Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B1/00—Nanostructures formed by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
  • B82B1/001—Devices without movable or flexible elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
  • B82B3/0009—Forming specific nanostructures
  • B82B3/0033—Manufacture or treatment of substrate-free structures, i.e. not connected to any support
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G41/00—Compounds of tungsten
  • C01G41/02—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/01—Particle morphology depicted by an image
  • C01P2004/03—Particle morphology depicted by an image obtained by SEM
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
  • C01P2004/13—Nanotubes

Definitions

• the invention relates to a method for the preparation of submicron and/or micron crystalline tungsten oxide tubes.
• the invention also relates to submicron and/or micron crystalline tungsten oxide tubes prepared by this method.
• Tungsten oxide (WO 3 ) is widely used due to its electrochromic [1 , 2] and photocatalytic [3] properties and the potential of being used as an active substance of gas sensors [4 to 7], nowadays, it is commonly prepared in several different submicron forms, such as nanoparticles, nanorods and nanofibres.
• a usual method for the preparation of WO3 nanofibres consists in electrospinning [5 to 12] of a suitable precursor solution and possible further processing of the thus prepared precursor fibres.
• the precursor solution contains a tungsten precursor, such as tungsten chloride [3,6,12], sodium [1] or ammonium [8] metatungstate salt, and a suitable carrier polymer, usually polyvinylpyrrolidone (PVP) [3,5, 6 7,10,11], polyvinyl alcohol (PVA) [8], etc.
• PVP polyvinylpyrrolidone
• PVA polyvinyl alcohol
• Another method for the preparation of WO3 nanofibres is a hydrothermal method [1], which results in preparing shorter nanofibres, more often referred to as nanorods.
• CN 104150537 discloses a method for the preparation of WO3 nanotubes hydrothermally, by using sodium tungstate dihydrate, acetic acid, acetamide and hydrochloric acid. The hydrothermal process lasts for 20 to 30 hours and results in WO 3 nanotubes with an outer diameter of 8 to 12 nm and a length of 50 to 200 nm.
• CN 105565385 discloses a method for the preparation of WO3 nanotubes hydrothermally on moulds followed by calcination to convert a precursor - ammonium tungstate - into WO 3 . The hydrothermal process lasts for 15 to 20 days and the resulting product is calcined after the mould removal at temperatures between 500 and 540 °C.
• CN 106018480 describes a method for the preparation of WS 2 nanoparticles.
• the starting material in this case is a solution of ammonium metatungstate, dimethylformamide (DMF), absolute ethanol and PVP. This solution is spun by electrospinning and formed precursor fibres are deposited on aluminium foil. These fibres are then calcined to be converted into WO3. The resulting WO 3 nanofibres are further vulcanized by sulfur in nitrogen atmosphere. This results in the formation of WS 2 nanoparticles, which are further decorated with Ag in an AgNOs solution.
• DMF dimethylformamide
• PVP absolute ethanol
• This solution is spun by electrospinning and formed precursor fibres are deposited on aluminium foil. These fibres are then calcined to be converted into WO3.
• the resulting WO 3 nanofibres are further vulcanized by sulfur in nitrogen atmosphere. This results in the formation of WS 2 nanoparticles, which are further decorated with Ag in an AgNOs solution.
• KR 20110085591 discloses the preparation of WO3 nanowires by a thermal evaporation method in which a tungsten sheet having dimensions of 10 x 10 x 1 mm is used as a substrate and WO 3 powder as a material for the growth of nanowires. These materials are deposited on a corundum substrate and, together with it, are placed in a furnace heated to 1 ,000 °C for a period of 1 hour. The resulting nanowires are about 100 pm long and their diameter is between 50 and 300 nm.
• the object of the present invention is to provide a method for the preparation of submicron and/or micron crystalline tungsten oxide tubes, which would remove the disadvantages of the background art.
