SE1100140A1 - Methods for producing metallized carbon nanoparticles - Google Patents

Abstract

Methods for modifying dispersed carbon nanoparticles using electrochemistry are described. First, a dispersion of CNT, graphene, graphite or the like is prepared in water or organic solvent. Then said dispersion is contacted with a solution of ionic compounds in a liquid, such as dissolved metal salts in water, where the dispersion of carbon nanoparticles is in electrical contact with one electrode, typically the minus pole, and the second solution is in contact with a second electrode , typically plus-poland. The most practical voltage for converting metal salt to each metal is between 0 and 10 volts. This voltage can be applied continuously or at intervals, such as every millisecond with a pause of one millisecond. A practical method is to pump the dispersion of carbon nanoparticles and allow it to flow into the second liquid in the form of growing droplets, similar to the dripping mercury electrode. After the electrochemical metal deposition, metallized carbon nanoparticles can be separated and used in various products such as composites, coatings, capacitors, cables and other products.

Description

The invention describes methods which make it possible to produce MCNP by electrochemical treatment of CNP dispersions in the presence of another liquid containing ionic compounds such as metal salts. The method involves the following steps: a) an electrically conductive dispersion of CNP is prepared, b) the CNP dispersion is contacted with an electrode for transporting electric current), c) the CNP dispersion is also contacted with another liquid, namely a solution of ionic compounds which in turn are in contact with the opposite electrode. The two mentioned electrodes are not in direct contact with each other through a homogeneous phase, d) an optional variable current is conducted between the electrodes so that the dissolved ionic compounds can be discharged, especially so that metal cations can be discharged and converted into pure metal in the vicinity of the electrode. the conductive CNP dispersion, e) the products containing MCNP are separated from the mixture of the dispersion and the solution of ionic compounds for purification, isolation for use, including reuse by electrochemical treatment.

The products thus obtained are metallized CNP or MCNP. Without wishing to speculate in terms of theory, the products can be nano-shaped metal wire, metallized CNPs, CNPs that carry metal clusters on the tips of CNTs, or mixtures of different conceivable products containing CNP and pure metal. The products may also contain functionalized CNPs such as oxidized or chlorinated CNPs, especially where the conductive dispersion has been in contact with the plus pole of the baffle, ie if anions such as sulfate or chloride have been discharged in the vicinity of the CNP dispersion.

A simple embodiment involves the dispersion of CNP in, for example, paraffin oil or silicone oil, and electrochemical treatment with another liquid, eg copper sulphate dissolved in water. The oil and water phases are separated by an interface. If an electric current is conducted through the electrodes located in each phase, copper metal is deposited in the vicinity of the CNP or CNT.

Careful agitation of the oil phase or both phases makes it possible to transport the MCNP away from the interface and into the oil phase. MCNP is separated and isolated, or further processed after the deposition of the desired amount of metal.

A preferred embodiment involves pumping the conductive dispersion of CNP through hollow stainless steel needles. The outside of the needles are coated with an electrically insulating material. The dispersion is typically in contact with the minus pole of a power supply, usually 1-10 V DC. The voltage can be applied in the pulse form, eg On for 1 millisecond (ms), Off for 1 ms, and so on, see below. The electrically conductive dispersion of CNP forms droplets on the tip of the needles, and since the dispersion is pumped through the needle, the surface of the droplets is constantly renewed. The dispersion is pumped into another liquid containing ionic compounds (eg copper sulphate CuSO4 in water). This second fluid is in contact with the opposite electrode, typically the plus pole of the power supply. In this arrangement (taking CuSO4 as an example), copper metal is formed because copper ions are discharged at the interface between the CNP dispersion and the other liquid. At the same time, oxygen is formed by oxidation on the counter electrode. The high field strength at the CNT tips leads to metal deposition mainly there, and further growth of copper is the preferred follow the deduction.

