Rare earth metal tungstate nanosheet material as well as preparation method and application thereof

Abstract

The invention relates to a rare earth metal tungstate nanosheet material as well as a preparation method and application thereof. The rare earth metal tungstate nanosheet material comprises a PO4 < 3->-LnWO4 nanosheet, and Ln is at least one of lanthanide series rare earth metals. The preparation method comprises the following steps: dissolving phosphotungstic acid and a precursor in a solvent, and stirring to form a solution; adding an organic amine ligand, and stirring to form a transparent solution; performing solvothermal reaction on the solution; and centrifuging, washing with ethanol and drying to obtain the rare earth metal tungstate nanosheet material. A solvothermal reaction method is adopted to successfully construct a two-dimensional sheet structure material formed by interweaving nanowires, the material has high specific surface area, abundant pores and excellent structural stability, and the problems that a traditional photocatalytic material is single in structure and insufficient in active site are effectively solved. The photocatalyst shows excellent degradation capability on various typical antibiotic pollutants, breaks through the limitation that most photocatalytic materials are only effective on single pollutants, and realizes relatively high pollutant degradation universality.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of catalyst nanomaterial, specifically to a kind of rare earth metal tungstate nanosheet material and its preparation method and application. BACKGROUND

[0002] Fluoroquinolones (FQs) are a class of broad-spectrum antibiotics widely used in medical clinics and livestock breeding industries. This class of antibiotics has strong stability, is not easy to decompose, and has other characteristics, resulting in persistent accumulation and difficulty in degradation in natural water bodies, and has become a typical emerging environmental pollutant. Traditional biodegradation and conventional chemical oxidation methods have limited efficiency in removing FQs, and are often accompanied by problems such as insufficient selectivity and complex products, so it is of great application value to develop a photocatalytic material that can efficiently and selectively degrade FQs under visible light conditions.

[0003] Metal tungstate semiconductors are widely studied for photocatalytic oxidation, reduction, and degradation of water pollutants due to their excellent chemical stability and redox capacity. However, traditional bulk tungstates generally have wide band gaps, weak visible light absorption, fast photo-generated carrier recombination, and limited active sites on the material surface, which limits their practical effect in efficient photocatalytic degradation of antibiotics. Therefore, existing research has attempted to improve the photoelectric properties of tungstates through size reduction, ion doping, and interface regulation.

[0004] Among the many regulation strategies, polyoxometalates (POMs) are widely used in the controllable preparation of metal tungstates due to their clear structure, adjustable composition, and ability to provide stable multi-metal oxygen clusters. Polyoxometalates can play a dual role in the formation of tungstates: on the one hand, as a uniform tungsten source, it participates in hydrolysis and condensation reactions, promoting the directional assembly of metal ions and tungsten oxygen clusters at the molecular scale, forming tungstate structures with nanometer or sub-nanometer characteristics; on the other hand, its internal heteroatoms (such as PO4 3- , BO3 3- , etc.) can introduce lattice or interface during material construction, adjusting the band structure, oxygen defect distribution, and surface electronic state of the material, thereby significantly improving the visible light absorption capacity and photo-generated carrier separation efficiency.

[0005] Although the above-mentioned construction strategy based on POMs promotes the development of tungstate photocatalytic materials, some systems still rely on toxic metals such as Cd as the central ion. Although such materials enhance visible light response through size effect and interface reconstruction, their metal composition has environmental risks and is difficult to meet the requirements of water pollution treatment for material safety. In addition, the surface chemical properties of Cd-based tungstates are more suitable for small molecule catalytic reactions, and the selective adsorption and directional reaction ability of complex FQs molecules with multiple functional groups is limited, making it difficult to achieve efficient and controllable photocatalytic degradation.

[0006] In contrast, rare earth elements La and similar metals (such as Gd, etc.) have the advantages of low toxicity, good chemical stability, strong hard acid properties, and easy formation of stable structures with tungsten oxygen clusters. La 3+ The larger ionic radius and special electronic structure enable it to construct a stable metal-oxygen-tungsten network under the regulation of POMs, while providing more Lewis acid sites on the material surface, which is beneficial to the adsorption, complexation and directional activation of complex antibiotic molecules. In addition, La-based tungstates have greater controllable space in terms of light absorption, band regulation and carrier behavior, and can induce lattice distortion, enhance interface polarization effect and improve the efficiency of photo-generated electron-hole separation through coordination with PO4 3- heteroatoms, thereby improving their photocatalytic performance in the visible light region.