• the object of the invention is submicron and/or micron crystalline tungsten oxide tubes having a diameter of 400 to 1600 nm prepared by this method.
• the object of the invention is achieved by a method for the preparation of submicron and/or micron crystalline tungsten oxide tubes with an outer diameter of 400 to 1600 nm, in which a precursor aqueous or aqueous-ethanol spinning solution is used, which contains 5 to 20 % by weight, preferably 8 to 15 % by weight of ammonium metatungstate as precursor of WO3 and 5 to 25 % by weight, preferably 10 to 20 % by weight, of a carrier polymer - polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) or polyethylene glycol (PEG), optionally a mixture of at least two of them.
• PVP carrier polymer - polyvinylpyrrolidone
• PVA polyvinyl alcohol
• PEG polyethylene glycol
• the ethanol concentration is 1 to 10 % by weight, wherein at a concentration higher than 5 % by weight it is advantageous to stabilize this solution by adding lactic acid in an amount of 1 to 12 % by weight of the resulting solution.
• the precursor solution thus obtained is transformed by centrifugal spinning into precursor fibres, which are subsequently calcined to remove organic components from them, and to convert ammonium metatungstate into crystalline WO 3 , which in addition attains a hollow tube structure or a hollow tube-in-tube structure (when a longitudinal structure, hollow or not, is housed in the cavity of the base tube), with a large available reaction surface.
• Another advantage of this process is the fact that the centrifugal spinning produces large tufts of fibres without residual electric charge, which substantially facilitates their handling, and also the fact that the solution used is chemically inert, and so it does not cause aging or corrosion of the device with which it comes into contact.
• the weight ratio of ammonium metatungstate to the carrier polymer or polymer mixture in the precursor solution is in the range from 1 :5 to 2:1 and, in a preferred embodiment, in the range from 1 :2 to 1 :1 .
• the precursor solution is preferably prepared by mixing separately prepared aqueous or aqueous-ethanol solution of ammonium metatungstate and an aqueous or aqueous ethanol solution of the carrier polymer/polymers.
• the precursor solution thus prepared is subjected to centrifugal spinning.
• the preferred parameters of the air flowing into the spinning chamber during centrifugal spinning are: a temperature of 25 to 45 °C and a relative humidity of 15 to 40 % RH.
• the spinning head rotates at a speed of 3,000 to 15,000 rpm.
• the resulting precursor fibres are collected on collectors and then calcined (burnt) in a furnace at temperatures between 300 and 500 °C for a period of 4 to 13 hours, preferably in two phases.
• the first phase of calcination takes place at temperatures between 300 and 400 °C for a period of 0.5 to 3 hours
• the second phase takes place at temperatures between 450 and 500 °C for a period of 4 to 10 hours.
• the result of this process are submicron and/or micron crystalline tungsten oxide tubes with an outer diameter of 400 to 1 ,600 nm, with a mean value around 1 ,000 to 1 ,500 nm, and an inner diameter of 100 to 1 ,400 nm, which, due to their high mechanical integrity and excellent textural properties and especially the large available reaction surface, have a higher potential for practical applications than, e.g., nanofibres or nanorods formed by any of the known methods.
• the diameter of the precursor fibres being prepared can be corrected by using a suitable carrier polymer and its concentration.
• PVP can be used advantageously, when it is possible to obtain diameters of the precursor fibres (before calcination) of 1 ,200 to 2,500 nm and diameters of the WO 3 tubes (after calcination) ranging from 1 ,000 to 1 ,600 nm.
• the diameters of the precursor fibres are between 400 and 2,000 nm and the diameters of WO 3 tubes are between 400 and 1200 nm; when using PEG, the diameters of the precursor fibres are between 700 and 1600 nm, and the diameters of WO3 tubes are between 500 and 1000 nm.
• PVP may have a molar weight in the range from 40,000 to 1 ,300,000 g/mol