To achieve a more uniform growth, or even metal deposition on all CNPs, the interface is renewed at a certain speed so that unmodified CNPs reach the interface, and in addition the biasing unit can be pulsed at certain intervals, eg 1000 Hz or other suitable frequency. Growing droplets of CNP dispersion eventually fall from the needle - or they rise from the needle in case the solvent is lighter than that used for the other liquid - and are then no longer in contact with the power supply, so that electrochemical metal deposition ceases. These droplets can be separated from the other liquid by different methods, depending on the solvents used. Practical methods are phase separation, centrifugation, decantation, filtration, solvent removal through membranes, washing of filtration cake, drying, etc. Some of the product can be returned to the metallization process.

The products obtained (MCNP) differ from CNP in that they contain a certain amount of metal which may vary, for example from the ppm (parts per million on weight) level to 100% or more.

Low levels of metal content (especially platinum, rhodium, silver, nickel, etc.) are typically practical for applications such as catalysis. Intermediate metal concentrations (such as copper, zinc, tin, lithium, etc.), for example at the percentage level, already increase the CNP bulk conductivity and change the electronic properties of the CNP. Different metals differ in electronegativity, therefore combinations of MCNP with different metals show the properties of pn junctions. High metal contents (eg copper), such as many percent, increase the bulk conductivity of CNP significantly, therefore it is advantageous to use MCNP in all applications where the already high conductivity of CNP is used. Such products include heating foils, conductors, both direct and special alternating current, electrical connections, cables, sensors, batteries, capacitor foils and super-capacitors.

Examples and Preferred Embodiments: 1. Preparation of Dispersions: Electrically conductive dispersions of CNP can be easily produced by applying very strong ultrasound to CNP agglomerates in a liquid such as water, alcohol, ketone, paraffin, silicone oil, epoxy, amine, ester or the like. . 0.5-1.5% by weight of CNT, commercially available for example from Bayer under the trade name Baytubes TM, can be dispersed by ultrasound within 5-30 minutes so that a resistance of 100-1000 Ohm is obtained (simple measurement between two electrodes, 1 cm distance, standard Ohm measuring device). These dispersions may, depending on the circumstances, contain additives, for example to regulate viscosity, to prevent re-agglomeration, or as preparation for later (after metallization) steps in product manufacturing. "Fumed silica" increases the viscosity. Cellulose, especially in micronized or nano-forms, stabilizes CNP and prevents re-agglomeration but slightly reduces the electrical conductivity of especially CNT. 2. Different reactors, two phases, stirring or needles: In a simple embodiment, the CNP dispersion and the solution of ionic compounds can be two different and incompatible phases. Electrochemical metal deposition therefore takes place at the interface from which MCNP can be isolated in dispersed form or as fi lm / thin film. The two phases can be stirred. In a more complex embodiment, the CNP dispersion is pumped into the second liquid, for example through a hollow needle or a plurality of hollow needles or channels.

If using incompatible phases, such as CNP in silicone oil and CuSO4 in water, it is practical to pump up the dispersion (from below) to form growing droplets where the surface is constantly renewed. As long as the droplets are in contact with the dispersion, electrochemical deposition takes place, but over-deposition is prevented as the surface is renewed.

Finally, the droplet leaves the dispersion and fl surfaces up (because the droplet has a lower density than the aqueous phase), and then metal deposition on the droplet also ceases. During treatment, the aqueous solution can also be stirred or pumped to prevent ion depletion. The dispersion may be based on the same fl uid as the other solution containing ionic compounds. In this case, a mixture takes place at the interface (shall be understood as the interface between different concentrations of CNP and ionic compounds), but the metal deposition is nevertheless effective. It is also possible to pump the second solution into the CNP dispersion, so that the second solution forms growing droplets, but in many practical cases the above-mentioned method is preferred.

. Different solvents, different metals: The following solvents are very practical for CNP dispersions: silicone oil, eg AK 50 from Wacker, paraffin oil (especially paraffins with 4-20 carbon atoms), ester, eg alkyl acetate, glycol. eg Carbitol TM, amines, arninester, eg Desmophen TM NH 1420 from Bayer, alcohol such as isopropanol, ketone such as acetone or MEK, epoxides and diepoxides as starting materials for epoxy composites, and water. The second liquid is preferably water containing water-soluble metal salts, where the metal especially includes copper, zinc, iron, chromium, noble metals such as gold, nickel, platinum, etc., but also alkali-alkaline earth and transition metals. Copper is generally suitable for improving the electrical conductivity of all CNPs. Nickel, platinum, rhodium, silver, etc. are metals suitable in the catalytic field. Zinc and copper are suitable for conductive coatings and coatings for anti-corrosive purposes. In some cases it is desirable to use solvents other than water.

