CN101665232A - Palladium nanoparticle/carbon nanofiber compound, preparation method and application thereof in electrocatalysis - Google Patents

Abstract

The invention relates to a palladium nanoparticle/carbon nanofiber composite, a preparation method and its application in electrocatalysis. The composite was directly prepared by a one-step electrospinning method. The complex-modified electrode was used for the direct electrochemical detection of hydrogen peroxide, β-nicotinyl adenine dinucleotide, dopamine, ascorbic acid and uric acid. The complex-modified electrode has a linear range of 0.2 μm-20 mm for hydrogen peroxide detection, with a detection limit of 0.2 μm; a linear range for β-nicotinoyl adenine dinucleotide detection of 0.2 μm-716.6 μm, with a detection limit of 0.2 μm. The peak-to-peak potential differences of ascorbic acid-dopamine, dopamine-uric acid, and ascorbic acid-uric acid are 244mV, 148mV and 392mV, respectively, indicating that the modified electrode can be used for simultaneous electrochemical detection of three substances. The composite material can be used in the fields of catalysis, fuel cells and sensing.

Description

Palladium Nanoparticle/Carbon Nanofiber Composite, Preparation Method and Its Application in Electrocatalysis

technical field

The invention relates to a palladium nanoparticle/carbon nanofiber composite, a preparation method and its application in electrocatalysis.

Background technique

Due to its unique structure, good electrical conductivity, large specific surface area, high chemical stability, and mechanical strength, carbon nanofibers (CNFs) can be used as ideal catalyst supports for catalytic reactions and the preparation of sensors. Using CNF as a carrier can significantly improve the activity and stability of the catalyst, and the application of the prepared metal nanoparticles/CNF composites in electrochemical biosensors and fuel cell electrode materials has been reported in a large number of literatures. Although CNF as a fuel cell catalyst carrier can significantly enhance the catalyst activity, its high price currently limits its practical application, and it is still mainly in the laboratory research stage. Moreover, in previous methods for preparing CNFs, metal catalysts were generally used to catalyze the growth of CNFs, and these metal catalysts often remained in the prepared products. Therefore, when CNF is applied, it must go through a purification process to remove residual metal particles, graphite particles and other forms of carbon nanomaterials, which is relatively cumbersome. Therefore, large-scale preparation of high-purity CNF is the basis for its application.

As an effective method for preparing nanoscale fibers, electrospinning technology has made great progress in theory and experiment in recent years, and has successfully prepared polymer, ceramic, metal and inorganic/organic composite nanofibers. People have also conducted research on the application of electrospun fibers in many fields, showing broad application prospects [1]. The stabilization and carbonization process of electrospun polymer fibers can be used as a fast and efficient method to prepare CNFs. Since there is no need to introduce a metal catalyst during the preparation process, no other impurities remain in the prepared CNF, and no cumbersome purification process is required during application. Therefore, electrospinning is a cost-effective method to prepare high-purity CNFs.

The preparation methods of metal nanoparticles/CNF composites mainly include chemical reduction method[2,3], self-assembly method[4,5], electrochemical deposition method[6,7], electroless deposition method[8,9] and Physical method [10] and so on. Since these preparation methods will destroy the structural integrity of CNFs, thereby affecting their conductivity and stability, it is of great significance to develop non-destructive methods for preparing metal nanoparticles/CNFs.

H ₂ O ₂ , β-nicotinyl adenine dinucleotide (NADH), dopamine (DA), ascorbic acid (AA) and uric acid (UA) are some important substances closely related to the life process, the analysis and detection of these substances is of great significance. Among various detection methods, electrochemical detection is one of the most commonly used methods. However, on bare solid-state electrodes, the detection of these substances requires a high detection potential, which will be interfered by some coexisting electroactive substances. Therefore, it is necessary to develop detection methods with good selectivity and high sensitivity to perform direct electrochemical detection of these substances at low potentials.

references:

[1] Greiner, A.; Wendorff J.H.Angew.Chem.Int.Ed.2007, 46, 2-36.

[2] Bessel, C.A.; Laubernds, K.; Rodriguez, N.M.; Baker, R.T.K.J.Phys.Chem.B2001, 105, 1115-1118.

[3] Van der Lee, M.K.; Van Dillen, A.J.; Bitter, J.H.; De Jong, K.P.J.Am.Chem.Soc.2005, 127, 13573-13582.

