NANOPARTICLES AND THEIR PREPARATION PROCESS

The present invention relates to the field of nanoparticles, more particularly to noble metal nanoparticles with well defined hollow interiors. In particular, the invention relates to noble metal nanoparticles with a multiple wall and with a hollow interior, the process to obtain them as well to the use as catalyst. It also relates to Pt/Ag single wall hollow interior nanoparticles, the process to obtain them, as well as to their uses. BACKGROUND ART

In recent years, noble metal nanoparticles have been extensively studied owing to their intriguing optical, electronic and catalytic properties. For most of the nanoparticles, the introduction of hollows into their interiors could offer some properties, such as resonant cavities, increased surfaces areas or reduced density.

Many attempts have been performed in order to produce noble metal nanoparticles with hollow interiors, but all of them present limited industrial applications since its preparation is either complicated or not reproducible. Thus, hollow metal nanostructures have been described by Xianmao et al. "Galvanic replacement reaction: a simple and powerful route to hollow and porous metal nanostructures" J. Nanoengineering and Nanosystems, vol. 221 , part N, pp. 1 -14. These nanoparticles are prepared by galvanic replacement. Unfortunately, the process needs relatively high temperatures (of about 100°C). The high temperature needed for the reaction implies a high energy cost. Additionally, by galvanic replacement in this condition is difficult to scale up the process for the production of large amounts of nanoparticles. Nanoparticles obtained by galvanic replacement reaction present an alloy of the metals all over the structure. On the other hand, other approach to produce noble metal nanoparticles has been described by Xiaohu et al. "Au- Ag alloy nanoporous nanotubes" Nano Research, 2009, vol. 2, pag. 386-393. In this document, it is described the obtention of bimetallic nanoporous nanotubes by dispersion in water of silver nanoparticles containing

cetyltrimethylammonium bromide (CTAB) and ascorbic acid, under magnetic stirring and at 40°C, followed by the addition of a salt of Au. For dealloying the sample is mixed with nitric acid. Unfortunately, the pores distribution and size of the nanoparticles obtained are irregular and the particles show signs of fragmentation and structural damage, suggesting that by this method, nanoparticles with sufficient quality can not be obtained.

Nanoparticles of Pt/Ag have been produced by the method described in Gao et al. "Bimetallic Ag-Pt hollow nanoparticles: synthesis and tunable surface plasmon resonance", Scripta Materialia, 2007, Vol. 57, pag 687, but when the nanoparticles are formed, the platinum nucleates in form of islands which growth in the surface without the alloying. So, the nanoparticle is not a smooth alloy. Similarly, in Chen et al. "Optical properties of Pd-Ag and Pt-Ag nanoboxes synthesized via galvanic replacement reactions", Nano Lett. 5, 2058 (2005), nanoboxes produced by galvanic replacement of Ag nanocubes dispersed in water with Na ₂ PtCI ₄ is disclosed. However, it is reported that Pt does not readily undergo solid-solid diffusion with Ag at temperatures below 900 K (626.85 °C). Thus, at the reaction conditions Pt and Ag do not alloy, and the nanobox formed after replacement of Ag with Pt is composed of distinct Pt nanoparticles. So, the nucleation and growth of Pt particles on the Ag nanocube results in the formation of rough, noncrystalline nanobox walls that collapse upon further addition of Pt salt.

Document US200500561 18A1 discloses the preparation of single wall nanoparticles with a hollow interior, wherein the wall is made of platinum and silver. Particularly, in Example 1 1 single wall Pt/Ag nanotubes are prepared by refluxing silver nanowires with Pt(CH ₃ COO) ₂ in water solution.

Nevertheless, it is stated that compared to Au/Ag nanotubes, the walls of Pt/Ag nanotubes seemed to be rougher and primarily composed of discrete nanoparticles, and that the wall of Pt/Ag nanotubes could not effectively be reconstructed to form a highly crystalline structure.

