High-sensitivity visible light full-spectrum activated sensitive material, NO2 gas sensor as well as preparation method and application of high-sensitivity visible light full-spectrum activated sensitive material

Abstract

The invention relates to the technical field of NO2 gas detection, and particularly discloses a high-sensitivity visible light full-spectrum activated sensitive material, the sensitive material is a g-C3N4 / SnS / Au nano composite material with a heterostructure, the g-C3N4 / SnS / Au nano composite material comprises g-C3N4 with a multi-lamellar structure and granular SnS growing on the surface of the g-C3N4, and the g-C3N4 / SnS / Au nano composite material is a high-sensitivity visible light full-spectrum activated sensitive material. The g-C3N4 / SnS composite material with a heterostructure is formed, Au nanoparticles are freely distributed on the surface and / or the edge of the g-C3N4 / SnS composite material, and a heterojunction is formed on a contact interface of the Au nanoparticles and the g-C3N4 / SnS composite material. The sensitive material disclosed by the invention has excellent absorption capacity on full-spectrum visible light, can better promote the generation of photon-generated carriers and improve the photon utilization rate under the irradiation of an external light source or natural light, and meanwhile provides activation energy required by surface reaction between target gas molecules and the sensitive material; sufficient energy is provided for gas-sensitive reaction at room temperature, and the comprehensive gas-sensitive performance of the gas sensor is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of NO2 gas detection, and specifically discloses a highly sensitive visible light full-spectrum activated sensitive material, a gas sensor, a preparation method thereof and an application thereof. Background Art

[0002] With the rapid development of technology, gas sensors play a key role in application scenarios such as environmental monitoring and industrial safety. The demand for high-sensitivity and low-power gas sensors is growing rapidly. Among them, metal oxide semiconductor-based gas sensors have been widely studied due to their superior reliability. However, the metal oxide semiconductor-based gas sensors show limited sensitivity at room temperature. They usually can only work under high-temperature modulation, which is difficult to meet the growing application requirements of working at room temperature, restricting the development of this type of sensor. In view of this, developing semiconductor gas sensors that can work stably at room temperature has become one of the research focuses in the field of gas detection.

[0003] Nitrogen dioxide (NO2), as a typical air pollutant, its emission sources mainly include the high-temperature combustion process of fossil fuels, motor vehicle exhaust emissions, as well as nitric acid manufacturing, metal smelting, etc. Nitrogen dioxide can participate in photochemical reactions in the atmospheric environment to form photochemical smog. At the same time, as an acidic precursor, it combines with moisture to form nitric acid, thereby causing acid rain. Some studies have shown that there is a significant correlation between the incidence of human respiratory system diseases and long-term exposure to a NO2 environment with a concentration level of 1 ppm, and there is a risk of inducing lung parenchymal damage. When the environmental concentration reaches the 8 ppm threshold, this gas will produce an acute toxic effect on the respiratory mucosa, specifically manifested as an aggravated bronchoconstriction reaction and impaired alveolar gas exchange function. Therefore, it is particularly important to detect nitrogen dioxide quickly and accurately. Publication No. CN 115974135 A discloses a highly selective NO2 gas sensor modulated by visible light based on an Au / SnS2 nanocomposite, which can achieve highly sensitive detection and specific recognition of NO2 gas in the room temperature detection mode. However, this gas sensor needs to be activated under illumination at a specific wavelength (420 nm), and its absorption range and intensity are limited, and its anti-interference ability and stability need to be further improved.

[0004] In recent years, graphitic carbon nitride (g-C3N4) has attracted extensive attention from researchers due to its unique layered structure, remarkable photoactivity, and high sensitivity to NO2, showing outstanding prospects in the development of next-generation room-temperature gas sensors and the detection of NO2. g-C3N4 exhibits efficient absorption capacity in the blue-violet light region with wavelengths less than 475 nm in the solar spectrum. However, due to the limited absorption wavelength, it cannot fully utilize the entire visible light spectrum, resulting in limited detection sensitivity and slow response and recovery speeds, which poses a huge challenge to improving the photon utilization efficiency to enhance the performance of g-C3N4 gas sensors.

[0005] The traditional sensitization strategy is to introduce second-phase particles into g-C3N4 to increase the number of active reaction sites in the sensitive material system, thereby effectively improving the gas-sensing response ability of g-C3N4 gas sensors. However, this method cannot fundamentally solve the problem of low photon utilization efficiency in the gas-sensing reaction at room temperature under natural light. Therefore, developing an effective and general method to improve the comprehensive gas-sensing performance of g-C3N4-based gas sensors under natural light excitation at room temperature is of great significance for its practical applications in environmental monitoring, industrial safety, and other fields. Summary of the Invention

[0006] The object of the present invention is to provide a highly sensitive visible light full-spectrum activated sensitive material aiming at the deficiencies of the existing technology. The sensitive material is a g-C3N4 / SnS / Au nanocomposite with a heterostructure. The sensitive material has excellent absorption capacity for the full-spectrum visible light. Under the irradiation of an external light source or natural light, it can better promote the generation of photo-generated carriers, improve the photon utilization efficiency, and provide sufficient energy for the gas-sensing reaction at room temperature. Applying it to a NO2 gas sensor is beneficial to achieving highly sensitive detection, excellent selectivity, and fast response / recovery rate of NO2 under the condition of natural light-assisted room-temperature operation of the gas sensor. The specific technical solutions are as follows:

