Preparation method and application of piezoelectric catalytic composite material for degrading pollutants

Abstract

The invention belongs to the technical field of environmental functional materials, and discloses a preparation method and application of a piezoelectric catalytic composite material for degrading pollutants. According to the scheme, stress dispersion, crack inhibition and efficient charge transmission are realized by in-situ construction of a nano aluminum oxide buffer layer with dual gradients of aperture and elasticity modulus between a piezoelectric substrate and a catalytic active component. The buffer layer is composed of a compact barrier layer, a transition layer and a porous surface layer, and 5-30 nm titanium dioxide or graphite phase carbon nitride is loaded as a catalytic component. The problem of catalyst stripping caused by interface stress concentration is solved, meanwhile, efficient charge transmission and high-density distribution of catalytic active sites are considered, and collaborative optimization of mechanical stability and electrochemical activity is achieved. According to the technical scheme, the performance bottleneck of an existing piezoelectric catalytic material in a dynamic service environment is broken through.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, and relates to a method for preparing and applying a piezoelectric catalytic composite material for degrading pollutants. Background Technology

[0002] Piezoelectric catalysis, as an emerging non-photodependent catalytic pathway, converts mechanical energy (such as ultrasonic vibration and water flow disturbance) into electrical energy to drive the catalyst to generate reactive oxygen species for pollutant mineralization, demonstrating unique application potential. The core of this technology lies in the composite structure of the piezoelectric matrix and the catalytically active component, and its performance is highly dependent on the interfacial stability and charge transfer efficiency between the two.

[0003] In existing technologies, physical mixing, in-situ growth, or surface loading methods are commonly used to attach nanocatalysts (such as TiO2, graphitic carbon nitride, or noble metal particles) to the surface of piezoelectric materials (such as BaTiO3, ZnO, or polyvinylidene fluoride) to construct efficient piezoelectric-catalytic synergistic systems. While these methods can initially achieve pollutant degradation under laboratory conditions and exhibit certain catalytic activity under static or short-term vibration conditions, their design philosophy mainly focuses on the selection of catalytically active components and the optimization of specific surface area, paying insufficient attention to the mechanical stability of the composite interface under dynamic service environments.

[0004] The weak interfacial bonding strength commonly found between piezoelectric substrates and catalysts is insufficient to effectively resist the shear stress and peeling force induced by repeated deformation. Piezoelectric materials continuously undergo lattice distortion in alternating stress fields, generating periodic changes in surface potential. Meanwhile, the rigid catalyst particles attached to them, due to mismatches in physical parameters such as thermal expansion coefficient and elastic modulus with the substrate, form significant stress concentration zones at the interface.

[0005] This localized high-stress state accelerates the initiation and propagation of microcracks, ultimately leading to the detachment of catalyst particles from the substrate surface. Catalyst loss not only directly reduces the number of active sites and weakens overall catalytic efficiency, but also disrupts internal charge transport pathways, lowering the effective conversion rate of piezoelectric potential to the catalytic reaction. The detached nanoparticles may cause secondary pollution and also threaten the long-term reliability of the system.

[0006] Although some studies have attempted to improve adhesion by introducing adhesives or surface modification, such methods often sacrifice the interfacial charge migration rate or fail to maintain structural integrity under strong vibration conditions, reflecting an inherent contradiction between mechanical stability and electrochemical activity. Summary of the Invention

[0007] This invention provides a method for preparing and applying a piezoelectric catalytic composite material for degrading pollutants, aiming to solve the technical problems of catalyst exfoliation, charge transport path disruption, and catalytic efficiency decline caused by interfacial stress concentration in existing piezoelectric-catalytic composite systems under long-term dynamic mechanical excitation conditions. This invention introduces a nanoscale alumina buffer layer with a dual gradient structure of pore size and elastic modulus between the piezoelectric matrix and the catalytically active component. This effectively disperses interfacial stress, inhibits crack propagation, and continuously constructs charge transport channels, thereby significantly improving the mechanical stability and service life of the composite material while ensuring high catalytic activity.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a method for preparing a piezoelectric catalytic composite material for degrading pollutants, comprising the following steps: First, pretreating the surface of a piezoelectric substrate to form a clean and activated surface; second, constructing a gradient alumina buffer layer with a thickness of 50-300 nm in situ on the surface of the piezoelectric substrate through a multi-step anodic oxidation process, wherein the buffer layer comprises, from the inside to the outside, a dense barrier layer, a transition layer, and a porous surface layer, wherein the dense barrier layer is in direct contact with the piezoelectric substrate, has a thickness of 10-30 nm, and a pore size of less than 2 nm; the transition layer has a thickness of 20-100 nm, and the pore size linearly increases from 2 nm to 20 nm; the porous surface layer has a thickness of 20-170 nm, and the pore size is stable in the range of 20-50 nm; third, loading a catalytically active component onto the porous surface layer of the gradient alumina buffer layer, wherein the catalytically active component is titanium dioxide nanoparticles with a particle size in the range of 5-30 nm; finally, heat-treating the obtained composite structure to enhance the interfacial bonding strength and complete the crystal phase regulation.

