A trivalent nickel-doped tungsten oxide hollow microsphere and its preparation method and application

Abstract

The present invention discloses trivalent nickel-doped tungsten oxide hollow microspheres, as well as a preparation method and application thereof. The method comprises the following steps: adding a calcium source to a mixed aqueous solution of a tungsten source and a surfactant, stirring uniformly, and then performing a hydrothermal reaction to produce a calcium tungstate hollow microsphere material; adding the calcium tungstate hollow microsphere material to an acid solution for reaction to obtain a precursor material; annealing the precursor material to produce tungsten oxide hollow microspheres; adding the tungsten oxide hollow microspheres to an ethanol solution of a nickel salt, continuing stirring until the ethanol solvent is completely evaporated; and after evaporation, annealing the resulting product to produce trivalent nickel-doped tungsten oxide hollow microspheres. The tungsten oxide hollow microspheres are prepared using a hydrothermal method and acid etching, and then a trivalent nickel-doped tungsten oxide gas-sensitive material is prepared using an oil bath evaporation method. The gas sensor prepared using the tungsten oxide hollow microspheres has the advantages of high response value, fast response recovery speed, excellent selectivity, and low detection limit for NO2 gas.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensing materials, and in particular relates to trivalent nickel-doped tungsten oxide hollow microspheres, a preparation method thereof, and applications in the field of gas sensing. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In today's world, nitrogen dioxide (NO2) is one of the most common pollutants, mainly coming from fossil fuel combustion, smelting processing, boiler exhaust and agricultural incineration. The concentration of nitrogen dioxide (NO2) has an important impact on air quality control, industrial health and environmental safety.

[0004] Metal-metal semiconductors (MOSs), such as SnO2, CuO, ZnO, In2O3, and WO3, are widely used in gaseous pollutant detection due to their low cost, ease of fabrication, and high stability. As an n-type semiconductor, WO3 offers advantages such as fast electron migration and non-toxicity, making it an excellent gas-sensing material. However, due to its unfilled 5d shell, WO3 sensors respond to a wide range of gases, including xylene, acetone, ethanol, sulfur dioxide, triethylamine, NH3, and NO2, resulting in generally poor selectivity. Furthermore, the slow response recovery and low response values of WO3 sensors further limit their practical applications.

[0005] In summary, the current tungsten oxide-based gas-sensitive materials still cannot meet the requirements of today's society for environmental protection. Therefore, it is very necessary to develop a tungsten oxide-based gas sensor with excellent gas-sensing properties. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention provides trivalent nickel-doped tungsten oxide hollow microspheres, their preparation method, and applications. The present invention utilizes a hydrothermal method and acid etching to prepare the tungsten oxide hollow microspheres. The trivalent nickel-doped tungsten oxide gas-sensing material is then prepared by oil-bath evaporation. The resulting gas sensor exhibits high NO2 response, rapid response recovery, excellent selectivity, and a low detection limit.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing trivalent nickel-doped tungsten oxide hollow microspheres, comprising the following steps:

[0009] A calcium source is added to a mixed aqueous solution of a tungsten source and a surfactant, stirred evenly, and then subjected to a hydrothermal reaction to prepare a calcium tungstate hollow microsphere material;

[0010] The calcium tungstate hollow microsphere material is added into an acid solution for reaction to obtain a precursor material, and the precursor material is annealed to obtain tungsten oxide hollow microspheres;

[0011] Add tungsten oxide hollow microspheres to the ethanol solution of nickel salt and continue stirring until the ethanol solvent is completely evaporated;

[0012] After the evaporation is completed, the obtained product is annealed to obtain trivalent nickel-doped tungsten oxide hollow microspheres.

[0013] In a second aspect, the present invention provides trivalent nickel-doped tungsten oxide hollow microspheres prepared by the aforementioned method, wherein the shell of the hollow microspheres is composed of randomly distributed nanosheets. The hollow microspheres have a diameter of approximately 3-5 μm and a shell thickness of 1 μm, and the shell is composed of randomly distributed nanosheets with a thickness of approximately 50 nm.

[0014] In a third aspect, the present invention provides a gas-sensitive element comprising a conductive substrate and a gas-sensitive layer, wherein the conductive substrate is a ceramic substrate provided with a gold conductive layer, the gas-sensitive layer is attached to the gold conductive layer, and the gas-sensitive material of the gas-sensitive layer is the trivalent nickel-doped tungsten oxide hollow microspheres.

