A nano-platinum / carbon nanotube / MXene fiber composite material and its preparation method and application

Abstract

The present invention discloses a nanoplatinum / carbon nanotube / MXene fiber composite material, its preparation method, and application. The composite material is formed by sequentially loading carbon nanotubes and platinum nanoparticles onto the surface of MXene fibers. This composite material, formed by loading platinum nanoparticles and carbon nanotubes onto the surface of MXene fibers, exhibits excellent mechanical properties, flexibility, and electrochemical characteristics. It is used as a working electrode for the electrocatalytic oxidation of applied ammonia, exhibiting a significant increase in the oxidation peak signal with increasing ammonia concentration. This allows the construction of a ratiometric electrochemical sensor for highly sensitive detection of ammonia content in urine.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial preparation, and in particular to a nano-platinum / carbon nanotube / MXene fiber composite material and a preparation method and application thereof. Background Art

[0002] MXene is an emerging two-dimensional nanomaterial. Since its discovery in 2011, it has become a research hotspot in the field of electrochemistry due to its excellent conductivity, hydrophilicity and outstanding thermal stability. It has been widely used in the field of electrochemical sensing.

[0003] Existing reports indicate that fiber electrodes have established a niche in the sensing field. Graphene and carbon fibers, similar to MXene fibers, have demonstrated excellent performance as substrate materials in electrochemical sensors. For example, Zhao et al. prepared graphene fibers as sensor substrates by wet spinning and then modified the graphene fiber surfaces with MnO2-NWs and Au-NPs to produce fiber sensors with high catalytic activity for hydrogen peroxide. Aziz et al. integrated spindle-shaped CuNiAl LDHs onto carbon fibers to achieve highly sensitive detection of nitrate.

[0004] MXene fibers as electrodes offer the advantages of small size and flexibility, enabling multi-angle and localized detection in practical applications. Miniaturized fiber electrodes can be easily fabricated into small, portable devices, offering greater operational advantages in integrated sensors. However, currently reported MXene fiber electrodes are typically composited with other materials, such as PEDOT, PU, ​​and PVA, significantly reducing their electrical conductivity. Therefore, developing a highly conductive sensor based on pure MXene fibers is of great significance. Summary of the Invention

[0005] In view of the above-mentioned deficiencies, the purpose of the present invention is to provide a nano-platinum / carbon nanotube / MXene fiber composite material and its preparation method and application to solve the problem of poor conductivity of existing MXene fiber electrodes.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a nano-platinum / carbon nanotube / MXene fiber composite material, which is formed by sequentially loading carbon nanotubes and platinum nanoparticles on the surface of MXene fibers.

[0008] Preferably, the average diameter of the MXene fibers is 100 to 200 μm.

[0009] The present invention also provides a method for preparing a nano-platinum / carbon nanotube / MXene fiber composite material, comprising the following steps:

[0010] S1. Preparation of MXene dispersion by etching-stripping method;

[0011] S2. Prepare MXene fibers by injecting MXene dispersion into a coagulation bath using a wet spinning method;

[0012] S3. In situ growth of ZIF-67 on the surface of MXene fibers to obtain MXene fiber@ZIF-67;

[0013] S4. Calcination of MXene fiber@ZIF-67 at high temperature under inert gas atmosphere to obtain MXene fiber@CNTs;

[0014] S5. Using MXene fiber@CNTs as the working electrode, platinum nanoparticles were loaded on the surface of MXene fiber@CNTs by electrodeposition to obtain a nano-platinum / carbon nanotube / MXene fiber composite material.

[0015] Preferably, the coagulation bath in step S2 is an acetic acid aqueous solution.

[0016] Preferably, in step S2, the concentration of the MXene dispersion is 30-70 mg·mL -1 , the concentration of the acetic acid aqueous solution is 60-80wt.%.

[0017] Preferably, in step S3, 2-methylimidazole, cobalt nitrate hexahydrate, and MXene fiber are mixed evenly, allowed to stand at room temperature, and dried to obtain MXene fiber@ZIF-67.

[0018] Preferably, in step S4, the mixture of MXene fiber @ ZIF-67 and melamine is calcined at high temperature; the conditions for high temperature calcination are: in an inert gas atmosphere at 2-3 ° C·min -1 The temperature was raised to 500-550℃ at a rate of 1-2℃·min and kept at that temperature for 2-3h. -1 The temperature is raised to 700-750°C at a rate of 0.1°C and kept at this temperature for 2-3 hours.

