Sandy piezoelectric electro-catalytic particles and preparation method thereof

Abstract

The invention aims to prepare a sandy piezoelectric electro-catalytic particle for degrading organic pollutants in wastewater, and the sandy piezoelectric electro-catalytic particle is wrapped by quartz sand serving as an inner core and a TiO2 / BaTiO3 composite material serving as an outer layer. The piezoelectric effect of the piezoelectric electro-catalytic material means that change and strain of charge distribution can be generated in the material when acting pressure is applied to the outside. The photocatalytic effect means that chemical reaction occurs on the surface of the material under the irradiation of an external light source. The two effects are coupled together by preparing the piezoelectric electro-catalytic composite material, the efficiency of degrading refractory organics in water through the photocatalytic reaction is improved, and the quartz sand is granular, so that the recycling of the photocatalytic material is facilitated, and the preparation method belongs to the technical field of environmental protection.

Description

Technical Field

[0001] The present invention relates to the preparation of a photocatalytic material, specifically to the preparation of a sandy piezoelectric photocatalytic particulate material, and a novel photocatalyst is prepared to remove organic or inorganic pollutants in wastewater, mainly to remove refractory organic pollutants, belonging to the fields of water purification and environmental protection. Background Art

[0002] The methods for removing organic pollutants in sewage are mainly divided into physical treatment methods, chemical treatment methods and biological treatment methods. Among them, physical methods include adsorption, filtration, reverse osmosis and membrane separation, etc. The physical method for treating organic matter in wastewater has the advantages of simple operation method, stable treatment effect and no secondary pollution. Common chemical treatment methods include chemical precipitation, oxidation-reduction, and complexation, etc. The chemical treatment method can quickly remove specific pollutants in sewage, and the chemical method for treating wastewater has the advantages of low treatment cost, rapid reaction and high efficiency. The principle of the biological treatment method is to degrade, adsorb or reduce organic pollutants in sewage by culturing microorganisms. Common biological treatment methods include activated sludge method, biological rotating disk, biofilm and biological filter, etc. The biological treatment technology has the advantages of good treatment effect and environmental friendliness without pollution. The principle of advanced oxidation technology (AOPs) is to utilize advanced oxidants to react with water to generate hydroxyl radicals ·OH and superoxide radicals (·O2 - ), and utilize their strong oxidizing property to oxidize and remove refractory organic pollutants in sewage. Common advanced oxidation treatment technologies include photocatalytic oxidation, Fenton oxidation and ozone oxidation, etc. The advanced oxidation technology is particularly remarkable for the removal of specific refractory organic pollutants, and the advanced oxidation technology often combines various photocatalytic materials to improve the degradation efficiency of organic matter.

[0003] All kinds of new pollutants include antibiotics, microplastics, new chemical substances and persistent refractory organic pollutants, etc. For such special new pollutants, the traditional wastewater treatment methods and processes are difficult to meet the treatment requirements of such new pollutants. As a new type of water treatment technology, photocatalytic technology can generate strong degradation ability for different refractory organic pollutants. The photocatalytic reaction speed is rapid and can occur under sunlight conditions, without adding chemical agents and without causing secondary pollution to the water body, and has great potential in the field of treating various wastewaters containing refractory organic matter and heavy metal pollutants. Most of the photocatalysts required for common photocatalytic reactions are composed of semiconductor materials. Such materials are rich in natural resources and have strong renewable properties and are difficult to be consumed completely.

[0004] Titanium dioxide (TiO2), as a commonly used semiconductor photocatalytic material, exists in three crystal forms in nature: rutile, anatase, and brookite. Because it can generate electron-hole pairs under the irradiation of visible light, ultraviolet light, and infrared light of some wavelengths during the photocatalytic reaction, and the material is inexpensive, easy to obtain, highly stable, and has strong corrosion resistance. The photocatalytic reaction produces non-toxic and harmless substances, which is widely favored in the field of water treatment. However, due to the disadvantages of easy recombination of electron-hole pairs generated inside titanium dioxide and narrow light response range, the material needs to be modified to improve the photocatalytic degradation efficiency of organic pollutants by titanium dioxide and broaden the light response wavelength range.

