JP4803396B2 - Metal porous structure - Google Patents

Description

  The present invention relates to a metal porous structure suitably used for, for example, a biosensor, a chemical reaction catalyst, and the like. More specifically, the present invention relates to a metal porous structure having a monolithic porous structure and having a size of a connection node. Is a metal porous structure which is a secondary aggregate composed of primary particles of 3 nm to 20 nm.

  A porous structure of metal / metal oxide having a macroporous internal communication with a large ratio of voids to the structure part, due to its remarkably large specific surface area, is used in various chemical fields including epoxy reactions. It has been applied as a catalyst. By forming a porous metal having internal communication on the substrate, and further reducing the minimum structure scale of the porous structure, it is possible to obtain electrodes for capacitors, electrodes of batteries such as wet solar cells, and chemical sensors. Applications as electrodes or electron emission sources are also expected.

  The following Patent Document 1 discloses a porous structure excellent in internal communication in which silver particles of about 2 μm are partially bound. This is produced by thermally decomposing a dextran paste in an aqueous metal salt solution in the atmosphere. It is described that the crystal grain size can be made 1 to 20 μm by controlling the firing temperature in the range of 500 to 900 ° C.

  In general, it is possible to obtain a metal porous structure or a metal oxide porous structure having internal communication with a very large specific surface area by sintering after forming metal particles in advance. is there. For example, the following Patent Document 2 discloses a technique in which a powder nanomaterial is sintered to construct an extremely fine porous structure, and a structure having a large surface area is obtained using the structure.

Patent Document 3 below discloses a spray reduction plating method in which a metal ion solution and a reducing agent are sprayed simultaneously by spraying to provide a metal layer on the surface of the structure.
JP-T-2006-509915 JP-T-2006-509918 JP-A-11-335858

  In the silver porous structure described in Patent Document 1 and the nano-powder material sintered body described in Patent Document 2, a high temperature is required for firing, so the support is limited to a material that can withstand high temperatures such as ceramics. ing. Therefore, a general synthetic resin could not be used as the support. In addition, the equipment is very expensive to cope with a large size. Further, the porous structure of Patent Document 1 has a large porosity, but has a minimum structural unit of 1 μm or more. In the porous structure of Patent Document 2, the minimum structural unit is submicron, but since the particles are simply bound, the porosity is not large.

  On the other hand, the spray reduction plating method described in Patent Document 3 can be applied to a large-sized structure. However, this method is only a method for obtaining a dense metal mirror, and a metal porous structure having a large specific surface area has not been obtained.

  The specific surface area is the surface area per unit mass of the object or the surface area per unit volume of the structure, and the internal communication porous structure has a significantly larger specific surface area than a simple concavo-convex structure. . Further, if the basic unit of the structure is reduced, the specific surface area is dramatically increased accordingly.

  An object of the present invention is to provide a metal porous structure having internal communication capable of providing a larger surface area and porosity even in a structural region of smaller tens of nanomails to hundreds of microns in view of the current state of the prior art described above. Is to provide.

  According to the present invention, there is provided a metal porous structure having a monolithic porous structure in which a large number of connecting nodes made of metal are connected to each other so as to form an internal communication gap. A metal porous structure having a size of 10 nm to 1000 nm is provided.

  In the present invention, the bonding node of the porous structure is preferably a secondary aggregate composed of primary particles having a size of 3 nm to 20 nm.

  In the present invention, preferably, the surface of the metal porous body is covered with a single layer with organic molecules.

  The porosity of the metal porous structure is preferably in the range of 35 to 65%. By being within this range, a metal porous structure having a sufficiently large surface area and good conductivity can be provided.

  In a specific aspect of the present invention, the metal porous structure is formed as a metal porous structure layer on the substrate.

  In the present invention, preferably, the surface of the substrate has a plurality of convex portions having a height of 10 to 1000 nm, and a part of the coupling nodes is coupled to the apex of the convex portion or the vicinity thereof.

  In the metal porous structure according to the present invention, the pitch between the protrusions on the substrate surface is preferably in the range of 10 to 1000 nm. When it is within this range, a plurality of coupling nodes are bonded and arranged on the substrate surface at the pitch at the above-mentioned pitch, and the porosity of the metal porous structure can be within an appropriate range. .

