HIGH-SPECIFIC SURFACE AREA AND SUPER-HYDROPHILIC GRADIENT BORON-DOPED DIAMOND ELECTRODE, METHOD FOR PREPARING SAME AND APPLICATION THEREOF

Abstract

A high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode is disclosed. The electrode directly uses a substrate as an electrode matrix; or a transition layer is disposed on a surface of the substrate and used as the electrode matrix. A gradient boron-doped diamond layer is disposed on a surface of the electrode matrix, and a contact angle of the electrode is θ<40°. The gradient boron-doped diamond layer includes: a gradient boron-doped diamond bottom layer, a gradient boron-doped diamond middle layer, and a gradient boron-doped diamond top layer, a boron content of which gradually increases, so the gradient boron-doped diamond layer has high adhesion, high corrosion resistance, and high catalytic activity. The high-content boron of the top layer is combined with a one-time high-temperature treatment, so the gradient boron-doped diamond electrode has a high-specific surface area and superhydrophilicity, which may greatly improve the mineralization and degradation efficiency of the electrode.

Claims

1. A high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode, wherein in the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode, a substrate is directly used as an electrode matrix; or a transition layer is disposed on a surface of the substrate and used as the electrode matrix, and a gradient boron-doped diamond layer is disposed on a surface of the electrode matrix, and wherein a contact angle θ of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode is less than 40°.

2. The high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 1, wherein the gradient boron-doped diamond layer comprises, in a succession from a bottom to a top, a gradient boron-doped diamond bottom layer, a gradient boron-doped diamond middle layer, and a gradient boron-doped diamond top layer, and boron contents of the gradient boron-doped diamond bottom layer, the gradient boron-doped diamond middle layer, and the gradient boron-doped diamond top layer gradually increase; wherein in the gradient boron-doped diamond bottom layer, an atomic ratio B/C is 3333 ppm-33333 ppm; in the gradient boron-doped diamond middle layer, an atomic ratio B/C is 10000 ppm-33333 ppm; and in the gradient boron-doped diamond top layer, an atomic ratio B/C is 16666 ppm-50000 ppm.

3. The high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 2, wherein the gradient boron-doped diamond layer is uniformly deposited on the surface of the substrate by a chemical vapor deposition, the gradient boron-doped diamond layer has a thickness of 5 μm-2 mm; and a thickness of the gradient boron-doped diamond middle layer accounts for 50/6-90% of the thickness of the gradient boron-doped diamond layer.

4. The high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 1, wherein a substrate material is selected from one of metals nickel, niobium, tantalum, copper, titanium, cobalt, tungsten, molybdenum, chromium, and iron or one of an alloy of the nickel, an alloy of niobium, an alloy of tantalum, an alloy of copper, an alloy of titanium, an alloy of cobalt, an alloy of tungsten, an alloy of molybdenum, an alloy of chromium, and an alloy of iron; or an electrode substrate material is selected from one of ceramics Al.sub.2O.sub.3, ZrO.sub.2, SiC, Si.sub.3N.sub.4, BN, B.sub.4C, AlN, TiB.sub.2, TiN, WC, Cr.sub.7C.sub.3, Ti.sub.2GeC, Ti.sub.2AlC and Ti.sub.2AlN, Ti.sub.3SiC.sub.2, Ti.sub.3GeC.sub.2, Ti.sub.3AlC.sub.2, Ti.sub.4AlC.sub.3, and BaPO.sub.3, or a doped ceramic of the Al.sub.2O.sub.3, a doped ceramic of the ZrO.sub.2, a doped ceramic of the SiC, a doped ceramic of the Si.sub.3N.sub.4, a doped ceramic of the BN, a doped ceramic of the B.sub.4C, a doped ceramic of the AlN, a doped ceramic of the TiB.sub.2, a doped ceramic of the TiN, a doped ceramic of the WC, a doped ceramic of the Cr.sub.7C.sub.3, a doped ceramic of the Ti.sub.2GeC, a doped ceramic of the Ti.sub.2AlC and the Ti.sub.2AlN, a doped ceramic of the Ti.sub.3SiC.sub.2, a doped ceramic of the Ti.sub.3GeC.sub.2, a doped ceramic of the Ti.sub.3AlC.sub.2, a doped ceramic of the Ti.sub.4AlC.sub.3, and a doped ceramic of the BaPO.sub.3; or the substrate material is selected from one of composite materials comprising the metals and the ceramics, or the substrate material is selected from a diamond or Si; the substrate is in a shape of a solid cylinder, a hollow cylinder, or a plate; and the substrate is in a three-dimensional continuous network structure, a two-dimensional continuous network structures, or a two-dimensional closed plate structure.

5. The high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 1, wherein a transition layer material is selected from at least one of titanium, tungsten, molybdenum, chromium, tantalum, platinum, silver, aluminum, copper, and silicon, and the transition layer has a thickness of 50 nm-10 μm.