[0015] In a fourth aspect, the present invention provides a method for preparing the gas sensor, comprising the following steps:

[0016] The trivalent nickel-doped tungsten oxide hollow microsphere material and water are prepared into a uniform slurry at a mass ratio of 1:1.5-5, and then the slurry is coated on a ceramic substrate with a gold conductive layer and dried to obtain a trivalent nickel-doped tungsten oxide hollow microsphere gas sensor.

[0017] The drying temperature is 60-150℃ and the drying time is 8-12h.

[0018] In a fifth aspect, the present invention provides the use of the trivalent nickel-doped tungsten oxide hollow microspheres or gas sensing elements in gas sensing detection.

[0019] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0020] 1) The present invention obtains trivalent nickel-doped tungsten oxide hollow microspheres, the disordered nanosheets on the surface of which constitute many voids and provide a large specific surface area, providing more adsorption sites for NO2 gas and facilitating the rapid diffusion of NO2 gas to the surface and interior of the hollow microspheres, thereby greatly improving its response value and response recovery speed.

[0021] 2) During the preparation process of the present invention, trivalent nickel-doped tungsten oxide hollow microspheres were successfully obtained by oil bath evaporation without changing the morphology; trivalent nickel ion doping effectively suppressed the amount of oxygen adsorbed on the surface of tungsten oxide, further improving the gas-sensing performance of the material.

[0022] 3) The trivalent nickel-doped tungsten oxide hollow microspheres prepared by the present invention were fabricated into gas sensors and subjected to gas sensitivity testing. The test results demonstrated that the gas sensor exhibited excellent performance for detecting NO₂ gas, including a high response value (396 for 10 ppm NO₂), a fast response recovery rate (13 s / 6 s), and excellent selectivity. This makes it suitable for rapidly detecting changes in NO₂ gas concentration, possessing a wide range of applications and promising prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 Scanning electron microscope (SEM) images of trivalent nickel-doped tungsten oxide hollow microspheres prepared in Examples 1-16 of the present invention;

[0025] Figure 2 X-ray diffraction (XRD) patterns of trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive materials prepared in Examples 4-7 of the present invention;

[0026] Figure 3 The spectrum of the strongest peak magnified area in the X-ray diffraction (XRD) pattern of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Examples 4-7 of the present invention;

[0027] Figure 4 Transmission electron microscope (TEM) images of trivalent nickel-doped tungsten oxide hollow microspheres prepared in Examples 4 and 6 of the present invention;

[0028] Figure 5 The X-ray photoelectron (XPS) spectrum of the strongest peak amplified region of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Examples 4-7 of the present invention;

[0029] Figure 6 is a nitrogen adsorption-desorption isotherm diagram of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention;

[0030] Figure 7 Schematic diagram of the gas sensor prepared by Example 6 of the present invention

[0031] Figure 8The response curves of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive materials prepared in Examples 4-7 of the present invention to 10 ppm NO2 at different temperatures are shown;

[0032] Figure 9 This is the response recovery curve of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 6 of the present invention to 10 ppm NO2 at 160°C;

[0033] Figure 10 This is a bar graph showing the response values of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 6 of the present invention to 10 ppm NO2 and 100 ppm other gases at 160°C;

[0034] Figure 11 This is a graph showing the stability of the gas-sensing performance of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention at 160°C with 10 ppm NO2;

[0035] Figure 12 This is a graph showing the continuous test of the gas-sensing performance of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention to different concentrations of NO2 at 160°C;

[0036] Figure 13 This is a response value curve of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 6 of the present invention to 10 ppm NO2 at 160°C within 30 days. DETAILED DESCRIPTION

[0037] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0038] In a first aspect, the present invention provides a method for preparing trivalent nickel-doped tungsten oxide hollow microspheres, comprising the following steps:

[0039] A calcium source is added to a mixed aqueous solution of a tungsten source and a surfactant, stirred evenly, and then subjected to a hydrothermal reaction to prepare a calcium tungstate hollow microsphere material;

[0040] The calcium tungstate hollow microsphere material is added into an acid solution for reaction to obtain a precursor material, and the precursor material is annealed to obtain tungsten oxide hollow microspheres;

[0041] Add tungsten oxide hollow microspheres to the ethanol solution of nickel salt and continue stirring until the ethanol solvent is completely evaporated;

[0042] After the evaporation is completed, the obtained product is annealed to obtain trivalent nickel-doped tungsten oxide hollow microspheres.

