Bismuth titanate nanomaterial, preparation method thereof and wastewater treatment method

Abstract

The application relates to the technical field of nanometer materials, and particularly discloses a bismuth titanate nanometer material, a preparation method thereof and a sewage treatment method. The preparation method of the bismuth titanate nanometer material comprises the following steps: uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride and potassium chloride according to a molar ratio of Bi:Ti:Ho:NaCl:KCl=(3.5-3.92):(2.8-3.2):(0.1-0.5):(40-55):(40-55) to obtain a precursor; calcining the precursor to obtain an intermediate product; and removing sodium chloride and potassium chloride in the intermediate product. By implementing the application, the polarity and piezoelectric response of the bismuth titanate nanometer material can be improved, and the piezoelectric-optical catalytic performance of the bismuth titanate nanometer material can be improved.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and in particular to a bismuth titanate nanomaterial, its preparation method, and a wastewater treatment method. Background Technology

[0002] With the acceleration of industrialization, the problem of organic pollutants in water bodies emitted by industries such as textiles, dyeing, and pharmaceuticals has become increasingly prominent. Dye pollutants such as Rhodamine B and antibiotic pollutants such as ciprofloxacin are characterized by high toxicity, poor degradation, and bioaccumulation, seriously threatening aquatic ecosystems and human health. Developing efficient, environmentally friendly, and stable pollutant treatment technologies has become a key research focus in the field of environmental governance.

[0003] Semiconductor photocatalysis technology, driven by solar energy, can completely convert organic pollutants into non-toxic small molecules such as CO2 and H2O under mild conditions, making it a highly promising environmental remediation technology. Bismuth titanate (Bi4Ti3O) 12 As an environmentally friendly lead-free piezoelectric material, bismuth titanate possesses a unique layered perovskite structure, excellent piezoelectric and ferroelectric properties, and certain visible light response characteristics, making it an ideal candidate for piezoelectric photocatalytic materials. However, its intrinsic characteristics include high photogenerated electron-hole recombination rate, small specific surface area, insufficient piezoelectric response intensity, and low visible light utilization rate, making it difficult for pure bismuth titanate to meet the piezoelectric photocatalytic activity required for practical applications. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a bismuth titanate nanomaterial and its preparation method, which can improve the polarity and piezoelectric response of the bismuth titanate nanomaterial and enhance its piezoelectric-photocatalytic performance.

[0005] Another technical problem that this invention aims to solve is to provide a method for treating wastewater containing organic pollutants.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing bismuth titanate nanomaterials, comprising: Bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride were mixed uniformly in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor. The precursor was calcined to obtain an intermediate product; Sodium chloride and potassium chloride are removed from the intermediate product.

[0007] As an improvement to the above technical solution, in the step of uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride according to the molar ratio Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor, Bi:Ti:Ho:NaCl:KCl = (3.5~3.91):3:(0.1~0.5):50:50; and / or In the step of calcining the precursor to obtain the intermediate product, the precursor is heated from 20-50°C to 450-550°C at a heating rate of 4-10°C / min, then heated to 750-820°C at a heating rate of 1-3°C / min, held at that temperature for 1.5-3.5 hours, and then cooled to 20-50°C within 2-3.5 hours to obtain the intermediate product; and / or In the step of removing sodium chloride and potassium chloride from the intermediate product, the intermediate product is washed with water and dried at 60~100℃ for 3~8 hours.

[0008] As an improvement to the above technical solution, in the step of uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride according to the molar ratio Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor, the ratio Bi:Ti:Ho:NaCl:KCl = 3.75:3:0.25:50:50; and / or In the step of calcining the precursor to obtain the intermediate product, the precursor is heated from 20-50°C to 480-520°C at a heating rate of 4-5°C / min, then heated to 790-810°C at a heating rate of 1.5-2.5°C / min, held at that temperature for 1.8-2.2 hours, and then cooled to 20-50°C within 2.5-3.5 hours to obtain the intermediate product.

[0009] As an improvement to the above technical solution, the step of uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor includes: Bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride were mixed in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain a mixture. The mixture was ball-milled to obtain a precursor slurry; The precursor slurry is dried to obtain the precursor.

[0010] As an improvement to the above technical solution, the step of ball milling the mixture to obtain the precursor slurry involves mixing the mixture with a dispersant and ball milling at 200-500 rpm for 1-3 hours; wherein the dispersant is water and / or ethanol, and the weight ratio of the mixture to the dispersant is 1:(1.2-1.5); and / or In the step of drying the precursor slurry to obtain the precursor, the precursor slurry is dried at 70~100℃ for 1~3h.

[0011] Accordingly, the present invention also discloses a bismuth titanate nanomaterial, which is prepared by the above-described preparation method.

[0012] As an improvement to the above technical solution, the (001) crystal plane exposure ratio of the bismuth titanate nanomaterial is ≥80%, and it has a nanosheet structure with a thickness of 20~50nm and a length of 0.5~2μm.

[0013] Accordingly, the present invention also discloses a method for treating wastewater containing organic pollutants, which includes the step of treating the wastewater using the aforementioned bismuth titanate nanomaterial.

