Preparation method of noble metal sensitized bimicroporous metal oxide microspheres

Abstract

The application belongs to the technical field of nanometer sensing material, and particularly relates to a preparation method of noble metal sensitized double mesoporous metal oxide microspheres. The application adopts a one-step method, first cross-linking polymerization of polymer monomers is carried out by using the hydrogen bond action between a surfactant and the polymer monomers; the chelation between the polymer monomers and noble metal and transition metal ions is used to form the composite microspheres by polymerization-induced self-assembly of the noble metal and transition metal ions chelated with the monomers; then the surfactant and the polymer are removed by sintering; the sintered surfactant forms the secondary mesoporous metal oxide loaded with the noble metal; the sintered polymer forms the primary mesoporous metal oxide loaded with the noble metal, and the noble metal sensitized metal oxide microspheres with double hierarchical mesopores are obtained. The application has controllable components in the preparation process, adjustable pore structure and pore wall microenvironment, universality, and can realize batch production.

Description

Technical Field

[0001] This invention belongs to the field of advanced porous materials and nanosensing materials, specifically relating to a method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres. Background Technology

[0002] With the rapid development of the Internet of Things (IoT), the demand for highly sensitive and selective gas sensors with low detection limits, fast response-recovery speeds, excellent long-term stability, and reversibility is increasing in smart cities, smart industries, and smart healthcare. Among various gas sensors, including electrochemical, infrared, thermal conductivity, and catalytic combustion types, resistive chemical gas sensors have attracted widespread research interest due to their unique advantages such as high sensitivity, small size, low cost, ease of operation, and high integration. Typically, gas sensors consist of a sensitive material, a sensing electrode, and a heating electrode. The sensitive material is considered the most critical component of a chemical gas sensor, and much effort has been invested in developing superior gas-sensitive materials. Metal oxide semiconductor nanomaterials (MOSs) are considered promising gas-sensitive materials due to their high specific surface area, abundant active adsorption sites, superior electrical properties, and low cost. However, single MOSs-based gas sensors suffer from low response, poor selectivity, and excessively high operating temperatures, limiting their practical application in a wider range of environments.

[0003] Researchers have extensively explored strategies to enhance gas sensing performance, such as constructing heterostructures, modifying heteroatoms, building porous materials, introducing molecular probes, and employing sieving effects. It is well known that gas molecule diffusion in mesoporous materials is primarily Knudsen diffusion, which helps increase the interaction frequency between gas molecules and pore walls. Therefore, constructing mesoporous channels is beneficial for improving the sensitivity and response speed of gas sensing. Furthermore, in gas-solid interface reactions, the pore structure of the material has a significant impact on the performance of porous materials. Dual-mesoporous structures have better pore connectivity than single-mesoporous structures, promoting the adsorption / diffusion of gas molecules within the sensitive layer and improving the accessibility of catalytic reaction active sites. The noble metal sensitization effect is another important strategy for enhancing gas sensing performance. It can not only adjust the electron depletion layer and carrier concentration by constructing heterostructures (electron sensitization), but also utilize the excellent catalytic activity of noble metals to lower the activation energy barrier and accelerate reaction kinetics (chemosensitization). However, noble metal-supported mesoporous metal oxide materials typically involve depositing noble metal nanoparticles onto a pre-synthesized support via photoreduction or chemical reduction after the mesoporous metal oxide support has been prepared. This process is cumbersome and time-consuming. Furthermore, the aggregation and deactivation of noble metal nanoparticles is another major obstacle limiting the development of gas sensing, especially at higher operating temperatures, where aggregation usually leads to a reduction in active sites, pore blockage, and decreased mass transfer rates. The design of dual-mesoporous metal oxide supports can utilize the mesoporous confinement effect to suppress nanoparticle migration and improve nanoparticle stability. In addition, the higher pore connectivity of dual-mesoporous materials can solve the pore blockage problem caused by noble metal nanoparticle aggregation, while also enhancing gas diffusion and catalytic conversion reactions at the gas-solid interface. This results in improved selectivity and sensitivity in the gas-sensitive reaction process and also contributes to enhancing the long-term operational stability of the device.

[0004] Chinese patent No. 202011015498.0 discloses an ordered dual-mesoporous metal oxide composite material loaded with noble metals and its preparation method, introducing dual mesopores into the metal oxide material loaded with noble metals. The patent employs a volatility-induced self-assembly (EISA) method to synthesize mesoporous metal oxides. EISA is a soft-templating method for synthesizing mesoporous materials. Compared to hard-templating methods, although soft-templating methods are simpler, more time-saving, and easier to operate, they have two major challenges: First, due to the uncontrollable hydrolysis rate of the mesoporous metal oxide precursor, the soft-templating agent is prone to phase separation from the metal precursor. Therefore, it is usually necessary to add chelating agents to the synthesis system to enhance the interaction between the template agent and the metal precursor, or add acids to inhibit the hydrolysis rate of the metal precursor; second, the severe shrinkage of the framework during the high-temperature crystallization of metal oxides easily leads to the collapse of the mesoporous structure. The patented EISA method dissolves the template agent and metal precursor together in an organic solvent, and may also add chelating agents or metal hydrolysis inhibitors to obtain a clear micelle solution. This solution is then poured into a petri dish for slow solvent evaporation, resulting in a uniform film. The template agent is then removed by calcination to obtain the mesoporous metal oxide material. However, due to the inherent limitations of the EISA method, the synthesized mesoporous metal oxide materials typically exhibit irregular bulk morphologies (as shown in SEM characterization). This irregular morphology, resulting from the uncontrollable hydrolysis rate of the transition metal precursor, is detrimental to the fabrication of reliable and reproducible sensors with good film regularity for gas sensing. Furthermore, this preparation method requires the pre-synthesis of the polymer used as a pore-forming agent, involving multiple steps, making it cumbersome, with low yields, and unsuitable for industrial mass production. In addition, this method uses a large amount of organic solvent, inevitably causing environmental pollution during the synthesis process. Summary of the Invention

