Paper-based detection method for rapidly detecting volatile methyl mercaptan

Abstract

The invention discloses a paper-based detection method for rapidly detecting volatile methyl mercaptan, which comprises the following specific steps: firstly, by taking silver acetate as a silver source, oleic acid as a modifier, xylene as an organic solvent and NaBH4 as a reducing agent, preparing hydrophobic silver nanoparticles through a phase transfer chemical reduction method, and then diluting the silver nanoparticles into different concentrations. A PVDF paper base is used as an immobilization substrate, silver nanoparticles with different concentrations are immobilized on the paper base, and a paper-based colorimetric sensor array with five sensing element points is obtained through printing. Finally, the paper-based sensor is exposed in methyl mercaptan gases with different concentrations, a methyl mercaptan standard colorimetric card is manufactured, a quantitative detection model M is established, and the lowest detection limit of methyl mercaptan is 55.8 ppb. The method disclosed by the invention has the characteristics of low cost, high efficiency, simplicity in operation, portability, high sensitivity and strong selectivity, and can realize on-site visual rapid quantitative detection of the methyl mercaptan gas.

Description

Technical Field

[0001] The present application relates to a paper-based detection method for rapidly detecting volatile methyl mercaptan, and belongs to the technical field of nanomaterial preparation and chemical analysis. Background Art

[0002] Methyl mercaptan (CH3SH) is a major environmental pollutant with high toxicity, extremely low vapor pressure and odor threshold, and it can easily vaporize to dangerous concentrations even at room temperature. Long-term exposure, even at ultra-low concentrations, increases the risk of cancer, respiratory diseases and cardiovascular diseases. The odor of methyl mercaptan is 2000 times that of NH3, and the odor threshold is only 0.002ppm. Leakage of CH3SH during transportation and storage, or chronic injury from the workplace, can be fatal because it may not be quickly identified or detected in advance. Methyl mercaptan is widely sourced from food processing, sewage and solid waste treatment, landfills, animal husbandry, petroleum refining, natural gas fractions and other fields. It can also be released from human bad breath, cheese products, meat products, wine maturation process, and milk. In addition, methyl mercaptan is also widely used in the preparation of pesticides, medicines, insecticides and organic polymerization catalysts. Therefore, it is crucial to develop technologies that can quickly and effectively monitor methyl mercaptan gas to protect humans from harmful chemicals in the working environment and monitor indoor air quality.

[0003] So far, a large number of methods for detecting thiols have been reported, including instrumental analysis methods, fluorescence methods, adsorption methods, electrochemical semiconductor sensors, etc. Although the measurement results of these methods are acceptable, there are also some obvious disadvantages. For example, real-time on-site monitoring cannot be performed in practical applications, especially in emergency situations, and heating is required during operation. In addition, multiple analytes cannot be detected at the same time, and the experimental results are easily interfered by the detection environment.

[0004] In contrast, the paper-based colorimetric array sensing method distinguishes and identifies analytes by the color change of the sensor before and after the analyte is detected. This method is simple to operate, low cost, high efficiency, portable, and visual. Moreover, the paper base is disposable, recyclable, and environmentally friendly.

[0005] Silver nanoparticles have played an important role in environmental monitoring, food safety, biomedicine, wearable technology, etc. due to their excellent colorimetric sensing performance. Compared with other precious metal nanoparticles, silver nanoparticles are simple to prepare, low cost, antibacterial, and have a larger extinction coefficient, narrower surface plasmon resonance band, better colorimetric performance, higher sensitivity, and higher reactivity. Therefore, they are the perfect platform for the development of colorimetric sensor devices. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention is based on the mechanism of strong hydrogen bonding formed by the interaction between -COOH groups and -SH groups, methyl mercaptan and the modifier containing -COOH groups on the surface of silver nanoparticles undergo chemical reactions, the surface modifier of the nanoparticles falls off, thereby causing the silver nanoparticles to agglomerate and produce the characteristics of colorimetric response, and provides a method for visual detection of methyl mercaptan by a hydrophobic silver nanoparticle paper-based colorimetric sensor array. This detection method is simple to operate, low in cost, high in efficiency, and portable, and has the advantages of on-site real-time monitoring without instruments.

[0007] The invention adopts a phase inversion chemical reduction method, uses silver acetate as a silver source and sodium oleate as a modifier to prepare hydrophobic silver nanoparticles. Using a PVDF hydrophobic paper substrate as a carrier, a visual rapid detection method for highly toxic volatile organic small molecule methyl mercaptan based on a silver nanoparticle paper-based colorimetric sensor array is provided.

