Patent Description:
<CIT> discloses a conventional method for preparing a hollow fiber composite, the method comprising preparing polyacrylonitrile nanofibers; providing a precursor containing aluminum oxide onto the polymer fiber; and heat-treating the polymer fiber provided with the precursor, wherein the precursor is heat-treated to be converted into a catalyst and the polymer fiber is heat-treated to have cavities formed therein.

<CIT> proposes a method for preparing a hollow fiber composite, the method comprising preparing a polymer fiber by electrospinning, wherein the fiber comprises a shell portion comprising a metal precursor and a sulfur salt; heat-treating the polymer fiber provided with the precursor, wherein the precursor is heat-treated to be converted into a catalyst and the polymer fiber is heat-treated to have cavities formed therein.

In general, a nanofiber may be defined as a fibrous material having a diameter of less than <NUM> and may be prepared by various methods such as phase separation, self-assembly, chemical vapor disposition (CVD), electrospinning or the like. However, it is known that the electrospinning is most effective in terms of convenient preparation or mass production and applicability of final products.

The electrospinning is a method for preparing a fibrous material having a diameter of less than <NUM> into a web or three-dimensional non-woven fabric by applying a high-voltage electric field to a polymer solution. The nanofiber prepared as above may be used for purposes such as a filter material for air or water purification, a medical anti-adhesive agent, a dressing material, a wiping cloth, a carbon nanofiber for artificial leather and energy storage, an inorganic nanofiber by organic/inorganic mixed spinning, etc., and thus various nanofiber-related technologies have been developed.

For example, Korean Unexamined Patent Publication No. <CIT> (Application No.: <CIT>and applicant: University-Industry Cooperation Group of Kyung Hee University) discloses a method for preparing a metal-coated nanofiber, including a) preparing an electrospinning solution containing a polymer with a fiber forming ability and an electroless plating catalyst, b) preparing a nanofiber having a diameter of <NUM> to <NUM> by electrospinning the electrospinning solution, and c) electrolessly plating the nanofiber. Besides, various nanofiber-related technologies have been developed now.

One technical object of the present invention is to provide a method for preparing a hollow fiber composite with an improved surface area.

Another technical object of the present invention is to provide a method for preparing a hollow fiber composite with an improved content of a catalyst.

Still another technical object of the present invention is to provide a method for preparing a hollow fiber composite, which may be applied to various applications.

The technical objects of the present invention are not limited to the above.

To solve the above technical objects, the present invention provides a method for preparing a hollow fiber composite with the features of claim <NUM>.

According to one embodiment of the invention, the method for preparing a hollow fiber composite includes preparing a polymer fiber, providing a precursor containing nitrogen onto the polymer fiber, and heat-treating the polymer fiber provided with the precursor, in which the precursor is heat-treated to be converted into a catalyst including g-C<NUM>N<NUM> and the polymer fiber is heat-treated to have cavities formed therein, wherein the polymer fiber provided with the precursor is heat-treated at a temperature of <NUM> or above and less than a temperature at which the polymer is carbonized.

According to one embodiment, in the method for preparing a hollow fiber composite, as the polymer fiber provided with the precursor is heat-treated, an adhesive strength between the catalyst and the polymer fiber may be enhanced so that the catalyst may be allowed to fix an outer wall of the polymer fiber, and the polymer fiber may be contracted toward the outer wall from a center of diameter of the polymer fiber so that cavities are formed within the polymer fiber, in which the adhesive strength between the catalyst and the polymer fiber may be stronger than a contraction force of the polymer fiber.

According to one embodiment, the providing of the precursor containing nitrogen onto the polymer fiber may be performed by a method of immersing the polymer fiber into a solution containing the precursor, and the catalyst may be provided onto the polymer fiber in a form of particle or layer depending on a ratio of a weight of the precursor to a weight of the polymer fiber.

According to one embodiment, in the method for preparing a hollow fiber composite, an amount of the precursor permeating into the polymer fiber may be increased as a thickness of the polymer fiber is decreased.

According to one embodiment, the polymer may include polyacrylo nitrile (PAN).

According to one embodiment, the precursor may include urea.

According to another embodiment, the method for preparing a hollow fiber composite may include that an adhesive strength between the catalyst and the polymer fiber is enhanced so that the catalyst is allowed to fix an outer wall of the polymer fiber, and the polymer fiber is contracted toward the outer wall from a center of diameter of the polymer fiber so that the cavities are formed within the polymer fiber.

