Photostimulated in2o3 / ppy / g-c3n4 heterojunction material for sensing co2 gas at room temperature and preparation method thereof

Abstract

The application relates to an In2O3 / PPy / g-C3N4 heterojunction material synthesized by a solvothermal method and an in-situ polymerization method, which is used for detecting CO2 gas under room temperature and visible light irradiation. The composite material combines the unique electronic properties of In2O3, the high conductivity of PPy and the good visible light absorption characteristics of g-C3N4, improves the photo-generated charge separation efficiency through the heterojunction effect, and significantly improves the detection performance of CO2. The sensing material not only has high sensitivity, low detection limit, good stability and reusability, but also is environment-friendly, conforms to the environmental protection development trend, and has wide application prospects in the fields of environmental monitoring and the like.

Description

I. TECHNICAL FIELD

[0001] The application relates to the field of environmental monitoring and sensing technology, in particular to a sensing material for detecting CO2 gas at room temperature by using a light-excited In2O3 / PPy / g-C3N4 heterojunction material and a preparation method thereof. II. BACKGROUND

[0002] With the acceleration of global industrialization, the large-scale combustion of fossil fuels such as coal and oil leads to the year-by-year increase of the CO2 concentration in the atmosphere, which not only aggravates the greenhouse effect, but also causes serious threats to the ecological system and human health. Therefore, it is particularly important to develop a high-efficiency, accurate and environment-friendly CO2 sensor. Most of the currently available CO2 sensors need to work at high temperatures, have high energy consumption and have an impact on the environment. Therefore, it is of great significance to develop a sensing material that can efficiently and sensitively detect CO2 at room temperature for environmental protection and energy saving.

[0003] PolyPyrrole (PPy) is a kind of conductive polymer material, which has high conductivity, controllable synthesis and good biocompatibility, and is widely used in various fields, including sensors, batteries, solar cells, optoelectronics and biomedical engineering. PPy can play a very important role in semiconductor heterojunction materials because PPy has high conductivity, which can effectively improve the charge transport performance of semiconductor materials. When PPy is added to semiconductor materials, it can form a continuous conduction channel, making it easier for electrons to migrate in the material. The nitrogen atoms and pyrrole rings in PPy can provide additional chemical adsorption sites, which can help to enhance the interaction between the material and CO2 gas. Due to its good conductivity and the provision of chemical adsorption sites, PPy can improve the sensitivity of semiconductor materials to CO2. At the same time, it can improve the selectivity of the material to CO2 and reduce the interference of other gases. Therefore, the introduction of PPy can significantly improve the gas sensing performance of semiconductor heterojunction materials to CO2. In addition, PPy has very excellent visible light absorption capacity, and the combination of PPy and In2O3 will significantly enhance the visible light absorption capacity, broaden the visible light response range and improve the CO2 gas response under visible light irradiation.

[0004] Due to the high electrical conductivity and rich chemical adsorption sites of PPy, it can generate a detection signal at a lower CO2 concentration, thereby increasing the range and accuracy of its application. Due to the enhanced charge transport efficiency and chemical adsorption capacity of PPy, the response speed of In2O3 / PPy / g-C3N4 to CO2 is faster, which is very important for application fields that require fast and accurate detection of CO2. The In2O3 / PPy / g-C3N4 with PPy added has improved material structure, resulting in enhanced gas sensing performance and stability. Therefore, in terms of sensitivity, response speed and stability, the gas sensing performance of In2O3 / PPy / g-C3N4 to CO2 is superior to that of In2O3 / g-C3N4.

[0005] Based on the above considerations, the present application uses in-situ chemical polymerization to successfully grow PPy on the surface of In2O3, and in-situ polymerization of g-C3N4 to obtain a sandwich structure of In2O3 / PPy / g-C3N4 ternary heterojunction gas sensing material. III. SUMMARY

[0006] The present application aims to provide a sensing material for detecting CO2 gas at room temperature by using light to excite In2O3 / PPy / g-C3N4 heterojunction material and a preparation method thereof. The sensing material is a one-dimensional tubular structure of In2O3 / PPy / g-C3N4 composite heterojunction material, which uses heterojunction to increase the number of carriers on the surface of the gas sensing material and improve the disadvantage of easy recombination of photo-generated electron-hole pairs of single semiconductor material, and uses visible light to excite the semiconductor heterojunction material to realize sensing of low concentration of CO2 gas at room temperature.

