TECHNICAF FIELD

The present invention pertains to a process for obtaining a metal or metalloid oxide porous material containing metal or metalloid nanoparticles selectively dispersed within the pores. This invention is also directed to the material thus obtained, wherein said nanoparticles have a mean diameter of 10 to 40 nm, and uses thereof.

BACKGROUND OF THE INVENTION

Porous materials have a high specific surface area and an organized or non-organized porosity. Such materials can also be functionalized: for instance, organic groups can be introduced so as to obtain organic-inorganic hybrid materials, and nanoparticles can be introduced so as to obtain composite or nano-composite materials. A wide range of structures and chemical compositions can be obtained for such functionalized porous materials, which make them useful in many applications, such as in optics or catalysis.

More particularly, mesoporous oxides, such as silica, are a well-suited support for metal nanoparticles. Insertion and dispersion of nanoparticles in this confined support allow a control of their growth and limit their aggregation.

The most common method for preparing nanoparticles-containing porous nanocomposite materials consists of impregnating a porous solid with a metal salt solution, and in situ reducing the metal salt. The step of reducing is typically carried out by using a chemical agent, such as dihydrogen or sodium borohydride, a physical agent such as UV- or g- radiation, or by thermal reduction under inert gas.

Bloch et al (J. Phys. Chem. C. 2010, 114, 22652) describe such an impregnating method, wherein the porous silica matrix is prepared by a sol-gel process in the presence of a triblock copolymer (poly styrene- h-poly ethylene oxidc-/?-poly styrene) as a pore-forming agent, and wherein the metal salt (silver nitrate) is reduced by UV irradiation.

Even though the impregnating method is a convenient method, it does not allow to control (i) the localization of the nanoparticles; (ii) the amount of nanoparticles incorporated within the material; and (iii) the size of the nanoparticles. Furthermore, the in situ reduction of the metal salt gives only access to nanoparticles of less than 10 nm, typically 2-6 nm. These drawbacks are closely related to the diffusion of the nanoparticle precursors within the porous material and to the nucleation/growth of the nanoparticles in a confined medium.

Bastakoti et al ( Chem . Commun. 2014, 50, 9101) describe a process comprising a step of mixing a metal complex, namely platin pentanedioate, with a poly(styrcnc-/?-vinylpyndinc-/?-cthylcnc oxide) pore-forming copolymer followed by a step of micellizing of the copolymer, and a step of forming the silica matrix by a sol-gel method. The solid is then heated to a temperature allowing the formation of the pores and the reduction of the metal complex into nanoparticles. However, the reduction being performed in situ, the above limitations cannot be overcome. Furthermore, since the block copolymer and the metal complex are not bound to each other, the selective dispersion of the nanoparticles within the pores cannot be guaranteed.

FR 2 901 715 discloses a process comprising (i) contacting a metal complex with a ligand consisting of a lipophilic alkyl block, a thiol end and an alkoxysilane end, (ii) in situ reducing the metal complex, (iii) polymerizing the silane moiety, and (iv) heating to a temperature allowing the formation of the pores. However, the lipophilic chain of the pore-forming agent is an alkyl chain, which tends to fold, and thus gives only access to very small pores, typically 2- 3 nm.

WO 2010/040926 discloses a process wherein metal nanoparticles coordinated by ligands are contacted with a pore-forming amphiphilic polymer and then with a silica precursor. Depending on the hydrophobic or hydrophilic nature of the ligands, and consequently, their affinity with the polymer, nanoparticles can be dispersed within the pores and/or the walls of the porous silica material. However, such affinities do not allow to reach a high selectivity regarding the localization of the nanoparticles.

Hence, there remains a need to provide a process for preparing a porous material containing nanoparticles, wherein the size of pores and nanoparticles can be tuned and controlled, and wherein the nanoparticles are selectively dispersed within the pores of the material. SUMMARY OF THE INVENTION

In this context, the inventors have developed an efficient process, which overcomes the aforementioned shortcomings. In addition, this process gives access for the first time to a porous nanocomposite material, which contains nanoparticles having a mean diameter of 10 to 40 nm selectively dispersed within the pores of the material. In this process, nanoparticles coordinated by an exchangeable ligand are prepared beforehand. Then, a substitution of this ligand by an end-functionalized amphiphilic copolymer is performed in order to form micelles of this polymer coordinated to nanoparticles through its functional end. Formation of a metal or metalloid oxide matrix by a sol-gel process, with a final calcination step, produces said material. This process allows a high control and versatility of the nanoparticles and pore sizes, but also a high selectivity in terms of dispersion of the nanoparticles, which make the material particularly useful and efficient in a wide range of applications. In particular, the inventors have demonstrated that the material obtained by this process is an efficient catalyst and enhances the dosage and detection of chemicals at very low concentrations, by spectroscopy.

This invention is thus directed to a process for forming a nanoparticles-containing porous material, said process comprising the following successive steps:

(a) providing metal or metalloid (M) nanoparticles coordinated by a ligand;

(b) contacting the nanoparticles obtained in step (a) with an amphiphilic block copolymer having at least one functionalized end, so as to obtain metal or metalloid nanoparticles coordinated by said amphiphilic block copolymer;

(c) contacting the nanoparticles obtained in step (b) with a metal or metalloid (M') oxide precursor; and

(d) heating the mixture obtained in step (c) at a temperature allowing the formation of a nanoparticles-containing metal or metalloid (M') oxide porous material.

This invention also pertains to a material obtainable by a process as defined herein, wherein said material comprises a porous metal or metalloid oxide matrix and, metal or metalloid nanoparticles selectively dispersed within the pores of the matrix, said nanoparticles having a mean diameter of 10 to 40 nm.

It is also directed to the use of a material obtainable by a process of the invention, and in particular a material as defined herein, as a catalyst. Another object of the present invention is the use of a material obtainable by a process of the invention, and in particular a material as defined herein, for dosing and/or detecting at least one chemical substance in a sample subjected to Raman spectroscopy.

FIGURES

Figure 1: ¹ H NMR spectrum of C H -POE ₄₅ -/7-PS ₇ 6-S H

Figure 2: a) Size distribution of gold nanoparticles stabilized by a citrate ligand

(Au5 _nm@ citrate) determined by DLS; b) TEM photograph of gold nanoparticles stabilized by a citrate ligand (Au5 _nm@ citrate).

Figure 3: a) Size distribution of gold nanoparticles stabilized by a citrate ligand

(Au20 _nm@ citrate) determined by DLS; b) TEM photograph of gold nanoparticles stabilized by a citrate ligand (Au20 _nm@ citrate).

