WO2021120359A1 - 单原子贵金属锚定缺陷型WO3/TiO2纳米管、其制备和应用 - Google Patents

单原子贵金属锚定缺陷型WO3/TiO2纳米管、其制备和应用 Download PDF

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WO2021120359A1
WO2021120359A1 PCT/CN2020/072111 CN2020072111W WO2021120359A1 WO 2021120359 A1 WO2021120359 A1 WO 2021120359A1 CN 2020072111 W CN2020072111 W CN 2020072111W WO 2021120359 A1 WO2021120359 A1 WO 2021120359A1
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tio
nanotubes
nanoparticles
defects
noble metal
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French (fr)
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张延荣
汪晓光
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华中科技大学
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • 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
    • B01J23/24—Chromium, molybdenum or tungsten
    • B01J23/30—Tungsten
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8678—Removing components of undefined structure
    • B01D53/8687—Organic components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/39—Photocatalytic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/348—Electrochemical processes, e.g. electrochemical deposition or anodisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/708—Volatile organic compounds V.O.C.'s
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/06—Polluted air

Definitions

  • the invention belongs to the field of photocatalytic materials, and more specifically, relates to a single-atom noble metal anchoring defect type WO 3 /TiO 2 nanotube, and its preparation and application.
  • TiO 2 has unique optical properties and high photocatalytic activity. It has been used in optical materials, photoelectrochemical and photoelectromagnetic fields. , Photocatalytic degradation of pollutants and other applications have been extensively developed. In 1991, Iijima et al. discovered carbon nanotubes. Due to their unique structure and excellent performance, one-dimensional nanomaterials (such as nanowires, nanotubes, and nanofilms) have received extensive attention and research.
  • TiO 2 nanotube arrays As a two-dimensional nanomaterial of TiO 2 , TiO 2 nanotube arrays have attracted more and more attention due to their highly ordered, size-controllable structural characteristics and unique electron transfer characteristics. Compared with other forms of TiO 2 nanomaterials, TiO 2 nanotube arrays have a larger specific surface area, better electron transport channels and adsorption capacity, so it can better improve the photoelectric conversion efficiency, photocatalytic performance, etc., especially in Modification of metal, non-metal particles or other semiconductor oxide materials in the tube will greatly improve the catalytic, photoelectric and electromagnetic properties of TiO 2. In 1999, Zwilling et al. obtained TiO 2 nanotubes with a highly ordered array structure through anodization. At present, the preparation methods of TiO 2 nanotubes also include sol-gel method, hydrothermal synthesis method and magnetron sputtering method.
  • this semiconductor material can only use solar resources with a wavelength in the visible light region, and the photo-generated electron-hole recombination problem that is unavoidable in photocatalysis.
  • TiO 2 nano The catalytic efficiency of the tube, especially in the visible light region, is low, so a large amount of modification work is started. It mainly includes surface modification of precious metals, excessive metal modification and ion doping, non-metal doping and co-doping, and semiconductor compounding.
  • WO 3 based on the low band gap semiconductor material, the advantages of non-toxic and inexpensive, since 2013, a lot of work in response to a wavelength of TiO 2 to WO nanotube-based material 3 is supported on TiO 2 nano-tubes, to form a heterojunction, improve , Thereby improving the photocatalytic efficiency.
  • the photocatalytic performance of the material has never reached the actual production standard.
  • single-atom catalysts have been developed rapidly as a new type of catalyst.
  • Single-atom noble metals can maximize the catalytic efficiency, improve the electron distribution and transmission, light absorption performance and chemical adsorption capacity of the photocatalyst, thereby increasing the photocatalytic efficiency, and It is used in oxidation and hydrogenation reactions.
  • single atoms due to the high surface energy of single atoms, single atoms are usually movable and easy to agglomerate, which makes the photocatalyst lose its activity. Therefore, in the design of high-efficiency photocatalysts, it is necessary to develop a single metal A suitable carrier with strong interaction of atoms.
  • the present invention provides a single-atom noble metal anchoring defect type WO 3 /TiO 2 nanotube, its preparation and application, which adopts noble metal single atom anchoring defect type WO 3 / TiO 2 nanotubes prevent the agglomeration of single atoms and improve their photocatalytic performance, thereby solving the problem of limited capacity of photo-responsive catalysts in the prior art, narrow response range to visible light, easy agglomeration of noble metal single atoms, poor photocatalytic performance and easy Technical issues such as deactivation.
  • a method for preparing a monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotube composite includes the following steps:
  • step (3) Using the WO 3 particle-loaded TiO 2 nanotube composite containing W 5+ defects obtained in step (2) as a working electrode, the noble metal monoatoms are loaded on the composite by electrochemical deposition. Surface defects of WO 3 nanoparticles Where, a single-atom noble metal-anchored defect-type WO 3 /TiO 2 nanotube composite is obtained.
  • the calcination in step (1) is specifically calcination at 400° C.-600° C. for 60 min-240 min.
  • the TiO 2 nanotubes in step (1) are obtained by the following method: the TiO 2 precursor is prepared by an anodic oxidation method, a sol-gel method, a hydrothermal method, a magnetron sputtering method or an atomic layer deposition method, Then the TiO 2 precursor is calcined at 400° C.-600° C. for 60 min-240 min to obtain TiO 2 nanotubes.
  • the method step (1) the deposition of WO 3 nanoparticles as electrochemical deposition, co-hydrothermal method, a spin coating method or a dipping method.
  • step (2) is specifically: using the TiO 2 nanotubes loaded with WO 3 nanoparticles on the inner and outer walls obtained in step (2) as the working electrode, and the reduction voltage is -1.0v ⁇ -1.6v, the reduced Electrochemical reduction is carried out under the condition of 200s-1000s, so that WO 3 nanoparticles are partially reduced to form W 5+ defects, and a composite of WO 3 nanoparticles loaded with TiO 2 nanotubes containing W 5+ defects is obtained.
  • the TiO 2 nanotubes loaded with WO 3 nanoparticles on the inner and outer walls obtained in step (2) are used as the working electrode, the platinum electrode is used as the counter electrode, and the saturated calomel electrode is used as the reference The electrode is subjected to the electrochemical reduction of step (2).
  • step (3) is specifically: in a three-electrode system, the WO 3 nanoparticle-loaded TiO 2 nanotubes containing W 5+ defects obtained in step (2) are used as the working electrode, and the square wave pulse method and the potentiostatic method are used. Or the constant current method loads the noble metal single atoms on the defects on the surface of the WO 3 nanoparticles in the composite.
  • the noble metal single atom is Au, Ag, Pt, Pd, Ir or Ru
  • step (3) is specifically: in a three-electrode system, step (2) to obtain WO 3 nanometers containing W 5+ defects
  • the particle-loaded TiO 2 nanotubes are used as the working electrode.
  • the square wave pulse method is used to load the noble metal single atoms on the defects on the surface of the WO 3 nano particles in the composite.
  • the high potential of the square wave pulse method is 0v ⁇ -0.2v, which is low.
  • the potential is -0.4v to -1.6v, the number of cycles is 1 to 50 times, and the pulse width is 1s to 20s.
  • the constant potential method is used to load the noble metal single atoms on the defects on the surface of the WO 3 nanoparticles in the composite.
  • the potential of the constant potential method is -0.2v ⁇ -1.6v
  • the reduction time is 2s ⁇ 100s
  • the electrolyte is
  • concentration of the precious metal source is 5 ⁇ mol/L ⁇ 1mmol/L.
  • a monoatomic noble metal anchored defect type WO 3 /TiO 2 nanotube composite prepared by the preparation method.
  • the monoatomic precious metal anchoring defect type WO 3 /TiO 2 nanotube composite includes TiO 2 nanotubes and WO 3 nanoparticles loaded on the inner and outer walls of the TiO 2 nanotube; the composite It contains W 5+ defects and oxygen vacancies accompanying the W 5+ defects, and noble metal single atoms are anchored at the surface defects of WO 3 nanoparticles.
  • the diameter of the TiO 2 nanotube is 100 nm-200 nm.
  • the application is an application in the photocatalytic degradation of volatile organic compounds.
  • the application is carried out under illumination conditions with a wavelength of less than or equal to 470 nm.
  • the concentration of the volatile organic compounds is 50 ppmv-500 ppmv.
  • the present invention provides a method for preparing a single-atom noble metal anchored defect-type WO 3 /TiO 2 nanotube composite, which directly reduces WO 3 /TiO 2 nanotubes by using an electrochemical method.
  • a large number of oxygen vacancy defects are generated, and the use of oxygen vacancies to promote the separation of photo-generated electron holes is beneficial to the anchoring of precious metal units.
  • the electrochemical self-doping method is efficient, safe, and easy to operate and control.
  • the present invention controls the electrochemical reduction process, such as by controlling the voltage and the reduction time of the electrochemical reduction of WO 3 /TiO 2 nanotubes, so that the reduction of WO 3 nanoparticles is the main factor to obtain W 5+ WO 3 nano-particles loaded with TiO 2 nanotube composites with defects and accompanying oxygen vacancies, further, by electrochemically depositing single-atom noble metals, a composite with single-atom noble metals mainly anchored on the surface defects of WO 3 nanoparticles is obtained .
  • the experiment of the present invention found that the noble metal single atom is loaded on the defect on the surface of the WO 3 nanoparticle in the composite. Compared with the sample where the noble metal is anchored on the surface defect of the WO 3 nanoparticle and the TiO 2 nanotube at the same time, its photocatalytic performance is similar. However, the precious metal loading decreased by 40-60%.
  • the present invention provides a single-atom noble metal anchoring defect type WO 3 /TiO 2 nanotube composite, which obtains abundant oxygen vacancies by electrochemical reduction and self-doping of WO 3 nanoparticle-supported TiO 2 nanotubes After the defect, the noble metal unit is doped to obtain a visible light catalyst that fully utilizes the hydroxyl radicals, superoxide radicals and other active oxygen generated by it to complete the degradation of volatile organic pollutants in the air.
  • the nanotube structure contains W 6+ -O bonds, Ti 4+ -O bonds, defects W 5+ and their accompanying oxygen vacancies and noble metal single atoms.
  • the monoatomic noble metal anchored defect type WO 3 /TiO 2 nanotube composite catalyst of the present invention has visible light responsiveness.
  • the WO 3 particles supported on TiO 2 and sharp Titanite TiO 2 forms a heterojunction and reduces the band gap of WO 3 /TiO 2 nanotubes.
  • the band gap width of this catalyst is 2.6eV ⁇ 2.8eV, which makes the maximum absorption edge extend in the direction of visible light, which can be used Visible light with lower energy completes the degradation reaction of organic matter.
  • the existence of WO 3 /TiO 2 nanotube heterojunction can significantly inhibit the recombination of photo-generated electrons and holes, thereby improving the photocatalytic performance.
