A method for preparing a three-dimensional silver surface-enhanced Raman spectroscopy substrate material for quantitative detection of trace hydrazine

Abstract

The present invention provides a method for preparing a three-dimensional silver surface enhanced Raman spectroscopy substrate material for quantitatively detecting trace hydrazine. The substrate material is Ag6[MnMo9O 32 ]∙8H2O can be used as a label-free quantitative SERS detection substrate for hydrazine molecules. The substrate material has high sensitivity and the detection limit of hydrazine can reach 2.37×10 ‑4 mg∙m ‑3 , which is far lower than the exposure limit of hydrazine for humans in the workplace stipulated in the National Occupational Health Standard of the People’s Republic of China (0.06 mg∙m ‑3 ). The three-dimensional framework material Ag6[MnMo9O 32 ]∙8H2O is mostly composed of MnMo9. The introduction of MnMo9 not only reduces the raw material cost of the SERS substrate, but MnMo9 itself is a signal molecule and can also be used as an internal standard, so there is no need to introduce additional signal molecules.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis of molecular detection materials, and in particular relates to the preparation of a three-dimensional silver surface enhanced Raman spectroscopy substrate material and its application in quantitative detection of hydrazine. Background Art

[0002] Hydrazine is widely used as a precursor of chemical products such as polymers and drug intermediates due to its suitable reducibility and alkalinity. However, with the widespread application of hydrazine, people have found that hydrazine is a highly toxic substance. When we are in a hydrazine environment for a long time, it will cause diseases of our nerves, blood and skin. In addition, hydrazine is also a potential carcinogen, so the detection of hydrazine, especially the detection of trace hydrazine in steam, is very important.

[0003] As people's understanding of hydrazine toxicity deepens, hydrazine detection technology has gradually developed. Currently, detection technologies mainly include fluorescent probe method, electrochemical detection method, titration method, etc. Although each detection method has its own advantages, it still faces some limitations, such as low sensitivity, long analysis time, and complex pretreatment process. In particular, most of these methods are limited to liquid phase detection of hydrazine, and rarely involve the detection of hydrazine gas in the air. At present, the only detection method based on gaseous hydrazine also uses fluorescence spectroscopy, and the lowest detection concentration of gaseous hydrazine so far is 0.86 mg∙m -3 , but still does not reach the exposure limit of hydrazine for humans in the workplace as stipulated in the National Occupational Health Standard of the People’s Republic of China (0.06 mg∙m -3 ) testing standards.

[0004] Surface enhanced Raman spectroscopy (SERS) has excellent development prospects in the field of detecting trace pollutants due to its high sensitivity, but the SERS detection method based on gaseous hydrazine has not been reported. Since silver is more easily excited by light in the visible to near-infrared region, it produces higher plasma quality and thus exhibits stronger electromagnetic coupling. Therefore, silver is currently the most ideal SERS substrate material. However, traditional ultra-sensitive SERS detection not only requires the use of a large number of dispersed silver nanoparticles as a detection substrate, but also requires the introduction of additional signal molecules, which leads to high detection costs and complex detection processes. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing a three-dimensional silver surface-enhanced Raman spectroscopy substrate material for quantitatively detecting trace hydrazine, thereby achieving the following invention objectives: reducing the amount of silver used, not requiring additional introduction of signal molecules, and having a low detection limit.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a three-dimensional silver surface enhanced Raman spectroscopy substrate material for quantitatively detecting trace hydrazine, wherein the substrate material is Ag 6 [MnMo 9 O 32 ]∙8H 2 O.

[0008] The preparation method comprises preparing solution A, preparing solution B, and adding dropwise;

[0009] The method for preparing solution A is to 4 ) 6 [MnMo 9 O 32 ]·8H 2 Dissolve O in distilled water, heat to 48-52°C, and stir until dissolved to prepare solution A;

[0010] The method for preparing solution B is to add AgNO 3 Dissolve in acetonitrile solution and stir for 4-6 minutes to prepare solution B;

[0011] The method of dropping is to drop solution B into solution A and stir at room temperature to obtain an orange clear solution, which is then placed in a dark place for crystallization, and the precipitated crystals are Ag. 6 [MnMo 9 O 32 ]∙8H 2 O.