[4] Carrillo, A.; Swartz, J.A.; Gamba, J.M.; Kane, R.S.; Chakrapani, N.; Wei, B.Q.;

[5] Han, X.; Li, Y.; Deng, Z. Adv. Mater. 2007, 19, 1518-1522.

[6] Guo, D.-J.; Li, H.-L.J. Electroanal. Chem. 2004, 573, 197-202.

[7] Zhao, Y; Fan, L.Z.; Zhong, H.Z.; Li, Y.F.; Yang, S.H. Adv. Funct. Mater.2007, 17, 1537-1541.

[8] Qu, L.T.; Dai, L.M.; Osawa, E.J.Am.Chem.Soc.2006, 128, 5523-5532.

[9] Arai, S.; Endo, M.; Hashizume, S.; Shimojima, Y. Electrochem. Commun. 2004, 6, 1029-1031.

[10] Kong, J.; Chapline, M.G.; Dai, H.J. Adv. Mater.2001, 13, 1384-1386.)

Contents of the invention

The palladium nanoparticle/carbon nanofiber composite provided by the invention is composed of palladium nanoparticle with particle diameter of 10-90nm uniformly dispersed on the surface of carbon nanofiber with diameter of 100-500nm.

The preparation method of the palladium nanoparticle/carbon nanofiber composite provided by the invention comprises the following steps:

1) Preparation of electrospinning solution: dissolve polyacrylonitrile (PAN) and palladium acetate in dimethylformamide (DMF) solution to obtain a uniform mixed solution; the content of polyacrylonitrile in the mixed solution is 5-15wt. %, palladium acetate content is 2-6wt.%;

2) Electrospinning: the uniform mixed solution obtained in step 1) is electrospun in an electric field with an electric field strength of 50-100kV/m to prepare polyacrylonitrile composite fibers containing palladium acetate, and the distance between the spinneret and the collecting plate is 10-50cm, the applied voltage is 5-50kV;

3) annealing the polyacrylonitrile composite fiber containing palladium acetate obtained in step 2) at 200-300° C. for 2-5 hours to partially oxidize the composite fiber;

4) Raise the temperature to 200-500°C at a rate of 2-6°C/min, and pass a mixed gas of _H2 and Ar for 1-3h at this temperature, wherein the volume ratio of _H2 :Ar is 1:3 to stabilize Palladium nanoparticles/polyacrylonitrile composite fibers and reduced metal ions;

5) Raise the temperature to 1000-1500°C at a rate of 2-6°C/min, keep at this temperature for 20-60min to palladium carbide nanoparticle/polyacrylonitrile composite fiber, and then cool to room temperature in Ar to obtain palladium nanoparticle / carbon nanofiber composite.

The following introduces the application of the metal nanoparticle/carbon nanofiber composite provided by the present invention in electrocatalysis.

The inventor's research shows that the palladium nanoparticle/carbon nanofiber composite material provided by the present invention has good electrocatalytic activity. The electrochemical redox reactions of H ₂ O ₂ , NADH, DA, AA, and UA have high electrocatalytic activity and good selectivity, and can significantly reduce the detection overpotential of these substances.

The method for the direct electrochemical detection of H ₂ O ₂ , NADH or DA, AA and UA for the electrode modified by the palladium nanoparticle/carbon nanofiber composite is as follows:

1. The detection steps of H ₂ O ₂ on the electrode modified by palladium nanoparticles/carbon nanofiber composites are as follows:

1. Preparation of Palladium Nanoparticle/Carbon Nanofiber Composite Modified Electrode

1) Weigh 0.5-2 mg of palladium nanoparticles/carbon nanofiber composites into a 5 mL beaker, add 1 mL of secondary water, and stir for 1 hour to obtain a black suspension of palladium nanoparticles/carbon nanofibers with a concentration of 0.5-2 mg/mL;

2) Take 2-20 μL of the black suspension described in step 1) and drop it on the surface of the electrode, place the electrode in a desiccator at room temperature to evaporate the solvent, and obtain a palladium nanoparticle/carbon nanofiber composite modified electrode;

3) The prepared palladium nanoparticle/carbon nanofiber composite modified electrode is rinsed with deionized water before use; when the modified electrode is not in use, it is stored in a desiccator at room temperature;

2. Preparation of phosphate buffer solution with pH value of 7

First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the Na ₂ HPO ₄ solution with a concentration of 100mmol/L, and then add the prepared NaH ₂ PO ₄ solution to the Na ₂ HPO ₄ solution until the pH of the solution is 7.0;

3. Detection of H ₂ O ₂

Deoxygenate the phosphate buffer solution with a pH value of 7 with N ₂ for 10-30 minutes, then add H ₂ O ₂ , and perform constant potential electrochemical detection under the stirring condition of 200-1000 rpm; select the detection potential as - 0.2V.