  • the present invention incorporates noble metal single atoms in the material preparation process. Compared with nano-particle noble metals, single-atom noble metals have a strong interaction with the carrier, which prevents noble metals from agglomerating, and has higher photocatalytic efficiency and greater durability. it is good.
  • the modified self-doped WO 3 particles in the present invention support TiO 2 nanotubes, which have a highly ordered array of nanotubes and a large specific surface area.
  • photocatalytic degradation of volatile organic compounds in the air occurs, the oxygen in the air
  • the molecules can effectively diffuse into the open channels in the nanotubes, thereby inhibiting the formation of "carbon beds" in the tubes.
  • the nanotube structure gives the invention excellent stability and is not easy to deactivate.
  • the modified self-doped WO 3 particle supported TiO 2 nanotubes in the present invention are macroscopically flaky, with adjustable flaky area. Compared with traditional powdered catalysts, this invention is easy to recycle and suitable as a catalyst.
  • the catalytic plate or catalytic bed is used for photocatalytic degradation of organic pollutants in the gas phase to further improve its catalytic performance.
  • (a) is the micro-topography of WO 3 /TiO 2 nanotubes (scanning electron microscope);
  • (b) is the modified anchoring defect type WO 3 /TiO 2 nanotubes in the precious metal transmission electron microscope of Example 1 Picture (bright field transmission electron microscope);
  • (c) is the single atom state of noble metal in the modified monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotubes (high angle ring dark field transmission electron microscope);
  • (d) It is a distribution map of noble metal single atoms in the modified single-atom noble metal anchoring defect type WO 3 /TiO 2 nanotubes (transmission electron microscope scan).
  • Figure 2 (a) is the electron paramagnetic resonance signal (RPE) of the monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotube (R-Au-W/T) modified in Example 1, (b) It is a high-resolution TEM image of defective WO 3 /TiO 2 nanotubes.
  • RPE electron paramagnetic resonance signal
  • Figure 3 shows the original WO 3 /TiO 2 nanotube (W/T), Au nanoparticle-supported WO 3 /TiO 2 nanotube (Au-W/T) and the modified monoatomic precious metal prepared in Example 1. UV-vis absorption spectra of anchor defect type WO 3 /TiO 2 nanotubes (R-Au-W/T).
  • FIG 4 is a raw WO 3 / TiO 2 nanotubes (W / T), comprising W5 + defect self-doped WO 3 / TiO 2 nanotubes, Au particles loaded nanoparticles WO 3 / TiO 2 nanotubes in Example 1 and modified Photoluminescence spectra of the defect-type WO 3 /TiO 2 nanotubes anchored by sexual monoatomic precious metals.
  • Figure 5 shows the WO 3 /TiO 2 nanotubes (RW/T) containing W 5+ defects and the monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotubes (R-Au-W/T) modified in Example 1. -1 and R-Au-W/T-2) photocurrent response graph.
  • FIG 6 is a defect WO W 5+ containing 3 TiO 2 nanotubes (RW / T), Au nanoparticles loaded teeth WO 3 / TiO 2 nanotubes (Au-W / T) Modified Example 1 Single / Atomic precious metal anchoring defect type WO 3 /TiO 2 nanotubes (R-Au-W/T) degradation curve of volatile organic compounds toluene;
  • FIG. 7 (a), (b) and (c) respectively WO 3 / TiO 2 nanotubes containing defects W5 +, Au nanoparticles particles supported WO 3 / TiO 2 nanotubes in Example 1 and the modified embodiment of monatomic Repeated degradation curves of toluene degradation by precious metal anchoring defect WO 3 /TiO 2 nanotubes.
  • Figure 8 (a) is a sample (Au-W/Au-T) in which monoatomic Au is simultaneously anchored to the surface defects of WO 3 nanoparticles and TiO 2 nanotubes and the modified monoatomic noble metal anchoring of Example 1 and WO 3 Single atom state diagram of nanoparticle (R-Au-W/T) (high-angle annular dark field transmission electron microscope); (b) is the single atom distribution diagram of Au-W/Au-T sample (transmission electron microscope scan) ; (C) is the mass fraction of the precious metal Au (EDS spectrum) of Au-W/Au-T and R-Au-W/T.
  • Figure 9 is a band gap diagram of WO 3 and TiO 2 composites (data ultraviolet photoelectron spectroscopy, UPS).
  • Figure 10 is a sample (Au-W/Au-T) in which monoatomic Au is simultaneously anchored to the surface defects of WO 3 nanoparticles and TiO 2 nanotubes and the modified monoatomic noble metal anchors and WO 3 nanoparticles ( R-Au-W/T) Comparison of degradation of toluene.
  • a preparation method of monoatomic precious metal anchoring defect type WO 3 /TiO 2 nanotube composite includes the following steps:
  • step (1) Electrochemically reduce the TiO 2 nanotubes loaded with WO 3 nanoparticles on the inner and outer walls obtained in step (1).
  • part of the WO 3 nanoparticles are reduced to form W 5+ defects, a WO 3 nanoparticle loaded TiO 2 nanotube composite containing W 5+ defects is obtained;
  • step (3) Using the WO 3 nanoparticle-loaded TiO 2 nanotube composite containing W 5+ defects obtained in step (2) as a working electrode, a single atom of noble metal is loaded on the surface of the WO 3 nanoparticle in the composite by electrochemical deposition At the defects, a single-atom noble metal-anchored defect-type WO 3 /TiO 2 nanotube composite is obtained.
  • the TiO 2 nanotubes of the present invention can be prepared by conventional methods.
  • the TiO 2 nanotubes in step (1) are obtained by the following methods: TiO 2 precursors are prepared by anodization, sol-gel, hydrothermal, magnetron sputtering, or atomic layer deposition. Then, the TiO 2 precursor is calcined at 400° C.-600° C. for 60 min-240 min to obtain TiO 2 nanotubes.
  • TiO 2 nanotubes are prepared by anodizing method.
  • the anodic oxidation method is to place a metal Ti sheet as a working electrode in an electrolyte solution containing F- under a two-electrode system, and etch for 2h-20h under the condition of a constant voltage of 20V-80V to obtain a TiO 2 precursor .
  • the titanium sheet as the working electrode was placed containing F - electrolyte solution, the etching 2 ⁇ 20h at 20V ⁇ 80V constant voltage conditions.
  • the obtained TiO 2 nanotube precursor is fired at a certain temperature of 400-600° C. for 60-240 min to obtain TiO 2 nanotubes.
  • the F - containing electrolyte solution is a mixed solution formed by an aqueous ammonium fluoride solution and an organic solvent; the concentration of ammonium fluoride in the mixed solution is 0.1 g/L-10 g/L; the ammonium fluoride The volume of the aqueous solution accounts for 5%-20% of the volume of the mixed solution; the organic solvent is ethylene glycol, glycerol, glycerol, dimethyl sulfoxide, dimethyl formamide, formamide, methyl formamide and One or more of diethylene glycol.
  • Step (1) First , deposit WO 3 nanoparticles on the inner and outer walls of the TiO 2 nanotubes, and calcinate to crystallize the WO 3 nanoparticles.
  • the calcination in step (1) is specifically calcination at 400° C.-600° C. for 60 min-240 min.
  • the method for depositing WO 3 nanoparticle precursors on the inner and outer walls of TiO 2 nanotubes in step (1) of the present invention may be methods commonly used in the prior art, such as electrochemical deposition, co-hydrothermal, and spin coating. Method or dipping method.
  • the electrochemical deposition method using WO 3 TiO 2 nanoparticles inner wall and an outer wall nanotubes specifically to: TiO 2 nanotubes as the working electrode, in the three-electrode system, ethylenediamine tetraacetic acid A mixed solution of ammonium acetate and sodium tungstate is used as an electrolyte, and WO 3 nanoparticle precursors are deposited on the surface of the TiO 2 nanotubes.
  • the concentrations of ethylenediaminetetraacetic acid, ammonium acetate, and sodium tungstate in the electrolyte are all 0.01mol/L-1mol/L;
  • the electrochemical deposition method is a galvanostatic polarization method, and the constant The current density of the current is -1mA/cm 2 ⁇ -10mA/cm 2 , and the deposition time is 400s ⁇ 1000s.
  • the obtained TiO 2 nanotube precursor is used as the working electrode.
  • the electrochemical deposition method is adopted, and the mixed solution of EDTA, ammonium acetate and sodium tungstate is used as the electrolyte.
  • a layer of WO 3 nanoparticle precursor is deposited on the surface of the TiO 2 nanotubes, and then fired at a temperature of 400-600° C. for 60-240 minutes, washed with water and dried to obtain WO 3 /TiO 2 nanotubes.
  • the co-hydrothermal method is used to deposit WO 3 nanoparticles on the inner and outer walls of TiO 2 nanotubes, specifically: placing the prepared TiO 2 nanotube film in 100 ml containing 0.01M sodium tungstate and 0.01M After fully stirring the mixed solution of oxalic acid, it is transferred to a reaction kettle and reacted at 150° C. for 24 hours. After natural cooling, the TiO 2 nanotube film is taken out, washed with water and dried, and the result is the product.
  • the spin-coating method is used to deposit WO 3 nanoparticles on the inner and outer walls of the TiO 2 nanotubes, specifically: the peroxy polymer produced by the mixed reaction of tungsten powder and hydrogen peroxide (mass fraction: 30%) Tungstic acid gel is used as a precursor. After diluting 10 times with water, apply an appropriate amount evenly on the surface of the TiO 2 nanotube film, and then spin-coat at 3000r/min with a spin coater. After spin-coating, the precursor will be loaded with peroxy polytungstic acid. The bulk TiO 2 nanotube film is placed in a muffle furnace and calcined at 450° C. for 2 hours, and the result is the product.
  • the peroxy polymer produced by the mixed reaction of tungsten powder and hydrogen peroxide (mass fraction: 30%) Tungstic acid gel is used as a precursor. After diluting 10 times with water, apply an appropriate amount evenly on the surface of the TiO 2 nanotube film, and then spin-coat at 3000r/min
  • the dipping method is used to deposit WO 3 nanoparticles on the inner and outer walls of the TiO 2 nanotubes, specifically: placing the prepared TiO 2 nanotube film in a 1 mM ammonium metatungstate aqueous solution, stirring and immersing for 2 hours Take it out and calcine in a muffle furnace at 450°C for 2h, and the result is the product.
  • step (2) is specifically: using the TiO 2 nanotubes with WO 3 nanoparticles loaded on the inner and outer walls obtained in step (2) as the working electrode, and the reduction voltage is -1.0v ⁇ -1.6v, The reduction time is 200 s-1000 s and electrochemical reduction is carried out, so that WO 3 nanoparticles are partially reduced to form W 5+ defects, and a composite of WO 3 nanoparticles loaded with TiO 2 nanotubes containing W 5+ defects is obtained.