[0009] In a preferred embodiment of the present invention, the piezoelectric matrix is ​​selected from any one of BaTiO3, ZnO, or polyvinylidene fluoride, and its geometric morphology is sheet-like, fibrous, or porous bulk structure, with a specific surface area greater than 1 m². 2 / g. When the piezoelectric matrix is ​​an inorganic ceramic material, its surface pretreatment includes sequentially performing acetone ultrasonic cleaning for 10 min, rinsing with deionized water, soaking in 5% nitric acid solution for 5 min, rinsing again with deionized water, and vacuum drying at 80°C for 2 hours; when the piezoelectric matrix is ​​a polymer material, its surface pretreatment includes plasma treatment for 10 min, with a power of 50 W, working gas of oxygen, and a pressure of 10 Pa.

[0010] The specific parameters of the multi-step anodizing process are as follows: a piezoelectric substrate is used as the anode, a platinum sheet as the cathode, and the electrolyte consists of 0.3 mol / L oxalic acid and 5 vol% ethylene glycol aqueous solution. The first stage of oxidation is carried out at 10V and 5℃ for 10 minutes to form a dense barrier layer. The second stage of oxidation is carried out at a voltage that linearly increases from 10V to 40V and a temperature maintained at 5℃ for 30 minutes to form a transition layer with gradually changing pore size. The third stage of oxidation is carried out at a constant voltage of 40V and a temperature of 5℃ for 20-60 minutes to form a porous surface layer with stable pore size. The entire oxidation process is carried out under magnetic stirring at a stirring rate of 200 rpm to ensure uniform electrolyte concentration.

[0011] As a key technical feature of this invention, the pore size gradient of the gradient alumina buffer layer is achieved by controlling the electric field intensity distribution and local dissolution rate during the anodic oxidation process. In the low-voltage stage, the high electric field intensity promotes rapid oxidation of aluminum atoms to form a non-porous, dense Al2O3 layer. As the voltage increases, the electric field-induced local breakdown effect intensifies, while the chemical dissolution of the oxide film by oxalate ions intensifies, leading to an increase in micropore nucleation density and a linear increase in pore size with oxidation time. In the constant high-voltage stage, pore formation and dissolution reach a dynamic equilibrium, and the pore size tends to stabilize. This gradient structure also causes the elastic modulus of the buffer layer to show a continuous decreasing trend from the inside to the outside. The elastic modulus of the dense barrier layer is 200-220 GPa, the transition layer is 80-150 GPa, and the porous surface layer is 30-60 GPa. This forms a modulus-matched transition region with the piezoelectric matrix (elastic modulus typically 50-150 GPa) and the catalytically active component (TiO2 elastic modulus approximately 230 GPa), effectively alleviating interfacial stress concentration caused by physical parameter mismatch.

[0012] In the loading step of the catalytically active component, an impregnation-calcination method was adopted: the piezoelectric matrix modified with a gradient alumina buffer layer was immersed in a 0.1 mol / L tetrabutyl titanate ethanol solution, allowed to stand for 2 hours, then removed and dried at 60°C for 1 hour, followed by calcination in air at 450°C for 2 hours, causing the tetrabutyl titanate to hydrolyze and crystallize into anatase phase titanium dioxide. During calcination, the porous surface of the gradient alumina buffer layer provides anchoring points for TiO2 nanoparticles, and its pore walls have a spatial confinement effect on particle growth, thereby controlling the particle size within the range of 5-30 nm and preventing agglomeration. In addition, the Al-O-Ti chemical bonds formed between alumina and titanium dioxide further enhance the interfacial bonding strength and provide low-resistance transport channels for photogenerated or piezoelectrically generated electrons.