[0007] However, although the lanthanide metals of Ln have natural advantages, there is still a lack of a material system in the current public technology that uses heteropolyacids as a structure and electronic regulation unit, uses lanthanide metals of Ln as the center to construct tungstate nanosheet structures, and can achieve high selectivity photocatalytic degradation of antibiotic pollutants. The existing metal tungstate materials still have obvious deficiencies in visible light response, structure controllability, material safety and selective degradation ability of complex antibiotic molecules, which are difficult to meet the application requirements of actual water pollution treatment.

[0008] Therefore, the present patent develops a new type of lanthanide tungstate nanosheet photocatalytic material with a nanoscale structure, which uses heteropolyacids (phosphotungstic acid) as a control unit and lanthanide elements (La, Gd, Ce, etc.) of Ln as a central metal, to solve the technical bottlenecks in the existing technology in terms of material toxicity, light response range, electronic structure regulation and antibiotic selective degradation. SUMMARY

[0009] To solve the problems in the above-mentioned technology, the present application provides a rare earth metal tungstate nanosheet material and a preparation method and application thereof.

[0010] The present application first provides a rare earth metal tungstate nanosheet material, which comprises PO4 3-- LnWO4nanoplatelets, wherein Ln is at least one of the lanthanide series of rare earth metals.

[0011] In a preferred embodiment, the PO4 3- - LnWO4nanoplatelets have a two-dimensional platelet structure comprising PO4 3- doped with Ln 3+ doped with Ln 2- to the WO4

[0012] In a preferred embodiment, Ln 3+ is at least one of the following: La 3+ , Gd 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3 + , Tb 3+ .

[0013] In a preferred embodiment, the PO4 12 - LnWO4nanoplatelets are prepared from a Ln precursor and a PW 3- ; the molar ratio of the Ln precursor to the PW 12 is X:1, wherein X ranges from 1 to 10, or X ranges from 3 to 30, or X is 5, 10, or 20.

[0014] The present application provides a method for preparing LnWO4nanoplatelets based on heteropoly acid regulation, comprising the following steps: Step 1: Dissolve phosphotungstic acid (H3PW 12 O 40 ) and rare earth metal salt Ln(CH3COO)3-xH2O in a mixed non-polar solvent composed of cyclohexane and long-chain alcohol (such as n-hexanol, n-octanol), wherein the volume ratio of cyclohexane to long-chain alcohol is (1:1)~(4:1). Stir continuously at 30-50°C for 30-60 minutes to form a uniform suspension. This step utilizes the weak coordination ability of long-chain alcohol to interact with rare earth ions, regulating the subsequent nucleation kinetics. Here, “nucleation kinetics” refers to the regulation of nanoplatelet generation rate in Step 3 below.

[0015] Step 2: Add a composite organic amine ligand to the system of Step 1 above, which is composed of a main amine (selected from oleylamine, hexadecylamine) and a small amount of auxiliary diamine (such as ethylenediamine, with a volume fraction of 5%-15%). Under an inert atmosphere (such as nitrogen or argon), stir vigorously at 60-80°C for 1-2 hours until a uniform, transparent amber solution is formed. Then, let the solution stand at room temperature for 2-4 hours to promote the formation of more stable metal-organic precursor complexes.

[0016] Step 3: The aged solution was transferred into a Teflon-lined autoclave, with a fill level of 60-75%. The reaction was carried out using a two-stage temperature program: First stage: temperature was increased to 140-160°C at a rate of 2-3°C / min, and kept for 2-4 hours to achieve slow nucleation; Second stage: temperature was further increased to the target temperature of 180-200°C, and kept for 12-20 hours to promote anisotropic growth and crystallization of the nanosheet structure.

[0017] The molar ratio X (Ln:PW 12 ) of the rare earth metal precursor to phosphotungstic acid was strictly controlled between 5 and 30, preferably X = 10, 20.