  • the present invention controls the voltage and time of electrochemical reduction so that the reduction is mainly based on the reduction of WO 3 nanoparticles. It does not rule out that a small amount of TiO 2 nanotubes are also reduced to form Ti 3+ defects at the same time, so that W 5+ defects are obtained. And a small amount of Ti 3+ defect WO 3 nanoparticles loaded TiO 2 nanotube composite.
  • the TiO 2 nanotubes with WO 3 nanoparticles loaded on the inner and outer walls obtained in step (2) are used as the working electrode, the platinum electrode is the counter electrode, and the saturated calomel electrode is used as the working electrode.
  • the electrochemical reduction in step (2) is performed.
  • the surface oxygen vacancy concentration and the degree of electrochemical reduction are in a normal distribution. In order to ensure the number of single-atom anchor sites and catalytic performance, it is necessary to control the oxygen vacancies accompanying W 5+ defects and Ti 3+ defects within an appropriate range.
  • the present invention controls the electrochemical reduction voltage and the reduction time, so that part of the WO 3 nanoparticles and part of the TiO 2 nanotubes are reduced to form W 5+ defects and Ti 3+ defects, respectively, and the reduction of WO 3 nanoparticles is the main component.
  • the defect content should not be too high. Ideally, only WO 3 nanoparticles can be partially reduced to obtain a modified self-doped WO 3 particle loaded TiO 2 nanotube composite with a certain defect content.
  • step (3) is specifically: in a three-electrode system, the WO 3 nanoparticles containing W 5+ defects obtained in step (2) are loaded with TiO 2 nanotubes as the working electrode, and the square wave pulse method, The potentiostatic method or the galvanostatic method loads the noble metal single atoms on the defects on the surface of the WO 3 nanoparticles in the composite.
  • the present invention controls the reduction of WO 3 nanoparticles and TiO 2 nanotubes by controlling the electrochemical reduction process. Since the reduction of TiO 2 nanotubes to Ti 3+ defects requires a higher voltage (about 2.0V), a preferred embodiment of the present invention By controlling the electrochemical reduction voltage to be lower than 1.6V, in order to reduce only part of the WO 3 nanoparticles to W 5+ defects, and then use electrochemical deposition to load the noble metal single atoms only on the surface defects of the WO 3 nanoparticles in the composite , the maximum lift of the present invention prepared in the case where the least amount of noble metal used to obtain a single noble metal atoms deficient WO 3 / TiO 2 composite nano-tube used in an amount photocatalytic performance, saving precious metal anchor.
  • the noble metal single atom of the present invention can be Au, Ag, Pt, Pd, Ir or Ru.
  • the square wave pulse method is used to load the noble metal single atom on the defect on the surface of the WO 3 nanoparticle in the composite.
  • the high potential of the square wave pulse method is 0v ⁇ -0.2v
  • the low potential is -0.4v ⁇ -1.6v
  • the number of cycles is 1 to 50 times
  • the pulse width is 1s ⁇ 20s
  • the concentration of the precious metal source in the electrolyte is 5 ⁇ mol/L ⁇ 10mmol/L.
  • the constant potential method is used to load the noble metal single atoms on the defects on the surface of the WO 3 nanoparticles in the composite.
  • the potential of the constant potential method is -0.2v ⁇ -1.6v, and the reduction time is 2s ⁇ 100s.
  • the concentration of the precious metal source in the electrolyte is 5 ⁇ mol/L to 1 mmol/L.
  • the present invention also provides a single-atom noble metal anchoring defect type WO 3 /TiO 2 nanotube composite, which includes TiO 2 nanotubes and WO 3 nanoparticles loaded on the inner and outer walls of the TiO 2 nanotubes; the composite There are W 5+ defects and oxygen vacancies accompanying the W 5+ defects, and noble metal single atoms are anchored at the surface defects of WO 3 nanoparticles.
  • the monoatomic noble metal anchored defect-type WO 3 /TiO 2 nanotube composite of the present invention can absorb light radiation with a wavelength less than or equal to 470 nm.
  • the diameter of the TiO 2 nanotubes in the composite is 100 nm-200 nm.
  • the invention also provides the application of the monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotube composite in photocatalysis.
  • the composite is applied to the photocatalytic degradation of volatile organic compounds.
  • it is preferably carried out under light conditions with a wavelength of less than or equal to 470 nm; and the concentration of the volatile organic compounds is 50 ppmv-500 ppmv.
  • WO 3 /TiO 2 nanotubes represent WO 3 particles loaded with TiO 2 nanotubes
  • R-WO 3 /TNTs represent self-doped WO 3 particles loaded with W 5+ defects and TiO 2 nanotubes
  • R-Au- WO 3 /TNTs stands for single-atom noble metal anchoring defect-type WO 3 /TiO 2 nanotubes.
  • the modified monoatomic noble metal anchored defect type WO 3 /TiO 2 nanotubes in the present invention refers to the modification of the self-doped WO 3 particle-loaded TiO 2 nanotubes containing W 5+ defects.
  • the modified monoatomic precious metal anchoring defect type WO 3 /TiO 2 nanotube is the monoatomic precious metal anchoring defect type WO 3 /TiO 2 nanotube composite of the present invention.
  • the present invention provides a noble metal monoatomic anchor deficient WO 3 / TiO 2 nanotube composite which TiO 2 nanotubes inner and outer walls of the WO 3 nanoparticles loaded enriched vacancies, WO 3 nanoparticles loaded with noble metal single surface Atom; the composite contains W 5+ defects and oxygen vacancies accompanying W 5+ defects, and may also contain a small amount of Ti 3+ defects and oxygen vacancies accompanying Ti 3+ defects, mainly on the surface of WO 3 nanoparticles There are noble metal single atoms anchored in the defects.
  • the WO 3 particles supported TiO 2 nanotubes were modified by electrochemical reduction, and the single-atom noble metal was further loaded by electrochemical treatment to improve its electron transport ability and hole-electron pair recombination performance, and improve its photocatalytic performance .
  • Oxygen vacancies on the surface of WO 3 particles stabilize single-atom noble metals, prevent noble metals from agglomerating and deactivate them, and apply the material to indoor photocatalytic degradation of volatile organic compounds, which has higher degradation efficiency and stability.
  • the present invention prepares monoatomic precious metal anchoring defect type WO 3 /TiO 2 nanotube composite, which is a binary phase composite material. Compared with the unit phase, the binary phase composite material has a longer response wavelength and can respond within a certain visible light range, the recombination rate of photogenerated electrons and holes is lower, and the photocatalytic performance is stronger.
  • part of the WO 3 nanoparticles are reduced to form W 5+ defects through an electrochemical reduction method, and by controlling the electrochemical reduction method, the obtained defects and the content of oxygen vacancies accompanying the defects are controlled. And further control the electrochemical deposition process conditions, so that the noble metal single atoms are anchored and loaded on the surface defects of the WO 3 nanoparticles in the composite.
  • the photocatalytic performance of the composite is improved while saving the use of precious metals to the greatest extent.
  • TiO 2 nanotubes as a carrier with an open channel structure, ensure the mass transfer of oxygen molecules and other substances in the tube, prevent the accumulation of VOCs degradation intermediate products, and improve the durability of the composite catalyst.
  • the noble metal single atom with 100% atom utilization rate anchored at the defect site has obtained a low-cost, efficient and stable single-atom noble metal/WO 3 /TiO 2 nanotube composite photocatalyst that is responsive to visible light. And applied to the degradation of VOCs.
  • a method for preparing a modified TiO 2 nanotube-based visible light photocatalyst includes the following steps: the photocatalyst is a visible light-responsive TiO 2 nanotube-based photocatalyst.
  • the Ti piece was cut into a size of 3cm ⁇ 3.5cm, and immersed in a glycol solution containing 3.119g/L ammonium fluoride and 13.75% (volume ratio) deionized water under a two-electrode system.
  • the platinum electrode was used as the counter electrode at 60V. Voltage etching for 8 hours.
  • the obtained TiO 2 nanotube precursor is put into a muffle furnace and calcined at 450° C. for 120 min to obtain anatase TiO 2 nanotubes.
  • the electrochemical deposition of WO 3 nanoparticles was carried out.
  • 0.1mol/L EDTA, ammonium acetate and sodium tungstate aqueous solution deposit 600s under the condition of -2mA/cm 2 constant current.
  • the WO 3 /TiO 2 nanotube precursor was placed in a muffle furnace and calcined at 450° C. for 120 min.
  • step (2) The material obtained in step (2) was used as the working electrode, the saturated calomel electrode was used as the reference electrode, the platinum sheet electrode was used as the counter electrode, and the electrolyte was a 0.1 M Na 2 SO 4 solution.
  • the reduction potential is set to -1.4V, and the reduction is 600s.
  • the WO 3 nanoparticles with oxygen-enriched vacancies obtained in step (3) are loaded with TiO 2 nanotubes as the working electrode, using the square wave pulse method, and the electrolyte is a mixed solution containing 25 ⁇ mol/L HAuCl 4 and 0.1 mol NaCl Under the conditions of -0.2v high potential, -0.6v low potential, 5s pulse width and 5 cycles, the Au monoatoms are loaded on the surface of the composite, and after drying, the oxygen vacancy stable Au monoatomic WO 3 /TiO 2 is obtained Nanotube catalyst.
  • TiO 2 nanotubes mentioned below refers to a step (2) TiO 450 °C firing nanotubes obtained in Example 2; WO 3 / TiO 2 is referring to the nanotubes Example 1 Step (2)
  • the catalyst obtained by step (3) of TiO 2 nanotubes calcined at 450°C; self-doped WO 3 particles with oxygen-rich vacancies supported TiO 2 nanotubes refers to the step (2) of Example 1
  • the TiO 2 nanotubes obtained by firing are subjected to step (3) to obtain a photocatalyst, and the modified monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotubes refers to the rich nanotubes obtained in step (3) of Example 1.
  • Oxygen vacancy self-doped WO 3 /TiO 2 nanotubes are modified catalysts obtained through step (4).
  • Example 1 Modified self-doped WO 3 particle-loaded TiO 2 nanotube microscopic morphology, single-atom state diagram and single-atom distribution diagram of the noble metal Au
  • (a) is the micro-topography of WO 3 /TiO 2 nanotubes (scanning electron microscope);
  • (b) is the noble metal in the modified anchoring defect type WO 3 /TiO 2 nanotubes in Example 1.
  • Transmission electron microscope image (bright field transmission electron microscope), as shown in Figure 1 (a), from the SEM micro-topography, it can be seen that WO 3 /TiO 2 nanotubes have a highly ordered nanotube array structure with a diameter of 150 nm , The thickness of the nanotube wall is about 10nm.
  • the wall of the TiO 2 nanotube tube is uniformly loaded with WO 3 particles with a particle diameter of 50-80 nm.
  • Figure 1(c) is the single-atom state of the precious metal in the monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotubes modified in Example 1 (high-angle annular dark field transmission electron microscope);
  • Figure 1 (d) is the implementation Example 1 The distribution map of the noble metal single atoms in the modified single-atom noble metal anchored defect-type WO 3 /TiO 2 nanotubes (transmission electron microscope scan).
