WO2024019102A1

WO2024019102A1 - Composite material carrying au nanocluster and manufacturing method for said composite material

Info

Publication number: WO2024019102A1
Application number: PCT/JP2023/026496
Authority: WO
Inventors: 寛岸
Original assignee: 田中貴金属工業株式会社
Priority date: 2022-07-22
Filing date: 2023-07-20
Publication date: 2024-01-25

Abstract

The present invention relates to a composite material formed by carrying Au nanoclusters, each containing two or more Au atoms, on carriers via ligands. In the present invention, hydrophobic bodies, such as carbon powder, are employed as the carriers and an L-cysteine or an L-cysteine derivative that has a nonpolar residue is employed as the ligands. Also, the present invention discloses a method for effectively carrying the Au nanoclusters on hydrophobic carriers. With the present invention, as a result of reacting an Au source and the L-cysteine or the like, serving as the ligands, in a state in which the hydrophobic carriers are dispersed in an aqueous solvent, Au nanocluster synthesis and carrying thereof on the hydrophobic carriers simultaneously proceed. With the present invention, it is possible to manufacture a composite material in which Au nanoclusters are carried on hydrophobic carriers in a highly dispersed manner.

Description

Composite material supporting Au nanoclusters and method for producing the composite material

The present invention relates to a composite material in which nanoclusters made of Au are supported on a suitable carrier. Specifically, the present invention relates to a composite material in which nano-order Au nanoclusters are supported on a hydrophobic carrier via a predetermined ligand. Furthermore, the present invention relates to a method for producing a composite material in which Au nanoclusters can be supported in a highly dispersed manner on a hydrophobic carrier in an aqueous solution system.

When metals are made into nanoparticles, they exhibit various properties not found in bulk materials, such as photoresponsive properties (photoluminescence properties), fluorescence emission properties, and light scattering/reflection properties. Therefore, metal nanoparticles are being considered for application in various fields such as light emitting elements and fluorescent materials used in display devices and the like, and electrode and wiring materials for various electronic and semiconductor devices.

Furthermore, as for the range of applications of metal nanoparticles, in addition to materials related to electrical and optical devices as mentioned above, they are also extremely effective as catalysts for various chemical reactions. Making metal into fine particles increases the surface area of the metal, so by making the metal fine to the nano-order, its catalytic activity can be greatly improved. These metal particles that have been made into nano-sized particles are called metal nanoclusters. Although there is no fixed definition, a nanocluster is usually a collection of several to several hundred metal atoms.

Metal nanoclusters are often synthesized in a wet manner (liquid phase), and their usage is generally in the form of a dispersion in which metal nanoclusters are dispersed in a solvent. Furthermore, a common method for synthesizing metal nanoclusters is to add a reducing agent and a ligand (organic ligand) to a solution of a metal salt. In this synthesis method, a ligand binds to a plurality of metal atoms generated by reduction, thereby forming particles in which metal atoms are clustered. The ligand is sometimes referred to as a protective agent/dispersant, and has the effect of suppressing aggregation of clustered metal nanoparticles and maintaining a dispersed state. The metal nanoclusters are utilized by applying a dispersion in which the metal nanoclusters are dispersed onto a carrier such as a catalyst, and then adsorbing the carrier by immersion, thereby adsorbing and fixing the metal nanoclusters onto the carrier.

The present invention relates to the application of nanoclusters made of Au (gold) among metal nanoclusters. In addition to the above-mentioned properties, noble metals such as Au and Ag are metals that significantly exhibit localized surface plasmon resonance (SPR). Further, Au is a metal that is chemically stable and has suitable electrical properties. Further, although Au does not exhibit catalytic activity in a bulk state, nano-order Au has a catalytic effect on various chemical reactions such as the oxidation reaction of carbon monoxide. For these reasons, Au nanoclusters are expected to be a precursor material that can contribute to improved performance in the various applications described above.

Examples of Au nanoclusters known so far include those in which Au atoms are clustered by applying phosphine, thiol-based organic ligands (thiolates), etc. as ligands. In particular, Au nanoclusters with the thiolate glutathione (GSH) as a ligand are highly stable due to strong Au-S bonds, and are also hydrophilic and stably dispersed in aqueous solvents. It is known.

Japanese Patent Application Publication No. 2019-513184 Japanese Patent Application Publication No. 2007-45791

As mentioned above, a common way of utilizing metal nanoclusters is to adsorb and support metal nanoclusters dispersed in a solvent on a carrier. At this time, in order to manufacture highly active catalysts and devices with high characteristics, it is necessary to efficiently transfer and support metal nanoclusters dispersed in a solvent onto a carrier. Since the usage pattern of Au nanoclusters is also similar, it is necessary to support a dispersion of Au nanoclusters synthesized by the above-described conventional method on a carrier.

However, according to studies by the present inventors, conventional dispersions of Au nanoclusters may not be able to be supported with sufficient efficiency depending on the type of carrier. For example, when a dispersion of Au nanoclusters with glutathione as a ligand is supported on carbon powder, which is often used as a catalyst carrier, many of the Au nanoclusters remain in the solvent without being adsorbed to the carrier. Sometimes.