Thus, from what is known in the art, there is a need of a simple process allowing for the preparation of Pt-Ag nanoparticles with homogeneous alloy between silver and platinum. Additionally, it is derived that the development of noble metal nanoparticles with a multiple wall and with an hollow interior at room temperature as well as the development of porous nanoparticles with regular pores is still of great interest.

SUMMARY OF THE INVENTION

Inventors have found a process to produce Pt/Ag nanoparticles with homogeneous alloy between silver and platinum at room temperature, the Pt/Ag nanoparticles having a single wall. Platinum silver nanoparticles of this kind are very difficult to produce due to the deficiency of interdiffusion between Pt and Ag, which is a fundamental issue in the process of epitaxial growth. Thus, an aspect of the invention relates to a Pt/Ag single wall nanoparticle with a hollow interior, wherein the nanoparticle has at least two dimensions at the nanoscale, particularly the nanoparticle has all three dimensions at the nanoscale, where the nanoscale is the range about 1 nm to about 100 nm. Particularly, the nanoparticle has a size from 5 nm to 100 nm, more

particularly from 30 nm to 100 nm. This Pt/Ag nanoparticle is of a

homogeneous Pt/Ag alloy.

Another aspect of the invention relates to a process for the preparation of Pt/Ag single wall nanoparticles as defined above at room temperature, the process comprising the steps of: a) adding benzyldodecyldimethylammonium chloride in a molar concentration from 3 x10 ^"2 M to 4 x10 ^"2 M in an aqueous medium comprising nanoparticles of silver, b) adding a salt of platinum in a molar concentration from 0,05 x 10 ^"2 to 4 x10 ^"2 M, particularly from 3 x 10 ^"2 to 4 x10 ^"2 M, and c) isolating the obtained nanoparticles. Particularly the salt of platinum is not soluble in water. As mentioned above, the Pt/Ag single wall nanoparticles are homogeneous, namely are nanoparticles with a

homogeneous alloy between silver and platinum. The nanoparticles obtainable by the process defined above also form part of the invention.

This process allows controlling the ratio between Pt and Ag in the alloy with high morphological and structural quality, and production at industrial scale. On the other hand, the production of homogeneous Pt-Ag hollow structures by the process of the invention, allowing minimizing the consumption of the expensive metal Pt, is a strategic contribution to materials with high catalytic activity. Additionally, the process is advantageous since it is carried out at room temperature, which results in a more cost-effective process. Also, Pt nanoparticles alloyed with Ag, not composed of distinct Pt nanoparticles, exhibit in some cases a higher catalytic activity than pure Pt. Consequently, a more efficient and cost-effective product is obtained. This fact is considered an important contribution to the art since the production of of Pt-Ag hollow structures known in the art had limited use mainly due to higher capital costs as a consequence of the use of high temperatures and the higher

consumption of Pt, as a consequence of nucleation and growth of Pt discrete nanoparticles.

Inventors have also found that noble metal nanoparticles, with multiple walls and with a hollow interior comprising two or three noble metals, the walls with a structure based on a layer of noble metals with a high concentration of one of the noble metals both in the exterior and interior face surfaces of the walls, and an alloy of two metals with specific features in the space between the two layers of the wall, advantageously are more stable than nanoparticles made of a simple metallic alloy all over the wall. The reason lies on the high chemical stability of the metal which is in a high concentration in the external faces of the wall. Particularly, when the highly concentrated in the faces noble metal is gold, as it is an inert metal, the nanoparticles are particularly suitable for their use in biological environments.

