WO2012012927A1

WO2012012927A1 - Methods for synthesizing noble metal ultrathin nanowires in aqueous phase and organizing noble metal nanoporous films by self-sedimentation

Info

Publication number: WO2012012927A1
Application number: PCT/CN2010/002238
Authority: WO
Inventors: 刘景富; 刘睿; 于素娟; 江桂斌
Original assignee: 中国科学院生态环境研究中心
Priority date: 2010-07-29
Filing date: 2010-12-31
Publication date: 2012-02-02
Also published as: CN101935017B; CN101935017A

Abstract

Methods for synthesizing noble metal (Au, Pd, Pt) nanowires and organizing noble metal nanoporous films by self-sedimentation are provided. The methods comprise the following steps: the non-ionic surfactant of 0.05% (W/V) is added into the noble metal precursor (HAuCl₄, H₂PtCl₆, Pd(NO3)₂) solution with a concentration of 1mmol-L^-1 which is then stirred and mixed. KBH₄(or NaBH₄) is added by 6 times, 4 times and 2 times the amount of the metal precursor for HAuCl₄, H₂PtCl₆ and Pd(NO3)₂ respectively, after the mixture has been stirred for 5-10 minutes in an ice-colded aqueous solution. The metal precursor in the mixture is reduced completely to synthesize the said metal ultrathin (≤3nm) mesh nanowires under vigorous stirring. By further adding the non-ionic surfactant of 0.05% (W/V) into the synthesized nanowires dispersion solution, mixing uniformly and centrifuging at 60⁰C for 10 minutes, the nanometer material can be separated and purified. The corresponding noble metal nanoporous films can be acquired by adding NaCl till 5mM ( the extra adding of NaCl is not necessary for the Au nanowire) into the synthesized nanowires aqueous dispersion solution and placing the solution still for 12 hours.

Description

Technical field

The invention relates to a method for constructing a precious metal nanoporous membrane by supercritical nanowire aqueous phase synthesis and ultrafine metal nanowire self-sedimentation, and particularly relates to a method suitable for the construction of nanowires and nanoporous membranes in the field of catalysis. Background technique

Controllable synthesis of various nanostructures is a hot topic in the field of materials science. The potential of nanocatalysts in chemical production, pollution control and energy conversion promotes this nano-hot. The catalytic properties of nanomaterials are generally believed to be strongly dependent on the size and morphology of the nanocatalyst. Because of its unique quantum confinement/small size benefits related to physicochemical properties and outstanding catalytic performance, precious metal ultrafine nanowires have received much attention as catalysts. For example, ultrafine nanowires of palladium and platinum catalyze the oxidation of CO significantly higher than that of the corresponding nanoparticles, and platinum nanowires also have higher activity in oxygen reduction (ORR) and methanol electrocatalytic reactions. In addition to controlling the morphology of nanomaterials, the use of stabilizers that bind weakly to nanomaterials can also increase the activity of nanocatalysts when synthesizing nanocatalysts. Although strong binding of stabilizers or polymers can effectively improve the stability of the catalyst, it has been reported that the catalytic activity of uncoated nano-gold particles in glucose oxidation is as high as 18043 moles of gluconic acid per mole of gold per hour, and surfactant-depleted palladium is removed. The activity of nanoparticles in electrocatalytic oxidation of formic acid is much higher than that of commercial palladium/carbon catalysts. It is still a problem to synthesize nanocatalysts with high activity and high stability.