[0005] In view of the above-mentioned defects or deficiencies in the prior art, the present invention aims to provide a method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres. This method synthesizes noble metal-sensitized metal oxide gas-sensitive materials with dual mesoporous structures in a one-step process. The one-step process involves the simultaneous co-assembly of two pore-forming agents, a metal oxide precursor, and a noble metal oxide precursor, without stepwise reactions. The resulting sensing material exhibits a dual mesoporous structure with different pore sizes, a noble metal-modified pore wall microenvironment, and a uniform microsphere morphology. Its composition is controllable, and the pore structure and pore wall microenvironment are tunable, enabling its wide application in the detection of various toxic, harmful, flammable, and explosive gases.

[0006] The method for preparing noble metal-sensitized mesoporous metal oxide microspheres provided by this invention employs a one-step synthesis method, comprising:

[0007] By utilizing the hydrophobic, hydrogen bond, and electrostatic interactions between surfactants and polymer monomers, the polymer monomers undergo cross-linking polymerization with the assistance of surfactants. Simultaneously, there is a chelation effect between polymer monomers and noble metal and transition metal ions. During the cross-linking polymerization of polymer monomers, the noble metal and transition metal ions chelated with polymer monomers undergo polymerization-induced self-assembly, controlling the hydrolysis of transition metal precursors and enhancing the interaction between surfactants and transition metal precursors, thus forming polymer-noble metal / metal composite microspheres.

[0008] The surfactant and polymer in the composite microspheres are removed by sintering. The surfactant acts as a co-templating agent for secondary mesopores, and the surfactant portion after sintering forms secondary mesopores loaded with noble metal oxides. The polymer, after sintering, forms primary mesopores loaded with noble metal oxides. The primary and secondary mesopores have different orders of magnitude, and the noble metal modifies the pore wall microenvironment of both primary and secondary mesopores. This results in noble metal-sensitized metal oxide microspheres with hierarchical dual mesopores, exhibiting uniform morphology. The specific surface area of ​​the formed microspheres is between 50 and 200 m². 2 ·g -1 The pore volume is 0.1–1.0 cm. 3 ·g -1 The primary mesopore diameter is 10–50 nm, and the secondary mesopore diameter is 2–10 nm.

[0009] In specific operations, the one-step method includes the following steps:

[0010] Step S1: Dissolve the surfactant in a mixed solution of ethanol and water, and stir to form a homogeneous solution A, wherein the volume ratio of ethanol to water is 1:9 to 1:1.

[0011] In this step, the surfactant is selected from one or more of the following: Pluronic F127 (PEO106PPO70PEO106), Pluronic P123 (PEO20PPO70PEO20), Pluronic F108 (PEO132PPO50PEO132), Pluronic P105 (PEO37PPO56PEO37), hexadecyltrimethylammonium bromide (CTAB), and hexadecyltrimethylammonium chloride (CTAC), all of which are soluble in water or ethanol. It must have a clear difference in hydrophilic / hydrophobic properties and be able to interact with the polymer monomer, metal oxide precursor, and noble metal precursor through electrostatic interactions, hydrogen bonding, or other forces. In step S2, a certain amount of polymer monomer is added to solution A, and after stirring, the metal oxide precursor and noble metal precursor are added sequentially. After stirring, a homogeneous solution B is obtained.

[0012] In this step, the polymer monomer corresponds to the polymerization-inducing reaction in step S3. The polymerization-inducing reaction includes one of the following: glucose condensation reaction, phenolic resin synthesis reaction, melamine resin synthesis reaction, urea-formaldehyde resin synthesis reaction, dopamine polymerization reaction, etc. Correspondingly, for glucose condensation reaction, the precursor is only glucose, with a feed amount of 1–5 g; for phenolic resin synthesis reaction, the precursor can be one of phenol and formaldehyde, or tannic acid and formaldehyde, with a feed amount of 0.1–1 g of phenol or tannic acid and 0.2–2 ml of formaldehyde aqueous solution, ensuring a phenol-formaldehyde mass ratio of 1:1–1:2; for melamine resin synthesis reaction, the precursor is melamine and formaldehyde, with a feed amount of 0.5–2 g of melamine and 1–3 ml of formaldehyde aqueous solution, ensuring a melamine-formaldehyde aqueous solution mass ratio of 1:2–1.3; for urea-formaldehyde resin synthesis reaction, the precursor is urea and formaldehyde, with a feed amount of 0.5–3 g of urea and 1–4 ml of formaldehyde aqueous solution, ensuring a urea-formaldehyde aqueous solution mass ratio of 1:1–1.3; for dopamine polymerization reaction, the precursor is only dopamine hydrochloride, with a feed amount of 0.3–2 g.

[0013] In this step, the hydrophobic, hydrogen bond, and electrostatic interactions between the polymer monomer and the surfactant, as well as the chelation between the polymer monomer and the metal ions, can enhance the interaction between the surfactant and the metal precursor and prevent phase separation.

