Titanium suboxide-based composite catalytic electrode and preparation method thereof

Abstract

This invention relates to the field of wastewater treatment technology and discloses a composite catalytic electrode based on titanium suboxide and its preparation method. The composite catalytic electrode consists of a titanium plate substrate, a conductive titanium suboxide transition layer, and a BDD catalytic layer grown under core-shell seed conditions. Its preparation method comprises five steps: titanium plate substrate pretreatment, preparation of the conductive titanium suboxide transition layer, surface composite modification, construction of the core-shell seed layer, and low-temperature CatCVD deposition. This invention solves the problems of high interfacial stress, insufficient bonding strength, high-temperature oxidation, and difficulty in bonding between the titanium substrate and BDD in existing BDD-based electrodes. The electrode interfacial bonding strength is ≥6.0 MPa, the BDD crystallinity is ≥88%, and in the treatment of high-concentration, recalcitrant organic wastewater with COD ≥1000 mg / L, the COD removal rate is ≥98.0%, with excellent cycle stability, demonstrating significant practical application value.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a composite catalytic electrode based on titanium suboxide and its preparation method. Background Technology

[0002] Electrochemical oxidation technology has gained widespread attention in wastewater treatment due to its advantages such as high efficiency and environmental friendliness. Among them, BDD (boron-doped diamond) electrodes have become ideal catalytic electrode materials due to their wide potential window, high oxygen evolution overpotential, and strong oxidation capacity. To solve the problems of high interfacial stress and high-temperature oxidation in the traditional multilayer structure of "titanium substrate + intermediate layer + BDD", the existing technology has developed a ternary structure electrode of "titanium plate substrate + conductive sub-titanium oxide transition layer + BDD catalytic layer". The initial design intention is to use the similar thermal expansion coefficient and interfacial compatibility between sub-titanium oxide and titanium substrate and BDD to alleviate the interlayer matching contradiction.

[0003] However, existing ternary electrode structures still suffer from several technical defects that urgently need to be addressed: 1) Insufficient interfacial bonding. The existing conductive sub-titanium oxide transition layer has limited physical intercalation sites with the titanium substrate, and its chemical interaction with the BDD catalyst layer is weak. During long-term electrolysis, delamination failures such as transition layer peeling and BDD coating detachment are prone to occur; 2) Imbalanced transition layer performance. Existing transition layers struggle to balance high conductivity and excellent mechanical strength. Single-doped or undoped designs can easily lead to high volume resistivity or insufficient fracture toughness in the transition layer, affecting the overall electrochemical performance and lifespan of the electrode; 3) Low BDD nucleation efficiency. In existing ternary structures, the surface modification process of the transition layer is simple, often involving only single acid etching or mechanical roughening. This results in low surface hydroxyl content and insufficient active sites, leading to high BDD nucleation activation energy, uneven crystallinity, and poor catalytic performance stability; 4) Insufficient optimization of the preparation process. In existing technologies, the matching degree between the coating and sintering process parameters of the transition layer is low, which can easily lead to excessively high or low porosity of the transition layer, further affecting the interface bonding effect and electron transport efficiency. Moreover, BDD deposition often relies on high-temperature processes, and there is still a risk of oxidation and deterioration of the transition layer.

[0004] Therefore, in view of the inherent defects of the existing ternary structure electrode of "titanium plate substrate + conductive sub-titanium oxide transition layer + BDD catalytic layer" in terms of interface bonding, transition layer performance, BDD nucleation and preparation process, it is necessary to develop a composite catalytic electrode with better performance and more reasonable process and its preparation method. This has important practical application value for improving the treatment efficiency of high-concentration recalcitrant organic wastewater. Summary of the Invention

[0005] In view of this, the present invention proposes a composite catalytic electrode based on titanium suboxide and its preparation method, aiming to solve the problems of interfacial stress, insufficient bonding force and high-temperature oxidation in the multilayer structure of BDD-based electrodes in the current technology. Through ternary structure design and innovative pretreatment process, low-temperature and high-efficiency deposition of BDD is achieved, improving the interfacial bonding force and electrochemical performance of the electrode, which is especially suitable for COD removal from wastewater.

[0006] The present invention provides a composite catalytic electrode based on titanium suboxide, wherein the composite catalytic electrode based on titanium suboxide is a ternary composite structure composed of a titanium plate substrate, a conductive titanium suboxide transition layer and a BDD catalytic layer induced by core-shell seed crystal growth. The conductive sub-titanium oxide transition layer is a yttrium-zirconium composite doped monolayer structure; The BDD catalytic layer induced by the core-shell seed crystal is a homogeneous structure doped with phosphorus, and the core-shell seed crystal is nanodiamond@boron nitride core-shell particles.

[0007] Preferably, the thickness of the titanium plate substrate is 0.5~1.5mm.

[0008] Preferably, the doping amount of the yttrium-zirconium composite dopant is 0.5~2wt% of the mass of titanium suboxide, and the molar ratio of yttrium to zirconium is 2:1.

[0009] Preferably, the porosity of the conductive titanium suboxide transition layer is 15-30%, and the particle size of the conductive titanium suboxide transition layer is 2-8 μm.

[0010] Preferably, in the nanodiamond@boron nitride core-shell particles, the core layer particle size is 50~100nm, the shell layer thickness is 10~20nm, and the total thickness of the BDD catalyst layer is 5~15μm.

[0011] Preferably, the boron doping amount in the BDD catalyst layer is 0.3~0.8% in atomic percentage.

[0012] Preferably, the phosphorus doping amount is 0.1~0.5% in atomic percentage.