According to another embodiment, the catalyst may be provided onto the surface of the polymer fiber in a form of particle or layer.

According to another embodiment, the polymer may include polyacrylo nitrile (PAN).

According to another embodiment, the catalyst may be formed prior to the cavities within the polymer fiber.

The method for preparing a hollow fiber composite according to an embodiment of the present invention includes preparing a polymer fiber, providing a precursor containing nitrogen onto the polymer fiber, and heat-treating the polymer fiber provided with the precursor.

Further, as the polymer fiber provided with the precursor is heat-treated, the precursor is converted into a catalyst, and an adhesive strength between the catalyst and the polymer fiber is enhanced, so that the catalyst is allowed to fix an outer wall of the polymer fiber. In this case, the polymer fiber is contracted toward the outer wall from a center of diameter of the polymer fiber, so that cavities are formed within the polymer fiber.

Accordingly, a surface area of the polymer fiber is increased to enhance a content of the catalyst. Further, the hollow fiber composite may be used as an artificial photosynthetic material, a photocatalyst responding to light, etc., depending on a type of the catalyst, and may be also used as a material which carries out reduction of contaminants such as carbon dioxide. Furthermore, the hollow fiber composite may be also used as a composite material, a conductive polymer composite material, a photoelectrochemical water-splitting material, etc., which are used in an electrode material with an improved rate of ionic adsorption, a gas sensor with an improved rate of gas adsorption, an energy storage, and a radiator panel of aircrafts, cars, etc..

When it is mentioned in the specification that one element is on another element, it means that the first element may be directly formed on the second element or a third element may be interposed between the first element and the second element. Further, in the drawings, the thicknesses of the membrane and areas are exaggerated for efficient description of the technical contents.

Further, in the various embodiments of the present invention, the terms such as first, second, and third are used to describe various elements, but the elements are not limited to the terms. The terms are used only to distinguish one element from another element. Accordingly, an element mentioned as a first element in one embodiment may be mentioned as a second element in another embodiment. The embodiments illustrated here include their complementary embodiments. Further, the term "and/or" in the specification is used to include at least one of the elements enumerated in the specification.

In the specification, the terms of a singular form may include plural forms unless otherwise specified. Further, the terms "including" and "having" are used to designate that the features, the numbers, the steps, the elements, or combination thereof described in the specification are present, and may be understood that one or more other features, numbers, step, elements, or combinations thereof may be added.

Further, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unnecessarily unclear.

<FIG> is a flowchart for explaining a method for preparing a hollow fiber composite according to an embodiment of the present invention, and <FIG> are views showing a process of preparing a hollow fiber composite according to an embodiment of the present invention.

Referring to <FIG> and <FIG>, a polymer fiber <NUM> may be prepared (S110). According to one embodiment, the polymer fiber <NUM> may be prepared by electrospinning a polymer solution. For example, the polymer may include polyacrylo nitrile (PAN). For example, the electrospinning process may be performed through a single nozzle. For example, the polymer fiber <NUM> may include a PAN nanofiber.

Referring to <FIG> and <FIG>, the precursor 200a may be provided onto the polymer fiber <NUM> to prepare a fiber composite <NUM> (S120). According to one embodiment, the precursor 200a may contain nitrogen. For example, the precursor 200a may include urea.

According to one embodiment, the fiber composite <NUM> may be prepared by a method of immersing the polymer fiber <NUM> into a solution containing the precursor 200a. For example, if the polymer fiber <NUM> includes PAN and the precursor 200a includes urea, the fiber composite <NUM> may be prepared by a method of immersing a PAN fiber having a weight of <NUM> into a solution containing urea having a weight of <NUM>.

According to one embodiment, as a thickness of the polymer fiber <NUM> is decreased, an amount of the precursor 200a permeating into the polymer <NUM> may be increased. Specifically, if the polymer fiber <NUM> is immersed into the solution containing the precursor 200a, the precursor 200a may permeate into the polymer fiber <NUM>. In this case, an amount of the precursor 200a permeating into the polymer fiber <NUM> having a small thickness may be more than an amount of the precursor 200a permeating into the polymer fiber <NUM> having a large thickness.

Referring to <FIG> and <FIG>, the polymer fiber <NUM> provided with the precursor 200a may be heat-treated (S130). In other words, the fiber composite <NUM> may be heat-treated. According to one embodiment, the fiber composite <NUM> may be disposed within a sintering device <NUM> and heat-treated. Accordingly, the fiber composite <NUM> may be subject to sintering.

