WO2017186201A1

WO2017186201A1 - Precursor fibers intended for preparation of silica fibers, method of manufacture thereof, method of modification thereof, use of silica fibers

Info

Publication number: WO2017186201A1
Application number: PCT/CZ2017/050019
Authority: WO
Inventors: Jana Ruzickova; Miroslav TEJKL; Andrea KUDROVA; Zdenek VOSATKA; Jan BUK
Original assignee: Pardam, S.R.O.
Priority date: 2016-04-26
Filing date: 2017-04-25
Publication date: 2017-11-02

Abstract

Precursor fibers for preparation of silica fibers that contain the earner polymer and have the silica content in fibers 60 to 95 wt% in the dry mass. Further the method of preparation thereof is described with the centrifugal or electrostatic spinning of aqueous solutions of the carrier polymers with the content of the salt of silicic acid. The obtained precursor fibers are then calcinated to remove the carrier polymer and form the silica fibers that may form the fiber material in a wide range of forms from areal shapes to bulky wool-like structure.

Description

PRECURSOR FIBERS INTENDED FOR PREPARATION OF SILICA

FIBERS, METHOD OF MANUFACTURE THEREOF,

METHOD OF MODIFICATION THEREOF, USE OF SILICA FIBERS

Field of the invention

The invention relates to precursor fibers intended for preparation of silica fibers, a method of manufacture thereof, further to a method of modification thereof resulting in a formation of nanofibers and/or submicron fibers of amorphous silicon dioxide.

Background of the invention

The popularity of silica as material in various branches of human activities is given by its ability to interact with other groups, it acts e.g. as proton donor or acceptor, further it is capable of dipole-dipole interactions, interactions of induced dipoles and interactions based on disperse forces (Reich, 2007). Nanofibers and submicron fibers have huge specific surface that gives this material large space to the above mentioned interactions. These fibers may be therefore used as carriers of catalyzers or battery separators. Because of high chemical stability and thermal endurance it may be used also for filtration in extreme conditions. In a combination with polymer materials, it may be used as special medicine means, membranes, sensors, extractive sorbents and chromatographic materials with high adsorption capacity (Keyur, 2008; Shao, 2002; Sawicka, 2006).

Currently, the most common process of Si0₂ nanofiber production is electrospinning. It is possible to spin a sol-gel (Freyer, 2014; He, 2013; Saha, 2013; Shao, 2002; Shao, 2003; When, 2010; Wang, 2012; Yamaguchi, 2008) either with the addition of a carrier polymer (Liu, 2008; Roh, 2008; Wen, 2010) or without it (Choi, 2003) or to spin the polymer solution with the content of particles on the basis of silicon (Chen L.-J., 2009; Ji, 2008; Wu, 2014). The manufacturing of Si0₂ fibers may be performed also with centrifugal fiber spinning of the sol- gel in the mixture with the carrier polymer (Ren, 2014). Pure Si0₂ fibers may be prepared from the described mixture fibers with following calcination, wherein the separation of the carrier polymer occurs at the high temperature.

There are further processes of preparation of silica fibers, e.g. synthesis (Jin, 2008; Wang, 2008; Xiao, 2008), self-assembly" technique (Lai, 2015) or spreading of silica onto the surface of nanofibers with following surface treating of pre-prepared polymer fibers (Jia, 2015; Patel, 2009), they are, however, long, complicated and little effective from a commercial point of view.

According to Newsome at al. (Newsome, 2014) the above stated sol-gel technique comprises hydrolysis of metal alkoxide such as tetraethyl orthosilicate (TEOS) and although the sol-gel may be spun separately, it is often mixed with polymer to achieve sufficient degree of entaglements of molecular chains that prevent an breakage of the polymer stream in the course of the electrospinning. An important fact is, that the disclosed sol-gel either in the mixture, or alone, may be spun only in a certain phase and that is neither before, nor after the sol-gel reaction, whereas large disadvantage of this process is accurate control of the above stated dynamic reaction of the spun solution and thus also chemical and physical properties of resulting product (Newsome, 2014). The use of TEOS in the spinning sol-gel solution usually demands the use of ethanol as a solution, which to a certain extent limits the commercial use of this spinning system.

From this perspective, the possibility to spin particles in the mixture with the earner polymer appears much more interesting. The carrier polymer may be e.g. polyvinyl alcohol (PVA) (Jin, 2009; Kanehata, 2007), polyethylene oxide (PEO) (Sharma, 2010), polyacrylonitrile (PAN) (Ji, 2008; Jung, 2009), polymethylmethacrylate (PMMA) (Chen Y., 2009), polyvinylbutyral (PVB) (Chen L.-J., 2009), polyethylene terephthalate (PET) (Ma, 2012), polyvinylidene fluoride (PVDF) (Chinnapan, 2011; Choi, 2003; Rambaud, 2009) and often used is also polyvinylpyrrolidone (PVP) (Newsome, 2014; Roh, 2008; Wang, 2012; Wu, 2014; Zhao, 2008). A problem of this process is a need of a homogenous disperse of inorganic particles that is often achievable only with suitable solvent, which often limits the choice of earner polymer to polymers soluble in water or alcohol (Chen L.-J., 2009) Alcoholic solutions are combustible, it is necessary to evaporate large amount of alcohol during the spinning, in the case of the electrospinning when discharge occurs easily, it brings about considerable risk.