[0008] According to one aspect of the present application, a paper-based detection method for rapid detection of volatile methyl mercaptan is provided, the paper-based detection method comprising the following steps:

[0009] (1) adding the silver acetate solution to the sodium oleate solution and stirring for 1 second to obtain a silver oleate solution;

[0010] (2) adding NaBH4 solution to the silver oleate solution for reduction, then adding an organic solvent and stirring for II to obtain oleic acid-modified hydrophobic nanoparticles;

[0011] (3) diluting the same oleic acid-modified hydrophobic nanoparticles with different volumes of xylene to obtain oleic acid-modified hydrophobic nanoparticles with different concentrations;

[0012] (4) taking the same volume of oleic acid-modified hydrophobic nanoparticles with different concentrations and immobilizing them on a paper substrate, and printing them to obtain a paper-based colorimetric sensor with multiple sensing elements;

[0013] (5) exposing a paper-based colorimetric sensor with multiple sensing elements to different concentrations of methyl mercaptan gas, observing the color response, and obtaining a methyl mercaptan gas standard colorimetric card;

[0014] (6) The unknown concentration of methyl mercaptan gas is placed in a paper-based colorimetric sensor with multiple sensing elements, and the color response is observed and compared with the methyl mercaptan gas standard colorimetric card to determine the concentration of the methyl mercaptan gas.

[0015] Optionally, in step (1), the concentration of the sodium oleate solution is 0.08-0.10M.

[0016] Optionally, the concentration of the sodium oleate solution is selected from any value among 0.08M, 0.085M, 0.09M, 0.095M, 0.10M or a range between any two of the above.

[0017] Optionally, the concentration of the silver acetate solution is 0.07-0.09M.

[0018] Optionally, in step (2), the concentration of the NaBH4 solution is 0.24-0.30M.

[0019] Optionally, the organic solvent is selected from at least one of toluene, xylene and n-hexane.

[0020] Optionally, in step (2), the reduction temperature is 60-70° C., and the reduction time is 2-3 h.

[0021] Optionally, in step (2), the volume ratio of the organic solvent to the NaBH4 solution is 1:1.

[0022] Optionally, in step (4), the same volume is used in an amount of 1 to 1.5 μL.

[0023] Optionally, the diameter of the sensing points of the paper-based colorimetric sensor with multiple sensing points is 2 to 3.5 mm.

[0024] Optionally, the paper base is selected from at least one of PVDF, whatman No. 1 filter paper, and whatman No. 2 filter paper.

[0025] Optionally, in step (4), the paper-based colorimetric sensor with multiple sensing elements has an anti-interference range of 10% to 90% to humidity.

[0026] Optionally, the detection limit of the paper-based colorimetric sensor with multiple sensing elements for methyl mercaptan is 55.8-57.00 ppb.

[0027] Optionally, in step (5), the methyl mercaptan gas standard colorimetric card is stored in an inactive atmosphere.

[0028] Optionally, the inert atmosphere is selected from at least one of nitrogen, helium and argon.

[0029] As a specific implementation, the present application is implemented through the following technical solutions:

[0030] A method for preparing a paper-based sensor for rapid visual detection of trace volatile methyl mercaptan comprises the following steps:

[0031] (1) Preparation of hydrophobic silver nanoparticles:

[0032] Sodium oleate is transferred into a 250ml flask containing 25ml ultrapure water, a magnet is placed, and a water bath is heated and magnetically stirred for a certain period of time to completely dissolve the sodium oleate, and the solution becomes clear and transparent. Silver acetate is dissolved in 25ml ultrapure water, and magnetic stirring in a water bath is performed for a certain period of time to completely dissolve the silver acetate. The silver acetate solution is then slowly added to the above-mentioned sodium oleate solution, and magnetic stirring in a water bath is continued for a certain period of time to obtain a silver oleate solution. Freshly prepared NaBH4 is dissolved in 25ml ultrapure water, added dropwise to the silver oleate solution, and the water bath is stirred for reduction for 2h. After the solution is cooled to room temperature, 25ml of organic solvent is added, magnetic stirring is performed for 30min, and the silver nanoparticles are transferred to the organic phase, the organic phase is extracted, centrifuged, and the supernatant is collected to obtain oleic acid-modified hydrophobic silver nanoparticles.

