Cerium-doped modified bismuth cupric oxide gas sensitive material, preparation method and application thereof

Abstract

The application belongs to the technical field of gas sensitive materials, and particularly relates to a cerium doped modified bismuth cuprate gas sensitive material and a preparation method and application thereof. The preparation method of the cerium doped modified bismuth cuprate gas sensitive material comprises the following steps: (1) adding a cerium source solution dropwise into a mixed solution of a copper source and a bismuth source, stirring uniformly, adding an alkaline substance as a precipitant, and stirring again to obtain a uniform suspension; (2) allowing the uniform suspension to react by warming; and (3) after the reaction is completed, performing solid-liquid separation, cleaning and drying the obtained solid, and thus the cerium doped modified bismuth cuprate gas sensitive material is obtained. The cerium doped modified bismuth cuprate gas sensitive material can help to solve or improve the problems of poor humidity resistance (failure when encountering water) and low response value when pure bismuth cuprate is used for detecting formaldehyde.

Description

Technical Field

[0001] This invention belongs to the field of gas-sensitive materials technology, specifically relating to a cerium-doped modified copper bismuthate gas-sensitive material, its preparation method, and its application. Background Technology

[0002] With increasing environmental pollution and growing concern for human health, highly sensitive detection of volatile organic compounds (VOCs), especially formaldehyde (HCHO), has become crucial. Formaldehyde is not only a common pollutant in indoor decoration but also a potential biomarker for lung cancer in human exhaled breath. Its median concentration is 83 ppb (parts per billion), higher than the level in healthy individuals (48 ppb). Therefore, gas-sensitive materials with a detection range covering the formaldehyde concentration range in the exhaled breath of both lung cancer patients and healthy individuals at 90% RH have the potential to detect lung cancer through breath tests.

[0003] The existing pure copper bismuthate (CuBi2O4) material has the following main defects, which limit its practical application: (1) Insufficient sensitivity: It is difficult to detect low concentrations (e.g., 10 ppb) of formaldehyde gas; (2) Poor moisture resistance: In the actual application environment (especially human breath detection, where the relative humidity is extremely high), the presence of water molecules will competitively adsorb onto the material surface, resulting in a significant decrease in gas sensitivity response, which seriously affects the accuracy and reliability of detection.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide cerium-doped modified copper bismuthate gas-sensitive materials, their preparation methods, and applications, so as to help solve or improve the problem that the detection effect of pure copper bismuthate (CuBi2O4) materials on formaldehyde in the prior art is easily affected by humidity.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a cerium-doped modified copper bismuthate gas-sensitive material, comprising the following steps: (1) adding a cerium source solution dropwise to a mixed solution of a copper source and a bismuth source, stirring evenly, adding an alkaline substance as a precipitant, and stirring again to obtain a uniform suspension; (2) heating the uniform suspension to react; (3) after the reaction is completed, separating the solid and liquid, washing and drying the obtained solid to obtain the cerium-doped modified copper bismuthate gas-sensitive material; in step (2), the temperature is raised to 120-240℃ and reacted for 3-24 hours.

[0007] Preferably, in step (1), the number of moles of cerium in the cerium source is 0.01%-5.0% of the number of moles of copper in the copper source; the molar ratio of copper in the copper source to bismuth in the bismuth source is 1:2.

[0008] Preferably, in step (1), the number of moles of cerium in the cerium source is 0.05%-0.45% of the number of moles of copper in the copper source.

[0009] Preferably, in step (1), the cerium source is a soluble cerium salt; the copper source is a soluble copper salt; and the bismuth source is a soluble bismuth salt.

[0010] Preferably, in step (1), the cerium source is at least one of cerium acetate, cerium nitrate, cerium chloride, cerium sulfate, and cerium ammonium nitrate; the copper source is at least one of copper nitrate, copper chloride, copper sulfate, and copper acetate; and the bismuth source is at least one of bismuth nitrate, bismuth chloride, and bismuth citrate.

[0011] Preferably, in step (1), the pH of the uniform suspension is >10; the alkaline substance is a metal hydroxide and / or a slow-release precipitant; the metal hydroxide is sodium hydroxide and / or potassium hydroxide; and the slow-release precipitant is ammonia.

[0012] Preferably, the solvent in the mixed solution of copper source and bismuth source is at least one of water, ethanol, ethylene glycol and glycerol; the solvent in the cerium source solution is at least one of water, ethanol, ethylene glycol and glycerol.

[0013] The present invention also provides a cerium-doped modified copper bismuthate gas-sensitive material, which adopts the following technical solution: a cerium-doped modified copper bismuthate gas-sensitive material, wherein the cerium-doped modified copper bismuthate gas-sensitive material is prepared by the method described above.

[0014] The present invention also provides a formaldehyde testing element, which adopts the following technical solution: a formaldehyde testing element, wherein the formaldehyde testing element contains cerium-doped modified copper bismuthate gas-sensitive material as described above.