The solution of silicic acid is not classified as a dangerous agent that is an advantage to TEOS. Water soluble carrier polymers may be successfully substituted also by water insoluble carrier polymers that have to be, however, dissolved in toxic solvents that again it complicates the eventual commercial production. Several authors deal with the spinning of water soluble polymers with colloid particles of silica (Jin, 2009; Kanehata, 2007; Sharma, 2010). Kanehata at al. (Kanehata, 2007) that worked with various sizes of colloid particles of Si0₂ spun together with an aqueous solution of PVA. Maximum content of silica in produced fibers was 57 wt%. A spinning solution was prepared by a dispersion of silica nanoparticles in water and forming a mixture with 10% aqueous solution of PVA. Dispergation of resulting particles against using of colloidal solutions brings about several disadvantages. First of all, there is an additional process step, that so as not to cause the increase of viscosity, must comprise homogenization and degassing, there agglomerates among particles easily occur and a quality control of the dispersion is very complicated. Also the manipulation with nanoparticles in a dry state is very problematic and in the case of the commercial production only hardly feasible. Jin at all. (Jin, 2009) prepared special PVA fibers with "bead-like structure" that are interesting in the term of photoelectric properties. These materials contain up to 77% silica particles in fibers. It must be noted that this process of preparation is not designed to the preparation of silica fibers regarding the bead-like fiber structure and neither it is usable as a precursor for the preparation of pure silica fibers, as the fibers would disintegrate after the removal of the carrier polymer in the calcination. Sharma et al. in his work did not exceed the concentration of 25 wt% of colloid Si0₂ particles in PEO fibers.

Patent documents concerning the production of nanofibers and the submicron fibers from Si0₂ deal in vast majority with different processes of preparation of these fibers with electrospinning of solutions containing TEOS (US20110049769, US2015224468, US2015240411, CN104056612, US20120171488, CN102652903, CN102674370, CN101603245, CN103882624, CN102826760) or the formation of the silica layer on the surface of fibers of carboxymethyl cellulose or alginate (WO2011112364) or other polymers (CN104111246, CN103981634) or carbon fibers (RU2012121044, RU2516409). For the formation of Si0₂ nanofibers may be used also the coaxial spinning, the authors used polymer PVP as carrier polymer in the document CN103102067. Worth mentioning it is also the technique for preparation of silica nano- and micro-fibers with electrolysis of Si0₂ from melted salts (RU2427526) or the manufacturing of nanofibers from silicon carbide from silicon monocrystals and at very high temperatures (RU2006117961, RU2328444, RU2393112) or the production of fibers from amorphous silicon dioxide in the reaction of chrysotile in an aqueous solution containing an agent control releasing protons and an agent complexing cations (US6692715, US2003044339) but they are probably difficult processes. Documents US2015211152 and WO2009038767 relate to silicon carbide. CN102502660 uses template synthesis for producing Si0₂ fibers, that is, however, not a commercially usable method of producing nanofibers.

Si0₂ nanofibers may be according to the document CN102791259 combined with other materials in the form of a composite suitable for medicine materials with hemostatic effect and the addition thereof may significantly improve the mechanic properties of inorganic coatings (CN104177877) or dental composites (CN103319832). Silica nanofibers may be part of bioactive materials (CN 102826760) and may be used for extraction of chemicals from organism (US2015126712).

The US8647557 relates to the preparation of nanofibers from water glass (also stated as KR20120082857 and KR20120076997), the authors thereof used water glass in the preparation of the spinning solution followed by adding propanol, hexane, trimethylchlorosilane to form hydrophobic gel. A carrier polymer in this mixture was PMMA, optionally PAN in dimethyl formamide, 40% silica content in the fibers is not high. PAN nanofibers with Si0₂ nanoparticle occur also in the documents CN103311523 and CN103305965. CN103467896 describes PTFE nanofibers doped with small amount of Si0₂ powder. Above mentioned composite nanofibers spun from non-aqueous solvents demand the use of toxic agents that complicate eventual commercial production of these fibers.

The aqueous solution was used according to the patent document marked with number KR20130075466 that describes the preparation of PVA nanofibers with the content of germanium and silica but the Si0₂ content was only 5%. PVA nanofibers with the content of silica nanoparticles are described in the document CN 103022442, nanoparticles are prepared by high-temperature pre-sintration and the developed material is used as a precursor for the preparation of a carbonate-silicon composite.

Summary of the invention The disadvantages and drawbacks of the prior art are overcome with precursor fibers intended for the preparation of silica fibers, characterized in that the silica content in the fibers is 60 to 95 wt%, preferably 65 to 95 wt% in the dry mass, more preferably 75 to 95 wt% in the dry mass. Further they contain at least one carrier polymer that is preferably selected from a group comprising polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyvinyl pyrolidone. Precursor fibers of the invention preferably contain one carrier polymer.

The term "carrier polymer" relates to a polymer that may be electrospun or centrifugally spun and that is soluble in an aqueous solution of silicic acid.