[0018] Step 4: After the reaction was completed, it was naturally cooled to room temperature. The product was collected by centrifugation, and then purified using an alternating washing method: first, it was washed twice with a mixed solvent of cyclohexane and acetone (1:1 by volume) to completely remove long-chain organic amines and residual organic matter; then it was washed twice with anhydrous ethanol. The obtained product was dried in a vacuum drying oven at 80°C for 8-12 hours to obtain a fluffy powder of rare earth metal tungstate nanosheet material.

[0019] In the preferred scheme: The rare earth metal Ln is selected from at least one of the following elements: La, Gd, Ce, Pr, Nd, Sm, Eu, Tb; The mixed non-polar solvent is cyclohexane and n-hexanol, with a volume ratio of 3:1; The complex organic amine ligand is a mixture of oleylamine and ethylenediamine, with ethylenediamine accounting for 10% of the total volume; In step 3, the solvothermal reaction uses a two-stage program: first, it is kept at 150°C for 3 hours, and then it is reacted at 190°C for 16 hours; The molar ratio X is 10.

[0020] The application also provides a use of rare earth metal tungstate nanosheet regulated by heteropoly acid as a photocatalyst for degrading antibiotic or drug-like pollutants containing heterocyclic structures. Drug-like substances refer to substances containing heterocyclic structures similar in structure to antibiotics, such as sulfonamides, organic dyes such as rhodamine B, etc.

[0021] In the preferred scheme, the antibiotic includes fluoroquinolone antibiotics; the fluoroquinolone antibiotic is at least one of the following substances: CIP, NOR, OFX, ENR, LOM.

[0022] In the preferred scheme, the CO32- photocatalytic degradation under the system.

[0023] The technical effects of the present application are summarized as follows: The present application focuses on the above technical problems and technical solutions, through material structure regulation, multi-element synergistic effect and photocatalytic behavior optimization, to achieve significant technical effects, as follows: (1) Technical effects in material design and structure regulation: The present application successfully constructs a two-dimensional sheet structure material formed by interweaving nanowires using a solvothermal reaction method. This structure has high specific surface area, rich porosity and excellent structural stability, effectively overcoming the problems of single structure and insufficient active sites of traditional photocatalytic materials.

[0024] By regulating the material composition, high uniform dispersion of C, N, O, P, Ln and W is achieved, and a controllable W 6+ / W 5+ redox pair and surface oxygen vacancies are formed in the material. The synergistic effect of the two significantly improves the separation efficiency of photo-generated electron-hole pairs and accelerates the carrier migration, effectively solving the technical bottleneck of easy phase separation and high carrier recombination rate in traditional single-component or multi-component systems.

[0025] (2) Technical effects in performance improvement: The material PO4 3- -LaWO4(X=10) prepared by the present application has a target pollutant degradation efficiency of 92% under optimal conditions (catalyst dosage 1.0 g / L), which is significantly better than most existing photocatalytic materials. The narrow band gap property (3.84 eV) and strong visible light absorption ability of the material effectively improve the solar energy utilization efficiency, making it exhibit more excellent photocatalytic activity in the visible light region, and solving the problem of narrow light absorption range and low degradation rate of traditional materials.

[0026] (3) Technical effects in environmental adaptability and application universality: The material prepared by the present application exhibits excellent degradation ability for multiple types of typical antibiotic pollutants (including CIP, NOR, OFX, ENR, LOM, etc.), breaking through the limitation of most photocatalytic materials being effective only for single pollutants, and achieving strong pollutant degradation universality. It can still maintain stable catalytic performance in water containing common inorganic anions such as Cl - , SO4 2- , NO3 - , etc., among which CO3 2-The presence of the above-mentioned elements can even promote the reaction process, effectively avoiding the technical defects of traditional photocatalytic systems that are susceptible to anion inhibition, leading to a decrease in activity, and thus being more suitable for complex actual water body environments. Compared with existing photocatalytic technologies that require high temperature, high pressure or rely on expensive additives, the present application is simple to operate, mild in conditions, low in operating cost, and more suitable for engineering scale applications.