[0015] The present invention also provides a formaldehyde sensor, which adopts the following technical solution: a formaldehyde sensor, wherein the formaldehyde sensor contains the formaldehyde testing element as described above.

[0016] Beneficial effects: The method for preparing the cerium-doped modified copper bismuthate gas-sensitive material of the present invention is simple and low-cost. The prepared material has a uniform morphology and is suitable for large-scale production.

[0017] The present invention helps to regulate the electronic structure and surface active sites of materials by introducing cerium, which can effectively inhibit the competitive adsorption of water molecules on the material surface, thereby helping to solve or improve the problems of poor moisture resistance (failure to function when exposed to water) and low response value of pure copper bismuthate when used for formaldehyde detection.

[0018] The cerium-doped modified copper bismuthate gas-sensitive material of the present invention is significantly less affected by humidity in its formaldehyde detection performance, which helps to improve the formaldehyde detection response value and improve the formaldehyde detection performance in high humidity environments.

[0019] Experimental data show that as the relative humidity (RH) increases from 10% to 90%, the response retention rate of pure copper bismuthate is only 11%, while the response retention rate of the cerium-doped copper bismuthate gas-sensitive material of this invention can be increased to 49%. This characteristic allows the material to be used directly for the detection of formaldehyde in human exhaled gas (high humidity environment) without the need for complex dehumidification devices.

[0020] Furthermore, the cerium-doped modified copper bismuthate gas-sensitive material of the present invention has a minimum detection limit of less than 50 ppb under conditions of 240°C and 90% RH, which can cover the abnormal range of formaldehyde concentration in the exhaled gas of lung cancer patients and has the potential to be applied to early cancer screening. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 The product characterizations of Examples 1-5 and Comparative Examples 1-2 are shown below; where a is an XRD pattern, b is a SEM image of Comparative Example 1, c is a SEM image of Example 3, d is a SEM image of Comparative Example 2, e is a dark-field TEM image of Example 3, f is an EDS elemental distribution map of Example 3, g and h are high-resolution TEM images of Example 3, and i is a selected area electron diffraction pattern of Example 3.

[0022] Figure 2The graph shows the formaldehyde gas sensitivity test results under 50% RH conditions. Specifically, a) shows the response values ​​of cerium-doped copper bismuthate from Examples 1-5 and pure copper bismuthate from Comparative Example 1 to 100 ppm formaldehyde at different temperatures; b) shows the resistance values ​​of cerium-doped copper bismuthate from Examples 1-5 and pure copper bismuthate from Comparative Example 1 at different temperatures; c) shows the response values ​​of CBO:Ce 0.25% (Example 3) and pure CBO (Comparative Example 1) to 100 ppm of different gases at 240℃; d) shows the response time and recovery time of CBO:Ce 0.25% and pure CBO at 240℃ for testing 500 ppb formaldehyde; e) shows the response values ​​of CBO:Ce 0.25% and pure CBO to different concentrations of formaldehyde at 240℃; and f) shows the response values ​​of CBO:Ce... The linear fit between the response values ​​of 0.25% CBO and pure CBO to 10-500 ppb formaldehyde at 240℃ and the formaldehyde concentration is shown. g represents the repeatability test results of the response values ​​of 0.25% CBO:Ce and pure CBO to 50 ppb formaldehyde at 240℃, and h represents the test results of the long-term stability of the response values ​​of 0.25% CBO:Ce and pure CBO to 50 ppb formaldehyde at 240℃.

[0023] Figure 3 The graph shows the test results of the effect of humidity on the formaldehyde gas sensing performance. Specifically, a) shows the test results of the response values ​​of CBO:Ce 0.25%, pure CBO, and CBO-FAS to 50 ppb formaldehyde at different relative humidityes and 240℃; b) shows the test results of the response values ​​of CBO:Ce 0.25% and pure CBO to 50 ppb formaldehyde at 90% RH and 240℃ for different gases; c) shows the test results of the response time and recovery time of CBO:Ce 0.25% and pure CBO for 50 ppb formaldehyde detection at 240℃; d) shows the repeatability test results of the response values ​​of CBO:Ce 0.25% and pure CBO to 100 ppb formaldehyde at 90% RH and 240℃; e) shows the repeatability test results of the response values ​​of CBO:Ce 0.25% and pure CBO to 50 ppb formaldehyde at 90% RH and 240℃; f) shows the response time of CBO:Ce... Test results of the long-term stability (continuous testing for 70 days) of the response values ​​of 0.25% and pure CBO to 50 ppb formaldehyde at 90% RH and 240℃.