  Although the substrate is formed of various materials, a substrate made of an insulating material is preferably used, and thereby a metal having a porous metal structure layer functioning as a conductive film or the like on the substrate made of an insulating material. A porous structure can be provided. As the insulating material, a synthetic resin is preferably used, whereby it is possible to easily perform surface shape processing such as substrate surface processing and embossing, and metal porous materials using substrates of various shapes. A structure can be provided.

  In the present invention, the metal constituting the metal particles is not particularly limited, but preferably Au, Ag, Pt, Pd, Rh, Ir, Ru, Fe, Cu, Ni, Co, Cr, Mn, Ti, Al, At least one metal selected from the group consisting of Sn and Mo. These metals are known to generate nanoparticles by mixing a complex ion and a reducing agent, and metal particles composed of at least one of these metals can be directly deposited on the surface of the substrate and bonded.

  The metal porous structure according to the present invention is a metal porous structure having a monolithic porous structure in which a large number of connecting nodes made of metal are connected to each other so as to form an internal communication void. In addition, since the size of the connecting node is 10 nm to 1000 nm, the surface area of the metal porous structure is remarkably increased as compared with a flat metal film formed by plating or a metal surface with unevenness. Can do. In particular, since the size of the connection node is within the specific range, the scale is about 100 times smaller than the conventionally known internal connection porous structure having a connection node of 1 μm to 10 mm. Therefore, when the porosity and weight are aligned, the surface area is about 10,000 times. In addition, since the structure is monolithic, electrical connection can be reliably achieved.

  Therefore, by using the metal porous structure of the present invention as, for example, an electrode of a battery or an electrode of a chemical sensor, the contact efficiency between the electrode and the electrolyte or specimen can be increased, thereby increasing the electromotive force of the battery. In addition, the sensitivity of the chemical sensor can be improved.

  Hereinafter, the present invention will be clarified by giving specific embodiments and examples of the present invention.

  FIG. 1 is a schematic partial cutaway front sectional view of a metal porous structure sample including a metal porous structure according to an embodiment of the present invention.

  In the metal porous structure sample 1, the metal porous structure 3 of the present embodiment is formed on the surface of the substrate 2 as a metal porous structure layer.

  Unevenness is formed on the surface of the substrate 2. The surface of the substrate 2 on which the metal porous structure 3 is formed has a plurality of convex portions 2a and 2a.

  The metal porous structure 3 includes a plurality of connecting nodes 4. The size (particle diameter) of a specific connecting node 4 can be defined as the diameter of a sphere that surrounds all the midpoints of adjacent connecting nodes. The particle size of the connecting node 4 is in the range of 10 to 1000 nm.

  Further, as shown in FIG. 1, a plurality of connecting nodes 4 are joined so as to be connected to each other, and at least a part thereof is appropriately joined. Further, some of the plurality of connecting nodes 4 are intensively coupled to the apex of the convex portion 2 a on the surface of the substrate 2 or the vicinity thereof. As a result, a metal porous structure 3 having a monolithic structure and having internally communicating voids is formed to form a metal porous structure layer. Since the plurality of connecting nodes 4 are appropriately bonded in the thickness direction or the plane direction of the metal porous structure layer, the metal porous structure 3 has conductivity as a state. That is, the metal porous structure 3 has conductivity sufficient to be used as an electrode or the like.

  In addition, in the metal porous structure sample 1 obtained by the manufacturing method described later, as schematically shown in FIG. 1, in the connection node 4, many primary particles X having a particle size of about 3 to 20 nm are aggregated. It is a form such as secondary particles having a particle size of about 10 to 1000 nm and exhibiting such an appearance, and is partially bound to adjacent connecting nodes.

  More specifically, this includes the formation of metal particles by reduction deposition of metal ions, the surface protection of metal particles by organic molecules, the formation of new metal particle nuclei with the unprotected surface as the growth point, and Formation of secondary particle forms by repetition, the secondary particles exhibit autocatalytic properties in the reduction reaction, and the growth from there is selectively promoted, and the adjacent secondary particles are partially bound The expression mechanism of the morphology can be explained by the expression of the monolithic porous structure.