[0019] Preferably, the electrodeposition conditions in step S5 are: a platinum electrode as a counter electrode, an Ag / AgCl electrode as a reference electrode, MXene fiber@CNTs as a working electrode, a sulfuric acid solution of chloroplatinic acid as an electrolyte, and a deposition potential of -0.2 to -0.25 V.

[0020] The present invention also provides a MXene fiber-based electrochemical sensor, which includes the nano-platinum / carbon nanotube / MXene fiber composite material described above.

[0021] The present invention also provides an application of the above-mentioned MXene fiber-based electrochemical sensor in ammonia nitrogen sensing detection.

[0022] The beneficial effects of the present invention are:

[0023] 1. The composite material formed by loading platinum nanoparticles and carbon nanotubes on the surface of MXene fibers in the present invention has excellent mechanical properties, flexibility and electrochemical characteristics. It can be used as a self-supporting microelectrode and independently inserted into cells or tissues, or attached to copper sheets to prepare electrochemical sensors.

[0024] 2. The present invention first prepares MXene fibers by wet spinning, then in situ grows a layer of ZIF-67 on the surface of the MXene fibers, pyrolyzes the ZIF-67 grown on the surface of the MXene fibers into carbon nanotubes at high temperature, and finally uses constant potential electrodeposition technology to grow platinum nanoparticles on the surface to obtain MXene fibers @CNTs@Pt, avoiding the high-risk gases such as acetylene and hydrogen required for traditional chemical vapor deposition of carbon nanotubes.

[0025] 3. The MXene fiber@CNTs@Pt prepared in the present invention is used as a sensor. The CNTs grown on the surface of the MXene fiber not only provide an efficient channel for the transmission of electrons, but also have a strong adsorption effect, which is beneficial to the conversion of ammonia from a water-soluble state to an adsorbed state, and has an excellent synergistic auxiliary effect on the electrochemical oxidation of ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments are briefly introduced below.

[0027] Figure 1 This is a scanning electron microscope image of the MXene nanosheets prepared in Example 1;

[0028] Figure 2 This is a scanning electron microscope image of the composite material prepared in Example 1;

[0029] Figure 3 This is the X-ray photoelectron spectrum of the MXene fiber@CNTs@Pt material prepared in Example 1;

[0030] Figure 4 DPV differential pulse voltammograms of the MXene fiber-based electrochemical sensor prepared in Example 4 to different ammonia concentrations;

[0031] Figure 5 CV curves of MXene fiber, MXene fiber@CNTs, and MXene fiber@CNTs@Pt prepared in Example 1 at a scan rate of 0.05 V / s;

[0032] Figure 6Impedance test fitting diagram of MXene fiber, MXene fiber@CNTs and MXene fiber@CNTs@Pt prepared in Example 1. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0034] The nano-platinum / carbon nanotube / MXene fiber composite material provided by the present invention is a composite material formed by sequentially loading carbon nanotubes and platinum nanoparticles on the surface of MXene fibers.

[0035] The present invention also provides a method for preparing a nano-platinum / carbon nanotube / MXene fiber composite material, comprising the following steps:

[0036] S1. MXene dispersion was prepared by etching-stripping method to obtain single-layer MXene nanosheets with an average lateral size of 1.5-3 μm.

[0037] S2. Prepare MXene fibers by wet spinning the MXene dispersion into an acetic acid aqueous solution;

[0038] The length and diameter of the MXene fibers prepared by the present invention are controllable, and the thickness of the MXene fibers can be controlled by controlling the size of the device during injection, such as the diameter of the syringe nozzle. Preferably, the concentration of the MXene dispersion is 30-70 mg·mL -1 , the concentration of the acetic acid aqueous solution is 60-80wt.%.

[0039] S3. After uniformly mixing 2-methylimidazole, cobalt nitrate hexahydrate, and MXene fibers, the mixture was allowed to stand at room temperature and dried. ZIF-67 was then in situ grown on the surface of the MXene fibers to obtain MXene fibers@ZIF-67.

[0040] S4. Mix MXene fiber @ ZIF-67 with melamine and calcine at high temperature under an inert gas atmosphere to obtain MXene fiber @ CNTs. The addition of melamine can increase the carbon source during pyrolysis, thereby growing denser carbon nanotubes. The high temperature calcination conditions are: 2-3°C·min under an inert gas atmosphere. -1 The temperature was raised to 500-550℃ at a rate of 1-2℃·min and kept at that temperature for 2-3h. -1 The temperature is raised to 700-750°C at a rate of 0.1°C and kept at this temperature for 2-3 hours.

