Patent Description:
As the industry has advanced, separation membrane technologies for obtaining separation ability for high purity can be recognized as a very important field. Such technologies are becoming increasingly important in a wide range of fields, including the chemical industry, food industry, pharmaceutical industry, medical care, biochemistry, and environmental fields. As the demand for clean water and awareness of water shortage particularly increase in the field of environment, the technologies using the separation membrane has attracted much attention as one of the solutions to address the issues.

Generally, the types of separation membranes used vary depending on the characteristics of the target substance. The materials of the separation membrane include, e.g., filter cloth, paper, felt, and sponge as a fiber type. Their values are comparatively cheap, the dust collection effect is good, and thus, the application range is wide. There are various kinds of materials for the filter cloth depending on natural fibers and man-made fibers.

Materials of porous membranes are carbon, metal, plastic, and so on. They have high mechanical strength and thus are used in industrial high pressure filter. In particular, the porous membranes composed of carbon are suitable for filters that must withstand corrosion. Recently, as interest in clean technology using functional materials has increased, researches on filters that purify various air pollutants and water pollutants have been actively conducted. These porous membranes have been developed in various forms in order to filter, e.g., suspended substances, harmful substances, and dusts present in gases or liquids. Among them, filters using active carbon fibers for removing fine dusts and organic adsorbates and metal fiber separation membranes using metal fibers for decomposing pathogens and organic matters have been widely spotlighted.

Separation membranes such as a micro filtration (MF) membrane, an ultrafiltration (UF) membrane, a nano filtration (NF) membrane, a reverse osmosis (RO) membrane, and an ion exchange membrane are used in the water treatment field and mainly used for industrial waste water treatment, water treatment, sewage treatment, wastewater treatment, and seawater desalination. The micro filtration membranes are mainly used in water treatment plants and are also used for sewage treatment by a membrane bio reactor (MBR). The ultrafiltration membrane is used for water treatment applications because of their ability to remove bacteria. The reverse osmosis membrane is used for seawater desalination facilities. The ion exchange membrane is mainly used for desalting processes. At Shizuoka Technology Center, a nano filtration membrane was successfully developed to separate green tea components. Yamamoto Group of Tokyo University has developed a membrane reactor for ultrahigh-water treatment. The ultrahigh water treatment technology is in the process of commercialization.

Meanwhile, carbon nanostructures can be classified into, e.g., carbon nanotubes, carbon nanohorns, and carbon nanofibers depending on the type thereof. In particular, carbon nanotubes can be applied to various fields such as energy, environment, and electronic materials due to their excellent mechanical strength, thermal conductivity, electrical conductivity, and chemical stability.

As an application for such a carbon nanostructure, a carbon nanostructure-metal composite induces a functional group on the carbon nanotube, and a metal (for example, cobalt, copper, nickel, and silver) is reacted with the functional group to be chemically bonded thereto. Due to the metal components contained, they have excellent properties for forming and molding of structures such as a field emission display, a hydrogen storage device combination, an electrode, a super capacitor, an electromagnetic wave shielding structure, and a lightweight high strength application product.

Methods of preparing materials for such carbon nanostructure-metal composites are disclosed in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

Further, it is attempted to produce the membranes using carbon nanostructures. Single-walled carbon nanotubes are applicable to renewable hybrid ceramic filters due to narrow diameter, high surface area, thermal resistance, and porous cohesive structure thereof. Recently, it has reported that multi-walled carbon nanotube filters have excellent effects on bacterial removal. Further, it has been known that high-penetrability single-walled carbon nanotube filters are highly efficient at removing bacterial and viral pathogens from water.

Further, the difficulty of adhering carbon nanotubes has been addressed to some extent by directly synthesizing and aligning multi-walled carbon nanotubes on a surface of a universal metal filter for filter applications. The reduction of the metal filter under high temperature hydrogen gas causes to produce the catalyst sites of the nanotube growth so that the carbon nanotubes are aligned to grow. At this time, direct manipulation of filter recovery efficiency and the shape of the carbon nanotubes were possible by controlling the flow rate of the reducing agent in the carbon nanotube synthesis process. However, the technology using the aligned carbon nanotubes is difficult to commercialize, and there are still many technical problems to deal with a large amount of actual pollutants.