  Since the metal porous structure 3 is composed of a plurality of connecting nodes 4, that is, the metal porous structure layer 3 is bonded and appropriately bonded so that at least a part of the plurality of connecting nodes 4 is continuous. Has a void A that communicates with the entire porous structure. The void A corresponds to a portion where no metal particles are present, and in this embodiment, the void ratio, which is the ratio of the void A to a specific volume, is in the range of 35 to 65%. When the porosity is less than 35%, the metal porous structure has an appearance as if the particles are simply packed and coalesced, and the surface area of the metal porous structure 3 is not easily increased. There is a possibility that the material constituting the porous structure layer 3 increases and the cost is high. If it exceeds 65%, it becomes structurally fragile. However, in the present invention, conductivity is ensured due to the monolithic structure, so that the porosity may be less than 35% or may exceed 65% depending on the purpose of use.

  The substrate 2 has irregularities on the surface, but the pitch between the convex portions 2a and 2a is in the range of 10 to 1000 nm. When the pitch between the convex portions 2a is less than 10 nm, the concave-convex structure is smaller than the unit structure (primary particles) of the deposited metal particles, so that an internal interconnecting porous structure is formed by secondary aggregation. There is a concern that the structure as a scaffold is too small to make sense, and there is a concern that the three-dimensional shape of the unevenness will be densely buried by the deposited metal porous structure. Is too wide, and the formation of the porous structure due to the joining of the connecting nodes as aggregates of the deposited metal particles may be impaired. However, since the size of the primary particles and their secondary aggregates can be controlled by factors such as surfactant, thickener, temperature, etc., in the present invention, the pitch between the convex portions 2a and 2a is less than 10 nm. Or may exceed 1000 nm. The preferable pitch of the convex portions is determined by the size of the secondary aggregate. The size of the secondary aggregates is the size of the primary particles, the protection of the metal surface by organic molecules and the new reduction growth rate balance, the ease of solvent polarization, temperature, surface activity, metal redox potential, It is thought to be affected by the type of reducing agent and additives. The pitch between the convex portions 2a and 2a is approximately in the range of 10 to 1000 nm because the size of the primary particles X is about 3 to 20 nm, but is not limited.

  The height of the convex part is preferably 10 to 1000 nm, more preferably 50 nm to 500 nm. From the ease of forming irregularities, the thickness is more preferably 100 nm to 300 nm.

  Although the substrate 2 has irregularities on the surface, a flat substrate may be prepared, the irregularities may be formed on the surface of the flat substrate, and the substrate 2 may be prepared. Concavities and convexities can be produced by a usual embossing method such as nanoimprint lithography, or by spraying seed particles. In general, polarizable solvents such as water and alcohol form a polarization boundary layer at the solid-liquid interface. Since the board | substrate 2 has an unevenness | corrugation about the polarization boundary layer thickness, it is guessed that a charge density differs for every place. As a result, unevenness occurs in the reduction environment at each location, and metal deposition preferentially occurs at or near the top of the convex portion, and the resulting metal fine particle structure induces further metal deposition in an autocatalytic manner. The secondary agglomerates and the monolithic interconnected metal porous structure that they are connected to may be formed.

  The substrate surface is preferably subjected to a general degreasing treatment or a weak reduction treatment with tannic acid or the like as a pretreatment. Moreover, it is also preferable that the substrate surface is pretreated with triazinedithiols as a coupling agent for strengthening the adhesion between the resin and the metal.

  Although the material which comprises the said board | substrate 2 is not specifically limited, Preferably, an insulating material is used. By using the substrate 2 made of an insulating material, the metal porous structure layer 3 can be used as an electrode or the like. That is, the present invention can provide a structure in which a substrate is used as a support supporting the electrodes, and an electrode composed of a metal porous structure layer is formed on the substrate.

  The insulating material is not particularly limited, and glass, ceramic, silicon oxide film, metal oxide film, diamond, cellulose, resin and the like are used, and preferably synthetic resin is used. When made of a synthetic resin, the substrate 2 having irregularities can be easily obtained by a known molding method or the like. Or in the case of the board | substrate which consists of synthetic resins, surface treatments, such as blasting, an etching, and dispensing, are also easy, and it can also provide the said unevenness | corrugation etc. easily.