[0007] In order to achieve the technical purpose of the present application, the technical scheme adopted by the present application is as follows:

[0008] 1. Preparation of In2O3 hollow tube: first, synthesize In-MIL-68 precursor by hydrothermal method, and then calcine in air atmosphere to obtain In2O3 hollow tubular structure.

[0009] 2. Preparation of g-C3N4 nanosheet: g-C3N4 nanosheet is prepared by simple heating treatment of urea, and pure g-C3N4 nanosheet is obtained by centrifugation and washing.

[0010] 3. Preparation of PPy: pyrrole is added to FeCl3·6H2O solution, ultrasonic reaction is carried out for 12h, after being washed with anhydrous ethanol and ultrapure water in a cycle, it is placed in a vacuum drying box for 12h, and black PPy powder is obtained.

[0011] 4. Preparation of In2O3 / PPy: Pyyrole was added to FeCl3-6H2O solution, then added dropwise to the suspension of In2O3 and pyrrole, and stirred for polymerization for 10 h. The product was centrifuged, washed with anhydrous ethanol and ultrapure water in a cycle, and then placed in a vacuum drying oven for 12 h to obtain gray-black In2O3 / PPy powder.

[0012] 5. Preparation of g-C3N4 / PPy: Pyyrole was added to the suspension of g-C3N4 nanosheets, and ultrasonically treated for 30 min. FeCl3-6H2O was added dropwise to the suspension of g-C3N4 and pyrrole for polymerization for 10 h, and then washed with anhydrous ethanol and ultrapure water in a cycle, and the precipitate was placed in a vacuum drying oven for 12 h to obtain black g-C3N4 / PPy powder.

[0013] 6. Preparation of In2O3 / PPy / g-C3N4 heterojunction material: In2O3 / g-C3N4 heterojunction material was prepared by in-situ growth and subsequent calcination treatment, wherein the light response performance of the material was optimized by adjusting the addition ratio of g-C3N4. In2O3 and g-C3N4 were ultrasonically treated, pyrrole was added dropwise to the suspension and ultrasonically dispersed, and then FeCl3-6H2O was added dropwise to the suspension of In2O3, pyrrole and g-C3N4, and the stirring reaction was continued for 10 h. The product was centrifuged, washed with anhydrous ethanol and ultrapure water in a cycle, and then placed in a vacuum drying oven for 12 h to obtain black In2O3 / PPy / g-C3N4 powder. The obtained In2O3 / PPy / g-C3N4 powder was placed in a tube furnace and heated to 350°C to obtain gray-black In2O3 / PPy / g-C3N4 heterojunction powder material.

[0014] 7. Characterization analysis: SEM and TEM were used to observe the morphology and confirm the microstructure of the material; XRD and FT-IR were used to determine the crystal structure and chemical composition of the material; and UV-Vis and PL tests were used to evaluate the optical performance and electron-hole separation efficiency of the material.

[0015] 8. Sensing performance test: Different concentrations of CO2 were detected under room temperature and visible light irradiation, and the results showed that the In2O3 / PPy / g-C3N4 heterojunction material had extremely high sensitivity to CO2 and a detection limit as low as ppm level, which was significantly better than single In2O3 material.

[0016] As preferred, in step 1, 468 mg of In(NO3)3-xH2O and 180 mg of H2BDC were weighed and added to 40 ml of DMF, respectively.

[0017] As preferred, in step 2, 10 g of urea was weighed and placed in a tube furnace, and the heating rate was set to 2 ℃ / min, heated to 550 ℃ for 4 h.

[0018] As preferred, in step 3, 2.96 g of FeCl3·6H2O was weighed and dissolved in 20 ml of ultrapure water, and 0.5 ml of pyrrole was gradually added to 30 ml of ultrapure water, and ultrasonic treatment was performed for 30 min.

[0019] As preferred, in step 3, the FeCl3·6H2O aqueous solution was gradually added to the pyrrole dispersion under a 3 ℃ water bath and the reaction was continued for 12 h.

[0020] As preferred, in step 4, 100 mg of In2O3 was weighed and placed in 35 ml of ultrapure water, and 40 μl of pyrrole was added and ultrasonic treatment was performed for 30 min. The FeCl3·6H2O aqueous solution was added to the In2O3 and pyrrole suspension, and stirring was performed for 10 h.

[0021] As preferred, in step 5, 100 mg of g-C3N4 nanosheet was weighed and placed in 35 ml of ultrapure water, and 40 μl of pyrrole was added and ultrasonic treatment was performed for 30 min. The FeCl3·6H2O aqueous solution was added to the g-C3N4 and pyrrole suspension at 40 ℃ and stirring was performed for 10 h.

