EP2611948A2 - Method for depositing nanoparticles on substrates - Google Patents

Abstract

The present invention is related to a method for depositing nanoparticles on a substrate, wherein the method comprises the steps of: forming a mixture of a precursor and a substrate, said precursor being in a liquid or a solid phase, said substrate being a nanoscopic or microscopic substrate, said mixture being formed outside a reactor after which said mixture is introduced into a reactor, or introducing said precursor and said substrate into a reactor and forming said mixture in said reactor, - exposing said mixture of said precursor and said substrate to a plasma in said reactor, wherein the temperature of the plasma during the step of exposing said mixture of said precursor and said substrate to a plasma is lower than 300°C.

Description

Method for depositing nanoparticles on substrates

Field of the Invention

[0001] The present invention relates to a method for (simultaneously forming and) depositing nanoparticles on nanoscopic and microscopic substrates, such as carbon nanotubes, or porous substrates.

[0002] More in particular, the present invention relates to a method for (simultaneously forming and) depositing nanoparticles using liquid or solid (organometallic) precursors and ((very) low temperature) plasma treatment.

Background of the Invention

[0003] Carbon nanotubes (CNTs) attract scientist attentions during more than last 15 years due to their extraordinary physical, chemical, and mechanical properties, and their, almost one-dimensional, structure.

[0004] However, weak reactivity and poor dispersability cause problems in their applications.

[0005] The properties of (single-wall (SW) and multi- wall (MW) ) CNTs, and their application, can be boosted (or improved) e.g. by preparing polymer-nanotube composites.

[0006] Moreover, various alternative applications can be found in the processing of nanoparticles (NPs) with their decoration (or deposition) onto (the external walls of) carbon nanotubes to form (nano ) hybrids .

[0007] The main reason for the interest in NPs is their significantly different bulk/surface ratio when compared to larger clusters. [0008] This leads to remarkable and miscellaneous properties which are used in (opto) electronics, biomedicine, composites, and chemistry.

[0009] As such, industrial applications of (nano ) hybrids of carbon nanotubes and nanoparticles can be employed in e.g. composites, catalysis, semiconductor devices, xerography, or as gas sensors due to the CNT large surface area .

[0010] However, the linking between for example metal NPs and CNTs is highly disputable and can vary regarding different synthesis methods and metals used.

[0011] Several different ways to decorate diverse nanometric, porous, or flat substrates by nanoparticles can be found in prior art.

[0012] Very common techniques known in prior art (as e.g. described in WO 03/086030, or in WO 2007/103829) are various modifications of Chemical Vapour Deposition (CVD) , e.g. Metallo-Organic Chemical Vapour Deposition (MOCVD) , Plasma-Enhanced Chemical Vapour Deposition (PECVD) , or Thermal CVD.

[0013] CVD of volatile organometallic compounds is widely used for formation of metallic and oxide coatings (or continuous films) on different substrates.

[0014] Multiple-steps chemical methods, sol-gel process (or chemical solution deposition) , microwave synthesis, or plasma torch treatment are often used in prior art as well.

[0015] JP 2009 167031 for example describes the use of an arc plasma at elevated temperatures (of not less than 3000 K) for the manufacturing of metal-including carbon nanotubes.

[0016] The use of a plasma together with organometallic precursors for the synthesis of (or for forming, or producing) nanopowders has been described in e.g. WO/2006/079213. [0017] However, the plasma deposition technique described in said document includes a high temperature synthesis of nanopowders using plasma temperatures far above 1000°C with precursors (for forming, or producing said nanopowders) injected into the plasma, resembling MOCVD and Plasma-Enhanced (PE)MOCVD.

[0018] Nanometer powders (or nanopowders) can be produced by microwave plasma, as described in e.g. TW248328, where the precursor gas is decomposed by the microwave plasma.

[0019] The precursor gas can even be decomposed by a dense fluid medium, as described in e.g. US2008169182.

[0020] In the case of using a microwave plasma as described in TW248328, a high temperature plasma (above 300°C) is used where iron and nickel (nano ) powders were inserted into the high temperature microwave plasma reactor using a hydrogen carrier gas.

[0021] Plasma, especially cold plasma (or low temperature plasma) , seems to be a very promising tool in the case of the decoration of carbon nanotubes.

[0022] Plasma kinetic studies show that the discharge generates ions and radicals which participate on the ion bombardment and etching of the sp² carbon-carbon bonds (with energy E_c-c= 3.5 eV) creating defects on the walls of carbon nanotubes.

[0023] It has been shown that the presence of defects plays an important role in the functionalization process (allowing to attach a number of groups to the carbon nanotubes) .

[0024] For example, the formation of C-O-Pt bonds has been observed by Bittencourt et al (Chemical Physics Letters 462 (2008) 260-264) when an oxygen plasma pre- treatment was used prior to a UHV (Ultra-High Vacuum) platinum evaporation on multi-wall carbon nanotubes. [0025] EP 1 323 846 describes a process for preparing metal coatings upon porous substrate surfaces from liquid solutions utilizing a cold plasma.

[0026] US 2008/0145553 describes a process for the in- flight surface treatment of powders using a Dielectric Barrier Discharge Torch operating at atmospheric pressures or soft vacuum conditions. The process comprises feeding a powder material into the Dielectric Barrier Discharge Torch yielding powder particles; in-flight modifying the surface properties of the particles; and collecting coated powder particles .

[0027] Despite the progress in the art, there is still a need for a method for depositing nanoparticles on nanoscopic and microscopic substrates, such as carbon nanotubes, or porous substrates, wherein the method involves fewer steps than the processes known in the art.

[0028] Other advantages of the invention will be immediately apparent to those skilled in the art, from the following description.

Summary of the Invention

[0029] The present invention provides a method particularly advantageous for (simultaneously forming and) depositing nanoparticles on nanoscopic and microscopic substrates, such as carbon nanotubes, or porous, or flat substrates, wherein the method involves fewer steps than the processes known in the art.

[0030] The present invention provides an improved method for depositing nanoparticles on nanoscopic and microscopic substrates, when compared to processes known in the art.

[0031] The method of the present invention has the advantage over existing methods in prior art that it is a simplified method. [0032] The method provided by the present invention avoids the use of a gas-comprising (or containing) precursor flow, and avoids the injection of the precursors into the plasma.

[0033] Furthermore, the method of the invention provides the advantage of avoiding (( electro ) chemical , and/or physical) pre-treatment (or functionalization) of the substrates, when compared to the processes known in the art .

[0034] In the context of the present invention, "functionalization of the substrate" refers to introducing chemical functional groups to a substrate (or allowing to attach a number of groups to the substrate) using for example acids, or crosslinking .

[0035] The method of the invention also avoids high- temperature heating, when compared to the processes known in the art .

[0036] More particularly, the method of the invention avoids high-temperature plasma treatment, when compared to the processes known in the art.

[0037] In the context of the present invention, a "high- temperature plasma" is a plasma having a temperature higher than (about) 300°C, preferably higher than (about) 600°C, more preferably higher than (about) 1000°C.

[0038] The method of the present invention provides the preparation of (nano ) hybrids by using precursors being in a liquid or a solid phase, and a plasma with (very) low temperature (i.e. a plasma temperature being lower than (about) 300°C) .

[0039] More particularly, in a method of the present invention, the plasma temperature is lower than (about) 300°C, preferably lower than (about) 200°C.

[0040] In a method of the invention, the plasma temperature can be close to ambient temperature. [0041] The method of the present invention has the advantage over existing methods in prior art that the (significantly) degradation (or melting) of the substrate is avoided.

[0042] In the context of the present invention, a "hybrid" (or hybrid material) refers to a microscopic substrate on which nanoparticles are deposited.

[0043] In the context of the present invention, "nanohybrid" (or nanos tructure ) refers to a nanoscopic substrate on which nanoparticles are deposited.

[0044] According to one aspect of the present invention, it is provided a method for (simultaneously forming and) depositing nanoparticles (or nanoclusters ) on a substrate, wherein the method comprises the steps of:

- forming (or preparing) a mixture of a precursor (for producing nanoparticles) and a substrate, said precursor being in a liquid or a solid phase (or state, or form) , said substrate being a nanoscopic or microscopic substrate, said mixture being formed outside a reactor after which said mixture is introduced into a reactor, or introducing said precursor and said substrate into a reactor and forming said mixture in (or inside) said reactor, - exposing (or subjecting) said mixture of said precursor and said substrate to a plasma in said reactor (or performing a plasma activation step, performing a plasma treatment, or applying a plasma onto said mixture of said precursor and said substrate in said reactor) ,

wherein the temperature of the plasma during the step of exposing said mixture of said precursor and said substrate to a plasma is lower than (about) 300°C.

[0045] More particularly, the plasma is a low temperature plasma (or a cold plasma, or a non-thermal plasma) (i.e. with a plasma temperature being lower than (about) 300°C) .

[0046] In the context of the present invention, a "low temperature plasma" (or a cold plasma, or a non-thermal plasma) refers to a plasma where the temperature of the neutral gas particles (or atoms, or molecules) is much lower than the temperature of the ions, which in turn is much lower than the temperature of the electrons (i.e. T_g < Ti<<T_e, wherein T_g is close to the ambient temperature) .