The diameter of precursor fibers of the invention is in the range from 50 to 5000 nm, preferably 50 to 3000 nm, more preferably 100 to 3000 nm. The precursor fiber of the invention may further contain a compound of a transition metal selected from a group comprising palladium(II) chloride, palladium(II) oxide, palladium(II) acetate, palladium(II) sulfide, palladium(II) iodide, palladium(II) bromide, palladium(II) sulfate, palladium(II) hydroxide, hexahydrate of chloroplatinic acid, platinum(II) oxide, platinum(II) chloride, platinum(II) sulfide, platinum(II) sulfate, platinum(II) bromide, platinum(II) iodide, ruthenium(III) chloride, ruthenium(III) iodide, ruthenium(III) bromide, ruthenium(IV) oxide, ruthenium(IV) hydroxide, titanium(IV) oxide. The content of the compound of transition metal in precursor fiber is preferably in the range 0.1 to 10 wt%. In the term of the commercial production, the use of aqueous solutions is much more practical and also environment friendlier because of low toxicity and small risk of fire during spinning.

Thus the method of production of precursor fibers of the invention proceeds in aqueous environment. The subject-matter of this method of the invention is a preparation of the spinning solution containing the aqueous solution of the salt of silicic acid of a general formula M₂Si0₃ x nH₂0, where M is selected from the group containing of any of the ions of alkali metals, preferably Na⁺, K⁺ or Li⁺, n is integer in the range 1 to 8, preferably n is 2 and at least one in an aqueous solution soluble carrier polymer and thereafter it is spun electrostatically or with centrifugal spinning. The spinning solution is made by blending the aqueous solution of the earner polymer, the aqueous solution of silicic acid and preferably also an adjuvant. The adjuvant is efficient after reaching higher output of spinning process. Between spinning solutions for the electrospinning and the centrifugal spinning is little difference in the composition which is given by the need of processing more viscous solutions in the case of the centrifugal spinning. The advantage of prepared colloid spinning solutions Si0₂ is the significant stability thereof. The solution of silicic acid is a cheap and non-toxic material. The processing of this raw material into nanofibers, either with the technology of the electrostatic spinning or the technology of centrifugal spinning, in the mixture with non-toxic water-soluble polymers enables a mass production of silica fibers with minimum impact on the environment. Because of not using concentrated ethanol as a solvent, there is no need to solve risk combustibility of this solvent and the vapor thereof.

Another advantage of the disclosed method mentioned previously is the high content of silica in the precursor fibers that decreases the amount of the carrier polymer in precursor fibers that is to be removed in the process of calcination. Thus the yield and the rate of the process are increased and the cost decreases. Precursor fibers prepared with the electrospinning are in the form of flat fabric, resulting nanofibers have diameter of the fiber in the tens to hundreds nanometers. Precursor fibers prepared with the centrifugal spinning may be also prepared as a membrane or as a cotton-woollike bulky fiber structures, the diameter of these fibers varies usually in the range from hundreds nanometers to ones micrometers. Resulting silica fibers retain the structure after calcination that the precursor fibers possessed before the calcination but minor reduction of the fiber diameter and increase of porosity occur that relates to the amount of carrier polymer that is removed by the calcination. Precursor and silica fibers of the invention thus form the fiber material that may be in the form of a layer or bulky cotton-wool. The possibility to process spinning solutions with the content of silicic acid with two different technologies brings about also the possibility of choice between different fiber structures. From bulky structures (bulky cotton-wool) obtained from the centrifugal spinning to flat structures (layers). Flat structures may be prepared either by the centrifugal spinning or the electrospinning. The materials prepared with disclosed technologies differ also in the fiber diameter that gives the opportunity to choose specific parameters according to the needs of the final product. Eventual combination of the materials obtained with these different technologies further broadens the range of properties that may be achieved.

According to preferred embodiment of the invention the molecular mass of the carrier polymer is in the range of 2xl0³ to 5xl0⁶ g/mol, preferably 2xl0⁴ to l .lxlO⁶ g/mol, more preferably 2x10⁵ to l .lxlO⁶ g/mol, whereas the carrier polymer is selected from the group comprising polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyvinyl pyrolidone. Molecular mass of polyvinyl alcohol is preferably in the range 2xl0⁴ to 1.5xl0⁵ g/mol.

According to another preferred embodiment of the invention the salt of silicic acid in the spinning solution is in the form of colloid particles or nanoparticles. The mass ratio thereof against the carrier polymer in the spinning solution is in the range 60/40 to 95/5. The formation of precursor fiber occurs at the temperature of 15 °C to 35 °C, preferably 20 °C to 30 °C. The spinning solution may further contain at least one adjuvant selected from a group comprising ethanol, n-butanol, izopropyl alcohol, formic acid, acetic acid, hydrochloric acid, lactic acid, oxalic acid. The adjuvant content in the spinning solution is preferably in the range 2 to 10 wt%.

According to yet another preferable embodiment of the invention the spinning solution further may contain at least one compound of transition metal selected from a group comprising palladium(II) chloride, palladium(II) oxide, palladium(II) acetate, palladium(II) chloride, palladium(II) sulfide, palladium(II) iodide, palladium(II) bromide, palladium(II) sulfate, palladium(II) hydroxide, chloroplatinic acid hexahydrate, platinum(II) oxide, platinum(II) chloride, platinum(II) sulfide, platinum(II) sulfate, platinum(Ii) bromide, platinum(II) iodide, ruthenium(III) chloride, ruthenium(III) iodide, ruthenium(III) bromide, ruthenium(IV) oxide, ruthenium(IV) hydroxide or titanium(IV) oxide. The content of the transition metal compound in the spinning solution is preferably in the range 2 to 12 wt%. The Pt, Pd or Ru compounds are preferably dissolved in the spinning solution. Ti0₂ is preferably in the form of suspension of aqueous solution and Ti0₂ nanoparticles in the spinning solution.