Therefore an aspect of the present invention relates to a noble metal nanoparticle with multiple walls and with a hollow interior, the nanoparticle comprising two or three noble metals, wherein each one of the walls comprises a layer of noble metals, with a concentration of one of the noble metals equal to or higher than 85%, both in the exterior and interior face surfaces of the walls, and an alloy of a first and a second noble metals in the space between the two layers of the wall, wherein the second noble metal has a higher reduction potential than the first noble metal, and the first and the second noble metals have different diffusion coefficients, and wherein the noble metal of the layer is made of the second noble metal or of a third noble metal. The process for the production of these nanoparticles with noble metal layers at room temperature makes possible the scale up the process to a large production scale. Thus, another aspect of the present invention relates to a process for the preparation of bimetallic nanoparticles at room temperature comprising the steps of: a) adding cetyltnmethylammonium bromide and ascorbic acid into an aqueous medium comprising nanoparticles of a first noble metal, b) adding a salt of a second noble metal in a molar concentration from 30 μΜ to 100 μΜ and with a flow rate from 20 μΙ/min to 50 μΙ/min, wherein the second noble metal has a higher reduction potential than the first noble metal, and wherein the first and the second noble metals have different diffusion coefficients, and c) isolating the obtained nanoparticles. The bimetallic nanoparticles obtainable by the process defined above also form part of the invention.

Another aspect of the present invention relates to a process for the

preparation of trimetallic nanoparticles, comprising carrying out the process for the preparation of bimetallic nanoparticles and further comprising adding before step c) a salt of a third noble metal in a molar concentration from 3.5x10 ^"3 M to 4x10 ^"3 M and with a flow rate from 200 μΙ/min to 270 μΙ/min. The trimetallic nanoparticles obtainable by the process defined above also form part of the invention.

It has also been found that it can be increased the level of complexity of the nanoparticles with respect to the simple interior hollow of double walls nanoparticles. This geometric pattern, which is formed by cavities

symmetrically distributed, can be obtained by a second process of carving. The process allows having a better control of the interior morphology of the nanoparticles.

Therefore another aspect of the present invention relates to a process for the preparation of trimetallic nanoparticles having two or more cavities at room temperature comprising the steps of: a) adding cetyltrimethylammonium bromide or a mixture of cetyltrimethylammonium bromide and ascorbic acid into an aqueous medium comprising nanoparticles of a first noble metal, b) adding a salt of a second noble metal in a molar concentration from 3.5x10 ^" M to 4x10 ^"3 M,

c) waiting for a period from 20 to 30 minutes, d) adding

cetyltrimethylammonium bromide and ascorbic acid, e) adding a salt of a third noble metal in a molar concentration from 55 μΜ to 100 μΜ, and f) isolating the obtained nanoparticles. The trimetallic nanoparticles having two or more cavities obtainable by the process defined above also forms part of the invention. The trimetallic nanoparticles have the two or more cavities uniformly distributed.

Another aspect of the present invention refers to the use of any of the nanoparticles disclosed above as a catalyst.

These nanoparticles can also be used as fuel cells, drug delivery carrier, sensor or plasmon resonators.

Another aspect of the present invention refers to the use of any of the nanoparticles disclosed above as a catalyst or drug delivery carrier.

When preparing bimetallic nanoparticles in the form of nanocages, the process of the invention ensures the formation of pores with control in the size and localization. This may be an important condition for its use as carrier and delivery system, on the other hand allows a fine modulation of the optical response. Accordingly, another aspect of the invention relates to a process for the preparation of bimetallic nanoparticles in the form of nanocages at room temperature the process comprising the steps of: a) adding

benzyldodecyldimethylammonium chloride in a molar concentration from 3 x 10 ^"2 M to 3.5 x 10 ^"2 M in an aqueous medium comprising nanoparticles of a first noble metal, b) adding a salt of a second noble metal in a molar concentration from 1 .4 x10 ^"4 M to 3 x10 ^"4 M and with a flow from 100- to 200 μΙ/min, herein the second noble metal has a higher reduction potential than the first noble metal, and wherein the first and the second noble metals have different diffusion coefficients, and c) isolating the obtained nanoparticles. It also forms part of the invention the bimetallic nanoparticles in the form of nanocages obtainable by the process as defined above.

On the one hand, the existence of pores in nanocages makes possible to load through the pores chemical compounds that can be delivered in a controlled manner.

