WO2014096556A2

WO2014096556A2 - Manufacture of noble metal nanoparticles

Info

Publication number: WO2014096556A2
Application number: PCT/FI2013/051201
Authority: WO
Inventors: Juha Rantala
Original assignee: INKRON Ltd
Current assignee: INKRON Ltd
Priority date: 2012-12-21
Filing date: 2013-12-23
Publication date: 2014-06-26
Anticipated expiration: 2015-06-21
Also published as: WO2014096556A3; EP2934793A2; EP2934793B1; FI126197B

Abstract

A method and an apparatus of extracting metal nanoparticles from electrolytic solutions containing metal ions through an electrochemical process on an electrode. The electrolytic solution undergoes potentiostatic pulse electrolysis in the presence of a first electrode and a second electrode, and the electrochemical nucleaction takes a place at the first electrode and the metal particles are extracted from the electrolytic solution. By means of the invention it is possible to produce nano-sized nobel metal or zinc particles in an efficient way.

Description

MANUFACTURE OF NOBLE METAL NANOPARTICLES

FIELD OF THE INVENTION The present invention relates to the manufacture of noble metal nanoparticles. In particular the present invention concerns a method of producing nanoparticles by electrodeposition.

BACKGROUND ART Electrodeposition provides a cost effective (G. Staikov, Electrocrystallisation in Nanotechnology, Wiley-VCH Verlag GmbH & Co KGaA, Weinheim, 2007) and non-equipment intensive method for the preparation of nanocrystalline and nanophase metallic materials (metals, alloys,

compositionally modulated alloys and composites) as free standing objects even in complex shapes. Electrodeposition can be used with conventional or modified electroplating baths and conditions to produce grain sizes in the range from essentially amorphous to micrometric. The production of nanostructured materials/nanoparticles by electrochemical procedures is very advantageous because of the crucial steps in nanocrystal formation, nuclei formation and nuclei growth, can be controlled by physical parameters i.e. current density, current characteristics and chemical parameters (grain refiners, complex formation) (Hatter et al., J. Phy. Chem. 100 (1996) 19525; Alfantazi et al., J. Mater. Sci. Letter, 15 (1996) 1361). Several groups have electrodeposited metallic nanoparticles on various substrates, such as glassy carbon (GC) (Isse et al., Electrochem. Commun. 8 (2006)), highly oriented pyrolitic graphite (HOPG) (Liu et al., Electrochim. Acta 47 (2001) 671-677), and indium doped tin Oxide (ITO) (Ueda et al., Electrochim. Acta 48 (2002) 377- 386).

The choice of electrodes is also an important aspect of the electrodeposition process. The reproducibility of results from electrodeposition experiments is quite poor when solid metal electrodes are used. Ultramicroelectrodes (UME) are the best tools to study concentrated electrolytes ( . M. Wightman, D. O. Wipf, "Voltammetry at Ultramicro-electrodes" in: A. J. Bard (Ed), Electroanalytical Chemistry, Vol. 15, Marcel Dekker, NY, 1988.). Ultramicroelectrodes arrays can be easily used in a commercial process and can be manufactured at low cost using well established methods. The usage of ultramicroelectrodes makes the electrodeposition process very efficient mostly due to the increase of mass transport of electroactive species. The application of ultrasound irradiation to electrochemistry process dates back to the early thirties (Moriguchi, J. Chem. Soc. Jpn, 55 (1934) 749-750). The fundamental basis of the pulsed sonoelectrochemical technique for the production of nanopowders is massive nucleation (Aqil et al., Ultrason Sonochem. 15 (2008) 1055-1061). The variety of induced effects on electrochemistry processes by ultrasound waves is attributed to the generation, growth and collapse of

microbubbles in the electrolyte.

The pulsed electrodeposition technique is a versatile method for the preparation of

nanostructured metals and alloys because this technique (Puippe and Leaman (Ed.), Theory and Practice of Pulse Plating, American Electroplaters and Surface Finishers Society, Orlando, Florida, 1986) allows for the preparation of large bulk samples with high purity, low porosity and enhanced thermal stability. This electrochemical process enables the adjustment of the nanostructure (grain-size, grain size distribution, microstress) which is responsible for physical and chemical properties. In this technique, metal nuclei are formed during a short nucleation pulse with a high overpotential. The nucleation pulse is followed by the growth pulse, where the nuclei slowly grow at low overpotential to their final size. Recently, gold nanoparticles have been prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron doped epitaxial 100-oriented diamond layers using a potentiostatic double pulse technique with a particle size in the range of 5 to 30 nm in case of HOPG. Also well-dispersed metallic nanoparticles in the mesoscopic range with average particle diameters of 50 nm and above and very narrow particle size distributions on HOPG (Penner et al., J. Phys. Chem. B 106 (2002) 3339-3353; Liu et al., 7. Phys.Chem. B 104 (2000) 9131-9139; Ueda et al., Electrochim. Acta 48 (2002) 377-386; Sandmann et al., 7. Electroanal. Chem. 491 (2000) 78-86) and indium tin oxide (ITO) could be obtained by a deposition method consisting of two potentiostatic pulses. It is possible to independently control the particle density and particle size using this technique. Recently, copper powders and nanopowders have been produced from industrial electrolytes by using

potentiostatic pulse electrolysis method (See US Published Patent Application No. 2012/0093680).