According to another embodiment of the invention the precursor fibers that do not contain transition metal compound and that are defined above, are modified using calcination at the 17 050019

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temperature 300 to 1400 °C, preferably 450 to 700 °C, for the period 30 to 240 minutes, preferably 60 to 180 minutes; whereas the heating rate is 0.5 to 20 °C/min, preferably 1 to 10 °C/min and thereafter the silica fibers formed contain 100 wt% silica.

According to another embodiment of the invention the precursor fibers containing transition metal compound and that are defined above, are modified using calcination at the temperature 300 to 1400 °C, preferably 450 to 700 °C; for the period 30 to 240 minutes, preferably 60 to 180 minutes; whereas the heating rate is 0.5 to 20 °C/min, preferably 1 to 10 °C/min, resulting in formation of silica fiber with the silica content of 85 to 99.9 wt% and transition metal content of 0.1 to 15 wt%. The content of Pt, Pd or Ru is preferably in the range of 0.1 to 10 wt% or the content of Ti is in the range of 10 to 15 wt%.

Silica fibers of the invention are thus made of precursor fibers produced in the method as is defined above, and the precursor fibers are thereafter modified with calcination in the method of the invention, as is defined above. The diameter of silica fibers of the invention is in the case of electrostatically spun fibers in the range 30 to 1000 nm, preferably 30 to 200 nm, more preferably 30 to 150 nm, and in the case of centrifugally spun fibers in the range of 100 to 4000 nm, preferably 200 to 2000 nm, more preferably 200 to 800 nm.

The high silica content in precursor fibers makes the method of silica fibers production more effective.

Silica fibers of the invention have further unique high porous structure that is apparent only at extreme magnification of the fibers using electron microscopy (see Fig. 20). This structure significantly increases surface of the fibers and broadens application possibilities thereof.

Precursor fibers or silica fibers of the invention may be used in chemistry, in filtration, in energetics or in medicine.

The fibers of the invention may be used in manufacturing filters, wound covering, drug carriers. Further, the fibers may be used because of the large surface and high porosity as sorbents, e.g. in water sorption or as catalyst carriers, e.g. for platinum (Fig. 22), palladium or ruthenium. Disclosed nanofibers with the content of noble metals bring about in the case of catalysts significant savings of noble metals and thus reduce the costs.

Fibers of the invention may be supplemented with the addition of Ti0₂ nanoparticles into spinning solution that leads to the formation of mixed precursor fibers Si0₂/Ti0₂ with photoactive effect. Because of this effect, the materials with the content of Ti0₂ are self- cleaning, efficiently degrade bacteria and viruses and eliminate odor. Ti0₂ nanoparticles themselves are difficult to use e.g. in industrial water treatment since they are difficult to remove afterwards. The incorporation thereof into Si0₂ nanoparticles enable to create special filtration materials that solve the above mentioned problem. It may degrade also hormones, the presence thereof is currently serious issue in the sewage treatment. The filtration material may be used also for the filtration of air or gases, where also liquidation of bacteria, viruses and VOC (volatile organic compound) occurs. Due to its high thermal stability the disclosed filtration material may be used to the filtration at high temperatures.

The term "silica content" in the fiber means the content of Si0₂ in the fiber. The term "titanium content" in the fiber means the content of Ti0₂ in the fiber. The term "compound of transition metal" means inorganic or organic compound of any transition metal belonging to 4^th, 5^th, or 6^th period of Mendeleev periodic table, they are preferably inorganic or organic compounds of Pt, Pd, Ru or Ti. As compounds of transition metal may be used oxides of Pt, Pd, Ru or Ti, halides, hydroxides, sulfides or sulfates of Pt, Pd or Ru. The compounds selected from the group ccomprising palladium(II) chloride, palladium(II) oxide, palladium(II) acetate, palladium(II) chloride, palladium(II) sulfide, palladium(II) iodide, palladium(II) bromide, palladium(II) sulfate, palladium(II) hydroxide, chloroplatinic acid hexahydrate, platinum(II) oxide, platinum(II) chloride, platinum(II) sulfide, platinum(II) sulfate, platinum(II) bromide, platinum(II) iodide, ruthenium(III) chloride, ruthenium(III) iodide, ruthenium(III) bromide, ruthenium(IV) oxide, ruthenium(IV) hydroxide, titanium(IV) oxide are preferably used.

Brief description of the drawings

Fig. 1 - SEM PVA of nanofibers with 65 wt% content of Si0 in the fibers produced with the technology of the electrospinning a) before the calcination and b) after the calcination. Fig. 2 - SEM of precursor PVA nanofibers with 65 wt% content of Si0₂ in the fibers and with the addition of ethanol into the spinning solution making 10 wt% in the final spinning solution, produced with the technology of the electrospinning.

