Tungsten-doped tin dioxide nanopowder, method for preparing the same, and application of the same in semiconductor-type gas sensing elements

Abstract

This invention relates to a tungsten-doped tin dioxide nanopowder, its preparation method, and its application in semiconductor-type gas-sensitive elements. The method for preparing the tungsten-doped tin dioxide nanopowder includes the following steps: dissolving a soluble tungsten compound and a soluble tin compound in an aqueous solution containing a surfactant, and adding a complexing agent to obtain a homogeneous metal ion mixed solution; adding a precipitant to the mixed solution under stirring conditions to adjust the pH to 2-6, causing a metal hydroxide precursor to precipitate; aging, solid-liquid separation, washing, and drying the precipitate to obtain a precursor powder; adding a dispersant to the precursor powder and mixing evenly; and calcining to obtain the tungsten-doped tin dioxide nanopowder. The tungsten-doped tin dioxide nanopowder of this invention can be used in the preparation of semiconductor-type gas-sensitive sensors, ultraviolet detectors, lithium-ion battery anode materials, catalysts, or transparent conductive films.

Description

Technical Field

[0001] This invention relates to the field of functional oxide materials and sensor technology, specifically to a tungsten-doped tin dioxide nanopowder, its preparation method, and its application in semiconductor-type gas-sensitive elements. Background Technology

[0002] Tin dioxide (SND) is a wide-bandgap n-type semiconductor oxide with a bandgap of approximately 3.6 eV, and has a long history of application in gas sensing. Due to its low manufacturing cost, good chemical stability, and mature processing technology, it is widely used in semiconductor-type gas sensors. During operation, oxygen adsorbed on the SND surface undergoes a redox reaction with the detected gas, altering the thickness of the depletion layer and thus changing the overall conductivity of the material. This mechanism is simple and reliable; however, undoped SND often exhibits weak output signals in low-concentration gas detection, shows little difference in response to different gases, and requires higher operating temperatures to achieve ideal sensitivity, leading to higher energy consumption and accelerated thermal aging of the material.

[0003] Under long-term operating conditions, undoped tin dioxide is prone to stability issues such as baseline drift and response decay. This is related to its unstable oxygen vacancy distribution and insufficient surface active sites. To improve these shortcomings, researchers have attempted to modify the device through doping to adjust carrier concentration, alter defect states, suppress grain growth, and to some extent optimize specific surface area and pore structure. These methods can improve the sensitivity and selectivity of gas-sensitive elements, and some doped systems can even lower the optimal operating temperature.

[0004] Tungsten is a high-melting-point transition metal element with multiple valence states. When incorporated into the tin dioxide lattice, W... 6+ Replace Sn 4+ Tungsten can form acceptor states, compensate for intrinsic electrons, reduce carrier concentration, and increase the Debye length, thereby enhancing the modulation effect of surface reactions on overall conductivity. Simultaneously, tungsten doping can stabilize oxygen vacancy distribution, improving response repeatability and long-term stability. Under suitable process conditions, tungsten ions can also suppress excessive grain growth, keeping the grain size within a range matching the Debye length, thus balancing sensitivity and response speed.

[0005] However, existing technologies still have shortcomings in the preparation and application of tungsten-doped tin dioxide. The lack of systematic optimization of process parameters such as doping ratio, precipitation conditions, and calcination procedures makes it difficult to replicate experimental results. The additive systems are mostly conventional choices, offering limited control over particle size and pore structure, making it difficult to overcome the bottlenecks in low-temperature response and long-term stability. Furthermore, the powder exhibits insufficient adhesion and poor uniformity during film formation and integration with packaged materials or wafers, making it difficult to guarantee inter-wafer performance consistency. Therefore, there is still a need to develop a tungsten-doped tin dioxide nanopowder with a clearly defined composition range, novel additive system, reproducible process, and direct compatibility with packaging production to comprehensively improve the overall performance of gas-sensitive components. Summary of the Invention

