SnO2 (at) g-C3N4 (at) CeO2 composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of functional materials and sensing, and discloses a SnO2 (at) g-C3N4 (at) CeO2 composite material and a preparation method and application thereof.The preparation method of the composite material comprises the steps that stannous chloride dihydrate, cerium nitrate hexahydrate and deionized water are mixed, sodium hydroxide and cetyltrimethylammonium bromide are added, and stirring and uniform dispersing are conducted; then adding g-C3N4, and stirring; carrying out hydrothermal reaction on the stirred mixed solution, centrifuging, washing and drying; and finally, carrying out high-temperature calcination to obtain the SnO2 (at) g-C3N4 (at) CeO2 composite material. The novel metal oxide-polymer semiconductor-rare earth oxide ternary composite gas sensitive material SnO2 (at) g-C3N4 (at) CeO2 is constructed and applied to a gas sensor, and rapid detection of target gas at low temperature can be realized by assisting light irradiation with certain wavelength and intensity.

Description

Technical Field

[0001] The present invention relates to the field of functional materials and sensing technology, and in particular to a SnO2@g-C3N4@CeO2 composite material, a preparation method and applications thereof. Background Art

[0002] In today's world, where environmental and safety issues are of increasing concern, accurate and efficient detection of harmful gases is crucial. As a crucial tool for gas detection, the performance of gas sensors directly impacts the accuracy and reliability of detection. Traditional single-material gas sensors have limitations in sensitivity, selectivity, and stability, making them difficult to meet detection requirements in complex environments.

[0003] SnO2, a typical n-type semiconductor metal oxide, exhibits excellent chemical stability and high electron mobility, showing promising potential in the field of gas sensing. g-C3N4, a polymer semiconductor with a two-dimensional layered structure, possesses a large surface area and abundant active sites, enhancing its adsorption capacity for gas molecules. CeO2, with its excellent oxygen storage capacity and catalytic activity, can effectively promote gas redox reactions.

[0004] The three materials mentioned above have a wide range of applications in gas sensors. However, existing research requires that they be used at relatively high temperatures to detect certain target gases. Testing at higher temperatures poses significant safety risks for flammable and explosive target gases. Therefore, combining these three materials, integrating their respective advantages, and achieving low-temperature detection of flammable and explosive target gases is of great practical significance. In particular, there remains a technological gap in achieving a synergistic improvement in both low-temperature operation and high selectivity. Summary of the Invention

[0005] Purpose of the Invention: To address the problems existing in the prior art, the present invention provides a SnO2@g-C3N4@CeO2 composite material, preparation method, and application thereof. By constructing a novel metal oxide-polymer semiconductor-rare earth oxide ternary composite gas-sensitive material SnO2@g-C3N4@CeO2 and using it in a gas sensor, assisted by light irradiation of a certain wavelength and intensity, rapid detection of target gases at low temperatures can be achieved. The light-irradiated low-temperature SnO2@g-C3N4@CeO2 ternary gas sensor provided by the present invention has important applications in environmental monitoring, industrial safety early warning, and other fields.

[0006] Technical solution: In the first aspect, the present invention provides a method for preparing a SnO2@g-C3N4@CeO2 composite material, comprising the following steps: S1 take stannous chloride dihydrate, cerium nitrate hexahydrate mixed with deionized water, add sodium hydroxide and cetyltrimethylammonium bromide, stir and evenly disperse; S2 S1 was added to the resulting mixture g-C3N4, stirring; S3 S2 obtained mixture was subjected to a hydrothermal reaction, centrifuged, washed and dried; S4. The product obtained in S3 is calcined at a high temperature to obtain a SnO2@g-C3N4@CeO2 composite material.

[0007] Furthermore, in S1, the mass ratio of the stannous chloride dihydrate, the cerium nitrate hexahydrate, the deionized water, the sodium hydroxide and the hexadecyltrimethylammonium bromide is 1:0.03-0.1:13.5:0.7:0.3.

[0008] Furthermore, in S2, the added amount of g-C3N4 accounts for 0.3-0.5.