Hereinafter, as the fiber composite <NUM> is heat-treated, a process of forming cavities within the polymer fiber <NUM> will be described with reference to <FIG>, <FIG> and <FIG>.

<FIG> is a view specifically showing a fiber composite formed in a process of preparing a hollow fiber composite according to an embodiment of the present invention, and <FIG> is a view for explaining that cavities are formed within a polymer fiber in a process of preparing a hollow fiber composite according to an embodiment of the present invention.

Referring to <FIG> and <FIG>, as the fiber composite <NUM> is heat-treated, the precursor 200a may be converted into a catalyst 200b (S140). In other words, if the fiber composite <NUM> is heat-treated, the precursor 200a provided onto the polymer fiber <NUM> may be converted into the catalyst 200b. Accordingly, the catalyst 200b may be provided onto the polymer fiber <NUM>. For example, as described above, if the precursor 200a includes urea, the catalyst 200b may include g-C<NUM>N<NUM>.

According to one embodiment, as shown in (a) of <FIG>, the catalyst 200b may be provided onto the polymer fiber <NUM> in a form of particle. According to another embodiment, as shown in (b) of <FIG>, the catalyst 200b may be provided onto the polymer fiber <NUM> in a form of layer. Specifically, the catalyst 200b may be provided onto the polymer fiber <NUM> in a form of particle or layer depending on a ratio of a weight of the precursor 200a to a weight of the polymer fiber <NUM> in the preparing of the fiber composite <NUM>. For example, the catalyst 200b may be provided onto the polymer fiber <NUM> in the form of layer, if the polymer fiber <NUM> includes a PAN fiber and the precursor 200a includes urea, and if a weight ratio between the PAN fiber and the urea exceeds <NUM> : <NUM>.

Although (a) and (b) of <FIG> show the polymer fiber <NUM> in a form of cylinder for convenience of explanation, a surface of the polymer fiber <NUM> may have a concavo-convex shape including concave and convex portions. Accordingly, the catalyst 200b may be provided onto the plurality of concave and convex portions in a form of particle, or may be provided in a form of layer, which conformally covers the surface of the concave and convex portions.

According to one embodiment, the fiber composite <NUM> may be heat-treated at a temperature of <NUM> or above and less than a temperature at which the polymer is carbonized. The temperature at which the polymer is carbonized may vary depending on a type of the polymer. For example, if the polymer includes PAN, the fiber composite <NUM> may be heat-treated at a temperature of <NUM>.

In contrast, if the fiber composite <NUM> is heat-treated at a temperature of less than <NUM>, a contraction of the polymer fiber <NUM>, which will be described below, may not occur, so that cavities may not be easily formed within the polymer fiber <NUM>. Further, if the fiber composite <NUM> is heat-treated at a temperature, at which the polymer is carbonized, or above, the precursor 200a may not be easily converted into the catalyst 200b, so that cavities may not be easily formed within the polymer fiber <NUM>, which will be described below.

Referring to <FIG> and <FIG>, as the fiber composite <NUM> is heat-treated, the catalyst 200b may fix an outer wall 100b of the polymer fiber <NUM> (S150). Specifically, if the fiber composite <NUM> is heat-treated, adhesion between the catalyst 200b and the polymer fiber <NUM> may be enhanced, and thus the catalyst 200b may fix the outer wall 100b of the polymer fiber <NUM>.

Further, as the fiber composite <NUM> is heat-treated, the polymer fiber <NUM> may be contracted to form cavities <NUM> within the polymer fiber <NUM>. Specifically, the polymer fiber <NUM> may be contracted toward the outer wall 100b of the polymer fiber <NUM> from a center 100a of diameter of the polymer fiber <NUM>. In this case, the adhesive strength between the polymer fiber <NUM> and the catalyst 200b may be stronger than a contraction force of the polymer fiber <NUM>. Accordingly, the cavities <NUM> may be formed within the polymer fiber <NUM>.

In other words, if the fiber composite <NUM> is heat-treated, the precursor 200a provided onto the polymer fiber <NUM> may be converted into the catalyst 200b and the adhesive strength between the catalyst 200b and the polymer fiber <NUM> may become strong. Further, as the polymer fiber <NUM> is heat-treated, a contraction phenomenon of the polymer fiber <NUM> may occur.

