CZ2008277A3 - Process for preparing inorganic nanofibers by electrostatic spinning - Google Patents

Abstract

The invention relates to a process for the production of inorganic nanofibres by electrostatic spinning of a solution comprising a metal alkoxide or a metalloid or non-metal dissolved in an alcohol-based solvent system. The solution is stabilized by a chelating agent which prevents the alkoxide hydrolysis and, after homogenization, is mixed with a solution of poly (vinylpyrrolidone) in the alcohol, whereupon the resulting solution is fed into an electrostatic field, in which electrostatic spinning continues, resulting in the formation of organic-inorganic nanofibres which they are subsequently calcined in an air atmosphere at a temperature of 500 degC to 1300 degC.

Description

The present invention relates to a process for the production of inorganic nanofibres by electrostatic spinning of a solution comprising a metal alkoxide or a metal or metalloid dissolved in an alcohol-based solvent system.

BACKGROUND OF THE INVENTION

Inorganic materials have a number of properties that make them suitable for use in many fields of technology, eg in electrical engineering, medicine, industry, etc. Major inorganic materials include TiO ₂ , SiO ₂₁ Al ₂ O 3, ZrO ₂ and B2O 3. In inorganic nanofibers, properties of nanofibrous materials such as organized one-dimensional structure are associated with properties of nanomaterials, especially high specific surface, and with physico-chemical properties of inorganic substances such as hardness, temperature resistance and structure of electron bands. The resulting nanofibers are therefore suitable for the production of composite materials, catalysts, electrochemical elements and the like.

Various methods for producing nanoparticles from inorganic materials are currently known. The production of inorganic nanoparticles, specifically from SiO ₂ and Al ₂ O 3, is described in WO2007 / 079841.

Nanoparticles of inorganic material, which can be produced by the above or other suitable method, can also be incorporated into the nanofiber structure, which can be realized eg by adding nanoparticles to the polymer solution and subsequent production of nanofibres from this solution. The presence of inorganic nanoparticles in polymer nanofibers gives these nanofibers specific properties. However, a substantial part of these nanofibres is the polymer component.

Pure inorganic nanofibers are currently produced by discontinuous electrostatic spinning methods using a jet or needle spinning electrode, which is fed with a solution which can be applied to it by means of a P63571OZ ··· • φ ·· φφ

be precursor of given inorganic elements, resp. a polymer solution containing the alkoxide of the metal or non-metal in question as a source of inorganic fiber base.

The known solutions used for the production of inorganic nanofibres by electrospinning from nozzles cannot be used for the continuous production of nanofibres, as the alkoxides are time-unstable and easily subject to alkoxide degradation by hydrolysis, even under the influence of atmospheric moisture, which occurs before their spinning. So far no electrolyte spinning solution has been used which is sufficiently stable and can be used for the continuous production of inorganic nanofibers.

It is an object of the present invention to provide a continuous process for the production of inorganic nanofibres by electrostatic spinning, which avoids the disadvantages of the prior art.

SUMMARY OF THE INVENTION

The object of the invention is achieved by the method of production of the inorganic nanofibres according to the invention, which is characterized in that the solution of metal alkoxide or metalloid or non-metal in alcohol-based solvent system is stabilized with a chelating agent to prevent hydrolysis of the alkoxide and mixed with poly (vinylpyrrolidone ) in alcohol, whereupon the resulting solution is fed into an electrostatic field, in which the electrostatic spinning takes place continuously for a long time, resulting in the formation of organic-inorganic nanofibres, which is then calcined outside the spinning apparatus in an air atmosphere at 500 ° C to 1300 ° C .

The stabilization of the solution prevents the hydrolysis of the alkoxides under the influence of atmospheric moisture and other influences of the working environment, so that the electrospinning process takes place continuously and in the long term. In the case of jet electrospinning in the published works they use solutions of metal alkoxide in alcohol in combination with poly (vinylpyrrolidone). The alkoxide is stabilized by the addition of acetic acid, (see Journal of America Ceramic Society 89 [6] 18611869 (2006), and Science and Technology of Advanced Materials 6 (2005) 240-245). Use of this solution in the case of electrospinning from open «♦ ♦

* · ·

PS3571EN ** · • 4 levels are possible on a laboratory scale, but with a process lasting more than half an hour, solution degradation and hydrolysis of the alkoxide begin to occur. This phenomenon prevents the industrial use of compositions of solutions for the production of ceramic nanofibres by the open-surface electrospinning method described in the literature.