Fig. 3 - SEM of precursor PVA nanofibers with 65 wt% content of Si0₂ in the fibers with the addition of acetic acid into the spinning solution making 10 wt% in the final spinning solution, produced with the technology of the electrospinning. Fig. 4 - SEM of precursor PVA nanofibers with 65 wt% content of Si0₂ in the fibers with the addition of formic acid into the spinning solution making 10 wt% in the final spinning solution, produced with the technology of the electrospinning.

Fig. 5 - SEM of PVA nanofibers with 82 wt% content of Si02 in the fibers produced with the technology of the electrospinning and with the addition of acetic acid making 10 wt% in the final spinning solution a) before the calcination and b) after the calcination.

Fig. 6 - SEM of PEO nanofibers with 67 wt% content of Si0₂ in the fibers produced with the technology of the electrospinning a) before the calcination and b) after the calcination.

Fig. 7 - SEM of PEO nanofibers with 92 wt% content of Si0₂ in the fibers produced with the technology of the electrospinning a) before the calcination and b) after the calcination.

Fig. 8 - SEM of precursor PAA nanofibers with 60 wt% content of Si0₂ in the fibers with the addition of acetic acid into the spinning solution making 2 wt% in the final spinning solution produced with the technology of the electrospinning.

Fig. 9 - SEM of precursor PVA submicron fibers with 76 wt% content of Si0₂ in the fibers and the addition of acetic acid into the spinning solution making 10 wt% in the final spinning solution produced with the technology of the centrifugal spinning.

Fib. 10 - SEM of precursor PVA submicron fibers with 76 wt% content of Si0₂ in the fibers with the addition of formic acid into the spinning solution making 10 wt% in the final spinning solution produced with the technology of the centrifugal spinning. Fig. 11 - SEM of PEO submicron fibers with 60 wt% content of Si0₂ in the fibers produced with the technology of centrifugal spinning a) before the calcination and b) after the calcination.

Fig. 12 - SEM of PEO precursor submicron fibers with 90 wt% content of Si0₂ in the fibers produced with the technology of the centrifugal spinning.

Fig. 13 - SEM of precursor PAA submicron fibers with 60 wt% content of Si0₂ in the fibers with the content of formic acid into the spinning solution making 2 wt% in the final spinning solution produced with the technology of the centrifugal spinning.

Fig. 14 - SEM of PVA nanofibers with 60 wt% content of Si0₂ in the fibers produced with the technology of the electrospinning from lithium salt of silicic acid a) before the calcination and b) after the calcination. Fig. 15 - SEM of PVA nanofibers with 60 wt% content of Si0₂ in the fibers produced with the technology of electrospinning from potassium salt of silicic acid a) before calcination and b) after calcination.

Fig. 16 - SEM of PVA submicron fibers with 60 wt% content of Si0₂ in the fibers produced with the technology of the centrifugal spinning from lithium salt of silicic acid a) before the calcination and b) after the calcination.

Fig. 17 - SEM of PVA submicron fibers with 60 wt% content of Si0₂ in the fibers produced with the technology of the centrifugal spinning from potassium salt of silicic acid a) before the calcination and b) after the calcination. Fig. 18 - SEM of precursor PVA nanofibers with 82 wt% content of Si0₂ in the fibers produced with the technology of the electrospinning.

Fig. 19 - SEM of PVA submicron fibers with 60 wt% content of Si0₂ in the fibers produced with the technology of centrifugal spinning a) before calcination, b) after calcination at 500 °C c) after calcination at 700 °C. Fig. 20 - SEM of calcinated PVA submicron fibers with 60 wt% content of Si0₂ in the fibers produced with the technology of the centrifugal spinning, calcinated at 700 °C a) magnification 2 OOOx, b) magnification 50 OOOx.

Fig. 21 -SEM of calcinated PVA nanofibers with 65 wt% content of Si0₂ in the fibers produced with the technology of electrospinning a) magnification 2 OOOx, b) magnification 20 OOOx. Fig. 22 - SEM of calcinated PVA submicron fibers with 90 wt% content of Si0₂ and 10 wt% content of Pt in the fibers produced with the technology of the centrifugal spinning a) magnification 2 OOOx b) magnification 100 OOOx.

Fig. 23 - SEM of PVA submicron fibers with 60 wt% content of Si0₂ with incorporated Ti0₂ nanoparticles produced with the technology of the centrifugal spinning a) before the calcination, b) after the calcination at 700 °C. The mass content of Ti0₂ nanoparticles in Si0₂ calcinated submicron fibers is 15 wt%. Examples of the embodiments of the invention Example 1

The spinning solution was mixed from the pre-prepared solution of PVA (16% solution, Sloviol®, Novacke chemicke zavody) and the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :1. The electrospinning proceeded on the laboratory machine NS Lab.

Conditions of the electrospinning:

Manufactured precursor nanofibers have the diameter in the range 50-200 nm and the silica content of 65 wt%. Productivity of the method on the lab device was 0.101 g precursor fibers per 10 min. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 1. The fiber diameter after the calcination varies in the range 30-150 nm.

Example 2 The spinning solution was mixed from the pre-prepared solution of PVA (16% solution, Sloviol®, Novacke chemicke zavody) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :1. Ethanol was added into the solution and it was in the final spinning solution in the concentration 10 wt%. The electrospinning proceeded on laboratory device NS Lab. Conditions of the electrospinning. 17 050019

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Manufactured precursor nanofibers have the fiber diameter in the range 100-250 nm and the silica content of 65 wt%. Productivity of the method on the lab device was 0.484 g fibers per 10 min. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 2. The addition of ethanol increased the productivity of the process almost five-fold in comparison to the output of the process with the solution without adjuvant stated in Example 1.