2. The detection steps of NADH by the palladium nanoparticle/carbon nanofiber composite modified electrode are as follows:

1. Preparation of Palladium Nanoparticle/Carbon Nanofiber Composite Modified Electrode

1) Weigh 0.5-2 mg of palladium nanoparticles/carbon nanofiber composites into a 5 mL beaker, add 1 mL of secondary water, and stir for 1 hour to obtain a black suspension of palladium nanoparticles/carbon nanofibers with a concentration of 0.5-2 mg/mL;

2) Take 2-20 μL of the black suspension described in step 1) and drop it on the surface of the electrode, place the electrode in a desiccator at room temperature to evaporate the solvent, and obtain a palladium nanoparticle/carbon nanofiber composite modified electrode;

3) The prepared palladium nanoparticle/carbon nanofiber composite modified electrode is rinsed with deionized water before use; when the modified electrode is not in use, it is stored in a desiccator at room temperature;

2. Preparation of phosphate buffer solution with pH value of 7

First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the Na ₂ HPO ₄ solution with a concentration of 100mmol/L, and then add the prepared NaH ₂ PO ₄ solution to the Na ₂ HPO ₄ solution until the pH of the solution is 7.0;

3. NADH detection

NADH is added to a phosphate buffer solution with a pH value of 7, and a constant potential electrochemical detection is performed under a stirring condition of 200-1000 rpm; the detection potential is selected as 0.5V.

3. The electrochemical detection steps of DA, AA and UA on the palladium nanoparticle/carbon nanofiber composite modified electrode are as follows:

1. Preparation of Palladium Nanoparticle/Carbon Nanofiber Composite Modified Electrode

1) Weigh 0.5-2 mg of palladium nanoparticles/carbon nanofiber composites into a 5 mL beaker, add 1 mL of secondary water, and stir for 1 hour to obtain a black suspension of palladium nanoparticles/carbon nanofibers with a concentration of 0.5-2 mg/mL;

2) Take 2-20 μL of the black suspension described in step 1) and add it dropwise on the surface of the electrode, place the electrode in a desiccator at room temperature to evaporate the solvent, and obtain a palladium nanoparticle/carbon nanofiber composite modified electrode;

3) The prepared palladium nanoparticle/carbon nanofiber composite modified electrode is rinsed with deionized water before use; when the modified electrode is not in use, it is stored in a desiccator at room temperature;

2. Preparation of phosphate buffer solution with a pH value of 4.5

First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the H ₃ PO ₄ solution with a concentration of 1.0mol/L, and then use the 1.0mol/L H ₃ PO ₄ solution to adjust the NaH ₂ PO ₄ solution to a pH value of 4.5 ;

3. Simultaneous electrochemical detection of DA, UA and AA

Add DA, AA and UA to the phosphate buffer solution with a pH value of 4.5 at the same time, and perform differential pulse voltammetry detection under static conditions; the selected differential pulse voltammetry conditions are: the sweep rate is 20mV/s; the pulse height is 50mV; pulse width is 50ms; pulse period is 200ms; differential pulse voltammetry scan range is -0.1-0.8V.

Beneficial effects: the present invention adopts a one-step electrospinning method to directly prepare palladium nanoparticles/carbon nanofiber composite materials, avoiding the destruction of the conductivity of carbon nanofibers in the preparation method of metal nanoparticles/carbon nanofiber composite materials reported in the literature and stability issues. Moreover, no other impurities are introduced during the preparation process, and no cumbersome purification process is required during application. The prepared palladium nanoparticles have good dispersion and stability on the surface of the carbon nanofibers, and, due to the existence of the metal nanoparticles, can catalyze the generation of graphitized carbon during the carbonization process. The prepared palladium nanoparticles/carbon nanofiber composite modified electrode showed high electrocatalytic activity for electrochemical redox reactions of H ₂ O ₂ , NADH, DA, AA and UA, and significantly reduced the detection overpotential of these substances .