Further, typical membrane filters require frequent backwashing, which limits the application of various temperatures when removing impurities, consumes a large amount of energy, and break the membrane or increase the pore size because the membrane itself is not strong. Among these membrane filters, in particular, a porous membrane using the carbon nanostructure is manufactured by layering or coating a material on a support. However, there are problems that the support and the carbon nanostructure film are not bonded, and desorption occurs, and the size of the formed nanoporous membrane is not constant. When the carbon nanotube-metal composite is used, the metal should be melted and bonded to the support. However, when a metal which is not formed of nanoparticles is used, it is not melted after the heat treatment and thus not bonded to the support. Further, even when a metal formed of nanoparticles is used, a phenomenon occurs in which the metal is melted to block all the pores.

As a result, the inventors of the present disclosure have found that a carbon nanostructure is layered on a porous membrane support, a solution containing a polymer binder and a solvent permeates into the composite, and the composite is subjected to a calcining treatment to form a carbon nanostructure-binder coupled nanoporous membrane. They have found that the nanoporous membrane can be applied to a separation membrane, a field emission display, a hydrogen storage device, a supercapacitor, etc., since strong coupling occurs between the support and the carbon nanostructure due to the use of the binder. Thus, they completed the present disclosure.

It is an object of the present disclosure to provide a binder-coupled carbon nanostructure nanoporous membrane and a method for manufacturing the same.

In order to achieve the above object, the present disclosure is to provide a binder-coupled carbon nanostructure nanoporous membrane in accordance with claim <NUM>.

In addition, the present disclosure is to provide a binder-coupled carbon nanostructure nanoporous membrane manufactured by the method.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Generally, the nomenclature used herein and the experiment methods, which will be described below, are those well known and commonly employed in the art.

In the present disclosure, a binder-coupled carbon nanostructure nanoporous membrane was prepared by mixing a binder and a solvent at various ratios, and the pore size was measured according to each ratio. As a result, it was confirmed that the size of the pores varied depending on the ratio of the binder and the solvent, and the resulting binder-coupled carbon nanostructure nanoporous membrane can be used as a separation membrane for various applications because of its strong bonding strength between the carbon nanotube porous membrane and the support.

Accordingly, an aspect of the present disclosure relates to a method of preparing a binder-coupled carbon nanostructure nanoporous membrane, consisting of: (a) preparing a suspension consisting of a carbon nanostructure, a first solvent and a surfactant, and then layering the suspension on a porous support thereby preparing a carbon nanostructure layer; (b) washing the prepared carbon nanostructure layer with a solvent and drying the carbon nanostructure layer; (c) preparing a binder solution by mixing a binder and a second solvent, and then preparing a complex porous membrane layer by infiltrating the binder solution into an upper portion of the carbon nanostructure layer; and (d) heat treating the aligned carbon nanostructure and the support layer by heating the layer, wherein viscosity of the binder solution is <NUM> to <NUM>,<NUM> cP.

According to the present disclosure, the surfactant may be selected from the group consisting of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and a mixture thereof. The surfactant may be, but not limited to, preferably used as one selected from the group consisting of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, sodium dodecyl sulfate, stearic acid, methyl glucoside, octyl glucoside, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, sorbitan monolaurate, ethylene glycol monolaurate, propylene glycol monolaurate, triglycerol monostearate, and a mixture thereof. DISPER-<NUM>, DISPER-<NUM>, DISPER-<NUM>, DISPER-<NUM>, DISPER-<NUM>, DISPER-<NUM>, DISPER-<NUM> of BYK product or a mixture thereof is, but not limited to, preferably used among the commercialized products. The surfactant is preferably added in an amount of <NUM> parts by weight to <NUM> parts by weight based on <NUM> parts by weight of the suspension so as to uniformly mix the carbon nanostructure without entanglement. When the amount of the surfactant is less than <NUM> part by weight, the carbon nanostructure does not easily disperse in the solvent. When the amount of the surfactant is more than <NUM> parts by weight, it is inefficient that a lot of solvent is consumed to clean the residual surfactant after the carbon nanostructure is layered on the support.

