Large-grain graphene epitaxial ammonia sensor, preparation method and application thereof

Abstract

The application discloses a large-crystalline-domain graphene epitaxial ammonia sensor, which has the characteristics of comprising a substrate layer, a graphene layer, a metal organic framework material layer and an electrode layer. The sensor epitaxially grows the metal organic framework material on the graphene with millimeter crystalline domains, has good conductivity (150-800 omega / squ) and super-sensitive response to ammonia (detection limit as low as 0.1 ppb), and can realize accurate detection of trace ammonia components in human breath. In addition, the sensor also has excellent flexibility and fatigue resistance, can withstand 5 million times of bending, and has the potential to be further developed into a wearable flexible sensor.

Description

Technical Field

[0001] This invention belongs to the field of wearable smart health electronics technology, specifically relating to a large-domain graphene epitaxial ammonia sensor, its preparation method, and its application. Background Technology

[0002] Human exhaled breath is closely related to human health. Besides N2, O2, and CO2, exhaled breath also contains low concentrations of H2O and trace gases. These trace gases are often metabolic intermediates or products, reflecting the body's health level to some extent. Therefore, the composition and content of exhaled breath can be used to determine a person's health status. This non-invasive and rapid detection method is of great significance for disease prevention and health management. Ammonia, a common small chemical molecule in human metabolism such as the urea cycle, is an important indicator of the function of metabolic organs and systems such as the liver and kidneys. However, the concentration of ammonia in exhaled breath is extremely low (50-1000 ppb), and it is inevitably affected by other respiratory components during detection. This makes the specific detection of ammonia in human breath a highly challenging task.

[0003] Metal-organic frameworks (MOFs) are a class of extended crystalline porous materials formed by the coordination of inorganic metal nodes and organic ligands. MOFs possess extremely high specific surface areas, open pore structures, and good chemical stability, and their unique metal sites can selectively recognize small chemical molecules. Currently, many MOF-based fluorescent sensors have been developed for ammonia detection; however, these sensors suffer from poor portability and operability. Compared to fluorescent sensors, resistive sensors have been widely used commercially due to their high accuracy, long lifespan, and simple structure. However, MOF materials have poor conductivity, making it difficult to read electrical signals at low ammonia concentrations. Therefore, resistive ammonia sensors still cannot achieve sensitive detection of trace amounts of ammonia exhaled by humans. Summary of the Invention

[0004] This invention is made to solve the above-mentioned problems, and aims to provide a large-domain graphene epitaxial ammonia sensor, its preparation method and its application.

[0005] This invention provides a large-domain graphene epitaxial ammonia sensor, characterized by comprising: a substrate layer, a graphene layer, a metal-organic framework material layer, and an electrode layer.

[0006] The large-domain graphene epitaxial ammonia sensor provided by this invention may also have the following features: the metal-organic framework material is formed by coordination between metal ions and organic ligands, belongs to the hexagonal or trigonal crystal system, has a one-dimensional channel structure with micropores or mesopores, and its cell parameters match those of graphene. The metal ions include at least iron, cobalt, nickel, and copper ions, and the organic ligands are fused-ring aromatic phenolic derivatives that coordinate with the metal ions through oxygen atoms.

[0007] The large-domain graphene epitaxial ammonia sensor provided by this invention may also have the following feature: in an ammonia atmosphere, the metal sites in the metal-organic framework material interact with ammonia as active centers, causing ammonia to be adsorbed on the metal-organic framework material and resulting in a change in the conductivity of the material.

[0008] The large-domain graphene epitaxial ammonia sensor provided by this invention may also have the following feature: wherein the metal-organic framework material is epitaxially grown and oriented on the surface of graphene using graphene as a template.

[0009] This invention provides an application of a large-domain graphene epitaxial ammonia sensor, characterized in that: the large-domain graphene epitaxial ammonia sensor is used for the precise detection of ammonia components in human respiration, responding to trace amounts of ammonia in human exhaled breath and reflecting the concentration of ammonia.

[0010] This invention provides a method for preparing a large-domain graphene epitaxial ammonia sensor, characterized by the following steps: Step 1, growing a large-domain monolayer graphene and transferring it onto a substrate; Step 2, epitaxially growing a metal-organic framework material layer on the graphene surface using a hydrothermal method to obtain a graphene-metal-organic framework composite material; Step 3, constructing electrodes on the surface of the graphene-metal-organic framework composite material to fabricate a resistive device.