  The metal constituting the metal porous structure is not particularly limited, but is composed of various metal elements or alloys, preferably Au, Ag, Pt, Pd, Rh, Ir, Ru, Fe, Cu, Ni, Co And at least one metal selected from the group consisting of Cr, Mn, Ti, Al, Sn and Mo.

  The bonding node of the porous structure is preferably a secondary aggregate composed of primary particles of 3 nm to 20 nm. When the size of the primary particle X is less than 3 nm, there is a concern about the quantum effect from the size of the metal particle or the disappearance of the metallic characteristics due to the display area becoming too large. If the size exceeds 20 nm, there is a concern that the process window for balancing the deposition rate and surface protection becomes narrow and it becomes difficult to create a uniform state over a large area. Accordingly, the size of the primary particles X is preferably in the range of 3 to 20 nm, but is not limited. The size of the primary particle X may be smaller than 3 nm or larger than 20 nm.

  The plurality of connecting nodes 4 having the specific particle diameter are coupled so that at least a part thereof is continuous, the connecting nodes 4 are joined together, and some of the connecting nodes 4 are connected to the substrate 2. The metallic porous structure 3 is formed by bonding to the apex of the convex portion 2a on the surface or the vicinity thereof. In this case, as shown schematically in FIG. 1, it is preferable that the plurality of connecting nodes 4 be arranged so as to overlap in the thickness direction and be bonded to the surface of the substrate 2. Thereby, a thick metal porous structure 3 can be obtained. However, when a thin metal porous structure is desired, the plurality of connecting nodes 4 may be bonded so as not to overlap in the thickness direction.

FIG. 2 is an electron micrograph showing the structure of Example 1 described later as a specific example in which the metal porous structure 3 shown in FIG. 1 is formed. Here, a monolithic interconnected metal porous structure having a porosity of about 50% in which connecting nodes having a particle size of about 100 nm are bonded to each other can be seen. The metal porous structure is formed on a substrate 2 on which convex portions 2a having a height of 400 nm arranged at a pitch of 200 nm are formed, and a part of a connecting node made of Ag having a particle size of about 100 nm to 200 nm is formed. It is combined with the convex portion. By examining the electron micrograph in detail, it can be seen that the connecting node has a form as if primary particles having a particle size of about 20 nm were aggregated. Note that an aqueous ammoniacal Ag ion solution having a concentration of 10 ⁻² mol / L is used as the metal ion or metal complex ion-containing solution to be sprayed.

  The method for producing the metal porous structure 3 is not particularly limited. After preparing the substrate 2 having irregularities on the surface, for example, a metal ion or metal complex ion-containing solution and the metal ion or metal complex are formed on the surface of the substrate 2. It can be formed by applying a reducing agent that reduces ions. The substrate 2 may be dissolved after the metal porous structure is formed.

  As a solvent for the metal ion or metal complex ion-containing solution, water is generally used, but alcohol or the like or a mixed solution thereof may be used. An appropriate liquid composed of molecularly polar molecules can be used. Preferably, water is used.

The metal ion concentration and the metal complex ion concentration in the metal ion or metal complex ion solution are preferably 1 × 10 ⁻⁶ to 1 × 10 ⁻³ mol / L. 10-6 possibility increases the formation of secondary aggregates in a connecting section 4 is not sufficiently less than ^{mol /} L, 1 × 10 exceeds -3 ^{mol /} L when the dense metal film or porosity Sometimes it becomes a small porous metal.

  More specifically, examples of the metal ion-containing solution include sulfate aqueous solutions, nitrate aqueous solutions, and hydrochloric acid aqueous solutions of the respective metals. Examples of the metal complex ion-containing solution include an ammonia complex aqueous solution, a cyano complex aqueous solution, and a hydroxy solution. A complex aqueous solution, a halogeno complex aqueous solution, various chelate solutions and the like can be mentioned. Alkali components such as sodium hydroxide, sodium thiosulfate having a buffering action, hydrogen bonding solvents such as ethanol, thickeners such as gelatin, dyes such as phthalocyanines, surfactants such as organic carboxylates, Commonly used for colloid protection, thiols such as dodecanethiol, choline bromide, thiouric acid, thiophenol, alkali metal sulfites such as sodium thiosulfate, allyl mercaptan, glutathione, etc. may be added for the purpose of metal surface protection. Good.

