Nonstoichiometric metal oxides with tunable oxygen vacancies

Abstract

A method for forming aggregates of non-stoichiometric metal oxide nanoparticles is disclosed, comprising the steps described herein.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This specification discloses a method for forming non-stoichiometric metal oxide nanoparticle agglomerates by aerosolizing a heated mixture comprising a flammable gas mixture and a volatile metal oxide precursor. The metal can be Ti. [Background technology]

[0002] (background) The listing or discussion of a prior-disclosure document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

[0003] Non-stoichiometric semiconductor materials have been identified as promising catalysts for efficient energy conversion and storage. Various semiconductors with defects, such as metal oxides (TiO2, ZnO, BiVO4, SrTiO3, etc.), metal sulfides (CdS, MoS2, ZnS, In2S3, etc.), and nitride materials (CN4, Ta3N5, etc.), have been developed and found to be active in catalytic reactions. Such materials are widely applied in the field of solar-to-chemical energy conversion (e.g., photocatalytic water splitting, CO2 reduction, N2 fixation, and dye-sensitized solar cells). Engineering such defects (defect engineering) is considered to be an effective approach for modulating surface chemistry, electronic structure, and charge transport.

[0004] Based on the dimensionality of the defect, crystal defects may be spatially classified into four types: 0D point defects (e.g., oxygen vacancies (OVs), doping) 1D line defects (e.g., dislocations) 2D planar defects (e.g., stacking faults, grain boundaries), and 3D volume defects (e.g., cracks, voids) Such defects can change the atomic coordination environment and generate vacancy states. These vacancy states affect light absorption, charge separation, and transport, and therefore catalytic or photocatalytic activity. A deep understanding of the defect nature through characterization is essential to clarify the relationship between the fundamental structure and activity.

[0005] Various strategies have been developed to synthesize oxygen-deficient TiO 2-x have been synthesized. These methods include hydrogen thermal treatment, high-energy particle bombardment, and heating of TiO2 (under reduced pressure or oxygen-deficient conditions). Although each method has its advantages, limitations include high-energy input, complex post-processing, and limited ability to tune the defect state. A one-step synthesis method that allows for easy tuning of the location and abundance of oxygen vacancies (OVs) has not been reported.

[0006] Flame synthesis has the advantages of high throughput, low waste, simple operation, and no post-processing required. The scalability and efficiency of flame synthesis make it a powerful fabrication method for producing functional nanostructured materials for a variety of applications (e.g., dye-sensitized solar cells, water treatment, and toxic gas detection). Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, there is a need for improved materials and methods for producing high performance catalysts, thereby solving the above problems. [Means for solving the problem]

[0008] (Summary of the Invention) Aspects and embodiments of the present invention are disclosed in the following numbered paragraphs (or claims):

[0009] 1. 1. A method for forming (or generating) aggregates of non-stoichiometric metal oxide nanoparticles, the method comprising the steps of: (a) aerosolizing a heated mixture through a nozzle of a burner, the heated mixture comprising a combustible gas mixture and a volatile metal oxide precursor, the combustible gas mixture having an oxygen-lean equivalence ratio (φ), the combustible gas mixture being ignited at an outlet of the nozzle to provide a flame whereby the volatile metal oxide precursor decomposes and rapidly undergoes nucleation and coagulation to form non-stoichiometric metal oxide nanoparticles in the presence of the flame; and (b) depositing non-stoichiometric metal oxide nanoparticles onto a surface of a substrate to form agglomerates of non-stoichiometric metal oxide nanoparticles on the surface of the substrate, the substrate being positioned at a distance from the nozzle for a period of nanoparticle aggregation and oxidation. Including, The oxygen lean equivalence ratio (φ) of the flammable gas mixture is 1.5 or less; At the nozzle of the burner, the velocity of the combustible gas mixture is 300 to 500 cm / s; method.

[0010] 2. 2. The method according to item 1, wherein the oxygen lean equivalent ratio (φ) is 1.05 to 1.5.

[0011] 3. 3. The method according to item 2, wherein the oxygen lean equivalent ratio (φ) is 1.1 to 1.4.

[0012] 4. 4. The method according to any one of claims 1 to 3, wherein the flammable gas mixture comprises an inert gas (e.g., argon), oxygen, and either or both of hydrogen gas and hydrocarbon gas (e.g., CH).

[0013] 5. 5. The method of claim 4, wherein the inert gas represents 70% or more by volume of the combustible gas mixture, with the balance being oxygen and either or both of hydrogen gas and hydrocarbon gas.

[0014] 6. the inert gas providing 75 to 79.9 vol% of the combustible gas mixture; the oxygen providing 10 to 17 vol% of the combustible gas mixture; The hydrogen gas and / or the hydrocarbon gas provide 5 to 10.1 vol% of the combustible gas mixture. The method according to paragraph 5.

[0015] 7. the inert gas providing 78 to 79.75 vol% of the combustible gas mixture; the oxygen providing 14.4 to 15 vol% of the combustible gas mixture; The hydrogen gas and / or the hydrocarbon gas provide 5.25 to 8 vol% of the combustible gas mixture. The method according to paragraph 6.

[0016] 8. (a) injecting the volatile metal oxide precursor into the heated mixture at a flow rate of 2 mL / h to 100 mL / h, for example 3 mL / h to 50 mL / h, for example 5 mL / h to 25 mL / h, for example 10 mL / h to 20 mL / h; and / or (b) 8. The method according to any one of items 1 to 7, wherein the concentration of the volatile metal oxide precursor in the combustible gas mixture is 100 to 1,500 ppm, for example, 250 to 900 ppm.

[0017] 9. 9. The method according to any one of items 1 to 8, wherein the temperature of the flame is 1,500 to 2,500K.

[0018] 10. 10. The method of any one of claims 1 to 9, wherein the substrate is a rotatable substrate and upon (or when) rotation, deposition of the non-stoichiometric metal oxide nanoparticle aggregates occurs only on a portion of the substrate in an area (or region) below the flame at any given time.

[0019] 11. 11. The method according to item 10, wherein the rotatable substrate rotates at a speed of 0.1 rpm to 500 rpm, for example 1 rpm to 300 rpm, or 1 rpm to 100 rpm, for example 0.1 rpm, 1 rpm, 100 rpm or 300 rpm.

[0020] 12. 12. The method according to claim 10 or 11, wherein the deposited agglomerates of non-stoichiometric metal oxide nanoparticles are substantially removed from the surface of the rotatable substrate by a collecting means (or collecting means or recovery means or collection means) or collecting device (or collecting device or recovery device or collection device), such that the deposited agglomerates of non-stoichiometric metal oxide nanoparticles are continuously collected (or collected or recovered or collected) from the surface of the rotatable substrate as the substrate rotates (or with each rotation), and the rotatable substrate is rotated at a speed (or speed) of 0.1 rpm to 20 rpm, for example, 0.2 rpm to 5 rpm or less, for example, 1 rpm or less, as necessary.

[0021] 13. 13. The method according to claim 12, wherein the method is operated (or actuated or run or operated) for a period of 1 minute to infinity, such as 5 minutes to 1 month, such as 15 minutes to 1 week, such as 25 minutes to 1 hour.

[0022] 14. 11. The method of claim 10, wherein the deposited non-stoichiometric metal oxide nanoparticle aggregates are deposited on the surface of the rotatable substrate over a period of 1 second to 15 minutes, and optionally rotating the rotatable substrate at a speed of 100 rpm to 500 rpm, for example 100 rpm to 300 rpm.

[0023] 15. 15. The method of claim 12 or 13 or the method of claim 14, wherein the rotatable substrate is actively cooled after passing through the flame, and optionally the rotatable substrate is cooled by a plurality of air nozzles, each of which delivers the air at 20 to 200 L / min, for example 50 to 150 L / min, for example 75 to 100 L / min.

[0024] 16. 16. The method according to any one of items 1 to 15, wherein the distance between the nozzle of the burner and the substrate is 5 to 25 mm, for example, 14 mm to 20 mm, for example, 14 mm or more to 15 mm.

[0025] 17. 17. The method according to any one of items 1 to 16, wherein the temperature of the substrate is 298K to 800K, for example, 350K to 780K, for example, 400K to 500K, and optionally the temperature of the substrate is measured at a point outside the flame.

[0026] 18. 18. The method of any one of items 1 to 17, wherein the volatile metal oxide precursor comprises a metal capable of forming (or generating) a stable, reducible oxide.

[0027] 19. 19. The method of claim 18, wherein the volatile metal oxide precursor comprises one or more metals selected from the group consisting of Ti, Ce, Co, Fe, Cu, and W, and optionally, the volatile metal oxide precursor comprises Ti.

[0028] 20. 20. The method according to any one of items 1 to 19, wherein the formed (or generated) aggregates of non-stoichiometric metal oxide nanoparticles contain oxygen vacancies, and optionally the oxygen vacancies are formed (or generated) at grain boundaries.

[0029] twenty one. 21. The method according to any one of items 1 to 20, wherein the deposition in step (b) is carried out in an oxygen-containing environment.

[0030] twenty two. A device (or apparatus or equipment) for forming (or generating) aggregates of non-stoichiometric metal oxide nanoparticles, the device comprising a burner, a rotatable stagnation plate (or retention plate or stagnation plate), and a trapping means (or collection means or recovery means or collection means) or trapping device (or collection device or recovery device or collection device); the burner comprising a nozzle and a feed intake (or feed inlet), the feed intake adapted to receive a combustible gas mixture and a volatile metal oxide precursor; the rotatable stagnation plate comprises a plate and a motor, the plate having a circular substrate holding area (or substrate hold area), and the motor is for rotating the rotatable stagnation plate; the burner nozzle is adapted to be positioned at a fixed position within a portion of the circular substrate-holding area, and in use, a flame is generated from the nozzle and causes non-stoichiometric metal oxide nanoparticle agglomerates to deposit on a surface of a substrate, the substrate being positioned within the circular substrate-holding area while the stagnation plate rotates; the collection means or device is positioned (or arranged) to remove the non-stoichiometric metal oxide nanoparticle aggregates from the surface of the substrate after deposition; device.

[0031] twenty three. The collecting means or collecting device comprises a collector head (or collection head or collection head or recovery head), a blowing mechanism (or blowing mechanism), and a collecting vessel (or collection vessel or recovery vessel or collection vessel), the collector head comprises a scraper adapted to be placed in contact with the substrate so as to remove (or dislodge) agglomerates of non-stoichiometric metal oxide nanoparticles deposited on the surface of the substrate; the blowing mechanism is adapted to supply gas (or vapor) to the collection vessel to remove the non-stoichiometric metal oxide nanoparticle agglomerates; 23. The device of claim 22.

[0032] twenty four. The collecting means or collecting device comprises a collector head (or collecting head or collecting head or recovery head), the collector head comprising a body portion (or body portion or body portion), a scraper, a plurality of holes (or apertures), a collecting container (or collecting container or recovery container or collection container), and a vacuum system (or reduced pressure system); the scraper extends from the body portion and is adapted to be positioned in contact with the substrate such that agglomerates of the non-stoichiometric metal oxide nanoparticles are removed (or dislodged) from a surface of the substrate; the plurality of holes are in the body portion; 23. The device of claim 22, wherein the vacuum system is in fluid communication with the plurality of holes in the body portion and the collection vessel, and in use the vacuum system transports the removed agglomerates of non-stoichiometric metal oxide nanoparticles from the substrate to the collection vessel via the plurality of holes in the body portion and deposits them in the collection vessel, and optionally the collection means or collector further comprises a cyclone separator.

[0033] twenty five. 25. A device as described in any one of paragraphs 22 to 24, wherein the device further comprises a plurality of jet nozzles for cooling the rotatable stagnation plate by blowing gas (e.g., dry air) onto the surface of the stagnation plate, the surface of the stagnation plate being the surface opposite to the surface that comes into contact with the flame (or flame) generated from the nozzles during use.

[0034] 26. A non-stoichiometric metal oxide nanoparticle aggregate containing a plurality of oxygen vacancies (or oxygen vacancies or oxygen vacancies or OVs), each nanoparticle having a size of 20 nm or less, for example 5 to 20 nm, and having a disordered (or irregular or disordered) surface layer.

[0035] 27. 27. The aggregate of non-stoichiometric metal oxide nanoparticles according to item 26, wherein the thickness of the disordered (or irregular or disordered) surface layer is 1 nm or less.