In this case, as the adhesive strength between the polymer fiber <NUM> and the catalyst 200b is stronger than the contraction force of the polymer fiber <NUM>, the polymer fiber <NUM> may be contracted while the outer wall 100b of the polymer fiber <NUM> is fixed by the catalyst 200b. Accordingly, the polymer fiber <NUM> may be contracted toward the outer wall 100b of the polymer fiber <NUM> from a center 100a of diameter of the polymer fiber, and the cavities <NUM> may be formed within the polymer fiber <NUM>.

If the cavities <NUM> are formed within the polymer fiber <NUM>, the catalyst 200b may be provided not only onto a surface of the polymer fiber <NUM>, but also within the cavities <NUM> of the polymer fiber <NUM>. However, an amount of the catalyst 200b provided onto the surface of the polymer fiber <NUM> may be more than an amount of the catalyst 200b provided within the cavities <NUM> of the polymer fiber <NUM>.

The method for preparing a hollow fiber composite according to an embodiment of the present invention as described above may include preparing the polymer fiber <NUM>, providing the precursor 200a containing nitrogen onto the polymer fiber <NUM>, and heat-treating the polymer fiber <NUM> provided with the precursor 200a.

Further, as the polymer fiber <NUM> provided with the precursor 200a is heat-treated, the precursor 200a may be converted into the catalyst 200b, and the adhesive strength between the catalyst 200b and the polymer fiber <NUM> may be enhanced, so that the catalyst 200b may fix the outer wall 100b of the polymer fiber <NUM>. In this case, the polymer fiber <NUM> may be contracted toward the outer wall 100b from a center 100a of diameter of the polymer fiber <NUM>, so that the cavities <NUM> may be formed within the polymer fiber <NUM>.

Accordingly, a surface area of the polymer fiber <NUM> may be increased to enhance a content of the catalyst 200b. Further, the hollow fiber composite may be used as an artificial photosynthetic material, a photocatalyst responding to light, etc., depending on a type of the catalyst 200b, and may be also used as a material which carries out reduction of contaminants such as carbon dioxide. Furthermore, the hollow fiber composite may be also used as a composite material, a conductive polymer composite material, a photoelectrochemical water-splitting material, etc., which are used in an electrode material with an improved rate of ionic adsorption, a gas sensor with an improved rate of gas adsorption, an energy storage, and a radiator panel of aircrafts, cars, etc..

Hereinafter, specific experimental examples and the results of property evaluation will be described with regard to the hollow fiber composite prepared in accordance with the method for preparing the hollow fiber composite according to an embodiment of the present invention.

A PAN nanofiber was prepared by electrospinning a polyacrylonitrile (PAN) solution through a single nozzle. After that, a fiber composite was prepared by immersing the PAN nanofiber having a weight of <NUM> into a solution containing urea having a weight of <NUM>, after which the fiber composite was heat-treated at a temperature of <NUM> under an atmosphere of argon (Ar) gas, so as to prepare a hollow fiber composite according to an embodiment, in which g-C<NUM>N<NUM> was provided onto the PAN nanofiber.

A PAN nanofiber was prepared by electrospinning a PAN solution.

A carbonized PAN nanofiber was prepared by carbonizing a PAN nanofiber which was prepared by electrospinning a PAN solution through a single nozzle. After that, a fiber composite was prepared by immersing the carbonized PAN nanofiber into a solution containing urea and thiourea, after which the fiber composite was heat-treated at a temperature of <NUM> under an atmosphere of argon (Ar) gas, so as to prepare a hollow fiber composite according to an embodiment, in which g-C<NUM>N<NUM> was provided onto the carbonized PAN nanofiber.

The hollow fiber composite according to the embodiment, the nanofiber according to Comparative Example <NUM>, and the hollow fiber composite according to Comparative Example <NUM> are summarized in the following Table <NUM>.

<FIG> is a view showing pictures of a hollow fiber composite according to an embodiment of the present invention.

Referring to (a) and (b) of <FIG>, the hollow fiber composite according to the embodiment was photographed through a scanning electron microscope (SEM) with magnification power of <NUM> and <NUM>. As can be understood from (a) and (b) of <FIG>, it might be confirmed that the hollow fiber composite according to the embodiment has cavities formed within the fiber composite. Further, the surface area (m<NUM>/g) and total pore volume (cm<NUM>/g) properties of the hollow fiber composite, which was photographed through the SEM with reference to (a) and (b) of <FIG>, and the PAN nanofiber according to Comparative Example <NUM> are summarized in the following Table <NUM>.