  • the particle size of the precious metal Au in the monoatomic noble metal anchoring defect type WO 3 /TiO 2 nanotubes modified in Example 1 is less than 0.2 nm, which is in a single atom state.
  • the distribution position of Au atoms is the same as the distribution position of W atoms, and single-atom Au is only distributed on the surface of WO 3 nanoparticles.
  • Example 1 Modified single-atom noble metal anchoring defect type WO 3 /TiO 2 nanotubes (R-Au-W/T) electron paramagnetic resonance signal pattern (RPE), and defect type WO 3 /TiO 2 High-resolution transmission electron microscope image of nanotubes.
  • R-TNTs defect state TiO 2 nanotubes
  • the oxygen vacancy signal of the modified monoatomic noble metal anchored defective WO 3 /TiO 2 nanotubes (R-Au-W/T) is relative to that of the defective WO 3 /TiO 2 nanotubes (RW/T).
  • Au proved monatomic oxygen vacancies anchored on the surface 3 of WO.
  • Figure 6 is the degradation curve of the sample degrading toluene, which is a volatile organic compound, under 375nm light;
  • the reaction system is: a sheet catalyst with an area of 4cm 2 is placed in a 15mL closed quartz reactor containing toluene at a concentration of 150ppmv, under dark conditions After 5 minutes of natural adsorption, it was irradiated with a 375nm LED light source with a power of 4W, and samples were taken every 5 minutes to measure the concentration of toluene and CO 2. It can be clearly seen from the figure that the modified R-Au-W/T has better catalytic performance than Au-W/T and RW/T and can be used in actual production.
  • Figure 7 (a), (b) and (c) are respectively RW/T, Au-W/T and modified R-Au-W/T prepared in Example 1 toluene degradation curves. It can be clearly seen from the figure that R-Au-W/T has better catalytic performance than RW/Th and Au-W/T. In addition, Au-W/T will show obvious deactivation. , And R-Au-W/T has good stability, indicating that the oxygen vacancy can anchor the Au single atom, that is, the oxygen vacancy can effectively inhibit the Au single atom agglomeration, so that the modified single-atom noble metal can anchor the defect type WO 3 /TiO 2 nanotubes are not easy to deactivate and are suitable for actual production processes.
  • the modified monoatomic noble metal anchored defect type WO 3 /TiO 2 nanotubes prepared by the method of this embodiment have strong photocatalytic activity and stability, and can effectively degrade organic pollutants in the gas phase.
  • the modified monoatomic noble metal anchored defect type WO 3 /TiO 2 nanotubes prepared in this example contain WO 3 nanoparticles on the inner and outer walls of the TiO 2 nanotubes.
  • the WO 3 nanoparticles of the composite contain Oxygen vacancies are anchored with noble metal single atoms, and the cost is lower than that of samples in which noble metal single atoms are simultaneously distributed in WO 3 nanoparticles and TiO 2 nanotubes.
  • a method for preparing a modified self-doped TiO 2 nanotube-based visible light photocatalyst includes the following steps: the photocatalyst is a visible light responsive TiO 2 nanotube-based photocatalyst.
  • TiO 2 nanotube precursor is put into a muffle furnace and calcined at 400° C. for 240 min to obtain anatase TiO 2 nanotubes.
  • the electrochemical deposition of WO 3 nanoparticles was carried out. 0.01mol/L EDTA, ammonium acetate and sodium tungstate aqueous solution, deposited 400s under the condition of -10mA/cm 2 constant current. Then the WO 3 /TiO 2 nanotube precursor was placed in a muffle furnace and calcined at 600° C. for 60 min.
  • the material obtained in (2) was used as the working electrode, the saturated calomel electrode was used as the reference electrode, the platinum sheet electrode was used as the counter electrode, and the electrolyte was a 0.1 M Na 2 SO 4 solution.
  • the reduction potential is set to -1.6V, and the reduction is 200s.
  • the WO 3 nanoparticles with oxygen-rich vacancies obtained in step (3) are loaded with TiO 2 nanotubes as the working electrode.
  • the square wave pulse method is used.
  • the electrolyte is a mixture containing 1mmol/L H 2 PtCl 6 and 0.1mol NaCl. Solution, under the conditions of -0.1v high potential, -1.2v low potential, 2s pulse width and 15 cycles, load Pt monoatoms on the surface of the composite, and after drying, the oxygen vacancy stabilized Pt monoatomic WO 3 /TiO 2 Nanotube catalyst.
  • a method for preparing a modified self-doped TiO 2 nanotube-based visible light photocatalyst includes the following steps: the photocatalyst is a visible light responsive TiO 2 nanotube-based photocatalyst.
  • TiO 2 nanotube precursor is put into a muffle furnace and calcined at 600° C. for 60 min to obtain anatase TiO 2 nanotubes.
  • the electrochemical deposition of WO 3 nanoparticles was carried out.
  • 1mol/L EDTA, ammonium acetate and sodium tungstate aqueous solution deposit 1000s under the condition of -1mA/cm 2 constant current.
  • the WO 3 /TiO 2 nanotube precursor was calcined in a muffle furnace at 400° C. for 240 min.
  • step (2) The material obtained in step (2) was used as the working electrode, the saturated calomel electrode was used as the reference electrode, the platinum sheet electrode was used as the counter electrode, and the electrolyte was a 0.1 M Na 2 SO 4 solution.
  • the reduction potential is set to -1.0V, and the reduction is 1000s.
  • the WO 3 nanoparticles with oxygen-rich vacancies obtained in step (3) are loaded with TiO 2 nanotubes as the working electrode.
  • the potentiostatic method is used, and the electrolyte is a mixed solution containing 1 mmol/L AgNO 3 and 0.1 mol NaCl. -1.0v constant potential reduction for 10s, the Ag single atom is loaded on the surface of the composite, and the oxygen vacancy stabilized Pt single atom WO 3 /TiO 2 nanotube catalyst is obtained after drying.
  • the present invention loads WO 3 on the surface of TiO 2 nanotubes, and constructs oxygen vacancies on the surface of WO 3 particles loaded with TiO 2 nanotubes by electrochemical reduction treatment, and further introduces noble metal units electrochemically, and uses WO 3
  • the oxygen vacancies on the surface anchor single atoms, prevent single atoms from reunion, improve its photocatalytic performance, and enable it to effectively and quickly degrade organic pollutants.
  • a method for preparing a modified TiO 2 nanotube-based visible light photocatalyst includes the following steps: the photocatalyst is a sample of single-atom Au anchored simultaneously on WO 3 nanoparticles and TiO 2 nanotube surface defects (Au-W/ Au-T).
  • the Ti piece was cut into a size of 3cm ⁇ 3.5cm, and immersed in a glycol solution containing 3.119g/L ammonium fluoride and 13.75% (volume ratio) deionized water under a two-electrode system.
  • the platinum electrode was used as the counter electrode at 60V. Voltage etching for 8 hours.
  • the obtained TiO 2 nanotube precursor is put into a muffle furnace and calcined at 450° C. for 120 min to obtain anatase TiO 2 nanotubes.
  • the TiO 2 nanotubes obtained in step (1) were used as the working electrode, the saturated calomel electrode was used as the reference electrode, the platinum sheet electrode was used as the counter electrode, and the electrolyte was a 0.1 M Na 2 SO 4 solution.
  • the reduction potential was set to -1.4V, and the reduction was performed for 600 s to obtain TiO 2 nanotubes rich in oxygen vacancies after electrochemical reduction.
  • the TiO 2 nanotubes with oxygen-rich vacancies obtained in step (2) are used as the working electrode, and the square wave pulse method is used.
  • the electrolyte is a mixed solution containing 25 ⁇ mol/L HAuCl 4 and 0.1 mol NaCl. Under the conditions of -0.2v high potential, -0.6v low potential, 5s pulse width and 5 cycles, single Au atoms are loaded on the surface of TiO 2 nanotubes, and after drying, single atoms of Au are anchored on the surface defects of TiO 2 nanotubes Sample (Au-TiO 2 ).
  • step (3) Using the Au-anchored TiO 2 nanotubes obtained in step (3) as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum sheet electrode as the counter electrode, electrochemical deposition of WO 3 nanoparticles was carried out, wherein the electrolyte was Aqueous solutions of EDTA, ammonium acetate and sodium tungstate with all the solubility of 0.1mol/L were deposited for 600s under the condition of -2mA/cm 2 constant current. The WO 3 /Au-TiO 2 nanotubes were obtained, which were then placed in a muffle furnace and calcined at 450° C. for 120 min.
  • the electrolyte was Aqueous solutions of EDTA, ammonium acetate and sodium tungstate with all the solubility of 0.1mol/L were deposited for 600s under the condition of -2mA/cm 2 constant current.
  • the WO 3 /Au-TiO 2 nanotubes were obtained, which were then placed in
  • step (4) The material obtained in step (4) was used as the working electrode, the saturated calomel electrode was used as the reference electrode, the platinum sheet electrode was used as the counter electrode, and the electrolyte was a 0.1 M Na 2 SO 4 solution.
  • the reduction potential was set to -1.4V, and the reduction was performed for 600 s to obtain WO 3 particles with oxygen-rich vacancies supporting Au-TiO 2 nanotubes.
  • the composite material with oxygen-rich vacancies obtained in step (5) is used as the working electrode.
  • the square wave pulse method is used.
  • the electrolyte is a mixed solution containing 25 ⁇ mol/L HAuCl 4 and 0.1mol NaCl at a high potential of -0.2v. , -0.6v low potential, 5s pulse width and 5 cycles conditions, the single Au atom is loaded on the surface of the composite, and after drying, the single atom Au is simultaneously anchored to the surface defects of WO 3 nanoparticles and TiO 2 nanotubes.
  • Sample (Au-W/Au-T) Sample (Au-W/Au-T).
  • Figure 8 (a) and (b) are the high-angle circular dark-field transmission electron microscope images of the sample (Au-W/Au-T) in which single-atom Au is simultaneously anchored to the surface defects of WO 3 nanoparticles and TiO 2 nanotubes.
  • the scanning image shows that the single-atom Au also exists as a single atom on the surface of TiO 2 and the single-atom Au is uniformly distributed on the surface of WO 3 nanoparticles and TiO 2 nanotubes at the same time.
  • Figure 8(c) is the EDS energy spectrum.
  • the graph and the integration results show that the mass percentages of the precious metal Au in the Au-W/Au-T and R-Au-W/T samples are 4.51% and 2.41%, respectively.
  • the preparation method of the sample (Au-W/Au-T) in which monoatomic Au is simultaneously anchored to the surface defects of WO 3 nanoparticles and TiO 2 nanotubes is: before carrying out the first step of the preparation method to load WO 3 , The TiO 2 nanotubes are chemically reduced and single-atom Au is electrochemically anchored. The subsequent steps are the same as the R-Au-W/T sample.
