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  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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Definitions

• the invention relates to a method for the preparation of submicron and/or micron fibers formed by a mixture of crystalline titanium dioxide (TiC ) and crystalline vanadium oxide (V2O5).
• the invention relates to submicron and/or micron fibers prepared by this method. art
• One of the oxides is either prepared in advance or both oxides are prepared together in a single step [1 to 4],
• the disadvantage of this method is that agglomeration of the resulting nanoparticles occurs, making this method very difficult to apply on an industrial scale.
• CN103706362A describes a process for the preparation of TiO2/V2Os fibers, in which tetrabutyl titanate (Ci6H4o04Ti) is used as a source of titanium, vanadium acetoacetonate (V0(Acac)2) as a source of vanadium, and polyvinylpyrrolidone (PVP) with a molecular weight of 1 ,300,000 as a carrier polymer. Absolute ethanol and dimethyl acetamide are used as solvents. A solution prepared by mixing stock titanium solution and stock vanadium solution with PVP is subjected to electrostatic spinning. During subsequent calcination, the prepared precursor fibers are converted to TiC A ⁇ Os fibers.
• tetrabutyl titanate Ca6H4o04Ti
• V0(Acac)2 vanadium acetoacetonate
• PVP polyvinylpyrrolidone
• CN109119636A discloses production of titanium and vanadium nitride nanofibers. It uses Ti(OC2Hs)4, TiO2, Ti4O?, TiCIs, TiCk or TiH4 as a titanium precursor and VO(OC2Hs)2, V(OC2Hs)3, NH4VO3, NasVCM, VCI2 or V2O5 as a vanadium precursor.
• PVP is used as a carrier polymer
• alcohol (ethanol) is used as a solvent.
• Precursor solution is spun by electrostatic spinning and the prepared precursor fibers are subsequently subjected to calcination in a nitrogen atmosphere, during which they are converted to TiChA ⁇ Os fibers.
• submicron and/or micron fibers themselves consisting of a mixture of TiO2 and V2O5 prepared by this method are also an object of the invention.
• the object of the invention is achieved by a method for the preparation of submicron and/or micron fibers with a diameter of 200 to 3,000 nm formed by a mixture of titanium dioxide (TiC>2) and vanadium oxide (V2O5), using ammonium bis(oxalate)oxo-titanate (C4HnN0nTi) as a TiO2 precursor, ammonium vanadate (NH4VO3) as a V2O5 precursor, and polyvinylpyrrolidone (PVP) with a molar mass of 360,000 to 1 ,300,000 g/mol, polyethylene glycol (PEG) with a molar mass of 200,000 to 700,000 g/mol, or a mixture of PVP and PEG at a ratio of 3:1 to 6:1 as a carrier polymer, wherein the diameter of the prepared fibers decreases as the molar mass of the carrier polymer/polymers increases.
• Stock vanadium solution with a vanadium concentration of 0.3 to 0.65 M is prepared by dissolving ammonium vanadate in a mixture of water and oxalic acid (C2H2O4).
• Ammonium vanadate in an amount of 4 to 15 wt. %, preferably 5 to 10 wt. %, is mixed with a mixture of water and oxalic acid, wherein the ratio of water and oxalic acid in this mixture is in the range of 1 :1 to 6:1 and the amount of oxalic acid is at least twice the molar concentration of ammonium vanadate.
• the mixture thus prepared is heated to a temperature of 50 ⁇ 5 °C and is stirred (preferably in a water bath) until the precipitate dissolves, and the color of the solution turns blue. It is then heated to a temperature of 60 ⁇ 5 to 80 ⁇ 5 °C, when ammonium vanadate is reduced and an oxalate complex of tetravalent vanadium is formed, accompanied by the release of CO2:
• the solution thus formed is cooled (preferably freely) to room temperature.