[0009] Furthermore, in S3, the specific conditions of the hydrothermal reaction are: reaction temperature of 160-200° C.; reaction time of 4-6 h.

[0010] Furthermore, in S3, the specific conditions of the drying are: drying temperature is 70-90° C.; reaction time is 2-4 h.

[0011] Furthermore, in S4, the specific operation of the high-temperature calcination is: heating to 350-450° C. at a heating rate of 2-4° C. / min and calcining for 2-4 hours.

[0012] In a second aspect, the present invention provides a SnO2@g-C3N4@CeO2 composite material prepared by any of the methods described above.

[0013] In a third aspect, the present invention provides an application of a SnO2@g-C3N4@CeO2 composite material prepared by any of the methods described above in a gas sensor, wherein the specific manufacturing method of the gas sensor is: (1) uniformly dispersing the SnO2@g-C3N4@CeO2 composite material in a mixed solution of ethanol and deionized water to form a slurry; coating the slurry on the surface of the ceramic tube and drying it to form a thin film layer with a thickness of 8-12 μm; (2) inserting the heating wire into the ceramic tube coated with the thin film layer in step (1), and welding the pins on the surface of the ceramic tube to the base respectively to obtain a sensor element; (3) Aging treatment of sensor components; (4) Using visible light to illuminate the thin film layer of the sensor element to detect formaldehyde; wherein the wavelength of the visible light is greater than 440 nm.

[0014] Furthermore, in step (4), a heating voltage of 0-3.3 V may be applied to the sensor element.

[0015] Furthermore, in step (3), the specific operation of the aging treatment is: 2.0-3.5V heating voltage treatment for 24-72h.

[0016] Theoretical explanation: This paper constructs a light-irradiated low-temperature SnO2@g-C3N4@CeO2 ternary gas sensor: SnO2, as the main gas-sensitive material, provides high electron mobility and abundant oxygen vacancies, which dominate gas adsorption and initial conductivity changes; g-C3N4, as a two-dimensional layered structure, increases the specific surface area and exposes more active sites. Its nitrogen-rich properties promote the chemical adsorption of gas molecules; CeO2 redox properties (Ce 3+ / Ce 4+ ) enhance the activity of surface oxygen species and promote the catalytic oxidation of gas molecules.

[0017] Due to the lamellar structure of g-C3N4, the interlayer gaps and the dispersion of SnO2 / CeO2 nanoparticles together provide more gas diffusion channels and adsorption sites. Under light, SnO2 generates electron-hole pairs, which promote the redox reaction of gas molecules on the surface and enhance the response speed. The narrow band gap of g-C3N4 absorbs visible light, expands the range of light excitation, and provides more photogenerated carriers. In addition, the lamellar structure of g-C3N4 can also prevent the agglomeration of SnO2 and CeO2 nanoparticles, which is beneficial to the adsorption and desorption effect of gases. 3+ / Ce 4+ Variable valence states introduce oxygen vacancies, which serve as active sites to capture formaldehyde gas molecules and promote lattice oxygen to participate in the reaction.