[0043] The preparation principle of the trivalent nickel-doped tungsten oxide hollow microsphere material in the present invention is:

[0044] The aqueous solution containing tungsten source, surfactant and calcium source is subjected to hydrothermal reaction. Under the action of high temperature, high pressure and surfactant, the generated tungstate ions combine with the calcium source to form a calcium tungstate hollow microsphere structure.

[0045] Calcium tungstate hollow microspheres are dissolved in an acid solution, where hydrogen ions react with calcium tungstate to produce tungstic acid. Annealing removes moisture, resulting in tungsten oxide hollow microspheres. Tungsten oxide is added to a nickel source solution. Because the ionic radius of trivalent nickel is smaller than that of oxygen ions, trivalent nickel ions readily replace tungsten ions under heating, with a small amount of nickel remaining attached to the surface of the tungsten oxide material as divalent nickel. Further annealing removes surface moisture, resulting in a trivalent nickel-doped tungsten oxide structure.

[0046] In some embodiments, the tungsten source is selected from Na2WO4·2H2O, Na2WO4·xH2O, or Na3PO4·12WO3·18H2O;

[0047] The surfactant is sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS);

[0048] The calcium source is selected from CaCl2 or Ca(NO3)2;

[0049] The nickel source is selected from Ni(CH3COO)·4H2O, NiCl2·6H2O or Ni(NO3)2·6H2O.

[0050] Preferably, the molar ratio of the tungsten source to the surfactant is 1:0.2-0.6.

[0051] In some embodiments, the mass ratio of the tungsten oxide hollow microspheres to the nickel salt is 1:0.01-0.05.

[0052] In some embodiments, the acid solution is selected from one or a mixture of two or more of HNO3, HCl, H2SO4 and H3PO4.

[0053] Preferably, H + The concentration is 1-3 mol / L.

[0054] In some embodiments, the mixed aqueous solution of the tungsten source and the surfactant is stirred for 10-90 min. If the stirring time is too short, the tungsten source and the surfactant are not fully dissolved; if the stirring time is too long, the hollow microspheres will rupture.

[0055] In some embodiments, the stirring time after adding the calcium source to the mixed aqueous solution of the tungsten source and the surfactant is 20-240 minutes. If the stirring time is too short, the calcium source will be unevenly dispersed; if the stirring time is too long, the guiding effect of the surfactant will be affected, thereby causing the hollow microspheres to rupture.

[0056] In some embodiments, the temperature of the hydrothermal reaction is 100-200° C., and the time is 2-30 h; preferably, the temperature of the hydrothermal reaction is 120-180° C., and the time is 18-24 h.

[0057] In some embodiments, the annealing temperature is 400-600° C., and the annealing time is 1.5-4.5 hours.

[0058] Preferably, the annealing temperature is 450-550° C. and the annealing time is 2-3 hours.

[0059] In some embodiments, the ethanol solvent is evaporated at a temperature of 60-150°C for 2.5-5.5 hours. Evaporation below 60°C results in slow ethanol evaporation, while evaporation above 150°C results in rapid ethanol evaporation, leading to nickel ion aggregation and negatively impacting performance.

[0060] Preferably, the ethanol solvent is evaporated at a temperature of 90-140° C. for 3.5-4.5 hours.

[0061] In a second aspect, the present invention provides trivalent nickel-doped tungsten oxide hollow microspheres prepared by the aforementioned method, wherein the shell of the hollow microspheres is composed of randomly distributed nanosheets. The hollow microspheres have a diameter of approximately 3-5 μm and a shell thickness of 1 μm, and the shell is composed of randomly distributed nanosheets with a thickness of approximately 50 nm.

[0062] In a third aspect, the present invention provides a gas-sensitive element comprising a conductive substrate and a gas-sensitive layer, wherein the conductive substrate is a ceramic substrate provided with a gold conductive layer, the gas-sensitive layer is attached to the gold conductive layer, and the gas-sensitive material of the gas-sensitive layer is the trivalent nickel-doped tungsten oxide hollow microspheres.