[0006] In view of the above-mentioned technical defects in the prior art, the present invention provides a tungsten-doped tin dioxide nanopowder with a clear composition range and reproducible process and its preparation method, and provides an application path that can be directly connected to gas-sensitive chip packaging to improve the sensitivity, selectivity and long-term stability of gas-sensitive elements.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for producing tungsten-doped tin dioxide nanopowder, comprising the following steps:

[0009] (1) Dissolve soluble tungsten compounds and soluble tin compounds in an aqueous solution containing surfactants, and add a complexing agent to obtain a homogeneous mixed solution of metal ions;

[0010] (2) Add a precipitant to the mixed solution under stirring conditions and adjust the pH to 2-6 to precipitate the metal hydroxide precursor;

[0011] (3) The precipitate is aged, separated into solid and liquid, washed and dried to obtain precursor powder;

[0012] (4) Add a dispersant to the precursor powder and mix thoroughly;

[0013] (5) The tungsten-doped tin dioxide nanopowder was obtained by calcination.

[0014] Preferably, the molar ratio of tin to tungsten is set to 1:1-12:1; more preferably 2:1-10:1; more preferably 3:1-8:1; and most preferably 4:1-8:1.

[0015] Preferably, the soluble tungsten compound is selected from: tungsten hexachloride, sodium metatungstate, ammonium metatungstate, metatungstic acid, and tungstate.

[0016] Preferably, the soluble tin compound is selected from: tin tetrachloride, stannous chloride, tin nitrate, tin sulfate and their hydrates.

[0017] Preferably, the surfactant is at least one of anionic, cationic, or nonionic surfactants, and more preferably sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, or polyoxyethylene alkyl ether.

[0018] Preferably, the complexing agent is an organic compound or its salt that can form a stable complex with tin and tungsten cations and inhibit premature hydrolysis, and is selected from one or more of polyphosphate complexing agents, phosphorylated cyclodextrin salts, polycarboxylic acids and their salts, polyamine polycarboxylic acid chelating agents, and organophosphonic acids.

[0019] More preferably, the polyphosphate complexing agent is at least one selected from phytic acid, sodium phytate, polyphosphate, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, and sodium metaphosphate.

[0020] The phosphorylated cyclodextrin salt is β-cyclodextrin sodium phosphate (CAS: 199684-61-2).

[0021] The polycarboxylic acids and their salts are at least one of citric acid or sodium citrate, tartaric acid or sodium tartrate, oxalic acid or sodium oxalate, malic acid, lactic acid, gluconic acid or their salts.

[0022] The polyamine polycarboxylic acid chelating agent is ethylenediaminetetraacetic acid and its salts, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(β-aminoethyl ether)tetraacetic acid, ethylenediaminedisuccinic acid, and iminotriacetic acid. The organophosphonic acid includes at least one of hydroxyethylidene diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, iminotrimethylenephosphonic acid, ethylenediaminedimethylenephosphonic acid, 1-hydroxypropylidene diphosphonic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0023] Most preferably, the complexing agent is composed of sodium citrate, sodium phytate, and sodium β-cyclodextrin phosphate, with a mass ratio of sodium citrate, sodium phytate, and sodium β-cyclodextrin phosphate of 10:(2-6):(1-3). Sodium citrate, with its moderately strong tricarboxylic acid ligand field, first balances the hydrolysis and condensation rates of tetravalent tin and hexavalent tungsten, causing both to enter critical supersaturation within the same time window. Sodium phytate, as a high-charge-density polyphosphate multidentate ligand, provides stronger and transmetallic bridging coordination for tin and tungsten in the same solution phase, and its multi-anionic shell imparts strong electrostatic repulsion, thereby inhibiting aggregation and tungsten-rich phase separation after nucleation at the nanoscale. Sodium β-cyclodextrin phosphate provides weak to moderate coordination and surface charge stability with its external phosphate groups, while its cyclic framework forms a spatial confinement of a soft template, allowing the solvated metal complex to undergo synergistic nucleation and confined growth within the nanocavity. The combined effect of these three factors results in the formation of a uniformly composed tin-tungsten coprecipitate precursor. During subsequent drying and calcination, the organic framework undergoes pyrolysis, forming interconnected micropores. Simultaneously, multidentate coordination inhibits abnormal growth and the precipitation of external tungsten oxide in the early stages of crystallization, making tungsten more inclined to enter the tin dioxide lattice through substitution sites and achieving controllable oxygen vacancy density and grain size. Ultimately, this achieves a match between Debye length and grain size, simultaneously optimizing surface reactivity and gas diffusion channels, thus exhibiting a higher response amplitude and shorter response time under the same conditions.