[0047] Preferably, the temperature of the plasma during the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma is lower than (about) 200°C, and more preferably comprised between (about) 50 °C and (about) 150 °C.

[0048] In the context of the present invention, the term "reactor" refers to a plasma reactor, reaction chamber, plasma chamber, or post discharge region.

[0049] Preferably, in a method of the invention, no (( electro ) chemical , and/or physical) pre-treatment (or functionalization) of the substrate is performed.

[0050] Preferably, in a method of the invention, no gas- comprising (or containing) precursor flow is used.

[0051] Preferably, in a method of the invention, no injection (e.g. by using a carrier gas) of the precursors into the plasma is performed.

[0052] Preferably, in a method of the invention, no high-temperature heating is performed.

[0053] More particularly, in a method of the invention, no high-temperature plasma treatment is performed.

[0054] Preferably, in a method of the invention, the substrate is not (significantly) degraded (or melted) .

[0055] In a method of the invention, said precursor and said substrate are mixed in said mixing step, said mixing step being performed outside or inside said reactor, thereby forming (or preparing) a mixture of said precursor and said substrate.

[0056] In a method of the invention, the precursor (s) and the substrate do not react with each other during said mixing step (or by performing said mixing step) .

[0057] More particularly, the precursor (s) and the substrate do not undergo any changes (e.g. decomposition, degradation, or melting) during said mixing step (or by performing said mixing step) .

[0058] More particularly, the precursor (s) is (are) (only) in (physical) contact with (or touches) the substrate after having performed said mixing step, and before performing said step of plasma exposure (or plasma activation, or plasma treatment) .

[0059] More particularly, the substrate is not coated by the precursor (s) during said mixing step (or by performing said mixing step) .

[0060] In other words, the mixing step is performed for (physically) "bringing together" the precursor (s) and the substrate in a recipient or a reactor, without (chemical) reaction between said precursor (s) and said substrate, or without coating said substrate by said precursor (s) .

[0061] Preferably, in a method according to the invention, the mixing step is performed at ambient temperature.

[0062] Preferably, in a method according to the invention, the mixing step is performed at atmospheric pressure .

[0063] In a method according to the invention, the mixing step is performed by any mixing process known in the art, more particularly, by sonication (using an ultrasonic bath) , by stirring, or by contacting the precursor with the substrate . [0064] Preferably, in a method according to the invention, the step of introducing said mixture into said reactor, or the step of introducing said precursor and said substrate to be mixed into said reactor, is performed at atmospheric pressure.

[0065] More particularly, in a method according to the invention, the step of introducing said mixture into said reactor, or the step of introducing said precursor and said substrate to be mixed into said reactor, is performed using a chemical dish comprising said mixture, or comprising said precursor and said substrate to be mixed, said chemical dish being placed into the reactor through the introduction chamber, or directly through the window in the plasma reactor .

[0066] Preferably, in a method according to the invention, after introducing said mixture into said reactor, or after introducing said precursor and said substrate to be mixed into the reactor and subsequently forming said mixture inside said reactor, said step being performed at atmospheric pressure, said reactor is pumped down for forming a low pressure in the reactor.

[0067] More particularly, in a method according to the invention, a low pressure of (about) 10E-2 mbar or less is formed .

[0068] Alternatively, in a method according to the invention, after introducing said mixture into said reactor, or after introducing said precursor and said substrate to be mixed into the reactor and subsequently forming said mixture inside said reactor, said step being performed at atmospheric pressure, the pressure in said reactor remains (or is kept) at atmospheric pressure.

[0069] In the context of the present invention, a "liquid precursor" refers to a precursor being present in a liquid phase (or state, or form) . In other words, no solid particles of said precursor are present.

[0070] In the context of the present invention, a "solid precursor" refers to solid particles of said precursor, or solid particles of said precursor being dissolved in a solvent (of e.g. isopropanol) forming a solution of solid particles in a solvent (in other words, solid particles of said precursor are present in solution) .

[0071] In a method of the invention, nanoparticles are (simultaneously) formed (or created) and deposited on (or onto) said substrate during said (one) step of plasma exposure, as a result of precursor decomposition during said step of plasma exposure.

[0072] More particularly, in a method according to the invention, nanoparticles are (simultaneously) formed (or created) and deposited on (or onto) the substrate during the decomposition of the (microsized) precursor, due to chemical reactions which occur in an electric discharge (or plasma) .

[0073] Simultaneously with (or by, or during) performing said (one) step of plasma exposure (or plasma activation, or plasma treatment) in a method of the invention, the nanoparticles are formed (or produced) by (or as a result of) the decomposition of the (microsized) precursor ( s ) , and said nanoparticles are deposited (and attached (or grown) ) on the substrate.

[0074] In other words, by not performing said step of plasma exposure (or plasma activation, or plasma treatment) , no nanoparticle formation (or production) occurs (or in other words, the (microsized) precursor (s) is (are) not decomposed) , and no nanoparticle deposition (on the substrate) occurs.

[0075] In a method according to the invention, the (simultaneously created and) deposited nanoparticles (or nanoclusters ) do not agglomerate on the substrate or do not form a continuous film (or layer or coating) on the substrate. In other words, no agglomeration of nanoparticles (or nanoclusters) or no continuous film (of (agglomerated) nanoparticles or nanoclusters) is formed (or deposited) on the substrate.

[0076] In the context of the present invention, the term "nanocluster" refers to a group of atoms (i.e. molecules) .

[0077] In a method according to the invention, the diameter of the (simultaneously created and) deposited nanoparticles can be smaller than (about) 1 μπι.

[0078] Preferably, in a method according to the invention, the diameter of the (simultaneously created and) deposited nanoparticles is comprised between (about) 1 nm and (about) 100 nm, preferably between (about) 1 nm and (about) 30 nm, more preferably between (about) 1 nm and (about) 10 nm.

[0079] In a method according to the invention, the diameter of the (simultaneously created and) deposited nanoclusters is comprised between (about) 1 nm and (about) 30 nm, preferably between (about) 1 nm and (about) 10 nm.

[0080] Preferably, in a method according to the invention, the (simultaneously created and deposited) nanoparticles (or nanoclusters) comprise (or consist of) metal nanoparticles, or metal oxide nanoparticles.

[0081] Preferably, in a method according to the invention, the (simultaneously created and) deposited nanoparticles (or nanoclusters) comprise (or consist of) monometallic nanoparticles, bimetallic nanoparticles, or trimetallic nanoparticle ( s ) .

[0082] Preferably, in a method according to the invention, said substrate comprises (or consists of) microscopic particles (or micropowders ) , nanoscopicparticles (or nanopowders ) , or flat substrates. [0083] In the context of the present invention, the term "substrate" refers to (a surface of) a support.

[0084] More preferably, in a method according to the invention, the substrate comprises (or consists of) carbon (nano) fibers, carbon nanotubes or inorganic nanotubes, carbon nanorods or inorganic nanorods, metal or polymer micropowders , metal or polymer nanopowders, or porous substrates .

[0085] In the context of the present invention, the term "nanopowder" refers to a powder with size of the particles of said powder being less than (about) Ιμπι.

[0086] Preferably, in a method of the invention, the inorganic nanotubes comprise (or consist of) metal oxides, Tungsten disulfide (WS₂) , Boron nitride (BN) , Silicon (Si), Molybdenum disulfide (M0S₂) , Copper (Cu) , or Bismuth (Bi) .

[0087] More particularly, said metal oxides comprise (or consist of) Vanadium pentoxide (V₂O₅) , Vanadium dioxide (VO2) , manganese dioxide (Μ^ηθ2) , or titanium dioxide (T1O2) .

[0088] Preferably, in a method of the invention, the carbon nanotubes comprise (or consist of) single-wall carbon nanotubes (SWCNTs), or multi-wall carbon nanotubes (MWCNTs) (i.e. either powders or nanotubes grown on solid substrates) .

[0089] More particularly, the carbon nanotubes (CNTs) comprise (or consist of) closed-ended CNTs (or closed-end CNTs) .

[0090] In a method of the invention, during said step of plasma exposure nanoparticles (NPs) are (simultaneously formed and) deposited onto (the external walls of) said carbon nanotubes to form (or for forming) (nano ) hybrids .

[0091] In a method of the invention, the carbon nanotubes comprise (or consist of) carbon nanotubes of various size (in diameter, and/or in length) . [0092] Preferably, the outer diameter of the single-wall carbon nanotubes is lower than (about) 5 nm.

[0093] Preferably, the outer diameter of the multi-wall carbon nanotubes is comprised between (about) 2 nm and (about) 200 nm.

[0094] Preferably, the inner diameter of the multi-wall carbon nanotubes is comprised between (about) 1 nm and (about) 50 nm.

[0095] Preferably, the length of the single-wall carbon nanotubes is comprised between (about) 1 μπι and (about) 10cm, more preferably between (about) 1 μπι and (about) 30μπι.

[0096] Preferably, the length of the multi-wall carbon nanotubes is comprised between (about) 1 μπι and (about) 10cm, more preferably between (about) Ιμπι and (about) 50μπι.

[0097] Preferably, the outer diameter of the carbon (nano) fibers is comprised between (about) 10 nm and (about) 100 μπι.

[0098] Preferably, the length of carbon (nano) fibers is comprised between (about) 1 μπι and (about) 1 m. More preferably, between (about) 10 μπι and (about) 500 μπι.

