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WO2012175990A1 - Nanoparticules revêtues et leurs procédés de production - Google Patents

Nanoparticules revêtues et leurs procédés de production Download PDF

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Publication number
WO2012175990A1
WO2012175990A1 PCT/GB2012/051466 GB2012051466W WO2012175990A1 WO 2012175990 A1 WO2012175990 A1 WO 2012175990A1 GB 2012051466 W GB2012051466 W GB 2012051466W WO 2012175990 A1 WO2012175990 A1 WO 2012175990A1
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Prior art keywords
metal
nanoparticles
liquid carrier
carrier medium
working electrode
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English (en)
Inventor
Richard Guy Compton
Neil Vaughan Rees
Yi-Ge ZHOU
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Oxford University Innovation Ltd
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Oxford University Innovation Ltd
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D7/00—Electroplating characterised by the article coated
    • C25D7/006—Nanoparticles
    • 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
    • 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
    • B22F1/17—Metallic particles coated with metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/26—Electroplating: Baths therefor from solutions of cadmium
    • 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
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • 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
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

  • the present invention relates to coated nanoparticles and a method for their production, particularly using an electrodeposition technique.
  • the method allows bulk deposition of a metal onto a nanoparticle.
  • Metal nanoparticles for example silver nanoparticles
  • Core-shell nanoparticles have also been researched extensively, since the differing properties of the materials of the core and shell can be tailored to meet different requirements.
  • core-shell particles where both the core and shell are elemental metals.
  • One example of producing core-shell nanoparticles having a metallic core and a metallic shell is described in WO 2009/156990, which is incorporated here by reference in its entirety.
  • nanoparticles having a copper core and a silver shell are produced by adding silver nitrate to a dispersion of copper nanoparticles, as described in Example 6 of this document.
  • the silver ions are reduced by copper atoms on the surface of the nanoparticles, resulting in a layer of elemental silver on the nanoparticles, with the copper atoms themselves being oxidised.
  • the present invention provides a method of electrochemically coating nanoparticles, the method comprising:
  • the elemental metal is the metal of the ions in solution in elemental form.
  • the present invention provides an apparatus for carrying out the method of the first aspect, the apparatus comprising:
  • the liquid carrier medium comprising:
  • the present invention provides a coated nanoparticle producible in accordance with the method described in the first aspect.
  • the present invention provides a nanoparticle having a core comprising a first elemental metal and an electrochemically-deposited coating of a second elemental metal on the core, wherein the coating is in the form of a bulk deposit of the second elemental metal.
  • the nanoparticle of the fourth aspect may be producible in accordance with the method of the first aspect.
  • the present inventors have found that they can produce coated nanoparticles by an electrochemical method, including core-shell metal nanoparticles.
  • the electrochemical nature of the deposition is such that the coating on the nanoparticles can be controlled, and such that a bulk deposition of the metal occurs.
  • the process can also be controlled such that substantially only the nanoparticles are coated, not the working electrode.
  • Figure 1 shows a comparative voltammogram of Cadmium deposition on a bare glassy carbon electrode (dotted lines, Example 1 ) and on a AgNP-modified glassy carbon electrode (solid lines, Example 2). (a) sets forth the full voltammograms, and (b) the underpotential deposition region.
  • Figure 2 shows (a) a typical impact transient at -0.55V for a glassy carbon microelectrode (of radius 1 1 ⁇ ) which has been placed in a degassed solution of 1 mM CdCI 2 and 0.1 M KCI, also to which solution an aliquot of dispersed AgNPs has been added and agitated by bubbling with N 2 (Example 3); and (b) a histogram showing the number of impacts in terms of layer coverage of an average AgNP.
  • Figure 3 shows (a) a potential step-sweep experiment of a glassy carbon electrode (of radius 1 1 ⁇ ) in 1 mM CdCI 2 and 0.10M NaCI (Example 5) in which the potential was held at -0.74V (vs Ag/AgCI) and scanned positive at 20 mV s "1 ; and (b) an enlargement of the "transient" region after noise reduction to confirm no spikes.