[0024] Preferably, the precipitant is an alkaline solution containing hydroxide ions, and more preferably ammonia water, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or ammonium carbonate aqueous solution.

[0025] Preferably, the dispersant is selected from polyethylene glycol, sodium polyacrylate, polyoxyethylene-polyoxypropylene block copolymer and combinations thereof, wherein the average molecular weight of the polyethylene glycol is 200-6000.

[0026] Preferably, the method for producing tungsten-doped tin dioxide nanopowder includes the following steps:

[0027] (1) Dissolve 1-6g of tungsten hexachloride and 5-15g of tin tetrachloride pentahydrate in 80-160mL of 0.4-1.2mol / L surfactant aqueous solution, and add 10-30mL of 80-140g / L complexing agent aqueous solution to obtain a homogeneous metal ion mixed solution; at the same time, control the molar ratio of tin to tungsten to be (1-12):1;

[0028] (2) Add a precipitant to the mixed solution under stirring conditions and adjust the pH to 2-6 to precipitate the metal hydroxide precursor;

[0029] (3) The precipitate is aged, separated into solid and liquid, washed and dried to obtain precursor powder;

[0030] (4) Add 0.02-0.08g of dispersant to the precursor powder and mix evenly;

[0031] (5) Calcination at 500-700℃ to obtain the tungsten-doped tin dioxide nanopowder.

[0032] The present invention also provides a tungsten-doped tin dioxide nanopowder, which is prepared by the above method. The nanopowder is mainly composed of tin dioxide, with tungsten as the dopant element, and the molar ratio of tin to tungsten is 1:1-12:1; preferably, the molar ratio of tin to tungsten is 2:1-10:1; more preferably, the molar ratio of tin to tungsten is 2:1-8:1.

[0033] The average grain size of the nanopowder is 5-100 nanometers, and the specific surface area is 10-150 m² / g.

[0034] The present invention also provides the use of the above-mentioned tungsten-doped tin dioxide nanopowder in the preparation of semiconductor gas sensors, ultraviolet detectors, lithium-ion battery anode materials, catalysts or transparent conductive films.

[0035] The present invention also provides a gas-sensitive device, including a substrate, a heating electrode and a detection electrode disposed on the substrate, and the aforementioned tungsten-doped tin dioxide nanopowder sensitive layer covering the detection electrode.

[0036] In the tungsten-doped tin dioxide nanopowder of this invention, the tin-tungsten molar ratio determines the carrier concentration and Debye length, thereby regulating the depletion region and carrier transport characteristics on the gas-sensitive layer surface. An excessively high tungsten ratio leads to a low carrier concentration and weakened response; an excessively high tin ratio results in an excessively high electron concentration, faster response speed but decreased sensitivity. Considering both stability and performance, this invention controls the tin-tungsten molar ratio between 1:1 and 12:1 to achieve a reasonable match between the Debye length and grain size. By introducing tungsten into the crystal lattice and combining it with controlled pH precipitation and segmented calcination, a porous structure with uniform particle size and controllable defect distribution can be obtained, improving gas adsorption activity, accelerating the reaction rate, and reducing operating temperature and power consumption.