• acetic acid CH 3 COOH
• acetic acid is preferably added to it in an amount of 6 to 22 wt.% to stabilize the formed oxalate complex of tetravalent vanadium, and, optionally, also water in an amount up to the required volume, wherein the total content of water in stock vanadium solution is up to 85 wt.%, preferably ranging from 20 to 85 wt.%.
• Stock titanium solution with a titanium concentration of 0.3 to 0.65 M is prepared by dissolving ammonium bis(oxalate)oxo-titanate in technical hydrogen peroxide (preferably 30% hydrogen peroxide).
• the ratio of ammonium bis(oxalate)oxo-titanate to hydrogen peroxide is in the range of 1 :2.5 to 1 :4, preferably 1 :3 to 1 :3.5.
• the mixture thus obtained is vigorously stirred at an elevated temperature (40 ⁇ 5 °C) until the bis(oxalate)oxo-titanate is completely dissolved and a clear solution of peroxo complex is formed.
• ammonium bis(oxalate)oxo-titanate is oxidized by hydrogen peroxide to ammonium bis(oxalate) peroxo-titanate to form a clear orange-red solution.
• acetic acid CH 3 COOH
• water is added to it in an amount up to the required volume, wherein the total water content in the stock solution is up to 80 wt. %, preferably 8 to 80 wt.%.
• acetic acid is not necessary when creating stock titanium solution for immediate consumption.
• acetic acid and/or water may be added to a mixture of ammonium bis(oxalate)oxo- titanate in technical hydrogen peroxide prior to preparing the solution.
• the order in which the individual components are added does not matter.
• Stock solutions of titanium and vanadium thus prepared are mixed according to the desired ratio of titanium to vanadium in the resulting submicron or micron fibers (atomic ratio of 0.1 :99.9 to 99.9:0.1 ). Subsequently, to the mixture of stock solutions thus prepared, PVP with a molar mass of 360 000 to 1 300 000 g/mol in an amount of 15 to 25 wt. % of the resulting solution or PEG with a molar mass of 200 000 to 700 000 g/mol in an amount of 5 to 16 wt. % of the resulting solution or a mixture of PVP and PEG at a ratio of 1 :3 to 1 :6 in an amount of 7 to 15 wt.
• % of the resulting solution is added, and the rest up to 100 wt. % is topped up with water.
• the order in which PVP and PEG are added does not matter.
• the mixture thus obtained is subsequently stirred until a homogeneous solution is formed.
• the concentration of the polymer/polymers in this solution is 5 to 25 wt. %; the stock solution of titanium and vanadium together represents 55 to 80 wt. % of this solution. If necessary, this solution is made up to the required volume with water.
• the proportion of water is in the range of 0 to 40 wt. %.
• ethanol may be added to the mixture at the expense of water in quantities of up to 25 wt. %.
• the solution for spinning thus prepared is subsequently spun by a suitable technology of spinning.
• the most suitable method appears to be centrifugal spinning, which does not require high electrical voltage and which produces large and easy-to-manipulate tufts of precursor fibers without an electrical charge which are deposited on collectors, so that there is no need to laboriously peel the fibers from the base material (e.g. non-woven textiles), the need existing in the case, for example, when using electrostatic spinning.
• Another advantage of centrifugal spinning is that it has a greater yield of fibers over time than the other methods, such as electrostatic spinning, hydrothermal processes, templating, drawing, etc., and enables the preparation of industrial quantities of material in a short time.
• any other known technology for the preparation of submicron or micron fibers, in particular electrostatic spinning can be used to produce submicron or micron fibers.
• centrifugal spinning conditions air with a temperature of 25 to 45 °C and a relative humidity of 15 to 40 % flows into the spinning chamber and the spinning head rotates at a speed of 3,000 to 15,000 rpm, preferably 4,500 to 9,500 rpm.
• the diameters of precursor fibers prepared by centrifugal spinning reach approximately 450 to 6,200 nm.