  • Figure 9 is the band gap diagram of WO 3 and TiO 2 composites (data from UV photoelectron spectroscopy UPS characterization).
  • the valence band positions of WO 3 and TiO 2 in the composite are 3.12 eV and 2.91 eV, respectively.
  • WO 3 has stronger The valence band oxidation ability of, and the coupling of single atom Au and WO 3 should have stronger oxidation ability.
  • Figure 10 is a sample (Au-W/Au-T) in which monoatomic Au is simultaneously anchored to the surface defects of WO 3 nanoparticles and TiO 2 nanotubes and the modified monoatomic precious metal of Example 1 is anchored to WO 3 nanoparticles ( R-Au-W/T) Comparison of degradation of toluene. Compared with R-Au-W/T, the toluene degradation efficiency of Au-W/Au-T is not significantly improved. Therefore, compared with Au-W/Au-T, the modified R-Au-W/T of Example 1 has a lower preparation cost.

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Abstract

一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管、其制备和应用，通过采用电化学还原对WO 3颗粒负载TiO 2纳米管进行改性，并通过对其进行电化学处理进一步负载单原子贵金属，改善其电子传输能力和空穴电子对复合表现，提高其光催化性能。WO 3颗粒表面氧空位稳定单原子贵金属，防止贵金属团聚使其失活，将材料应用于室内挥发性有机物的光催化降解，具有更高的降解效率和稳定性。

Description

单原子贵金属锚定缺陷型WO 3/TiO 2纳米管、其制备和应用 【技术领域】
本发明属于光催化材料领域，更具体地，涉及一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管、其制备和应用。
【背景技术】
自1972年，日本科学家Fujishima和Honda首次发表在n-半导体TiO 2电极上发现水的光电催化分解的报道以来，TiO 2以独特的光学性质和较高光催化活性，在光学材料、光电化学和光电磁、光催化降解污染物等领域的应用中得到广泛的发展。1991年Iij ima等人发现了碳纳米管，由于其独特的结构和优异的性能，一维纳米材料(如纳米线、纳米管、纳米膜)受到了人们的广泛关注和研究。TiO 2纳米管阵列作为TiO 2的二维纳米材料，因其高度有序、尺寸可控的结构特征和独特的电子转移特性而引起越来越多的关注。与其他形态TiO 2纳米材料相比，TiO 2纳米管阵列有着更大的比表面积、更好的电子传输通道及吸附能力，因此可更好的提高光电转换效率、光催化性能等，特别是在管中修饰金属、非金属粒子或其他半导体氧化物材料，将会极大改善TiO 2的催化、光电及电磁性能。1999年Zwilling等通过阳极氧化法获得了具有高度有序阵列结构的TiO 2纳米管。目前，TiO 2纳米管的制备方法还包括溶胶-凝胶法、水热合成法以及磁控溅射法等。
然而，受限于TiO 2半导体本身较宽的禁带(3.2eV)，该半导体材料仅能利用波长在可见光区的太阳能资源，以及光催化难以避免的光生电子-空穴复合问题，TiO 2纳米管的催化效率，特别是在可见光区的催化效率较低，因此大量的改性工作就此展开。主要包括贵金属的表面修饰、过度金属修饰及离子掺杂、非金属掺杂与共掺杂以及半导体复合等。
基于WO 3半导体材料禁带宽度低、无毒廉价等优点，2013年以来，大 量的工作将WO 3负载于TiO 2纳米管上，以形成异质结，提高TiO 2纳米管基材料的响应波长，进而提高光催化效率。然而，由于不可避免的光生电子-空穴的复合现象，该材料的光催化性能始终不能达到实际生产的标准。
近年来，单原子催化剂作为一种新型的催化剂得到迅猛发展，单原子贵金属能将催化效率最大化，改善光催化剂的电子分布及传输、光吸收性能以及化学吸附能力，从而提高光催化效率，并应用于氧化和加氢等反应，然而，由于单原子的高表面能，单个原子通常是可移动的且易于团聚，使光催化剂失去活性，故在高效光催化剂的设计中，需要开发与单一金属原子具有强相互作用的合适载体。
发明内容
针对现有技术的以上缺陷或改进需求，本发明提供了一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管、其制备和应用，其通过采用贵金属单原子锚定缺陷型WO 3/TiO 2纳米管，防止单原子团聚，提高其光催化性能，由此解决现有技术中光响应型催化剂缺陷容量有限、对可见光的响应范围窄、贵金属单原子易团聚、光催化性能差以及易失活等的技术问题。
为实现上述目的，按照本发明的一个方面，提供了一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物的制备方法，包括如下步骤：
(1)在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，煅烧使所述WO 3纳米颗粒晶化，得到内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管；
(2)对步骤(1)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管进行电化学还原，使部分WO 3纳米颗粒被还原形成W 5+缺陷，得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物；
(3)以步骤(2)获得的含有W 5+缺陷的WO 3颗粒负载TiO 2纳米管复合物作为工作电极，通过电化学沉积将贵金属单原子负载于该复合物中WO 3纳米颗粒表面缺陷处，得到单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物。
优选地，步骤(1)所述煅烧具体为在400℃-600℃条件下煅烧60min-240min。
优选地，步骤(1)所述TiO 2纳米管通过如下方法获得：采用阳极氧化法、溶胶-凝胶法、水热法、磁控溅射法或原子层沉积法制备得到TiO 2前驱体，然后将该TiO 2前驱体在400℃-600℃条件下煅烧60min-240min，得到TiO 2纳米管。
优选地，步骤(1)所述沉积WO 3纳米颗粒的方法为电化学沉积法、共水热法、旋涂法或浸渍法。
优选地，步骤(2)具体为：以步骤(2)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管为工作电极，在还原电压为-1.0v～-1.6v，还原的时间为200s-1000s的条件下进行电化学还原，使WO 3纳米颗粒被部分还原形成W 5+缺陷，得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物。
优选地，在三电极体系下，以步骤(2)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管为工作电极，以铂电极为对电极，以饱和甘汞电极为参比电极，进行步骤(2)的电化学还原。
优选地，步骤(3)具体为：在三电极体系下，将步骤(2)得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用方波脉冲法、恒电位法或恒电流法将贵金属单原子负载于复合物中WO 3纳米颗粒表面的缺陷处。
优选地，所述的贵金属单原子为Au、Ag、Pt、Pd、Ir或Ru，步骤(3)具体为：在三电极体系下，将步骤(2)得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用方波脉冲法将贵金属单原子负载于复合物中WO 3纳米颗粒表面的缺陷处，所述方波脉冲法的高电位为0v～-0.2v，低电位为-0.4v～-1.6v，循环次数为1次～50次，脉冲宽度为1s～20s。
优选地，采用恒电位法将贵金属单原子负载于复合物中WO 3纳米颗粒 表面的缺陷处，采用的恒电位法的电位为-0.2v～-1.6v，还原时间为2s～100s，电解质中的贵金属源的浓度为5μmol/L～1mmol/L。
按照本发明的另一个方面，提供了一种所述的制备方法制备得到的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物。
优选地，所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物，其包括TiO 2纳米管以及在该TiO 2纳米管内壁和外壁上负载的WO 3纳米颗粒；该复合物中含有W 5+缺陷以及由所述W 5+缺陷伴随产生的氧空位，且WO 3纳米颗粒表面缺陷处锚定有贵金属单原子。
优选地，所述TiO 2纳米管的直径为100nm-200nm。
按照本发明的另一个方面，提供了一种所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物在光催化中的应用。
优选地，所述应用为在挥发性有机物的光催化降解方面的应用。
优选地，所述应用在波长小于等于470nm的光照条件下进行。
优选地，所述挥发性有机物的浓度为50ppmv-500ppmv。
总体而言，通过本发明所构思的以上技术方案与现有技术相比，能够取得下列有益效果：
(1)本发明提供了一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物的制备方法，其通过使用电化学方法直接阴极耦合还原WO 3/TiO 2纳米管，在还原后产生大量的氧空位缺陷，利用氧空位对光生电子空穴的分离促进作用，有利于贵金属单元子的锚定。与目前传统的还原气氛热处理(如在氢气气氛中煅烧)方法相比，电化学自掺杂方法高效、安全，易于操作与控制。
(2)本发明通过控制电化学还原过程工艺，比如通过控制电化学还原WO 3/TiO 2纳米管的电压和还原时间，使得主要以其中WO 3纳米颗粒还原为主，获得富含W 5+缺陷及其伴随产生的氧空位的WO 3纳米颗粒负载TiO 2纳米管复合物，进一步地，通过电化学沉积单原子贵金属，获得单原子贵金 属主要锚定在WO 3纳米颗粒表面缺陷处的复合物。本发明实验发现将贵金属单原子负载于复合物中WO 3纳米颗粒表面的缺陷处，与贵金属同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品相比，其光催化性能相似，但贵金属负载量下降40-60％。
(3)本发明提供的一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物，通过对WO 3纳米颗粒负载的TiO 2纳米管进行电化学还原自掺杂获得丰富的氧空位缺陷后，掺杂贵金属单元，得到了一种充分利用其产生的羟基自由基、超氧自由基等活性氧完成现有空气中挥发性有机污染物降解的可见光催化剂。该纳米管结构中包含W 6+-O键、Ti 4+-O键、缺陷W 5+及其伴随产生的氧空位以及贵金属单原子。
(4)本发明的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物催化剂具有可见光响应性，其应用于光催化降解有机污染物时，负载于TiO 2上的WO 3颗粒与锐钛矿的TiO 2形成异质结，并降低WO 3/TiO 2纳米管的禁带宽度，该催化剂的带隙宽度为2.6eV～2.8eV，使其最大吸收边向可见光方向扩展，从而可以利用能量更低的可见光来完成有机物的降解反应。此外，WO 3/TiO 2纳米管异质结的存在可显著抑制光生电子空穴的复合，从而提高光催化性能。
(5)本发明在材料制备过程中掺入贵金属单原子，与纳米颗粒态的贵金属相比，单原子态的贵金属与载体发生强相互作用，防止贵金属团聚，光催化效率更高，耐久性更好。
