CN1199853C - Loaded metal catalyst suitable for low-temperature thermochemical vapor deposition synthesis of carbon nanotubes and method for synthesizing carbon nanotubes using the catalyst - Google Patents

Abstract

The present invention relates to a synthesis method of carbon nanotubes , particularly to a supported metal catalyst suitable for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition. The invention discloses a metal-loaded catalyst suitable for synthesizing carbon nanotubes by low-temperature (lower than 600 ℃) thermochemical vapor deposition, which comprises noble metal particles with the particle size of 0.01 to 10 microns, which are used as a supporter; and a metal catalyst deposited on the noble metal particles, wherein the metal catalyst may be iron, cobalt, nickel or an alloy thereof, and the weight ratio of the metal catalyst to the noble metal particles is between 0.1: 100 and 10: 100. The invention also discloses a method for directly synthesizing carbon nanotubes on a substrate at low temperature by using the metal catalyst of the supporter, wherein the catalyst supporter is not required to be removed after the carbon nanotubes are synthesized.

Description

Loaded metal catalyst suitable for synthesis of carbon nanotubes by low-temperature thermochemical vapor deposition and synthesis method of carbon nanotubes using the catalyst

Technical field

The invention relates to a method for synthesizing carbon nanotubes, in particular to a supported metal catalyst suitable for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition.

Background technique

Carbon nanotubes have very special properties, such as low density, high strength, high toughness, flexibility, high surface area, large surface curvature, high thermal conductivity, specific conductivity, etc., so they attract a lot of research work Researchers focus on developing its possible applications, such as composite materials, microelectronic components, flat-panel displays, wireless communications, fuel cells, and lithium-ion batteries, among others. Carbon nanotube field emission displays (CNT-FED) with carbon nanotubes as the electron emission source is a new type of flat panel display with great potential. Usually, the larger CNT-FED process is based on the purification and grinding of nano-carbon The tube is mixed with conductive colloid, which is planted on the surface of the conductive glass substrate by mixing paste, screen printing and other technologies, and then undergoes a sintering step at 350 to 500 degrees Celsius to remove the polymer substances in the paste to form an electronic with good conductivity. radiation film. Such a CNT-FED manufacturing process requires several steps and the technology is cumbersome, and carbon nanotubes are not easy to disperse uniformly in the conductive colloid.

At present, the methods for synthesizing carbon nanotubes with field emission electron function include arc discharge method (arc discharge), laser evaporation method (laser vaporization) and thermal chemical vapor deposition method (thermal chemical vapor deposition, thermal CVD) and so on. The arc discharge method and the laser evaporation method not only cannot control the length and diameter of the carbon nanotube product, but also have a rather low yield. In addition, a considerable amount of amorphous carbon (amorphous carbon) will be produced, which requires further purification. In addition, the operating temperature of these processes exceeds 1000 degrees Celsius, and it is impossible to directly synthesize carbon nanotubes on glass substrates. Therefore, it is generally believed that the thermal chemical vapor deposition method has the most potential to become the mainstream technology for low-temperature production of carbon nanotubes.

In the past, carbon nanotubes were synthesized by thermal chemical vapor deposition, mainly based on porous silica, zeolite, aluminum oxide or magnesium oxide, and impregnated. An active metal catalyst deposited on the support is prepared. The main reason for choosing the above supports is that such supports are quite stable inert oxides, which are not easy to react with the active metal catalyst when heated, so that the active metal catalyst loses its activity, and the synthesis reaction of carbon nanotubes cannot be carried out. The active metals selected are mainly iron, cobalt or nickel, and trace metals such as copper, molybdenum, manganese, zinc or platinum are added to adjust the reactivity. Use the active metal catalyst deposited on the carrier to carry out catalytic carbon deposition reaction in the reactor to generate carbon nanotubes. The reaction conditions include: introducing inert gas (helium, argon, nitrogen), hydrogen, and carbon source gas to the reactor, and the reaction temperature Usually, the temperature is 650 to 1000° C., the pressure is 1 to 2 atmospheres, and the reaction time is 1 to 120 minutes. Carbon sources used include hydrocarbons or carbon monoxide. After the reaction, the carrier needs to be removed with an acid solution to obtain relatively pure carbon nanotubes for use in the CNT-FED process or other purposes.