[0011] The method for preparing a large-domain graphene epitaxial ammonia sensor provided by this invention may also have the following features: In step 1, the graphene layer thickness is on the nanometer scale, and the maximum size of the crystal domains can reach the millimeter scale. It is prepared on a copper substrate by chemical vapor deposition. The specific preparation steps are as follows: Step 1-1, using an aqueous phosphoric acid solution as an electrolyte, the copper foil is briefly polished under rated voltage; Step 1-2, the copper foil is cleaned and thoroughly dried, and then annealed in a high-temperature and hydrogen atmosphere; Step 1-3, methane and hydrogen are introduced, and growth is carried out in a low-pressure and high-temperature environment to obtain a large-domain monolayer graphene.

[0012] The method for preparing a large-domain graphene epitaxial ammonia sensor provided by the present invention may also have the following features: In step 1, polymethyl methacrylate is used to assist in graphene transfer. Before the transfer, a layer of polymethyl methacrylate is spin-coated on the graphene surface, and the copper foil is etched with an acidic copper chloride solution. Then, it is transferred to a substrate, which can be any one of silicon wafer, quartz or flexible substrate. The flexible substrate can be any one of polyethylene terephthalate, polyimide or polydimethylsiloxane.

[0013] The method for preparing a large-domain graphene epitaxial ammonia sensor provided by this invention may also have the following features: In step 2, the name of the metal-organic framework material is M-CAT-1, the molecular formula is M3(HHTP)2(H2O)6, M is a transition metal element, which is any one of iron, cobalt, nickel, and copper, HHTP is 2,3,6,7,10,11-hexahydroxytriphenyl, and the metal-organic framework material belongs to the trigonal crystal system and space group P-3c1.

[0014] The method for preparing a large-domain graphene epitaxial ammonia sensor provided by this invention may also have the following features: In step 2, the specific steps for epitaxially growing the metal-organic framework material are as follows: Step 2-1, dissolving the metal salt and organic ligand 2,3,6,7,10,11-hexahydroxytriphenyl in water; Step 2-2, placing the graphene-loaded substrate into the solution, sealing the system, and reacting at 85°C for 12 hours; In step 3, constructing a sensor by building a conductive electrode on the surface of the graphene-metal-organic framework composite material. Each sensor requires the construction of two electrodes, source and drain. The conductive electrode is a conductive metal or a composite electrode composed of multiple metals. Common conductive metals are any one or more of copper, silver, gold, and indium.

[0015] The role and effect of invention

[0016] The large-domain graphene epitaxial ammonia sensor according to this invention comprises a substrate layer, a graphene layer, a metal-organic framework (MOF) material layer, and an electrode layer. Graphene, a honeycomb-like two-dimensional material composed of carbon atoms, not only possesses excellent electrical conductivity but can also combine with MOFs through π-π interactions to form a highly conductive composite material, making the material's electrical signals easily read. Based on this concept, this invention epitaxially grows MOFs on a large-domain monolayer graphene to obtain a graphene-MOF composite material, which is then fabricated into a resistive ammonia sensor with excellent conductivity. This sensor has a detection limit for ammonia as low as 0.1 ppb, enabling accurate detection of trace ammonia components in human respiration. It also exhibits excellent flexibility and fatigue resistance, withstanding 5 million bends, and has the potential to be further developed into a wearable flexible sensor.

[0017] Based on the principle of lattice symmetry matching, a metal-organic framework material with consistent domain orientation within a range of tens of micrometers was epitaxially grown using large-domain monolayer graphene as a template. This sensor exhibits excellent selectivity for ammonia, with a response range of 0.1-1000 ppb and an actual detection limit of 0.1 ppb, achieving accurate detection of ammonia components in human respiration. The sensor possesses excellent flexibility and fatigue resistance, and can still output a good current signal under low voltage, demonstrating its potential as a low-power wearable electronic device. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of graphene in this embodiment, wherein... Figure 1 (a) and Figure 1 (b) is a schematic diagram of graphene obtained at different growth times, with copper foil as the substrate; Figure 1 (c) is a schematic diagram of the optical microscope showing the graphene transferred onto the silicon wafer;