Therefore, another aspect of the present invention relates to the use of Pt/Ag nanoparticles, in particular, in form of nanocages, nanoboxes or nanotubes, more particularly in form of nanocages, as defined above as a drug delivery carrier, as catalytic cathode in fuel cells or as a catalyst in oxidation reactions. This aspect can also be formulated as a method of use of the mentioned nanoparticles as a drug delivery carrier, as catalytic cathode in fuel cells or as a catalyst in oxidation reactions.

Finally, it is known that the durability under cycling regimes in systems of proton exchange membrane fuel cells is one of the most important problems that must be resolved. When platinum nanoparticles are used as cathode, amorphous carbon clusters are utilized as support. Unfortunately, the corrosion of the support limits the duration and efficiency of the system. Due at its high surface area, advantages offered by its morphology, and the facility to be aligned and assembled in 2D configurations, the Pt/Ag nanoparticles in form of nanotubes of the invention can be used for its implementation as catalytic cathode in fuel cells. Thus, it is also an aspect of the present invention the use of Pt/Ag nanoparticles as defined above in form of nanotubes as catalytic cathodes in fuel cells. This aspect can also be formulated as a method of use of the mentioned nanoparticles as catalytic cathodes in fuel cells. It can be prepared a colloidal solution of AuAg nanoparticles, in particular blue colour. For its preparation, Au nanocages are prepared. The gold nanocage may be prepared by the method explained in the Example 10 of this document. The gold nanoparticle may be prepared also by other methods known in the art. It is also prepared oxidized polyvinylpyrrolidone (PVP). For its preparation PVP is oxidized during two days in the presence of air. Other method known in the art for oxidizing the polyvinylpyrrolidone may also be used.

It is also considered an aspect of the present invention a process for the preparation of a colloidal solution of Pt/Ag nanoparticles of blue colour which comprises the steps of:

a) adding between 0.5 ml and 1 ml of oxidized polyvinylpyrrolidone with a molar concentration between 1 .5 M and 2.5 M, to an aqueous medium comprising the gold nanocages; b) leaving to stand the solution at least during one day; and c) removing the supernatant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a Transmission electron microscopy (TEM) image of double walled nanocubes Au/Ag.

FIG. 2 shows an Energy-dispersive X-ray spectroscopy (EDX) map of double walled nanocubes Au/Ag.

FIG 3 shows a schematic representation of double walled nanocubes with an open window.

FIG. 4 shows a TEM image for Pt-Ag nanoboxes.

FIG. 5 shows a TEM image of Au-Ag nanocages.

FIG. 6 show a schematic representation of a trimetallic Pd-Au-Ag triple walled nanocubes with five cavities

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, Pt/Ag single wall nanoparticles with a hollow interior of the invention, as well as their preparation process, are part of the invention. Also as mentioned above, the process is carried out at room temperature, and comprises the steps of: a) adding benzyldodecyldimethylammonium chloride until obtaining a molar concentration from 3 x 10 ^"2 M to 4 x 10 ^"2 M in an aqueous medium comprising nanoparticles of silver, b) adding a non-water soluble salt of platinum until obtaining a molar concentration from 0,05 x 10 ^"2 M to 4 x10 ^"2 M, particularly from 3 x 10 ^"2 M to 4 x 10 ^"2 M, in the aqueous medium, and isolating the obtained nanoparticles. Particularly the salt of platinum is not soluble in water.

This process leads to the mentioned Pt/Ag nanoparticles where the Pt mass is extremely reduced and high index planes -highly reactive low coordinated Pt atoms- for increased reactivity, stabilized. Particularly, a stable

homogeneous alloy between silver and platinum coated by a thin layer of platinum is formed, the nanoparticles having a very high catalytic activity.