  • Figure 4 shows similar information to Figure 3, except that, in this example, 9 x 10 12 particles dm "3 of AgNPs was also present (Example 6).
  • Figure 5 shows (a) a potential step-sweep experiment of a glassy carbon electrode (of radius 1 1 ⁇ ) in 1 mM CdCI 2 and 0.10M NaCI (Example 7), in which the potential was held at -0.73V (vs Ag/AgCI) and scanned positive at 20 mV s "1 ; and (b) an enlargement of the "transient" region after noise reduction showing spikes.
  • Figure 6 shows a histogram of the number of impacts in terms of layer coverage of an average AgNP of Example 7. It sets forth the distribution of nanoparticle coverages, confirming that multilayers of Cd are deposited onto the AgNPs during collision.
  • the present invention provides the first to fourth aspects described above.
  • Optional and preferred features of the various aspects are described below. Unless otherwise stated, any optional or preferred feature may be combined with any other optional or preferred feature, and with any of the aspects of the invention mentioned herein.
  • the nanoparticles, in step (i) of the method may be particles having a diameter of from 1 to 500 nm, optionally from 1 to 200 nm, optionally from 10 to 90 nm, optionally from 20 to 80 nm, optionally from 30 to 70 nm.
  • the liquid carrier medium, in step (i) may comprise nanoparticles having a mean diameter of from 1 to 500 nm, optionally from 1 to 200 nm, optionally from 10 to 90 nm, optionally from 20 to 80 nm, optionally from 30 to 70 nm.
  • the diameter of a nanoparticle can be determined by scanning electron microscope (SEM) imaging, as would be appreciated by the skilled person.
  • the nanoparticle can be any suitable shape, including spherical, and elongated, for example a rod-shaped nanoparticle. If a nanoparticle is non-spherical, the diameter of the nanoparticle as measured herein will be the smallest diameter across the particle.
  • the mean diameter of nanoparticles in the liquid carrier medium can be measured using SEM imaging of a sample of the nanoparticles, and calculating the number average (i . e. mean) diameter for 1 00 nanoparticles or more, optional ly 200 nanoparticles or more, optionally 300 nanoparticles or more.
  • the nanoparticles, in step (i), may comprise, consist essentially of, or consist of, a first material. If a particle consists essentially of the first material, this indicates that preferably the particle comprises at least 95 % by weight of the first material, preferably 98 % by weight, preferably 99 % by weight, of the first material.
  • the first material is an electrically-conducting material.
  • the first material may be selected from a metal, a semi-metal, and a semi-conductor.
  • the first material comprises a metal, preferably in elemental form, which is preferably a different type of metal from the metal of the metal ions in solution.
  • the metal of the first material may be any suitable metal, including, but not limited to, a metal selected from any of groups 3 to 14 of the periodic table.
  • the metal of the first material may be selected from a transition metal of any of groups 3 to 12 of the periodic table.
  • the first material comprises a metal selected from a group 1 1 of the periodic table.
  • the first material comprises a metal in elemental form selected from copper, silver, gold, ruthenium, osmium, rhodium, iridium, palladium and platinum.
  • the first material comprises a metal in elemental form selected from silver and gold.
  • the nanoparticles are adsorbed on the working electrode and/or dispersed in liquid carrier medium.
  • the nanoparticles are dispersed in the carrier medium.
  • the particles are dispersed in the liquid carrier medium, e.g. by addition to the liquid carrier medium and agitation of the liquid carrier medium (e.g. by ultrasound), and step (ii) is initiated less than 20 minutes after the particles are dispersed in the liquid carrier medium, optionally 15 minutes or less, optionally 10 minutes or less, optionally 5 minutes or less, optionally 2 minutes or less, after the particles are dispersed in the liquid carrier medium.
  • the first material is or comprises a first metal, which is in elemental form, and the metal of the ions in solution is a second metal, the first and second metal being different to one another.
  • the first and second metals are each independently selected from the transition metals, but are different from one another.