[0019] Figure 2 This is a schematic diagram of the epitaxial growth of metal-organic framework materials (MOFs) on the graphene surface in this embodiment;

[0020] Figure 3 This is an optical microscope image of graphene after epitaxial growth of MOFs in this embodiment, wherein... Figure 3 (a) is a schematic diagram of MOFs transmission electron microscopy (TEM); Figure 3 (b) Schematic diagram of MOFs with equidistant points within a 70μm*70μm range; Figure 3 (c) represents the subgraphs corresponding to... Figure 3 (b) Schematic diagram of high-resolution real-time Fourier transform (FFT) analysis of the central region; Figure 3 (d) is Figure 3 (c) is an overlay of all subgraphs in the graph;

[0021] Figure 4 This is a schematic diagram of the sensor device in an embodiment of the present invention;

[0022] Figure 5 This is a sensor test result diagram from Example 1 of the present invention, wherein... Figure 5 (a) is a real-time curve of the sensor response during actual testing; Figure 5 (b) is a graph showing the relationship between the sensor's response and the ammonia concentration.

[0023] Figure 6 This is a test graph of sensor adsorption / desorption stability under a 1ppb ammonia atmosphere in Test Example 1 of the present invention;

[0024] Figure 7These are sensor response result diagrams at different times in Example 1 of the present invention, wherein... Figure 7 (a) is a graph showing the change in sensor response from 0 to 200 seconds under a 1ppb ammonia atmosphere; Figure 7 (b) is a graph showing the change in sensor response from 0 to 10 seconds under a 1ppb ammonia atmosphere;

[0025] Figure 7 (b) is a graph showing the change in sensor response from 0 to 10 seconds in a 1ppb ammonia atmosphere in Test Example 1 of the present invention.

[0026] Figure 8 This is a schematic diagram of the sensor's response signals to different gases in Test Examples 2-5 of the present invention;

[0027] Figure 9 This is a diagram illustrating the sensor bending and viewing process in Example 6 of the present invention, wherein... Figure 9 (a) is a schematic diagram of the sensor bending test; Figure 9 (b) is a top view of the sensor during the bending test; Figure 9 (c) is a side view of the sensor during the bending test; Figure 9 (d) is a model diagram of the sensor bending test;

[0028] Figure 10 This is a schematic diagram showing the change in sensor performance with the number of bends when the deformation is 1% and 2.4% in Test Example 6 of the present invention.

[0029] Figure 11 This is a comparative schematic diagram of scanning electron microscopy (SEM) images of the sensor before and after the bending test in Test Example 6 of the present invention. Figure 11 (a) is a schematic diagram of the sensor under a scanning electron microscope (SEM) before the bending test; Figure 11 (b) is a schematic diagram of the sensor after the bending test using a scanning electron microscope (SEM).

[0030] Figure 12 This is a schematic diagram of the human exhalation test results in Example 7 of the present invention, wherein... Figure 12 (a) is a schematic diagram of ammonia exhaled by the human body; Figure 12 (b) is a schematic diagram of the concentration of ammonia in the test subject's exhaled breath sample and the corresponding ammonium ion nuclear magnetic resonance.

[0031] Figure 13 This is a comparison chart of the signals obtained by the sensor from human exhaled breath at different times of day and the results of nuclear magnetic resonance analysis in Test Example 7 of the present invention. Figure 13 (a) is a graph of the response signal detected by the sensor; Figure 13 (b) is a schematic diagram of the ammonia concentration corresponding to the response signal;

[0032] Figure 13 (c) is a schematic diagram of ammonia concentration obtained by nuclear magnetic resonance analysis. Detailed Implementation

[0033] To make the technical means, creative features, objectives and effects of this invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate a large-domain graphene epitaxial ammonia sensor, its preparation method and application.

[0034] <Example>

[0035] In this embodiment, a method for preparing a large-domain graphene epitaxial ammonia sensor is provided.

[0036] The fabrication method of the large-domain graphene epitaxial ammonia sensor involved in this embodiment includes the following steps:

[0037] Step S1: Grow large-domain monolayer graphene and transfer it onto the substrate.