[0027] (4) Technical effects in terms of social and economic value: The successful development of the technology provides an efficient, stable, economical and environmentally friendly technical path for the treatment of antibiotic pollution in water environments. Its excellent comprehensive performance not only promotes new progress in the design of photocatalytic materials, but also contributes to new solutions for improving efficiency and reducing costs in water treatment processes. With its reliable performance in complex water body systems, the present application has wide application potential in the fields of municipal sewage treatment, medical wastewater purification, industrial wastewater treatment, etc. The popularization and application of the technology will help to improve the ecological environment governance capacity and provide strong support for maintaining water ecological safety and public health, and has far-reaching social value. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the synthesis steps of the samples of embodiments 1-3 of the present application; OAm in the figure represents oleylamine; Figure 2 is a SEM and TEM image of the sample of embodiment 1 of the present application; Figure 3 is an XRD spectrum of the samples of embodiments 1-3 of the present application and a standard card; Figure 4 is a UV-Vis-DRS spectrum of the samples of embodiments 1-3 of the present application; Figure 5 is an XPS spectrum of the samples of embodiments 1-3 of the present application; Figure 6 is a degradation performance graph of the samples of embodiments 1-3 of the present application; Figure 7 is a morphology and degradation performance graph of embodiment 4 of the present application; Figure 8 is a morphology and degradation performance graph of embodiment 5 of the present application. DETAILED DESCRIPTION

[0029] Embodiment 1: PO4 3- Preparation of LaWO4(X=10): (1) Take 0.5 g of PW 12Add 24 mL of n-hexane to 0.5486 g of La(CH3COO)3·xH2O and stir for 10 min; Note that the mass of xH2O is not included in the 0.5486 g of La(CH3COO)3·xH2O, and this is also the case in the following examples to maintain the correct conversion of dosage and molar ratio.

[0030] (2) Add 5.7 mL of oleylamine and continue stirring for 10 min; (3) The solution was transferred to a reaction vessel and reacted at 180 °C for 12 h using a solvothermal method; (4) After cooling, centrifuge at 8000 rpm and wash three times with ethanol; (5) Vacuum drying at 60 °C yields PO4. 3- –LaWO4 (X=10) nanosheets.

[0031] Example 2: PO4 3- Preparation of LaWO4 (X=5): Same as Example 1, except that the feeding ratio of La(CH3COO)3·xH2O is different, which is 0.27743g.

[0032] Example 3: PO4 3- Preparation of LaWO4 (X=20): Same as Example 1, except that the feeding ratio of La(CH3COO)3·xH2O is different, which is 1.0973g.

[0033] Example 4: PO4 3- Preparation of GdWO4 (X=10): This embodiment is used to verify the applicability of the method of the present invention to other lanthanide metals (Ln). Same as Example 1, but the amount of Gd(CH3COO)3·xH2O added is adjusted to 0.5805 g. The preparation steps are the same as in Example 1, except that the rare earth precursor is replaced with Gd(CH3COO)3·xH2O, and the amount added is 0.5805 g. All other reaction conditions are completely identical, yielding two-dimensional PO4. 3- –GdWO4 (X = 10) nanosheets.

[0034] Example 5: PO4 3- Preparation of CeWO4 (X=10): To further extend this invention to more lanthanide metals (Ln=Ce), the same steps as in Example 1 were used, except that the amount of rare earth precursor was adjusted to 0.5507 g of Ce(CH3COO)2·xH2O, thus PO4 could be prepared. 3- –CeWO4 (X = 10) nanosheets.

[0035] The synthesis methods for other lanthanide metals are the same as in Example 1, except that the rare earth precursor is replaced with the precursor corresponding to the desired lanthanide metal element, which will not be described in detail here; and, according to the required X ratio, the corresponding mass of rare earth precursor is selected.

[0036] Reagents and instruments: Reagent: n-hexane (C6H) 14 Anhydrous ethanol (C2H6O) and phosphotungstic acid (H3PW) were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). 12 O 40 -6H2O, PW 12 Lanthanum acetate hydrate (La(CH3COO)3–xH2O), oleylamine (OLA), potassium persulfate (PMS), ciprofloxacin (CIP), norfloxacin (NOR), ofloxacin (OFX), enrofloxacin (ENR), and lomefloxacin (LOM) were purchased from Aladdin (Shanghai, China). All chemical reagents used in the experiments were analytical grade and had not undergone further purification. Deionized water was used in all experimental procedures.