(6)本发明中改性的自掺杂型WO 3颗粒负载TiO 2纳米管，具有高度有序的纳米管阵列，比表面积大，在光催化降解空气中挥发性有机物时，空气中的氧气分子能有效扩散至纳米管中的开放通道中，从而抑制管内“碳床”的形成，纳米管结构赋予该发明具备优异的稳定性，不易失活。
(7)本发明中改性的自掺杂型WO 3颗粒负载TiO 2纳米管宏观上表现为薄片状，薄片面积可调，与传统的粉末状催化剂相比，该发明易于回收， 且适合作为催化板或催化床应用于光催化降解气相中的有机污染物，进一步提高其催化性能。
【附图说明】
图1中(a)为WO 3/TiO 2纳米管的微观形貌图(扫描电子显微镜)；(b)为实施例1改性的锚定缺陷型WO 3/TiO 2纳米管中贵金属透射电镜图(明场透射电镜)；(c)为实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管中贵金属的单原子状态(高角环形暗场透射电镜)；(d)为实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管中贵金属单原子分布图(透射电镜面扫图)。
图2中(a)为实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)的电子顺磁共振信号图(RPE)，(b)为缺陷型WO 3/TiO 2纳米管高分辨透射电镜图。
图3为原始的WO 3/TiO 2纳米管(W/T)、Au纳米颗粒负载的WO 3/TiO 2纳米管(Au-W/T)和实施例1制得的改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)的UV-vis吸收光谱图。
图4为原始WO 3/TiO 2纳米管(W/T)、含有W5+缺陷的自掺杂WO 3/TiO 2纳米管、Au颗纳米粒负载的WO 3/TiO 2纳米管和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管的光致发光光谱图。
图5为含有W 5+缺陷的WO 3/TiO 2纳米管(R-W/T)和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T-1和R-Au-W/T-2)的光电流响应图。
图6为含有W 5+缺陷的WO 3/TiO 2纳米管(R-W/T)、Au颗纳米粒负载的WO 3/TiO 2纳米管(Au-W/T)和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)降解挥发性有机物甲苯的降解曲线图；
图7中(a)、(b)和(c)分别为含有W5+缺陷的WO 3/TiO 2纳米管、Au颗纳米粒负载的WO 3/TiO 2纳米管和实施例1改性的单原子贵金属锚定 缺陷型WO 3/TiO 2纳米管降解甲苯的重复降解曲线图。
图8中(a)为单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)和实施例1改性的单原子贵金属锚定与WO 3纳米颗粒(R-Au-W/T)的单原子状态图(高角环形暗场透射电镜)；(b)为Au-W/Au-T样品的单原子分布图(透射电镜面扫图)；(c)为Au-W/Au-T和R-Au-W/T的贵金属Au的质量分数(EDS能谱)。
图9为WO 3和TiO 2复合物的带隙图(数据紫外光电子能谱，UPS)。
图10为单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)和实施例1改性的单原子贵金属锚定与WO 3纳米颗粒(R-Au-W/T)降解甲苯对比。
【具体实施方式】
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物的制备方法，包括如下步骤：
(1)在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，煅烧使所述WO 3纳米颗粒晶化，得到内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管；
(2)对步骤(1)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管进行电化学还原，通过控制电化学还原的电位和时间，使部分WO 3纳米颗粒被还原形成W 5+缺陷，得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物；
(3)以步骤(2)获得的含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物作为工作电极，通过电化学沉积将贵金属单原子负载于该复合物 中WO 3纳米颗粒表面缺陷处，得到单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物。
本发明所述的TiO 2纳米管可以采用常规的方法制得。一些实施例中，步骤(1)所述TiO 2纳米管通过如下方法获得：采用阳极氧化法、溶胶-凝胶法、水热法、磁控溅射法或原子层沉积法制备得到TiO 2前驱体，然后将该TiO 2前驱体在400℃-600℃条件下煅烧60min-240min，得到TiO 2纳米管。
一些实施例中，采用阳极氧化法制备TiO 2纳米管。所述阳极氧化法为在两电极体系下，将金属Ti片作为工作电极置于含有F -的电解质溶液中，在恒电压为20V-80V的条件下刻蚀2h-20h，得到TiO 2前驱体。
一些优选实施例中，在两电极体系下，将钛片作为工作电极置于含有F -的电解质溶液中，在20V～80V恒电压条件下刻蚀2～20h。将得到的TiO 2纳米管前驱体在一定400～600℃温度下烧制60～240min，得到TiO 2纳米管。
优选实施例中，所述含F -电解质溶液为氟化铵水溶液与有机溶剂形成的混合溶液；所述混合溶液中氟化铵的浓度为0.1g/L-10g/L；所述氟化铵水溶液的体积占混合溶液的体积的5％-20％；所述有机溶剂为乙二醇、丙三醇、甘油、二甲基亚砜、二甲基甲酰胺、甲酰胺、甲基甲酰胺和二乙二醇中的一种或多种。
步骤(1)首先在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，煅烧使所述WO 3纳米颗粒晶化。一些实施例中，步骤(1)所述煅烧具体为在400℃-600℃条件下煅烧60min-240min。
本发明步骤(1)所述在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒前驱体的方法可以为现有技术通常采用的方法，比如电化学沉积法、共水热法、旋涂法或浸渍法。
一些实施例中，采用电化学沉积法在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，具体为：将TiO 2纳米管作为工作电极，在三电极体系下， 以乙二胺四乙酸、醋酸铵和钨酸钠的混合溶液为电解质，在所述TiO 2纳米管表面沉积WO 3纳米颗粒前驱体。
优选实施例中，所述电解质中乙二胺四乙酸、醋酸铵和钨酸钠的浓度均为0.01mol/L-1mol/L；所述电化学沉积法为恒电流极化法，所述恒电流的电流密度为-1mA/cm 2～-10mA/cm 2，沉积时间400s～1000s。
另一些优选实施例中，将所得的TiO 2纳米管前驱体作为工作电极，在三电极体系下，采用电化学沉积法，以EDTA、醋酸铵以及钨酸钠混合溶液为电解质，在恒电流条件下，在TiO 2纳米管表面沉积一层WO 3纳米颗粒前驱体，然后在400～600℃温度下烧制60～240min，水洗后烘干得到WO 3/TiO 2纳米管。
一些实施例中，采用共水热法在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，具体为：将制备好的TiO 2纳米管薄膜置于100ml含有0.01M钨酸钠和0.01M草酸的混合溶液中，充分搅拌后，转移至反应反应釜中，在150℃下反应24h，待自然冷却后取出TiO 2纳米管薄膜，水洗后烘干，所得即为产物。
一些实施例中，采用旋涂法在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，具体为：将钨粉和过氧化氢(质量分数:30％)混合反应后产生的过氧聚钨酸凝胶作为前驱体，用水稀释10倍后，取适量均匀涂抹在TiO 2纳米管薄膜表面，后采用旋涂机在3000r/min旋涂，旋涂后将载有过氧聚钨酸前驱体的TiO 2纳米管薄膜置于马弗炉中，在450℃下煅烧2h，所得即为产物。
一些实施例中，采用浸渍法在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，具体为：将制备好的TiO 2纳米管薄膜置于1mM偏钨酸铵水溶液中，搅拌浸渍2h后取出，在马弗炉中450℃下煅烧2h，所得即为产物。
一些实施例中，步骤(2)具体为：以步骤(2)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管为工作电极，在还原电压为-1.0v～-1.6 v，还原的时间为200s-1000s的条件下进行电化学还原，使WO 3纳米颗粒被部分还原形成W 5+缺陷，得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物。
本发明通过控制电化学还原的电压和时间，使得该还原主要以WO 3纳米颗粒的还原为主，不排除少量的TiO 2纳米管也同时被还原形成Ti 3+缺陷，得到含有W 5+缺陷和少量Ti 3+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物。
一些实施例中，在三电极体系下，以步骤(2)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管为工作电极，以铂电极为对电极，以饱和甘汞电极为参比电极，进行步骤(2)的电化学还原。
表面氧空位浓度与电化学还原程度成正态分布，为了确保单原子锚定位点数量和催化性能，需要将W 5+缺陷和Ti 3+缺陷伴随产生的氧空位控制在合适的范围内。本发明通过控制电化学还原电压和还原时间，使得部分WO 3纳米颗粒和部分TiO 2纳米管分别被还原形成W 5+缺陷和Ti 3+缺陷，且主要以WO 3纳米颗粒的还原为主。缺陷含量也不宜太高，理想情况下仅将WO 3纳米颗粒部分还原，得到具有一定缺陷含量的改性的自掺杂型WO 3颗粒负载TiO 2纳米管复合物。
一些优选实施例中，步骤(3)具体为：在三电极体系下，将步骤(2)得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用方波脉冲法、恒电位法或恒电流法将贵金属单原子负载于复合物中WO 3纳米颗粒表面的缺陷处。
实验中发现将贵金属单原子同时负载于复合物中WO 3纳米颗粒表面缺陷和TiO 2纳米管表面缺陷处时，相对于单独负载于复合物中WO 3纳米颗粒表面缺陷处，对甲苯光降解性能并没有明显的提升。贵金属单原子与WO 3耦合带来的光催化氧化能力远大于贵金属单原子与TiO 2耦合，可能是由于WO 3的价带位置比TiO 2更正，禁带宽度比TiO 2更窄，具有更强的氧化能力和更长的响应波长。
本发明通过控制电化学还原过程工艺，控制WO 3纳米颗粒和TiO 2纳米管的还原，由于TiO 2纳米管还原为Ti 3+缺陷要求的电压更高(约2.0V)，本发明优选实施例中通过控制电化学还原电压低于1.6V，以期仅将部分WO 3纳米颗粒还原为W 5+缺陷，进而采用电化学沉积法将贵金属单原子仅负载于复合物中WO 3纳米颗粒表面缺陷处，在贵金属使用量最少的情况下最大程度提升本发明制备得到的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物用于光催化性能，节省了贵金属的使用量。
本发明所述的贵金属单原子可以为Au、Ag、Pt、Pd、Ir或Ru，一些实施例中，采用方波脉冲法将贵金属单原子负载于复合物中WO 3纳米颗粒表面的缺陷处，其方波脉冲法的高电位为0v～-0.2v，低电位为-0.4v～-1.6v，循环次数为1次～50次，脉冲宽度为1s～20s，电解质中的贵金属源的浓度为5μmol/L～10mmol/L。
一些实施例中，采用恒电位法将贵金属单原子负载于复合物中WO 3纳米颗粒表面的缺陷处，采用的恒电位法的电位为-0.2v～-1.6v，还原时间为2s～100s，电解质中的贵金属源的浓度为5μmol/L～1mmol/L。