In a particular embodiment of this process, the salt of platinum is PtCI ₂ . The

PtCI ₂ provides a high standard potential, favoring the inherent reactivity in addition to its insolubility in water, aspect that allows a kinetic control on reaction via a sustained release of Pt ions in the reacting mixture. It is known that PtCI ₂ is soluble in HCI or ammonia, so, with the use of

amphyphilic/tensioactives/surfactant molecules as

benzyldodecyldimethylammonium chloride (BDAC) in aqueous media it is possible to create a chemical environment to solubilise the salt slowly. Under these conditions, the diffusion of platinum in silver is favored and it leads to the formation of a homogeneous alloy.

In a particular embodiment, the wall ot the Pt/Ag single wall nanoparticles with a hollow interior as defined above has a thickness from 3 to 10 nm, particularly of around 5 nm.

In an embodiment of the process for the preparation of Pt/Ag single wall nanoparticles with a hollow interior as defined above, the nanoparticle of silver is a nanocube and, consequently, the obtained nanoparticle is a nanobox. In another particular embodiment of the same process, the nanoparticle of silver is a nanowire and the obtained nanoparticle is a nanotube. As mentioned above, the Pt/Ag single wall nanoparticles are homogeneous. Pt/Ag single wall nanoparticles with a hollow interior in form of nanoboxes or in form of nanotubes obtainable by this process also form part of the invention. As mentioned above, like with Pt/Ag nanocages, Pt/Ag nanotubes show a great potential in their use as catalytic agents. Particularly, with Pt/Ag nanotubes it is not necessary having an additional substrate to form the catalytic cathode.

In another preferred embodiment, the salt of platinum is H ₂ PtCI ₆ . With H ₂ PtCI ₆ appear a formation of Pt-Ag nanocages with porous symmetrically distributed.

The isolation of the obtained nanoparticles can be carried out by conventional methods known to those skilled in the art, such as by filtration or

centrifugation.

Also as mentioned above, another aspect of the present invention relates to a noble metal nanoparticle with multiple walls and with a hollow interior, the nanoparticle comprising two or three noble metals, wherein each one of the walls comprises a layer of a noble metals with a concentration of one of the noble metals equal to or higher than 85% both in the exterior and interior face surfaces of the walls, and an alloy of a first and a second noble metals in the space between the two layers of the wall, wherein the second noble metal has a higher reduction potential than the first noble metal, and the first and the second noble metals have different diffusion coefficients, and wherein the noble metal of the layer is made of the second noble metal or of a third noble metal. Preferably, the layer of noble metals has a concentration of one of the noble metals equal to or higher than 90%, more preferably, metals equal to or higher than 95%, still more preferably equal to or higher than 97%, and even still more preferably equal to or higher than 99%. The term "nanoparticle" as used herein, refers to a particle with at least two dimensions at the nanoscale, particularly with all three dimensions at the nanoscale, where the nanoscale is the range about 1 nm to about 100 nm. Particularly, when the nanoparticle is substantially rod-shaped with a substantially circular cross-section, such as a nanowire or a nanotube, the "nanoparticle" refers to a particle with at least two dimensions at the nanoscale, this two dimensions being the cross-section of the nanoparticle.

As used herein, the term "size" refers to a characteristic physical dimension. For example, in the case of a nanoparticle that is substantially spherical, the size of the nanoparticle corresponds to the diameter of the nanoparticle. In the case of a nanoparticle that is substantially rod-shaped with a substantially circular cross-section, such as as nanowire or a nanotube, the size of the nanoparticle corresponds to the diameter of the cross-section of the

nanoparticle. In the case of a nanoparticle that is substantially box-shaped, such as a nanocube, a nanobox, or a nanocage, the size of the nanoparticle corresponds to the maximum edge length. When referring to a set of nanoparticles as being of a particular size, it is contemplated that the set of nanoparticles can have a distribution of sizes around the specified size. Thus, as used herein, a size of a set of nanoparticles can refer to a mode of a distribution of sizes, such as a peak size of the distribution of sizes.

The term "noble metal" as used herein, refers to metals that are resistant to corrosion and oxidation in moist air. Examples of noble metal are palladium, silver, platinum and gold.

