A method for preparing a carbon nanoelectrode

Abstract

The present application relates to the technical field of nanometer material, and particularly provides a preparation method of carbon nanometer electrode. The preparation method of the carbon nanometer electrode comprises the following steps: under the condition of no oxygen, a gaseous carbon source is introduced into a nanometer template, and heating is performed to obtain the carbon nanometer electrode; the nanometer template is a nanometer tube with a tip; and the cross section of the nanometer template is parallel to the horizontal line. The current preparation process of the nanometer electrode is complex, time-consuming, high in cost and low in success rate. The preparation process of the nanometer electrode is convenient and low in cost, and the carbon nanometer electrode with a regular tip morphology, stable conductivity and long-term preservation can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials, and more particularly to a preparation method of a carbon nanoelectrode. BACKGROUND

[0002] Nanoelectrodes have a wide range of applications in fundamental electrochemistry (kinetics and thermodynamics) and electroanalytical detection (sensors) due to their nanoscale advantages and ultra-high spatial and temporal resolution. Carbon nanoelectrodes have good application prospects due to their advantages of high-temperature resistance (> 3500 DEG C), high conductivity and wide potential window. For example, they are used as probes for electrochemical detection to be applied to electrochemical scanning imaging, micro / nanoscale sensors and sensing carriers, electrocatalytic testing and electrocatalyst inert carriers, biological detection probes, and precision micro / nano processing devices. At the same time, due to the high chemical stability of carbon materials, carbon nanoelectrodes are suitable for being used as a basic carrier to load various metal and non-metal elements to jointly build a composite electrode.

[0003] At present, the preparation process of nanoelectrodes is very complicated, especially the thin insulating layer protected disc nanoelectrode. Etching or pulling a metal (or carbon) wire is a representative method for preparing nanoelectrodes at present. For example, the White group adopts the strategy of electrochemically etching a metal wire and sealing it in glass, while the Schuhmann and Mirkin groups use the method of simultaneously stretching glass and sealing the metal wire. Mechanical grinding under impedance or optical microscope monitoring can achieve the purpose of exposing the tip of the nanoelectrode. Scanning electron microscopy (SEM), atomic force microscopy and transmission electron microscopy are used to image these nanoelectrodes to reveal the fine structure of the tip.

[0004] Chemical vapor deposition is often used to prepare carbon nanoelectrodes. This method originated from the Ewing group, which used quartz nanotubes and methane as templates and carbon sources, respectively, for vapor phase pyrolysis deposition to prepare carbon nanoelectrodes with a diameter of more than 1 micrometer. The Gogotsi and Bau groups improved this method and developed a scheme for selective deposition of carbon on the inner wall of quartz nanotubes (i.e. space-limited deposition). Although this method reduces the size of the electrode, the preparation process is complex, difficult to operate and time-consuming (≥ 1 h), which makes it difficult to meet the demand for batch production.

[0005] At present, there is almost no commercial version of nanodisc electrodes below 200 nm, so researchers with experimental needs cannot obtain them by purchase. Most methods for preparing nanoelectrodes have the problems of complex operation process, long time consumption and high cost, and it is difficult to obtain multifunctional electrodes with regular tip morphology, stable conductivity and long-term preservation. SUMMARY

[0006] Therefore, the present application aims to provide a preparation method of carbon nanoelectrode, which is convenient and low in cost, and can obtain carbon nanoelectrode with regular tip morphology, stable conductivity and long-term preservation.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A preparation method of carbon nanoelectrode comprises: under oxygen-free condition, introducing gaseous carbon source into nanotemplate, heating to obtain carbon nanoelectrode.

[0009] The nanotemplate is a nanotube with a tip.

[0010] The cross section of the nanotemplate is parallel to the horizontal line.

[0011] In the present application, the nanotemplate is made of high-temperature-resistant material, and the material of the nanotemplate is preferably quartz; the inner diameter of the tip of the nanotemplate is 10-1000 nm, i.e. the minimum diameter of the nanotemplate is 10-1000 nm; in an embodiment of the present application, the inner diameter of the tip of the nanotemplate is 10-1000 nm, and the outer diameter of the tip is greater than the inner diameter, preferably 10-1000 nm. The nanotemplate is preferably made by drawing machine.