[0024] Figure 4 for 1 H NMR proton spectroscopy analysis and mechanism of cerium doping for enhanced moisture resistance and gas sensitivity; where a is the proton spectroscopy analysis results of CBO:Ce 0.25% and pure CBO, b is the water vapor interference mechanism diagram of pure CBO surface, and c is the moisture resistance and gas sensitivity enhancement mechanism diagram of CBO:Ce 0.25%; Figure 5The electronic structure analysis results are for pure CBO and CBO:Ce 0.25%; where a is the high-resolution Bi 4f XPS spectrum of pure CBO and CBO:Ce 0.25%, b is the high-resolution Cu 2p XPS spectrum of pure CBO and CBO:Ce 0.25%, c is the high-resolution O 1s XPS spectrum of pure CBO and CBO:Ce 0.25%, and d is the high-resolution Ce 3d spectrum of CBO:Ce 0.25%. XPS spectra: e is the spin-resolved band structure and total density of states (TDOS) diagram of the pure CBO model; f is the spin-resolved band structure and total density of states (TDOS) diagram of the Ce-doped CBO model with Ce atoms substituted with Bi atoms; g is the spin-resolved band structure and total density of states (TDOS) diagram of the Ce-doped CBO model with Ce atoms substituted with Cu atoms; h is the partial density of states (PDOS) diagram of the pure CBO model, the Ce-doped CBO model with Ce atoms substituted with Bi atoms, and the Ce-doped CBO model with Ce atoms substituted with Bu atoms. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0026] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0027] This invention addresses the problem that the formaldehyde detection performance of pure copper bismuthate (CuBi2O4) material in the prior art is easily affected by humidity, and provides a method for preparing a cerium-doped modified copper bismuthate gas-sensitive material.

[0028] The preparation method of cerium-doped modified copper bismuthate gas-sensitive material according to the present invention includes the following steps: (1) adding cerium source solution dropwise to a mixed solution of copper source and bismuth source, stirring evenly, adding an alkaline substance as a precipitant, and stirring again to obtain a uniform suspension; (2) heating the uniform suspension to react; (3) after the reaction is completed, separating the solid and liquid, washing and drying the obtained solid to obtain the cerium-doped modified copper bismuthate gas-sensitive material; in step (2), the temperature is raised to 120-240℃ (e.g., 120℃, 150℃, 180℃, 210℃ or 240℃) and reacted for 3-24h (e.g., 3h, 6h, 9h, 12h, 15h, 18h, 21h or 24h). If the temperature of the reaction in step (2) is too high or too low, the product will be impure and other by-products other than copper bismuthate will be generated. If the reaction time is too short or too long, it will affect the microstructure and defect state of the product, which in turn will affect its sensitivity to formaldehyde.

[0029] This invention introduces Ce element into the copper bismuthate lattice. The introduction of Ce element can regulate the electronic structure and surface active sites of the material, effectively inhibiting the competitive adsorption of water molecules on the material surface, thereby helping to solve or improve the problem of pure copper bismuthate failing when exposed to water.

[0030] The preparation method of the cerium-doped modified copper bismuthate gas-sensitive material of the present invention is simple, low-cost, and produces materials with uniform morphology suitable for large-scale production.

[0031] Preferably, in step (2), the temperature is raised to 170-190℃ (e.g., 170℃, 175℃, 180℃, 185℃ or 190℃) and the reaction is carried out for 4-6 hours (e.g., 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours).

[0032] In a preferred embodiment of the preparation method of the cerium-doped modified copper bismuthate gas-sensitive material of the present invention, in step (1), the molar number of cerium in the cerium source is 0.01%-5.0% of the molar number of copper in the copper source (e.g., 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%); the molar ratio of copper in the copper source to bismuth in the bismuth source is 1:2. An inappropriate proportion of cerium will cause a decrease in the response value of the prepared cerium-doped modified copper bismuthate gas-sensitive material for detecting formaldehyde gas.

[0033] In a preferred embodiment of the method for preparing cerium-doped modified copper bismuthate gas-sensitive material of the present invention, in step (1), the number of moles of cerium in the cerium source is 0.05%-0.45% of the number of moles of copper in the copper source (e.g., 0.05%, 0.15%, 0.25%, 0.35% or 0.45%).

[0034] In a preferred embodiment of the preparation method of the cerium-doped modified copper bismuthate gas-sensitive material of the present invention, in step (1), the cerium source is a soluble cerium salt; the copper source is a soluble copper salt; and the bismuth source is a soluble bismuth salt.

[0035] In a preferred embodiment of the method for preparing cerium-doped modified copper bismuthate gas-sensitive material of the present invention, in step (1), the cerium source is at least one of cerium acetate, cerium nitrate, cerium chloride, cerium sulfate and cerium ammonium nitrate; the copper source is at least one of copper nitrate, copper chloride, copper sulfate and copper acetate; and the bismuth source is at least one of bismuth nitrate, bismuth chloride and bismuth citrate.

[0036] In a preferred embodiment of the preparation method of the cerium-doped modified copper bismuthate gas-sensitive material of the present invention, in step (1), the pH of the uniform suspension is >10; the alkaline substance is a metal hydroxide and / or a slow-release precipitant; the metal hydroxide is sodium hydroxide and / or potassium hydroxide; the slow-release precipitant is ammonia. The alkaline substance, after dissolving in the solvent, should be alkaline. Hydroxide ions react with copper ions and bismuth ions to generate metal hydroxide, which, after dehydration, generates metal oxide. The pH of the uniform suspension (the amount of alkaline substance) will affect the microstructure and defect state of the product, thereby affecting the formaldehyde sensitivity.