In order to increase the electrical conductivity of the solution and to increase the productivity of the manufacturing process, a concentrated acid, preferably selected according to claim 3, is selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid.

In a preferred embodiment of the method, the chelating agent is a β-diketone, wherein the most suitable β-diketone appears to be acetylacetone in which the stabilization of the solution is permanent.

The alcohol in the poly (vinylpyrrolidone) solution is selected from the group of ethanol, 1-propanol, 2-propanol or mixtures thereof.

In a preferred embodiment, the poly (vinylpyrrolidone) has an average molar mass in the range of 1000000 - 1500000 g / mol and its weight concentration in the solution is in the range of 4 to 9%, poly (vinylpyrrolidone) having an average molecular weight of 1300000 g / mol.

The metal alkoxide is preferably selected from titanium tetrabutoxide, titanium tetraisopropoxide, aluminum tri-sec-butoxide, aluminum triisopropoxide or zirconium tetraisopropoxide.

The metalloxide is preferably tetraethoxysilane or boron triethoxide.

In order to achieve good stabilization of the alkoxide solution, it is preferred that the ratio of the alkoxide to the chelating agent in the solution be in the range of 1: 0.8 to 1: 2.2.

For the electrospinning itself, the alkoxide solution in the electrostatic field is located on the core surface of the spinning agent spinning electrode.

In this case, it is advantageous if the alkoxide solution is transported to the electrostatic field for spinning by the surface of the spinning electrode, which is preferably this to this. To to to · 4 4 4 4 4 4 4 4 4 4 4 35 35 35 35 35 35 35 PS3571CZ .......

formed by a rotary spinning electrode of elongated shape which extends through a part of its periphery into the spinning solution.

Overview of the drawings

The drawing shows in Fig. 1 produced TiO ₂ nanofibres and in Fig. 2 their XRD spectrum, Fig. 3 shows Al ₂ O ₃ nanofibres and Fig. 4 their XRD spectrum, Fig. 5 shows B ₂ O ₃ nanofibres and Fig. 6 their XRD spectrum, Fig. 7 shows ZrO ₂ nanofibers and Fig. 8 their XRD spectrum.

DETAILED DESCRIPTION OF THE INVENTION

The spinning solution for the production of inorganic nanofibres, in particular TiO ₂ , SiO ₂ , Al ₂ O ₃ , ZrO ₂ and B ₂ O ₃ , by electrospinning contains, as an inorganic base source, a metal alkoxide, a metal or non-metal dissolved in a suitable solvent in ethanol, 1-propanol or 2-propanol. The addition of a chelating agent as a stabilizer is necessary to stabilize the alkoxide solution, in particular to prevent its hydrolysis. The most suitable chelating agents include β-diketones, such as acetylacetone. The molar ratio between the alkoxide and the chelating agent should be in the range of 1: 0.8 to 1: 2.2. To improve the spinning ability of the solution, a support polymer, such as poly (vinylpyrrolidone) having a molar mass of 1300000 g / mol or a viscosity number of K-90, is added to it, its concentration by weight relative to the total weight of the solution being 4-9. % wt.

The electrospinning process depends on the concentration, respectively. viscosity, surface tension and other parameters of the alkoxide solution. The exact composition of the alkoxide solution depends on the temperature and humidity of the environment and the electrospinning parameters such as rotation and electrode type, the distance between the electrodes and the applied voltage.

In a specific embodiment of the production of SiO ₂ nanofibres, a mixture of 250 g of ethanol and 39 g of acetylacetone, in which 100 g of tetraethoxysilane was carefully dissolved, was used to produce the solution. After homogenization, the solution obtained was carefully mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of molecular weight φ ·

Φ ΦΦ · ♦ · · · · · 9 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35

weight 1300000 g / mol in 747.9 g ethanol. After subsequent homogenization, the resulting solution was acidified with concentrated hydrochloric acid.