[0037] This invention utilizes the multidentate coordination and buffering effect of complexing agents to suppress differential hydrolysis of tin and tungsten salts, achieving molecular-level mixing and uniform doping. Some of the complexing agents can also form micro / mesopores in situ during calcination, further improving specific surface area and pore connectivity. The resulting powder exhibits higher response values, faster response speeds, and good device consistency and stability under the same conditions. The overall inventive concept lies in controlling the synthesis system of tin-tungsten precursors, introducing a complexation-dispersion synergistic mechanism, and combining it with programmed temperature calcination to obtain dense, uniformly doped tungsten-doped tin dioxide nanoparticles, thereby achieving efficient and sensitive detection of ozone. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 Here is a SEM image of tungsten-doped tin dioxide nanopowder from Example 1;

[0040] Figure 2 This is a distribution diagram of O element in tungsten-doped tin dioxide nanopowder in Example 1;

[0041] Figure 3 The distribution diagram of Sn element in tungsten-doped tin dioxide nanopowder in Example 1;

[0042] Figure 4 This is a distribution diagram of W element in tungsten-doped tin dioxide nanopowder in Example 1;

[0043] Figure 5 The image shows the XRD pattern of tungsten-doped tin dioxide nanopowder from Example 1. Detailed Implementation

[0044] The invention will now be described in further detail with reference to specific embodiments, but it should not be construed as limiting the scope of the invention to the following embodiments.

[0045] Example 1:

[0046] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, and add 20 mL of 120 g / L sodium citrate aqueous solution. Place the solution in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0047] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0048] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0049] like Figure 1 As shown, this is a SEM image of the prepared tungsten-doped tin dioxide nanoparticles observed using a scanning electron microscope, followed by SEM-EDS elemental analysis. Figure 2 , Figure 3 and Figure 4 As shown, O, Sn and W elements are uniformly distributed inside the material, and the tungsten-doped tin dioxide nanopowder prepared by this method has high doping uniformity.

[0050] By performing XRD analysis on the prepared material, such as Figure 4 The XRD pattern of tungsten-doped tin dioxide nanoparticles is shown, with the crystal corresponding to the peak in the spectrum marked in the upper right corner. The XRD pattern reveals that tungsten doping significantly shifts the peaks of tin dioxide and forms a new Sn-W oxide crystal structure. Tungsten is an effective dopant incorporated into the tin dioxide crystal.

[0051] Example 2:

[0052] Weigh 1.32 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 8:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L sodium citrate aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0053] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0054] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 8:1.

[0055] Example 3

[0056] Weigh 1.76 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 6:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L sodium citrate aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0057] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0058] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 6:1.

[0059] Example 4

[0060] Weigh 5.28 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 2:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L sodium citrate aqueous solution, and place in a 60 °C water bath and stir thoroughly to obtain a transparent solution.

[0061] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0062] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 2:1.

[0063] Example 5:

[0064] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L complexing agent aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0065] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0066] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0067] The complexing agent is sodium phytate.

[0068] Example 6:

[0069] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L complexing agent aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0070] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0071] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0072] The complexing agent is sodium β-cyclodextrin phosphate.

[0073] Example 7:

[0074] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L complexing agent aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0075] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0076] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0077] The complexing agent is a compound of sodium citrate and sodium phytate in a mass ratio of 10:6.

[0078] Example 8:

[0079] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L complexing agent aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0080] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0081] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0082] The complexing agent is a compound of sodium citrate and sodium β-cyclodextrin phosphate in a mass ratio of 10:6.

[0083] Example 9:

[0084] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1), dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution, add 20 mL of 120 g / L complexing agent aqueous solution, and place in a water bath at 60 °C and stir thoroughly to obtain a transparent solution.

[0085] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the transparent solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0086] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0087] The complexing agent is a compound of sodium citrate, sodium phytate, and sodium β-cyclodextrin phosphate in a mass ratio of 10:4:2.