[0037] In a preferred embodiment of the method for preparing cerium-doped modified copper bismuthate gas-sensitive material of the present invention, the solvent in the mixed solution of copper source and bismuth source is at least one of water, ethanol, ethylene glycol and glycerol; the solvent in the cerium source solution is at least one of water, ethanol, ethylene glycol and glycerol.

[0038] This invention also proposes a cerium-doped modified copper bismuthate gas-sensitive material, which is prepared by the method described above.

[0039] The cerium-doped modified copper bismuthate gas-sensitive material of the present invention exhibits excellent moisture resistance, enabling it to be directly used for formaldehyde detection in high-humidity environments (for example, the cerium-doped modified copper bismuthate gas-sensitive material of the present invention is expected to be directly used for the detection of formaldehyde content in human exhaled breath), without the need for complex dehumidification devices. Furthermore, the cerium-doped modified copper bismuthate gas-sensitive material of the present invention has a higher response value to formaldehyde than pure copper bismuthate, and can be used for low-limit detection of trace formaldehyde at the ppb level.

[0040] The present invention also proposes a formaldehyde testing element, wherein the formaldehyde testing element of the present invention contains the cerium-doped modified copper bismuthate gas-sensitive material as described above.

[0041] The present invention also proposes a formaldehyde sensor, wherein the formaldehyde sensor of the present invention embodiment contains the formaldehyde testing element as described above.

[0042] The cerium-doped modified copper bismuthate gas-sensitive material of the present invention, its preparation method, and its application are described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0043] Example 1 The preparation method of the cerium-doped modified copper bismuthate gas-sensitive material in this embodiment includes the following steps: (1) Preparation of cerium acetate solution: Weigh 0.5 mmol of cerium acetate hydrate (Ce(CH3COO)3·xH2O) and dissolve it in 100 mL of deionized water. Stir magnetically until completely dissolved to prepare a cerium acetate solution with a concentration of 5 mmol / L for later use. (2) Preparation of mixed reaction solution: Place 1 mmol of copper nitrate (Cu(NO3)2) and 2 mmol of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) in a reaction vessel (such as a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene), add 29.9 mL of deionized water to the reaction vessel to dissolve the metal salt, and then add 100 µL of the cerium acetate solution prepared in step (1) (the molar amount of cerium is 0.05% of the molar amount of copper). Stir the above 30 mL mixed solution magnetically at room temperature for 30 min; then add 4 g of sodium hydroxide (NaOH) at once and stir vigorously for 1 h until a uniform suspension is formed.

[0044] (3) Hydrothermal reaction: The suspension obtained in step (2) was transferred to a polytetrafluoroethylene-lined high-pressure reactor, the reactor was sealed, and placed in an electric heating drying oven for 5 hours at 180°C.

[0045] (4) After the reaction is completed, the mixture is naturally cooled to room temperature, the precipitate is collected, and the mixture is washed several times by alternating centrifugation with deionized water and anhydrous ethanol until the pH of the supernatant drops to about 7. Finally, the product is dried at 60°C for 12 hours to obtain the cerium-doped copper bismuthate gas-sensitive material (in powder form) of this embodiment, denoted as CBO:Ce 0.05%.

[0046] Example 2 The only difference between the cerium-doped modified copper bismuthate gas-sensitive material in this embodiment and that in Example 1 is that in step (2), the molar amount of cerium is 0.15% of the molar amount of copper (i.e., in step (2), the amount of deionized water used is 29.7 mL and the amount of cerium nitrate solution used is 300 µL); the rest are the same as in Example 1.

[0047] The cerium-doped copper bismuthate gas-sensitive material in this embodiment is denoted as CBO:Ce 0.15%.

[0048] Example 3 The only difference between the cerium-doped modified copper bismuthate gas-sensitive material in this embodiment and that in Example 1 is that in step (2), the molar amount of cerium is 0.25% of the molar amount of copper (i.e., in step (2), the amount of deionized water used is 29.5 mL and the amount of cerium nitrate solution used is 500 µL); the rest are consistent with Example 1.

[0049] The cerium-doped copper bismuthate gas-sensitive material in this embodiment is denoted as CBO:Ce 0.25%.

[0050] Example 4 The only difference between the cerium-doped modified copper bismuthate gas-sensitive material in this embodiment and that in Example 1 is that in step (2), the molar amount of cerium is 0.35% of the molar amount of copper (i.e., in step (2), the amount of deionized water used is 29.3 mL and the amount of cerium nitrate solution used is 700 µL); the rest are consistent with Example 1.

[0051] The cerium-doped copper bismuthate gas-sensitive material in this embodiment is denoted as CBO:Ce 0.35%.