[0005] Piezo-photocatalysis is a new photocatalytic technology that combines the piezoelectric effect and the photocatalytic effect. Piezoelectric materials are divided into inorganic piezoelectric materials and organic piezoelectric materials. In piezo-photocatalysis, due to the asymmetric internal structure of the crystal of the piezoelectric material, when the crystal is affected by an external force, deformation occurs, resulting in charge separation and macroscopic polarization of the crystal. The principle of the photocatalytic reaction is to use light energy to excite the active sites of the semiconductor catalyst, and the electrons undergo transitions to promote the progress of chemical reactions. In the present invention, by combining the piezoelectric material barium titanate (BaTiO3) and the photocatalytic material titanium dioxide (TiO2), the coupling of the two effects can be realized, compensating for the defects of a single photocatalytic material, thereby increasing the rate of the photocatalytic reaction. When an external force (such as ultrasonic or vibration) is applied to the piezoelectric material barium titanate, charge separation occurs inside the piezoelectric material, forming an electric field effect that can enhance the migration of charges. This causes changes in the electronic structure and reaction activity on the surface of the photocatalyst, thereby enhancing the progress of the photocatalytic reaction. Currently, Michael et al. synthesized a new ZnO / SiO2 composite material to improve the catalytic performance of a single catalyst. However, the silica used for loading in the samples was all synthesized, with high preparation costs, environmental defects, and poor conductivity (Nazarkovsky M, Czech B, A,et al. Structural, optical and catalytic properties of ZnO-SiO2 colored powders with the visible light-driven activity[J]. Journal of Photochemistry and Photobiology A: Chemistry, 2021, 421: 113532.). The La-doped TiO2 / modified quartz sand composite photocatalytic material reported in the literature can effectively improve the photocatalytic performance of semiconductor catalysts, but its catalytic performance still needs further exploration (Chen Chao, Liu Xinwei, Chen Yong. Preparation and photocatalytic performance of La-doped TiO2 / modified quartz sand composite photocatalytic material[J]. Journal of Functional Materials, 2019, 50(03): 3096-3100+3106.). Summary of the Invention

[0006] Aiming at the shortcomings of the above technologies, the present invention proposes a sandy piezoelectric photocatalytic particle and its preparation method. On the one hand, through the action of external mechanical force, a polarization electric field is generated inside, and the piezoelectric material BaTiO3 is used to convert mechanical energy into electrical energy; on the other hand, the micro-piezoelectric effect of the piezoelectric material is used to inhibit the recombination of electrons and holes, so that the separation efficiency of photo-generated carriers of the TiO2 / BaTiO3 composite particles is high, improving the piezoelectric photocatalytic effect and achieving the removal of organic pollutants. Finally, the composite particles are loaded on the quartz sand core. Under the external force of water flow disturbance, the collision probability between the sandy piezoelectric photocatalytic particles increases, and the degree of micro-deformation of the piezoelectric material intensifies, inducing internal charge transfer. Using the strong adsorption capacity of quartz sand, the pollutants in water are adsorbed onto the surface of the catalyst, providing a microenvironment with a high concentration for piezoelectric photocatalytic degradation, solving the problems of low reaction efficiency and difficult recycling of photocatalysts, preventing them from polluting the environment, and meeting the requirements of environmental engineering applications.

[0007] To solve the above technical problems, the purpose of the present invention is to provide a piezoelectric photocatalytic composite material, its preparation method and application to solve the problems of low photocatalytic reaction efficiency and difficult recycling.

[0008] The present invention adopts the following technical solution: A preparation method of sandy piezoelectric photocatalytic particles TiO2 / BaTiO3@quartz sand.