Besides the pulse electrodeposition technique, other synthesis techniques are of large industrial interest for the synthesis of metal nanoparticles. Recently, sol-flame synthesis has been used as a general strategy to decorate nanowires with metal oxide/ noble metal nanoparticles. The nanoparticle-decorated nanowires serve as a desirable structure for applications including batteries, dye-sensitized solar cells, photoelectrochemical water splitting and catalysis (Feng et al. 2012). Silver nanoparticles obtained by chemical reduction technique display appealing properties such as catalytic and antibacterial activity (Mukherjee et al., Nanoletters, 10 (2001) 515; Soudi et al. J. Colloid. Interface Sci. 275 (2004) 177) which open perspectives in medical applications (Chen, et al., Toxicol Letter 176 (2008) 1). Collodial PT NPS synthesized by reduction of H₂PtCI₂ in the presence of a citrate capping agent acts as a novel hydrogen storage medium (Yamauchi et al. Chem. Phys. Chem. 2009, 10:2566). Furthermore, Au NPS exhibit excellent optical properties (Hostetler et al. Langmuir, 14 (1998) 17). And also known for their high chemical stability, catalytic use and size dependent properties (Sardar et al., Langmuir, 25 (2009) 13840). Further applications of metal nanoparticles are inkjet printing with the use of inks. Most of the conductive inks at present are based on Ag NPS since Ag possesses the highest electrical conductivity among metals. Cu- NP based inkjet sets are of commercial interest due to its long term stability under ambient conditions (Magdass et al. NIP 25 and Digital Fabrication, Tech Program 2009 611-613, Grouchko et al. J. Mater. Chem. 19 (2009) 3057-3062).

Noble metal nanoparticles exhibit increased photochemical activity because of their high surface/volume ratio and unusual electronic properties. Noble metal nanoclusters in the nanometer scale display numerous interesting optical, electronic and chemical properties that depend on size enabling them for manifold applications in the development of biological nanosensors and optoelectronic devices. Also, inorganic nanoparticles especially bimetallic nanoparticles have attracted much interest among the broad scientific community since the catalytic properties and electronic structures of such nanomaterials can be tuned by varying their compositions and structures (Schmid et al., Angew Chem. Int. Ed. 30 (1991) 874; Joshima et al. Langmuir 1994, 104574. 1994; Sinfelt, J. Catal. 29 (1973) 308).

Currently, noble metal nanoparticles are produced by a series of different processes depending on the necessary product size and parts. Much attention has been devoted in recent years to develop methods of synthesizing monodispersed and size/shape controlled noble metal nanoparticles ( ioux et al., Topics in Catalysis 39 (2006) 167-174; Chen et al, Chemical Reviews, 110 (2010), No. 6, 3767-3804; Seo et al., 7. Am Chem. Soc. 128 (2006), No. 46, 14863-14870; Tao et al., Angewandte Chemie Int. Edn, 45 (2006), No. 28, 4597-4601). Many effective methods (physical and chemical) have been developed which include seeded growth by polyol reduction (Hoefelmeyer et al., Nanoletters, 5 (2005), No. 3, 435-438), thermolysis of organometallics (Park et al., Proceedings of the Combustion Institute 31 (2007) 2643-2652), modified polyol methods (Zettsu et al., Angewandte Chemie International Edition, 118 (2006), No. 46, 7988-7992), micelle techniques (Lee et al., Angewandte Chemie International Edition, 118 (2006), No. 46, 6990) and physical methods such as vapor deposition, laser ablation, grinding etc. Physical synthesis methods often require expensive equipment and can thus have a high initial cost. In the chemical methods, many anions, such as CI , N0₃ and S0₄ ² , often remain in the prepared solution and removal of these anions adds to the cost. Therefore, the development of low cost, low environmental load and high yield process is important for the synthesis of metal nanoparticles. Methods such as microemeulsion method yield narrow particle size distributions, but the variation of particle sizes is difficult. Sputtering followed by thermal treatment is a convenient deposition method allowing adjustment of different coverage, however the distribution of particle sizes is rather broad.

It is therefore of great industrial interest to have a production method which best combines cost efficiency and versatility.

