Highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite material and its preparation method

Abstract

The present invention provides a highly selective NO2 gas sensor based on visible light modulation of an Au / SnS2 nanocomposite material and a preparation method thereof. The Au / SnS2 nanocomposite material with a heterogeneous structure is used as a sensitive material and is drop-coated on an interdigitated electrode to form a sensitive layer to prepare the gas sensor. A light source is arranged above the gas sensor to emit light of a 420nm wavelength to the gas sensor. External light field modulation enhances the sensor's response to NO2 and suppresses the sensor's response to interfering gases such as NH3, thereby achieving enhanced selectivity of the Au / SnS2 gas sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of NO2 gas sensors, and in particular to a highly selective NO2 gas sensor modulated by visible light based on Au / SnS2 nanocomposite materials and a preparation method thereof. Background Art

[0002] Nitrogen dioxide (NO2) is a major source of pollution that harms the environment and human health. Not only can NO2 form photochemical smog and acid rain under certain conditions, damaging ecosystems, but long-term exposure to NO2 can also increase the risk of illness and harm human health. Due to the wide variety of toxic and harmful gases in the environment, sensors often have cross-responses to different gases, making it difficult to achieve highly selective and specific identification of target gases in complex gas environments. This presents a technical challenge in the field of gas sensing. Therefore, developing high-performance gas sensors for highly selective NO2 detection holds significant practical value.

[0003] Among current sensor technologies, gas sensors made from metal oxide semiconductors (MOS) are the most widely used. For example, Chinese patent publication number CN113125385A discloses a localized surface plasmon-enhanced NO2 gas sensor based on Au@MoS2 and its preparation method. By incorporating the localized surface plasmon resonance (LSPR) effect of gold nanoparticles, a visible light-assisted MoS2 gas sensor with a low detection limit and strong resistance to moisture interference was developed, improving the gas-sensing performance and detection accuracy of the light-assisted gas sensor. However, this sensor primarily utilizes the LSPR effect stimulated by gold nanoparticles under an applied light field to enhance the gas sensor's response to NO2 gas, and does not involve regulating its gas-sensitive selectivity.

[0004] SnS2 sensitive materials have excellent electron transport properties and abundant molecular active sites, making them sensitive not only to oxidizing gases that readily acquire electrons (such as NO2), but also to reducing gases that are more susceptible to losing electrons (such as NH3 and VOCs). However, due to cross-sensitivity between gases, SnS2-based gas sensors have poor selectivity for detecting NO2 in complex atmospheres and still cannot meet the application requirements of high-precision detection. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the existing technology and provide a highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite materials and a preparation method thereof. By introducing visible light to regulate the adsorption and reaction behavior of gas molecules on the surface of sensitive materials, light field-regulated gas detection technology is developed to achieve highly sensitive detection and specific identification of NO2 gas in room temperature detection mode.

[0006] In a first aspect, the present invention relates to a highly selective NO2 gas sensor based on visible light modulation of an Au / SnS2 nanocomposite material, comprising a gas sensor composed of an Al2O3 substrate having a plurality of interdigital electrodes and a sensitive material on the interdigital electrodes. A light source is provided above the gas sensor for emitting light in a 420 nm wavelength range toward the gas sensor during detection, providing a visible light modulation environment. The gas sensor selectively detects NO2 in a mixture of NO2 and NH3 gas under visible light modulation at 420 nm.

[0007] Wherein, the sensitive material is an Au / SnS2 nanocomposite material with a heterogeneous structure.

[0008] In an optional embodiment, the Au / SnS2 nanocomposite material having a heterostructure includes SnS2 nanosheets having a hexagonal sheet structure, and Au nanoparticles are attached to the surface of the SnS2 nanosheets to form a heterojunction.

[0009] In an optional embodiment, the diameter of the Au nanoparticles is 5 nm.

[0010] In a second aspect, the present invention relates to a method for preparing the aforementioned highly selective NO2 gas sensor based on visible light modulation of the Au / SnS2 nanocomposite material, comprising the following steps:

[0011] Preparation of SnS2 nanosheets, wherein the prepared SnS2 nanosheets exhibit a hexagonal sheet structure;

[0012] SnS2 nanosheets were modified with Au nanoparticles to obtain Au / SnS2 nanocomposites with heterogeneous structures.

[0013] A sensitive film is prepared using Au / SnS2 heterostructure as a sensitive material, specifically comprising: dispersing Au / SnS2 powder in anhydrous ethanol to prepare a dispersion liquid, then drop-coating the dispersion liquid on an Al2O3 substrate having a plurality of interdigital electrodes, and forming a sensitive film on the interdigital electrodes after drying, thereby preparing a gas sensor using Au / SnS2 as a sensitive material;

[0014] A light source is set above the gas sensor to emit light in the 420 nm wavelength range towards the gas sensor during detection, providing a visible light modulation environment. Through visible light modulation at 420 nm, the gas sensor can achieve selective detection of NO2 in a mixture of NO2 and NH3.