本发明还提供了一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物，其包括TiO 2纳米管以及在该TiO 2纳米管内壁和外壁上负载的WO 3纳米颗粒；该复合物中含有W 5+缺陷以及由所述W 5+缺陷伴随产生的氧空位，且WO 3纳米颗粒表面缺陷处锚定有贵金属单原子。
一些实施例中，本发明所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物能吸收波长小于或等于470nm的光辐射。
本发明一些实施例中，所述复合物中的TiO 2纳米管的直径为100nm-200nm。
本发明还提供了所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物在光催化中的应用。
一些实施例中，将该复合物应用在挥发性有机物的光催化降解方面， 应用时，优选在波长小于或等于470nm的光照条件下进行；且所述挥发性有机物的浓度为50ppmv-500ppmv。
本发明中WO 3/TiO 2纳米管表示WO 3颗粒负载TiO 2纳米管，R-WO 3/TNTs表示含有W 5+缺陷的自掺杂型WO 3颗粒负载TiO 2纳米管，R-Au-WO 3/TNTs表示单原子贵金属锚定缺陷型WO 3/TiO 2纳米管。本发明中所述的改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管是指相对于含有W 5+缺陷的自掺杂型WO 3颗粒负载TiO 2纳米管进行的改性，改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管即为本发明所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物。
本发明提供的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物，其TiO 2纳米管内壁和外壁上负载了富氧空位的WO 3纳米颗粒，WO 3纳米颗粒表面负载有贵金属单原子；所述复合物中含有W 5+缺陷以及W 5+缺陷伴随产生的氧空位，也可能含有少量Ti 3+缺陷以及Ti 3+缺陷伴随产生的氧空位，且主要在WO 3纳米颗粒表面的缺陷处锚定有贵金属单原子。通过采用电化学还原对WO 3颗粒负载TiO 2纳米管进行改性，并通过对其进行电化学处理进一步负载单原子贵金属，改善其电子传输能力和空穴电子对复合表现，提高其光催化性能。WO 3颗粒表面氧空位稳定单原子贵金属，防止贵金属团聚使其失活，将材料应用于室内挥发性有机物的光催化降解，具有更高的降解效率和稳定性。
本发明制备单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物，其为一种二元相复合材料。二元相复合材料相对于单元相，响应波长更长，可在一定的可见光范围内响应，光生电子和空穴的复合率更低，光催化性能更强。
本发明通过电化学还原法使部分WO 3纳米颗粒被还原形成W 5+缺陷，且通过控制电化学还原方法，控制得到的缺陷和缺陷伴随产生的氧空位含量。并进一步控制电化学沉积工艺条件，使得贵金属单原子锚定负载于该 复合物中WO 3纳米颗粒表面缺陷处。在最大程度节省贵金属使用量的情况下提升了该复合物光催化性能。另一方面，TiO 2纳米管作为具有开放通道结构的载体，确保了氧分子等物质的管内传质，防止VOCs降解中间产物的积累，提高了该复合催化剂的耐久性，配合WO 3纳米颗粒表面缺陷处锚定负载的，具有100％原子利用率的贵金属单原子，获得了一种较低成本的，高效稳定的的，可见光响应的单原子贵金属/WO 3/TiO 2纳米管复合光催化剂，并应用于VOCs降解。
以下为实施例：
实施例1
一种改性的TiO 2纳米管基可见光光催化剂的制备方法，包括如下步骤：该光催化剂为可见光响应型TiO 2纳米管基光催化剂。
(1)制备TiO 2纳米管
将Ti片剪裁为3cm×3.5cm大小，在两电极体系下浸入含有3.119g/L氟化铵以及13.75％(体积比)去离子水的乙二醇溶液中，以铂电极为对电极在60V电压刻蚀8小时。将得到的TiO 2纳米管前驱体放入马弗炉中，在450℃下煅烧120min，以获得锐钛矿型TiO 2纳米管。
(2)制备WO 3/TiO 2纳米管
将步骤(1)中所得的TiO 2纳米管作为工作电极，饱和甘汞电极作为参比电极，铂片电极做为对电极，进行WO 3纳米颗粒的电化学沉积，其中电解质为溶度均为0.1mol/L的EDTA、醋酸铵以及钨酸钠水溶液，在-2mA/cm 2恒电流条件下沉积600s。后将WO 3/TiO 2纳米管前驱体置于马弗炉中，在450℃下煅烧120min。
(3)制备富氧空位的自掺杂型WO 3颗粒负载TiO 2纳米管
将步骤(2)中所得的材料作为工作电极，饱和甘汞电极作为参比电极，铂片电极为对电极，电解质为0.1M的Na 2SO 4溶液。还原电位设置为-1.4V，还原600s。
(4)制备单原子贵金属锚定缺陷型WO 3/TiO 2纳米管
在三电极体系下，将步骤(3)得到富氧空位的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用方波脉冲法，电解质为含有25μmol/L HAuCl 4和0.1mol NaCl的混合溶液，在-0.2v高电位、-0.6v低电位、5s脉冲宽度和5次循环条件下，将Au单原子负载于复合物表面，烘干后得到氧空位稳定Au单原子型WO 3/TiO 2纳米管催化剂。
对本实施例制备的光催化剂进行结果分析：以下提到的TiO 2纳米管是指实施例1步骤(2)在450℃烧制得到的TiO 2纳米管；WO 3/TiO 2纳米管是指实施例1步骤(2)在450℃烧制得到的TiO 2纳米管经步骤(3)得到的催化剂；富氧空位的自掺杂型WO 3颗粒负载TiO 2纳米管是指实施例1步骤(2)在烧制得到的TiO 2纳米管经步骤(3)得到光催化剂，改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管是指是指实施例1步骤(3)得到的富氧空位的自掺杂型WO 3/TiO 2纳米管经步骤(4)得到的改性催化剂。
(1)实施例1改性的自掺杂型WO 3颗粒负载TiO 2纳米管的微观形貌图、贵金属Au的单原子状态图和单原子分布图
图1中(a)图为WO 3/TiO 2纳米管的微观形貌图(扫描电子显微镜)；(b)图为实施例1改性的锚定缺陷型WO 3/TiO 2纳米管中贵金属透射电镜图(明场透射电镜)，如图1的(a)图所示，从SEM微观形貌图可以看出WO 3/TiO 2纳米管具有的150nm直径的高度有序的纳米管阵列结构，纳米管壁的厚度约为10nm。如图1中(b)图所示，TiO 2纳米管管壁均匀负载有WO 3颗粒，颗粒直径50-80nm。
图1的(c)为实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管中贵金属的单原子状态(高角环形暗场透射电镜)；图1中(d)为实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管中贵金属单原子分布图(透射电镜面扫图)。如图1中(c)所示，实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管中贵金属Au的粒径小于为0.2nm，为单 原子状态。如图1中(d)所示，Au原子的分布位置与W原子的分布位置相同，单原子Au仅分布于WO 3纳米颗粒表面。
(2)实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)的电子顺磁共振信号图(RPE)，和缺陷型WO 3/TiO 2纳米管高分辨透射电镜图。
如图2中(a)图所示，实施例1改性缺陷型R-WO 3/TiO 2纳米管在g＝2.002处存在明显氧空位信号，且在图2的(b)图中能观察到明显的WO 3晶格扭曲以及氧空位，仅对进行缺陷处理的得到的缺陷态TiO 2纳米管(R-TNTs)没有明显的氧空位信号，说明氧空位仅存在于WO 3表面。而实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)的氧空位信号相对于缺陷型WO 3/TiO 2纳米管(R-W/T)有所下降，证明单原子Au锚定在WO 3表面的氧空位上。
(3)原始的WO 3/TiO 2纳米管(W/T)、Au纳米颗粒负载的WO 3/TiO 2纳米管(Au-W/T)和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)的UV-vis吸收光谱图
从图3中可以看出，相比原始的WO 3/TiO 2纳米管和Au纳米颗粒负载的WO 3/TiO 2纳米管，实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管的最高响应光波长为470nm，且可见及红外吸光度有明显上升，说明本发明通过对材料的改进，增加了其对于可见光的响应，提高了催化剂光催化能力。
(4)原始WO 3/TiO 2纳米管(W/T)、含有W 5+缺陷的自掺杂WO 3/TiO 2纳米管、Au颗纳米粒负载的WO 3/TiO 2纳米管和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管的光致发光光谱图
从光致发光光谱图图4中可以很明显的看出，原始的WO 3/TiO 2纳米管和Au颗纳米粒负载的WO 3/TiO 2纳米管发光强度很高，说明其电子和空穴复合率较高，光催化反应时真正发挥作用的电子和空穴很少。而改性的单 原子贵金属锚定缺陷型WO 3/TiO 2纳米管发光强度变弱，说明其电子和空穴的复合率降低，提高了光催化效率。
(5)富氧空位的自掺杂WO 3/TiO 2纳米管(R-W/T)和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T-1和R-Au-W/T-2，重复实验的两个样品)的光电流响应图
通过对样品的光电流响应图对比分析，如图5所示，可以发现，改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管具有最强的光电活性，改性方方法显著增强了材料中载流子的迁移效率。
(6)含有W 5+缺陷的WO 3/TiO 2纳米管(R-W/T)、Au颗纳米粒负载的WO 3/TiO 2纳米管(Au-W/T)和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)降解挥发性有机物甲苯的降解曲线图
图6为样品在375nm光照下降解挥发性有机物甲苯的降解曲线图；反应体系为：面积为4cm 2的片状催化剂被放入在含有浓度为150ppmv甲苯的15mL密闭石英反应器内，黑暗条件下自然吸附5分钟后，用具有功率为4W的375nmLED光源照射，每隔5min取样测甲苯及CO 2的浓度。从图中可以很明显看出，改性的R-Au-W/T相比于Au-W/T和R-W/T具有更优异的催化性能，可应用于实际生产之中。
(7)含有W 5+缺陷的WO 3/TiO 2纳米管(R-W/T)、Au颗纳米粒负载的WO 3/TiO 2纳米管(Au-W/T)和实施例1改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管(R-Au-W/T)降解甲苯的重复降解曲线图。
图7中(a)、(b)和(c)分别为R-W/T、Au-W/T和实施例1制得的改性R-Au-W/T的甲苯降解曲线图。从图中可以很明显看出，R-Au-W/T相比于R-W/Th和Au-W/T具有更优异的催化性能，此外，Au-W/T会表现出明显的失活现象，而R-Au-W/T具有良好的稳定性，表明氧空位对Au单原子的锚定作用，即氧空位能有效抑制Au单原子团聚，使改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管不易失活，适用于实际生产过程中。
(8)为单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)和实施例1改性的单原子贵金属锚定与WO 3纳米颗粒(R-Au-W/T)的单原子状态图(高角环形暗场透射电镜)，Au-W/Au-T样品的单原子分布图(透射电镜面扫图)，以及Au-W/Au-T和R-Au-W/T的贵金属Au的质量分数(EDS能谱)。
通过上述分析可知，本实施例的方法制备的改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管具有很强的光催化活性和稳定性，能够有效降解气相中的有机污染物。
