Spiral BDD electrode and preparation method and application thereof

Abstract

The invention discloses a spiral type BDD electrode and a preparation method and application thereof, and belongs to the field of electrode materials.The preparation method comprises the steps that firstly, pretreatment is conducted to obtain a spiral type silicon rod, then a BDD film is deposited through an HFCVD method, and the obtained spiral type BDD electrode is made into a row reactor. The preparation technology is simple, the cost is low, and safety is high; through theoretical calculation, the prepared spiral BDD row rod-shaped electrode shows high selectivity, high stability and high sensitivity when being used for treating organic molecules in wastewater, and has a wide application prospect in the field of wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the field of electrode materials, and particularly to a spiral BDD electrode, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of water treatment, the BDD electrode (i.e., boron-doped diamond electrode) is a commonly used electrochemical material with excellent physical and chemical properties. At present, the commonly used preparation method of the BDD electrode is mainly the chemical vapor deposition method (CVD method). At present, when the BDD electrode is used for wastewater treatment, especially for treating organic molecules in wastewater, there is still a large room for improvement in terms of selectivity, stability, and sensitivity. Summary of the Invention

[0003] One of the purposes of the present invention is to provide a preparation method of a spiral BDD electrode to solve the above problems.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A preparation method of a spiral BDD electrode includes the following steps; (1) Pretreatment: Using a silicon rod as a substrate material, first perform pretreatment on the silicon rod. The pretreatment method is to form spiral lines on the surface of the silicon rod to obtain a spiral silicon rod; Appropriately pretreating the Si substrate before deposition, the mechanical damage and defects formed can provide the high free energy position required for nucleation, effectively reducing the free energy of nucleation; (2) Depositing a BDD film by the HFCVD method: Using the spiral silicon rod obtained after the pretreatment in step (1) as a substrate, depositing a BDD film. The deposition atmosphere uses CH4 as a carbon source, B2H6 as a boron source, and hydrogen as an auxiliary gas, which is divided into three stages in sequence: 1) Tantalum wire carbonization treatment stage; 2) Diamond film nucleation stage; 3) Diamond film growth stage.

[0005] Tantalum carbide has a higher melting point and can provide a higher temperature compared to the tantalum wire before carbonization treatment; at the same time, overheating the tantalum wire will cause it to deform, thereby destroying the uniform thermal field; therefore, it is preferably to carbonize the tantalum wire before deposition to carbonize it into tougher tantalum carbide.

[0006] As a preferred technical solution, in step (1), the size of the spiral lines is: spiral lines with a height of 47 - 53 mm, a spiral coil radius of 1 - 1.5 mm, a spiral line radius of 0.8 - 0.85 mm, 4 - 5 turns, and a pitch of 15 - 20 mm.

[0007] As a preferred technical solution, in step (1), the pretreatment further includes embedding diamond seeds on the surface of the spiral silicon rod, and then performing deposition.

[0008] As a further preferred technical solution, the method for embedding diamond seeds on the surface of the spiral silicon rod is as follows: First, grind the growth surface of the spiral silicon rod with diamond micropowder having a particle size of 0.9 - 1.1 μm for 3 - 5 min, and then perform ultrasonic treatment.

[0009] As a preferred technical solution, in step (2), the treatment method in the tantalum wire carbonization treatment stage is as follows: Place 6 - 8 tantalum wires around the substrate to completely cover it, then pump the chamber pressure to below 0.1 Pa, introduce methane and hydrogen, adjust through a pump to maintain the chamber pressure at 3.0 kPa, the carbon source concentration is 4.7 - 5.3 vol.%, the total gas flow rate is 380 - 420 sccm, gradually increase the power to 0.75 - 0.85 kW / wire, and then perform carbonization for 28 - 32 min.

[0010] As a preferred technical solution, in step (2), the treatment method in the diamond thin film nucleation stage is as follows: Raise the substrate table to a distance of 7.5 - 8.5 mm from the hot wire, then rotate the substrate table at a speed of 9 - 11 rpm, the carbon source concentration is 4.7 - 5.3 vol.%, the total gas flow rate is 380 - 420 sccm; subsequently, gradually increase the power to 1.1 - 1.3 kW / wire, the substrate temperature is 850 - 900 °C, and this process is maintained for 50 - 70 min.

[0011] As a preferred technical solution, in step (2), the treatment method in the diamond thin film growth stage is as follows: When maintaining the wire - substrate distance Df - s at 7.5 - 8.5 mm, introduce diborane as the boron source into the chamber, the carbon source concentration is 2.8 - 3.2 vol.%, the boron source concentration is 7400 - 7600 ppm, the total gas flow rate is 380 - 420 sccm, adjust the equipment power to 1.4 - 1.6 kW / wire, the substrate temperature is 840 - 860 °C, and perform thin film growth for 450 - 500 min to obtain the product.

