Preparation method of ag nanoparticle modified w03 nanospheres for high-sensitivity detection of h2s gas

Abstract

The application relates to a preparation method of Ag nanoparticle modified WO3 nanospheres for high-sensitivity detection of H2S gas, which comprises the following steps: 1) preparation of a mixed solution; 2) preparation of a precursor solution; 3) hydrothermal reaction; 4) centrifugal precipitation; and 5) preparation of Ag-WO3 nanospheres. The application adopts a simple solvent-thermal reduction method with sodium borohydride (NaBH4) to synthesize a noble metal Ag nanoparticle (NPs) modified WO3 nanosphere gas sensor with controllable morphology and size. The AgNPs modified WO3 nanospheres of the application can realize detection of H2S gas at room temperature (25 DEG C), and the response value of 10ppm H2S gas is as high as 2849, which is about 235 times of that of pure WO3 (Ra / Rg=12.14); meanwhile, the sensor also has the advantages of rapid response capability (6s), low detection lower limit (10ppb), wide detection range (10ppb-40ppm) and excellent selectivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas sensors, and particularly relates to a preparation method of Ag nanoparticle modified WO3 nanospheres for high-sensitivity detection of H2S gas. BACKGROUND

[0002] Hydrogen sulfide (H2S) is a toxic, harmful, flammable and explosive acid gas, and long-term exposure to it can cause harm to human life and health [1] . When inhaling low-concentration H2S gas, it can cause inflammation, pulmonary edema, respiratory tract infection and other physiological diseases. Once the concentration exceeds 10 ppm, high concentration, it can cause people to lose their sense of smell, have difficulty breathing, and even death [2] . Therefore, for safety reasons, the Occupational Safety and Health Administration (OSHA) has set the H2S safe exposure limit to 20 ppm [3 ] In addition, H2S can also be used as a biomarker for medical disease diagnosis, for example, the gas exhaled by patients with general halitosis contains about 0.1-0.5 ppm H2S, which can be used as a biomarker for diagnosing diseases such as tongue coating, mucosal disease, periodontal disease, etc. [4] The H2S concentration in the exhaled gas of patients with hepatocellular carcinoma (HCC) is 23 ppb [5] . Traditionally, halitosis can be monitored by the sensory system, but for H2S at a concentration as low as ppb, it cannot be detected by the human olfactory system. Fortunately, the use of gas sensors to detect biomarkers such as H2S has become a new technology, which has also promoted the rapid development of gas sensors and smart medical fields [6] .

[0003] WO3 is a typical n-type MOS, which is widely used in gas sensor research due to its low price, easy-to-control structure, non-stoichiometric characteristics, and high gas sensitivity [7-9 ] Through literature research, it can be known that although pure-phase WO3 can effectively detect toxic and harmful gases, it still has the disadvantages of high working temperature, low response value, and poor selectivity, which limits its detection of H2S gas [10-1 2] At present, WO3 materials with different morphological structures have been widely used to detect H2S gas. Zhu et al.

[13] prepared WO3 nanofilms on electrode sheets by magnetron sputtering technology, and in two consecutive months of H2S testing, the response value of the WO3 sensor only decreased by 3.1%, showing good long-term stability. In addition, our research group

[14] synthesized hierarchical WO3 nanoflowers, which showed high sensitivity and low working temperature to H2S gas.

[0004] Although the gas sensing performance can be improved by changing the morphology of WO3, this improvement is limited. We can also further improve the sensing performance of WO3 by adding precious metal catalysts. [15 ]. Currently, common noble metal modified WO3-based H2S gas sensors mainly include Au, Pt, Pd, Ru, etc., while there are very few reports on Ag-modified WO3-based gas sensors. Choi et al. [16 ] prepared Pt nanoparticle-modified WO3 nanofibers for pattern recognition of simulated respiratory gas components. The results showed that the response value of 5 ppm H2S at 350 ° C was as high as 834.2, and the sensitivity and selectivity were significantly improved. Guo et al. [1 7] used electron beam evaporation to deposit WO3 and Pd sequentially on an alumina substrate, providing an effective strategy for achieving a high-performance H2S sensor with a detection limit at the ppb level. Kruefu et al. [18 ] synthesized a series of WO3 sensors with different Ru concentrations. The Ru-functionalized WO3 nanomaterials optimized the sensor's response value, response / recovery time, and selectivity. In addition to single noble metal modification, dual noble metal modification also showed excellent gas sensing performance. Zhang et al. [19 ] used Pt and Pd co-modified hexagonal WO3 nanorods to evaluate the gas sensing performance of H2S gas. At 120℃, the response value of PtPd@h-WO3 sensor to H2S was about 49.47 times that of pure WO3 sensor. In addition, Gui et al.