[0015] In an optional embodiment, the preparation process of the SnS2 nanosheets includes:

[0016] Step 1-1, dissolve tin chloride pentahydrate (SnCl4·5H2O) and thioacetamide (CH3CSNH2) in ultrapure water with a resistivity of >18.2MΩ·cm;

[0017] Step 1-2, magnetically stirring the mixed solution at room temperature for 30 min to obtain a transparent homogeneous solution;

[0018] Steps 1-3, ultrasonically oscillating the resulting homogeneous solution for 20 min;

[0019] Step 1-4: transfer the solution to a polytetrafluoroethylene Teflon autoclave and heat it in a vacuum heating box at 200°C for 12 h;

[0020] Step 1-5: After the solution in the reactor has cooled to room temperature, centrifuge the solution at 5500 rad / min for 3 min, and then wash the resulting precipitate with deionized water and ethanol;

[0021] Step 1-6: Place the yellow precipitate in a vacuum drying oven and place it at 60°C for 8 hours to finally obtain SnS2 nanosheets with hexagonal phase and yellow powder.

[0022] In an optional embodiment, the preparation process of the Au / SnS2 heterostructure includes:

[0023] Step 2-1, dissolving the prepared SnS2 nanosheets in ultrapure water with a resistivity of >18.2 MΩ·cm;

[0024] Step 2-2, ultrasonically vibrate the solution for 10 min;

[0025] Step 2-3, add HAuCl4 solution, stir and heat to boiling;

[0026] Step 2-4: After boiling, add sodium citrate trihydrate, heat for 10 minutes, stop heating and wait for cooling to room temperature;

[0027] Step 2-5, washing with deionized water and anhydrous ethanol 3 to 4 times;

[0028] Step 2-6: Finally, the obtained dark green precipitate was placed in a vacuum drying oven and dried at 60°C for 8 h to obtain a heterostructured Au / SnS2 in the form of dark green powder.

[0029] In an optional embodiment, the Au / SnS2 is in the form of a hexagonal sheet, and Au nanoparticles are attached to its surface to form a heterojunction; the diameter of the Au nanoparticles is 5 nm.

[0030] In an optional embodiment, the distance between the fingers of the interdigitated electrodes is 200 microns.

[0031] In an optional embodiment, during the preparation of the sensitive film, the final sensitive film is formed by repeatedly dropping and drying.

[0032] In an optional embodiment, the gas sensor and the light source above the gas sensor are assembled in a housing, and a channel for gas to flow through is provided on a side of the housing.

[0033] Compared with the prior art, the present invention has the following significant beneficial effects:

[0034] The NO2 sensor of the present invention successfully prepares a highly selective NO2 gas sensor modulated by visible light based on Au / SnS2 nanocomposite materials by forming a heterojunction with SnS2 two-dimensional nanosheets with poor gas selectivity and gold nanoparticles. The heterostructured Au / SnS2 is obtained by modifying SnS2 with Au, which is used as a sensitive material. Under visible light conditions, the adsorption type of gas molecules on the surface of the sensitive material is regulated by the light field to affect its electronic interaction process, thereby enhancing the NO2 response value while reducing the NH3 response value, enabling the sensor to achieve highly selective and specific recognition of NO2 gas under low concentrations of NO2 and NH3 mixed gas.

[0035] The highly selective NO2 gas sensor, fabricated by the present invention and based on visible light modulation using an Au / SnS2 nanocomposite material, is a 420 nm light-modulated gas sensor. Testing with light from multiple wavelengths demonstrates that the sensor can accurately detect NO2 in a mixture of NO2 and NH3 gases under visible light modulation at 420 nm. The combined effect of 420 nm illumination and the Au / SnS2 heterojunction significantly enhances sensor selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of a highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite materials of the present invention.

[0037] Figure 2 This is the experimental flow chart of the preparation of SnS2 and Au / SnS2 materials in the present invention.

[0038] Figure 3 It is the XRD test pattern of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention.

[0039] Figure 4 and Figure 5 They are SEM images of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention respectively.

[0040] Figure 6 and Figure 7 They are TEM images of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention respectively.

[0041] Figure 8 This is a high-resolution TEM image of Au / SnS2 of Example 2 of the present invention.

[0042] Figure 9 It is the XPS spectrum of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention.

[0043] Figure 10 3d of SnS2 in Example 1 and Au / SnS2 in Example 2 of the present invention.

[0044] Figure 11 1 and 2 are high-resolution XPS spectra of S 2p of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention.

[0045] Figure 12 This is a high-resolution XPS spectrum of Au / SnS2Au 4f of Example 2 of the present invention.

[0046] Figure 13 It is the Raman spectrum of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention.

[0047] Figure 14 It is the ultraviolet-visible absorption spectrum of SnS2 of Example 1 and Au / SnS2 of Example 2 of the present invention.

[0048] Figure 15 and Figure 16 The dynamic response curves of the SnS2 sensor of the present invention were tested for NO2 and NH3 1-50 ppm respectively.

[0049] Figure 17 is the response value of SnS2 sensor exposed to 1-50 ppm concentration of NO2 and NH3.