[0022] As preferred, in step 6, 100 mg of In2O3 and 50 mg of g-C3N4 were added to ultrapure water and ultrasonic dispersion was performed; 20 μl, 40 μl, and 60 μl of pyrrole were weighed and added to a beaker and ultrasonic dispersion was performed for 30 min.

[0023] As preferred, in step 6, the FeCl3·6H2O aqueous solution was added to the In2O3, pyrrole, and g-C3N4 suspension, and stirring was continued for 10 h.

[0024] As preferred, in step 6, the In2O3 / PPy / g-C3N4 powder was placed in a tube furnace and annealed at 350 ℃ for a short time (30 min).

[0025] As preferred, in step 8, an electrochemical workstation I-t test was used to obtain a current-time curve, data conversion was performed to obtain resistance-time information, and CO2 concentration change information was obtained.

[0026] Figure 1SEM and TEM images of In2O3 / PPy / g-C3N4 heterojunction material. PPy nanoparticles are uniformly dispersed and loaded on the surface of g-C3N4 nanosheets. It is proved that PPy nanoparticles are successfully in-situ polymerized on g-C3N4. The hollow structure of the material can be seen in the TEM image of the composite material, but the tube wall is not obvious. The in-situ polymerization of PPy and g-C3N4 has an impact on the hollow tubular structure of In2O3. From the HRTEM image, it can be observed that the interplanar spacing is 0.291 nm corresponding to the In2O3(222) crystal plane, and it can be observed that the outer layer of In2O3 is wrapped with PPy, and the outer layer of PPy is wrapped with g-C3N4.

[0027] Figure 2 XRD pattern of In2O3 / PPy / g-C3N4 heterojunction material. It is found that the addition of g-C3N4 has an impact on the crystallization performance of PPy. Due to the large specific surface area of g-C3N4 and other reasons, there is a certain interface interaction between PPy and g-C3N4, which hinders the regular arrangement of PPy polymer chain, resulting in the change of crystallinity.

[0028] Figure 3 FT-IR pattern of In2O3 / PPy / g-C3N4 heterojunction material. The characteristic peak of PPy at 1548 cm -1 -1 is the C=C vibration peak of the pyrrole ring, 1017 cm -1 -1 corresponds to the stretching vibration of C-N, and the characteristic peaks of g-C3N4 appearing at 1239, 1316, 1406, 1637 cm -1 -1 are consistent with the stretching vibration peaks of aromatic C-N and C=N heterocycle, which proves the successful synthesis of PPy and g-C3N4.

[0029] Figure 4 XPS spectrum of In2O3 / PPy / g-C3N4 heterojunction material. After the composite PPy, the characteristic peaks of In2O3 / PPy / g-C3N4 move to the direction of higher binding energy, lattice oxygen (530.3 eV), vacancy oxygen (531.9 eV) and adsorbed oxygen (533.2 eV). It is proved that there is a strong electron transfer between PPy and g-C3N4, In2O3.

[0030] Figure 5UV-vis DRS test analysis of PPy, g-C3N4, g-C3N4 / PPy, In2O3 / g-C3N4 and In2O3 / PPy / g-C3N4 can be used to analyze the visible light absorption range, the separation efficiency of photo-generated carriers and the semiconductor band gap, etc. The absorption band edge of In2O3 / PPy / g-C3N4 heterojunction material has a red shift, and has a significantly enhanced visible light absorption ability compared with In2O3 / g-C3N4, which is extended to the entire visible light absorption range. This is due to the high carrier transport capacity, strong visible light absorption capacity of PPy and the formation of heterojunction.

[0031] Figure 6 In2O3, PPy, g-C3N4 and In2O3 / PPy / g-C3N4 heterojunction materials were tested under visible light irradiation and dark conditions, respectively. The heterojunction material significantly improves the condition that the single material cannot completely recover without visible light irradiation. It is proved that the heterojunction and visible light irradiation can improve the response and recovery ability. Among them, PPy shows p-type response, that is, the resistance decreases after contacting with oxidizing gas.

[0032] Figure 7 In order to further prove that In2O3 / PPy / g-C3N4 mainly responds to CO2 in the air, CO2 gas sensing performance test of In2O3 / PPy / g-C3N4 under visible light irradiation at room temperature was carried out. Different concentrations of CO2 and N2 were used alternately to obtain dynamic response curve. With the increase of CO2 gas concentration, the sensitivity also increases.