[0038] The graphene layer has a thickness on the nanometer scale and a maximum crystal domain size on the millimeter scale. It is prepared on a copper substrate by chemical vapor deposition. The specific steps of its preparation are as follows:

[0039] Step S1-1: Using phosphoric acid aqueous solution as electrolyte, the copper foil is briefly polished under rated voltage. The specific process is as follows: two 25μm thick copper foils are cut and immersed in a solution with a volume ratio of H3PO4 to H2O of 3:1. The two copper foils are connected to the two poles of an external power supply, and a voltage of 5V is applied by the power supply. The distance between the two copper foils is adjusted so that the current passing through the system is always 2A for 40 seconds.

[0040] Step S1-2: Clean the copper foil and dry it thoroughly, then anneal it at high temperature in a hydrogen atmosphere. The specific process is as follows:

[0041] Remove the copper foil connected to the positive terminal of the power supply and clean it with pure water. Consider the side facing the other copper foil as the front side, and place the copper foil face up in the quartz tray. Place the quartz tray inside the heating zone of the muffle furnace, introduce hydrogen gas at a flow rate of 500 sccm under vacuum conditions using a mechanical pump, and raise the temperature of the muffle furnace to 1050℃. Anneal for 30 minutes.

[0042] Steps S1-3 involve introducing methane and hydrogen gas and growing the graphene under low pressure and high temperature to obtain large-domain monolayer graphene. The specific process is as follows:

[0043] The hydrogen flow was stopped and maintained for 2 minutes, then hydrogen was introduced again at a flow rate of 500 sccm, followed by 1% methane at a flow rate of 60 sccm for 30 minutes. The quartz tray was then removed from the heating zone and rapidly cooled to obtain a graphene film loaded on the copper foil surface.

[0044] A copper foil loaded with a single-layer graphene film was placed face up on a coating machine. A few drops of a 6% (molecular weight) polymethyl methacrylate (PMMA) solution with a molecular weight of 50,000 were dropped onto the face. The film was rotated at 800 rpm for 6 seconds, followed by 3000 rpm for 30 seconds. The copper foil was then removed and air-dried for 10 minutes. 29 g of CuSO4 was dissolved in 100 mL of hydrochloric acid and 100 mL of pure water. The copper foil was gently placed face up on the surface of this solution until it was completely etched, leaving only a transparent film. The film was lifted with a clean glass slide and transferred to a pure water solution, held for 10 minutes, and then slowly removed using a substrate. The substrate was heated at 85°C for 6 hours, followed by immersion in acetone at 70°C to remove the PMMA. The acetone was replaced every half hour, for a total of four immersions. Finally, the substrate was removed and air-dried.

[0045] Figure 1 This is a schematic diagram of graphene in this embodiment, wherein... Figure 1 (a) and Figure 1 (b) is a schematic diagram of graphene obtained at different growth times, with copper foil as the substrate; Figure 1 (c) is an optical microscope schematic diagram of graphene transferred onto a silicon wafer.

[0046] Figure 2 This is a schematic diagram of the epitaxial growth of metal-organic framework (MOF) materials on the graphene surface in this embodiment.

[0047] Step S2, as follows Figure 2 As shown, a graphene-metal-organic framework composite material was obtained by epitaxially growing MOFs layers on the surface of graphene using a hydrothermal method.

[0048] In this embodiment, MOFs are formed by the coordination of metal ions and organic ligands, belonging to the hexagonal or trigonal crystal system, and have a one-dimensional channel structure with micropores or mesopores. The cell parameters are matched with those of graphene. The organic ligands are fused-ring aromatic phenolic derivatives, which coordinate with metal ions through oxygen atoms. The specific process is as follows:

[0049] This embodiment takes the epitaxial growth of Ni-CAT-1 on graphene as an example: 0.005 mmol / L nickel acetate and 0.001 mmol / L HHTP aqueous solutions were prepared, and 10 mL of each was placed in a 20 mL glass bottle. A graphene-loaded substrate was then placed in the bottle, the bottle was sealed, and the mixture was heated at 85°C for 12 hours. The substrate was then removed and washed with pure water to obtain a composite material with a metal-organic framework epitaxially grown on graphene. HHTP is 2,3,6,7,10,11-hexahydroxytriphenyl, and the MOFs belong to the trigonal crystal system with space group P-3c1.