The reason for this is considered to be the difference in polarity (hydrophilicity and hydrophobicity) between the Au nanoclusters and the carrier. To explain using the above example, since Au nanoclusters having glutathione as a ligand are hydrophilic and stable in aqueous solvents, they are difficult to be adsorbed and supported on hydrophobic carbon powder. Therefore, most of the Au nanoclusters remain in the solvent without being supported on the hydrophobic carrier. Many catalyst carriers and device substrates have hydrophobic surfaces. Even if Au nanoclusters can stably maintain their nanoparticle state in a solvent, their significance will be diminished if they cannot be supported on these carriers.

If the reason why it is difficult to support is the hydrophobicity of the carrier, one solution is to use Au nanoclusters that can be dispersed in non-aqueous solvents such as organic solvents. In fact, Au nanoclusters that can stably exist in organic solvents are also known. For example, it has been reported that Au nanoclusters having phenylethanethiol as a ligand as described in Non-Patent Document 2 are stable in the state of nanoparticles of about 1 nm in an organic solvent. However, in order to apply the supporting process using an organic solvent to manufacturing sites for catalysts, etc., it is necessary to manage the working environment during use, treat waste liquid, etc. and take into consideration the environmental burden, which is not an easy measure.

As described above, although there are many studies regarding Au nanoclusters related to their synthesis, there are few studies that consider the process of supporting synthesized Au nanoclusters on a carrier. However, in order to apply Au nanoclusters to functional materials such as catalysts, it is also important to consider efficient methods of supporting them.

The present invention was made against the above background, and relates to a composite material in which Au nanoclusters, which are fine particles, are highly dispersed and supported on a hydrophobic carrier at an appropriate supporting density. An object of the present invention is to clarify a method for supporting Au nanoclusters on a hydrophobic carrier while using an aqueous solvent, and to provide a method for manufacturing the above-mentioned composite material.

In order to study how to solve the above problem, the present inventors first studied the behavior of Au clusters synthesized with various thiolate-based ligands including glutathione in an aqueous solvent. As a result, it was found that L-cysteine and L-cysteine derivatives having a predetermined residue can synthesize Au nanoclusters in an aqueous solvent without the action of a reducing agent. It was also confirmed that Au nanoclusters synthesized using these ligands have hydrophobicity. However, since Au nanoclusters have hydrophobicity, it is difficult to stably disperse them in an aqueous solvent. The Au nanoclusters made of L-cysteine and L-cysteine derivatives studied by the present inventors cause precipitation and precipitation due to aggregation and the like in a solvent after synthesis, and cannot maintain a stable dispersion state.

Even if Au nanoclusters have hydrophobicity in an aqueous solvent, if the dispersion state after synthesis is unstable, it is difficult to support this solution on a hydrophobic carrier. Therefore, as a result of further study and consideration, the present inventors found that a hydrophobic carrier exists in the aqueous solvent at the time when the above-mentioned ligand reacts with the Au source (Au ion) to synthesize Au nanoclusters. It has been found that Au nanoclusters can be adsorbed and supported on a carrier at the same time as synthesis. This is thought to be because Au nanoclusters synthesized from L-cysteine and L-cysteine derivatives have good adsorption to hydrophobic carriers, and adsorption to the carrier takes precedence over aggregation of nanoclusters.

As a result of studying the structure and characteristics of a composite material in which Au nanoclusters are supported on a hydrophobic carrier at the same time as described above, the present inventors found that this composite material has Au nanoclusters supported on a hydrophobic carrier. After confirming that it was supported at high density and high dispersion, we came up with the present invention.

That is, the present invention provides a composite material in which Au nanoclusters containing two or more Au atoms are supported on a carrier via a ligand, wherein at least the portion on which the Au nanoclusters are supported is hydrophobic. and the ligand is a composite material that is L-cysteine or an L-cysteine derivative with a non-polar residue.

Hereinafter, the structure of the composite material supporting Au nanoclusters according to the present invention and the method for manufacturing the composite material based on the method of supporting Au nanoclusters on a hydrophobic carrier will be explained.

(A) Composite material supporting Au nanoclusters according to the present invention The composite material according to the present invention is composed of a carrier, Au nanoclusters supported on the carrier, and a ligand that binds the two.

(A-1) Hydrophobic carrier The carrier is a member for supporting the Au nanoclusters in a dispersed state. The carrier of the composite material according to the present invention is a carrier that has hydrophobicity at least in the portion on which the Au nanoclusters are supported. Hydrophobicity is a property that has a low affinity for water and is difficult to dissolve or mix with water. Examples of the constituent material of the carrier include carbon, cellulose, nitrocellulose, hydrophobic polymers (fluororesin, acrylic, epoxy, polyethylene, polystyrene, polyvinyl chloride, etc.), metal nitrides, and the like. There are no particular limitations on the shape and dimensions of the carrier. Particulate carriers are often used in catalysts. In addition, bulk carriers such as plate-shaped, sheet, and film-shaped carriers are sometimes used as carriers for material applications related to electrical and optical devices. In the present invention, specific criteria for the hydrophobicity of the carrier can be set for each of the particulate carrier and the bulk carrier as follows.