[0014] As an improvement to the above technical solution, the following are included: The bismuth titanate nanomaterials described above were added to wastewater containing organic pollutants and reacted under visible light excitation conditions. The weight ratio of the bismuth titanate nanomaterial to the volume of the wastewater is (0.5~0.7) g:1L; the wavelength of the visible light is 400~1100nm; and the reaction temperature is 20~50℃.

[0015] As an improvement to the above technical solution, The bismuth titanate nanomaterials as described in claim 6 or 7 are added to wastewater containing organic pollutants and reacted under visible light and mechanical stress excitation conditions. The mechanical stress excitation conditions are ultrasonic treatment or low-frequency water flow stress treatment, wherein the power of ultrasonic treatment is 100~300W and the frequency is 50~60kHz.

[0016] Implementing this invention has the following beneficial effects: In one embodiment of the present invention, a method for preparing bismuth titanate nanomaterials involves first mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride, then calcining the mixture, and finally removing sodium chloride and potassium chloride to obtain the final product. Based on the above preparation method, one approach involves introducing holmium oxide (Ho₂O₃) to make Ho₂O₃... 3+ Replaced Bi in the finished crystal lattice 3+This induces lattice distortion, optimizes the band structure, and strengthens the finished bismuth titanate nanomaterials (Bi). 4-x Ho x Ti3O 12 The spontaneous polarization and piezoelectric response characteristics of Ho. 3 + Doping also optimizes the band structure, making the conduction band potential more negative, providing favorable thermodynamic conditions for the generation of active free radicals; moreover, oxygen vacancies can serve as trapping sites for photogenerated carriers, improving carrier separation efficiency. Therefore, Ho 3+ Doping achieves a synergistic enhancement of the polarity and piezoelectric photocatalytic performance of bismuth titanate nanomaterials. Secondly, by using sodium chloride and potassium chloride as molten salts, the exposed proportion of the (001) crystal plane in the finished bismuth titanate nanomaterials can be increased, increasing the specific surface area of ​​the material and providing a large number of active sites for the catalytic reaction. Furthermore, it shortens the transport distance of photogenerated carriers, reduces carrier recombination losses, and improves photocatalytic performance. In addition, sodium chloride and potassium chloride are easy to remove later, avoiding coverage of active sites. The combination of these two factors effectively improves the polarity and piezoelectric properties of the finished bismuth titanate nanomaterials, enhances their response to ultraviolet-visible light, and thus significantly improves the degradation rate of organic pollutants. This allows the finished bismuth titanate nanomaterials obtained by this invention to be applied to the treatment of wastewater containing organic waste. Thirdly, the preparation method of this invention is simple, the conditions are mild, the raw materials are readily available, and it is easy to industrialize. Attached Figure Description

[0017] Figure 1 These are SEM and TEM images of the bismuth titanate nanomaterials prepared in Example 2 of this invention, as well as the comparative preparations. Wherein, a is the SEM image of BTO, b is the SEM image of 0.25Ho-BTO, c is the TEM image of 0.25Ho-BTO, d is the HRTEM image of 0.25Ho-BTO, and e is the EDS elemental mapping image of 0.25Ho-BTO. Figure 2 These are XPS spectra of bismuth titanate nanomaterials prepared in Example 2 of this invention, as well as comparative samples; where a is the full XPS spectrum of BTO and 0.25Ho-BTO, b is the high-resolution spectrum of Bi 4f, c is the high-resolution spectrum of Ti 2p, d is the high-resolution spectrum of O 1s, and e is the high-resolution spectrum of Ho 4d. Figure 3 This is the UV-Vis diffuse reflectance spectrum and (αhv) of the bismuth titanate nanomaterials prepared in Example 2 and the comparative example of this invention. 1 / 2 Tauc diagram with photon energy; Figure 4 This is the Nyquist electrochemical impedance spectroscopy (EIS) of the bismuth titanate nanomaterials prepared in Example 2 of this invention, as a comparative example. Figure 5 This is a comparison of the piezoelectric photocatalytic degradation curves of Rhodamine B by different bismuth titanate nanomaterials in Application Example 1 of this invention; where a is the photocatalytic activity curve, b is the piezoelectric catalytic activity curve, c is the piezoelectric-photocatalytic synergistic activity curve, and d is a comparison of the apparent rate constants under different catalytic conditions. Figure 6 This is a graph showing the cycle stability test results of 0.25Ho-BTO in Application Example 2 of this invention; Figure 7 This is a piezoelectric photocatalytic degradation activity diagram of 0.25Ho-BTO for antibiotic pollutants in Application Example 3 of the present invention; wherein, TC is tetracycline, CIP is ciprofloxacin, and LVX is levofloxacin; Figure 8 This is an experimental diagram of free radical capture in the piezoelectric photocatalytic degradation of Rhodamine B using 0.25Ho-BTO in this invention.

[0018] To facilitate understanding of the present invention, it will now be described in more detail. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0020] The following embodiments are provided for the purpose of illustrating various embodiments of the present invention and are not intended to limit the invention in any way. Those skilled in the art will understand that variations and other uses as defined in the claims are included within the spirit and scope of the invention. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available.