[0063] In a fourth aspect, the present invention provides a method for preparing the gas sensor, comprising the following steps:

[0064] The trivalent nickel-doped tungsten oxide hollow microsphere material and water are prepared into a uniform slurry at a mass ratio of 1:1.5-5, and then the slurry is coated on a ceramic substrate with a gold conductive layer and dried to obtain a trivalent nickel-doped tungsten oxide hollow microsphere gas sensor.

[0065] The drying temperature is 60-150℃ and the drying time is 8-12h.

[0066] In a fifth aspect, the present invention provides the use of the trivalent nickel-doped tungsten oxide hollow microspheres or gas sensing elements in gas sensing detection.

[0067] Trivalent nickel-doped tungsten oxide hollow microspheres have excellent detection performance for NO2, such as higher response value, faster response recovery speed and excellent selectivity.

[0068] The applications include indoor air pollution monitoring, industrial gas detection, vehicle exhaust emission detection, battery pre-combustion gas emission detection, etc.

[0069] The present invention will be further described below with reference to the embodiments.

[0070] Example 1

[0071] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0072] 1) Add 6 mmol Na2WO4·2H2O, 0.4 g SDS, and 0.1 g SLS to 30 mL deionized water;

[0073] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 25 ml of CaCl2 solution (0.2 M) was added.

[0074] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0075] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0076] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0077] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0078] Example 2

[0079] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0080] 1) Add 6 mmol of Na2WO4·2H2O and 0.5 g of SDS to 30 mL of deionized water;

[0081] 2) The solution in 1) was stirred at 25°C for 30 min, and then 25 ml of Ca(NO3)2 solution (0.2 M) was added.

[0082] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0083] 4) Add the powder described in 3) to 15 ml of 3M H2SO4 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 450°C for 2 hours to obtain a powdered tungsten oxide material.

[0084] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 3 h until the ethanol is completely evaporated.

[0085] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0086] Example 3

[0087] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0088] 1) Add 6 mmol Na2WO4·2H2O, 0.6 g SDS, and 0.1 g SLS to 30 mL deionized water;

[0089] 2) The solution in 1) was stirred at 25°C for 30 min, and then 25 ml of Ca(NO3)2 solution (0.2 M) was added.

[0090] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0091] 4) Add the powder from 3) to 20 ml of 2M HCl and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 550°C for 2 hours to obtain a powdered tungsten oxide material.

[0092] 5) Add the powder described in 4) to NiCl2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0093] 6) The powder produced in 5) was calcined at 450° C. for 2 h.

[0094] Example 4

[0095] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0096] 1) Add 6 mmol of Na2WO4·2H2O, 0.7 g of SDS, and 0.2 g of SLS to 30 mL of deionized water;

[0097] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 25 ml of CaCl2 solution (0.2 M) was added.

[0098] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0099] 4) Add the powder described in 3) to 10 ml of 4M H3PO4 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 550°C for 2 hours to obtain a powdered tungsten oxide material.

[0100] 5) Add the powder described in 4) to NiCl2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0101] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0102] Example 5

[0103] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0104] 1) Add 6 mmol Na2WO4·2H2O, 0.4 g SDS, and 0.1 g SLS to 30 mL deionized water;

[0105] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 25 ml of CaCl2 solution (0.2 M) was added.

[0106] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0107] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0108] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0109] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0110] Example 6

[0111] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0112] 1) Add 6 mmol Na2WO4·2H2O, 0.4 g SDS, and 0.1 g SLS to 30 mL deionized water;

[0113] 2) The solution in 1) was stirred at 25°C for 30 min, and then 25 ml of Ca(NO3)2 solution (0.2 M) was added.

[0114] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0115] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0116] 5) Add the powder described in 4) to Ni(CH3COO)·4H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0117] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0118] Example 7

[0119] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0120] 1) Add 6 mmol Na2WO4·2H2O, 0.4 g SDS, and 0.1 g SLS to 30 mL deionized water;

[0121] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 25 ml of CaCl2 solution (0.2 M) was added.