[0099] More particular, said carbon nanotubes or said carbon (nano) fibers comprise (or consist) of graphite.

[0100] Preferably, in a method according to the invention, the micropowders comprise (or consist of) silicon carbide (SiC), silicon dioxide (S1O₂), tungsten carbide (WC) , gold (Au) , eudragit, polycaprolactone, or polystyrene (PS) micropowders.

[0101] Preferably, in a method according to the invention, the nanopowders comprise (or consist of) silicon carbide (SiC), silicon dioxide (S1O₂), tungsten carbide (WC) , gold (Au) , eudragit, polycaprolactone, or polystyrene (PS) nanopowders. [0102] Preferably, the diameter of SiC is comprised between (about) 10 nm and (about) 500 nm.

[0103] Preferably, the diameter of WC is comprised between (about) 0.1 μπι and Ιμπι.

[0104] Preferably, the diameter of PS powders (nanopowders or micropowders ) is comprised between (about) lOnm and (about) 30μπι.

[0105] More preferably, the diameter of PS nanopowders is comprised between (about) lOnm and (about) 500nm.

[0106] In the context of the present invention, a "porous substrate" refers to a substrate with high porosity (i.e. a porosity of (about) 50% or higher) , or with a continuous network of voids. A porous substrate can be flat.

[0107] Preferably, in a method according to the invention, the porous substrate is selected from the group consisting of microporous material, mesoporous material, or macroporous material.

[0108] More preferably, in a method according to the invention, the porous substrate comprises (or consists of) clay, nanoporous aluminum powder, porous ceramic powder, or zeolites .

[0109] Preferably, in a method according to the invention, the porosity of said porous substrate is (about) 50% or higher.

[0110] Preferably, the porosity of clay is (about) 60%.

[0111] Preferably, the size of clay is comprised between (about) 50 nm and (about) 5 μπι.

[0112] In the context of the present invention, "a flat substrate" refers to a layer, a sheet, or plate of substrate (or in other words, a flat substrate is not a powder substrate) .

[0113] Preferably, in a method according to the invention, the flat substrate comprises (or consists of) Highly Ordered (or oriented) Pyrolytic Graphite (HOPG) , graphene (i.e. a single layer or sheet of graphite), flat glass, stainless steel, silicon layers provided with films (or coatings) on the surface of said layers, metal sheets, or polymer sheets.

[0114] In the context of the present invention, graphite is composed of graphene layers.

[0115] In a method according to the invention, said metal sheets can comprise (or consist of) any metal sheet known in the art, more particularly, said metal sheets comprise (or consist of) an aluminum sheet, a copper sheet, a (stainless) steel sheet, a carbon steel perforated sheet, a brass sheet, or a titanium sheet.

[0116] In a method according to the invention, said polymer sheets can comprise (or consist of) any polymer sheet known in the art, more particularly, said polymer sheets comprise (or consist of) a Polyvinyl chloride (PVC) sheet, a BOPP film (Biaxial-oriented Polypropylene film) , or an acrylic polymer sheet.

[0117] In a method according to the invention, said films (or coatings) on the surface of said layers of silicon can comprise (or consist of) titanium nitride (TiN) , titanium dioxide (ΊΊΟ₂) , or hydrogenated silicon nitride (Si₃N-_x:H, with x ranging from 0 to 3 (or x=<0, 3>) ) .

[0118] More preferably, in a method according to the invention, the flat substrate comprises (or consists of) Highly Ordered (or oriented) Pyrolytic Graphite (HOPG) , or graphene .

[0119] In the context of the present invention, said "precursor" (or "nanoparticle precursor") refers to (microsize) molecules (or precursors) for producing (or forming) nanoparticles . [ 0120 ] In other words, in the context of the present invention, said molecules (or precursors) act as a source for producing (or forming) nanoparticles (i.e. nanoparticles are formed as a result of precursor decomposition during the step of plasma exposure) .

[ 0121 ] More particularly, in a method according to the invention, said nanoparticles are (simultaneously) formed and deposited on the substrate during the (one) step of plasma exposure (as a result of precursor decomposition during said step of plasma exposure) .

[ 0122 ] By performing a method of the invention, (nano ) hybrids are formed.

[ 0123 ] Preferably, in a method according to the invention, said precursor comprises (or consists of) an organometallic compound (or an organometallic precursor, or an organometallic) .

[ 0124 ] In a method of the invention, said precursor has microsize dimensions (or in other words, said precursor has no nanosize dimensions) .

[ 0125 ] More preferably, in a method according to the invention, said organometallic precursor comprises (or consists of) nickel (II) acetylacetonate (Ni (C5H7O2) 2) , bis (methylcyclopentadienyl ) nickel (II) (C₁₂H₁₄N1), palladium acetylacetonate (Pd (C₅H₇O₂) ₂) , palladium (II) propionate ( , rhodium (III) acetylacetonate (Rh (C5H7O2) 3) , ruthenium acetylacetonate, iron acetylacetonate, e t hyny 1 f e r r o c ene (Ci₂Hi₀Fe), silver acetylacetonate, zinc acetylacetonate, titanium oxy acetylacetonate, bis (2, 4-cyclopentadien-l-yl) [(4- methylbicyclo [ 2.2.1 ] heptane-2.3-diyl ) methylene] titanium (IV) (Ci₉H₂ Ti) , ( 1 , 5-cyclooctadiene ) dimethyl platinum (II) ( ( CH₃ ) ₂Pt ( C₈Hi₂ ) ) , or any combination of two (or more) thereof . [0126] Even more preferably, in a method of the invention, said organometallic precursor comprises (or consists of) nickel (II) acetylacetonate (Ni (C5H7O2) 2) , bis (methylcyclopentadienyl ) nickel (II) (C₁₂H₁₄N1), palladium acetylacetonate (Pd (C₅H₇O₂) ₂) , palladium (II) propionate (C₆Hi₀O₄Pd) , rhodium (III) acetylacetonate (Rh (C₅H₇0₂) 3) , ruthenium acetylacetonate, iron acetylacetonate, ethynylferrocene (Ci₂Hi₀Fe) , silver acetylacetonate, zinc acetylacetonate, titanium oxy acetylacetonate, bis (2,4- cyclopentadien-l-yl ) [ ( 4-methylbicyclo [ 2.2.1 ] heptane-2.3- diyl) methylene] titanium (IV) (Ci₉H₂₄Ti), (1,5- cyclooctadiene ) dimethyl platinum (II) ( (CH₃) ₂Pt (C₈Hi₂) ) , or any combination of two (or more) thereof.

[0127] Most preferably, in a method of the invention, said organometallic precursor comprises (or consists of) metal acetylacetonates .

[0128] More particularly, said metal acetylacetonates comprise (or consist of) nickel (II) acetylacetonate (Ni (C5H₇C>2) 2) , palladium acetylacetonate (Pd (CsH₇02) 2) , rhodium (III) acetylacetonate (Rh (CsH₇02) 3) , ruthenium acetylacetonate, iron acetylacetonate, silver acetylacetonate, zinc acetylacetonate, titanium oxy acetylacetonate, or any combination of two (or more) thereof .

[0129] In a method according to the invention, two or more organometallic precursors can be combined.

[0130] More particularly, two organometallic precursors can be combined, or three organometallic precursors can be combined .

[0131] By combining two organometallic precursors in a method of the invention, bimetallic nanoparticles are deposited on the substrate.

[0132] More particularly, by combining two organometallic precursors in a method of the invention, bimetallic nanoparticles are deposited on SWCNTs or MWCNTs, in case the substrate comprises (or consists of) SW or MW carbon nanotubes.

[0133] By combining three organometallic precursors in a method of the invention, trimetallic nanoparticles are deposited on the substrate.

[0134] More particularly, when using substrates comprising (or consisting of) SWCNTs or MWCNTs, combining three organometallic precursors in a method of the invention, produces trimetallic nanoparticles which are deposited on SWCNTs or MWCNTs.

[0135] A suitable (combination of) (OM) precursor (s) for use in a method according to the invention depends on the substrate, the (nano ) hybrids to be prepared, and/or the use (or type of application) of said prepared (nano ) hybrids .

[0136] Finding a suitable (combination of) (OM) precursor (s) for use in a method according to the present invention is well within the practice of those skilled in the art .

[0137] Preferably, the method according to the invention is performed at (very) low temperature.

[0138] More preferably, the method according to the invention is performed at a temperature lower than (about) 300°C, even more preferably lower than (about) 200°C, and most preferably comprised between (about) 50 °C and (about) 150 °C.

[0139] The plasma (or electric discharge) used (or applied) in a method of the invention can be any plasma (or electric discharge) known in the art, more particularly, Radio-Frequency (RF) glow discharge plasmas, Direct Current (DC) glow discharge plasmas, Dielectric Barrier Discharge (DBD) plasmas, atmospheric Plasma Jet, microwave discharge plasmas, Inductively Coupled RF Plasmas (ICP RF) , Capacitively Coupled RF Plasmas (CCP RF) , hollow cathode glow discharge plasmas, pulsed glow discharge plasmas, or electron cyclotron resonance discharge plasmas can be used.