(i) Particulate carrier The particulate carrier is a particulate or powdery solid with a particle size of 10 μm or less that can be dispersed in a solvent such as water. As an index for determining the hydrophobicity of a particulate carrier, the R _SP value obtained from pulsed NMR (TD-NMR) measurement is suitable. The hydrophobicity of a carrier dispersed in an aqueous solvent can be evaluated by the magnitude of interaction between the carrier surface and solvent molecules. According to pulse NMR, it is possible to measure the relaxation time of a solvent having protons (H) in its molecules, such as water, and the shorter the relaxation time, the stronger the interaction between the carrier and the solvent. In determining hydrophobicity by pulsed NMR, the _RSP value is determined by measuring the relaxation time in each state of a solvent only state and a state in which a particulate carrier is dispersed in a solvent. The R _SP value is calculated from the following formula, and the smaller the R _SP value, the higher the hydrophobicity tends to be.

The hydrophobicity of the carrier used in the present invention is determined by measuring the relaxation time (transverse relaxation time (spin-spin relaxation time)) by pulsed NMR using water as the solvent and calculating the R _SP value using the above formula. . At this time, it is preferable to judge hydrophobicity using a correction value (R _SP /TSA: hereinafter referred to as R _{SP (c)) obtained by dividing the R SP} _value by the total surface area (TSA) of the carrier at the time of measurement. In the present invention, a carrier having an R _{SP (c)} value of 0.5 or less is defined as a hydrophobic carrier. Note that the total surface area (TSA) of the carrier during pulsed NMR measurement can be calculated using the following formula.

In the above formula, it is preferable to apply the BET specific surface area as the specific surface area SA of the carrier. The present invention is intended to be applied to catalysts, and carbon particles or the like are often used as catalyst carriers. Carbon particles take various forms, such as a structure with countless fine pores on the surface and a hollow structure. Application of the BET specific surface area is suitable for determining the specific surface area of these various forms of particulate carriers. For the BET specific surface area, it is preferable to apply a value measured by a gas adsorption method, and it is preferable to apply a value measured by nitrogen gas. Further, the mass-to-volume ratio concentration of the carrier during pulse NMR measurement is preferably 0.1% or more (0.001 g/mL or more) and 10% or less (0.1 g/mL or less).

(ii) Bulk-like carrier The bulk-like carrier is intended to exclude the above-mentioned particulate carriers, and is a plate-like, lump-like, or thin-film-like solid with a minimum size of 10 μm or more. The hydrophobicity of a bulk carrier can be defined by the contact angle with water. In the present invention, a hydrophobic carrier is one that has a contact angle with water of 90° or more. Note that for a bulk carrier whose minimum size is larger than that of a particulate carrier, it is sufficient that at least the surface portion supporting the Au nanoclusters has the above-mentioned hydrophobicity. Materials other than the above-mentioned hydrophobic materials may be used as long as the surface on which the Au nanoclusters are supported is treated to impart hydrophobicity. Examples of the hydrophobic treatment include a treatment for modifying the carrier surface with a nonpolar functional group (alkyl group, etc.), a firing treatment in an inert atmosphere, and coating with the above-mentioned hydrophobic material.

(A-2) Au nanocluster Au nanocluster is a particle containing a group of two or more Au atoms. The particle size of the Au nanoclusters supported on the hydrophobic carrier in the composite material of the present invention is preferably 0.5 nm or more and 5 nm or less, more preferably 3 nm or less. The particle size of the Au nanocluster can be obtained, for example, by calculating the average value by measuring the particle size of a plurality of particles based on an image observed by electron microscopy such as TEM. The particle size in an observed image can be measured by image analysis in addition to visual observation. Furthermore, the particle size distribution can also be analyzed by statistical calculation of the measured particle size. In addition, from the viewpoint of measuring the particle size distribution, it is preferable to arbitrarily select 100 or more particles and measure the particle size. Furthermore, the term "particle diameter" shall mean the maximum distance (diameter equivalent to a circumscribed circle) among the distances between any two points on the contour line of a particle.

Furthermore, the Au nanocluster may be composed only of Au atoms, but may also contain atoms of other elements. For example, atoms of elements that have a high bonding property with Au, such as S (sulfur), O (oxygen), N (nitrogen), C (carbon), Cu (copper), and Ag (silver), stabilize the Au nanocluster. It may contribute to sexual activity and high activation. It is preferable that atoms other than Au be contained in an amount of 50% or less in terms of number of atoms.

The amount of Au nanoclusters supported (supporting density) in the present invention is adjusted depending on the use of the composite material. According to the supporting method according to the present invention described below, the amount of Au nanoclusters supported can be 0.1% by mass or more and 50% by mass or less based on the entire composite material such as a catalyst. be.

(A-3) Ligand (L-cysteine and L-cysteine derivative)
The ligand is an organic ligand that coordinates to the Au atoms in order to maintain the collective state of the clustered Au atoms. In addition, in the present invention, the ligand acts as an aid for binding the Au nanoclusters to the hydrophobic carrier when the Au nanoclusters are synthesized. The ligand of the present invention is L-cysteine and L-cysteine derivatives represented by the following formula.

In the above formula, R is a residue (substituent), and is hydrogen or a nonpolar residue. According to the studies of the present inventors, when L-cysteine in which R is hydrogen or an L-cysteine derivative in which R is a nonpolar residue coordinates to an Au atom in an aqueous solvent to form a nanocluster. , imparts hydrophobicity to the Au nanoclusters.