[0036] 28. 28. The non-stoichiometric metal oxide nanoparticle aggregate of claim 26 or 27, wherein the metal of the metal oxide is one or more selected from the group consisting of Ti, Ce, Co, Fe, Cu and W, and optionally the metal is Ti.

[0037] 29. the non-stoichiometric metal oxide nanoparticle aggregates are blue non-stoichiometric titanium oxide nanoparticle aggregates; the titanium oxide nanoparticles of the aggregates comprise a heterogeneous phase (or heterophase) of rutile and anatase; Optionally, the proportion of rutile phase is 65% to 85% and / or the nanoparticles further comprise a TiO2-II phase. 29. An aggregate of non-stoichiometric metal oxide nanoparticles according to any one of items 26 to 28.

[0038] (drawing) Certain embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0039] [Figure 1] Figure 1 shows the FSRS synthesis process of TiO2-x ((a) in-frame and (b) post-frame (subjected to thermal sintering and oxidation on a hot glass substrate)). [Figure 2] Figure 2 shows the XRD patterns of TiO2-x samples (as prepared) and commercial P25 TiO2 obtained at different deposition times. [Figure 3] Figure 3 shows (a) FESEM, (b) TEM, and (c) HRTEM images of TiO2-x (6 min), (d) TiO2-x (10 min), (e) TiO2-x (15 min), and (f) TiO2-x (30 min). [Figure 4]Figure 4 shows (a) a structural model of rutile TiO2 from the

[0111] projection. The light gray spheres represent Ti atoms, and the dark gray spheres represent O atoms. (b) HAADF-STEM images (corrected by atomic resolution ablation) of TiO2-x (15 min) from the

[0111] projection. (c) and (d) are enlargements of the area (dashed line) in (b). (e) HAADF-STEM images of TiO2-x (30 min). [Figure 5] Figure 5 shows (a) Raman spectrum (inset: expanded spectrum from 110 to 200 cm-1) (A: anatase, R: rutile), (b) EPR spectrum of flame-made TiO2-x, (c) XPS spectrum of Ti 2p, and (d) XPS spectrum of O 1s. [Figure 6] FIG. 6 is a TEM image of TiO2-x (1 min) (having a disordered core and an amorphous layer). [Figure 7] Figure 7 shows (a) UV-visible DRS spectra (inset: expanded spectrum from 340 to 380 nm), (b) bandgap analysis, (c) transient photocurrent density of flame-made TiO2-x and P25 TiO2 (300 W xenon lamp (λ ≥ 400 nm)), and (d) time-resolved PL decay of the reacted TiO2-x sample (0.1 wt% Pt loaded). [Figure 8] Figure 8 shows (a) H2 generated after 4 h of photoreaction (20 mg TiO2, 0.1 wt% Pt, 25 vol% methanol, 300 W Xe lamp, ≥ 400 nm), (b) stability test. [Figure 9] Figure 9 shows TEM images of (a) TiO2-x (6 min), (b) TiO2-x (10 min), (c) TiO2-x (15 min), and (d) TiO2-x (30 min). [Figure 10]Figure 10 shows the Raman spectrum of P25, the Raman spectrum of anatase TiO2, and the Raman spectrum of rutile TiO2. [Figure 11] Figure 11 shows the HAADF images of 0.1 wt% Pt loaded (a) TiO2-x (6 min), (b) TiO2-x (10 min), (c) TiO2-x (15 min), (d) TiO2-x (30 min), and (e) P25 (after photocatalytic H2 generation). [Figure 12] Figure 12 shows a flame reactor set up with a rotatable stagnation plate with interval particle collection (IPC). [Figure 13A] FIG. 13A is a prototype 1 of a continuous particle collection (CPC) system. [Figure 13B] FIG. 13B is a plan view of prototype 1 (noting important dimensions). [Figure 14] Figure 14 shows the prototype 2 of the continuous particle collection (CPC) system. [Figure 15] FIG. 15 is a plan view of the CPC system showing the average plate temperatures at various locations (or sections) of the plate. [Figure 16]Figure 16 shows (A) photographs of powders collected after varying deposition times using the IPC and CPC methods ((a) CPC (1 rpm), (b) IPC (1 rpm, 5 min), (c) IPC (1 rpm, 15 min), (d) IPC (1 rpm, 25 min) (from left to right)). (B) Powder XRD patterns (NiO (approximately 14%) was added as an internal standard). (The intensity scale was adjusted to the largest NiO peak to allow direct comparison between samples). (C) XPS spectrum of Ti 2p (Ti 2p3 / 2 peak was set at 458.6 eV) (a magnified shoulder area is shown in the inset) (455-457 eV) (the Ti3+ 2p3 / 2 peak is expected at 457 eV). (D) Ti Fitted FWHM values ​​for the 2p3 / 2 peak (peak broadening is reported, which corresponds to the presence of defects / Ti3+), (E) Elemental analysis results. [Figure 17] Figure 17 shows (A) photographs of powders collected at varying rotation speeds using the IPC and CPC methods ((a) CPC (1 rpm), (b) IPC (300 rpm, 15 min), (c) IPC (100 rpm, 15 min), (d) IPC (1 rpm, 15 min) (from left to right). (B) Powder XRD patterns (NiO (approximately 14%) was added as an internal standard). (The intensity scale is adjusted to the largest NiO peak to allow direct comparison between samples.) (C) XPS spectrum of Ti 2p (Ti 2p3 / 2 peak set at 458.6 eV) (The enlarged shoulder area is shown in the inset) (455-457 eV) (Ti3+ 2p3 / 2 peak is expected at 457 eV). (D) Ti Fitted FWHM values ​​for the 2p3 / 2 peak (peak broadening is reported, which corresponds to the presence of defects / Ti3+). [Figure 18]Figure 18 shows (A) photographs of powders collected using the CPC method with varying equivalence ratios of premixed gases ((a) 1.20, (b) 1.10, (c) 1.05, (d) 1.00, (e) 0.90 (from left to right)), and (B) powder XRD patterns (NiO (approximately 14%) was mixed in as an internal standard) (intensity scaled to the largest NiO peak to allow direct comparison between samples). [Figure 19] Figure 19 shows the effect of particle layers formed (or accumulated or constructed or built up) at stagnation temperatures. [Figure 20] Figure 20 compares (A) the median particle diameter (or median particle diameter or median particle size) and (B) the GSD of the particle size distribution in this (or current or current or related) method (see Table 8) and a previous study (J. Aerosol Sci. 133, 96-112). [Figure 21]Figure 21 shows (A) photographs of powders collected at different rotation speeds using the CPC method ((a) 1 rpm, (b) 0.5 rpm, (c) 0.3 rpm, (d) 0.2 rpm, (e) 0.1 rpm) (from left to right). (Note that the color of the sample is slightly different compared to that shown in other figures (e.g., CPC 1 rpm). This is because the sample shown here was mixed using a mortar and pestle to make the powder homogeneous and dense after synthesis.) (B) Powder XRD pattern; (C) XPS spectrum of Ti 2p (Ti 2p3 / 2 peak is set at 458.6 eV) (enlarged shoulder area is shown in the inset) (455-457 eV) ((Ti3+ 2p3 / 2 peak is expected at 457 eV)); (D) Ti This is the fitted FWHM value for the 2p3 / 2 peak (peak broadening is reported, which corresponds to the presence of defects / Ti3+). Note that the absolute FWHM values ​​cannot be directly compared with those in other figures because the XPS spectrum in this figure was acquired at a later time than the spectra in the other figures. This is due to the fact that maintenance and service of the equipment (or facilities) was performed between the two. Therefore, the FWHM values ​​may have been affected by the equipment (or facilities) service. [Figure 22] Figure 22 shows (a) BET adsorption-desorption isotherms and (b) pore size distributions of flame-made TiO2-x and P25 TiO2. DETAILED DESCRIPTION OF THE INVENTION

[0040] (explanation) Surprisingly, it has been found that non-stoichiometric metal oxides can be produced by a one-step method as described herein. This method allows for control of defect content (e.g., oxygen vacancies) and location by varying simple parameters (e.g., deposition time), while providing consistent particle size. In particular, it has been found that moderate defect levels can effectively promote charge separation, thereby improving performance in catalytic, photocatalytic, or photoelectrochemical processes (e.g., photocatalytic activity for H2 production).

[0041] In a first aspect of the present invention, there is provided a method for forming (or producing) non-stoichiometric metal oxide nanoparticle agglomerates, the method comprising the steps of: (a) aerosolizing a heated mixture through a nozzle of a burner, the heated mixture comprising a combustible gas mixture and a volatile metal oxide precursor, the combustible gas mixture having an oxygen-lean equivalence ratio (φ), the combustible gas mixture being ignited at an outlet of the nozzle to provide a flame whereby the volatile metal oxide precursor decomposes and undergoes rapid nucleation and coagulation to form non-stoichiometric metal oxide nanoparticles in the presence of the flame; and (b) depositing non-stoichiometric metal oxide nanoparticles onto a surface of a substrate to form (or generate) aggregates of non-stoichiometric metal oxide nanoparticles on the surface of the substrate, the substrate being positioned (or arranged or positioned) at a distance from the nozzle for a period of nanoparticle aggregation and oxidation; The oxygen lean equivalence ratio (φ) of the combustible gas mixture is less than or equal to 1.5. At the nozzle of the burner, the velocity of the combustible gas mixture is 300-500 cm / s.

[0042] In embodiments of the present disclosure, the term "comprising" may be interpreted as requiring the recited features, but without limiting the presence of other features. Alternatively, the term "comprising" may relate to a situation in which it is intended that only the recited components / features may be present (e.g., the term "comprising" may be replaced with the phrase "consists of" or "consists essentially of"). It is expressly expected that both broader and narrower interpretations may apply to all aspects and embodiments of the present invention. In other words, the term "comprising" and its equivalents may be replaced with the phrase "consisting of" or "consists essentially of" or their equivalents, and vice versa.

[0043] The phrase "consists essentially of" or variants thereof may be construed in the present disclosure to refer to a material in which low or minor impurities may be present. For example, such a material may be 90% or more pure, such as 95% or more pure, such as 97% or more pure, such as 99% or more pure, such as 99.9% or more pure, such as 99.99% or more pure, such as 99.999% or more pure, such as 100% pure.

[0044] The equivalence ratio (φ) is defined as the ratio of the actual fuel / air (or other oxidizer / oxidizer) ratio to the stoichiometric fuel / air (or other oxidizer / oxidizer) ratio (or actual fuel / air (or other oxidizer / oxidizer) ratio / stoichiometric fuel / air (or other oxidizer / oxidizer) ratio). Stoichiometric combustion occurs when all of the oxygen is consumed in the reaction, and there is no molecular oxygen (O2) in the products. If the equivalence ratio = 1, the combustion is stoichiometric. If the equivalence ratio < 1, the combustion is lean with excess fuel and excess air. For equivalence ratios >1, the combustion is rich in fuel or lean in oxygen (or O), resulting in incomplete combustion. Therefore, oxygen-lean equivalence ratio (or oxygen-lean equivalence ratio or O-lean equivalence ratio) as used in this disclosure means an equivalence ratio greater than 1 (>1).

[0045] As described above, the oxygen lean equivalence ratio (or oxygen lean equivalence ratio or O2-lean equivalence ratio) (φ) is 1.5 or less. For example, the oxygen lean equivalence ratio (φ) may be 1.05 to 1.5. In more specific embodiments that may be mentioned in the present disclosure, the oxygen lean equivalence ratio (φ) may be 1.1 to 1.4. Without wishing to be bound by theory, it is believed that an oxygen lean equivalence ratio (φ>1) may enable the formation (or generation) of blue non-stoichiometric titanium dioxide nanoparticle aggregates (or blue TiO2). Meanwhile, the generation (or generation) of large amounts of smoke (or soot) and carbon contaminants (or carbon contaminants) can be avoided. This oxygen lean equivalence ratio also prevents the formation (or generation) of secondary flames (or flames). The secondary flame (or flame) can increase the temperature and promote the oxidation of the blue TiO2.