[0012] In the preparation of solution A, (NH 4 ) 6 [MnMo 9 O 32 ]·8H 2 The mass ratio of O to water is 1:295-296; in the preparation of solution B, AgNO 3 The mass volume ratio of acetonitrile solution is 1 g:220-221 mL.

[0013] In the dropwise addition step, the stirring time at room temperature is 5.8-6.2 h.

[0014] The (NH 4 ) 6 [MnMo 9 O 32 ]·8H 2The preparation method of O is as follows: dissolve ammonium molybdate in distilled water, adjust the pH to 5 with glacial acetic acid; then add manganese sulfate monohydrate, stir and heat to 58-62°C, a yellow precipitate appears, and a yellow suspension is obtained; then, add ammonium persulfate to the yellow suspension under stirring, and raise the temperature to 78-82°C, keep stirring at this temperature for 28-32 minutes, and then filter while hot, and place the filtrate at room temperature overnight to precipitate crystals, which is (NH 4 ) 6 [MnMo 9 O 32 ]·8H 2 O.

[0015] The mass ratio of ammonium molybdate to water is 1:24-25; the mass ratio of ammonium molybdate to manganese sulfate monohydrate is 1.04-1.05:1;

[0016] The stirring speed is 450-500 r / min;

[0017] The mass ratio of the ammonium molybdate to ammonium persulfate is 2.6-2.8:1.

[0018] This application synthesizes a polyacid-based three-dimensional silver framework material Ag 6 [MnMo 9 O 32 ]∙8H 2 O (abbreviated as Ag 6 MnMn 9 ). Each [MnMo 9 O 32 ] 6- (abbreviated as MnMo 9 ) anion as a dodecanoate inorganic metal ligand is connected by 12 covalently bonded Ag + Surrounded by silver ions, a three-dimensional framework structure with two-dimensional channels (along the a-axis and c-axis) is formed through the connection of silver ions. + Most of the coordinated oxygen atoms are MnMo 9 The terminal oxygen atom of Mn 4+ Wrapped in MnMo 9 Center and Ag + Therefore, when using Ag 6 MnMn 9When used as a SERS substrate, the Mo-O chemical bond signal connected to the silver ions will be more sensitive to changes in the coordination environment or redox processes of the silver ions. And silver is the connection point of the three-dimensional framework material. When hydrazine comes into contact with silver ions, the generated silver nanoparticles will be fixed in the two-dimensional channels, so that the silver nanoparticles are well dispersed. For highly dispersed silver nanoparticles, each particle can emit the same strong SERS signal, so that a uniform and repeatable SERS signal can be obtained. The signal of the internal Mn-O chemical bond far away from the silver ions remains basically unchanged. Therefore, MnMo 9 When used as SERS substrate, polyacid anions can serve as both signal molecules and internal standard molecules to achieve ratiometric SERS quantitative detection of reduced hydrazine gas molecules.

[0019] In summary, the MnMo designed by the present invention 9 Silver-doped SERS substrate three-dimensional framework material, due to MnMo 9 The introduction of not only reduces the cost of raw materials for SERS substrates, but also eliminates the need for doping with other signal molecules. At the same time, the presence of a two-dimensional pore structure in the three-dimensional framework material is also more conducive to the dispersion of reduced silver nanoparticles. These structural features give the three-dimensional framework material Ag 6 MnMn 9 Excellent performance as a SERS substrate for quantitative detection of hydrazine.

[0020] The present invention designs a new MnMo-based 9 and silver three-dimensional framework material Ag 6 MnMn 9 , which can be used as a label-free quantitative SERS detection substrate for hydrazine molecules. The substrate material has high sensitivity, and the detection limit of hydrazine can reach 2.37×10 -4 mg∙m -3 , which is much lower than the exposure limit of hydrazine for humans in the workplace stipulated by the National Occupational Health Standard of the People’s Republic of China (0.06 mg∙m -3 ), which can be fully applied to the environmental monitoring of gaseous hydrazine concentration in the air.