• PVA may have a molar weight in the range from 31 ,000 to 190,000 g/mol
• PEG may have a molar weight in the range from 200,000 to 1 ,000,000 g/mol.
• the diameter of the precursor fibres increases with an increasing content of polymer in the precursor solution.
• Fig. 1 a is a SEM image of precursor fibres in a first variant of embodiment at 1 ,000x magnification
• Fig. 1 b is a SEM image of a WO 3 tube obtained by calcination of precursor fibre according to Fig. 1 a at 50,000x magnification;
• Fig. 2a is a SEM image of precursor fibres in a second variant of embodiment at 500x magnification
• Fig. 2b is a SEM image of a WO3 tube obtained by calcination of precursor fibre according to Fig. 2a at 50,000x magnification;
• Fig. 3a is a SEM image of precursor fibres in a third variant of embodiment at 1 ,000x magnification
• Fig. 3b is a SEM image of a WO3 tube obtained by calcination of precursor fibre according to Fig. 3a at 50,000x magnification;
• Fig. 4a is a SEM image of precursor fibres in a fourth variant of embodiment at 1 ,000x magnification
• Fig. 4b shows a SEM image of a WO 3 tube obtained by calcination of precursor fibre according to Fig. 4a at 50,000x magnification
• Fig. 5a is a SEM image of precursor fibres in a fifth variant of embodiment at 1 ,000x magnification
• Fig. 5b is a SEM image of a WO3 tube obtained by calcination of precursor fibre according to Fig. 5a at 100,000x magnification
• Fig. 4a is a SEM image of precursor fibres in a fourth variant of embodiment at 1 ,000x magnification
• Fig. 4b shows a SEM image of a WO 3 tube obtained by calcination of precursor fibre according to Fig. 4a at 50,000x magnification
• Fig. 5a is a SEM image of precursor fibres in a fifth variant of embodiment at 1 ,000
• Fig. 6a is a SEM image of precursor fibres in a sixth variant of embodiment at 2,000x magnification
• Fig. 6b shows a SEM image of a WO3 tube obtained by calcination of precursor fibre according to Fig. 6a at 50,000x magnification.
• a method for the preparation of submicron and/or micron crystalline tungsten oxide (WO3) tubes according to the invention is based on using ammonium metatungstate as a precursor of WO 3 .
• ammonium metatungstate as a precursor of WO 3 .
• the advantage of this precursor is the fact that unlike other precursors, such as sodium metatungstate or tungsten chloride, it does not contain Na, Cl or Br ions, which would be difficult, if not impossible, to remove from the final product and which thus reduce its utility value.
• the products of thermal decomposition of ammonium metatungstate are tungsten oxide, nitrogen oxides and water vapour. During the calcination of the precursor fibres, gases escape to the environment and only pure tungsten oxide remains.
• Polyvinylpyrrolidone (PVP) with a molar weight of 40,000 to 1 ,300,000 is used as a carrier polymer, or polyvinyl alcohol (PVA) with a molar weight of 31 ,000 to 190,000, or polyethylene glycol (PEG) with a molar weight of 200,000 to 1 ,000,000 or a mixture of at least two of them.
• PVP polyvinylpyrrolidone
• PVA polyvinyl alcohol
• PEG polyethylene glycol
• the weight ratio of the precursor of WO3 to the carrier polymer or to a mixture of polymer in the precursor solution is in the range from 1 :5 to 2:1 , preferably from 1 :2 to 1 :1 .
• the absolute amount of ammonium metatungstate in the precursor solution is in the range from 5 to 20 % by weight, preferably from 8 to 15 % by weight
• the absolute amount of the carrier polymer or the mixture of carrier polymers is in the range from 5 to 25 % by weight, preferably from 10 to 20 % by weight, whereby with an increasing content of the carrier polymer the diameter of the subsequently formed precursor fibres as well as of the final tubes increases.
• This precursor solution is prepared by mixing all the components into one aqueous or aqueous-ethanol solution or, more preferably, by mixing a separately prepared solution of the precursor and a separately prepared solution of the carrier polymer or of a mixture of polymers.
• the resulting solution is then spun on a device for producing fibres working on the principle of centrifugal spinning to prepare crude precursor fibres.