Among all nanomaterials, precious metal nanoporous materials (metal parts and voids between several nanometers and tens of nanometers) have both nanoscale microstructures and microscale macrostructures. Therefore, nanoporous materials have a large specific surface area, a higher atomic ratio of unsaturated atoms, and better stability. These advantages make this nanoporous material an excellent catalyst/electrocatalyst, sensor and energy conversion building unit. At present, the means for obtaining such nanostructures are chemical/electrochemical corrosion alloys, metallization of non-metallic nanoporous structures, and self-assembly of stencil-controlled nanoparticles. Methods for synthesizing precious metal nanowires which have been reported in the literature include a hard stencil method and a soft stencil method. The former uses mesoporous silicon or carbon nanotubes as a hard template to limit/inducing the growth of nanowires, or to have nanometers with reducibility Lines (such as selenium nanowires) as sacrificial templates; the latter include micelles/reverse micelles, DNA or bacteria) stenciling, and directional bonding under the control of amines (oleylamine, octadecylamine, hexadecylamine) (Oriented Attachment) ₀ In addition to very few methods, these synthetic methods require the use of organic solvents, strongly bound stabilizers/ligands, and higher synthesis temperatures have been aged for extended periods of time. Recently, Bigall et al. added a stabilizer such as ethanol or hydrogen peroxide to the colloidal colloid of the corresponding metal to obtain a similar nanostructure through long-term aging (NC Bigall, Anne-Kristin Herrmann, M. Vogel, M. Rose, P. Simon, W. Carrillo-Cabrera, D. Dorfs, S. Kaskel, N. Gaponik, A. Eychmuller, Angew. Chem. Int. Ed. 2009, 48, 9731-9734). However, the strong acid used for de-alloying, the removal of organic solvents or plasma during the stencil process, and the aging time of more than ten days limit the promotion of the above method. Although the solution sedimentation method has the advantages of convenient operation, easy control of thickness, and the like, it has been widely used for obtaining metal oxides, halides, and hydroxide films, but as of now, this method has not been used to construct noble metal nanoporous films. Summary of the invention

The object of the present invention is to provide a method for synthesizing precious metal ultrafine nanowires in an aqueous phase, which can synthesize ultrafine nanowires of metal, such as gold, palladium, platinum and the like, which have application prospects in the aqueous phase, and the synthesis cost Low cost, one hundred milligrams of nanowires can be synthesized at one time, and the synthesized nanowires have high activity in electrocatalytic oxidation of methanol/ethanol. Another object of the present invention is to provide a method for constructing a precious metal nanoporous material (nanoporous film), which can obtain a nanoporous film having a thickness of several tens of nanometers to several micrometers by self-precipitation of the corresponding precious metal ultrafine nanowires. The obtained nanoporous membrane has a large specific surface area and a metal fraction size of less than 5 nm, and is expected to be used in catalytic and analytical chemical related fields such as surface enhanced Raman spectroscopy (SERS) and surface assisted laser desorption ionization mass spectrometry (SADLI-MS). ).

The present inventors have completed the present invention through intensive research.

According to one aspect of the invention, a method of synthesizing precious metal ultrafine nanowires is provided, the method comprising the steps of:

(a) adding a nonionic surfactant to a precious metal precursor (HAuCl ₄ , H ₂ PtCl ₆ , Pd(N03) ₂ ) solution, thereby obtaining a mixture;

(b) stirring the mixture obtained in the step (a) in an ice bath; (c) adding 6 times (relative to HAuCl ₄ ), 4 times (relative to H ₂ PtCl ₆ ) and 2 times (relative to Pd(N03) ₂ ) reducing agent to the mixture obtained above, And vigorously stirring for 10 seconds to 1 minute, the metal precursor in the mixture is sufficiently reduced to synthesize the ultrafine network nanowire of the above metal;

(d) adding a nonionic surfactant in an amount of 0.05 to 1% by weight based on the weight percent of the aqueous dispersion of the nanomaterial to the aqueous dispersion of the nanomaterial synthesized as described above to obtain a mixture;

(e) centrifuging the mixture obtained in step (d) at a temperature of 50-70 ° C, and separating the mixture into a supernatant liquid and a two-phase system containing the lower cloud point phase of the nano material; with

(f) discarding the supernatant liquid, adding ultrapure water to the lower layer cloud point containing the nano material, and redispersing the nanowires in the lower layer cloud point phase in water.

In an embodiment of the above aspect, the stirring speed is 1000 rpm.

In one embodiment of the above aspect, the centrifugation temperature is 50 °C.

In one embodiment of the above aspect, the agitation time in step (b) is 5 minutes. In one embodiment of the above aspect, the precious metal precursor has a concentration of 1 mmol'I

In one embodiment of the above aspect, the ratio is 0.05 ° /. The amount of (w/v) is the nonionic surfactant added in the step (a).