[20] The prepared Ag / WO3 / rGO sensor also exhibited good gas-sensing performance to H2S gas, which was significantly better than that of WO3 / rGO.

[0005] This shows that the strategy of noble metal-modified WO3 gas sensors can fully improve the gas-sensing performance of H2S detection, but it also has disadvantages such as high operating temperature. Therefore, the development of highly sensitive, highly selective, fast-response gas sensors that can detect H2S at room temperature has become an urgent problem to be solved.

[0006] References

[0007] [1]M.Yu,J.Li,D.Yin,Z.Zhou,C.Wei,Y.Wang,J.Hao,Enhanced oxygen anionsgeneration on Bi(2)S(3) / Sb(2)S(3)heterostructure by visible light for trace H(2)S detection at room temperature,JHazard Mater,476(2024)134932.

[0008] [2] P. Hu, J. Chen, Q. Ma, J. Yin, D. Zhou, C. Kou, J. Xu, J. Xu, One-step thermal compensation decomposition synthesis of ZnWO4 / WO3 composite with synergy of multiple structural effects for efficient trace H2S detection, Sensors and Actuators B: Chemical, 381 (2023) 133388.

[0009] [3] S. Kundu, G. Gorthala, R. Ghosh, Room Temperature Detection of H2S by Two Dimensional WS2 based Chemiresistive Sensors, Sensors and Actuators B: Chemical, 416 (2024) 136018.

[0010] [4] D. Feng, L. Du, X. Xing, C. Wang, J. Chen, Z. Zhu, Y. Tian, D. Yang, Highly Sensitive and Selective NiO / WO3 Composite Nanoparticles in Detecting H2S Biomarker of Halitosis, ACS Sensors, 6 (2021) 733-741.

[0011] [5] X. R. Zhu, J. Q. Zhu, Y. F. Chen, Y. Y. Liu, J. J. Lu, J. Sun, S. Q. Peng, M. B. Chen, Y. P. Du, Bioinformatics analysis and experimental verification of the prognostic and biological significance mediated by fatty acid metabolism related genes for hepatocellular carcinoma, Frontiers in oncology, 12 (2022) 972744.

[0012] [6]M.M.a.A.J.Baeumner*,A Megatrend Challenging Analytical Chemistry:Biosensor and Chemosensor Concepts Ready for the Internet of Things,Chemicalreviews,119(2019)7996-8027.

[0013] [7]Y.Wang,S.Zhang,D.Xiao,S.Wang,T.Zhang,X.Yang,S.Heng,M.Sun,CuO / WO3hollow microsphere P-N heterojunction sensor for continuous cycle detectionofH2S gas,Sensors andActuators B:Chemical,(2022)132823.

[0014] [8]S.S.Shendage,V.L.Patil,S.A.Vanalakar,S.P.Patil,N.S.Harale,J.L.Bhosale,J.H.Kim,P.S.Patil,Sensitive and selective NO2 gas sensor based onWO3nanoplates,Sensors andActuators B:Chemical,240(2017)426-433.

[0015] [9]G.-L.Chen,H.-Y.Jiang,Z.-P.Deng,Y.-M.Xu,L.-H.Huo,S.Gao,Controllableassembly ofcorn cob-like h / γ-WO3 hierarchical structure for enhancedsensitive detection of dibutylamine vapor,Sensors and Actuators B:Chemical,415(2024)135981.

[0016]

[10] Y.Ren,Y.Deng,Z.Wang,Y.Li,H.Yu,Y.Zou,L.Wu,Y.Deng,Lab-on-DeviceSynthesis ofHierarchical Macro / Mesoporous WO(3)Semiconducting Films for High-Performance H(2)S Sensing,Small,(2024)e2311659.

[0017]

[11] X.-T.Yin,P.Lv,J.Li,A.Jafari,F.-Y.Wu,Q.Wang,D.Dastan,Z.Shi,S.Yu,H.Garmestani,Nanostructured tungsten trioxide prepared at various growthtemperatures for sensing applications,Journal ofAlloys and Compounds,825(2020)154105.

[0018]

[12] T.Zhao,Y.Fan,Z.Sun,J.Yang,X.Zhu,W.Jiang,L.Wang,Y.Deng,X.Cheng,P.Qiu,W.Luo,Confined interfacial micelle aggregating assembly oforderedmacro–mesoporous tungsten oxides for H2S sensing,Nanoscale,12(2020)20811-20819.

[0019]

[13] C.Zhu,T.Lv,H.Yang,X.Li,X.Wang,X.Guo,C.Xie,D.Zeng,Influence ofmagnetron sputtering process on the stability of WO3 thin film gas sensor,Materials Today Communications,34(2023)105116.

[0020]

[14] M.Sun,S.Zhang,Z.Zhang,H.Zhang,Y.Wang,X.Jing,X.Song,Effect ofC6H14N2O7 and reaction temperature on sensing properties ofhierarchical WO3for H2S sensor,Journal ofMaterials Science,56(2021)11801-11813.