[0018] Under illumination (visible light), g-C3N4 and SnO2 / CeO2 jointly excite carriers to compensate for insufficient thermal excitation at low temperatures, and the local heating of CeO2 oxygen vacancies can further reduce the operating temperature requirement. In addition, the SnO2@g-C3N4@CeO2 ternary heterostructure builds a multi-level band structure, in which a heterojunction is formed between SnO2 and g-C3N4 or CeO2, and the electrons transfer from g-C3N4 (or CeO2) to SnO2 under thermal excitation, reducing the electron concentration of SnO2, expanding the depletion layer, and significantly improving the initial resistance (baseline). When the gas is adsorbed, the resistance change amplitude increases and the sensitivity is improved. CeO2 releases / stores oxygen (O 2- O - ), dynamically adjust the oxygen adsorption amount on the surface of the composite material and optimize the gas reaction kinetics.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following specific beneficial effects: 1. Multi-interface heterojunction design, constructing a "metal oxide-polymer-rare earth oxide" hierarchical structure to achieve synergistic enhancement of electron transport and surface reaction; 2. Utilize the oxygen storage effect of CeO2 and the molecular recognition characteristics of g-C3N4 to optimize the selective adsorption of target gas; 3. Use hydrothermal-calcination two-step method to ensure nano-level uniform compounding; 4. By irradiating light of a certain wavelength and intensity, rapid detection of formaldehyde gas can be achieved at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Schematic diagram of the device of the light-irradiated low-temperature SnO2@g-C3N4@CeO2 ternary gas sensor prepared by the present invention; Figure 2 The sensitivity of the SnO2@g-C3N4@CeO2 ternary gas sensor to formaldehyde at different heating voltages under light and no light irradiation; Figure 3 The response recovery curves of the SnO2@g-C3N4@CeO2 ternary gas sensor to 20, 50, 100, 200, 300, 400, 500, 1000, and 2000 ppm formaldehyde gas at a heating voltage of 3.3 V (200°C) in the absence of light. Figure 4 The response recovery curve of SnO2@g-C3N4@CeO2 ternary gas sensor to 2, 5, 10, 20, 50, 100, 200, 300, 400, and 500 ppm formaldehyde gas at a heating voltage of 3.3 V (200°C) under light irradiation; Figure 5 The response recovery curves of the SnO2@g-C3N4@CeO2 ternary gas sensor to 20, 50, 100, 200, 300, 400, 500, 1000, and 2000 ppm formaldehyde gas at a heating voltage of 0.6 V (37°C) under light and no light irradiation; Figure 6 (a) SEM characterization of SnO2@g-C3N4@CeO2 ternary composite material; Figure 6 (b) SEM characterization of lamellar g-C3N4; Figure 7 Schematic diagram of the gas-sensing mechanism of SnO2@g-C3N4@CeO2 ternary composite material to formaldehyde gas under light. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the embodiments.

[0021] Implementation method 1: This embodiment provides a method for preparing a SnO2@g-C3N4@CeO2 ternary composite material, comprising the following steps: 1. Solution preparation: Weigh 4.432 g of stannous chloride dihydrate (SnCl2·2H2O) and 0.137 g of cerium nitrate hexahydrate (Ce(NO3)2·6H2O), completely dissolve them in 30 mL of deionized water, and stir thoroughly with a magnetic stirrer for 30 min.

[0022] 2. Add sodium hydroxide: Add 3.204 g of sodium hydroxide (NaOH) to the mixed solution and continue stirring for 20 min.

[0023] 3. Adding a surfactant: Add 1.443g of cetyltrimethylammonium bromide (CTAB) as a surfactant and stir vigorously for 3 hours to ensure uniform dispersion and promote subsequent reactions. CTAB reduces the surface tension between particles in the solution, preventing agglomeration of SnO2, CeO2, and other particles, as well as the subsequently added g-C3N4. CTAB adsorbs on the particle surface, imparting the same charge to the particles. Electrostatic repulsion maintains the dispersion of the particles in the solution, ensuring uniform distribution of SnO2, CeO2, and g-C3N4 in the mixed solution.

[0024] 4. Add g-C3N4: Add 2.072 g of g-C3N4 to the above system and mechanically stir for 2 h to obtain a uniformly dispersed mixed solution.

[0025] 5. Hydrothermal reaction: Transfer the above solution to a 50 mL polytetrafluoroethylene-lined reaction vessel, place it in a high-pressure reactor, and treat it at a constant temperature of 180°C in a forced air drying oven for 5 h.

[0026] 6. Centrifugal washing: After the reaction is completed, the product is separated by a centrifuge and washed alternately with deionized water and ethanol multiple times to remove impurity ions.

[0027] 7. Drying and calcination: The washed precipitate was transferred to a porcelain boat, dried in a drying oven at 80°C for 3 h, and then placed in a muffle furnace, heated to 400°C at a heating rate of 2°C / min and calcined for 3 h to obtain the SnO2@g-C3N4@CeO2 ternary composite material.