The resulting tetraethoxysilane solution was used for the production of SiO ₂ nanofibres by electrospinning. An electrostatic spinning device of polymer solutions comprising a spinning electrode and a collecting electrode opposed thereto was used, wherein the spinning electrode comprised a rotatable spinning means extending part of its perimeter into a solution of tetraethoxysilane present in the container. The spinning spinning means brought through its rotation a solution of tetraethoxysilane into an electrostatic field formed between the spinning electrode and the collecting electrode, wherein a portion of the surface of the rotating spinning means opposite the collecting electrode represents the active spinning zone of the spinning agent. Thus, during spinning, the tetraethoxysilane solution was located in an electrostatic field on the surface of the active spinning zone of the spinning agent of the spinning electrode. The rotatable spinning means may be formed, for example, according to CZ patent 294274 or according to CZ PV 2006-545 or CZ PV 2007-485. In the particular spinning of the tetraethoxysilane solution described above, a portion of the solution, about 125 ml, was poured into a stock tray and this was fitted with a spinning rotary cylindrical electrode. The electrode tray was placed in a device for producing nanofibers by electrostatic spinning. As a backing material, any fabric, film or the like can be used. The obtained organic-inorganic nanofiber layer contained nanofibres with thicknesses of 30-1000 nm.

The nanofibrous organic-inorganic layer was subsequently calcined in the furnace in an air atmosphere at a temperature of 600 to 800 ° C to form pure amorphous SiO ₂ nanofibres.

Similarly, the following alkoxide solutions were electrospinned.

For the production of TiO ₂ nanofibres, a mixture of 250 g of ethanol and 29.4 g of acetylacetone was used in the preparation of the solution, in which 100 g of titanium tetrabutoxide was dissolved. After homogenization, the solution obtained was carefully mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of 1300000 g / mol in 758.8 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. Nanofibrous organic • · ·· «44 ♦« · <

9 94 «(° PS3571EN .......)

the inorganic layer was calcined in an air furnace at 500 ° C. The crystalline form (structure) of the resulting T1O2 inorganic nanofibres was purely anatase.

In another exemplary embodiment, a mixture of 250 g of ethanol and 29.4 g of acetylacetone in which 100 g of titanium tetrabutoxide was dissolved was used to prepare the solution of Li 4 Ti 15 O 12 nanofibers. After homogenization, the solution obtained was carefully mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of 1300000 g / mol and 24 g of lithium acetate dihydrate in 758.8 g of ethanol. The resulting solution was spun by electrostatic spinning. The nanofibrous organic-inorganic layer was calcined in an air furnace at 750 ° C. The resulting inorganic fibers exhibited a Li 4 Ti 15 O 12 phase with anatase and rutile admixture of less than 5%.

In another embodiment, a mixture of 250 g of 2-propanol and 29.4 g of acetylacetone in which 100 g of titanium tetrabutoxide was dissolved was used to produce a solution for producing ΊΊΟ2 nanofibers. After homogenization, the obtained solution was mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of 1300000 g / mol in 758.8 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 700 ° C. The crystalline form of the resulting nanofibres was partly anatase and partly rutile, which is confirmed by the image shown in Fig. 1 and the XRD spectrum of the nanofibers shown in Fig. 2.

In another exemplary embodiment, a mixture of 250 g of 1-propanol and 29.4 g of acetylacetone acidified with 0.3 g of phosphoric acid was used to produce a solution for the production of T1O2 nanofibres. 100 g of titanium tetrabutoxide were dissolved in the mixture. After homogenization, the obtained solution was mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of 1300000 g / mol in 758.8 g of ethanol. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 500 ° C. The crystalline form of the resulting inorganic T1O2 nanofibres was purely anatase.