The term "multiple walls" as used herein, refers to at least a double wall, for example double wall, triple wall or quadruple wall. The term "hollow interior" as used herein, refers to the presence of one or more cavities in the interior of the nanoparticle, such as two, three, four or five cavities.

The term "metallic alloy" as used herein, refers to a homogeneous mixture of two or more metals, wherein each of the metals may be in different or equal amounts.

The term "homogeneous" as used herein is understood according to the common understanding of the term. Namely, in the context of composite metals, it relates to an alloy of metals which forms a solid solution, i.e., to a homogeneous mixture of two or more than two metals. Thus, a "homogeneous Pt-Ag nanoparticle" is a nanoparticle with a single phase alloy between silver and platinum. A "solid solution" is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase. The nanoparticle of the invention refers to a nanobox, nanotube or a nanocage. The nanobox, nanotube or nanocage may have different morphologies depending on the sacrificial template, which can have different shapes such as cubes, spheres, wires, rods, prisms and so on. The term "nanobox" as used herein, refers to nanoparticles with hollow interior and solid walls, or with one pore in one of the walls.

The term "nanocages" as used herein, refers to nanoparticles with hollow interior and porous walls and/or porous corners.

The term "nanotubes" as used herein, refers to cylindrical nanoparticles with porous walls or solid walls.

The term "sacrificial template" as used herein, refers to nanoparticles that participate as reactant and are partially or totally consumed during the process. The final product takes the same shape as the template, aspect that allows controlling the geometry of the hollow structure.

In a preferred embodiment of the first aspect of the invention, the first novel metal is silver. In another preferred embodiment of the first aspect, the second and third noble metals are selected from the group consisting of gold, platinum, and palladium.

In another preferred embodiment the nanoparticle is a bimetallic double walled nanoparticle and has an opening giving access to the hollow interior. In a particular embodiment of this aspect the nanoparticle is a Au/Ag double walled nanocube. This nanoparticle is shown in FIG. 1 . FIG 2 shows the metalic distribution of the nanoparticle of FIG. 1 . In other particular embodiment of this aspect the nanoparticle is a Au/Ag double walled nanosphere. In another particular embodiment of this aspect the nanoparticle is a double walled nanotube.

The sentence "opening giving access to the hollow interior" refers to a hole that allows direct access to the interior of the nanoparticle. A schematic representation of this access is shown in FIG. 3.

In other preferred embodiment of the first aspect of the invention the nanoparticle is a trimetallic double wall nanoparticle nanoparticle and has an opening giving access to the hollow interior. In a particular embodiment, the nanoparticle is Pd/Au/Ag double walled nanocube.

To increase the levels of complexity in the double walled nanoparticles with hollow interior the inventors have development trimetallic nanoparticles with interior cavities, symmetrically distributed in the nanoparticles.

In a preferred embodiment of the first aspect of the invention the nanoparticle is a trimetallic nanoparticle having two or more cavities such as two, four or five central cavities. In a particular embodiment of this aspect, the

nanoparticle is Pd/Au/Ag triple walled with five cavities. A schematic representation of this nanoparticle is shown in FIG. 6.

The term "cavities" as used herein refers to interior voids surrounded by only one wall of noble metals in the centre symmetrically distributed. The term cavities does not include the gaps between the walls or the gaps around the cavities.

The bimetallic nanoparticles as defined above may be prepared by a process carried out at room temperature comprising the steps of: a) adding

cetyltrimethylammonium bromide and ascorbic acid into an aqueous medium comprising nanoparticles of a first noble metal, b) adding a salt of a second noble metal in a molar concentration from 30 μΜ to 100 μΜ and with a flow rate from 20 μΙ/min to 50 μΙ/min, wherein the second noble metal has a higher reduction potential than the first noble metal, and wherein the first and the second noble metals have different diffusion coefficients, c) isolating the obtained nanoparticles.