Brief Summary of the invention

As is apparent from the above, there are considerable problems associated with the known technology. In order to address these issues, there is need for improved control of nanoparticle growth controlled by the composition of the deposition solution, deposition overpotential, actual overpotential at the electrode/electrolyte interface, current density and temperature.

Thus, it is an aim and to provide a novel method of producing of metal nanoparticles by electrodeposition. It is also an aim to provide an apparatus for producing such nanoparticles from metal containing electrolytes. It is further an aim to provide a method and apparatus for production of nanoparticles from polymetallic electrolytes,

The present invention is based on the idea of extracting metal nanoparticles from electrolytic solutions containing ions of the corresponding metals through an electrochemical process on an electrode, wherein the electrolytic solution is subjected to potentiostatic pulse electrolysis in the presence of a first electrode and a second electrode such that electrochemical nucleaction takes a place at the first electrode. Metal particles are extracted from the electrolytic solution. In an embodiment, metal particles having a maximum dimension of 1 micron or less, are produced from a first and a second salt in aqueous solution, the first salt comprising transition metal or semi-metal and the second salt comprising alkali metal or alkaline earth metals, and both of the salts further comprising N0₃ ^~, S0₄ ^2~, P0₄ ^3~, B0₃ ^3~, CI0₄ ^~, (COO)₂ ^2~ or halo. The aqueous is subjected to a voltage between electrodes such that transition metal or semi-metal particles are formed and dispersed within the aqueous solution, said particles having an average maximum dimension of less than 1 micron; and said particles are separated from the solution, e.g. by filtering.

The present invention provides an apparatus for producing metal nanoparticles by

electrodeposition of an electrolyte containing metal ions, comprising

- an electrolytic chamber for the electrolyte;

- means for providing a potentiostatic pulse electrolysis in the electrolytic chamber;

- an ultramicroelectrode cathode in the electrolytic chamber;

- an anode in the electrolytic chamber; and

- means for regulating the processing temperature of the electrolytic chamber.

More specifically, the present method is characterized by what is stated in the characterizing parts of claims 1 and 26, and the present apparatus is characterized by what is stated in the characterizing part of claim 33.

Considerable advantages are obtained by the present invention. Thus, the present invention provides for efficient production of metal particles, in particular of particles in one embodiment, nanoparticles, consisting at least to 95% or more of a desired element, are extracted from electrolytic solutions containing two or more metals or metal ions. In a further embodiment, nanoparticles of other elements, consisting at least to 95% or more of a desired element, are sequentially extracted from electrolytic solutions containing two or more metals or metal ions.

This allows for selective removal of the desired metal. In such an embodiment, it is possible to continue the process when the first metal has been removed by removing a second (and third etc.) metal. Thus, for example, it is possible first to remove Ag and then to continue by removing Cu in order to produce particles or either or both of said metal.

Brief Description of the Drawings

Figures 1A and IB show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 1;

Figures 2A and 2B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 2; Figures 3A and 3B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 3;

Figures 4A and 4B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 4;

Figures 5A and 5B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 5;

Figures 6A and 6B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 6;

Figures 7A and 7B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 7;

Figure 8 shows an SEM image of the Cu particles formed in Example 8;

Figures 9A and 9B show an SEM image of Cu particles formed and the rate of electrodeposition of particles as a function of energy (in keV) for Example 9;

Figure 10A and 10B show an SEM image of Ag particles formed and the rate of electrodeposition of said particles as a function of energy (in keV) for Example 10; and

Figure 11 shows an SEM image of Ag particles formed in Example 11.

Description of Embodiments The present invention relates to the manufacture of metal or metalloy nanoparticles from multimetal electrolytes/complex matrix industrial electrolytes by using potentiostatic pulse electrodeposition process. In particular the process is suitable for noble metals and transition metals. Examples include Ag, Sn, Cu, Au, and Ni; preferred are noble metals, such as Ag, Au and Pt, as well as transition metals, such as Sn and Ni. The invention further relates to an apparatus specifically adapted to the said process, to the metal nanoparticles obtained by the said process and the use of said metal nanoparticles.

As discussed above, the present technology comprises the steps of extracting metal nanoparticles from electrolytic solutions through an electrochemical process on an electrode, comprising that the metal ions containing electrolytic solution undergoes potentiostatic pulse electrolysis in the presence of a first electrode, which for example is an array electrode containing plurality of micrometer or sub-micrometer sized electrodes, and a second electrode. The electrochemical nucleaction takes a place at the first electrode and the metal particles are or extracted, preferably continuously, from the electrolytic solution. In one embodiment, nanoparticles, consisting at least to 95% or more of a desired element, are extracted from electrolytic solutions containing two or more metals or metal ions. The desired metal nanoparticles are formed through an electrochemical process on an electrode, wherein the electrolytic solution is subjected to potentiostatic pulse electrolysis in the presence of a first electrode and a second electrode such that electrochemical nucleaction takes a place at the first electrode. Metal particles, containing 95% or more of desired metal, can be extracted from the electrolytic solution leaving undesired metals in the electrolyte.