In an embodiment of the above aspect, wherein the reducing agent used is potassium borohydride or sodium borohydride.

In one embodiment of the above aspects, wherein water is used as the solvent.

In an embodiment of the above aspect, wherein the nonionic surfactant is selected from the group consisting of

Triton TX-114, or Triton TX-100.

In an embodiment of the above aspect, wherein the synthetic environment is an ice bath.

In one embodiment of the above aspect, the synthesized nanowires are ultrafine, networked, and polycrystalline nanowires of 3 nanometers or less. Compared with the existing synthetic methods of ultrafine nanowires, the method has the following advantages: 1. Wide applicability: It can synthesize three different metal nanowires such as Au, Pd and Pt; 2. Greenness of the method: It is not necessary to use chemicals that are toxic (such as chloroform), odor (amines), expensive or not yet commercialized (Triton TX-114 has good biocompatibility);

3. Save energy and time: The method can be carried out in normal temperature or ice bath, and only takes a few minutes, and does not need to react for several tens of hours in high temperature;

4. This method is based on the very weak interaction between the benzene ring and the precious metal on TX-114 to control the morphology, which is beneficial to the retention of active sites.

5. The method uses cloud point extraction as a separation stabilization method, and the nanowires can be preserved for a long time (several weeks) because there is no corrosion effect of Cr.

According to another aspect of the invention, a method for constructing a precious metal nanoporous membrane is provided, the method comprising the steps of:

(a) placing the cleaned substrate (silicon wafer, ITO slide, optical slide, etc.) on the bottom of the flat-bottomed container and adding the synthetic precious metal nanowires to the desired depth;

(b) The container is allowed to stand in an environment of 4 ° C for 12 hours (Au), 24 hours (Pt) or after being added with C1-salt for 24 hours (Pd);

(c) carefully removing the supernatant to dry the underlying colloidal layer at 50% relative humidity to obtain the noble metal nanoporous film;

(d) Wash the dried film with ethanol.

In one embodiment of the above aspects, it is desirable to add 6 mM CI-containing salts to the synthesized palladium nanowires, preferably NaCl, KClo

In one embodiment of the above aspect, the concentration of ethanol used therein is 50% (V/V). An ultrafine nanoporous membrane synthesized by the method of the above aspect, characterized in that it has a large specific surface area, an ultrafine nanoporous membrane constructed by self-precipitation of ultrafine nanowires, wherein the size of the metal mesh portion is less than 5 nm, The nanopore portion is 5 to 20 nm. Compared with the existing synthetic methods of precious metal nanoporous membranes, the method has the following advantages:

1. Wide applicability: It can synthesize three different metal nanoporous membranes such as Au, Pd and Pt;

2. Greenness of the method: No need to use strong acid or organic solvent (Triton TX-114 has good biocompatibility);

3. Low cost and time saving: The method only takes about 12 hours, and the precursor used It can be completely converted into a nanoporous membrane without the waste of other methods (a large amount of energy is required in the alloying or plasma removal stencil process, and a metal needs to be dissolved when alloying);

4. The method is based on the very weak interaction between the benzene ring and the precious metal on the TX-114. It is very easy to clean and has a simple ethanol cleaning. The metal content can be as high as 94% (EDS, energy scattering spectrometry);

5. The method obtains a controllable thickness of the nanopore film, and by changing the depth of the solution, obtaining a nanopore film thickness of several tens of nanometers to several micrometers;

6. The constructed nanoporous membrane has a large specific surface and a low relative density, such as a gold nanoporous membrane with a specific surface area of up to 14.7 m ² /g and a relative density as low as 7.5%. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a corresponding transmission electron micrograph (left image) and size distribution (right panel) of the synthesis of the gold ultrafine nanowire of Example 1.

Fig. 2 is a corresponding transmission electron micrograph (left image) and size distribution (right image) of the Pt ultrafine nanowires synthesized in Example 2.