[0046] The flammable gas mixture (or gas mixture) may include any suitable combination of an inert gas (e.g., argon), oxygen, and a flammable gas (or gases). For example, the flammable gas mixture may include an inert gas (e.g., argon), oxygen, and one or both of hydrogen gas and hydrocarbon gas (e.g., CH). Any suitable combination of gases (or gases) that provides the oxygen lean equivalence ratio (φ) described above may be used. In certain embodiments that may be mentioned in this disclosure, the inert gas may represent 70 vol% (or volume % or volume % or volume %) or more of the flammable gas mixture. Oxygen and one or both of hydrogen gas and hydrocarbon gas provide the balance (or represent the balance or remainder). More specifically, the inert gas may provide 75 to 79.9 vol% of the flammable gas mixture. Oxygen may provide 10 to 17 vol% of the flammable gas mixture. The hydrogen gas and / or hydrocarbon gas provides 5 to 10.1 vol% of the combustible gas mixture. In further embodiments that may be mentioned in the present disclosure, the inert gas may provide 78 to 79.75 vol% of the combustible gas mixture. The oxygen provides 14.4 to 15 vol% of the combustible gas mixture. The hydrogen gas and / or hydrocarbon gas provides 5.25 to 8 vol% of the combustible gas mixture.

[0047] It is important to note that the velocity of the combustible gas mixture at the nozzle must be greater than the flame speed to stabilize the flame, thereby providing a stable flame for use in the process. This can be achieved by using a velocity of the combustible gas mixture at the burner nozzle of 300-500 cm / s. Importantly, this velocity range may be used with a nozzle of any appropriate size. An alternative way to view gas velocity is to consider the flow rate of the combustible gas mixture. For example, if the nozzle diameter is 1.4 cm (14 mm), the flow rate of the combustible gas mixture may be 18-30 liters per minute (SLPM). This provides a velocity of 300-500 cm / s. It is understood that a larger or smaller nozzle will result in an increased or decreased flow rate, respectively, to maintain the same velocity range. Standard liters per minute (SLM or SLPM) is a unit of volumetric flow rate of a gas at standard conditions of temperature and pressure (STP; typically defined as a temperature of 273.15 K (0°C) and an absolute pressure of 101.325 kPa (1 atm)). As used in this disclosure, the flow rate of a gas is measured before preheating. MFCs are also calibrated at standard conditions (0°C, 1 atm).

[0048] Any suitable volatile metal oxide precursor (or metal oxide precursor) can be used, provided that the metal used can provide a non-stoichiometric metal oxide. More specifically, the volatile metal oxide precursor can include a metal capable of forming a stable, reducible oxide. Examples of suitable volatile metal oxide precursors include metal salts and metal complexes (or metal composites) with other metals. Suitable metals that may be included as part of the volatile metal oxide precursor include, but are not limited to, Ti, Ce, Co, Fe, Cu, W, and combinations thereof. In a specific embodiment that may be included in the present disclosure, the metal included in the volatile metal oxide precursor can be Ti. The volatile metal oxide precursors used in the present disclosure can be solid or liquid. The boiling point or sublimation point can be 350°C or less, for example, 120-300°C, for example, 150-250°C. Additionally or alternatively, the volatile metal oxide precursor can be solid or liquid. The gas (or vapor) supplied to the burner may have a significant vapor pressure at the temperature used. For example, it may have a significant vapor pressure at temperatures below 350°C, such as 120-300°C, for example, 150-250°C. The higher the vapor pressure of the precursor, the higher the loading rate (or loading rate, loading rate, packing rate, or carrying rate) that can be used in the system. As a general rule, the higher the vapor pressure of the precursor, the better. For example, the vapor pressure of titanium(IV) isopropoxide at 150°C may be approximately 77 mmHg.

[0049] Examples of specific volatile metal oxide precursors that may be mentioned in the present disclosure include, but are not limited to, titanium(IV) isopropoxide, titanium tetrachloride, WF6, and combinations thereof. In specific embodiments that may be mentioned in the present disclosure, the volatile metal oxide precursor may be titanium(IV) isopropoxide and / or titanium tetrachloride (e.g., titanium(IV) isopropoxide).

[0050] Any suitable amount of volatile metal oxide precursor may be used in the methods disclosed herein. For example, the volatile metal oxide precursor may be injected into the heated mixture at a flow rate of 2 mL / h to 100 mL / h, e.g., 3 mL / h to 50 mL / h, e.g., 5 mL / h to 25 mL / h, e.g., 10 mL / h to 20 mL / h. Additionally or alternatively, the volatile metal oxide precursor may have a concentration in the combustible gas mixture of 100 to 1,500 ppm, e.g., 250 to 900 ppm. As will be appreciated, the latter may not be affected by the size of the burner nozzle, while the former may be affected by this feature of the physical equipment. For example, a flow rate of 20 mL / h of titanium(IV) isopropoxide (the flow rate of the flammable gas mixture is 28 sL / min) (using a 14 mm nozzle) corresponds to 900 ppm of titanium(IV) isopropoxide. Similarly, a flow rate of 3 mL / h of titanium(IV) isopropoxide (the flow rate of the flammable gas mixture is 15 sL / min) (using a 14 mm nozzle) corresponds to 250 ppm of titanium(IV) isopropoxide.

[0051] The flame used in the method may have any suitable temperature, for example, a temperature of 1,500 to 2,500 K. Such a temperature may be related to the theoretical adiabatic flame temperature that can be achieved based on the combustion gas mixture.

[0052] Any suitable substrate may be used in the process. For example, the substrate may be a rotatable substrate. This may refer to a flat disk or a conveyor belt. In situations where the substrate is rotatable, it is understood that at any given time, only the portion of the substrate below the flame will be subject to deposition of non-stoichiometric metal oxide nanoparticle agglomerations. However, if the substrate rotates, this allows a "fresh" portion of the substrate to be subjected to deposition. The rotation of the rotatable substrate may be at any suitable speed. For example, the rotatable substrate may be rotated at a speed of 0.1 rpm to 500 rpm, such as 0.2 rpm to 350 rpm, such as 1 rpm to 300 rpm, or 1 rpm to 100 rpm, such as 0.1 rpm, 1 rpm, 100 rpm or 300 rpm.

[0053] For the avoidance of doubt, when this disclosure refers to multiple numerical ranges relating to the same characteristic, it is expressly intended that the endpoints of each range be combined in any order to provide the further intended range (and implicitly disclosed range).

[0054] Thus, such a rotatable substrate may rotate at the following speeds: 0.1rpm~1rpm, 0.1rpm~100rpm, 0.1rpm~300rpm, 0.1rpm~500rpm; 1rpm~100rpm, 1rpm~300rpm, 1rpm~500rpm; 100 rpm to 300 rpm, 100 rpm to 500 rpm; and 300rpm~500rpm.

[0055] As will be appreciated, if the rotatable substrate is in motion, portions of the substrate already undergoing deposition will undergo additional rounds of deposition unless the method is stopped or the substrate is cleaned after one rotation (or cycle). Thus, over time, nanoparticles may form (or accumulate or build up) on the surface of the substrate. Using such methods, aggregates of deposited non-stoichiometric metal oxide nanoparticles can be deposited on the surface of the rotatable substrate over a period of 1 second to 15 minutes. The duration (or deposition time) selected for nanoparticle deposition can allow for the formation (or generation) of a desired material, such as blue TiO. The rotatable substrate in such methods may be rotated at a speed (or speed) of 100 rpm to 500 rpm, e.g., 100 rpm to 300 rpm.

[0056] In an alternative embodiment, the deposited agglomerates of non-stoichiometric metal oxide nanoparticles may be substantially removed from the surface of the rotatable substrate by a collecting means or a collecting device. In this way, the deposited agglomerates of non-stoichiometric metal oxide nanoparticles are continuously collected from the surface of the rotatable substrate with each rotation. The rotation speed used in the present disclosure may be 0.1 rpm to 20 rpm, for example, 0.2 rpm to 5 rpm or less, for example, 1 rpm to 4.5 rpm or less, for example, 1 rpm.

[0057] As will be appreciated, various of the above collections may be performed, for example, the collections may be arranged to occur after a set time and / or a set number of rotations.

[0058] As used herein, the term "substantially removed" may mean that 95% or more (e.g., 97% or more, e.g., 98% or more, e.g., 99% or more, e.g., 99.5% or more, e.g., 99.9% or more) of the non-stoichiometric metal oxide nanoparticle population deposited on the surface of the substrate is removed.

[0059] When the method uses a rotatable substrate, it can be operated on a "continuous flow" basis. This is particularly the case when the deposited non-stoichiometric metal oxide nanoparticle ensemble is continuously collected from the surface of the rotatable substrate with each rotation (or at a set number of rotations per hour). In such an arrangement, the method can be operated for a period of time ranging from 1 minute to indefinite, e.g., 5 minutes to 1 month, e.g., 15 minutes to 1 week, e.g., 25 minutes to 1 hour.

[0060] One limitation of the extended operation of the method may be due to the equipment used, which may deform or deteriorate over time. This can be overcome, for example, by using two or more scrapers (see the description of suitable devices below). Here, if the first scraper deteriorates and can no longer be used, a second scraper can be placed in its place. The first scraper can then be replaced, and thereby replaced by a second scraper, allowing for continuous collection over an extended period of time.

[0061] When the method uses a rotatable substrate, convection (or reflux) due to rotation may act to cool the substrate after passing through the flame. Alternatively, the rotatable substrate may be actively cooled after passing through the flame. As will be appreciated, any suitable number of nozzles (with any suitable flow rate) may be used. For example, the rotatable substrate may be cooled by multiple air nozzles, each delivering air at 20 to 200 L / min, e.g., 50 to 150 L / min, e.g., 75 to 100 L / min. In a specific embodiment disclosed herein, active cooling may be achieved using four nozzles, each delivering air at a flow rate of 25 L / min above the substrate. As will be appreciated, the number of nozzles and flow rate actually used will depend on the size of the nozzle / flame and the composition / size of the substrate. For example, for a 30 cm diameter plate combined with a 1.4 cm diameter nozzle, a flow rate of 20-200 L / min from each nozzle may be appropriate.

[0062] Any suitable size (or dimension or size) of nozzle can be used. The size (or dimension or size) of the nozzle used can be one that can generate (or form) a stable flame (or flame), provided that a relatively uniform velocity (or speed) can be achieved at the burner nozzle for a combustible gas mixture of 300 to 500 cm / s. There is no limit to the size (or size) of the nozzle.

[0063] The burner nozzle may be positioned at any suitable distance from the substrate to provide the desired non-stoichiometric deposition of metal oxide nanoparticle aggregates. For example, the distance between the burner nozzle and the substrate may be 5 mm to 25 mm, e.g., 14 mm to 20 mm, e.g., 14 mm or more to 15 mm. Thus, the distance between the burner nozzle and the substrate may be: 5~14mm, 5~15mm, 5~20mm, 5~25mm; 14~15mm, 14~20mm, 14~25mm; 15-20mm, 15-25mm; and It may be 20 to 25 mm.

[0064] The distance of the burner nozzle from the substrate may affect the stability of the flame, but may not directly affect the properties of the resulting particles. Thus, one skilled in the art can determine, through routine trial and error, the appropriate distance for any setup, as they seek a stable flame for use in the method.

[0065] As will be appreciated, the substrate is subjected to a flame (or flame), and as such, the substrate may be at or near room temperature, or may be at an elevated temperature. For example, the temperature of the substrate may be between 298K and 800K, such as between 350K and 780K, such as between 400K and 500K. The temperature of the substrate may be measured at any suitable point on the substrate (e.g., inside the flame or flame or outside the flame). In certain embodiments, the temperature of the substrate may be measured at a point that is no longer under the flame (e.g., a portion of the substrate that was under the flame during the process).

[0066] As described above, the methods disclosed herein produce aggregates (or agglomerates) of non-stoichiometric metal oxide nanoparticles. The aggregates (or agglomerates) of non-stoichiometric metal oxide nanoparticles thus produced may contain oxygen vacancies. In certain embodiments, the oxygen vacancies may be formed at grain boundaries.

[0067] In the methods disclosed herein, the deposition in step (b) may be carried out in an oxygen-containing environment, i.e., the ambient environment outside the flame and burner may be an oxygen-containing environment (e.g., the ambient environment may be air).

[0068] The flame generated in the methods disclosed herein may be accompanied by a sheath of inert gas (e.g., argon or nitrogen). Further details on the sheath gas can be found in the experimental section below. This can be adapted according to the nozzle, velocity, and flame to be used in any particular embodiment, based on the knowledge of one skilled in the art.