In a further embodiment, nanoparticles of other elements, consisting at least to 95% or more of a desired element, are sequentially extracted from electrolytic solutions containing two or more metals or metal ions. The desired metal nanoparticles are formed through an electrochemical process on an electrode, wherein the electrolytic solution is subjected to potentiostatic pulse electrolysis in the presence of a first electrode and a second electrode such that electrochemical nucleaction takes a place at the first electrode. Metal particles, containing 95% or more of desired metal, can be extracted from the electrolytic solution leaving undesired metals in the electrolyte. Once the first desired metal has been extracted, process parameters are adjusted to permit removal of a second or further elements.

In a preferred embodiment, metal particle extraction is achieved by combining potentiostatic pulse electrodeposition technique using ultramicroelectrodes (UME) and synchronized ultrasound in the presence of a megasonic transducer.

In one embodiment, the electrolyte is formed by metal ions and corresponding anions of a soluble metal salt in an aqueous medium. The electrolyte preferably additionally comprises an acid. It is particularly preferred to employ salts and corresponding acids. In advantageous embodiments, mineral acids and corresponding metal salts are employed such as hydrochloric acid and chlorides, or suitably nitric acid and nitrates of sulphuric acid and sulphates.

In one preferred embodiment, the electrolytic solution has a pH of less than 7. The pH lies in particular in the range from 1 to 6.

One embodiment of the invention relates to the formation of Ag nanoparticles on the stainless steel (SS) substrate. Metal in the form of nanopowders are deposited on the SS surface by potentiostatic pulse electrodeposition from a solution comprising metal nitrate and nitric acid. One of the pulse electrodeposition processes includes applying a number of electrical pulses having a pulse width. The number of electrical pulse cycles may be up to 400 and the pulse duration may be from 0-O.ls.

In another embodiment, the number of nanoparticles formed per unit area of the stainless steel surface may be affected by controlling the duration of electrical pulses used for deposition. The composition of the nanoparticles placed on the surface of SS substrate may be affected by controlling the chemical composition of the precursor solution.

One embodiment comprises producing nanoparticles of a Di₀o of less than 100 nm.

In one embodiment, only one type of the metals is extracted from the electrolytic solution.

In another embodiment, only one type of the metals is extracted from the polymetallic electrolytic solution selectively. In a preferred embodiment, several types of metals are sequentially and selectively extracted from the polymetallic electrolytic solution. The polymetallic solution may contain impurities as such or other metal salts may have been added in the solution to alter the electrolyte

conductivity. The number of electrical pulses or pulse cycles is, preferably, less than 450.

The electrolytic process comprises an ultrasonic or megasonic transducer.

In one preferred embodiment, the first electrode is a diode. For example, the diode is a photo diode. Further, one the first electrode is a diode, the first electrode passes the current once the diode is activated by a light.

In one embodiment, the potentiostatic pulse changes current direction. Generally, the anodic potential E_a can be about 2.5 V. The cathodic potential E_c can be about -1.0 V. In one embodiment, the pulse in the anodic potential is for a period (t_a) of about 0.1 s. The pulse in the cathodic potential is for a period (t_c) of about 0.1 s

In another embodiment, the potentiostatic pulse changes current direction. Generally, the anodic potential E_a is regulated to permit selective production of metal nanoparticles with elemental purity of 95% or more. The cathodic potential E_c can similarly be regulated. In one embodiment, the pulse in the anodic potential is for a period (t_a) of about 0.1 s. The pulse in the cathodic potential is for a period (t_c) of about 0.1 s

In one particular embodiment, the extracted metal nucleates does not adhere on the cathode and returns back to the plating solution as free particles or nanoparticles.

The present method makes it possible to regulate the size of the particles by simply adjusting the distance between the electrodes. Thus, in one embodiment, wherein the electrodes are spaced apart at a first distance in order to produce particles having a first size, the electrodes are shifted so as to be spaced apart at a second distance in order to produce particles having a second size, second size being greater than the first size when the second distance is smaller than the first distance.

The metal particles formed have an average maximum dimension of less than 1 micron.

In a particularly preferred method, the method is carried out in an apparatus for obtaining Ag or Sn nanopowders from industrial electrolytes through electrochemical deposition of Ag or Sn on the cathode. In the case of Ag, the electrolytic solution comprises Ag ions, for example at a concentration of about 5 g/L to 80 g/L. In the case of Sn, the electrolytic solution comprises Sn ions for example at a concentration of about 1.19 g/L to 45 g/L.