. Dispersion on the plus (pole) - for oxidation: In one embodiment, the CNP dispersion is in contact with the Plus pole of the baffle, and the other solution is in contact with the minus pole and contains sulfate or chloride ions. The electrochemical discharge leads to the formation of oxygen or chlorine in a very reactive form. This means that CNPs are oxidized and halogenated, respectively.

. Dispersion on minus (pole) - H2SO4 or other acids such as medium, hydrogen, reduction: In one embodiment, an acid such as sulfuric acid is used as the ionic compound in the other solution. The CNP dispersion is in electrical contact with the negative pole. Electrochemical treatment causes hydrogen atoms to form in the vicinity of the CNP and thus causes a chemical reduction of the CNP. This chemical reduction of CNP improves the electrical conductivity of CNP, and the products are therefore suitable for the production of (among other things) transparent electrodes for photovoltaic purposes. Graphene in particular is often available as oxidized graphene, and the electrochemical treatment according to the invention is very suitable for increasing the conductivity of graphene oxide.

. Voltage units: For deposits of metal, voltages between 0-10 V are particularly suitable. Higher voltages than the theoretically necessary potential differences are suitable for overcoming surges ("überspannung") and for increasing the metal deposition rate. Constant voltage can lead to local metallization, probably as a consequence of the lower resistance in areas where metal has already been deposited. This can happen even if the surface is constantly renewed, as in the example where the droplets are formed from (ie pumped through) needles. In such cases, it is a preferred method to pulse the voltage in intervals, eg On for 1 ms and Off for 1 ms. The most practical frequency and the length of the On / Off periods can vary greatly, and depend on the solvent, metal salts, the desired polydispersity (evenness and statistical variation in the metallization) and other parameters. 7. Separation: After metallization or other electrochemical modification (eg reduction, oxidation, halogenation), MCNP must be cleaned for the next step or use in the final product. If incompatible phases have been used, it is practical to phase separate, for example, the oil and water phases, and to concentrate MCNP, for example by centrifugation, continuous decanting, washing with solvent or the like. If the phases were compatible, as in the example where both (CNP) dispersion and the other liquid were aqueous, the following methods are practical: centrifugation, decantation, filtration.

Additional water extraction is suitable for removing metal salt or acids. Some MCNPs can again be used for further electrochemical treatment. The products can be dried, washed, concentrated by solvent distillation, they can be dispersed in other solvents or further processed by known methods. 8. The product examples: In one embodiment, MCNP (where the metal is preferably copper) is used as the conductive component in electric heating foils, where silicone rubber is preferred as the surrounding matrix. A practical composition for a preferred use, de-icing for wind turbine blades, is 30-90% by weight silicone rubber, 5-50% by weight carbon black, 0.1-10% by weight MCNP and 5-30% by weight fillers such as fumed silica.

MCNP provides higher volume conductivity than CNP, therefore the heating foil can be made thinner than without the addition of MCNP. The twine foil is preferably covered by a thin (eg 100 micrometers) gelcoat, based on epoxy or polyurethane, on the upper side (to the outside, against the wind). The heating foil is preferably covered by a thermally insulating layer such as gelcoat in foam form on the underside. The heating foil may have holes so that the two gelcoat layers can be crosslinked. The lower gel coat can in turn be covered with a self-adhesive tape that can be used to upgrade existing wind turbines or similar installations.

In one embodiment, MCNPs based on CNP dispersions with cellulose, especially micronized or nanocellulose, are used as raw materials for conductive paper-like sheets. For this, 2 parts of cellulose, 1 part of CNT, graphene, cones, discs, etc. and optionally a quantity of fumed silica are mixed, and dispersed in water or alcohol.

