JP4639364B2 - Nano-multilayer film and manufacturing method thereof - Google Patents

Description

The present invention relates to a nano-multilayer film expected to be applied to fields such as highly efficient catalysts and optoelectronic devices, and a method for producing the same , and more specifically, a film composed of a titanate nanotube and a polycation film are laminated. The present invention relates to a nano multilayer film and a manufacturing method thereof.

Nano-sized fine metal particles obtained by impregnating porous silica or titanium oxide with gold, silver, platinum or other metals are known as highly efficient heterogeneous catalysts (see, for example, Non-Patent Documents 1 and 2). ).
In addition, since the nanotube has surfaces on both the hollow part and the outer side, a high specific surface area can be obtained as compared with a rod-like structure having no hollow part. Among them, the titanium oxide nanotubes are produced by a method using a template (for example, see Non-Patent Document 3) or a reaction in an alkaline aqueous solution (for example, see Non-Patent Documents 4 to 6). Titanium oxide nanotubes obtained by reaction in an alkaline aqueous solution are also called titanate nanotubes.

D.R.Rolison, 2003, Science, 299, 1698 Y. Guari et al., 2001, Chem. Commun., P. 1374 P. Hoyer, 1996, Langmuir, 12, 1411 T. Kasuga et al., 1998, Langmuir, 14, 3160 Qing Chen et al., 2002, Adv. Mater. 14: 1208 H. Tokudome et al., 2004, Chem. Comm, page 958

However, a multilayered film of composite nanotubes in which titanate nanotubes are filled with a noble metal such as silver or gold is not known, and there is a problem of how to manufacture this multilayered film.
Accordingly, an object of the present invention is to provide a nano-multilayer film having a titanate nanotube to which a noble metal useful as a highly efficient catalyst, an optoelectronic device or the like is attached, and a method for producing the same.

In order to achieve the above object, the nano-multilayer film of the present invention 1 is a nano-multilayer film in which a film made of titanate nanotubes and a polycation film are laminated, and the titanate nanotubes have inner and outer surfaces. One or both of them hold a noble metal.
Invention 2 is characterized in that in the nano-multilayer film of Invention 1, the noble metal is silver or gold.
Invention 3 is characterized in that in the nano-multilayer film of Invention 1 or 2, the outermost surface of the laminated film is a film made of titanate nanotubes.

Invention 4 is a method for producing a nano-multilayer film according to Inventions 1 to 3, wherein titanate nanotubes are dispersed in an aqueous solution containing a noble metal compound, and the noble metal compound is reduced with a reducing agent to form inner and outer surfaces of the titanate nanotube. Either or both of them hold a noble metal and are dispersed in a liquid to form a dispersion, and a substrate with a polycation film is immersed in the dispersion to form the titanate nanotube in a film form on the polycation film. The first step and the second step of forming the polycation film on the titanate nanotube film by immersing the substrate that has undergone the first step in a polycation solution are repeated one or more times.
Invention 5 is a method for producing a noble metal-containing titanate nanotube multilayer film, characterized in that, in the method for producing a nano-multilayer film of Invention 4, the reducing agent for the reduction treatment is an aqueous sodium borohydride solution.
Invention 6 adjusts the pH of the dispersion in the first step to 7 to 12 and adjusts the pH of the polycation solution in the second step to 8 to 12 in the method for producing a nano-multilayer film of Invention 4 or 5. It is characterized by that.
Invention 7 is characterized in that in the method for producing a nano-multilayer film of any one of Inventions 4 to 6, silver nitrate or tetrachloroauric (III) acid is used as the noble metal compound.
Invention 8 is the method for producing a nano-multilayer film according to any one of Inventions 4 to 7, wherein the substrate immersion time in the dispersion liquid in the first step and the substrate immersion time in the polycation solution in the second step are as follows. The time for immersing the substrate is 20 minutes or more, respectively.
Invention 9 is the method for producing a nano-multilayer film according to any one of Inventions 4 to 8, after the substrate immersion treatment in the dispersion liquid in the first step and after the substrate immersion treatment in the polycation solution in the second step. Each of the substrates is washed with deionized water.
Invention 10 is characterized in that, in the method for producing a nano-multilayer film of any one of Inventions 4 to 9, the concentration of the dispersion is 0.36 g / ltr or more.