[0052] Example 5 The only difference between the cerium-doped modified copper bismuthate gas-sensitive material in this embodiment and that in Example 1 is that in step (2), the molar amount of cerium is 0.45% of the molar amount of copper (i.e., in step (2), the amount of deionized water used is 29.1 mL and the amount of cerium nitrate solution used is 900 µL); the rest are consistent with Example 1.

[0053] The cerium-doped copper bismuthate gas-sensitive material in this embodiment is denoted as CBO:Ce 0.45%.

[0054] Comparative Example 1 The only difference between this comparative example and Example 1 is that the step of adding cerium nitrate solution in steps (1) and (2) is omitted (the amount of deionized water used is 30 mL); the rest are the same as in Example 1.

[0055] The pure copper bismuthate gas-sensitive material used in this comparative example is denoted as CBO.

[0056] Comparative Example 2 This comparative example uses fluorosilane to modify copper bismuthate (hydrophobic modification). The fluorosilane-modified copper bismuthate in this comparative example is surface hydrophobic modified by a vapor-phase self-assembly method, including the following steps: the pure copper bismuthate prepared in Comparative Example 1 and one drop of fluorosilane (specifically tridecafluorooctyltriethoxysilane; hereinafter referred to as FAS) solution are placed in a semi-closed cavity, vacuum sealed and left to stand for 30 min, allowing the fluorosilane to uniformly self-assemble on the surface of the pure copper bismuthate. The resulting sample is named CBO-FAS.

[0057] Experimental Example 1. Characterization of the products from Examples 1-5 and Comparative Examples 1-2: (1) XRD patterns of cerium-doped copper bismuthate in Examples 1-5 and pure copper bismuthate in Comparative Example 1 are shown below. Figure 1 As shown in Figure a, the XRD diffraction peaks of all samples (pure CBO and CBO:Ce with different Ce doping ratios) correspond to the standard card JCPDS No. 72-0493, indicating that they are pure CuBi2O4 phase with no impurity peaks.

[0058] This indicates that as the Ce doping ratio increases from 0 to 0.45%, the diffraction peaks do not shift significantly; this suggests that low-concentration Ce doping does not change the main phase structure of CBO crystal, and that Ce ions may enter the lattice through interstitial or substitutional means without forming a new crystal phase.

[0059] (2) SEM microstructure: Figure 1 Figures b, c, and d show the microstructures of copper bismuthate (pure CBO) from Comparative Example 1, Ce-doped copper bismuthate (CBO:Ce 0.25%) from Example 3, and fluorosilane-modified copper bismuthate (CBO-FAS) from Comparative Example 2, respectively. Figure 1 Both b and 1c appear as spheres composed of clearly defined quadrangular prisms, with no obvious difference in appearance; Figure 1 Due to the surface load of fluorosilane, the sharp edges of the tetragonal prisms on the d surface become blurred.

[0060] (3) Element distribution (EDS mapping): like Figure 1 As shown in f, the surface scan results of the CBO:Ce 0.25% sample show that Cu, Bi, and O elements are uniformly distributed in the microspheres, and Ce element is also uniformly doped without local enrichment. This indicates that Ce element was successfully introduced and uniformly distributed in the CBO matrix, providing a foundation for subsequent oxygen vacancy control and electronic structure optimization.

[0061] (4) HRTEM and SAED crystal structure analysis: Pure CBO and CBO:Ce 0.25% HRTEM Figure 1 As shown in gh; in pure CBO, the characteristic interplanar spacing of CuBi2O4 can be observed: 0.319nm corresponds to the (211) crystal plane and 0.270nm corresponds to the (310) crystal plane; in CBO:Ce 0.25% (h), in addition to the above crystal planes, the (420) crystal plane of 0.190nm and the (321) crystal plane of 0.216nm are also observed. The interplanar spacing has no obvious distortion, indicating that doping has not destroyed the periodic arrangement of the crystal.

[0062] Selected area electron diffraction revealed polycrystalline diffraction rings (Fig. i), corresponding to the (211), (102), (312), (530), and (721) crystal planes of CuBi2O4, further verifying the polycrystalline structure and pure phase characteristics of the material.

[0063] 2. Formaldehyde gas sensitivity test under 50% RH conditions: (1) The test results of the response values ​​of cerium-doped copper bismuthate in Examples 1-5 and pure copper bismuthate in Comparative Example 1 to 100 ppm formaldehyde gas at 50% RH and different temperatures are as follows: Figure 2 As shown in a: Depend on Figure 2 As can be seen from a, the response values ​​(Rg / Ra) of cerium-doped copper bismuthate in Examples 1-5 and pure copper bismuthate in Comparative Example 1 to 100 ppm formaldehyde all increased and then decreased with increasing temperature, with 240℃ being the optimal operating temperature; Ce doping significantly improved the response value, with CBO:Ce 0.25% showing the highest response value, which was far superior to pure CBO and other doping ratios.