[0013] Another object of the present invention is to provide a method for preparing the aforementioned titanium suboxide-based composite catalytic electrode, comprising the following steps: 1) The titanium plate is subjected to sandblasting and oxalic acid etching in sequence to obtain a pretreated titanium plate substrate; 2) Yttrium-zirconium composite doped titanium suboxide powder was coated on the surface of a pretreated titanium plate substrate and sintered by gradient heating to obtain a composite substrate containing a conductive titanium suboxide transition layer. 3) The surface of the conductive sub-titanium oxide transition layer of the composite substrate was mechanically roughened, subjected to composite acid etching, and activated by low-temperature plasma in sequence to obtain the modified composite substrate; 4) The modified composite substrate was immersed in a nanodiamond@boron nitride core-shell suspension and formed a uniform seed layer by ultrasonic-assisted self-assembly. 5) The composite substrate with a uniform seed layer obtained in step 4) is deposited with a pure diamond transition layer at 400°C, and then boron source gas and phosphorus source gas are simultaneously introduced at 500~550°C to deposit a homogeneous BDD catalyst layer, and finally a composite catalytic electrode is formed.

[0014] Preferably, the sandblasting treatment in step 1) uses 80~120 mesh quartz sand and the sandblasting pressure is 0.3~0.5MPa; the oxalic acid concentration in the oxalic acid etching is 8~12wt%, the etching temperature is 50~70℃, and the etching time is 20~40min.

[0015] Preferably, the coating thickness of the yttrium-zirconium composite-doped titanium suboxide powder in step 2) is 1.5~3mm.

[0016] Preferably, the gradient heating sintering is performed by heating to 800°C at a rate of 5°C / min and holding for 1 hour; then heating to 1200°C at a rate of 8°C / min and holding for 2 hours; and finally heating to 1400°C at a rate of 10°C / min and holding for 1 hour; the sintering pressure is controlled to be 8~12 MPa during the gradient heating sintering.

[0017] Preferably, the etching solution for the composite acid etching in step 3) is composed of citric acid, ammonium hydrofluoride, and aminosulfonic acid in a concentration ratio of 0.2:0.1:0.05 mol / L, with an etching temperature of 50~70℃ and an etching time of 40~80 min.

[0018] Preferably, the low-temperature plasma activation uses an argon-oxygen mixed gas with a volume ratio of 9:1, an activation power of 150~250W, an activation time of 10~20min, and an activation temperature of 80~120℃.

[0019] Preferably, the concentration of the nanodiamond@boron nitride core-shell suspension in step 4) is 1~3g / L, containing 0.3~0.8wt% polydopamine dispersant, with an ultrasonic power of 200~300W, an ultrasonic time of 40~80min, a self-assembly temperature of 60~80℃, and a seed layer coverage of ≥95% after drying.

[0020] Preferably, the boron source gas in step 5) is gaseous trimethyl borate; the phosphorus source gas is phosphine.

[0021] Preferably, the preparation method of the sub-titanium oxide powder in step 2) is as follows: titanium dioxide and titanium are mixed, kept at a temperature in an air atmosphere, then calcined in a nitrogen atmosphere, cooled, and obtained by ball milling.

[0022] Preferably, the mass ratio of titanium dioxide to titanium is (1~3):1; the heat preservation is specifically at 1600~1650℃ for 20~40 min; the calcination is specifically at 1350~1450℃ for 8~10 h.

[0023] Preferably, the nanodiamond@boron nitride core-shell particles are prepared by the following method: a) The core layer material is nanodiamond powder with a particle size of 50~100nm, which is pretreated by boiling with 1mol / L nitric acid for 2h, washing with deionized water until neutral, and drying at 80℃ for 4h for hydroxylation; the shell layer material is boric acid, urea, and polyvinylpyrrolidone, and the solvent is deionized water; the raw material ratio is nanodiamond:boric acid:urea:PVP=1g:0.8g:2g:0.05g, and the amount of deionized water added is 10 times the total mass of solid material; b) Add nano-diamond, boric acid, urea, and PVP sequentially to deionized water, stir magnetically at 500 r / min for 30 min, and then ultrasonically disperse at 200 W for 60 min to form a uniform suspension. Transfer the suspension to a 50 mL polytetrafluoroethylene-lined autoclave, keep it at 180 °C for 12 h, cool it naturally to room temperature, centrifuge at 8000 r / min for 10 min, wash it three times with deionized water and once with ethanol, and vacuum dry it at 60 °C for 8 h to obtain diamond@boron-nitrogen precursor composite powder. c) The diamond@boron-nitrogen precursor composite powder was placed in a graphite boat, placed in a tube furnace, and high-purity nitrogen gas was introduced at a flow rate of 50 sccm. The temperature was increased to 800℃ at 5℃ / min and held for 6 hours. Nitrogen gas was continued to be introduced until it cooled naturally to room temperature. Nanodiamond@boron nitride core-shell particles were collected.

[0024] Another object of the present invention is to provide the application of the titanium suboxide-based composite catalytic electrode in the removal of COD from high-concentration, recalcitrant organic wastewater with a COD ≥ 1000 mg / L.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention employs a ternary structure of "titanium substrate + conductive sub-titanium oxide transition layer + BDD catalyst layer". The titanium substrate provides stable mechanical support, while the conductive sub-titanium oxide transition layer possesses a thermal expansion coefficient similar to that of the titanium substrate and interface characteristics matching those of BDD, fundamentally eliminating the problem of thermal expansion mismatch between different materials and completely solving the problem of coating peeling and delamination failure caused by interfacial stress. Simultaneously, yttrium-zirconium composite doping synergistically optimizes the matrix properties. Yttrium ions strengthen the lattice and improve mechanical strength, while zirconium ions optimize the electron conduction path and reduce volume resistivity, balancing matrix strength, conductivity, and interfacial bonding ability, achieving a fracture toughness of 4.5~4.9 MPa·m. 1 / 2 .

[0026] 2) This invention employs a "sandblasting + oxalic acid etching" pretreatment on the titanium substrate. Sandblasting creates a rough surface, increasing physical interlocking sites, while oxalic acid etching removes the surface oxide film and introduces hydroxyl groups, significantly improving the interfacial bonding between the titanium substrate and the sub-titanium oxide transition layer. The transition layer surface is then treated with a three-step modification process: "mechanical roughening + composite acid etching + low-temperature plasma activation." Composite acid etching forms uniform nanopores, and plasma activation ensures that the hydroxyl content on the transition layer surface is ≥5 mmol / m². 2 This provides sufficient binding sites for seed adsorption; the core layer of the nanodiamond@boron nitride core-shell seed has the same crystallization habit as BDD, reducing the nucleation activation energy; the boron nitride shell layer forms hydrogen bonds with the hydroxyl groups of the transition layer and is resistant to high-temperature oxidation; after ultrasonic-assisted self-assembly, the seed coverage rate is ≥95%, ultimately making the overall interface bonding force of the electrode ≥6.0MPa.