[0069] As will be appreciated, the methods disclosed above may be achieved by using a suitable device. Accordingly, a further aspect of the present invention provides a device for forming (or generating) non-stoichiometric metal oxide nanoparticle agglomerates. The device (or equipment or apparatus) 100 comprises a burner 110, a rotatable stagnation plate (or retention plate or stagnation plate) 120, and a collection means (or collection means or recovery means or collection means) or trapping apparatus (or collection apparatus or recovery apparatus or collection apparatus) 130. Burner 110 comprises a nozzle 115 and a feed intake (or feed inlet or feed intake or feed inlet) (not shown), the feed intake adapted to receive the combustible gas mixture and the volatile metal oxide precursor. The rotatable stagnation plate 120 comprises a plate and a motor 125, the plate having a circular substrate holding area (or substrate hold area), and the motor 125 for rotating the rotatable stagnation plate 120. The burner nozzle 115 is adapted to be positioned at a fixed position within a portion of the circular substrate-holding area so that, in use, a flame emerges from the nozzle and deposits non-stoichiometric metal oxide nanoparticle agglomerates onto a surface of a substrate, the substrate being positioned within the circular substrate-holding area while the stagnation plate rotates. The collection means or device is positioned (or arrayed or arranged) to remove agglomerates of non-stoichiometric metal oxide nanoparticles from the surface of the substrate after deposition.

[0070] Examples of suitable devices (or equipment or apparatus) are shown in Figures 13 and 14.

[0071] FIG. 13 (considering both FIGS. 13A and 13B) discloses a device (or apparatus or equipment) 100. The device (or equipment or apparatus) 100 comprises a burner 110, a rotatable stagnation plate (or retention plate or stagnation plate) 120, and a collection means (or collection means or recovery means or collection means) or trapping apparatus (or collection apparatus or recovery apparatus or collection apparatus) 130. The burner 110 comprises a nozzle 115 and a feed intake (or feed inlet or feed intake or feed inlet), the feed intake adapted to receive the combustible gas mixture and the volatile metal oxide precursor. The rotatable stagnation plate 120 comprises a plate and a motor 125, the plate having a circular substrate holding area (or substrate hold area), and the motor 125 for rotating the rotatable stagnation plate 120. The burner nozzle 115 is adapted to be positioned at a fixed position within a portion of the circular substrate-holding area such that, in use, a flame 104 emerges from the nozzle and deposits non-stoichiometric metal oxide nanoparticle agglomerates 144 onto a surface 145 of a substrate 140, the substrate 140 being positioned within the circular substrate-holding area while the stagnation plate 120 rotates. The collecting means 130 or collecting device 130 comprises a collector head 131, a blowing mechanism 133 and a collecting vessel (or collection vessel or recovery vessel or collection vessel) 134. The collector head 131 comprises a scraper 132 adapted to be placed in contact with the substrate 140 so as to remove (or dislodge) agglomerates 144 of non-stoichiometric metal oxide nanoparticles deposited on the surface of the substrate 140. The blowing mechanism is adapted to deliver a vapor (or gas) towards a collection vessel to collect the removed (or stripped) non-stoichiometric metal oxide nanoparticle agglomerates. As will be understood, the collection vessel may include a device that serves to direct the removed (or scraped) agglomerates of non-stoichiometric metal oxide nanoparticles into the collection vessel. This may be a device that simply deposits the removed (or scraped) particles into the collection vessel. Alternatively, it may simply be present on the side of the scraper. The blowing mechanism may include an air blowing machine and a plurality of channels. The channels direct blow air (or air) toward the substrate and the scraper, thereby urging the removed (or scraped) agglomerates of non-stoichiometric metal oxide nanoparticles into the collection vessel. As shown in Figure 13, the channel may simply be a tube 134a that runs along the upper edge of the scraper and then bends in a U-shape to provide the desired directionality of the blow air / gas.

[0072] FIG. 14 discloses a device (or apparatus or equipment) 100 . The device (or equipment or apparatus) 100 comprises a burner 110, a rotatable stagnation plate (or retention plate or stagnation plate) 120, and a collection means (or collection means or recovery means) or collector (or collector or recovery apparatus) 130. The burner 110 comprises a nozzle 115 and a feed intake (or feed inlet or feed intake or feed inlet), the feed intake adapted to receive the combustible gas mixture and the volatile metal oxide precursor. The rotatable stagnation plate 120 comprises a plate and a motor 125, the plate having a circular substrate holding area (or substrate hold area), and the motor 125 for rotating the rotatable stagnation plate 120. The burner nozzle 115 is adapted to be positioned at a fixed position within a portion of the circular substrate-holding area such that, in use, a flame 104 emerges from the nozzle and deposits non-stoichiometric metal oxide nanoparticle agglomerates 144 onto a surface 145 of a substrate 140, the substrate 140 being positioned within the circular substrate-holding area while the stagnation plate 120 rotates. The collection means 130 or collection device 130 is composed of a collector head (or collection head or collection head or recovery head) 131, which comprises a body portion (or body part or body portion) 135, a scraper 132, a plurality of holes (or apertures) 136, a collection container (or collection container or recovery container or collection container) 134, and a vacuum system (or reduced pressure system). The scraper 132 extends from the body portion and is adapted to be placed in contact with a substrate such that agglomerates of non-stoichiometric metal oxide nanoparticles are removed (or dislodged) from the surface of the substrate. A plurality of holes 136 are in the body portion. A vacuum system is in fluid communication with the plurality of holes in the body portion and the collection vessel such that, in use, the vacuum system transfers (or transports) removed (or scavenged) non-stoichiometric metal oxide nanoparticle agglomerates from the substrate through the plurality of holes in the body portion and deposits them in the collection vessel. As shown in FIG. 14, the collection means or device may further include a cyclone separator 138a.

[0073] In FIG. 14, the vacuum system (or decompression system) includes a number of vacuum pumps (or decompression pumps) 138b (e.g., one or two) to provide a suction effect. The suction effect causes the removed (or removed) non-stoichiometric metal oxide nanoparticle agglomerates to be sucked through a plurality of holes (or apertures) 136 and connected tubes (or pipes or tubing) 138c and enter a cyclone separator 138a. The cyclone separator 138a is intended to separate air from the removed (or removed) non-stoichiometric metal oxide nanoparticle agglomerates. The latter (agglomerates) are deposited in a collection vessel (or collection vessel) 134. Some of the removed non-stoichiometric metal oxide nanoparticle agglomerates may not be separated from the air through the cyclone separator, and a filter 138b may be present before the vacuum pump 138b to separate and collect (or recover or recover) any non-stoichiometric metal oxide nanoparticle agglomerates that are not deposited in the collection vessel (or collection vessel).

[0074] Those skilled in the art will understand that the above device (or equipment or apparatus) can be easily adapted. For example, an equivalent of a rotatable plate may be used (e.g., a conveyor belt system). While the described device only uses a single scraper, the system may be designed with two or more scrapers. If more than one scraper is present, two or more scrapers may be used in series (or tandem) (one scraper may precede the other). This ensures that non-stoichiometric metal oxide nanoparticle agglomerates are completely removed (or as close to this as possible) from the substrate surface. Additionally or alternatively, using more than one scraper may allow the scrapers to be replaced without stopping production.

[0075] The device (or apparatus or equipment) may also include a plurality of jet nozzles 150, which allow the rotatable stagnation plate (or retention plate or stagnation plate) to be cooled by blowing a gas (e.g., dry air) onto the surface of the rotatable stagnation plate (or retention plate), the surface of the stagnation plate being the surface opposite to the surface that comes into contact with the flame (or flame) generated (or produced) from the nozzles in use.

[0076] Yet another aspect of the present invention provides aggregates of non-stoichiometric metal oxide nanoparticles containing a plurality of oxygen vacancies, wherein the nanoparticles each have a size of 20 nm or less, e.g., 5-20 nm, and a disordered surface layer. As will be appreciated, the oxygen vacancies may occur within the nanoparticles and / or at the grain boundaries of the aggregates. The particle size can be measured by the methods described in the Examples below.

[0077] The disordered surface layer may have any suitable thickness, for example, the disordered surface layer may have a thickness of 1 nm or less.

[0078] As noted above in this disclosure, any metal capable of providing a non-stoichiometric metal oxide can form (or produce) the metal in the non-stoichiometric metal oxide nanoparticle aggregates disclosed herein. For example, the metal may be one or more selected from the group consisting of Ti, Ce, Co, Fe, Cu, and W. Optionally, the metal is Ti.

[0079] In certain embodiments that may be mentioned in the present disclosure, the non-stoichiometric metal oxide nanoparticle aggregates (or agglomerates) may be blue non-stoichiometric titanium dioxide nanoparticle aggregates (or agglomerates), wherein the titanium dioxide nanoparticles within the aggregates (or agglomerates) comprise a heterogeneous phase (or heterophase) of rutile and anatase. Optionally, the rutile phase ratio (or percentage (%)) is 65% to 85%. And / or the nanoparticles further comprise a TiO2-II phase (or TiO2-II phase).

[0080] Further aspects and embodiments of the present invention are provided in the following non-limiting examples. [Example]

[0081] (Example) In this disclosure, we present a method for producing TiO2 for photocatalysis using a flame stabilized on a rotating surface (FSRS). 2-xA method for the preparation of nanoparticles is disclosed. In this method, a thin flame is stabilized above a convection-cooled substrate, resulting in the formation of a steep temperature gradient near the substrate. While the FSRS method is used in this example, other substrates may be used as long as the substrate surface can be cooled sufficiently quickly. Particles formed in the flame are subjected to a short residence time and a fast cooling rate during deposition. This results in the formation of highly monodisperse, ultrafine nanoparticles. Furthermore, particle growth in a flame under high temperature and oxygen-deficient conditions results in a high concentration of defects, including oxygen vacancies (OVs), in the deposited particles. However, with prolonged deposition, particles on a rotatable substrate can grow further due to the formation of grain boundaries (GBs) through thermal sintering, which can react with atmospheric oxygen and reduce the concentration of OVs. Therefore, simply changing the deposition time can provide a convenient way to control the location and abundance of OVs.

[0082] Example 1 Blue TiO prepared by flame synthesis 2-x Production of nanoparticles Blue TiO containing oxygen vacancies (OVs) was synthesized by a one-step method using a flame stabilized on a rotating surface (FSRS) as shown in Figure 1a. 2-x was prepared (or manufactured).

[0083] In a typical procedure, a premixed gas mixture consisting of 7.2% CH, 14.4% O, and 78.4% Ar (oxygen-lean or oxygen-lean mixture with an equivalence ratio (φ) of 1.5 (defined as the ratio of the actual fuel / air ratio to the stoichiometric fuel / air ratio)) was preheated to 150 °C at a total flow rate of 18 L / min (STP) (corresponding to an equivalent velocity of 304 cm / s). Titanium chloride (TiCl, Aldrich, 99.9%) was injected into the heated gas mixture at a flow rate of 3 mL / h using a syringe pump. The premixed gas containing evaporated TiCl4 was then released from an aerodynamic nozzle (with a 1 cm diameter outlet) and impinged on a rotating disk (or disc). The rotating disk (30.5 cm diameter) was placed 1.5 cm below the nozzle outlet and maintained at a rotational speed of 300 rpm. Upon ignition, a flat, laminar flame was formed and stabilized above the rotating disk. Within the flame, the TiCl4 vapor rapidly reacted to form liquid TiO2 droplets. Ultrafine TiO2 droplets were then formed. 2-x Nanoparticles of TiO were formed. The nanoparticles were deposited on a glass substrate placed in the slot of the rotating disk. Due to heat transfer from the flame, the temperature of the glass substrate gradually increased from room temperature to approximately 450 K within 15 minutes (measured with an infrared thermometer from the bottom of the rotating disk). At the end of the process, the powder was scraped off from the substrate and used directly for cocatalyst loading without further post-treatment. The sample was then coated with TiO. 2-xThe deposition times are listed as (deposition time) (x = 6, 10, 15, or 30 min). The observed colors in these samples range from dark blue (6 min), to light blue (10 min), to pale blue (15 min), to almost colorless (30 min).

[0084] Example 2 blue TiO 2-x Physicochemical characteristics (or properties) of (XRD) Powder X-ray diffraction (XRD) patterns were obtained on a Bruker D2 Phaser diffractometer (Cu Kα (λ = 1.54184 Å) radiation, 30 kV, 10 mA). Brunauer-Emmett-Teller (BET) surface area measurements were obtained using a Quantachrome Autosorb-6 sorption system (N adsorption and desorption at 77 K).