[0050] Figure 18 and Figure 19 The dynamic response curves of the Au / SnS2 sensor of the present invention exposed to 1-50 ppm NO2 and NH3 respectively.

[0051] Figure 20 is the response value of the Au / SnS2 sensor of the present invention when exposed to NO2 and NH3 at concentrations of 1-50 ppm.

[0052] Figure 21 and Figure 22 These are the light response curves of the Au / SnS2 sensor of the present invention to 1 ppm NO2 at different light wavelengths and light intensities.

[0053] Figure 23 and Figure 24 The dynamic response curves of 1-50 ppm NO2 and NH3 were tested for the Au / SnS2 sensor of the present invention under optimal illumination conditions.

[0054] Figure 25 It is the response value of the Au / SnS2 sensor of the present invention under optimal lighting conditions when exposed to NO2 and NH3 at concentrations of 1-50 ppm.

[0055] Figure 26 The selectivity of SnS2 and Au / SnS2 of the present invention, as well as the Au / SnS2 sensor under light assistance, to different gases (5ppmNO2, 50ppmNH3, 50ppmC2H5OH, 50ppmHCHO, 50ppmCH3COCH3).

[0056] Figure 27 A comprehensive comparison was made from five aspects: response value, selectivity, response time, recovery time and sensitivity. Figure 26 Gas sensing performance diagram of the sensor.

[0057] Figure 28 These are the four cycle test graphs of the Au / SnS2 sensor under 1 ppm NO2 on the first, fifth, ninth and fifteenth days under light-assisted conditions.

[0058] Figure 29 This is a graph showing the long-term stability of the Au / SnS2 sensor under 1 ppm NO2 for 17 days under light-assisted conditions.

[0059] Figure 30 shows the NO2 sensing mechanism of Au / SnS2 heterostructure under 420 nm conditions; Figure 30a The interaction between the Au / SnS2 sensor and oxygen molecules under light and no light conditions; Figure 30b The interaction between the Au / SnS2 sensor and NO2 gas in the presence and absence of light. Figure 30c The interaction between the Au / SnS2 sensor and NH3 gas in the presence and absence of light. DETAILED DESCRIPTION

[0060] In order to better understand the technical content of the present invention, specific embodiments are given and described below with reference to the accompanying drawings.

[0061] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to be comprehensive. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of a number of ways.

[0062] In recent years, gas sensors prepared from two-dimensional layered chalcogenides (such as SnS2) are not only sensitive to gases under room temperature working conditions, but also have low energy consumption and are easy to integrate, showing broad prospects in the emerging field of gas sensors.

[0063] Therefore, the present invention provides a highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite materials. The gas sensor is prepared by using Au / SnS2 as the sensitive material and drop-coating it on the interdigital electrodes to form a sensitive layer. A light source is arranged above the gas sensor to emit light of 420 nm wavelength to the gas sensor. The external light field modulation enhances the sensor's response to NO2 and suppresses the sensor's response to interfering gases such as NH3, thereby achieving enhanced selectivity of the Au / SnS2 gas sensor.

[0064] The modulation in the present invention refers to a detection mode, and the visible light modulation refers to changing the adsorption type of gas molecules on the sensitive material in the visible light adding mode, thereby enhancing the selectivity of the sensor.

[0065] Visible light modulation can also be understood as regulation through visible light; a further understanding is that under visible light conditions, through the regulation of visible light, the response of Au / SnS2 to NO2 is enhanced, while the response to NH3 is weakened, thereby greatly improving the selectivity of Au / SnS2 to the target gas NO2.

[0066] like Figure 1 As shown, in an exemplary embodiment of the present invention, a highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite materials is provided, comprising a gas sensor composed of an Al2O3 substrate having a plurality of interdigital electrodes 1 and a sensitive material 2 on the interdigital electrodes. A light source 3 is provided above the gas sensor for emitting light in a wavelength range of 420 nm toward the gas sensor during detection, providing a visible light modulation environment. The gas sensor selectively detects NO2 in a mixture of NO2 and NH3 gas under visible light modulation at 420 nm.

[0067] Wherein, the sensitive material is an Au / SnS2 nanocomposite material with a heterogeneous structure.

[0068] In an optional embodiment, the Au / SnS2 nanocomposite material having a heterostructure includes SnS2 nanosheets having a hexagonal sheet structure, and Au nanoparticles are attached to the surface of the SnS2 nanosheets to form a heterojunction.

[0069] In an optional embodiment, the size of the SnS2 nanosheets is 50nm~200nm.

[0070] In an optional embodiment, the diameter of the Au nanoparticles is 5 nm.

[0071] In another exemplary embodiment of the present invention, a method for preparing the aforementioned highly selective NO2 gas sensor based on visible light modulation of the Au / SnS2 nanocomposite material is provided, comprising the following steps:

[0072] Preparation of SnS2 nanosheets, wherein the prepared SnS2 nanosheets exhibit a hexagonal sheet structure;

[0073] SnS2 nanosheets were modified with Au nanoparticles to obtain Au / SnS2 nanocomposites with heterogeneous structures.