When R in the above formula is a nonpolar residue, the nonpolar residue is an acyl group (acetyl group (CH ₃ CO: Ac), ethylcarbonyl group (CH ₃ CH ₂ CO), linear or branched propylcarbonyl group (C ₃ H ₇ CO), linear or branched butyl carbonyl group (C ₄ H ₉ CO)), or carbon number 1 Alkoxycarbonyl group having ~4 aliphatic hydrocarbon chains (methoxycarbonyl group (CH ₃ OCO), ethoxycarbonyl group (CH ₃ CH ₂ OCO), linear or branched propoxycarbonyl group (C ₃ H ₇ OCO), linear or branched butoxycarbonyl group (C ₄ H ₉ OCO)) are preferred. Among these, acetyl group (CH ₃ CO:Ac), isopropylcarbonyl group ((CH ₃ ) ₂ CHCO), and tert-butoxycarbonyl group ((CH ₃ ) ₃ COCO) are more preferred.

Furthermore, when an L-cysteine derivative having a non-polar residue is applied as a ligand, the non-polar residue exhibits an anchoring effect to a hydrophobic carrier and has the effect of suppressing the movement of Au nanoclusters in a high-temperature environment. It is believed that there is. This effect suppresses the aggregation of Au nanoclusters and the resulting coarsening of the particles.

Particularly preferred ligands are L-cysteine, where R is hydrogen, and N-acetyl-L-cysteine, where R is an acetyl group. This is because these have a small molecular weight and can be easily decomposed and removed by heat.

In the composite material according to the present invention, the content of the ligand is preferably 0.1% by mass or more and 50% by mass or less based on the entire composite material such as the catalyst. More preferably, it is 20% by mass or less.

The ligand only needs to be bonded to at least a portion of the Au nanocluster, and does not need to be bonded to the entire surface or all Au atoms. In addition, regarding the composite material according to the present invention, the presence of the ligand L-cysteine or an L-cysteine derivative in which R is a non-polar residue can be detected by gas chromatography-mass spectrometry (GC/MS), especially thermal decomposition-gas It can be qualitatively confirmed by chromatography-mass spectrometry (Py-GC/MS). Non-polar residues of L-cysteine derivatives can also be confirmed using this analytical method.

(B) Method for manufacturing a composite material according to the present invention (method for supporting Au nanoclusters)
Next, a method for manufacturing a composite material supporting Au nanoclusters according to the present invention will be explained. As described above, the present invention synthesizes hydrophobic Au nanoclusters by using L-cysteine or an L-cysteine derivative having a predetermined residue as a ligand, and simultaneously transfers the Au nanoclusters to a hydrophobic carrier. It is produced by supporting on. In order to simultaneously generate and advance the synthesis and support of Au nanoclusters, it is necessary to coexist the carrier in the aqueous solvent that is the reaction system at the time of contact between the Au source and the ligand, which is the starting point of the synthesis reaction.

That is, in the method for producing a composite material supporting Au nanoclusters according to the present invention, after forming a state in which at least a portion of the support is in contact with an aqueous solvent containing either an Au source or a ligand, the aqueous solvent is the step of synthesizing Au nanoclusters in the aqueous solvent and supporting the Au nanoclusters on the carrier by adding the other of the Au source and the ligand, wherein the ligand is L-cysteine. Alternatively, it is a method of producing an L-cysteine derivative having a nonpolar residue.

In the examples of studies regarding metal nanoclusters (Au nanoclusters) so far, the subject matter is the synthesis of Au nanoclusters, and the loading on a carrier is based on the premise that the synthesis of Au nanoclusters has been completed. In contrast, in the present invention, the loading on the carrier is completed simultaneously with the synthesis of the Au nanoclusters or immediately after the synthesis of the Au nanoclusters. In the present invention, before synthesizing Au nanoclusters, a reaction system is formed in which either the Au source or the ligand and a carrier coexist, and the other of the Au source or the ligand is allowed to act on this reaction system to synthesize Au nanoclusters. and supported on a carrier. The present invention differs from the prior art in the timing of synthesis and loading of Au nanoclusters. Hereinafter, a method for manufacturing a composite material based on this method of supporting Au nanoclusters will be explained.

In the present invention, it is first necessary to form a state in which the carrier is in contact with an aqueous solvent containing either the Au source or the ligand. In this step, a state in which the aqueous solvent and the carrier are in contact may be formed, or a solution in which either the Au source or the ligand is added to the aqueous solvent is prepared in advance, and this solution and the carrier are brought into contact. Also good. The state in which the carrier is in contact with the aqueous solvent or solution is preferably formed by immersing part or all of the carrier in the aqueous solvent or solution. This is because a sufficient amount of solvent is required in order to uniformly proceed with the subsequent Au nanocluster synthesis reaction that is started by adding the other of the Au source and the ligand. However, an aqueous solvent or solution may be dropped/coated onto the carrier as long as a state in which the Au nanocluster synthesis reaction can occur can be maintained. As the carrier, the above-mentioned carrier having hydrophobicity is applied.