Fig. 3 is a corresponding transmission electron micrograph (left image) and size distribution (right image) of the Pd ultrafine nanowires synthesized in Example 3.

Figure 4 is a high resolution scanning electron micrograph (left) of the gold nanopore film constructed on a silicon wafer in Example 4 and the corresponding solution depth/nanoporous film thickness relationship (right).

Fig. 5 is a view showing the construction of a palladium nanopore film on the basis of a silicon wafer in Example 6.

Fig. 6 is a view showing the construction of a platinum nanopore film on the basis of a silicon wafer in Example 7.

detailed description

In the present inventors' research, it was found that when synthesizing precious metal nanostructures, the nanostructure morphology can be controlled by controlling the concentration ratio of the reducing agent to the metal precursor in the presence of a suitable nonionic surfactant, when the concentration ratio is At 1 o'clock, only the nanoparticles are formed. As the concentration of the reducing agent increases, the proportion and length of the nanowires in the product increase simultaneously. Finally, when the concentration ratio reaches 6, 4 and 2, respectively, the obtained product is completely gold nanowires, platinum nanowires. And palladium nanowires. Further research found that TX-114 is weakly bonded to the surface of nanomaterials through the benzene ring, and this combination has a choice. Sexuality, and mainly combined on the (100) crystal plane, and the corresponding (111) plane is relatively clean. In order to reduce the surface energy of the whole system, the synthesized nanocrystals tend to connect through (111) planes and finally obtain nanowires. Because the stabilizer TX-114 is weakly bound to the surface of the nanowire, if the Cr in the solution is not removed by cloud point extraction, ( ¹ will compete with TX-114 for the adsorption site of the metal surface, resulting in the surface hydrate layer of the metal nanowire. The decrease in thickness and the increase in the particle size of the nanowires eventually begin to precipitate from the dispersion to form a nanoporous film at the bottom of the container.

In one aspect of the invention, a method of synthesizing precious metal ultrafine nanowires is provided, the method comprising the steps of:

(a) adding 0.05% (w/v) of a nonionic surfactant to a solution of ¹ mmol 'L' ¹ precious metal precursor (HAuCl ₄ , H ₂ PtCl ₆ , Pd(N03) ₂ ) to obtain a mixture;

(b) stirring the mixture in an ice bath for 5 minutes;

(c) adding to the resulting mixture 6 times (relative to HAuC), 4 times (relative to H ₂ PtCl ₆ ) and 2 times (relative to Pd(N03) ₂ ) of potassium borohydride (or Sodium borohydride), and vigorously stirred for 10 seconds to 1 minute, the metal precursor in the mixture is sufficiently reduced to synthesize the ultrafine network nanowire of the above metal;

(d) adding 0.05 to 1% by weight of the aqueous dispersion of the nanomaterial to the aqueous dispersion of the synthetic nanomaterial to obtain a mixture;

(e) centrifuging the mixture at 60 ° C to separate the mixture into a supernatant and a two-phase system containing the lower cloud point phase of the nanomaterial;

(f) discarding the supernatant liquid, adding ultrapure water to the lower layer cloud point containing the nano material, and redispersing the nanowires in the lower layer cloud point phase in water. According to some preferred embodiments of the present invention, the nonionic surfactant is selected from the group consisting of Triton TX-114 (polyoxyethylene (8) nonylphenyl ether, available from Acros Oganic, USA), Triton TX-100 ( Polyoxyethylene (10) octylphenyl ether, available from Acros Oganic, Inc., USA, preferably Triton TX-114, preferably at a concentration of 0.05% (w/v).

According to certain preferred embodiments, the metal precursor is HAuCl ₄ , H ₂ PtCl ₆ and Pd(N0 ₃ ) _2o

The present invention also provides a method for constructing a precious metal nanoporous membrane, the method comprising the steps of: (a) placing the cleaned substrate (silicon wafer, ITO slide, optical slide, etc.) on the bottom of the flat-bottomed container and adding the synthetic precious metal nanowires to the desired depth;

(b) The container is allowed to stand at 4 ° C for 12 hours (Au), 24 hours (Pt) or after adding C1-salt and allowed to stand for 24 hours (Pd);

(c) Carefully remove the supernatant and dry the lower gelatinous layer at 50% relative humidity; and

(d) Wash the dried film with 50% (V/V) ethanol.