[0041] S5. Using a platinum electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a sulfuric acid solution of chloroplatinic acid as the electrolyte, platinum nanoparticles were loaded on the surface of the MXene fiber@CNTs by electrodeposition at a deposition potential of -0.2 to -0.25 V to obtain MXene fiber@CNTs@Pt.

[0042] In step S4, melamine can be placed at the bottom of the MXene fiber @ZIF-67 or the MXene fiber @ZIF-67 can be laid flat on the melamine powder.

[0043] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1

[0045] A method for preparing a nano-platinum / carbon nanotube / MXene fiber composite material comprises the following steps:

[0046] (1) Preparation of monolayer large-scale MXene dispersion (30 mg / mL)

[0047] MXene dispersion was prepared by an improved etching-stripping two-step method. The main steps are as follows: 1) 3g LiF was dissolved in 40mL hydrochloric acid (9mol·L -1 ), after LiF was completely dissolved, 2g of Ti3AlC2MAX phase ceramic powder was added in small amounts several times, and the mixture was stirred and etched at 35°C for 5 days to obtain Ti3C2T X ; 2) The mixed solution after etching is repeatedly centrifuged (3500rpm, 5min) and washed with water until the pH is 6. At this time, no water washing is performed but it is continued to be shaken and centrifuged 3 times, and finally the bottom solid, i.e., the MXene phase, is collected; 3) The collected MXene phase is transferred to a beaker and deionized water is added. After ice bath ultrasonication for 10min, centrifugation (4000rpm, 20min) is performed to collect the liquid phase containing the single-layer MXene, and the solid at the bottom is repeated with the above steps until all the MXene is completely peeled off; 4) Finally, the collected single-layer MXene dispersion is centrifuged (6000rpm, 20min) and the single-layer large-size MXene at the bottom is collected; 5) The concentration of the prepared MXene is calibrated by the membrane extraction method, and then an appropriate amount of deionized water is added to dilute its concentration to 30mg / mL. Figure 1 This is a scanning electron microscope image of MXene nanosheets. It can be seen that the prepared MXene material is a single-layer sheet with an average lateral size of 1.5-3μm.

[0048] (2) Preparation of MXene fibers by wet spinning

[0049] 1) The MXene dispersion was loaded into a 5 mL syringe connected to a polyetheretherketone (PEEK) tube. The other end of the PEEK tube was connected to a spinning nozzle with an inner diameter of 610 μm. 2) The MXene dispersion was pumped into the spinneret at a rate of 100 μL min-1 using a syringe pump (LongerPump, LSP02-1B). -1 % acetic acid into a coagulation bath containing an aqueous solution; 3) after standing for 10 minutes, the mixture was collected on a polytetrafluoroethylene roller and vacuum-dried at 40°C for 30 minutes, and finally washed with water and vacuum-dried at 40°C to obtain MXene fibers. Figure 2 A is a scanning electron microscope image of MXene fiber. It can be seen that the average diameter of the prepared MXene fiber is 100 μm, and the fiber surface has a wrinkled structure. This special structure gives the MXene fiber a huge specific surface area.

[0050] (3) 0.87 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 1.97 g of 2-methylimidazole (C4H6N2) were dissolved in 30 mL of deionized water respectively. After complete dissolution, the two solutions were mixed and added to the MXene fiber. After stirring for 10 min, the mixture was allowed to stand at room temperature for 12 h. Finally, the mixture was washed with water three times and dried in vacuum at 40 °C to obtain MXene fiber@ZIF-67. Figure 2 B is a scanning electron microscope image of MXene fiber @ZIF-67. It can be seen that after in situ growth of ZIF-67 nanosheets on the surface of MXene fiber, the obtained MXene fiber @ZIF-67 still retains the initial wrinkled structure.

[0051] (4) MXene fiber @ ZIF-67 was mixed with melamine powder in a mass ratio of 1:2 under a nitrogen atmosphere, and calcined at a high temperature under a nitrogen atmosphere to obtain MXene fiber @ CNTs; the calcination process conditions were: 3 ° C·min under a nitrogen atmosphere (100 sccm) -1 The temperature was raised to 500℃ at a rate of 2℃·min and kept at that temperature for 2h. -1 The temperature was raised to 750°C at a rate of 1000 ℃ and kept at this temperature for 2 h.