6. The high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 1, wherein micropores and/or spikes are distributed on a surface of the gradient boron-doped diamond layer, and wherein the micropores have a diameter of 500 nm-0.5 mm, and the spikes have a diameter of 1 μm-30 μm.

7. A method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 1, comprising the following steps: step I: pretreating the electrode matrix putting the electrode matrix into a suspension containing nanocrystalline and/or microcrystalline diamond mixed particles; carrying out an ultrasonic treatment and drying; obtaining the electrode matrix with nanocrystalline and/or microcrystalline diamonds adsorbed to the surface of the electrode matrix; step II: depositing the gradient boron-doped diamond layer putting the electrode matrix obtained in the step I into a chemical vapor deposition reactor, and carrying out a three-stage deposition on the surface of the electrode matrix to obtain the gradient boron-doped diamond layer, wherein in a first-stage deposition process, a carbon-containing gas accounts for 1%-5% of a mass flow rate of all gasses in the chemical vapor deposition reactor, and a boron-containing gas accounts for 0.005%-0.05% of the mass flow rate of all the gasses in the chemical vapor deposition reactor; in a second-stage deposition process, the carbon-containing gas accounts for 1%-5% of the mass flow rate of all the gasses in the chemical vapor deposition reactor, and the boron-containing gas accounts for 0.015%-0.05% of the mass flow rate of all the gasses in the chemical vapor deposition reactor; and in a third-stage deposition process, the carbon-containing gas accounts for 1%-5% of the mass flow rate of all the gasses in the chemical vapor deposition reactor, and the boron-containing gas accounts for 0.025%-0.075% of the mass flow rate of all the gasses in the chemical vapor deposition reactor; and step III: performing a high-temperature treatment carrying out a heat treatment on the electrode matrix with the gradient boron-doped diamond layer at a temperature of 400° C.-1200° C. for 5 min-110 min, wherein the heat treatment is carried out under a pressure of 10 Pa-10.sup.5 Pa in an etching atmosphere.

8. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 7, wherein in the step II, the first-stage deposition process is carried out at a temperature of 600° C.-1000° C. under a pressure of 10.sup.3 Pa-10.sup.4 Pa for 1 h-3 h; the second-stage deposition process is carried out at a temperature of 600° C.-1000° C. under a pressure of 10.sup.3 Pa-10.sup.4 Pa for 3 h-48 h; and the third-stage deposition process is carried out at a temperature of 600° C.-1000° C. under a pressure of 10.sup.3 Pa-10.sup.4 Pa for 1 h-12 h.

9. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 7, wherein in the step III, the heat treatment is carried out at the temperature of 500° C.-800° C. for 15 min-40 min.

10. A method of an application of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 1, wherein the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode is applied to an electrochemical oxidation treatment of a wastewater, a sterilization, and an organic pollutant removal of various types of a daily water, water purifiers, or electrochemical biosensors.

11. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 7, wherein the gradient boron-doped diamond layer comprises, in a succession from a bottom to a top, a gradient boron-doped diamond bottom layer, a gradient boron-doped diamond middle layer, and a gradient boron-doped diamond top layer, and boron contents of the gradient boron-doped diamond bottom layer, the gradient boron-doped diamond middle layer, and the gradient boron-doped diamond top layer gradually increase; wherein in the gradient boron-doped diamond bottom layer, an atomic ratio B/C is 3333 ppm-33333 ppm; in the gradient boron-doped diamond middle layer, an atomic ratio B/C is 10000 ppm-33333 ppm; and in the gradient boron-doped diamond top layer, an atomic ratio B/C is 16666 ppm-50000 ppm.

12. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 11, wherein the gradient boron-doped diamond layer is uniformly deposited on the surface of the substrate by a chemical vapor deposition, the gradient boron-doped diamond layer has a thickness of 5 μm-2 mm; and a thickness of the gradient boron-doped diamond middle layer accounts for 50%-90% of the thickness of the gradient boron-doped diamond layer.

13. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 7, wherein a substrate material is selected from one of metals nickel, niobium, tantalum, copper, titanium, cobalt, tungsten, molybdenum, chromium, and iron or one of an alloy of the nickel, an alloy of niobium, an alloy of tantalum, an alloy of copper, an alloy of titanium, an alloy of cobalt, an alloy of tungsten, an alloy of molybdenum, an alloy of chromium, and an alloy of iron; or an electrode substrate material is selected from one of ceramics Al.sub.2O.sub.3, ZrO.sub.2, SiC, Si.sub.3N.sub.4, BN, B.sub.4C, AlN, TiB.sub.2, TiN, WC, Cr.sub.7C.sub.3, Ti.sub.2GeC, Ti.sub.2AlC and Ti.sub.2AlN, Ti.sub.3SiC.sub.2, Ti.sub.3GeC.sub.2, Ti.sub.3AlC.sub.2, Ti.sub.4AlC.sub.3, and BaPO.sub.3, or a doped ceramic of the Al.sub.2O.sub.3, a doped ceramic of the ZrO.sub.2, a doped ceramic of the SiC, a doped ceramic of the Si.sub.3N.sub.4, a doped ceramic of the BN, a doped ceramic of the B.sub.4C, a doped ceramic of the AlN, a doped ceramic of the TiB.sub.2, a doped ceramic of the TiN, a doped ceramic of the WC, a doped ceramic of the Cr.sub.7C.sub.3, a doped ceramic of the Ti.sub.2GeC, a doped ceramic of the Ti.sub.2AlC and the Ti.sub.2AlN, a doped ceramic of the Ti.sub.3SiC.sub.2, a doped ceramic of the Ti.sub.6GeC.sub.2, a doped ceramic of the Ti.sub.3AlC.sub.2, a doped ceramic of the Ti.sub.4AlC.sub.3, and a doped ceramic of the BaPO.sub.3; or the substrate material is selected from one of composite materials comprising the metals and the ceramics, or the substrate material is selected from a diamond or Si; the substrate is in a shape of a solid cylinder, a hollow cylinder, or a plate; and the substrate is in a three-dimensional continuous network structure, a two-dimensional continuous network structure, or a two-dimensional closed plate structure.

14. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 7, wherein a transition layer material is selected from at least one of titanium, tungsten, molybdenum, chromium, tantalum, platinum, silver, aluminum, copper, and silicon, and the transition layer has a thickness of 50 nm-10 μm.

15. The method for preparing the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 7, wherein micropores and/or spikes are distributed on a surface of the gradient boron-doped diamond layer, and wherein the micropores have a diameter of 500 nm-0.5 mm, and the spikes have a diameter of 1 μm-30 μm.

16. The method of the application of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 10, wherein the gradient boron-doped diamond layer comprises, in a succession from a bottom to a top, a gradient boron-doped diamond bottom layer, a gradient boron-doped diamond middle layer, and a gradient boron-doped diamond top layer, and boron contents of the gradient boron-doped diamond bottom layer, the gradient boron-doped diamond middle layer, and the gradient boron-doped diamond top layer gradually increase; wherein in the gradient boron-doped diamond bottom layer, an atomic ratio B/C is 3333 ppm-33333 ppm; in the gradient boron-doped diamond middle layer, an atomic ratio B/C is 10000 ppm-33333 ppm; and in the gradient boron-doped diamond top layer, an atomic ratio B/C is 16666 ppm-50000 ppm.

17. The method of the application of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 16, wherein the gradient boron-doped diamond layer is uniformly deposited on the surface of the substrate by a chemical vapor deposition, the gradient boron-doped diamond layer has a thickness of 5 μm-2 mm; and a thickness of the gradient boron-doped diamond middle layer accounts for 50/0-90% of the thickness of the gradient boron-doped diamond layer.

18. The method of the application of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 10, wherein a substrate material is selected from one of metals nickel, niobium, tantalum, copper, titanium, cobalt, tungsten, molybdenum, chromium, and iron or one of an alloy of the nickel, an alloy of niobium, an alloy of tantalum, an alloy of copper, an alloy of titanium, an alloy of cobalt, an alloy of tungsten, an alloy of molybdenum, an alloy of chromium, and an alloy of iron; or an electrode substrate material is selected from one of ceramics Al.sub.2O.sub.3, ZrO.sub.2, SiC, Si.sub.3N.sub.4, BN, B.sub.4C, AlN, TiB.sub.2, TiN, WC, Cr.sub.7C.sub.3, Ti.sub.2GeC, Ti.sub.2AlC and Ti.sub.2AlN, Ti.sub.3SiC.sub.2, Ti.sub.3GeC.sub.2, Ti.sub.3AlC.sub.2, Ti.sub.4AlC.sub.3, and BaPO.sub.3, or a doped ceramic of the Al.sub.2O.sub.3, a doped ceramic of the ZrO.sub.2, a doped ceramic of the SiC, a doped ceramic of the Si.sub.3N.sub.4, a doped ceramic of the BN, a doped ceramic of the B.sub.4C, a doped ceramic of the AlN, a doped ceramic of the TiB.sub.2, a doped ceramic of the TiN, a doped ceramic of the WC, a doped ceramic of the Cr.sub.7C.sub.3, a doped ceramic of the Ti.sub.2GeC, a doped ceramic of the Ti.sub.2AlC and the Ti.sub.2AlN, a doped ceramic of the Ti.sub.3SiC.sub.2, a doped ceramic of the Ti.sub.3GeC.sub.2, a doped ceramic of the Ti.sub.3AlC.sub.2, a doped ceramic of the Ti.sub.4AlC.sub.3, and a doped ceramic of the BaPO.sub.3; or the substrate material is selected from one of composite materials comprising the metals and the ceramics, or the substrate material is selected from a diamond or Si; the substrate is in a shape of a solid cylinder, a hollow cylinder, or a plate; and the substrate is in a three-dimensional continuous network structure, a two-dimensional continuous network structure, or a two-dimensional closed plate structure.