[0021]

[15] L.-Y.Zhu,L.-X.Ou,L.-W.Mao,X.-Y.Wu,Y.-P.Liu,H.-L.Lu,Advances inNoble Metal-Decorated Metal Oxide Nanomaterials for Chemiresistive GasSensors:Overview,Nano-micro letters,15(2023).

[0022]

[16] S.-J.Choi,K.H.Ku,B.J.Kim,I.-D.Kim,Novel Templating Route Using PtInfiltrated Block Copolymer Microparticles for Catalytic Pt FunctionalizedMacroporous WO3 Nanofibers and Its Application in Breath Pattern Recognition,ACS Sensors,1(2016)1124-1131.

[0023]

[17] Y.Guo,B.Liu,Z.Duan,Z.Yuan,Y.Jiang,H.Tai,Batch fabrication ofH2Ssensors based on evaporated Pd / WO3 film with ppb-level detection limit,Materials Chemistry and Physics,302(2023)127768.

[0024]

[18] V.Kruefu, A.Wisitsoraat, A.Tuantranont, S.Phanichphant, Ultra-sensitive H2S sensors based on hydrothermal / impregnation-made Ru-functionalized WO3nanorods, Sensors and Actuators B: Chemical, 215 (2015) 630-636.

[0025]

[19] Y.Zhang, J.Chang, Y.Wang, Mechanism analysis of PtPd-decoratedhexagonal WO3 nanorods for H2S sensing application with ppt-level detectionlimit, Journal of Alloys and Compounds, 892(2022)162133.

[0026]

[20] Y. Gui, J. Wu, K. Tian, ​​H. Guo, X. Qin, Summary of the Invention

[0027] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas. The method adopts a simple solvent thermal plus sodium borohydride (NaBH4) reduction method to synthesize WO3 nanospheres modified with controllable morphology and size. The electronic sensitization and chemical sensitization effects of Ag NPs accelerate the charge transfer rate and reduce the reaction activation energy, thereby significantly improving the gas sensing performance of the gas sensor.

[0028] The present invention solves the technical problem by the following technical solutions:

[0029] A method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas, comprising the following steps:

[0030] S1. Measure 20-40 mL of ethanol and pour it into a 100 mL beaker. Then add 1.30-1.34 g of WCl6 to the beaker and stir with a magnetic stirrer to fully dissolve it in the ethanol solution to obtain a mixed solution.

[0031] S2, add 2.4~2.6mmol of diammonium hydrogen citrate C6H 14 O7N2, polyvinyl pyrrolidone PVP and silver nitrate AgNO3, the amount of silver nitrate AgNO3 added is 0.002828~0.01131g, stirring continuously to make it fully mixed, and finally adding sodium borohydride NaBH4 to obtain a precursor solution;

[0032] S3. Transfer the precursor solution to a 50 mL polytetrafluoroethylene reaction vessel and place it in an oven for hydrothermal reaction;

[0033] S4. After the reaction is completed, the mixture is cooled naturally and washed by centrifugation with deionized water and anhydrous ethanol to obtain a precipitate A;

[0034] S5. Dry the precipitate A in a constant temperature vacuum drying oven for 6 to 10 hours, and calcine it in a muffle furnace to obtain light yellow Ag-WO3 nanospheres.

[0035] Moreover, the magnetic stirring time in S1 is 25 to 35 minutes.

[0036] Moreover, the stirring time in S2 is 85 to 95 min, and the molar ratio of AgNO 3 : NaBH 4 : PVP is 1:1.2:5.

[0037] Moreover, the oven temperature in S3 is set to 90-110° C., and the hydrothermal reaction time is 23-25 ​​h.

[0038] Moreover, the centrifugal speed in S4 is 2000-4000 r / min, and the product is first centrifugally washed with deionized water for 2-4 times, and then centrifugally washed with anhydrous ethanol for 2-4 times.

[0039] Moreover, the temperature of the constant temperature vacuum drying oven in S5 is 50-70°C, the vacuum degree is 700-800 Pa, the heating rate of the muffle furnace calcination is 2°C / min, and the calcination time at 440-460°C is 110-130 min.

[0040] The positive effects that the present invention can produce are:

[0041] 1. The present invention uses solvent heat plus sodium borohydride NaBH4 reduction method to synthesize WO3 nanospheres with controllable morphology and size.

[0042] 2. The Ag-WO3 sensor of the present invention has an ultra-high response value (Ra / Rg=2849) to 10 ppm H2S gas, which is about 235 times that of pure WO3, and is superior to the Ag-WO3 sensors on the market.