[0014] The metal oxide precursor includes one or more of tin chloride, sodium stannate, nickel chloride, zinc chloride, tungsten chloride, indium chloride, zirconium chloride, titanium chloride, niobium oxide, ferric chloride, and cobalt chloride. The amount of material added is determined according to the selected polymerization induction reaction and the required pH.

[0015] The noble metal precursor includes one or more noble metal compounds that are soluble in water or ethanol, such as chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, potassium chloropalladiumate, ammonium chloropalladiumate, sodium hexachloropalladiumate, platinum acetylacetonate, palladium acetylacetonate, chloroauric acid, silver nitrate, and rhodium chloride, and provides the corresponding noble metal, including one or an alloy of Pt, Pd, Au, Ag, and Rh.

[0016] Step S3: A predetermined amount of catalyst is added to solution B to adjust the pH of the solution. The mixture is stirred at a predetermined reaction temperature for 1–24 h to induce a polymerization reaction. The reaction product is collected by centrifugation and washed alternately with water and ethanol. After drying, polymer-noble metal / metal composite microspheres are obtained. The diameter of the composite microspheres is related to the type of metal oxide and the type of polymer. Preferably, the diameter of the composite microspheres is 100 nm to 2 μm.

[0017] In this step, the catalyst is an acid or base catalyst, including one or more of hydrochloric acid, nitric acid, sulfuric acid, ammonia, and sodium hydroxide. The amount of catalyst added is determined based on the pH required for the selected polymerization-inducing reaction. The solution pH and reaction temperature are determined according to the polymerization-inducing reaction conditions: for glucose condensation reaction, the solution pH needs to be adjusted to 6–8, and the reaction temperature is 60–100℃; for phenolic resin synthesis reaction, the solution pH needs to be adjusted to 8–9, and the reaction temperature is 25–80℃; for melamine resin synthesis reaction, the solution pH needs to be adjusted to 4–6, and the reaction temperature is 60–90℃; for urea-formaldehyde resin synthesis reaction, the solution pH needs to be adjusted to 4–6, and the reaction temperature is 25–80℃; for dopamine polymerization reaction, the solution pH needs to be adjusted to 8.5–9.5, and the reaction temperature is 25–40℃.

[0018] In this step, the polymerization and crosslinking process of the polymer can inhibit the hydrolysis of the metal precursor to a certain extent, thereby controlling the hydrolysis and allowing it to slowly hydrolyze and crosslink during the polymerization induction process.

[0019] Step S4: The composite microspheres are transferred to a muffle furnace and calcined in air at a heating rate of 1-10°C / min to 350-700°C and held for 1-3 hours to remove surfactants and polymers, thereby obtaining noble metal-sensitized hierarchical porous metal oxide microspheres.

[0020] In this step, the polymer acts as a pore-forming agent during sintering. After the polymer is removed by calcination, a hierarchical mesoporous structure is generated.

[0021] The present invention has the following beneficial technical effects:

[0022] (1) The soft template method of liquid-phase polymerization assembly synthesis has higher flexibility and controllability, and can assemble mesoporous materials with rich microstructures. Compared with the traditional liquid-phase assembly synthesis method, it is not easy to assemble microspheres due to the uncontrollable hydrolysis rate of metal oxide precursors and the large differences in the hydrolysis rate of different metal oxide precursors. The present invention adopts the liquid-phase polymerization assembly synthesis method, which utilizes the polymer to enhance the interaction between the template agent and the metal precursor, and can also control the hydrolysis process of the metal precursor. In addition, the polymer can leave rich mesoporous structures after calcination, which is conducive to constructing hierarchical mesoporous channels to improve mass transfer capacity.

[0023] (2) By utilizing the interaction between polymer monomers, surfactants and metal ions, a one-step synthesis of metal oxide microspheres with a double mesoporous structure anchored by noble metal is achieved. This overcomes the cumbersome and complex multi-step process of traditional noble metal-modified double mesoporous materials, avoids the post-loading process of noble metal after the synthesis of metal oxides, and the raw materials are cheap and readily available. They can be used in practical engineering applications of gas sensing and are suitable for mass production. At the same time, the uniform microsphere structure is conducive to the preparation of gas-sensitive films with adjustable thickness and uniform interparticle voids, thereby improving the reproducibility and reliability of gas-sensitive elements.

[0024] (3) The noble metal-sensitized dual mesoporous metal oxide microspheres have the advantages of controllable composition, adjustable pore structure and pore wall microenvironment. Various single or composite dual mesoporous metal oxide gas-sensitive materials can be obtained by changing the type of metal oxide precursor. The pore wall microenvironment can be controlled by selecting different noble metal precursors. The pore size of the dual mesoporous microspheres can be flexibly controlled by controlling the polymerization reaction rate and surfactant. Therefore, the noble metal-sensitized dual mesoporous metal oxide gas-sensitive materials provided by this invention can be widely used in the detection of various toxic, harmful, flammable and explosive gases.