[0027] 3) By seeding and laying a pure diamond transition layer, the BDD catalyst layer is deposited at low temperature, avoiding the oxidation of the titanium substrate and the deterioration of the titanium suboxide transition layer caused by high temperature. At the same time, a boron-phosphorus co-doping strategy is adopted. Boron doping forms effective active sites to improve the generation efficiency of ·OH free radicals, and phosphorus doping adjusts the Fermi level to optimize the electron transport rate. The two work together to make the BDD catalyst layer have both high catalytic activity and uniformity.

[0028] 4) The composite catalytic electrode of this invention achieves a COD removal rate of ≥98.0% and up to 99.2% for high-concentration, recalcitrant organic wastewater with COD ≥1000 mg / L. After 100 hours of use, the performance retention rate is ≥97.0%, and the stability is significantly better than that of traditional electrodes. The preparation process, including gradient heating sintering, ultrasonic-assisted self-assembly, and low-temperature CatCVD deposition (catalytic chemical vapor deposition), is easy to scale up. It combines technological innovation with industrial applicability, providing a new solution for the efficient treatment of high-concentration, recalcitrant organic wastewater. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0030] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] The present invention provides a composite catalytic electrode based on titanium suboxide, wherein the composite catalytic electrode based on titanium suboxide is a ternary composite structure composed of a titanium plate substrate, a conductive titanium suboxide transition layer and a BDD catalytic layer induced by core-shell seed crystal growth. The conductive sub-titanium oxide transition layer is a yttrium-zirconium composite doped monolayer structure; The BDD catalytic layer induced by the core-shell seed crystal is a homogeneous structure doped with phosphorus, and the core-shell seed crystal is nanodiamond@boron nitride core-shell particles.

[0035] In this invention, the titanium substrate provides stable mechanical support, and the conductive sub-titanium oxide transition layer is mainly composed of sub-titanium oxide and is doped with yttrium-zirconium composite. Yttrium ions strengthen the lattice by solid solution to improve mechanical strength, and zirconium ions optimize the electronic conduction path to improve conductivity. The two work together to solve the contradiction of traditional transition layers in terms of "strength-conductivity-bonding force" and achieve a dual stable bond with the titanium substrate and the BDD catalyst layer.

[0036] In this invention, the thickness of the titanium plate substrate is 0.5~1.5mm.

[0037] In this invention, the doping amount of the yttrium-zirconium composite doping is preferably 0.5~2wt% of the mass of titanium suboxide, more preferably 1~1.5wt%; the molar ratio of yttrium to zirconium is preferably 2:1.

[0038] In this invention, the porosity of the conductive titanium suboxide transition layer is preferably 15-30%, more preferably 20-25%; the particle size of the conductive titanium suboxide transition layer is preferably 2-8 μm, more preferably 4-6 μm.

[0039] In this invention, the porosity design of 15-30% avoids both insufficient bonding sites due to excessively low porosity and excessively high porosity that could affect mechanical strength.

[0040] In this invention, the core layer particle size of the nanodiamond@boron nitride core-shell particles is preferably 50~100nm, more preferably 60~80nm; the shell layer thickness is preferably 10~20nm, more preferably 12~16nm; and the total thickness of the BDD catalyst layer is preferably 5~15μm, more preferably 8~12μm.

[0041] In this invention, the surface roughness Ra of the conductive titanium suboxide transition layer is 100~300 nm, and the surface hydroxyl content is ≥5 mmol / m after plasma activation. 2 Volume resistivity ≤200μΩ·m, interfacial bonding strength ≥6MPa.

[0042] In this invention, the boron doping amount in the BDD catalyst layer is preferably 0.3 to 0.8% in atomic percentage, more preferably 0.4 to 0.6%.

[0043] In this invention, the phosphorus doping amount is preferably 0.1 to 0.5% in atomic percentage, more preferably 0.2 to 0.4%.

[0044] In this invention, the boron doping amount is controlled at 0.3~0.8 at%, which can form effective active sites in the BDD lattice and improve the ·OH radical generation efficiency; the phosphorus doping amount is controlled at 0.1~0.5 at%, which can adjust the Fermi level of the BDD and optimize the electron transport rate. The synergistic effect of the two makes the catalyst layer have both high catalytic activity and high electron conduction efficiency. The homogeneous structure ensures the uniformity of the catalytic reaction and avoids electrode loss caused by excessive local activity.

[0045] Another object of the present invention is to provide a method for preparing the aforementioned titanium suboxide-based composite catalytic electrode, comprising the following steps: 1) The titanium plate is subjected to sandblasting and oxalic acid etching in sequence to obtain a pretreated titanium plate substrate; 2) Yttrium-zirconium composite doped titanium suboxide powder was coated on the surface of a pretreated titanium plate substrate and sintered by gradient heating to obtain a composite substrate containing a conductive titanium suboxide transition layer. 3) The surface of the conductive sub-titanium oxide transition layer of the composite substrate was mechanically roughened, subjected to composite acid etching, and activated by low-temperature plasma in sequence to obtain the modified composite substrate; 4) The modified composite substrate was immersed in a nanodiamond@boron nitride core-shell suspension and formed a uniform seed layer by ultrasonic-assisted self-assembly. 5) The composite substrate with a uniform seed layer obtained in step 4) is deposited with a pure diamond transition layer at 400°C, and then boron source gas and phosphorus source gas are simultaneously introduced at 500~550°C to deposit a homogeneous BDD catalyst layer, and finally a composite catalytic electrode is formed.