[0043] 3. The Ag-WO3 sensor of the present invention can continuously detect 0.01-40ppm H2S gas with a detection limit as low as 10ppb and a response time of only 6s, which has strong engineering practicality.

[0044] 4. The present invention realizes the development of room temperature sensors. Due to the electronic sensitization and chemical sensitization effects of Ag NPs catalysts, the adsorption rate is improved and the operating temperature is reduced, realizing the detection of H2S at room temperature (25°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 (a) is a synthetic diagram of WO3 and Ag-WO3 of the present invention, Figure 1 (b) is a diagram of the test system of the Ag-WO3 gas sensor of the present invention;

[0046] Figure 2 XRD spectra of WO3 and Ag-WO3 materials of the present invention;

[0047] Figure 3 (ab) is the SEM scanning electron microscope image of WO3 of the present invention, Figure 3 (cd) is the SEM scanning electron micrograph of 0.5 mol% Ag-WO3 of the present invention, Figure 3 (e) is the SEM scanning electron microscope of 1.0 mol% Ag-WO3 of the present invention, Figure 3 (f) is the SEM scanning electron microscope of 1.5 mol% Ag-WO3 of the present invention, Figure 3 (gh) is the SEM scanning electron microscope of 2.0 mol% Ag-WO3 of the present invention, Figure 3 (i-1) is the elemental mapping diagram of 1.0 mol% Ag-WO3 of the present invention;

[0048] Figure 4 (a) is a transmission electron microscope image of WO3 of the present invention, Figure 4 (bc) is the transmission electron microscopy image of 1.0 mol% Ag-WO3 of the present invention, Figure 4 (d) is a high-resolution transmission electron micrograph of 1.0 mol% Ag-WO3 of the present invention;

[0049] Figure 5 (a) is the full XPS spectrum of WO3 and Ag-WO3 of the present invention, Figure 5 (b) to (d) are high-resolution XPS spectra of W4f, Ag 3d, and O1s, respectively;

[0050] Figure 6 (a) is a graph showing the change of response value of WO3 and Ag-WO3 sensor with working temperature at H2S gas concentration of 10 ppm according to the present application, Figure 6 (b) is a graph showing the resistance (Ra) of sensor in air at different working temperature according to the present application;

[0051] Figure 7 (a-d) are graphs showing the dynamic sensing characteristics of 0.5-2.0 mol% Ag-WO3 sensor at 25°C to 1-40-1 ppm H2S gas, Figure 7 (e) is a graph showing the dynamic sensing characteristics of WO3 sensor at 40°C to 1-30-1 ppm H2S gas, Figure 7 (f) is a graph showing the response of 0.5-2.0 mol% Ag-WO3 sensor at 25°C to 1-40 ppm H2S gas, Figure 7 (g) is a graph showing the statistical response of 1.0 mol% Ag-WO3 sensor at 25°C to 0.01-1 ppm H2S concentration, Figure 7 (h-k) are graphs showing the response / recovery of 0.5-2.0 mol% Ag-WO3 sensor at room temperature (25°C) to 10 ppm H2S gas, Figure 7 (l) is a graph showing the response / recovery of WO3 sensor at 40°C to 10 ppm H2S gas;

[0052] Figure 8 (a) is a graph showing the selective response of WO3 and 0.5-2.0 mol% Ag-WO3 to different concentration of target gas, Figure 8 (b-f) are graphs showing the response of 0.5-2.0 mol% Ag-WO3 sensor to 10 ppm H2S at room temperature and different relative humidity;

[0053] Figure 9 (a) is a graph showing the long-term stability of WO3 and 1.0 mol% Ag-WO3 sensor at 10 ppm H2S, Figure 9 (b) is a graph showing the continuous response of 1.0 mol% Ag-WO3 sensor for 10 times on the 2nd day and for 6 times on the 26th day at 10 ppm H2S. DETAILED DESCRIPTION

[0054] The present application will be further described in the following specific examples, which are only illustrative and not restrictive, and should not be used to limit the scope of the present application.

[0055] As Figure 1As shown, the present invention relates to a method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas. A simple solvent thermal plus sodium borohydride (NaBH4) reduction method is used to synthesize a WO3 nanosphere gas sensor modified with precious metal Ag nanoparticles (NPs) with controllable morphology and size. The electronic sensitization and chemical sensitization effects of Ag NPs accelerate the charge transfer rate and reduce the reaction activation energy, significantly improving the gas sensing performance of the gas sensor.

[0056] Example 1

[0057] (1) Pour 20 mL of ethanol into a 100 mL beaker. Then add 1.30 g of WCl6 and stir with a magnetic stirrer for 20 minutes to allow it to fully dissolve in the solution.

[0058] (2) Then add 2.4 mmol of diammonium hydrogen citrate (C6H 14 The precursor solution was transferred to a 50 mL polytetrafluoroethylene reaction vessel and hydrothermally reacted at 90°C for 23 h.