[0013] In another preferred embodiment of the present invention, the catalytically active component can also be graphitic carbon nitride nanosheets, which are grown in situ on the surface of a gradient alumina buffer layer via thermal polymerization: melamine powder is placed at the bottom of a crucible, and the modified piezoelectric substrate is inverted on top of it. The crucible is heated to 550°C at a rate of 5°C / min and held for 4 hours. After cooling, a ternary composite structure of graphitic carbon nitride / Al2O3 / BaTiO3 is obtained. In this structure, the gradient alumina layer not only provides mechanical buffering, but its surface hydroxyl groups also form hydrogen bonds with the edge amino groups of the graphitic carbon nitride, enhancing adhesion stability.

[0014] This invention also provides the application of the piezoelectric catalytic composite material in the degradation of organic pollutants. Specifically, the composite material is placed in water containing organic pollutants, and an application frequency of 20-100 kHz and a power density of 0.5-2 W / cm² are used. 2 The catalytic reaction is carried out under ultrasonic vibration conditions. Under ultrasound, the piezoelectric matrix generates an alternating surface potential due to periodic deformation. This potential is efficiently transferred to the surface of the catalytically active component through a gradient alumina buffer layer, driving water molecules or dissolved oxygen to generate hydroxyl radicals and superoxide radicals, thereby mineralizing pollutants. Due to the presence of the gradient buffer layer, even after 100 hours of continuous ultrasonic treatment, the shedding rate of the catalytically active component is low.

[0015] The preparation method described in this invention has the advantages of strong process controllability, good repeatability, and applicability to various piezoelectric substrates and catalytic systems. By adjusting the voltage program and time parameters of anodic oxidation, the thickness, pore size distribution, and modulus gradient slope of the gradient buffer layer can be precisely controlled to adapt to the mechanical excitation intensity and contaminant type under different application scenarios. For example, in high-frequency, low-amplitude vibration environments, a thinner buffer layer (total thickness of approximately 80 nm) can be used to reduce the charge transport distance; in low-frequency, high-amplitude impact conditions, a thicker buffer layer (total thickness of approximately 250 nm) can be used to enhance the anti-peeling ability.

[0016] As an extension of the present invention, the piezoelectric catalytic composite material can also be integrated into a flow reactor for treating industrial wastewater or microplastic suspensions. Under the disturbance of water flow at a velocity of 0.5-2 m / s, the material surface continuously generates a piezoelectric potential due to shear force, enabling in-situ degradation of pollutants without the need for external energy input.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. By constructing a nano-alumina buffer layer with dual gradients in pore size and elastic modulus in situ between the piezoelectric matrix and the catalytically active component, the problems of catalyst exfoliation, charge transport path breakage and catalytic activity decay caused by interfacial stress concentration are solved in a coordinated manner, and the mechanical stability and electrochemical activity of the composite material under dynamic service environment are optimized in a coordinated manner.

[0018] 2. The gradient buffer layer, through its dual gradient of pore size and modulus, constructs a continuous mechanical property transition zone between heterogeneous interfaces, significantly reducing and dispersing the local stress peaks caused by physical parameter mismatch (for example, according to finite element simulation analysis, the maximum principal stress value is reduced by about 70% compared to the structure without buffer layer). 3. The porous surface of the gradient buffer layer provides a high specific surface area and ordered channels, which not only provides abundant loading sites for catalytically active components and achieves a high-density distribution of active sites, but also facilitates efficient mass transfer between reactants and products. 4. The heterojunction interface formed between alumina and the catalytically active components promotes the effective separation of electron-hole pairs driven by piezoelectric potential, which significantly improves the catalytic reaction efficiency. Detailed Implementation

[0019] This invention provides a method for preparing and applying a piezoelectric catalytic composite material for degrading pollutants. The core of this method lies in constructing a nanoscale alumina buffer layer with a dual gradient structure of pore size and elastic modulus in situ between a piezoelectric matrix and the catalytically active component. This addresses the technical problems in existing technologies where interfacial stress concentration leads to catalyst particle detachment under continuous mechanical vibration, charge transport path disruption, and catalytic efficiency degradation. This method achieves a continuous gradient structure in the buffer layer from the inside out—from a dense barrier layer, a transition layer to a porous surface layer—through precise control of the anodic oxidation process parameters. Based on this, a highly dispersed catalytically active component is loaded, ultimately yielding a composite material that combines high catalytic activity, excellent mechanical stability, and long-term service reliability.