[0074] A sensitive film is prepared using Au / SnS2 heterostructure as a sensitive material, specifically comprising: dispersing Au / SnS2 powder in anhydrous ethanol to prepare a dispersion liquid, then drop-coating the dispersion liquid on an Al2O3 substrate having a plurality of interdigital electrodes, and forming a sensitive film on the interdigital electrodes after drying, thereby preparing a gas sensor using Au / SnS2 as a sensitive material;

[0075] A light source is set above the gas sensor to emit light in the 420 nm wavelength range towards the gas sensor during detection, providing a visible light modulation environment. Through visible light modulation at 420 nm, the gas sensor can achieve selective detection of NO2 in a mixture of NO2 and NH3.

[0076] Combine Figure 2 As shown in (Part A), in an optional embodiment, the preparation process of the SnS2 nanosheets includes:

[0077] Step 1-1, dissolve tin chloride pentahydrate (SnCl4·5H2O) and thioacetamide (CH3CSNH2) in ultrapure water with a resistivity of >18.2MΩ·cm;

[0078] Step 1-2, magnetically stirring the mixed solution at room temperature for 30 min to obtain a transparent homogeneous solution;

[0079] Steps 1-3, ultrasonically oscillating the resulting homogeneous solution for 20 min;

[0080] Step 1-4: transfer the solution to a polytetrafluoroethylene Teflon autoclave and heat it in a vacuum heating box at 200°C for 12 h;

[0081] Step 1-5: After the solution in the reactor is cooled to room temperature, the resulting mixed solution is centrifuged at a speed of 5500 rad / min to collect the SnS2 precipitate, and the precipitate is washed 2 to 3 times with deionized water and anhydrous ethanol by centrifugation;

[0082] Steps 1-6: Finally, the obtained yellow precipitate is placed in a vacuum drying oven and dried at 60°C for 8 h to obtain hexagonal SnS2 nanosheets in the form of yellow powder.

[0083] In a preferred embodiment, in step 1-1, the molar ratio of Sn to S is (1:3) to (1:5). For example, 1.753 g (5 mmol) of tin chloride pentahydrate and 1.126 g (15 mmol) of thioacetamide are dissolved in 60 mL of ultrapure water with a resistivity of >18.2 MΩ·cm.

[0084] Combine Figure 2 As shown in (Part B), in an optional embodiment, the preparation process of the Au / SnS2 heterostructure includes:

[0085] Step 2-1, dissolving the prepared SnS2 nanosheets in ultrapure water with a resistivity of >18.2 MΩ·cm;

[0086] Step 2-2, ultrasonically vibrate the solution for 10 min;

[0087] Step 2-3, add HAuCl4 solution, stir and heat to boiling;

[0088] Step 2-4: After boiling, add sodium citrate trihydrate (TA), heat for 10 minutes, stop heating and wait for cooling to room temperature;

[0089] Step 2-5, washing with deionized water and anhydrous ethanol 3 to 4 times;

[0090] Step 2-6: Finally, the obtained dark green precipitate was placed in a vacuum drying oven and dried at 60°C for 8 h to obtain a heterostructured Au / SnS2 in the form of dark green powder.

[0091] In a preferred embodiment, in step 2-1, the molar concentration of the SnS2 solution is 0.005 mmol / L~0.01 mmol / L.

[0092] In another preferred embodiment, in step 2-3, the molar ratio of Au to SnS2 is 1:5.

[0093] In another preferred embodiment, in steps 2-4, sodium citrate trihydrate is a sodium citrate aqueous solution with a mass fraction of 1%, that is, sodium citrate trihydrate is dissolved in deionized water.

[0094] In an optional embodiment, the Au / SnS2 is in the form of a hexagonal sheet, and Au nanoparticles are attached to its surface to form a heterojunction; the diameter of the Au nanoparticles is 5 nm.

[0095] In an optional embodiment, the spacing between the interdigital electrodes is 200 microns, 5 Ag / Pd interdigital electrodes are used, and the size of the Al2O3 substrate is 6.8 mm×3 mm×0.5 mm.

[0096] In an optional embodiment, during the preparation of the sensitive film, the final sensitive film is formed by repeatedly dropping and drying.

[0097] In an optional embodiment, the gas sensor and the light source above the gas sensor are assembled in a housing, and a channel for gas to flow through is provided on a side of the housing.

[0098] In a preferred example, the gas sensor is fixedly disposed in the first cavity of the detection box;

[0099] A light source is provided in the second cavity of the detection box. During detection, the light source emits light in the 420 nm wavelength range to the sensor, which is the light source required for the light modulation of Au / SnS2.

[0100] In this way, a gas sensor made of Au / SnS2 as the sensitive material is placed in one part of the detection box cavity. A light source is fixed in another part of the detection box cavity. The detection box has a built-in power supply or an external power supply. During detection, the light source provides a 420nm light-assisted excitation environment, improving the gas sensor's gas selectivity and sensitivity, and ensuring detection stability and consistency.