  • the first metal may be a metal higher up or lower down in the electrochemical series than the second metal .
  • the first metal is a metal higher up in the electrochemical series than the second metal.
  • the first metal is less strongly reducing (has a more positive value for its standard reduction electrode potential) than the second metal.
  • the electrochemical series is known to the skilled person, and is found in many text books, for example as described on page 343 of Physical Chemistry, authored by P. W Atkins, 5 th Edition, which is incorporated herein by reference in its entirety.
  • the ions of a metal dissolved in the liquid carrier medium are ions of a metal selected from any one of groups 3 to 13 of the periodic table.
  • the ions of a metal dissolved in the liquid carrier medium are ions of a metal selected from group 12 and 13 of the periodic table, including, but not limited to, zinc, cadmium, mercury, indium and thallium.
  • the ions of a metal dissolved in the liquid carrier medium are ions of a transition metal selected from any one of groups 3 to 12 of the periodic table.
  • the ions of the metal dissolved in the liquid carrier medium are ions of a transition metal other than silver, and the first material comprises or is silver.
  • the ions of the metal dissolved in the liquid carrier medium are ions of cadmium and the first material comprises or is silver.
  • a bulk deposit of a metal onto a substrate is understood in the art to mean a deposit of more than a monolayer of atoms of the metal onto the substrate (e.g. nanoparticle).
  • the bulk deposition in the method of the first aspect results in a plurality of layers of atoms of the elemental metal on the nanoparticle.
  • the bulk deposition of the elemental metal on the particles may result in a partial or complete coating of the elemental metal on the surface of the nanoparticle.
  • the particle density of the nanoparticles in the liquid carrier medium may be at any suitable density that allows deposition on the nanoparticles of the metal from the metal ions in the liquid carrier medium.
  • the particle density of the nanoparticles in the liquid carrier medium may be at least 1 x 10 6 particles dm "3 of the liquid carrier medium, optionally at least 1 x 10 8 particles dm "3 of the liquid carrier medium, optionally at least 1 x 10 10 particles dm "3 of the liquid carrier medium, optionally at least 1 x 10 11 particles dm "3 of the liquid carrier medium.
  • the particle density of the nanoparticles in the liquid carrier medium may be from 1 x 10 10 particles dm "3 of the liquid carrier medium to 1 x 10 15 particles dm “3 of the liquid carrier medium, optionally from 1 x 10 12 particles dm “3 of the liquid carrier medium to 1 x 10 14 particles dm “3 of the liquid carrier medium, optionally 5 x 10 12 particles dm “3 of the liquid carrier medium to 5 x 10 13 particles dm "3 of the liquid carrier medium.
  • the particle density of nanoparticles can be measured using any known technique. I n one embodiment, the particle density of metal nanoparticles in the liquid carrier medium is measured is follows:
  • a sample of nanoparticles suspended in the liquid carrier medium e.g. using ultrasound
  • an aliquot e.g. 20 ⁇ _
  • the liquid of the liquid carrier medium is then allowed to evaporate, to form a nanoparticle-modified GC electrode.
  • the number of metal atoms present on the GC electrode surface can be determined from Faraday's Law. Knowing the mean nanoparticle size and density of the nanoparticles, we can convert the number of atoms of metal into a number of nanoparticles. Thus, the number of nanoparticles in the original aliquot (e.g. 20 ⁇ _) can be found, from which the nanoparticles in a dm 3 of the liquid carrier medium can be calculated.
  • the ions of the metal dissolved in the liquid carrier medium may be at any suitable concentration to allow deposition of the elemental form of this metal on to the nanoparticles.
  • the ions of the metal may have a concentration in the liquid carrier medium, before step (ii) in the method, of at least 0.01 mM, optionally at least 0.1 mM, optionally at least 0.5 mM.
  • the ions of the metal may have a concentration in the liquid carrier medium, before step (ii) in the method, of from 0.01 mM to 100 mM, optionally from 0.1 mM to 10 mM, optionally from 0.5 mM to 5 mM, optionally from 0.5 mM to 3 mM.