[0021] In this invention, terms such as "first aspect" and "second aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0022] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0023] Unless otherwise specified, the percentage contents mentioned in this invention refer to solid-liquid mixtures and solid phases. Solid-phase mixing refers to mass percentage; for liquid phases... Liquid phase mixing refers to volume percentage.

[0024] Unless otherwise specified, all percentage concentrations mentioned in this invention refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0025] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument.

[0026] As a first aspect of the present invention, the present invention provides a method for preparing bismuth titanate nanomaterials, which includes the following steps: S10: Bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride are mixed uniformly in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor; S11: Calcine the precursor to obtain the intermediate product; S12: Remove sodium chloride and potassium chloride from the intermediate product.

[0027] Based on the above preparation methods, one approach involves introducing holmium oxide (Ho₂O₃) to make Ho₂O₃... 3+ Replaced Bi in the finished crystal lattice 3+ This induces lattice distortion, introduces oxygen vacancies, and strengthens the finished bismuth titanate nanomaterials (Bi). 4-x Ho x Ti3O 12 The piezoelectric response characteristics of Ho. 3+ Doping also optimizes the band structure, making the conduction band potential more negative and providing favorable thermodynamic conditions for the generation of active free radicals; moreover, oxygen vacancies can serve as trapping sites for photogenerated carriers, improving carrier separation efficiency. Therefore, Ho 3+Doping achieves a synergistic enhancement of the polarity and piezoelectric photocatalytic performance of bismuth titanate nanomaterials. Secondly, by using sodium chloride and potassium chloride as molten salts, the exposed proportion of the (001) crystal plane in the finished bismuth titanate nanomaterials can be increased, increasing the specific surface area of ​​the material and providing a large number of active sites for the catalytic reaction. Furthermore, it shortens the transport distance of photogenerated carriers, reduces carrier recombination losses, and improves photocatalytic performance. In addition, sodium chloride and potassium chloride are easy to remove later, avoiding coverage of active sites. The combination of these two factors effectively improves the polarity and piezoelectric properties of the finished bismuth titanate nanomaterials, enhances their response to ultraviolet-visible light, and thus significantly improves the degradation rate of organic pollutants. This allows the finished bismuth titanate nanomaterials obtained by this invention to be applied to the treatment of wastewater containing organic waste. Thirdly, the preparation method of this invention is simple, the conditions are mild, the raw materials are readily available, and it is easy to industrialize.

[0028] Specifically, in step S11, bismuth oxide (Bi2O3), titanium oxide (TiO2), and holmium oxide (Ho2O3) are used as the bismuth source, titanium source, and holmium source, respectively, to prevent the introduction of impurity ions (such as Cl). - NO3 - Using organic carbon, etc., can avoid the generation of corrosive impurities during calcination, which can lead to excessive lattice defects. It can also prevent the formation of photogenerated carrier recombination centers by residual impurity ions. If other types of raw materials are used (such as bismuth nitrate, titanium chloride, etc.), the lattice porosity will increase abnormally after calcination, and the catalytic active sites will be covered, thereby reducing the polarization intensity, piezoelectric response and photocatalytic efficiency of the material.

[0029] Specifically, in step S11, sodium chloride and potassium chloride are used as a composite molten salt, which can provide an isotropic ionic environment for the growth of bismuth titanate crystals, induce the crystals to grow oriented along the (001) crystal plane, effectively increase the specific surface area of ​​the material, increase the number of catalytic active sites, and shorten the photogenerated carrier transport distance; at the same time, the composite molten salt has a low melting temperature, which can inhibit the agglomeration of bismuth titanate nanomaterials at a lower calcination temperature and improve the exposure ratio of the (001) crystal plane; in addition, the lower calcination temperature is beneficial to Ho 3+ Uniform substitution of Bi in the crystal lattice 3+ This avoids lattice distortion caused by uneven doping and allows for appropriate control of oxygen partial pressure during calcination, promoting oxygen vacancy generation and enhancing the material's polarization intensity and carrier trapping ability. Furthermore, sodium chloride and potassium chloride can be removed later by simple water washing.

[0030] Specifically, in step S11, the molar ratio of bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride, calculated as Bi:Ti:Ho:NaCl:KCl, is (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55). Examples of such ratios are 3.51:2.9:0.5:50:50, 3.61:3:0.4:42:42, 3.7:3.1:0.3:45:45, 3.82:3.05:0.2:51:51, 3.85:3:0.15:54:54, 3.55:3:0.45:50:50, 3.65:3:0.35:50:50, or 3.85:3:0.15:50:50, but not limited to these. Preferably, in some embodiments, the molar ratio of bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride, calculated as Bi:Ti:Ho:NaCl:KCl, is (3.5~3.91):3:(0.1~0.5):50:50; more preferably (3.6~3.9):3:(0.1~0.4):50:50; further preferably (3.7~3.9):3:(0.1~0.3):50:50; and even more preferably 3.75:3:0.25:50:50.

[0031] Specifically, in step S11, bismuth oxide, titanium oxide, and holmium oxide can be mixed first, and then mixed with sodium chloride and potassium chloride. Alternatively, the components can be mixed directly, but this is not the only option.