The dispersion is electrochemically treated to deposit metals such as copper, silver, zinc, nickel, etc. on the dispersed and preferably cellulose-coated CNPs. (The obtained) MCNP dispersion is washed, excess metal salt is removed, the dispersion is filtered and spread for drying in the form of leaves of any length and thickness (eg between 10 and 50 micrometers). The dried paper is useful as a capacitor foil.

Incorporation of other metals such as lithium opens up for use as a battery component.

In one embodiment, hydrogenated CNPs, i.e. CNPs, which have been subjected to hydrogen atoms formed by electrochemical reduction of H + or H3 O + (acid in water), are used as raw material for transparent electrodes in a photovoltaic device.

In one embodiment, two different types of MCNP are combined, eg MCNP based on zinc and MCNP based on copper, in thin film or layers. Such a combination shows properties of p-n junctions, ie the resistance through the double layer is dependent on the polarity.

In one embodiment, the MCNP is used to transport electrical current. MCNP shows an even lower "percolation threshold" than the CNPs on which the said MCNP is based.

The resistance is also very pressure dependent, especially if it is measured in an elastic medium (matrix) such as rubber. Very low resistance is measured if you compress the rubber / MCNP combination. Furthermore, the resistance to high frequency alternating current, especially with frequencies above 1 MHz, is extremely low. Electrical conductivity (by MCNP) can be used in analytical chemistry, where the falling mercury electrode (potentiometry) can be replaced by falling CNP or MCNP drip electrodes. These are also useful in unusual solvents. The CNP dispersion can be used in synthetic electrochemistry as a substitute for surface mercury, for example in a modification of the chlor-alkali electrolysis process. CNP and MCNP are directly useful as catalysts in electrochemical reactions. Electron transport through the CNT tips gives very high current density locally, therefore reactions that require a very high current density can take place at the interface of the CNP (especially CNT) dispersion. An example (of such a reaction) is the formation of peroxodisulfate (S2082-) from two sulfate ions (SO42-).

In one embodiment, MCNPs are used as components in coatings and paint. Zinc MCNP and copper MCNP are both useful in marine paint / coating, the first as an anti-corrosion agent, the second as an anti-fouling additive. MCNP as an additive generally gives some conductive color, with the advantage that the corrosion protection is better because the contact with the sacrificial anode is better. MCNP also protects against radiation.

In one embodiment, MCNP is used as a reinforcing additive in composites. MCNP shows significantly stronger adhesion to or compatibility with common matrix materials such as epoxy, polyurethane, PET and other preferably polar plastics and "thermoset" s.

Therefore, composites with MCNP show higher tensile strength and higher resistance to fatigue (or fatigue) compared to composites based on the respective CNP.

Pure MCNP can be compressed and heated to melt the metal phase. As a product, a metal / CNP nano-composite with mechanical properties between the pure metal and CNP results. This opens up for uses in ballistic and similar protection. Similarly, MCNP, preferably with metals such as nickel, silver, platinum, rhodium, iron, manganese, etc., can be formed into larger structures such as a mesh, optionally with a supporting structure, which can be used as a catalyst or catalyst support for chemical reactions.

In one embodiment, relatively large amounts of metal, such as twice the weight of the dispersed CNPs, are deposited on or near the CNP. At the same time, a low pump speed is used so that the growth of metal through electrochemical deposition is favored where growth has already begun.

Highly metallized CNP is available as a product that can be used where the traditional way metal nano wires have been used, eg sensors or in applications described above.

This list should not be construed as complete or limiting as far as possible applications are concerned.

Advantages of the invention: The described methods make it possible to produce MCNP using a simple, safe and efficient technology. The production process can be scaled up in a simple way. The products can be used in many areas, such as nano-technology, electronics, catalysis, photovoltaics, composite materials, coatings, energy storage, etc. Compared to CNP used today in these applications, and compared to CNP on which the respective MCNPs are based, MCNP shows higher electrical conductivity, higher thermal conductivity, less tendency to re-agglomeration, better compatibility with most plastics and thermosets and therefore better ability to strengthen composite systems.

Due to the metal content, MCNP enables new effects, such as the formation of p-n junctions after the combination of two different MCNPs, or catalysis.