[0085] First, XRD was performed to characterize the flame-made (or flame-prepared) TiO. 2-x The phase composition of the flame-made TiO was analyzed. 2-x , especially TiO 2-x (6 min) is significantly less crystalline than P25 TiO2, suggesting that its structure contains defects and disorder. 2-x The samples consist of a predominant rutile phase and a minor anatase phase. In addition, a small amount of TiO2-II phase is also present. The calculated phase compositions based on Rietveld refinement are shown in Table 1 below. All flame-made TiO 2-xcontains more than 70% rutile. In comparison, P25 TiO2 is composed of approximately 80% anatase and approximately 20% rutile. XRD results show that the deposition time does not significantly affect the phase composition. However, the color of the sample changes abruptly from dark blue (6 min) to white (30 min). This is associated with a slight increase in crystallinity.

[0086] [Table 1]

[0087] Effect of deposition time on morphology Field emission scanning electron microscopy (FESEM) was performed using a JEOL JSM 6701F microscope. Transmission electron microscope (TEM) images and high-angle annular dark field (HAADF) images were obtained using a JEOL JEM-2100F TEM / STEM and a JEOL JEM-ARM200F / 300F equipped with a Cs corrector (or Cs corrector).

[0088] Figure 3 shows the flame-made TiO film. 2-x In Figure 3a, the morphology of the TiO sample is shown. 2-xThe FESEM image at 6 min shows the formation of loosely agglomerated nanoparticles with particle sizes of approximately 10–20 nm. In the TEM image (Figure 3b), the spherical nanoparticle outlines are easily visible, indicating minimal interparticle sintering due to the short time on the substrate. The nanoparticles have a crystalline core, and the surface / subsurface exhibits amorphous and disordered layers. These features are further demonstrated in the HRTEM image. As shown in Figure 3c, disordered domains are clearly observed, especially at the particle surface. The core exhibits lattice fringes with interplanar spacings of 0.322 nm and 0.249 nm. These are attributed to the (110) and (101) planes of rutile TiO2, respectively. This disordered surface layer has a thickness of about 1 nm. Within the flame (or flame), the vaporized TiCl4 precursor reacts rapidly with O2 and other radical species to form Ti-containing intermediate species, which act as precursors for TiO2 nanoparticles. Because the flame is in oxygen-lean (or oxygen-lean or O2-lean) conditions (calculated equilibrium O2 mole fraction is 5.83 × 10 -5 ), such intermediate species may be oxygen deficient (Ti x O y ,y / x<2). Therefore, it is expected that the nanoparticles formed will contain a high concentration of oxygen vacancies (or oxygen vacancies or OVs). Since oxygen vacancies are introduced into the particles very early (not from the stoichiometric reduction of TiO2 at a later stage), the TiO2 nanoparticles formed at short deposition times are more likely to have high oxygen vacancies. 2-x As demonstrated in Figure 6, oxygen vacancies should be distributed throughout the particle, both in the bulk and on the surface. The TiO formed at such a short deposition time is 2-xThe (1 min) sample exhibits the most disordered structure, with the outer amorphous layer measured to be about 2.1 nm.

[0089] As the deposition time increases, oxygen vacancies (OVs) in the particles deposited on the substrate can react with atmospheric O2, given the temperature of the substrate. As a result, the OV concentration, especially the surface OVs, decreases with increasing deposition time. Also, the crystallinity of the particles improves with increasing oxidation time. For example, in Figure 3d, the TiO 2-x (10 min) TiO 2-x Compared to the TiO film deposited for 6 min, the bulk phase exhibits lattice disorder and a thinner amorphous layer. Further increasing the deposition time reduces the surface defects observed in Figure 3e, resulting in a TiO film with a more crystalline core. 2-x (15 min). Figure 3f shows the TiO 2-x (30 min) HRTEM images are shown. Here, TiO 2-x At 30 minutes, the lattice defects are so few that the amorphous surface layer is barely observable.

[0090] Based on qualitative HRTEM observations for all samples, the degree of both bulk and surface defects decreased well with deposition time. The measured substrate temperature was relatively low (450 K). However, the actual temperature of the upper layer of the particles exposed to the flame is expected to be much higher (calculated adiabatic flame temperature of 2376 K). The adiabatic flame temperature was calculated using the USC-II chemical mechanism for H2 / CO / C1-C4 compounds by Wang et al. using the software package (Kinetics®) assuming constant enthalpy and pressure (USC Mech Version II. High-Temperature Combustion Reaction Model of H2 / CO / C1-C4 Compounds). As a result, as observed in Figures 3c-3f, the particles may undergo further thermal sintering after deposition on the substrate, resulting in the formation of grain boundaries (GBs) between adjacent nanoparticles. The GBs may be more pronounced in samples with longer deposition times due to the longer sintering.

[0091] As further shown by the TEM images in Figures 9a-d, the nanoparticles collected beyond 6 min of deposition time lose their spherical shape and form aggregated structures. Consistent with the morphological features, all flame-made TiO nanoparticles 2-x Brunauer-Emmett-Teller (BET) surface area (100-120 m 2 g -1 ) is P25 TiO2 (50m 2 g -1 ), the surface area is much larger than that of TiO (Table 1). 2-x (10 and 15 min) compared to TiO 2-xThe decrease in surface area (30 min) is due to prolonged sintering and agglomeration. All TiO2 samples exhibit Type H3 hysteresis isotherms. This type of isotherm indicates non-limiting adsorption at high P / P (Figure 22a). This type of isotherm is derived from plate-like nanoparticles or non-rigid aggregates with numerous slit-shaped pores. This is consistent with the characteristics of our samples, which consist of aggregated nanoparticles, as shown in Figure 9. Correspondingly, the measured pore size (Figure 22b), i.e., the distance between particles, is very large, typically exceeding 20 nm, indicating that the TiO2 samples are not adsorption-limited. 2-x The average pore size (or average pore diameter or average pore diameter) of TiO is in the range of 43-48 nm. However, the pore volume (or pore volume) varies depending on the sample (Table 1). In particular, TiO 2-x At 30 min, a significant decrease in pore volume was observed due to more intense sintering.

[0092] (TiO 2-x (15 min) and TiO 2-x (30 mins STEM analysis) TiO 2-x The structural analysis (15 min) was performed by applying atomic-resolution aberration-corrected STEM, which showed the defects in the sample in more detail. 1 The structural model of rutile TiO2 projected from the [1] direction is shown. This shows the structure of TiO 2-xThis is in good agreement with the STEM image (Figure 4b) taken at 15 min. Here, defects (e.g., step planes and stacking faults) can be easily observed. Atoms at edges, corners, and steps exhibit low coordination sites, serving as active sites for anchoring metal cocatalysts and for adsorption and activation of reactive species. In addition to surface defects, large areas of bulk defects (disordered regions) can also be observed in Figure 4b. This reduces crystallinity and disrupts the well-ordered arrangement of atoms. Bulk defects throughout the nanocrystal induce stacking faults. Careful inspection of the stacking sequence of the lattice planes reveals that some planes of atoms are shifted from their original regular positions, as shown in Figures 4c and 4d. The formation of stacking faults could be related to the sintering of nanoparticles or the removal of vacancies during crystal growth. 2-x STEM analysis (at 30 min) reveals that the nanocrystals exhibit a well-ordered lattice without obvious bulk defects (Fig. 4e).

[0093] (chemical properties) Spectroscopic techniques such as Raman, EPR, and XPS have been used to characterize flame-made TiO. 2-xThe chemical properties of the compounds were further investigated. Raman spectra were recorded on a Renishaw InVia Raman Spectrometer at an excitation wavelength of 514.5 nm. X-ray photoelectron spectroscopy (XPS) was performed on a Kratos AXIS Ultra DLD spectrometer. The binding energy was calibrated to the C 1s peak at 284.7 eV. Electron spin resonance (EPR) was performed at 9.363 GHz using a Bruker EMX-10 / 12 EPR spectrometer.

[0094] The Raman spectra of flame-made TiO are compared with those of pure anatase TiO and pure rutile TiO (Figure 10). 2-x The rutile phase exhibits a mixed vibration mode. The mixed vibration mode contains both phases and exhibits a fairly broad signal due to the lower crystallinity, as shown in Figure 5a. The rutile phase exhibits two first-order vibration modes (E g (445cm -1 ) and A 1g (611cm -1 )). The anatase phase is E g (144cm -1 ) vibration mode. E of anatase and rutile gThe modes, attributed to Ti-O vibrations, shift to higher and lower frequencies with shorter deposition times of 6 and 10 minutes, respectively, accompanied by a peak broadening effect (see inset in Figure 5a). This demonstrates the presence of more oxygen vacancies (OVs) in both phases in the defective sample. Removal of one oxygen atom triggers the three nearest-neighbor Ti atoms to relax away from the oxygen vacancy in order to strengthen their bonds with other oxygen atoms. This outward relaxation induces a disordered structure and locally shortens the Ti-O bond length. Therefore, the anatase E g This results in a blue shift and broadening of the signal. g The mode is associated with the out-of-phase and liberation motion of oxygen atoms along the c-axis. The red-shift of this mode is thought to arise from the lattice distortion in the rutile phase and the motion of oxygen atoms along the c-axis.

[0095] blue TiO 2-x Ti in 3+ The presence of Ti can be further confirmed by EPR. As shown in Figure 5b, the broad signal at g = 1.93 corresponds to the surface-exposed Ti. 3+ This phenomenon becomes stronger as the deposition time becomes shorter. In particular, TiO 2-x At (6 min), the strongest signal corresponds to the dark blue color (Fig. 1b). This indicates that in a reducing flame environment, a large amount of Ti 3+ This means that defects (or defects) of Ti are formed. When the temperature exceeds the ambient temperature and the contact time of the substrate with air is long, 3+ gradually Ti 4+ It is oxidized to TiO 2-x (30 min) and P25, almost no signal was detected.

[0096] To investigate the surface and subsurface (or subsurface) chemical states of the sample, XPS analysis was performed. As shown in Figure 5c, two peaks at binding energies of 458.7 eV and 464.4 eV correspond to Ti and TiO, respectively. 4+ Ti 2p 3 / 2 and Ti 2p 1 / 2 It is attributed to TiO 2-x (6 min and 15 min) 3+ The existence of Ti 3+ Ti 2p 3 / 2 and Ti 2p 1 / 2 This is evidenced by shoulder peaks (457.4 eV and 463.1 eV) attributed to TiO. 2-x On the surfaces of TiO (30 min) and P25, almost no charge was observed. Correspondingly, oxygen vacancies (OVs) exist on the surface to balance the charge. In the O 1s spectrum (Figure 5d), the main O 1s peak (529.9 eV) is assigned to Ti-O lattice bonds (with no OVs nearby). The shoulder peak (531.8 eV) is assigned to O atoms (located in the vicinity (or vicinities) of the O vacancies). TiO 2-x The larger shoulder peak at (6 min) is consistent with the presence of more oxygen vacancies (OVs) on its surface compared to the other samples.

[0097] (Abstract) Based on the above results, TiO 2-x A mechanism for the formation of oxygen vacancies (OVs) in TiO2 has been proposed, as shown in Figure 1b. In a fuel-rich reducing flame, nucleation and particle growth occur in TiO2. 3+ and the formation of oxygen vacancies (OVs). At short residence times of 6–7 ms, TiO 2-xNanoparticles grow rapidly, reaching sizes of around 10-20 nm. During this process, defects originally present in the outer layer "migrate" to the core, resulting in a random distribution of oxygen vacancies (OVs) throughout the particle. During precipitation, the nanoparticles undergo thermal sintering and oxidation by atmospheric O2. Finally, after prolonged exposure to air (30 min), the amount of OVs decreases and the sample becomes colorless.

[0098] Example 3 blue TiO 2-x Photophysical properties of Blue TiO obtained in Example 2 2-x Quantitative results of oxygen vacancies (OV) in SiC provide a deeper understanding of the correlation between the oxygen vacancy (OV) distribution and its photophysical properties (e.g., bandgap energy, transient photocurrent density, charge carrier kinetics).

[0099] (Bandgap Energy) UV-visible diffuse reflectance spectra (UV-vis DRS) were collected using a UV-2450 spectrophotometer (Shimadzu Corporation).