[0064] (2) The resistance test results of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 100ppm formaldehyde gas at 50%RH and different temperatures are as follows: Figure 2 As shown in b: Depend on Figure 2 As shown in b, the resistance of cerium-doped copper bismuthate in Examples 1-5 and pure copper bismuthate in Comparative Example 1 decreases exponentially with increasing temperature, exhibiting typical semiconductor characteristics. Ce doping first increases and then decreases the initial resistance of the material, with the CBO:Ce 0.15% sample showing the highest resistance; further increases in concentration decrease the material resistance. The inset in the upper right corner shows the resistance changes of samples with different composite concentrations at the optimal operating temperature of 240°C.

[0065] (3) The test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 100 ppm of different gases at 50%RH and 240℃ are as follows: Figure 2 As shown in c: Depend on Figure 2 As can be seen from c, the response value of CBO:Ce 0.25% to formaldehyde is much higher than that of other interfering gases (acetone, ethanol, isopropanol, etc.), and significantly higher than that of pure CBO to formaldehyde. Pure CBO itself has a higher response to formaldehyde than other gases, but Ce doping further amplifies this selectivity difference.

[0066] (4) The test results of the response time and recovery time of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 500 ppb formaldehyde at 50% RH and 240℃ are as follows: Figure 2 As shown in d: Depend on Figure 2 As can be seen from d: the response time of CBO:Ce 0.25% is 25s and the recovery time is 164s; the response time of pure CBO is 28s and the recovery time is 130s; although the recovery time of CBO:Ce 0.25% is longer, the response value is significantly higher than that of pure CBO.

[0067] (5) The test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to different concentrations of formaldehyde at 50%RH and 240℃ are as follows: Figure 2 As shown in e: Depend on Figure 2 As can be seen from the results, both samples showed significant responses to formaldehyde concentrations ranging from 10 ppb to 100 ppm. The response value of CBO:Ce 0.25% was consistently higher than that of pure CBO, and the signal baseline remained stable without significant drift. Furthermore, at a concentration of 10 ppb, the response of CBO:Ce 0.25% was significantly higher than that of pure CBO (the response value of CBO:Ce 0.25% to 10 ppb formaldehyde increased from 1.05 for pure CBO to 1.15).

[0068] (6) The linear fitting test results of the relationship between the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 10-500 ppb formaldehyde at 50% RH and 240℃ and the formaldehyde concentration are as follows: Figure 2 As shown in f: Depend on Figure 2 As can be seen from f, within the range of 10ppb to 500ppb, the response values ​​of CBO:Ce 0.25% and pure CBO show a good linear relationship with the logarithm of formaldehyde concentration; CBO:Ce 0.25% has high sensitivity and good linearity for formaldehyde detection, and can realize the quantitative detection of formaldehyde from the ppb level.

[0069] (7) The repeatability test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 50 ppb formaldehyde at 50% RH and 240 °C are as follows: Figure 2 As shown in g: Depend on Figure 2 As can be seen from g, the response curve of CBO:Ce 0.25% has good repeatability, with no significant changes in the peak value and baseline, indicating that the material has excellent reversibility and repeatability.

[0070] (8) The long-term stability test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 50 ppb formaldehyde at 50% RH and 240℃ are as follows: Figure 2 As shown in h: Depend on Figure 2 As can be seen from h, the response values ​​of CBO:Ce 0.25% and pure CBO to 50ppb formaldehyde remain stable. The response value of CBO:Ce 0.25% is always about twice that of pure CBO, with no significant attenuation.

[0071] 3. Formaldehyde gas sensitivity test at 90% RH: (1) The test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3, pure copper bismuthate (pure CBO) in Comparative Example 1, and fluorosilane-modified copper bismuthate (CBO-FAS) in Comparative Example 2 to 50 ppb formaldehyde at different humidity and 240℃ are as follows: Figure 3 As shown in a: Depend on Figure 3 As can be seen from a, the response value of pure CBO decreases rapidly with increasing humidity; humidity has little effect on the response value of CBO:Ce 0.25%, and it can still maintain a relatively high response value under high humidity (when the humidity increases from 10%RH to 90%RH, the response retention rate of CBO:Ce 0.25% to 50ppb formaldehyde increases to 49%; while the response retention rate of pure CBO to 50ppb formaldehyde is only 11%); although high humidity has little effect on the response value of CBO-FAS, its response value is small under different humidity levels.

[0072] (2) The test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 50 ppb of different gases at 90%RH and 240℃ are as follows: Figure 3 As shown in b: Depend on Figure 3 b shows that the response value of CBO:Ce 0.25% to formaldehyde is much higher than that of other interfering gases (acetone, ethanol, isopropanol, etc.), and significantly higher than that of pure CBO to formaldehyde. Pure CBO has a higher response to formaldehyde than other gases, but Ce doping further amplifies this selectivity difference.