[0025] (4) Due to the strong coordination between various metal ions and polymer molecules, the one-step method has strong universality and can be applied to the synthesis of a series of single metal (such as W, Sn, Nb, In, Co, Fe, Ni, Cu, Zn), bimetallic (such as W-Sn, In-Nb, Fe-Ni, Co-Zn), and multimetallic (such as W-Sn-Nb-In-Fe-Co-Ni-Cu) oxide microspheres, as well as the in-situ modification of various highly dispersed noble metal nanoparticles (such as Pt, Pd, Rh, Au, Ag) and their alloys (such as Pt-Pd, Pd-Ag, Au-Rh). The obtained noble metal-sensitized double mesoporous metal oxide microspheres can be used for gas sensing of toxic and harmful gases (CO, H2S, etc.), volatile organic compounds (VOCs) (benzene, formaldehyde, etc.), human exhaled gases (acetone, NH3, etc.), and flammable and explosive gases (CH4, H2), exhibiting excellent gas-sensing performance. Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0027] Figure 1The N2 adsorption-desorption isotherm of the Au-sensitized double mesoporous SnO2 microspheres prepared in Example 1 of this invention.

[0028] Figure 2 The image shows the pore size distribution curve of the Au-sensitized double mesoporous SnO2 microspheres prepared in Example 1 of this invention.

[0029] Figure 3 This is a gas-sensitizing performance test diagram of Au-sensitized dual mesoporous SnO2 microspheres prepared in Example 1 of the present invention for 10 ppm methane.

[0030] Figure 4 This is a gas-sensitizing performance test diagram of Au-sensitized dual mesoporous SnO2 microspheres prepared in Example 1 of the present invention for 4000ppm methane.

[0031] Figure 5 This is a scanning electron microscope image of the Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres prepared in Example 2 of the present invention.

[0032] Figure 6 This is a transmission electron microscope image of the Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres prepared in Example 2 of the present invention.

[0033] Figure 7 The N2 adsorption-desorption isotherm of the Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres prepared in Example 2 of this invention.

[0034] Figure 8 The image shows the pore size distribution curve of the Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres prepared in Example 2 of this invention.

[0035] Figure 9 The methane sensing performance of the Pt-Pd alloy-sensitized dual mesoporous SnO2 microspheres prepared in Example 2 of this invention was tested at 50-3000 ppm.

[0036] Figure 10 Cyclic stability test of Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres prepared in Example 2 of this invention against 3000ppm methane.

[0037] Figure 11 This is a scanning electron microscope image of the Pd-sensitized double mesoporous WO3 microspheres prepared in Example 3 of the present invention.

[0038] Figure 12 This is a transmission electron microscope image of the Pd-sensitized double mesoporous WO3 microspheres prepared in Example 3 of the present invention.

[0039] Figure 13The H2 sensing performance of the Pd-sensitized dual mesoporous WO3 microspheres prepared in Example 3 of this invention was tested at 10-100 ppm.

[0040] Figure 14 The test results show the cyclic stability of the Pd-sensitized dual mesoporous WO3 microspheres prepared in Example 3 of this invention against 50 ppm H2. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can also be combined with each other.

[0042] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, the terms "first," "second," "third," "fourth," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0043] Example 1

[0044] This embodiment uses polydextrose as the primary mesoporous pore-forming agent and F127 as the secondary mesoporous cotemplating agent to provide a one-step synthesis strategy for Au-sensitized dual mesoporous SnO2 microspheres.

[0045] Step S1: Dissolve 0.05g F127 in a mixed solution of 10ml ethanol and 40ml water, stir for 5min to form homogeneous solution A.

[0046] Step S1: Add 1g of glucose to solution A, stir for 10min, then add 0.5g of sodium stannate and 3mg of chloroauric acid in sequence, stir for 30min to obtain homogeneous solution B.

[0047] Step S1: Add ammonia to solution B to adjust the pH of the solution to about 8. Stir at 70°C for 12 hours, then centrifuge at 10000 r / min to collect the reaction product. Wash the product twice with water and ethanol alternately, and finally dry it in an oven at 70°C for 12 hours to obtain glucose-SnO2 composite microspheres.

[0048] Step S1: Transfer the glucose-SnO2 composite microspheres obtained in step S3 to a muffle furnace and calcine them in air at 350°C for 2 hours with a heating rate of 2°C / min to finally obtain Au-sensitized double mesoporous SnO2 microspheres.

[0049] The N2 adsorption-desorption isotherm and pore size distribution curve of the Au-sensitized dual-mesoporous SnO2 microspheres (Au / SnO2) obtained in this embodiment are shown in the figure below. Figure 1 and Figure 2 As shown, its specific surface area is 54.21 m². 2 ·g -1 The pore volume is 0.24 cm. 3 ·g -1 The primary mesopores have a diameter of 45.6 nm and are produced by the decomposition of polydextrose, while the secondary mesopores have a diameter of 5.1 nm and are produced by the decomposition of F127. The Au / SnO2 obtained in this embodiment was used as the sensitive material for methane sensing. The sensitive material was integrated onto a MEMS device using an automated dispensing method. The sensing performance for methane at 10 and 4000 ppm at 300°C was as follows: Figure 3 and Figure 4 As shown in the figure. The results show that Au / SnO2 exhibits excellent methane gas sensing performance at both low and high concentrations, and has a fast response-recovery speed. Therefore, the Au / SnO2 in this example can be applied to methane sensing in different scenarios.

[0050] Example 2

[0051] This embodiment uses urea-formaldehyde resin as the primary mesoporous pore-forming agent and F127 as the secondary mesoporous cotemporal agent to provide a one-step synthesis strategy for Pt-Pd alloy-sensitized dual mesoporous SnO2 microspheres.

[0052] Step S1: Dissolve 0.2g F127 in a mixed solution of 10ml ethanol and 40ml water, stir for 20min to form homogeneous solution A.