Generally speaking, the strain temperature (strain temperature) of calcined heat-resistant glass can reach up to 650°C, and the strain temperature of poor soda glass is about 550°C or lower. If carbon tubes grow on the surface of the substrate, the reaction temperature cannot exceed the deformation temperature of the substrate, that is, preferably lower than 600°C. However, the process temperature is too low, and the catalyst activity is not enough to synthesize carbon nanotubes. Therefore, it is necessary to develop a special catalyst system with high activity to synthesize carbon nanotubes at a low temperature below 600°C.

European patent application EP 1061041 A1 discloses a low-temperature thermal CVD device and a method for synthesizing carbon nanotubes using the device, wherein the reaction tube in the device is divided into a first section for thermally decomposing the input gas, which is spatially adjacent to the gas input part. A zone, and a second zone spatially adjacent to the exhaust portion, are used for synthesizing carbon nanotubes using the aforementioned decomposition gas, and the temperature of both zones is maintained such that the temperature of the second zone is lower than that of the first zone. Two different catalyst substrates are used in the generation reaction area of carbon nanotubes, one of which is used as a co-catalyst, the main function is to accelerate the cracking of acetylene, and the components are Pd, Cr and Pt, etc., and the other is deposited with iron, cobalt, nickel or The alloy catalyst film is the catalyst that mainly generates carbon nanotubes. The catalyst substrate with iron, cobalt, nickel or its alloy catalyst film is corroded with etching gas to form nano-scale catalytic particles, and the above-mentioned equipment is used to decompose the carbon source gas with high heat in the first zone, and then pass through the second zone at equal to or At a temperature lower than the deformation temperature of the substrate, the carbon source gas decomposed by the catalyst is used to grow vertically arranged carbon nanotubes on each isolated nanometer-scale catalytic metal particle on the substrate through thermal chemical vapor deposition reaction. In addition to using a low-temperature reaction zone of 450 to 650 degrees Celsius, the technology in the previous proposal still needs to use a high temperature of 700 to 1000 degrees Celsius for thermal decomposition of carbon source gas (the first zone), which is not a purely low-temperature process. The technique necessitates the use of special CVD reactors. In addition, in the prior art, two different metal catalyst layers must be formed on the two substrates, and then the two substrates are placed in a thermal CVD reactor with a distance between the metal layers. Obviously, the manufacturing process of the prior art is complicated, the cost is high, and it is not easy to implement.

European patent application EP 1061043 A1 discloses a method for low-temperature synthesis of carbon nanotubes using a metal catalyst layer. In this synthesis method, a metal catalyst layer is formed on a substrate, which is etched to form isolated nanoscale catalytic metal particles. Vertically aligned carbon nanotubes are then grown on each isolated nanoscale catalytic metal particle on the substrate by thermal chemical vapor deposition using a decomposed carbon source gas at a temperature equal to or lower than the deformation temperature of the substrate . The decomposed carbon source gas uses a carbon source gas to decompose the metal catalyst layer. In the prior art, two different metal catalyst layers must be formed on the two substrates, and then the two substrates are placed in a thermal CVD reactor at a distance with the metal layers facing each other. Obviously, the technology in the previous proposal is to improve the process patent of EP1061041 A1. The main progress is to change the two-stage heating system to a one-stage heating system, but there is no obvious progress for the catalyst system, and it still needs to be installed on two substrates. Two different catalyst systems are used.

Contents of invention

A main purpose of the present invention is to provide a supported metal catalyst suitable for synthesis of carbon nanotubes by thermal chemical vapor deposition at low temperature, which can be easily prepared.

Another object of the present invention is to provide a supported metal catalyst suitable for synthesizing carbon nanotubes by thermal chemical vapor deposition at low temperature. The supported metal catalyst has the advantage of easy adjustment and control of catalyst composition.

Another object of the present invention is to provide a method for directly synthesizing carbon nanotubes on a substrate at low temperature, which does not have the disadvantages of the aforementioned prior art.