Example 3

The spinning solution was mixed from the pre-prepared solution of PVA (16% solution, Sloviol®, Novacke chemicke zavody) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :1. 75% acetic acid, that it was in the final spinning solution in the concentration 10 wt%, was added into the solution. Electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Voltage [kV]: 81.9

Current [mA] : 0.03-0.07

Electrode distance [cm]: 18-24

Temperature [°C]: 20-28

Humidity [% RH]: 25-35

Speed of the fabric movement [mm/min] : 40-100

Speed of revolving of the spinning electrode [rev/min]: 2.7 The manufactured precursor nanofibers have the fiber diameter in the range 50-200 nm and the silica content of 65 wt%. Productivity of the method on the lab device was 0.697 g fibers per 10 min. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 3 and Fig. 21. The addition of acetic acid increased the productivity of the process almost seven-fold in comparison to the output of the process with the solution without the adjuvant stated in Example 1.

Example 4

The spinning solution was mixed from the pre-prepared solution of PVA (16% solution, Sloviol®, Novacke chemicke zavody) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :1. 98% formic acid that it was in the final spinning solution in the concentration 10 wt%, was added into the solution. The electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Produced precursor nanofibers have the fiber diameter in the range 50-250 nm and the silica content of 65 wt%. Productivity of the method on the lab device was 0.583 g fibers per 10 min. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 4. The addition of acetic acid increased the productivity of the process almost six-fold in comparison to the output of the process with the solution without the adjuvant stated in Example 1.

Example 5

The spinning solution was mixed from the pre-prepared solution of PVA (20% solution, Poval 18-88, Kuraray) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :3.2. 75% acetic acid that it was in the final spinning solution in the concentration 10 wt%, was added into the solution. The electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Produced precursor nanofibers have the fiber diameter in the range 50-150 nm and the silica content of 82 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 5. The fiber diameter after the calcination varies in the range 30-120 nm.

Example 6 The spinning solution was mixed from the pre-prepared solution of PEO (5% solution, Mw 400 000 g/mol, Scientific Polymer Products) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in mass ratio 3:1. Ethanol was added to the solution and it was in the solution in the final concentration 10 wt%, was added into the solution. Electrospinning proceeded on lab device NS Lab. Conditions of the electrospinning.

Voltage [kV]: 45

Current [mA] : 0.03

Electrode distance [cm]: 18-24

Temperature [°C]: 20

Humidity [% RH]: 42 Z2017/050019

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Produced precursor nanofibers have the fiber diameter in the range 100-300 nm and the silica content 67 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 6. The fiber diameter after the calcination varies in the range 70-200 nm.

Example 7

The spinning solution was mixed from the pre-prepared solution of PEO (5% solution, Mw 900 000 g/mol, Scientific Polymer Products) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :2. Ethanol was added to this solution and it was in the solution in the final concentration 10 wt%. The electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Produced precursor nanofibers have the fiber diameter in the range 200-800 nm and the silica content 92 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 7. The fiber diameter after the calcination varies in the range 150-600 nm. Example 8

The spinning solution was mixed from the pre-prepared solution of PAA (25% solution, Mw 250 000 g/mol, Scientific Polymer Products) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 : 1.5. Acetic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Produced precursor nanofibers have the fiber diameter in the range 100-300 nm and the silica content 60 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 8.

Example 9

The spinning solution was mixed from the pre-prepared solution of PVA (20% solution, Poval 18-88, Kuraray) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :3.2. 75% Acetic acid was added to this solution and it was in the solution in the final concentration 10 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 20.2 °C and humidity 26.8%RH. Revolving rate was 8 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 300-800 nm and the silica content 76 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 9. Example 10

The spinning solution was mixed from the pre-prepared solution of PVA (20% solution, Poval 18-88, Kuraray) and from the pre-prepared 30%> aqueous solution of sodium salt of silicic acid in the mass ratio 1 :3.2. 98%> formic was added to this solution and it was in the solution in the final concentration 10 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 20.2 °C and humidity 26.8%RH. The rate of spinneret revolving was 8 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 300-1000 nm and the silica content 76 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 10.

Example 11

The spinning solution was mixed from the pre-prepared solution of PEO (5% solution, Mw 400.000 g/mol, Scientific Polymer Products) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 3:1. Ethanol was added to this solution and itwas in the solution in the final concentration 10 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 32 °C and humidity 22% H. The rate of spinneret revolving was 8 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 1000-5000 nm and the silica content 60 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 1 1. The fiber diameter after the calcination varies in the range 800-3000 nm.

Example 12

The spinning solution was mixed from the pre-prepared solution of PEO (5%> solution, Mw 900.000 g/mol, Scientific Polymer Products) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 2:3. Ethanol was added to this solution and it was in the solution in the final concentration 10 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for centrifugal spinning at the temperature 22 °C and humidity 54%RH. The rate of spinneret revolving was 4 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 1000-5000 nm and the silica content 90 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 12. Example 13

The spinning solution was mixed from pre-prepared solution of PA A (25% solution, Mw 1.080.000 g/mol, Acros Organics) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 : 1.5. Acetic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 32 °C and humidity 22%RH. The rate of spinneret revolving was 8 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 100-1000 nm and the silicon content 60 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shot of the produced sample is in Fig. 13.