[0059] (3) After the reaction is completed, the mixture is naturally cooled to room temperature, the supernatant is removed, and the mixture is centrifuged and washed twice with deionized water and then twice with anhydrous ethanol to obtain precipitate A.

[0060] (4) The sample was then placed in a constant temperature vacuum drying oven and dried at 50 °C for 6 h, and calcined at 440 °C for 110 min with a heating rate of 2 °C / min, finally obtaining light yellow WO3 nanoflower powder.

[0061] (5) Pour 20 mL of ethanol into a 100 mL beaker. Then add 1.30 g of WCl6 and stir with a magnetic stirrer for 20 min.

[0062] (6) Then 2.4 mmol of diammonium hydrogen citrate (C6H 14 Add 0.07N2), polyvinyl pyrrolidone (PVP), and silver nitrate (AgNO3) and stir continuously to mix thoroughly. Finally, add sodium borohydride (NaBH4). The amount of AgNO3 added is 0.002828-0.01131g, and the molar ratio of AgNO3:NaBH4:PVP is 1:1.2:5.

[0063] (7) The precursor solution was transferred to a 50 mL polytetrafluoroethylene reaction vessel and subjected to hydrothermal reaction at 90 °C for 23 h.

[0064] (8) After cooling, the supernatant was removed and the mixture was washed twice by centrifugation with deionized water and then twice by centrifugation with anhydrous ethanol to obtain precipitate B.

[0065] (9) The sample was then placed in a constant temperature vacuum drying oven and dried at 50 °C for 6 h, and calcined at 440 °C for 110 min with a heating rate of 2 °C / min, finally obtaining light yellow Ag-WO3 nanospheres.

[0066] Example 2

[0067] (1) Pour 30 mL of ethanol into a 100 mL beaker. Then add 1.32 g of WCl6 and stir with a magnetic stirrer for 30 minutes to allow it to fully dissolve in the solution.

[0068] (2) Then add 2.5 mmol of diammonium hydrogen citrate (C6H 14 The precursor solution was transferred to a 50 mL polytetrafluoroethylene reaction vessel and hydrothermally reacted at 100°C for 24 h.

[0069] (3) After the reaction is completed, the mixture is naturally cooled to room temperature, the supernatant is removed, and the mixture is first centrifuged and washed three times with deionized water and then centrifuged and washed three times with anhydrous ethanol to obtain precipitate A.

[0070] (4) The sample was then placed in a constant temperature vacuum drying oven and dried at 60 °C for 8 h, and calcined at 450 °C for 120 min with a heating rate of 2 °C / min, finally obtaining light yellow WO3 nanoflower powder.

[0071] (5) Pour 30 mL of ethanol into a 100 mL beaker. Then add 1.32 g of WCl6 and stir with a magnetic stirrer for 30 min.

[0072] (6) Then 2.5 mmol of diammonium hydrogen citrate (C6H 14 Add 0.07N2), polyvinyl pyrrolidone (PVP), and silver nitrate (AgNO3) and stir continuously to mix thoroughly. Finally, add sodium borohydride (NaBH4). The amount of AgNO3 added is 0.002828-0.01131g, and the molar ratio of AgNO3:NaBH4:PVP is 1:1.2:5.

[0073] (7) The precursor solution was transferred to a 50 mL polytetrafluoroethylene reaction vessel and subjected to hydrothermal reaction at 100 °C for 24 h.

[0074] (8) After cooling, the supernatant was removed and the mixture was washed three times with deionized water and then three times with anhydrous ethanol to obtain precipitate B.

[0075] (9) The sample was then placed in a constant temperature vacuum drying oven and dried at 60 °C for 8 h, and calcined at 450 °C for 120 min with a heating rate of 2 °C / min, finally obtaining light yellow Ag-WO3 nanospheres.

[0076] Example 3

[0077] (1) Pour 40 mL of ethanol into a 100 mL beaker. Then add 1.34 g of WCl6 and stir with a magnetic stirrer for 40 minutes to allow it to fully dissolve in the solution.

[0078] (2) Then add 2.6 mmol of diammonium hydrogen citrate (C6H 14 The precursor solution was transferred to a 50 mL polytetrafluoroethylene reaction vessel and hydrothermally reacted at 110°C for 25 h.

[0079] (3) After the reaction is completed, the mixture is naturally cooled to room temperature, the supernatant is removed, and the mixture is first centrifuged and washed four times with deionized water and then with anhydrous ethanol to obtain precipitate A.

[0080] (4) The sample was then placed in a constant temperature vacuum drying oven and dried at 70 °C for 10 h, and calcined at 460 °C for 130 min with a heating rate of 2 °C / min, finally obtaining light yellow WO3 nanoflower powder.