Another object of the present invention is to provide a method for directly synthesizing carbon nanotubes on a substrate at low temperature, which has the advantage of easy preparation of the catalyst system.

In order to achieve the purpose of the above invention, a supported metal catalyst suitable for synthesis of carbon nanotubes by low-temperature thermochemical vapor deposition according to the present invention includes:

Precious metal particles ranging in size from 0.01 to 10 microns; and

A metal catalyst deposited on the noble metal particles, wherein the metal catalyst is selected from the group consisting of iron, cobalt, nickel and alloys thereof, and the weight ratio of the metal catalyst to the noble metal particles is from 0.1:100 to 10:100 between.

Preferably, the noble metal particles are silver, gold, platinum, palladium and copper or their alloys, among which silver is more preferred.

Preferably, the supported metal catalyst of the present invention is obtained by mixing the noble metal particles with a salt solution of the metal catalyst, and then heating the obtained mixture, so that the metal catalyst is deposited on the noble metal particles. preparation. The salt solution of the metal catalyst can be nitrate solution and sulfate solution, and the nitrate solution and sulfate solution can be water or alcohol solution.

Preferably, the loaded metal catalyst of the present invention is prepared by a deposition precipitation method comprising the following steps:

a) dispersing the noble metal particles in a solvent;

b) adding a salt solution of the metal catalyst to the dispersion of the noble metal particles in step a);

c) adding a precipitating agent to the mixture of step b) and heating the obtained mixture; and

d) adding a reducing agent to the mixture of step c) to reduce the metal catalyst ions so that the metal catalyst is deposited on the noble metal particles.

Preferably, the solvent in step a) is water or alcohols.

Preferably, the precipitation agent in step c) is ammonia water or sodium bicarbonate.

Preferably, the reducing agent in step d) is hydrazine, formaldehyde, hypophosphite or benzaldehyde.

The present invention also provides a method for synthesizing carbon nanotubes by low-temperature thermochemical vapor deposition, comprising the following steps:

a) dispersing the loaded metal catalyst of the present invention on a substrate; and

b) Depositing a carbon source gas on the supported metal catalyst to grow carbon nanotubes by means of thermal chemical vapor deposition.

Preferably, step a) of the method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention includes dispersing the loaded metal catalyst in a glue solution containing a polymer and an organic solvent, and coating the obtained dispersion glue solution On the substrate, the obtained coating is heated to remove polymers and organic solvents therein. More preferably, the temperature for heating the obtained coating to remove the polymer and the organic solvent therein is between 350°C and 500°C.

Preferably, step a) of the method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention includes adding the supported metal catalyst in an organic solvent, and dispersing it by ultrasonic vibration for a period of time, and dispersing the obtained The liquid is poured onto a quartz boat substrate to form a thin layer thereon, and the thin layer is dried by heating.

Preferably, the base material of step a) of the method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention is selected from ITO conductive glass, strengthened glass, soda glass, quartz, silicon oxide, silicon wafer, aluminum and metal foil composed of groups.

Preferably, the thermal chemical vapor deposition in step b) of the method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention is carried out at a reaction temperature ranging from 400 to 600°C.

Preferably, the thermal chemical vapor deposition in step b) of the method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention is carried out at a pressure of 0.5 to 2 atmospheres for a reaction time of 1 to 120 minutes; and the The carbon source gas contains hydrocarbons or carbon monoxide. The hydrocarbon preferably contains 1 to 12 carbons. More preferably, the carbon source gas is methane, acetylene or carbon monoxide.

Preferably, the thermal chemical vapor deposition in step b) of the method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention is carried out in the presence of hydrogen; and the carbon source gas contains hydrocarbons or carbon monoxide.

Compared with the previous case, the main advantages of the present invention are as follows: 1. The carrier metal catalyst of the present invention can be used for the synthesis of carbon nanotubes deposited by thermal chemical vapor deposition at low temperature (less than 600° C.). 2. The supported metal catalyst of the present invention can be used in the method of directly synthesizing carbon nanotubes at a low temperature on a substrate without removing the catalyst support. 3. The present invention uses a single highly active catalyst system instead of two catalyst systems, which can reduce costs. 4. The present invention uses a one-stage low-temperature heating method, and does not need to process the carbon source gas through the high-temperature zone of the previous stage. 5. Using the same conductive layer as the carrier with the existing thick film (thick film) process, it can be directly embedded in the original process of CNT-FED, with full compatibility.