According to the present disclosure, the carbon nanostructure may be mixed with <NUM> part by weight to <NUM> parts by weight based on <NUM> parts by weight of the suspension. When the amount of the carbon nanostructure is less than <NUM> part by weight, the porous membrane of the carbon nanostructure is not formed on the support. When the amount of the carbon nanostructure is more than <NUM> parts by weight, a membrane of the carbon nanostructure is formed on the support, but all of the pores are blocked.

According to the present disclosure, the first solvent may be selected from the group consisting of water, alcohol, polyhydric alcohol, glycol ethers, isophorone, and mixtures thereof.

According to the present disclosure, the binder may include a hardening resin comprising one or more selected from the group consisting of an epoxy-based resin, an acrylic-based resin, a phenol-based resin, a polyimide-based resin, a silicone-based resin, a ceramic-based resin, a polyurethane-based resin, a polyvinyl chloride polyvinyl acetate copolymer, a polyester resin, and an unsaturated polyester resin.

The binder may be a ceramic binder. The ceramic binder may be, but is not limited to, preferably used as RSN-<NUM> resin, RSN-<NUM> HS resin, RSN-<NUM> HS resin, RSN-<NUM> resin, RSN-<NUM> resin, RSN-<NUM> resin, RSN-<NUM> resin, RSN-<NUM> resin, RSN-<NUM> flake resin, RSN-<NUM> flake resin, RSN-<NUM> flake resin, RSN-<NUM> flake resin, or mixtures thereof, which are products manufactured by Dow Corning Co. on the market.

Further, the binder solution is required to be filtered through a porous membrane support having a carbon nanostructure layered thereon. Thus, the binder must be a substance having a viscosity low enough to be permeable to the membrane before hardening. Further, after hardening, the properties of the binder must remain, and the binder must be changed firmly. Therefore, the viscosity of the binder solution used is <NUM> cP to <NUM>,<NUM> cP. When the viscosity of the binder solution is less than <NUM> cP, it is relatively thinly layered on the carbon nanostructure layer and thus is not bonded to the support, and hardness thereof is also low. When the viscosity of the binder solution is more than <NUM>,<NUM> cP, the viscosity of the carbon nanostructure is too high to pass through the layered support, and thereby blocking all pores.

According to the present disclosure, the weight ratio of the polymer binder to the second solvent in the binder solution is <NUM> : <NUM> to <NUM> : <NUM>. When the amount of the binder is greater than that of the second solvent upon preparation of the binder solution, the viscosity of the binder solution increases, and thus the binder cannot penetrate into the carbon nanostructure layer. On the other hand, when the amount of the binder is too lower than that of the second solvent, the binder solution can penetrate into the carbon nanostructure layer, but hardness thereof decreases or the pores thereof are formed nonuniformly upon calcining.

The pore size of the binder-coupled carbon nanostructure nanoporous membrane can be controlled depending on the size of the carbon nanostructure, the amount of the carbon nanostructure, or the ratio of the binder and the solvent. More specifically, the carbon nanostructure has a different diameter depending on kinds thereof. In spite of the same carbon nanostructure, since the carbon nanostructures can have different sizes thereof, the size of the pores can be controlled by controlling the size and type of the carbon nanostructure. By adjusting the amount of the carbon nanostructure added, the thickness of the carbon nanostructure bonded to the binder can be controlled to adjust size of the pores. In addition, the pore size can be controlled depending on the mixing ratio of the binder and the solvent. The function of the binder in the carbon nanostructure-binder bonded nanoporous membrane is to penetrate the network structure in which one or more carbon nanostructures are layered, attaching to the surfaces of the structures, and crosslinking them to each other to form a rigid network structure. The binder also bonds the support and the network structure of the carbon nanostructure firmly to form a nanoporous membrane on the support. In other words, when the binder attached on the surface of the carbon nanostructure and the support is calcined, the binder on the surface thereof is hardened to couple the carbon nanostructure with neighboring carbon nanostructures and thus to form a network structure.

According to the present disclosure, the second solvent may be selected from the group consisting of water, alcohol, polyhydric alcohol, glycol ethers, isophorone, and mixtures thereof.