[0046] In this invention, the titanium plate substrate is pretreated by "sandblasting + oxalic acid etching". Sandblasting forms a rough surface to increase physical interlocking sites, and oxalic acid etching removes the surface oxide film and introduces hydroxyl groups, providing a stable bonding basis for the deposition of the transition layer. The transition layer is uniformly coated and vacuum hot-pressed into one piece, with the porosity controlled at 15~30%, which not only ensures the overall mechanical stability, but also provides sufficient physical interlocking sites for the subsequent BDD catalyst layer.

[0047] In this invention, pretreatment introduces a large number of hydroxyl groups onto the surface of the nanodiamond, enhancing its interaction with the boron-nitrogen precursor. During the hydrothermal reaction, boric acid polymerizes with urea to form a uniform coating layer, which, after high-temperature nitriding, transforms into a highly stable boron nitride shell, thus achieving core-shell structure regulation. The nanodiamond core layer exhibits the same crystallization habit as BDD, lowering the BDD nucleation activation energy. The layered structure of the boron nitride shell forms hydrogen bonds with the hydroxyl groups on the substrate surface, while its high-temperature resistance prevents the seed crystals from oxidizing during deposition, significantly improving the crystallinity of BDD and ensuring the uniformity of the homogeneous catalyst layer.

[0048] In this invention, during composite acid etching, citrate complexes titanium ions to prevent product deposition, ammonium hydrofluoric acid selectively etches to form uniform nanopores, and aminosulfonic acid regulates the etching rate; high-energy particles generated by plasma activation bombard the surface, increasing the hydroxyl content to 5 mmol / m 2 In summary, the hydroxyl groups form covalent bonds with the amino groups of the core-shell seed crystals, which significantly improves the adsorption stability of the seed crystals and lays the foundation for the continuous deposition of a homogeneous BDD layer.

[0049] In this invention, the sandblasting treatment in step 1) preferably uses 80-120 mesh quartz sand, more preferably 90-110 mesh; the sandblasting pressure is preferably 0.3-0.5 MPa, more preferably 0.3-0.4 MPa; the oxalic acid concentration in the oxalic acid etching is preferably 8-12 wt%, more preferably 9-11 wt%; the etching temperature is preferably 50-70℃, more preferably 55-65℃; and the etching time is preferably 20-40 min, more preferably 25-35 min.

[0050] In this invention, the coating thickness of the yttrium-zirconium composite-doped titanium suboxide powder in step 2) is preferably 1.5~3mm, more preferably 2~2.5mm.

[0051] In this invention, the gradient heating sintering is preferably performed by heating to 800°C at a rate of 5°C / min and holding for 1 hour; then heating to 1200°C at a rate of 8°C / min and holding for 2 hours; and finally heating to 1400°C at a rate of 10°C / min and holding for 1 hour. The sintering pressure is preferably controlled at 8~12 MPa, more preferably 9~10 MPa during the gradient heating sintering.

[0052] In this invention, the etching solution for the composite acid etching in step 3) is preferably composed of citric acid, ammonium hydrofluoride, and aminosulfonic acid in a concentration ratio of 0.2:0.1:0.05 mol / L; the etching temperature is preferably 50~70℃, more preferably 55~65℃; and the etching time is preferably 40~80 min, more preferably 50~70 min.

[0053] In this invention, the low-temperature plasma activation preferably uses an argon-oxygen mixed gas with a volume ratio of 9:1, the activation power is preferably 150~250W, more preferably 180~220W; the activation time is preferably 10~20min, more preferably 12~16min; and the activation temperature is preferably 80~120℃, more preferably 90~110℃.

[0054] In this invention, the concentration of the nanodiamond@boron nitride core-shell suspension in step 4) is preferably 1~3 g / L, more preferably 1.5~2.5 g / L; the suspension also preferably contains 0.3~0.8 wt% polydopamine dispersant, more preferably 0.4~0.6 wt%; the ultrasonic power is preferably 200~300 W, more preferably 220~280 W; the ultrasonic time is preferably 40~80 min, more preferably 50~70 min; the self-assembly temperature is preferably 60~80℃, more preferably 65~75℃; and the seed layer coverage after drying is preferably ≥95%, more preferably ≥96%.

[0055] In this invention, the boron source gas in step 5) is preferably gaseous trimethyl borate; the phosphorus source gas is preferably phosphine.

[0056] In this invention, the preparation method of the sub-titanium oxide powder in step 2) is as follows: titanium dioxide and titanium are mixed, kept at a temperature in an air atmosphere, then calcined in a nitrogen atmosphere, cooled, and obtained by ball milling.

[0057] In this invention, the preferred mass ratio of titanium dioxide to titanium is (1~3):1, more preferably 2:1; the preferred heat preservation is at 1600~1650℃ for 20~40 min, more preferably at 1620~1640℃ for 25~35 min; the preferred calcination is at 1350~1450℃ for 8~10 h, more preferably at 1380~1420℃ for 8.5~9 h.

[0058] In this invention, the nanodiamond@boron nitride core-shell particles are prepared by the following method: a) The core layer material is preferably nanodiamond powder with a particle size of 50~100nm, which is pretreated by boiling with 1mol / L nitric acid for 2h, washing with deionized water until neutral, and drying at 80℃ for 4h for hydroxylation; the shell layer material is boric acid, urea, and polyvinylpyrrolidone, and the solvent is deionized water; the raw material ratio is nanodiamond:boric acid:urea:PVP=1g:0.8g:2g:0.05g, and the amount of deionized water added is 10 times the total mass of solid material; b) Add nano-diamond, boric acid, urea, and PVP sequentially to deionized water, stir magnetically at 500 r / min for 30 min, and then ultrasonically disperse at 200 W for 60 min to form a uniform suspension. Transfer the suspension to a 50 mL polytetrafluoroethylene-lined autoclave, keep it at 180 °C for 12 h, cool it naturally to room temperature, centrifuge at 8000 r / min for 10 min, wash it three times with deionized water and once with ethanol, and vacuum dry it at 60 °C for 8 h to obtain diamond@boron-nitrogen precursor composite powder. c) The diamond@boron-nitrogen precursor composite powder was placed in a graphite boat, placed in a tube furnace, and high-purity nitrogen gas was introduced at a flow rate of 50 sccm. The temperature was increased to 800℃ at 5℃ / min and held for 6 hours. Nitrogen gas was continued to be introduced until it cooled naturally to room temperature. Nanodiamond@boron nitride core-shell particles were collected.