[0007] A highly sensitive visible light full-spectrum activated sensitive material, the sensitive material is a g-C3N4 / SnS / Au nanocomposite with a heterostructure. The g-C3N4 / SnS / Au nanocomposite includes g-C3N4 presenting a multi-layered structure and granular SnS grown on its surface, forming a g-C3N4 / SnS composite with a heterostructure. Au nanoparticles are freely distributed on the surface and / or edge of the g-C3N4 / SnS composite, and a heterojunction is formed at the contact interface between the Au nanoparticles and the g-C3N4 / SnS composite.

[0008] The technical principle of the technical solution of the present invention is as follows: The sensitive material of the present invention has excellent absorption capacity for the full-spectrum visible light. Under the irradiation of an external light source or natural light, it can better promote the generation of photo-generated carriers, improve the photon utilization rate, and is applied to a NO2 gas sensor. By natural light assistance or by setting a light source above the gas sensor, it is used to emit full-band visible light towards the gas sensor during detection, excite the sensitive material system, provide the activation energy required for the reaction between the target gas molecules and the sensitive material, provide sufficient energy for the gas-sensing reaction under room temperature conditions, and enhance the comprehensive gas-sensing performance of the NO2 gas sensor under room temperature working conditions.

[0009] On the other hand, the present invention also provides a preparation method of the above-mentioned highly sensitive visible light full-spectrum activated sensitive material, including the following steps:

[0010] (1) Prepare multiple laminated g-C3N4 nanosheets;

[0011] (2) Grow granular SnS on the surface of the g-C3N4 nanosheets to obtain a g-C3N4 / SnS composite material with a heterostructure;

[0012] (3) Load Au nanoparticles on the g-C3N4 / SnS composite material, and a heterojunction is formed at the contact interface between the Au nanoparticles and the g-C3N4 / SnS composite material to obtain a g-C3N4 / SnS / Au nanocomposite material with a heterostructure.

[0013] Preferably, in the preparation method of the above-mentioned highly sensitive visible light full-spectrum activated sensitive material, in the step (1), the preparation process of the g-C3N4 nanosheets includes:

[0014] Step 1-1: Mix melamine powder and ascorbic acid powder evenly to obtain a mixed powder;

[0015] Step 1-2: Heat the mixed powder at a heating rate of 2 °C / min to 500-600 °C and keep it warm for 3-5 h;

[0016] Step 1-3: After the heat preservation ends, cool it naturally to room temperature to obtain porous g-C3N4 nanosheets.

[0017] Preferably, in the preparation method of the above-mentioned highly sensitive visible light full-spectrum activated sensitive material, in the step (2), the preparation process of the g-C3N4 / SnS composite material with a heterostructure includes:

[0018] Step 2-1: Dissolve SnCl2·2H2O in a mixed solvent of dilute HCl solution and deionized water, and stir for 10-30 min until a transparent mixed solution is formed;

[0019] Step 2-2: Uniformly disperse the prepared g-C3N4 nanosheets in the mixed solution obtained in Step 2-1 to obtain a suspension;

[0020] Step 2-3: Dissolve Na2S·9H2O in deionized water, slowly add it dropwise to the suspension obtained in Step 2-2, and then react with stirring at 45-55 °C for 2-3 h to obtain a mixture;

[0021] Step 2-4: Centrifuge and separate the precipitate from the mixture obtained in Step 2-3, then wash it 3-5 times with deionized water and absolute ethanol, and finally dry it in a vacuum drying oven at 50-65 °C for 9-15 h to obtain the g-C3N4 / SnS composite material.

[0022] Preferably, in the preparation method of the above high-sensitivity visible light full-spectrum activated sensitive material, the mass ratio of SnCl2·2H2O to g-C3N4 nanosheets is 40-50:28-35.

[0023] Preferably, in the preparation method of the above high-sensitivity visible light full-spectrum activated sensitive material, in Step (3), the preparation process of the g-C3N4 / SnS / Au nanocomposite material with a heterostructure includes:

[0024] Step 3-1: Add the prepared g-C3N4 / SnS composite material to deionized water, and continuously oscillate it in an ultrasonic instrument until it is uniformly dispersed to obtain a mixture;

[0025] Step 3-2: Add sodium citrate (C6H5Na3O7·2H2O) and tannic acid (C 76 H 52 O 46 ) to the mixture obtained in Step 3-1, stir magnetically for 30-50 min, and then add the HAuCl4·3H2O solution and continue stirring for 2-4 h to obtain a mixed solution;

[0026] Step 3-3: Centrifuge the mixed solution obtained in Step 3-2, collect the black precipitate, wash it 3-5 times with deionized water and absolute ethanol, and then dry it in a vacuum drying oven at 50-65 °C for 9-15 h to obtain the g-C3N4 / SnS / Au nanocomposite material.