As the aqueous solvent, in addition to pure water, a mixed solvent of water and a water-soluble polar solvent (alcohol, N-methylpyrrolidone, etc.) can be used. The amount of the aqueous solvent is preferably 2 times or more and 1000 times or less relative to the weight of the carrier.

As the Au source, Au salts such as tetrachloride gold (III) acid, gold halide, and potassium gold (I) cyanide can be used. The amount of the Au source added here (Au concentration in the aqueous solvent) is related to the amount of Au nanoclusters supported on the carrier, so the concentration of the Au source should not be limited. For example, when considering catalyst applications, it is possible to obtain the above-mentioned supporting density of Au nanoclusters by setting the Au source to 0.1% by mass or more and 50% by mass or less based on the carrier weight in terms of Au mass. can.

As the ligand, L-cysteine or an L-cysteine derivative having a nonpolar residue is added as described above. The amount of the ligand added is preferably from 1 to 10 times the number of moles of Au ions on a molar basis, taking into consideration the amount of Au nanoclusters to be supported. The ligand, L-cysteine, etc. also acts as a reducing agent, and if the amount is less than 1 time, Au ions may not be completely reduced. The lack of ligand also reduces the stability of Au nanoclusters. On the other hand, if the amount of ligand is 10 times or more, the nanocluster synthesis efficiency will decrease because the Au atom will tend to be stabilized in a complex state in which the ligand is coordinated with the ligand.

Then, after bringing the carrier into contact with the aqueous solvent to which either one of the Au source and the ligand is added, Au nanoclusters are synthesized by adding the other of the Au source and the ligand. At this time, L-cysteine or an L-cysteine derivative functions not only as a ligand but also as a reducing agent. Therefore, in the present invention, when the Au source and the ligand coexist in the reaction system without adding a reducing agent, the synthesis of Au nanoclusters starts and progresses at the same time. The synthesized Au nanoclusters are then adsorbed and supported on a hydrophobic carrier. This support of Au clusters progresses instantaneously to such an extent that they cannot be distinguished by visual observation at the same time as or after the synthesis of Au clusters.

The temperature conditions of the reaction system in the synthesis and support of the above Au nanoclusters are preferably 0° C. or higher and 50° C. or lower, and room temperature may also be used. Further, the reaction atmosphere may be either air atmosphere or inert gas atmosphere.

A composite material can be obtained by completing the synthesis of Au nanoclusters and supporting them on a hydrophobic carrier. The carrier carrying Au nanoclusters may be recovered by drying or filtration, and may be washed, dried, and heat treated as necessary. The heat treatment is performed to control the particle size by decomposing and removing excess ligands and by associating Au nanoclusters. The atmosphere for the heat treatment is preferably an atmospheric atmosphere, a mixed gas atmosphere of oxygen gas and an inert gas, a reduced pressure atmosphere (preferably a reduced pressure atmosphere of 100 Pa or less), or an inert gas atmosphere. Further, the heat treatment temperature is preferably 100°C or more and 800°C or less, more preferably 120°C or more and 400°C or less.

As explained above, the composite material according to the present invention is a composite material in which Au nanoclusters are supported on a hydrophobic carrier. The composite material according to the present invention supports fine Au nanoclusters at a high density, and can effectively exhibit the unique characteristics of the Au nanoclusters.

The present invention also reveals a method for manufacturing a composite material by efficiently supporting Au nanoclusters in an aqueous solvent. According to the present invention, a composite material can be produced by supporting Au nanoclusters on a hydrophobic carrier without relying on organic solvents that are difficult to use from the viewpoint of environmental impact.

By forming Au into nanoclusters, it has catalytic activity not found in bulk. Au nanoclusters have catalytic activity for the oxidation reaction of carbon monoxide, alcohol, and styrene, and the hydrogenation reaction of unsaturated ketones. The present invention can be applied as a catalyst for these chemical reactions. Examples include carbon monoxide removal catalysts and exhaust gas purification catalysts for producing reformed hydrogen gas. Moreover, Au nanoclusters have catalytic activity for oxygen reduction reaction (ORR) as an electrode catalyst. The present invention can also be used as an electrode catalyst for fuel cells.

TEM images of composite materials on which Au nanoclusters of Examples 1 to 3 are supported. MS spectra of the composite material supporting Au nanoclusters (Au(C)/C) of Example 1 before and after heat treatment. MS spectra of the composite material supporting Au nanoclusters (Au(NAC)/C) of Example 2 before and after heat treatment. MS spectra of the composite material supporting Au nanoclusters (Au(C)/C) of Example 3 before and after heat treatment. FIG. 3 is a diagram comparing the MS spectra of the composite materials of Example 1 and Example 2 before heat treatment. FIG. 3 is a diagram comparing the MS spectra of the composite materials of Example 1 and Example 2 after heat treatment. TEM images of composite materials supporting Au nanoclusters of Examples 4 and 5. TEM images of composite materials supporting Au nanoclusters of Examples 6 and 7.

First Embodiment : Hereinafter, an embodiment of the present invention will be described. In this embodiment, carbon powder was used as the hydrophobic carrier. In addition, a composite material was manufactured using L-cysteine and N-acetyl-L-cysteine (hereinafter referred to as acetylcysteine) as ligands for synthesizing Au nanoclusters.