The term "room temperature" as used in the present invention, refers to a temperature between 20°C to 30°C, for example 25°C. Hydrochloric acid may be optionally added in step a.

Hydrochloric acid improves quality surface, smoothness, regularity and monodispersity of the nanoparticle. The trimetallic nanoparticles as defined above, may be prepared by a process comprising carrying out the process of the second aspect of the present invention and further comprising adding before step c) a salt of a third noble metal in a molar concentration from 3.5x10 ^"3 M to 4x10 ^"3 M and with a flow rate from 200 μΙ/min to 270 μΙ/min.

In a particular embodiment, the third noble metal has a lower reduction potential than the second noble metal, thereby a nanocage is obtained. In another particular embodiment, the third noble metal has a higher reduction potential than the second noble metal, thereby a nanobox is obtained.

Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Reference signs related to drawings and placed in parentheses in a claim, are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein. EXAMPLES Example 1 : Production of bimetallic Au-Ag double walled nanoboxes

In Mili Q water (2ml) at room temperature under magnetic stirring, silver nanocubes (200 μΙ_, 7 nM) were added. The silver nanocubes were prepared as the method described in Skrabakak et al. "Nature Protocols", 2007, vol. 2, 2182-2190 and stabilized with polyethylene glycol. Immediately after Cetyl Trimethyl Ammonium Bromide (CTAB) (1 .4 10 ^"2 M) and L- ascorbic acid (1 .4 10- ⁴ M) were added, the two products dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (5.5 10 ^"5 mM) was injected with syringe pump a flow of 30 μΙ/min. After 10 min the product was centrifuged at 14000 rpm and was washed several times with water to eliminate the residues of the synthesis.

Example 2: Production of bimetallic Au-Ag double walled spheres

In Mili Q water (2 ml) at room temperature under magnetic stirring, silver nanospheres (250 μΙ, 7 nM) were added. The silver nanospheres were prepared as the method described in Kim et al. "J. Phys. Chem. C", 2008, vol. 1 12, 7872-7876. Immediately after CTAB (1 ml, 0.1 M) and L- ascorbic acid (10 μΙ, 0.1 M) were added, the two products dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (4 ml, 0.1 mM) was injected with syringe pump a flow of 300 μΙ/min. The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis.

Example 3: Production of trimetallic Pd-Au-Ag double walled nanoboxes

In Mili Q water (2 ml) at room temperature under magnetic stirring, silver nanocubes (250 μΙ, 7 nM) were added. The silver nanocubes were prepared as the method described in Kim et al. "J. Phys. Chem. C", 2008, vol. 1 12, 7872-7876. Immediately after CTAB (1 ml, 0.1 M) and L- ascorbic acid (10 μΙ, 0.1 M) were added, the two products dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (4 ml, 0.1 mM) was injected with syringe pump a flow of 300μΙ/Γηϊη. Immediately after Na ₂ PdCI ₄ (4 ml) was injected with syringe pump a flow of 300 μΙ/min.The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis. The sample was re-dispersed in Mili-Q water (18.2 ΜΩ cm) for storage until use.

Example 4: Production of bimetallic Au-Ag double walled nanocages

In Mili Q water (2 ml) at room temperature under magnetic stirring, silver nanocubes (250 μΙ, 7 nM) were added. The silver nanocubes were prepared as the method described in Kim et al. "J. Phys. Chem. C", 2008, vol. 1 12, 7872-7876. Immediately after, benzyldodecyldimethylammonium chloride (BDAC) (1 ml, 0.1 M) was added dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (500-1000 μΙ, 1 mM) was injected with syringe pump a flow of 45 μΙ/min.The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis. The sample was re-dispersed in Mili-Q water (18.2 ΜΩ cm) for storage until use. Example 5: Production of bimetallic Pt-Ag single walled nanoboxes