Detailed ways

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention discloses a supported metal catalyst suitable for synthesis of carbon nanotubes by thermal chemical vapor deposition at low temperature (below 600°C), which is different from the destructive method of synthesizing nano-metal catalysts disclosed in the aforementioned EP application. Synthetic method to prepare the catalyst. First, select a carrier that can be applied to a downstream product together with carbon nanotubes, that is, the carrier will not affect the downstream product and its manufacturing process. Taking CNT-FED as an example, the silver particles in the silver colloid can be used as a catalyst carrier. Because the silver colloid is a conductive surface adhesive that must be used in the CNT-FED manufacturing process, the carrier can be directly put into the CNT without removing it. -FED process. The active metal catalyst is implanted on the surface of such a support by deposition or impregnation method, and then the loaded metal catalyst is dispersed or coated on the surface of the substrate, and then the carbon nanotubes can be generated by thermal chemical vapor deposition reaction, and the A large amount of carbon nanotubes can still be synthesized when the reaction temperature is controlled below 600°C.

The catalyst carrier of the present invention is precious metal particles, such as gold, silver, copper, palladium, platinum, etc., and its particle size distribution is between 0.01-10 microns. There are two methods for preparing the active catalyst, the first is the impregnation method, and the second is the deposition-precipitation method. Both methods require the precious metal particles to be dispersed in water first.

In the impregnation method, the aqueous solution of silver particles is vibrated with ultrasonic waves for a period of time, such as 10 minutes, and then added with an active metal salt solution, such as an aqueous solution of nickel nitrate, wherein the active metal includes transition metal elements, such as iron, cobalt, nickel, etc., and the salt can be as nitrate or sulfate. After the two solutions are mixed evenly, the mixed solution is heated and concentrated to remove the solvent, and the active metal catalyst is distributed on the carrier to become a loaded metal catalyst.

The precipitation precipitation method is to add an aqueous solution containing silver particles to an alkaline aqueous solution (such as ammonia water) to make the pH of the solution 8 to 9, and then boil it for a period of time, such as 30 minutes, to modify the surface of the support to be alkaline, and then add the active metal salts The aqueous solution is added, stirred evenly, and then a precipitant and a chemical reducing agent are added to precipitate and reduce the active metal. The precipitating agent is ammonia water, the reducing agent is such as formaldehyde, and then the solvent is removed by filtration to obtain the supported metal catalyst.

A method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition of the present invention includes dispersing the aforementioned supported metal catalyst on a substrate; and using a carbon source gas to grow on the supported metal catalyst by thermal chemical vapor deposition carbon nanotubes.

One way of dispersing the aforementioned supported metal catalyst on a substrate is as follows. Take a piece of substrate, soak it in acetone, shake it with an ultrasonic oscillator for about 10 minutes and clean it, then take it out and dry it for later use. This step is pretreatment, which can increase the adhesion of the catalyst system on the surface of the substrate. The aforementioned substrate can be silicon wafer, quartz glass, strengthened glass, soda glass, ITO conductive glass, metal sheet or silicon oxide. The prepared loaded metal catalyst and polymer glue are evenly mixed, and the mixing ratio (weight) of the loaded metal catalyst to the polymer glue is from 1:10 to 3:1. A suitable polymer glue comprises 35wt% of a cellulose resin (Celluloseresin), 50wt% of dl-1-p-alpha-terpineol (dl-α-terpineol) as a solvent, and sodium phosphate as a dispersant (dispersant) (sodium phosphate) 10wt% and glass powder (glass powder) 15wt%. The function of the glass powder is to increase adhesion. Apply the mixed colloid on the surface of the substrate by screen printing, dry at 110°C for 30 minutes, and then sinter at 350-500°C for 30 minutes in an air atmosphere to remove the polymer glue. Another method of dispersing the supported metal catalyst of the present invention on a substrate includes adding the supported metal catalyst in an organic solvent, such as ethanol, and dispersing with ultrasonic waves for a period of time, such as 10 minutes, and pouring the mixture Bake at 110°C for 30 minutes on a quartz boat substrate.