[0101] The adsorption model of NO2 is physical adsorption, a process that does not require the participation of electrons, while the adsorption of NH3 requires the presence of adsorbed oxygen ions on the sensor surface to react. The Au / SnS2 sensor of the present invention absorbs light at a wavelength of 420 nm, generating positively charged holes and negatively charged electrons in the Au and SnS2. The negatively charged electrons of the SnS2 can be transferred to the Au surface, enhancing the response to NO2. The excess positively charged holes react with the adsorbed oxygen ions on the sensor surface to generate O2. Therefore, the adsorbed oxygen ions required for NH3 are reduced, making the reaction difficult to continue, reducing the response to NO2, and thus enabling selective recognition of NO2 and NH3.

[0102] The implementation of the above preparation method will be described in more detail below with reference to specific examples. Example 1

[0103] [Preparation of SnS2 nanosheets]

[0104] Step 1-1: Dissolve 1.753 g of tin chloride pentahydrate (SnCl4·5H2O) and 1.1269 g of thioacetamide (CH3CSNH2) in 60 mL of ultrapure water with a resistivity of >18.2 MΩ·cm.

[0105] Step 1-2: Stir the solution on a magnetic stirrer at room temperature (25°C) for 30 min to obtain a clear and transparent homogeneous solution.

[0106] Step 1-3: The obtained homogeneous solution was shaken in an ultrasonic oscillator with a power of 200 W for 20 min.

[0107] Steps 1-4: Transfer the solution to a 100 mL polytetrafluoroethylene-lined autoclave, place it in a vacuum drying oven and heat it at 200°C for 12 h.

[0108] Step 1-5: After the solution cools to room temperature, the resulting mixed solution is centrifuged at a centrifugal speed of 5500 rad / min to collect the SnS2 precipitate, and the mixture is centrifuged and washed 2 to 3 times with deionized water and anhydrous ethanol.

[0109] Step 1-6: Finally, place the obtained dark green precipitate in a vacuum drying oven and dry it at 60°C for 12 hours to finally obtain yellow SnS2 powder.

[0110] Among them, the yellow SnS2 powder has a typical hexagonal structure. Example 2

[0111] [Preparation of Au / SnS2 composite materials]

[0112] Step 2-1: Take 0.0278 g of prepared SnS2 and dissolve it in 30 mL of ultrapure water with a resistivity of >18.2 Ω·cm.

[0113] Step 2-2: Oscillate the solution in an ultrasonic oscillator at a power of 200 W for 10 min.

[0114] Step 2-3: Add 600 μL of 50 mM HAuCl4 solution to the above solution, stir and heat to boiling.

[0115] Step 2-4: After boiling, add 620 μL of 1% sodium citrate and cook for 7 minutes before stopping heating.

[0116] Step 2-5: Cool the resulting solution to room temperature and wash with deionized water and anhydrous ethanol 2 to 3 times.

[0117] Step 2-6: Finally, the obtained dark green precipitate was placed in a vacuum drying oven and dried at 60°C for 8 h to obtain a dark green powder of Au / SnS2 heterostructure. Example 3

[0118] [Preparation of the sensitive layer of NO2 gas sensor]

[0119] Step 3-1: Disperse 0.01 g of Au / SnS2 in 2 mL of ethanol using ultrasonication.

[0120] Step 3-2: 2 μl of the dispersion was drop-coated on an Al2O3 substrate (6.8 mm × 3 mm × 0.5 mm) with five Ag / Pd interdigital electrodes and dried at 60°C for 30 min to prepare a sensitive film layer.

[0121] During the preparation process, the drop coating and drying process was repeated 5 times.

[0122] The electrodes were directly purchased commercial electrodes, and the spacing between the forks was 200 μm.

[0123] The materials used in the following tests are all from Examples 1-3.

[0124] Microstructure testing

[0125] like Figure 3 The XRD patterns shown in the figure show the crystal phase information of SnS2 and Au / SnS2. The main diffraction peaks of Au / SnS2 match well with those of single SnS2 (PDF#23-0677), and no other impurity diffraction peaks are observed, indicating that the prepared SnS2 is relatively pure. Compared with the main diffraction peaks of single SnS2, the other peaks of Au / SnS2 correspond to those of the standard card (PDF#04-0784).

[0126] Figure 4 The surface morphology of SnS2 is shown, which is a typical two-dimensional flake structure with a size of 50-200 nm and a thickness of about 10 nm.

[0127] Figure 5 This is the surface morphology of Au / SnS2. It can be clearly seen that gold particles are attached to the surface of SnS2. Au particles tend to grow on its edges and defects because these areas have high energy.

[0128] Figure 6 and Figure 7TEM images of SnS2 and Au / SnS2 are shown. It can be seen from the images that the present invention successfully synthesized hexagonal flake-shaped SnS2, and Au was successfully grown on its surface.

[0129] Figure 8 This is a high-resolution TEM image of Au / SnS2. The two lattice spacings of 0.31 nm and 0.24 nm correspond to the (100) plane of SnS2 and the (111) plane of Au, respectively. It can be clearly seen that Au grows on its surface with a size of about 5 nm.