[0028] This embodiment also provides a specific step of preparing a gas sensor using the SnO2@g-C3N4@CeO2 ternary composite material prepared above: 1. The SnO2@g-C3N4@CeO2 ternary composite material is dispersed in a mixed solution of ethanol and deionized water to form a slurry; the slurry is coated on a ceramic tube and dried to form a 10 μm thick sensitive film layer; 2. Insert the Cr-Ni heating wire into the ceramic tube coated with the gas-sensitive material, and weld the four Pt wire pins on the surface of the ceramic tube to the hexagonal base respectively; 3. The sensor element is aged for 48 hours using a constant heating voltage of 2.9V. 4. Use visible light to illuminate the thin film layer of the sensor. The wavelength of visible light must be greater than 440nm.

[0029] Performance testing: The SnO2@g-C3N4@CeO2 ternary composite material gas sensor prepared above was used for the detection of formaldehyde gas: 1. Compared with traditional SnO2 sensors, detailed parameters are shown in the table below:

[0030] 2. The sensitivity of SnO2@g-C3N4@CeO2 ternary composite gas sensor to formaldehyde was tested under different heating voltages under light and no light irradiation. The results are as follows: Figure 2 As shown; wherein, the abscissa is the heating voltage and the ordinate is the sensitivity; the sensitivity of the sensor prepared by the present invention to 200 ppm formaldehyde gas is 1 under no light irradiation and no heating voltage; the sensitivity to 200 ppm formaldehyde gas under light irradiation and no heating voltage is 5.3, and the detection limit is 50 ppm; the sensitivity to 200 ppm formaldehyde gas under light irradiation and 0.6 V (37°C) is 18.2, and the detection limit is 20 ppm; the sensitivity to 200 ppm formaldehyde gas under no light irradiation and 3.3 V heating voltage (200°C) is 68.5, and the detection limit is 20 ppm; the sensitivity to 200 ppm formaldehyde gas under light irradiation and 3.3 V heating voltage (200°C) is 94.6, and the detection limit is 2 ppm.

[0031] 3. Response recovery curves of SnO2@g-C3N4@CeO2 ternary composite gas sensor to formaldehyde gas at different heating voltages under light and no light irradiation Figure 3-5 As shown: Figure 3 The response recovery curve of the SnO2@g-C3N4@CeO2 ternary gas sensor to 20, 50, 100, 200, 300, 400, 500, 1000, and 2000 ppm formaldehyde gas at a heating voltage of 3.3 V (200°C) under no light irradiation; Figure 4 The response recovery curve of SnO2@g-C3N4@CeO2 ternary gas sensor to 2, 5, 10, 20, 50, 100, 200, 300, 400, and 500 ppm formaldehyde gas at a heating voltage of 3.3 V (200°C) under light irradiation; Figure 5 The following are the response recovery curves of the SnO2@g-C3N4@CeO2 ternary gas sensor to 20, 50, 100, 200, 300, 400, 500, 1000, and 2000 ppm formaldehyde gas at a heating voltage of 0.6 V (37°C) under light and no light irradiation; the horizontal axis is the test time and the vertical axis is the test voltage value; it can be seen that in the absence of light irradiation, the SnO2@g-C3N4@CeO2 ternary gas sensor has no response to different concentrations of formaldehyde gas at a heating voltage of 0.6 V (37°C).

[0032] 4. Characterize the SnO2@g-C3N4@CeO2 ternary composite material, such as Figure 6 As shown: Among them, Figure 6 (a) SEM characterization of SnO2@g-C3N4@CeO2 ternary composite material, in which SnO2 / CeO2 nanoparticles are attached to the surface of g-C3N4 sheets or filled in the gaps between g-C3N4 sheets, forming a complex three-dimensional structure; Figure 6 (b) is a lamellar structure of g-C3N4, stacked and staggered. The lamellar layers have a certain thickness and size, and their edges are irregular, showing natural tearing or growth boundaries. The lamellar surface is undulating and wrinkled, not completely smooth. In the present invention, SnO2, g-C3N4, and CeO2 are composited. The lamellar structure of g-C3N4, the interlayer voids therein, and the dispersion of SnO2 / CeO2 nanoparticles together provide more gas diffusion channels and adsorption sites.