19. The method of the application of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 10, wherein a transition layer material is selected from at least one of titanium, tungsten, molybdenum, chromium, tantalum, platinum, silver, aluminum, copper, and silicon, and the transition layer has a thickness of 50 nm-10 μm.

20. The method of the application of the high-specific surface area and super-hydrophilic gradient boron-doped diamond electrode according to claim 10, wherein micropores and/or spikes are distributed on a surface of the gradient boron-doped diamond layer, and wherein the micropores have a diameter of 500 nm-0.5 mm, and the spikes have a diameter of 1 μm-30 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 shows SEM images of a BDD electrode material prepared in Embodiment 1 before and after high-temperature treatment. The left image is the SEM image of the BDD electrode material before the high-temperature treatment, and the right image is the SEM image of the finished BDD electrode material after the high-temperature treatment.

[0056] FIG. 2 shows images showing hydrophilicity of the BDD electrode material prepared in Embodiment 1 before and after the high-temperature treatment. The left image shows the room-temperature contact angle of the BDD electrode material before the high-temperature treatment, and the right image shows the room-temperature contact angle of the BDD electrode material after the high-temperature treatment.

[0057] FIGS. 3A-3B show degradation efficiency curves of reactive blue 19 by the BDD electrode material prepared in Embodiment 1 before and after the high-temperature treatment: FIG. 3A shows a color remove versus time curve; and FIG. 3B shows a COD (chemical oxygen demand) remove versus time curve.

[0058] FIG. 4 shows SEM images of a BDD electrode material prepared in Embodiment 2 before and after high-temperature treatment. The left image is the SEM image of the BDD electrode material before the high-temperature treatment, and the right image is the SEM image of the finished BDD electrode material after the high-temperature treatment.

[0059] FIG. 5 shows images showing Raman spectra of the BDD electrode material prepared in Embodiment 2 before and after the high-temperature treatment. The lower curve is the Raman spectrum of the BDD electrode material before the high-temperature treatment, and the upper curve is the Raman spectrum of the finished BDD electrode material after the high-temperature treatment.

[0060] FIG. 6 shows images showing hydrophilicity of the BDD electrode material prepared in Embodiment 2 before and after the high-temperature treatment. The left image shows the room-temperature contact angle of the BDD electrode material before the high-temperature treatment, and the right image shows the room-temperature contact angle of the BDD electrode material after the high-temperature treatment.

[0061] FIG. 7 shows SEM images of a BDD electrode material prepared in Embodiment 3 before and after high-temperature treatment. The left image is the SEM image of the BDD electrode material before the high-temperature treatment, and the right image is the SEM image of the finished BDD electrode material after the high-temperature treatment.

[0062] FIG. 8 shows images of surface morphology of the finished BDD electrode material prepared in Embodiment 3 before and after 300 hours of accelerated life testing. The left image shows the morphology of the material before the 300 hours of accelerated life testing, and the right image shows the morphology of the material after the 300 hours of accelerated life testing.

[0063] FIG. 9 shows degradation efficiency curves of organic wastewater by the BDD electrode material prepared in Embodiment 3 before and after the high-temperature treatment.

[0064] FIG. 10 shows a structure of a water purifier in Embodiment 3: 1, housing; 2, separator; 3, metal electrode; 4, BDD electrode; 5, conductive clip; 6, sealed insulator; and 7, wire.

[0065] FIG. 11 shows a room-temperature contact angle of the finished BDD electrode material prepared in Comparative Embodiment 1.

[0066] FIG. 12 shows an SEM image of the finished BDD electrode material prepared in Comparative Embodiment 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiment 1

[0067] BDD Electrode Material with Ti Substrate.

[0068] This BDD electrode used titanium (Ti) as the substrate for BDD deposition. This is because it is easy to form a carbide transition layer on the surface of Ti, and Ti has a thermal expansion coefficient matched with that of C, so it is easy to form a BDD thin film with good bonding. Both Ti and C have good corrosion resistance and stability. The preparation process is as follows.

[0069] 2. Preparation of BDD Material.

[0070] 2.1 Pretreatment of Substrate Material.

[0071] First, Ti was cut into a plate-like sample with a size of 30×20×2 mm, which was polished with 600-grit, 800-grit and 1000-grit metallographic abrasive papers. The polished Ti substrate was immersed in acetone (CH.sub.3COCH.sub.3) and anhydrous ethanol (C.sub.2H.sub.5OH) and subjected to ultrasonic oscillation for 10 min. Then, the Ti substrate was placed in a nano-diamond suspension, and seed crystals were grown for 30 min under the action of ultrasound to enhance the nucleation. Finally, the Ti substrate was rinsed with deionized ultrapure water and dried for later use.

[0072] 2.2 Deposition of BDD Thin Film.