[0009] The present invention uses the sol-gel method to couple the photocatalytic material TiO2 with the piezoelectric material BaTiO3 to produce the TiO2 / BaTiO3 composite material, including the following steps:

[0010] (1) The present invention pre-treats quartz sand. The quartz sand is successively added to absolute ethanol, an acid solution and an alkali solution, soaked and washed, and then filtered, washed and dried for standby.

[0011] (2) Add 20 - 50 ml of tetrabutyl titanate, 20 - 25 ml of glacial acetic acid and 80 ml of absolute ethanol to a beaker and mix them. Stir magnetically at a constant temperature for 0.5 h.

[0012] (3) Dropwise add absolute ethanol and pure water to the mixed solution in step (2), and stir magnetically at a constant temperature for 0.5 h to obtain a TiO2 sol.

[0013] (4) Place the TiO2 sol prepared in step (3) in a drying oven at 60 °C and dry it for 24 h to obtain a nano-TiO2 solid gel.

[0014] (5) Place the TiO2 solid gel in a muffle furnace and calcine it at 450 °C for 1 h, then grind it to obtain white nano-TiO2 powder.

[0015] (6) Add ethylene glycol to the oxalic acid solution and adjust the pH to 3.

[0016] (7) Add the TBOT solution to the mixed solution obtained in step (6) and stir magnetically at a constant temperature for 1 h.

[0017] (8) Add the sodium hydroxide solution to the mixed solution obtained in step (7). The molar ratio of sodium hydroxide to TBOT is 1:1, and stir magnetically for 30 min.

[0018] (9) Transfer the mixed solution obtained in step (8) to a constant-temperature oven and age it at 80 °C for 4 h.

[0019] (10) Filter, wash and ultrasonically disperse the precipitate in step (9), and place it in a drying oven for drying.

[0020] (11) Place the precipitate in a muffle furnace and calcine it at 900 °C for 2 h, then cool and grind it to obtain white BaTiO3 nano powder.

[0021] (12) Prepare a mixed solution containing absolute ethanol and TBOT, add a certain amount of dilute nitric acid, and stir magnetically to form a gel.

[0022] (13) Prepare a mixed solution containing barium titanate, absolute ethanol and pure water, and stir ultrasonically.

[0023] (14) Add the mixed solution prepared in step (13) to the gel system, and add acetylacetone to inhibit hydrolysis. Stir magnetically for 30 min.

[0024] (15) Place the gel prepared in step (14) in a drying oven at 80 °C and age it for 3 - 4 h.

[0025] (16) Place the gel in a muffle furnace and calcine it for 2 h to obtain the TiO2 / BaTiO3 composite material.

[0026] The present invention uses the sol-gel method to coat TiO2 / BaTiO3 on the outer layer of modified quartz sand to form sandy piezoelectric photocatalytic particles, which includes the following steps:

[0027] (17) Mix the mixed gel obtained in step (15) with the pretreated quartz sand, stir magnetically for 10 - 12 h, and place it in a drying oven for constant-temperature drying.

[0028] (18) Place the quartz sand and the mixed gel in a muffle furnace at 500 °C and calcine for 2 h to obtain the sandy piezoelectric photocatalytic particles TiO2 / BaTiO3@quartz sand.

[0029] The external mechanical force applied in the piezoelectric catalytic reaction system can be one or more of ultrasonic waves, mechanical forces, magnetic field forces, water flow stirring forces, etc. to initiate the piezoelectric catalytic reaction.

[0030] Optionally, the particle size of the carrier quartz sand is 8 - 26 mesh. When the mesh number of the quartz sand is fine, the particle size of the quartz sand is more uniform, the content of quartz minerals inside is high, it is not easy to generate bubbles and other structural defects, and the transparency and whiteness of the quartz sand are high.