[0088] Example 10:

[0089] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1) and dissolve them in 100 mL of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution. Add 20 mL of 120 g / L complexing agent aqueous solution and 0.12 g of 1-ethyl-3-methylimidazolium dihydrogen phosphate ionic liquid [EMIM][H2PO4] (CAS: 262297-14-3). Place the solution in a water bath at 60 °C and stir thoroughly to obtain a homogeneous solution.

[0090] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0091] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0092] The complexing agent is a compound of sodium citrate, sodium phytate, and sodium β-cyclodextrin phosphate in a mass ratio of 10:4:2.

[0093] Comparative Example 1:

[0094] Weigh 2.64 g of tungsten hexachloride and 9.35 g of tin tetrachloride pentahydrate (the molar ratio of tin to tungsten is 4:1) and dissolve them in 100 ml of 0.8 mol / L sodium dodecylbenzenesulfonate aqueous solution. Place the solution in a water bath at 60 °C and stir thoroughly until homogeneous.

[0095] Ammonia solution with a volume fraction of 25% was used as a precipitant and added dropwise to the solution at a uniform rate. The pH of the solution was adjusted to 3, and stirring was continued until the precipitation reaction was complete. After the reaction was completed, the solution was aged for 2 hours, then filtered and washed with deionized water until no chloride ions were detected. The resulting precipitate was the precursor of tin-tungsten mixed hydroxide.

[0096] The precursor was placed in a vacuum drying oven and dried to constant weight at 80℃. After grinding into powder, 0.05g of polyethylene glycol-600 was added and ground evenly. Finally, the mixture was placed in a muffle furnace and heated at a rate of 5℃ / min. The temperature was first raised to 100℃ and held for 1 hour, then raised to 600℃ and calcined for 2 hours. After natural cooling, the powder was removed to obtain tungsten-doped tin dioxide nanopowder with a tin to tungsten molar ratio of 4:1.

[0097] Test Example 1:

[0098] Device fabrication:

[0099] Weigh 10.00 g of ethyl cellulose, add 90.00 g of α-terpineol, and mechanically stir in a water bath at 65°C for 90 min until completely dissolved to obtain a 10 wt% ethyl cellulose / α-terpineol solution, which is the binder solution.

[0100] Weigh 1.000 g of tungsten-doped tin dioxide nanoparticles prepared in the embodiments and comparative examples of the present invention, add 0.100 g of the above binder solution, that is, control the mass ratio of powder to binder solution = 10:1, add 0.20 g of anhydrous ethanol for rheological fine adjustment, grind in an agate mortar for 30 min, let stand to degas for 10 min, and obtain a uniform slurry.

[0101] It uses a 5 mm × 5 mm × 0.25 mm alumina ceramic substrate, with pre-fabricated platinum interdigitated electrodes on the surface. The electrode fingers are 200 μm wide and 200 μm apart, and a platinum heating resistor is integrated on the back.

[0102] Using a 325-mesh stainless steel wire mesh, a squeegee speed of 50 mm / s, a squeegee pressure of 0.30 MPa, and a mesh spacing of 1.5 mm, the paste is printed on the electrode area. The printed pattern is a circular sensitive film area with a diameter of 3.0 mm. The printing is repeated 3 times, with a 2-minute hot air treatment at 50°C between each printing.

[0103] The film was dried on a hot plate at 80℃ for 30 min; then placed in an air-atmosphere muffle furnace and heated to 400℃ at a rate of 3℃ / min, held at that temperature for 2 h, and then cooled to room temperature with the furnace to obtain a firmly attached sensitive layer device. The dry film thickness was measured to be 10 μm using a white light interferometer.

[0104] The device was aged at 200°C in air for 24 hours to stabilize the baseline and contact interface.