[0140] More preferably, in a method of the invention, the plasma used (or applied) is a Radio-Frequency (RF) glow discharge plasma, a Dielectric Barrier Discharge (DBD) plasma, or an atmospheric Plasma Jet.

[0141] The plasma gas used (or applied) in a method according to the invention can be any plasma gas known in the art .

[0142] More particularly, the plasma gas used (or applied) in a method according to the invention comprises (or consists of) Argon (Ar) , Helium (He) , Oxygen (O₂) , Nitrogen (N₂) , Hydrogen (¾) , Xenon (Xe) , and/or carbontetrafluoride (or tetrafluoromethane ) (CF₄) .

[0143] In a method according to the invention, the He (comprising) plasma gas can further comprise air.

[0144] A suitable plasma gas for use in a method according to the invention depends on the (nano ) hybrids to be prepared.

[0145] Finding (or selecting) a suitable plasma gas (or finding a suitable composition and ratio of the gas to form said plasma) for use in a method according to the present invention is well within the practice of those skilled in the art .

[0146] A suitable gas flow for preparing (or for forming) the plasma according to a method of the invention depends on the experimental conditions (or set-up configuration) .

[0147] Finding (or selecting) a suitable gas flow for use in a method according to the present invention is well within the practice of those skilled in the art.

[0148] According to a method of the invention, the upper temperature limit (or the maximum temperature) of the applied plasma during the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma depends on (or is determined by) the melting temperature of the substrate (or the degradation of the substrate) .

[0149] During the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma in a method of the invention, the melting (or (significantly) degradation or decomposition) of the substrate is avoided.

[0150] During the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma in a method of the invention, an instable plasma is avoided.

[0151] According to a method of the invention, the lower plasma power limit (or the minimum plasma power) of the applied plasma during the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma depends on (or is determined by) the stability of the applied plasma.

[0152] Suitable plasma temperatures for use in the method of the invention will be apparent to those skilled in the art.

[0153] Suitable plasma powers for use in the method of the invention will be apparent to those skilled in the art.

[0154] A suitable combination of plasma power, gas flow, pressure of the plasma gas (or partial pressure of plasma gases in case a mixture of gases is used to provide the plasma) , and (type of) plasma gas for use in a method according to the present invention is a combination of plasma power, gas flow, pressure of the plasma gas (or partial pressure of plasma gases in case a mixture of gases is used to provide the plasma) , and (type of) plasma gas being sufficient for decomposing (or degrading, or melting) of the organometallic precursor ( s ) and for (simultaneously) forming and depositing the nanoparticles on the substrate. [0155] Finding a suitable combination of plasma power, gas flow, pressure of the plasma gas (or partial pressure of plasma gases in case a mixture of gases is used to provide the plasma) , and (type of) plasma gas for use in a method according to the present invention is well within the practice of those skilled in the art.

[0156] Preferably, in a method according to the invention, the (lower) plasma power during the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma is comprised between (about) 15 W and (about) 200 W, more preferably between (about) 100 W and (about) 200 W.

[0157] Preferably, in a method according to the invention, the time (or duration) of the plasma exposure is sufficient for (simultaneously) decomposing (or degrading) the organometallic precursor (s) for forming the nanoparticles) and for depositing the (formed) nanoparticles onto the substrate.

[0158] Suitable time (or duration) of the plasma exposure for use in the method of the invention will be apparent to those skilled in the art.

[0159] Preferably, in a method according to the invention, the pressure in the reactor during the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma is comprised between a low pressure and atmospheric pressure.

[0160] More particularly, in a method according to the invention, the pressure in the plasma (in the reactor) during the step of exposing (or subjecting) said mixture of said precursor and said substrate to a plasma is comprised between (about) 10 Pa and (about) 102000 Pa.

[0161] Preferably, in a method according to the invention, the frequency of the discharge is comprised between (about) 1 kHz and (about) 20 GHz. [0162] Preferably, in a method according to the invention, an organic solvent is added during said mixing step .

[0163] More particularly, one organic solvent is added during said mixing step.

[0164] In a method of the invention, one organic solvent is added during said mixing step when combining two precursors .

[0165] Alternatively, two different (types of) organic solvents can be added during said mixing step when combining two precursors in a method of the invention.

[0166] Preferably, in a method of the invention, said organic solvent is added to (or mixed with) the organometallic precursor (thereby obtaining a liquid organometallic solution), after which the substrate is added to said solution.

[0167] Alternatively, in a method of the invention, said organic solvent is added to (or mixed with) the substrate (thereby obtaining a liquid solution) , after which the organometallic precursor is added to said solution.

[0168] Preferably, according to a method of the invention, the organic solvent depends on (or is determined by) the (OM) precursor.

[0169] Suitable organic solvents for use in the method of the invention will be apparent to those skilled in the art .

[0170] More particularly, in a method according to the invention, the organic solvent comprises (or consists of) n-hexane, ethanol, or isopropanol.

[0171] Preferably, in a method according to the invention, the mixture of said precursor and said substrate is heated before performing the step of plasma treatment. [0172] More preferably, the step of heating said mixture is performed before or after the step of introducing said mixture into the reactor.

[0173] Preferably, according to a method of the invention, the temperature of the heating of the mixture of said precursor and said substrate depends on (or is determined by) the melting temperature of the organometallic precursor (or the degradation (or decomposition) of the organometallic precursor) .

[0174] Preferably, according to a method of the invention, the temperature of the heating of the mixture of said precursor and said substrate is lower than or equal to the melting temperature of the organometallic precursor (or the degradation (or decomposition) of the organometallic precursor) .

[0175] During the step of heating the mixture of said precursor and said substrate in a method of the invention, the degradation (or the decomposition, or the melting) of the substrate is avoided.

[0176] More particularly, in a method of the invention, the temperature of the heating of the mixture of said precursor and said substrate is lower than the melting point of the substrate (or is chosen to avoid melting, or (significantly) damaging (or degradation, or decomposition) of the substrate) .

[0177] Preferably, in a method of the invention, said heating is performed by any type of heating known in the art, more preferably using a heating technique under inert atmosphere, or under air atmosphere and atmospheric pressure, or by using a hot plate.

[0178] Suitable temperatures for heating the mixture of said precursor and said substrate for use in the method of the invention will be apparent to those skilled in the art. [0179] Preferably, said heating of said mixture is performed at a temperature lower than (about) 300°C, more preferably lower than (about) 200°C, and most preferably comprised between (about) 50°C and (about) 150°C.

[0180] Preferably, in a method of the invention, the duration (or the time) of said heating of said mixture depends on the heating device used for performing said heating .

[0181] More preferably, the duration (or the time) of said heating of said mixture is comprised between (about) 10 minutes and (about) 120 minutes.

[0182] According to another aspect, the present invention is directed to nanostructures (or nanohybrids ) , wherein said nanostructures (or nanohybrids) have different properties (e.g. size, abundance, oxidation state, etc.) when compared with those known in the art.

[0183] According to still another aspect, the present invention is related to nanostructures (or nanohybrids) obtainable by a method according to the present invention.

[0184] The nanostructures (or nanohybrids) (obtainable by a method) of the present invention may find particular use for various industrial applications.

[0185] More particularly, nanohybrids of NPs on CNTs can be employed in e.g. composites, catalysis for a variety of reactions, semiconductor devices, xerography, substrates for Surface Enhanced Raman Spectroscopy, or as gas sensors due to the CNT large surface area.

[0186] Furthermore, nanohybrids of NPs on CNTs can be employed in optical electronics, or as electrocatalyst , proton exchange membrane fuel cells (PEMFC) , photovoltaics , UV lasers, light-emitting diodes, or, due to their high emission performance, in X-ray tubes, flat panel displays, or vacuum gauges. [0187] More specifically, nanohybrids of bimetallic NPs on CNTs can be employed in methanol fuel cell applications, in hydrogenation of anthracene, as engineering catalysts (e.g. in pollution control, or alcohol oxidation), or as electrodes for hydrogen electro absorption.

[0188] Decorated clay (with NPs) can be employed in catalysis (e.g. in oxidation of benzene), or in hydrogenation of alkenes and alkynes.

[0189] Decorated polystyrene NPs can be employed as substrates for Surface Enhanced Raman Spectroscopy, in calibration of various measuring instruments and techniques, or in various immunoassays on medical diagnostic tests.

[0190] SiC nanopowder decorated with (Ni) NPs improves hydrogen absorption and/or desorption kinetics.

[0191] Pd0/Si0₂ nanopowders are used for visible-light- activated photocatalysis using different bacterial indicators .

[0192] According to yet another aspect, the present invention is related to the use of a method according to the present invention for the manufacture of nanostructures (or nanohybrids) .

Short Description of the Drawings

[0193] All figures/drawings are intended to illustrate some aspects and embodiments of the present invention. Devices are depicted in a simplified way for reason of clarity. Not all alternatives and options are shown and therefore the invention is not limited to the content of the given drawings .

[0194] Figure 1 shows an example of an inductively coupled radio-frequency (RF) plasma (1) quartz reactor, (2) inox vacuum chamber, (3) primary pump, (4) turbo pump, (5) mass-flow controller, (6) needle valve for monomers (not used in this work), (7) Baratron gauge, (8) Advenced Energy RFX-600 RF generator (13.56 MHz), (9) ENI Power Systems Matchwork matching unit, (10) atmosphere release valve.

[0195] Figure 2 shows an example of a dielectric barrier discharge (DBD) reactor. A glass tube and two external electrodes of the reactor are used for the deposition of metal nanoparticles .

[0196] Figure 3 shows another example of a dielectric barrier discharge (DBD) reactor.

[0197] Figure 4 shows an example of an atmospheric plasma jet reactor.

[0198] Figure 5 represents an HRTEM image of Ni/CNTs (synthesis conditions : PP = 30W, oxygen flow Q₀2 = 10 seem, pressure P = 0.1 Torr and time t = 15 minutes) .

[0199] Figure 6a represents XPS wide scan of Ni/CNTs prepared in plasma RF chamber.

[0200] Figure 6b represents Ni2p XPS spectrum prepared in plasma RF chamber.

[0201] Figure 7 represents Cls XPS core level spectra recorded on RF-oxygen plasma treated MWCNTs and the result of the fitting analysis. Dotted line stands for untreated MWCNTs .

[0202] Figure 8a represents HRTEM image of PdRh/MWCNTs (nanocyl™ MWCNTs) prepared in plasma RF. Figure 8b represents a TEM image of PdRh/MWCNTs (SES ( SESResearch) MWCNTs) prepared in plasma RF chamber.

[0203] Figure 9 represents an XPS wide scan spectrum of PdRh/MWCNTs prepared in plasma RF chamber.

[0204] Figure 10a represents XRD patterns of Pd nanoparticles on CNTs (CNTsPd) . Figure 10b represents XRD patterns of Pd/Rh bimetals on CNTs (CNTsPdRh) . Figure 10c represents XRD patterns of Rh nanoparticles on CNTs (CNTsRh) . [0205] Figure 11 represents XRD patterns. The inset shows an enlargement of (111) reflection.

[0206] Figure 12 Enlargement of the EDX spectrum of the individual bimetallic nanoparticle (TEM image shown in the inset) attached to the multiwall carbon nanotubes.

[0207] Figure 13 represents a TEM images of Pt metal nanoparticles deposited on MWCNTs in DBD reactor a) in He plasma b) in He (95%) + 0₂(5%) plasma.

[0208] Figure 14 represents a TEM image of SiC nanopowder decorated by Pt nanoparticles using DBD discharge .

[0209] Figure 15 represents a Pt/Si0₂ nanopowder prepared by DBD discharge.

[0210] Figure 16 represents a TEM image of Pt nanoparticles on tungsten carbide nanopowder prepared in DBD reactor.

[0211] Figure 17 represents a Field Emission Scanning Electron Microscope image of Rh/HOPG prepared by atmospheric plasma jet.

[0212] Figure 18 represents a TEM image of clay decorated by palladium nanoparticles .

[0213] Figure 19 represents a TEM image of polystyrene beads decorated by silver nanoparticles.

[0214] Figure 20 represents a TEM image of graphene decorated by iron nanoparticles.

Description of the Invention

[0215] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention and how it may be practiced in particular embodiments. However it will be understood that the present invention may be practiced without these specific details. In other instances, well- known methods, procedures and techniques have not been described in detail, so as not to obscure the present invention. While the present invention will be described with respect to particular embodiments and with reference to certain drawings, the reference is not limited hereto. The drawings included and described herein are schematic and are not limiting the scope of the invention. It is also noted that in the drawings, the size of some elements may be exaggerated and, therefore, not drawn to scale for illustrative purposes.

[0216] Furthermore, particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0217] Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention .

[0218] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0219] The present invention provides a method for (simultaneously forming and) depositing nanoparticles on a substrate, wherein the method comprises the steps of:

forming a mixture of a precursor and a substrate, said precursor being in a liquid or a solid phase, said substrate being a nanoscopic or microscopic substrate, said mixture being formed outside a reactor after which said mixture is introduced into a reactor, or introducing said precursor and said substrate into a reactor and forming said mixture in said reactor, - exposing said mixture of said precursor and said substrate to a plasma in said reactor (so as to

(simultaneously) form and deposit nanoparticles or nanoclusters on the substrate during said step of plasma exposure) ,

wherein the temperature of the plasma during the step of exposing said mixture of said precursor and said substrate to a plasma is lower than (about) 300°C.

[0220] In the method of the invention, the step of plasma exposure is performed at low temperature (i.e. with a plasma temperature being lower than (about) 300°C) .

[0221] Preferably, in the method of the invention, the step of plasma exposure is performed at a temperature lower than (about) 200 °C, and even more preferably comprised between (about) 50 °C and (about) 150 °C.

[0222] More particularly, the temperature is close to ambient temperature.

[0223] Said substrate comprises (or consists of) microscopic particles (or micropowders ) , or nanoscopic particles (or nanopowders ) , or flat substrates. [0224] Preferably, said substrate comprises (or consists of) carbon (nano) fibers, carbon nanotubes or inorganic nanotubes, carbon nanorods or inorganic nanorods, metal or polymer micropowders , metal or polymer nanopowders, or porous substrates.

[0225] More particularly, the substrate comprises (or consists of) carbon (nano) fibers, carbon nanotubes or inorganic nanotubes, metal or polymer micropowders, metal or polymer nanopowders, or porous substrates.

[0226] According to a preferred method of the invention, the substrate comprises (or consists of) single-wall carbon nanotubes or multi-wall carbon nanotubes.

[0227] In said preferred method of the invention, the outer diameter of the single-wall carbon nanotubes is lower than 5 nm, and the outer diameter of the multi-wall carbon nanotubes is comprised between 2 nm and 200 nm.

[0228] In said preferred method of the invention, the inner diameter of the single-wall carbon nanotubes is 0.7 nm, and the inner diameter of the multi-wall carbon nanotubes is comprised between 1 nm and 50 nm.

[0229] In said preferred method of the invention, the length of the single-wall carbon nanotubes is comprised between 1 μπι and 30 μπι, and the length of the multi-wall carbon nanotubes is comprised between 1 μπι and 50 μπι.

[0230] According to another preferred method of the invention, said nanopowders comprise (or consist of) silicon carbide, silicon dioxide, tungsten carbide, gold, eudragit, polycaprolactone, or polystyrene nanopowders.

[0231] In said preferred method of the invention, the diameter of SiC is comprised between 20 nm and 50 nm, the diameter of WC is 0.4 μπι, and the diameter of PS nanopowders is 0.1 μπι.

[0232] According to yet another preferred method of the invention, the substrate is a porous substrate, such as clay, nanoporous aluminum powder, porous ceramic powder, or a zeolite.

[0233] More particularly, in said preferred method of the invention, said porous substrate is clay, having a porosity of 60%, and a size comprised between 50 nm and 5 μπι.

[0234] According to still another preferred method of the invention, the substrate is a flat substrate, such as Highly Ordered (or Oriented) Pyrolytic Graphite (HOPG) , graphene, flat glass, stainless steel, a silicon layer provided with a film (or a coating) on the surface of said layer, a metal sheet, or a polymer sheet.

[0235] More particularly, in said preferred method of the invention, said flat substrate is HOPG, or graphene.

[0236] In a method of the invention, said (microsize) precursor(s) act(s) as a source for producing nanoparticles . By carrying out a method of the invention, said nanoparticles are (simultaneously formed and) deposited on a substrate.

[0237] According to a preferred method of the invention, said precursor comprises (or consists of) an organometallic compound .

[0238] In said preferred method of the invention, said organometallic precursor preferably comprises (or consists of) n i c ke l ( I I ) a c e t yl a c e t on a t e , b i s ( me t hy 1 c yc 1 op en t a di e ny 1 ) nickel (II) , palladium acetylacetonate, palladium (II) propionate, rhodium (III) acetylacetonate, ruthenium acetylacetonate, iron acetylacetonate, ethynylferrocene, silver acetylacetonate, zinc acetylacetonate, titanium oxy acetylacetonate, bis (2, 4-cyclopentadien-l-yl ) [ ( 4-methylbicyclo

[ 2.2.1 ] heptane-2.3-diyl ) methylene] titanium (IV), (1,5- cyclooctadiene ) dimethyl platinum (II), or any combination of two (or more) thereof. [0239] In said preferred method of the invention, said organometallic precursor has microsize dimensions.

[0240] More particularly, in said preferred method of the invention, said organometallic precursor comprises (or consists of) metal acetylacetonates , said metal being preferably nickel, palladium, rhodium, ruthenium, iron, silver, zinc, or titanium.

[0241] In a method of the invention, two organometallic precursors can be combined, depositing bimetallic nanoparticles on a substrate.

[0242] In a method of the invention, three organometallic precursors can be combined, depositing trimetallic nanoparticles on a substrate.

[0243] In a method of the invention, said mixing step can be performed by any mixing process known in the art, more particularly, by sonication (using an ultrasonic bath) , by stirring, or by contacting the precursor with the substrate, at ambient temperature, and at atmospheric pressure .

[0244] According to a method of the invention, the precursor and the substrate do not react with each other during said mixing step. In other words, the precursor and the substrate do not undergo any changes during said mixing step .

[0245] More particularly, the precursor (s) is (are) (only) in (physical) contact with the substrate after having performed said mixing step, and before performing said step of plasma exposure.

[0246] More particularly, in a method of the invention, the substrate is not coated by the precursor (s) during said mixing step (or by performing said mixing step) .