The prepared palladium nanoparticles/carbon nanofibers modified electrode has a low detection limit and a wide linear range for the detection of H ₂ O ₂ and NADH, and the linear range for the detection of H ₂ O ₂ is 0.2μM-20mM, and the detection limit is 0.2μM; the linear range of NADH detection is 0.2μM-716.6μM, and the detection limit is 0.2μM. On the modified electrode, the peak-to-peak potential differences of AA-DA, DA-UA and AA-UA are 244mV, 148mV and 392mV, respectively, indicating that the modified electrode can be used for simultaneous electrochemical detection of three substances.

Description of drawings

Figure 1 is the scanning electron micrograph (a) and transmission electron micrograph (b) of the palladium nanoparticle/carbon nanofiber composite (Pd/CNF) prepared by electrospinning;

Figure 2(a) is the it curve of the Pd/CNF modified electrode in response to the continuous addition of a certain concentration of H ₂ O ₂ , the inset is the linear regression curve of the H ₂ O ₂ concentration in the range of 0.2μM-20mM; (b) Pd/CNF The it curve of the modified electrode in response to low concentration H ₂ O ₂ ; supporting electrolyte: 100mmol/L phosphate buffer solution (pH 7.0); detection potential: -0.2V.

Figure 3(a) is the i-t curve of the Pd/CNF modified electrode in response to the continuous addition of a certain concentration of NADH, the inset is the linear regression curve of the NADH concentration in the range of 0.2μM-716.6μM; The i-t curve of NADH response; supporting electrolyte: 100mmol/L phosphate buffer solution (pH 7.0); detection potential: +0.5V.

Figure 4 is the differential pulse voltammetry (DPV) curve of the Pd/CNF modified electrode in 100mmol/L phosphate buffer solution (pH 4.5) containing 2mM AA, 50μMDA and 100μMUA; DPV conditions: sweep rate 20mV/s; pulse height 50mV ; Pulse width 50ms; Pulse period 200ms.

Detailed ways

Embodiment 1, electrospinning prepares Pd/CNF composite material

1) Preparation of electrospinning solution: polyacrylonitrile (PAN) and palladium acetate are dissolved in dimethylformamide (DMF) solution to obtain a uniform mixed solution; the content of polyacrylonitrile in the mixed solution is 8wt.%. Palladium acetate content is 4.8wt.%;

2) Electrospinning: the uniform mixed solution obtained in step 1) is electrospun in an electric field with an electric field strength of 100kV/m to prepare polyacrylonitrile composite fibers containing palladium acetate, and the distance between the spinneret and the collecting plate is 30cm. The applied voltage is 30kV;

3) annealing the polyacrylonitrile composite fiber containing palladium acetate obtained in step 2) at 230° C. for 3 hours to partially oxidize the PAN nanofiber;

4) Raise the temperature to 300°C at a rate of 5°C/min, and pass a mixed gas of H ₂ and Ar for 2 hours at this temperature, wherein, H ₂ :Ar=1:3 (v/v) to reduce Pd ²⁺ and stabilized palladium nanoparticles/polyacrylonitrile composite fibers;

5) The temperature was raised to 1100° C. at a rate of 5° C./min, and kept at this temperature for 30 minutes to carbonize PAN nanofibers, and then cooled to room temperature in Ar to obtain Pd nanoparticles/carbon nanofiber composites.

The SEM and TEM images of the prepared Pd nanoparticles/carbon nanofiber composites are shown in Figure 1. It shows that metal Pd nanoparticles have good dispersion and stability on the surface of carbon nanofibers, and there is no obvious aggregation. The average particle size of Pd nanoparticles is 76nm, and the diameter of carbon nanofibers is between 200-500nm. X-ray diffraction analysis shows that there are cubic Pd nanoparticles in the generated product, and the presence of Pd nanoparticles promotes the formation of graphitized carbon during carbonization.

Embodiment 2, electrospinning prepares Pd/CNF composite material

1) Preparation of electrospinning solution: polyacrylonitrile (PAN) and palladium acetate are dissolved in dimethylformamide (DMF) solution to obtain a uniform mixed solution; the content of polyacrylonitrile in the mixed solution is 15wt.%. Palladium acetate content is 6wt.%;

2) Electrospinning: the uniform mixed solution obtained in step 1) is electrospun in an electric field with an electric field strength of 100kV/m to prepare polyacrylonitrile composite fibers containing palladium acetate, and the distance between the spinneret and the collecting plate is 30cm. The applied voltage is 30kV;

3) annealing the polyacrylonitrile composite fiber containing palladium acetate obtained in step 2) at 230° C. for 3 hours to partially oxidize the PAN nanofiber;

4) Raise the temperature to 300°C at a rate of 5°C/min, and pass a mixed gas of H ₂ and Ar for 2 hours at this temperature, wherein, H ₂ :Ar=1:3 (v/v) to reduce Pd ²⁺ and stabilized palladium nanoparticles/polyacrylonitrile composite fibers;

5) The temperature was raised to 1100° C. at a rate of 5° C./min, and kept at this temperature for 30 minutes to carbonize PAN nanofibers, and then cooled to room temperature in Ar to obtain Pd nanoparticles/carbon nanofiber composites.