According to some preferred embodiments of the present invention, the nonionic surfactant is selected from the group consisting of Triton TX-114 (polyoxyethylene (8) nonylphenyl ether, available from Acros Oganic, USA), Triton TX-100 ( Polyoxyethylene (10) octylphenyl ether, available from Acros Oganic, Inc., USA, preferably Triton TX-114, preferably at a concentration of 0.05% (w/v).

According to certain preferred embodiments, the metal precursors are HAuCl ₄ , 3⁄4^03⁄4 and Pd(N0 ₃ ) ₂ .

According to certain preferred embodiments, the C1-salt is a water-soluble salt of a Group I element or a Group II element, such as NaCl, LiCK KCK CaCl ₂ , MgCl _{2 ,} etc., wherein NaCl is preferred.

According to certain preferred embodiments, the C1-salt is used in an amount of from 0.01 to 1% by weight, preferably 0.2% by weight, based on the weight percent of the mixture obtained in the step (b).

In certain preferred embodiments, the C1-salt is NaCl or KC1. The invention will now be described in greater detail with reference to the embodiments. It is to be understood that the description and the examples are intended to be illustrative and not restrictive. The scope of the invention is defined by the appended claims. The materials used in the examples are as follows:

Triton TX-114 (available from Acros Oganic, USA);

Triton TX-100 (available from Acros Oganic, USA);

HAuC, H ₂ PtCl _{6 was} purchased from Sinopharm Chemical Reagent Co., Ltd.;

Pd(N0 ₃ ) _{2 was} purchased from Xitou Chemical Plant, Shantou, Guangdong;

The water used is Millipore ultrapure water (18.2 ΜΩ)

Other reagents are from Beijing Chemical Plant. Example 1: Synthesis of gold ultrafine nanowires

Use TX-114 as a stabilizer and structure control agent, and KB as a reducing agent. 0.05 mmol of HAuCl ₄ and 25 mg of TX-114 were dissolved in 47 ml of Millipore ultrapure water, and then added to a sealed 50 ml Erlenmeyer flask. After stirring for 5 minutes at 1000 rpm in an ice bath, 3 ml of 100 mM KBH ₄ solution was quickly injected into the solution with a syringe. Continue stirring for 10 seconds, the color of the solution changes from bright yellow to brown, and the red finally turns dark gray. After the reaction was completed, 25 mg of TX-114 was added to the solution, mixed uniformly, and centrifuged at 1500 rpm for 10 minutes at 60 ° C, the supernatant was discarded, and the lower layer of the cloud point was redispersed in Millipore ultrapure water to regain the corresponding valuable. Metal nanowire aqueous solution/dispersion. It was observed by transmission electron microscopy (TEM, H-7500, Hitachi) and high-resolution transmission electron microscopy (HRTEM, JEM-2100F, JEOL) and processed using image plus software with a diameter of 3.01 ± 0.61 nm. (Figure 1, the left picture shows the corresponding transmission electron micrograph, the scale is 10nm, the right picture shows the size distribution)) Example 2: Synthesis of Pt ultrafine nanowires

Use TX-114 as a stabilizer and structure control agent, and KB as a reducing agent. 0.05 mmol H ₂ PtCl ₆ and 25 mg TX-114 were dissolved in 48 ml of Millipore ultrapure water, and then added to a sealed 50 ml Erlenmeyer flask. After stirring for 5 minutes at 1000 rpm in an ice bath, 2 ml of 100 mM KBH was quickly injected into the solution with a syringe. ₄ solution, continue to stir for 10 seconds. After the reaction was completed, 25 mg of TX-114 was added to the solution, and the mixture was homogenized. The mixture was centrifuged at 1500 rpm for 10 minutes at 60 ° C, the supernatant was discarded, and the lower layer of the cloud phase was redispersed in Millipore ultrapure water to obtain a solution. /Dispersions. It was observed by transmission electron microscopy (TEM, H-7500, Hitachi) and high-resolution transmission electron microscopy (HRTEM, JEM-2100F, JEOL) and processed using image plus software with a diameter of 2.04 ± 0.36 nm. (Figure 2, the left picture shows the corresponding transmission electron micrograph, the scale is 10nm, and the right picture shows the size distribution.) Example 3: Synthesis of Pd ultrafine nanowires