[0050] In this embodiment, the MOFs synthesized by this method were characterized and analyzed by transmission electron microscopy (TEM). The results showed that the MOFs were epitaxially grown and oriented on the surface of graphene, and the orientation of the crystal domains could be kept consistent within a range of tens of micrometers.

[0051] Step S3: Construct electrodes on the surface of graphene-metal-organic framework composite material to fabricate resistive devices. In this process, a sensor is built by constructing conductive electrodes on the surface of graphene-metal-organic framework composite material. Each sensor requires the construction of two electrodes: a source electrode and a drain electrode. The conductive electrodes are conductive metals or composite electrodes composed of multiple metals.

[0052] Figure 3 This is an optical microscope image of graphene after epitaxial growth of MOFs in this embodiment, wherein... Figure 3 (a) is a schematic diagram of MOFs transmission electron microscopy (TEM); Figure 3 (b) Schematic diagram of MOFs with equidistant points within a 70μm*70μm range; Figure 3 (c) represents the subgraphs corresponding to... Figure 3 (b) Schematic diagram of high-resolution real-time Fourier transform (FFT) analysis of the central region; Figure 3 (d) is Figure 3 (c) is an overlay of all subgraphs.

[0053] MOFs are epitaxially grown and oriented on the surface of graphene using graphene as a template. Transmission electron microscopy (TEM) diffraction patterns show that they can maintain consistent domain orientation within a range of hundreds of micrometers. MOFs are tightly bound to graphene through π-π interactions and can remain stable in atmospheric, vacuum, and aqueous environments. This sensor possesses excellent flexibility, capable of being bent more than 5 million times continuously, and has the potential to become a wearable electronic device.

[0054] Figure 4 This is a schematic diagram of the sensor device in an embodiment of the present invention.

[0055] This sensor is a resistive sensor, and the participation of large-domain graphene gives it excellent conductivity, with a sheet resistance of only 150-800Ω / squ. The low resistance not only facilitates signal readout but also enables it to output a good current signal at low voltages, thus allowing it to operate at low power consumption (milliwatt level).

[0056] <Test Example 1>

[0057] The large-domain graphene epitaxial ammonia sensor in this test example was prepared according to the above embodiments. In this test example, the sensor's response to ammonia was tested. The specific test process is as follows:

[0058] Electrodes were welded to the surface of the composite material, and the electrodes were connected to a resistance tester with wires. The sensor was placed in a sealed test tube, and ammonia gas (0.1-1000 ppb) was introduced for gas sensitivity testing. Throughout the test, the resistance value of the sensor was read in real time by the measuring circuit, and the sensor's response to the corresponding gas was calculated using the following formula:

[0059] Response = (R g -R i ) / R i ×100%

[0060] In the formula, R i R is the initial resistance value of the sensor. g This represents the resistance value of the sensor in the gas being detected.

[0061] Figure 5 This is a graph showing the sensor test results from Example 1. Figure 5 (a) is a real-time curve of the sensor response during actual testing; Figure 5 (b) is a graph showing the relationship between the sensor's response and the ammonia concentration.

[0062] like Figure 5 As shown in the figure, the test results indicate that the curve shows a linear relationship between the sensor's response value and the gas concentration, which suggests that the composite material has a good response to ammonia.

[0063] The sensor has a response range of 0.1-1000 ppb for ammonia, with an actual detection limit of 0.1 ppb, and exhibits good selectivity for ammonia.

[0064] The sensor of this invention possesses extremely high sensitivity, enabling selective detection of low concentrations of ammonia gas within a detection range of 0.1 ppb to 1000 ppb, with a detection limit of 0.1 ppb. For ammonia gas at a concentration of 1 ppb, the sensor's response signal is higher than 0.2%, and the signal-to-noise ratio is not lower than 100. Furthermore, it can respond to trace amounts of ammonia gas in human exhaled breath and reflect the concentration of ammonia, and the response results are consistent with those obtained through precise quantitative analysis methods such as nuclear magnetic resonance analysis.

[0065] Figure 6 This is a graph showing the adsorption / desorption stability test of the sensor under a 1ppb ammonia atmosphere in Test Example 1.