[0059] Another object of the present invention is to provide the application of the titanium suboxide-based composite catalytic electrode in the removal of COD from high-concentration, recalcitrant organic wastewater with a COD ≥ 1000 mg / L.

[0060] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] Example 1 1) Titanium plate substrate pretreatment: Take a titanium plate with a thickness of 0.5 mm, sandblast it with 80 mesh quartz sand at a pressure of 0.3 MPa for 10 min, then immerse it in 8 wt% oxalic acid solution, etch it at 50℃ for 40 min, take it out and rinse it with deionized water until neutral, and dry it at 80℃ for 4 h to obtain the pretreated titanium plate substrate.

[0062] 2) Preparation of conductive sub-titanium oxide transition layer: Titanium dioxide and titanium were mixed at a mass ratio of 1:1, and then heated at 1600℃ for 20 min in an air atmosphere. After that, the mixture was calcined at 1350℃ for 8 h in a nitrogen atmosphere, cooled, and ball-milled to obtain titanium suboxide powder with an average particle size of 2 μm. The above-mentioned titanium suboxide powder (particle size 2 μm) was mixed with 1.2 wt% yttrium-zirconium composite dopant (molar ratio 2:1), followed by 1 wt% polyethylene glycol (dispersant) and 2 wt% polyvinyl alcohol (binder) by weight of the powder. The mixture was then coated onto the surface of a pretreated titanium substrate to a thickness of 3 mm. The composite substrate was placed in a vacuum hot-pressing sintering furnace, with a gradient heating process: room temperature → 800℃ (heating rate 5℃ / min, holding for 1 h) → 1200℃ (heating rate 8℃ / min, holding for 2 h) → 1400℃ (heating rate 10℃ / min, holding for 1 h), sintering pressure 8 MPa. After natural cooling, a composite substrate with a conductive titanium suboxide transition layer was obtained, exhibiting a porosity of 22%, a volume resistivity of 200 μΩ·m, and a fracture toughness of 4.5 MPa·m. 1 / 2 .

[0063] 3) Surface modification of the transition layer: First, the surface of the conductive titanium suboxide transition layer of the composite substrate was mechanically roughened with 400-grit sandpaper, then immersed in a composite acid etching solution (0.2 mol / L citric acid, 0.1 mol / L ammonium hydrofluoride, and 0.05 mol / L aminosulfonic acid) for 80 min at 50 °C. After removal, it was rinsed with deionized water until neutral and dried at 80 °C for 4 h. Subsequently, plasma activation was performed (argon:oxygen = 9:1, 150 W, 80 °C for 20 min). The surface roughness Ra was measured to be 100 nm, and the hydroxyl content was 5 mmol / m. 2 .

[0064] 4) Construction of core-shell seed layer: Preparation of core-shell particles: 1g of nanodiamond powder was taken according to the formula, boiled in 1mol / L nitric acid for 2h, washed with deionized water until neutral, and dried at 80℃ for 4h. Then, it was added to 10mL of deionized water along with 0.8g boric acid, 2g urea, and 0.05g PVP. The mixture was stirred at 500r / min for 30min and sonicated at 200W for 60min. The mixture was then transferred to a 50mL autoclave and kept at 180℃ for 12h. After centrifugation and washing, it was vacuum dried at 60℃ for 8h. Then, it was nitrided in a tube furnace at 800℃ for 6h. Nitrogen gas was continued to be introduced until it cooled naturally to room temperature to obtain nanodiamond@boron nitride core-shell particles (core diameter 50nm, shell thickness 10nm).

[0065] Suspension preparation and self-assembly: Prepare a 1 g / L core-shell suspension (containing 0.3 wt% polydopamine), immerse the modified composite substrate in the suspension, sonicate at 200 W for 80 min, self-assemble at 60 °C for 1 h, dry at 100 °C for 4 h, and the seed crystal coverage rate is 95%.

[0066] 5) Low-temperature CatCVD deposition: The composite substrate is placed in the CatCVD reaction chamber and evacuated to a vacuum of 1×10⁻⁶. -3 Pa, firstly, methane (flow rate 20 sccm) was introduced, and a pure diamond transition layer was deposited at 400℃ for 2 h; then, gaseous trimethyl borate (flow rate 6 sccm) and phosphine (flow rate 1 sccm) were simultaneously introduced, and co-doping deposition was carried out at 500℃ for 5 h, resulting in a composite catalytic electrode with a total BDD catalyst layer thickness of 5 μm (boron doping amount 0.5 at%) and phosphorus doping amount 0.3 at%), and an interfacial bonding force of 6.0 MPa.

[0067] Example 2 1) Titanium plate substrate pretreatment: Take a titanium plate with a thickness of 1.0 mm, sandblast it with 100 mesh quartz sand at a pressure of 0.4 MPa for 8 min, then immerse it in a 10 wt% oxalic acid solution and etch it at 60℃ for 30 min. After taking it out, rinse it with deionized water until neutral, and dry it at 80℃ for 4 h to obtain the pretreated titanium plate substrate.

[0068] 2) Preparation of conductive sub-titanium oxide transition layer: Titanium dioxide and titanium were mixed at a mass ratio of 2:1, and then heated at 1610℃ for 25 min in an air atmosphere. After that, they were calcined at 1450℃ for 9 h in a nitrogen atmosphere, cooled, and ball-milled to obtain titanium suboxide powder with an average particle size of 5 μm. Titanium suboxide powder (particle size 5 μm) was mixed with 1.2 wt% yttrium-zirconium composite dopant (molar ratio 2:1), followed by 1 wt% polyethylene glycol (dispersant) and 2 wt% polyvinyl alcohol (binder) by weight of the powder. The mixture was then coated onto the surface of a pretreated titanium substrate to a thickness of 3 mm. The composite substrate was placed in a vacuum hot-pressing sintering furnace, and the temperature was gradually increased: room temperature → 800℃ (heating rate 5℃ / min, holding for 1 h) → 1200℃ (heating rate 8℃ / min, holding for 2 h) → 1400℃ (heating rate 10℃ / min, holding for 1 h). The sintering pressure was 10 MPa. After natural cooling, a composite substrate with a conductive titanium suboxide transition layer was obtained, exhibiting a porosity of 22%, a volume resistivity of 170 μΩ·m, and a fracture toughness of 5.0 MPa·m. 1 / 2 .