According to the present disclosure, the calcining temperature may be <NUM> to <NUM>. When the calcining temperature is lower than <NUM>, the desired hardness is not obtained, and thus the carbon nanostructure layer is desorbed. When the calcining temperature is higher than <NUM>, the support is burnt or the binder membrane is cracked. When a ceramic binder is used, the calcining temperature is preferably <NUM> to <NUM>.

According to the present disclosure, the carbon nanostructure may be selected from a single wall carbon nanotube, a double wall carbon nanotube, a multi-wall carbon nanotube, a carbon nanohorn, a carbon nanofiber, or a mixture thereof.

According to the present disclosure, the porous support may be a porous filter made of polyethersulfone, polyethylene, polystyrene, polypropylene, paper, metal, cotton, glass fiber or carbon fiber. Further, the porous support preferably has a pore size of <NUM> to <NUM>. When the pore size is less than <NUM>, the solvent does not escape when the carbon nanostructure is layered on the porous membrane support, so that it is difficult to form the membrane. When the pore size is more than <NUM>, the carbon nanostructure in the dispersion solution passes all, and thus the carbon nanostructure layer cannot be formed on the carbon nanostructure layer.

According to the present disclosure, the porous filter may be a HEPA filter, a ULPA filter, a glass fiber filter, a glass powder sintering filter, a polymer nonwoven filter, a Teflon membrane filter, a sintered metal powder filter, or a metal wire weave filter.

In another aspect, the present disclosure relates to a binder-coupled carbon nanostructure nanoporous membrane prepared by the method as described above.

According to the present disclosure, the binder-coupled carbon nanostructure nanoporous membrane has a pore size of <NUM> to <NUM>. The pore size can be controlled depending the type, size or amount of the carbon nanostructure, and the ratio of the binder and the second solvent, as described above.

According to the present disclosure, the binder-coupled carbon nanostructure nanoporous membrane may be characterized in that the amount of the carbon nanostructure layered on the support is <NUM>/cm<NUM> to <NUM>/cm<NUM>. When the amount of the carbon nanostructure layered on the support is <NUM>/cm<NUM> or less, the pores are not formed in the nano-size. When the amount of the carbon nanostructure layered on the support is <NUM>/cm<NUM> or more, since the size of the pores decreases, water permeability and air permeability are drastically reduced or the pores are completely clogged.

Hereinafter, the present invention will be described in further detail with reference to examples.

<NUM> of carbon nanotubes, <NUM> of ultrapure water, and <NUM> of a surfactant (product name: DISPER-<NUM>, manufactured by BYK) were put in a <NUM> flask and subjected to dispersion treatment at <NUM> to <NUM> for <NUM> hours using ultrasonic waves. A HEPA filter paper having a pore size of <NUM> was cut into a <NUM> diameter circle and mounted on a filtration apparatus (Advantec KP-<NUM>). Then, <NUM> of the dispersion liquid dispersed using the ultrasonic wave was put therein and then filtered. The surfactant and the fine residue were then washed with <NUM> of ethanol and <NUM> of ultrapure water and dried in an oven set at a temperature of <NUM>. The dried HEPA support was fixed again to the filtration apparatus, and <NUM> of a polymer binder, specifically, a ceramic binder (RSN805, manufactured by Dow Corning Co. ) and toluene was mixed at a ratio of <NUM>: <NUM>, and the mixture was penetrated thereinto. The support was thermally hardened at <NUM> for <NUM> hour.

As shown in <FIG>, the SEM analysis image of the binder-coupled carbon nanostructure nanoporous membrane shows that the porous membrane of the carbon nanotube was almost clogged by the binder, and new fine pores were formed. The prepared porous membrane was analyzed using an automated capillary flow porometer. As a result, the average pore size was <NUM>, which showed a pore size of a nanofilter region, and the pore distribution was <NUM> to <NUM> (See <FIG>).

The binder-coupled carbon nanostructure nanoporous membrane was prepared in the same scheme as in Example <NUM>, except that the ratio of the ceramic binder (RSN805, manufactured by Dow Corning Co. ) to toluene was <NUM> : <NUM>.