• a laboratory device Cyclone Pilot G1 (PARDAM NANO4FIBRES) was used to produce these precursor fibres, however, in general, any other device based on the principle of centrifugal spinning can be used to create the fibres.
• the precursor fibres thus prepared are subsequently calcined in a calcination furnace, during which all the organic components are released and ammonium metatungstate is converted into pure crystalline WO 3 , which attains a hollow tubular structure (see, e.g., Fig. 1 b), or a hollow tube-in-tube structure (see, e.g., Fig. 2b), with an outer diameter between 400 and 1600 nm, an inner diameter between 100 and 1400 nm and a wall thickness between 50 to 400 nm.
• the calcination may take place in the range of temperatures from 300 °C, when the carrier polymer(s) is/are decomposed, to 500 °C, when intense conversion of ammonium metatungstate into crystalline WO 3 takes place, for a period of 4 to 13 hours.
• the most suitable process of calcination of the precursor fibres appears to be two- phase calcination, when the precursor fibres are first heated to a temperature of 300 to 400 °C (preferably with a temperature rise rate of 0.5 to 2 °C/min), at which they remain for 0.5 to 3 hours, and then are heated to a temperature of 450 to 500 °C (preferably with a temperature rise rate of 5 to 20 °C/min), at which they remain for 4 to 10 hours.
• a hollow tubular structure or a tube-in-tube structure is formed from the precursor fibres, whereby in a tube-in-tube structure, a longitudinal structure, hollow or not, is housed in the cavity of the base tube.
• tungsten oxide WO3
• the organic material burns out even more intensely and WO3 crystallizes towards the centre of the precursor fibre, which leads to a volume contraction of the material inside the fibre, which in combination with the escape of gases which are formed during the combustion of the organic part of the precursor fibre, creates a hollow structure. Its final shape and dimensions are subsequently completed after the complete combustion of all the remaining organic substance from inside the fibres and after the complete crystallization of WO 3 .
• the resulting WO 3 submicron and/or micron tubes have a higher specific surface area and available reaction surface, e. g., for catalytic applications, than solid fibres with the same outer diameter would have.
• This process is advantageous due to the simplicity of the preparation of WO3 submicron and micron tubes, when ammonium metatungstate, carrier polymer and water are sufficient for their preparation. No combustibles, toxic solvents, precursors containing unwanted cations (e. g. Na + ) and anions (Cr, Br) are used, which would contaminate both the submicron and/or micron tubes formed and the devices used for their production.
• the preparation of precursor fibres by the method of centrifugal spinning has a higher fibre yield over time than other methods, such as electrostatic spinning, hydrothermal process, templating, drawing, etc.
• centrifugal spinning large and easily portable tufts of fibres are created without residual electric charge, and at the same time the need to peel the fibres laboriously off the substrate material (e. g. non-woven textile) is eliminated.
• the centrifugal spinning technique has lower operating costs than electrostatic spinning since it always consumes the entire amount of precursor solution.
• the metatungstate solution was poured into the PVA solution to form a mixed solution which contained ammonium metatungstate in an amount of 12 % by weight and PVP in an amount of 20 % by weight. This mixed solution was further stirred until completely mixed and homogeneous.
• the precursor solution thus prepared was then spun on a Cyclone Pilot G1 centrifugal spinning machine. The revolutions of the spinning head were set at 11 ,000 revolutions per minute. The temperature of the air which flowed to the spinning chamber during the centrifugal spinning was 41.5 °C, its humidity was 15.2 % RH.
• 8.5 g of precursor fibres were prepared, the fibres having a diameter of 2632 ⁇ 1091 nm - see Fig. 1 a, which shows a SEM image of these fibres at 1000x magnification.
• the metatungstate solution was poured into the PVA solution to form a mixed solution which contained ammonium metatungstate in an amount of 20 % by weight a PVA in an amount of 12 % by weight.