[0020] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0021] Example 1: The piezoelectric substrate was BaTiO3; the total thickness of the gradient alumina buffer layer was 180 nm (20 nm dense layer + 60 nm transition layer + 100 nm porous layer); the catalytically active component was titanium dioxide (particle size 20 nm); the ultrasonic frequency was 50 kHz and the power density was 1 W / cm². 2 ; Preparation process: piezoelectric substrate pretreatment → multi-step anodic oxidation to construct buffer layer → impregnation-calcination of loaded catalytic components → heat treatment → finished product.

[0022] Example 2: The piezoelectric matrix is ​​ZnO, and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0023] Example 3: The piezoelectric matrix is ​​polyvinylidene fluoride, and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1 (pretreatment is changed to plasma treatment).

[0024] Example 4: The total thickness of the gradient alumina buffer layer is 50nm (10nm dense layer + 20nm transition layer + 20nm porous layer), and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0025] Example 5: The total thickness of the gradient alumina buffer layer is 300 nm (30 nm dense layer + 100 nm transition layer + 170 nm porous layer), and the rest of the formulation and process are the same as in Example 1; Preparation process: Same as in Example 1.

[0026] Example 6: The catalytically active component is graphitic carbon nitride nanosheets, and the remaining formulation and process are the same as in Example 1; Preparation process: Same as in Example 1 (the load was changed to thermal polymerization).

[0027] Example 7: Ultrasonic power density 2W / cm² 2 The remaining formulas and processes are the same as in Example 1; Preparation process: Same as in Example 1.

[0028] Example 8: Ultrasonic power density 0.5 W / cm² 2 The remaining formulas and processes are the same as in Example 1; Preparation process: Same as in Example 1.

[0029] Comparative Example 1: No gradient alumina buffer layer, titanium dioxide directly loaded onto BaTiO3 matrix; other formulations and processes are the same as in Example 1; Preparation process: piezoelectric matrix pretreatment → direct impregnation-calcination of supported catalytic components → heat treatment → finished product.

[0030] Comparative Example 2: The surface of the piezoelectric substrate is a homogeneous alumina layer (thickness 180nm, pore size 20nm), and the rest of the formulation and process are the same as in Example 1; Preparation process: piezoelectric substrate pretreatment → homogeneous layer construction by single anodic oxidation → loading of catalytic components → heat treatment → finished product.

[0031] Test method: Catalytic performance test: The degradation rate of Rhodamine B was determined by UV-Vis spectrophotometer; the degradation rate was retested after continuous sonication for 100 hours.

[0032] Stability and mechanical testing: Inductively coupled plasma mass spectrometry was used to determine the shedding rate of the catalytic components; an electrochemical workstation was used to test the charge transfer resistance.

[0033] Application testing: Integrated into a flow reactor, the bisphenol A removal efficiency was measured over 30 days; stability under water flow disturbance was evaluated.

[0034] The test data comparisons are shown in Table 1 and Table 2.

[0035] Table 1. Comparison of Rhodamine B degradation rate, 100-hour shedding rate, and degradation rate after 100 hours. Table 2 Comparison of Charge Transfer Resistance and Bisphenol A Removal Rate after 30 Days In Examples 1-8, the shedding rate was ≤2.8% and the degradation rate remained ≥91% after 100 hours, which was far better than the comparative examples. Comparative Example 1 had an extremely high shedding rate due to the lack of a buffer layer, and Comparative Example 2 had insufficient stress dispersion in the homogeneous layer and poor stability, which confirms that the gradient buffer layer is the key to stability and high efficiency.

[0036] Increasing the thickness of the buffer layer (Examples 4→1→5) reduces the shedding rate and improves stability; different piezoelectric substrates can be adapted to the system, with BaTiO3 showing the best performance; high ultrasonic power (Example 7) increases the degradation rate but does not affect stability.

[0037] The embodiment features low charge transfer resistance and high charge transport efficiency; a removal rate of ≥84% for 30 consecutive days in a flow reactor with minimal pressure drop; no secondary pollution; and is suitable for actual wastewater treatment.

[0038] Compared to the direct loading process (Comparative Example 1), the detachment rate of the example was reduced by 94%, and the degradation rate retention rate was increased by 60%; compared to the homogeneous layer process (Comparative Example 2), the detachment rate was reduced by 86%, solving the problem of easy catalyst detachment caused by interfacial stress concentration.