[0100] As shown in Figure 7a, compared to P25 TiO2 (bandgap energy: 3.2 eV), flame-made TiO 2-x All of these samples exhibit an absorption edge on the long wavelength side due to the dominance of the rutile phase. 2-x Among them, TiO 2-x The TiO (6 min) sample has the smallest bandgap energy of 2.8 eV. The rest all have bandgap energies of about 3.0 eV, which is the bandgap energy of the rutile phase (Figure 7b and Table 1). 2-x(6 min) exhibits a large absorption tail in the visible and near-infrared (NIR) regions. 2-x (6 min) In other frames, TiO 2-x The clear decrease in band gap energy and the tail-up phenomenon compared to TiO indicate that surface disorder (an amorphous outer layer about 1 nm thick) plays an important role in these properties. On the other hand, bulk defects are also important for TiO. 2-x (10 and 15 min) (TiO 2-x It appears to have little effect, as shown by samples containing bulk defects similar to or greater than 6 min.

[0101] (Photocurrent density) Photoelectrochemical measurements were performed using a three-electrode cell system controlled by a CHI 660E electrochemical workstation. The working electrode was a TiO coated ITO (Sigma-Aldrich, L × W × T: 25 mm × 25 mm × 1.1 mm). 2-x A Pt electrode was used as the counter electrode. An Ag / AgCl electrode was used as the reference electrode. 5 mg of TiO was used to obtain the catalyst ink. 2-x (prepared from Example 1) and 20 μL of Nafion solution (5 wt%) were added to 980 μL of ethanol solution and sonicated for 15 minutes to form a homogeneous ink. To prepare the working electrode, a portion (40 μL) of such catalyst ink was applied to a 0.196 cm2 area on an ITO conductive glass. 2 The film was deposited over an area of ​​100 μm and dried at 40°C for 2 h. A 300 W xenon lamp (Newport) equipped with a cut-off filter (λ ≥ 400 nm) was used as the light source. Photocurrents were recorded at an applied potential of 0.6 V vs. Ag / AgCl in a 0.5 M Na2SO4 solution.

[0102] Figure 7c shows the measurement results of the transient photocurrent density. 2-x (6 min) has the smallest band gap and the largest absorption tail in the visible light. However, under visible light irradiation (λ ≥ 400 nm), all flame-made TiO 2-x The photocurrent density is lowest among TiO. 2-x (15 min), which was obtained from TiO 2-x This observation suggests that TiO has a moderate amount of oxygen vacancies (OVs). 2-x It has been suggested that a time of 15 minutes has the maximum charge separation efficiency.

[0103] (Charge Carrier Kinetics) TiO 2-x To further investigate the charge carrier kinetics at the interface between the catalyst and the Pt cocatalyst, time-resolved photoluminescence (PL) spectroscopy was performed. After the photoreaction, 0.1 wt% Pt was loaded. Time-resolved PL spectra were collected using an Edinburgh Instruments FLS920 PL spectrometer (excitation: 375 nm).

[0104] Double exponential decay function (or biexponential decay function):

[0105]

number

[0106] By fitting the spectrum using the following relationship:

[0107]

number

[0108] The PL lifetime was calculated by (41). In the equation, the parameters are the fast decay (τ1), the slow decay (τ2), and the amplitudes (A1, A2), respectively. The fast decay process is 2-x The slow decay process is attributed to the radiative recombination of electrons migrating back to the ground state. (42) Therefore, to obtain better photocatalytic performance, it is desirable to have a smaller fast decay (τ) to further increase the electron extraction rate at the interface and a larger amplitude A to increase the overall contribution of the quenching process. As shown in Figure 7d and Table 2, the fast decay (τ) of TiO is 2-x (15 min) indicates the minimum τ1 and maximum A1 values. This gives the shortest mean lifetime (or average lifetime) (tau average (τ average P25 TiO2 yields the longest tau average (τ average These results indicate that photoexcited electrons trapped and stored in grain boundary oxygen vacancies (GB OVs) can be efficiently transferred to the Pt cocatalyst, allowing the photoreduction reaction to occur. The presence of such interfacial defects is advantageous for minimizing the radiative coupling between electrons and holes.

[0109] [Table 2]

[0110] Example 4 Frame-made TiO 2-x Photocatalytic activity for H2 evolution using Photocatalysis was carried out under visible light irradiation (λ ≥ 400 nm) in aqueous solution, where methanol served as a sacrificial agent.

[0111] (Photocatalytic measurement) Photocatalytic H2 evolution measurements were performed using a 300 mL top-irradiation Pyrex glass cell connected to a closed gas circulation and exhaust system. The reaction cell was maintained at 18 °C by external cooling water circulation. A 300 W xenon lamp (Newport) with a cut-off filter (λ ≥ 400 nm) was applied as the light source. In a typical experiment, 20 mg of TiO2 was added. 2-x The cation exchange catalyst (prepared according to Example 1) was dispersed in 120 mL of aqueous methanol (25 vol%). Then, 20 μL of a 1 mg Pt / mL HPtCl solution (Sigma-Aldrich) was added to in situ photodeposit 0.1 wt% Pt as a cocatalyst. Prior to photoirradiation, the reaction system was evacuated and purged with argon several times to remove air. Finally, it was refilled with argon to reach approximately 30 Torr. The evolved H was analyzed using an online gas chromatograph (Agilent 6890N, thermal conductivity detector).

[0112] TiO 2-x For stability tests of the photoreactor (15 min) (loaded with 0.1 wt% Pt), three consecutive runs of 12 h each were performed under the same conditions. After each run, the photoreactor system was evacuated and purged with Ar several times to remove evolved H2 before the next run.

[0113] ICP measurements were performed (Prodigy High Dispersion ICP). During the preparation, the Pt-loaded photocatalyst was heated at 300 °C for 4 h in H (30 mL min −1 ). -1 ) and PtO x Seeds Pt 0 After hydrogenation, each sample (0.02 g) was dissolved in 2 mL of aqua regia and filtered to remove TiO2. 4+ The concentration was analyzed by ICP instrument.

[0114] (result) As shown in Figure 8a, when 0.1% Pt was used as a cocatalyst, flame-made TiO 2-x All samples show superior photocatalytic activity compared to P25 TiO2. The activity trends for H2 evolution are consistent with those of photocurrent density and photoluminescence decay (or PL decay). TiO 2-x (15 min) had the highest activity (960 μmol h -1 g -1 This activity is approximately 12 times that of P25 TiO2. 2-x Since there was no significant variation in surface area and phase composition among the samples (Table 1), the defect state should be the primary factor contributing to the activity differences.

[0115] Consistently, TiO 2-x (6 min) shows the lowest photoactivity. TiO 2-xComparing the activities (10 min, 15 min, and 30 min) with respect to the properties of the respective oxygen vacancies (OVs), it can be concluded that a moderate amount of bulk oxygen vacancies (OVs) is desirable to achieve higher photocatalytic activity. Furthermore, it was found that Pt promoter nanoparticles preferentially deposit at or near the grain boundaries (GBs) due to the higher electron concentration at the GBs (Figure 11). Also, the oxygen vacancies (OVs) at the GBs should effectively anchor the Pt species, and the Pt 6+ From Pt 0 Even when some single Pt atoms are identified, the average cluster size (or cluster diameter or cluster dimension) of Pt is the smallest (Table 3). 0 The proportion (or percentage (%)) of TiO 2-x Based on the inductively coupled plasma (ICP) data (Table 3), TiO 2-x The Pt loading (0.076 wt%) of the sample (15 min) is the highest among all samples. However, the Pt 0 %, TiO 2-x (15 min) 0 Loading is TiO 2-x (10 min) and TiO 2-x (30 min) Pt 0 loadings are approximately 13% and 44%, respectively. 2-x (6 min) and Pt on P25 TiO2 0 The loading of Pt is substantially lower. These results indicate that oxygen vacancies (OVs) locked at the grain boundaries (GBs) due to thermal sintering of the nanoparticles during synthesis can facilitate the immobilization and reduction of Pt species. Also, even when several single Pt atoms are identified, the average Pt size is larger than that of TiO. 2-x It was found to be smallest at (15 min).

[0116] [Table 3]

[0117] Our best 0.1% Pt-TiO 2-x The photocatalytic activity is comparable to that of some of the best OV-containing TiO2 photocatalysts reported to date (those containing 0.5–1% Pt (or Pd)) under visible light irradiation (Table 4). Some previous studies have suggested that fewer bulk defects and more surface defects are beneficial for photocatalysis. However, based on our current study, a balanced concentration of both surface and bulk defects, coupled with the promotion of grain boundary oxygen vacancies (GB OVs), clearly improves performance.

[0118] [Table 4]

[0119] TiO 2-x A recycling test (15 min) (0.1 wt% Pt loading) shows that this photocatalyst has good stability (Fig. 8b). After three 12-h reaction runs in each run, the activity only decreased by 9.7%, which is mainly due to the evaporation and consumption of the sacrificial agent during the reaction.

[0120] Example 5 Continuous particle collection (CPC) methods and mechanisms for achieving collection As described above, particles may be formed by the FSRS method. In a typical setup, as shown in Figure 12, a rotatable stagnation plate 120 (100-300 rpm) is positioned a fixed distance below the burner nozzle 115 (5-25 mm) of the burner 110. This plate 120 forces the flow of premixed gases (or premixed gases or vapors) emitted from the burner nozzle 115 to diverge. As a result, a flat flame 104 is formed and stabilized above the stagnation plate 120. When particle precursors (or particle precursors) are mixed into the premixed gas mixture, particles 144 are formed within the flame 104 and then deposited on the plate 120. The rotation of the plate is suggested to cool the deposited particles 144 by convection and prevent further sintering during deposition. Additional cooling may be provided by multiple jet nozzles 150 (dry air) positioned below the plate, as shown in FIG.

[0121] Typically, deposition of these particles occurs over a specific period of time (typically 10-60 minutes). The flame is then extinguished and the deposited particles are collected from the stagnation plate. This method (or approach) may be called interval particle collection (IPC), but it has two main drawbacks:

[0122] 1. Despite the convective cooling provided by the plate rotation, the deposition time can affect the properties of the deposited particles (e.g., crystal phase, defect concentration, etc.). In other words, particle properties may be limited by the synthesis yield. For example, the defect concentration of TiO particles prepared using the IPC method decreases with increasing deposition time, based on the observed color of the samples. This may be due to the gradual change in particle properties as the particles are periodically exposed to a flame during synthesis. Furthermore, the deposited particles typically form a porous layer on the plate surface. This porous layer of oxide particles acts as a poor thermal conductor, creating a strong thermal gradient in the particle layer. As a result, the stagnation temperature gradually increases as the particle layer forms, as shown in Figure 19. These effects are easily amplified by the relatively long deposition times, typically 10-60 minutes, required to collect sufficient sample for a typical application (e.g., catalyst testing) or material characterization (e.g., powder X-ray diffraction). Experiments can require multiple runs to collect sufficient sample. However, such methods are extremely time- and resource-intensive due to the manual labor required to periodically scrape the sample and the pre-treatment period required after each flame extinguishing for particle collection.

[0123] 2. As a result of the deposition time and the effects of thermal gradients that develop in the particle layer, it is reasonable to expect that the particle properties of the synthesis batch will be non-uniform, which may adversely affect the performance of the material in its intended application.

[0124] (Prototype 1 and Prototype 2 implementing the CPC method) The above drawbacks of the IPC method can be overcome by the continuous particle collection method (CPC method). Two prototypes of the CPC method are shown in Figures 13 and 14.

[0125] Both of the illustrated prototypes use the same collection mechanism. The collector head 131, consisting of a scraper 132, is fixed above the plate 120. The collector head 131 is used to scrape and remove particles 144. During synthesis, the plate 120 rotates. The scraper 132 is made of a heat-resistant material. This is a material with a lower hardness than the plate 120 (made of stainless steel) so as not to scratch the plate 120. In this case, the scraper 132 is made of 0.25 mm Nomex TM It is made by fixing two pieces of polymer (heat-resistant polymer) perpendicular to the plate surface.

[0126] Two different mechanisms may be employed to remove particles 144 using a scraper, thereby directing them to a final particle collector. In Prototype 1 (Figures 13A and 13B), a small flow of compressed dry air (CDA, 3.5 lpm) 133 through a 1 / 16-inch stainless steel tube 134a was used to push scraped particles from the stagnation plate 120 to the particle collector 134. In the collector 134, the particles easily settle due to gravity. In Prototype 2 (Figure 14), a vacuum pump 138b was used to suck particles through holes or orifices 136 in a tube 138c in the collector head 131. The particles were then separated using a cyclone separator 138a and a filter 138d. The main advantage of this method is that particles can be removed from the scraper 132 more quickly by suction (compared to using the CDA blower 133 in Prototype 1) to prevent them from contacting the hot stagnation plate 120 for a long time. However, the strong suction generated by the pump creates an aerosolized flow that is difficult to separate. As a result, the collection efficiency is reduced.