[0027] On the other hand, the present invention also provides the application of the above high-sensitivity visible light full-spectrum activated sensitive material in the preparation of a NO2 gas sensor.

[0028] On the other hand, the present invention also provides a high-sensitivity visible light full-spectrum activated NO2 gas sensor, the NO2 gas sensor includes a substrate with a plurality of interdigital electrodes and a sensitive material on the interdigital electrodes, and the sensitive material is the above sensitive material.

[0029] A light source is arranged above the NO2 gas sensor, which is used to emit full-spectrum visible light towards the NO2 gas sensor during detection, providing an excitation environment closest to natural light assistance. Under the irradiation of an external light source or natural light, it can better promote the generation of photo-generated carriers, improve the photon utilization rate, provide the activation energy required for the reaction system between the target gas molecules and the sensitive material, provide sufficient energy for the gas-sensing reaction at room temperature, and enhance the comprehensive gas-sensing performance of the NO2 gas sensor under room-temperature working conditions.

[0030] Preferably, in the above-mentioned highly sensitive visible light full-spectrum activated NO2 gas sensor, the average size of the Au nanoparticles is 30 - 35 nm, the interdigital electrode is an Ag-Pd electrode, the line width is 0.2 mm, the spacing is 0.2 mm, and the substrate material is Al2O3.

[0031] On the other hand, the present invention also provides a preparation method of the above-mentioned highly sensitive visible light full-spectrum activated gas sensor, including the following steps: dispersing g-C3N4 / SnS / Au powder in absolute ethanol to prepare a dispersion liquid, then drop-coating the dispersion liquid on an Al2O3 substrate with multiple interdigital fingers, and drying to form a sensitive film on the interdigital electrode, thus preparing a gas sensor with g-C3N4 / SnS / Au as the sensitive material; in an alternative embodiment, during the preparation of the sensitive film, the final sensitive film is formed by repeating the drop-coating and drying process 3 - 5 times.

[0032] On the other hand, the present invention also provides an application of the above-mentioned highly sensitive visible light full-spectrum activated gas sensor in the detection of NO2.

[0033] Preferably, in the above-mentioned application, the detection is carried out under natural light, or a light source is arranged above the gas sensor, which is used to emit full-spectrum visible light towards the NO2 gas sensor during detection, providing an excitation environment.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. The heterostructured g-C3N4 / SnS / Au nanocomposite of the present invention has excellent absorption capacity for full-spectrum visible light. Under the irradiation of an external light source or natural light, it can better promote the generation of photo-generated carriers, improve the photon utilization rate, and at the same time provide the activation energy required for the surface reaction between the target gas molecules and the sensitive material, providing sufficient energy for the gas-sensing reaction at room temperature. When applied to a gas sensor, it enhances the comprehensive gas-sensing performance of the gas sensor under room-temperature working conditions.

[0036] 2. The present invention uses the in-situ grown composite g-C3N4 / SnS / Au heterostructure material as the sensitive material, and successfully fabricates a room-temperature highly sensitive NO2 gas sensor activated by the full spectrum of natural light. In the environment assisted by natural light, the g-C3N4 / SnS / Au composite material enhances the light absorption and charge separation ability, increases the carrier lifetime, enhances the local surface plasmon resonance effect of the composite material system, elevates the temperature within the nanoscale range while raising the temperature of the entire material system, provides sufficient energy for the gas-sensing reaction, and the optimized g-C3N4 / SnS / Au heterostructure gas-sensing element has excellent comprehensive gas-sensing properties such as good NO2 sensitivity, fast response / recovery rate, excellent selectivity, reliable moisture resistance and stability.

[0037] 3. The highly sensitive visible-light full-spectrum activated NO2 gas sensor of the present invention is tested under light of multiple wavelengths. The test results show that it can achieve ultra-high sensitivity and fast response-recovery speed to NO2 under full-spectrum visible-light irradiation. It is activated by the full spectrum of visible light and can be excited under natural light, making full use of the energy of the solar spectrum and improving the light utilization efficiency.

[0038] 4. The composite g-C3N4 / SnS / Au heterostructure sensitive material system provided by the present invention not only reduces the activation energy of the reaction between the target gas molecules and the sensitive material, but also enhances the light absorption and charge separation ability, increases the carrier lifetime, and thus provides sufficient energy to accelerate the gas-sensing reaction process, ultimately contributing to enhancing the comprehensive gas-sensing performance of the sensor under room-temperature working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for description in the embodiments. Obviously, the drawings below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0040] Figure 1 It is a schematic structural diagram of the highly sensitive visible-light full-spectrum activated NO2 gas sensor of the present invention.

[0041] Figure 2 It is a schematic diagram of the preparation process of the g-C3N4 / SnS / Au composite material of the present invention.

[0042] Figure 3 It is the XRD pattern of g-C3N4, g-C3N4 / SnS and g-C3N4 / SnS / Au prepared in Examples 1 - 3 of the present invention.