[0033] Figure 8 The air with increased CO2 concentration of 200 ppm was tested under different humidity to evaluate the influence of humidity on the sensing performance of the gas sensitive material. The pyrrole nitrogen in PPy can provide additional adsorption sites for CO2, and accordingly, In2O3 / PPy / g-C3N4 is less affected by humidity compared with In2O3 / g-C3N4.

[0034] Figure 9 The air with increased CO2 concentration of 120 ppm and air were continuously contacted with the gas sensitive material to evaluate the sensing performance of the gas sensitive material. After multiple continuous tests, the sensitivity curve of the heterojunction material does not show obvious deviation, and In2O3 / PPy / g-C3N4 has higher sensitivity.

[0035] The excellent effect of the application is that: 1, the In2O3 / PPy / g-C3N4 heterojunction material in the application shows a one-dimensional outer uniform loading of nanoparticles and nanosheet sandwich structure, PPy has good adsorption effect on CO2, can produce higher photocurrent, can improve the sensitivity and response time of gas response, and is obviously superior to single semiconductor gas sensitive material. The heterojunction material has great application potential in CO2 quantitative detection sensing.

[0036] 2, PPy is in-situ polymerized between In2O3 and g-C3N4 by in-situ polymerization. A series of In2O3 / PPy / g-C3N4 heterojunction materials are obtained by further short-time calcination to remove the excess PPy on the surface. Due to the loading of PPy, the transmission mode of carriers between In2O3 / g-C3N4 heterojunction is changed, and the visible light absorption capacity of the material is greatly improved. These changes can improve the charge separation efficiency of In2O3 / g-C3N4, increase the number of electrons on the surface of the material, and further improve its sensing response to CO2.

[0037] 3, the In2O3 / PPy / g-C3N4 heterojunction material of the application realizes the sensing response of CO2 under visible light irradiation at room temperature. And the air with different concentrations of CO2 and CO2 concentration change all have good fitting function relationship. It is proved that the heterojunction material has great application potential in low concentration CO2 detection, such as plant respiration detection, human respiration detection, CO2 gas leakage detection, etc. IV. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 SEM and TEM images of the heterojunction material;

[0039] Figure 2 XRD image of the heterojunction material;

[0040] Figure 3 FT-IR image of the heterojunction material;

[0041] Figure 4 XPS spectrum of the heterojunction material;

[0042] Figure 5 UV-vis DRS and Tauc plot image of the heterojunction material;

[0043] Figure 6 CO2 gas sensing response curve of the heterojunction material to 50ppm;

[0044] Figure 7 Dynamic response curve of the heterojunction material to different concentrations of CO2 under visible light irradiation;

[0045] Figure 8 for gas selectivity of the heterojunction material under visible light irradiation;

[0046] Figure 9 for continuous multiple dynamic detection response curve and long-term stability test of the heterojunction material; V. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below. The following examples facilitate better understanding of the present application, but do not limit the present application. The experimental methods in the following examples are all conventional methods, unless otherwise specified.

[0048] Example 1

[0049] A preparation method of a heterojunction sensing material for CO2 gas detection at room temperature, characterized by comprising the following operation steps:

[0050] (1) Preparation of In-MIL-68: 468 mg of In(NO3)3·xH2O and 180 mg of H2BDC were weighed and added to 40 ml of DMF to dissolve thoroughly, and then reacted at 120℃ in an autoclave for 2 h, followed by centrifugation at 3500 r / min for 10 min. The white precipitate was washed and filtered with anhydrous ethanol and ultrapure water alternately, and then placed in a vacuum drying box for 12 h to obtain a white powder sample, i.e. In-MIL-68.

[0051] (2) Preparation of In2O3 hollow tube: the obtained In-MIL-68 was placed in a tube furnace and heated to 120℃ for 2 h, and then calcined at 400℃ for 2 h to obtain a white powder sample, i.e. In2O3 hollow tube.

[0052] (3) Preparation of g-C3N4 nanosheet: 10 g of urea was weighed and placed in a tube furnace and heated to 550℃ for 4 h to obtain light yellow g-C3N4. The g-C3N4 was stirred in ultrapure water for 4 h and ultrasonically dispersed for 1 h, and then dried in a vacuum drying box for 12 h to obtain light yellow g-C3N4 nanosheet.