The apparatus comprises an electrolytic chamber (such as an ultrasonic bath as mentioned below) for the electrolyte; means for providing a potentiostatic pulse electrolysis; an ultramicroelectrode cathode, such as a microelectrode comprising of stainless steel; an anode for example comprising Pt coated titanium mesh plates; and means for regulating the processing temperature of the electrolytic chamber. Typically, the process is carried out at a temperature of about 5 to 90 °C, for example about 10 to 70 °C, in particular about 15 to 50 °C, for example 20 to 30 °C, or about 25 °C.

Another embodiment of the invention relates to a method of making Ag nanoparticles including performing pulse electrodeposition in a solution comprising of a nanoparticle precursor placed in an ultrasonic bath to form a metal powder/precipitate at the bottom of the electrochemical cell during the potentiostatic cycles and annealing the filtered precipitate to form the nanoparticles wherein the average diameter of Ag nanoparticles is capable of being arbitrarily controlled during processing from about 200 nm-325 nm. Another aspect of the invention is to produce Sn nanoparticles with particle sizes of up to 200 nm.

Formed or precipitate metal particles are separated from the electrodes. In order to avoid or mitigate entanglement of such particles to the electrodes for example ultrasound can be directed to the electrolyte or electrodes or both.

Based on the above, one embodiment for making metal particles, comprises the steps of

- mixing with water, together or separately,

a) a transition metal salt, and

b) a soluble conductivity enhancing compound, so as to form an electrolyte solution;

- providing the electrolyte solution between electrodes;

- performing potentiostatic pulse electrolysis so as to cause the formation of metal oxide particle at the first or second electrode;

wherein the metal oxide particles become separated from the first or second electrode back into the electrolytic solution; and

- separating the metal oxide particles from the electrolytic solution.

The electrolytic solution has a pH of less than 7, preferably a pH of from 1 to 6.

The potentiostatic electrolysis comprises a series of voltage pulses having a pulse width of less than 1 second, for example the pulse width is less than 0.5 second, in particular less than 0.1 second. The transition metal salt comprises a transition metal selected from Ni, W, Pb, Ti, Zn, V, Fe, Co, Cr, Mo, Mn and u. The transition metal salt is a nitrate, sulphate, carbonate, phosphate or halogen salt.

The soluble conductivity enhancing compound is an acid, in particular the conductivity enhancing compound is, for example, a water soluble acid, such as sulphuric acid, nitric acid, a chlorine containing acid, phosphoric acid or carbonic acid.

Alternatively, the soluble, conductivity enhancing compound is a halogen containing salt or acid. The soluble conductivity enhancing compound is a salt, for example .a transition metal salt comprises a late transition metal. Both the transition metal salt and the soluble conductivity enhancing compound may comprise the same nitrate, sulphate, carbonate, phosphate or halogen group element or ion derived therof. In another embodiment, a method for forming metal particles having a maximum dimension of less than 1 micron, comprises the steps of:

- adding into water a first salt comprising a metal or semi-metal;

- adding to water a second salt comprising an alkali metal or alkaline earth metal, wherein the first and second salts are added to water together or separately to form at least one aqueous electrolyte solution;

- providing the at least one aqueous electrolyte solution between an anode and cathode;

- providing an anode and cathode, and providing the at least one aqueous electrolyte

solution there between;

- providing electrical pulses through the electrolyte solution so as to form metal particles in the solution having a maximum dimension of less than 1 micron.

In still a further embodiment, a method of forming metal particles having a maximum dimension of 1 micron or less, comprises:

- providing to water a first salt having a) a transition metal or semi-metal, and b) a N0₃ ^~, S04², P0₄ ^3~, B0₃ ^3~, CI0₄ ^~, (COO)₂ ^2~ or a halogen group, and providing to water a second salt having a) an alkali metal or alkaline earth metal, and b) a N03, S04, P04, B03, CL04, (COOH)2 or a halogen group, so as to form an at least one aqueous solution;

disposing the aqueous solution between electrodes;

- providing a voltage across the electrodes such that transition metal or semi-metal

particles are formed and dispersed within the aqueous solution having an average maximum dimension of less than 1 micron; and

- filtering out the transition or semi-metal particles from the solution.

The first salt may comprise a noble metal and Y may be N0₃ ^~ or (COOH)₂.

The first salt may comprise Sn, or the first salt may comprise a metal selected from group 10 or group 11 of the periodic table.

The voltage provided across the electrodes is provided as alternating positive and negative potentials between the electrodes. Further ultrasound may be directed to the electrolyte solution.

The transition metal or semi-metal is Ag, Sn, Cu, Au, Cu or Ni. The alkali metal is Na or K.

The voltage is provided across the electrodes as a series of voltage pulses. Preferably the voltage pulses are provided as a series of alternating positive and negative pulses.