[0032] Specifically, in step S11, bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride can be uniformly mixed by ball milling, grinding, sand milling, etc., but are not limited to these methods. Preferably, in some embodiments, step S10 includes: S111: Bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride are mixed in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain a mixture; S112: Ball mill the mixture to obtain a precursor slurry; Specifically, the mixture is mixed with a dispersant and ball-milled at 200-500 rpm for 1-3 hours; the dispersant is water and / or ethanol, and the weight ratio of the mixture to the dispersant is 1:(1.2-1.5).

[0033] S113: Dry the precursor slurry to obtain the precursor.

[0034] Specifically, the precursor slurry can be dried by spray drying, oven drying, or freeze drying, but is not limited to these methods. Preferably, in some embodiments, the drying method is oven drying at a temperature of 70-100°C for 1-3 hours. By using ball milling-drying to prepare the precursor, the reactants can be homogenized and thoroughly mixed, providing a good foundation for the subsequent formation of a uniformly distributed crystal structure.

[0035] Specifically, in step S12, the calcination temperature is 750~820℃. If the calcination temperature is too low, the crystal phase will not form completely; if the calcination temperature is too high, the Bi and Ho components will easily volatilize, destroying the crystal lattice structure. For example, the calcination temperature is 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, or 820℃.

[0036] Specifically, in step S12, the calcination atmosphere is air or oxygen, and the heating rate is 3~15℃ / min, exemplarily 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min or 12℃ / min, but not limited thereto.

[0037] Specifically, in step S12, the calcination time (i.e., the holding time at the highest temperature) is 1 to 5 hours, exemplarily 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, but not limited to these.

[0038] Preferably, in some embodiments, in step S12, the precursor is heated from 20-50°C to 450-550°C at a heating rate of 4-10°C / min, then heated to 750-820°C at a heating rate of 1-3°C / min, held at this temperature for 1.5-3.5 hours, and cooled to 20-50°C within 2-3.5 hours to obtain the intermediate product. Based on the above temperature control curve, the proportion of (001) crystal planes can be effectively increased, thereby improving catalytic performance. More preferably, the precursor is heated from 20-50°C to 480-520°C at a heating rate of 4-5°C / min, then heated to 790-810°C at a heating rate of 1.5-2.5°C / min, held at this temperature for 1.8-2.2 hours, and cooled to 20-50°C within 2.5-3.5 hours to obtain the intermediate product.

[0039] Specifically, in step S13, the intermediate product is washed with water and dried at 60~100℃ for 3~8 hours.

[0040] As a second aspect of the present invention, the present invention also provides a bismuth titanate nanomaterial, which is prepared by the above-described method for preparing bismuth titanate nanomaterials. The preparation method of the present invention uses the molten salt method as its core to prepare bismuth titanate nanomaterials with exposed (001) crystal planes (Bi). 4-x Ho x Ti3O12 Holmium doping significantly enhances the spontaneous polarization characteristics and photogenerated electron-hole separation efficiency of bismuth titanate nanomaterials, resulting in a substantial increase in both the internal electric field strength and the photogenerated carrier separation efficiency. The prepared material exhibits excellent polarization and piezoelectric properties, with a bandgap that perfectly matches the UV-Vis light response range, demonstrating superior UV-Vis light response. Under the synergistic effect of piezoelectricity and photocatalysis, the degradation rate constant of this material for Rhodamine B reaches as high as 0.0607 min⁻¹. -1 It is an undoped bismuth titanate nanomaterial (Bi4Ti3O) 12 It is 3.99 times more potent than other organic pollutants, including tetracycline, ciprofloxacin, and levofloxacin. It also exhibits high degradation efficiency for organic pollutants such as tetracycline, ciprofloxacin, and levofloxacin. Even after being recycled four times, the degradation rate remains high, and the crystal structure is stable. This provides a new approach for the treatment of organic pollutants in water bodies, such as dye wastewater and antibiotic wastewater.

[0041] Specifically, the bismuth titanate nanomaterial has a (001) crystal plane exposure ratio of ≥80%, and it has a nanosheet structure with a thickness of 20~50nm and a length of 0.5~2μm.

[0042] As a third aspect of the present invention, the present invention provides a method for treating wastewater containing organic pollutants, comprising the step of treating the wastewater using the aforementioned bismuth titanate nanomaterials. Specifically, the present invention prepares bismuth titanate nanomaterials (Bi) with predominantly (001) crystal plane exposed. 4-x Ho x Ti3O 12 This material possesses excellent polarization and piezoelectric properties, and exhibits superior response to ultraviolet-visible light. Consequently, it can achieve the catalytic degradation of conventional organic pollutants. Furthermore, the bismuth titanate nanomaterial of this invention is a lead-free and environmentally friendly material, and the catalytic degradation process produces no secondary pollution, meeting the development needs of green environmental governance.

[0043] Specifically, organic pollutants can be common dyes, antibiotics, and phenolic organic pollutants containing structures such as benzene rings, amino groups, or carboxyl groups. Examples include rhodamine B, tetracycline, levofloxacin, and p-nitrophenol, but they are not limited to these.