  • the liquid carrier medium will comprise counter ions for the dissolved ions of the metal. These counter ions may be selected from any suitable counter ions.
  • the counter ions preferably are selected such that they will not themselves be oxidised or reduced under the conditions at which the method is carried out.
  • the counter ions are preferably selected such that a compound of the metal ions and the counter ions will dissolve in the liquid carrier medium, for example such that the metal ions can dissolve at the concentrations mentioned above.
  • the counter ions may, for example, be selected from the halides, including, but not limited to, chlorides, bromides and iodides.
  • the liquid carrier medium may be any suitable medium.
  • the liquid carrier medium comprises, consists essentially of, or consists of (excluding any dissolved solutes and suspended nanoparticles), water.
  • the carrier med i u m consists essentially of water, preferably the liquid carrier medium (excluding any dissolved solutes and suspended nanoparticles) comprises at least 98% by weight water, preferably at least 99% by weight water, preferably at least 99.5% by weight water.
  • the water, before the addition of the metal ions, counter ions and the nanoparticles may have a resistivity of at least 18 MQ.cm, preferably at least 18.2 MQ.cm.
  • the liquid carrier medium is degassed before the addition of the metal ions, any counter ions and the nanoparticles.
  • the liquid carrier medium may be degassed using any suitable technique, for example degassing using N 2 under an atmosphere of N 2 .
  • the nanoparticles may be dispersed in the liquid carrier medium using any suitable technique.
  • the nanoparticles are added to the liquid carrier medium and then dispersed in the liquid carrier medium using ultrasound, optionally stirring or otherwise agitating the liquid carrier medium as required.
  • the working electrode may comprise any suitable material.
  • the surface of the working electrode comprises an inert material, such that it is not itself oxidised or reduced under the conditions at which the method is carried out. Suitable electrodes are available to the skilled person.
  • the working electrode may have a surface comprising a metal or carbon.
  • the whole of the electrode comprises a metal or carbon.
  • the working electrode may comprise a metal selected from gold, silver and platinum.
  • the working electrode may comprise a carbon-containing material, which may be selected from edge plane pyrolytic graphite, basal plane pyrolytic graphite, glassy carbon, boron doped diamond, highly ordered pyrolytic graphite, carbon powder and carbon nanotubes.
  • the working electrode is a glassy carbon electrode.
  • the counter electrode may be made of any suitable material, for example a metal or carbon. If the counter electrode is in contact with the liquid carrier medium, preferably the material of the counter electrode is selected such that it is not itself oxidised or reduced under the conditions at which the method is carried out.
  • the counter electrode may comprise a metal selected from gold, silver and platinum.
  • the counter electrode may comprise a carbon-containing material, which may be selected from edge plane pyrolytic graphite, basal plane pyrolytic graphite, a glassy carbon, boron doped diamond, highly ordered pyrolytic graphite, carbon powder and carbon nanotubes.
  • the counter electrode is a graphite electrode.
  • both the working electrode and the counter electrode are carbon-containing electrodes.
  • a reference electrode for example an Ag/AgCI reference electrode or a saturated calomel reference electrode, may be connected to the worki ng and/or counter electrodes as is known in the art.
  • the working electrode, the counter electrode and the reference electrode may be controlled by a potentiostat, as is known by the skilled person.
  • a means for applying a potential is electrically connected to the working and counter electrodes.
  • the means for applying a potential can be any suitable means, for example a potentiostat, as mentioned above.
  • the potential applied to the working electrode is more than, i.e. a value more positive than, the potential at which the deposition of the elemental metal occurs on the working electrode in the absence of the nanoparticles, but otherwise the conditions being the same as the method.
  • the potential at which the deposition of the elemental metal occurs on the working electrode in the absence of the nanoparticles can be determined in a cyclic voltamogram by the single cathodic deposition peak in the sweep from the most positive potential to the most negative potential, using a sweep rate of 100 mVs "1 or less, e.g. 50 mVs "1 .