• This mixed solution was further stirred until completely mixed and homogeneous.
• the precursor solution thus prepared was then spun on a Cyclone Pilot G1 centrifugal spinning machine. The revolutions of the spinning head were set at 9,000 rpm. The temperature of the air which flowed to the spinning chamber during the centrifugal spinning was 36.8 °C, its humidity was 18 % RH.
• 8.6 g of the precursor fibres with a diameter of 775 ⁇ 355 nm were prepared - see Fig. 2a, which shows a SEM image of these fibres at 500x magnification.
• the metatungstate solution was poured into the PVA solution to form a mixed solution which contained ammonium metatungstate in an amount of 10 % by weight a PVA in an amount of 5 % by weight.
• This mixed solution was further stirred until completely mixed and homogeneous.
• the precursor solution thus prepared was then spun on a Cyclone Pilot G1 centrifugal spinning machine. The revolutions of the spinning head were set at 4,000 rpm. The temperature of the air which flowed to the spinning chamber during the centrifugal spinning was 39 °C, its humidity was 15 % RH.
• 8.7 g of precursor fibres with a diameter of 1498 ⁇ 411 nm were prepared - see Fig. 3a, which shows a SEM image of these fibres at 1000x magnification.
• the metatungstate solution was poured into the PVA solution to form a mixed solution which contained ammonium metatungstate in an amount of 8 % by weight and PVP in an amount of 15 % by weight. This mixed solution was further stirred until completely mixed and homogeneous.
• the precursor solution thus prepared was then spun on a Cyclone Pilot G1 centrifugal spinning machine. The revolutions of the spinning head were set at 12,000 revolutions per minute. The temperature of the air which flowed to the spinning chamber during the centrifugal spinning was 35 °C, its humidity was 30 % RH.
• 7.7 g of the precursor fibres having a diameter of 1596 ⁇ 543 nm were prepared - see Fig. 4a, which shows a SEM image of these fibres at 1000x magnification.
• PVA polyvinyl alcohol
• the metatungstate solution was poured into the PVA solution to form a mixed solution which contained ammonium metatungstate in an amount of 5 % by weight and PVA in an amount of 25 % by weight. This mixed solution was further stirred until completely mixed and homogeneous.
• the precursor solution thus prepared was then spun on a Cyclone Pilot G1 centrifugal spinning machine. The speed of the spinning head was set at 15,000 rpm. The temperature of the air that flowed into the spinning chamber during centrifugal spinning was 28.8 0 C, its humidity was 25 % RH.
• PVA polyvinyl alcohol
• PEG polyethylene glycol
• the metatungstate solution was poured into the solution of PVA and PEG to form a mixed solution, which contained ammonium metatungstate in an amount of 10 % by weight and PVA + PEG in an amount of 10 % by weight.
• This mixed solution was further stirred until completely mixed and homogeneous.
• the precursor solution thus prepared was then spun on a Cyclone Pilot G1 centrifugal spinning machine. The revolutions of the spinning head were set at 7,000 rpm. The temperature of the air which flowed to the spinning chamber during the centrifugal spinning was 38.8 °C, its humidity was 22 % RH.
• 8.5 g of the precursor fibres were prepared, the fibres having a diameter of 701 ⁇ 411 nm - see Fig. 6a, which shows a SEM image of these fibres at 2,000 magnification.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Nanotechnology (AREA)
• Crystallography & Structural Chemistry (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Inorganic Chemistry (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Composite Materials (AREA)
• Materials Engineering (AREA)
• Inorganic Fibers (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=74180886

Family Applications (1)

Country Status (2)

Cited By (1)

Families Citing this family (1)

Citations (1)

Family Cites Families (4)

• 2020
  • 2020-11-03 CZ CZ2020-592A patent/CZ2020592A3/cs unknown
  • 2020-11-23 WO PCT/CZ2020/050086 patent/WO2022096040A1/en not_active Ceased

Patent Citations (1)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events