[0053] Step S1: Add 2g of urea and 4ml of formaldehyde solution to solution A, stir for 40min, then add 0.2g of tin chloride, 0.5mg of chloroplatinic acid and 0.5mg of potassium chloropalladate in sequence, stir for 60min to obtain homogeneous solution B.

[0054] Step S1: Add hydrochloric acid to solution B to adjust the pH of the solution to about 5. After stirring at 35°C for 3 hours, centrifuge at 6000 r / min to collect the reaction product. Wash the product twice with water and ethanol alternately. Finally, dry it in an oven at 60°C for 24 hours to obtain urea-formaldehyde resin-SnO2 composite microspheres.

[0055] In step S1, the urea-formaldehyde resin-SnO2 composite microspheres obtained in step S3 are transferred to a muffle furnace and calcined in air at 500°C for 2 hours with a heating rate of 5°C / min, finally obtaining Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres.

[0056] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the Pt-Pd alloy-sensitized double mesoporous SnO2 microspheres (Pt-Pd / SnO2) obtained in this embodiment are shown below. Figure 5-6 As shown in the figure, the Pt-Pd / SnO2 obtained in this embodiment exhibits a distinct microsphere morphology with a size of approximately 400–500 nm. The surface is rough, and its abundant mesoporous channels are clearly visible in the TEM image. The N2 adsorption-desorption isotherms and pore size distribution curves of the Pt-Pd / SnO2 microspheres are shown in the figure. Figure 7 As shown. Its N2 adsorption-desorption isotherm exhibits a typical isotherm IV, indicating its mesoscopic structure, and its specific surface area is calculated to be 56.5 m². 2 ·g -1 The pore volume is 0.143 cm³. 3 ·g -1 .like Figure 8 The pore size distribution curves show that the primary mesopores of the Pt-Pd / SnO2 microspheres have a diameter of 13.9 nm, which is generated by the decomposition of urea-formaldehyde resin, and the secondary mesopores have a diameter of 6.6 nm, which is generated by the decomposition of F127.

[0057] The Pt-Pd / SnO2 obtained in this embodiment was used as the sensitive material for methane sensing. After thorough grinding, it was mixed with anhydrous ethanol to form a uniform slurry, which was then uniformly coated onto a ceramic tube. The methane sensing performance at 400°C for 50-3000 ppm was as follows: Figure 9 As shown in the figure. The results show that Pt-Pd / SnO2 exhibits excellent methane sensing performance in the concentration range of 50-3000 ppm, with a sensing sensitivity (R0.05) for 3000 ppm methane. a / R g The value is as high as 10, far exceeding most methane sensors reported to date. Additionally, Figure 10 The cyclic stability of Pt-Pd / SnO2 with 3000ppm methane was demonstrated. The test results show that the methane sensor with Pt-Pd / SnO2 as the gas-sensitive material has excellent repeatability and reusability.

[0058] Example 3

[0059] This embodiment uses melamine resin as the primary mesoporous pore-forming agent and F108 as the secondary mesoporous cotemporal agent to provide a one-step synthesis strategy for Pd-sensitized dual mesoporous WO3 microspheres.

[0060] Step S1: Dissolve 0.1g F108 in a mixed solution of 15ml ethanol and 35ml water, and stir for 30min to form a homogeneous solution A.

[0061] Step S1: Add 0.5g of melamine and 1.5ml of formaldehyde solution to solution A, stir for 40min, then add 0.3g of tungsten chloride and 3mg of sodium hexachloropalladium in sequence, stir for 60min to obtain homogeneous solution B.

[0062] Step S1: Add hydrochloric acid to solution B to adjust the pH of the solution to about 6. After stirring at 80°C for 10 hours, centrifuge at 9000 r / min to collect the reaction product. Wash the product with water and ethanol alternately 4 times. Finally, dry it in an oven at 70°C for 10 hours to obtain melamine resin-WO3 composite microspheres.

[0063] Step S1: Transfer the melamine resin-WO3 composite microspheres obtained in step S3 to a muffle furnace and calcine them in air at 400°C for 3 hours with a heating rate of 2°C / min to finally obtain Pd-sensitized double mesoporous WO3 microspheres.

[0064] The SEM and TEM images of the Pd-sensitized double mesoporous WO3 microspheres (Pd / WO3) obtained in this embodiment are shown below. Figure 11 and Figure 12 As shown in the figure, the Pd / WO3 obtained in this embodiment has a uniform and well-dispersed microsphere morphology with a rough and porous surface and a diameter of approximately 1 μm. The Pd / WO3 obtained in this embodiment was used as a sensitive material for H2 sensing. After thorough grinding, it was mixed with anhydrous ethanol to form a uniform slurry, which was then uniformly coated onto a ceramic tube. The sensing performance for 10-100 ppm H2 at 210°C was as follows: Figure 13 and Figure 14 As shown in the figure. The results show that Pd / WO3 exhibits excellent H2 sensing performance in the concentration range of 10-100 ppm, with a response value as high as 33.5 for H2 at 50 ppm. Figure 14 The cycling stability of Pd / WO3 for 50ppm H2 was demonstrated. The results showed that the sensitivity of Pd / WO3 microspheres to H2 sensing fluctuated little during more than 23 cycles, indicating its excellent repeatability and reusability.

[0065] Example 4

[0066] This embodiment uses tannic acid polymer as a primary mesoporous pore-forming agent and P123 as a secondary mesoporous cotemporal agent to provide a one-step synthesis strategy for Pt-sensitized dual mesoporous WO3 microspheres.