  • the absence of nanoparticles indicates that the nanoparticles are neither present on the working electrode nor in the liquid carrier medium. Otherwise the conditions being the same as the method” indicates that, for example, the working and counter electrodes, any reference electrodes, the liquid carrier medium, and its content of metal ions and counter ions, and the temperature and pressure are the same as in the method.
  • the potential applied to the working electrode has a value at least 0.02 V more positive than the potential at which the deposition of the elemental metal occurs on the working electrode in the absence of the nanoparticles, but otherwise the conditions being the same as the method.
  • the potential applied to the working electrode has a value at least 0.05 V more positive than, optionally at least 0.08 V more positive than, optionally at least 0.1 V more positive than, optionally at least 0.2 V more positive than, optionally at least 0.3 V more positive than, optionally at least 0.4 V more positive than, the potential at which the deposition of the elemental metal occurs on the working electrode in the absence of the nanoparticles, but otherwise the conditions being the same as the method.
  • the nanoparticles are dispersed in the liquid carrier medium and, in step (i i) , the potential applied to the working electrode is (a) less than the underpotential at which deposition of the elemental metal occurs onto the nanoparticles when adsorbed onto the surface of the electrode and are absent from the liquid carrier medium, but otherwise the conditions being the same as the method.
  • the potential applied to the working electrode preferably has a value less positive than the underpotential for the deposition of the elemental metal onto the surface of the nanoparticle.
  • the potential applied to the working electrode preferably has a value of at least 0.02V less positive than the underpotential for the deposition of the elemental metal onto the surface of the nanoparticle.
  • the potential applied to the working electrode preferably has a value of at least 0.04V less positive, optionally a value of at least 0.08 V less positive, a value of at least 0.1 V less positive, a value of at least 0.2 V less positive, a value of at least 0.3 V less positive, a value of at least 0.4 V less positive, than the underpotential for the deposition of the elemental metal onto the surface of the nanoparticle.
  • the nanoparticles are dispersed in the liquid carrier medium and the potential applied to the working electrode in step (ii) is (a) less than the underpotential at which deposition of the elemental metal occurs onto the nanoparticles when adsorbed onto the surface of the electrode and are absent from the liquid carrier medium, but otherwise the conditions being the same as the method and (b) more than the potential at which the deposition of the elemental metal occurs on the working electrode in the absence of the nanoparticles, but otherwise the conditions being the same as the method.
  • the amount of nanoparticles adsorbed onto the electrode can be any amount, since it is the nature of the material of the nanoparticles, not the amount, that will affect the underpotential as described above.
  • the underpotential of the deposition of the elemental metal onto the nanoparticles from the metal ions in the liquid carrier medium can be determined using any known technique, for example cyclic voltametry. This may be determined, for example, by adsorbing the nanoparticles onto the electrode and placing it in the liquid carrier medium containing the metal ions (but not the nanoparticles), and carrying out a cyclic voltametry experiment by sweeping the voltage between set points either side of the standard electrode potential for the deposition of the metal from the metal ions in the solution onto the electrode; on sweeping from the most positive potential to the most negative potential, it is possible to identify the underpotential at which deposition of the metal from the metal ions occurs on the working electrode on which the nanoparticles are adsorbed; this may be indicated by a small minimum (sometimes termed a shoulder) on right-hand side of the largest peak on the sweep from the most positive potential to most negative potential.
  • a small minimum sometimes termed a shoulder
  • the underpotential at which deposition of the cadmium from the cadmium ions occurs onto the working electrode havi ng the silver nanoparticles adsorbed thereon was determined to be -0.46 V (vs Ag/AgCI).
  • the underpotential of the deposition of the elemental metal onto the nanoparticles may be determined by measuring the most positive potential at which collisions of the nanoparticles are observed using a potentiostat; i.e. the most positive potential at which spikes are observed, indicating charge transfer is occurring during collisions.