[0073] (3) The test results of response time and recovery time of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 for the detection of 50 ppb formaldehyde at 90%RH and 240℃ are as follows: Figure 3 As shown in c: Depend on Figure 3From c, we can see that: the response time of CBO:Ce 0.25% is 32s and the recovery time is 137s; the response time of pure CBO is 24s and the recovery time is 65s; although the recovery time of CBO:Ce 0.25% is longer, the response value is significantly higher than that of pure CBO.

[0074] (4) The repeatability test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 100 ppb formaldehyde at 90% RH and 240℃ are as follows: Figure 3 As shown in d; the repeatability test results of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 50 ppb formaldehyde at 90% RH and 240 °C are shown in d. Figure 3 As shown in e; Depend on Figure 3 As shown in d and e, the response curve of CBO:Ce 0.25% exhibits excellent repeatability, with no significant drift in peak height and baseline across multiple cycles; the response value of pure CBO remains consistently low.

[0075] (5) The long-term stability (continuous testing for 70 days) of the response values ​​of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 to 50 ppb formaldehyde at 90% RH and 240℃ is as follows: Figure 3 As shown in f: Depend on Figure 3 As can be seen from f, the response value of CBO:Ce 0.25% to 50 ppb formaldehyde remains around 4, with no significant attenuation; the response value of pure CBO remains around 1.8.

[0076] The above experimental results show that the cerium-doped modified copper bismuthate gas-sensitive material of the present invention has a detection limit of less than 50 ppb under the conditions of 240℃ and 90% RH, which can cover the formaldehyde concentration range in the exhaled gas of lung cancer patients and healthy people, and has the potential to be applied to early cancer screening (direct detection of lung cancer through exhalation without the need for exhalation treatment).

[0077] 4. 1 H NMR proton spectroscopy analysis and mechanism of enhanced moisture resistance and gas sensitivity: (1) The proton spectrum analysis results of cerium-doped copper bismuthate (CBO:Ce 0.25%) in Example 3 and pure copper bismuthate (pure CBO) in Comparative Example 1 are as follows: Figure 4 As shown in a; Depend on Figure 4 From a, we can see that pure CBO (red curve) exhibits three characteristic peaks: 6.38 ppm (acidic H+). +The concentrations of adsorbed water (H2O) and surface hydroxyl groups (-OH) were 4.74 ppm and 0.87 ppm, respectively. This indicates that the pure CBO surface contains a large amount of adsorbed water and hydroxyl groups, which easily form a strong hydrogen bond network and compete for formaldehyde adsorption sites. At the same time, water vapor in a high humidity environment can interfere with the gas-sensitive reaction.

[0078] CBO:Ce 0.25% (blue curve): Peak shape changes significantly: 6.38 ppm acidic H+ + The peaks disappeared, and a weak water adsorption peak appeared at 4.66 ppm, while the intensity of the hydroxyl peak at 0.76 ppm decreased significantly. This indicates that Ce doping significantly reduced the strong adsorption of water and hydroxyl groups on the material surface, weakened the hydrogen bond network, and reduced the competitive interference of water vapor on formaldehyde adsorption. This is the key basis for performance improvement under high humidity conditions.

[0079] (2) Water vapor interference mechanism of pure CBO surface, such as Figure 4 As shown in b; Under high humidity, H2O molecules form a dense hydrogen bond network on the surface of pure CBO: water vapor is adsorbed on the material surface and converted into hydroxyl groups (-OH), occupying active sites; formaldehyde molecules (HCHO) have difficulty penetrating the hydrogen bond network to reach the active sites, resulting in a decrease in response value; the hydroxyl desorption reaction has poor reversibility, and water vapor continues to be adsorbed under high humidity, further inhibiting the gas-sensitive reaction.

[0080] (3) The mechanism of enhanced moisture resistance and gas sensitivity of CBO:Ce 0.25% is as follows: Figure 4 As shown in c; Ce doping fundamentally solves the water vapor interference problem through oxygen vacancy regulation and redox cycle, which can be divided into two main paths: Path 1: Directly fill oxygen vacancies (pink arrow): Ce 4+ / Ce 3+ Redox pairs provide a dynamic oxygen source: O2 in the environment is converted by Ce. 3+ Captured and converted into lattice oxygen (O L） Directly fill oxygen vacancies (O) V Maintaining a dynamic balance of oxygen vacancy concentration and inhibiting excessive water vapor from passing through the "O2" oxygen vacancy zone. V The reaction "+H2O→2OH" generates hydroxyl groups, thereby promoting the formation of a hydrogen bond network on the surface to block the approach of target molecules.

[0081] Path 2: Lattice oxygen migration to fill oxygen vacancies (blue-green arrow): Ce doping lowers the migration barrier of lattice oxygen, allowing lattice oxygen (MO) to migrate and fill oxygen vacancies. L They can migrate to oxygen vacancies to maintain surface oxygen balance.