[0012] By the method of the present application, the carbon nanoelectrode prepared has regular tip morphology consistent with the geometric morphology of the tip opening of the nanotemplate, and this morphology can be embedded in the insulating layer, so that the electrical signal and the geometric size can be one-to-one corresponding.

[0013] In the present application, the tip of the nanotemplate faces upward. The nanotemplate has two openings, i.e. upper and lower openings, and the gaseous carbon source is introduced from the lower side of the nanotemplate and discharged from the upper side.

[0014] In the present application, the gaseous carbon source comprises one or more of propane, butane, propylene and butene; in an embodiment of the present application, the gaseous carbon source is preferably petroleum gas.

[0015] In the present application, the pressure of the gaseous carbon source is 0.1-0.3 MPa, preferably 0.18-0.3 MPa; the heating temperature is 1100-1500 K, preferably 1100-1200 K, and more preferably 1100 K; and the heating time is 0.5-15 s.

[0016] The repeated growth and oxidation of carbon on the inner wall of the quartz tube is very unfavorable to the stability in the process of preparing the electrode when the pressure of the gaseous carbon source is not enough. The nanometer scale quartz will collapse and burst at high temperature of about 1300K without internal sustained growth of carbon as support. Although the quartz is resistant to high temperature, the temperature resistance of the material body and the nanometer scale decreases exponentially, resulting in a great change in the geometric morphology of the nanometer quartz tube before and after preparation, losing the significance of the nanometer tube as a template for preparing the carbon nanoelectrode, that is, using a nanometer quartz tube with a tip diameter of 50nm, the diameter of the obtained carbon nanoelectrode may be 50nm or 10nm.

[0017] The heating method is not particularly limited in the present application, and a temperature of 1100-1500K can be reached. Preferably, a butane flame gun is used for heating, and the outer flame temperature of the butane flame gun is relatively high.

[0018] In the present application, the oxygen-free condition is realized by the following ways:

[0019] A protective tube is arranged outside the nanotemplate, and inert gas is introduced into the protective tube.

[0020] The nanotemplate is made of a high-temperature resistant material.

[0021] In the present application, the flow rate of the inert gas is 20-200mL / min, preferably 25-200mL / min; and the inert gas is preferably argon.

[0022] In the present application, the cross section of the nanotemplate is parallel to the horizontal line, so that the carbon source is not oxidized again due to the possible air in the protective tube after being reduced by high-temperature thermal decomposition. In addition, the inert gas is uniformly distributed in the protective tube, so that the prepared electrode is symmetric about the center of the cone. If the cross section of the nanotemplate is arranged vertically to the horizontal line, that is, the nanotube is arranged horizontally, the symmetry of the nanoelectrode is poor, mainly manifested as thick carbon on one side and thin carbon on the other side.

[0023] In the present application, the air in the nanotemplate is discharged before the gaseous carbon source is introduced into the nanotemplate; preferably, the air in the nanotemplate is discharged by vacuumizing; and the time for vacuumizing is 3-5min.

[0024] In the present application, the material of the nanotemplate and the protective tube is quartz. The minimum diameter of the protective tube is greater than that of the quartz nanotube. In an embodiment of the present application, the protective tube is a quartz protective tube, the inner diameter is 0.5-3mm, the outer diameter is 1-4mm, and the length is 80-100mm.

[0025] The carbon nanodisk electrode can be obtained through the above method, the carbon nanodisk electrode is etched by hydrofluoric acid for different time to obtain carbon nanotaper electrodes with different sizes; and different sizes and types of metal nanoelectrodes are obtained by using the embedded carbon nanoelectrode combined with electrodeposition.

[0026] The electrocatalytic activity, electrochemical window, and anti-fouling property, and stability of the carbon nanoelectrode and the metal nanoelectrode are different, for example, the carbon nanoelectrode has high stability, a wide electrochemical window, is suitable for long-time testing in a large voltage range, or is used as a catalyst carrier, and is especially resistant to high temperature.