[0044] Preferably, in some embodiments, bismuth titanate nanomaterials are added to wastewater containing organic pollutants and reacted under visible light excitation conditions. Specifically, the bismuth titanate nanomaterials prepared by this invention exhibit strong reactivity under visible light irradiation, enabling the degradation of target organic pollutants. Specifically, the weight ratio of bismuth titanate nanomaterials to wastewater volume is (0.5~0.7) g:1L; the wavelength of visible light is 400~1100nm; and the reaction temperature is 20~50℃.

[0045] More preferably, the aforementioned bismuth titanate nanomaterials are added to wastewater containing organic pollutants, and the reaction is carried out under visible light and mechanical stress excitation conditions. Specifically, by introducing mechanical stress, a piezoelectric-photocatalytic synergistic effect can be achieved, thereby significantly improving the treatment efficiency. Specifically, under the piezoelectric-photocatalytic synergistic effect, the degradation rate constant of this material for Rhodamine B is as high as 0.0607 min. -1 It is an undoped bismuth titanate nanomaterial (Bi4Ti3O) 12 It is 3.99 times more potent than other organic pollutants, including tetracycline, ciprofloxacin, and levofloxacin. It also exhibits high degradation efficiency for organic pollutants such as tetracycline, ciprofloxacin, and levofloxacin. Even after being recycled four times, the degradation rate remains high, and the crystal structure is stable. This provides a new approach for the treatment of organic pollutants in water bodies, such as dye wastewater and antibiotic wastewater.

[0046] The mechanical stress excitation conditions are ultrasonic treatment or low-frequency water flow stress treatment. The ultrasonic treatment power is 100~300W and the frequency is 50~60kHz. Low-frequency water flow refers to water flow with a velocity of 0.1~0.5m / s and a periodic pulsation frequency of 0.5~2Hz, such as streams and slow-moving rivers in nature. The bismuth titanate nanomaterial of this invention can be excited by the weak mechanical stress of natural water bodies such as low-frequency water flow to induce a piezoelectric effect, without the need for additional high-power ultrasonic equipment. This expands the practical application scenarios of the material in natural water environments and reduces the energy consumption of pollutant treatment. The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides a method for preparing bismuth titanate nanomaterials, the specific steps of which are as follows: 1. Weigh out bismuth trioxide, titanium dioxide, holmium trioxide, sodium chloride and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl=3.9:3:0.1:50:50, add them to a planetary ball mill jar, add an appropriate amount of anhydrous ethanol as a dispersant, and ball mill at 250 rpm for 4 hours to obtain the precursor slurry.

[0047] 2. After drying the precursor slurry at 75℃ for 2 hours, it is placed into an alumina crucible and calcined in a muffle furnace with programmed temperature rise: room temperature → 500℃ (120 min) → 800℃ (150 min), held for 2 hours, and cooled to room temperature for 180 minutes.

[0048] 3. After grinding the sintered product, it is washed with deionized water by vacuum filtration until no Cl is detected by AgNO3 detection. - Dry at 80℃ for 6 hours to obtain the product. The sample in this example is denoted as 0.1Ho-BTO.

[0049] Example 2 This embodiment provides a method for preparing bismuth titanate nanomaterials, the specific steps of which are as follows: 1. Weigh out bismuth trioxide, titanium dioxide, holmium trioxide, sodium chloride and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl=3.75:3:0.25:50:50, add them to a planetary ball mill jar, add an appropriate amount of anhydrous ethanol as a dispersant, and ball mill at 250 rpm for 4 hours to obtain the precursor slurry.

[0050] 2. After drying the precursor slurry at 75℃ for 2 hours, it is placed into an alumina crucible and calcined in a muffle furnace with programmed temperature rise: room temperature → 500℃ (120 min) → 800℃ (150 min), held for 2 hours, and cooled to room temperature for 180 minutes.

[0051] 3. After grinding the sintered product, it is washed with deionized water by vacuum filtration until no Cl is detected by AgNO3 detection. - Dry at 80℃ for 6 hours to obtain the product. The sample in this example is denoted as 0.25Ho-BTO.

[0052] Example 3 This embodiment provides a method for preparing bismuth titanate nanomaterials, the specific steps of which are as follows: 1. Weigh out bismuth trioxide, titanium dioxide, holmium trioxide, sodium chloride and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl=3.6:3:0.4:50:50, add them to a planetary ball mill jar, add an appropriate amount of anhydrous ethanol as a dispersant, and ball mill at 250 rpm for 4 hours to obtain the precursor slurry.

[0053] 2. After drying the precursor slurry at 75℃ for 2 hours, it is placed into an alumina crucible and calcined in a muffle furnace with programmed temperature rise: room temperature → 500℃ (120 min) → 800℃ (150 min), held for 2 hours, and cooled to room temperature for 180 minutes.

[0054] 3. After grinding the sintered product, it is washed with deionized water by vacuum filtration until no Cl is detected by AgNO3 detection. - Dry at 80℃ for 6 hours to obtain the product. The sample in this example is denoted as 0.4Ho-BTO.

