated, thereby forming an inorganic film. FIG. 6 is a diagram clarified based on an X-ray diffraction pattern showing the relationship between the cumulative number of manganate nanosheets / PDDA ultrathin films and the heating process. In this figure, an arrow indicates a Bragg peak indicating a stacking period (0.8 nm) of the cumulative multilayer film, and a black circle indicates 222 reflection of Mn ₂ O ₃ . The halo at 2θ of 15 to 30 ° is derived from the quartz glass substrate. As shown in FIG. 6, a diffraction peak reflecting the nanostructure of the manganate nanosheet / polymer is seen up to 100 ° C., but this diffraction line disappears by heating at 200 ° C. or higher. This is because the polymer was thermally decomposed and removed, indicating that an inorganic film was obtained. When further heated, Mn ₂ O ₃ crystallizes at 500 ° C. or higher, and a manganese oxide thin film is obtained.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, according to the present invention, the film thickness is self-supporting by simply immersing the colloidal solution and the polymer solution of the manganese nanosheet obtained by subjecting the layered manganese oxide to a specific chemical treatment in the substrate. By controlling the number of times, etc., we succeeded in forming a manganese oxide film whose thickness can be easily controlled in the sub-nanometer range. Next, the present invention will be specifically described based on examples. However, this embodiment is only for the purpose of explaining the aspect of the present invention based on a specific example and assisting the understanding of the present invention, and is not intended to limit the present invention.
[0020]
[Example 1]
0.4 g of layered manganate powder (H _0.13 MnO ₂ .0.7H ₂ O) obtained by acid treatment of layered potassium manganate represented by composition formula K _0.45 MnO ₂ was added to 100 cm ³ of tetrabutylammonium hydroxide solution. In addition, the mixture was shaken at room temperature for about 1 week (150 rpm) to obtain a colloidal solution in which the manganate nanosheets were dispersed. This was diluted to a concentration of 0.08 g dm ⁻³ , and hydrochloric acid was further added to adjust the pH to 9. On the other hand, a 2 wt% polydimethyldiallylammonium (PDDA) chloride aqueous solution was prepared, and its pH was adjusted to 9. Next, the quartz glass plate (5 cm × 1 cm) was washed with Merck's ExtraMA022% solution, and then immersed in a 1: 1 solution of concentrated sulfuric acid and methanol for 30 minutes. After 30 minutes, the solution was taken out from the solution and thoroughly washed with Milli-Q pure water.
[0021]
Next, this substrate was immersed in a polyethyleneimine aqueous solution having a concentration of 0.25 wt% for 20 minutes and thoroughly washed with Milli-Q pure water.
The substrate thus cleaned and pretreated was immersed in (1) the manganic acid nanosheet colloid solution. (2) After 20 minutes, it was thoroughly washed with Milli-Q pure water and dried by blowing an argon stream. (3) Next, this substrate was immersed in a PDDA solution for 20 minutes, and (4) was then thoroughly washed with Milli-Q pure water. By repeating the above operations (1) to (4), an ultrathin manganate nanosheet was synthesized.
[0022]
When the above-described film formation cycle was repeated once, the ultraviolet / visible absorption spectrum was measured. As a result, broad absorption due to the manganate nanosheet was observed (FIG. 1), and the absorbance was almost linear for each adsorption cycle. (Fig. 2). As a result, it was found that almost the same amount of nanosheets was adsorbed and accumulated on the substrate. Further, from the X-ray diffraction data shown in FIG. 4, a black peak having a periodic structure of about 0.8 nm appeared, and the intensity increased as the number of adsorptions increased.
From the above data, it was confirmed that a multilayer ultrathin film in which manganate nanosheets and PDDA were alternately repeated in the nanometer scale range could be constructed.
[0023]
[Example 2]
A quartz glass substrate that had been cleaned and pretreated in the same procedure as in Example 1 was immersed in (1) a manganic acid nanosheet colloidal solution (pH = 9) having a concentration of 0.01 g dm ⁻³ . (2) After 20 minutes, it was thoroughly washed with Milli-Q pure water and dried by blowing an argon stream. (3) Next, the substrate was immersed in the PDDA solution of Example 1 for 20 minutes, and (4) was then thoroughly washed with Milli-Q pure water.
As a result of repeating the above operations (1) to (4) and examining the film forming process in the same manner as in Example 1 (FIG. 5), the cumulative amount of manganate nanosheets was ¼ of that in Example 1. The production of the multilayer ultrathin film suppressed to the following was confirmed.
[0024]
[Example 3]
The manganate nanosheet / PDDA multilayer ultra-thin film synthesized according to Example 1 was placed in a platinum crucible and heated in an electric furnace. Heating was performed from room temperature at a rate of 5 ° C. min ⁻¹ , held at the target temperature for 1 hour, and then the heater was turned off and allowed to cool. After returning to room temperature, a sample was taken out and its X-ray diffraction pattern was measured (FIG. 6). As a result, it was revealed that the nanostructure of the multilayer film was destroyed at 200 ° C. This is probably because PDDA was thermally decomposed, and the formation of an inorganic film was confirmed. It was also found that the film was changed to a Mn ₂ O ₃ thin film by heating at 500 ° C. or higher.
[0025]
【The invention's effect】
As disclosed above, the present invention succeeded in providing a thin film of manganese oxide by an unprecedented film forming method. The operation consists of preparing a colloidal solution of manganic acid nanosheets and an organic polymer solution, and immersing the material substrate to be deposited alternately in this solution. This is made possible by a very simple and reproducible unique method that can be controlled automatically, and its significance is extremely large.
[Brief description of the drawings]
FIG. 1 shows an ultraviolet / visible absorption spectrum of a cumulative process of a manganate nanosheet / PDDA multilayer ultrathin film.
FIG. 2 is a graph showing the relationship between the absorbance (340 nm) in the accumulation process of manganate nanosheets / PDDA ultrathin films and the number of accumulations.
FIG. 3 is a diagram observing the relationship between the number of accumulated manganate nanosheets / PDDA ultrathin films and the color tone.
FIG. 4 is an X-ray diffraction pattern of a cumulative process of a manganate nanosheet / PDDA multilayer ultrathin film.
FIG. 5 shows an ultraviolet / visible absorption spectrum of a cumulative process of a manganate nanosheet / PDDA multilayer ultrathin film.
FIG. 6 is an X-ray diffraction pattern of a heating process of a manganate nanosheet / PDDA multilayer ultrathin film (10 layers).