[0027] The shape of the carbon nanotaper electrode has a difference in orders of magnitude in mass transfer capacity and conductive area compared with the nanodisk electrode, and the carbon nanotaper electrode is suitable for being used in a case where a large reaction area is required, and the detection limit is higher than that of the nanodisk electrode with the same size, but the sample preparation amount and the test current scale are much larger than those of the nanodisk electrode, and the two belong to a progressive relationship in geometric size and are complementary in the measurement range.

[0028] At present, the carbon nanotaper electrode is relatively difficult to preserve and transport, and the best effect is achieved by preparing and using it immediately.

[0029] The beneficial effects of the technical scheme of the present application are as follows:

[0030] (1) The RG ratio (the ratio of the radius of the insulating layer to the radius of the conductive layer of the electrode) has a significant influence on the diffusion field, and the smaller the size is, the more obvious the influence is. The small RG ratio is one of the necessary conditions for the high mass transfer of the nanoelectrode, and there is almost no carbon nanoelectrode with small size and small RG ratio in the prior art.

[0031] The carbon nanoelectrode of the present application has a diameter of 10-1000 nm and a small RG ratio of about 1.1, which is the smallest in the carbon nanoelectrode and is almost unattainable by the metal nanodisk electrode prepared by other methods at present.

[0032] (2) The current nanoelectrode preparation process is complex, time-consuming, high in cost, and low in success rate. The nanoelectrode preparation platform of the present application has a perfect structure, is convenient to use, can prepare various nanoelectrodes (including but not limited to carbon nanodisk electrodes, carbon nanotaper electrodes, and metal nanoelectrodes), is easy to preserve, and has wide application. The average time consumption for preparing the carbon nanoelectrode is about 2 min per electrode, and the cost is low (2 RMB per electrode). The product has a regular tip morphology and uniform carbon distribution at the tip; the product can be preserved for a long time while maintaining good performance, the surface roughness factor is less than 1.5, and the conductive capacity local density is close to that of metal materials. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a schematic diagram of a carbon nanoelectrode preparation platform in Example 1 of the present application: vertical type.

[0034] Figure 2 is the SEM image of the carbon nanodisk electrode in Example 2 of the present application: (A) the overall view of the carbon nanodisk electrode; (B) the tip morphology of the carbon nanodisk electrode;

[0035] Figure 3 is the schematic diagram of the carbon nanodisk electrode preparation platform in Comparative Example 1 of the present application: horizontal type;

[0036] Figure 4 is the SEM image of the tip morphology of the carbon nanodisk electrode in Comparative Example 1 of the present application;

[0037] Figure 5 is the SEM image of the carbon nanodisk electrode in Example 1 of the present application: (A) the overall view of the carbon nanodisk electrode; (B) the tip morphology of the carbon nanodisk electrode;

[0038] Figure 6 is the SEM image of the embedded gold nanodisk electrode in Example 2 of the present application. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] In order to further illustrate the present application, the following examples are used for detailed description. The raw materials used in the following examples of the present application are all commercially available.

[0041] The quartz nanotube used in the embodiments of the present application is prepared by a Sutter P-2000 laser drawing machine. According to the size of the quartz tube and the running program, the quartz nanotube with a tip diameter ranging from several nanometers to several microns can be obtained. The commonly used raw material is a quartz nanotube with an inner diameter of 0.7 mm, an outer diameter of 1.0 mm and a length of 80-150 mm; the program for preparing a laser drawing machine with a tip diameter of 100 nm is: HEAT 700 PUL 4 VEL 40 DEL 130 PUL 090; adjusting DEL and PUL, quartz nanotube with different sizes can be obtained. The quartz nanotube is consistent with the diameter size of the target prepared electrode, for example, a 10 nm inner diameter is used to prepare a 10 nm diameter carbon nanodisk.

[0042] The size of the quartz protective tube can be selected in many ways. The most common size is an inner diameter of 1.6 mm, an outer diameter of 2.2 mm, a length of 80-100 mm, a maximum size of no more than an inner diameter of 3 mm, an outer diameter of 4 mm, and a minimum diameter greater than that of the quartz nanotube.