• the precursor fibers thus prepared are subsequently calcined, their organic components being removed from them by heat, ammonium bis(oxalate)oxo-titanate being transformed into crystalline TiO2 and ammonium vanadate into crystalline V2O5, wherein these oxides retain the fiber structure of the precursor fibers and create submicron and/or micron fibers, which can be optionally hollow, with a diameter in the range of 200 to 3,000 nm.
• Calcination can generally take place in the temperature of 390 to 450 °C, when both the decomposition of the carrier polymer(s) and the transformation of bis(oxalate)oxo-titanate and ammonium vanadate take place.
• the precursor fibers are kept at the calcination temperature for 45 to 75 minutes. The preferred increase of temperature during the calcination is 0.5 to 5 °C/min.
• the submicron and/or micron fibers thus prepared have a high mechanical integrity and excellent textural properties with a unique porous 3D structure consisting of V2O5 crystals up to 20 nm in size, supplemented by smaller and evenly distributed TiO2 crystals - see Figs. 5 and 6, which are transmission electron microscope images of submicron fibers showing the uniform distribution of titanium and vanadium in the submicron fibers according to the invention with a Ti:V ratio of 90:10.
• the submicron and/or micron fibers thus prepared have a large specific surface area (up to 100 m 2 /g), which is crucial for their activity and reactivity in the considered applications.
• the V2O5 crystals are evenly distributed in the TiO2 matrix and vice versa.
• the oxides of one type are present in small amounts as dopants also in the crystal lattice of oxides of the other type.
• V2O5 content is higher than 20 wt. %, hollow fibers are formed due to the larger size of the V2O5 crystals - see, e.g., Fig. 1 and Fig. 2.
• Fig. 1 shows an SEM image of submicron fibers formed by a mixture of TiO2 and V2O5 according to the invention with a Ti:V atomic ratio of 1 :99 at a magnification of 25,000
• Fig. 2 shows an SEM image of submicron fibers formed by a mixture of TiO2 and V2O5 according to the invention with a Ti:V atomic ratio of 10:90 at a magnification of 20,000
• Fig. 3 shows an SEM image of submicron fibers formed by a mixture of TiO2 and V2O5 according to the invention with a Ti:V atomic ratio of 90:10 at a magnification of 60,000
• Fig. 1 shows an SEM image of submicron fibers formed by a mixture of TiO2 and V2O5 according to the invention with a Ti:V atomic ratio of 1 :99 at a magnification of 25,000
• Fig. 2 shows an SEM image of submicron fibers formed by a mixture of TiO2
• FIG. 4 shows an SEM image of submicron fibers formed by a mixture of TiO2 and V2O5 according to the invention with a Ti:V atomic ratio of 99:1 at a magnification of 500.
• Figs. 5 and 6 are transmission electron microscope images of submicron fibers formed by a mixture of TiO2 and V2O5 with a Ti:V atomic ratio of 90:10 from, which demonstrate that the fibers are composed of the relevant chemical elements (Ti, V, O).
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 15,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C.
• 7.5 g of precursor fibers with a diameter of 1095 ⁇ 405 nm was prepared by spinning.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 7,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C. 6.9 g of precursor fibers with a diameter of 1462 ⁇ 538 nm was prepared by spinning.
• these precursor fibers was then placed in a ceramic crucible. In it, these fibers were heated to a temperature of 390 °C at a rate of 0.5 °C/min and kept at this temperature for 60 minutes. During this process, the polymers were burned out, the vanadium oxalate complex decomposed, vanadium oxidized to V2O5, the ammonium bis(oxalate) peroxo-titanate decomposed and titanium oxidized to TiO2.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 7,000 rpm, the relative humidity in the chamber of the device was 20 % and the temperature was 30 °C.
• 7.1 g of precursor fibers with a diameter of 1205 ⁇ 446 nm was prepared by spinning. 0.739 g of these precursor fibers was then placed in a ceramic crucible. In it, these fibers were heated to a temperature of 390 °C at a rate of 5 °C/min and kept at this temperature for 45 minutes.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 7,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C. 6.8 g of precursor fibers with a diameter of 1353 ⁇ 396 nm was prepared by spinning.