[0012] The second object of the present invention is to provide a spiral BDD electrode prepared by the above - mentioned method.

[0013] The third object of the present invention is to provide a continuous - row reactor made of the above - mentioned spiral BDD electrode. The continuous - row reactor includes a substrate, and several of the spiral BDD electrodes are arranged on the substrate.

[0014] Preferably, the substrate is a copper substrate, and preferably, the spiral BDD electrodes are arranged at equal intervals; by inserting the spiral electrodes into the copper substrate, the continuous reactor is convenient for disassembly and replacement, reducing the maintenance cost. In the case of the conventional sheet electrode, if the middle part falls off, corrodes, etc., only the whole replacement can be carried out, with a higher cost.

[0015] The fourth object of the present invention is to provide an application of the spiral BDD electrode prepared by the above method, that is, for wastewater treatment.

[0016] Compared with the prior art, the advantages of the present invention are as follows: the preparation process of the present invention is simple, with low cost and high safety; through theoretical calculation, the prepared spiral BDD continuous rod-shaped electrode can change the flow trend of the waste liquid and improve the conversion efficiency, having a broad application prospect in the field of wastewater treatment. Description of the Drawings

[0017] Figure 1 Structural diagram of the spiral silicon rod of Embodiment 1 of the present invention; Figure 2 Schematic diagram of the hot wire chemical vapor deposition principle of Embodiment 1 of the present invention; Figure 3 Raman spectrum diagram of Embodiment 2 of the present invention; Figure 4 XRD spectrum diagram of Embodiment 2 of the present invention; Figure 5 Schematic diagram of the continuous reactor of Embodiment 3 of the present invention; Figure 6 Schematic diagram of the reaction tank body of Embodiment 3 of the present invention; Figure 7 Flow streamline diagram of the conventional sheet electrode - 40 L / h - 4 mm of Embodiment 3 of the present invention; Figure 8 Flow velocity streamline diagram of the spiral electrode - 40 L / h - 4 mm prepared in Embodiment 1 of the present invention; Figure 9 Velocity contour diagram of the conventional sheet electrode flowing through the surface of Embodiment 3 of the present invention; Figure 10 Velocity contour diagram of the spiral electrode flowing through the surface prepared in Embodiment 1 of the present invention. Detailed Description of the Invention

[0018] The present invention will be further described below with reference to the accompanying drawings.

[0019] Embodiment 1:

[0020] A spiral BDD electrode, the preparation method thereof includes the following steps: 1.1 Pretreatment The substrate material for preparing the BDD-coated electrode is a helical silicon rod. The main body is a cylinder with a height of 50 mm and a radius of 0.0014 mm. Helical grooves with a height of 50 mm, a helical coil radius of 1.25 mm, a helical line radius of 0.83 mm, 3 turns, and a pitch of 17 mm are added to the edges in four opposite directions of the cylinder, as Figure 1 shown; The substrate growth surface is polished with diamond micropowder (1 μm) for 3 - 5 min, and then the diamond micropowder in absolute ethanol is ultrasonically treated for 30 min to embed a certain number of diamonds as "seed crystals" on the surface of the Si substrate, so as to reduce the nucleation time and improve the uniformity of the BDD-coated electrode; finally, the diamond powder floating on the substrate surface is washed with absolute ethanol and dried for use; 1.2 Preparation of silicon-based BDD-coated electrode by HFCVD method It is prepared by using the HF-650 CVD deposition device developed by Beijing Taikenuo Company, as Figure 2 shown, which is mainly composed of a vacuum system, a frame, a substrate table lifting mechanism, a reaction chamber, a hot wire power supply, a reaction gas supply system, an electrical control system, etc. This equipment can uniformly deposit 6-inch high-purity and highly conductive BDD electrodes on Si, graphite, Nb / Mo metal transition layers, and carbon cloth substrates; A helical BDD rod-shaped electrode is prepared on the HFCVD equipment. The substrate is the helical silicon substrate prepared in step 1.1. CH4 is used as the carbon source, B2H6 is used as the boron source, and hydrogen is used as the auxiliary gas in the deposition atmosphere; the growth process parameters are a pressure of 2.5 - 2.6 kPa and a total gas flux of 400 SCCM; the hot wire used in the device is a tantalum wire with a diameter of 0.6 mm, and the power is controlled by regulating the power supply, and then the temperature of the tantalum wire is controlled; 7 wires are arranged during the film growth, the power is adjusted to 1.5 kW / wire, the temperature of the tantalum wire is controlled at about 2100 °C, the wire-substrate distance Df-s is 8 mm, and the substrate growth temperature is 850 - 900 °C; the film growth process is mainly divided into three stages: 1.2.1 Tantalum wire carbonization treatment stage Seven tantalum wires are placed around the substrate to completely cover it to ensure uniform distribution of the thermal temperature field; the chamber pressure is pumped to below 0.1 Pa, methane and hydrogen are introduced, and the chamber pressure is maintained at about 3.0 kPa by adjusting with a pump; the power is gradually increased to 0.8 kW / wire, and then carbonized for 30 min; 1.2.2 Diamond film nucleation stage The substrate table is raised to a position about 8 mm away from the hot wire, and then the substrate table is rotated at a speed of 10 rpm to make the surface heat conduction uniform, so that the growth and nucleation are more uniform, and the substrate table continues to rotate stably in the subsequent growth stage; then the power is gradually increased to 1.2 kW / wire, and this process is maintained for 1 h; 1.2.3 Growth Stages of Diamond Films After the nucleation stage, the formal growth stage (8 h) begins: When maintaining the distance between the filament and the substrate Df-s at 8 mm, diborane as the boron source is introduced into the chamber, and the equipment power is adjusted to 1.5 kW / filament; at this time, the performance of the hot filament is more stable, the power supply power basically no longer changes, and the film begins to grow; The optimal process parameters for the above three stages are shown in Table 1 below: Table 1 Optimal Process Parameters for Deposition by HFCVD Method