[0033] 5. Figure 7 Schematic diagram of the gas-sensitive mechanism of SnO2@g-C3N4@CeO2 ternary composite material to formaldehyde gas under light; in air, the free electrons on the surface of the SnO2@g-C3N4@CeO2 ternary composite material come into contact with the adsorbed oxygen in the air to form oxygen anions, which leads to an increase in the surface resistance of the material and a thickening of the electron depletion layer; in formaldehyde gas, the formaldehyde gas reacts with the oxygen anions to generate free electrons that are re-injected into the SnO2@g-C3N4@CeO2 ternary composite material, thereby reducing the surface resistance of the material and thinning the electron depletion layer.

[0034] Implementation 2: This embodiment is substantially the same as Embodiment 1, except that, in this embodiment, the masses of other substances remain unchanged, and the doping mass of cerium nitrate hexahydrate (Ce (NO3)2·6H2O) is changed, wherein the doping mass of Ce (NO3)2·6H2O is 0.233 g.

[0035] Apart from this, this embodiment is identical to Embodiment 1 and will not be described in detail here.

[0036] Implementation 3: This embodiment is substantially the same as embodiment 1, except that in this embodiment, the masses of other substances remain unchanged, and the doping mass of cerium nitrate hexahydrate (Ce (NO3)2·6H2O) is changed, wherein the doping mass of Ce (NO3)2·6H2O is 0.385 g.

[0037] Apart from this, this embodiment is identical to Embodiment 1 and will not be described in detail here.

[0038] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a SnO2@g-C3N4@CeO2 composite material, characterized in that: The following steps are involved: S1 take stannous chloride dihydrate, cerium nitrate hexahydrate mixed with deionized water, add sodium hydroxide and cetyltrimethylammonium bromide, stir and evenly disperse; S2 S1 was added to the resulting mixture g-C3N4, stirring; S3 S2 obtained mixture was subjected to a hydrothermal reaction, centrifuged, washed and dried; S4. The product obtained in S3 is calcined at a high temperature to obtain a SnO2@g-C3N4@CeO2 composite material.

2. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 1, characterized in that: In S1, the mass ratio of stannous chloride dihydrate, cerium nitrate hexahydrate, deionized water, sodium hydroxide and hexadecyltrimethylammonium bromide is 1:0.03-0.1:13.5:0.7:0.

3.

3. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 1, characterized in that: In S2, the added amount of g-C3N4 is 0.3-0.

5.

4. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 1, characterized in that: In S3, the specific conditions of the hydrothermal reaction are: reaction temperature of 160-200° C.; reaction time of 4-6 h.

5. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 1, characterized in that: In S3, the specific conditions of the drying are: drying temperature is 70-90° C.; and reaction time is 2-4 h.

6. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 1, characterized in that: In S4, the specific operation of the high-temperature calcination is: heating to 350-450° C. at a heating rate of 2-4° C. / min and calcining for 2-4 hours.

7. A SnO2@g-C3N4@CeO2 composite material prepared by the method according to any one of claims 1 to 6.

8. Use of the SnO2@g-C3N4@CeO2 composite material prepared by the method according to any one of claims 1 to 6 in a gas sensor, characterized in that: The specific manufacturing method of the gas sensor is: (1) uniformly dispersing the SnO2@g-C3N4@CeO2 composite material in a mixed solution of ethanol and deionized water to form a slurry; coating the slurry on the surface of the ceramic tube and drying it to form a thin film layer with a thickness of 8-12 μm; (2) inserting the heating wire into the ceramic tube coated with the thin film layer in step (1), and welding the pins on the surface of the ceramic tube to the base respectively to obtain a sensor element; (3) Aging treatment of sensor components; (4) Detecting formaldehyde by irradiating a thin film layer of a sensor element with visible light, wherein the wavelength of the visible light is greater than 440 nm.

9. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 8, characterized in that: In step (4), a heating voltage of 0-3.3 V may also be applied to the sensor element.

10. The method for preparing the SnO2@g-C3N4@CeO2 composite material according to claim 8, characterized in that: In step (3), the specific operation of the aging treatment is: 2.0-3.5V heating voltage treatment for 24-72h.

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