[0039] The composite material described in this invention achieves stress dispersion and charge transport synergy through a gradient alumina buffer layer. Different parameter combinations can meet the requirements for efficient and stable degradation of pollutants, and it is suitable for wastewater treatment scenarios driven by ultrasound or disturbed by water flow.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a piezoelectric catalytic composite for degrading pollutants, characterized in that, Includes the following steps: Pre-treating the surface of the piezoelectric substrate to form a clean and activated surface; A gradient alumina buffer layer with a thickness of 50-300 nm is constructed in situ on the surface of the piezoelectric substrate through a multi-step anodizing process. The buffer layer consists of a dense barrier layer, a transition layer and a porous surface layer from the inside to the outside. The dense barrier layer is in direct contact with the piezoelectric substrate and has a thickness of 10-30 nm and a pore size of less than 2 nm. The thickness of the transition layer is 20-100 nm, and the pore size increases linearly from 2 nm to 20 nm. The thickness of the porous surface layer is 20-170 nm, and the pore size is stable in the range of 20-50 nm. A catalytically active component is loaded on the porous surface of the gradient alumina buffer layer. The catalytically active component is titanium dioxide nanoparticles with a particle size in the range of 5-30 nm. The resulting composite structure was subjected to heat treatment to enhance the interfacial bonding strength and achieve crystal phase control.

2. The piezocatalytic composite material preparation method of claim 1, wherein, The piezoelectric matrix is ​​selected from any one of BaTiO3, ZnO or polyvinylidene fluoride, and its geometric shape is sheet-like, fibrous or porous bulk structure.

3. The method for preparing piezoelectric catalytic composite materials according to claim 2, characterized in that, When the piezoelectric substrate is an inorganic ceramic material, its surface pretreatment includes sequentially performing acetone ultrasonic cleaning, deionized water rinsing, immersion in 5% nitric acid solution, deionized water rinsing again, and vacuum drying; when the piezoelectric substrate is a polymer material, its surface pretreatment includes plasma treatment.

4. The method for preparing piezoelectric catalytic composite materials according to claim 1, characterized in that, The multi-step anodizing process uses an electrolyte composed of 0.3 mol / L oxalic acid and 5 vol% ethylene glycol aqueous solution, with a piezoelectric substrate as the anode and a platinum sheet as the cathode, and is carried out under magnetic stirring at a stirring rate of 200 rpm. The first stage of oxidation is carried out at a voltage of 10V and a temperature of 5℃ for 10 min; the second stage of oxidation is carried out at a voltage that is linearly increased from 10V to 40V and a temperature of 5℃ for 30 min; and the third stage of oxidation is carried out at a constant voltage of 40V and a temperature of 5℃ for 20-60 min.

5. The method for preparing piezoelectric catalytic composite materials according to claim 1, characterized in that, The elastic modulus of the gradient alumina buffer layer decreases continuously from the inside to the outside, with the elastic modulus of the dense barrier layer being 200-220 GPa, the transition layer being 80-150 GPa, and the porous surface layer being 30-60 GPa.

6. The method for preparing piezoelectric catalytic composite materials according to claim 1, characterized in that, The catalytically active component is loaded by an impregnation-calcination method: the piezoelectric matrix modified with a gradient alumina buffer layer is immersed in a 0.1 mol / L tetrabutyl titanate ethanol solution and left to stand for 2 hours, then dried at 60°C for 1 hour and calcined in air at 450°C for 2 hours to form anatase phase titanium dioxide.

7. The method for preparing piezoelectric catalytic composite materials according to claim 6, characterized in that, During calcination, the pore walls of the porous surface exert a spatial confinement effect on the growth of titanium dioxide nanoparticles and enhance the interfacial bonding strength through Al-O-Ti chemical bonds.

8. The method for preparing piezoelectric catalytic composite materials according to claim 1, characterized in that, The catalytically active component is graphitic carbon nitride nanosheets, which are grown in situ on the surface of a gradient alumina buffer layer by thermal polymerization: melamine powder is placed at the bottom of a crucible, the modified piezoelectric substrate is inverted on top of it, and the mixture is kept at 550°C for 4 hours. After cooling, a graphitic carbon nitride / Al2O3 / BaTiO3 composite structure is obtained.

9. The method for preparing piezoelectric catalytic composite materials according to claim 8, characterized in that, Hydroxyl groups on the surface of the gradient alumina buffer layer form hydrogen bonds with the amino groups at the edge of the graphitic carbon nitride, thereby improving adhesion stability.

10. A piezoelectric catalytic composite material prepared by the method according to any one of claims 1-9, characterized in that, For degradation of organic pollutants in water under ultrasonic vibration conditions, the ultrasonic frequency is 20-100 kHz, the power density is 0.5-2 W / cm 2 .

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