[0082] Key synergies (red arrows at the bottom): Under high humidity conditions, maintaining the stability of oxygen vacancies preserves the dynamic balance of surface hydroxyl groups, preventing the formation of surface hydrogen bond networks that could interfere with the gas-sensitive reaction. Surface hydroxyl desorption reaction (2OH→O) L +O V The reaction of H2O(gas) is more likely to occur, reducing the residence of water vapor on the surface; formaldehyde molecules can directly reach the active sites and react with adsorbed oxygen, greatly improving the response value and selectivity in high humidity environments.

[0083] 5. Figure 5 ad represents the XPS spectra of cerium-doped copper bismuthate from Example 3 and pure copper bismuthate from Comparative Example 1. Figure 5 ab indicates that Bi is stably present in both samples. 3+ and Cu 3+ ;in, Figure 5 a indicates that the binding energy shifts to a lower value by 0.1 eV after doping, which suggests that the charge density near the Bi atom has increased. Figure 5 c indicates that the content of lattice oxygen species and adsorbed oxygen species increases after doping; Figure 5 d indicates that Ce exists in a mixed valence state of trivalent and tetravalent in Example 3.

[0084] Figure 5 Spin-resolved band structure, density of states (DOS), and partial-wave density of states (PDOS) were calculated for three models: pure CBO, Ce@Bi, and Ce@Cu. All models preserved semiconductor properties. PDOS analysis showed that Ce... 3+ (4f) 1 This provides an unpaired electron in the spin-up channel, and the Ce 4f orbital hybridizes with the Cu 3d and O 2p orbitals at the top of the valence band. Ce@Cu narrows the band gap to 0.76 eV, where the Ce 4f state hybridizes with the O 2p (spin-up) and Cu 3d (spin-down) orbitals at the bottom of the conduction band, which is consistent with Ce 4+ (4f) 0 These results confirm that Ce is consistent with Ce. 4+ / Ce 3+ The presence of mixed valence states introduces excess electrons, increases the electron density around Bi sites, induces lattice distortion, increases oxygen vacancy concentration, and effectively narrows the band gap through site-dependent orbital hybridization, providing more active sites and optimizing carrier transport.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a cerium-doped modified copper bismuthate gas-sensitive material, characterized in that, Includes the following steps: (1) Add cerium source solution dropwise to the mixed solution of copper source and bismuth source, stir evenly, add alkaline substance as precipitant, and stir again to obtain a uniform suspension; (2) The uniform suspension is heated to react; (3) After the reaction is completed, the solid and liquid are separated, and the obtained solid is washed and dried to obtain the cerium-doped modified copper bismuthate gas-sensitive material. In step (2), the temperature is raised to 120-240℃ and the reaction is carried out for 3-24 hours.

2. The preparation method of the cerium-doped modified copper bismuthate gas-sensitive material as described in claim 1, characterized in that, In step (1), the molar number of cerium in the cerium source is 0.01%-5.0% of the molar number of copper in the copper source; The molar ratio of copper in the copper source to bismuth in the bismuth source is 1:

2.

3. The preparation method of the cerium-doped modified copper bismuthate gas-sensitive material as described in claim 2, characterized in that, In step (1), the number of moles of cerium in the cerium source is 0.05%-0.45% of the number of moles of copper in the copper source.

4. The preparation method of the cerium-doped modified copper bismuthate gas-sensitive material as described in claim 1, characterized in that, In step (1), the cerium source is a soluble cerium salt; The copper source is a soluble copper salt; The bismuth source is a soluble bismuth salt.

5. The preparation method of the cerium-doped modified copper bismuthate gas-sensitive material as described in claim 4, characterized in that, In step (1), the cerium source is at least one of cerium acetate, cerium nitrate, cerium chloride, cerium sulfate, and cerium ammonium nitrate; The copper source is at least one of copper nitrate, copper chloride, copper sulfate, and copper acetate; The bismuth source is at least one of bismuth nitrate, bismuth chloride, and bismuth citrate.

6. The method for preparing the cerium-doped modified copper bismuthate gas-sensitive material as described in claim 1, characterized in that, In step (1), the pH of the homogeneous suspension is >10; The alkaline substance is a metal hydroxide and / or a slow-release precipitant; The metal hydroxide is sodium hydroxide and / or potassium hydroxide; The slow-release precipitant is ammonia.

7. The method for preparing the cerium-doped modified copper bismuthate gas-sensitive material as described in claim 1, characterized in that, The solvent in the mixed solution of copper and bismuth sources is at least one of water, ethanol, ethylene glycol and glycerol; The solvent for the cerium source solution is at least one of water, ethanol, ethylene glycol, and glycerol.

8. A cerium-doped modified copper bismuthate gas-sensitive material, characterized in that, The cerium-doped modified copper bismuthate gas-sensitive material is prepared by the method described in any one of claims 1-7.

9. A formaldehyde testing element, characterized in that, The formaldehyde testing element contains a cerium-doped modified copper bismuthate gas-sensitive material as described in claim 8.

10. A formaldehyde sensor, characterized in that, The formaldehyde sensor contains the formaldehyde testing element as described in claim 9.

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