[0073] The hot filament used in this example was φ0.5 mm straight tungsten wire, which completely covered the substrate. The pretreated substrate was placed into a chamber of HFCVD equipment, and the distance between the hot filament and the substrate was adjusted (to 10 mm). After the completion of the installation, the door was closed, and the chamber was vacuumized. Then, hydrogen, methane and borane (diborane used in this experiment was a gas mixture of B.sub.2H.sub.6 and H.sub.2 in a ratio of 5:95) were introduced according to a set concentration ratio of gas sources of the experiment. After the reactive gas sources were uniformly mixed, a suction valve was closed, and a micrometering valve was adjusted to adjust the pressure in the chamber to a set pressure. Then, the HFCVD equipment was powered on, the current was adjusted such that the hot filament was heated to a preset temperature, and at the same time, the pressure in the deposition chamber was observed. If the pressure changed, the micrometering valve was used to adjust the pressure. Then, the deposition of the boron-doped diamond thin film was started. After the completion of the deposition, the temperature of the deposition chamber was reduced by adjusting the magnitude of the current. At this time, CH.sub.4 and B.sub.2H.sub.6 needed to be stopped, only H.sub.2 was used to etch the graphite phase on the surface of the diamond. In this example, the BDD electrode material was subjected to a three-stage deposition process. The first-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.1 sccm:3.0 sccm under a pressure of 2 kPa at a temperature of 850° C. for 4 h. The second-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.4 sccm:3.0 sccm under a pressure of 2 kPa at a temperature of 850° C. for 8 h. The third-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:1.0 sccm:3.0 sccm under a pressure of 2 kPa at a temperature of 850° C. for 12 h.

[0074] 2.3 High-Temperature Oxidation Treatment of BDD Thin Film.

[0075] After the completion of the deposition, the obtained BDD electrode material was placed in a crucible. A heating program of a tube furnace was set: in an air atmosphere, the temperature was raised at a rate of 10° C./min to 800° C., and then held for 35 minutes. The crucible containing the BDD material was pushed into a resistance heating area. After 30 times of treatment, the crucible was pushed out of the tube furnace, and cooled at room temperature, thereby obtaining the finished BDD electrode.

[0076] 2. Performance Testing.

[0077] 1) The BDD electrode not subjected to high-temperature treatment and the finished BDD electrode subjected to high-temperature treatment were respectively tested for their microstructure (by a field emission electron scanning microscope). As can be seen from FIG. 1, after the high-temperature treatment, morphology distributed with irregular micropores and spikes was formed on the surface of the thin film by etching. These irregular micropores and spikes could greatly increase the specific surface area of the material.

[0078] 2) The BDD electrode not subjected to high-temperature treatment and the finished BDD electrode subjected to high-temperature treatment were respectively tested for their room-temperature contact angle. As shown in FIG. 2, the contact angle of the BDD electrode not subjected to high-temperature treatment was 83.2°, and the contact angle of the finished BDD electrode subjected to high-temperature treatment was 33.4°.

[0079] The contact angle is of great significance to the application of a diamond electrode material. On the one hand, the improved hydrophilicity can improve the degradation efficiency in the degradation process. On the other hand, when the material is used in the field of electrochemical analysis, the surface hydrophilicity of the electrode material will affect the molecular weight to be detected adsorbed by the electrode material, which will restrict the degree of electrochemical catalytic reaction and further control the strength of the electrochemical signal.

[0080] 3) Encapsulation of BDD electrode: The surface of the matrix on which BDD had not been deposited was first polished with abrasive paper, in order to remove oil stains and impurities on the matrix. Then, a copper wire was spread on the surface of the Ti substrate, and bonded to the back surface of the BDD sample with a silver conductive adhesive to avoid the copper wire from being exposed. The silver conductive adhesive was allowed to stand for about 2 h until it was completely solidified. Finally, epoxy resin AB glue was uniformly applied to the surface of the BDD electrode except where the diamond was deposited. After about 6 hours, the strength of the insulating glue would reach its maximum. The encapsulation effect was tested with a multimeter.

[0081] 4) The encapsulated electrodes (including the finished BDD electrode subjected to high-temperature oxidation treatment and the electrode not subjected to high-temperature oxidation treatment in Embodiment 1) were used to degrade reactive blue. The results are shown in FIGS. 3A-3B. FIG. 3A shows color remove in the water sample in the degradation process: the color remove of the treated electrode material was 100%, and the color remove of the untreated material was 90.2%. The color remove can reflect the degree of destruction of organic chromophores. As can be seen, the electrode material subjected to high-temperature oxidation treatment had a larger specific surface area in the degradation process, and thus, could produce more active substances (such as hydroxyl radicals, active chlorine, etc.) on its surface, which thereby further oxidized the organic pollutants in the water body. FIG. 3B shows the change of COD (chemical oxygen demand) in the water body as a function of time in the degradation process. After 120 min of degradation, the COD remove of the electrode material subjected to high-temperature treatment could reach 79.5%, and the COD remove of the untreated electrode was only 50.1%. COD could further reflect the organic content in the water body, and thus was used as the evaluation indicator. Both the color remove and the COD remove showed that the treated electrode material had a significantly improved degradation efficiency.