Example 14

The spinning solution was mixed from the pre-prepared solution of PVA (16% solution, Sloviol®, Novacke chemicke zavody) and from the pre-prepared 30% aqueous solution of lithium salt of silicic acid in the mass ratio 1 : 1. 98% formic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning:

Produced precursor nanofibers have the fiber diameter in the range 50-200 nm and the silica content 65 wt%. Productivity of the process on the lab device was 0.101 g of precursor fibers per 10 min. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. The fiber diameter varies in the range 30-150 nm. Example 15

The spinning solution was mixed from the pre-prepared solution of PVA (16% solution, Sloviol®, Novacke chemicke zavody) and from the pre-prepared 30% aqueous solution of potassium salt of silicic acid in the mass ratio 1 :1. 98% formic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The electrospinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Produced precursor nanofibers have the fiber diameter in the range 50-200 nm and the silica content 65 wt%. Productivity of the process on the lab device was 0.101 g of precursor fibers per 10 min. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 14. The fiber diameter varies in the range 30-150 nm.

Example 16 The spinning solution was mixed from the pre-prepared solution of PVA (20% solution, Poval 13-88, Kuraray) and from the pre-prepared 30% aqueous solution of lithium salt of silicic acid in the mass ratio 1 :3. 75% acetic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 20.2 °C and humidity 26.8%RH. The rate of spinneret revolving was 9 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 300-800 nm and the silica content 66 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 2017/050019

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hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 16. The fiber diameter varies in the range 200-600 nm.

Example 17

The spinning solution was mixed from the pre-prepared solution of PVA (20% solution, Poval 13-88, Kuraray) and from the pre-prepared 30% aqueous solution of potassium salt of silicic acid in the mass ratio 1 :3. 98% acetic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 20.2 °C and humidity 26.8%RH. The rate of spinneret revolving was 9 000 rev/min. Produced precursor nanofibers have the fiber diameter in the range 300-800 mil and the silica content 66 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of produced sample are in Fig. 17. The fiber diameter varies in the range 200-600 nm.

Example 18 The spinning solution was mixed from the pre-prepared solution of PVA (20% solution, Poval 13-88, Kuraray) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :3.2. Electro spinning proceeded on lab device NS Lab.

Conditions of the electrospinning.

Produced precursor nanofibers have the fiber diameter in the range 200-800 nm and the silica content 82 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of the produced sample are in Fig. 18. Example 19

The spinning solution was mixed from the pre-prepared solution of PVA (18% solution, Poval 13-88, Kuraray) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the. mass ratio 1 : 1. 98%) formic acid was added to this solution and it was in the solution in the final concentration 2 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab device for the centrifugal spinning at the temperature 26 °C and humidity 25%RH. The rate of spinneret revolving was 8 500 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 300-1000 nm and the silica content 63 wt%. The calcination proceeded in the batch oven in the first case at the temperature 500 °C for 2 hours, whereas the heating rate was 1 °C/min and in the second case at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. SEM shots of produced sample are in Fig. 19 and Fig. 20.

Example 20

The spinning solution was mixed from the pre-prepared solution of PVA (18% solution, Poval 13-88, Kuraray) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 : 1. 98%) formic acid was added to this solution and it was in the solution in the final concentration 2 wt% and chloroplatinic acid hexahydrate that it was in the final spinning solution in the concentration 3 wt%. The centrifugal spinning proceeded on a prototype of large- scale lab device for the centrifugal spinning at the temperature 26 °C and humidity 25%>RH. The rate of spinneret revolving was 8 500 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 200-800 nm and the silica content 65 wt% and chloroplatinic acid content 12 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. The final silica content in the calcinated fibers is 90 wt% and the final platinum content in the calcinated fibers is 10 wt%. SEM shots of the produced sample are in Fig. 22.

Example 21

The spinning solution was mixed from the pre-prepared solution of PVA (18% solution, Poval 13-88, Kuraray) and from the pre-prepared 30% aqueous solution of sodium salt of silicic acid in the mass ratio 1 :1. 98% formic acid was added to this solution and it was in the solution in the final concentration 3 wt% and nanoparticles Ti0₂ of 4 nm that they were in the final solution in concentration 3 wt%. The centrifugal spinning proceeded on a prototype of large-scale lab Z2017/050019

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device for the centrifugal spinning at the temperature 21 °C and humidity 31%RH. The rate of spinneret revolving was 8 000 rev/min.

Produced precursor nanofibers have the fiber diameter in the range 200-2000 irm and the silica content 60 wt% and titanium dioxide 3 wt%. The calcination proceeded in the batch oven at the temperature 700 °C for 2 hours, whereas the heating rate was 1 °C/min. The final silica content in the calcinated fibers is 85 wt% and the final titanium content in the calcinated fibers is 15 wt%. SEM shots of the produced sample are in Fig. 23.

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Claims

1. Precursor fiber intended for preparation of a silica fiber characterized in that a silica content in the fiber is 60 to 95 wt% in the diy mass, containing at least one carrier polymer.

2. Precursor fiber according to claim 1 characterized in that the silica content in the fiber is preferably 65 to 95 wt% in the dry mass, more preferably 75 to 95 wt% in the dry mass.