[0033] (2) Construction of Paper-Based Colorimetric Sensor Array Device

[0034] The silver nanoparticles prepared in step (1) are extracted with the same volume of stock solution, and are diluted with different volumes of xylene to obtain silver nanoparticle solutions of different concentrations. A certain volume of silver nanoparticle solutions of different concentrations is manually transferred with a pipette, and fixed on a PVDF paper substrate to print a paper-based colorimetric sensor array with multiple sensing elements. Finally, the paper-based sensor is placed in a screw-mouth glass bottle, N2 is introduced to isolate oxygen, and stored at room temperature for later use.

[0035] (3) Preparation of Methyl Mercaptan Standard Colorimetric Card and Quantitative Detection Model M

[0036] The sensor was exposed to different concentrations of methyl mercaptan gas for 10 minutes. Different concentrations of methyl mercaptan gas reacted with the sensor to produce different color responses. The sensor images with different color responses were matched with different concentrations of methyl mercaptan gas, and arranged in order from small to large methyl mercaptan concentrations to establish a standard colorimetric test paper card for detecting methyl mercaptan gas. The ΔRGB values ​​of the images before and after the response were extracted to establish a model M for quantitative detection of methyl mercaptan.

[0037] (4) Specific recognition and detection of methyl mercaptan gas by paper-based sensors.

[0038] The specific identification and detection of methyl mercaptan gas by paper-based sensors includes: the influence of common potential interfering gases on methyl mercaptan gas detection and the influence of environmental humidity.

[0039] Optionally, in step (1), the water bath temperature is 60° C.; the centrifugal parameters are: rotation speed 5000-6000 r / min, 5 min.

[0040] Optionally, in step (2), the same volume of the stock solution is extracted to be 500ul, and different volumes of xylene are 0, 2, 4, 8, and 12ml, respectively, to obtain 5 different concentrations of silver nanoparticles. The volume of the pipette is 1-1.5ul, the diameter of the sensing element is 2-3.5mm, and the paper-based sensor is passed through N2 for 1h and placed at room temperature for 12h.

[0041] Optionally, in step (3), the concentrations of methyl mercaptan gas are 0.1 ppm, 0.5 ppm, 1.0 ppm, 1.5 ppm, 2.0 ppm, 2.5 ppm, 3.0 ppm, and 3.5 ppm, respectively.

[0042] Optionally, in step (4), the interfering gas is selected from one of trimethylamine, ammonia, formic acid, hydrogen chloride, dimethyl sulfide, dimethyl disulfide, ethanol, and styrene.

[0043] Optionally, in step (4), the ambient humidity is 10% to 90%.

[0044] In the present application, the specific construction steps of the paper-based colorimetric sensor for rapid visual detection of trace volatile methyl mercaptan are as follows: first, using silver acetate as a silver source, oleic acid as a modifier, xylene as an organic solvent, and NaBH4 as a reducing agent, hydrophobic silver nanoparticles are prepared by phase transfer chemical reduction, and then the silver nanoparticles are diluted to different concentrations. Using PVDF paper as a solid support matrix, silver nanoparticles of different concentrations are fixed on the paper base, and a paper-based colorimetric sensor array with 5 sensing element points is printed. Finally, the paper-based sensor is exposed to methyl mercaptan gas of different concentrations, a methyl mercaptan standard colorimetric card is made, and a quantitative detection model M is established to obtain a minimum detection limit of 55.8ppb for methyl mercaptan. The paper-based sensor has excellent specific recognition ability for methyl mercaptan, high sensitivity, and good moisture resistance. The method of the present invention has the characteristics of low cost, high efficiency, simple operation, portability, high sensitivity, and strong selectivity, and can realize on-site visualization and rapid quantitative detection of methyl mercaptan gas.

[0045] The beneficial effects of this application include:

[0046] 1) The silver nanoparticle paper-based colorimetric sensor array provided in the present application has an obvious specific recognition response to the detection of methyl mercaptan gas and can be used for the detection of methyl mercaptan gas in complex environments.

[0047] 2) The present application provides a method for visual detection of methyl mercaptan using a silver nanoparticle paper-based colorimetric sensor array. The method is low-cost, simple to operate, portable, and can be used for on-site real-time monitoring, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1This is a TEM image of the morphology of oleic acid-modified silver nanoparticles prepared in Example 1 of the present application, with a scale of 20 nm.

[0049] Figure 2 This is the silver nanoparticle paper-based colorimetric sensor array in Example 1 of the present application.

[0050] Figure 3 This is the standard colorimetric test paper card for detecting methyl mercaptan in Example 1 of the present application.

[0051] Figure 4 This is a diagram of the linear fitting equation of the model M for quantitative detection of methyl mercaptan by the paper-based sensor in Example 1 of the present application.