In another embodiment, a mixture of 250 g of ethanol and 58.8 g of acetylacetone in which 100 g of titanium tetrabutoxide was dissolved was used to produce a solution for the production of T1O2 nanofibres. After homogenization, the solution obtained was mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of 1300000 g / mol in 729.4 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 700 ° C. The crystalline form of the resulting TiO ₂ nanofibres was partly anatase and partly rutile.

A mixture of 150 g of ethanol and 29.4 g of acetylacetone, in which 100 g of titanium tetrabutoxide was dissolved, was used to produce a solution for the production of TiO ₂ nanofibres. After homogenization, the obtained solution was mixed with a solution of 35.2 g of poly (vinylpyrrolidone) of 1300000 g / mol in 272.1 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 500 ° C. The crystalline form of the resulting inorganic TiO ₂ nanofibres was purely anatase.

In another embodiment, a mixture of 250 g of ethanol and 35.2 g of acetylacetone in which 100 g of titanium tetraisopropoxide was dissolved was used to produce a solution for the production of TiO ₂ nanofibres. After homogenization, the obtained solution was mixed with a solution of 42.2 g of poly (vinylpyrrolidone) having a molecular weight of 1300000 g / mol in

977.7 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 500 ^e C. The crystalline form of the resulting inorganic TiO ₂ nanofibres was pure pineapple.

For the production of Al2O3 nanofibres, a mixture of 500 g of 2-propanol a was used

40.7 g of acetylacetone in which 100 g of aluminum tri-sec-butoxide was dissolved. After homogenization, the obtained solution was mixed with a solution of 62.1 g of poly (vinylpyrrolidone) of 1300000 g / mol in 1366.9 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 700 ° C. The resulting inorganic fibers showed a pure γ-Al ₂ O ₃ crystalline structure, as confirmed by the image shown in Figure 3 and the XRD spectrum shown in Figure 4.

• w «V» V 4 · · · 35 PS PS 35 35 35 35 35 35 35 PS3571C2 .. .....

In another embodiment, a mixture of 350 g of 2-propanol and 40.7 g of acetylacetone in which 100 g of aluminum tri-sec-butoxide was dissolved was used to produce a solution for producing Al 2 O 3 nanofibres. After homogenization, the solution obtained was mixed with a solution of 62.1 g of poly (vinylpyrrolidone) of 1300000 g / mol in 827 g of ethanol and then acidified with concentrated hydrochloric acid. The nanofibrous layer was calcinated at the temperature of 800 ^e C. The resultant inorganic fibers showed a pure yA = CH crystalline structure.

In another embodiment, a mixture of 500 g of 2-propanol and 49 g of acetylacetone in which 100 g of aluminum triisopropoxide was dissolved was used to produce a solution for producing Al2O3 nanofibres. After homogenization, the solution obtained was mixed with a solution of 74.9 g of poly (vinylpyrrolidone) of 1300000 g / mol in 1772.2 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 700 ° C. The resulting inorganic fibers showed a pure γ-Al ₂ O ₃ crystalline structure.

A mixture of 500 g of ethanol and 68.6 g of acetylacetone was used for the production of B2O3 nanofibres in which 100 g of boron triethoxide was dissolved. After homogenization, the obtained solution was mixed with a solution of 71.5 g of poly (vinylpyrrolidone) of 1300000 g / mol in 1644.3 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 500 ° C. The resulting inorganic fibers exhibited a B ₂ O ₃ crystalline structure with an amorphous impurity, as confirmed by the image shown in Figure 5 and the XRD spectrum shown in Figure 6.

For the production of ZrO ₂ nanofibres a mixture of 500 g of ethanol and 30.6 g of acetylacetone was used, to which a solution of 142.9 g of zirconium tetraisopropoxide in 1-propanol was added. After homogenization, the obtained solution was mixed with a solution of 56.4 g of poly (vinylpyrrolidone) of 1300000 g / mol in 1193.8 g of ethanol and then acidified with concentrated hydrochloric acid. The resulting solution was spun by electrostatic spinning. The nanofibrous layer was calcined at 700 ° C. The resulting inorganic fibers showed ZrO ₂

1 V 1 • «« · · v · · I

- PS3571CJ *** mixture of monoclinic and tetragonal crystalline structure, as confirmed by the image shown in Fig. 7 and the XRD spectrum shown in Fig. 8.