[0105] Test method:

[0106] The device was installed in a sealed test chamber with an effective volume of 50 mL, and the operating temperature was set to 150℃. A mass flow controller was used to dispense gas at a total flow rate of 200 mL / min; an ultraviolet ozone generator was used to dispense ozone, which was calibrated to 100 ppb using an ozone analyzer; and a membrane humidifier was used to adjust the relative humidity to 25%.

[0107] Introduce dry air, control RH=25%, stabilize for 30 min, and record the steady-state baseline resistance R_air (a change rate <1% / 5 min is considered stable).

[0108] Switch to ozone 100 ppb / relative humidity 25% / total flow rate 200 mL / min, denoted as t=0; continuous sampling resistance (≥1 Hz).

[0109] After 5 minutes of ozone exposure, switch back to air cleaning for 10 minutes; repeat 3 times.

[0110] Evaluation indicators and calculations:

[0111] Response value S (n-type): S=R air / R gas .

[0112] Where R gas To expose the terminal resistance for 5 minutes;

[0113] Response time T 90 The time required for the resistance to reach 90% of the total change from t=0.

[0114] If the resistance returns to ≥90% of its initial value within a preset 10 minutes during the cleaning phase, it is considered reversible; recovery time is not counted separately.

[0115] The S and T90 values ​​for each device are taken as the arithmetic mean of three cycles; the measured values ​​of operating temperature, ozone concentration, humidity and total flow rate are recorded.

[0116] Example 1 4:1 12.4 9.0 Example 2 8:1 12.0 8.6 Example 3 6:1 13.1 9.1 Example 4 2:1 10.5 10.8 Example 5 4:1 12.7 8.8 Example 6 4:1 12.9 8.5 Example 7 4:1 13.0 8.3 Example 8 4:1 13.3 8.2 Example 9 4:1 14.0 7.1 Example 10 4:1 14.6 6.7 Comparative Example 1 4:1 9.5 12.2

[0117] Compared to Examples 1-9 which used complexing agents, the overall performance of Comparative Example 1 without complexing agents was significantly lower under the same process and testing conditions. In the weak acid system, tin salts and tungsten salts undergo differential hydrolysis and sudden nucleation, resulting in a wider precursor particle size distribution and easy agglomeration. Tungsten tends to form enriched phases or local oxides, leading to insufficient uniformity and depth of the tin dioxide lattice. In the subsequent temperature-programmed and high-temperature calcination stages, due to the lack of complexation-confinement and soft template constraints, the particles grow abnormally, the channels are prone to collapse or become disconnected, and the local tungsten-rich phases become further stabilized, making it difficult to obtain a reasonable oxygen vacancy distribution and a connected micro-mesoporous network. Ultimately, the effective specific surface area and active sites decrease, the Debye length and grain size are mismatched, and mass transfer within the film is hindered and charge redistribution is delayed, which macroscopically manifests as a lower response amplitude and a slower response speed.

[0118] A comparison of Examples 1-4 shows that, under the same complexing agent, the tin-tungsten molar ratio has a significant impact on the gas-sensing performance. The device exhibits the highest response value when the tin / tungsten ratio is 6:1, while an excessively high tungsten ratio of 2:1 leads to excessively low carrier concentration and excessively large Debye length, resulting in decreased sensitivity and slower response. Therefore, controlling the tin-tungsten molar ratio within the range of 4:1-8:1 achieves a good balance between sensitivity and response speed.