[0055] Comparative Example This comparative example provides a method for preparing bismuth titanate nanomaterials, the specific steps of which are as follows: 1. Weigh out bismuth trioxide, titanium dioxide, sodium chloride and potassium chloride in a molar ratio of Bi:Ti:NaCl:KCl=4:3:50:50, add them to a planetary ball mill jar; add an appropriate amount of anhydrous ethanol as a dispersant, and ball mill at 250 rpm for 4 hours to obtain the precursor slurry.

[0056] 2. After drying the precursor slurry at 75℃ for 2 hours, it is placed into an alumina crucible and calcined in a muffle furnace with programmed temperature rise: room temperature → 500℃ (120 min) → 800℃ (150 min), held for 2 hours, and cooled to room temperature for 180 minutes.

[0057] 3. After grinding the sintered product, it is washed with deionized water by vacuum filtration until no Cl is detected by AgNO3 detection. - Dry at 80℃ for 6 hours to obtain the product. The sample in this comparative example is denoted as BTO.

[0058] Example 2: SEM and TEM images of the bismuth titanate nanomaterials obtained in the comparative example are as follows. Figure 1 As shown in the figure, the 0.25Ho-BTO prepared in Example 2 is in the form of flakes with uniform and controllable particle size morphology, and the Ti, Bi, Ho, and O elements are evenly distributed without local enrichment or agglomeration.

[0059] Example 2, XPS spectra of bismuth titanate nanomaterials obtained in Comparative Example 1 are as follows: Figure 2 As shown in the figure, new oxygen vacancies are formed in 0.25Ho-BTO, and the concentration of oxygen vacancies is significantly higher than that of pure bismuth titanate (BTO).

[0060] Example 2, the UV-Vis diffuse reflectance spectrum and Tauc plot of the bismuth titanate nanomaterials obtained in Comparative Example 1 are shown below. Figure 3 As shown in the figure, the band gaps of BTO and 0.25Ho-BTO are 2.83 eV and 2.94 eV, respectively (corresponding to absorption edges of 438 nm and 422 nm). The absorption edge of 0.25Ho-BTO exhibits a blue shift relative to BTO, with a band gap increase of approximately 0.11 eV, mainly attributed to Ho. 3+ The doping-induced quantum confinement effect; the resulting 0.25 Ho-BTO bandgap is well-suited to the UV-Vis response range, enabling effective photoexcitation and carrier generation. Example 2, the Nyquist electrochemical impedance spectroscopy of the bismuth titanate nanomaterials obtained in Comparative Example 1 is shown below. Figure 4 As shown in the figure, the impedance arc radius of 0.25Ho-BTO is significantly smaller than that of pure BTO (comparative example), indicating that 0.25Ho-BTO has a lower interfacial charge transfer resistance and more rapid migration of photogenerated electrons on the material surface, which is beneficial to improving the efficiency of catalytic reaction.

[0061] Application Example 1: Piezoelectric photocatalytic degradation of Rhodamine B by bismuth titanate nanomaterials Take 0.04 g of each of the bismuth titanate nanomaterials prepared in Examples 1 to 3 and the comparative example, and add them to 60 mL of Rhodamine B aqueous solution with a concentration of 10 mg / L. Stir for 20 min in the dark until adsorption equilibrium is reached. Then turn on the xenon lamp (equipped with a 400 nm cutoff filter) and apply 200 W, 53 kHz ultrasonic vibration. Perform piezoelectric-photocatalytic synergistic reaction at 30 °C. Take a sample every five minutes to detect the concentration of Rhodamine B.

[0062] Furthermore, the reactions were conducted under conditions of xenon lamp irradiation only (photocatalytic), ultrasonic vibration treatment only (Piezocatalytic), and simultaneous xenon lamp irradiation and ultrasonic vibration treatment (Piezo-Photocatalytic). Detection was performed after 30 minutes.

[0063] The results of Rhodamine B degradation by different bismuth titanate nanomaterials are shown in Table 1.

[0064] Table 1. Experimental results of piezoelectric photocatalytic degradation of Rhodamine B by bismuth titanate nanomaterials.

[0065] As can be seen from the table, when Ho 3+ When the doping concentration is 0.25%, the piezoelectric photocatalytic activity of the material is optimal, which is 3.99 times that of pure bismuth titanate. Furthermore, after 50 minutes of reaction, the degradation rate of the sample in Example 2 reached 94.2%. In addition, a comparison between Examples 2 and 3 shows that when Ho... 3+ When the doping amount is too high, it can lead to an increase in lattice defects and a decrease in catalytic activity.

[0066] The degradation rates of Rhodamine B under different activation conditions are as follows: Figure 5 As shown in the figure. It can be seen from the figure that: (1) Photocatalytic performance: Under visible light excitation, the degradation rate of Rhodamine B by 0.25Ho-BTO reached 63% within 40 min, and the reaction rate constant k was 0.0256 min. -1 It is a pure BTO (k=0.0064min) -1 4.02 times that of Ho indicates that Ho 3+ Doping effectively enhances the photocatalytic activity of the material.

[0067] (2) Piezoelectric catalytic performance: Under simple ultrasonic mechanical stress excitation conditions, the degradation rate of 0.25Ho-BTO was 25%, and the reaction rate constant k was 0.0057 min. -1 It is a pure BTO (k=0.0026min) -1 2.19 times that of Ho indicates that 3+ Doping enhances the piezoelectric response of the material.