[0021] In addition, compared with the traditional SERS detection method which uses pure silver nanoparticles as the detection substrate and requires the additional introduction of signal molecules during detection, the three-dimensional framework material Ag of the present invention 6 MnMn 9 The majority of the composition is MnMo 9 , due to MnMo 9 The introduction of MnMo not only reduces the raw material cost of SERS substrate, but also 9 It is a signal molecule itself and can also be used as an internal standard, so there is no need to introduce additional signal molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Ag 6 MnMn 9 and MnMo 9 Infrared spectrum of

[0023] Figure 2 Ag under optical microscope 6 MnMn 9 Block crystal diagram

[0024] Figure 3 Ag 6 MnMn 9 exist a Axis and c Axis-directed ball-and-stick polyhedron 3D structure

[0025] Figure 4 Ag 6 MnMn 9 and MnMo 9 Raman spectrum of

[0026] Figure 5 is Ag before and after hydrazine vapor reduction 6 MnMn 9 XRD pattern of

[0027] Figure 6 Ag before (a) and after (b) hydrazine vapor reduction 6 MnMn 9 TEM image

[0028] Figure 7 Ag before and after hydrazine vapor reduction 6 MnMn 9 XPS chart of silver element

[0029] Figure 8 Ag 6 MnMn 9 SERS spectra after reacting with different concentrations of hydrazine and the correlation between the absolute intensity of Raman signals at different wavelengths and the hydrazine concentration:

[0030] Where (a) is Ag 6 MnMn 9 SERS spectra after reaction with different concentrations of hydrazine; (b) I 630 and C [N2H4] / 7.5 logarithmic response diagram; (c) is I 945 and C [N2H4] / 7.5 logarithmic response diagram; (d) is I 945 / I630 and C [N2H4] Response plot of / 7.5 logarithm. DETAILED DESCRIPTION

[0031] Example 1 A method for preparing a three-dimensional silver surface-enhanced Raman spectroscopy substrate material for quantitative detection of trace hydrazine

[0032] The following steps are involved:

[0033] Step 1: (NH 4 ) 6 [MnMo 9 O 32 ]·8H 2 O (abbreviated as MnMo 9 ) preparation and infrared characterization:

[0034] MnMn 9 The preparation of J. Inorg. Nucl. Chem .1966, 28, 447-454].

[0035] 12.359 g of ammonium molybdate (NH 4 ) 6 Mo 7 O 24 ∙4H 2 O) was dissolved in 300 mL of distilled water and the pH was adjusted to 5 with glacial acetic acid; then 11.83 g of manganese sulfate monohydrate (MnSO 4 ∙H 2 O), stirred and heated to 60 °C, a yellow precipitate appeared, and a yellow suspension was obtained.

[0036] Then, 4.56 g of ammonium persulfate (NH 4 ) 2 S 2 O 8 ), and the temperature was raised to 80°C. At this time, the solution was orange-red. The temperature was maintained and stirred (480 r / min) for 30 minutes. Finally, the solution was filtered while hot and the filtrate was placed at room temperature overnight. The orange-red crystals precipitated were MnMo 9 , the yield is about 71% (based on Mo). Infrared spectrum test shows that MnMo 9 At 400 cm -1 To 1000 cm -1 The characteristic peaks between the two are consistent with those reported in the literature for MnMo 9 At 940 and 900 cm -1 (attributed to the stretching vibration peak of M=O), 680, 590 and 540 cm -1The infrared characteristic peaks generated by the bending vibration of Mo-O-Mo are basically consistent (see Figure 1 Gray solid line). 9 was successfully prepared.

[0037] Step 2: Ag 6 [MnMo 9 O 32 ]∙8H 2 O (abbreviated as Ag 6 MnMn 9 ) preparation and structural characterization:

[0038] MnMo 9 (0.01 mmol, 0.0169 g) was dissolved in 5 mL (5 g) of distilled water, heated to 50 °C and stirred until dissolved to prepare solution A; AgNO 3 (0.08 mmol, 0.0136 g) was dissolved in 3 mL of acetonitrile solution and stirred for 5 min to prepare solution B.

[0039] Solution B was added dropwise to solution A and stirred at room temperature for 6 hours. The resulting orange clear solution was placed in a dark place for crystallization (because silver ions are photosensitive). After two weeks, light orange rhombus crystals were precipitated. Figure 2 , the yield is about 34% (based on Mo).

[0040] The light orange rhombus crystals were precisely tested using an X-ray single crystal diffractometer, the intensity was empirically corrected using the SADABS program, and the solution was obtained using the SHELXS97 program. The data analysis results show that the light orange rhombus crystals belong to the orthorhombic system, C222 1 Space group, unit structure is [MnMo 9 O 32 ] 6- Anion, Ag + and water molecules. Each [MnMo 9 O 32 ] 6- The anion is a dodecanoate inorganic metal ligand with 12 covalently linked Ag + Surrounded by silver ions, a two-dimensional pore (along a Axis and c axis), according to the van der Waals surface calculation along a Axis and c The pore sizes in the axial direction are approximately 5.34×5.71Å and 5.87×5.87Å, respectively, with a porosity of 26.4%. The ball-and-stick-polyhedron three-dimensional structure is shown in the figure below: Figure 3 .