According to the nano multilayer film of the present invention, the titanate nanotube film and the polycation film to which the noble metal is attached are alternately formed, and the titanate nanotube is modified with a noble metal having a desired size of several nm. Therefore, by adopting gold or silver as a noble metal, it can be used for highly efficient catalysts and optoelectronic devices.
According to the production method of the present invention, it is possible to form a multi-layer film of titanate nanotubes film and a polycation film attached to the desired size of the noble metal titanate nanotubes. Therefore, by adopting gold or silver as the noble metal, a noble metal-containing titanate nanotube multilayer film useful as a highly efficient catalyst or an optoelectronic device can be produced.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of a multilayer film composed of a titanate nanotube film and a polycation film to which a noble metal is attached according to the present invention. Nano multilayer film 10 of the present invention, in advance on a substrate 11 with a polycation film 12, made of a film 13 and a polycation layer 14 of titanate nanotubes adhering the noble metal is formed by alternately stacking. That is, the nano multilayer film 10 has a multilayer film structure in which polycation films 12 and 14 and titanate nanotube films 13 to which a noble metal is attached are alternately formed in one or more layers.
In Figure 1, the thickness of the polycationic film 12 on the substrate 11 t0, film thickness t1 of the titanate nanotube film 13, although the film thickness t2 of the polycation film 13, these thicknesses chosen arbitrarily can do.
Here, quartz glass, a silicon substrate, or the like can be used for the substrate 11. The polycation films 12 and 14 are formed of polyethyleneimine hydrochloride, polydiallyldimethylammonium chloride, polyallylamine hydrochloride, and the like, and are positively charged films.
The titanate nanotube film 13 is made of a noble metal such as gold or silver attached to and filled in a hollow portion of a titanate nanotube having an outer diameter of 8 to 12 nm, an inner diameter of 3 to 5 nm, and a length of several hundred nm, or attached to the surface of the titanate nanotube The film surface has a negative charge. The composition of the obtained titanate nanotube film 13 is, for example, HxTi2-x / 4 □ x / 4O4 · H2O (x˜0.7, □ indicates a vacancy). The composition of the titanate nanotube film 13 of the present invention is a substance that also includes titanium oxide and HxTi2-x / 4 □ x / 4O4 · H2O (□ indicates a vacancy).
In FIG. 1, the uppermost layer of the nano-multilayer film 10 is the titanate nanotube film 13, but may be a polycation film 14. When the nano multilayer film 10 is used as a catalyst, the uppermost layer of the nano multilayer film 10 is preferably the titanate nanotube film 13.
Although FIG. 1 shows a form in which only one surface of the substrate 11 is laminated, a form in which it is laminated on both the front surface and the back surface of the substrate 11 may be used.
Furthermore, on the substrate 11, to a polycation film 12 and the titanate nanotube film 13 may be formed, further, a polycation layer 14 and the titanate nanotube film 13 may be formed only one layer, respectively, Each layer may be repeatedly laminated.

Here, the manufacturing method of the nano multilayer film 10 is demonstrated.
Anatase-type titanium oxide powder was previously heat-treated at 150 ° C. in a sodium hydroxide NaOH aqueous solution having a concentration of 10 mol (mol) / ltr (liter) to obtain an outer diameter of 8 to 12 nm, an inner diameter of 3 to 5 nm, and a length of several hundred nm. An aggregate of titanate nanotubes is prepared.
First, a noble metal is attached to the titanate nanotube by the following procedure.
As a first procedure, titanate nanotubes are dispersed in an aqueous solution of a noble metal compound such as silver nitrate AgNO3 and tetrachloroauric (III) acid HAuCl4 having a concentration of 0.1 mol / ltr, and this dispersion is stirred for 12 hours or more. As a result, the noble metal compound solution can sufficiently penetrate into the hollow portion of the titanate nanotube, and the noble metal can be filled in the hollow portion, or the noble metal compound can be attached to the surface of the titanate nanotube by 2 to 3 nm. Thereafter, the titanate nanotube impregnated with the noble metal compound is separated from the dispersion using a centrifuge.
As a second procedure, a titanate containing a noble metal simple substance by reducing a noble metal compound by adding a reducing agent such as a sodium borohydride NaBH4 aqueous solution having a concentration of 0.1 mol / ltr to a titanate nanotube filled with a noble metal compound. Nanotubes, that is, titanate nanotubes with precious metals attached are produced.
Next, a dispersion for a multilayer film containing this titanate nanotube (hereinafter referred to as “a dispersion for forming a noble metal-containing titanate nanotube film”) is prepared. That is, to prepare a dispersion suspended the titanate nanotubes dispersed with distilled water, which together loosen aggregates of titanate nanotubes by ultrasonic dispersion, the dispersion with dilute tetrabutylammonium hydroxide (TBAOH) Adjust the pH. This titanate nanotube film-forming dispersion is negatively charged.
At this time, pH of the titanate nanotube film forming dispersions 7 to 12, preferably particularly 9. This is because a stable and good film can be obtained within this pH range. The concentration of the dispersion is preferably 0.36 g / ltr or more. This is because, as the concentration is increased, the thickness of the titanate nanotube film 13 to which the noble metal formed when the substrate 11 is immersed increases, but the film thickness t1 is constant when the concentration is 0.36 g / ltr or more. Because it becomes.