[0043] Figure 4SEM images of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention; among them, (a) is g-C3N4; (b) is g-C3N4 / SnS; (c) is g-C3N4 / SnS / Au.

[0044] Figure 5 TEM image of g-C3N4 / SnS / Au prepared in Example 3 of the present invention; among them, (f) is the HRTEM image.

[0045] Figure 6 EDS elemental mapping spectra of C, N, Sn, S, and Au of g-C3N4 / SnS / Au prepared in Example 3 of the present invention.

[0046] Figure 7 XPS spectra of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention.

[0047] Figure 8 High-resolution XPS spectra of N1s of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention.

[0048] Figure 9 High-resolution XPS spectra of S2p of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention.

[0049] Figure 10 UV-visible absorption spectra of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention.

[0050] Figure 11 PL spectra of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention.

[0051] Figure 12 Dynamic response curves of gas sensors using g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention as sensitive materials to 1-50 ppm NO2 over time.

[0052] Figure 13 Correspondence between the response values of gas sensors using g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au prepared in Examples 1-3 of the present invention as sensitive materials and the NO2 concentration.

[0053] Figure 14are the response / recovery curves of the g-C3N4 / SnS / Au gas sensor prepared in Example 4 of the present invention to 1 ppm NO2 under different light conditions (i.e., without light, 365 nm, 405 nm, 450 nm, 550 nm, 650 nm, and FSVL).

[0054] Figure 15 are the dynamic response / recovery curves of the g-C3N4 / SnS / Au sensor prepared in Example 4 of the present invention to 1-50 ppm NO2 under full-band visible light assistance.

[0055] Figure 16 is the corresponding relationship between the response value of the g-C3N4 / SnS / Au sensor prepared in Example 4 of the present invention to NO2 and the NO2 concentration under full-band visible light assistance.

[0056] Figure 17 is the histogram of the selectivity comparison of the g-C3N4, g-C3N4 / SnS, g-C3N4 / SnS / Au, and g-C3N4 / SnS / Au-FSVL sensors prepared by the present invention to different gases.

[0057] Figure 18 are the repeated response / recovery curves of the g-C3N4 / SnS / Au sensor prepared in Example 4 of the present invention to three different concentrations of NO2 under full-band visible light assistance.

[0058] Figure 19 is the response / recovery curve of the g-C3N4 / SnS / Au sensor prepared in Example 4 of the present invention to 1 ppm NO2 under natural light.

[0059] Figure 20 is the moisture resistance and long-term stability diagram of the g-C3N4 / SnS / Au sensor prepared in Example 4 of the present invention.

[0060] Figure 21 is the normalized electric field diagram of g-C3N4 and g-C3N4 / SnS / Au prepared by the present invention under 380 nm light.

[0061] Figure 22 is the normalized electric field diagram of g-C3N4 / SnS / Au prepared by the present invention under 530 nm and 680 nm light.

[0062] Figure 23 is the schematic diagram of the NO2 sensing mechanism of the g-C3N4 / SnS / Au sensor prepared by the present invention without natural light irradiation and with natural light irradiation. Detailed implementation manners

[0063] The following is a detailed description of the specific embodiments of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0064] Example 1

[0065] A preparation method of a multi-layered g-C3N4 material, comprising the following steps:

[0066] Step 1-1: Mix 5 g of melamine powder and 0.25 g of ascorbic acid powder evenly to obtain a mixed powder;

[0067] Step 1-2: Put the mixed powder into a muffle furnace, set the muffle furnace to heat from room temperature to 550 °C at a heating rate of 2 °C / min in an air atmosphere, and keep it at this temperature for 4 h;

[0068] Step 1-3: After the heat preservation, cool it naturally to room temperature, take it out and grind it to obtain a porous g-C3N4 material.

[0069] It can be seen from Figure 4 that the prepared g-C3N4 material presents a multi-layered structure.

[0070] Example 2

[0071] A preparation method of a heterostructured g-C3N4 / SnS nanocomposite, comprising the following steps:

[0072] Step 2-1: Dissolve 45 mg of SnCl2·2H2O in a mixed solvent of 5 ml of 0.1 M dilute HCl solution and 15 ml of deionized water, stir for 10 min to make the solution evenly dispersed until a transparent mixed solution is formed;

[0073] Step 2-2: Uniformly disperse 32 mg of prepared g-C3N4 nanosheets in the mixed solution obtained in Step 2-2;

[0074] Step 2-3: Dissolve 48 mg of Na2S·9H2O in 20 ml of deionized water, slowly drop it into the suspension obtained in Step 2-3, heat and stir in a 50 °C water bath for 2 h to obtain a mixture;

[0075] Step 2-4: Centrifuge and separate the precipitate from the mixture obtained in Step 2-3, then wash it 5 times with deionized water and anhydrous ethanol respectively, and finally dry it in a vacuum drying oven at 60 °C for 12 h to obtain the g-C3N4 / SnS composite material.