[0041] In addition, for Ag 6 MnMn 9 The compounds were subjected to infrared spectroscopy (see Figure 1 black solid line) and Raman spectra (see Figure 4 The black solid line). Figure 1 , Ag 6 MnMn 9 The compounds were at 933, 900, 673, 590, and 539 cm -1 The infrared characteristic absorption peak at 9 At 400 cm -1 To 1000 cm -1 The characteristic peaks of molybdenum oxygen vibration between them are similar, but each corresponding characteristic peak has a certain shift. This is due to the 9 The oxygen atoms on the Ag ions are bound to silver ions, which results in the restriction of the corresponding molecular vibrations. 6 MnMn 9 was successfully synthesized; similarly, Raman spectroscopy ( Figure 4 ) further proved that Ag + The addition of MnMo 9 The Raman vibration peak of Mo=O in the compound changes from 957 cm -1 Offset to 945 cm -1 (Ag + and the oxygen atom on the molybdenum oxygen bond); while MnMo 9 and Ag 6 MnMn 9 The characteristic peaks of Mn–O in the structure are all at 630 cm -1 This indicates that the oxygen atom in the Mn–O bond is not coordinated with the silver ion.

[0042] Example 2 Quantitative detection of hydrazine:

[0043] Since hydrazine has a low flash point and is volatile, hydrazine hydrate can be converted into hydrazine vapor by heating for SERS detection.

[0044] First, Ag 6 MnMn 9 The crystals were ground into powder (particle size was about 2.5 μm) and placed in a vacuum drying oven and dried at 50 °C for 8 h; subsequently, 0.05 g of the completely dried powder was pressed into a 0.5 × 0.5 cm sheet sample using a hydraulic press (5 MPa, 30 s).

[0045] Then, the hydrazine reagent (80%) was diluted with deionized water to obtain 8.25×10 -4 , 8.25×10 -5, 8.25×10 -6 , 8.25×10 -7 , 8.25×10 -8 , 8.25×10 -9 g∙cm -3 Five concentrations of hydrazine solution (the density of 80% hydrazine reagent is 1.032 g∙cm -3 ). Take 1 uL of the above solution and drop it into five clean, sealed wide-mouth bottles with a volume of 1.1 L, and then press the Ag 6 MnMn 9 The flake samples were quickly placed in wide-mouth bottles (one flake sample was placed in each bottle), sealed quickly, and heated in an oven to 60°C (at this time, the concentration of hydrazine vapor in the wide-mouth bottles was 7.5×10 -1 , 7.5×10 -2 , 7.5×10 -3 , 7.5×10 -4 , 7.5×10 -5 mg∙m -3 ), and keep for 2 hours to obtain Ag after hydrazine vapor treatment 6 MnMn 9 Sample.

[0046] In order to prove that Ag 6 MnMn 9 Whether the sample was partially reduced before hydrazine vapor treatment and when the hydrazine vapor concentration was 7.5×10 -1 mg∙m -3 Ag after treatment at concentration 6 MnMn 9 The samples were tested by XRD, TEM and XPS.

[0047] like Figure 5 It can be clearly seen that Ag 6 MnMn 9 The skeleton and crystallinity of the hydrazine-reduced Ag 6 MnMn 9 Four weaker characteristic diffraction peaks appeared at 38.08°, 44.22°, 64.75° and 77.42°, which were similar to Ag. 0 The (111), (200), (220) and (311) faces of the nanostructured carbon are consistent, indicating that some silver ions in the structure are reduced.

[0048] Figure 6 The TEM images shown show that Ag after hydrazine vapor treatment 6 MnMn 9Silver nanoparticles of about 5 nm appeared on the surface (the silver nanoparticles are numerous and evenly distributed, resulting in uniform and repeatable SERS signals).