[0119] Examples 5-9 demonstrate that, under a fixed tin to tungsten molar ratio, the type and formulation of the complexing agent have a decisive influence on the doping uniformity and pore structure of the precursor. Compared with sodium citrate alone, sodium phytate or sodium phosphocyclodextrin can further improve the response value and shorten the response time; the binary systems of sodium citrate with sodium phytate and sodium citrate with sodium phosphocyclodextrin show better performance. During the subsequent programmed temperature rise and high-temperature calcination, the above systems inhibit abnormal grain growth and reduce local tungsten-rich phases through confined nucleation and controlled pyrolysis of the organic framework, forming interconnected micropores and mesopores in situ, while obtaining uniformly distributed and moderately adequate oxygen vacancies; thereby achieving deeper and more uniform substitution of tungsten in the tin dioxide lattice, increasing the specific surface area and pore connectivity, matching the Debye length with the grain size and deepening the modulation of conductivity by the surface depletion layer, while shortening the mass transfer path and charge redistribution time of the gas in the film. Based on the above mechanism, Example 9 uses a ternary compound system of sodium citrate, sodium phytate and sodium phosphate cyclodextrin salt, which can maintain and amplify the structural advantages after calcination, and presents the best overall performance of simultaneously improving sensitivity and significantly accelerating response.

[0120] In Example 10, a small amount of 1-ethyl-3-methylimidazolium dihydrogen phosphate provides multi-point complexation and soft template confinement in a weakly acidic aqueous phase, converging the synchronous nucleation time window of tin and tungsten and promoting uniform doping and interconnected micropores. After appropriate calcination, the structural and defect features of these precursor layers are transformed and solidified into fine grains and a more reasonable oxygen vacancy distribution, which deepens the modulation of the surface depletion layer and reduces the mass transfer resistance within the film, thus improving the response value and making the response faster.

Claims

1. A method for producing tungsten-doped tin dioxide nanopowder, characterized in that, Includes the following steps: (1) Dissolve soluble tungsten compounds and soluble tin compounds in an aqueous solution containing surfactants, and add a complexing agent to obtain a homogeneous mixed solution of metal ions; (2) Add a precipitant to the mixed solution under stirring conditions and adjust the pH to 2-6 to precipitate the metal hydroxide precursor; (3) The precipitate is aged, separated into solid and liquid, washed and dried to obtain precursor powder; (4) Add a dispersant to the precursor powder and mix thoroughly; (5) Calcination yields the tungsten-doped tin dioxide nanopowder; The complexing agent is composed of sodium citrate, sodium phytate and phosphorylated β-cyclodextrin sodium phosphate, and the mass ratio of sodium citrate, sodium phytate and phosphorylated β-cyclodextrin sodium phosphate is 10:(2-6):(1-3).

2. The method for producing tungsten-doped tin dioxide nanopowder as described in claim 1, characterized in that, The molar ratio of tin to tungsten is controlled to be set between 4:1 and 8:

1.

3. The method for producing tungsten-doped tin dioxide nanopowder as described in claim 1, characterized in that, The soluble tungsten compound is selected from: tungsten hexachloride, sodium metatungstate, ammonium metatungstate, metatungstic acid, and tungstate.

4. The method for producing tungsten-doped tin dioxide nanopowder as described in claim 1, characterized in that, The soluble tin compound is selected from: tin tetrachloride, stannous chloride, tin nitrate, tin sulfate and their hydrates.

5. The method for producing tungsten-doped tin dioxide nanopowder as described in claim 1, characterized in that, The surfactant is at least one of anionic, cationic, or nonionic surfactants.

6. The method for producing tungsten-doped tin dioxide nanopowder as described in claim 1, characterized in that, The precipitant is ammonia water, sodium hydroxide, potassium hydroxide or ammonium carbonate solution; The dispersant is selected from polyethylene glycol, sodium polyacrylate, polyoxyethylene-polyoxypropylene block copolymers, and combinations thereof.

7. A tungsten-doped tin dioxide nanopowder, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The use of the tungsten-doped tin dioxide nanopowder as described in claim 7 in the preparation of semiconductor gas sensors, ultraviolet detectors, lithium-ion battery anode materials, catalysts, or transparent conductive films.

9. A gas-sensitive device, characterized in that, It includes a substrate, a heating electrode and a detection electrode disposed on the substrate, and a tungsten-doped tin dioxide nanopowder sensitive layer as described in claim 7 covering the detection electrode.

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