[0081] (5) Pour 40 mL of ethanol into a 100 mL beaker. Then add 1.34 g of WCl6 and stir with a magnetic stirrer for 40 min.

[0082] (6) Then 2.6 mmol of diammonium hydrogen citrate (C6H 14 Add 0.07N2), polyvinyl pyrrolidone (PVP), and silver nitrate (AgNO3) and stir continuously to mix thoroughly. Finally, add sodium borohydride (NaBH4). The amount of AgNO3 added is 0.002828-0.01131g, and the molar ratio of AgNO3:NaBH4:PVP is 1:1.2:5.

[0083] (7) The precursor solution was transferred to a 50 mL polytetrafluoroethylene reaction vessel and subjected to hydrothermal reaction at 110 °C for 25 h.

[0084] (8) After cooling, the supernatant was removed and the mixture was washed four times by centrifugation with deionized water and then four times by centrifugation with anhydrous ethanol to obtain precipitate B.

[0085] (9) The sample was then placed in a constant temperature vacuum drying oven and dried at 70 °C for 10 h, and calcined at 460 °C for 130 min with a heating rate of 2 °C / min, finally obtaining light yellow Ag-WO3 nanospheres.

[0086] like Figure 2As shown in the figure, the crystal structure and phase purity of WO3 and Ag-WO3 nanospheres were obtained by XRD analysis. These diffraction peaks have similar characteristics. The main XRD peaks of pure WO3 and Ag-WO3 materials correspond to monoclinic WO3 (JCPDS No.72-0677). The diffraction peaks are located at 23.109°, 23.579°, 24.349°, 33.252°, 34.151°, 49.893° and 55.894°, corresponding to the (002), (020), (200), (022), (202), (400) and (420) crystal planes of monoclinic WO3, respectively. In addition, the characteristic peaks of Ag observed in the Ag-WO3 material are not obvious, which may be due to the low content of Ag NPs, the small crystal size of Ag NPs, and the high dispersion of AgNPs on the surface of WO3 nanospheres, which makes it difficult to detect. However, it can be found that with the increase of Ag NPs content, the diffraction peaks near 35.50°, 44.75°, and 76.6° are significantly enhanced. This is because the diffraction peaks at 35.891°, 45.305°, and 76.807° correspond to the (004), (103), and (201) crystal planes of hexagonal Ag (JCPDS No. 41-1402), respectively.

[0087] Figure 3 The microstructure and phase composition of the material were analyzed using a scanning electron microscope. It is clear that the original WO3 presents a three-dimensional (3D) nanoflower shape self-assembled by nanosheets. The nanosheets grow outward, which helps to increase the reaction sites of the target gas on the surface of the material ( Figure 3 (ab)). With the addition of AgNO3, PVP and reducing agent NaBH4, the nanosheets on the 0.5mol% Ag-WO3 nanospheres were eroded to a certain extent, the diameter of the nanoflowers was slightly reduced, gaps appeared on the nanoflowers, and there was a tendency for them to break into nanoparticles ( Figure 3 (cd)). Figure 3SEM images of (e-g) are 1.0 mol% Ag-W03, 1.5 mol% Ag-W03 and 2.0 mol% Ag-W03, respectively. With the addition of AgN03, PVP and reducing agent NaBH4, the nanoparticles are broken into nanoparticles. The shape of this material becomes a 3D sphere self-assembled by nanoparticles. Specifically, 1.0 mol% Ag-W03 is a 750 nm diameter sphere grown on a nanoflower by assembling 21.1-65.8 nm nanoparticles. This special complex structure not only retains the large gas diffusion channels and large specific surface area of the nanoflower. It also provides more surface active sites for gas adsorption. 1.5 mol% Ag-W03 is a sphere with a diameter of about 1.17 μm, self-assembled by 20.7-41.4 nm nanoparticles. However, 2.0 mol% Ag-W03 is a sphere with a diameter of 1.05 μm, assembled by 39.7-62.2 nm nanoparticles. In addition, it can be found in the magnified SEM image of 2.0 mol% Ag-W03 that the presence of Ag NPs can be clearly seen Figure 3 h) Typical elemental mapping analysis of 1.0 mol% Ag-W03 sample Figure 3 (i-1)) further indicates that W, O and Ag are present in the sample and that W, O and Ag are uniformly distributed in the sample.

[0088] To further verify the structure of the sample, TEM test was also carried out, as shown in Figure 4 Pure phase W03 is a nanoflower self-assembled by nanosheets, while 1.0 mol% Ag-W03 is a solid sphere assembled by nanoparticles, and there are also sheet structures. This is completely consistent with the SEM image characterization. Figure 4 d is the HRTEM image of 1.0 mol% Ag-W03, the lattice spacing of 0.431 and 0.365 nm corresponds to the (111) and (200) crystal planes of monoclinic W03, and the lattice spacing of 0.250 nm corresponds to the (004) crystal plane of hexagonal Ag.