Embodiment 2

[0082] Preparation of BDD Material with Nickel Substrate.

[0083] Nickel (Ni), as a common electrocatalytic material that can be easily electrodeposited, can be processed into complex structures and shapes. Therefore, a BDD thin film was prepared on a Ni substrate in this example.

[0084] 2. Preparation of BDD Material.

[0085] 2.1 Pretreatment of Substrate Material.

[0086] First, Ni was cut into a plate-like sample with a size of 25×30×2 mm. Then, the Ni substrate was immersed in acetone (CH.sub.3COCH.sub.3) and anhydrous ethanol (C.sub.2H.sub.5OH) and subjected to ultrasonic oscillation for 10 min. Finally, the Ni substrate was rinsed with deionized ultrapure water and dried for later use.

[0087] 2.2 Preparation of Transition Layer.

[0088] Ni can easily catalyze the reaction of diamond to form other amorphous carbon, so it is impossible to directly deposit a boron-doped diamond film. Due to the big difference in thermal expansion coefficient between Ni and C, it impossible to form an effective carbide transition layer, and foam has poor bonding with the substrate. During the degradation experiment, Ni is easily sacrificed, resulting in a reduced service life of the BDD electrode. Therefore, in the disclosure, a Ti film that could completely cover the matrix was first sputtered on the foam Ni matrix. Ti not only could easily form a TiC layer with C, thus solving the problem of thermal mismatch, but also had good bonding with Ni.

[0089] Deposition of BDD Thin Film.

[0090] The hot filament used in this example was a φ0.5 mm straight tungsten wire, which completely covered the substrate. The pretreated substrate was placed into a chamber of HFCVD equipment, and the distance between the hot filament and the substrate was adjusted (to 8 mm). After the completion of the installation, the door was closed, and the chamber was vacuumized. Then, hydrogen, methane and borane (diborane used in this experiment was a gas mixture of B.sub.2H.sub.6 and H.sub.2 in a ratio of 5:95) were introduced according to a set concentration ratio of gas sources of the experiment. After the reactive gas sources were uniformly mixed, a suction valve was closed, and a micrometering valve was adjusted to adjust the pressure in the chamber to a set pressure. Then, the HFCVD equipment was powered on, the current was adjusted such that the hot filament was heated to a preset temperature, and at the same time, the pressure in the deposition chamber was observed. If the pressure changed, the micrometering valve was used to adjust the pressure. Then, the deposition of the boron-doped diamond thin film was started. After the completion of the deposition, the temperature of the deposition chamber was reduced by adjusting the magnitude of the current. At this time, CH.sub.4 and B.sub.2H.sub.6 needed to be stopped, only H.sub.2 was used to etch the graphite phase on the surface of the diamond. In this example, the BDD electrode material was subjected to a three-stage deposition process. The first-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.1 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 4 h. The second-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.4 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 8 h. The third-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:1.0 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 2 h.

[0091] 2.3 High-Temperature Oxidation Treatment of BDD Thin Film.

[0092] After the completion of the deposition, the obtained BDD electrode material was placed in a crucible. A heating program of a tube furnace was set: in an air atmosphere, the temperature was raised at a rate of 10° C./min to 500° C., and then held for 20 minutes. The crucible containing the BDD material was pushed into a resistance heating area. After 15 times of treatment, the crucible was pushed out of the tube furnace, and cooled at room temperature.

[0093] 2. Performance Testing.

[0094] 1) The BDD electrode not subjected to high-temperature treatment and the finished BDD electrode subjected to high-temperature treatment were respectively tested for their microstructure (by a field emission electron scanning microscope). As can be seen from FIG. 4, after the high-temperature treatment, morphology distributed with irregular micropores and spikes was formed on the surface of the thin film by etching. These irregular micropores and spikes could greatly increase the specific surface area of the material. Besides, as can be seen, after 10 min of treatment at 500° C., the graphite phase and stains on the surface of the material were effectively removed.

[0095] The existence of sp.sup.2 carbon (graphitic carbon) will destroy the weak surface adsorption of the electrode material. On the one hand, this will make the electrode material easily adsorb organic matters when being used for electrochemical oxidation treatment of organic pollutants in a water body, causing reduced active area and reduced degradation and mineralization efficiency of the electrode. On the other hand, the active substance (OH) produced by the electrode during working will be adsorbed, which will lead to reduced mineralization efficiency of the active substance and thus reduced degradation efficiency. Besides, compared with the sp.sup.3 carbon (diamond phase), the sp.sup.2 carbon are more easily corroded, which will reduce the oxygen evolution potential of the electrode and thereby lead to a large amount of energy consumed during actual service in favor of side reactions (i.e., oxygen evolution, etc.), causing a significant increase in useless and wasteful energy consumption. Therefore, the removal of the sp.sup.2 phase is crucial to the performance of the BDD electrode material.