Claims (7)

An ultra-thin film comprising a manganese oxide nanosheet and a polymer, wherein two-dimensional crystallites (hereinafter referred to as manganate nanosheets) obtained by peeling off layered manganese oxide microcrystals and polymers are alternately laminated. . Ultrathin film the two-dimensional crystallite composed of a manganese oxide nanosheets and polymer according to claim 1, characterized in that it consists manganate nanosheet represented by MnO _2. By repeating the operation of alternately immersing the substrate in the colloidal solution and the cationic polymer solution in which the manganic acid nanosheet is suspended, the nanosheet and the polymer are adsorbed on the substrate, respectively, and the two components are spaced at a sub-nm to nm level. A method for producing an ultrathin film comprising a manganic acid nanosheet and a polymer, wherein a multilayer film that repeats alternately is accumulated. Manganic acid characterized in that two-dimensional crystallites (manganate nanosheets) obtained by peeling off layered manganese oxide microcrystals and polymers are alternately laminated, and then the polymer is removed to obtain an ultrathin manganate nanosheet Nanosheet ultra-thin film. 5. The ultrathin manganate nanosheet according to claim 4, wherein the two-dimensional crystallite comprises a manganate nanosheet represented by MnO ₂ . By repeating the operation of alternately immersing the substrate in the colloidal solution and the cationic polymer solution in which the manganic acid nanosheet is suspended, the nanosheet and the polymer are adsorbed on the substrate, respectively, and the two components are spaced at a sub-nm to nm level. A method for producing an ultra-manganese nanosheet ultrathin film, comprising laminating alternately repeating films and then removing the polymer to obtain an ultrathin manganate nanosheet. The method for producing an ultrathin manganese oxide film according to claim 6, wherein the means for removing the polymer is performed by heating and is removed by decomposition.

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