3. Precursor fiber according to claim 1 or claim 2 characterized in that the fiber diameter is in the range 50 to 5 000 nm, preferably 50 to 3 000 nm, more preferably 100 to 3 000 nm.

4. Precursor fiber according to any one of claims 1 to 3 characterized in that the carrier polymer is selected from a group comprising polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyvinyl pyrolidone.

5. Precursor fiber according to any one of claims 1 to 4 characterized in that it further contains a transition metal compound selected from a group comprising palladium(II) chloride, palladium(II) oxide, palladium(II) acetate, palladium(II) sulfide, palladium(II) iodide, palladium(II) bromide, palladium(II) sulfate, palladium(II) hydroxide, chloroplatinic acid hexahydrate, platinum(II) oxide, platinum(II) chloride, platinum(II) sulfide, platinum(II) sulfate, platinum(II) bromide, platinum(II) iodide, ruthenium(III) chloride, ruthenium(III) iodide, ruthenium(III) bromide, ruthenium(IV) oxide, ruthenium(IV) hydroxide, titanium(IV) oxide.

6. Precursor fiber according to claim 5 characterized in that the content of the transition metal compound in the fiber is in the range 0.1 to 10 wt%.

7. Method for production of precursor fibers defined in any one of claims 1 to 6, characterized in that the spinning solution is prepared, containing an aqueous solution of silicic acid of general formula M₂Si0₃ x nH₂0, where M is selected from a group comprising any of alkali metal ions, preferably Na⁺, L⁺ or Li⁺, n is an integer in the range of 1 to 8, preferably 2, and containing at least one in the water soluble earned polymer followed by the electrostatic or centrifugal spinning of the solution.

8. Method of production according to claim 7, characterized in that the carrier polymer is selected from a group comprising polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyvinyl pyrolidone, the molecular mass being in the range 2x10³ to 5x10⁶ g/mol, preferably 2xl0⁴ to l . l l 0⁶ g/mol, more preferably 2x10⁵ to l .lxl 0⁶ g/mol.

9. The method of production according to any one of claims 7 to 8 characterized in that the mass ratio of the salt of silicic acid to the carrier polymer is in the range 60/40 to 95/5 in the spinning solution.

10. Method of production according to any one of claims 7 to 9 characterized in that the spinning proceeds at the temperature 15 °C to 35 °C, preferably 20 °C to 30 °C.

11. Method of production according to any one of claims 7 to 10 characterized in that the spinning solution further contains at least one adjuvant selected from a group comprising ethanol, isopropyl alcohol, n-butanol, formic acid, acetic acid, hydrochloric acid, lactic acid, oxalic acid.

12. Method of production according to claim 11, characterized in that the content of the adjuvant in the spimiing solution is in the range 2 to 10 wt%.

13. Method of production according to claim 1 1 to 12 characterized in that the spinning solution further contains at least one transition metal compound selected from a group comprising palladium(II) chloride, palladium(II) oxide, palladium(II) acetate, palladium(II) sulfide, palladium(II) iodide, palladium(II) bromide, palladium(II) sulfate, palladium(II) hydroxide, chloroplatinic acid hexahydrate, platinum(II) oxide, platinum(II) chloride, platinum(II) sulfide, platinum(II) sulfate, platinum(II) bromide, platinum(II) iodide, ruthenium(III) chloride, ruthenium(III) iodide, ruthenium(III) bromide, ruthenium(IV) oxide, ruthenium(IV) hydroxide or titanium(IV) oxide.

14. Method of production according to claim 13 characterized in that the content of the transition metal compound is in the range 2 to 12 wt% in spinning solution.

15. Method of production according to any one of claims 7 to 14 characterized in that the salt of silicic acid is in the form of colloid particles or nanoparticles in the spinning solution.

16. Method of modification of the precursor fiber defined according to any one of claims 1 to 4 characterized in that the precursor fiber is calcinated at the temperature 300 to 1400 °C, preferably 450 to 700 °C; for the period 30 to 240 minutes, preferably 60 to 180 minutes; the heating rate being 0.5 to 20 °C/min, preferably 1 to 10 °C/min., to form the silica fiber with the silica content 100 wt%.

17. Method of modification of the precursor fiber defined according to claim 5 or claim 6 characterized in that the precursor fiber is calcinated at the temperature 300 to 1400 °C, preferably 450 to 700 °C; for the period 30 to 240 minutes, preferably 60 to 180 minutes; the heating rate being 0.5 to 20 °C/min, preferably 1 to 10 °C/min., to form the silica fiber with the silica content in the range 85 to 99.9 wt% and transition metal content 0.1 to 15 wt%.

18. Method of modification of the precursor fiber defined according to claim 17, characterized in that Pt, Pd or Ru content is in the range 0.1 to 10 wt%.

19. Method for modification of the precursor fiber defined according to claim 17, characterized in that Ti content is in the range 10 to 15 wt%.

20. Use of the precursor fiber according to any one of claims 1 to 6 or the silica fiber prepared using the method defined according to any one of claims 16 to 19 as a material in chemistry, filtration, energetics or medicine.

21. Use of the precursor fiber according to claim 20 as a sorbent or a catalyst.

22. Use of the fiber according to claim 20 as a material for production of filter, wound cover or drug carrier.