[0049] Ag 6 MnMn 9 XPS test ( Figure 7 ), the two peaks at 368.1 and 374.1 eV correspond to Ag + Ag3d 5 / 2 and Ag 3d 3 / 2 Binding energy; and in the XPS spectrum after hydrazine vapor reduction, except for Ag + Ag 3d 5 / 2 and Ag 3d 3 / 2 In addition to the binding energy, there is also Ag 0 Ag 3d 5 / 2 and Ag 3d 3 / 2 The binding energies are 368.6 and 374.2 eV, respectively. 6 MnMn 9 Ag appears in the structure 0 . (Due to Ag 0 It is easier to be excited, produce higher plasma quality, and show stronger electromagnetic coupling, so Ag 0 The presence of hydrazine can realize the detection of trace amounts of hydrazine).

[0050] The Ag after hydrazine vapor treatment 6 MnMn 9 The sample was pasted on a glass plate and tested with a confocal Raman spectrometer. The laser power of the experiment was 5 mW, and a 50-mesh objective was used to collect spectral data for 4 seconds. The test results are shown in Figure 2. Figure 8 a shows that the hydrazine vapor concentration is 7.5×10 -5 ~7.5×10 -1 mg∙m -3 Raman spectra in the range of 630 cm -1 The absolute intensity of the Raman signal at 630 It is little affected by the change of hydrazine concentration, and the signal is relatively stable, which is a good signal reference (see Figure 8 b); and at 945cm -1 SERS intensity I 945 It increases with the increase of hydrazine concentration, but its linear correlation coefficient is low (see Figure 8 c, R 2 =0.8691). Further research found that I 945 / I 630 It has a good linear relationship with the logarithm of hydrazine concentration, and the correlation coefficient R2 is 0.9897, such as Figure 8 d, the standard curve equation is y = 7.3633 + 0.1959 x ( y I 945 / I 630 The ratio strength, x express C [N2H4] / 7.5). According to 3 σ / k ( σ is the standard deviation of the blank, k The detection limit of hydrazine vapor was calculated to be 2.37×10 -4 mg∙m -3 , which is much lower than the exposure limit of hydrazine for humans in the workplace stipulated by the National Occupational Health Standard of the People’s Republic of China (0.06 mg∙m -3 ).

Claims

1. A method for preparing a three-dimensional silver surface enhanced Raman spectroscopy substrate material for quantitatively detecting trace amounts of hydrazine, characterized in that: The substrate material is Ag6[MnMo9O 32 ]·8H2O; The method for preparing the base material comprises preparing solution A, preparing solution B, and adding dropwise; The method for preparing solution A is to add (NH4)6[MnMo9O 32 ]·8H2O is dissolved in distilled water, heated to 48-52°C, and stirred until dissolved to obtain solution A; The method for preparing solution B is to dissolve AgNO3 in acetonitrile solution and stir for 4-6 minutes to obtain solution B; The method of dropping is to drop solution B into solution A and stir at room temperature to obtain an orange clear solution, which is then placed in a dark place for crystallization to precipitate crystals, namely Ag6[MnMo9O 32 ]·8H2O.

2. The preparation method according to claim 1, characterized in that: In the preparation of solution A, (NH4)6[MnMo9O 32 ]·8The mass ratio of H2O to water is 1:295-296; in the preparation of solution B, the mass volume ratio of AgNO3 to acetonitrile solution is 1g:220-221mL.

3. The preparation method according to claim 1, characterized in that: In the dropwise addition step, the stirring time at room temperature is 5.8-6.2 h.

4. The preparation method according to claim 1, characterized in that: The (NH4)6[MnMo9O 32 ]·8H2O is prepared by dissolving ammonium molybdate in distilled water and adjusting the pH to 5 with glacial acetic acid; then adding manganese sulfate monohydrate, stirring and heating to 58-62°C until a yellow precipitate appears, and obtaining a yellow suspension; Then, ammonium persulfate was added to the yellow suspension under stirring, and the temperature was raised to 78-82°C. The temperature was maintained and stirred for 28-32 minutes, and then filtered while hot. The filtrate was left at room temperature overnight to precipitate crystals, which were (NH4)6[MnMo9O 32 ]·8H2O.

5. The preparation method according to claim 4, characterized in that: The mass ratio of ammonium molybdate to water is 1:24-25; the mass ratio of ammonium molybdate to manganese sulfate monohydrate is 1.04-1.05:1; The stirring speed is 450-500r / min; The mass ratio of the ammonium molybdate to ammonium persulfate is 2.6-2.8:1.

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