Figure 4: TEM photograph of gold nanoparticles stabilized by a citrate ligand

(Au40nm@ citrate).

Figure 5: SEM photograph of a porous material (Au _5nm @Si0 ₂ ) prepared by a process of the invention.

Figure 6: SEM photograph of a porous material (Au20 _nm @SiO2) prepared by a process of the invention.

Figure 7: TEM photograph of a porous material (Au _5nm @Si0 ₂ ) prepared by a process of the invention.

Figure 8: TEM photograph of a porous material (Au20 _nm @SiO2) prepared by a process of the invention.

Figure 9: TEM photograph of a porous material (Au40 _nm @SiO2) prepared by a process of the invention.

Figure 10: Nitrogen adsorption/desorption isotherm at 77K of a porous material (Au20nm@SiC>2)

Figure 11: Evolution of an Au@Si0 ₂ -catalyzed nitro-reduction of 4-nitrophenol by UV-vis spectroscopy.

Figure 12: Raman spectroscopy detection of oxazepam with Au@Si0 ₂ materials. DETAILED DESCRIPTION

In the process of the present invention, metal or metalloid (M) nanoparticles coordinated (or "stabilized") by a ligand (L) are first provided (step (a)).

The "ligand (L)" refers to a neutral or anionic ligand, which is able to stabilize nanoparticles. Said ligand is preferably organic. Advantageously, said ligand (L) has a long alkyl chain and/or at least one neutral or anionic functional group, preferably two, three or four neutral or anionic functional groups.

Exemplary functional groups include, but are not limited to, an oxo (=0), alcohol (-OH), thiol (-SH), disulfide (-S-S-), amine (-Nth), carboxylic acid (-C(O)OH), alcoholate (-0-), thiolate (- S ), carboxylate (-C(O)O-), phosphorous-based functions, or xanthate (-O-C(S)S-).

As used herein, an alkyl group refers to a linear or branched, saturated hydrocarbon chain. Preferably, an alkyl group has 1 to 20 carbon atoms (noted “C ₁ -C ₂₀ alkyl”), for instance 1 to 12 carbon atoms (noted “C ₁ -C ₁₂ alkyl”), or 1 to 6 carbon atoms (noted “C ₁ -C ₆ alkyl”), or 3 to 20 carbon atoms (noted “C ₃ -C ₂₀ alkyl”).

As used herein, a long alkyl chain refers to a C ₃ -C ₂₀ alkyl.

In a particular embodiment, said ligand (L) is selected from the group consisting of carboxylates (e.g. trisodium citrate), phosphines (e.g. triphenylphosphine), phosphine oxide (e.g. tri-n- octylphosphine oxide), amines (e.g. alkylamines), (C3-C2o)alkyl thiols, xanthates (e.g. alkylxanthates), and disulfides (e.g. alkyldisulfides). Preferably, said ligand (L) is trisodium citrate.

The metal or metalloid (M) of the nanoparticles is advantageously a transition metal, a post transition metal, an actinide, a lanthanide, or a combination thereof, preferably a transition metal.

Examples of transition metals are vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, molybdenum, niobium, zirconium, yttrium, tungsten, tantalum, gold, platinum, palladium, rhodium, osmium, iridium, silver, and ruthenium.

Examples of post-transition metals are gallium, aluminum, tin, indium, lead and bismuth. Examples of actinides are actinium and uranium. Examples of lanthanides are cerium, lanthanum, samarium, europium, neodymium, erbium and ytterbium.

Examples of metalloids are silicon, germanium, antimony, tellurium, and selenium.

In a particular embodiment, the metal or metalloid (M) is selected from the group consisting of gold, platinum, palladium, rhodium, osmium, iridium, silver, ruthenium, silicon, germanium, antimony, tellurium, and selenium.

In another particular embodiment, M is a metal.

Preferably, M is selected from the group consisting of gold, platinum, palladium, rhodium, osmium, iridium, silver, ruthenium, and a mixture thereof. More preferably, M is palladium, gold, silver, or a gold/silver mixture. Even more preferably, M is gold.

Said metal or metalloid (M) nanoparticles coordinated by a ligand (L) may be prepared by any process known to the skilled artisan, such as photochemistry (e.g. UV, near IR), sonochemistry, radiolysis or thermolysis.

In a particular embodiment, step (a) comprises contacting a metal or metalloid (M) precursor with a ligand (L), and optionally a reducing agent.

As used herein, the expression "reducing agent" refers to a compound which is able to reduce a cationic metal atom into a neutral metal atom.

In a first embodiment, metal or metalloid (M) nanoparticles coordinated by a ligand (L) are prepared by contacting a metal or metalloid (M) precursor with a ligand (L). In such embodiment, the conditions of the contacting step are chosen such that the ligand (L) can act itself as a reducing agent.

In such an embodiment, the ligand (L) is advantageously in excess with respect to the metal or metalloid (M) precursor. For instance, the amount of ligand (L) may be comprised between 3 and 20 equivalents with respect to the metal or metalloid (M) precursor. The metal or metalloid (M) precursor and the ligand (L) may be contacted at a temperature comprised between 70 °C and 120 °C, preferably between 85 °C and 105 °C. In a second embodiment, metal or metalloid (M) nanoparticles coordinated by a ligand (L) are prepared by contacting a metal or metalloid (M) precursor with a ligand (L) and a reducing agent, wherein the reducing agent is different from the ligand (L).

An example of such reducing agent is sodium borohydride, hydrazine, or dihydrogen, preferably sodium borohydride.

The ligand (L) and the reducing agent are typically contacted with the metal or metalloid (M) precursor successively, in this given order: (i) ligand (L), (ii) reducing agent.

In this second embodiment, the amount of ligand (L) may be comprised between 1 and 5 equivalents, preferably between 1 and 1.5 equivalents, with respect to the metal or metalloid (M) precursor. The amount of said reducing agent may be comprised between 3 and 20 equivalents with respect to the metal or metalloid (M) precursor. The metal or metalloid (M) precursor, the ligand (L) and the reducing agent may be contacted at a temperature comprised between 0 °C and 40 °C, preferably between 10 °C and 30 °C.

In the first and second embodiments, the metal or metalloid (M) precursor, the ligand (L) and the optional reducing agent are advantageously contacted in water.