[0052] Figure 2 C is a scanning electron microscope image of MXene fiber@CNTs. It can be seen that dense and interlaced carbon nanotubes grow on the surface of the MXene fiber. The grown carbon nanotubes not only increase the specific surface area of ​​the microelectrode, which is conducive to exposing more active sites and improving electrochemical activity, but also promote the adsorption of the object to be detected, accelerate the electron transfer rate in the catalytic process, and provide more channels for electron transmission.

[0053] (5) Using a platinum electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and MXene fiber@CNTs as the working electrode, deposition was performed at a potential of −0.25 V for 200 s in a 0.5 M H2SO4 solution containing 4 mM H2PtCl6 to obtain MXene fibers loaded with platinum nanoparticles and carbon nanotubes, namely, MXene fiber@CNTs@Pt.

[0054] Figure 2 D is a scanning electron microscope image of MXene fiber@CNTs@Pt, showing that platinum nanoparticles grown by constant voltage electrodeposition are coated on the carbon nanotubes, and the surface of the spherical platinum nanoparticles is rough.

[0055] Figure 3 This is the X-ray photoelectron spectrum of the MXene fiber@CNTs@Pt prepared in this example.

[0056] in Figure 3 A is the X-ray photoelectron spectrum of C, N, O, Pt, and Ti in MXene fiber@CNTs@Pt. In the full spectrum, binding energies of 74.4 eV, 284.8 eV, 400.0 eV, 459.0 eV, and 531.1 eV are attributed to Pt, C, N, Ti, and O in MXene fiber@CNTs@Pt, respectively. This indicates that MXene fiber@CNTs@Pt primarily contains five elements: Pt, C, N, Ti, and O. O comes from TiO2 generated by partial oxidation of MXene, and N comes from N-CNTs formed by doping CNTs with NH3 gas generated by pyrolysis of melamine.

[0057] Figure 3 B is the X-ray photoelectron spectrum of C1s in MXene fiber@CNTs@Pt, and the binding energies of 284.8eV, 285.9eV, 286.7eV and 288.1eV correspond to CC(sp 2 hybridized graphitic carbon), CN, CO and OC=O. Figure 3 C is the X-ray photoelectron spectrum of N1s in MXene fiber@CNTs@Pt, and the binding energies of 398.6 eV, 399.2 eV, 400.6 eV, 402.0 eV, and 403.9 eV are attributed to N-Co, pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, and nitrogen oxides, respectively. Figure 3 D is the X-ray photoelectron spectrum of Pt 4f in MXene fiber@CNTs@Pt, showing two peaks of Pt, corresponding to Pt 4f 5 / 2 and Pt4f 7 / 2 , these two peaks can be further divided into two pairs of double peaks: at 71.4eV and 72.8eV respectively attributed to Pt 4f 7 / 2 and Pt 2+4f 7 / 2 , located at 74.7eV and 75.5eV respectively, which are attributed to Pt 4f 5 / 2 and Pt 2+ 4f 5 / 2 .

[0058] Example 2

[0059] A method for preparing a nano-platinum / carbon nanotube / MXene fiber composite material comprises the following steps:

[0060] (1) Preparation of single-layer large-size MXene dispersion

[0061] The preparation method of MXene dispersion is basically the same as that in Example 1, except that in step 5), the concentration of the prepared MXene is calibrated by the film extraction method, and then an appropriate amount of deionized water is added to dilute its concentration to 50 mg / mL.

[0062] (2) MXene fibers were obtained by wet spinning a 50 mg / mL MXene dispersion into a 70 wt.% acetic acid aqueous solution, washing with water and then drying in a vacuum at 40 °C.

[0063] 1) The MXene dispersion was loaded into a 5 mL syringe connected to a polyetheretherketone (PEEK) tube. The other end of the PEEK tube was connected to a spinning nozzle with an inner diameter of 610 μm. 2) The MXene dispersion was pumped into the spinneret at a rate of 100 μL min-1 using a syringe pump (LongerPump, LSP02-1B). -1 % acetic acid at a rate of 100 μm; 3) after standing for 10 min, the resulting mixture was collected on a polytetrafluoroethylene roller and vacuum-dried at 40°C for 30 min. Finally, the resulting mixture was washed with water and vacuum-dried at 40°C to obtain MXene fibers with a diameter of 150 μm.