[0130] The above characterization methods can prove that the present invention successfully prepared Au / SnS2.

[0131] XPS spectra and optical characterization of SnS2 and Au / SnS2

[0132] Figure 9 The XPS spectra of SnS2 and Au / SnS2 show that no other elements are detected except Sn, S, Au, C, and O, which is consistent with the EDS results.

[0133] Figure 10 and Figure 11 The high-resolution XPS spectra of Sn 3d and S 2p are shown in Figure 2, where two strong peaks are located at 486.6 eV and 495.1 eV, corresponding to Sn 3d 5 / 2 and Sn 3d 3 / 2 , which belongs to Sn with a valence of +4. The two obvious peaks at 161.7 eV and 162.9 eV in the S 2p spectrum correspond to the S 2p 3 / 2 and S 2p 1 / 2 After Au modification, the peaks of Sn 3d and S 2p shift slightly to lower binding energy (red shift), which is related to the p-type modification effect of Au.

[0134] Figure 12 The high-resolution XPS graph of Au 4f is shown, in which there are two peaks at 83.9 eV and 87.6 eV in the Au / SnS2 sample corresponding to Au 4f 7 / 2 and Au 4f 5 / 2 , indicating that Au functionalization was successful. In order to further study the effect of Au surface modification on SnS2, the Raman spectrum and UV-visible absorption spectrum of the samples were also characterized.

[0135] Figure 13 This is the Raman spectrum, with an obvious strong peak at 313 cm -1 A corresponding to SnS2 1g Phonon mode. After Au modification, the A of SnS2 1gThe weakening of the mode intensity indicates that Au forms a covalent bond with S, resulting in a decrease in the electron density of SnS2. At the same time, a slight red shift can be observed, indicating that there is electronic interaction between Au and SnS2, proving the formation of a heterojunction.

[0136] Figure 14 The UV-visible absorption spectra of the samples show that SnS2 has strong absorption in the visible light region. After modification with Au, the visible light absorption of SnS2 is enhanced and red-shifted due to the LSPR effect of Au. The band gaps of SnS2 and Au / SnS2 can be estimated to be 2.52 eV and 2.41 eV, respectively, indicating that Au modification does not significantly alter the band gap of SnS2.

[0137] The above tests have demonstrated that the elemental composition of the Au / SnS2 prepared by the present invention is free of other impurities and substances.

[0138] The above-mentioned microstructure test, XPS spectrum, and optical characterization can prove that the present invention successfully prepared Au / SnS2 nanomaterials with heterogeneous structure.

[0139] Gas Sensing Performance Test of SnS2 and Au / SnS2

[0140] Figure 15 and Figure 16 The dynamic response curves for the SnS2 sensor were tested for NO2 and NH3 at 1-50 ppm. The response gradually reached saturation with increasing gas concentration. NO2 is an oxidizing gas. When adsorbed on the material surface, it removes electrons from SnS2, reducing the carrier concentration in n-type SnS2 and causing an increase in resistance. NH3, on the other hand, is a reducing gas and donates electrons to SnS2, causing a decrease in resistance. Figure 17 The purpose is to calculate the response of a SnS2 sensor exposed to 1-50 ppm concentrations of NO2 and NH3. Obviously, NH3 is an interfering gas for SnS2 and it is difficult to distinguish it from NO2.

[0141] Figure 18 and Figure 19 The dynamic response curves of an Au-functionalized SnS2 sensor exposed to 1-50 ppm NO2 and NH3 are shown. Au modification increases the sensor's sensitivity to NO2, and also accelerates its response and recovery rates, likely due to the catalytic and spillover effects of Au. The NH3 response also increases. This is because NH3 is primarily chemically adsorbed and requires reaction with pre-adsorbed oxygen ions on the material surface. The introduction of Au increases the amount of surface-adsorbed oxygen. Figure 20The above are the responses of the Au / SnS2 sensor when exposed to NO2 and NH3 at concentrations of 1-50 ppm. Although the selectivity for NO2 is greatly improved at high concentrations, it is still affected by NH3 at concentrations of 1 ppm or even lower.

[0142] pass Figure 15-17 and Figure 18-20 From the comparison, it can be seen that the SnS2 modified by Au has better performance to NO2 and lower response to NH3. Therefore, it can be concluded that the prepared Au / SnS2 has better performance and stronger anti-interference ability than SnS2.

[0143] Gas sensing performance test of Au / SnS2 under different light irradiation

[0144] The gas sensing properties of Au / SnS2 under different wavelengths and illumination intensities were studied.

[0145] Figure 21 and Figure 22 The light response curves of 1 ppm NO2 under different light wavelengths and intensities were tested. Figure 21 The following plots the dynamic response curves of the Au / SnS2 sensor to 1 ppm NO2 at different wavelengths (365-620 nm). The maximum response is achieved at 420 nm. When light shines on the surface of a sensitive material, both photoadsorption and photodesorption occur simultaneously. As light intensity increases, the reaction between gas molecules and the sensitive material shifts from being dominated by photoadsorption to being dominated by photodesorption. Therefore, it is important to select the optimal light intensity to achieve the maximum photoresponse.