[0122] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0123] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0124] 5) Add the powder described in 4) to NiCl2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0125] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0126] Example 8

[0127] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0128] 1) Add 6 mmol of Na2WO4·2H2O and 0.5 g of SDS to 30 mL of deionized water;

[0129] 2) The solution in 1) was stirred at 25°C for 30 min, and then 25 ml of Ca(NO3)2 solution (0.2 M) was added.

[0130] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0131] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0132] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0133] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0134] Example 9

[0135] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0136] 1) Add 6 mmol of Na2WO4·2H2O and 0.5 g of SDS to 30 mL of deionized water;

[0137] 2) The solution in 1) was stirred at 25°C for 30 min, and then 25 ml of Ca(NO3)2 solution (0.2 M) was added.

[0138] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0139] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0140] 5) Add the powder described in 4) to NiCl2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0141] 6) The powder produced in 5) was calcined at 500° C. for 2 h.

[0142] Example 10

[0143] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0144] 1) Add 4 mmol of Na2WO4·2H2O and 0.5 g of SDS to 30 mL of deionized water;

[0145] 2) The solution in 1) was stirred at 25°C for 30 min, and then 25 ml of Ca(NO3)2 solution (0.3 M) was added.

[0146] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 21 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0147] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0148] 5) Add the powder described in 4) to Ni(CH3COO)·4H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0149] 6) The powder produced in 5) was calcined at 450° C. for 2 h.

[0150] Example 11

[0151] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0152] 1) Add 5 mmol of Na2WO4·2H2O, 0.6 g of SDS, and 0.1 g of SLS to 30 mL of deionized water;

[0153] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 25 ml of CaCl2 solution (0.2 M) was added.

[0154] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 28 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0155] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0156] 5) Add the powder described in 4) to Ni(CH3COO)·4H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0157] 6) The powder produced in 5) was calcined at 450° C. for 2 h.

[0158] Example 12

[0159] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0160] 1) Add 4 mmol of Na2WO4·2H2O, 0.6 g of SDS, and 0.1 g of SLS to 30 mL of deionized water;

[0161] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 25 ml of CaCl2 solution (0.2 M) was added.

[0162] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 22 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0163] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0164] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0165] 6) The powder produced in 5) was calcined at 500° C. for 2 h.

[0166] Example 13

[0167] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0168] 1) Add 6 mmol of Na2WO4·2H2O, 0.7 g of SDS, and 0.2 g of SLS to 30 mL of deionized water;

[0169] 2) The solution prepared in 1) was stirred at 25°C for 30 min, and then 15 ml of CaCl2 solution (0.3 M) was added.

[0170] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 160° C. for 26 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0171] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0172] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0173] 6) The powder produced in 5) was calcined at 500° C. for 2 h.

[0174] Example 14

[0175] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0176] 1) Add 5 mmol of Na2WO4·2H2O, 0.7 g of SDS, and 0.2 g of SLS to 30 mL of deionized water;

[0177] 2) The solution prepared in 1) was stirred at 30°C for 30 min, and then 35 ml of CaCl2 solution (0.1 M) was added.

[0178] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 150° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0179] 4) Add the powder from 3) to 15 ml of 3M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0180] 5) Add the powder described in 4) to Ni(CH3COO)·4H2O in ethanol and stir for 2 h until the ethanol is completely evaporated.

[0181] 6) The powder produced in 5) was calcined at 400° C. for 2 h.

[0182] Example 15

[0183] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0184] 1) Add 6 mmol of Na2WO4·2H2O and 0.5 g of SDS to 30 mL of deionized water;

[0185] 2) The solution in 1) was stirred at 25°C for 30 min, and then 15 ml of Ca(NO3)2 solution (0.3 M) was added.

[0186] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 170° C. for 24 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0187] 4) Add the powder from 3) to 10 ml of 4M HNO3 and stir for 24 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0188] 5) Add the powder described in 4) to NiCl2·6H2O in ethanol and stir for 3 h until the ethanol is completely evaporated.

[0189] 6) The powder produced in 5) was calcined at 450° C. for 2 h.

[0190] Example 16

[0191] A method for preparing a trivalent nickel-doped tungsten oxide hollow microsphere material, the preparation method comprising the following steps:

[0192] 1) Add 7 mmol of Na2WO4·2H2O, 0.7 g of SDS, and 0.2 g of SLS to 30 mL of deionized water;

[0193] 2) The solution in 1) was stirred at 25°C for 30 min, and then 30 ml of Ca(NO3)2 solution (0.3 M) was added.