  • the potential at which the deposition of the elemental metal occurs on the working electrode in the absence of the nanoparticles can be determined in the same manner (as the underpotential at which deposition of the elemental metal occurs onto the nanoparticles when adsorbed onto the surface of the electrode), and under the same conditions, i.e. the nature and concentration of the metal ions in solution is the same, except that the electrode is free from adsorbed nanoparticles.
  • the potential at which deposition of the cadmium from the cadmium ions occurs on the bare glassy carbon working electrode i.e.
  • the potential applied to the working electrode is +/- 0.05 V, preferably +/- 0.025 V, of the potential at which the peak of maximum current is determined by adsorbing the nanoparticles onto the working electrode and placing it in the liquid carrier medium containing the metal ions (but not the nanoparticles), and carrying out a cyclic voltametry experiment by sweeping the voltage between set points either side of the standard electrode potential for the deposition of the metal from the metal ions in the solution onto the electrode; on sweeping from the most positive potential to the most negative potential, the peak of maximum current can be identified; the conditions in the cyclic voltametry, apart from the absence of nanoparticles in the liquid carrier medium, being the same as in the method.
  • the peak of maximum current was determined to be - 0.75 V.
  • the potential applied to the working electrode is at or more than the potential at which the peak of maximum current is determined by adsorbing the nanoparticles onto the working electrode and placing it in the liquid carrier medium containing the metal ions (but not the nanoparticles), and carrying out a cyclic voltametry experiment by sweeping the voltage between set points either side of the standard electrode potential for the deposition of the metal from the metal ions in the solution onto the electrode; on sweeping from the most positive potential to the most negative potential, the peak of maximum current can be identified; the conditions during the cyclic voltametry, apart from the absence of nanoparticles in the liquid carrier medium, being the same as in the method.
  • +/- 0.05 V of a potential X indicates that the potential is in the range of from X-0.05
  • the nanoparticles comprise silver, the metal of the metal ions in the liquid carrier medium is cadmium, and the method is carried out such that the potential at the working electrode in step (ii) is from about - 0.47 V to about - 0.75 V.
  • the liquid carrier medium is agitated during step (ii). This may be, for example, by passing a gas, for example an inert gas such as nitrogen, through the liquid carrier medium, preferably such that the gas passes near to and optionally contacts the working electrode.
  • the liquid carrier medium may be induced to flow past the working electrode.
  • a plurality of atomic layers of the elemental metal are coated onto the nanoparticles.
  • at least 5 atomic layers of the elemental metal are coated onto the nanoparticles.
  • at least 10 atomic layers of the elemental metal are coated onto the nanoparticles.
  • at least 15 atomic layers of the elemental metal are coated onto the nanoparticles.
  • the number of atomic layers deposited can be calculated by determining the amount of charge transferred to a nanoparticle during a collision with the electrode, by which method the number of electrons transferred can be calculated.
  • the amount of charge transferred per collision can be determined by plotting the current against time and integrating the period during a collision of a nanoparticle with an electrode (generally shown by a spike).
  • the surface area for a nanoparticle can also be calculated. From this, a monolayer coverage of the metal to be deposited, in terms of the number of atoms of this metal, can also be calculated. For example, as is illustrated in the Examples, a monolayer coverage of cadmium on a silver nanoparticle with fee geometry used in the Examples was calculated to be 10 5 atoms cadmium. Such calculations can be applied to other nanoparticles and metals to be deposited by analogy.
  • the conditions of the method are adapted such that, for at least some collisions, at least 1 x 10 "12 C is transferred per collision, optionally at least 1 x 10 "11 C is transferred per collision, optionally at least 1 x 10 "10 C is transferred per collision, optionally at least 2 x 10 "10 C is transferred per collision, optionally at least 3 x 10 "10 C is transferred per collision, optionally at least 4 x 10 "10 C is transferred per collision, optionally at least 5 x 10 "10 C is transferred per collision, optionally at least 1 x 10 "9 C is transferred per collision, optionally at least 1 x 10 "8 C is transferred per collision.
  • the collisions can be observed using a potentiostat, and, as mentioned above, the amount of charge transferred per collision can be determined by plotting the current against time and integrating the period during a collision of a nanoparticle with an electrode (generally shown by a spike).