[0146] At the same time, the effects of different light intensities on gas sensing performance were also tested, such as Figure 22 As the light intensity increases, the response value of the Au / SnS2 sensor to 1 ppm NO2 first increases and then decreases. 2 Therefore, here we choose the light intensity to be 3.6 mW / cm 2 420 nm light was used as a subsequent test.

[0147] Figure 23 and Figure 24 The dynamic response curves of NO2 and NH3 at 1-50 ppm were tested under optimal light conditions. Figure 25 It can be seen that under the stimulation of visible light, Au / SnS2 achieved further improvement in the selectivity for NO2.

[0148] It can be seen from this that at a wavelength of 420 nm, the response of Au / SnS2 to NO2 is much greater than that to NH3, which proves that the sensor prepared in the present invention has higher selectivity under the condition of adding visible light.

[0149] Gas Sensing Performance of SnS2, Au / SnS2 and 420 nm Light-Modulated Au / SnS2 Gas Sensors

[0150] Figure 26 The selectivity of SnS2, Au / SnS2, and light-assisted Au / SnS2 sensors for different gases (5 ppm NO2, 50 ppm NH3, 50 ppm C2H5OH, 50 ppm HCHO, and 50 ppm CH3COCH3) is described. The SnS2 sensor exhibited similar responses to all tested gases, indicating poor selectivity and inability to accurately identify NO2. After modification with Au nanoparticles, the sensor's response to NO2 was significantly enhanced due to the catalytic effect of the noble metal, and the response was greater than that of other gases. Under 420 nm light excitation, the sensor's response to NO2 was further enhanced, reaching 4.4 times that of the SnS2 sensor. This suggests that the introduction of light increases the gap between the responses to NO2 and other gases, thereby improving its selectivity.

[0151] Figure 27 The gas-sensing performance of the sensors was comprehensively compared across five dimensions: response value, selectivity, response time, recovery time, and sensitivity. As shown in the figure, the Au / SnS2 sensor with light assistance exhibited the highest response value, the shortest response time, the highest selectivity, and the highest sensitivity, resulting in the largest coverage area, indicating that the Au / SnS2 sensor with light assistance performed best.

[0152] From the above tests, it can be seen that compared with SnS2, the response ability of Au / SnS2 to different gases has been improved, but the selectivity is still poor; the modification of Au promotes the absorption of visible light by SnS2, so under the excitation of 420 nm light, the response value of Au / SnS2 to NO2 is greatly improved, but at the same time the response value to other gases has not changed, especially the response value to NH3 has decreased, thereby increasing the gap between the response of NO2 and other gases, especially the response gap with NH3.

[0153] Thus, when detecting a mixed gas of NO2 and NH3, the Au / SnS2 gas sensor of the present invention can achieve selective detection of NO2.

[0154] Figure 28 The light-assisted Au / SnS2 sensor was tested under 1 ppm NO2 for four cycles on the first, fifth, ninth and fifteenth days, indicating that the sensor of the present invention has good repeatability.

[0155] Figure 29The long-term stability of the Au / SnS2 sensor under 1 ppm NO2 under light assistance was tested for 17 days, and its resistance and response values did not change significantly, indicating that the sensor prepared in the present invention has good stability.

[0156] NO2 sensing mechanism of 420 nm Au / SnS2 heterostructure based on visible light modulation

[0157] Figure 30 depicts the reaction process of NO2 and NH3 with Au / SnS2 under light and light-free conditions, respectively.

[0158] Combined with Figure 30a, Figure 30b and Figure 30c As shown, SnS2, a typical n-type semiconductor, removes electrons from the sensor when exposed to the oxidizing gas NO2. This increases the carrier concentration and resistance. Conversely, NH3, a reducing gas, donates electrons to SnS2, decreasing resistance. After Au surface modification of SnS2, due to the work function of SnS2 (4.4-4.95 eV) being lower than that of Au (5.1 eV), electrons in the SnS2 conduction band transfer to Au until their Fermi energies reach equilibrium, leading to the formation of a heterojunction. In the dark, the overflow of Au provides more electrons for interaction with gas molecules (Equations 1 and 2), further enhancing the NO2 response.

[0159]

[0160] As for NH3, in addition to acting as an electron donor, it also reacts with the adsorbed oxygen on the surface (Equation 3), further reducing the sensor resistance and enhancing the response to NH3.

[0161] Au / SnS2 responds to both gases regardless of light conditions. However, visible light excitation further enhances the response of Au / SnS2 to NO2 and reduces its response to NH3, thereby increasing its selectivity for NO2. This phenomenon is related to the adsorption mechanism of these two gases.

[0162] SnS2's sensing mechanism for NO2 is based on a physical adsorption model, and the reaction does not require the presence of adsorbed oxygen. However, for NH3, its sensing process relies on surface adsorbed oxygen. Under 420 nm wavelength light excitation, because the photon energy exceeds the band gap of SnS2, electrons in the SnS2 valence band are excited and transition to the conduction band, allowing more electrons to interact with NO2 (Equations 4 and 5). Furthermore, due to the LSPR effect of Au, hot electrons from Au are transferred to the SnS2 surface, further enhancing the NO2 response.