In Mili Q water (2 ml) at room temperature under magnetic stirring, silver nanocubes (250 μΙ. 7 nM) were added. The silver nanocubes were prepared as the method described in Kim et al. "J. Phys. Chem. C", 2008, vol. 1 12, 7872-7876. Immediately after, BDAC (1 ml, 0.1 M) dissolved in water Mili-Q, and an aqueous solution of PtCI ₂ (2 ml, 10 mM) were added. The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis. The sample was re-dispersed in Mili-Q water (18.2 ΜΩ cm) for storage until use. Example 6: Production of bimetallic Au-Ag double walled nanotubes

In Mili Q water (2.8 ml) at room temperature under magnetic stirring, silver nanowires (0.28 ml, 7 nM) were added. Immediately after CTAB (1 .4 ml, 0.1 M) and ascorbic acid (0.013 ml, 0.1 M) were added, the two products dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (3 ml, 0.01 mM) was injected with syringe pump a flow of 225 μΙ/min, then an aqueous solution of H ₂ AuCI ₄ (2.3 ml, 1 mM) was injected with syringe pump a flow of 172 μΙ/min and finally H ₂ AuCI ₄ (0.2 ml, 10 mM) was injected with syringe pump a flow of 15μΙ/Γηίη. The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis. The sample was re-dispersed in Mili-Q water (18.2 ΜΩ cm) for storage until use. Example 7: Production of bimetallic Pt-Ag nanotubes

In Mili Q water (2 ml) at room temperature under magnetic stirring, silver nanowires (1 ΟΟμΙ, 7 nM) were added. Immediately after BDAC dissolved in water (1 ml, 0.1 M) was added. An aqueous solution of PtCI ₂ (200μΙ, 10mM) was added drop by drop. The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis. The sample was re-dispersed in Mili-Q water (18.2 ΜΩ cm) for storage until use.

Example 8: Production of trimetallic Pd-Au-Ag triple walled nanocubes with five cavities

In Mili Q water (2ml) at room temperature under magnetic stirring, silver nanocubes (250μΙ, 7 nM) were added. Immediately after CTAB (1 ml, 0.1 M) and ascorbic acid (10 μΙ, 0.1 M) were added, the two products dissolved in water Mili-Q. An aqueous solution of Na ₂ PdCI ₄ (400 μΙ, 1 mM) was injected with syringe pump a flow of 300 μΙ/min. Twenty minutes after an CTAB (1 ml, 0.1 M) and ascorbic acid (10 μΙ, 0.1 M) were added, the two products dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (400 μΙ, 1 mM) was injected with syringe pump a flow of 300 μΙ/min.

Example 9: Production of bimetallic Au-Ag hybrid nanotubes

In Mili Q water at room temperature under magnetic stirring, silver nanowires

(100 μΙ_, 7 nM) were added. Immediately after BDAC (3 10 ^"2 M) was added dissolved in water Mili-Q. An aqueous solution of H ₂ AuCI ₄ (1 .4 10 ^"5 M) was injected with syringe pump a flow of 0.075 μΙ/min, then an aqueous solution of H ₂ AuCI ₄ (1 .4 10 ^"4 M) was injected with syringe pump a flow of 0.075 μΙ/min. The product was centrifuged at 200 rpm and was washed several times with water to eliminate the residues of the synthesis. The sample was re-dispersed in Mili-Q water (18.2 ΜΩ cm) for storage until use.

Example 10: Production of a blue color

In Mili Q water (2 ml) at room temperature under magnetic stirring, silver nanocubes (250μΙ, 7 nM) were added. Immediately after BDAC dissolved in water (1 ml, 0.1 M) was added. An aqueous solution of H ₂ AuCI ₄ (600 μΙ, 1 mM) was injected with syringe pump a flow of 45 μΙ/min. When the resonance peak of the colloid show 800 nm in a spectrophotometer UV-vis the product was centrifuged at 14000 rpm. The supernatant was removed. Distillated water (1 ml) was added. Then oxidised polyvinylpyrrolidone was added (2 M, 0.5 ml) settling the solution al least one day and finally removing the supernatant.