[0068] (3) Synergistic catalytic performance: Under the synergistic excitation conditions of piezoelectric-photocatalysis, the degradation rate of 0.25Ho-BTO reached 86% within 30 min, and the reaction rate constant k was 0.0607 min. -1The results showed that the synergistic effect was 2.37 times that of pure photocatalysis and 10.65 times that of pure piezocatalysis, respectively; the synergistic factor S=k_synergy / (k_photo+k_piezo)=1.94, which was significantly greater than 1, confirming the existence of a significant piezo-photocatalytic synergistic effect.

[0069] (4) Material comparison: The catalytic performance of 0.25Ho-BTO under synergistic excitation conditions is significantly better than that of pure BTO (3.99 times better) and 0.1Ho-BTO (about 1.5 times better), confirming that the preferred Ho of this invention is superior. 3+ The doping ratio (x=0.25) provides the optimal piezoelectric-photocatalytic synergistic performance.

[0070] The 0.1Ho-BTO and 0.25Ho-BTO prepared by this invention both exhibit good catalytic performance under photoexcitation, and their catalytic performance is significantly improved after piezoelectric-photocatalytic synergistic excitation. In contrast, the catalytic activity of BTO under simple photocatalysis, ultrasonic stress excitation alone, and synergistic conditions is significantly lower than that of the material prepared by this invention. Among these, 0.25Ho-BTO shows the best performance, with an activity 3.99 times that of pure BTO under synergistic conditions.

[0071] Application Example 2: Cyclic Stability Testing of 0.25Ho-BTO Take 0.04 g of the 0.25 Ho-BTO nanomaterial prepared in Example 2 and add it to 60 mL of an aqueous solution of Rhodamine B with a concentration of 10 mg / L. Perform a piezoelectric-photocatalytic degradation reaction according to the reaction conditions of Application Example 1. Each reaction lasts for 25 min. After the reaction is completed, centrifuge to recover the catalyst, wash it three times with deionized water, dry it at 80 °C and then perform the next cycle experiment. A total of 4 cycles are performed.

[0072] The results are as follows Figure 6 As shown, the results indicate that after four cycles, the 30-min degradation rate of Rhodamine B by 0.25Ho-BTO decreased only slightly by 7.06%, and the XRD patterns of the samples before and after the cycles were basically consistent, indicating that the crystal structure remained stable. This suggests that the material has excellent reusability and structural stability.

[0073] Application Example 3: Piezoelectric photocatalytic degradation of various antibiotic pollutants by 0.25Ho-BTO 0.04 g of the 0.25 Ho-BTO nanomaterial prepared in Example 2 was added to 60 mL of aqueous solutions of tetracycline, ciprofloxacin, and levofloxacin at a concentration of 10 mg / L, respectively. After stirring in the dark for 20 min to reach adsorption equilibrium, a xenon lamp (equipped with a 400 nm cutoff filter) was turned on. The beaker containing the reaction solution was then placed in the cleaning tank of an ultrasonic cleaner, allowing it to float freely in the water (the liquid level in the beaker was below the rim). The ultrasonic cleaner was turned on, but the heating function was not activated, and the reaction was carried out at room temperature. Ultrasonic vibrations were coupled into the beaker through the water medium in the cleaning tank, inducing cavitation in the reaction solution. After the cavitation bubbles grew to a critical size, they collapsed rapidly, releasing shock wave pressure pulses with peak values ​​reaching megapascals. This drove the 0.25 Ho-BTO nanosheets to undergo reciprocating bending deformation, thereby generating a piezoelectric polarization field. This field, in synergy with photogenerated charge carriers, achieved efficient degradation of organic pollutants. After 30 min, the pollutant concentration was measured, and the degradation rate was calculated. Specific results are shown in Table 2. Figure 7 .

[0074] Table 2. Experimental results of piezoelectric photocatalytic degradation of antibiotics by bismuth titanate nanomaterials.

[0075] The results show that the 0.25Ho-BTO nanomaterials prepared in this invention also have good piezoelectric photocatalytic degradation effects on a variety of antibiotic-type organic pollutants, demonstrating the catalytic universality of the material and its applicability to water treatment of complex organic pollutants.

[0076] Application Example 4: Free Radical Scavenging Experiment Four scavenging agents were added to the piezoelectric photocatalytic degradation system of Rhodamine B: silver nitrate (AgNO3, 1 mmol / L) was used to capture photogenerated electrons (electrons). - p-Benzoquinone (BQ, 1 mmol / L) is used to capture superoxide radicals (O2). - Methanol (MT, 10 mmol / L) was used to capture holes (h + ); tert-butanol (TBA, 10 mmol / L) was used to capture hydroxyl radicals (·OH). Other reaction conditions were the same as in Application Example 1: 0.25 Ho-BTO 0.04 g / 60 mL Rhodamine B (10 mg / L), xenon lamp (>400 nm) + 200 W ultrasound (53 kHz), reaction at 30 °C for 30 min. Rhodamine B concentration changes were measured every 5 minutes.