[0052] Figure 5 This is the effect of interfering gas on methyl mercaptan gas detection in Example 2 of the present application.

[0053] Figure 6 This is the effect of ambient humidity on the detection of methyl mercaptan gas by the paper-based sensor in Example 3 of the present application. DETAILED DESCRIPTION

[0054] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0055] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0056] Example 1

[0057] A method for preparing a paper-based colorimetric sensor for rapid visual detection of trace volatile methyl mercaptan gas comprises the following steps:

[0058] Transfer 0.08M sodium oleate into a 250ml flask containing 25ml ultrapure water, put in a magnetic bar, and stir magnetically in a water bath at 60℃ for 30min to completely dissolve the sodium oleate and make the solution clear and transparent. Dissolve 0.08M silver acetate in 25ml ultrapure water, and stir magnetically in a water bath at 60℃ for 20min to completely dissolve the silver acetate. Then slowly add the silver acetate solution to the above sodium oleate solution, and continue to stir magnetically in a water bath at 60℃ for 30min to obtain a silver oleate solution. Dissolve 0.24M NaBH4 in 25ml ultrapure water, add dropwise to the silver oleate solution, and continue to stir and reduce in a water bath at 60℃ for 2h. After the solution is cooled to room temperature, add 25ml of xylene, stir magnetically for 30min, transfer the silver nanoparticles to the organic phase, extract the organic phase, and centrifuge at 5000-6000r / min for 5min. Collect the supernatant to obtain oleic acid-modified hydrophobic silver nanoparticles. Figure 1 As shown, TEM shows that the prepared silver nanoparticles are spherical.

[0059] (2) Construction of paper-based colorimetric sensor device

[0060] The oleic acid-modified hydrophobic silver nanoparticles prepared in step (1) were extracted with the same volume of 500ul stock solution, and diluted with 0, 2, 4, 8, and 12ml of xylene respectively to obtain 5 silver nanoparticle solutions with different concentrations. Then, 1μL of the different oleic acid-modified hydrophobic silver nanoparticle solutions were manually transferred by a pipette, immobilized on a PVDF paper substrate, and printed to obtain a paper-based colorimetric sensor array with 5 sensing elements (such as Figure 2 The sensor was placed in a screw-top glass bottle, and N2 was introduced for 1 hour and then placed at room temperature for 12 hours.

[0061] (3) Preparation of Methyl Mercaptan Standard Colorimetric Card and Quantitative Detection Model M

[0062] The sensor was exposed to methyl mercaptan gas with concentrations of 0.1ppm, 0.5ppm, 1.0ppm, 1.5ppm, 2.0ppm, 2.5ppm, 3.0ppm, and 3.5ppm for 10 minutes. The methyl mercaptan gas of different concentrations reacted with the sensor to produce different color responses. The sensor images with different color responses were matched with the methyl mercaptan gas of different concentrations, and arranged in order from small to large in terms of methyl mercaptan concentration, to establish a standard colorimetric test paper card for detecting methyl mercaptan gas (such as Figure 3 shown).

[0063] A flatbed scanner was used to extract the spectra before and after the sensor response, and Photoshop was used to extract the ΔRGB value of the image. ΔR is the difference in red color values ​​before and after the response, ΔG is the difference in green color values ​​before and after the response, and ΔB is the difference in blue color values ​​before and after the response.

[0064] The ED value was plotted as the ordinate and the methyl mercaptan concentration was plotted as the abscissa to establish a model for quantitative detection of methyl mercaptan: the linear fitting equation y=20.43x+42.96 (e.g. Figure 4 ), where x is the concentration of methyl mercaptan. The LOD of the gas is calculated by the formula LOD = 3δ / K. Where K is the slope of the fitting curve, and δ = 0.38 is the relative standard deviation of the blank group. Figure 4 It can be seen that the minimum detection limit of methyl mercaptan is 55.8 ppb.

[0065] Example 2

[0066] The influence of interfering gases on the detection of methyl mercaptan

[0067] Place the paper-based colorimetric sensor array in an 18L sealed gas box, and then use a micro-injector to transfer 0.5ppm methyl mercaptan stock solution and drop it on the heating plate in the gas box. At this time, methyl mercaptan evaporates quickly, and the sensor responds to the methyl mercaptan gas, and the detection is carried out for 10 minutes. Using the same steps, the sensor is used to detect trimethylamine, ammonia, formic acid, hydrogen chloride, methyl sulfide, dimethyl disulfide, ethanol, and styrene at a concentration of 5ppm, and the detection is carried out for 10 minutes. Finally, a flatbed scanner is used to collect the spectra of the sensor before and after the response to the above 9 gases, and the colorimetric response fingerprint is extracted using the ChemEye older software. By Figure 5 It can be seen that the sensor responds very well to methyl mercaptan, but has no response to other interfering gases, even when the concentration is 10 times greater (5 ppm), indicating that the sensor has excellent selectivity in responding to methyl mercaptan.