[0066] like Figure 6 As shown, the initial response signal of the sensor in an ammonia atmosphere with a concentration at the ppb level is consistent with the zero-order reaction kinetics of gas adsorption.

[0067] Figure 7 These are the sensor response results at different times in Example 1 of the measurement, where... Figure 7(a) is a graph showing the change in sensor response from 0 to 200 seconds under a 1ppb ammonia atmosphere; Figure 7 (b) is a graph showing the change in sensor response from 0 to 10 seconds under a 1ppb ammonia atmosphere.

[0068] <Test Example 2>

[0069] In this test case, the response of the large-domain graphene epitaxial ammonia sensor to nitrogen was tested, with high-purity nitrogen as the test gas.

[0070] Figure 8 This is a schematic diagram of the sensor's response signals to different gases in test example 2-5.

[0071] like Figure 8 As shown, the test results indicate that the sensor has almost no response to nitrogen gas.

[0072] <Test Example 3>

[0073] In this test case, the response of the large-domain graphene epitaxial ammonia sensor to water vapor was tested. The test gas was 1% water vapor (nitrogen as the carrier).

[0074] like Figure 8 As shown, the test results indicate that the sensor has almost no response to water vapor.

[0075] <Test Example 4>

[0076] In this test case, the response of the large-domain graphene epitaxial ammonia sensor to oxygen was tested. The test gas was 16% oxygen (nitrogen as the carrier).

[0077] like Figure 8 As shown, the test results indicate that the sensor has almost no response to oxygen.

[0078] <Test Example 5>

[0079] In this test example, the response of the large-domain graphene epitaxial ammonia sensor to carbon dioxide was tested. The test gas was 4% carbon dioxide (nitrogen was used as the carrier).

[0080] like Figure 8 As shown, the test results indicate that the sensor has a weak negative response to carbon dioxide.

[0081] <Test Example 6>

[0082] This test example demonstrates the bending and tensile testing of a large-domain graphene epitaxial ammonia gas sensor, with the gas sensor fabricated using PET as a substrate.

[0083] Figure 9 This is a diagram of the sensor bending and viewing process in Example 6, where... Figure 9(a) is a schematic diagram of the sensor bending test; Figure 9 (b) is a top view of the sensor during the bending test; Figure 9 (c) is a side view of the sensor during the bending test; Figure 9 (d) is a model diagram of the sensor bending test.

[0084] like Figure 9 As shown, the sensor is fixed on the bending and tensile testing machine, and parameters such as bending and tensile frequency, test duration and deformation are set. The instrument is then turned on to perform high-frequency bending and tensile cycle test.

[0085] Figure 10 This is a schematic diagram showing the change in sensor performance with the number of bends when the deformation is 1% and 2.4% respectively in Test Example 6.

[0086] Figure 11 This is a comparative schematic diagram of scanning electron microscopy (SEM) images of the sensor before and after the bending test in Test Example 6. Figure 11 (a) is a schematic diagram of the sensor under a scanning electron microscope (SEM) before the bending test; Figure 11 (b) is a schematic diagram of the sensor after the bending test using a scanning electron microscope (SEM).

[0087] like Figures 10-11 As shown in the figure, tests indicate that the sensor can withstand up to 5 million bending and tensile cycles under a deformation rate as high as 1%, demonstrating excellent flexibility and fatigue resistance. At a deformation rate of 2.4%, it can withstand 1 million cycles.

[0088] <Test Example 7>

[0089] This test example demonstrates a human breath test on the large-domain graphene epitaxial ammonia sensor prepared in the above embodiments. The specific process is as follows:

[0090] First, after connecting the sensor to the external measurement circuit, place it in an open system. The measurement circuit measures the sensor's resistance signal in real time. Then, the tester blows air towards the sensor at a relatively stable rate (1000 mL / s) and holds for about 5 seconds, recording the average resistance R of the sensor within 5-10 seconds after the exhalation ends. g And substitute it into the formula "Response = (R) g -R i ) / R i The response signal of the sensor is calculated as ×100%, where R is the response signal of the sensor. i R is the initial resistance value of the sensor. g The average resistance of the sensor is measured within 5 to 10 seconds after the test subject exhales.