[0247] In other words, the mixing step is performed for (physically) "bringing together" the precursor (s) and the substrate in a recipient or a reactor, without (chemical) reaction between said precursor (s) and said substrate, or without coating said substrate by said precursor (s) .

[0248] According to a preferred method of the invention, an organic solvent, such as n-hexane, ethanol, or isopropanol, is added during said mixing step. Adding said organic solvent improves said mixing process.

[0249] In said preferred method of the invention, said organic solvent is added to the organometallic precursor, after which the substrate is added to said solution.

[0250] Alternatively, in said preferred method of the invention, said organic solvent is added to the substrate, after which the organometallic precursor is added to said solution .

[0251] When combining two precursors, one organic solvent or two different (types of) organic solvents, can be added during said mixing step.

[0252] When combining three precursors, one organic solvent, or two or three different (types of) organic solvents can be added during said mixing step.

[0253] Alternatively, in said preferred method of the invention, said mixing process is improved by dispersing a powder substrate such as a nanosized substrate in a solvent, such as n-hexane, prior to performing said mixing step .

[0254] According to another preferred method of the invention, the mixture of said precursor and said substrate is heated before performing the step of plasma treatment.

[0255] In said preferred method, any type of heating known in the art can be used, such as a heating technique under inert atmosphere, under air atmosphere and atmospheric pressure, or by using a hot plate.

[0256] Performing said heating step before performing the step of plasma treatment results in a more homogeneous distribution of deposited nanoparticles on the substrate, and/or further enhances (or further improves) the yield of the deposited nanoparticles on the substrate.

[0257] In the context of the present invention, a "homogeneous distribution" of the deposited nanoparticles refers to an even (or uniform) distribution (or deposition) of nanoparticles on the surface of the substrate.

[0258] More particularly, a homogeneous distribution is not a continuous film.

[0259] In said preferred method of the invention, the step of heating said mixture is performed before or after the step of introducing said mixture into the reactor.

[0260] In said preferred method of the invention, the temperature of the heating of said mixture is lower than or equal to the melting temperature of the organometallic precursor.

[0261] Preferably, the temperature of the heating of said mixture is lower than the melting point of the substrate .

[0262] More particularly, said heating of said mixture is performed at a temperature lower than 300°C, more preferably lower than 200°C, and most preferably comprised between 50°C and 150°C.

[0263] The duration of said heating of said mixture is comprised between 10 minutes and 120 minutes.

[0264] Alternatively, in a preferred method of the invention, an organic solvent is added during the mixing step, and the mixture of said precursor, said substrate, and said organic solvent is heated before performing the step of plasma treatment.

[0265] In a preferred method according to the invention, the step of introducing said mixture into said reactor, or the step of introducing said precursor and said substrate to be mixed into said reactor, is performed using a chemical dish comprising said mixture, or comprising said precursor and said substrate to be mixed, said chemical dish being placed into the reactor through the introduction chamber, or directly through the window in the plasma reactor .

[0266] Alternatively, in a preferred method according to the invention, the step of introducing said precursor and said substrate to be mixed into said reactor is performed by spreading said precursor and said substrate into the glass tube of the treatment module (or reactor) to form a bed with uniform thickness (figure 2) .

[0267] Alternatively, in a preferred method according to the invention, the step of introducing said precursor and said substrate to be mixed into said reactor is performed by solubilising the precursor in an organic solvent, such as isopropanol, and spraying it between the substrate and the plasma torch (figure 4), or by drop deposition directly on the surface (figure 3) .

[0268] In a method of the invention, the step of introducing said mixture into the reactor, or the step of introducing said precursor and said substrate to be mixed into the reactor and subsequently forming said mixture inside said reactor, can be performed at atmospheric pressure, after which said reactor can be pumped down for forming a low pressure in the reactor, such as a pressure of 10E-2 mbar or less.

[0269] Alternatively, after the step of introducing said mixture into said reactor, or after the step of introducing said precursor and said substrate to be mixed into the reactor and subsequently forming said mixture inside said reactor, the pressure in said reactor can be kept at atmospheric pressure.

[0270] In a method of the invention, performing said step of plasma exposure results in forming the nanoparticles (by the decomposition of said (microsize) precursor ( s ) ) and depositing said nanoparticles on the substrate, thereby forming (nano ) hybrids .

[0271] According to a preferred method of the invention, the applied plasma gas comprises (or consists of) Argon, Helium, Oxygen, Nitrogen, Hydrogen, Xenon, and/or carbon tetrafluoride . The Helium comprising plasma gas can further comprise air.

[0272] In said preferred method of the invention, the gas flow for preparing the plasma is comprised between 5 slm and 20 slm.

[0273] According to a more preferred method of the invention, the plasma is provided by a mixture comprising (or consisting of) Ar gas and O₂ gas, for (further) increasing the nanocluster distribution over the substrate (increasing the number (or yield) of deposited nanoparticles and improving their homogeneous distribution) . The amount of said O₂ gas is maximum 10% (v/v) of the total volume of the gas mixture, to avoid (or for avoiding) plasma quenching.

[0274] Alternatively, in said more preferred method of the invention, the plasma is provided by a mixture comprising (or consisting of) He gas and O₂ gas, for (further) increasing the nanocluster distribution over the substrate (increasing the number (or yield) of deposited nanoparticles and improving their homogeneous distribution) . The amount of said O₂ gas is maximum 10% (v/v) of the total volume of the gas mixture, to avoid (or for avoiding) plasma quenching.

[0275] According to a preferred method of the invention, the plasma power during the step of plasma exposure is comprised between 15 W and 200 W, more preferably between (about) 100 W and (about) 200 W.

[0276] According to a preferred method of the invention, the pressure in the reactor during the step of plasma exposure is comprised between a low pressure and atmospheric pressure.

[0277] More particularly, in said preferred method of the invention, the pressure in the plasma (in the reactor) during the step of plasma exposure is comprised between (about) 10 Pa and (about) 102000 Pa.

[0278] According to a preferred method of the invention, the frequency of the discharge is comprised between 1 kHz and 20 GHz.

[0279] According to a method of the invention, the diameter of the deposited nanoparticles can be smaller than (about) 1 μπι.

[0280] Preferably, according to a method of the invention, the diameter of the deposited nanoparticles can be comprised between 1 nm and 100 nm, more preferably between 1 nm and 30 nm, and even more preferably between 1 nm and 10 nm.

[0281] According to a method of the invention, the deposited nanoparticles can comprise (or consist of) monometallic nanoparticles, bimetallic nanoparticles, or trimetallic nanoparticles.

[0282] According to a preferred method of the invention, the deposited nanoparticles comprise (or consist of) metal nanoparticles, or metal oxide nanoparticles.

[0283] More particularly, the metal oxide nanoparticles comprise (or consist of) partially oxidized metal oxide nanoparticles, or fully oxidized metal oxide nanoparticles.

[0284] According to a preferred method of the invention, the method is performed at low temperature, more particularly, the temperature is close to ambient temperature .

[0285] In said preferred method of the invention, the method is preferably performed at a temperature lower than 300°C, even more preferably lower than 200°C, and most preferably comprised between 50 °C and (about) 150 °C.

[0286] A preferred embodiment of the invention, comprises as a first step preparing a mixture of organometallic precursors and CNTs.

[0287] In said preferred embodiment, said mixing step is performed by sonication. The duration of said sonication is comprised between 5 minutes and 10 minutes.

[0288] Optionally, in said preferred embodiment, an organic solvent, such as n-hexane, ethanol, or isopropanol, is added during said mixing step.

[0289] Optionally, in said preferred embodiment, the mixture of said precursor and said substrate (and/or said organic solvent) is heated before performing the step of plasma treatment. Said heating of said mixture is performed at a temperature lower than 300°C, more preferably lower than 200°C, and most preferably comprised between 50°C and 150°C. The duration of said heating of said mixture is comprised between 10 minutes and 120 minutes.

[0290] In said preferred embodiment, said organometallic precursors comprise (or consist of) metal acetylacetonates , said metal being preferably nickel, palladium, rhodium, ruthenium, iron, silver, zinc, or titanium.

[0291] Said preferred embodiment comprises as a second step exposing said mixture to a plasma, such as an oxygen, argon, or helium comprising plasma.

[0292] In said preferred embodiment, the gas flow for preparing the plasma is comprised between 5 slm and 20 slm.

[0293] In said preferred embodiment, the power of said plasma is comprised between 10 W and 200 W. The duration of said plasma treatment is comprised between 5 minutes to 30 minutes .

[0294] In said preferred embodiment, said plasma treatment is performed at a temperature lower than 300°C, preferably lower than 200°C, and more preferably comprised between 50 °C and 150 °C.

[0295] Carrying out a method of the invention results in nano s t ruc tur e s (or nanohybrids) , also object of the invention, having different properties when compared with those known in the art.

[0296] A method of the invention can be used for improving the deposition of nanoparticles on microscopic and nanoscopic substrates, when compared to processes known in the art.

[0297] In particular, a method of the invention is a simplified method, involving fewer steps, when compared to existing methods in prior art.

[0298] More particularly, carrying out a method of the invention, avoids the use of a gas-comprising precursor flow, and the injection of the precursors into the plasma.