TX-114 is used as a stabilizer and structure control agent, and KBH ₄ is a reducing agent. 0.05 mmol of Pd(N0 ₃ ) ₂ and 25 mg of TX-114 were dissolved in 49 ml of Millipore ultrapure water, and then added to a sealed 50 ml Erlenmeyer flask. After stirring for 5 minutes at 1000 rpm in an ice bath, a lml was quickly injected into the solution with a syringe. 100 mM BH ₄ solution, stirring was continued for 10 seconds. After the reaction was completed, 25 mg of TX-114 was added to the solution and mixed uniformly at 60. After centrifugation at 1500 rpm for 10 minutes at C, the supernatant was discarded, and the lower cloud point phase was redispersed in Millipore ultrapure water to obtain a solution/dispersion. It was observed by transmission electron microscopy (TEM, H-7500, Hitachi) and high-resolution transmission electron microscopy (HRTEM, JEM-2100F, JEOL) and processed using image plus software with a diameter of 2.48 ± 0.42 nm. (Figure 3, the left picture shows the corresponding transmission electron micrograph, the scale is lOnm, and the right picture shows the size distribution.) Example 4: Constructing a gold nanopore film on a silicon wafer basis

The ultrafine gold nanowires were synthesized as described in Example 1. The lcm x lcm silicon wafer which had been ultrasonically cleaned with hydrochloric acid, ethanol and ultrapure water was placed at the bottom of the crystallizing dish, and the synthesized gold nanowire solution was added to the depth. 0.5cm, lcm, 2cm, 3cm and 4cm (because it is added to the inside of the crystallizing dish, the height of the solution can be measured), and it is allowed to stand at 4 °C for 12 hours. The upper gray-brown solution becomes colorless, and the upper layer is discarded. The supernatant is dried by drying the lower gel at 40% relative humidity, and after washing with ethanol, a gold nanopore film is obtained. Top-view scanning electron microscopy (SEM S-3000, S-4800, Hitachi) observed that the nanoporous film consisted of gold nanowires with a diameter of about 5 nm and pores of about 5-20 nm. Cross-section view SEM observation found that five The thickness of the gold nanopore film obtained by the deep deposition solution was 0.51μηη, 1.27μιη, 2.79μιη, 3.85μιη and 5.18μιη, and the nanopore film thickness showed a good linear relationship with the depth of the deposition solution. The nanopore film was estimated by the slope. The relative density is 7.5% (see Figure 4, the left picture shows the high resolution SEM image of the constructed gold nanopore film, and the right picture shows the corresponding solution depth/nanoporous film thickness relationship). Example 5: Construction of a gold nanoporous film based on bismuth glass

The gold nanopore film was synthesized as described in Example 4, and the substrate was changed from a silicon wafer to a bismuth glass. The obtained gold nanopore film was subjected to cyclic voltammetry in 0.1 M HC10 ₄ , and the specific surface area of the gold nanopore film was 15.6 m ² /g as measured by the amount of reduction of gold. Example 6: Based on silicon wafer Construction of palladium nanoporous membrane

The ultrafine palladium nanowires were synthesized as described in Example 2, and NaCl was added to a concentration of 6 mM, and the mixture was stirred and mixed. The lcm x lcm silicon wafer which had been ultrasonically cleaned with hydrochloric acid, ethanol and ultrapure water was placed at the bottom of the crystallizing dish. Add the synthetic palladium nanowire solution/dispersion to a depth of 1 cm (because it is added to the crystallizer, the height of the solution can be measured), and let it stand at 4 ° C for 24 hours, the upper solution becomes colorless. The supernatant was discarded, and the lower gel was dried at 40% relative humidity. After washing with ethanol, a palladium nanopore film was obtained. Top-view scanning electron microscope (SEM S-3000, S-4800, Hitachi) observed that the palladium nanopore film consisted of palladium nanowires having a diameter of about 3 nm and pores of about 5-20 nm (see Fig. 5). Example 7: Construction of a platinum nanoporous film based on a silicon wafer