[0043] The carbon nanometer electrode preparation platform used in the embodiment of the present application is shown in Figure 1 The carbon nanometer electrode preparation platform used in the embodiment of the present application is shown in

[0044] Embodiment 1

[0045] The carbon nanometer electrode preparation method of the present embodiment uses the device in Figure 1 , and specifically includes the following steps:

[0046] (1) After the experimenter detects that the environment is well ventilated and wears an electrostatic protection device, the high-purity argon protection gas path is opened, and the argon flow rate is controlled through the rotor flowmeter (120-150 mL / min);

[0047] (2) A 10 nm inner diameter quartz nanometer cone tube is connected to the peristaltic pump tube (the interface is sealed with sealing film), and is fixed on the support loaded by the three-dimensional displacement platform. The tip of the quartz nanometer cone tube is sent into the quartz protection tube by adjusting the three-dimensional displacement platform;

[0048] (3) The three-way valve is switched to the state of connecting the peristaltic pump tube and the vacuum pump, and the vacuum pump is opened for 3 min. After the air in the quartz nanometer cone tube is exhausted, the three-way valve is switched to the state of connecting the peristaltic pump tube and the high-pressure liquefied petroleum gas, and the liquefied petroleum gas is continuously introduced, keeping the pressure at 0.3 MPa;

[0049] (4) The butane flame gun is opened towards a safe open space. After the flame is stable, the position of the flame is moved. The heating of the butane flame gun is the outer layer of the flame, and the temperature is 1100 K. The tip of the quartz nanometer cone tube is heated for 0.5-1 s, and a carbon nanometer electrode with a minimum diameter of 10 nm at the tip is obtained. The butane flame gun is immediately turned off;

[0050] (5) After the prepared carbon nanometer electrode is naturally cooled in the quartz protection tube, it is removed from the quartz protection tube by the three-dimensional displacement platform and taken off.

[0051] The method for preparing the carbon nanoelectrode of the embodiment takes 2 minutes per electrode and has low cost (2 RMB per electrode). The carbon nanodisk electrode obtained in the embodiment has a small RG ratio (ratio of radius of the electrode containing the insulating layer to radius of the conductive layer), which is 1.1. The carbon nanodisk electrode can be used immediately or embedded at the tail end in an anti-static sponge, and stored in a clean and moist (humidity of 50% to 60%) oxygen-free sealed box under the premise that the tip of the nanodisk electrode is not touched. The stored carbon nanodisk electrode can maintain good performance for more than half a year in a suitable environment, including that the tip morphology does not change, the surface roughness factor is less than 1.5, the conductive ability local density of states D Ef is 1023 cm -3 -1eV -1 , close to that of metal materials.

[0052] Embodiment 2

[0053] The method for preparing the carbon nanoelectrode of the embodiment uses the device in Figure 1 , and specifically includes the following steps:

[0054] (1) After the experimenter detects that the environment is well ventilated and wears an electrostatic protection device, the high-purity argon protection gas path is opened, and the argon flow rate is controlled through the rotor flowmeter (100-120 mL / min);

[0055] (2) A 100 nm inner diameter quartz nanotaper tube is connected to the peristaltic pump tube (the interface is sealed with sealing film), and is fixed on the support loaded by the three-dimensional displacement platform. The tip of the quartz nanotaper tube is sent into the quartz protection tube by adjusting the three-dimensional displacement platform;

[0056] (3) The three-way valve is switched to a state of communication between the peristaltic pump tube and the vacuum pump, and the vacuum pump is opened for 3 minutes. After the air in the quartz nanotaper tube is exhausted, the three-way valve is switched to a state of communication between the peristaltic pump tube and the high-pressure liquefied petroleum gas, and the liquefied petroleum gas is continuously introduced to maintain a pressure of 0.26 MPa;

[0057] (4) A butane flame gun is opened towards a safe open space. After the flame is stable, the position of the flame is moved. The heating of the butane flame gun is the outer layer of the flame, and the temperature is 1100 K. The tip of the quartz nanotaper tube is heated, and the butane flame gun is immediately turned off after 5 seconds, so that a carbon nanoelectrode with a minimum diameter of 100 nm at the tip is obtained, as shown in Figure 2

[0058] (5) After the prepared carbon nanoelectrode is naturally cooled in the quartz protection tube, it is removed from the quartz protection tube by the three-dimensional displacement platform.