[0076] Example 3

[0077] A method for preparing a heterostructured g-C3N4 / SnS / Au nanocomposite material, comprising the following steps:

[0078] Step 3-1: Add the prepared 16 mg of g-C3N4 / SnS and 60 ml of deionized water to a beaker, and continuously oscillate in an ultrasonic instrument for 30 minutes to obtain a suspension;

[0079] Step 3-2: Add 0.128 g of sodium citrate (C6H5Na3O7·2H2O) and 0.56 mg of tannic acid (C 76 H 52 O 46 ) to the suspension obtained in Step 3-1, magnetically stir at room temperature for 40 min, and then add 720 μL of a 100 mM HAuCl4·3H2O solution and continue stirring for 3 h to obtain a mixture;

[0080] Step 3-3: Centrifuge the mixture obtained in Step 3-2, collect the black precipitate, wash it 5 times with deionized water and anhydrous ethanol respectively, and then dry it in a vacuum drying oven at 60 °C for 12 h to obtain the g-C3N4 / SnS / Au composite material.

[0081] Example 4

[0082] A method for preparing a sensitive layer of a NO2 gas sensor, comprising the following steps:

[0083] Step 4-1: Uniformly disperse 0.01 g of the g-C3N4 / SnS / Au gas-sensitive material in 2 mL of anhydrous ethanol, and then perform ultrasonic treatment for 20 min to obtain a uniformly dispersed suspension;

[0084] Step 4-2: Drop-coat 2 μL of the suspension on an Al2O3 substrate (13.4 mm × 7 mm × 0.653 mm) with 5 Ag / Pd interdigital electrodes. After drying at 60 °C for 30 min, repeat the drop-coating and drying processes 5 times to prepare a sensitive film layer, and obtain a g-C3N4 / SnS / Au gas sensor.

[0085] The interdigital electrodes are commercially available electrodes purchased directly, and the spacing between the interdigital electrodes is 200 microns.

[0086] The preparation of the g-C3N4 gas sensor and the g-C3N4 / SnS gas sensor is the same as that of the g-C3N4 / SnS / Au gas sensor, except that g-C3N4 or g-C3N4 / SnS is used to replace g-C3N4 / SnS / Au.

[0087] The materials used in the following tests are all from Examples 1-4.

[0088] Microstructure Test

[0089] Figure 3 XRD patterns of the g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au materials prepared for Examples 1-3. In the XRD pattern of g-C3N4, all diffraction peaks point to g-C3N4 (JCPDS No: 87-1526), and no diffraction peaks related to impurities are observed. In the XRD pattern of g-C3N4 / SnS, in addition to the diffraction peaks that can be indexed to g-C3N4, five new characteristic peaks can be indexed, which can be associated with SnS (JCPDS No: 39-0354), corresponding to the (111), (040), (041), (211), and (151) crystal planes of SnS respectively. In the XRD spectrum of g-C3N4 / SnS / Au, in addition to the diffraction peaks of g-C3N4 and SnS, five new diffraction peaks are added, which can be associated with Au (JCPDS No: 04-0784), corresponding to the (111), (200), (220), (311), and (222) crystal planes of Au respectively. No other impurity components are found in the g-C3N4 / SnS / Au heterostructure, indicating the successful formation of the g-C3N4 / SnS / Au composite.

[0090] Figure 4 (a)-(c) are SEM images of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au respectively. Compared with the multi-layered flaky g-C3N4 in (a), the surface of the g-C3N4 nanosheets in (b) has obvious granularity, indicating that SnS is attached to the surface of g-C3N4 in the form of quantum dots, and the granular structure in (c) increases significantly, indicating the successful attachment of Au nanoparticles.

[0091] Figure 5 is the TEM image of g-C3N4 / SnS / Au, where the g-C3N4 nanosheets are uniformly modified with SnS nanosheets (purple circles) and Au nanoparticles (red circles); Au nanoparticles with an average size of 30-35 nm are randomly distributed throughout the Ti3C2T xThere is no obvious aggregation on the surface or edge of the g-C3N4 / SnS / Au composite material. The lattice plane spacing of the nanoparticles with a diameter of 4 nm is 0.28 nm, corresponding to the (040) crystal plane of SnS nanoparticles. The lattice plane spacing of the nanoparticles with a diameter of 30 nm is 0.24 nm, corresponding to the (111) crystal plane of Au nanoparticles. The lattice spacing of the substrate nanosheets is 0.34 nm, corresponding to the (002) crystal plane of g-C3N4, further verifying the successful preparation of the g-C3N4 / SnS / Au composite sensitive material.

[0092] Figure 6 Figure is the EDS diagram of g-C3N4 / SnS / Au. It can be seen from the figure that the spatial distribution of elements C, N, Sn, S, and Au is uniform, further verifying the uniform distribution of SnS and Au nanoparticles.

[0093] Through the above characterization results, it can be proved that the g-C3N4 / SnS / Au composite material was successfully prepared in this invention.

[0094] XPS Spectroscopy and Optical Characterization of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au

[0095] Figure 7 Figures are the XPS spectra of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au. It can be seen that the chemical compositions of the g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au samples are consistent with the XRD measurement results, and the corresponding elemental components exist in the samples.