[0069] 3) Surface modification of the transition layer: First, the surface of the conductive titanium suboxide transition layer of the composite substrate was mechanically roughened with 600-grit sandpaper, then immersed in a composite acid etching solution (0.2 mol / L citric acid, 0.1 mol / L ammonium hydrofluoride, and 0.05 mol / L aminosulfonic acid) for 60 min at 60 °C. After removal, it was rinsed with deionized water until neutral and dried at 80 °C for 4 h. Subsequently, plasma activation was performed (argon:oxygen = 9:1, activation power 200 W, activation temperature 100 °C, activation time 15 min). The surface roughness Ra was measured to be 200 nm, and the hydroxyl content was 6.5 mmol / m. 2 .

[0070] 4) Construction of core-shell seed layer: Preparation of core-shell particles: 1g of nanodiamond powder (core diameter 80nm) was taken according to the specified ratio, boiled in 1mol / L nitric acid for 2h, washed with deionized water until neutral, and dried at 80℃ for 4h; then mixed with 0.8g boric acid, 2g urea, and 0.05g... PVP was added to 10 mL of deionized water, magnetically stirred at 500 r / min for 30 min, and then ultrasonically dispersed at 200 W for 60 min to form a uniform suspension. The suspension was transferred to a 50 mL PTFE-lined autoclave, kept at 180 °C for 12 h, and allowed to cool naturally to room temperature. The suspension was then centrifuged at 8000 r / min for 10 min, washed three times with deionized water and once with ethanol, and vacuum dried at 60 °C for 8 h. The diamond@boron-nitrogen precursor composite powder was placed in a graphite boat, placed in a tube furnace, and high-purity nitrogen gas with a purity ≥99.99% was introduced at a flow rate of 50 sccm. The temperature was increased to 800 °C at 5 °C / min and kept at that temperature for 6 h. Nitrogen gas was continued to be introduced until the suspension cooled naturally to room temperature. Nanodiamond@boron nitride core-shell particles (core diameter 80 nm, shell thickness 15 nm) were collected.

[0071] Suspension preparation and self-assembly: Prepare a 2 g / L core-shell suspension (containing 0.5 wt% polydopamine), immerse the modified composite substrate in the suspension, use an ultrasonic power of 250 W, an ultrasonic time of 60 min, a self-assembly temperature of 70 ℃, keep warm for 1 h, remove and dry at 100 ℃ for 4 h, with a seed coverage rate of 98%.

[0072] 5) Low-temperature CatCVD deposition: The composite substrate is placed in the CatCVD reaction chamber and evacuated to a vacuum of 1×10⁻⁶. -3 First, methane (flow rate 25 sccm) is introduced, and a pure diamond transition layer is deposited at 400℃ for 3 hours; then, gaseous trimethyl borate (flow rate 10 sccm) and phosphine (flow rate 2 sccm) are simultaneously introduced, and co-doping deposition is carried out at 520℃ for 6 hours to obtain a homogeneous BDD catalyst layer (thickness 10 μm, boron doping amount 0.5 at%, phosphorus doping amount 0.3 at%), finally forming a composite catalytic electrode with an interfacial bonding force of 6.8 MPa.

[0073] Example 3 1) Titanium plate substrate pretreatment: Take a titanium plate with a thickness of 1.5 mm, sandblast it with 120 mesh quartz sand at a pressure of 0.5 MPa for 5 min, then immerse it in 12 wt% oxalic acid solution, etch it at 70℃ for 20 min, take it out and rinse it with deionized water until neutral, and dry it at 80℃ for 4 h to obtain the pretreated titanium plate substrate.

[0074] 2) Preparation of conductive sub-titanium oxide transition layer: Titanium dioxide and titanium were mixed at a mass ratio of 3:1, and then heated at 1640℃ for 40 min in an air atmosphere. After that, they were calcined at 1380℃ for 10 h in a nitrogen atmosphere, cooled, and ball-milled to obtain titanium suboxide powder with an average particle size of 8 μm. The above-mentioned titanium suboxide powder (particle size 8 μm) was mixed with 2 wt% yttrium-zirconium composite dopant (molar ratio 2:1), followed by 1 wt% polyethylene glycol (dispersant) and 2 wt% polyvinyl alcohol (binder) by weight of the powder. The mixture was then coated onto the surface of a pretreated titanium substrate to a thickness of 3 mm. The composite substrate was placed in a vacuum hot-pressing sintering furnace, and the temperature was gradually increased: room temperature → 800℃ (heating rate 5℃ / min, holding for 1 h) → 1200℃ (heating rate 8℃ / min, holding for 2 h) → 1400℃ (heating rate 10℃ / min, holding for 1 h). The sintering pressure was 12 MPa. After natural cooling, a composite substrate with a conductive titanium suboxide transition layer was obtained, exhibiting a porosity of 30%, a volume resistivity of 150 μΩ·m, and a fracture toughness of 4.7 MPa·m. 1 / 2 .

[0075] 3) Surface modification of the transition layer: First, the surface of the conductive titanium suboxide transition layer of the composite substrate was mechanically roughened with 800-grit sandpaper, then immersed in a composite acid etching solution (0.2 mol / L citric acid, 0.1 mol / L ammonium hydrofluoride, and 0.05 mol / L aminosulfonic acid) for 40 min at 70℃. After removal, it was rinsed with deionized water until neutral and dried at 80℃ for 4 h. Subsequently, plasma activation was performed (argon:oxygen = 9:1, activation power 250 W, activation temperature 120℃, activation time 10 min). The surface roughness Ra was measured to be 300 nm, and the hydroxyl content was 8 mmol / m. 2 .