[0031] Optionally, the acid solution is hydrochloric acid or sulfuric acid solution. The purpose is to effectively remove the impurity components such as iron oxide and clay minerals that are soluble in acid in the quartz sand by the acid leaching method. Sulfuric acid can effectively dissolve impurity ions such as iron and calcium. The mass fraction of the acid solution is 4 - 8 wt%. The alkali solution is sodium hydroxide or potassium hydroxide solution. The purpose is to remove clay minerals and other organic impurities in the quartz sand particles by the alkali method. The strong alkali solution can react with the impurity component iron oxide in the quartz sand to form ferrate and react with aluminum oxide in the quartz sand to form aluminate. Since the ferrate and aluminate formed by the reaction are both soluble in the strong alkali solution, the effective separation of the quartz sand from its impurity components is realized. The mass fraction of the alkali solution is 2 - 4 wt%, and the soaking and cleaning pretreatment time is 2 - 5 h.

[0032] Optionally, for the sandy piezoelectric photocatalytic particles, BaTiO3 is preferably used as the piezoelectric material, and other piezoelectric materials such as MoS2, WS2, MoSe2, WSe2, ZnO, CdS, etc. can also be used. For the sandy piezoelectric photocatalytic particles, the photocatalytic layer can be selected from TiO2 or ZnO coatings, or the photocatalyst can be modified by doping modification, noble metal deposition, etc. Further optionally, the mass ratio of BaTiO3 to TiO2 is (0.4 - 1.0):1.

[0033] Optionally, it further includes adding an acetylacetone crosslinking agent to participate in the sol-gel method, and the mass ratio of acetylacetone to pure water is 5:1.

[0034] The photocatalytic light source required by the present invention is an artificial light source or a natural light source, and organic pollutants are degraded under this reaction system. Description of the Drawings

[0035] Figure 1 It is a three-dimensional schematic diagram of the sandy piezoelectric photocatalytic particles prepared by the present invention.

[0036] Figure 2 It is a scanning electron microscope photograph and an element distribution map of the sandy piezoelectric photocatalytic particles prepared by the present invention.

[0037] Figure 3 It is an X-ray diffraction spectrum of the sandy piezoelectric photocatalytic particles prepared by the present invention. Detailed Embodiments

[0038] The following further describes the detailed embodiments of the present invention in combination with the drawings and technical solutions.

[0039] Example 1

[0040] 1) Pretreatment of quartz sand: Add quartz sand to anhydrous ethanol, acid solution and alkali solution in sequence and soak for 2 h, then wash with pure water until the supernatant is neutral, and finally dry in an oven at 100 °C for 1 h to obtain pretreated quartz sand.

[0041] 2) Take a certain amount of TBOT, pure water, anhydrous ethanol, and barium titanate, and their molar ratio is 2:4:20:1.

[0042] 3) Dilute TBOT with half of the specified amount of ethanol, place it in a 250 mL beaker, and stir at 600 rpm for 5 min.

[0043] 4) Add 3.5 mL of dilute nitric acid to the system in step 3) and continue stirring to allow evaporation to form a gel.

[0044] 5) Add barium titanate to the remaining ethanol and pure water, ultrasonically stir to dissolve it completely, then add it dropwise to the gel system in step 4), and add acetylacetone at the same time to inhibit hydrolysis. Magnetically stir for 30 min to allow sufficient reaction to form a sol.

[0045] 6) Transfer the sol in step 5) to a constant temperature oven and age at 80 °C for 3 h to obtain a deep orange-colored colloid that no longer flows.

[0046] 7) Add the pretreated quartz sand in a certain proportion, stir well for 12 h, and transfer it to the oven for drying at a constant temperature and for a fixed time.

[0047] 8) After drying, transfer it to a crucible and calcine it in a muffle furnace at 500 °C for 2 h. After natural cooling, sandy piezoelectric photocatalytic particles TiO2 / BaTiO3@quartz sand will be obtained.

[0048] 9) Measure 200 mL of the water sample containing 20 mg / L of tetracycline, add 10 g of the sandy piezoelectric photocatalytic particles, and carry out catalytic degradation under the irradiation of a xenon lamp for 60 min.

[0049] 10) Every 10 min, use a disposable syringe to suck out the supernatant, filter it, and then measure the efficiency of the sandy piezoelectric photocatalytic particles in removing tetracycline. The removal effect is shown in Table 1.