[0194] 3) The solution in 2) was transferred to a 100 mL autoclave, hydroheated at 130° C. for 26 h, cooled, centrifuged, washed, washed three times with water and three times with anhydrous ethanol, and dried in an oven at 80° C. for 12 h to obtain a powdered calcium tungstate material.

[0195] 4) Add the powder from 3) to 20 ml of 4M HNO3 and stir for 15 hours. Collect the yellow product, centrifuge it with distilled water and ethanol, dry it at 60°C for 12 hours, and anneal it at 500°C for 2 hours to obtain a powdered tungsten oxide material.

[0196] 5) Add the powder described in 4) to Ni(NO3)2·6H2O in ethanol and stir for 3 h until the ethanol is completely evaporated.

[0197] 6) The powder produced in 5) was calcined at 550° C. for 2 h.

[0198] Example 17

[0199] The powdered tungsten oxide and trivalent nickel-doped tungsten oxide hollow microspheres prepared in Examples 1-16 were prepared into gas sensors. The preparation method is as follows:

[0200] A certain amount of the prepared powdered tungsten oxide and trivalent nickel-doped tungsten oxide hollow microspheres were weighed and added to a mortar. The prepared powder was mixed with 3 ml of water to obtain a uniform slurry. The slurry was then applied to a ceramic substrate and dried at 80°C for 10 minutes. After applying 3 to 5 times, it was sintered at 100°C for 10 hours, and the substrate was welded to the base to make a gas sensor. The sensor was aged at 200°C for 30 days to stabilize the resistance. Ra is the stable resistance of the sensor in air, Rg is the stable resistance of the sensor in NO2, and Rg / Ra represents the response value (S) of the sensor at an ambient temperature of 25°C and a humidity of 50%. Generally, the response time and recovery time are characterized by the time it takes to inject or pump out the gas when the response value changes to 90% of the stable condition. Figure 5 The gas sensor used in Example 15 is shown - an alumina ceramic substrate. The ceramic substrate is connected to the circuit via four platinum wires 3 for gas sensor testing. The two ends of the ceramic substrate are respectively 1 test electrode and 4 gold heating electrodes. A layer of powdered tungsten oxide prepared in Example 1-16 and trivalent nickel-doped tungsten oxide hollow microspheres are coated on one side of the test electrode.

[0201] Performance testing:

[0202] Application test of tungsten oxide and trivalent nickel-doped tungsten oxide hollow microspheres as gas-sensitive materials.

[0203] Figure 1Scanning electron microscope (SEM) photos of trivalent nickel-doped tungsten oxide hollow microspheres prepared in Examples 1-16 of the present invention. It can be seen that all the microspheres have a diameter between 3 and 5 μm, the wall thickness of the hollow microspheres is about 1 μm, and they are composed of nanosheets with a thickness of about 50 nm. 3+ After that, the layered hollow structure was still maintained, and the surface morphology did not change with the Ni 3+ The concentration of Ni 3+ The layered hollow structure can be maintained.

[0204] Figure 2 The X-ray diffraction (XRD) patterns of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive materials prepared in Examples 4-7 of the present invention are shown in Table 1. 3+ All diffraction peaks of the WO3 sample are consistent with the monoclinic structure of WO3 (JCPDS 83-0950). In addition, there are no obvious nickel-related diffraction peaks, indicating that trivalent nickel ions exist in the tungsten oxide lattice in the form of doping, and the doping amount is low.

[0205] Figure 3 The X-ray diffraction (XRD) pattern of the strongest peak magnified region of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 4-7 of the present invention. The peak in this region first shifts to a larger angle with the increase of Ni concentration, indicating that Ni 3+ May occupy W 6+ After that, the peak of 5wt% Ni-WO3 shifts to a smaller angle than that of pure WO3, indicating that Ni 3+ It may be integrated into the interstitial position of the WO3 lattice.