The surface morphology of the prepared Pd nanoparticles/carbon nanofiber composites is similar to that of Example 1, except that the diameters of the carbon nanofibers are all greater than 400 nm, and the average particle diameter of the Pd nanoparticles is 84 nm. At the same time, Pd nanoparticles partially aggregated on the surface of carbon nanofibers to form larger particles. X-ray diffraction analysis shows that there are cubic Pd nanoparticles in the generated product, and the presence of Pd nanoparticles promotes the formation of graphitized carbon during carbonization.

Embodiment 3, electrospinning prepares Pd/CNF composite material

1) Preparation of electrospinning solution: polyacrylonitrile (PAN) and palladium acetate are dissolved in dimethylformamide (DMF) solution to obtain a uniform mixed solution; the content of polyacrylonitrile in the mixed solution is 5wt.%. Palladium acetate content is 2wt.%;

2) Electrospinning: the uniform mixed solution obtained in step 1) is electrospun in an electric field with an electric field strength of 100kV/m to prepare polyacrylonitrile composite fibers containing palladium acetate, and the distance between the spinneret and the collecting plate is 30cm. The applied voltage is 30kV;

3) annealing the polyacrylonitrile composite fiber containing palladium acetate obtained in step 2) at 230° C. for 3 hours to partially oxidize the PAN nanofiber;

4) Raise the temperature to 300°C at a rate of 5°C/min, and pass a mixed gas of H ₂ and Ar for 2 hours at this temperature, wherein, H ₂ :Ar=1:3 (v/v) to reduce Pd ²⁺ and stabilized palladium nanoparticles/polyacrylonitrile composite fibers;

5) The temperature was raised to 1100° C. at a rate of 5° C./min, and kept at this temperature for 30 minutes to carbonize PAN nanofibers, and then cooled to room temperature in Ar to obtain Pd nanoparticles/carbon nanofiber composites.

The surface morphology of the prepared Pd nanoparticle/carbon nanofiber composite is similar to that of Example 1, except that the diameter of the carbon nanofiber is between 100nm and 200nm, the average particle diameter of the Pd nanoparticle is 40nm, and the density of the nanoparticle lower. Metal Pd nanoparticles have good dispersion and stability on the surface of carbon nanofibers, without obvious aggregation. X-ray diffraction analysis shows that there are cubic Pd nanoparticles in the generated product, and the presence of Pd nanoparticles promotes the formation of graphitized carbon during carbonization.

Example 4, Pd/CNF Modified Electrode Used for Direct Electrochemical Detection of H ₂ O ₂

The Pd/CNF composite prepared in Example 1 was used to prepare a modified electrode, and then used for direct electrochemical detection of H ₂ O ₂ .

1. The preparation of Pd/CNF modified electrode is carried out according to the following steps:

1) Weigh 1mg of Pd/CNF complex into a 5mL beaker, add 1mL of secondary water, and stir vigorously for 1h to obtain a black suspension of Pd/CNF with a concentration of 1mg/mL;

2) 10 μL of the black suspension described in step 1) was added dropwise on the surface of the electrode, and placed in a desiccator at room temperature to evaporate the solvent, thereby preparing a Pd/CNF composite modified electrode.

3) The prepared Pd/CNF modified electrode was carefully rinsed with deionized water before use, and when the modified electrode was not in use, it was stored in a desiccator at room temperature.

The prepared Pd/CNF modified electrode has a relatively smooth surface morphology, and Pd/CNF forms a three-dimensional network porous structure on the electrode surface, which can significantly increase the electroactive surface area of the electrode.