[0096] Figure 8 and Figure 9 Figures are the high-resolution XPS spectra of N1s and S2p of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au respectively. In the N1s spectrum, three peaks appear in the spectrum of g-C3N4 / SnS / Au at 398.8 eV, 399.8 eV, and 401.3 eV, corresponding to C-NH bonds, N-C3 bonds, and C-N═C bonds respectively. In the S2p spectrum, two high-intensity peaks corresponding to S2p 1 / 2 and S2p 3 / 2 are located at 161.4 eV and 162.3 eV respectively. The successful preparation of the g-C3N4 / SnS / Au sensitive material was further confirmed by the XPS spectrum. Compared with the single g-C3N4, the peak positions of N 1s, C 1s, Sn 3d, and S2p shift slightly towards the direction of lower binding energy, indicating that electron transfer occurs after the introduction of SnS and Au, and a heterostructure and built-in electric field are formed at the interface.

[0097] Figure 10These are the UV-visible absorption spectra of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au. As can be seen from the figure, compared with g-C3N4 / SnS and g-C3N4, between the wavelengths of 300 nm and 900 nm, the absorption efficiency of the sensitive material g-C3N4 / SnS / Au for visible light has been significantly improved, further verifying that the g-C3N4 / SnS / Au composite material may be suitable for natural light absorption.

[0098] Figure 11 These are the PL spectra of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au. The emission peak centered at 425 - 600 nm is due to the emission of photoexcited charge recombination. The PL emission intensity on the g-C3N4 / SnS heterojunction is lower than that of g-C3N4, indicating that the heterojunction between g-C3N4 nanosheets and SnS nanoparticles contributes to the transfer and separation of photogenerated electrons and holes. The PL emission spectral intensity of g-C3N4 / SnS / Au is the lowest, indicating that the introduction of Au nanoparticles can effectively reduce the recombination of photoinduced electron-hole pairs, prolong the lifetime of photogenerated electrons, is beneficial to improving the utilization rate of photogenerated carriers, and thus effectively improves the gas-sensing performance of the sensor.

[0099] From the above microstructure tests, XPS spectra, and optical characterizations, it can be demonstrated that the present invention has successfully prepared g-C3N4 / SnS / Au nanomaterials with a heterostructure.

[0100] Gas Sensitivity of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au to NO2 at Different Concentrations and under Different Light Illuminations Energy Level Comparison

[0101] Figure 12 These are the dynamic response curves of gas sensors based on g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au sensitive materials to 1 - 50 ppm NO2 over time. As can be seen from the figure, the response value of the g-C3N4 / SnS sensor after compounding with SnS nanoparticles is higher than that of the g-C3N4 sensor. In comparison, the response increase of the g-C3N4 / SnS / Au sensor after compounding with Au nanoparticles is more obvious. There are more pores on the surface of g-C3N4 nanosheets, creating more active sites for the adsorption of NO2 gas molecules. The SnS nanoparticles modified on the surface of g-C3N4 nanosheets occupy the surface defects of g-C3N4 and generate new active sites, effectively improving the response / recovery rate and sensitivity of the sensor. After attaching Au nanoparticles to the surface of g-C3N4 / SnS, due to the high catalytic activity of Au, the response of the sensor is further enhanced.

[0102] Figure 13It is the corresponding relationship diagram between the response values of g-C3N4, g-C3N4 / SnS, and g-C3N4 / SnS / Au sensors and the NO2 concentration. It can be seen from the figure that the response values of the three gas sensors increase linearly with the NO2 concentration at low concentrations and gradually approach saturation at high concentrations.

[0103] Figure 14 It is the response / recovery curve of the g-C3N4 / SnS / Au sensor to 1 ppm NO2 under different light conditions (i.e., without light, 365 nm, 405 nm, 450 nm, 550 nm, 650 nm, and FSVL). It can be seen that under the condition of 1 ppm NO2, visible light of different wavelengths can improve the response of the g-C3N4 / SnS / Au gas sensor, and the full-spectrum visible light (FSVL) has the most obvious improvement in its response, which is about 1 time higher than the response value without light.

[0104] Figure 15 and Figure 16 They are respectively the dynamic response / recovery curve of the g-C3N4 / SnS / Au sensor to 1-50 ppm NO2 under the assistance of full-spectrum visible light and the linear corresponding relationship between the response value of the g-C3N4 / SnS / Au sensor and the NO2 concentration under the assistance of full-spectrum visible light. It can be seen from the figure that the g-C3N4 / SnS / Au sensor based on full-spectrum visible light assistance has high sensitivity and large response values in the entire detection concentration range, and the response value of the g-C3N4 / SnS / Au sensor increases with the increase of the NO2 concentration, showing a linear growth, and almost no baseline drift phenomenon occurs, indicating that the sensor has excellent consistency and reversibility and high sensitivity.