Putting the base material dispersed with the loaded metal catalyst in a reactor for thermal chemical vapor deposition reaction can grow carbon nanotubes on the loaded metal catalyst. The reaction gas includes inert gas (such as helium, argon, nitrogen), hydrogen and carbon source gas, the carbon source gas used includes hydrocarbon or carbon monoxide, the reaction temperature is 400-600 degrees Celsius, and the reaction time is 1-120 minutes. The pressure is 0.5-2 atmospheres. After the reaction, carbon nanotubes are formed on the surface of the catalyst carrier, and the diameters of the tubes are distributed between 1 and 200 nanometers.

Example 1

1 gram of silver particles with a particle size distribution between 1-5 microns was added to 50 ml of water, followed by ultrasonic treatment of the solution for 10 minutes. 1 g of an aqueous solution of nickel nitrate at a concentration of 1% was added to the obtained silver aqueous solution, and stirred to mix. The obtained mixture was then heated to remove the solvent therein to obtain 1.01 g of a semi-finished product containing 1% nickel metal as a silver-supported catalyst.

Example 2:

Take 1.0 g of silver particle powder with a particle size distribution between 0.05-0.1 micron, add 50 ml of deionized water and stir for 15 minutes, then add 0.05 g of ammonia water with a concentration of 28% and stir for 5 minutes, then heat and reflux for 30 minutes, and then slowly add Add 0.5 g of nickel nitrate aqueous solution with a concentration of 10%, add 0.08 g of ammonia water with a concentration of 28%, continue stirring and boiling for 4 hours, then add 0.44 g of a 37% formaldehyde solution, and boil for another 30 minutes. After cooling, filter and take the filter cake and dry it at 110° C. for 4 hours to obtain 1.05 g of silver-supported catalyst containing 5% nickel metal.

Example 3:

The loaded metal catalyst prepared in Example 1 was mixed evenly with the polymer glue, and the mixing ratio (weight) of the loaded metal catalyst to the polymer glue was 1:1. A suitable macromolecular glue comprises a cellulose resin (Cellulose resin) 35wt%, dl-1-to-alpha-terpineol (dl-α-terpineol) 50wt% as a solvent, a phosphoric acid as a dispersant (dispersant) Sodium phosphate 10wt% and glass powder 15wt%. After the substrate coated with the catalyst glue solution was dried at 110°C for 30 minutes, it was placed in a thermal chemical vapor deposition reactor, and then the temperature in the reactor was raised to 500°C, and sintered in an air atmosphere for 30 minutes to remove polymers and solvents. Argon gas was introduced for 10 minutes at a flow rate of 1500ml/min, and the air was driven out of the reactor. Before starting the reaction, argon (500ml/min) and hydrogen (75ml/min) were mixed and passed into the system for 5 minutes, then acetylene (25ml/min) was added and mixed to start the thermal chemical vapor deposition reaction. After 6 minutes of reaction, first turn off the acetylene and hydrogen, then turn off the heating power, and then turn off the argon after the system cools down to below 100°C, and then take out the substrate. At this time, black can be observed at the place where the catalyst is coated on the substrate. sediment. The black deposit is observed by an electron microscope as carbon nanotubes with a diameter between 20 and 60 nanometers.

Example 4:

Repeat the steps of Example 3, but replace the one prepared in Example 1 with the carrier metal catalyst obtained in Example 2. The diameter distribution of carbon nanotubes grown on the substrate surface is between 20 and 60 nanometers.

Example 5:

Spread 0.01 g of the supported metal catalyst prepared in Example 2 on a quartz boat substrate. Then the quartz boat substrate was placed in a thermal chemical vapor deposition reactor to grow carbon nanotubes under the same conditions and steps as in Example 3. The diameter distribution of carbon nanotubes grown on the substrate surface is between 20 and 60 nanometers.