The precursor may for instance be selected from the group consisting of inorganic salts, organic salts or alkoxides of at least one metal or metalloid or of a combination of at least one metal with at least one metalloid. Examples of inorganic salts are halides (fluorides, chlorides, bromides or iodides, especially chlorides), oxyhalides (especially oxychlorides), hydrogen halides (especially hydrogen chloride), sulfates, and nitrates. Organic salts may be selected from oxalates and acetates, for instance, while alkoxides are typically of formula (RO) _n M where M denotes a metal or metalloid, n represents the number of ligands (OR) linked to M which corresponds to the valency of M and R represents a linear or branched alkyl chain having from 1 to 10 carbon atoms or a phenyl group; organometallic compounds of formula X _y R ¹ _Z M wherein M represents a metal or metalloid, X represents a hydrolysable group chosen from halogen atoms, acrylate, acetoxy, acyl or OR' groups where R' is a linear or branched alkyl group comprising from 1 to 10 carbon atoms or a phenyl group, R ¹ represents a non-hydrolysable group selected from optionally perfluorinated linear or branched alkyl groups comprising from 1 to 10 carbon atoms or a phenyl group, and y and z are integers chosen so that y + z is equal to the valency of M.

The precursor may be a solvate, for instance, a hydrate. A "hydrogen halide salt" refers to a salt of formula H _m MX _n , wherein M represents a metal, X represents a halide, m represents the number of hydrogen atoms (typically 1 or 2) and n represents the number of halides (typically, n is an integer from 1 to 7). Halides include fluoride, chloride, bromide and iodide. A preferred halide is chloride.

Preferably, when M is a metal, the metal or metalloid (M) precursor is an inorganic salt of said metal, and more preferably, a halide or a hydrogen halide of said metal.

The nanoparticles preferably have a mean diameter from 2 to 50 nm, preferably from 5 to 45 nm, more preferably from 10 to 40 nm, even more preferably from 10 to 25 nm, or from 15 nm to 40 nm. The mean diameter of the nanoparticles can be determined by any techniques known to the skilled artisan. For instance, said mean diameter can be determined by microscopy, such as Transmission Electron Microscopy (TEM) or atomic force microscopy (AFM), dynamic light scattering (DLS), or small-angle X-ray scattering (SAXS). Preferably, the mean diameter is determined by TEM. The mean diameter of the nanoparticles, as used herein, refers to the mean diameter of the non-coordinated nanoparticles, as determined by TEM.

The reaction conditions, and in particular the reducing agent (i.e. ligand L, or a reducing agent different therefrom), may judiciously be chosen in order to obtain the desired mean diameter of nanoparticles.

Step (b) of the process of the invention comprises contacting the nanoparticles obtained in step (a) (i.e. metal or metalloid (M) nanoparticles coordinated by a ligand (L)) with an amphiphilic block copolymer having at least one functionalized end. In particular, the ligand (L) being exchangeable, the contacting step (b) can also be described as a step comprising substituting (or equivalently “exchanging”) the ligand (L) of said nanoparticles with an amphiphilic block copolymer having at least one functionalized end.

As used herein, an "amphiphilic block copolymer" refers to a polymer comprising at least two (preferably two) different polymer chains or "blocks", wherein at least one (preferably one) of the blocks is hydrophilic and at least one (preferably one) of the blocks is hydrophobic. Amphiphilic block copolymers are able to form micelles, typically by evaporation-induced self- assembly. The amphiphilic block copolymers may be block copolymers of poly (ethylene oxide) with a polyolefin or poly(propylene oxide); block copolymers of polystyrene with poly(ethylene oxide), poly(lactic acid) or polyvinylpyridine; and their mixtures. Examples of such amphiphilic block copolymers are (polyethylene oxide)-block-(polystyrene), (polybutadiene)-block-(polyethylene oxide), [poly(ethylene-co-butadiene)-block-

(polyethylene oxide)], (propylene-based elastomer)-block-(polyethylene oxide), (poly styrene) - block- (poly lactic acid), (polystyrene)-block-(poly(4-vinyl pyridine)), (polyethylene oxide)- block- (polypropylene oxide)-block-(polyethylene oxide), and mixtures thereof.

Preferably, the amphiphilic block copolymer is a block copolymer of polystyrene with poly(ethylene oxide), more preferably a (polyethylene oxide)-block-(polystyrene) or (polystyrene)-block-(polyethylene oxide)-block-(polystyrene), even more preferably a (polystyrene)-block-(polyethylene oxide).

It is understood that each block of the amphiphilic block copolymer can be directly linked to each other, or by a linker, which may be any suitable organic chemical group.

The amphiphilic block copolymer used in the process of the invention comprises at least one functionalized end (preferably one or two functional ends, more preferably one functional end).

The functionalized end is a reactive group which is able to substitute the ligand (L) of said metal or metalloid nanoparticles coordinated by the ligand (L), so as to obtain metal or metalloid nanoparticles coordinated by the functionalized amphiphilic block copolymer, organized in the form of micelles.

In a preferred embodiment, the at least one functionalized end is linked to a hydrophobic block of said amphiphilic block copolymer.

In particular embodiment, the at least one functionalized end is selected from the group consisting of carboxylate (-C(O)O-), amine (-Nth), phosphine (e.g. -PR2 wherein each R represents independently an alkyl, cycloalkyl, or aryl), isocyanide (-NC), xanthate (e.g. -O- C(S)S or -0-C(S)SR’ wherein R’ represents a hydrogen atom, alkyl, cycloalkyl or aryl), and thiol (-SH). Preferably, the at least one functionalized end is a thiol (-SH) group.

As used herein, a “cycloalkyl” refers to a mono- or polycyclic saturated hydrocarbon chain. Preferably, said cycloalkyl has 3 to 12 carbon atoms (noted C3-C12 cycloalkyl). Examples of C3-C12 cycloalkyl include, but are not limited to, cyclopropyl, cyclopentyl, cyclohexyl, or cyclododecyl.

As used herein, an “aryl” refers to a mono- or bi-cyclic aromatic hydrocarbon group having between 5 and 14 atoms, such as phenyl, biphenyl, or naphthyl.

For instance, the amphiphilic block copolymer having at least one functionalized end may be HS-(polystyrene)-block-(polyethylene oxide)-block-(polystyrene)-SH, or (polyethylene oxide)-block-(polystyrene)-SH, preferably (polyethylene oxide)-block-(polystyrene)-SH. In a more particular embodiment, the amphiphilic block copolymer having at least one functionalized end is represented by the following formula (1-0): wherein n is an integer comprised between 10 and 1000, m is an integer comprised between 10 and 1000, and

R is a (Ci-C ₆ )alkyl (preferably a methyl) or a group of formula (II): wherein m’ is an integer comprised between 10 and 1000. In an embodiment where R is of formula (II), it is preferred that m’ and m are identical.