The particles formed are crystalline particles.

The following examples are given for illustrative purposes only. Example 1 A stainless steel plate serving as a cathode and a Pt-coated titanium mesh plate serving as a reference electrode (anode) were placed in an electrochemical cell. The width of the electrodes was: anode 1 mm, cathode 1 mm). The cathode and the anode were immersed at equivalent depth into the electrolyte yielding an area ratio of 1:1. The electrolyte consisted of 80 g/L of AgN0₃ and 120 g/L of HN0₃. The distance between the anode and cathode was adjusted to 2 cm.

The pulse cycle was as follows: E_a= 2.5V, t_a= 0.1 s, E_c= -1.0V, t_c = 0.1 s. A total of 400 cycles were run.

A precipitate formed during the electrodeposition on the cathode. The precipitate continuously settled toward the bottom of the electrochemical cell during the potentiostatic cycles. The precipitate was removed from the solution by filtration, dried and analyzed using SEM-EDS. The analysis confirmed that the precipitate was 100 % Ag and the smallest Ag- particles exhibited a size of ca. 300 nm, determined by SEM. The particle size was determined to be 1400 nm with a polydispersity index of 0.81 by DLS after re-dispersion and dilution.

Example 2

The procedure in Example 1 was repeated with an altered configuration. Into an electrochemical cell was placed a stainless steel plate serving as a cathode and a Pt-coated titanium mesh as a reference electrode (anode). The width of the electrodes was the same as in Example 1. The cathode and the anode were immersed to equivalent depth into the electrolyte yielding an area ratio of 1:2 resulting from the holes in the anode structure. The distance between the anode and cathode was adjusted to 3.5 cm. The electrolyte consisted of 80 g/L of AgN0₃ and 120 g/L of HN0₃. The electrolyte and the pulse sequence was held as in Example 1. The precipitate was removed from the solution by filtration, dried and analyzed using SEM-EDS. The analysis confirmed that the precipitate was 100% Ag and the smallest ag particles size determined by SEM- measurement was ca 200 nm. The particle size was determined to be 750 nm with a

polydispersity index of 0.90 by DLS after re-dispersion and dilution. The distance between anode and cathode has an influence on the particle size nucleation.

Example 3

The procedure in Example 2 was repeated. The electrochemical cell was placed in an ultrasonic bath during the nanoparticle synthesis. SEM-EDS analysis confirmed that the collected precipitate was 100 % Ag and the size of the smallest Ag-particles determined by SEM-measurement was ca. 200 nm. The particle size was determined to be 325 nm with a polydispersity index of 0.91 by DLS after re-dispersion and dilution. The ultrasound has an influence on the particles size and morphology Example 4

The procedure in Example 3 was repeated. The electrolyte was diluted to 5 g/L of AgN0₃ and 15 g/L of HNO3. The electrochemical cell was placed in an ultrasonic bath during the nanoparticle synthesis. The cathode and the anode were immersed to equivalent depth into the electrolyte yielding an area ratio of 1:2 SEM-EDS analysis confirmed that the collected precipitate was 100 % Ag and the smallest Ag-particles size determined by SEM-measurement was ca 200 nm. The particle size was determined to be 325 nm with a polydispersity index of 0.91 by DLS after re- dispersion and dilution. Example 5

The procedure in Example 4 was repeated. The electrolyte was diluted to 5 g/L of AgN0₃ and 15 g/L of HNO3. The electrochemical cell was placed without ultrasonic bath during the nanoparticle synthesis. SEM-EDS analysis confirmed that the collected precipitate was 100 % Ag and the smallest Ag-particles size determined by SEM-measurement was ca. 200 nm. The particle size was determined to be 164 nm with a polydispersity index of 0.81 by DLS after re-dispersion and dilution.

Example 6

Into an electrochemical cell was placed a stainless steel plate serving as a cathode and a Pt-coated titanium mesh plate as a reference electrode (anode). The width of the electrodes was (anode 1 mm, cathode 1 mm). The cathode and the anode were immersed to equivalent depth into the electrolyte yielding an area ratio of 1:2. The electrolyte consisted of = 45g/l Sn 120g/l H₂S0₄. The distance between the anode and cathode was adjusted to 3.5cm. The pulse cycle was as follows: E_a= 2.5 V, t_a= 0.1 s, E_c= -1.0 V, t_c= 0.1 s. A total of 400 cycles were run. A precipitate formed during the electrodeposition at the cathode. The precipitate continuously settled toward the bottom of the electrochemical cell during the potentiostatic cycles. The precipitate was removed from the solution by filtration, dried and analyzed using SEM-EDS. The analysis confirmed that the precipitate was 97 % Sn and its smallest particle had a size, determined by

SEM, to be ca. 200 nm. The particle size was determined to be 740 nm with a polydispersity index of 0.81 by DLS after re-dispersion and dilution.

