Magnetic piezoelectric photocatalytic hollow particle for degrading organic pollutants in water body

Abstract

The invention discloses a magnetic piezoelectric photocatalytic hollow particle for degrading organic pollutants in a water body, and the photocatalytic oxidation technology has the defects of high photon-generated carrier recombination rate, low visible light utilization rate, low cyclic utilization rate and the like, so that the development of the photocatalytic technology is seriously limited. By introducing BaTiO3 to construct a piezoelectric-photocatalytic coupling system, the performance of the catalyst is further improved, and the ZnFe2O4 material prolongs the absorption wavelength of the photocatalyst to a visible light region to make up for the defect of poor utilization rate of visible light. Besides, the piezoelectric photocatalytic composite material is loaded on the surfaces of the aluminum oxide hollow spheres, so that surface active sites of the composite material are improved, the dispersity of the catalyst material in a to-be-treated solution is improved, and the aluminum oxide hollow particles are beneficial to recycling and reusing of the photocatalytic material, and the method belongs to the technical field of environmental protection.

Description

Technical Field

[0001] In the present invention, hollow millimeter-sized (0.5 mm) particles are subjected to continuously changing pressures in water flow, thereby generating a micro piezoelectric effect. Under the action of the micro piezoelectric effect, when light illumination occurs, electron-hole pairs are generated on the surface of the catalyst, and the micro piezoelectric effect of the piezoelectric material inhibits the recombination of electron-hole pairs, thereby promoting the photocatalytic degradation of water pollutants. This invention belongs to the field of environmental protection technologies. Background Art

[0002] With the acceleration of the industrialization and urbanization processes, the discharge of waterborne organic pollutants (such as dyes, pesticides, drug residues, etc.) has become a global environmental problem. Traditional photocatalytic technologies utilize semiconductor materials (such as TiO2, g-C3N4) to generate electron-hole pairs under light illumination and degrade pollutants through redox reactions, but they have the following defects: 1. High electron-hole recombination rate: The rapid recombination of photo-generated carriers leads to low catalytic efficiency; 2. Single energy input: Dependence on continuous light illumination results in a significant decline in performance under weak light or no-light conditions; 3. Difficult recovery: Nano-sized catalysts are easily washed away by water flow, causing secondary pollution and resource waste.

[0003] In recent years, composite systems of piezoelectric materials (such as BaTiO3, ZnO) and photocatalysts have received attention. The piezoelectric effect can generate an internal electric field through mechanical stress (such as water flow impact, ultrasonic waves) to directionally separate electron-hole pairs, thereby improving the photocatalytic efficiency. However, the existing technologies have limitations such as insufficient structural design: The piezoelectric response of solid particles is weak and it is difficult to effectively transfer stress; Limited synergy mechanism: The interfacial bonding between the piezoelectric material and the photocatalyst is not tight, and the charge transfer efficiency is low; High recovery cost: Nano-composites require complex centrifugation or membrane separation processes and are difficult to apply on a large scale.

[0004] In addition, the introduction of magnetic materials (such as Fe3O4, CoFe2O4) can simplify the catalyst recovery, but their combination with piezoelectric / photocatalytic components often results in the coverage of active sites, and magnetic particles are prone to agglomeration, reducing the catalytic performance.

[0005] Piezoelectric catalysis is a newly emerging research field in recent years. It can generate a surface electric potential in piezoelectric materials under the action of external forces, and thus promote the formation of active free radicals through the internal potential difference, thereby achieving the efficient degradation of pollutants in water, but its degradation efficiency still needs to be improved.

[0006] CN119186606A discloses a microsphere piezoelectric-photocatalyst and its preparation method, which improves the carrier concentration by the electron capture effect of oxygen vacancies to enhance its photocatalytic, piezoelectric catalytic and photo-piezoelectric synergistic catalytic efficiency, but does not integrate magnetic function and relies on external mechanical stress; while CN119114108A realizes the recovery of magnetic photocatalyst, but lacks piezoelectric synergistic effect. In contrast, the millimeter-scale magnetic piezoelectric-photocatalytic hollow particles utilized in the present invention generate a piezoelectric electric field through the spontaneous deformation of the hollow structure in water flow, coupling with the photocatalytic reaction to achieve efficient separation of electrons and holes. At the same time, a magnetic core is used to achieve rapid recovery, with characteristics of self-energy supply (no additional input other than ultrasonic / light irradiation), high catalytic activity (piezoelectric-photocatalytic synergy) and engineering applicability (millimeter-scale size suitable for large-flow water bodies), significantly breaking through the bottlenecks of single material function, dependence on external energy sources and difficult recovery in the prior art. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of traditional photocatalytic materials such as high electron-hole recombination rate, single energy utilization and difficult recovery, and provide a hollow particle composite material with enhanced piezoelectric effect, improved photocatalytic activity and magnetic recovery function. The piezoelectric effect is excited by the deformation of the hollow alumina carrier under water flow pressure, and the built-in electric field of the piezoelectric material (BaTiO3) is used to inhibit the recombination of photo-generated carriers; at the same time, the rapid separation and recovery of the catalyst are realized through the magnetic component (ZnFe2O4) to prevent environmental pollution and meet the engineering requirements of large-flow water body treatment.