  • the conditions of the method are adapted such that, for at least some collisions, at least 1 x 10 4 atoms of the metal are deposited from the metal ions in the liquid carrier medium per collision, preferably at least 1 x 10 5 atoms of the metal are deposited from the metal ions in the liquid carrier medium per collision, preferably at least 5 x 10 5 atoms of metal are deposited from the metal ions in the liquid carrier medium per collision, preferably at least 1 x 10 6 atoms of the metal are deposited from the metal ions in the liquid carrier medium per collision, preferably at least 2 x 10 6 atoms of the metal are deposited from the metal ions in the liquid carrier medium per the liquid carrier medium per collision, preferably at least 4 x 10 6 atoms of the metal are deposited from the metal ions in the liquid carrier medium per collision.
  • the method may be carried out at any suitable temperature and pressure.
  • the method is carried out at a temperature of from 0 °C to 50 °C, optionally from 10 °C to 30 °C.
  • the method is carried out at a pressure of from 90 kPa to 1 10 kPa, optionally from 95 KPa to 105 kPa, optionally from 98 kPa to 102 kPa.
  • the present invention provides a nanoparticle having a core comprising a first elemental metal and an electrochemical ly-deposited coating of a second elemental metal on the core, wherein the coating is in the form of a bulk deposit of the second elemental metal.
  • the nanoparticle of the fourth aspect may be producible in accordance with the method of the first aspect.
  • the first elemental metal may be the first metal as described above and the second elemental metal may be the second metal described above.
  • the core of the nanoparticle may be as described above for the nanoparticles, in step (i) of the method.
  • AgNPs Silver Nanoparticles
  • SEM imaging to have a mean radius of 45 nm, with the standard deviation being 3 nm (the mean radius is a number average over 300 or more nanoparticles in an SEM image of them; and the standard deviation is calculated as known in the art).
  • AgNPs were dispersed by ultrasound prior to their addition to the solution.
  • An aliquot of AgNPs was determined to give a particle density of 9 ⁇ 10 12 particles dm "3 in the volume of electrolyte used in the reaction cell.
  • the particle density was determined as follows:
  • the AgNP-modified GC electrode was placed into an electrochemical cell containing a suitable counter and reference electrode and electrolyte solution. An oxidative scan was then run, and the stripping voltammogram of the AgNPs being exhaustively oxidised from the surface into Ag + ions recorded.
  • GC electrode surface was determined using Faraday's Law. Knowing the approximate mean NP size and density of Ag, the number of atoms of Ag was converted into a number of AgN Ps. This provided the number of AgNPs in the original aliquot of 20 ⁇ _, from which the density in a dm 3 can be calculated.
  • Cadmium chloride and sodium chloride were used as received.
  • Deposition solutions were made of 1 mM CdCI 2 and 0.10 NaCI, using ultrapure water of resistivity ⁇ 18.2MQ.cm (Millipore) and degassed thoroughly with N 2 (oxygen free, BOC Gases pic) and an atmosphere of N 2 maintained during the experiment.
  • Figure 1 shows Cadmium deposition on a bare GC electrode (dotted lines, Example 1) a n d a Ag N P-modified GC electrode (solid lines, Example 2): (a) shows full voltammograms, whilst (b) shows only the underpotential deposition region.
  • Example 3 Impact transients were recorded for Example 3 and these are shown in Figure 2. The impact transients were observed as sharp, reductive spikes of duration 1-10 ms and peak heights of several nA, similar to those previously recorded for nanoparticle impact events [4,1 1-13]. Over one hundred impact spikes were recorded and analysed according to the procedure published in Zhou et al.
  • Figure 2 therefore, shows a) a typical impact transient at -0.55V, and b) a histogram showing the number of impacts in terms of layer coverage of an average AgNP.
  • the present inventors consider that the appearance of particles having an apparent coverage of ⁇ greater than 1 is in fact the monolayer or sub-monolayer coverage of clusters of AgNPs. This is in agreement with the findings in the paper by Zhou et al entitled Nanoparticle-Electrode Collision Processes: The Underpotential deposition of Thallium on Silver Nanoparticles in Aqueous Solution (ChemPhysChem).