[0068] Example 3

[0069] Effect of environmental humidity on the detection of methyl mercaptan gas by paper-based sensor

[0070] Through the humidifier, the humidity of the 18L gas measuring box was adjusted to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%. Then the paper-based colorimetric sensor array was placed in the above different humidity for 10 minutes, and the sensor spectra before and after the reaction at the above 9 humidity were collected using a flatbed scanner. 0.5ppm methyl mercaptan gas was added to the gas measuring boxes with different humidity, and the paper-based colorimetric sensor array was placed in the above different humidity containing methyl mercaptan gas for 10 minutes, and the sensor spectra before and after the response were collected using a flatbed scanner. The ΔRGB value of the spectrum was extracted through photoshop, and the formula was used. ΔR is the difference in red color value before and after the response, ΔG is the difference in green color value before and after the response, and ΔB is the difference in blue color value before and after the response; the sensor color change value ED is calculated. Figure 6 It can be seen that the sensor has excellent moisture resistance, and the ambient humidity has no effect on the sensor's detection of methyl mercaptan gas.

[0071] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A paper-based detection method for rapid detection of volatile methyl mercaptan, characterized in that: The paper-based detection method comprises the following steps: (1) adding the silver acetate solution to the sodium oleate solution and stirring for 1 second to obtain a silver oleate solution; (2) adding NaBH4 solution to the silver oleate solution for reduction, then adding an organic solvent and stirring for II to obtain oleic acid-modified hydrophobic nanoparticles; (3) diluting the same oleic acid-modified hydrophobic nanoparticles with different volumes of xylene to obtain oleic acid-modified hydrophobic nanoparticles with different concentrations; (4) taking the same volume of oleic acid-modified hydrophobic nanoparticles with different concentrations and immobilizing them on a paper substrate, and printing them to obtain a paper-based colorimetric sensor with multiple sensing elements; (5) exposing a paper-based colorimetric sensor with multiple sensing elements to different concentrations of methyl mercaptan gas, observing the color response, and obtaining a methyl mercaptan gas standard colorimetric card; (6) The unknown concentration of methyl mercaptan gas is placed in a paper-based colorimetric sensor with multiple sensing elements, and the color response is observed and compared with the methyl mercaptan gas standard colorimetric card to determine the concentration of the methyl mercaptan gas.

2. The paper-based detection method according to claim 1, characterized in that: In the step (1), the concentration of the sodium oleate solution is 0.08-0.10M.

3. The paper-based detection method according to claim 1, characterized in that: The concentration of the silver acetate solution is 0.07-0.09M.

4. The paper-based detection method according to claim 1, characterized in that: In the step (2), the concentration of the NaBH4 solution is 0.24-0.30M; Preferably, the organic solvent is selected from at least one of toluene, xylene and n-hexane.

5. The paper-based detection method according to claim 1, characterized in that: In the step (2), the reduction temperature is 60-70° C., and the reduction time is 2-3 hours.

6. The paper-based detection method according to claim 1, characterized in that: In the step (2), the volume ratio of the organic solvent to the NaBH4 solution is 1:

1.

7. The paper-based detection method according to claim 1, characterized in that: In the step (4), the dosage of the same volume is 1 to 1.5 μL; Preferably, the diameter of the sensing points of the paper-based colorimetric sensor with multiple sensing points is 2 to 3.5 mm.

8. The paper-based detection method according to claim 1, characterized in that: The paper base is selected from at least one of PVDF, whatman No. 1 filter paper and whatman No. 2 filter paper.

9. The paper-based detection method according to claim 1, characterized in that: In the step (4), the paper-based colorimetric sensor with multiple sensing elements has an anti-interference range of 10% to 90% to humidity; Preferably, the detection limit of the paper-based colorimetric sensor with multiple sensing elements for methyl mercaptan is 55.8-57.00 ppb.

10. The paper-based detection method according to claim 1, characterized in that: In the step (5), the methyl mercaptan gas standard colorimetric card is stored in an inert atmosphere; Preferably, the inert atmosphere is selected from at least one of nitrogen, helium and argon.

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