[0076] 4) Construction of core-shell seed layer: Preparation of core-shell particles: 1g of nanodiamond powder (core diameter 100nm) was taken according to the specified ratio, boiled in 1mol / L nitric acid for 2h, washed with deionized water until neutral, and dried at 80℃ for 4h; then mixed with 0.8g boric acid, 2g urea, and 0.05g... PVP was added to 10 mL of deionized water, magnetically stirred at 500 r / min for 30 min, and then ultrasonically dispersed at 200 W for 60 min to form a uniform suspension. The suspension was transferred to a 50 mL PTFE-lined autoclave, kept at 180 °C for 12 h, and allowed to cool naturally to room temperature. The suspension was then centrifuged at 8000 r / min for 10 min, washed three times with deionized water and once with ethanol, and vacuum dried at 60 °C for 8 h. The diamond@boron-nitrogen precursor composite powder was placed in a graphite boat, placed in a tube furnace, and high-purity nitrogen gas with a purity ≥99.99% was introduced at a flow rate of 50 sccm. The temperature was increased to 800 °C at 5 °C / min and kept at that temperature for 6 h. Nitrogen gas was continued to be introduced until the suspension cooled naturally to room temperature. Nanodiamond@boron nitride core-shell particles (core diameter 100 nm, shell thickness 20 nm) were collected.

[0077] Suspension preparation and self-assembly: Prepare a 3 g / L core-shell suspension (containing 0.8 wt% polydopamine), immerse the pretreated matrix in the suspension, use an ultrasonic power of 300 W, an ultrasonic time of 40 min, a self-assembly temperature of 80 ℃, keep warm for 1 h, remove and dry at 100 ℃ for 4 h, with a seed coverage of 99%.

[0078] 5) Low-temperature CatCVD deposition: The composite substrate is placed in the CatCVD reaction chamber and evacuated to a vacuum of 1×10⁻⁶. -3 First, methane (flow rate 30 sccm) is introduced, and a pure diamond transition layer is deposited at 400℃ for 4 h. Then, gaseous trimethyl borate (flow rate 15 sccm) and phosphine (flow rate 4 sccm) are simultaneously introduced, and co-doping deposition is carried out at 550℃ for 7 h to obtain a homogeneous BDD catalyst layer (thickness 15 μm, boron doping amount 0.8 at%, phosphorus doping amount 0.5 at%), which finally forms a composite catalytic electrode with an interfacial bonding force of 7.5 MPa.

[0079] Example 4 Except for the yttrium-zirconium molar ratio of 1:1 in the preparation of the conductive titanium suboxide transition layer, all other parameters are completely consistent with those in Example 2.

[0080] Example 5 Except for the "boron doping amount of 0.6 at% and phosphorus doping amount of 0.2 at%" in the low-temperature CatCVD deposition, the other parameters are completely consistent with those in Example 2.

[0081] Example 6 Except for the "co-doping deposition temperature of 510°C" in the low-temperature CatCVD deposition, the other parameters are completely consistent with those in Example 2.

[0082] Comparative Example 1 Except for the yttrium-zirconium composite doping amount of 0.3 wt% in the preparation of the conductive titanium suboxide transition layer, the other parameters are completely consistent with those in Example 2.

[0083] Comparative Example 2 Except for the "composite acid etching temperature of 75°C" in the composite modification of the transition layer surface, the other parameters are completely consistent with those in Example 2.

[0084] Comparative Example 3 Except for the omission of the low-temperature plasma activation step in the surface composite modification of the transition layer, the other parameters are completely consistent with those in Example 2.

[0085] Comparative Example 4 Except for the core-shell seed layer construction, where the core-shell suspension concentration is 0.5 g / L, all other parameters are completely consistent with those in Example 2.

[0086] Comparative Example 5 Except for the "co-doping deposition temperature of 480°C" in the low-temperature CatCVD deposition, the other parameters are completely consistent with those in Example 2.

[0087] Comparative Example 6 Except for the fact that "the seed crystal is pure nanodiamond (without boron nitride shell)" in the construction of the core-shell seed layer, the other parameters are completely consistent with those in Example 2.

[0088] Comparative Example 7 Except for the omission of the 400℃ pure diamond transition layer deposition step and the direct boron-phosphorus co-doping deposition in the low-temperature CatCVD deposition, the other parameters are completely consistent with those in Example 2.

[0089] Comparative Example 8 Except for the phosphorus doping amount of 0.7 at% in the low-temperature CatCVD deposition, the other parameters are completely consistent with those in Example 2.

[0090] Performance testing The performance test data of Examples 1-6 and Comparative Examples 1-8 are shown in Table 1 below: Table 1. Performance test data of Examples 1-6 and Comparative Examples 1-8

[0091] As shown in Table 1, the composite catalytic electrodes prepared in Examples 1-6 exhibit excellent performance, with an interfacial bonding strength ≥6.0 MPa, a COD removal rate ≥98.0%, a cycle stability ≥97.0%, and a BDD crystallinity ≥88%. They also demonstrate good COD removal efficiency from wastewater. In contrast, the comparative examples, deviating from the technical solution of this invention, show a significant decrease in all performance characteristics.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A composite catalytic electrode based on titanium suboxide, characterized in that, The composite catalytic electrode based on titanium suboxide is a ternary composite structure consisting of a titanium plate substrate, a conductive titanium suboxide transition layer, and a BDD catalytic layer grown by seed crystals in a core-shell structure. The conductive sub-titanium oxide transition layer is a yttrium-zirconium composite doped monolayer structure; The BDD catalytic layer induced by the core-shell seed crystal is a homogeneous structure doped with phosphorus, and the core-shell seed crystal is nanodiamond@boron nitride core-shell particles.

2. The composite catalytic electrode based on sub-titanium oxide according to claim 1, characterized in that, The thickness of the titanium plate substrate is 0.5~1.5mm; The doping amount of the yttrium-zirconium composite doping is 0.5~2wt% of the mass of titanium suboxide, and the molar ratio of yttrium to zirconium is 2:

1. The porosity of the conductive titanium suboxide transition layer is 15-30%, and the particle size of the conductive titanium suboxide transition layer is 2-8 μm.