[0067] Step S1: Dissolve 0.1g P123 in a mixed solution of 20ml ethanol and 30ml water, and stir for 15min to form a homogeneous solution A.

[0068] In step S2, 0.2g of tannic acid and 0.2ml of formaldehyde solution are added to solution A and stirred for 30min. Then, 0.1g of tungsten chloride and 0.2mg of chloroplatinic acid are added sequentially and stirred for 60min to obtain homogeneous solution B.

[0069] Step S3: Add ammonia to solution B to adjust the pH of the solution to about 9. After stirring at 30°C for 24 hours, centrifuge at 8000 r / min to collect the reaction product. Wash the product three times alternately with water and ethanol. Finally, dry it in an oven at 80°C for 24 hours to obtain phenolic resin-WO3 composite microspheres.

[0070] In step S4, the phenolic resin-WO3 composite microspheres obtained in step S3 are transferred to a muffle furnace and calcined in air at 450°C for 1 hour with a heating rate of 5°C / min, finally obtaining Pt-sensitized double mesoporous WO3 microspheres.

[0071] The Pt-sensitized dual-mesoporous WO3 microspheres (Pt / WO3) obtained in this embodiment were used as the sensitive material for ethanol sensing. After thorough grinding, they were mixed with anhydrous ethanol to form a uniform slurry, which was then uniformly coated onto a ceramic tube. At a relatively low temperature of 110°C, they exhibited excellent gas-sensing performance for ethanol concentrations ranging from 0.5 to 500 ppm. Test results showed that the Pt / WO3 response value to 50 ppm ethanol was as high as 132. Transient response test results showed that the Pt / WO3 dual-mesoporous microspheres, as the sensitive material for ethanol sensing, had fast response-recovery times of 17 s and 7 s, respectively. Furthermore, in the cyclic test results, the Pt / WO3 ethanol sensor exhibited good cyclic stability and reversibility; during more than 11 cycles, the sensitivity fluctuation of the Pt / WO3 microspheres for ethanol sensing did not exceed 5%.

[0072] Example 5

[0073] This embodiment uses melamine resin as a primary mesoporous pore-forming agent and F108 as a secondary mesoporous cotemporal agent to provide a one-step synthesis strategy for Ag-Pd alloy-sensitized dual mesoporous Nb2O5 / WO3 composite microspheres.

[0074] Step S1: Dissolve 0.3g F108 in a mixed solution of 25ml ethanol and 25ml water, and stir for 20min to form a homogeneous solution A.

[0075] In step S2, 1g of melamine and 2ml of formaldehyde solution are added to solution A and stirred for 60min. Then, 0.2g of tungsten chloride, 0.2g of niobium chloride, 2mg of silver nitrate and 2mg of sodium hexachloropalladium are added in sequence and stirred for 120min to obtain homogeneous solution B.

[0076] Step S3: Add hydrochloric acid to solution B to adjust the pH of the solution to about 4. After stirring at 70°C for 12 hours, centrifuge at 10000 r / min to collect the reaction product. Wash the product with water and ethanol alternately 5 times. Finally, dry it in an oven at 60°C for 12 hours to obtain melamine resin-Nb2O5 / WO3 composite microspheres.

[0077] In step S4, the melamine resin-Nb2O5 / WO3 composite microspheres obtained in step S3 are transferred to a muffle furnace and calcined in air at 500°C for 2 hours with a heating rate of 8°C / min, finally obtaining Ag-Pd alloy-sensitized double mesoporous Nb2O5 / WO3 microspheres.

[0078] The Ag-Pd alloy-sensitized dual mesoporous Nb₂O₅ / WO₃ microspheres (Ag-Pd / Nb₂O₅-WO₃) obtained in this embodiment were used as the sensing material for CO sensing. The sensing material was integrated onto a MEMS device using an automated dispensing method. At a relatively low temperature of 65°C, it can detect CO in a low concentration range (1-50 ppm). Gas-sensing test results showed that Ag-Pd / Nb₂O₅-WO₃ had a response value as high as 53 for 25 ppm ethanol. Furthermore, in the cyclic test results, Ag-Pd / Nb₂O₅-WO₃ exhibited good cyclic stability and reversibility for CO sensing. During more than 22 cycles, the sensitivity fluctuation of the Ag-Pd / Nb₂O₅-WO₃ microspheres for CO sensing did not exceed 5%.

[0079] Example 6

[0080] This embodiment uses urea-formaldehyde resin as the primary mesoporous pore-forming agent and P105 as the secondary mesoporous co-templating agent to provide a one-step synthesis strategy for Au-Rh alloy-sensitized dual mesoporous ZnO / NiO / SnO2 composite microspheres.

[0081] Step S1: Dissolve 0.5g P105 in a mixed solution of 20ml ethanol and 30ml water, stir for 10min to form homogeneous solution A.

[0082] Step S2: Add 1g of urea and 2ml of formaldehyde solution to solution A, stir for 20min, then add 0.1g of zinc chloride, 0.1g of nickel chloride, 0.1g of tin chloride, 1mg of chloroauric acid and 1mg of rhodium chloride in sequence, stir for 90min to obtain homogeneous solution B.

[0083] Step S3: Add nitric acid to solution B to adjust the pH of the solution to about 6. After stirring at 25°C for 5 hours, centrifuge at 8000 r / min to collect the reaction product. Wash the product three times alternately with water and ethanol. Finally, dry it in an oven at 70°C for 24 hours to obtain urea-formaldehyde resin-ZnO / NiO / SnO2 composite microspheres.