In a preferred embodiment, the amphiphilic block copolymer having at least one functionalized end is represented by the following formula (I): wherein n is an integer comprised between 10 and 1000, and m is an integer comprised between 10 and 1000.

In a particular embodiment, n is an integer comprised between 40 and 500.

In another particular embodiment, m is an integer comprised between 50 and 300.

Contacting in step (b) may be carried out by mixing the metal or metalloid nanoparticles coordinated by ligand (L) and the amphiphilic block copolymer, in solution, preferably in an organic solvent, water, or a mixture thereof.

General examples of organic solvents include, but are not limited to, aliphatic hydrocarbons such as pentane or hexane, alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as benzene, styrene, toluene, ortho-xylene, meta-xylene or para-xylene, halogenated hydrocarbons such as dichloromethane, chloroform or chlorobenzene, nitrogen-based solvents such as acetonitrile or triethylamine, oxygen-based solvents, in particular ketones such as acetone, ethers such as diethyl ether, methyl tert-butyl ether or tetrahydrofuran (THF) and alcohols such methanol or ethanol, esters or amides, such ethyl acetate or dimethylformamide (DMF), and mixtures thereof.

In a particular embodiment, the solvent in step (b) is a mixture of THF and water, wherein the ratio THF:water is preferably comprised between 1:10 and 10:1, more preferably between 4:6 and 6:4.

The molar ratio of the nanoparticles coordinated by ligand (L) to the amphiphilic block copolymer in step (b) may be comprised between 0.01 and 10, preferably between 0.1 and 1. Contacting in step (b) may be carried out a temperature comprised between 5 °C and 40 °C, preferably between 15 °C and 30 °C.

Step (b) allows to obtain metal or metalloid (M) nanoparticles coordinated by said amphiphilic block copolymer, organized in the form of micelles. Successive steps (c) and (d) of the process of the invention consist of forming, typically by a sol-gel method, a porous matrix consisting of a metal or metalloid oxide, said matrix containing metal or metalloid nanoparticles within its pores.

Step (c) comprises contacting the metal or metalloid (M) nanoparticles coordinated by the amphiphilic block copolymer, obtained in step (b), with a metal or metalloid (NT) oxide precursor.

The expression "metal or metalloid oxide precursor(s)" refers to any metal oxide precursor, metalloid oxide precursor or combination thereof, which is conventionally used in sol-gel processes. The precursors may for instance be selected from the group consisting of inorganic salts, organic salts or alkoxides of at least one metal or metalloid or of a combination of at least one metal with at least one metalloid. Examples of inorganic salts are halides (fluorides, chlorides, bromides or iodides, especially chlorides), oxyhalides (especially oxychlorides), hydrogen halides (especially hydrogen chloride), sulfates, and nitrates. Organic salts may be selected from oxalates and acetates, for instance, while alkoxides are typically of formula (RO) _n M’ where M’ denotes a metal or metalloid, n represents the number of ligands linked to M’ which corresponds to the valency of M’ and R represents a linear or branched alkyl chain having from 1 to 10 carbon atoms or a phenyl group; organometallic compounds of formula X _y R^M’ wherein M’ represents a metal or metalloid, X represents a hydrolysable group chosen from halogen atoms, acrylate, acetoxy, acyl or OR' groups where R' is a linear or branched alkyl group comprising from 1 to 10 carbon atoms or a phenyl group, R ¹ represents a non- hydrolysable group selected from optionally perfluorinated linear or branched alkyl groups comprising from 1 to 10 carbon atoms or a phenyl group, and y and z are integers chosen so that y + z is equal to the valency of M’ .

M’ may be selected from titanium, hafnium, zirconium, aluminum, copper, iron, scandium, vanadium, chromium, manganese, cobalt, nickel, copper, yttrium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, rutherfordium, dubnium, seaborgium, bohrium, hassium, copemicium, cerium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium and their mixtures, whereas suitable metalloids include for instance silicon, selenium and tellurium. In a particular embodiment, M and M’ are different from each other.

In another particular embodiment, M’ is a metalloid.

In a preferred embodiment, the metal or metalloid (M’) is selected from silicon, titanium, zirconium and a combination thereof, more preferably M’ is silicon.

Examples of silicon oxide precursors are tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), tetrapropoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, ally ltrimethoxy silane, propyltriethoxy silane, phenyltriethoxy silane, 1,4- bis(triethoxysilyl)benzene, vinyltriethoxysilane, phenylaminomethyltriethoxysilane (PAMS), triethoxysilane, triethoxy(octyl)silane, methyltrimethoxysilane, phenyltrimethoxysilane, methyltriisopropoxysilane, or mixtures thereof, preferably tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS).

Examples of titanium oxide precursors are TiCU, Ti(OPr)4, Ti(N0 ₃ ) ₄ , Ti(S0 ₄ ) ₂ and titanium acetate.

The metal or metalloid (M’) oxide precursor(s) may further be present as a solvate, preferably a hydrate.

In particular embodiment, contacting in step (c) comprises the following substeps:

(cl) mixing said metal or metalloid nanoparticles coordinated by the amphiphilic block copolymer with said metal or metalloid (M') oxide precursor, in solution, preferably in an organic solvent (e.g. THF), so as to obtain a pre-solid; and

(c2) aging the pre-solid obtained in step (cl) for 1 day to 30 days, preferably for 2 days to 10 days, so as to obtain a solid.

The solid obtained in substep (c2) may be dried at a temperature comprised between 20 °C and 150 °C, and preferably for 5 hours to 10 days.

The mass ratio of the nanoparticles coordinated by the amphiphilic block copolymer to metal or metalloid (M’) oxide precursor(s) in step (c) may typically be comprised between 0.2 and 1. Such ratio can be tuned by the skilled artisan depending on the nanoparticle size and the copolymer structure. Step (c) (or substeps (cl) and (c2)) may be carried out at a temperature comprised between 5 °C and 40 °C, preferably between 15 °C and 30 °C.

In a preferred embodiment, step (c) (and in particular, substep (cl)) is carried out at a pH comprised between 0.5 and 5, preferably between 1 and 3. The pH may be controlled by using an acid.