The carbon powder used in this embodiment has an average particle size of 40 nm and a BET specific surface area of 800 m ² /g. A slurry in which 0.1 g of this carbon powder was dispersed in 100 mL of pure water was used as a measurement sample, and analyzed by pulsed NMR to measure the R _SP value. The measurement was performed using a pulsed NMR device manufactured by Resonance Systems, Inc., using a measurement sample volume of 1 mL, a measurement temperature of 30°C, a resonance frequency of about 20 MHz, and ^{a 1} H-NMR observation nucleus to measure the relaxation time (transverse relaxation time T ₂ ) (CMPG law).

The R _SP value of the carbon powder of this embodiment with respect to water was 0.28. Further, from the BET specific surface area (800 m ² /g) of the carbon powder, the total surface area (TSA) of the carrier is 0.8 m ² . Therefore, the TSA correction value R _{SP (c)} of the carbon powder of this embodiment was 0.35, and it was determined that the carbon powder was a hydrophobic carrier.

Example 1 (ligand: L-cysteine (C)) : 1 g of the above carbon powder was added and dispersed in 100 mL of pure water as an aqueous solvent. In the aqueous solvent in which this carbon powder carrier was dispersed, 0.75 g (2.2 mmol of Au) of tetrachloride gold (III) acid as an Au source was dissolved.

Then, 20 mL of an aqueous solution in which 1.2 g (9.3 mmol) of L-cysteine, a ligand, was dissolved was added to the Au aqueous solution in which the carrier was dispersed to synthesize Au nanoclusters, which were simultaneously supported on carbon powder to form a composite material ( Au(C)/C) was produced. The ambient temperature in the above operations was set to room temperature (25° C.) in an air atmosphere.

After supporting Au nanoclusters on carbon powder, the reaction solution was filtered to recover the composite material and filtrate. The recovered composite material was subjected to two types of treatment: one was dried under reduced pressure (100 Pa or less), and the other was heat-treated after drying at 150° C. for 4 hours under reduced pressure (100 Pa or less) to complete the composite material.

Example 2 (ligand: acetylcysteine (NAC)) : Carbon powder was dispersed in the same amount of pure water as in Example 1, and 0.75 g (2.2 mmol of Au) of tetrachloride gold (III) acid, which is an Au source, was dissolved. After that, 20 mL of an aqueous solution containing 1.5 g (9.3 mmol) of acetylcysteine as a ligand was added to produce a composite material (Au(NAC)/C). Thereafter, the composite material was collected and heat treated at 150°C in the same manner as in Example 1.

Example 3 (Ligand: L-cysteine (C)) : In this example, the order of addition of the Au source and the ligand was reversed with respect to Example 1, and Au nanoclusters were synthesized and supported. After dispersing carbon powder in the same amount of pure water as in Example 1 and adding 1.2 g (9.3 mmol) of L-cysteine as a ligand, 0.75 g of tetrachloride gold (III) acid as an Au source was added. (2.2 mmol of Au) was added to produce a composite material (Au(C)/C). Thereafter, the composite material was collected and heat treated at 150°C in the same manner as in Example 1.

The Au nanocluster supported composite materials produced in Examples 1 to 3 were observed using STEM (JEM-ARM200F manufactured by JEOL Ltd.) immediately after production (before heat treatment) and after heat treatment. STEM images of each example are shown in FIG. In the state in which Au nanoclusters are supported, in both Examples 1 and 2, fine Au nanoclusters of around 1 nm are supported. When this was heat-treated at 150°C, slight aggregation occurred, resulting in Au nanoclusters of 1.0 nm (Example 1), 1.0 nm (Example 2), and 0.9 nm (Example 3). . The particle size of these nanoclusters was calculated by fitting a scattering curve obtained when measuring with a camera length of 600 mm using a small-angle X-ray scattering device (NANOPIX manufactured by Rigaku Co., Ltd.).

Next, the composite materials of Examples 1 and 2 were analyzed by pyrolysis GC/MS to confirm the presence of the ligand and to determine whether nonpolar residues could be identified. Thermal decomposition GC/MS was performed using a device named 7890A/5975C manufactured by Agilent Technologies, and the components decomposed at a heating furnace temperature of 600°C were introduced into the GC, separated, and analyzed by MS. As analysis results, MS spectra of the composite materials of Examples 1 to 3 before and after heat treatment are shown in FIGS. 2 to 4. Furthermore, a comparison of the MS spectra of Example 1 and Example 2 using different ligands is shown in FIGS. 5 and 6.

From FIGS. 2 to 4, a peak derived from L-cysteine was detected in all of Examples 1 to 3, and this peak was detected even after heat treatment at 150°C. - The presence of cysteine and L-cysteine derivatives can be confirmed. In addition, since there is no difference in the spectra between Examples 1 and 3 although the order of mixing the Au source and the ligand is different, it is assumed that the structure of the Au nanoclusters is the same depending on the order of mixing with the solvent and carrier. be done. Furthermore, since FIGS. 5 and 6 show acetic acid and acetamide peaks derived from non-polar residues, which are different between the ligands of Examples 1 and 2, it is possible to identify the type of L-cysteine derivative.