As said reducing agent, the appropriate reducing agent according to the metal ion or metal complex ion to be used can be used. Such reducing agents include, for example, alkali metal borohydrides, quaternary ammonium borohydrides (NR4 ⁺ ), aldehydes such as diborane, hydrazine, formaldehyde, glucose, fructose, mannose, lactose, maltose, sucrose, and the like. Sugars such as sugar, starch, formic acid, citric acid, oxalic acid, ascorbic acid, tannic acid, gallic acid and other organic carboxylic acids and their salts, hydroquinone, t-butyl-hydroquinone and other polyhydroxybenzenes, anthracene aldehyde phenylhydrazone Examples include hydrazones of aldehydes or ketones, sulfonamidoanilines, hindered phenols, alcohols and polyols, alcohol amines, and tertiary amines.

  Application of the solution containing the metal ion or metal complex ion and application of the reducing agent can be performed by an appropriate application method. As such a coating method, an appropriate coating method such as a doctor blade method, a coating method using a die coater, or a coating method using a spray can be used. In coating, the above metal ion or metal complex ion-containing solution and the reducing agent may be applied to the substrate surface at the same time using different coating apparatuses for coating each of them. Then, the other may be applied. Preferably, a spray is used.

  More preferably, as shown in FIG. 7, a metal ion or metal complex ion-containing solution is applied to the surface of the substrate 2 by the first spray 21, and the reducing agent is added to the second spray 22 at the same time or before and after. The method of spraying using and applying to the surface of the board | substrate 2 is mentioned. According to the spraying / coating method using a spray, the metal ion or the metal complex ion is effectively dispersed on the substrate surface, and the particle size is 10 to 10 such that primary particles having a particle size of 3 to 20 nm aggregate. The 1000 nm coupling node 4 can be easily reduced and deposited on the substrate.

  In this case, since a large number of connecting nodes 4 are coupled to the surface of the substrate 2, as shown in the partially cutaway front sectional views in FIGS. 3A and 3B, the particle size is about 20 nm on the surface of the substrate 2. A large number of metal particles as primary particles X are bonded to form a connection node 4 as a secondary aggregate, and are bonded together. Therefore, a monolithic metal porous structure 3 composed of a large number of connecting nodes 4 is formed. The metal porous structure 3 has a void A that communicates internally with the entire metal porous structure except for a portion where the connection nodes 4 are joined.

  In the metal porous structure 3, when the convex portions 2a as described above are provided at a pitch of 10 to 1000 nm, metal reduction takes place more preferentially at the apex of the convex portions 2a or in the vicinity thereof. Can be formed.

  FIG. 8 is a partially cutaway front sectional view showing another example of the method for manufacturing the metal porous structure 3 according to one embodiment of the present invention. Here, although not shown, a reducing agent is applied to the surface of the substrate 2 in advance. Then, the metal ion or metal complex ion-containing ion solution is applied to the surface of the substrate 2 using one spray 23. In this way, some of the coupling nodes 4 of the plurality of coupled nodes 4 having a particle diameter of 10 to 1000 nm are effectively dispersed on the substrate surface and the particle size is 10 to 1000 nm by the reaction with the reducing agent. The nodes 4 are bonded to the convex portions 2a on the surface of the substrate 2 to form a porous structure layer.

  Next, specific examples will be described.

Example 1
A periodic sub-micrometer-scale microstructure is imprinted on a part of a flat substrate, and the microstructure has many conical convex structures whose height from the base is 400 nm and whose base has a diameter of 200 nm. A substrate 2 arranged on the surface at a pitch of 200 nm and made of polymethyl methacrylate (PMMA) was prepared by a normal nanoimprinting lithography method. An aqueous ammoniacal silver ion solution containing Ag ions at a concentration of 1 × 10 ⁻⁵ mol / L was sprayed. At the same time, an aqueous glucose solution as a reducing agent was sprayed onto the region where the metal ion solution was sprayed. Thereafter, the substrate was air-dried, heated at 60 ° C. for 10 minutes, and dried. The surface of the obtained metal porous structure was observed with an electron micrograph. An electron micrograph of this metal porous structure layer is shown in FIG. A metal porous structure layer having internal communication that is bonded to the surface of the substrate so that a part of the plurality of connection nodes is continuous and appropriately bonded is formed. Some of the plurality of connection nodes are connected to the apex of the convex structure on the substrate surface or the vicinity thereof.