[0084] In step S4, the urea-formaldehyde resin-ZnO / NiO / SnO2 composite microspheres obtained in step S3 are transferred to a muffle furnace and calcined in air at 400°C for 3 hours with a heating rate of 2°C / min, finally obtaining Au-Rh alloy-sensitized dual mesoporous ZnO / NiO / SnO2 composite microspheres.

[0085] The Au-Rh alloy-sensitized dual-mesoporous ZnO / NiO / SnO2 composite microspheres (Au-Rh / ZnO-NiO-SnO2) obtained in this embodiment were used as the sensitive material for formaldehyde sensing. After thorough grinding, they were mixed with anhydrous ethanol to form a uniform slurry, which was then uniformly coated onto a ceramic tube. At a relatively low temperature of 100℃, they exhibited excellent gas-sensing performance for formaldehyde concentrations ranging from 0.1 to 500 ppm. Test results showed that the Au-Rh / ZnO-NiO-SnO2 response value to 50 ppm formaldehyde was as high as 85.6. Transient response test results showed that the Au-Rh / ZnO-NiO-SnO2 dual-mesoporous microspheres, as the sensitive material for formaldehyde sensing, had rapid response-recovery times of 23 s and 18 s, respectively. Furthermore, in the cyclic test results, the Au-Rh / ZnO-NiO-SnO2 formaldehyde sensor exhibits good cyclic stability and reversibility. During more than 18 cycles of testing, the sensitivity fluctuation of Au-Rh / ZnO-NiO-SnO2 microspheres for formaldehyde sensing does not exceed 5%.

[0086] Example 7

[0087] This embodiment uses polydopamine as a primary mesoporous pore-forming agent and CTAB as a secondary mesoporous cotemplating agent to provide a one-step synthesis strategy for Ag-sensitized dual mesoporous In2O3 / Nb2O5 / ZnO / WO3 / SnO2 composite microspheres.

[0088] Step S1: Dissolve 0.2g CTAB in a mixed solution of 10ml ethanol and 40ml water, stir for 20min to form homogeneous solution A.

[0089] In step S2, 1g of dopamine hydrochloride is added to solution A and stirred for 40 minutes. Then, 0.1g of indium chloride, 0.1g of niobium chloride, 0.1g of zinc chloride, 0.1g of tungsten chloride, 0.1g of tin chloride and 2mg of silver chloride are added sequentially and stirred for 100 minutes to obtain homogeneous solution B.

[0090] Step S3: Add ammonia to solution B to adjust the pH of the solution to about 8.5. After stirring at 40°C for 12 hours, centrifuge at 10000 r / min to collect the reaction product. Wash the product twice with water and ethanol alternately. Finally, dry it in an oven at 90°C for 12 hours to obtain polydopamine-In2O3 / Nb2O5 / ZnO / WO3 / SnO2 composite microspheres.

[0091] In step S4, the polydopamine-In2O3 / Nb2O5 / ZnO / WO3 / SnO2 composite microspheres obtained in step S3 are transferred to a muffle furnace and calcined in air at 600℃ for 1 h with a heating rate of 10℃ / min, finally obtaining Ag-sensitized double mesoporous In2O3 / Nb2O5 / ZnO / WO3 / SnO2 composite microspheres.

[0092] The Ag-sensitized dual mesoporous In₂O₃ / Nb₂O₅ / ZnO / WO₃ / SnO₂ composite microspheres (Ag / In₂O₃ / Nb₂O₅-ZnO-WO₃-SnO₂) obtained in this embodiment were used as the sensitive material for H₂S sensing. After thorough grinding, the microspheres were mixed with anhydrous ethanol to form a uniform slurry, which was then uniformly coated onto a ceramic tube. At a relatively low temperature of 150°C, the microspheres exhibited excellent gas-sensing performance for H₂S concentrations ranging from 0.25 to 50 ppm. Test results showed that the response value of Ag / In₂O₃ / Nb₂O₅-ZnO-WO₃-SnO₂ to 50 ppm H₂S reached as high as 382. In the cyclic test results, the Ag / In2O3 / Nb2O5-ZnO-WO3-SnO2 hydrogen sulfide sensor showed good cyclic stability and reversibility. During more than 28 cycles of testing, the sensitivity fluctuation of Ag / In2O3 / Nb2O5-ZnO-WO3-SnO2 microspheres for H2S sensing did not exceed 5%.

[0093] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed, and is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments of the invention. Those skilled in the art should understand that the scope of the invention is not limited to the specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres, characterized in that, A one-step method was used to synthesize noble metal-sensitized dual-mesoporous metal oxide microspheres. The specific steps are as follows: Step S1: Dissolve the surfactant in a mixed solution of ethanol and water, and stir to form a homogeneous solution A, wherein the volume ratio of ethanol to water is 1:9 to 1:

1. Step S2: Add a certain amount of polymer monomer to the solution A, stir, and then add metal oxide precursor and noble metal precursor in sequence. After stirring, a homogeneous solution B is obtained. Step S3: Add a predetermined amount of catalyst to the solution B and adjust the pH of the solution. Stir at a predetermined reaction temperature for 1-24 h to induce polymerization reaction. Collect the reaction product by centrifugation and wash the reaction product alternately with water and ethanol. After drying, obtain polymer-noble metal / metal composite microspheres. Step S4: The composite microspheres are transferred to a muffle furnace and calcined in air at a rate of 1-10 °C / min to 350-700 °C and held for 1-3 h to remove surfactants and polymers, thereby obtaining noble metal-sensitized hierarchical mesoporous metal oxide microspheres. The surfactant is soluble in water and / or ethanol, has a clear difference in hydrophilicity / hydrophobicity, and can interact with polymer monomers, metal oxide precursors and noble metal precursors through electrostatic interactions, hydrogen bonding or other forces. The polymer monomer corresponds to the polymerization-inducing reaction in step S3; wherein... The polymerization-inducing reaction is one of the following: glucose condensation reaction, phenolic resin synthesis reaction, melamine resin synthesis reaction, urea-formaldehyde resin synthesis reaction, and dopamine polymerization reaction; Correspondingly, for glucose condensation reaction, the precursor is only glucose, with a feed amount of 1-5 g; for phenolic resin synthesis reaction, the precursor is one of phenol and formaldehyde, or tannic acid and formaldehyde, with a feed amount of 0.1-1 g of phenol or tannic acid and 0.2-2 ml of formaldehyde aqueous solution, ensuring a phenol-formaldehyde mass ratio of 1:1-1:2; for melamine resin synthesis reaction, the precursor is melamine and formaldehyde, with a feed amount of 0.5-2 g of melamine and 1-3 ml of formaldehyde aqueous solution, ensuring a melamine-formaldehyde aqueous solution mass ratio of 1:2-1.3; for urea-formaldehyde resin synthesis reaction, the precursor is urea and formaldehyde, with a feed amount of 0.5-3 g of urea and 1-4 ml of formaldehyde aqueous solution, ensuring a urea-formaldehyde aqueous solution mass ratio of 1:1-1.3; for dopamine polymerization reaction, the precursor is only dopamine hydrochloride, with a feed amount of 0.3-2 g.

2. The method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres according to claim 1, characterized in that, The surfactant is selected from one or more of Pluronic F127, Pluronic P123, Pluronic F108, Pluronic P105, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride.

3. The method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres according to claim 1, characterized in that, The metal oxide precursor is selected from one or more of the following: tin chloride, sodium stannate, nickel chloride, zinc chloride, tungsten chloride, indium chloride, zirconium chloride, titanium chloride, niobium oxide, ferric chloride, and cobalt chloride.

4. The method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres according to claim 1, characterized in that, The noble metal precursor is one or more noble metal compounds that can be dissolved in water or ethanol, and provides the corresponding noble metal.

5. The method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres according to claim 4, characterized in that, The noble metal precursor is selected from one or more of chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, potassium chloropalladiumate, ammonium chloropalladiumate, sodium hexachloropalladiumate, platinum acetylacetonate, palladium acetylacetonate, chloroauric acid, silver nitrate, and rhodium chloride; the noble metal is one or more of Pt, Pd, Au, Ag, and Rh.

6. The method for preparing noble metal-sensitized dual mesoporous metal oxide microspheres according to claim 1, characterized in that, The catalyst is an acid or base catalyst, selected from hydrochloric acid, nitric acid, sulfuric acid, ammonia, and sodium hydroxide. Its dosage is determined based on the pH required for the selected polymerization-inducing reaction, and the solution pH and reaction temperature are determined based on the polymerization-inducing reaction conditions; wherein: For glucose condensation reaction, the solution pH needs to be adjusted to 6-8, and the reaction temperature is 60-100 ℃; For the synthesis reaction of phenolic resin, the solution pH needs to be adjusted to 8-9, and the reaction temperature is 25-80℃; For the synthesis reaction of melamine resin, the solution pH needs to be adjusted to 4-6, and the reaction temperature is 60-90 ℃; For the synthesis reaction of urea-formaldehyde resin, the solution pH needs to be adjusted to 4-6, and the reaction temperature is 25-80℃; For dopamine polymerization, the solution pH needs to be adjusted to 8.5~9.5, and the reaction temperature should be 25~40 ℃.

7. A method for preparing noble metal-sensitized bimesoporous metal oxide microspheres according to any one of claims 1 to 6, characterized in that, include: By utilizing the hydrophobic, hydrogen bond, and electrostatic interactions between surfactants and polymer monomers, the polymer monomers undergo cross-linking polymerization with the assistance of surfactants. Simultaneously, there is a chelation effect between polymer monomers and noble metal and transition metal ions. During the cross-linking polymerization of polymer monomers, the noble metal and transition metal ions chelated with the monomers undergo polymerization-induced self-assembly, controlling the hydrolysis of transition metal precursors and enhancing the interaction between surfactants and transition metal precursors, thus forming polymer-noble metal / metal composite microspheres. By sintering to remove surfactants and polymers from the composite microspheres, the surfactants act as co-templators for secondary mesopores. After sintering, the surfactant portion forms secondary mesopores loaded with noble metal oxides. Meanwhile, the polymer forms primary mesopores loaded with noble metal oxides after sintering. The primary and secondary mesopores have different orders of magnitude, and the noble metal modifies the microenvironment of the pore walls, thus obtaining noble metal-sensitized metal oxide microspheres with hierarchical dual mesopores.

8. The noble metal-sensitized dual mesoporous metal oxide microspheres according to claim 7, characterized in that, The specific surface area of ​​the formed metal oxide microspheres is 50~200 m². 2 ·g -1 The pore volume is 0.1 ~ 1.0 cm. 3 ·g -1 The primary mesopores have a diameter of 10~50 nm, and the secondary mesopores have a diameter of 2~10 nm.

Images