[0096] 2) The BDD electrode not subjected to high-temperature treatment and the finished BDD electrode subjected to high-temperature treatment were respectively subjected to Raman spectroscopy. The results are shown in FIG. 5. The intensity at 1580 cm.sup.−1 shows the sp.sup.2 content in the material, and the intensity at 1332 cm.sup.−1 shows the content of sp; (diamond phase) in the material. As can be seen, after 10 min of treatment at 500° C., the content of the sp.sup.2 phase in the material significantly decreased, indicating an improved purity of the diamond phase, which was consistent with the analysis results obtained by SEM.

[0097] 3) The BDD electrode not subjected to high-temperature treatment and the finished BDD electrode subjected to high-temperature treatment were respectively tested for their room-temperature contact angle. As shown in FIG. 6, the contact angle of the BDD electrode not subjected to high-temperature treatment was 66.5°, and the contact angle of the finished BDD electrode subjected to high-temperature treatment was 38.5°.

[0098] The contact angle is of great significance to the application of a diamond electrode material. On the one hand, the improved hydrophilicity can improve the degradation efficiency in the degradation process. On the other hand, when the material is used in the field of electrochemical analysis, the surface hydrophilicity of the electrode material will affect the molecular weight to be detected adsorbed by the electrode material, which will restrict the degree of electrochemical catalytic reaction and further control the strength of the electrochemical signal.

[0099] 4) Encapsulation of BDD electrode: The surface of the matrix on which BDD had not been deposited was first polished with abrasive paper, in order to remove oil stains and impurities on the matrix. Then, a copper wire was spread on the surface of the Ti substrate, and bonded to the back surface of the BDD sample with a silver conductive adhesive to avoid the copper wire from being exposed. The silver conductive adhesive was allowed to stand for about 2 h until it was completely solidified. Finally, epoxy resin AB glue was uniformly applied to the surface of the BDD electrode except where the diamond was deposited. After about 6 hours, the strength of the insulating glue would reach its maximum. The encapsulation effect was tested with a multimeter.

Embodiment 3

[0100] BDD Electrode Material with Silicon Substrate.

[0101] Silicon (Si), as the most common substrate material, has high lattice matching and bonding ability with the BDD thin film due to its good corrosion resistance and low thermal expansion coefficient. In this example, plate-like p-type silicon was used as the substrate material for the experiment.

[0102] 2. Preparation of BDD Material.

[0103] 2.1 Pretreatment of Substrate Material.

[0104] First, Si was cut into a plate-like sample with a size of 20×30×0.5 mm. Then, the Si substrate was immersed in acetone (CH.sub.3COCH.sub.3) and anhydrous ethanol (C.sub.2H.sub.5OH) and subjected to ultrasonic oscillation for 10 min. Finally, the Si substrate was rinsed with deionized ultrapure water and dried for later use.

[0105] 2.2 Deposition of BDD Thin Film.

[0106] The hot filament used in this example was a φ0.5 mm straight tungsten wire, which completely covered the substrate. The pretreated substrate was placed into a chamber of HFCVD equipment, and the distance between the hot filament and the substrate was adjusted (to 10 mm). After the completion of the installation, the door was closed, and the chamber was vacuumized. Then, hydrogen, methane and borane (diborane used in this experiment was a gas mixture of B.sub.2H.sub.6 and H.sub.2 in a ratio of 5:95) were introduced according to a set concentration ratio of gas sources of the experiment. After the reactive gas sources were uniformly mixed, a suction valve was closed, and a micrometering valve was adjusted to adjust the pressure in the chamber to a set pressure. Then, the HFCVD equipment was powered on, the current was adjusted such that the hot filament was heated to a preset temperature, and at the same time, the pressure in the deposition chamber was observed. If the pressure changed, the micrometering valve was used to adjust the pressure. Then, the deposition of the boron-doped diamond thin film was started. After the completion of the deposition, the temperature of the deposition chamber was reduced by adjusting the magnitude of the current. At this time, CH.sub.4 and B.sub.2H.sub.6 needed to be stopped, only H.sub.2 was used to etch the graphite phase on the surface of the diamond. In this example, the BDD electrode material was subjected to a three-stage deposition process. The first-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.1 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 4 h. The second-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.5 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 8 h. The third-stage deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:1.5 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 1.5 h.

[0107] 2.3 High-Temperature Oxidation Treatment of BDD Thin Film.

[0108] After the completion of the deposition, the obtained BDD electrode material was placed in a crucible. A heating program of a tube furnace was set: in an air atmosphere, the temperature was raised at a rate of 10° C./min to 800° C., and then held for 45 minutes. The crucible containing the BDD material was pushed into a resistance heating area. After 40 times of treatment, the crucible was pushed out of the tube furnace, and cooled at room temperature. The stability of the electrode is crucial for the service cost of the material, and is also a key link in the industrial chain of the material. In this example, by controlling the treatment temperature and time, the BDD electrode material was etched into porous morphology, and then tested for its stability.