[0089] The elemental configuration and chemical valence of the material were studied by XPS. From Figure 5 (a) The full spectrum of 1.0 mol% Ag-W03 composite surface measured by XPS is composed of Ag, W and O elements, while the measured XPS spectrum of W03 surface is composed of W and O elements. In the XPS test, C is used as the reference object. Figure 5 (b) shows that W 4f7 / 2 and W 4f5 / 2 belong to 1.0 mol% Ag-W03 at 34.96 and 37.09 eV, respectively, and W 4f7 / 2 and W 4f5 / 2 belong to W03 at 34.94 and 37.14 eV, respectively. W +6The existence of has been confirmed. Figure 5 As can be seen in (c), the two peaks at 367.60eV and 373.60eV belong to Ag3d5 / 2 and Ag 3d3 / 2, respectively, confirming the presence of Ag. Figure 5 In (d), the O1s spectrum of 1.0 mol% Ag-WO3 has three peaks at 529.70, 530.43 and 532.54 eV, representing lattice oxygen (O L ), oxygen vacancies (O V ) and adsorbed water molecules (O C In WO3, the binding energies of these three peaks are 529.75, 531.09 and 532.97 eV respectively. Compared with WO3, the three O1s peaks of 1.0 mol% Ag-WO3 show negative shifts, and the oxygen vacancies increase. In addition, the relative oxygen content is also different. It can be seen that the oxygen vacancies (O V ) content is higher than that of WO3, which is beneficial to improve gas sensitivity. XPS spectrum confirms that Ag-WO3 is composed of WO3 and metallic Ag, which is consistent with the XRD results.

[0090] The contact between the sensitive layer and the gas is closely related to the operating temperature and is an important factor affecting the gas sensing performance of the gas sensor. Figure 6 (a) shows the response curves of the WO3 and Ag-WO3 sensors as a function of operating temperature at a H2S gas concentration of 10 ppm. The response of the 0.5-2.0 mol% Ag-WO3 sensor decreases with increasing operating temperature, reaching a maximum at room temperature. As the operating temperature increases, the response of pure WO3 exhibits a "volcano-like" response, reaching a maximum at 40°C. Therefore, subsequent gas-sensing performance tests were conducted at room temperature. More notably, under the same room temperature conditions, the gas-sensing performance of the 0.5-2.0 mol% Ag-WO3 sensors varies slightly. The response values ​​(Ra / Rg) of the 0.5-2.0 mol% Ag-WO3 sensors to 10 ppm H2S are 395, 2849, 1570, and 946, respectively, significantly higher than those of pure WO3 (Ra / Rg = 12.14). The 2.0 mol% Ag-WO3 sensor exhibits the highest response, approximately 235 times that of WO3. This indicates that the WO3 nanosphere sensor modified with AgNPs surface significantly improves the response value of the sensor. Figure 6 (b) shows the relationship between operating temperature and sensor Ra. As the operating temperature increases, the Ra of all sensors decreases, demonstrating typical semiconductor properties. Furthermore, it can be clearly seen that at the same operating temperature, the Ra of the Ag-WO3 sensor is significantly higher than that of the pure WO3 sensor. This is due to the formation of a Schottky barrier and a thicker electron depletion layer at the interface between Ag and WO3.

[0091] Figure 7 (ae) Continuous response cycle performance of Ag-WO3 and WO3 sensors to H2S gas of different concentrations at 25℃ and 40℃, respectively. In H2S gas of different concentrations, the resistance of the gas sensor loaded with AgNPs drops faster and more sharply than that of the pure WO3 sensor. The response amplitude increases with the increase of H2S concentration. At the same time, in the dynamic test of H2S gas cycle of different concentrations, the concentration response values ​​corresponding to the four sensors are basically the same, indicating that the Ag-WO3 sensor has good short-term reproducibility. It is worth noting that the response value of the 1.0mol% Ag-WO3 sensor is the largest ( Figure 7 (f)), which is much higher than that of pure WO3. The response value of 1.0mol% Ag-WO3 is a function of H2S concentration. More importantly, in the minimum detection limit test ( Figure 7 (g)), 0.5-2.0mol% Ag-WO3 sensors showed good response even in the presence of H2S gas at ppb level, with the minimum detection limit as low as 10ppb and response values ​​of 1.32, 1.74, 1.3, and 1.09, respectively.