  In the obtained metal porous structure, the particle size of the connection node was measured with an electron microscope. The results are shown in FIG. As a result, the average particle size was 100 nm. Moreover, the porosity of the obtained metal porous structure layer was calculated | required based on the image analysis result. As a result, the porosity was about 50%.

  When the electron micrograph was examined in detail, the 100 nm connecting node had a secondary aggregate-like structure in which primary particles of about 20 nm gathered. In order to confirm this fact, the spraying time was finished at 1/5, the substrate was washed with water in the initial stage of the spray plating process, and observed with an electron microscope. The results are shown in FIG. The primary particles were about 10 to 20 nm, and it was presumed that metal precipitation preferentially occurred around the primary particles during the growth process to form a secondary aggregate-like structure. In addition, since the lower limit of the diameter of the sprayed droplet is about 10 μm, it is assumed that the primary particle structure is expressed in a self-organized manner.

(Comparative Example 1)
Except for using a substrate having a flat surface, silver plating was performed under exactly the same conditions as in Example 1 to obtain a metal porous structure. An electron micrograph of the surface is shown in FIG. Internal connectivity was not confirmed, and the average particle size of the connecting nodes was about 10 to 20 nm.

(Comparative Example 2)
Using another PMMA substrate produced from the exact same mold as the substrate used in Example 1, an Ag gold film was formed to a thickness of about 30 nm by vacuum deposition. In the structure in which the metal film was formed on the substrate in this way, as shown in FIG. 6, even when observed with an electron microscope, no connection node was confirmed, and no porous structure was observed.

The typical partial notch front sectional drawing of the metal porous structure formed on the board | substrate which has an unevenness | corrugation which concerns on one Embodiment of this invention. The figure which shows the electron micrograph of the metal porous structure formed on the uneven | corrugated area | region of Example 1 of this invention. It is each typical partial notch front sectional drawing for demonstrating the formation state of the connection node of a metal porous structure layer, (a) is an initial state, (b) shows the mode of the growth of a secondary particle. Figure. The figure which shows the electron micrograph of the surface when the spray time of Example 1 is cut up by 1/5. The figure which shows the electron micrograph of the surface of the comparative example 1. FIG. The figure which shows the electron micrograph of the surface of the comparative example 2. FIG. The partial notch front sectional drawing for demonstrating the method to manufacture the metal porous structure which concerns on one Embodiment of this invention. The partial notch front sectional drawing for demonstrating the other method of manufacturing the metal porous structure which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal porous structure sample 2 ... Board | substrate 2a ... Convex part 3 ... Metal porous structure 4 ... Connection node 21 ... 1st spray 22 ... 2nd spray 23 ... Spray X ... Primary particle

Claims (10)

  A metal porous body having a monolithic porous structure in which a large number of connecting nodes made of metal are connected to each other so as to form an internal communication gap, and the size of the connecting nodes is 10 nm to 1000 nm. A metallic porous structure.   The metal porous structure according to claim 1, wherein the bonding node of the porous structure is a secondary aggregate composed of primary particles of 3 nm to 20 nm.   The metal porous structure according to claim 1 or 2, wherein the surface of the metal porous body is covered with a single layer with an organic molecule.   The metal porous structure according to any one of claims 1 to 3, wherein the porosity is in the range of 35 to 65%.   The metal porous structure of any one of Claims 1-4 currently formed as a metal porous structure layer on a board | substrate.   The surface of the substrate has a plurality of convex portions having a height in the range of 10 to 1000 nm, and a part of the connecting nodes is coupled to the apex of the convex portion or the vicinity thereof, The metal porous structure according to claim 5.   The metal porous structure according to claim 6, wherein a pitch between convex portions on the surface of the substrate is in a range of 10 to 1000 nm.   The metal porous structure according to claim 5, wherein the substrate is made of an insulating material.   The metal porous structure according to claim 8, wherein the insulating material is a synthetic resin.   The primary particles are at least one metal selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, Fe, Cu, Ni, Co, Cr, Mn, Ti, Al, Sn, and Mo. The metal porous structure according to any one of claims 2 to 9, comprising: