WO2023031111A1 - Synthèse colloïdale sans tensioactif de nanomatériaux à base d'or - Google Patents

Synthèse colloïdale sans tensioactif de nanomatériaux à base d'or Download PDF

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WO2023031111A1
WO2023031111A1 PCT/EP2022/073930 EP2022073930W WO2023031111A1 WO 2023031111 A1 WO2023031111 A1 WO 2023031111A1 EP 2022073930 W EP2022073930 W EP 2022073930W WO 2023031111 A1 WO2023031111 A1 WO 2023031111A1
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aunps
surfactant
free
less
mono
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PCT/EP2022/073930
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English (en)
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Jonathan Quinson
Kirsten Marie Ørnsbjerg JENSEN
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University Of Copenhagen
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0545—Dispersions or suspensions of nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/48—Silver or gold
    • B01J23/52—Gold
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/391—Physical properties of the active metal ingredient
    • B01J35/393—Metal or metal oxide crystallite size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions

Definitions

  • the present invention relates to a method for preparing gold nanoparticles and nanomaterials without the need for organic adsorbates having a molar mass above 100 g/mol.
  • the present invention also relates to a colloidal dispersion of the gold nanoparticles obtained by the methods according to the invention, solid and redispersed nanomaterials and products comprising gold nanoparticles.
  • Precious metal nanomaterials and in particular gold (Au) based nanomaterials are widely used in various fields of applications, such as catalysis, water/air treatment, optics, electronics, sensing, bio-medical applications, antibacterial applications, and medicine (e.g. diagnostics and treatments).
  • the preparation of Au nanomaterials is achieved by physical or chemical methods.
  • Physical methods such as sputtering, coating, plasma treatment, ball milling, laser ablation etc. often suffer the drawback to require specific infrastructures and typically require energy consuming processes like high temperature.
  • Chemical methods typically comprise the reduction of a gold precursor in a liquid or supercritical solvent, in the presence of a reducing agent and various surfactants, additives, and/or stabilizers.
  • chemical species play the multiple roles of both solvent and/or reducing agent and/or surfactants.
  • surfactants are used to avoid the undesirable agglomeration of the nanomaterials.
  • the presence of surfactants or residual surfactants reduces the available surface area of the nanomaterials which is detrimental to unlocking the full potential of the nanomaterials.
  • a support may be used to avoid the use of surfactants and also has the potential to stabilize the nanomaterials.
  • the formation of Au nanomaterials directly on a support suffer several drawbacks.
  • One of the disadvantages of such process is that particle loading on the support and particle size cannot easily be optimized independently. It is commonly observed in so called ‘one-pot’ syntheses that the support material affects the particle size resulting for instance in an undesirably broad particle size distribution. Due to the potentially inhomogeneous surface of the support, particles are also formed in small pores of the support material which reduces their surface accessibility, thus lowering the overall catalytic activity potential.
  • the impregnation method that is considered the state-of-the-art method to produce nanoparticles directly on a support often requires to conduct multiple soaking and/or impregnation steps in case a high loading of the active material on the support is desired. This approach often leads to poor size control of the resulting supported nanomaterials. Moreover, subjecting the support and catalyst precursor to the high temperature thermal treatments associated with this method, can change the chemical properties of the supported nanoparticles.
  • bare nanomaterials are desired, and are often provided for in a colloidal suspension.
  • the methods used in the prior art to obtain gold colloidal nanoparticles are still facing various limitations.
  • Three main approaches can be identified: firstly, the use of an organic solvent, with a state-of-the- art example being the House— Schiffrin method; secondly, the use of aqueous solutions in the presence of surfactants like the trisodium citrate where the Turkevich-Frens method is a state-of-the-art example; and thirdly, to use strong reducing agent like NaBH4, hydrazine or hydroxylamine which allow for the synthesis to be performed at room temperature at the expense of using hazardous chemicals.
  • a drawback of using organic solvents is the associated cost and hazards. In addition to the cost of the chemicals, high temperature is often needed to perform the synthesis which renders the procedure cost-expensive. Also these chemicals are hazardous, which hampers scalability to industrial applications.
  • Aqueous solvents allow the synthesis to be performed at relatively medium temperature (ca. 100 °C) without the need of strong reducing agents.
  • the synthesis typically requires surfactants, often derived from fossil fuels, often hazardous and possibly costly and challenging to recycle.
  • Stabilizers like thiols, molecules with amine groups, polymers like polyvinylpyrrolidone (PVP) or sodium citrate are commonly used but often raise concern on safety.
  • plant extracts, biomolecules or bio-derived stabilizers can be used but their properties depend on the source of the plant or biological feedstock used which varies a lot across different geographical zones. This last approach then suffers from relatively poor reproducibility.
  • These surfactants are often claimed to be essential to stabilize the nanoparticles and control the properties like size.
  • surfactants are however undesirable since they either block the active sites (relevant for catalysis and/or sensing), or because the presence of surfactants on the nanomaterial surface can prevent further functionalization with desired molecules expressing desired functionalities (relevant for optical and medicinal applications).
  • Removing the surfactants is possible with various chemical and physical methods but all are energy, time and cost intensive, or generate waste, or are not scalable, or often show limited effectiveness.
  • the present invention is directed at methods for preparing surfactant-free Au-based nanomaterials, such as nanoparticles, with size control to overcome the aboveidentified disadvantages and limitations and which allow in an easy, efficient and reliable way to produce Au-based nanomaterials, in particular those which provide unexpected advantages over nanoparticles prepared according to the methods known in the prior art.
  • the present invention is also directed at surfactant-free Au-based nanoparticles (abbreviated: AuNPs) with improved properties, such as stability, size control and catalysis.
  • one aspect of the present invention relates to a method for preparing surfactant- free colloidal dispersion of AuNPs, comprising the steps: a. Providing at least one inorganic gold precursor for the AuNPs, at least one mono-alcoholic solvent system, and at least one base; b. Mixing the at least one inorganic gold precursor for the AuNPs, the at least one mono-alcoholic solvent system, and the at least one base in the absence of any polymers, ligands, capping agents, and surfactants, thereby obtaining a reaction mixture, so as to reduce the at least one inorganic gold precursor for the AuNPs with the at least one monoalcoholic solvent system; and c. Reducing the at least one inorganic gold precursor, thereby obtaining the surfactant-free colloidal dispersion of AuNPs.
  • the at least one base is added, preferably as a stabilizer, instead of the surfactants, e.g. polymers, used in the prior art.
  • the at least one mono-alcoholic solvent system acts preferably as a mild reducing agent enabling the reduction of the nanoparticle precursor to the nanoparticle.
  • a second aspect of the present invention is a surfactant-free colloidal dispersion of AuNPs.
  • a third aspect of the present invention is isolated surfactant-free AuNPs isolated from the colloidal dispersion as described herein.
  • Further aspects of the present invention include products comprising the surfactant- free AuNPs as described above, as well as the use of the AuNPs as described above in fields such as catalysis, sensing, medical applications, and methods of treatment, such as anticancer treatment.
  • Figure 1 TEM micrographs of Au nanoparticles obtained by (a) the prior art Turkevich method and (b) the surfactant-free synthesis detailed here. Upon drying on the TEM grid the Au nanoparticles obtained by the Turkevich method agglomerate due to citrate interactions.
  • Figure 2 Representative TEM micrographs of the AuNPs obtained using (a) methanol and (b) ethanol. Both (a) and (b) are synthesized in an alcohokwater mixture of 30:70 (v:v) using 0.5 mM HAuCL and a molar ratio LiOH/HAuCL of 4.
  • the synthesis was performed at room temperature, (c) is the resulting size distribution and (d) UV-Vis characterization normalized to the absorbance at the surface plasmon resonance wavelength of the as-synthesized AuNPs. (e) XRD characterization of as-synthesized AuNPs confirms a fee structure.
  • Figure 3 TEM of the different nanomaterials obtained using LiOH in mixture of ethanokwater (30:70, v:v) for different LiOH/HAuCL molar ratios and 0.5 mM HAuCL, as indicated on the upper right corner of each micrograph.
  • Figure 4 Characterization of AuNPs obtained using an alcohokwater mixture of 30:70 (v:v) but with different ratio of ethanol and methanol as indicated, (a, b) UV-Vis (a) obtained at room temperature and (b) using a 50 °C treatment for 1 hour. (c,d) Mean size obtained from TEM analysis for the different conditions as indicated (c) for a room temperature synthesis and (d) for a synthesis using a treatment at 50 °C treatment for 1 hour. (e,f) Size distribution obtained from TEM analysis (e) for a room temperature synthesis and (f) for a synthesis using a treatment at 50 °C treatment for 1 hour. * volume ratio before volume contraction. 0.5 mM HAuCL and 2 mM LiOH were used.
  • Figure 5 TEM of Au nanoparticles obtained using an alcohokwater mixture of 30:70 (v:v) at room temperature but with different ratio of ethanol and methanol as indicated using 0.5 mM HAuCL and 2 mM LiOH. * volume ratio before volume contraction.
  • Figure 6 TEM micrograph of AuNPs produced in an exemplary large-scale synthesis as described in Example 2.
  • Figure 7 XRD characterization of Au x Pd y nanoparticles obtained by (a-b) a room temperature synthesis or (c-d) using 1 hour treatment at 50 °C, with composition as indicated, (a, c) Diffractograms with an offset for readability and (b,d) peak position of the main peak around 38-40 ° (20) as a function of Au or Pd composition.
  • Figure 8 Cyclic voltammograms au Au x Pd y nanoparticles prepared surfactant at room temperature in ethanokwater mixture (30:70, v:v) using LiOH for the ethanol oxidation reaction in alkaline media (1 M ethanol and 1 M KOH) recorded at room temperature at a scan rate of 50 mV s -1 , the 2 nd and 50 th scans are displayed.
  • Figure 9 TEM micrographs of Au nanoparticles directly obtained on TiOs. The grey features are the TiOs whereas the darker features are the Au nanoparticles.
  • Figure 10 TEM micrographs of Au nanoparticles obtained from colloidal dispersion after solvent removal on MnOs. The grey features are the MnOs whereas the darker features are the Au nanoparticles.
  • Figure 11 (a) Cyclic voltammograms of Au nanoparticles prepared by the prior art Turkevich method (NasC) or without surfactant in ethanokwater mixture (30:70, v:v) using LiOH at room temperature by the method of the present invention, for the ethanol oxidation reaction in alkaline media (1 M ethanol and 1 M KOH) recorded at room temperature at a scan rate of 50 mV s -1 , the 10 th scan is displayed, (b) Chronoamperometry for the ethylene glycol oxidation performed at 1 .27 VRHE for 1 hour.
  • Figure 12 Mass activity for the (a) ethanol and (b) ethylene glycol electro-oxidation in 1 M KOH and (a) 1 M ethanol or (b) 1 M ethylene glycol.
  • the Au nanoparticles used as catalysts were prepared at room temperature with 0.5 mM HAuCLand 2 mM LiOH using 30 v.% of the alcohol indicated on the X axis.
  • the present disclosure is directed to a method for preparing a surfactant-free colloidal dispersion of AuNPs, comprising the steps: a. Providing at least one inorganic gold precursor for the AuNPs, at least one mono-alcoholic solvent system, and at least one base; b. Mixing the at least one inorganic gold precursor for the AuNPs, the at least one mono-alcoholic solvent system, and the at least one base in the absence of any polymers, ligands, capping agents, and surfactants, thereby obtaining a reaction mixture, so as to reduce the at least one inorganic gold precursor for the AuNPs with the at least one monoalcoholic solvent system; and c. Reducing the at least one inorganic gold precursor, thereby obtaining the surfactant-free colloidal dispersion of AuNPs.
  • the Au nanoparticles (AuNPs) as defined herein are surfactant-free.
  • colloidal dispersion refers to a heterogeneous system having a dispersed phase and a dispersion medium, i.e., microscopically dispersed insoluble particles are suspended throughout another substance (e.g., an aqueous composition such as water or aqueous solution of at least one mono-alcohol ).
  • an aqueous composition such as water or aqueous solution of at least one mono-alcohol
  • An example of a colloidal dispersion herein is wherein the insoluble particles are surfactant-free AuNPs.
  • step b. of the method as described herein may be performed in any order.
  • the mixing in step b. of the method as described herein is to be performed in the following order: i. Mixing the at least one mono-alcoholic solvent system and the at least one base in a first instance, and ii. Mixing the at least one inorganic gold precursor with the mixture obtained in step i., in the absence of any polymers, ligands, capping agents, and surfactants.
  • the at least one monoalcoholic solvent system is mixed with the at least one base prior to the introduction of the at least one inorganic gold precursor.
  • the robust method of the present disclosure does not necessitate the use of inert atmospheres as is often the case in fabrication of well-dispersed and well- characterized nanomaterials, although it may still be performed in an inert atmosphere as a safe guard.
  • the method as described herein is optionally conducted in an inert atmosphere, wherein the inert atmosphere consists essentially of Nitrogen (N 2 ) or Argon (Ar).
  • the method as described herein produces in surfactant-free colloidal dispersion of AuNPs, comprising AuNPs with an average size of less than 50 nm.
  • the AuNPs have an average size less than 40 nm, such as less than 30 nm, such as less than 25 nm, such as less than 20 nm, such as less than 15 nm, such as less than 10 nm.
  • the surfactant-free AuNPs may be isolated from the colloidal dispersion by any suitable manipulation known to a person of ordinary skill in the art.
  • the surfactant-free AuNPs may be isolated by any combination of centrifugation, distillation, fractionation, solvent evaporation, drying, and mechanical separation so as to obtain isolated surfactant-free AuNPs.
  • the surfactant-free AuNPs as described herein does not change size when isolated from a colloidal dispersion, nor when re-dispersed into a colloidal dispersion.
  • the isolated surfactant-free AuNPs as described herein are not prone to agglomeration. In one embodiment, the isolated surfactant-free AuNPs as described herein are not prone to agglomeration upon drying.
  • agglomeration refers to any process in which nanoparticles dispersed on a substrate, such as a surface are fused or bunched together.
  • the surfactant-free AuNPs of the present invention are not prone to agglomeration, which means that upon surface deposition they will stay as isolated nanoparticles, and not bunch together into larger clusters.
  • the surfactant-free AuNPs of the present invention can easily be re-dispersed in organic solvents or aqueous media such as water, aqueous buffers or aqueous saline solutions to reconstitute a colloidal dispersion.
  • organic solvents or aqueous media such as water, aqueous buffers or aqueous saline solutions to reconstitute a colloidal dispersion.
  • the isolated surfactant-free AuNPs as described herein do not agglomerate upon drying.
  • Nanoparticles based on gold are characterized by the presence of a surface plasmon resonance band which can be identified when investigating the nanoparticles with means of optical spectroscopy.
  • the surfactant-free AuNPs of the present disclosure demonstrate a maximum peak absorbance as measured using standard UV- Vis measurements at a wavelength ranging from 500 to 600 nm.
  • the maximum peak absorbance is located at a wavelength ranging from 500 nm to 515 nm, such as from 515 nm to 530 nm, such as from 530 nm to 545 nm, such as from 545 nm to 560 nm, such as from 560 nm to 575 nm, such as from 575 nm to 600 nm.
  • the surfactant-free AuNPs as described herein are characterized by an electrochemically active surface area which may be accessed in connection with applications such as catalysis, sensing, imaging and photothermal therapy.
  • the absence of surfactants means that the available surface area is larger for the surfactant-free AuNPs as described herein compared to prior art AuNPs.
  • the surfactant-free AuNPs present an average electrochemically active surface area of more than 5.0 m 2 g -1 , such as more than 5.5 m 2 g -1 , such as more than 6.0 m 2 g -1 , such as more than 6.5 m 2 g -1 , such as more than 7.0 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 .
  • the surfactant-free AuNPs present an average electrochemically active surface area of 8.2 ⁇ 1 .1 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 .
  • One embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in any one of catalysis, imaging, optics, electronics and sensing.
  • One embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in any one of sensing, bio-sensing, inorganic sensing, metal ion sensing.
  • One embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in galvanostatic displacement.
  • One embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in solvent remediation.
  • One embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in antibacterial food packaging.
  • One embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in catalysis.
  • the catalysis is homogeneous catalysis or heterogeneous catalysis. In one embodiment, the catalysis is electrocatalysis. In one embodiment, the catalysis is heterogeneous electrocatalysis. In one embodiment, the catalysis is homogeneous electrocatalysis. In one embodiment, the catalysis involves an oxidation reaction, such as alcohol oxidation. In one embodiment, the catalysis involves a reduction reaction such as CO2 reduction.
  • the catalysis involves activation of any one epoxides, carbonyls, alcohols, alkynes, hydrosilanes, and dihydrogen. In one embodiment, the catalysis is coupled to a reaction resulting in the formation of C-C bonds.
  • Another embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use as a medicament.
  • Another embodiment of the present disclosure is the surfactant-free colloidal dispersion of AuNPs, or the isolated surfactant-free AuNPs, or the re-dispersed surfactant-free AuNPs as described herein, for use in the treatment of cancer, such as by photothermal therapy, such as photothermal cancertherapy.
  • alloyed nanomaterials such as heterometallic nanoparticles, more specifically such as surfactant-free heterometallic AuNPs.
  • the AuNPs described herein may be heterometallic AuNPs.
  • the metallic nanoparticle precursors comprise a metal or the salt of a metal selected from the group consisting of Platinum (Pt), Palladium (Pd), Ruthenium (Ru), Rhodium (Rh), Silver (Ag), Copper (Cu), and Manganese (Mn).
  • the metallic nanoparticle precursor comprises Palladium (Pd) or a salt thereof, such as PdCIs or a hydrate thereof.
  • the heterometallic AuNPs described herein are formed by a combination of gold (Au) and palladium (Pd).
  • the heterometallic AuNPs described herein are formed by a combination of gold (Au) and at least one of Platinum (Pt), Palladium (Pd), Ruthenium (Ru), Rhodium (Rh), Silver (Ag), Copper (Cu), and Manganese (Mn).
  • the surfactant-free AuNPs of the present disclosure may be impregnated on a support, such as a solid support.
  • the solid support may be introduced into the reaction mixture prior to the formation of surfactant-free AuNPs.
  • one embodiment of the present disclosure is the method as described herein, wherein the solid support is provided in step a. of the method, and step b. is conducted in the presence of the solid support, so as in step c. to reduce the at least one inorganic gold precursor onto the solid support, thereby obtaining supported surfactant- free AuNPs.
  • the solid support may be introduced to the surfactant-free AuNPs following successful reduction of the inorganic gold precursor into surfactant-free AuNPs. In one embodiment, the solid support may be introduced into a re-dispersion of isolated surfactant-free AuNPs as described herein.
  • the method disclosed herein comprises a method of contacting the surfactant-free colloidal dispersion of AuNPs with a solid support, to obtain solid supported surfactant-free AuNPs.
  • the solid support is either 1) an inorganic porous oxide, such as selected from MnOs, TiOs, CeOs, SiOs, AI2O3, FesOs, zeolites such as Zeolite A or ZMS-5, and spinels such as MgAhC or other aluminium and iron spinels; or 2) a carbon-based support, such as selected from graphite nanofibers (GNF), carbon black (CB), carbon aerogels, and carbon nanotubes (CNTs).
  • an inorganic porous oxide such as selected from MnOs, TiOs, CeOs, SiOs, AI2O3, FesOs, zeolites such as Zeolite A or ZMS-5, and spinels such as MgAhC or other aluminium and iron spinels
  • a carbon-based support such as selected from graphite nanofibers (GNF), carbon black (CB), carbon aerogels, and carbon nanotubes (CNTs).
  • the solid support is an inorganic porous oxide selected from MnOs, TiOs, CeOs, SiC>2, AI2O3, Fe2Os, zeolites such as Zeolite A or ZMS-5, and spinels such as MgAhC or other aluminium and iron spinels.
  • the method of the present disclosure may be influenced by ambient light conditions. Without being bound by theory, the inventors believe this to be a result of activation of the inorganic gold precursors in the early stages of the reaction. If the mono-alcoholic component is ethanol, the reaction is usually completed and carried out over ca. 2 hours, but may be even faster; whereas the reaction may take up to 24 hours to complete if performed in the dark. It has also been noticed that the kinetics of the reaction are always slower when methanol is used instead of ethanol. This difference in reaction kinetics may be used to tune the size of the obtained surfactant-free AuNPs.
  • the method as described herein may be performed under ambient light conditions.
  • the method as described herein may be performed under UV- radiation.
  • the method as described herein may be performed under IR- radiation.
  • the method as described herein is carried out or completed over a time period ranging from 1 minutes to 24 hours when the method is performed in the presence of a light source. In one embodiment, the method as described herein is carried out or completed over a time period of less than 8 hours, such as less than 5 hours, such as less than 3 hours, such as less than 2 hours, such as less than 1 .5 hours, such as less than 1 hours, such as less than 30 minutes, such as less than 15 minutes, when the method is performed in the presence of a light source.
  • the method as described herein may be performed in the dark. In one embodiment, the method as described herein is carried out or completed over a time period ranging from 5 minutes to 24 hours when the method is performed in the dark.
  • a thermal pretreatment step may be performed to offset any ambient light impact on the reaction product.
  • Example 1 For samples subjected to a thermal pre-treatment step, the general procedure of Example 1 may be used but the at least one mono-alcoholic solvent system comprising a specified amount of base may be left to equilibrate at the desired temperature in a water bath before adding the gold precursor. Following the addition of the gold precursor, the reaction mixture may be left at a moderate temperature between 40 to 70°C for a shortened period of time, followed by reaction completion at room temperature.
  • the method as described herein may be performed at a temperature between 5 and 70°C, such as 5 to 15°C, such as 15 to 30°C, such as 30 to 45°C, such as 45 to 60°C, such as 60 to 70°C.
  • the method as described herein may be performed at ambient temperature, such as room temperature.
  • the method as described herein may comprise a thermal pretreatment step.
  • the thermal pre-treatment step may be performed at a temperature between 40 to 70°C, such as 40 to 50°C, such as 50 to 60°C, such as 60 to 70°C.
  • the thermal pre-treatment step may have a duration of 0.25 to 3 h, such as 0.25 to 0.5 h, such as 0.5 to 1 h, such as 1 .0 to 2.0 h, such as 2.0 to 3.0 h.
  • the method of the present disclosure may be performed with or without stirring. In either case, small well-dispersed surfactant-free AuNPs may be produced.
  • the method as described herein is performed with stirring. In one embodiment, the method as described herein is performed without stirring.
  • the method of the present disclosure may be performed with varying the base/Au ratio.
  • surfactant-free AuNPs may be formed using base/Au ratios ranging from 2 to 10. It is noted that the colloids formed at a base/Au ratio of 2 are rather unstable if stored for extended periods of time (more than 2 days), in particular if the mono-alcoholic component is methanol. Also at higher base/Au ratios of 8 to 10, the colloids may tend to agglomerate (also evidenced by a lower A 3 8o/A 8 oo ratio in the UV-Vis characterization). Consequently it is preferred to conduct the synthesis using a base/Au ratio centered around 4.
  • the base/Au ratio may be less than 20, such as less than 15, such as less than 10, such as less than 8, such as less than 5.
  • the base/Au ratio may range from 2 to 10, such as 2 to 3, such as 3 to 3.5, such as 3.5 to 4, such as 4 to 4.5, such as 4.5 to 5, such as 5 to 6, such as 6 to 8, such as 8 to 10.
  • the concentration of the inorganic gold precursor in the final reaction mixture varies between 0.1 mM to 5.0 mM, such as between 0.1 mM and 0.5 mM, such as between 0.5 mM and 1 .0 mM, such as between 1 .0 mM and 2.0 mM, such as between 2.0 mM and 3.0 mM, such as between 3.0 mM and 4.0 mM, such as between 4.0 mM and 5.0 mM.
  • the concentration of the inorganic gold precursor in the final reaction mixture is around 0.5 mM, such as 0.5 mM.
  • the concentration of the base in the final reaction mixture varies between 0.1 mM to 5.0 mM, such as between 0.5 mM and 1 .0 mM, such as between 1 .0 mM and 2.0 mM, such as between 2.0 mM and 3.0 mM, such as between 3.0 mM and 4.0 mM, such as between 4.0 mM and 5.0 mM.
  • the concentration of the base in the final reaction mixture is around 2.0 mM, such as 2.0 mM.
  • the base/Au ratio may also be tuned for size control of the surfactant-free AuNPs.
  • the at least one inorganic gold precursor can be selected from any suitable gold precursor which is capable of undergoing a reduction reaction in the at least one monoalcoholic solvent system.
  • the at least one inorganic gold precursor is selected from the group consisting of HAuCL, AuCI, AuBr, Aul, AuCI(C4H4S), as well as salts, hydrates and solvates thereof.
  • the method of the present disclosure may be performed with varying the mono- alcohol/water ratio.
  • the combination of a specific mono-alcohol/water ratio with a specific base can be used to tune the size of the surfactant-free AuNPs as described herein.
  • the mono-alcoholic solvent system may comprise water in an amount corresponding to 90% (v/v) or less, such as 80% (v/v) or less, such as 70% (v/v) or less, such as 50% (v/v) or less, such as 30% (v/v) or less, the remaining volume being the at least one mono-alcohol component.
  • the mono-alcoholic solvent system is based only on ethanol and the solvent system may comprise 90% (v/v) water or less, such as 80% (v/v) water, such as 70% (v/v) water, such as 60% (v/v) water, such as 50% (v/v) water.
  • the mono-alcoholic solvent system is based only on methanol and the solvent system may comprise 70% (v/v) water or less, such as 60% (v/v) water, such as 50% (v/v) water, such as 40% (v/v) water, such as 30% (v/v) water.
  • the ratio (v/v) of the at least one mono-alcohol to water in the at least one mono-alcoholic solvent system ranges from 5:95 to 95:5, such as from 10:90 to 90:10, such as from 10:90 to 80:20, such as from 10:90 to 70:30, such as from 20:80 to 70:30, such as from 30:70 to 70:30, such as from 40:60 to 60:40, such as 50:50.
  • the ratio (v/v) of the at least one mono-alcohol to water in the at least one mono-alcoholic solvent system ranges from 10:90 to 90:10, such as from 10:90 to 80:20, such as from 10:90 to 70:30, such as from 10:90 to 60:40, such as from 10:90 to 50:50.
  • the ratio (v/v) of the at least one mono-alcohol to water in the at least one mono-alcoholic solvent system is 30:70.
  • the mono-alcoholic solvent system comprises water at 70% (v/v) and comprises one or more of methanol or ethanol to make up the remaining volume.
  • mono-alcohols may be comprised in the mono-alcoholic solvent system such as mono-alcohols selected from isopropanol, n-propanol, n- butanol, and tert-butanol. Influence of combination of mono-alcohols in solvent system
  • the method of the present disclosure may be performed with varying the monoalcoholic solvent system so as to comprise more than one mono-alcoholic component.
  • the size control may be realized using different base/Au ratios or by tuning pH of the reaction mixture.
  • different base concentrations and thereby increasing pH there is also a risk of nanoparticle agglomeration and no fine size control can be achieved.
  • increasing the base concentration can be hazardous.
  • complex solvent mixtures of 3 or more solvents allows to achieve size control in a simpler way.
  • Results presented in Fig. 2 illustrates that the change in AuNP size observed when changing mono-alcohol from methanol to ethanol was significant and drastically decreasing.
  • a solvent system comprising water and two mono-alcoholic components in a controlled ratio, such as ethanol and methanol, keeping the total volume of alcohol to 30% (v/v) and the base concentration at 2 mM for 0.5 mM HAuCk
  • the average diameter of the nanoparticles can be finely tuned in the range IQ- 25 nm.
  • reaction time is generally shortened when the mono-alcohol is ethanol, compared to when the mono-alcohol is methanol. As such the reaction time may be tuned by combination of the two mono-alcohols in the at least one monoalcoholic solvent system.
  • the at least one mono-alcoholic solvent system may comprise one or more mono-alcoholic compounds.
  • the one or more mono-alcoholic compounds are selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol and tert-butanol.
  • the method of the present disclosure may be performed with varying the cation of the at least one base.
  • the base may be selected from a number sources, known to the person of ordinary skill in the art.
  • AuNPs may be formed following the (in Example 1 ) disclosed general method, with different cations such as Li + , Na + , K + , Cs and more.
  • the at least one base is selected from amines, amides, metal oxides, metal hydroxides, and alkolates.
  • the at least one base is selected from lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), Caesium hydroxide (CsOH), or mixtures thereof.
  • the at least one base is selected from lithium hydroxide (LiOH) and sodium hydroxide (NaOH).
  • the surfactant-free AuNPs as obtained as a colloid dispersion by following the previously described general procedure may be dried or otherwise separated from solution by any means known to a person of ordinary skill in the art, such as to obtain dried isolated surfactant-free AuNPs.
  • the surfactant-free AuNPs have the advantage over prior art AuNPs obtained by the state-of-the-art “Turkevich method” that they do not agglomerate upon drying as also evidenced in Fig. 1 (a: prior art Turkevich method, b: present disclosure).
  • the surfactant-free colloidal dispersion of AuNPs obtained by the method of the present disclosure has a dispersed stability of at least 1 hour when stored at 5°C in the dark , such as at least 2 hours, such as at least 4 hours, such as at least 8 hours, such as at least 12 hours, such as at least 24 hours, such as at least 2 days, such as at least 4 days, such as at least 7 days, when stored at 5°C in the dark.
  • the re-dispersed colloid of surfactant-free AuNPs obtained by redispersion of the isolated surfactant-free AuNPs of the present disclosure has a dispersed stability of at least 1 hour when stored at 5°C in the dark , such as at least 2 hours, such as at least 4 hours, such as at least 8 hours, such as at least 12 hours, such as at least 24 hours, such as at least 2 days, such as at least 4 days, such as at least 7 days, when stored at 5°C in the dark.
  • the surfactant-free AuNPs as described herein are re-dispersed in organic solvents or aqueous media.
  • the surfactant-free AuNPs as described herein are re-dispersed in a medium having a pH ranging from 2.5 to 12.5, selected from water, aqueous buffers and aqueous saline solutions.
  • Metal hydroxide as used in the present application also covers in situ formed metal hydroxides. Consequently the use of LiOH may be equivalent to the combined use of NaOH and LiCL Similarly, alkoholates such as NaOtBu may be formed in situ from NaCI and KOtBu.
  • Nanoparticle as used in the present application also covers rods, spheres, shells, discs, cluster globules, polyhedra, spike-like and other structures otherwise characterized by nanoregime dimensions, and is not intended as being limited to any particular shape or structure of the nanoparticle.
  • Mono-alcoholic solvent systems as used herein does not encompass solvent systems in which polyols (such as ethylene glycol, glycerol and more) are present.
  • the term mono-alcohol as used herein refers to an alcohol having a single hydroxy group.
  • the alcohol is often of formula R-OH where R is an alkyl.
  • the at least one monoalcoholic solvent system comprises a mixture of at least one mono-alcohol and water.
  • v/v as used herein refers to the volume percentage of a chemical solute in a liquid mixture. Also as used herein, the volume percentage is calculated without taking any volume contraction into account.
  • a herein disclosed 10 ml solvent mixture of 30% (v/v) ethanol and 70% (v/v) water may be obtained by combination of 3 ml ethanol and 7 ml water.
  • the resulting mixture may in reality comprise less than 10 ml of solvent mixture due to volume contraction.
  • Surfactant-free as used herein, and especially in relation to the AuNPs of the present invention, refers to being free of organic adsorbates that have a molar weight above 100 g/mol.
  • Base/Au ratio refers to the molar ratio of the at least one base to the at least one inorganic gold precursor (correlated for the number of gold atoms per formula unit in the inorganic gold precursor) in the final reaction mixture with reference to the herein disclosed method.
  • TEM Transmission electron microscopy
  • EDS energy dispersive X-ray spectroscopy
  • the AuNPs were dropped onto Nickel or Copper grids and left to dry at room temperature before being imaged on a Jeol 2100 operated at 200 kV.
  • the samples were characterized by taking micrographs in at least three randomly selected areas of the grid at a minimum of three different magnifications.
  • the size of the AuNPs was evaluated using the Imaged software by measuring at least 30 AuNPs for the largest particles (> 50 nm), and more typically at least 100-200 AuNPs for smaller particles.
  • the size reported correspond to the average diameter size and the related deviation, in addition the Sauter mean diameter (surface weighted) and the De Brouckere mean diameter (volume weighted) are indicated.
  • UV-Vis spectra were acquired with a Lambda UV/VIS/NIR-absorption spectrometer (PerkinElmer). A solvent mixture with the same water:alcohol ratio as the sample, but with no AuNPs was used as a baseline. The solutions were placed in dedicated quartz with 1 cm width cuvette for absorption measurements.
  • AuNPs show a strong signal in UV-Vis characterization that correspond to size dependent surface plasmon resonance.
  • the smaller nanoparticles from around 5 nm will show a surface plasmon resonance at a wavelength around 520 nm.
  • the peak-position and general UV-Vis spectra features to the size of the investigated AuNPs is solvent and nanomaterial shape dependent and so extremely complex. Therefore an absolute comparison of sizes is challenging, nevertheless several metrics used in the literature that capture different features of the UV-Vis data are reported.
  • the position A spr (wavelength at the surface plasmon resonance) of the maximum absorption peak intensity A spr is reported.
  • the relative width at 90% of the maximum absorption at the surface plasmon resonance is indicated (AA/A sp @ 90% of A spr ).
  • the size of the corresponding nanomaterials was evaluated by the follo ; where the value A sp r/A 4 5o (where A450 is the intensity measured at 450 nm wavelength) gives an indication of the size of the nanomaterials.
  • the relative intensity measured at 400 nm was suggested to indicate the relative amount of Au° in the sample and when relevant, the relative value for different samples regrouped in different section of the Tables below are reported (Hendel et aL, 2014).
  • the ratio of the absorption peak intensity at 650 nm and at the surface plasmon resonance A 6 5o/A sp r is reported to indicate the extend of aggregation of the nanoparticless (Ye et aL, 2015 and Agarwal et aL, 2015), the higher this ratio, the more aggregated the nanoparticles (it must be noted that this is technically relevant only if the nanoparticles are characterized by a well-defined surface plasmon resonance peak).
  • X-ray powder diffraction was measured on a Broker D8 diffractometer with a Cu anode equipped with a Ni filter in Bragg-Brentano geometry.
  • the samples were prepared by drop-casting a suspension of the nanoparticles onto a microscope slide and washed with water. Each sample was measured from 5-80° in 20 and background corrected for presentation and analysis.
  • the electrochemical testing was performed in a three electrode set up using a glassy carbon tip (5 mm diameter) as working electrode, a saturated calomel electrode (SCE) as reference electrode and a carbon rod as counter electrode in Teflon cells.
  • the as-prepared dispersion of surfactant-free Au or mixed alloy AuPd nanoparticles were dropped on the glassy carbon electrode (total of 30 pL) and left to dry.
  • the surface area of the AuNPs was evaluated by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm -2 (Padayachee et aL, 2014).
  • the mass activity was evaluated based on the nominal content of Au in the colloidal dispersion. The mass activities were corrected by a factor -3% to take into account the fact that for the ethanokwater content used (30:70, v:v) the volume contraction is around 3%.
  • Each sample of surfactant-free Au, Pd and Au x Pd y NPs was then tested following the general protocol A:
  • protocol B For the comparison of the surfactant-free AuNPs obtained from different alcohols the electrochemical protocol, protocol B, was:
  • the electrocatalytic properties of the AuNPs were evaluated for the ethanol oxidation and ethylene glycol oxidation in alkaline media in respectively 1 M ethanol with 1 M KOH in water and 1 M ethylene glycol with 1 M KOH. This correspond to step (3) of the protocol A above and steps (2) and (3) in the protocol B for testing surfactant free AuNPs prepared using different alcohols for the synthesis.
  • AuNPs gold-based nanoparticles
  • base reagent were prepared in water at 20 mM and 57 mM concentrations respectively.
  • a specified amount of a mono-alcoholic solvent system was provided by mixing of at least one mono-alcohol and water in a transparent plastic container (polypropylene, PP) and the specified amount of base stock solution was added, together with a magnetic stirrer.
  • the container was closed with a dedicated cover and the solution was shaken manually or left to stir for few seconds on a magnetic plate at ambient light and pressure.
  • a specified amount of chloroauric acid stock solution was then added, the sample container closed and the solution were left to stir for 24 hours at room temperature. After 24 hours the samples were prepared for transmission electron microscopy (TEM) and/or the samples stored in a fridge at ca. 5 °C until further characterization was performed e.g. by UV-Visible spectroscopy (UV-Vis) or X-ray diffraction (XRD).
  • UV-Vis UV-Visible spectroscopy
  • XRD X-ray diffraction
  • the best compromise found for the experimental conditions in an approach to minimise the amount of base and yet obtain stable colloidal dispersions is a ratio of base/Au of less than 10, preferably 3 to 8, more preferably 3 to 6.
  • the final volume is typically between 5 to 20 mL, preferably between 10 to 15 ml, but is not limited to these volumes.
  • the general procedure is not limited for further scalability (see Example 2).
  • the same reaction mixture is influenced by ambient light conditions. Without being bound by theory, the inventors believe this to be a result of UV activation of the AuNP precursors in the early stages of the reaction. If the mono-alcoholic component is ethanol, the reaction is generally completed in ca. 2 hours, whereas the reaction may take up to 24 hours to complete if performed in the dark. It has also been noticed that the kinetics of the reaction are always slower when methanol is used instead of ethanol. This difference in reaction kinetics may be used to tune the size of the obtained surfactant-free AuNPs.
  • a thermal pretreatment step may be performed to offset any ambient light impact on the reaction product.
  • the at least one mono-alcoholic solvent system comprising a specified amount of base was left to equilibrate at the desired temperature in a water bath for 15 minutes before adding the gold precursor.
  • the reaction mixture was left at a moderate temperature between 40 to 70°C for one hour and then left for 23 hours at room temperature.
  • the same reaction mixture can be converted into surfactant-free AuNPs with or without stirring.
  • stirring was used, however if the reaction mixture is subjected to the same conditions without stirring, small well-dispersed AuNPs are produced with a mean size of approximately 7 to 10 nm as verified by TEM analysis.
  • surfactant-free AuNPs may be formed using base/Au ratios ranging from 2 to 10. It is noted that the colloids formed at a base/Au ratio of 2 are rather unstable, in particular if the mono-alcoholic component is methanol. Also at higher base/Au ratios of 8 to 10, the colloids may tend to agglomerate (also evidenced by a lower A 3 8o/A 8 oo ratio). Consequently it is preferred to conduct the synthesis using a base/Au ratio from 3 to 6, such as 4.
  • the same reaction mixture can be converted into surfactant-free AuNPs with varying the mono-alcohol/water ratio.
  • the same reaction mixture can be converted into surfactant-free AuNPs with varying the mono-alcoholic solvent system so as to comprise more than one mono-alcoholic component.
  • the same reaction mixture can be converted into surfactant-free AuNPs with varying the cation of the at least one base.
  • AuNPs may be formed following the previously disclosed general method, with different cations such as Li + , Na + , K + , Cs + and more. All these monovalent cations have the same formal charge, however since lithium is the smallest ion, it has a higher charge density and is therefore expected to interact more strongly with the AuNP surface. Consequently, use of LiOH leads to formation of the most stable AuNP dispersions (i.e., colloids), with decreasing stability associated with increasing cation size.
  • the surfactant-free AuNPs as obtained as a colloid dispersion by following the previously described general procedure may be dried or otherwise separated from solution by any means known to a person of ordinary skill in the art, such as to obtain dried solid surfactant-free AuNPs.
  • the surfactant-free AuNPs have the advantage over prior art AuNPs obtained by the state-of-the-art “Turkevich method” that they do not agglomerate upon drying. This has the effect that the surfactant-free AuNPs of the present disclosure can easily be re-dispersed in organic solvents or aqueous media such as water, aqueous buffers or aqueous saline solutions. This facilitates transport of the product, since the AuNPs can be shipped dry which is more economical.
  • One immediate advantage of the present invention is that the herein provided synthesis is readily scalable to large volumes, which facilitates the industrial applicability.
  • the following exemplary large-scale synthesis is given for a reaction mixture of inorganic gold precursor at 0.5 mM, a LiOH/Au ratio of 4 and the at least one mono- alcoholic solvent system comprises 70% (v/v) water and 30% (v/v) ethanol in a total volume of 1018 ml.
  • the at least one solvent system was mixed in a glass container with the required amount of LiOH and heated to 50°C before the inorganic gold precursor was added. The final reaction mixture was allowed to stir for 1 hour at this temperature before heating was turned off, and the reaction was stirred for another 23 hours.
  • the as- synthesized colloidal AuNPs were characterized by UV-Vis spectroscopy and TEM as previously described. The results are summarized in Table 2 below.
  • the size estimated from UV-Vis is based on the peak position of the surface plasmon resonance as previously described.
  • the peak position is however also influenced by solvent, particle shape, composition, size, aggregation, all of which contributes to the interaction between the AuNPs.
  • the AuNPs produced in the present example are much smaller than estimated from UV-Vis spectroscopy and underlines the need for TEM in size analysis of nanoparticles.
  • the inventors have demonstrated that the claimed process can be scaled to an industrially relevant range and to obtain colloidally dispersed AuNPs of approximately 7 nm in size as depicted in Fig. 6.
  • the formed surfactant-free AuNPs display optical phenomena, appearing red in ambient light, and purple when held in front of a source emitting white light.
  • the present example is directed to the synthesis of mixed AuPd nanomaterials with different Au and Pd ratios, but can be expanded to other Au-alloyed NPs.
  • the synthesis follows the general procedure described in Example 1 , using a combination of HAuCL stock solution at 20 mM in water and a stock solution of PdCh in ethanol or water at 20 mM to obtain mixed alloy AuNPs as characterized below in Table 3 and illustrated in Fig. 7.
  • the Au x Pd y nanoparticles thereby obtained are readily electroactive and the mass activity and potential at which the maximum mass activity are observed can be tuned by alloying the Au with Pd as reported in Fig. 8.
  • the synthesis approach is suitable to develop bi/multi metallic nanoparticles.
  • An illustrative example is the case of Au x Pd y nanoparticles in which the size generally decreases as the amount of Pd increases as documented in Table 3 above.
  • Example 4 AuNPs supported on a solid support
  • Supported AuNPs were obtained by directly performing the synthesis following the previously described general protocol in the presence of a solid support with the desired Au:support ratio. Following the completed synthesis, the dispersion comprising the solid support was centrifuged, washed with water and air-dried. Supported AuNPs of the present invention were also obtained by mixing the required amount of colloidally dispersed AuNPs (obtained according to the previously described general protocol) with the appropriate amount of solid support to arrive at the desired Au loading, followed by solvent evaporation at room temperature to obtain a powder which was washed with water and air-dried.
  • Example 5 improved catalysis properties of novel AuNPs compared to prior art
  • the as-synthesized AuNPs were tested for catalytic properties in the electro-oxidation of alcohols, specifically ethanol or ethylene glycol (EG) in alkaline media (1 M KOH).
  • the Au nanoparticles present an electrochemically active surface area of 8.2 ⁇ 1.1 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 VSCE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 , which is higher than for nanoparticles prepared by the Turkevich method (7.1 ⁇ 0.4 m 2 g -1 ) and the specific activity (activity per available site) for the ethanol oxidation reaction is higher as illustrated in Fig. 11 . This is explained by the surfactant-free synthesis allowing a better access to the nanoparticle surface.
  • the mass activity (activity per mass) of gold e.g. for the ethylene glycol oxidation in alkaline media, is also higher and more stable over time for the AuNPs prepared by the method of the present invention.
  • a comparison of the catalytic activity was also made with surfactant-free AuNPs obtained from polyol mixtures.
  • the AuNPs used as catalysts were prepared at room temperature following the protocol of Example 1 with 0.5 mM HAuCLand 2 mM LiOH using 30% (v/v) of the alcohol indicated on the x-axis in Fig. 12.
  • the AuNPs of the present invention have improved properties compared to AuNPs obtained by the prior art “Turkevich” method.
  • a higher mass activity in electro-oxidation of alcohols is also realized for surfactant-free AuNPs obtained from a reaction implementing mono-alcohols such as methanol or ethanol, compared to reactions using polyols such as ethylene glycol or glycerol.
  • the trend is the same for electrooxidation of both mono-alcohols (Fig. 12(a)) and polyols (Fig. 12(b)) exemplified by oxidation of ethanol and ethylene glycol, and shows that the AuNPs of the present invention provides superior properties compared to prior art AuNPs.
  • a method for preparing a surfactant-free colloidal dispersion of AuNPs comprising the steps: a. Providing at least one inorganic gold precursor for the AuNPs, at least one mono-alcoholic solvent system, and at least one base; b. Mixing the at least one inorganic gold precursor for the AuNPs, the at least one mono-alcoholic solvent system, and the at least one base in the absence of any polymers, ligands, capping agents, and surfactants, thereby obtaining a reaction mixture, such as to reduce the at least one inorganic gold precursor for the AuNPs with the at least one monoalcoholic solvent system; and c. Reducing the at least one inorganic gold precursor, thereby obtaining the surfactant-free colloidal dispersion of AuNPs.
  • the inert atmosphere essentially consists of or comprises Nitrogen (N 2 ) or Argon (Ar).
  • the surfactant-free colloidal dispersion of AuNPs comprise AuNPs with an average size of less than 50 nm such as less than 40 nm, such as less than 30 nm, such as less than 25 nm, such as less than 20 nm, such as less than 15 nm, such as less than 10 nm.
  • step b. may be performed with and without stirring.
  • step b. is performed at a temperature ranging from 5 to 70°C.
  • step b. is performed at a temperature ranging from 5 to 70°C, such as 5 to 15°C, such as 15 to 30°C, such as 30 to 45°C, such as 45 to 60°C, such as 60 to 70°C.
  • step b. is performed at ambient temperature, such as room temperature.
  • step b. may comprise a thermal pre-treatment step, which takes place at a temperature between 40 to 70°C, such as 40 to 50°C, such as 50 to 60°C, such as 60 to 70°C.
  • thermo pre-treatment step has a duration of 0.25 to 3 h, such as 0.25 to 0.5 h, such as 0.5 to 1 h, such as 1 .0 to 2.0 h, such as 2.0 to 3.0 h.
  • step c. reducing the at least one inorganic gold precursor for the AuNPs is carried out or completed over a time period ranging from 5 minutes to 24 hours.
  • step c. reducing the at least one inorganic gold precursor for the AuNPs is carried out or completed over a time period ranging from 5 minutes to 24 hours when the method is performed in the dark.
  • step c. reducing the at least one inorganic gold precursor for the AuNPs is carried out or completed over a time period ranging from 5 minutes to 24 hours when the method is performed in ambient light.
  • the base/Au ratio is less than 20. 16. The method according to any one of the preceding items, wherein the base/Au ratio is less than 20, such as less than 15, such as less than 10, such as less than 8, such as less than 5.
  • the base/Au ratio is 2 to 8, such as 2 to 3, such as 3 to 3.5, such as 3.5 to 4, such as 4 to 4.5, such as 4.5 to 5, such as 5 to 6, such as 6 to 8.
  • the at least one inorganic gold precursor for the AuNPs is selected from the group consisting of HAuCL, AuCI, AuBr, Aul, AuCI(C4H 4 S), as well as salts, hydrates and solvates thereof.
  • step c. The method according to any one of the preceding items, wherein the surfactant-free colloidal dispersion of AuNPs, obtained in step c. has a dispersed stability of at least 7 days, when stored at 5°C in the dark.
  • step c. The method according to any one of the preceding items, wherein the surfactant-free colloidal dispersion of AuNPs, obtained in step c. has a maximum peak absorbance as measured using standard UV-Vis measurements at a wavelength ranging from 500 to 600 nm.
  • the surfactant-free colloidal dispersion of AuNPs, obtained in step c. has a maximum peak absorbance as measured using standard UV-Vis measurements at a wavelength ranging from 500 to 600 nm, such as from 500 nm to 515 nm, such as from 515 nm to 530 nm, such as from 530 nm to 545 nm, such as from 545 nm to 560 nm, such as from 560 nm to 575 nm, such as from 575 nm to 600 nm.
  • the at least one mono-alcoholic solvent system comprises a mixture of at least one monoalcohol and water.
  • the ratio (volume:volume) of the at least one mono-alcohol to water in the at least one mono-alcoholic solvent system ranges from 5:95 to 95:5.
  • ratio (volume:volume) of the at least one mono-alcohol to water in the at least one mono-alcoholic solvent system ranges from 10:90 to 90:10, such as from 10:90 to 80:20, such as from 10:90 to 70:30, such as from 20:80 to 70:30, such as from 30:70 to 70:30.
  • ratio (volume:volume) of the at least one mono-alcohol to water in the at least one mono-alcoholic solvent system ranges from 10:90 to 90:10, such as from 10:90 to 80:20, such as from 10:90 to 70:30, such as from 10:90 to 60:40, such as from 10:90 to 50:50.
  • the mono-alcohol of the at least one mono-alcoholic solvent system is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol.
  • the at least one base is selected from amines, amides, metal oxides, metal hydroxides, and alkolates.
  • the at least one base is selected from lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), Caesium hydroxide (CsOH), or mixtures thereof.
  • the at least one base is selected from lithium hydroxide (LiOH) and sodium hydroxide (NaOH).
  • step a at least one additional metallic nanoparticle precursor is provided, wherein the at least one additional metallic nanoparticle precursor comprises a metal or the salt of a metal selected from the group consisting of Platinum (Pt), Palladium (Pd), Ruthenium (Ru), Rhodium (Rh), Silver (Ag), Copper (Cu), and Manganese (Mn), so as to in step c. obtain a surfactant-free colloidal dispersion of heterometallic AuNPs.
  • the solid support is either 1 ) an inorganic porous oxide, such as selected from MnO 2 , TiO 2 , CeO 2 , SiOs, AI2O3, Fe 2 Os, zeolites such as Zeolite A or ZMS-5, and spinels such as MgAI 2 C>4 or other aluminium and iron spinels; or 2) a carbon-based support, such as selected from graphite nanofibers (GNF), carbon black (CB), carbon aerogels, and carbon nanotubes (CNTs).
  • an inorganic porous oxide such as selected from MnO 2 , TiO 2 , CeO 2 , SiOs, AI2O3, Fe 2 Os, zeolites such as Zeolite A or ZMS-5, and spinels such as MgAI 2 C>4 or other aluminium and iron spinels
  • a carbon-based support such as selected from graphite nanofibers (GNF), carbon black (CB), carbon aerogels, and carbon nanotubes (CNTs).
  • step a. wherein the solid support is provided in step a., and step b. is conducted in the presence of the solid support, so as in step c. to reduce the at least one inorganic gold precursor onto the solid support, thereby obtaining supported surfactant-free AuNPs.
  • step c any combination of centrifugation, distillation, fractionation, evaporation, drying, and separation may be performed so as to obtain solid surfactant-free AuNPs.
  • step b. The method according to any one of the preceding items, wherein the mixing in step b. may be performed in any order.
  • step b. The method according to any one of the preceding items, wherein the mixing in step b. is to be performed in the following order: i. Mixing the at least one mono-alcoholic solvent system and the at least one base in a first instance, and ii. Mixing the at least one inorganic gold precursor with the mixture obtained in step i., in the absence of any polymers, ligands, capping agents, and surfactants.
  • the surfactant-free AuNPs according to items 39 to 41 wherein the surfactant-free AuNPs have an average size of less than 50 nm such as less than 40 nm, such as less than 30 nm, such as less than 25 nm, such as less than 20 nm, such as less than 15 nm, such as less than 10 nm.
  • the surfactant-free AuNPs according to any one of items 39 to 43, wherein the surfactant-free AuNPs present an average electrochemically active surface area of more than 5.0 m 2 g -1 , such as more than 5.5 m 2 g -1 , such as more than 6.0 m 2 g -1 , such as more than 6.5 m 2 g -1 , such as more than 7.0 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 .
  • the surfactant-free AuNPs according to any one of items 39 to 43, wherein the surfactant-free AuNPs present an average electrochemically active surface area of 8.2 ⁇ 1.1 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 .
  • Re-dispersed surfactant-free AuNPs prepared by re-dispersing the solid AuNPs according to any one of items 39 to 45.
  • the re-dispersed surfactant-free AuNPs according to any one of items 46 to 47, wherein the AuNPs are re-dispersed in a medium having a pH ranging from 2.5 to 12.5, selected from water, aqueous buffers and aqueous saline solutions.
  • re-dispersed surfactant-free AuNPs according to any one of items 46 to 48, wherein the re-dispersed surfactant-free AuNPs have a dispersed stability of at least 7 days, when stored in aqueous buffer at 5°C in the dark
  • a product comprising the surfactant-free AuNPs according to any one of items 39 to 45 or the re-dispersed surfactant-free AuNPs according to any one of items 46 to 49.
  • Surfactant-free AuNPs wherein the surfactant-free AuNPs present an average electrochemically active surface area of more than 5.0 m 2 g -1 , such as more than 5.5 m 2 g -1 , such as more than 6.0 m 2 g -1 , such as more than 6.5 m 2 g -1 , such as more than 7.0 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 .
  • the surfactant-free AuNPs according to item 61 wherein the surfactant-free AuNPs, comprise AuNPs with an average size of less than 50 nm such as less than 40 nm, such as less than 30 nm, such as less than 25 nm, such as less than 20 nm, such as less than 15 nm, such as less than 10 nm.
  • the surfactant-free AuNPs according to any one of items 61 to 62 for use in any one of catalysis, imaging, optics, electronics and sensing.
  • a method for preparing a surfactant-free colloidal dispersion of AuNPs comprising the steps: a. Providing at least one inorganic gold precursor for the AuNPs, at least one mono-alcoholic solvent system, and at least one base; b. Mixing the at least one inorganic gold precursor for the AuNPs, the at least one mono-alcoholic solvent system, and the at least one base in the absence of any polymers, ligands, capping agents, and surfactants, thereby obtaining a reaction mixture, such as to reduce the at least one inorganic gold precursor for the AuNPs with the at least one monoalcoholic solvent system; and c. Reducing the at least one inorganic gold precursor, thereby obtaining the surfactant-free colloidal dispersion of AuNPs.
  • step b. is performed at a temperature ranging from 5 to 70°C, such as 5 to 15°C, such as 15 to 30°C, such as 30 to 45°C, such as 45 to 60°C, such as 60 to 70°C.
  • step b. is performed at ambient temperature, such as room temperature.
  • the base/Au ratio is 2 to 8
  • the at least one mono-alcoholic solvent system comprises a mixture of at least one mono-alcohol and water
  • the at least one base is selected from lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), Caesium hydroxide (CsOH), or mixtures thereof.
  • step a at least one additional metallic nanoparticle precursor is provided, so as to in step c. obtain a surfactant-free colloidal dispersion of heterometallic AuNPs.
  • the surfactant-free AuNPs according to item 8 wherein the surfactant-free AuNPs, comprise AuNPs with an average size of less than 50 nm such as less than 40 nm, such as less than 30 nm, such as less than 25 nm, such as less than 20 nm, such as less than 15 nm, such as less than 10 nm.
  • the surfactant-free AuNPs according to any one of items 8 to 10, wherein the surfactant-free AuNPs present an average electrochemically active surface area of more than 5.0 m 2 g -1 , such as more than 5.5 m 2 g -1 , such as more than 6.0 m 2 g -1 , such as more than 6.5 m 2 g -1 , such as more than 7.0 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm 2 .
  • Surfactant-free AuNPs wherein the surfactant-free AuNPs present an average electrochemically active surface area of more than 5.0 m 2 g -1 , such as more than 5.5 m 2 g -1 , such as more than 6.0 m 2 g -1 , such as more than 6.5 m 2 g -1 , such as more than 7.0 m 2 g -1 , when evaluated using scans at 50 mV s -1 in 0.5 M H2SO4 between 0.00 and 1 .50 V S CE by the charge passed under the reduction peak of gold in H2SO4 converted to an electrochemically active surface area using a conversion factor of 386 pC cm' 2 .

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Abstract

La présente invention concerne un procédé de préparation de nanoparticules et de nanomatériaux d'or ne nécessitant pas d'adsorbats organiques ayant une masse molaire supérieure à 100 g/moL. La présente invention concerne également une dispersion colloïdale des nanoparticules d'or obtenues par les procédés selon l'invention, des nanomatériaux solides et redispersés et des produits comprenant des nanoparticules d'or.
PCT/EP2022/073930 2021-08-30 2022-08-29 Synthèse colloïdale sans tensioactif de nanomatériaux à base d'or WO2023031111A1 (fr)

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US20170304902A1 (en) * 2016-04-22 2017-10-26 The Board Of Trustees Of The Leland Stanford Junior University Synthesis of water-soluble thiolate-protected gold nanoparticles of uniform size and conjugates thereof
EP3329990A1 (fr) * 2016-11-30 2018-06-06 Sebastian Kunz Nanoparticules de métal précieux améliorées
EP3587009A1 (fr) * 2018-06-29 2020-01-01 Université de Tours Procédé de fabrication de nanofleurs d'or et leurs utilisations

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Publication number Priority date Publication date Assignee Title
US20130264198A1 (en) * 2012-04-10 2013-10-10 Brookhaven Science Associates, Llc Synthesis of Nanoparticles Using Ethanol
US20170304902A1 (en) * 2016-04-22 2017-10-26 The Board Of Trustees Of The Leland Stanford Junior University Synthesis of water-soluble thiolate-protected gold nanoparticles of uniform size and conjugates thereof
EP3329990A1 (fr) * 2016-11-30 2018-06-06 Sebastian Kunz Nanoparticules de métal précieux améliorées
EP3587009A1 (fr) * 2018-06-29 2020-01-01 Université de Tours Procédé de fabrication de nanofleurs d'or et leurs utilisations

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