In all cases a long-term continuous spinning process was achieved and the thickness of produced nanofibres ranged from 30 to 1000 nm.

The production of nanofibres of the above-described alkoxide solutions is not limited to the described electrostatic spinning apparatus with a rotating spinning electrode, but other types of spinning electrodes can be used, in which the alkoxide solution in the electrostatic spinning field is on the surface of the active spinning zone of the spinning electrode. The spinning of the alkoxide solution also takes place successfully on the string spinning electrodes according to CZ PV 2007-485, in which the active spinning zone of the string has a stable position against the collecting electrode during spinning and the alkoxide solution is transported to the active spinning zone of the string either by deposition or by its length. In this case, the solution of alkoxides in the electrospinning field is located on the core surface of the spinning agent string. However, the described alkoxide solutions can also be used for the discontinuous production of nanofibres using a nozzle or needle as a spinning electrode.

Industrial applicability

Said method of production of nanofibres ensures sufficient stability of the spinning solution during the whole spinning and is crucial for the continuous production of inorganic nanofibres. The use of layers of inorganic nanofibres is important in many fields of technology and industry, for example for the production of composite materials, catalysts and electrochemically active elements.

Claims (15)

Process for the production of inorganic nanofibres by electrostatic spinning of a solution comprising a metal alkoxide or a metal or metalloid dissolved in an alcohol-based solvent system, characterized in that the solution is stabilized with a chelating agent which prevents the hydrolysis of the alkoxide and (vinylpyrrolidone) in alcohol, whereupon the resulting solution is fed to an electrostatic field in which electrospinning is continuously carried out, resulting in the formation of organic-inorganic nanofibres, which are subsequently calcined outside the spinning apparatus in an air atmosphere at a temperature of 500 ° C to 1300 ° C. 2. The process of claim 1 wherein concentrated acid is added to the solution to increase the conductivity of the solution. The process according to claim 2, wherein the acid is selected from the group of hydrochloric acid, nitric acid, phosphoric acid. Process according to any one of claims 1 to 3, characterized in that the chelating agent is acetylacetone. Process according to any one of claims 1 to 5, characterized in that the alcohol in the poly (vinylpyrrolidone) solution is selected from ethanol, 1-propanol, 2-propanol or mixtures thereof. Method according to any one of claims 1 to 5, characterized in that the poly (vinylpyrrolidone) has an average molar mass in the range of 10000001500000 g / mol and its mass concentration in the solution is in the range of 4 to 9%. The process according to claim 6, wherein the poly (vinylpyrrolidone) has an average molecular weight of 1300000 g / mol. The method according to any one of claims 1 to 7, wherein the poly (vinylpyrrolidone) has a viscosity number K in the range of K-70 to K-95 and its concentration in solution is in the range of 4 to 9%. The method of claim 8, wherein the poly (vinylpyrrolidone) has a viscosity number of K-90. • * * V Φ · φ · «·« φ φ • • • • • • •φ · »Ρ ^ 357Κ5Ζ ··· ·· ·· The process according to any one of claims 1 to 9, wherein the metal alkoxide is selected from titanium tetrabutoxide, titanium tetraisopropoxide, aluminum trisec-butoxide, aluminum triisopropoxide, zirconium tetraisopropoxide. A method according to any one of claims 1 to 9, characterized in that The metal alkoxide is selected from tetraethoxysilane, boron triethoxide. The method of any one of claims 1 to 11, wherein the molar ratio of alkoxide to chelating agent in solution is in the range of 1: 0.8 to 1: 2.2. Method according to any one of the preceding claims, characterized by 10 in that the alkoxide solution is in the electrospinning field on the surface of the active spinning zone of the spinning agent of the spinning electrode. Method according to claim 12, characterized in that the alkoxide solution is transported to the electrostatic spinning field by the surface of the spinning machine. 15 electrodes. Method according to claim 12, characterized in that the spinning electrode is formed by a rotary spinning electrode of elongated shape, which extends a part of its periphery into the spinning solution.