2. Preparation of phosphate buffer solution with a pH value of 7.0:

First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the Na ₂ HPO ₄ solution with a concentration of 100mmol/L, and then add the prepared NaH ₂ PO ₄ solution to the Na ₂ HPO ₄ solution until the pH of the solution is 7.0;

3. Direct electrochemical detection of H ₂ O ₂ at Pd/CNF modified electrode

The prepared Pd/CNF modified electrode was used for the direct electrochemical detection of H ₂ O ₂ . The detection was carried out in a phosphate buffer solution with a pH of 7.0. The phosphate buffer solution was deoxygenated with N ₂ for 20 minutes before adding H ₂ O _2. Under the stirring condition of 500 rev/min, the potentiostatic electrochemical detection was carried out at the detection potential of -0.2V.

The modified electrode can be used for direct electrochemical detection of H ₂ O ₂ at a lower potential, with a detection linear range of 0.2 μM-20 mM and a detection limit of 0.2 μM ( FIG. 2 ). The detection potential used is -0.2V, and at such a low detection potential, the interference of the co-existing high concentrations of AA and UA on the detection can be effectively avoided. The method has the characteristics of high sensitivity, good selectivity and short response time for the detection of H ₂ O ₂ .

Example 5, Pd/CNF modified electrode for direct electrochemical detection of NADH

The Pd/CNF complex prepared in Example 1 was used to prepare a modified electrode, and then used for direct electrochemical detection of NADH.

1. The preparation of Pd/CNF modified electrode is carried out according to the following steps:

1) Weigh 1mg of Pd/CNF complex into a 5mL beaker, add 1mL of secondary water, and stir vigorously for 1h to obtain a Pd/CNF black suspension with a concentration of 1mg/mL;

2) 10 μL of the black suspension described in step 1) was added dropwise on the surface of the electrode, and placed in a desiccator at room temperature to evaporate the solvent, thereby preparing a Pd/CNF composite modified electrode.

3) The prepared Pd/CNF modified electrode was carefully rinsed with deionized water before use, and when the modified electrode was not in use, it was stored in a desiccator at room temperature.

The prepared Pd/CNF modified electrode has a relatively smooth surface morphology, and Pd/CNF forms a three-dimensional network porous structure on the electrode surface, which can significantly increase the electroactive surface area of the electrode.

2. Preparation of phosphate buffer solution with a pH value of 7.0:

First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the Na ₂ HPO ₄ solution with a concentration of 100mmol/L, and then add the prepared NaH ₂ PO ₄ solution to the Na ₂ HPO ₄ solution until the pH of the solution is 7.0;

3. Direct electrochemical detection of NADH at Pd/CNF modified electrode

The prepared Pd/CNF modified electrode was used for the direct electrochemical detection of NADH. The detection is carried out in a phosphate buffer solution with a pH of 7.0. Under the stirring condition of 500 rpm, NADH is added to the phosphate buffer solution, and the constant potential electrochemical detection is performed at a detection potential of 0.5V.

The modified electrode was used for direct electrochemical detection of NADH, and compared with the bare electrode, the oxidation peak potential of NADH was significantly reduced, indicating that Pd/CNF has a higher catalytic activity for the oxidation of NADH. At a detection potential of 0.5V, the linear range of NADH detection is 0.2 μM-716.6 μM, and the detection limit is 0.2 μM ( FIG. 3 ). The Pd/CNF modified electrode has a large electroactive surface area and a fast electron transfer rate, which can significantly reduce the detection overpotential, inhibit the surface contamination of the electrode, and have good stability for the detection of NADH.

Example 6, Pd/CNF modified electrode is used for simultaneous electrochemical detection of DA, UA and AA

The Pd/CNF composite prepared in Example 1 was used to prepare modified electrodes, and then used for simultaneous electrochemical detection of DA, UA and AA.

1. The preparation of Pd/CNF modified electrode is carried out according to the following steps:

1) Weigh 1mg of Pd/CNF complex into a 5mL beaker, add 1mL of secondary water, and stir vigorously for 1h to obtain a Pd/CNF black suspension with a concentration of 1mg/mL;

2) 10 μL of the black suspension described in step 1) was added dropwise on the surface of the electrode, and placed in a desiccator at room temperature to evaporate the solvent, thereby preparing a Pd/CNF composite modified electrode.

3) The prepared Pd/CNF modified electrode was carefully rinsed with deionized water before use, and when the modified electrode was not in use, it was stored in a desiccator at room temperature.

The prepared Pd/CNF modified electrode has a relatively smooth surface morphology, and Pd/CNF forms a three-dimensional network porous structure on the electrode surface, which can significantly increase the electroactive surface area of the electrode.