[0109] 2. Performance Testing.

[0110] 1) The BDD electrode not subjected to high-temperature treatment and the finished BDD electrode subjected to high-temperature treatment were respectively tested for their microstructure (by a field emission electron scanning microscope). As can be seen from FIG. 7, after the high-temperature treatment, morphology distributed with irregular micropores and spikes was formed on the surface of the thin film by etching.

[0111] 2) The finished BDD electrode was tested for its stability using accelerated life testing. After the finished BDD electrode was run in a 1 mol/L sulfuric acid solution at a current density of 1 A/cm2 for 300 hours, the surface topography was characterized. As shown in FIG. 8, there was no significant thin film falling off the electrode, and the surface topography was still stable.

[0112] 3) Encapsulation of BDD electrode: The surface of the matrix on which BDD had not been deposited was first polished with abrasive paper, in order to remove oil stains and impurities on the matrix. Then, a copper wire was spread on the surface of the Ti substrate, and bonded to the back surface of the BDD sample with a silver conductive adhesive to avoid the copper wire from being exposed. The silver conductive adhesive was allowed to stand for about 2 h until it was completely solidified. Finally, epoxy resin AB glue was uniformly applied to the surface of the BDD electrode except where the diamond was deposited. After about 6 hours, the strength of the insulating glue would reach its maximum. The encapsulation effect was tested with a multimeter.

[0113] 4) The encapsulated electrodes (including the finished BDD electrode subjected to high-temperature oxidation treatment and the electrode not subjected to high-temperature oxidation treatment in Embodiment 3) were used to degrade organic wastewater. Actual wastewater has a more complex composition and provides a more hostile experimental environment (pH, etc.). As a result, in this example, the electrode materials (subjected to high-temperature oxidation treatment and not subjected to high-temperature oxidation treatment) were used to degrade actual wastewater (pharmaceutical wastewater from a factory in Gansu Province), so as to verify the promotion effect of high-temperature oxidation on degradation efficiency after increasing the specific surface area and sp.sup.2 purity of the electrode. Due to the complex composition of the actual wastewater as well as complex types and contents of organic pollutants and salts, TOC (total organic carbon) was used as the evaluation indicator. TOC remove can reflect the degree to which organic pollutants in the water body are mineralized to water and carbon dioxide. It can be clearly seen from FIG. 9 that after the wastewater was degraded with the electrode material subjected to high-temperature oxidation treatment, the degree of mineralization of the organic matters in the water body was significantly increased. After 120 min of degradation, the TOC remove of the electrode material subjected to high-temperature oxidation treatment could reach 73.4%, and the TOC remove of the untreated electrode material was only 47.3%, indicating that the treated electrode material had a significantly improved degradation efficiency.

[0114] 5) The BDD electrode prepared in Embodiment 3 was applied to a water purifier. The water purifier, as shown in FIG. 10, included a housing 1, a separator 2, a metal electrode 3, a BDD electrode 4, a conductive clip 5, a sealed insulator 6 and a wire 7.

[0115] In actual application, an electrode assembly formed by the BDD electrode prepared in Embodiment 3 as an anode, a titanium electrode as a cathode, and a perfluorinated ion-exchange membrane as a separator was installed in a water purifier (FIG. 10), and the water purifier was placed in a water sample to be treated (in a fishbowl containing live fish) and run under a voltage of 3 V for 5 h. The COD in the water sample to be treated was reduced from 983 mg/L to 50 mg/L.

Comparative Embodiment 1

[0116] The conditions were the same as in Embodiment 2, except that gradient doping was not used in the deposition of the thin film. The deposition was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:0.4 sccm:3.0 sccm under a pressure of 3 kPa at a temperature of 850° C. for 14 h. The material was tested for its surface hydrophilicity. As shown in FIG. 11, the room-temperature contact angle of the material was 82.4°.

Comparative Embodiment 2

[0117] The conditions were the same as those in Embodiment 2, except that the deposition of the top layer of the material was carried out at a gas flow rate ratio H.sub.2:B.sub.2H.sub.6:CH.sub.4 of 97 sccm:1.0 sccm:3.0 sccm. The room-temperature water contact angle of the gradient boron-doped sample was 66.7°, indicating a significant decrease of the hydrophilicity.

Comparative Embodiment 3

[0118] The conditions were the same as in Embodiment 3, except that the high-temperature treatment was carried out for 120 min. The surface topography of the electrode material obtained after high-temperature treatment is shown in FIG. 12. Due to the excessive treatment time, the thin film was damaged seriously (over a large area), and the substrate material was exposed. At this time, the material was no longer able to perform normally, exhibiting a significant decrease in both performance and service life.