[0127] One difference between the IPC and CPC methods is the range of rotational speeds that can be achieved. Due to contact between the scraper and the rotatable plate, the CPC method imposes significantly higher off-axis loads on the motor. As a result (for the current motor 125 used in this setup), the rotational speed of the CPC is limited to <5 rpm, compared to a maximum of 300 rpm for the IPC.

[0128] Example 6 Effect of various parameters on particle properties A series of experiments were conducted using the IPC and CPC prototype 1 methods (as described in Example 5). The effects of deposition time and plate rotation speed on particle properties were demonstrated. Furthermore, the effect of flame equivalence ratio (FER) in the CPC method was also investigated. The synthesis conditions are summarized in Tables 5 and 6.

[0129] [Table 5]

[0130] Based on the conditions in Table 6, the premixed gas velocity is 473 cm / s. This is based on a premixed gas flow rate of 28 slpm delivered through a 14 mm (1.4 cm) diameter nozzle and a nozzle temperature of 150°C. It should be noted that nozzles of various sizes can be used. However, the premixed gas velocity at the nozzle must be greater than the flame speed to stabilize the flame.

[0131] The precursor is injected into the heated mixture at a flow rate of 900 ppm based on the conditions in Table 6. This flow rate is calculated from the injection rate of the precursor and the flow rate of the premixed gas.

[0132] [Table 6]

[0133] The flame with ER = 1.20 (#1-11) was selected as the standard flame because the prepared particles exhibited a very strong color (dark blue). This allowed us to clearly demonstrate the changes due to the different collection methods. Table 7 summarizes the average plate temperatures after the pretreatment period (approximately 10 min) for various flame conditions (without precursor).

[0134] [Table 7]

[0135] The prepared samples were then characterized using digital photography, powder X-ray diffraction, and X-ray photoelectron spectroscopy. Powder X-ray diffraction (XRD) patterns were recorded using a D8 Advance diffractometer (Bruker) with Cu Ka radiation (40 kV, 30 mA), a 217.5 mm radius, a 0.6 mm / 0.3° divergence slit, and a 2.5° Soller slit. The 2θ scan range was 10–80° (step size 0.025, 0.8 s per step). A zero-background silicon sample holder (cavity 10 mm x 0.2 mm) was used. X-ray photoelectron spectroscopy (XPS) was recorded using a Kratos AXIS Ultra photoelectron spectrometer (Kratos Analytical) equipped with a monochromated Al Ka ​​source (1486.71 eV, 5 mA, 15 kV). Photoelectrons were collected at an electron emission angle of 90°. The binding energy shift is 3 / 2 The binding energy was corrected by setting it to 458.6 eV (Biesinger et al., 2010).

[0136] (Shorter deposition times favor the formation of blue TiO2) Figure 16 summarizes the effects of varying deposition time (IPC) compared with the sequential method (CPC). These results suggest that the dark blue coloration is only obtained with the CPC method or with IPC at very short deposition times (5 min). Because the blue coloration is associated with defect centers in the TiO crystals (Breckenridge et al., 1953), the blue coloration tends to gradually disappear with longer deposition times (IPC-15 min, IPC-25 min). While not wishing to be bound by theory, the disappearance of the blue coloration with longer deposition times may be due to oxidation and sintering processes during the continuous exposure of the deposited particles to the flame. For example, sintering is evidenced by the sharpening of the rutile peak at 2θ = 27.4° with increasing deposition time (Figures 16B and 16D, XRD). Furthermore, the presence of defects / TiO on the particle surface may also contribute to the formation of sintered TiO. 3+ (or Defect / Ti 3+ The relative amount of Ti 2p ions also decreases as a function of deposition time. This is reflected by the Ti 2p ions in the XPS spectra of Figures 16C and 16E. 3 / 2 This is evidenced by peak broadening (or broadening).

[0137] (The rotation speed of the plate does not significantly affect the coloring of the particles.) Figure 17 shows the results of varying the rotation speed on the CPC (vs. IPC), using a rotation speed of 1 rpm as a reference. The coloration of the particles (Figure 17A) and the defect / Ti from the XPS spectrum. 3+ (or Defect / Ti 3+ The effect of rotation speed is not very pronounced, as shown by the relative amounts of ρ (Figure 17C), suggesting that plate rotation is not a very effective cooling mechanism (see Table 7).

[0138] (The flame equivalence ratio (ER or φ) significantly affects the crystalline phase and particle coloration.) The effect of flame equivalence ratio (ER) is summarized in Figure 18 (CPC method). This result is consistent with our previous results, and shows that the crystalline phase composition is strongly dependent on the blend equivalence ratio. Furthermore, as the equivalence ratio decreases (the oxygen concentration increases), the blue color disappears.

[0139] Based on these results, and without wishing to be bound by theory, it appears that there are two main requirements for producing blue TiO2. First, the fuel-to-oxidizer ratio (or flame equivalence ratio) must be sufficiently high. Specifically, the flame equivalence ratio must be approximately 1.1 or higher. However, significantly higher equivalence ratios (approximately 2.0 or higher) are undesirable because such flames tend to produce large amounts of soot and carbon contaminants. A high equivalence ratio can cause excess fuel to mix with the surrounding air, potentially forming a secondary flame. Without additional cooling mechanisms, the secondary flame can significantly increase plate temperatures, potentially accelerating the oxidation of the blue TiO2.

[0140] Second, prolonged exposure of the deposited particles to high temperatures should be minimized, as blue TiO2 is easily oxidized under these conditions. This can be achieved by efficient cooling of the plate or by using short deposition times (as described in the Detailed Description). (The exact cooling or deposition time required depends on the flame, precursor, precursor loading rate, collection mechanism, etc.)

[0141] (Particle size measurement) Particle size measurements from selected collection methods are shown in Table 8. These data are also compared to a previous study (J. Aerosol Sci. 133, 96-112) shown in Figure 20. In Figure 20, particles were collected in situ and immediately quenched, resulting in an equivalent deposition time close to zero (see the original study for further details).

[0142] This result seems to indicate that the collection method or deposition time has little effect on particle size, which indicates that particle size is primarily controlled by precursor loading.

[0143] [Table 8]

[0144] (Effect of rotation speed on CPC system) The effect of rotation speed on the CPC system is summarized in Figure 21. The results show that the blue coloration gradually disappears with decreasing rotation speed (Figure 21a). This is accompanied by a slight sharpening of the XRD peaks corresponding to higher crystallinity as the defects are oxidized (Figure 21b). As the rotation speed decreases, the defect concentration decreases. This is due to the Ti 2p peaks in the XPS results. 3 / 2 This is reflected in a smaller full width half maximum (FWHM) (Fig. 21c, 21d).

[0145] Comparative Example Use of high oxygen lean equivalence ratio All samples obtained at very high equivalence ratios (>2) (i.e., very oxygen-lean or O2-lean) and deposition times of 20 minutes were found to be colorless, which is consistent with the blue TiO formed in the above examples. 2-x In contrast to the comparative examples, these samples have some surface defects as detected by XPS and EPR, but the performance of the optimal comparative sample was inferior to that of the optimal sample in the present example in terms of photocurrent density and photocatalytic activity for hydrogen evolution from water. This indicates that the defects promote the separation and transport of charges. The disclosure of this specification may include the following aspects. (Aspect 1) 1. A method for forming aggregates of non-stoichiometric metal oxide nanoparticles, the method comprising the steps of: (a) dissolving a metal oxide nanoparticle in a solution of a non-stoichiometric metal oxide nanoparticle; (a) aerosolizing a heated mixture through a nozzle of a burner, the heated mixture comprising a combustible gas mixture and a volatile metal oxide precursor, the combustible gas mixture having an oxygen-lean equivalence ratio (φ), the combustible gas mixture being ignited at an outlet of the nozzle to provide a flame whereby the volatile metal oxide precursor decomposes and undergoes rapid nucleation and condensation to form non-stoichiometric metal oxide nanoparticles in the presence of the flame; and (b) depositing non-stoichiometric metal oxide nanoparticles onto a surface of a substrate to form aggregates of non-stoichiometric metal oxide nanoparticles on the surface of the substrate, the substrate being positioned at a fixed distance from the nozzle for a period of nanoparticle aggregation and oxidation. Including, The oxygen lean equivalence ratio (φ) of the flammable gas mixture is 1.5 or less; The velocity of the combustible gas mixture at the burner nozzle is 300 to 500 cm / s; method. (Aspect 2) The method according to aspect 1, wherein the oxygen lean equivalent ratio (φ) is 1.05 to 1.5. (Aspect 3) 3. The method according to aspect 2, wherein the oxygen lean equivalent ratio (φ) is 1.1 to 1.4. (Aspect 4) The combustible gas mixture is a mixture of an inert gas (e.g., argon), oxygen, hydrogen gas, and a hydrocarbon gas (e.g., C 2 H 4 4. The method of any one of aspects 1 to 3, comprising either or both of: (Aspect 5) 5. The method of embodiment 4, wherein the inert gas represents 70 vol.% or more of the combustible gas mixture, with the balance being oxygen and either or both of hydrogen gas and hydrocarbon gas. (Aspect 6) the inert gas provides 75 to 79.9 vol% of the combustible gas mixture; the oxygen providing 10 to 17 vol% of the combustible gas mixture; The hydrogen gas and / or the hydrocarbon gas provides 5 to 10.1 vol% of the combustible gas mixture. The method according to embodiment 5. (Aspect 7) the inert gas providing 78 to 79.75 vol% of the combustible gas mixture; the oxygen providing 14.4 to 15 vol% of the combustible gas mixture; The hydrogen gas and / or the hydrocarbon gas provide 5.25 to 8 vol% of the combustible gas mixture. The method of embodiment 6. (Aspect 8) (a) injecting the volatile metal oxide precursor into the heated mixture at a flow rate of 2 mL / h to 100 mL / h, for example 3 mL / h to 50 mL / h, for example 5 mL / h to 25 mL / h, for example 10 mL / h to 20 mL / h; and / or (b) Aspect 8. The method of any one of aspects 1 to 7, wherein the concentration of the volatile metal oxide precursor in the combustible gas mixture is 100 to 1,500 ppm, for example, 250 to 900 ppm. (Aspect 9) Aspect 9. The method according to any one of aspects 1 to 8, wherein the temperature of the flame is 1,500 to 2,500K. (Aspect 10) 10. The method of any one of aspects 1-9, wherein the substrate is a rotatable substrate and, upon rotation, deposition of the non-stoichiometric metal oxide nanoparticle aggregates occurs only on a portion of the substrate in an area below the flame at any given time. (Aspect 11) 11. The method of embodiment 10, wherein the rotatable substrate rotates at a speed of from 0.1 rpm to 500 rpm, such as from 1 rpm to 300 rpm, or from 1 rpm to 100 rpm, such as 0.1 rpm, 1 rpm, 100 rpm, or 300 rpm. (Aspect 12) The method of any one of claims 10 to 11, wherein the deposited non-stoichiometric metal oxide nanoparticle agglomerates are substantially removed from the surface of the rotatable substrate by a collection means or device, such that the deposited non-stoichiometric metal oxide nanoparticle agglomerates are continuously collected from the surface of the rotatable substrate as the rotatable substrate rotates, and the rotatable substrate is rotated at a speed of 0.1 rpm to 20 rpm, for example, 0.2 rpm to 5 rpm or less, for example, 1 rpm or less, as necessary. (Aspect 13) 13. The method of embodiment 12, wherein the method is operated for a period of from 1 minute to infinity, such as from 5 minutes to 1 month, such as from 15 minutes to 1 week, such as from 25 minutes to 1 hour. (Aspect 14) 11. The method of claim 10, wherein the deposited non-stoichiometric metal oxide nanoparticle aggregates are deposited on the surface of the rotatable substrate for a period of 1 second to 15 minutes, and optionally rotating the rotatable substrate at a speed of 100 rpm to 500 rpm, e.g., 100 rpm to 300 rpm. (Aspect 15) 15. The method of claim 12 or 13, or the method of claim 14, wherein the rotatable substrate is actively cooled after passing through the flame, and optionally the rotatable substrate is cooled by a plurality of air nozzles, each of which delivers the air at 20 to 200 L / min, for example, 50 to 150 L / min, for example, 75 to 100 L / min. (Aspect 16) Aspect 16. The method according to any one of aspects 1 to 15, wherein the distance between the nozzle of the burner and the substrate is 5 to 25 mm, for example, 14 mm to 20 mm, for example, 14 mm or more to 15 mm. (Aspect 17) 17. The method of any one of aspects 1 to 16, wherein the temperature of the substrate is 298 K to 800 K, for example, 350 K to 780 K, for example, 400 K to 500 K, and optionally the temperature of the substrate is measured at a point outside the flame. (Aspect 18) 18. The method of any one of embodiments 1 to 17, wherein the volatile metal oxide precursor comprises a metal capable of forming a stable, reducible oxide. (Aspect 19) 19. The method of embodiment 18, wherein the volatile metal oxide precursor comprises one or more metals selected from the group consisting of Ti, Ce, Co, Fe, Cu, and W, and optionally, the volatile metal oxide precursor comprises Ti. (Aspect 20) 20. The method of any one of aspects 1 to 19, wherein the formed non-stoichiometric metal oxide nanoparticle aggregates contain oxygen vacancies, and optionally the oxygen vacancies are formed at grain boundaries. (Aspect 21) Aspect 21. The method of any one of aspects 1 to 20, wherein the depositing in step (b) is carried out in an oxygen-containing environment. (Aspect 22) 1. A device for forming aggregates of non-stoichiometric metal oxide nanoparticles, the device comprising: a burner; a rotatable stagnation plate; and a collection means or device; the burner comprising a nozzle and a feed intake adapted to receive a combustible gas mixture and a volatile metal oxide precursor; the rotatable stagnation plate comprises a plate and a motor, the plate having a circular substrate holding area, the motor for rotating the rotatable stagnation plate; the burner nozzle is adapted to be positioned at a fixed position within a portion of the circular substrate-holding area, and in use, a flame is generated from the nozzle such that aggregates of non-stoichiometric metal oxide nanoparticles are deposited on a surface of a substrate, the substrate being positioned within the circular substrate-holding area while the stagnation plate rotates; the collection means or device is configured to remove the non-stoichiometric metal oxide nanoparticle agglomerates from the surface of the substrate after deposition; device. (Aspect 23) the collection means or collection device comprises a collector head, a blowing mechanism, and a collection vessel; the collector head comprising a scraper adapted to be placed in contact with the substrate so as to remove agglomerates of non-stoichiometric metal oxide nanoparticles deposited on a surface of the substrate; the blowing mechanism is adapted to deliver gas toward the collection vessel to remove the non-stoichiometric metal oxide nanoparticle agglomerates; 23. The device of embodiment 22. (Aspect 24) the collecting means or collecting device comprises a collector head, the collector head comprising a body portion, a scraper, a plurality of holes, a collecting container, and a vacuum system; the scraper extends from the body portion and is adapted to be placed in contact with the substrate such that agglomerates of the non-stoichiometric metal oxide nanoparticles are removed from a surface of the substrate; the plurality of holes are in the body portion; The device of embodiment 22, wherein the vacuum system is in fluid communication with the plurality of holes in the main body portion and the collection vessel, and wherein, in use, the vacuum system transports the removed agglomerates of the non-stoichiometric metal oxide nanoparticles from the substrate through the plurality of holes in the main body portion and deposits them in the collection vessel, and optionally the collection means or collection apparatus further comprises a cyclone separator. (Aspect 25) 25. The device of any one of aspects 22 to 24, further comprising a plurality of jet nozzles for cooling the rotatable stagnation plate by blowing gas (e.g., dry air) onto a surface of the stagnation plate, the surface of the stagnation plate being the surface opposite to the surface that comes into contact with the flame generated from the nozzles during use. (Aspect 26) A non-stoichiometric metal oxide nanoparticle aggregate containing a plurality of oxygen vacancies, each nanoparticle having a size of 20 nm or less, e.g., 5-20 nm, and having a disordered surface layer. (Aspect 27) 27. The non-stoichiometric metal oxide nanoparticle aggregate of embodiment 26, wherein the disordered surface layer has a thickness of 1 nm or less. (Aspect 28) 28. The non-stoichiometric metal oxide nanoparticle aggregate of claim 26 or 27, wherein the metal of the metal oxide is one or more selected from the group consisting of Ti, Ce, Co, Fe, Cu, and W, and optionally the metal is Ti. (Aspect 29) the non-stoichiometric metal oxide nanoparticle aggregates are blue non-stoichiometric titanium oxide nanoparticle aggregates; the titanium oxide nanoparticles of the aggregates comprise a heterogeneous phase of rutile and anatase; Optionally, the proportion of rutile phase is 65% to 85% and / or the nanoparticles are TiO 2 -Further comprising phase II, 29. An aggregate of non-stoichiometric metal oxide nanoparticles according to any one of embodiments 26 to 28.