[0206] Figure 4 Transmission electron microscope (TEM) photos of trivalent nickel-doped tungsten oxide hollow microspheres prepared in Examples 4 and 6 of the present invention. The brightness contrast between the spherical shell and the center in the figure further confirms that pure WO3 and 3wt% Ni-WO3 are hollow microspheres. The lattice fringes of pure WO3 are about 0.377nm, corresponding to the (020) crystal plane of pure WO3 (JCPDS83-0950). The (020) crystal plane spacing of 3wt% Ni-WO3 is 0.372nm, and the (020) crystal plane spacing of 3wt% Ni-WO3 is significantly smaller than that of pure WO3, further confirming that Ni 3+ Replaced W 6+ At the same time, no NiO was found in the transmission electron microscope, which may be due to the low Ni content.

[0207] Figure 5This is the X-ray photoelectron (XPS) spectrum of the strongest peak amplified region of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 4-7 of the present invention. Figure 1 As can be seen from the XPS spectra of all samples, O, W and C elements were found, and Ni 2p peaks were observed, confirming the presence of Ni element in 1-5wt% doped WO3 samples. Figure 2 There are two peaks at 35.3eV and 37.5eV, proving the presence of W 6+ In addition, compared with pure WO3 samples, the W 4f peaks of WO3 samples doped with 1-5wt% Ni shift to lower binding energies, which may be affected by the electronegativity of Ni. Figure 3 As shown, the peaks at 855.44eV, 859.66eV and 872.25eV binding energy prove that Ni 3+ and Ni 2+ The existence of Ni 3+ Occupy W 6+ lattice site, Ni 2+ NiO is formed and loaded onto the WO3 surface. Figure 4 As shown. O1s can be fitted into three components: lattice oxygen (530±0.1eV), vacancy oxygen (531.8±0.1eV) and chemically adsorbed oxygen (533.3±0.1eV). The proportion of chemically adsorbed oxygen in the 3wt% Ni-WO3 sample is low, and the proportion of vacancy oxygen is higher than that in the pure WO3 sample, indicating that Ni 3+ The doping of α-doped ...

[0208] Figure 6 The nitrogen adsorption-desorption isotherm of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 6 of the present invention is shown in FIG. The adsorption isotherm is type-III, the hysteresis loop is type-H3, and the BET specific surface area of the sample is 29.134 m 2 / g, providing a larger specific surface area for gas reaction.

[0209] Figure 7 This is a schematic diagram of a gas sensor fabricated in Example 6 of the present invention. Four platinum wires serve as connecting electrodes, and a gold coating serves as a conductive electrode. The front of the ceramic substrate serves as a test electrode, onto which the prepared gas-sensing material slurry is applied. The back of the ceramic substrate serves as a heating electrode, providing heat.

[0210] Figure 8The following are curves showing the response values of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive materials prepared in Examples 4-7 of the present invention to 10 ppm NO2 at different temperatures. The responses of all sensors were highest at 160°C and decreased after exceeding 160°C. Obviously, the optimal operating temperature is 160°C. Compared with the pure WO3 sensor, the response values of the 1-5wt% Ni-WO3 sensors increased to varying degrees. At 160°C, the 3wt% Ni-WO3 sensor had the highest response value (396) to 10 ppm NO2, which was approximately 6 times that of the pure WO3 sensor (66).

[0211] Figure 9 This is the response recovery curve of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensitive material prepared in Example 6 of the present invention to 10ppm NO2 at 160℃. The recovery time (6s) of 3wt% Ni-WO3 is much shorter than that of pure WO3 (32s), and the response time (13s) is also significantly shorter than that of pure WO3 (20s), indicating that the appropriate amount of Ni 3+ Doping improves the response recovery speed.

[0212] Figure 10 This is a bar graph showing the responses of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention to 10 ppm NO2 and 100 ppm other gases at 160°C. The selectivity graph shows that the trivalent nickel-doped tungsten oxide hollow microspheres have a high response to NO2, but almost no response to several other interfering gases such as CO and CH4, indicating that trivalent nickel doping greatly improves the selectivity of the gas-sensing material.

[0213] Figure 11 This graph shows the stability of the gas-sensing performance of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention at 160°C in the presence of 10 ppm NO₂. Five cycles of testing revealed no significant changes in the sample's response value or corresponding recovery time, demonstrating the excellent repeatability of this gas-sensing sample.