[0008] To solve the above technical problems, the present invention aims to provide a preparation method of a lightweight piezoelectric-photocatalytic composite material to solve the problems of low efficiency and difficult recovery of single-phase photocatalysts.

[0009] The purpose of the present invention is achieved by the following technical solutions: The ZnFe2O4 / BaTiO3@hollow alumina composite material is constructed step by step by the sol-gel method, and then the structure of the composite material is stabilized by the calcination process.

[0010] The present invention uses the sol-gel method to prepare ZnFe2O4 and BaTiO3, and prepare the ZnFe2O4 / BaTiO3@alumina hollow sphere composite material, including the following steps:

[0011] (1) The present invention pre-treats the alumina hollow spheres, adds the alumina hollow spheres to pure water for washing, filtering and drying, and sets aside.

[0012] (2) Weigh 0.02 mol of barium hydroxide and dissolve it in a certain amount of acetic acid solution

[0013] (3) Take 0.02 mol of tetrabutyl titanate and dissolve it in twice the volume of absolute ethanol, and slowly add it drop by drop to the mixed solution in step (2).

[0014] (4) Place the solution from step (3) on a magnetic stirrer and stir vigorously for 0.5 h to form a BaTiO3 sol.

[0015] (5) Place the sol obtained in step (4) in a vacuum drying oven and dry at a constant temperature of 80 °C for 2 h to form a BaTiO3 gel.

[0016] (6) Place the gel obtained in step (5) in a muffle furnace and calcine at 900 °C for 2 h, then grind to obtain a nano BaTiO3 catalyst.

[0017] (7) Disperse the nano BaTiO3 catalyst prepared in step (6) in pure water and sonicate for 0.5 h.

[0018] (8) Weigh a certain amount of zinc nitrate, iron nitrate and citric acid and dissolve them in water, where the ratio of iron nitrate:zinc nitrate:citric acid is 2:1:4.5.

[0019] (9) Add the solution from step (8) to the mixed solution from step (7).

[0020] (10) Heat the mixed solution from step (9) in a water bath at 90 °C until a sol is formed, and add hollow alumina and mix well.

[0021] (11) Place the sol from step (10) in a vacuum drying oven and age at a constant temperature of 100 °C for 3 h to form a gel.

[0022] (12) Place the gel from step (11) in a muffle furnace and calcine at 500 °C to obtain a ZnFe2O4 / BaTiO3@hollow alumina sphere composite material.

[0023] The present invention preferably uses the sol-gel method to synthesize BaTiO3 nanoparticles with high purity, good dispersibility, good crystallinity and saturation.

[0024] The present invention preferably uses the sol-gel method to load the ZnFe2O4 / BaTiO3 composite material, uses zinc nitrate and iron nitrate as precursors, combines with a citric acid complexing agent, and in-situ grows a ZnFe2O4 / BaTiO3 catalyst on the surface of hollow alumina.

[0025] The present invention preferably selects hollow alumina as the carrier, and its hollow structure generates periodic deformation under the water flow pressure, stimulating the piezoelectric effect of BaTiO3, thereby enhancing the charge separation efficiency of the photocatalytic reaction.

[0026] The described piezoelectric-photocatalytic synergistic reaction system can be triggered by external stresses such as water flow stirring force, ultrasonic wave or mechanical vibration, without additional energy input.

[0027] Optionally, the particle size of the photocatalytic support alumina hollow spheres is selected to be 0.5 - 1 mm. It is characterized in that when the particle size of the alumina hollow spheres is small, the hollow sphere structure is complete, with few defects and high mechanical strength.