Claims

1. 1. A method for forming aggregates of non-stoichiometric metal oxide nanoparticles, the method comprising the steps of: (a) dissolving a metal oxide nanoparticle in a solution of a non-stoichiometric metal oxide nanoparticle; (a) aerosolizing a heated mixture through a nozzle of a burner, the heated mixture comprising a combustible gas mixture and a volatile metal oxide precursor, the combustible gas mixture having an oxygen-lean equivalence ratio (φ), the combustible gas mixture being ignited at an outlet of the nozzle to provide a flame whereby the volatile metal oxide precursor decomposes and undergoes rapid nucleation and condensation to form non-stoichiometric metal oxide nanoparticles in the presence of the flame; and (b) depositing non-stoichiometric metal oxide nanoparticles onto a surface of a substrate to form aggregates of non-stoichiometric metal oxide nanoparticles on the surface of the substrate, the substrate being positioned at a fixed distance from the nozzle for a period of nanoparticle aggregation and oxidation. Including, The oxygen lean equivalence ratio (φ) of the combustible gas mixture is 1.5 or less; the velocity of the combustible gas mixture at the burner nozzle is 300-500 cm / s; the substrate is a rotatable substrate, and when rotated, deposition of the non-stoichiometric metal oxide nanoparticle agglomerates occurs only on a portion of the substrate in an area below the flame at any given time; the deposited non-stoichiometric metal oxide nanoparticle agglomerates are substantially removed from the surface of the rotatable substrate by a collection means or device, such that the deposited non-stoichiometric metal oxide nanoparticle agglomerates are continuously collected from the surface of the rotatable substrate as it rotates. method.

2. 2. The method of claim 1, wherein the oxygen lean equivalence ratio (φ) is 1.05 to 1.

5.

3. 3. The method of claim 2, wherein the oxygen lean equivalence ratio (φ) is 1.1 to 1.

4.

4. The method according to any one of claims 1 to 3, wherein the combustible gas mixture comprises an inert gas, oxygen, and either or both of hydrogen gas and hydrocarbon gas.

5. 5. The method of claim 4, wherein the inert gas represents 70% or more by volume of the combustible gas mixture, with the balance being oxygen and either or both of hydrogen gas and hydrocarbon gas.

6. the inert gas providing 75 to 79.9 vol% of the combustible gas mixture; the oxygen providing 10 to 17 vol% of the combustible gas mixture; the hydrogen gas and / or the hydrocarbon gas provides 5 to 10.1 vol% of the combustible gas mixture; The method of claim 5.

7. the inert gas providing 78 to 79.75 vol% of the combustible gas mixture; the oxygen providing 14.4 to 15 vol% of the combustible gas mixture; the hydrogen gas and / or the hydrocarbon gas provides 5.25 to 8 vol% of the combustible gas mixture; The method of claim 6.

8. (a) Injecting the volatile metal oxide precursor into the heated mixture at a flow rate of 2 mL / h to 100 mL / h; and / or (b) The method of any one of claims 1 to 7, wherein the concentration of the volatile metal oxide precursor in the combustible gas mixture is from 100 to 1,500 ppm.

9. 9. The method according to claim 1, wherein the temperature of the flame is between 1,500 and 2,500 K.

10. The method of any one of claims 1 to 9, wherein the rotatable substrate rotates at a speed of from 0.1 rpm to 500 rpm.

11. The method of claim 10, wherein the rotatable substrate is rotated at a speed of from 0.1 rpm to 20 rpm.

12. 12. The method of claim 11, wherein the method is operated for a period of time ranging from 1 minute to indefinite.

13. 10. The method of claim 1, wherein the deposited non-stoichiometric metal oxide nanoparticle aggregates are deposited on the surface of the rotatable substrate for a period of time between 1 second and 15 minutes.

14. 14. The method of claim 11 or 12 or the method of claim 13, wherein the rotatable substrate is actively cooled after passing through the flame.

15. The method according to any one of claims 1 to 14, wherein the distance between the nozzle of the burner and the substrate is 5 to 25 mm.

16. The method of any one of claims 1 to 15, wherein the temperature of the substrate is between 298K and 800K.

17. The method of any one of claims 1 to 16, wherein the volatile metal oxide precursor comprises a metal capable of forming a stable, reducible oxide.

18. 18. The method of claim 17, wherein the volatile metal oxide precursor comprises one or more metals selected from the group consisting of Ti, Ce, Co, Fe, Cu, and W.

19. The method of any one of claims 1 to 18, wherein the formed non-stoichiometric metal oxide nanoparticle aggregates contain oxygen vacancies.

20. The method of any one of claims 1 to 19, wherein the deposition in step (b) is carried out in an oxygen-containing environment.

21. 1. A device for forming aggregates of non-stoichiometric metal oxide nanoparticles, the device comprising: a burner; a rotatable stagnation plate; and a collection means or device; the burner comprising a nozzle and a feed intake adapted to receive a combustible gas mixture and a volatile metal oxide precursor; the rotatable stagnation plate comprises a plate and a motor, the plate having a circular substrate holding area, the motor for rotating the rotatable stagnation plate; the burner nozzle is adapted to be positioned at a fixed position within a portion of the circular substrate-holding area, and in use, a flame is generated from the nozzle such that aggregates of non-stoichiometric metal oxide nanoparticles are deposited on a surface of a substrate, the substrate being positioned within the circular substrate-holding area while the stagnation plate rotates; the collection means or device is configured to remove the non-stoichiometric metal oxide nanoparticle agglomerates from the surface of the substrate after deposition; device.

22. the collection means or collection device comprises a collector head, a blowing mechanism, and a collection vessel; the collector head comprises a scraper adapted to be placed in contact with the substrate so as to remove agglomerates of non-stoichiometric metal oxide nanoparticles deposited on a surface of the substrate; the blowing mechanism is adapted to supply gas to direct the removed agglomerates of non-stoichiometric metal oxide nanoparticles toward the collection vessel.

22. The device of claim 21.

23. the collecting means or collecting device comprises a collector head, the collector head comprising a body portion, a scraper, a plurality of holes, a collecting container, and a vacuum system; the scraper extends from the body portion and is adapted to be placed in contact with the substrate such that agglomerates of the non-stoichiometric metal oxide nanoparticles are removed from a surface of the substrate; the plurality of holes are in the body portion; 22. The device of claim 21, wherein the vacuum system is in fluid communication with the plurality of holes in the body portion and the collection vessel, and wherein, in use, the vacuum system transports the removed agglomerates of non-stoichiometric metal oxide nanoparticles from the substrate through the plurality of holes in the body portion and deposits them in the collection vessel.

24. 24. The device of any one of claims 21 to 23, further comprising a plurality of jet nozzles for cooling the rotatable stagnation plate by blowing gas onto a surface of the stagnation plate, the surface of the stagnation plate being opposite to the surface that comes into contact with a flame generated from the nozzles in use.

25. A non-stoichiometric metal oxide nanoparticle aggregate comprising a plurality of oxygen vacancies, each nanoparticle being 20 nm or less in size and having a disordered surface layer, the non-stoichiometric metal oxide nanoparticle aggregate being a blue non-stoichiometric titanium oxide nanoparticle aggregate, the titanium oxide nanoparticles of the aggregate comprising a heterogeneous phase of rutile and anatase.

26. 26. The non-stoichiometric metal oxide nanoparticle aggregate of claim 25, wherein the disordered surface layer has a thickness of 1 nm or less.

27. ​​The proportion of rutile phase is 65% to 85%, and / or the nanoparticles are TiO ２ 27. The non-stoichiometric metal oxide nanoparticle aggregate of claim 25 or 26, further comprising a -II phase.

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