2. Preparation of phosphate buffer solution with a pH value of 4.5:

First prepare NaH ₂ PO ₄ solution with a concentration of 100mmol/L and H ₃ PO ₄ solution with a concentration of 1.0mol/L, and then adjust the NaH ₂ PO ₄ solution to pH 4.5 with 1.0mol/L H ₃ PO ₄ solution.

3. Simultaneous electrochemical detection of DA, UA and AA on Pd/CNF modified electrode

The prepared Pd/CNF modified electrode was used for the simultaneous electrochemical detection of DA, UA and AA. The supporting electrolyte used was 100 mmol/L phosphate buffer solution with a pH value of 4.5. The selected differential pulse voltammetry conditions are: sweep rate, 20mV/s; pulse height, 50mV; pulse width, 50ms; pulse period, 200ms. The differential pulse voltammetry scan range is -0.1-0.8V.

Differential pulse voltammetry (DPV) was used to detect DA, UA and AA simultaneously, and the DPV curve of the mixture of the three substances on the Pd/CNF modified electrode is shown in Figure 4. The oxidation peaks of DA, UA and AA on the Pd/CNF modified electrode were completely separated from each other, and the corresponding oxidation peak potentials were 402mV, 550mV and 158mV, respectively. On the Pd/CNF modified electrode, the peak-to-peak potential differences of AA-DA, DA-UA and AA-UA were 244 mV, 148 mV and 392 mV, respectively, indicating that the modified electrode can be used for the simultaneous detection of three substances. The detection limits of the modified electrode for DA, UA and AA were 0.2 μM, 0.7 μM and 15 μM, respectively (S/N=3). The simultaneous detection of these three substances will not interfere with each other, and the detection has good reproducibility and high sensitivity.

Claims (6)