Through the above preparation, first, the polycation film 12 is formed on the substrate 11 in the nano-multilayer film 10 shown in FIG.
For example, a preliminarily cleaned substrate 11 is dipped in a polyethyleneimine aqueous solution having a concentration of 1.25 g / ltr adjusted to pH 8-12, particularly pH 9 with hydrochloric acid HCl, and the surface is positively charged with a polyethyleneimine cation having a thickness t0. A substrate with a film is formed. Instead of the polyethyleneimine aqueous solution, other polycation aqueous solutions such as polydiallyldimethylammonium chloride and polyallylamine hydrochloride may be employed. The substrate 11 can be a quartz glass substrate or a silicon substrate. Undesirable Here, the pH of the aqueous polyethyleneimine solution outside the above range, the amount of the titanate nanotubes adsorbed to polycation membrane decreases.

Next, the titanate nanotube film 13 on the polycation film 12 is formed by the next first step.
That is, as a first step, the titanate nanotube film forming dispersion with a negative charge, after the polycation film 12 with a substrate 11 having a positively charged immersed predetermined time, washed with deionized water. Here, the predetermined time is preferably 20 minutes. Increasing the immersion time in the titanate nanotube film forming dispersion, although the thickness t1 of the titanate nanotube film 13 is increased, the predetermined time elapses thickness t1 of the titanate nanotube film 13 is constant, especially polycationic film 12 , 14 when the pH of the polycation aqueous solution used is 9, the film thickness t1 becomes constant after immersion for 20 minutes or more.
Next, a polycation film 14 is formed by the following second step on the titanate nanotube film 13. That is, in the second step, the polycation film 14 is formed by, for example, making a 20 g / ltr aqueous solution of polydiallyldimethylammonium chloride containing 0.5 mol / ltr sodium chloride NaCl basic with tetrabutylammonium hydroxide. adjusted aqueous solution (hereinafter referred to as "polycation membrane forming solution".), the said titanate nanotube film 13 by immersing the substrate 11 is formed, the surface to form a positively charged layer of thickness t2 was. Here, the aqueous solution for forming a polycation film is preferably adjusted to basic pH 8 to 12, particularly pH 9. If the pH is out of the range, the adsorption amount of the noble metal-containing titanate nanotubes on the polycation film 14 is decreased in the next step, which is not preferable. The polycation film formed in the second step has counter ions for self-assembly.
Thereafter, by repeating the first step and the second step of the appropriate, on the substrate 11 with a polycation film 12, the titanate nanotube film 13 and a polycation layer 1 4 (12) and are alternately stacked The nano multilayer film 10 can be produced.

As Example 1, a nano-multilayer film composed of a titanate nanotube film and a polycation film with silver attached thereto was produced.
In advance, 2 g of anatase-type titanium oxide powder was dispersed in 40 cm 3 of an aqueous sodium hydroxide solution having a concentration of 10 mol / ltr, placed in an autoclave lined with polytetrafluoroethylene, heated at 150 ° C. for 48 hours, and an outer diameter of 8 to 12 nm. Titanate nanotubes having a length of 3 to 5 nm and a length of several hundred nm were produced.
Next, a suspension in which 50 mg of titanate nanotubes were dispersed in 100 ml of a 0.1 molar aqueous silver nitrate solution was placed in a round bottom flask and stirred for 12 hours using a magnetic stirrer. Thereafter, the suspension was separated with a centrifugal separator at a rotation speed of 6000 rpm to obtain a titanate nanotube containing a filler. To this titanate nanotube containing the filler, 5 cm 3 of an aqueous solution of sodium borohydride having a concentration of 0.1 mol / ltr was added little by little over about 10 minutes. The silver filled titanate nanotubes were separated with a centrifuge and washed with deionized water. A dilute tetrabutylammonium hydroxide aqueous solution was added to a 0.36 g / ltr distilled water suspension of silver-filled titanate nanotubes to adjust the pH to 9 to obtain a film-forming dispersion of titanate nanotubes adhered with silver . .