Examples of acids include, but are not limited to, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, trifluoroacetic acid, methanesulfonic acid, benzenesulfonic acid or p-toluenesulfonic acid. Hydrochloric acid is particularly preferred.

The solid obtained in step (c) may be described as a non-porous material, comprising a metal or metalloid (M’) oxide matrix and metal or metalloid (M) nanoparticles coordinated by the amphiphilic block copolymer dispersed within the matrix.

Step (d) of the process of the invention allows the formation of pores within the material, by removal of organic entities (namely, the amphiphilic block copolymer) of the solid obtained in step (c).

Step (d) comprises heating the solid obtained in step (c) at a temperature allowing the formation of a nanoparticles-containing metal or metalloid (M’) oxide porous material.

Said temperature in step (d) is advantageously comprised between 300 °C and 1200 °C, preferably between 400 °C and 800 °C.

Heating in step (d) may be maintained for 1 hour to 24 hours, preferably for 2 hours to 10 hours.

In a particular embodiment, the process of the invention comprises the following steps of:

(a) providing metal or metalloid (M) nanoparticles coordinated by a ligand (L);

(b) substituting the ligand (L) of the nanoparticles obtained in step (a) with an amphiphilic block copolymer having at least one functionalized end, so as to obtain metal or metalloid nanoparticles coordinated by said amphiphilic block copolymer through said at least one functional end; (c) contacting the nanoparticles obtained in step (b) with a metal or metalloid (NT) oxide precursor, so as to obtain a solid; and

(d) heating the solid obtained in step (c) at a temperature allowing the formation of a nanoparticles-containing metal or metalloid (M’) oxide porous material.

The material obtained by the process of the invention is porous. Such material comprises a porous matrix of a metal or metalloid (M’) oxide and, metal or metalloid (M) nanoparticles dispersed within the pores. Removal of the amphiphilic block copolymers coordinating the metal or metalloid (M) nanoparticles in step (d) of the process of the invention creates the pores, and thus allows to reach a highly selectivity in terms of localization of the nanoparticles. Typically, the nanoparticles are (selectively) dispersed within pores, and not within the walls of the matrix. In a particular embodiment, at least 60%, 70%, 80%, 90%, 95%, 98%, 99% or 100% of the nanoparticles are dispersed within the pores of the matrix.

The pores of said material may have a mean diameter from 2 to 50 nm, preferably from 5 to 45 nm, more preferably from 10 to 40 nm, and even more preferably from 10 to 25 nm, or from 15 nm to 40 nm. The mean diameter of the pores can be determined by any techniques known to the skilled artisan. For instance, said mean diameter can be determined by microscopy, such as Transmission Electron Microscopy (TEM).

The mean diameter of the pores depends on the molecular weight of the amphiphilic block copolymer and the mean diameter of the nanoparticles. Generally speaking, the longer the amphiphilic block copolymer, the higher the mean diameter of the pores. Thus, the skilled artisan can control the mean diameter of the pores, by adjusting the length (or the molecular weight) of the amphiphilic block copolymer. By such adjustment, a high control of the size of the pores can be obtained.

Typically, the mean diameter of the pores of the material obtained by the process of the invention is larger than (or slightly larger than) that of the nanoparticles within the pores.

As used herein, “larger” or “slightly larger” may refer to 1% to 400% larger, preferably from 2% to 300% larger. The mean diameter of the nanoparticles of the material obtained by the process of the invention is similar (or substantially similar) to the mean diameter of the nanoparticles provided in step (a). In other words, the mean diameter of the nanoparticles is preserved (or substantially preserved) throughout the process of the invention.

The material obtained by the process of the invention may have a specific surface area of from 50 to 500 m ² /g, preferably from 100 to 300 m ² /g, as measured by the BET method.

Another object of the invention is a material obtainable by the process of the invention, wherein said material comprises a porous metal or metalloid (M’) oxide matrix and, metal or metalloid (M) nanoparticles selectively dispersed within the pores of the matrix, said nanoparticles having a mean diameter of 10 to 40 nm. In such material, the mean diameter of the pores is larger (or slightly larger) than that of the nanoparticles.

The particular and preferred embodiments described above for the process of the invention, for instance particular and preferred M or M', can apply to the material of the invention.

The present invention also relates to the use of a material obtainable by the process of the invention, and in particular a material as defined herein, as a catalyst. In particular, said material may be used as a heterogeneous catalyst. The material of the invention may particularly be used in metallo-catalysed organic reactions. For instance, the material may be used as a catalyst for converting the nitro (-NO2) group of nitro-containing compounds into an amino (-NH2) group. The catalytic loading in such reactions may typically be comprised between 0.1 and 10 mmol of metal or metalloid (M) per mol of reactant.

The present invention also relates to the use of a material obtainable by the process of the invention, and in particular a material as defined herein, for dosing and/or detecting at least one chemical substance in a sample subjected to Raman spectroscopy, and more particularly, Surface-enhanced Raman Spectroscopy (SERS).

The present invention also relates to a method for dosing and/or detecting at least one chemical substance in a sample comprising contacting said sample with a material obtainable by the process of the invention, and in particular a material as defined herein, and subjecting the material having been contacted with said sample to Raman spectroscopy (and more particularly, Surface-enhanced Raman Spectroscopy).

In a typical procedure, said material is contacted with a sample comprising at least one chemical substance, for a period of time allowing the at least one chemical substance to be adsorbed on said material, and then the resulting material is subjected to a SERS analysis.

This invention will be better understood in light of the following examples which are given for illustrative purposes only and are not intended to limit the scope of the invention, which is defined by the attached claims.

EXAMPLES

Methods

¹ H NMR was performed on a BRUKER Avance DPX-300 spectrometer.

SEM were obtained using Microscope MEB Zeiss GeminiSEM 500.

TEM micrographs were obtained using a JEOL 2000FX microscope. In case of solid materials, samples were ground and afterward suspended in methanol. The suspension was added to a carbon grid and dried in air.

Nitrogen sorption measurements were carried out using an ASAP 2010 Micromeritics apparatus at -196°C. Prior to adsorption, samples (~ 80-100 mg) were outgassed at 120°C during 12 h under the vacuum of 2.10-3 mbar. The specific surface area was determined with Brunauer, Emmet, and Teller (BET) method, the pore size distribution was calculated from the adsorption branch using the Barrett- Joyner-Halenda (BJH) method (Rouquerol, F.; Rouquerol, J.; Sing, K. S. W. Adsorption by powders and porous solids: principles, methodology and applications, Academic Press: London, 1999).