The ultrafine platinum nanowires were synthesized as described in Example 2. The lcm x lcm silicon wafer which had been ultrasonically cleaned by using hydrochloric acid, ethanol and ultrapure water was placed at the bottom of the crystallizing dish, and the above synthesized platinum nanowire solution/dispersion was added. To a depth of lcm, let stand at 4 ° C for 24 hours, the upper solution becomes colorless, discard the supernatant, the lower gel is dried at 40% relative humidity, and after washing with ethanol, platinum nanopores can be obtained. membrane. A Top-view scanning electron microscope (SEM S-3000, S-4800, Hitachi) observed that the nanoporous film consisted of platinum nanowires with a diameter of about 2.5 nm and pores of about 5-20 nm (see Figure 6).

Claims

A method for the synthesis of precious metal, gold, palladium, platinum ultrafine nanowires, the method comprising the steps of:

(a) adding a nonionic surfactant to a noble metal gold, palladium, platinum precursor solution, thereby obtaining a mixture;

(b) stirring the mixture obtained in (a) in an ice bath;

(c) adding 6 times (relative to HAuCl ₄ ), 4 times (relative to 3⁄4 to ₁₆ ) and 2 times (relative to Pd(N0 ₃ ) ₂ ) reducing agent to the mixture obtained above as the metal precursor And vigorously stirring for 10 seconds to 1 minute, the metal precursor in the mixture is sufficiently reduced to synthesize the ultrafine network nanowire of the above metal;

(e) centrifuging the mixture obtained in the step (d) at a temperature of 50 to 70 ° C to separate the mixture into a supernatant liquid and a two-phase system containing the lower cloud point phase of the nano material ; with

(f) discarding the supernatant liquid, adding ultrapure water to the lower layer cloud point containing the nano material, and redispersing the nanowires in the lower layer cloud point phase in water. '

2. A method according to claim 1 wherein water is used as the solvent.

3. The method of claim 1 wherein the centrifugation temperature of step (d) is 60 °C.

4. The method according to claim 1, wherein the stirring speed is 1000 rpm.

5. The method according to claim 1, wherein the nonionic surfactant is selected from the group consisting of Triton TX-U4, or Triton TX-100.

The method according to any one of claims 1 to 5, wherein the concentration of the precious metal precursor solution is lmmoH^

The method according to any one of claims 1 to 5, wherein the concentration of the nonionic surfactant added in the step (a) is 0.05% (W/V).

The method according to any one of claims 1 to 5, wherein the reducing agent used is potassium borohydride or sodium borohydride.

9. The method of claim 1 wherein the synthetic environment is an ice bath.

10. The method of claim 1, wherein the synthesized nanowires are ultrafine, networked, and polycrystalline nanowires of less than or equal to 3 nanometers.

11. A method of synthesizing a precious metal nanoporous membrane, the method comprising the steps of:

(b) The container is allowed to stand at 4 ° C for 12 hours (Au), 24 hours (Pt) or after adding CI-containing salt and allowed to stand for 24 hours (Pd);

(d) Wash the dried film with ethanol.

12. The method of claim 11 wherein the precious metal nanowires used are precious metal nanowires synthesized in an aqueous phase.

13. The method according to claim 11, wherein 6 mM CI-containing salts, preferably NaCl, KClo are required to be added to the synthesized palladium nanowires.

14. A method according to claim 11 wherein the concentration of ethanol used is 50% (V/V).

An ultrafine nanoporous membrane synthesized by the method of claim 11, characterized by having a large specific surface area, which is constructed by self-precipitation of ultrafine nanowires, wherein the metal network portion has a size of about 5 nm, and the nanoporous portion It is 5 to 20 nanometers.