[0105] To study the selectivity of the g-C3N4 / SnS / Au gas sensor under the assistance of full-spectrum visible light, four sensors (g-C3N4, g-C3N4 / SnS, g-C3N4 / SnS / Au gas sensors under no light condition, and g-C3N4 / SnS / Au gas sensor under the assistance of full-spectrum visible light) were tested for their responses to different gases (1 ppm NO2, 10 ppm H2S, 10 ppm NH3, 10 ppm SO2, 10 ppm CH3COCH3, and 100 ppm CH4), and the results are as Figure 17 shown. It can be seen from the figure that by comparison, the response value of g-C3N4 / SnS / Au under the assistance of full-spectrum visible light to NO2 is significantly higher than that of other test gases, indicating that the device has good selectivity for NO2.

[0106] Figure 18 It is the repeated response / recovery curve of the g-C3N4 / SnS / Au sensor to three different concentrations of NO2 under the assistance of full-spectrum visible light.Figure 19 The response / recovery curves of the g-C3N4 / SnS / Au sensor to 1 ppm NO2 under natural light are shown. All show that the sensor has good repeatability, further confirming the high reliability and stability of the g-C3N4 / SnS / Au sensor in a natural light environment.

[0107] Figure 20 The moisture resistance and long-term stability diagram of the g-C3N4 / SnS / Au sensor is shown. It can be seen that the sensor has good moisture resistance and there are no obvious fluctuations in the response and baseline resistance of the sensor, indicating its good long-term stability.

[0108] As can be seen from the above, the g-C3N4 / SnS / Au heterostructure has a high degree of compatibility with natural light. The increase in photon utilization rate leads to a significant increase in the number of photo-generated carriers, providing the activation energy required for the surface reaction between NO2 and the sensitive material, providing sufficient energy for the gas-sensing reaction at room temperature, and greatly improving the sensing performance of the g-C3N4 / SnS / Au sensor to achieve the improvement of the gas-sensing performance of the g-C3N4 / SnS sensor under natural light irradiation.

[0109] NO2 Sensing Mechanism Driven by Localized Surface Plasmon Resonance Effect of Natural Light-Assisted Heterostructure g-C3N4 / SnS / Au

[0110] Figure 21 The normalized electric field diagrams of g-C3N4 and g-C3N4 / SnS / Au under 380 nm light are shown. Figure 22 The normalized electric field diagrams of g-C3N4 / SnS / Au under 530 nm and 680 nm light are shown. From Figure 21 it can be seen that the maximum normalized electric field intensity |E / E0| of the g-C3N4 / SnS / Au composite material max reaches 5.1, which is significantly higher than the electric field intensity of g-C3N4 (0.69). This significant enhancement of the electric field intensity greatly improves the light absorption efficiency. Combining with Figure 22 it can be found that g-C3N4 / SnS / Au has obvious electric field enhancement under three different wavelengths of light, indicating that the light absorption ability is enhanced. In particular, the |E / E0| value max is the largest at 530 nm, due to the great enhancement of the local electric field intensity and the improvement of the light absorption efficiency.

[0111] Figure 23 The schematic diagrams of the NO2 sensing mechanisms of the g-C3N4 / SnS / Au sensor without and with natural light irradiation are shown. When the g-C3N4 / SnS / Au sensor is exposed to ambient air without light irradiation, oxygen molecules (O 2(gas) ) capture electrons (e - ) from the sensitive material and are converted into chemisorbed oxygen. When NO2 gas is introduced, due to the strong oxidation ability of NO2, the adsorbed NO2 molecules (NO 2(gas) ) directly capture electrons from the surface of the sensitive material The above reaction process continuously consumes electrons, resulting in a decrease in conductivity, an increase in the sensor resistance, and a positive response, which is consistent with the trend of the response curve in the above text. During the response process, a desorption process occurs synchronously

[0112] When irradiated by natural light, the photo-generated carriers generated due to the enhanced electric field participate in the gas-sensing reaction through an additional reaction path At the same time, the photo-generated carriers can promote gas desorption and pre-adsorbed oxygen molecules to refresh the surface, releasing the reaction sites for adsorbed NO2 gas molecules Thereby improving the sensitivity of the sensor and reducing the detection limit of the sensor. In addition, photo-generated holes can also participate in the adsorption reaction Accelerate the desorption of NO2, so that the sensor has excellent recoverability.

[0113] In summary, the g-C3N4 / SnS / Au composite sensitive material of the present invention has the characteristic of enhanced absorption in a wide wavelength band, has excellent absorption ability for the entire spectrum of visible light, and the efficient matching of the light absorption wavelength with natural light significantly improves the light absorption efficiency of the gas sensor, thereby promoting the enhancement of the gas-sensing performance; under the irradiation of an external light source or natural light, it can better promote the generation of photo-generated carriers, improve the photon utilization rate, and at the same time provide the activation energy required for the surface reaction between the target gas molecules and the sensitive material, providing sufficient energy for the gas-sensing reaction under room temperature conditions, and enhancing the comprehensive gas-sensing performance of the gas sensor under the condition of natural light excitation and room temperature operation. The gas sensor of the present invention can achieve high-sensitivity detection, excellent selectivity, and fast response / recovery rate for NO2 under the condition of natural light-assisted room temperature operation.