As can be understood from Table <NUM>, it may be seen that the hollow fiber composite according to the embodiment has a surface area value about seven times more than that of the PAN nanofiber, and has a total pore volume value about <NUM> times more than that of the PAN nanofiber. In other words, it may be seen that the hollow fiber composite according to the embodiment, in which g-C<NUM>N<NUM> is provided onto the PAN nanofiber, has excellent surface area and total pore volume properties.

<FIG> is a view showing pictures of a nanofiber composite according to Comparative Example <NUM> of the present invention.

Referring to (a) and (b) of <FIG>, a side and a surface of the nanofiber composite according to above Comparative Example <NUM> were photographed through a transmission electron microscope (TEM) with magnification power of <NUM>. As can be understood from (a) and (b) of <FIG>, it may be confirmed that the nanofiber composite according to above Comparative Example <NUM> does not have cavities formed therein. Further, it may be confirmed that the nanofiber composite according to above Comparative Example <NUM> has a carbonized PAN surface coated with g-C<NUM>N<NUM>.

<FIG> are views showing pictures of hollow fiber composites according to embodiments of the present invention, which are prepared at mutually different temperatures.

Referring to <FIG>, the PAN nanofiber according to the embodiment, which was immersed in urea, was heat-treated at temperatures of <NUM>, <NUM> and <NUM> to prepare hollow fiber composites, which were then photographed through the SEM respectively.

As can be confirmed from <FIG>, the hollow fiber composites prepared by being heat-treated at temperatures of <NUM> and <NUM> do not have cavities formed in a part thereof. On the other hand, as can be confirmed from <FIG>, it might be confirmed that the hollow fiber composite prepared by being heat-treated at a temperature of <NUM> has cavities easily formed therein. Accordingly, in case of preparing the hollow fiber composite according to the embodiment, it may be seen that it is easy to heat-treat the PAN nanofiber immersed in urea at a temperature of <NUM> or above.

<FIG> is a graph showing a change in properties of a hollow fiber composite according to an embodiment of the present invention depending on a concentration of urea.

Referring to <FIG>, in a process of preparing a hollow fiber composite according to the embodiment, a concentration of urea was adjusted in a step of immersing a PAN fiber into a solution containing urea. Next, the hollow fiber composite was prepared when there is no urea (PAN@<NUM>) and when there are <NUM>, <NUM>, <NUM> and <NUM> of urea, after which a transmittance (%)depending on wavenumbers (cm-<NUM>) was measured, and the results were shown in a graph of FT-IR (Fourier transform infrared spectroscopy).

As can be understood from <FIG>, it might be confirmed that the hollow fiber composite (PAN@<NUM>) without urea does not show any peak and the hollow fiber composite prepared through immersion into the solution containing <NUM> of urea shows one peak at <NUM>-<NUM>-<NUM>. On the other hand, it might be confirmed that the hollow fiber composites prepared through immersion into the solutions containing <NUM>, <NUM> and <NUM> of urea show two peaks at <NUM>-<NUM>-<NUM> and <NUM>-<NUM>-<NUM>.

In other words, in case of generally measuring FT-IR, a peak related to g-C<NUM>N<NUM> may be confirmed at <NUM>-<NUM>-<NUM> and <NUM>-<NUM>-<NUM>. However, in case of the hollow fiber composites prepared through immersion into the solutions containing <NUM>, <NUM> and <NUM> of urea, it is confirmed that a peak is shown in the range described above. Thus, it may be seen that the hollow fiber composite prepared through immersion into the solutions containing <NUM>, <NUM> and <NUM> of urea have g-C<NUM>N<NUM> easily formed therein. Accordingly, in case of preparing the hollow fiber composite according to the embodiment, it may be seen that g-C<NUM>N<NUM> is easily formed by immersing the PAN fiber into the solution containing at least <NUM> of urea.

Claim 1:
A method for preparing a hollow fiber composite (<NUM>), the method comprising:
preparing a polymer fiber (<NUM>);
providing a precursor (200a) containing nitrogen onto the polymer fiber (<NUM>); and
heat-treating the polymer fiber (<NUM>) provided with the precursor (200a),
wherein the precursor (200a) is heat-treated to be converted into a catalyst (200b) including g-C<NUM>N<NUM> and the polymer fiber (<NUM>) is heat-treated to have cavities (<NUM>) formed therein,
wherein the polymer fiber (<NUM>) provided with the precursor (200a) is heat-treated at a temperature of <NUM> or above and less than a temperature at which the polymer is carbonized.