[0091] The actual ammonia concentration in exhaled breath was verified by quantitative analysis using nuclear magnetic resonance (NMR). The test subject filled four 5L gas collection bags at a relatively stable blowing rate (1000 mL / s), collecting a total of 20L of gas. After each bag was filled, a short rest was taken before continuing. The 20L of gas was then bubbled into 10mL of ultrapure water, with an internal standard added. The concentration of ammonium ions in the water was then analyzed using 1H NMR spectroscopy, which allowed for the estimation of the ammonia concentration in the exhaled breath.

[0092] Figure 12 This is a schematic diagram of the human exhalation test results in Example 7, in which... Figure 12 (a) is a schematic diagram of ammonia exhaled by the human body; Figure 12 (b) is a schematic diagram of the concentration of ammonia in the test subject's exhaled breath sample and the corresponding ammonium ion nuclear magnetic resonance.

[0093] Figure 13 This is a comparison chart of the signals obtained by the sensor from human exhaled breath at different times of day in Test Example 7, and the results of nuclear magnetic resonance analysis. Figure 13 (a) is a graph of the response signal detected by the sensor; Figure 13 (b) is a schematic diagram of the ammonia concentration corresponding to the response signal; Figure 13 (c) is a schematic diagram of ammonia concentration obtained by nuclear magnetic resonance analysis.

[0094] like Figure 12 As shown in (a), ammonia molecules are exhaled from the lungs and then expelled through the trachea, thus ammonia concentration can be detected by breath testing. By collecting ammonia, dissolving it in water, and analyzing the sample using nuclear magnetic resonance (NMR), corresponding peak signals can be observed (e.g., Figure 12 (b)). Figure 13 Breath tests were conducted on the test subjects at different times of the day, and each test was performed using a sensor. Figure 13 (a) Figure 13 (b) and nuclear magnetic resonance ( Figure 13 (c) The concentration of ammonia in exhaled breath was obtained by analysis. Figure 13 In (a), the vertical axis represents the sensor's response signal intensity, which can be converted from the response curve. Figure 13 (b) Ammonia concentration.

[0095] The role and effect of the embodiments

[0096] The large-domain graphene epitaxial ammonia sensor, its preparation method, and its application according to the present invention comprise a substrate layer, a graphene layer, a metal-organic framework (MOF) material layer, and an electrode layer. Graphene is a honeycomb-like two-dimensional material composed of carbon atoms. It not only possesses excellent electrical conductivity but can also combine with MOFs through π-π interactions to form a highly conductive composite material, making the material's electrical signals easily read. Based on this concept, this embodiment epitaxially grows MOFs on a large-domain monolayer of graphene to obtain a graphene-MOF composite material, which is then fabricated into a resistive ammonia sensor with excellent conductivity. This sensor has a detection limit for ammonia as low as 0.1 ppb, enabling accurate detection of trace ammonia components in human respiration. It also exhibits excellent flexibility and fatigue resistance, withstanding 5 million bends, and has the potential to be further developed into a wearable flexible sensor.

[0097] Based on the principle of lattice symmetry matching, a metal-organic framework material with consistent domain orientation within a range of tens of micrometers was epitaxially grown using large-domain monolayer graphene as a template. This sensor exhibits excellent selectivity for ammonia, with a response range of 0.1-1000 ppb and an actual detection limit of 0.1 ppb, achieving accurate detection of ammonia components in human respiration. The sensor possesses excellent flexibility and fatigue resistance, and can still output a good current signal under low voltage, demonstrating its potential as a low-power wearable electronic device.