[0059] ​The method for preparing the carbon nanoelectrode of the embodiment takes an average time of 2 minutes per branch and has low cost (2 RMB per branch). The carbon nanodisk electrode obtained in the embodiment has an RG ratio of about 1.1-1.2; the carbon nanodisk electrode can be used immediately or embedded at the tail end in an anti-static sponge, and placed in a clean and moist (humidity of 50%-60%) oxygen-free sealed box for storage under the premise that the tip of the nanodisk electrode is not touched. The stored carbon nanodisk electrode can maintain good performance for more than half a year in a suitable environment, including no change in the tip morphology, a surface roughness factor of less than 1.5, and a conductive ability local density close to that of metal materials.

[0060] Embodiment 3

[0061] The method for preparing the carbon nanoelectrode of the embodiment uses the device in Figure 1 , and specifically includes the following steps:

[0062] (1) After the experimenter detects that the environment is well ventilated and wears an electrostatic protection device, the high-purity argon protection gas path is opened, and the argon flow rate is controlled through the rotor flowmeter (25-40 mL / min);

[0063] (2) The 1000 nm inner diameter quartz nanotaper tube is connected to the peristaltic pump tube (the interface is sealed with a sealing film), and is fixed on the support loaded by the three-dimensional displacement platform. The tip of the quartz nanotaper tube is sent into the quartz protection tube by adjusting the three-dimensional displacement platform;

[0064] (3) The three-way valve is switched to a state of communication between the peristaltic pump tube and the vacuum pump, and the vacuum pump is opened for 3 minutes. After the air in the quartz nanotaper tube is exhausted, the three-way valve is switched to a state of communication between the peristaltic pump tube and the high-pressure liquefied petroleum gas, and the liquefied petroleum gas is continuously introduced to maintain a pressure of 0.18-0.2 MPa;

[0065] (4) The butane flame gun is opened towards a safe open space. After the flame is stable, the position of the flame is moved. The heating of the butane flame gun is the outer layer of the flame, and the temperature is 1100 K. The tip of the quartz nanotaper tube is heated for 15 seconds, and a carbon nanoelectrode with a minimum diameter of 1000 nm at the tip is obtained. The butane flame gun is immediately turned off;

[0066] (5) After the prepared carbon nanoelectrode is naturally cooled in the quartz protection tube, it is removed from the quartz protection tube by the three-dimensional displacement platform and taken off.

[0067] The method for preparing the carbon nanoelectrode of the present embodiment takes an average time of 2 minutes per electrode and has a low cost (2 RMB per electrode). The carbon nanodisk electrode obtained in the present embodiment has an RG ratio of about 1.2. The carbon nanodisk electrode can be used immediately or embedded at the tail end in an anti-static sponge, and stored in a clean and moist (humidity of 50% to 60%) oxygen-free sealed box under the premise that the tip of the nanodisk electrode is not touched. The stored carbon nanodisk electrode can maintain good performance for more than half a year in a suitable environment, including no change in the tip morphology, a surface roughness factor of less than 1.5, and a conductive ability local density close to that of a metal material.

[0068] Comparative Example 1

[0069] The method for preparing the carbon nanoelectrode of the present embodiment takes an average time of 2 minutes per electrode and has a low cost (2 RMB per electrode). The carbon nanodisk electrode obtained in the present embodiment has an RG ratio of about 1.2. The carbon nanodisk electrode can be used immediately or embedded at the tail end in an anti-static sponge, and stored in a clean and moist (humidity of 50% to 60%) oxygen-free sealed box under the premise that the tip of the nanodisk electrode is not touched. The stored carbon nanodisk electrode can maintain good performance for more than half a year in a suitable environment, including no change in the tip morphology, a surface roughness factor of less than 1.5, and a conductive ability local density close to that of a metal material.