Example 7

The procedure of Example 6 was repeated. The electrolyte was diluted to Sn 1.1 g/l + 2.9 g/l H₂S0₄. The electrochemical cell was placed with ultrasonic bath during the nanoparticle synthesis. SEM-EDS analysis confirmed that the collected precipitate was 40 % Sn (ca. 50 % impurities due to the dissolution of anode and cathode material during the electrodeposition, see EDS-curves) and the size of the smallest Sn-particles was determined, by SEM-measurement, to be ca. 100 nm. After re-dispersion and dilution, the particle size was determined to be 1240 nm with a polydispersity index of 0.81 by DLS.

Example 8

An electrolyte solution of CuS0₄ in aqueous H₂S0₄ was prepared by weighing 200g of CuS0₄-5H₂0 and 240g of concentrated H₂S0₄ into de-ionized water and the total volume was diluted to 3L. A stainless steel plate serving as a cathode and a Pt-coated titanium mesh plate serving as a reference electrode (anode) were placed in an electrochemical cell. The width of the electrodes was: anode 1 mm, cathode 1 mm). The cathode and the anode were immersed at equivalent depth into the electrolyte yielding an area ratio of 1:1. The distance between the anode and cathode was adjusted to 5 cm. The pulse cycle was as follows: E_a= 2.5V, t_a= 3 ms, E_c= -1.0V, t_c = lms. A precipitate formed during the electrodeposition on the cathode. After 2min, the precipite was collected, washed with water, dried and analyzed using SEM-EDS. The analysis confirmed that the precipitate was 100 % Cu and the diameter of smallest Cu-particles were less than 100 nm, determined by SEM. Example 9

An electrolyte solution containing CuS0₄ was prepared by weighing lOOg of a enriched ore and allowing the components to dissolve in 300g of 8% aqueous aqueous H₂S0₄. Main elements in this ore were Cu (673 mg/g), Al (7 mg/g), Fe (31 mg/g), Mg (2 mg/g) and Zn (1 mg/g). The process in example 8 was repeated for 3h. A precipitate formed during the electrodeposition on the cathode. After 2min, the precipitate was collected, washed with water, dried and analyzed using SEM-EDS. The EDS analysis confirmed that the precipitate was pure Cu.

Example 10

The procedure in Example 2 was repeated. The electrolyte consisted of 20 g/L of AgN0₃ and 30 g/L of HN0₃. CuS0₄ was added into the electrolyte as an impurity to obtain a 20% metal ion impurity level. The electrolyte and the pulse sequence was held as in Example 1 and the experiment was carried out for 3h. The precipitate was removed from the solution by filtration, dried and analyzed using SEM-EDS. The EDS-analysis confirmed that the precipitate was pure Ag.

Example 11

An aqueous electrolyte solution containing 20g/L Ag (as nitrate) and 40g/L of KN03 was prepared. The pulse cycle was as follows: E_a= 2.5V, t_a= 3 ms, E_c= -1.0V, t_c = lms. The precipitate formed was removed from the solution by filtration, dried and analyzed using SEM-EDS. The EDS-analysis confirmed that the precipitate was pure Ag. References:

Patent Literature: US Published Patent Application No. 2012/0093680). Non Patent Literature:

G. Staikov, Electrocrystallisation in Nanotechnology, Wiley-VCH, Verlag GMBH & Co KGaA, Weinheim, 2007.

Hatter et al., J. Phy. Chem. 100 (1996) 19525.

Alfantazi et al., J. Mater. Sci. Letter, 15 (1996) 1361.

Isse et al., Electrochem. Commun. 8 (2006).

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Claims

1. A method of extracting metal nanoparticles from electrolytic solutions containing metal ions through an electrochemical process on an electrode, wherein the electrolytic solution undergoes potentiostatic pulse electrolysis in the presence of a first electrode and a second electrode, and the electrochemical nucleaction takes a place at the first electrode and the metal particles are extracted from the electrolytic solution.

2. The method of claim 1, wherein the metals are extracted from the electrolytic solution as a powder or nano powder.

3. The method of claim 1 or 2, wherein the first electrode is an array and contains a plurality of micrometer or sub-micrometer sized electrodes.

4. The method of any of claims 1 to 3, wherein the ultramicroelectrode is a static

ultramicroelectrode

5. The method of any of claims 1 to 4, wherein the nanopowder comprises at least one of the metals silver, gold and tin.

6. The method of any of the preceding claims, wherein the nanoparticles are less than Di₀o 100 nm.

7. The method of any of the preceding claims, wherein only one type of the metals is extracted from the electrolytic solution selectively.

8. The method of any of the preceding claims, wherein the metallic nanoparticle composition is determined by the chemistry of the electrolytic bath.