[0214] Figure 12 This graph shows the gas-sensing performance of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention, tested continuously at 160°C for various NO₂ concentrations. It can be seen that the response value increases with increasing NO₂ concentration. Furthermore, the detection limit for 3wt% Ni-WO₃ is 100 ppb, with a response value of 1.92, which is higher than that of pure WO₃. This demonstrates that trivalent nickel doping has a positive impact on the gas-sensing material's ability to detect ppb-level NO₂.

[0215] Figure 13This is a graph showing the response of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material prepared in Example 6 of the present invention to 10 ppm NO2 at 160°C over 30 days. As can be seen from the graph, the response of the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material did not change significantly over the 30 days, indicating that the trivalent nickel-doped tungsten oxide hollow microsphere gas-sensing material has excellent long-term stability.

[0216] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing trivalent nickel-doped tungsten oxide hollow microspheres, characterized by: The steps include: A calcium source is added to a mixed aqueous solution of a tungsten source and a surfactant, stirred evenly, and then subjected to a hydrothermal reaction to prepare a calcium tungstate hollow microsphere material; The calcium tungstate hollow microsphere material is added into an acid solution for reaction to obtain a precursor material, and the precursor material is annealed to obtain tungsten oxide hollow microspheres; Add tungsten oxide hollow microspheres to the ethanol solution of nickel salt and continue stirring until the ethanol solvent is completely evaporated; After the evaporation is completed, the obtained product is annealed to obtain trivalent nickel-doped tungsten oxide hollow microspheres; The tungsten source is selected from Na2WO4·2H2O, Na2WO4·xH2O or Na3PO4·12WO3·18H2O; The calcium source is selected from CaCl2 or Ca(NO3)2; The nickel salt is selected from Ni(CH3COO)·4H2O, NiCl2·6H2O or Ni(NO3)2·6H2O.

2. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, wherein: The surfactant is sodium dodecyl sulfate or sodium lauryl sulfate; the molar ratio of the tungsten source to the surfactant is 1:0.2-0.

6.

3. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, characterized in that: The mass ratio of tungsten oxide hollow microspheres to nickel salt is 1:0.01-0.

05.

4. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, wherein: The acid solution is selected from one or a mixture of two or more of HNO3, HCl, H2SO4 and H3PO4; + The concentration is 1-3 mol / L.

5. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, wherein: The time for stirring and mixing the mixed aqueous solution of the tungsten source and the surfactant is 10-90 minutes; the time for stirring after adding the calcium source to the mixed aqueous solution of the tungsten source and the surfactant is 20-240 minutes.

6. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 100-200°C and the time is 2-30h.

7. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 6, characterized in that: The temperature of the hydrothermal reaction is 120-180°C and the time is 18-24 hours.

8. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, characterized in that: The annealing temperature is 400-600°C and the time is 1.5-4.5h.

9. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 8, characterized in that: The annealing temperature is 450-550℃ and the time is 2-3h.

10. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 1, characterized in that: The ethanol solvent is evaporated at a temperature of 60-150° C. for 2.5-5.5 hours.

11. The method for preparing trivalent nickel-doped tungsten oxide hollow microspheres according to claim 10, characterized in that: The ethanol solvent is evaporated at a temperature of 90-140° C. for 3.5-4.5 hours.

12. A trivalent nickel-doped tungsten oxide hollow microsphere, characterized by: The hollow microspheres are prepared by the preparation method according to any one of claims 1 to 11, and the shells of the hollow microspheres are composed of disorderly distributed nanosheets.

13. A gas sensor, characterized in that: It includes a conductive substrate and a gas-sensitive layer, wherein the conductive substrate is a ceramic substrate provided with a gold conductive layer, the gas-sensitive layer is attached to the gold conductive layer, and the gas-sensitive material of the gas-sensitive layer is the trivalent nickel-doped tungsten oxide hollow microspheres described in claim 12.

14. The method for preparing the gas sensor according to claim 13, characterized in that: The steps include: The trivalent nickel-doped tungsten oxide hollow microsphere material and water are mixed in a mass ratio of 1:1.5-5 to prepare a uniform slurry, and then the slurry is coated on a ceramic substrate with a gold conductive layer and dried to obtain a trivalent nickel-doped tungsten oxide hollow microsphere gas sensor; The drying temperature is 60-150℃ and the drying time is 8-12h.

15. Use of the trivalent nickel-doped tungsten oxide hollow microspheres according to claim 12 or the gas sensor according to claim 13 in gas sensing detection.

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