• these precursor fibers was then placed in a ceramic crucible. In it, these fibers were heated to a temperature of 450 °C at a rate of 0.5 °C/min and kept at this temperature for 75 minutes. During this process, the polymers were burned out, the vanadium oxalate complex decomposed, vanadium oxidized to V2O5, the ammonium bis(oxalate) peroxo-titanate decomposed and titanium oxidized to TiO2. This was followed by free cooling to room temperature.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 4,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C.
• 6.5 g of precursor fibers with a diameter of 1257 ⁇ 530 nm was prepared by spinning.
• these precursor fibers was then placed in a ceramic crucible. In it, these fibers were heated to a temperature of 420 °C at a rate of 1 °C/min and kept at this temperature for 60 minutes. During this process, the polymers were burned out, the vanadium oxalate complex decomposed, vanadium oxidized to V2O5, the ammonium bis(oxalate) peroxo-titanate decomposed and titanium oxidized to TiO2. This was followed by free cooling to room temperature.
• the thus prepared solution for spinning was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 10,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C.
• 8.2 g of precursor fibers with a diameter of 1145 ⁇ 512 nm was prepared by spinning.
• Figs. 5 and 6 are transmission electron microscope images, showing the uniform distribution of titanium and vanadium in the structure of these fibers.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 9,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C. 7.9 g of precursor fibers with a diameter of 1123 ⁇ 476 nm was prepared by spinning.
• a mixture with an atomic ratio of vanadium to titanium of 7.2:92.8 was prepared by mixing the entire batch of 9.6 g of stock titanium solution (2.17 mmol of titanium) with 2 g of stock vanadium solution (0.8 mmol of vanadium). The mixture thus formed was stirred for a period of 12 hours. Then 2.4 g (14.65 wt. %) of ethanol and 2.4 g (14.65 wt. %) of PVP were added to it. This mixture was subsequently stirred until a homogeneous solution was created. 70.7 wt. % of this solution was made up of stock solutions of titanium and vanadium.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 7,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C.
• 1 .9 g of precursor fibers with a diameter of 854 ⁇ 394 nm was prepared by spinning. 0.513 g of these precursor fibers was then placed in a ceramic crucible. In it, these fibers were heated to a temperature of 390 °C at a rate of 3 °C/min and kept at this temperature for 60 minutes.
• a mixture with an atomic ratio of vanadium to titanium of 99.51 :0.49 was prepared by mixing the entire batch of 22.9 g of stock vanadium solution (21 .07 mmol of vanadium) and 2.3 g of stock titanium solution (1.08 mmol of titanium). The mixture thus formed was stirred for a period of 12 hours. Subsequently, 5 g (12.38 wt. %) of ethanol and 10.2 g (25.25 wt. %) of PVP were added to it and this mixture was then stirred until a homogeneous solution was created. 62.4 wt. % of this solution consisted of stock solutions of titanium and vanadium.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 7,000 rpm, the relative humidity in the chamber of the device was 25 % and the temperature was 30 °C. 1 .13 g of precursor fibers with a diameter of 5126 ⁇ 1054 nm was prepared by spinning.
• micron fibers with a diameter of 2062 ⁇ 689 nm consisting of a mixture of V2O5 and TiO2 with a V:Ti atomic ratio of 99.5:0.5.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 3,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C. 0.67 g of precursor fibers with a diameter of 1564 ⁇ 538 nm was prepared by spinning.
• the solution for spinning thus prepared was spun on a laboratory centrifugal spinning device Cyclone G1.
• the speed of the spinning head was set at 5,000 rpm, the relative humidity in the chamber of the device was 15 % and the temperature was 40 °C. 1 .67 g of precursor fibers with a diameter of 793 ⁇ 254 nm was prepared by spinning.

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