[0037] Instruments: Scanning electron microscope (SEM, JEOL JSM-7800F), transmission electron microscope (TEM, Talos F200X G2), UV-Vis spectrophotometer (solid-state UV-vis-DRS, Shimadzu UV-2405), X-ray photoelectron spectroscopy (XPS, Thermo Scientific Escalab OXi), xenon lamp light source (PLS-SEX300D).

[0038] Experimental Analysis and Explanation: 1. PO4 prepared in Example 1 3- -Analysis was conducted on the synthesis of LaWO4 (X=10) material.

[0039] Figure 1 This provides an overview of i.) PO4 3- - Synthesis route of LaWO4 (X=10). This synthesis process uses a one-step solvothermal method to successfully prepare La-based doped WO3 nanosheets. First, in the nonpolar solvent n-hexane, PW 12 A stable metal-amine complex is formed with the lanthanum acetate precursor under the strong coordination of OLA. This complex not only provides spatial confinement for the hydrolysis-condensation of tungstate ions, but also realizes the La... 3+Uniform doping at the molecular scale was achieved. Subsequently, OLA, acting as a reducing agent and structure-directing agent, induced partial reduction of tungsten in a high-temperature, high-pressure solvothermal environment, promoting the preferential growth of two-dimensional nanosheet structures along specific crystal planes. Centrifugation and washing processes after the reaction effectively removed unreacted precursors and organic residues. Finally, vacuum drying yielded fully crystallized and uniformly doped PO4. 3- -LaWO4 nanosheet material.

[0040] 2. PO4 prepared in Example 1 3- -LaWO4 (X=10) material was characterized.

[0041] Figure 2 These are SEM and TEM images of samples from embodiments of the present invention. Figure 2 Image a is a SEM image of an example of this invention. The sample exhibits a layered stacked structure with relatively uniform layer thickness and certain porosity between the layers. PO4 3- -LaWO4 (X=10) exhibits a balance between aggregation and dispersion, achieving synergistic optimization of light absorption, carrier separation, and reaction site exposure. It enhances light capture and carrier separation efficiency through lamellar aggregation, while retaining sufficient active sites and mass transfer channels through appropriate dispersion, thereby improving photocatalytic degradation performance.

[0042] (2) Transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM): TEM Figure 2 (b) shows that the material exhibits a two-dimensional sheet-like aggregate structure composed of interwoven nanowires. The sheets are relatively thin and have a certain degree of porosity, providing a structural basis for the uniform dispersion of multiple components. The uniform elemental distribution achieved through the solvothermal method can avoid the formation of defects caused by phase separation, thereby improving the stability of the material structure.

[0043] like Figure 3 As shown, via PO4 3- X-ray diffraction (XRD) patterns of LaWO4 nanosheets confirm the existence of their crystal structure. From... Figure 3 The given XRD patterns show that different Ln / PW 12 The diffraction peaks of the samples synthesized at scales (X=5, 10, 20) all highly coincided with the peak positions of the standard PDF card (#34-0652, La2W2O9), with (200), (210), (321), and (420) being the main characteristic diffraction peaks of this structure. This result directly indicates that the main crystal structure of the obtained material belongs to the La2W2O9 type tungstate lattice. More importantly, PO4 3- and Ln 3+The introduction of these substances did not change the basic crystal structure of the material, indicating that they entered WO4 in the form of doping or substitution. 2- It exists within the base lattice, rather than forming an independent impurity phase.

[0044] (3) Ultraviolet-Vis absorption spectrum (solid) UV-Vis-DRS: Figure 4 The UV-Vis-DRS spectra of samples from Examples 1-3 of this invention are shown. In the UV-Vis-DRS spectra ( Figure 4 In (a), all samples exhibited strong absorption in the ultraviolet region. PO4 3- -LaWO4 (X=5), PO4 3- -LaWO4 (X=10) and PO4 3- The absorption edges of the LaWO4 (X=20) samples were located at 326 nm, 342 nm, and 367 nm, respectively. With increasing component content, the absorption edges exhibited a red shift, indicating enhanced visible light absorption, which is beneficial for improving the utilization rate of solar energy in photocatalytic degradation reactions. In the optical property characterization of photocatalytic materials, the absorption edge refers to the critical wavelength (λ) at which a sharp increase in absorbance or absorption coefficient occurs in the material's light absorption spectrum (usually ultraviolet-visible diffuse reflectance spectrum, UV-Vis DRS) (i.e., absorption begins to significantly increase). g In simpler terms, it is the "turning point" wavelength at which a material goes from absorbing almost no photons to beginning to strongly absorb them.