UV- Visible spectroscopy measurements in the liquid phase were performed on a Varian Cary 300 spectrometer in the 300-800 nm range.

Raman spectra were acquired using a LabRAM HR800 (Horiba-Jobin-Yvon) micro spectrometer (laser excitation source 632.8 nm; 50x objective; numerical aperture 0.5). Raman spectra are an average of 16 spectra, each recorded during 25 s.

Abbreviations

POE: polyethylene oxide / POE _x : polyethylene oxide having x -CH2CH2O- units PS: polystyrene / PS _X : polystyrene having x -CH2CH(C6Hs)- units ATC: Chain Transfer! Agent (dodecylthiocarbonothioylthio group)

SEC: size exclusion chromatography PI: Polydispersity Index

Example 1 - Preparation of a nanoparticles-containing metal or metalloid oxide porous material by a process of the invention

1.1. Preparation of amphiphilic block copolymers of formula (1-0) or (I)

1.1.1. Preparation of CH3-POE _n -ATC or ATC-POE _n -ATC compounds

CH3-POE45-ATC

In a 50 ml flask containing an agitator, 2.006 g (5.50 mmol) of 2- (dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) were dissolved in 10 ml of anhydrous dichloromethane conditioned in molecular sieves. The flask was immersed in an ice bath and the contents were deoxygenated for 15 minutes. An excess of 5 molar equivalents of oxalyl chloride (3.759 g, 27.5 mmol) was added dropwise to the flask under a stream of argon. The reaction medium was stirred at room temperature for 3 hours under an argon atmosphere. The unreacted oxalyl chloride was then removed under vacuum for 5 hours. Subsequently, 4.390 g of CH3-POE45-OH (Mn = 2000 g/mol, 2.20 mmol) were dissolved in 10 ml of anhydrous dichloromethane before being added to the reaction medium. The reaction was carried out for 24 hours at room temperature under argon. At the end of the reaction, the solution obtained was precipitated from a cold mixture of 50/50 by volume of pentane / diethyl ether and was then filtered through a Biichner filter. After drying under vacuum at 30 °C, a yellowish powder was obtained and characterized by ¹ H NMR (400MHz, CDCI3) and by SEC (RI and UV detectors, THF).

CH ₃ -POE ₁₁₄ -ATC, CH ₃ -POE ₂₂₇ -ATC, CH ₃ -POE ₄₅₄ -ATC, ATC-POE ₂₂₇ -ATC were prepared according to a similar method. CH ₃ -POEii ₄ -ATC

1.055 g (2.89 mmol) of DDMAT dissolved in 10 mL of dichloromethane, 3.006 g (22.0 mmol) of oxalyl chloride, 4.319 g of CH ₃ -POEn4-OH (Mn = 5000 g/mol, 0.86 mmol) dissolved in 10 mL of dichloromethane.

CH ₃ -POE ₂₂₇ -ATC

2.005 g (5.540 mmol) of DDMAT dissolved in 10 mL of dichloromethane, 3.759 g (27.5 mmol) of oxalyl chloride, 10.976 g of CH ₃ -POE227-OH (Mn = 10000 g/mol, 1.10 mmol) dissolved in 10 mL of dichloromethane.

CH ₃ -POE ₄₅₄ -ATC

0.354 g (0.97 mmol) of DDMAT dissolved in 10 mL of dichloromethane, 0.659 g (4.81 mmol) of oxalyl chloride, 5.764 g of CH ₃ -POE454-OH (Mn = 20000 g / mol, 0.29 mmol) dissolved in 10 mL of dichloromethane.

ATC-POE227-ATC

2.003 g (5.49 mmol) of DDMAT dissolved in 10 mL of dichloromethane, 3.759 g (27.5 mmol) of oxalyl chloride, 11.003 g of HO-POE227-OH (Mn = 10000 g / mol, 1.10 mmol) dissolved in 10 mL of dichloromethane.

1.1.2. Preparation of CH3-POE _n -b-PS _m -ATC or ATC-PS _m -b-POE _n -b-PS _m -ATC compounds

CH ₃ -POE ₄₅ -b-PS ₇₆ -ATC

3.526 g (1.50 mmol) of CH ₃ -POE ₄₅ -ATC, 0.075 g (0.45 mmol) of AIBN, 19.784 g (0.19 mmol) of styrene and 14 mL of toluene were introduced into a flask fitted with an agitator magnetic. The solution obtained was deoxygenated for 15 minutes. The reaction was conducted at 75 ⁰ C under argon for 24 h. At the end of the reaction, the solution was precipitated three times in a cold mixture of 50/50 by volume of pentane / diethyl ether. A yellowish powder was obtained after filtration on Buchner. This product was then dried under vacuum at 30 ⁰ C to finally be characterized by ¹ H NMR (400MHz, CDC1 ₃ ) and by SEC (RI and UV detectors, THE).

CH ₃ -POEii ₄ -b-PS ₉ o-ATC, CH -POE ₂₂₇ -b-PS ₇₉ -ATC, CH ₃ -POE ₄₅₄ -b-PSi ₈₉ -ATC, ATC-PS - b-POE227-b-PSi5 ₃ -ATC were prepared according to a similar method. CH ₃ -POEii4-b-PS ₉ o-ATC

2.504 g (0.47 mmol) of CH ₃ -POEn ₄ -ATC, 24.6 mg (0.15 mmol) of AIBN, 8.005 g (76.9 mmol) of styrene and 7 mL of toluene.

CH ₃ -POE ₂₂₇ -b-PS ₇₉ -ATC 3.005 g (0.29 mmol) of CH ₃ -POE ₂₂ 7-ATC, 14.3 mg (0.087 mmol) of AIBN, 7.671 g (73.7 mmol) of styrene and 15 mL of toluene.

CH ₃ -POE ₄₅₄ -b-PS ₁₈₉ -ATC 1.005 g (0.049 mmol) of CH ₃ -POE ₄₅ 4-ATC, 2.89 mg (0.018 mmol) of AIBN, 3.008 g (28.9 mmol) of styrene and 6 mL of toluene.

ATC-PS i ₅₃ -b-POE ₂₂₇ -b-PS -ATC

2.005 g (0.019 mmol) of ATC-POE227-ATC, 18.7 mg (0.11 mmol) of AIBN, 21.387 g (0.205 mol) of styrene and 35 mL of toluene.