Quartz glass was used as the substrate 11. The substrate 11 was immersed in a 1: 1 mixed solution of methanol and concentrated hydrochloric acid for 30 minutes, then immersed in concentrated sulfuric acid for 30 minutes, and then washed with distilled water.
The substrate 11 after cleaning was immersed in a polyethyleneimine aqueous solution having a concentration of 1.25 g / ltr adjusted to pH 9 with hydrochloric acid for 20 minutes, and then immersed in distilled water for cleaning, and the polyethyleneimine cation membrane as the polycation membrane 12 was washed. The attached substrate 11 was produced.
The substrate 11 with a polyethyleneimine cationic film as polycation film 12 was immersed for 20 minutes in the film-forming dispersion of the titanate nanotubes described above, and washed with deionized water, polyethylene as polycation film 12 on imine cationic film, silver was formed film 13 of titanate nanotubes filled.
Thereafter, the polycationic film forming aqueous solution was adjusted to pH9 with a solution at a by tetrabutylammonium hydroxide of polydiallyldimethylammonium chloride 20 g / ltr containing sodium chloride aqueous solution having a concentration of 0.5 mol / ltr, the titanate The substrate 11 on which the nanotube film 13 was formed was immersed for 20 minutes and then washed with deionized water. Thus, polydiallyldimethylammonium cation membrane as polycation film 14 is formed on the titanate nanotube film 13.
Thereafter, by repeating this process, on a substrate 11 with a polycation film 12, to produce a nano-multilayered film 10 of silver and a layer 13 of titanate nanotubes attached and a polycation layer 14 are alternately laminated . The titanate nanotube film 13 of 10 layers were stacked across the polycationic film 14. After the formation of the uppermost layer of the titanate nanotube film 13 is washed with deionized water and blown dry with nitrogen gas.

  2 is a transmission electron microscope image of the silver-containing titanate nanotube produced as Example 1. FIG. From FIG. 2, it can be seen that silver particles are present in the hollow portion and the outer surface of the titanate nanotube.

FIG. 3 is a diagram showing measurement results of energy-dispersive X-ray analysis (EDX) of titanate nanotubes attached with silver prepared as Example 1. FIG. In the figure, the vertical axis represents the X-ray intensity (arbitrary scale), and the horizontal axis represents the X-ray energy (keV).
As can be seen from FIG. 3, silver (Ag), titanium (Ti), and oxygen (O) signals appear and are composed of silver and titanate nanotubes.
In FIG. 3, the copper (Cu) signal is derived from the copper grid used to attach the sample of titanate nanotubes with silver attached to the sample stage.

FIG. 4 is a diagram showing a light absorption spectrum of a nano-multilayer film composed of a titanate nanotube film and a polycation film to which silver is attached . The vertical axis is the absorption intensity (arbitrary scale), the horizontal axis is the wavelength (nm), and the parameter is the number of times the nano-multilayer film 10 is stacked (hereinafter referred to as “cumulative number”).
FIG. 4 shows that there is an absorption peak with a wavelength of 228 nm derived from titanate nanotubes, and this absorption peak increases with the cumulative number.

FIG. 5 is a diagram showing the cumulative number dependence of the absorption intensity at a wavelength of 228 nm in FIG. The vertical axis represents the absorption intensity at a wavelength of 228 nm, and the horizontal axis represents the cumulative number.
FIG. 5 shows that the absorption intensity increases linearly as the cumulative number increases. Thus, it can be seen that the titanate nanotube film 13 to which each silver is adhered is formed with a uniform film thickness t1.

As Example 2, a titanate nanotube multilayer film to which gold was attached was manufactured.
When preparing a dispersion for forming a film of titanate nanotubes with a precious metal attached, 100 cm 3 of an aqueous solution of 0.1 mol of tetrachloroauric (III) acid was used instead of 100 cm 3 of an aqueous solution of 0.1 mol of silver nitrate. Others are the same as in the first embodiment.

FIG. 6 is a view showing a transmission electron microscope image of a titanate nanotube attached with gold prepared by filling a titanate nanotube with a tetrachloroauric (III) acid aqueous solution and causing a reduction reaction with an aqueous sodium borohydride solution. It is.
FIG. 6 shows that gold particles are present in the hollow portion and the outer surface of the titanate nanotube.

FIG. 7 is a diagram showing measurement results of energy-dispersive X-ray analysis (EDX) of titanate nanotubes with gold attached . In the figure, the vertical axis represents the X-ray intensity (arbitrary scale), and the horizontal axis represents the X-ray energy (keV).
From FIG. 7, it can be seen that gold (Au), titanium (Ti), and oxygen (O) signals appear, and that titanate nanotubes to which gold is attached are formed. Moreover, since the signal of chlorine (Cl) did not appear in FIG. 7, it was also confirmed that tetrachloroauric (III) acid was completely reduced to gold.
Note that the copper (Cu) signal in FIG. 7 is derived from the copper grid used to attach the sample of titanate nanotubes with gold attached to the sample stage.