[0092] In addition, the response / recovery capabilities of 0.5–2.0 mol% Ag-WO3 and WO3 sensors were investigated, as Figure 7 (h-1) At the optimal operating temperature, the response times of 0.5-2.0 mol% Ag-WO3 and WO3 to 10 ppm H2S gas were 23, 6, 46, 17, and 30 s, respectively. Compared to WO3, the 1.0 mol% Ag-WO3 material exhibited a significantly enhanced response signal amplitude and a shorter response time from 30 s to 6 s. This is likely due to the silver providing catalytic centers for the oxidation of adsorbed H2S molecules, injecting electrons into the conduction band of WO3 and altering its conductivity. After the reaction, the strong adsorption of H2S prevented rapid sensor recovery at room temperature. Therefore, a pulsed heating current was applied externally to the sensor to accelerate the strong adsorption of Ag and S, thereby separating the H2S molecules from the AgNPs. The 0.5-2.0 mol% Ag-WO3 samples were heated at 170, 150, 190, and 140°C for 90 s, respectively, while the WO3 sample was heated at 80°C for 60 s.

[0093] Ideally, a gas sensor should have the ability to screen specific gases, so selectivity is a key parameter of a gas sensor, such as Figure 8The selectivity of the sensors was analyzed by measuring the response of WO3 and 1.0 mol% Ag-WO3 sensors to 10 ppm H2S, SO2, CO, NO2 and 100 ppm EG, ethanol, methanol gases. The 0.5-2.0 mol% Ag-WO3 experiments were carried out at room temperature, and the WO3 experiment was carried out at 40 °C, and the results are shown in Fig. Figure 8 (a) and (b) show that all 0.5-2.0 mol% Ag-WO3 sensors exhibit a high contrast in the relative response to the test gases, with the highest response to H2S and negligible responses to the other gases. In addition, the relative humidity of the environment also has an effect on the performance of the gas sensors. Figure 8 (a) and (b) show that all 0.5-2.0 mol% Ag-WO3 sensors exhibit a high contrast in the relative response to the test gases, with the highest response to H2S and negligible responses to the other gases. In addition, the relative humidity of the environment also has an effect on the performance of the gas sensors.

[0094] In the stability tests, the short-term repeatability and long-term stability of the sensors were studied. Figure 9 (b) show the response / recovery curves for 10 and 6 exposures to 10 ppm H2S at room temperature, on day 2 and day 26, respectively. The results show that the response values remain essentially unchanged and the baseline resistance can be recovered to the original state, with good short-term repeatability. In addition, the long-term stability of the WO3 and 1.0 mol% Ag-WO3 sensors was also tested, with at least three cycles for each over a period of one month, as shown in Figure 9 (a) and (b) show that all 0.5-2.0 mol% Ag-WO3 sensors exhibit a high contrast in the relative response to the test gases, with the highest response to H2S and negligible responses to the other gases. In addition, the relative humidity of the environment also has an effect on the performance of the gas sensors.

[0095] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas, characterized by: The steps of the method are: S1. Measure 20-40 mL of ethanol and pour it into a 100 mL beaker. Then add 1.30-1.34 g of WCl6 to the beaker and stir with a magnetic stirrer to fully dissolve it in the ethanol solution to obtain a mixed solution. S2, add 2.4~2.6mmol of diammonium hydrogen citrate C6H 14 O7N2, polyvinyl pyrrolidone PVP and silver nitrate AgNO3, the amount of silver nitrate AgNO3 added is 0.002828~0.01131g, stirring continuously to make it fully mixed, and finally adding sodium borohydride NaBH4 to obtain a precursor solution; S3. Transfer the precursor solution to a 50 mL polytetrafluoroethylene reaction vessel and place it in an oven for hydrothermal reaction; S4. After the reaction is completed, the mixture is cooled naturally and washed by centrifugation with deionized water and anhydrous ethanol to obtain a precipitate A; S5. Dry the precipitate A in a constant temperature vacuum drying oven for 6 to 10 hours, and calcine it in a muffle furnace to obtain light yellow Ag-WO3 nanospheres.

2. The method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas according to claim 1, characterized in that: The magnetic stirring time in S1 is 25 to 35 minutes.

3. The method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas according to claim 1, characterized in that: The stirring time in S2 is 85-95 min, and the molar ratio of AgNO3:NaBH4:PVP is 1:1.2:

5.

4. The method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas according to claim 1, characterized in that: In the step S3, the oven temperature is set to 90-110° C., and the hydrothermal reaction time is 23-25 ​​hours.

5. The method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas according to claim 1, characterized in that: The centrifugal speed in S4 is 2000-4000 r / min, and the product is first centrifugally washed 2-4 times with deionized water, and then centrifugally washed 2-4 times with anhydrous ethanol.

6. The method for preparing Ag nanoparticle-modified WO3 nanospheres for high-sensitivity detection of H2S gas according to claim 1, characterized in that: The temperature of the constant temperature vacuum drying oven in S5 is 50-70° C., the vacuum degree is 700-800 Pa, the heating rate of the muffle furnace calcination is 2° C. / min, and the calcination time at 440-460° C. is 110-130 min.

Images