The method makes it possible to produce MCNP with high productivity and specific deposition of the desired metal compared to electroplated deposition (“electroless plating”).

Solvents for the CNP dispersion and additives can be selected with only a few limitations so that electrochemically treated dispersions can be used fairly immediately, possibly after washing and drilling of unwanted salts and water, and converted to final product according to the examples above.

Compared to the prior art (US 2010/0122910), the method avoids unwanted co-deposition of metal and CNT on an electrode. With this invention it is possible to metallize only the nanoparticles.

Claims (1)

A method of producing MCNP (Metallized Carbon Nano Particles) by electrochemical treatment of dispersions of CNP (Carbon Nano Particles, such as carbon nanotubes, graphene cones, disks, sheets, carbon black, gray) in the presence of a second liquid containing ionic compounds such as metal salts, the method comprising the following steps: a. an electrically conductive dispersion of CNP is prepared, b. the CNP dispersion is contacted with an electrode for transporting electric current), c. The CNP dispersion is also in contact with another liquid, namely a solution of ionic compounds which in turn are in contact with the opposite electrode. The two mentioned electrodes are not in direct contact with each other through a homogeneous phase, d. An optional variable current is conducted between the electrodes so that the dissolved ionic compounds can be discharged, especially so that metal cations can be discharged and converted to pure metal in the vicinity of the conductive The CNP dispersion, i.e. the products containing MCNP are separated from the mixture of the dispersion and the solution of ionic compounds for purification, isolation for use, including reuse by electrochemical treatment. A method according to claim 1 characterized in that the CNP dispersion is prepared using silicone oil, paraffin or ester oil, or an organic solvent such as isopropanol, or leaching raw material for epoxy or polyurethane polymer including epoxy, arnine, amine ester, or water, or mixtures of these, and that optionally other additives are used and dispersed together with CNP such as fumed silica, cellulose, glycol, TiO2 (titanium dioxide) powder and others. . A method according to claim 1 or claim 2 characterized in that the second liquid according to claim 1c) is preferably water, and that the ionic compounds are water-soluble salts of metals including copper, zinc, sodium, potassium, calcium, palladium, platinum, rhodium, iron , nickel, manganese, silver, or mineral acids such as sulfuric acid. A method according to any one of claims 1-3 wherein either the dispersion (1a) or the second liquid (1c) is pumped into the second liquid, preferably through at least one hollow needle or a plurality of needles, so that the contact surface between the dispersion and the second liquid constantly fömyas and is as large as possible. . A method according to any one of claims 1-4 wherein the dispersion is in contact with the negative pole of a direct current voltage supply and where the second liquid is in contact with the positive pole of the same voltage supply, and where the preferred voltage is between 0-20 V, preferably between 0 -10 V, and where the voltage can be pulsed (Off and On) at a certain frequency, for example at 100 or 1000 Hz, and where the arrangement is used to deposit metal on or near the CNP, or used to produce reactive hydrogen atoms for chemical reduction of CNP. A method according to any one of claims 1-5 wherein the dispersion is in contact with the positive terminal of the power supply (according to claim 5), and wherein the arrangement is used to form reactive oxygen or halogen atoms on or near the CNP, to effect an electrochemical oxidation, halogenation or functionalization of CNP where functionalization also includes chemical derivatization using alcohol, amine, acid, epoxide and isocyanate. A method according to any one of claims 1-6 wherein the electrochemically treated CNP dispersion is separated by filtration, decantation, centrifugation, solvent distillation or other classical methods from the second liquid, and wherein isolated MCNPs are used for further and repeated electrochemical treatment to the degree of metallization is sufficiently high, and where MCNP after such adequate electrochemical treatment is incorporated into technical products. Use of MCNP according to any one of claims 1 to 7 in products including capacitors, batteries, transparent electrodes, electronic connections, electric heating foils, cables, catalysts, in particular in gas diffusion electrodes and catalyst supports, photovoltaics, coatings and paints, composites containing epoxy / amine or polyurethane or other thermosets (permanently cross-linked plastics), and ballistic protective materials in which case MCNP is treated at high temperature to fuse metallic areas.