[0053] (4) Preparation of PPy: 2.96 g of FeCl3·6H2O was weighed and added to 20 ml of ultrapure water. 0.5 ml of pyrrole was gradually added to 30 ml of ultrapure water, and ultrasonically treated for 30 min. The FeCl3·6H2O aqueous solution was gradually added to the pyrrole dispersion under a 3℃ water bath, and the reaction was continued for 12 h. The black product was placed in a 40℃ vacuum drying box for 12 h to obtain black PPy powder.

[0054] (5) Preparation of In2O3 / PPy: 100 mg of In2O3 hollow tube was weighed and placed in 35 ml of ultrapure water, 40 μl of pyrrole was taken and added, and ultrasonic treatment was performed for 30 min. 100 mg of FeCl3 6H2O was weighed and added to 5 ml of ultrapure water and stirred to dissolve completely, and was gradually added to the suspension of In2O3 and pyrrole at 40℃, and polymerization was performed for 10 h. The product was centrifuged, and after washing with anhydrous ethanol and ultrapure water in a cycle, it was placed in a vacuum drying oven at 40℃ for 12 h to obtain a gray-black In2O3 / PPy powder.

[0055] (6) Preparation of g-C3N4 / PPy: 100 mg of g-C3N4 nanosheet was weighed and placed in 35 ml of ultrapure water, 40 μl of pyrrole was taken and added, and ultrasonic treatment was performed for 30 min. 100 mg of FeCl3 6H2O was weighed and added to 5 ml of ultrapure water and stirred to dissolve completely, and was gradually added to the suspension of g-C3N4 and pyrrole at 40℃, and polymerization was performed for 10 h. The product was washed with anhydrous ethanol and ultrapure water in a cycle, and was placed in a vacuum drying oven at 40℃ for 12 h to obtain a black g-C3N4 / PPy powder.

[0056] (7) Preparation of In2O3 / PPy / g-C3N4 heterojunction material: 100 mg of In2O3 and 50 mg of g-C3N4 were weighed and added to 35 ml of ultrapure water, 40 μl of pyrrole was taken and gradually added to the beaker and continued to be ultrasonically dispersed for 30 min. 100 mg of FeCl3 6H2O was weighed and added to 5 ml of ultrapure water and stirred to dissolve completely, and was gradually added to the suspension of In2O3, pyrrole and g-C3N4 at 40℃, and stirring was continued for 10 h. The product was centrifuged, washed with anhydrous ethanol and ultrapure water in a cycle, and placed in a vacuum drying oven at 40℃ for 12 h to obtain a black In2O3 / PPy / g-C3N4 powder. The obtained powder was placed in a tube furnace, heated to 350℃ at a rate of 5℃ / min under a static air atmosphere, and annealed for a short time (30 min) to obtain a gray-black In2O3 / PPy / g-C3N4 heterojunction powder material.

[0057] The sensitivity of the preferred embodiment 1 of the present application to CO2 gas under visible light irradiation is the highest. Since the pyrrole nitrogen of PPy and the like has an adsorption effect on CO2, the influence of humidity is reduced, and it is proved that a suitable proportion of heterojunction material can achieve the best response to CO2 gas.

[0058] Example 2

[0059] Other conditions are the same as in example 1, and the difference is that in step (7), the amount of pyrrole added is 20 μl.

[0060] Example 3

[0061] Other conditions and Example 1 are the same, except that in step (7), the amount of pyrrole added is 60 μl.

Claims

1. A method for preparing an In2O3 / PPy / g-C3N4 heterojunction sensing material for CO2 gas detection at room temperature, characterized in that, (1) The In-MIL-68 precursor was synthesized by hydrothermal method and then calcined in air to obtain In2O3 hollow tubular structure. (2) g-C3N4 nanosheets were prepared by heating urea. (3) Pyrrole was added dropwise to the In2O3 and g-C3N4 suspension, and then FeCl3·6H2O was added dropwise to the suspension. After reacting for a period of time, the mixture was centrifuged and vacuum dried, and then calcined to obtain In2O3 / PPy / g-C3N4 powder.

2. The preparation method according to claim 1, characterized in that, In step (3), the amount of In2O3 added is 100mg, the amount of g-C3N4 added is 50mg, the amount of FeCl3·6H2O added is 100mg, and the amount of pyrrole added is 20-60μl.

3. An application of an In2O3 / PPy / g-C3N4 heterojunction material prepared according to the method of any of the preceding claims, characterized in that... Applications of room temperature CO2 gas sensing materials.

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