3. The composite catalytic electrode based on sub-titanium oxide according to claim 2, characterized in that, In the aforementioned nanodiamond@boron nitride core-shell particles, the core layer particle size is 50~100nm, and the shell layer thickness is 10~20nm; the total thickness of the BDD catalyst layer is 5~15μm. The boron doping content in the BDD catalyst layer is 0.3-0.8% in atomic percentage. The phosphorus doping amount is 0.1-0.5% in atomic percentage.

4. A method for preparing a composite catalytic electrode based on titanium suboxide as described in any one of claims 1 to 3, characterized in that, Includes the following steps: 1) The titanium plate is subjected to sandblasting and oxalic acid etching in sequence to obtain a pretreated titanium plate substrate; 2) Yttrium-zirconium composite doped titanium suboxide powder was coated on the surface of a pretreated titanium plate substrate and sintered by gradient heating to obtain a composite substrate containing a conductive titanium suboxide transition layer. 3) The surface of the conductive sub-titanium oxide transition layer of the composite substrate was mechanically roughened, subjected to composite acid etching, and activated by low-temperature plasma in sequence to obtain the modified composite substrate; 4) The modified composite substrate was immersed in a nanodiamond@boron nitride core-shell suspension and formed a uniform seed layer by ultrasonic-assisted self-assembly. 5) The composite substrate with a uniform seed layer obtained in step 4) is deposited with a pure diamond transition layer at 400°C, and then boron source gas and phosphorus source gas are simultaneously introduced at 500~550°C to deposit a homogeneous BDD catalyst layer, and finally a composite catalytic electrode is formed.

5. The method for preparing the composite catalytic electrode based on sub-titanium oxide according to claim 4, characterized in that, In step 1), the sandblasting process uses 80-120 mesh quartz sand and a sandblasting pressure of 0.3-0.5 MPa; the oxalic acid concentration for the oxalic acid etching is 8-12 wt%, the etching temperature is 50-70℃, and the etching time is 20-40 min. In step 2), the coating thickness of the yttrium-zirconium composite-doped sub-titanium oxide powder is 1.5~3mm; The gradient heating sintering process involves heating to 800℃ at a rate of 5℃ / min and holding for 1 hour; then heating to 1200℃ at a rate of 8℃ / min and holding for 2 hours; and finally heating to 1400℃ at a rate of 10℃ / min and holding for 1 hour. The sintering pressure is controlled at 8~12MPa during the gradient heating sintering process.

6. The method for preparing the composite catalytic electrode based on sub-titanium oxide according to claim 4 or 5, characterized in that, The etching solution for the composite acid etching described in step 3) is composed of citric acid, ammonium hydrofluoride, and aminosulfonic acid in a concentration ratio of 0.2:0.1:0.05 mol / L, with an etching temperature of 50~70℃ and an etching time of 40~80 min; The low-temperature plasma activation uses an argon-oxygen mixture with a volume ratio of 9:1, an activation power of 150~250W, an activation time of 10~20min, and an activation temperature of 80~120℃.

7. The method for preparing the composite catalytic electrode based on sub-titanium oxide according to claim 6, characterized in that, The concentration of the nanodiamond@boron nitride core-shell suspension in step 4) is 1~3 g / L, containing 0.3~0.8 wt% polydopamine dispersant, with an ultrasonic power of 200~300 W, an ultrasonic time of 40~80 min, a self-assembly temperature of 60~80℃, and a seed layer coverage of ≥95% after drying; The boron source gas mentioned in step 5) is gaseous trimethyl borate; the phosphorus source gas is phosphine.

8. The method for preparing the composite catalytic electrode based on sub-titanium oxide according to claim 4, 5, or 7, characterized in that, The method for preparing the sub-titanium oxide powder in step 2) is as follows: titanium dioxide and titanium are mixed, kept at a temperature in an air atmosphere, then calcined in a nitrogen atmosphere, cooled, and obtained by ball milling. The mass ratio of titanium dioxide to titanium is (1~3):1; the heat preservation is specifically at 1600~1650℃ for 20~40 min; the calcination is specifically at 1350~1450℃ for 8~10 h.

9. The method for preparing the composite catalytic electrode based on sub-titanium oxide according to claim 8, characterized in that, The nanodiamond@boron nitride core-shell particles were prepared by the following method: a) The core layer material is nanodiamond powder with a particle size of 50~100nm, which is pretreated by boiling with 1mol / L nitric acid for 2h, washing with deionized water until neutral, and drying at 80℃ for 4h for hydroxylation; the shell layer material is boric acid, urea, and polyvinylpyrrolidone, and the solvent is deionized water; the raw material ratio is nanodiamond:boric acid:urea:PVP=1g:0.8g:2g:0.05g, and the amount of deionized water added is 10 times the total mass of solid material; b) Add nano-diamond, boric acid, urea, and PVP sequentially to deionized water, stir magnetically at 500 r / min for 30 min, and then ultrasonically disperse at 200 W for 60 min to form a uniform suspension. Transfer the suspension to a 50 mL polytetrafluoroethylene-lined autoclave, keep it at 180 °C for 12 h, cool it naturally to room temperature, centrifuge at 8000 r / min for 10 min, wash it three times with deionized water and once with ethanol, and vacuum dry it at 60 °C for 8 h to obtain diamond@boron-nitrogen precursor composite powder. c) The diamond@boron-nitrogen precursor composite powder was placed in a graphite boat, placed in a tube furnace, and high-purity nitrogen gas was introduced at a flow rate of 50 sccm. The temperature was increased to 800℃ at 5℃ / min and held for 6 hours. Nitrogen gas was continued to be introduced until it cooled naturally to room temperature. Nanodiamond@boron nitride core-shell particles were collected.

10. The application of the titanium suboxide-based composite catalytic electrode according to any one of claims 1 to 3 in the removal of COD from high-concentration, recalcitrant organic wastewater, characterized in that, The high-concentration, recalcitrant organic wastewater has a COD ≥ 1000 mg / L.

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