[0050] 11) From the attached Figure 2 scanning electron microscope images, it can be seen that the surface of the prepared sandy piezoelectric photocatalytic particles is evenly distributed with the TiO2 / BaTiO3 piezoelectric photocatalytic layer, and no agglomeration occurs. From the EDX-Mapping diagram, it can be seen that Ti and Ba elements are evenly distributed on the surface of the material. From the attached Figure 3 it can be known that under the action of visible light irradiation and mechanical stirring force, the crystal structure of the piezoelectric material of the prepared sandy piezoelectric photocatalytic particles is distorted, thereby generating charges, inhibiting the recombination of electrons and holes, making the separation efficiency of photo-generated carriers of the sandy piezoelectric photocatalytic particles high, improving the photocatalytic effect, and being able to effectively remove tetracycline in water.

[0051] Example 2

[0052] This example first provides a kind of sandy piezoelectric photocatalytic particles, and the difference in its preparation method from Example 1 is only that: the molar ratio of TBOT to barium titanate is changed to 1:1.

[0053] This example further provides the efficiency of the sandy piezoelectric photocatalytic particles in removing tetracycline, and its method is the same as that of Example 1. The removal effect is shown in Table 1.

[0054] Example 3

[0055] This example first provides a kind of sandy piezoelectric photocatalytic particles, and the difference in its preparation method from Example 1 is only that: the molar ratio of TBOT to barium titanate is changed to 1:3.

[0056] This example further provides the efficiency of the sandy piezoelectric photocatalytic particles in removing tetracycline, and its method is the same as that of Example 1. The removal effect is shown in Table 1.

[0057] Comparative Example 1

[0058] The pure TiO2 photocatalytic material is used to remove tetracycline in water as follows: 0.2 g of pure TiO2 powder is added to 200 mL of a water sample containing 20 mg / L of tetracycline that is being stirred uniformly on a magnetic stirrer, and catalytic degradation is carried out under xenon lamp irradiation for 60 min. Samples are taken every 10 min to determine the efficiency of the pure TiO2 photocatalytic material in removing tetracycline.

[0059] Comparative Example 2

[0060] The TiO2 / BaTiO3 photocatalytic material is used to remove tetracycline in water as follows: 0.2 g of TiO2 / BaTiO3 powder is added to 200 mL of a water sample containing 20 mg / L of tetracycline that is being stirred uniformly on a magnetic stirrer, and catalytic degradation is carried out under xenon lamp irradiation for 60 min. Samples are taken every 10 min to determine the efficiency of the TiO2 / BaTiO3 photocatalytic material in removing tetracycline.

[0061] When irradiated with natural light or artificial light, when the light hits the surface of the photocatalyst, the energy is absorbed, electrons are excited from the ground state to the excited state, thereby generating electron-hole pairs, which react with surrounding substances.

[0062] The piezoelectricity generated by the piezoelectric material will inhibit the recombination of electron-hole pairs generated by the photocatalyst, thereby improving the treatment efficiency of the photocatalyst.

[0063] To address the problem that the photocatalyst is difficult to recycle, the piezoelectric composite material is loaded on the surface of quartz sand to facilitate its recycling.

[0064] Table 1 Efficiency of each material in removing tetracycline in water

[0065] Implementation number Removal rate / % Example 1 83.60 Example 2 64.49 Example 3 58.33 Comparative example 1 51.59 Comparative example 2 73.79

Claims

1. A piezoelectric photocatalytic particle for the degradation of organic matter in wastewater, characterized by The core is quartz sand, and the outer layer is a TiO2 / BaTiO3 piezoelectric photocatalytic layer.

2. The piezoelectric photocatalytic particles according to claim 1, wherein The core uses quartz sand (SiO2) as the catalyst carrier.

3. The piezoelectric photocatalytic particles according to claim 1, wherein The outer layer uses TiO2 / BaTiO3 piezoelectric photocatalytic material.

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