Comparative Example : Next, as a comparative example for confirming the supporting efficiency of Au nanoclusters for Examples 1 to 3, Au nanoclusters were synthesized using glutathione as a ligand and supported on carbon powder. In order to keep the conditions the same, in this comparative example, Au nanoclusters were synthesized and supported in a solvent in which the carrier was dispersed, as described below.

2.85 g (9.3 mol) of glutathione was added to an aqueous solution in which 0.75 g (2.2 mmol of Au) of tetrachloride gold (III) acid as an Au source was dissolved in pure water in which the same amount of carbon powder as in Example 1 was dispersed. ) was added to the mixture. After adding glutathione, the composite material was collected and heat treated at 150° C. in the same manner as in Example 1.

[Study of supporting efficiency of Au nanoclusters]
After producing the Au nanocluster-supported composite material of the above comparative example, the amount of remaining Au nanoclusters remaining in the reaction solution after supporting the Au nanoclusters was investigated for Examples 1 to 3 and the comparative example. . In this study, the filtrate after recovering the composite material from the reaction solution after supporting Au nanoclusters was analyzed by ICP-OES (ICP emission spectrometry: ICPE-9820 manufactured by Shimadzu Corporation), and the amount of Au in the filtrate was determined. It was measured. Then, the ratio (%) of the amount of Au in the filtrate to the charged amount (the amount of Au added to the solvent before synthesis of Au nanoclusters) was calculated.

From this study result, the proportion of Au in the filtrate was 0.03% in Example 1 (Au(C)/C), 0.015% in Example 2, and 0.075% in Example 3. there were. From these results, it was confirmed that most of the charged Au source was supported on the carrier as Au nanoclusters. On the other hand, the proportion of Au in the filtrate of the comparative example was 32.8%, which was clearly higher than that of Examples 1 to 3, confirming that there was a considerable amount of Au that was not supported on the carrier. It was done. It can be seen that the Au nanoclusters synthesized using glutathione, which is a ligand in the comparative example, are water-soluble and difficult to support on a hydrophobic carbon powder carrier.

[Evaluation of catalyst activity]
Next, the Au nanocluster-supported composite materials of Examples 1 to 3 were tested to evaluate their catalytic activity. In the activity evaluation test, 10 mg of the catalysts (composite materials) of each example and comparative example were collected after heat treatment, and 2 mL of tetramethylbenzidine solution (manufactured by SeraCare Life Sciences Inc. (KPL)) and 30% hydrogen peroxide solution were added to each sample. 0.1 mL was added and stirred at room temperature (25°C) for 1 minute. After that, 4 mL of 1M hydrochloric acid was added as a reaction stop solution, and the reaction solution was passed through a 0.45 μm filter to remove catalyst powder, and the absorbance at a wavelength of 452 nm was measured using an absorption photometer (V-770DS manufactured by JASCO Corporation). It was measured. The catalytic reaction here is an oxidative decomposition reaction of hydrogen peroxide, and the catalytic activity is evaluated by the intensity of the absorbance of the resulting tetramethylbenzidine dimer.

As a result of the evaluation test, the absorbance intensity was 2.26 in Example 1 (Au(C)/C), 1.97 in Example 2 (Au(NAC)/C), and 1.97 in Example 3 (Au(C)/C). )/C) was 1.95, and it was confirmed that each Example exhibited equivalent oxidation catalytic activity.

Second embodiment : In this embodiment, the same carbon powder as in the first embodiment (average particle size 40 nm, BET specific surface area 800 m ² /g, R _{SP (c)} 0.35) is used as the hydrophobic carrier, and Au Acetylcysteine (NAC) was applied as a ligand for synthesizing nanoclusters, and a composite material was manufactured under manufacturing conditions different from those of the first embodiment.

Example 4 (ligand: acetylcysteine (NAC)) : 4 g of carbon powder was added and dispersed in 400 mL of pure water, which is an aqueous solvent. After adding 6 g (37.2 mmol) of acetyl cysteine, which is a ligand, to the aqueous solvent in which this carbon powder carrier is dispersed, 20 mL of an aqueous solution in which 3 g (8.8 mmol Au) of tetrachloride gold (III) acid, which is an Au source, is dissolved is added. was added to produce a composite material (Au(NAC)/C). Thereafter, in the same manner as in Example 1, the composite material was collected and dried, and then heat-treated at 150° C. under reduced pressure (100 Pa or less) for 4 hours to complete the composite material.

Example 5 (Ligand: Acetylcysteine (NAC)) : Under the same conditions as Example 4, after adding the ligand (NAC) to the aqueous solvent in which the carbon powder is dispersed, the Au source (tetrachloride gold (III) acid) was added. A composite material (Au(NAC)/C) was manufactured by adding an aqueous solution of. After collecting and drying the composite material, the composite material was heat-treated at 400° C. for 4 hours under reduced pressure (100 Pa or less) to complete the composite material.

The Au nanocluster-supported composite materials produced in Examples 4 and 5 were observed using a TEM. TEM images of these composite materials are shown in FIG. As in the first embodiment, the particle sizes of Au nanoclusters in these Au nanocluster-supporting composite materials were measured using a small-angle X-ray scattering device, and the results were 0.8 nm (Example 4) and 4.3 nm (Example 4). 5). It was confirmed that the particle size of Au nanoclusters can be changed by adjusting the heat treatment temperature.