[0163]

[0164] The photoinduced holes combine with pre-adsorbed oxygen ions, causing the adsorbed oxygen to desorb (Equation 6), thereby exposing more active sites for NO2 reaction. However, this is detrimental to NH3, which requires adsorbed oxygen ions to participate in the reaction, resulting in a reduced response to NH3. Ultimately, the selectivity of the Au / SnS2 sensor for NO2 is improved at room temperature.

[0165] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite material, characterized in that: The invention comprises a gas sensor composed of an Al2O3 substrate having a plurality of interdigital electrodes and a sensitive material on the interdigital electrodes. A light source is provided above the gas sensor for emitting light in a wavelength range of 420 nm toward the gas sensor during detection, providing a visible light modulation environment. The gas sensor selectively detects NO2 in a mixture of NO2 and NH3 gas under visible light modulation at 420 nm. The sensitive material is an Au / SnS2 nanocomposite material with a heterogeneous structure, in which Au nanoparticles are attached to the (100) surface of SnS2. The Au / SnS2 nanocomposite material with a heterogeneous structure includes SnS2 nanosheets with a hexagonal flaky structure, and Au nanoparticles are attached to the surface of the SnS2 nanosheets to form a heterojunction.

2. The highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite material according to claim 1, characterized in that: The diameter of the Au nanoparticles is 5 nm.

3. A method for preparing a highly selective NO2 gas sensor based on visible light modulation of Au / SnS2 nanocomposite materials according to any one of claims 1-2, characterized in that: The following steps are involved: Preparation of SnS2 nanosheets, wherein the prepared SnS2 nanosheets exhibit a hexagonal sheet structure; SnS2 nanosheets were modified with Au nanoparticles to obtain Au / SnS2 nanocomposites with heterogeneous structures. A sensitive film is prepared using Au / SnS2 heterostructure as a sensitive material, specifically comprising: dispersing Au / SnS2 powder in anhydrous ethanol to prepare a dispersion liquid, then drop-coating the dispersion liquid on an Al2O3 substrate having a plurality of interdigital electrodes, and forming a sensitive film on the interdigital electrodes after drying, thereby preparing a gas sensor using Au / SnS2 as a sensitive material; A light source is set above the gas sensor to emit light in the 420 nm wavelength range towards the gas sensor during detection, providing a visible light modulation environment. Through visible light modulation at 420 nm, the gas sensor can achieve selective detection of NO2 in a mixture of NO2 and NH3.

4. The preparation method according to claim 3, characterized in that The preparation process of the SnS2 nanosheets includes: Step 1-1, dissolve tin chloride pentahydrate (SnCl4·5H2O) and thioacetamide (CH3CSNH2) in ultrapure water with a resistivity of >18.2 MΩ·cm; Step 1-2, magnetically stirring the mixed solution at room temperature for 30 min to obtain a transparent homogeneous solution; Steps 1-3, ultrasonically oscillating the resulting homogeneous solution for 20 min; Step 1-4: transfer the solution to a polytetrafluoroethylene Teflon autoclave and heat it in a vacuum heating box at 200°C for 12 h; Step 1-5: After the solution in the reactor has cooled to room temperature, centrifuge the solution at 5500 rad / min for 3 min, and then wash the resulting precipitate with deionized water and ethanol; Step 1-6: Place the yellow precipitate in a vacuum drying oven and place it at 60°C for 8 hours to finally obtain SnS2 nanosheets with hexagonal phase and yellow powder.

5. The preparation method according to claim 3, characterized in that The preparation process of the Au / SnS2 heterostructure includes: Step 2-1, dissolving the prepared SnS2 nanosheets in ultrapure water with a resistivity of >18.2 MΩ·cm; Step 2-2, ultrasonically vibrate the solution for 10 min; Step 2-3, add HAuCl4 solution, stir and heat to boiling; Step 2-4: After boiling, add sodium citrate trihydrate, heat for 10 minutes, stop heating and wait for cooling to room temperature; Step 2-5, washing with deionized water and anhydrous ethanol 3 to 4 times; Step 2-6: Finally, the obtained dark green precipitate was placed in a vacuum drying oven and dried at 60°C for 8 h to obtain a heterostructured Au / SnS2 in the form of dark green powder.

6. The preparation method according to claim 3, characterized in that The Au / SnS2 is in the shape of a hexagonal sheet, and Au nanoparticles are attached to its surface to form a heterojunction; the diameter of the Au nanoparticles is 5 nm.

7. The preparation method according to claim 3, characterized in that The distance between the fingers of the interdigital electrodes is 200 micrometers.

8. The preparation method according to claim 3, characterized in that In the process of preparing the sensitive film, the final sensitive film is formed by repeatedly dropping and drying.

9. The preparation method according to claim 3, characterized in that The gas sensor and the light source above the gas sensor are assembled in a housing, and a channel for gas to flow through is provided on the side of the housing.

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