该实施例制备得到的改性的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管的TiO 2纳米管内壁和外壁上负载有WO 3纳米颗粒，该复合物的WO 3纳米颗粒上中含有氧空位，且锚定有贵金属单原子，且相比于贵金属单原子同时分布于WO 3纳米颗粒和TiO 2纳米管的样品，成本更低。
实施例2
一种改性的自掺杂型TiO 2纳米管基可见光光催化剂的制备方法，包括如下步骤：该光催化剂为可见光响应型TiO 2纳米管基光催化剂。
(1)制备TiO 2纳米管
将Ti片剪裁为3cm×3.5cm大小，在两电极体系下浸入含有0.1g/L氟化铵以及20％(体积比)去离子水的乙二醇溶液中，以铂电极为对电极在20V电压刻蚀20小时。将得到的TiO 2纳米管前驱体放入马弗炉中，在400℃下煅烧240min，以获得锐钛矿型TiO 2纳米管。
(2)制备WO 3/TiO 2纳米管
将步骤(1)中所得的TiO 2纳米管作为工作电极，饱和甘汞电极作为参比电极，铂片电极做为对电极，进行WO 3纳米颗粒的电化学沉积，其中电解质为溶度均为0.01mol/L的EDTA、醋酸铵以及钨酸钠水溶液，在-10mA/cm 2恒电流条件下沉积400s。后将WO 3/TiO 2纳米管前驱体置于马弗炉中，在600℃下煅烧60min。
(3)制备富氧空位的自掺杂型WO 3颗粒负载TiO 2纳米管
将(2)中所得的材料作为工作电极，饱和甘汞电极作为参比电极，铂片电极为对电极，电解质为0.1M的Na 2SO 4溶液。还原电位设置为-1.6V，还原200s。
(4)制备单原子贵金属锚定缺陷型WO 3/TiO 2纳米管
在三电极体系下，将步骤(3)得到富氧空位的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用方波脉冲法，电解质为含有1mmol/L H 2PtCl 6和0.1mol NaCl的混合溶液，在-0.1v高电位、-1.2v低电位、2s脉冲宽度和15次循环条件下，将Pt单原子负载于复合物表面，烘干后得到氧空位稳定Pt单原子型WO 3/TiO 2纳米管催化剂。
实施例3
一种改性的自掺杂型TiO 2纳米管基可见光光催化剂的制备方法，包括如下步骤：该光催化剂为可见光响应型TiO 2纳米管基光催化剂。
(1)制备TiO 2纳米管
将Ti片剪裁为3cm×3.5cm大小，在两电极体系下浸入含有10g/L氟化铵以及5％(体积比)去离子水的乙二醇溶液中，以铂电极为对电极在80V电压刻蚀2小时。将得到的TiO 2纳米管前驱体放入马弗炉中，在600℃下煅烧60min，以获得锐钛矿型TiO 2纳米管。
(2)制备WO 3/TiO 2纳米管
将步骤(1)中所得的TiO 2纳米管作为工作电极，饱和甘汞电极作为参比电极，铂片电极做为对电极，进行WO 3纳米颗粒的电化学沉积，其中电解质为溶度均为1mol/L的EDTA、醋酸铵以及钨酸钠水溶液，在-1mA/cm 2恒电流条件下沉积1000s。后将WO 3/TiO 2纳米管前驱体置于马弗炉中在400℃下煅烧240min。
(3)制备富氧空位的自掺杂型WO 3颗粒负载TiO 2纳米管
将步骤(2)中所得的材料作为工作电极，饱和甘汞电极作为参比电极， 铂片电极为对电极，电解质为0.1M的Na 2SO 4溶液。还原电位设置为-1.0V，还原1000s。
(4)制备单原子贵金属锚定缺陷型WO 3/TiO 2纳米管
在三电极体系下，将步骤(3)得到富氧空位的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用恒电位法，电解质为含有1mmol/L AgNO 3和0.1mol NaCl的混合溶液，-1.0v恒电位下还原10s，将Ag单原子负载于复合物表面，烘干后得到氧空位稳定Pt单原子型WO 3/TiO 2纳米管催化剂。
本发明将WO 3负载于TiO 2纳米管表面，并利用电化学还原处理的方法在WO 3颗粒负载TiO 2纳米管表面构建氧空位，进一步地通过电化学方式引入贵金属单元子，并利用WO 3表面的氧空位锚定单原子，防止单原子团聚，提高其光催化性能，使其能有效并快速地降解用于有机污染物的降解。
对比例1
一种改性的TiO 2纳米管基可见光光催化剂的制备方法，包括如下步骤：该光催化剂为单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)。
(1)制备TiO 2纳米管
将Ti片剪裁为3cm×3.5cm大小，在两电极体系下浸入含有3.119g/L氟化铵以及13.75％(体积比)去离子水的乙二醇溶液中，以铂电极为对电极在60V电压刻蚀8小时。将得到的TiO 2纳米管前驱体放入马弗炉中，在450℃下煅烧120min，以获得锐钛矿型TiO 2纳米管。
(2)电化学还原TiO 2纳米管
将步骤(1)中所得的TiO 2纳米管作为工作电极，饱和甘汞电极作为参比电极，铂片电极为对电极，电解质为0.1M的Na 2SO 4溶液。还原电位设置为-1.4V，还原600s，得到电化学还原后富氧空位的TiO 2纳米管。
(3)在三电极体系下，将步骤(2)得到富氧空位的TiO 2纳米管作为工作电极，采用方波脉冲法，电解质为含有25μmol/L HAuCl 4和0.1mol  NaCl的混合溶液，在-0.2v高电位、-0.6v低电位、5s脉冲宽度和5次循环条件下，将Au单原子负载于TiO 2纳米管表面，烘干后得到单原子Au锚定于TiO 2纳米管表面缺陷的样品(Au-TiO 2)。
(4)负载WO 3纳米颗粒
将步骤(3)中所得的Au锚定的TiO 2纳米管作为工作电极，饱和甘汞电极作为参比电极，铂片电极做为对电极，进行WO 3纳米颗粒的电化学沉积，其中电解质为溶度均为0.1mol/L的EDTA、醋酸铵以及钨酸钠水溶液，在-2mA/cm 2恒电流条件下沉积600s。得到WO 3/Au-TiO 2纳米管，后将其置于马弗炉中，在450℃下煅烧120min。
(5)制备富氧空位的WO 3颗粒负载Au-TiO 2纳米管
将步骤(4)中所得的材料作为工作电极，饱和甘汞电极作为参比电极，铂片电极为对电极，电解质为0.1M的Na 2SO 4溶液。还原电位设置为-1.4V，还原600s，得到富氧空位的WO 3颗粒负载Au-TiO 2纳米管。
(6)制备单原子贵金属锚定缺陷型WO 3/TiO 2纳米管
在三电极体系下，将步骤(5)得到富氧空位的复合材料作为工作电极，采用方波脉冲法，电解质为含有25μmol/L HAuCl 4和0.1mol NaCl的混合溶液，在-0.2v高电位、-0.6v低电位、5s脉冲宽度和5次循环条件下，将Au单原子负载于复合物表面，烘干后得到单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)。
图8中(a)和(b)分别为单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)的高角环形暗场透射电镜图和面扫图，图中表明，单原子Au在TiO 2表面同样以单原子形式存在，且单原子Au在WO 3纳米颗粒和TiO 2纳米管表面同时均匀分布，图8(c)为EDS能谱图及积分结果，表明Au-W/Au-T与R-Au-W/T样品的贵金属Au的质量百分数分别为4.51％和2.41％。其中，其中单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)的制备方法为：在进行 制备方法第一步负载WO 3之前，电化学还原TiO 2纳米管并电化学锚定单原子Au，此后的步骤与R-Au-W/T样品相同。
WO 3和TiO 2复合物的带隙图和单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)和实施例1改性的单原子贵金属锚定于WO 3纳米颗粒(R-Au-W/T)降解甲苯对比。
图9为WO 3和TiO 2复合物的带隙图(数据来自紫外光电子能谱UPS表征)，复合物中WO 3和TiO 2的价带位置分别为3.12eV和2.91eV，WO 3具有更强的价带氧化能力，与单原子Au与WO 3耦合后应具有更强的氧化能力。
图10为单原子Au同时锚定于WO 3纳米颗粒和TiO 2纳米管表面缺陷的样品(Au-W/Au-T)和实施例1改性的单原子贵金属锚定于WO 3纳米颗粒(R-Au-W/T)降解甲苯对比。相比于R-Au-W/T，Au-W/Au-T的甲苯降解效率并没有明显的提升。因此，实施例1改性的R-Au-W/T相比于Au-W/Au-T，制备成本更低。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (10)

  1. 一种单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物的制备方法，其特征在于，包括如下步骤：
    (1)在TiO 2纳米管的内壁和外壁上沉积WO 3纳米颗粒，煅烧使所述WO 3纳米颗粒晶化，得到内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管；
    (2)对步骤(1)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管进行电化学还原，使部分WO 3纳米颗粒被还原形成W 5+缺陷，得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物；
    (3)以步骤(2)获得的含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物作为工作电极，通过电化学沉积将贵金属单原子负载于该复合物中WO 3纳米颗粒表面缺陷处，得到单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物。
  2. 如权利要求1所述的制备方法，其特征在于，步骤(1)所述煅烧具体为在400℃-600℃条件下煅烧60min-240min。
  3. 如权利要求1所述的制备方法，其特征在于，步骤(2)具体为：以步骤(2)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管为工作电极，在还原电压为-1.0v～-1.6v，还原的时间为200s-1000s的条件下进行电化学还原，使WO 3纳米颗粒被部分还原形成W 5+缺陷，得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管复合物。
  4. 如权利要求1所述的制备方法，其特征在于，步骤(2)所述电化学还原为在如下条件下进行：在三电极体系下，以步骤(2)得到的内壁和外壁上负载了WO 3纳米颗粒的TiO 2纳米管为工作电极，以铂电极为对电极，以饱和甘汞电极为参比电极。
  5. 如权利要求1所述的制备方法，其特征在于，步骤(3)具体为：在三电极体系下，将步骤(2)得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2 纳米管作为工作电极，采用方波脉冲法、恒电位法或恒电流法将贵金属单原子负载于复合物中WO 3纳米颗粒表面缺陷处。
  6. 如权利要求1所述的制备方法，其特征在于，所述的贵金属单原子为Au、Ag、Pt、Pd、Ir或Ru，步骤(3)具体为：在三电极体系下，将步骤(2)得到含有W 5+缺陷的WO 3纳米颗粒负载TiO 2纳米管作为工作电极，采用方波脉冲法将贵金属单原子负载于复合物中WO 3纳米颗粒表面缺陷处，所述方波脉冲法的高电位为0v～-0.2v，低电位为-0.4v～-1.6v，循环次数为1次～50次，脉冲宽度为1s～20s。
  7. 如权利要求5所述的制备方法，其特征在于，采用恒电位法将贵金属单原子负载于复合物中WO 3纳米颗粒表面缺陷处，采用的恒电位法的电位为-0.2v～-1.6v，还原时间为2s～100s，电解质中的贵金属源的浓度为5μmol/L～1mmol/L。
  8. 如权利要求1至7任一项所述的制备方法制备得到的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物。
  9. 如权利要求8所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物，其特征在于，其包括TiO 2纳米管以及在该TiO 2纳米管内壁和外壁上负载的WO 3纳米颗粒；该复合物中含有W 5+缺陷以及由所述W 5+缺陷伴随产生的氧空位，且WO 3纳米颗粒表面缺陷处锚定有贵金属单原子。
  10. 如权利要求8或9所述的单原子贵金属锚定缺陷型WO 3/TiO 2纳米管复合物在光催化中的应用。
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