1.1.3. Preparation of CH ₃ -POE _n -b-PS _m -SH or HS-PS _m -b-POE _n -b-PS _m -SH compounds (formula (1-0) or (I))

CH ₃ -POE ₄₅ -b-PS ₇₆ -SH

Into a flask fitted with a magnetic stirrer, 5.948 g (0.59 mmol) of CH ₃ -POE45-b-PS76-ATC, 1.723 g (10.4 mmol) of triethylphosphite and 15 ml of DML were introduced. After deoxygenation for 20 minutes, 1.240 g (12.3 mmol) of n-hexylamine were added via a syringe. The reaction medium was then stirred at room temperature under argon for 4 h. The solution obtained was precipitated three times in a cold mixture of 50/50 by volume of pentane / diethyl ether. After filtration through Buchner, a whitish powder was obtained. The latter was dried under vacuum at 40 ⁰ C to be characterized by ¹ H NMR (400MHz, CDC1 ₃ ) and by SEC (RI and UV detectors, THF) (Figure 1).

Mn, theoretical ⁼ 10000 g/mol; Mn (SEC - experimental) ⁼ 9 050 g/mol; Mn (NMR - experimental) = 11 760 g/mol; PI = 1.10

CH3-POEii4-b-PS ₉ o-SH, CH -POE ₂ 27-b-PS ₇ 9-SH, CH ₃ -POE ₄ 54-b-PSi89-SH, and HS-PS -b- POE227-b-PSi5 ₃ -SH were prepared according to a similar method. CH ₃ -POEii ₄ -b-PS ₉ o-SH

3.379 g (0.23 mmol) of CH ₃ -POEii4-b-PS9o-ATC, 0.473 g (2.85 mmol) of triethylphosphite and 16 mL DMF, 0.308 g (3.04 mmol) of n-hexylamine.

Mn, theoretical = 14500 g/ ITlOl ; Mn (SEC - experimental) = 16 390 g/ ITIOI ( PI = 1.10; Mn (NMR - experimental) ⁼ 15 980 g/mol;

¹ H NMR: the resonance at d = 3,7 ppm corresponding to -CH2-CH2-O- of poly(ethylene oxide) represents 456 protons and the resonance between 7,2 - 6,2 ppm corresponding to aromatic protons of polystyrene exhibits 527 protons.

CH -POE ₂₂₇ -b-PS ₇₉ -SH 3.000 g (0.16 mmol) of CH ₃ -POE227-b-PS ₇ 9-ATC, 0.269 g (E62 mmol) of triethylphosphite and 14 mL DMF, 0.164 g (1.62 mmol) n-hexylamine.

Mn, theoretical ⁼ 18288 g/mol; Mn (SEC - experimental) = 16 390 g/mol; PI = 1.17; Mn (NMR - experimental) ⁼ 15 980 g/mol;

¹ H NMR: the resonance at d = 3,7 ppm corresponding to -CH2-CH2-O- of poly(ethylene oxide) represents 908 protons and the resonance between 7,2 - 6,2 ppm corresponding to aromatic protons of polystyrene exhibits 287 protons.

CH ₃ -POE ₄₅₄ -b-PS ₁₈₉ -SH 1.563 g (0.039 mmol) of CH ₃ -POE454-b-PSi89-ATC, 0.065 g (0.39 mmol) of triethylphosphite and 14 mL DMF, 0.040 g (0.39 mmol) of n-hexylamine.

Mn, theoretical ⁼ 39750 g/mol; Mn (SEC experimental) ⁼ 40 180 g/mol; PI = 1.19, Mn (NMR - experimental) ⁼ 37 650 g/mol;

¹ H NMR: the resonance at d = 3,7 ppm corresponding to -CH2-CH2-O- of poly(ethylene oxide) represents 1816 protons and the resonance between 7,2 - 6,2 ppm corresponding to aromatic protons of polystyrene exhibits 848 protons.

HS-PS i ₅₃ -b-POE ₂₂₇ -b-PS -SH

3.000 g (0.070 mmol) of ATC-PSi ₅₃ -b-POE ₂ 27-b-PSi5 ₃ -ATC, 0.2339 g (1.41 mmol) of triethylphosphite and 14 mL of DMF, 0.1424 g (1.41 mmol) of n-hexylamine.

Mn, theoretical ⁼ 42 140 g/mol; Mn (SEC experimental) ⁼ 42 840 g/mol; PI = 1.25; Mn (NMR - experimental) ⁼ 44 130 g/mol; ¹ H NMR: the resonance at d = 3,7 ppm corresponding to -CH2-CH2-O- of poly(ethylene oxide) represents 908 protons and the resonance between 7,2 - 6,2 ppm corresponding to aromatic protons of polystyrene exhibits 1640 protons.

1.2. Preparation of metal or metalloid nanoparticles stabilized by a ligand

1.2.1. Gold nanoparticles - 5 nm (Aus _nm@ citrate)

A 200 ml aqueous solution containing 0.25 mM HAuCU.3H ₂ 0 and 0.25 mM of tricitrate sodium was prepared in an Erlenmeyer flask fitted with a magnetic stirrer and kept in an ice bath. The ice bath was then removed and a volume of 6 mL of NaBPL with a concentration of 0.1 M was then added to the solution dropwise while stirring at room temperature. A pink solution was obtained immediately after the addition of NaBPL, indicating the formation of nanoparticles. A mono-population of spherical nanoparticles was obtained. The size of the nanoparticles was determined by dynamic light scattering (DLS) (Figure 2a). Nanoparticles were also observed by Transmission Electron Microscopy (TEM) (Figure 2b).

1.2.2. Gold nanoparticles - 20 nm (Au20 _nm@ citrate)

A volume of 22 mL of trisodium citrate with a concentration of 60 mM was diluted to a final volume of 600 mL with deionized water in a flask fitted with a magnetic stirrer and of a condenser. The solution was stirred and heated to reflux for 15 min. A volume of 4 mL of HAUCU.3H2O with a concentration of 25 mM in deionized water was added quickly in the flask. After 10 min, a pink-colored solution was obtained. The temperature was then lowered to 90 ⁰ C. An additional volume of 4 mL of trisodium citrate (60 mM) was added to the solution in the flask while maintaining the stirring. After 2 min, a volume of 4 mL of HAuCL.3H ₂ 0 (25 mM) was added thereto. The nanoparticle solution was stirred vigorously at 90 ⁰ C for 30 min and was cooled to room temperature. A mono-population of spherical nanoparticles was obtained. Particle size was determined by DLS (Figure 3a). Nanoparticles were also observed by TEM (Figure 3b). 1.2.3. Gold nanoparticles - 40 nm