[0064] (3) 0.87 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 1.97 g of 2-methylimidazole (C4H6N2) were dissolved in 30 mL of deionized water respectively. After complete dissolution, the two solutions were mixed and added to the MXene fiber. After stirring for 10 min, the solution was allowed to stand at room temperature for 12 h. Finally, the solution was washed with water three times and dried in vacuum at 40 °C to obtain MXene fiber@ZIF-67.

[0065] (4) MXene fiber @ ZIF-67 was mixed with melamine powder in a mass ratio of 1:2 under a nitrogen atmosphere, and calcined at a high temperature under a nitrogen atmosphere to obtain MXene fiber @ CNTs; the calcination process conditions were: 3 ° C·min under a nitrogen atmosphere (100 sccm) -1 The temperature was raised to 500℃ at a rate of 2℃·min and kept at that temperature for 2h.-1 The temperature was raised to 750°C at a rate of 1000 ℃ and kept at this temperature for 2 h.

[0066] (5) Using a platinum electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and MXene fiber@CNTs as the working electrode, deposition was performed at a potential of -0.25 V for 200 s in a 0.5 M H2SO4 solution containing 4 mM H2PtCl6 to obtain MXene fibers loaded with platinum nanoparticles and carbon nanotubes.

[0067] Example 3

[0068] A method for preparing a nano-platinum / carbon nanotube / MXene fiber composite material comprises the following steps:

[0069] (1) Preparation of single-layer large-size MXene dispersion

[0070] The preparation method of MXene dispersion is basically the same as that in Example 1, except that in step 5), the concentration of the prepared MXene is calibrated by the film extraction method, and then an appropriate amount of deionized water is added to dilute its concentration to 70 mg / mL.

[0071] (2) MXene fibers were obtained by wet spinning a 70 mg / mL MXene dispersion into an 80 wt.% acetic acid aqueous solution, washing with water and then drying in a vacuum at 40 °C.

[0072] 1) The MXene dispersion was loaded into a 5 mL syringe connected to a polyetheretherketone (PEEK) tube. The other end of the PEEK tube was connected to a spinning nozzle with an inner diameter of 610 μm. 2) The MXene dispersion was pumped into the spinneret at a rate of 100 μL min-1 using a syringe pump (LongerPump, LSP02-1B). -1 % acetic acid into a coagulation bath of aqueous solution at a rate of 100 μm; 3) after standing for 10 min, the resulting mixture was collected on a polytetrafluoroethylene roller and vacuum-dried at 40°C for 30 min. Finally, the resulting mixture was washed with water and vacuum-dried at 40°C to obtain MXene fibers with a diameter of 200 μm.

[0073] (3) 0.87 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 1.97 g of 2-methylimidazole (C4H6N2) were dissolved in 30 mL of deionized water respectively. After complete dissolution, the two solutions were mixed and added to the MXene fiber. After stirring for 10 min, the solution was allowed to stand at room temperature for 12 h. Finally, the solution was washed with water three times and dried in vacuum at 40 °C to obtain MXene fiber@ZIF-67.

[0074] (4) MXene fiber @ ZIF-67 was mixed with melamine powder in a mass ratio of 1:2 under a nitrogen atmosphere, and calcined at a high temperature under a nitrogen atmosphere to obtain MXene fiber @ CNTs; the calcination process conditions were: 3 ° C·min under a nitrogen atmosphere (100 sccm) -1 The temperature was raised to 500℃ at a rate of 2℃·min and kept at that temperature for 2h. -1 The temperature was raised to 750°C at a rate of 1000 ℃ and kept at this temperature for 2 h.

[0075] (5) Using a platinum electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and MXene fiber@CNTs as the working electrode, deposition was performed at a potential of -0.25 V for 200 s in a 0.5 M H2SO4 solution containing 4 mM H2PtCl6 to obtain MXene fibers loaded with platinum nanoparticles and carbon nanotubes.

[0076] Example 4

[0077] A MXene fiber-based electrochemical sensor, prepared as follows:

[0078] 1) Take 2 cm of the MXene fiber@CNTs@Pt prepared in Example 2 and attach it to a copper sheet using conductive silver paste to form a MXene fiber@CNTs@Pt electrode.