[0299] Furthermore, by carrying out a method of the invention, a pre-treatment of the substrates, a high- temperature heating, a high-temperature plasma treatment, and a degradation of the substrate is avoided, when compared to processes known in the art.

EXAMPLES

Example 1 : Nickel nanoparticles on MWCNTs

[0300] First, the deposition of nickel nanoparticles on MWCNTs using RF low pressure, low temperature plasma reactor will be described (reactor in Fig. 1) . In this case electric discharge is used as the only ignition element. To improve the mixing process of organometallic (OM) + CNTs, OM (usually 50-200mg) were diluted in 3 - 5 ml of organic solvent, sonicated in ultrasonic bath for 15 minutes and later on mixed with CNTs (40 - 80 mg) and again sonicated for 15 minutes. The prepared mixture was introduced to the reactor via inox vacuum chamber and exposed to the low pressure atmosphere in the reactor to vaporize the alcohol, followed by the plasma treatment for 5-30 minutes.

[0301] Solution of 40 mg Nickel (II) ace t ylace tonat e Ni(C5H7C>2)2 + 2.5 ml ethanol was used to decorate 50 mg carbon nanotubes with Ni NPs with diameter ~1 nm as it is shown in figure 5. The deposition was performed in RF oxygen plasma with power P_P = 30W , oxygen flow Q₀₂ = lOsccm, pressure P = 0.1 Torr and time t = 15 minutes, corresponding to the gas temperature about55°C.

[0302] XPS wide scan spectra analysis (figure 6a) of the prepared powder shows that Ni content is about 2 % (with carbon 79 % and oxygen up to 19 % due to the O2 plasma treatment) . From Ni 2p photoelectron spectra shown in figure 6b main peak at 856.1 eV can be assigned to N1₂O₃ and it is followed by two satellites. Small peak observed at 853.3 eV is hardly to assign, it can be either NiO or N13C.

[0303] Interesting features can be found in the C Is XPS spectra (Figure 7) . The most dominant peak at 284.5 eV corresponds to the sp² bonding in carbon nanotubes. Peaks at 285.1 eV, 286.1 eV and 287.4 eV are attributed to sp³ bonds (defects and pentagons in CNTs and amorphous carbon) , hydroxyl and carbonyl (or ether) groups, respectively. Contribution at 283 eV and 281.5 eV can be in this case clearly assigned to the Ni_xC and Ni₃C, respectively [Kovacs et al, Thin Solid Films 516 (2008) 7942-7946, Czekaj et al, Applied Catalysis A: General 329 (2007) 68-78]. This suggests that unknown peak from Ni 2p spectra is due to nickel carbide contribution. It should be highlighted that occurrence of carbide was observed only in the case of nickel deposition and this could be due to the very small size of deposited particles. Example 2: Bimetallic Palladium Rhodium nanoparticles on MWCNTs

[0304] For the synthesis of bimetallic NPs on multi-wall carbon nanotubes the same experimental steps were used, except as for the OM precursor the mixture of two (1:1) organome t a 11 i c s was prepared. The solution of lOOmg Pdo.5 ho.5 acetylacetonates with 3 ml isopropanol was sonicated for 15 minutes and afterwards 80mg MWCNTs (Nanocyl™ nanotubes with diameter about 20nm or SES ( SESResearch) nanotubes with diameter 40-100 nm) was added and dispersed in solution by ultrasonic bath for additional 15 minutes. This was followed by heating of the prepared mixture by the hot plate in atmosphere at 270 °C (higher melting point of one of the OM precursors) during 90 minutes. After this heating process, the sample in chemical dish was introduced into the plasma RF reactor and plasma treatment was employed same way as it was mentioned in the previous example, however with slightly different parameters; oxygen plasma with power P_P = 100W , oxygen flow Qo2 = 10 seem, pressure P = 0.1 Torr and time t = 30 minutes, corresponding to the gas temperature of about 150°C.

[0305] As it could be seen from TEM analysis (Fig 8a and 8b), nanoparticles with diameter 5 -10 nm are deposited on carbon nanotubes. The XPS spectrum in figure 9 indicates the presence of rhodium (~ 5%) and palladium (~ 7%) .

[0306] To confirm that the deposited nanoparticles are Pd+Rh bimetals and not the monometallic mixture of palladium and rhodium nanoparticles, the x-ray diffraction (XRD) and TEM (together with EDX) analyses were used. XRD patterns of prepared powders, shown in figure 10, present Pd/MWCNTs, Rh/MWCNTs and PdRh/MWCNT s nanohybrids. XRD spectrum of multiwall carbon nanotubes decorated by palladium nanoparticles (figure 10a) indicates that the palladium is present in face centered cubic {fee) phase with peaks at 2Θ = 40.1°, 46.6° and 68.2° corresponding to (111), (110) and (100) crystallographic planes, respectively, which is in very good agreement with study of Guo et al [Guo et al, Journal of Colloid and interface Science 286 (2005), 274-279] on the Pd/SWNT composites. Tetragonal form of PdO [Simplicio et al, Applied Catalysis A, General 360 (2009), 2-7] was detected as well (peaks at 2Θ = 33.7°, 54.7°, 60.6°) and broad peak at 2Θ = 25.5° corresponds to MWCNTs diffraction peak [Lu, Carbon 45 (2007) 1599-1605] . The broadening of the main (111) Pd peak is due to the small contribution of PdO and MWCNTs peaks at around 2Θ = 42° which are hardly to distinguish. Similarly, the XRD pattern of Rh/CNTs (figure 10c) shows the reflection of fee Rh at 2Θ = 41.1°, 47.7° and 69.9° which can be assigned to (111), (200) and (220), respectively, in agreement with Tzitzios [Tzitzios et al, Carbon 44 (2006) , 848-853] . Again the MWCNTs and broader RhO diffraction peaks can be seen. To declare the bimetallic nature of the NPs, the inset of XRD patterns shown in figure 11, is very useful. PdRh/CNTs XRD pattern (figure 10b) shows that the (111) diffraction peak of PdRh NPs (at 2Θ = 40.4°) is lying between the Pd (111) and Rh (111) peaks. Position of the PdRh (111) peak and the evident merging of the two contributions raising from the monometallic peaks confirms the bimetallic nature of the PdRh nanoparticles on MWCNTs. It turns down the possibility of the physical (aggregate) mixture of two monometals where the both characteristic peaks of Pd and Rh should be observed without a shift [Devarajan et al, Journal of colloid and interface science, 2005, 290, 117-129, Li et al, Journal of Molecular Catalysis A: Chemical 284 (2008) 1-7, Wu et al, Chem. Mater. 2001, 13, 599-606] . Due to the low crystallinity of NPs diffraction peaks are not well defined, so to determine the diameter of nanoparticles using Scherrer equation is not evident. Anyway, it is clear that sharper (111) peak of Pd nanoparticles is observed which confirms the TEM observations that Pd forms larger nanoparticles than Rh NPs. Concerning the FWHM (Full Width at Half Maximum) of the bimetallic particles, it should be noted that the diffractograms generally show broader bands than their monometallic counterparts [Devara an et al, Journal of colloid and interface science, 2005, 290, 117-129] which was also observed in this study.

[0307] Bimetallic structure was confirmed by TEM using Energy Dispersive X-ray analysis of the individual NP/CNT as well. Insets in figure 12 shows TEM image of the individual Pd/Rh bimetallic nanoparticle (diameter ~ 10 nm) deposited on the separated multiwall carbon nanotube and corresponding EDX spectrum of the nanoparticle (with the probe of the nanoparticle size) . The enlargement of the EDX spectrum clearly shows that the nanoparticle consists of the palladium and rhodium elements.

Example 3: Platinum nanoparticles on MWCNTs

[0308] Iron, titanium and palladium oxide nanoparticles on MWCNTs were successfully deposited also by DBD reactor (Figure 2) . In this example, the deposition of platinum metal nanoparticles with diameter of 2-3 nm on MWCNTs is presented. In this case OMs (precursors) are used in the solid form (by mixing them with the CNTs in the reactor before the treatment in a DBD plasma module) or in the liquid form.

[0309] Preparation of the liquid OM platinum solution (0.3M) includes the mixing of lg of (1,5- Cyclooctadiene ) dimethyl platinum (II) (CH₃) ₂Pt (C₈Hi₂ ) with 10 ml of n-hexane . The resulting solution is then sonicated for 5 minutes at 30°C [0310] 20 mg of MWCNTs were mixed with the desired volume of the OM. The ensemble is then spread into the glass tube of the treatment module to form a bed with uniform thickness.

[0311] The discharge characteristics are as follows (i) the frequency is adjusted at 20 kHz. (ii) the plasma power should be between 100 and 200 W. (iii) Ar or He gas have been tested. The admixture of small amount of oxygen into the plasma gas, leads to the increasing of the nanoclusters distribution over the nanopowder (increasing the number (or yield) of deposited nanoparticles and improving their homogeneous distribution) . A maximum of 5% oxygen (in 95% He) can be used. Further increasing of the oxygen partial pressure leads to the plasma quenching, (iv) the gas flow is fixed at 5 slm; above 10 slm the nanopowders are blown into the exhaust line. The treatment duration is fixed at a maximum of t=10 minutes. For the treatment settings used (P_P=150W, f=20kHz, He) , CNTs are damaged in the case of treatment duration longer than 10 minutes. The optimal treatment time was found to be 5 minutes, (v) the OM/CNTs ratio: the amount of nanopowders is kept constant (20 mg) , the quantity of precursor is varied (from 0.25 to 1 ml for the liquid OM) .