[0114] The foregoing description of specific exemplary embodiments of the present invention is for the purposes of illustration and exemplification. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many changes and variations are possible in light of the above teaching. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the invention and its practical applications, so that those skilled in the art can implement and utilize the various different exemplary embodiments of the invention as well as various different selections and changes. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A highly sensitive visible light full spectrum activation sensitive material, characterized in that: The sensitive material is a g-C3N4 / SnS / Au nanocomposite material with a heterogeneous structure. The g-C3N4 / SnS / Au nanocomposite material includes g-C3N4 with a multi-layer structure and granular SnS grown on its surface, constituting a g-C3N4 / SnS composite material with a heterogeneous structure. Au nanoparticles are freely distributed on the surface and / or edge of the g-C3N4 / SnS composite material, and a heterojunction is formed at the contact interface between the Au nanoparticles and the g-C3N4 / SnS composite material.

2. A method for preparing a highly sensitive visible light full spectrum activation sensitive material as claimed in claim 1, characterized in that: The following steps are involved: (1) Preparation of multi-layered g-C3N4 nanosheets; (2) growing granular SnS on the surface of g-C3N4 nanosheets to obtain a g-C3N4 / SnS composite material with a heterogeneous structure; (3) Au nanoparticles are loaded on the g-C3N4 / SnS composite material, and a heterojunction is formed at the contact interface between the Au nanoparticles and the g-C3N4 / SnS composite material to obtain a g-C3N4 / SnS / Au nanocomposite material with a heterogeneous structure.

3. The method for preparing a highly sensitive visible light full spectrum activation sensitive material according to claim 2, characterized in that: In the step (1), the preparation process of g-C3N4 nanosheets includes: Step 1-1, mixing melamine powder and ascorbic acid powder uniformly to obtain a mixed powder; Step 1-2, heating the mixed powder to 500-600°C at a heating rate of 2°C / min, and keeping the temperature for 3-5h; Step 1-3: After the heat preservation is completed, the mixture is naturally cooled to room temperature to obtain g-C3N4 nanosheets.

4. The method for preparing a highly sensitive visible light full spectrum activated sensitive material according to claim 2, characterized in that: In the step (2), the preparation process of the g-C3N4 / SnS composite material with a heterogeneous structure includes: Step 2-1, dissolving SnCl2·2H2O in a mixed solvent of dilute HCl solution and deionized water, and stirring for 10 to 30 minutes until a transparent mixed solution is formed; Step 2-2, uniformly dispersing the g-C3N4 nanosheets in the mixed solution obtained in step 2-1 to obtain a suspension; Step 2-3, dissolving Na2S·9H2O in deionized water, slowly adding the solution dropwise to the suspension obtained in step 2-2, and then reacting at 45-55° C. with stirring for 2-3 hours to obtain a mixture; Step 2-4, centrifuge the mixture obtained in step 2-3 to precipitate, then wash it with deionized water and anhydrous ethanol for 3 to 5 times, and finally dry it in a vacuum drying oven at 50 to 65° C. for 9 to 15 hours to obtain a g-C3N4 / SnS composite material.

5. The method for preparing a highly sensitive visible light full spectrum activated sensitive material according to claim 2, characterized in that: In the step (3), the preparation process of the heterogeneous g-C3N4 / SnS / Au nanocomposite material comprises: Step 3-1, adding the prepared g-C3N4 / SnS composite material into deionized water, and continuously ultrasonically oscillating until uniformly dispersed to obtain a mixture; Step 3-2, adding sodium citrate and tannic acid to the mixture obtained in step 3-1, stirring for 30 to 50 minutes, then adding HAuCl4·3H2O solution and continuing to stir for 2 to 4 hours to obtain a mixed solution; Step 3-3, centrifuge the mixed solution obtained in step 3-2, collect the black precipitate, wash it with deionized water and anhydrous ethanol for 3 to 5 times, and then dry it in a vacuum drying oven at 50 to 65° C. for 9 to 15 hours to obtain a g-C3N4 / SnS / Au nanocomposite material.

6. Use of the highly sensitive visible light full spectrum activation sensitive material as claimed in claim 1 in the preparation of NO2 gas sensors.

7. A highly sensitive visible light full spectrum activated NO2 gas sensor, the NO2 gas sensor comprising a substrate having a plurality of interdigital electrodes and a sensitive material on the interdigital electrodes, the sensitive material being the sensitive material according to claim 1.

8. A method for preparing a highly sensitive visible light full spectrum activated NO2 gas sensor as claimed in claim 7, characterized in that: include: The g-C3N4 / SnS / Au nanocomposite material is dispersed in anhydrous ethanol to prepare a dispersion liquid, and then the dispersion liquid is drop-coated on an Al2O3 substrate having a plurality of interdigital electrodes, and a sensitive film is formed on the interdigital electrodes after drying to obtain a gas sensor.

9. Use of the NO2 gas sensor according to any one of claim 7 in detecting NO2.

10. The use according to claim 9, characterized in that: The detection is performed under natural light, or a light source is arranged above the NO2 gas sensor to emit full-band visible light toward the NO2 gas sensor during detection to provide an excitation environment.

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