[0079] 2) Using the MXene fiber@CNTs@Pt electrode as the working electrode, Hg / HgO as the reference electrode, and platinum wire as the counter electrode, a 1 M KOH solution was used as the electrolyte. The current response curves of different NH4Cl concentrations were measured by differential voltammetry. The linear relationship between the NH4Cl concentration and the corresponding current was fitted to construct a ratiometric electrochemical sensor for the MXene fiber@CNTs@Pt electrode sensing interface.

[0080] Specifically, differential pulse voltammetry was used, and the potential range was set to -0.5 to 0 V, as shown in FIG. Figure 4 As shown in the figure, the oxidation peak appears at -0.3V, and the oxidation peak current value increases with the increase of ammonia concentration. From the above results, it can be seen that the electrochemical sensor prepared by MXene fibers loaded with platinum nanoparticles and carbon nanotubes has good electrochemical sensing performance, high sensitivity and low detection. Among them, the detection line is as low as 73.2nmol / L and the sensitivity is 0.41μA μM -1 cm -2 .

[0081] To investigate the practical application potential of the MXene fiber@CNTs@Pt microelectrode, the detection accuracy of the prepared MXene fiber@CNTs@Pt microelectrode was studied by adding different amounts of NH4Cl to artificial urine without urinary ammonia using the standard addition method. Each sample group was tested five times in parallel. The results are shown in Table 1. The spiked recovery of NH4Cl in artificial urine samples ranged from 98.7% to 102.5%, indicating that this method has high accuracy. The MXene fiber@CNTs@Pt microelectrode constructed in this invention can be used to accurately detect the content of urinary ammonia in urine.

[0082] Table 1 Test results of ammonia content in artificial urine using MXene fiber@CNTs@Pt microelectrode

[0083]

[0084]

[0085] Electrochemical performance test of composite materials

[0086] The electrochemical properties of the MXene fiber, MXene fiber@CNTs and MXene fiber@CNTs@Pt electrodes prepared in Example 1 were tested. The three electrodes were used as working electrodes in a 3- / 4- Cyclic voltammetry was performed under the conditions of redox probe, and the test solution contained 5mM Fe(CN)6 3- / 4- 0.1 M KCl solution.

[0087] The test results are as follows Figure 5 As shown in the figure, it can be seen that the CV test graphs of the three different microelectrodes all show a pair of reversible redox peaks, which are attributed to the Fe 2+ and Fe 3+ The redox peaks are generated by the electron transfer process between the electrodes. It can be clearly seen from the figure that the oxidation peak current of the pure MXene fiber electrode in the test curve at the same scan rate is significantly lower than that of the other two electrodes, and the oxidation peak current of the MXene fiber@CNTs@Pt electrode is the largest. This is because the CNTs grown on the surface of the MXene fiber can greatly increase the specific surface area of ​​the microelectrode, and the CNTs can also play an adsorption role on the reactants, which can improve the ion conversion efficiency. After platinum nanoparticles are loaded on the surface of CNTs by electrodeposition, the platinum nanoparticles can promote the rapid transmission of electrons on the surface of the microelectrode. The electrochemical active area (ECSA) of different microelectrodes was calculated according to the Randles-Sevcik equation. It was calculated that the electrochemical active areas of MXene fiber, MXene fiber@CNTs and MXene fiber@CNTs@Pt were 0.072cm-2 、0.160cm -2 and 0.299cm -2 .

[0088] The interfacial charge transfer behavior of different MXene fiber electrodes was studied by electrochemical impedance spectroscopy (EIS). Figure 6 Different MXene fiber electrodes in the presence of 5mM Fe(CN)6 3- / 4- The impedance test fitting plots in 0.1M KCl solution show that the fitted Nyquist plots of all MXene fiber-based electrodes consist of a semicircle in the high-frequency region and a straight line in the low-frequency region. The semicircle in the high-frequency region represents the charge transfer process, and its diameter corresponds to the charge transfer resistance (Rct). The straight line in the low-frequency region represents the diffusion process. The fitting shows that the Rct value of the MXene fiber electrode is 68.3Ω, indicating that MXene fiber electrodes prepared from pure MXene have excellent conductivity and are well-suited as sensor substrates. The Rct value of the MXene fiber@CNTs electrode drops to 39.7Ω, indicating that the introduction of CNTs significantly improves the electrode's conductivity. The Rct value of the MXene fiber@CNTs@Pt electrode drops to 11.9Ω. This is because the electrodeposition of highly conductive platinum nanoparticles significantly improves the electrode's conductivity, effectively promoting charge transfer between the microelectrode and the reactants.