[0028] Optionally, barium hydroxide is selected as the raw material for preparing BaTiO3, or barium acetate can also be selected as one of the synthesis raw materials.

[0029] The light source required for the present invention is a 150W xenon lamp to simulate visible light source and solar light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a three-dimensional schematic diagram of the piezoelectric photocatalytic hollow particles prepared by the present invention.

[0031] Figure 2 It is a scanning electron microscope image of the piezoelectric photocatalytic hollow particles prepared by the present invention.

[0032] Figure 3 It is an X-ray diffraction pattern of the piezoelectric photocatalytic hollow particles prepared by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] The following further illustrates the specific embodiments of the present invention in conjunction with the drawings and technical solutions.

[0034] Example 1

[0035] (1) Pretreatment of alumina hollow particles: Add alumina hollow particles to absolute ethanol and pure water, wash and screen them, and place them in a vacuum drying oven for heating and drying at 60°C.

[0036] (2) Take a certain amount of BaTiO3, pure water, zinc nitrate, iron nitrate, and citric acid, where the molar ratio of zinc nitrate, iron nitrate, and citric acid is 2:1:4.5.

[0037] (3) Place the mixed solution in step (2) in a magnetic stirrer water bath and heat it at 90°C in a water bath, allowing evaporation to form a sol.

[0038] (4) Add the pretreated alumina hollow spheres in a certain proportion, stir and mix them, and place them in a vacuum drying oven for constant temperature aging at 100°C for 3 h.

[0039] (5) After forming a gel, transfer it to a muffle furnace and calcine it at 500°C for 2 h, and then naturally cool it to obtain piezoelectric photocatalytic hollow sphere particles.

[0040] (6) Take 200 ml of tetracycline solution with a concentration of 10 mg / L, add the piezoelectric photocatalytic hollow particles prepared in step (5), and react for 60 min using a xenon lamp to simulate sunlight.

[0041] (7) By the appendix Figure 2From the scanning electron microscope image of the sample, it can be seen that the ZnFe2O4 / BaTiO3 composite particles are uniformly embedded in the uneven surface structure of the alumina hollow spheres in the form of nano-microspheres. The aggregation of the nano-particles is alleviated. This loading method can expose more active sites, accelerate the reaction process, and reduce the agglomeration of nano-particles.

[0042] (8) By attachment Figure 3 From the X-ray diffraction pattern of the sample, it can be observed that the diffraction angles 2θ = 22.18, 30.16, 31.60, 35.18, 37.78, 43.32, 45.29, 56.20, 57.54, 62.45, 66.60 of the ZnFe2O4 / BaTiO3@alumina hollow sphere spectrum correspond to the (100), (110), (111), (210), (211), (220) crystal planes of tetragonal barium titanate and the (220), (311), (400), (511), (440) crystal planes of spinel ZnFe2O4. The characterization results show that the main components of the prepared composite material are tetragonal BaTiO3 and spinel-structured ZnFe2O4. However, the sharpness of the diffraction peaks of the composite material relative to those of a single substance is reduced, and the crystallinity decreases.

[0043] For the magnetic piezoelectric photocatalytic material as described above, the photocatalytic active layer preferably uses ZnFe2O4 / BaTiO3 to construct a photocatalytic-piezoelectric field, and can also be extended to a composite system of ZnFe2O4 and other piezoelectric materials (such as ZnO, CdS).

[0044] For the magnetic piezoelectric photocatalytic material as described above, the photocatalytic layer can use a TiO2 or ZnO coating, or the photocatalyst can also be modified by doping modification, noble metal deposition, etc.

[0045] Under natural light or artificial light source irradiation, the hollow particles can degrade organic pollutants through the synergistic effect of piezoelectric-photocatalysis, and at the same time, achieve rapid magnetic separation and recovery by virtue of the magnetism of ZnFe2O4, and the recycling rate ≥ 95%.

Claims

1. A magnetic piezoelectric photocatalytic hollow particle for degrading organic pollutants in water bodies, characterized in that an alumina hollow sphere is used as the core, and nano-photocatalytic particles ZnFe2O4 / BaTiO3 are embedded in the outer layer.

2. The magnetic piezoelectric photocatalytic hollow particles for degrading organic pollutants in water according to claim 1, wherein Using an alumina hollow sphere as the inner core.

3. The magnetic piezoelectric photocatalytic hollow particles for degrading organic pollutants in water body according to claim 1 are characterized in that Selecting alumina hollow spheres with a particle size of 0.5 mm.

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