Third Embodiment : In this embodiment, a composite material was manufactured by using carbon powder different from that in the first embodiment as a hydrophobic carrier and applying L-cysteine (C) as a ligand.

The carbon powder used in this embodiment has an average particle size of 40 nm and a BET specific surface area of 220 m ² /g. A slurry in which 1 g of this carbon powder was dispersed in 100 mL of pure water was used as a measurement sample, and analyzed by pulsed NMR to measure the _RSP value. The measurement was carried out using a pulse NMR device manufactured by Bruker, using a sample volume of 2 mL, a measurement temperature of 30° C., a resonance frequency of about 20 MHz, and ^{a 1} H-NMR observation nucleus to measure the relaxation time (transverse relaxation time T ₂ ). The R _SP value of the carbon powder of this embodiment with respect to water was 1.70. Since the total surface area (TSA) of the carrier was 4.4 m ² , the R _{SP (c)} of the carbon powder of this embodiment was 0.39, and it was determined to be a hydrophobic carrier.

Example 6 (ligand: L-cysteine (C)) : 4 g of carbon powder was added and dispersed in 80 mL of pure water, which is an aqueous solvent. After adding 4.8 g (37.2 mmol) of L-cysteine as a ligand to the aqueous solvent in which this carbon powder carrier is dispersed, 3 g (8.8 mmol of Au) of tetrachloride gold (III) acid as an Au source is dissolved. 20 mL of the aqueous solution was added to produce a composite material (Au(C)/C). Thereafter, in the same manner as in Example 1, the composite material was collected and dried, and then heat-treated at 150° C. under reduced pressure (100 Pa or less) for 4 hours to complete the composite material.

Example 7 (ligand: L-cysteine (C)) : Under the same conditions as Example 6, after adding the ligand (C) to the aqueous solvent in which the carbon powder is dispersed, the Au source (tetrachloride gold (III) acid ) was added to produce a composite material (Au(C)/C). After collecting and drying the composite material, the composite material was heat-treated at 230° C. for 4 hours under reduced pressure (100 Pa or less) to complete the composite material.

The Au nanocluster-supported composite materials produced in Examples 6 and 7 were observed using a TEM. TEM images of these composite materials are shown in FIG. As in the first embodiment, the particle diameters of the Au nanoclusters in these Au nanocluster-supporting composite materials were measured using a small-angle X-ray scattering device, and the results were 0.7 nm (Example 6) and 2.0 nm (Example 6). 7). In this embodiment, although a hydrophobic carrier different from that in the first embodiment was used, it was confirmed that a composite material supporting fine Au nanoclusters could be manufactured in the same manner as in the first embodiment. Furthermore, in this embodiment as well, it was confirmed that the particle size of the Au nanoclusters could be changed by adjusting the heat treatment temperature.

As explained above, the present invention relates to a composite material in which Au nanoclusters are supported on a hydrophobic carrier in a suitable state. The present invention also reveals a method for supporting Au nanoclusters on a hydrophobic carrier in an aqueous solvent. According to the present invention, Au nanoclusters can be efficiently supported on a hydrophobic carrier such as carbon powder.

The composite material according to the present invention can have a high surface area by applying Au nanoclusters and can exhibit catalytic activity that bulk Au does not have. Therefore, the present invention can be expected to be used as a catalyst for chemical reactions such as oxidation reactions of carbon monoxide, electrode catalysts for fuel cells, and amplification materials for photocatalysts. In addition, the present invention can be expected to be applied to various devices that utilize quantum effects, surface plasmon resonance, optical properties, etc. of Au nanoclusters.

Claims

A composite material in which Au nanoclusters containing two or more Au atoms are supported on a carrier via a ligand,
The support is hydrophobic at least in a portion on which the Au nanoclusters are supported,
A composite material, wherein the ligand is L-cysteine or an L-cysteine derivative having a nonpolar residue.
The composite material according to claim 1, wherein the ligand is an L-cysteine derivative having any one of an acetyl group, an isobutyl group, and a tert-butoxycarbonyl group as the nonpolar residue.
The carrier is a particulate carrier, and the particulate carrier has an R SP (c) value of 0.000, which is obtained by correcting the R SP value determined by pulse NMR measurement using water as a solvent by the total surface area of the particulate carrier. 3. The composite material according to claim 1 or claim 2, which has a molecular weight of 5 or less.
The composite material according to claim 1 or 2, wherein the carrier is a bulk carrier, and the bulk carrier has a contact angle with water of 90° or more.
The composite material according to claim 1 or 2, wherein the material of the carrier is carbon, cellulose, nitrocellulose, hydrophobic polymer, metal nitride, or hydrophobized material.
A method for producing a composite material according to claim 1 or 2, comprising:
After forming a state in which at least a portion of the carrier is in contact with an aqueous solvent containing either an Au source or a ligand,
adding the other of the Au source and the ligand to the aqueous solvent, thereby synthesizing Au nanoclusters in the aqueous solvent and supporting the Au nanoclusters on the carrier;
The method for producing a composite material, wherein the ligand is L-cysteine or an L-cysteine derivative having a nonpolar residue.