As shown in <FIG>, the SEM analysis image of the binder-bonded carbon nanostructure nanoporous membrane showed that the pores of the carbon nanotubes were coated by the binder to form pores. As a result of analyzing the prepared porous membrane using an automated capillary flow porometer, the average pore size was <NUM>, which showed the pore size of the nanofilter region. The pore distribution was <NUM> to <NUM>, which was the narrowest so that it can be used as a separation membrane (See <FIG>).

As shown in <FIG>, the SEM analysis image of the binder-bonded carbon nanostructure nanoporous membrane showed that the pores of the carbon nanotubes were coated by the binder to form pores. As a result of analyzing the prepared porous membrane using an automated capillary flow porometer, the average pore size was <NUM>, which showed the pore size of the nanofilter region. The pore distribution was <NUM> to <NUM> (See <FIG>).

Except for the polymer binder, the Comparative Example was carried out in the same scheme as in Example <NUM>.

A carbon nanotube porous membrane was formed on a HEPA support in the same manner as in Example as described above, and then a SEM photograph was taken. As shown in <FIG>, it was confirmed that the carbon nanotube porous membrane was formed on the support. The prepared porous membrane was analyzed using an automated capillary flow porometer. As a result, the average pore size was <NUM>, which showed a pore size of a microfilter region, but the pore distribution was very broad, which was in the range of <NUM> to <NUM>, so that it is difficult to be used as a separation membrane (See <FIG>).

As illustrated in <FIG>, it was found that the pore size and pore distribution of the binder-coupled carbon nanostructure nanoporous membrane were varied depending on the ratio of the ceramic binder and the toluene. The carbon nanostructure nanoporous membrane obtained by the binder solution without coating has a broad pore distribution with a maximum pore size of <NUM> and a minimum pore size of <NUM> and has an average pore size of <NUM>, which is a micro size. However, it can be found that the breadth of the minimum pore size and the maximum pore size are sharply reduced when the ceramic binder is mixed with an appropriate amount of a solvent and the diluted solution is coated. Here, it can be found that the smaller the amount of toluene mixed with the ceramic binder, the smaller the pore size. However, when the amount of toluene is too small, the viscosity of the ceramic binder becomes relatively high, and thus the pores formed by the carbon nanostructure may be clogged. Therefore, it is necessary to increase the dilution ratio of toluene. As a result, it was coated when the ratio of ceramic binder to toluene was <NUM> : <NUM>, the pore size and pore distribution were the best.

In order to test the binding strength between a support and a carbon nanotube porous membrane formed on the support, the carbon nanotube porous membrane and the binder-coupled carbon nanostructure nanoporous membrane were prepared by the same method, and water was permeated therethrough at a pressure of <NUM> bar to test the binding strength. As shown in <FIG>, it can be seen that the carbon nanotube porous membrane layer is separated from the support after water is permeated through the porous membrane without using a binder. Conversely, as shown in <FIG>, it can be conformed that the binder-coupled carbon nanostructure nanoporous membrane formed by passing through a binder and calcining the same is not desorbed even after permeation of water at a high pressure, and the binder is bonded to the support and the carbon nanotube porous membrane layer so that they are stably maintained.

Claim 1:
A method of preparing a binder-coupled carbon nanostructure nanoporous membrane, consisting of:
(a) preparing a suspension consisting of a carbon nanostructure, a first solvent and a surfactant, and then layering the suspension on a porous support thereby preparing a carbon nanostructure layer;
(b) washing the prepared carbon nanostructure layer with a solvent and drying the carbon nanostructure layer;
(c) preparing a binder solution by mixing a binder and a second solvent, and then preparing a complex porous membrane layer by infiltrating the binder solution into an upper portion of the carbon nanostructure layer; and
(d) heat treating the carbon nanostructure and the support layer by heating the layer, characterized in that viscosity of the binder solution is <NUM> to <NUM>,<NUM> cP; and weight ratio between the binder and the second solvent in the binder solution is <NUM> : <NUM> to <NUM> : <NUM>,
wherein the binder penetrates the network structure,
the binder attaches to the surfaces of the structures,
the binder crosslinks them to each other to form a rigid network structure,
and the binder bonds the support and the network structure of the carbon nanostructure.