[0070] The device in Figure 3 is used.

[0071] In order to avoid the problem of a too-thin carbon wall caused by uneven heating, the corresponding argon flow rate is reduced to 25-50 ml / min, and a long straight quartz protection tube with an inner diameter of 3 mm and an outer diameter of 4 mm is preferably used to slow down the growth and oxidation speed of the carbon layer.

[0072] During the heating process, heating is stopped every 10 seconds and vacuum is re-pumped for more than 1 minute to remove oxygen as much as possible. This process is repeated 2-3 times.

[0073] The carbon nanodisk electrode obtained in the present comparative example has a diameter of 250 nm, as shown in Figure 4 It can be seen that the carbon distribution at the tip is not uniform, especially at the tip part, and the middle part is recessed due to the absence of carbon, which affects the mass transfer rate of the carbon nanoelectrode. The CV graph has a peak value, and parameters such as the electrochemical equivalent area cannot be calculated using a theoretical model. Therefore, it cannot be applied to electrochemical imaging.

[0074] Application Example 1

[0075] The carbon nanodisk electrode obtained in Example 1 is immersed in HF (commercial original liquid) to etch the quartz wall. After immersion for 1 minute, a carbon nanotaper electrode with a taper length of about 12 μm is obtained. After immersion for 2 minutes, a carbon nanotaper electrode with a taper length of 50 μm is obtained. After immersion for 4-5 minutes, a carbon nanotaper electrode with a taper length of 100 μm is obtained, as shown in Figure 5 After immersion for 10 minutes, a carbon nanotaper electrode with a taper length of >200 μm is obtained.

[0076] Application Example 2

[0077] When preparing carbon nanodisc electrode, under the same conditions, the pressure of liquefied petroleum gas is reduced, a carbon nanoelectrode with V-shaped inwardly recessed tip can be obtained, and metal materials (including but not limited to gold, silver, platinum, ruthenium, copper, etc.) are deposited in the recessed carbon nanoelectrode by electrodeposition. The electrode filled with deposited metal materials is fixed on the carbon nanoelectrode preparation platform, and is heated to the melting point of metal nanoparticles under the protection of argon to make the structure of metal materials dense, and the corresponding embedded metal nanoelectrode is obtained, as shown in Figure 6 Au: 1 mM HAuCl4+ 0.1 M HCl, -0.5 V vs Ag / AgCl (3 M KCl), i-t electrodeposition; Ag, 1 mM AgNO3+ 0.1 M NH3·H2O, -0.3 V vs Ag / AgCl (3 M KCl); Ru, 1 mM RuCl3+ 0.1 M KCl, -0.6 V vs Ag / AgCl (3 M KCl).

[0078] The above description of disclosed embodiments enables one skilled in the art to make or use the application. Numerous modifications to these embodiments will be apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Therefore, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a carbon nanoelectrode, characterized by, The application relates to a carbon nanoelectrode and a preparation method thereof. The gaseous carbon source is introduced into a nanotemplate under an oxygen-free condition, and heating is performed to obtain the carbon nanoelectrode; The nanotemplate is a nanotube with a tip; The cross section of the nanotemplate is parallel to the horizontal line; The inner diameter of the tip of the nanotemplate is 10-1000 nm; The gaseous carbon source comprises one or more of propane, butane, propylene and butene; The pressure of the gaseous carbon source is 0.18-0.3 MPa; The heating temperature is 1100 K; The heating time is 0.5-15 s; The tip of the nanotemplate faces upwards.

2. The method of claim 1, wherein the carbon nanoelectrode is prepared by the steps of: The oxygen-free condition is realized by the following mode: A protective tube is arranged outside the nanotemplate, and an inert gas is introduced into the protective tube.

3. The method for preparing carbon nanoelectrodes according to claim 2, characterized in that, The flow rate of the inert gas is 20-200 mL / min.

4. The method for preparing carbon nanoelectrodes according to claim 1, characterized in that, The material of the nanotemplate and the protective tube is quartz.

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