  • Figure 3 shows a) a potential step-sweep experiment of a GC electrode (of radius 11 ⁇ ) in 1 mM CdCI 2 and 0.10M NaCI (Example 5).
  • the potential was held at -0.74V (vs Ag/AgCI) and scanned positive at 20 mV s ' (b) shows an enlargement of the "transient" region after noise reduction to confirm no spikes.
  • Example 6 The addition of aliquots of AgN Ps under the same conditions (Example 6) as for Example 5 resulted in numerous reductive collision spikes being recorded: these are illustrated in Figure 4. These spikes were considerably larger than those observed for UPD processes and were of the order of 10 "12 C per spike. In this case, Cd has clearly been deposited, due to the clear cadmium stripping peak observed in the anodic sweep. The charge passed under the Cd stripping peak was found to be ca. 6.5 x 10 "10 C (an average of 5 experiments): 6-60 times greater than the total charge passed under the impact spikes, leading to the conclusion that at -0.74V the majority of the Cd bulk deposition occurs at adsorbed AgN Ps. Analysis of the Ag stripping peak at +0.05V indicated that an average of 5.2 x 10 "10 C charge is passed, corresponding to ca. 168 single AgNPs.
  • Figure 4 shows similar information to Figure 3 (Example 5), except that 9 x 10 12 particles dm "3 of AgNPs is also present, (b) shows an enlargement of the "transient" region post-noise reduction.
  • Example 7 shows similar information to Figure 3 (Example 5), except that 9 x 10 12 particles dm "3 of AgNPs is also present, (b) shows an enlargement of the "transient" region post-noise reduction.
  • Example 7 shows similar information to Figure 3 (Example 5), except that 9 x 10 12 particles dm "3 of AgNPs is also present, (b) shows an enlargement of the "transient" region post-noise reduction.
  • Example 7 An experiment almost identical to that in Example 6 was performed, but at a potential of -0.73V: this is Example 7.
  • FIG. 5 shows (a) a potential step-sweep experiment of a GC electrode (of radius 1 1 ⁇ ) in 1 mM CdCI 2 and 0.10M NaCI (Example 7). The potential was held at -0.73V (vs Ag/AgCI) and scanned positive at 20 mV s "1 - no Cd stripping feature was observed; and (b) an enlargement of the "transient" region after noise reduction showing spikes. Analysis of the deposition spikes at -0.73V yielded a distribution of charges passed per impact, which can be converted into an approximate coverage of an average single nanoparticle using Equations 1 and 2 (as described above).
  • Figure 6 is a histogram showing the number of impacts in terms of layer coverage of an average AgNP. It sets forth the distribution of NP coverages confirming that multilayers of Cd are deposited onto the AgNPs during collision, i.e. a bulk deposit of Cd on the nanoparticles.

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Abstract

La présente invention concerne un procédé pour le revêtement électrochimique de nanoparticules, le procédé comprenant les étapes suivantes: (i) la fourniture d'une électrode de travail, d'une contre-électrode, et d'un milieu porteur liquide en contact avec l'électrode de travail, le milieu porteur liquide comportant: (a) les nanoparticules, les nanoparticules comprenant un premier matériau ; (b) des ions d'un métal dissout dans le milieu porteur liquide ; (ii) l'application d'un potentiel entre l'électrode de travail et la contre-électrode, de sorte que, au niveau de l'électrode de travail, les ions du métal soient réduits et qu'il y ait un dépôt de masse du métal élémentaire sur les nanoparticules. L'invention concerne également des nanoparticules fabriquées selon le procédé de l'invention. L'invention concerne en outre un appareil pour la mise en œuvre du procédé.
PCT/GB2012/051466 2011-06-23 2012-06-22 Nanoparticules revêtues et leurs procédés de production Ceased WO2012175990A1 (fr)

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Citations (2)

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