9. The method of any of the preceding claims, wherein the number of electrical pulses or pulse cycles is less than 450.

10. The method of any of the preceding claims, wherein the electrolytic process comprises an ultrasonic or megasonic transducer.

11. The method of any of the preceding claims, wherein the first electrode is a cathode and the second is an anode.

12. The method of any of the preceding claims, wherein the first electrode is a diode.

13. The method of claim 12, wherein the diode is a photo diode.

14. The method of any of the preceding claims, wherein the first electrode is a diode and the first electrode passes the current once the diode is activated by a light.

15. The method of any of the preceding claims, wherein the electrolytic solution extracted metal is an alloy.

16. The method of any of the preceding claims, wherein the potentiostatic pulse changes current direction.

17. The method of any of the preceding claims, wherein the anodic potential E_a is about 2.5 V

18. The method of any of the preceding claims, wherein the cathodic potential E_c is about -1.0 V

19. The method of any of the preceding claims, wherein the pulse in the anodic potential is for a period (t_a) of about 0.1 s.

20. The method of claim 19, wherein the pulse in the cathodic potential is for a period (t_c) of about 0.1 s

21. The method according to any of the preceding claims, wherein the extracted metal nucleates does not adhere on the cathode and returns back to the plating solution as free particles or nanoparticles.

22. The method according to any of the preceding claims, wherein the electrodes are spaced apart at a first distance in order to produce particles having a first size and then the electrodes are shifted so as to be spaced apart at a second distance in order to produce particles having a second size, second size being greater than the first size when the second distance is smaller than the first distance.

23. The method according to any of the preceding claims, comprising producing Ag or Sn nanopowders from industrial electrolytes through electrochemical deposition of Ag on the cathode, comprising an electrolytic solution of Ag ions of a concentration of 5 g/L - 80 g/L, based on the weight of the corresponding Ag salt, or an electrolytic solution of Sn ions of a

concentration of 1.19 g/L - 45 g/L based on the weight of the corresponding Sn salt.

24. The method according to any of the preceding claims, comprising producing metal, for example Ag or Sn, nanoparticles including performing pulse electrodeposition in a solution comprising of a nanoparticle precursor placed in an ultrasonic bath to form a metal powder or precipitate at the bottom of the electrochemical cell during the potentiostatic cycles and annealing the filtered precipitate to form the nanoparticles.

25. The method according to claim 24, wherein the average diameter of Ag nanoparticles is about 200 nm-325 nm, and the average diameter of Sn nanoparticles is up to 200 nm.

26 A method of forming metal particles having a maximum dimension of 1 micron or less, comprising:

providing to water a first salt having a) a cation selected from transition metal and semi- metal ions, and b) an anion selected from N0₃ ^~, S0₄ ^2~, P0₄ ^3~, B0₃ ^3~, CI0₄ ^~, (COO)₂ ^2~ and ions of a halogen group element, and providing to water a second salt having a) a caion selected from alkali metal and alkaline earth metal ions, and b) an anion selected from N0₃ ^~, S0₄ ^2~, P0₄ ^3~, B0₃ ^3~, CI0₄ ^~, (COO)₂ ^2~ or a halogen group, so as to form an at least one aqueous solution;

disposing the aqueous solution between electrodes;

providing a voltage across the electrodes such that transition metal or semi-metal particles are formed and dispersed within the aqueous solution having an average maximum dimension of less than 1 micron; and

filtering out the transition or semi-metal particles from the solution.

27 The method according to claim 26, wherein the first salt comprises a noble metal and Y is N0₃ ^~ or (COO)₂ ^2~.

28. The method according to claim 26 or 27, wherein the first salt comprises Sn, or the first salt comprises a metal selected from group 10 or group 11 of the periodic table.

29. The method according to any of claims 26 to 28, wherein the voltage provided across the electrodes is provided as alternating positive and negative potentials between the electrodes.

30. The method according to any of claims 26 to 39, further comprising providing ultrasound to the electrolyte solution.

31. The method according to any of claims 26 to 30, wherein the transition metal or semi-metal is Ag, Sn, Cu, Au, Cu or Ni.

32. The method according to any of claims 26 to 31, wherein the alkali metal is Na or K.

33. An apparatus for producing metal nanoparticles by electrodeposition of an electrolyte containing metal ions, comprising

- an electrolytic chamber for the electrolyte;

- an ultramicroelectrode cathode in the electrolytic chamber;

- an anode in the electrolytic chamber; and

- means for regulating the processing temperature of the electrolytic chamber.

34. The apparatus according to claim 33, wherein the ultramicroelectrode cathode, comprises a microelectrode of stainless steel

35. The apparatus according to claim 33 or 34, wherein the anode comprises Pt coated titanium mesh plates.