[0077] Free radical capture experiment results as follows Figure 8 As shown, the degree of inhibition of the degradation of Rhodamine B by different trapping agents on the piezoelectric photocatalytic process of 0.25Ho-BTO is as follows: AgNO3 > BQ > MT > TBA.

[0078] After the addition of AgNO3, the degradation efficiency of Rhodamine B dropped sharply from 86% to 8%, indicating that photogenerated electrons (e) were significantly reduced. - Superoxide radicals (O2) play a dominant role in the degradation process; after the addition of BQ, the degradation rate decreased to 40%, indicating that superoxide radicals (O2) play a dominant role. - Holes are also important bioactive species; after the addition of MT and TBA, the degradation rates decreased to 65% and 69%, respectively, indicating that holes (h) are also important bioactive species. + The contributions of photogenerated electrons (PEN) and hydroxyl radicals (·OH) are relatively small. Mechanistically, photogenerated electrons migrate to the material surface and reduce adsorbed oxygen to (O2) radicals. - This leads to the oxidative degradation of Rhodamine B molecules.

[0079] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of the present invention to facilitate a specific and detailed understanding of the technical solution of the present invention, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

[0080] It should be understood that any technical solutions obtained by those skilled in the art based on the technical solutions provided in this invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for preparing bismuth titanate nanomaterials, characterized in that, include: Bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride were mixed uniformly in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor. The precursor was calcined to obtain an intermediate product; Sodium chloride and potassium chloride are removed from the intermediate product.

2. The method for preparing bismuth titanate nanomaterials as described in claim 1, characterized in that, In the step of uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor, the molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.91):3:(0.1~0.5):50:50; and / or In the step of calcining the precursor to obtain the intermediate product, the precursor is heated from 20-50°C to 450-550°C at a heating rate of 4-10°C / min, then heated to 750-820°C at a heating rate of 1-3°C / min, held at that temperature for 1.5-3.5 hours, and then cooled to 20-50°C within 2-3.5 hours to obtain the intermediate product; and / or In the step of removing sodium chloride and potassium chloride from the intermediate product, the intermediate product is washed with water and dried at 60~100℃ for 3~8 hours.

3. The method for preparing bismuth titanate nanomaterials as described in claim 1, characterized in that, In the step of uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor, the molar ratio of Bi:Ti:Ho:NaCl:KCl is 3.75:3:0.25:50:50; and / or In the step of calcining the precursor to obtain the intermediate product, the precursor is heated from 20-50°C to 480-520°C at a heating rate of 4-5°C / min, then heated to 790-810°C at a heating rate of 1.5-2.5°C / min, held at that temperature for 1.8-2.2 hours, and then cooled to 20-50°C within 2.5-3.5 hours to obtain the intermediate product.

4. The method for preparing bismuth titanate nanomaterials as described in claim 1, characterized in that, The step of uniformly mixing bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain the precursor includes: Bismuth oxide, titanium oxide, holmium oxide, sodium chloride, and potassium chloride were mixed in a molar ratio of Bi:Ti:Ho:NaCl:KCl = (3.5~3.92):(2.8~3.2):(0.1~0.5):(40~55):(40~55) to obtain a mixture. The mixture was ball-milled to obtain a precursor slurry; The precursor slurry is dried to obtain the precursor.

5. The method for preparing bismuth titanate nanomaterials as described in claim 4, characterized in that, The step of ball milling the mixture to obtain the precursor slurry involves mixing the mixture with a dispersant and ball milling at 200-500 rpm for 1-3 hours; wherein the dispersant is water and / or ethanol, and the weight ratio of the mixture to the dispersant is 1:(1.2-1.5); and / or In the step of drying the precursor slurry to obtain the precursor, the precursor slurry is dried at 70~100℃ for 1~3h.

6. A bismuth titanate nanomaterial, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.

7. The bismuth titanate nanomaterial as described in claim 6, characterized in that, The bismuth titanate nanomaterial has an (001) crystal plane exposure ratio of ≥80%, and it has a nanosheet structure with a thickness of 20~50nm and a length of 0.5~2μm.

8. A method for treating wastewater containing organic pollutants, characterized in that, The method includes the step of treating wastewater using bismuth titanate nanomaterials as described in claim 6 or 7.

9. The method for treating wastewater containing organic pollutants as described in claim 8, characterized in that, include: The bismuth titanate nanomaterial as described in claim 6 or 7 is added to wastewater containing organic pollutants and reacted under visible light excitation conditions. The weight ratio of the bismuth titanate nanomaterial to the volume of the wastewater is (0.5~0.7) g:1L; the wavelength of the visible light is 400~1100nm; and the reaction temperature is 20~50℃.

10. The method for treating wastewater containing organic pollutants as described in claim 9, characterized in that, The bismuth titanate nanomaterials as described in claim 6 or 7 are added to wastewater containing organic pollutants and reacted under visible light and mechanical stress excitation conditions. The mechanical stress excitation conditions are ultrasonic treatment or low-frequency water flow stress treatment, wherein the power of ultrasonic treatment is 100~300W and the frequency is 50~60kHz.

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