Gold nanoparticles of 40 nm were prepared by the seeding growth procedure that consists in the first step the synthesis of gold seeds (10 nm) and in the second step the seeded growth of gold nanoparticles:

A volume of 5,5 mL of trisodium citrate with a concentration of 60 mM was diluted to a final volume of 150 mL with deionized water in a flask fitted with a magnetic stirrer and of a condenser. The solution was vigorously stirred for 15 min and heated to boiling. After boiling had commenced, 1 mL of HAuCLGtbO with a concentration of 25 mM in deionized water was added quickly in the flask. After 10 min, a pink-colored solution was obtained. Immediately after the synthesis of the Au seeds and in the same reaction vessel, the reaction was cooled until the temperature of the solution reached 90 °C. Then, 1 mL of HAuCLGtbO with a concentration of 25 mM in deionized water was added quickly in the flask. After 30 min, the reaction was completed. This operation was repeated twice to obtain gold nanoparticles of 40 nm (Ligure 4).

1.3. of metal or metalloid coordinated by a block

Au ₅ „ _m @POE ₄₅ -b-PS ₇₆ -SH

While stirring in a flask, 1.100 g of POE45-b-PS76-SH dissolved in 130 mL of THE were added dropwise to a volume of 130 mL of Au5 _nm @citrate aqueous solution having a gold concentration of 0.0835 mg/mL. Stirring was maintained for 2 hours. A bluish and homogeneous solution was obtained. This solution was then extracted with 50 mL of dichloromethane. The extraction was repeated three times and the extracted fractions were collected in a flask. The organic phase was then evaporated on a rotary evaporator. A bluish powder was obtained. This powder was then dried under vacuum at 40 ⁰ C. The size of the nanoparticles was determined by dynamic light scattering of 10 mg of the powder in 1.5 mL of THE.

Au ₂₀ n _m @POE ₂₂₇ -b-PS ₇ 9-SH, Au ₄₀ n _m @POE ₄₅₄ -b-PS I89-SH, and Au ₄₀ n _m @HS-PS _l53 -POE ₂₂₇ -b- PS153-SH were prepared according to a similar method. Au _20nm @POE ₂₂₇ -b-PS ₇₉ -SH

0.834 g of POE ₂ 27-b-PS ₇ 9-SH dissolved in 83 mL of THF, 83mL of a Au20 _nm @ citrate solution having a gold concentration of 0.0642 mg/mL.

AU _40iini @POE ₄₅₄ -b-PS _{l S9} -SH

0.887 g of POE ₄ 54-b-PSi89-SH dissolved in 10 mL of THF, 8 mL of a Au40 _nm @ citrate solution having a gold concentration of 0.286 mg/mL.

AU40nm@HS-PSl53-POE227-b-PSl53-SH

1.100 g of HS-PSi53-POE ₂ 27-b-PSi53-SH dissolved in 40 mL of THF, 40 mL of a Au40 _nm @ citrate solution having a gold concentration of 0.0642 mg/mL.

1.4. Preparation of a nanoparticles-containing metal or metalloid oxide porous material

Au5nm@SiC>2

At room temperature, 196 mg of Au5 _nm @POE45-PS76-SH were weighed in a flask fitted with a magnetic stirrer. 2 mL of THF and 402 mg (2.64 mmol) of Si(OCH3)4 were successively added to the flask while maintaining agitation. The pH of the medium was adjusted to 2 by adding 203 mg of HC1. The reaction was stirred for a few hours to form a purple/mauve solid. Then, this solid was left for 5 days for the aging step, dried in an oven for 2 days and calcined at a temperature at 600 ⁰ C for 5 hours. The calcined product was characterized by TEM and by manometric nitrogen adsorption (BET method).

Au20 _nm @SiO2 was prepared according to a similar method

Characterization of the materials

The porous structure of the materials was characterized by scanning (SEM) and transmission (TEM) electron microscopy. SEM photographs showed a porous structure organized on a large scale (Figure 5 and 6). TEM photographs show that the nanoparticles are inside the pores (Figures 7, 8, and 9). TEM analyzes in tomography mode confirmed this point. In addition, microscopy showed that the size of the incorporated nanoparticles was only slightly modified by heat treatment. The specific surface area of porous materials prepared as described above, was between 100 m ² /g and 300 m ² /g and the pore diameter between 10 and 25 nm (Figure 10). Example 2 - Catalysis experiments with Au@Si0 ₂ nanocomposites (5 nm): reduction of a nitro group

50 mL of a solution of 4-nitrophenol freshly prepared (41.73 mg; 0.30 mmol; in 50 mL of demineralized water) were mixed with 50 mL of a freshly prepared solution of NaBFL (567.54 mg; 150 mmol; in 50mL of water deionized). The mixture was homogenized by magnetic stirring for a few minutes. Then, 12.2 mg of Au@Si0 ₂ (10 ³ mmol of Au nanoparticles of 5 nm) were added to the solution and was stirred at room temperature. lmL of the solution was taken at regular time intervals, diluted with 9 mL of cold water (<5 °C) and immediately analyzed by UV spectrometry between 250 - 500 nm. As shown in Figure 11, after 90 min of reaction, the absorbance band of 4-nitrophenol at 400 nm completely disappeared while a new absorbance band at 300 nm appeared corresponding to the new molecule 4-aminophenol.*

*No reaction occurred in the absence of catalyst, for a same reaction time of 90 min.

Example 3 - Raman spectroscopy detection experiments with Au@Si0 ₂ materials (5 nm and 20 nm)

Solutions of oxazepam having a concentration between 1. 10 ⁶ M and 1. 10 ⁴ M were used as sample, and Au@Si0 ₂ materials (5 nm and 20 nm particles) were used as a detection solid. Solids and solutions of oxazepam were in contact for 12 hours in an enclosure thermostatically controlled and under stirring.

Results were compared with those obtained with a S1O2 matrix alone.

As shown in Figure 12, the detection threshold for oxazepam is greatly lowered when the molecule is adsorbed on the materials compared to silica alone (3.5 pg / ml vs 170 pg / ml). In addition, the relative intensity of the Raman band characteristic of the presence of oxazepam is multiplied by a factor comprised between 40 and 50 for a similar adsorbed amount when oxazepam is adsorbed on Au@Si0 ₂ material containing gold nanoparticles of 20 nm. The factor is comprised between 4 and 5 when oxazepam is adsorbed on Au@Si0 ₂ material containing gold nanoparticles of 5 nm.