1. The palladium nanoparticle/carbon nanofiber composite is characterized in that it is composed of palladium nanoparticles with a particle size of 10-90nm uniformly dispersed on the surface of carbon nanofibers with a diameter of 100-500nm. 2. The preparation method of the palladium nanoparticle/carbon nanofiber composite according to claim 1, characterized in that the steps and conditions are as follows: 1) Preparation of electrospinning solution: polyacrylonitrile and palladium acetate are dissolved in dimethylformamide solution to obtain a uniform mixed solution; the content of polyacrylonitrile in the mixed solution is 5-15wt.%, and the palladium acetate content is 2-6wt.%; 2) Electrospinning: the uniform mixed solution obtained in step 1) is electrospun in an electric field with an electric field strength of 50-100kV/m to prepare polyacrylonitrile composite fibers containing palladium acetate, and the distance between the spinneret and the collecting plate is 10-50cm, the applied voltage is 5-50kV; 3) annealing the polyacrylonitrile composite fiber containing palladium acetate obtained in step 2) at 200-300° C. for 2-5 hours to partially oxidize the composite fiber; 4) Raise the temperature to 200-500°C at a rate of 2-6°C/min, and feed a mixed gas of H2 and Ar for 1-3h at this temperature, wherein the volume ratio of _H2 :Ar is 1:3 to stabilize palladium Nanoparticles/polyacrylonitrile composite fibers and reduced metal ions; 5) Raise the temperature to 1000-1500°C at a rate of 2-6°C/min, keep at this temperature for 20-60min to palladium carbide nanoparticle/polyacrylonitrile composite fiber, and then cool to room temperature in Ar to obtain palladium nanoparticle / carbon nanofiber composite. 3. The application of the palladium nanoparticle/carbon nanofiber composite as claimed in claim 1, characterized in that, the palladium nanoparticle/carbon nanofiber composite is used for modifying electrodes, and the modified electrode is used for process Direct electrochemical detection of hydrogen oxide, β-nicotinyl adenine dinucleotide or dopamine, ascorbic acid and uric acid. 4. The palladium nanoparticle/carbon nanofiber composite modified electrode used for direct electrochemical detection of hydrogen peroxide as claimed in claim 3, characterized in that the steps and conditions are as follows: A. Preparation of Palladium Nanoparticle/Carbon Nanofiber Composite Modified Electrode 1) Weigh 0.5-2 mg of palladium nanoparticles/carbon nanofiber composites into a 5 mL beaker, add 1 mL of secondary water, and stir for 1 hour to obtain a black suspension of palladium nanoparticles/carbon nanofibers with a concentration of 0.5-2 mg/mL; 2) Take 2-20 μL of the black suspension described in step 1) and drop it on the surface of the electrode, place the electrode in a desiccator at room temperature to evaporate the solvent, and obtain a palladium nanoparticle/carbon nanofiber composite modified electrode; 3) The prepared electrode modified by the palladium nanoparticle/carbon nanofiber composite is rinsed with deionized water before use; when the modified electrode is not in use, it is stored in a desiccator at room temperature; B. Preparation of phosphate buffer solution with pH value of 7 First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the Na ₂ HPO ₄ solution with a concentration of 100mmol/L, and then add the prepared NaH ₂ PO ₄ solution to the Na ₂ HPO ₄ solution until the pH of the solution is 7.0; Detection _{of CH2O2} Deoxygenate the phosphate buffer solution with a pH value of 7 with N ₂ for 10-30 minutes, then add H ₂ O ₂ , and perform constant potential electrochemical detection under the stirring condition of 200-1000 rpm; select the detection potential as - 0.2V. 5. The palladium nanoparticle/carbon nanofiber composite modified electrode used for direct electrochemical detection of β-nicotinyl adenine dinucleotide as claimed in claim 3, characterized in that the steps and conditions are as follows: A. Preparation of Palladium Nanoparticle/Carbon Nanofiber Composite Modified Electrode 1) Weigh 0.5-2 mg of palladium nanoparticles/carbon nanofiber composites into a 5 mL beaker, add 1 mL of secondary water, and stir for 1 hour to obtain a black suspension of palladium nanoparticles/carbon nanofibers with a concentration of 0.5-2 mg/mL; 2) Take 2-20 μL of the black suspension described in step 1) and drop it on the surface of the electrode, place the electrode in a desiccator at room temperature to evaporate the solvent, and obtain a palladium nanoparticle/carbon nanofiber composite modified electrode; 3) The prepared electrode modified by the palladium nanoparticle/carbon nanofiber composite is rinsed with deionized water before use; when the modified electrode is not in use, it is stored in a desiccator at room temperature; B. Preparation of phosphate buffer solution with pH value of 7 First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the Na ₂ HPO ₄ solution with a concentration of 100mmol/L, and then add the prepared NaH ₂ PO ₄ solution to the Na ₂ HPO ₄ solution until the pH of the solution is 7.0; C. Detection of β-nicotinoyl adenine dinucleotide β-Nicotinyl adenine dinucleotide is added to a phosphate buffer solution with a pH value of 7, and a constant potential electrochemical detection is performed under the stirring condition of 200-1000 rpm; the detection potential is selected as 0.5V. 6. The palladium nanoparticle/carbon nanofiber composite modified electrode as claimed in claim 3 is used for the direct electrochemical detection of dopamine, ascorbic acid and uric acid, characterized in that the steps and conditions are as follows: A. Preparation of Palladium Nanoparticle/Carbon Nanofiber Composite Modified Electrode 1) Weigh 0.5-2 mg of palladium nanoparticles/carbon nanofiber composites into a 5 mL beaker, add 1 mL of secondary water, and stir for 1 hour to obtain a black suspension of palladium nanoparticles/carbon nanofibers with a concentration of 0.5-2 mg/mL; 2) Take 2-20 μL of the black suspension described in step 1) and add it dropwise on the surface of the electrode, place the electrode in a desiccator at room temperature to evaporate the solvent, and obtain a palladium nanoparticle/carbon nanofiber composite modified electrode; 3) The prepared palladium nanoparticle/carbon nanofiber composite modified electrode is rinsed with deionized water before use; when the modified electrode is not in use, it is stored in a desiccator at room temperature; B. Preparation of phosphate buffer solution with a pH value of 4.5 First prepare the NaH ₂ PO ₄ solution with a concentration of 100mmol/L and the H ₃ PO ₄ solution with a concentration of 1.0mol/L, and then use the 1.0mol/L H ₃ PO ₄ solution to adjust the NaH ₂ PO ₄ solution to a pH value of 4.5 ; C. Simultaneous electrochemical detection of dopamine, ascorbic acid, and uric acid Dopamine, ascorbic acid and uric acid were added to the phosphate buffer solution with a pH value of 4.5 at the same time, and the differential pulse voltammetry was detected under static conditions; the selected differential pulse voltammetry conditions were: the sweep rate was 20mV/s; the pulse height was 50mV; pulse width is 50ms; pulse period is 200ms; differential pulse voltammetry scan range is -0.1-0.8V.

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