[0098] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. Use of a large-grain graphene epitaxial ammonia sensor for accurate detection of ammonia components in human breath, characterized in that, The large-crystalline-domain graphene epitaxial ammonia sensor is used for responding to trace ammonia in human exhaled breath and reflecting the concentration of ammonia, and the large-crystalline-domain graphene epitaxial ammonia sensor can be continuously bent more than 5 million times and has an ammonia detection limit of 0.1 ppb, The preparation method of the large-crystalline-domain graphene epitaxial ammonia sensor comprises the following steps: Step 1, growing large-crystalline-domain monolayer graphene and transferring it to a substrate to obtain a large-crystalline-domain monolayer graphene layer, The large-crystalline-domain monolayer graphene layer has a nanoscale thickness and a millimeter-scale maximum crystalline domain size, and is prepared by a chemical vapor deposition method on a copper substrate, and the specific steps are as follows: Step 1-1, using a solution with a volume ratio of phosphoric acid to water of 3:1 as an electrolyte, performing a short polishing treatment on a copper foil at a rated voltage, the voltage is 5V, the current is 2A, and the treatment lasts for 40 seconds, Step 1-2, washing the copper foil and drying it sufficiently, and then annealing it in a hydrogen atmosphere at a temperature of 1050 DEG C for 30 minutes, Step 1-3, introducing methane and hydrogen, and growing under a low-pressure high-temperature environment to obtain the large-crystalline-domain monolayer graphene, The operation of transferring the large-crystalline-domain monolayer graphene to the substrate is as follows: the large-crystalline-domain monolayer graphene is transferred with the assistance of polymethyl methacrylate, before the transfer, a layer of polymethyl methacrylate solution with a molecular weight of 50000 and a mass fraction of 6% is spin-coated on the surface of the large-crystalline-domain monolayer graphene, then the copper foil is etched with an acidic copper chloride solution, and then transferred to the substrate; Step 2, epitaxially growing a metal organic framework material layer on the surface of the graphene by a hydrothermal method to obtain a graphene-metal organic framework composite material, The metal organic framework material in the metal organic framework material layer is formed by coordination between metal ions and organic ligands, belongs to a trigonal system, a P-3c1 space group, has a one-dimensional pore structure with a micropore or mesopore pore size, and has a unit cell parameter matched with the graphene, the metal ions at least include iron, cobalt, nickel and copper ions, and the organic ligands are condensed ring aromatic phenolic derivatives which are coordinated with the metal ions through oxygen atoms; Step 3, constructing an electrode on the surface of the graphene-metal organic framework composite material to make a resistance device, and finally obtaining the large-crystalline-domain graphene epitaxial ammonia sensor, The large-crystalline-domain graphene epitaxial ammonia sensor comprises a substrate layer, a large-crystalline-domain monolayer graphene layer, a metal organic framework material layer and an electrode layer.

2. Application of the large-crystalline-domain graphene epitaxial ammonia sensor in precise detection of ammonia components in human respiration according to claim 1, characterized in that: wherein Under an ammonia atmosphere, metal sites in the metal organic framework material act as active centers to interact with ammonia, so that the ammonia is adsorbed on the metal organic framework material and causes a change in the conductivity of the material.

3. Application of the large-crystalline-domain graphene epitaxial ammonia sensor in precise detection of ammonia components in human respiration according to claim 1, characterized in that: wherein The metal organic framework material is epitaxially grown and directionally arranged on the surface of the graphene as a template.

4. The use of the large domain graphene epitaxial ammonia sensor according to claim 1 in the accurate detection of ammonia components in human breath, characterized in that: wherein In step 1, the substrate is a flexible substrate, The flexible substrate is any one of polyethylene terephthalate, polyimide or polydimethylsiloxane.

5. The use of the large domain graphene epitaxial ammonia sensor according to claim 1 in the accurate detection of ammonia components in human breath, characterized in that: wherein In step 2, the metal organic framework material is named M-CAT-1, and the molecular formula is M3(HHTP)2(H2O)6, M is a transition metal element, and the transition metal element is any one of iron, cobalt, nickel or copper, HHTP is 2,3,6,7,10,11-hexahydroxytriphenyl.

6. The use of the large domain graphene epitaxial ammonia sensor according to claim 1 in the accurate detection of ammonia components in human breath, characterized in that: wherein In step 2, the specific steps for epitaxial growth of the metal organic framework material are as follows: Step 2-1, dissolve the metal salt and the organic ligand 2,3,6,7,10,11-hexahydroxytriphenyl in water; Step 2-2, place the graphene-loaded substrate into the solution, seal the system, and react at 85 ℃ for 12 hours, In step 3, the sensor is built by constructing a conductor electrode on the surface of the graphene-metal organic framework composite material, and each sensor needs to construct two electrodes, source and drain, the conductor electrode is a composite electrode composed of a conductor metal or multiple layers of metal, The conductor metal is any one or more of copper, silver, gold or indium.

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