[0021] Through the above steps, a spiral BDD electrode is prepared.

[0022] Example 2:

[0023] Characterization of Spiral Silicon-based BDD Coated Electrodes The surface morphology, purity, and crystallinity of the spiral silicon-based BDD electrode prepared in Example 1 are determined by various characterization and testing methods such as SEM morphology, Raman spectra, and XRD patterns.

[0024] 2.1 Raman Spectroscopy Measurement of Spiral Silicon-based BDD Coated Electrodes The Raman spectrum is as Figure 3 shown. From Figure 3 it can be determined that the sharp peak at 1332 cm -1 is the characteristic peak of diamond, and two vibration characteristic peaks appear near 500 cm -1 and 1200 cm -1 , representing B-B bonds and B-C bonds respectively; obviously, it is observed that there is no characteristic peak of sp2 carbon near 1580 cm -1 and no D peak of amorphous carbon is seen in the range of 1450 - 1700 cm-1, indicating that the BDD film has high crystallinity and high purity.

[0025] 2.2 XRD Measurement of Spiral Silicon-based BDD Coated Electrodes X-ray diffraction analysis can help study the crystal orientation and crystallinity of BDD; the performance of BDD in treating wastewater is significantly affected by the crystal orientation, and boron doping mainly exists in the grains with (111) orientation. The diamond film dominates the 111 orientation and exhibits excellent electrocatalytic performance in wastewater treatment. The XRD pattern of BDD is measured using the grazing incidence XRD mode, and the measurement results are shown in Figure 4, all diffraction peaks can be found in JCPDS Card No. 99 - 0043. The (111), (220), and (311) planes of diamond correspond to diffraction peaks at 43.93°, 75.3°, and 91.50° respectively; it is particularly noteworthy that in the sample, BDD exhibits an obvious (111) peak. Through the analysis of scanning electron microscopy technology, it can be known that BDD mainly grows along the (111) plane as the main growth direction; this indicates that the BDD thin film prepared in Example 1 is highly pure and well - crystallized.

[0026] Example 3:

[0027] 3.1 Preparation of the continuous - row reactor On a copper substrate with a length of 400 mm, a width of 17 mm, and a height of 10 mm, pores with a radius of 2.5 mm and a depth of 5 mm are drilled, and the distance between adjacent pores is 0.1 mm; then the spiral BDD rod - shaped electrode prepared in Example 1 is inserted into the pores on the reactor, and the assembly of the continuous - row reactor is completed, as Figure 5 shown; 3.2 Assembly of the reaction tank body The length of the tank body is 400 mm, the width is 17 mm, and the height is 150 mm; the tank body is made of a 1 - mm - thick stainless - steel plate, which can be used as the cathode for the electrolysis reaction; on the left side of the reaction tank body, an inlet with a radius of 2.5 mm is set 5 mm away from the copper substrate, and on the right side of the reaction tank body, an outlet with a radius of 2.5 mm is set 5 mm away from the upper - layer stainless - steel encapsulation plate, so that the sewage enters and exits the cavity from low to high, as Figure 6 shown; 3.3 Influence of the electrode on the fluid movement trend: Using the k - ω turbulence steady - state model simulation calculation function of computational fluid dynamics simulation software, through the single - variable simulation test results (as Figure 7 and Figure 8 shown), it can be known that when the fluid flow rate is 40 L / h and the distance between the cathode and the anode is 4 mm, a large vortex will be generated when the fluid flows through the spiral electrode of Example 1 of the present invention, so that the fluid can be electrolytically treated multiple times in the electrolytic cell; while for a flat - sheet electrode with a thickness of 5 mm (including the substrate), no vortex will be generated, and the fluid will flow out of the electrolytic cell only after staying in the electrolytic cell for a short time; 3.4 Experiment on the conversion efficiency of the electrode: Using the k - ω turbulence steady - state model simulation calculation function of computational fluid dynamics simulation software, through the single - variable simulation test results (as Figure 7 and Figure 8 shown), under the condition that the fluid flow rate is 40 L / h and the distance between the cathode and the anode is 4 mm, the velocity cloud map of the fluid flowing through the anode surface (as Figure 9 and Figure 10As can be seen from the figure (not shown), when the fluid flows through the flat sheet electrode with a thickness of 5 mm (including the substrate), it tends to be bounced off; while when it flows through the spiral electrode prepared in Example 1, the fluid will flow along the thread direction and be closer to the anode surface, so better conversion efficiency can be obtained.

[0028] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a spiral BDD electrode, characterized in that: The method comprises the following steps: (1) Pretreatment: using a silicon rod as a substrate material, the silicon rod is first pretreated, wherein the pretreatment method is to form spiral patterns on the surface of the silicon rod to obtain a spiral silicon rod; (2) Deposition of BDD film by HFCVD method: The spiral silicon rod obtained after pretreatment in step (1) is used as the substrate to deposit the BDD film. The deposition atmosphere is CH4 as the carbon source, B2H6 as the boron source, and hydrogen as the auxiliary gas. It is divided into three stages, namely: 1) Tantalum wire carbonization treatment stage; 2) Diamond film nucleation stage; 3) Diamond film growth stage.

2. The method according to claim 1, characterized in that In step (1), the dimensions of the spiral pattern are: height 47-53 mm, spiral coil radius 1-1.5 mm, spiral line radius 0.8-0.85 mm, number of turns 4-5, and spiral pitch 15-20 mm.

3. The method according to claim 1, characterized in that In step (1), the pretreatment further includes embedding diamond seeds on the surface of the spiral silicon rod and then performing deposition.

4. The method according to claim 3, characterized in that The method for embedding diamond seeds on the surface of the spiral silicon rod is: firstly grind the growth surface of the spiral silicon rod for 3 to 5 minutes with diamond micro powder with a particle size of 0.9-1.1 μm, and then perform ultrasonic treatment.

5. The method according to claim 1, characterized in that In step (2), the treatment method of the tantalum wire carbonization stage is: 6-8 tantalum wires are placed around the substrate to completely cover it, and then the chamber pressure is pumped down to below 0.1 Pa. Methane and hydrogen are introduced and the chamber pressure is maintained at 3.0 kPa by pump adjustment. The carbon source concentration is 4.7-5.3 vol.%, the total gas flow rate is 380-420 sccm, and the power is gradually increased to 0.75-0.85 kW / wire, followed by carbonization for 28-32 min.

6. The method according to claim 1, characterized in that In step (2), the processing method of the diamond film nucleation stage is: Place the substrate stage at a distance of 7.5-8.5 mm from the hot wire, then rotate the substrate stage at 9-11 rpm, with a carbon source concentration of 4.7-5.3 vol.%, and a total gas flow rate of 380-420 sccm; then gradually increase the power to 1.1-1.3 kW / filament, with a substrate temperature of 850-900°C, and maintain this process for 50-70 min.

7. The method according to claim 1, characterized in that In step (2), the processing method of the diamond film growth stage is: While maintaining the wire-substrate distance Df-s at 7.5-8.5 mm, introduce boron source diborane into the chamber, the carbon source concentration is 2.8-3.2 vol.%, the boron source concentration is 7400-7600 pmm, the total gas flow rate is 380-420 sccm, the equipment power is adjusted to 1.4-1.6 kW / wire, the substrate temperature is 840-860°C, and the film is grown for 450-500 min.

8. The spiral BDD electrode prepared by the method according to claims 1 to 7.

9. A series reactor made of the spiral BDD electrode according to claim 8, characterized in that: The tandem reactor comprises a substrate, on which a plurality of the spiral BDD electrodes are arranged.

10. Application of the spiral BDD electrode prepared by the method according to claims 1 to 7, characterized in that: Used for wastewater treatment.

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