[0312] The decoration was performed using (CH₃) ₂Pt (CsH^) as the solid or liquid (solution in n-hexane) precursor. TEM images of Pt/MWCNTs regarding the dependence on the plasma gas for helium and helium + oxygen (95/5) are shown in figure 13a and 13b, respectively. It is evident that the abundance of platinum nanoparticles is higher in the case of 5% O₂ is admixed into the He plasma (confirmed for the lower magnification as well) . This can be again assigned to the formation of defects or vacancies in the graphite sheets of MWCNTs due to the oxygen etching. Example 4 : Platinum nanoparticles on SiC & Si0₂ & WC

[0313] To show a wide-range of possible applications of this experimental procedure the deposition on various substrates by low temperature plasma using organonometallic precursor (s) is now shown. The steps taken to decorate nanopowders (such as SiC, S1O₂, WC, Au , eudragit, polycaprolactone ) , polystyrene nanopowders and porous system were exactly the same and can be still described as a plasma low temperature experiment, unlike classical vapour or liquid deposition processes.

[0314] DBD discharge reactor (Figure 2) described in more details in previous example was used to decorate SiC, S1O₂, WC using (CH₃) ₂Pt (CsH^) in solid or liquid form keeping the same experimental conditions as in the example 3. For the SiC substrate 2-3 nm metal platinum NPs homogeneously distributed over the substrate were found ( igure 14 ) .

[0315] In the case of S i O₂ nanopowder substrate, relatively larger nanoparticles about 5-15 nm and 5-30 nm were prepared from the solid and liquid precursor, respectively (figure 15) and XPS (not shown) confirmed that NPs are mainly metallic.

[0316] Tungsten carbide (WC) nanopowder, which is widely used in material research and catalysis, was tested as well as the substrate for the DBD decoration by Pt nanoparticles. However, evidence of agglomerated Pt metal oxide nanoparticles can be seen from figure 16, which can be due to the larger size of the substrate (-400 nm) . Example 5: Rhodium nanoparticles on HOPG

[0317] To decorate highly oriented pyrolytic graphite by titanium and rhodium nanoparticles, two reactors shown in figure 3 where used. [0318] Atmospheric plasma jet reactor (Figure 4) generates electric discharge with an Atomflo™-250 plasma source from Surfx Technologies LLC. This method has been already used to deposit gold clusters onto HOPG surfaces [F. Demoisson et al, Surface and Interface Analysis, 40, 566-570, 2008.] as well as to deposit Au , Pt, Rh nanoparticles onto MWCNTs. The plasma activation and the deposition processes using colloidal solution are described in [F. Reniers et al, PCT/EP2008/060676] . In this case (the present invention) the substrate with the OM precursor was exposed to a 5 min atmospheric plasma (Plasma gas: Ar (30 1/min) / O2 (20ml/min) , plasma power P_P= 80 W at atmospheric pressure) . After the plasma treatment, the resulting nanomaterials were plunged into the ethanol solution for up to 5 min and were submitted to ultrasonication before characterisation.

[0319] For the rhodium nanoparticle deposition, atmospheric plasma jet was employed with Rh (acac) 3 as a precursor. Solubilised rhodium acetylacetonate powder in isopropanol was sprayed between the HOPG and the plasma torch followed by the plasma treatment which resulted in the decoration of Rh particles on HOPG (figure 17) .

[0320] The sample quality was ZYB grade characterized by a mosaic spread angle of 0.8° ± 0.2° and the lateral grain size up to 1 mm. The size was 10 mm x 10 mm x 1 mm. The fresh surface of HOPG was obtained before each experiment by first pealing off few layers with an adhesive tape and then by soaking the surface in an ethanol solution for up to 5 min.

Example 6: Palladium nanoparticles on clay

[0321] To prepare clay doped by Pd nanoparticles, RF plasma chamber (figure 1) was again employed. For this procedure, the same steps as for the decoration of MWCNTs by Ni nanoparticles were taken (example 1), it means no pre-heating was used. 160 mg of palladium acetylacetonate is diluted in 3 ml of isopropanol and sonicated in the ultrasonic bath for 20 minutes. 200 mg of clay is admixed into the as prepared OM precursor and again sonicated for 20 minutes. Such prepared mixture is introduced into the reactor in chemical dish. After pumping down the reactor and vaporisation of isopropanol, plasma treatment, which resulted in deposition of Pd NPs on the clay substrate, is performed (plasma P=100W, oxygen flow of 9 seem, time t=15 min and pressure 0.15 Torr, corresponding to 150°C) . Besides XPS analysis which confirmed presence of Pd (not shown) the TEM microscopy was performed (Fig 18) . Example 7: Silver nanoparticles on polystyrene beads latex nanoparticles

[0322] Described invention was employed to decorate polystyrene latex beads nanoparticles (diameter of 100 nm) as well. This time silver acetylacetonate was used as a precursor for silver nanoparticles. As in the previous example (example 6) RF plasma was the main driven force to prepare nanohybrids using the same experimental process. 90 mg of Ag(acac) is diluted in 5 ml of isopropanol and sonicated for 20 minutes in ultrasonic bath. However this time the substrate is already in undefined solvent, so 300 microl (μΐ) of the polystyrene beads solution is admixed into the precursor followed by 20 minutes of ultrasonic treatment. Afterwards, as prepared liquid mixture is introduced into the quartz reactor plasma RF chamber via inox vacuum chamber and after pumping down and evaporation of the isopropanol and undefined solvent the plasma treatment is performed. This time argon gas plasma was used with time t=15minutes, plasma power P = 60W, pressure P= 0.1 Torr and Ar flow of 12 seem what resulted into Ag/PS nanohybrids as shown in figure 19.

Example 8: Iron nanoparticles on graphene

[0323] Nanohybrids of few-layered graphene decorated by iron nanoparticles (iron acetylacetonate as precursor) were prepared by RF discharge at low pressure. STXM(NEXAFS) analysis confirmed the presence of iron on graphene sheets (figure 20) .

Claims

1. A method for depositing nanoparticles on a substrate, wherein the method comprises the steps of:

forming a mixture of a precursor and a substrate, said precursor being in a liquid or a solid phase, said substrate being a nanoscopic or microscopic substrate, said mixture being formed outside a reactor after which said mixture is introduced into a reactor, or introducing said precursor and said substrate into a reactor and forming said mixture in said reactor,

- exposing said mixture of said precursor and said substrate to a plasma in said reactor,

wherein the temperature of the plasma during the step of exposing said mixture of said precursor and said substrate to a plasma is lower than 300°C.

2. A method according to claim 1, wherein the nanoparticles comprise metal nanoparticles, or metal oxide nanoparticles .

3. A method according to claim 1 or 2, wherein the substrate comprises micropowders , nanopowders, or flat substrates .

4. A method according to claim 3, wherein the substrate comprises carbon nanofibers, carbon nanotubes or inorganic nanotubes, carbon nanorods or inorganic nanorods, metal or polymer micropowders, metal or polymer nanopowders, or porous substrates.

5. A method according to claim 3 or 4, wherein the nanopowders comprise silicon carbide, silicon dioxide, tungsten carbide, gold, eudragit, polycaprolactone, or polystyrene nanopowders.

6. A method according to claim 3 or 4, wherein the micropowders comprise silicon carbide, silicon dioxide, tungsten carbide, gold, eudragit, polycaprolactone, or polystyrene micropowders.

7. A method according to claim 3, wherein the flat substrate comprises Highly Ordered Pyrolytic Graphite, graphene, flat glass, stainless steel, silicon layers provided with films on the surface of said layers, metal sheets, or polymer sheets.

8. A method according to claim 4, wherein the porous substrate comprises clay, nanoporous aluminum powder, porous ceramic powder, or zeolites.

9. A method according to any of the preceding claims, wherein said precursor comprises an organometallic compound .

10. A method according to claim 9, wherein said organometallic precursor comprises nickel (II) acetylacetonate, bis (methylcyclopentadienyl ) nickel (II), palladium acetylacetonate, palladium (II) propionate, rhodium (III) acetylacetonate, ruthenium acetylacetonate, iron acetylacetonate, ethynylferrocene, silver acetylacetonate, zinc acetylacetonate, titanium oxy acetylacetonate, bis (2, 4-cyclopentadien-l-yl) [(4- methylbicyclo [ 2.2.1 ] heptane-2.3-diyl ) methylene] titanium (IV), ( 1 , 5-cyclooctadiene ) dimethyl platinum (II), or any combination of two or more thereof.

11. A method according to any of the preceding claims, wherein an organic solvent is added during said mixing step.

12. A method according to any of the preceding claims, wherein the mixture of said precursor and said substrate is heated before performing the step of plasma treatment.

13. A method according to claim 12, wherein the temperature of the heating of the mixture of said precursor and said substrate is lower than or equal to the melting temperature of the organometallic precursor.

14. A method according to claim 13, wherein the temperature of the heating of the mixture of said precursor and said substrate is lower than the melting point of substrate .

15. A nanostructure obtainable by a method according any of the preceding claims.