Claims (18)

1. A supported metal catalyst suitable for low-temperature thermochemical vapor deposition synthesis of carbon nanotubes, comprising: noble metal silver, gold, platinum, palladium and copper or their alloy particles with a particle size ranging from 0.01 to 10 microns; and The metal catalyst deposited on the noble metal silver, gold, platinum, palladium and copper or their alloy particles, wherein the metal catalyst is selected from the group consisting of iron, cobalt, nickel and their alloys, and the metal catalyst is used for the noble metal The weight ratio of the particles is between 0.1:100 and 10:100. 2. The supported metal catalyst as claimed in claim 1, wherein the noble metal particles are silver. 3. The loaded metal catalyst as claimed in claim 1, it is by means of adding a salt solution of the noble metal silver, gold, platinum, palladium and copper or their alloy particles and the metal catalyst to mix, then heating the The obtained mixture is prepared by depositing the metal catalyst on the noble metal particles. 4. The loaded metal catalyst as claimed in claim 3, wherein the salt solution of the metal catalyst is a nitrate solution and a sulfate solution. 5. The loaded metal catalyst as claimed in claim 4, wherein the salt solution of the metal catalyst is water or alcohol solution. 6. The loaded metal catalyst as claimed in claim 1, prepared by means of a deposition-precipitation method comprising the steps of: a) dispersing the precious metal silver, gold, platinum, palladium and copper or their alloy particles in a solvent; b) adding a salt solution of the metal catalyst to the dispersion of the precious metal silver, gold, platinum, palladium and copper or their alloy particles in step a); c) adding a precipitant to the mixture of step b) and heating the mixture obtained; and d) adding a reducing agent to the mixture in step c) to reduce the metal catalyst ions so that the metal catalyst is deposited on the noble metal silver, gold, platinum, palladium and copper or their alloy particles. 7. The supported metal catalyst as claimed in claim 6, wherein the solvent in step a) is water or alcohols. 8. The loaded metal catalyst as claimed in claim 6, wherein the precipitation agent in step c) is ammonia or sodium bicarbonate. 9. The supported metal catalyst as claimed in claim 6, wherein the reducing agent in step d) is hydrazine, formaldehyde, hypophosphite or benzaldehyde. 10. A method for synthesizing carbon nanotubes by low-temperature thermal chemical vapor deposition, comprising the following steps: a) dispersing the supported metal catalyst according to claim 1 on a substrate; and b) Depositing a carbon source gas on the supported metal catalyst to grow carbon nanotubes by means of thermal chemical vapor deposition; wherein the thermal chemical vapor deposition is performed at a reaction temperature between 400 and 600°C. 11. The method according to claim 10, wherein step a) comprises dispersing the loaded metal catalyst in a glue solution containing a polymer and an organic solvent, coating the obtained dispersion glue solution on the substrate, and heating The obtained coating is used to remove polymers and organic solvents therein. 12. The method as claimed in claim 11, wherein the temperature for removing the polymer and the organic solvent is between 350°C and 500°C. 13. The method as claimed in claim 10, wherein step a) comprises adding the loaded metal catalyst in an organic solvent, and dispersing it for a period of time through ultrasonic vibration, and pouring the obtained dispersion on a quartz boat substrate to form a thin layer thereon, and heat to dry the thin layer. 14. The method of claim 10, wherein the substrate of step a) is selected from the group consisting of ITO conductive glass, strengthened glass, soda glass, quartz, silicon oxide, silicon wafer, aluminum and metal foil. 15. The method of claim 10, wherein the thermal chemical vapor deposition of step b) is carried out at a pressure of 0.5 to 2 atmospheres for a reaction time of 1 to 120 minutes; and the carbon source gas comprises hydrocarbons or carbon monoxide. 16. The method of claim 15, wherein the hydrocarbon contains 1 to 12 carbons. 17. The method of claim 15, wherein the carbon source gas is methane, acetylene or carbon monoxide. 18. The method of claim 10, wherein the thermal chemical vapor deposition in step b) is performed in the presence of hydrogen; and the carbon source gas comprises hydrocarbons or carbon monoxide.