FIG. 8 is a diagram showing a light absorption spectrum of a titanate nanotube film to which gold is attached . The vertical axis represents absorption intensity (arbitrary scale), the horizontal axis represents wavelength (nm), and the parameter is the cumulative number.
FIG. 8 shows that there is an absorption peak with a wavelength of 228 nm derived from the titanate nanotube, and this absorption peak increases with the cumulative number.

FIG. 9 is a diagram illustrating the cumulative number dependence of the light absorption intensity at a wavelength of 228 nm in FIG. The vertical axis represents the absorption intensity at a wavelength of 228 nm, and the horizontal axis represents the cumulative number of titanate nanotube films attached with gold.
FIG. 9 shows that the absorption intensity increases linearly as the cumulative number increases. Thereby, it can be seen that the titanate nanotube film 13 to which each noble metal is adhered is formed with a uniform film thickness t1.

The nano multilayer film of the present invention can be used for highly efficient catalysts, optoelectronic devices, and the like.

It is a schematic sectional drawing of the nano multilayer film of this invention. 3 is a view showing a transmission electron microscope image of silver-containing titanate nanotubes produced as Example 1. FIG. It is a figure which shows the measurement result by energy dispersive X-ray analysis (EDX: Energy-Dispersive X-ray Analysis) of the silver containing titanate nanotube produced as Example 1. FIG. 1 is a diagram showing a light absorption spectrum of a silver-containing titanate nanotube multilayer film produced as Example 1. FIG. FIG. 5 is a diagram showing the cumulative number dependence of absorption intensity at a wavelength of 228 nm in FIG. 6 is a view showing a transmission electron microscope image of a gold-containing titanate nanotube produced as Example 2. FIG. FIG. 4 is a diagram showing measurement results of an energy-dispersive X-ray analysis (EDX) of gold-containing titanate nanotubes produced as Example 2. 6 is a diagram showing a light absorption spectrum of a gold-containing titanate nanotube multilayer film produced as Example 2. FIG. It is the figure which showed the cumulative number dependence of the absorption intensity in wavelength 228nm in FIG.

Explanation of symbols

10 nano multilayer film 11 substrate 12 polycation film (polyethyleneimine cation film)
13 of titanate nanotubes adhering the noble metal film 14 polycation membrane (polydiallyldimethylammonium cation membrane)

Claims (10)

A nano-multilayer film in which a film composed of a titanate nanotube and a polycation film are laminated, wherein the titanate nanotube holds a noble metal on either or both of its inner and outer surfaces. The nano multilayer film according to claim 1, wherein the noble metal is silver or gold. In the nano multilayer film according to claim 1 or 2, the outermost surface of the laminated film, characterized in that it is a film made of titanate nanotubes. 4. The method for producing a nano-multilayer film according to claim 1 , wherein the titanate nanotube is dispersed in an aqueous solution containing a noble metal compound , and the noble metal compound is reduced with a reducing agent, and either one of the inner and outer surfaces of the titanate nanotube or first step of both are held the noble metal, the dispersion is dispersed in a liquid to form the titanate nanotubes on said polycation membrane substrate with a polycation layer is immersed in the dispersion into a film When, a second step of forming a polycation layer on the titanate nanotube film by immersing the substrate after the first step to the polycation solution, and repeating one or more times. 5. The method for producing a noble metal-containing titanate nanotube multilayer film according to claim 4, wherein the reducing agent for the reduction treatment is an aqueous sodium borohydride solution. The method for producing a nano-multilayer film according to claim 4 or 5, wherein the pH of the dispersion in the first step is set to 7 to 12, and the pH of the polycation solution in the second step is adjusted to 8 to 12. It is characterized by. The method for producing a nano multilayer film according to any one of claims 4 to 6, wherein silver nitrate or tetrachloroauric (III) acid is used as the noble metal compound. In the manufacturing method of the nano multilayer film according to any one of claims 4 to 7, respectively , the substrate immersion time in the dispersion liquid in the first step and the substrate immersion time in the polycation solution in the second step, respectively. The time for immersing the substrate is 20 minutes or more, respectively . The method of manufacturing a nano-multilayered film according to any one of claims 4 to 8, after the substrate immersion treatment in polycation solution at the substrate immersion treatment and after the second step of the dispersion in the first degree Each of the substrates is washed with deionized water. 10. The method for producing a nano multilayer film according to claim 4, wherein the concentration of the dispersion liquid is 0.36 g / ltr or more.