[0089] In summary, the present invention uses wet spinning to prepare MXene fibers. ZIF-67 is grown in situ on the MXene fiber surface using a simple method. This is followed by high-temperature pyrolysis to produce MXene fiber@CNTs. Finally, platinum nanoparticles are loaded onto the MXene fiber@CNTs surface via potentiostatic electrodeposition in a sulfuric acid solution of chloroplatinic acid, resulting in a MXene fiber loaded with platinum nanoparticles and carbon nanotubes. This MXene fiber serves as a working electrode for the electrocatalytic oxidation of added ammonia. The resulting MXene fiber exhibits a significant increase in the oxidation peak signal with increasing ammonia concentration, thereby constructing a ratiometric electrochemical sensor for highly sensitive detection of ammonia content in urine.

[0090] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.

[0091] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A nano-platinum / carbon nanotube / MXene fiber composite material, characterized in that: The nano-platinum / carbon nanotube / MXene fiber composite material is formed by sequentially loading carbon nanotubes and platinum nanoparticles on the surface of MXene fibers; the preparation method of the nano-platinum / carbon nanotube / MXene fiber composite material comprises the following steps: S1. Preparation of MXene dispersion by etching-stripping method; S2. MXene fibers were prepared by wet spinning by injecting a MXene dispersion into a coagulation bath; S3. In situ growth of ZIF-67 on the surface of MXene fibers to obtain MXene fiber@ZIF-67. S4. calcining the MXene fiber@ZIF-67 at high temperature under an inert gas atmosphere to obtain MXene fiber@CNTs; S5. Platinum nanoparticles were loaded on the surface of the MXene fiber@CNTs using electrodeposition as a working electrode to obtain the nanoplatinum / carbon nanotube / MXene fiber composite.

2. The nano-platinum / carbon nanotube / MXene fiber composite material according to claim 1, characterized in that The average diameter of the MXene fiber is 100-200 μm.

3. A method for preparing the nano-platinum / carbon nanotube / MXene fiber composite material according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Preparation of MXene dispersion by etching-stripping method; S2. MXene fibers were prepared by wet spinning by injecting a MXene dispersion into a coagulation bath; S3. In situ growth of ZIF-67 on the surface of MXene fibers to obtain MXene fiber@ZIF-67. S4. calcining the MXene fiber@ZIF-67 at high temperature under an inert gas atmosphere to obtain MXene fiber@CNTs; S5. Platinum nanoparticles were loaded on the surface of the MXene fiber@CNTs using electrodeposition as a working electrode to obtain the nanoplatinum / carbon nanotube / MXene fiber composite.

4. The preparation method according to claim 3, characterized in that The coagulation bath in step S2 is an acetic acid aqueous solution.

5. The preparation method according to claim 4, wherein In step S2, the concentration of the MXene dispersion is 30-70 mg·mL -1 , the concentration of the acetic acid aqueous solution is 60-80 wt.%.

6. The preparation method according to claim 3, characterized in that In step S3, 2-methylimidazole, cobalt nitrate hexahydrate, and MXene fiber are mixed evenly, allowed to stand at room temperature, and dried to obtain MXene fiber@ZIF-67.

7. The preparation method according to claim 3, wherein In step S4, the mixture of MXene fiber @ ZIF-67 and melamine is calcined at high temperature; the conditions of the high temperature calcination are: 2-3 ° C·min under an inert gas atmosphere. -1 The temperature was raised to 500~550℃ at a rate of 1~2℃·min and kept at that temperature for 2~3h. -1 The temperature was raised to 700~750℃ at a rate of 0.5~1.5 and kept at this temperature for 2~3 h.

8. The preparation method according to claim 3, wherein The electrodeposition conditions in step S5 are as follows: a platinum electrode is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, MXene fiber@CNTs is used as a working electrode, a sulfuric acid solution of chloroplatinic acid is used as an electrolyte, and the deposition potential is -0.2~-0.25 V.

9. A MXene fiber-based electrochemical sensor, characterized in that The electrochemical sensor comprises the nano-platinum / carbon nanotube / MXene fiber composite material according to any one of claims 1 to 2.

10. Application of the MXene fiber-based electrochemical sensor according to claim 9 in ammonia nitrogen sensing detection.

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