[0045] PO4 was calculated using the Tauc plots method. 3- -LaWO4 (X=5), PO4 3- -LaWO4 (X=10) and PO4 3- -Band gap width of LaWO4 (X=20) sample ( E g () Figure 4 b, where the horizontal axis "hν" represents photon energy, and the vertical axis "αhν" represents the relationship between the absorption coefficient (α) and photon energy (hν), with band gaps of 4.02 eV, 3.84 eV, and 4.17 eV, respectively. PO4 3- -LaWO4 (X=10) has the narrowest band gap, which is beneficial for promoting the excitation of electrons from the valence band to the conduction band under light irradiation, thereby generating more photogenerated electron-hole pairs. Combined with enhanced visible light absorption properties, PO4... 3- -LaWO4 (X=10) exhibits excellent photocatalytic degradation performance.

[0046] (4) X-ray photoelectron spectroscopy (XPS): Depend on Figure 5XPS spectra of samples from Examples 1-3 of this invention. Full spectrum scan ( Figure 5 a) Confirmed that all samples contained C, N, O, P, La, and W elements, consistent with EDS results. (Using PO4) 3- -LaWO4 (X=10) as an example. In the La3d spectrum ( Figure 5 In b), the two peaks at 835.28 eV and 838.88 eV correspond to La3d, respectively. 3 / 2 The two peaks at 852.18 eV and 855.68 eV correspond to La3d. 5 / 2 La mainly consists of La 3+ La exists in the form of [missing information]. Slight shifts in binding energy between different samples indicate that variations in component content can modulate La. 3+ The electronic environment affects its coordination state and chemical reactivity. W4f spectrum ( Figure 5 c) It can be divided into two pairs of peaks, located at 34.68 eV, 36.78 eV and 35.68 eV, 37.78 eV respectively, corresponding to W 5+ and W 6+ Of the three samples, PO4 3- -LaWO4 (X=10) of W 5+ The highest proportion of PO4 provides the catalyst with more sites for photocatalytic degradation. However, it can be calculated that PO4... 3- -LaWO4 (X=10) of W 6+ Peak and W 5+ The energy separation between the peaks was not significantly different, indicating that PO4 3- -LaWO4 (X=10) did not exhibit a phase shift due to different reaction times. O1s spectrum ( Figure 5 The peaks of d) can be fitted to lattice oxygen (529.88 eV, 530.78 eV and 530.98 eV) and oxygen defects (531.58 eV, 532.28 eV and 532.38 eV).

[0047] The synthesis method provided by this invention can effectively introduce "very small amounts" of W. 5+ (Typically less than 5%), this is a very sophisticated "defect engineering" strategy. 5+ The presence of these ions, by introducing associated oxygen vacancies, synergistically forms active defect centers, which can effectively capture photogenerated electrons, inhibit charge recombination, and enhance surface adsorption, thus significantly improving the light absorption and catalytic degradation performance of the material.

[0048] It should be noted that the elements "C" and "N" mentioned above are derived from organic amine ligands added to the precursors used in the synthesis. These ligands are adsorbed on the surface of the nanosheets and play a stabilizing role.

[0049] 3. PO4 prepared in Examples 1-3 3- -LaWO4 (X=5), PO4 3- -LaWO4 (X=10) and PO4 3- The degradation performance of the LaWO4 (X=20) material was tested. The specific experimental procedure was as follows: a certain mass of ciprofloxacin (CIP) standard was weighed and dissolved in deionized water to prepare a 10 mg / L ciprofloxacin aqueous solution as the working solution; 50 mg of PO4 prepared in Examples 1-3 was weighed. 3- -LaWO4 (X=5), PO4 3- -LaWO4 (X=10) and PO4 3- -LaWO4 (X=20) material was placed in a 100 mL reactor, and 50 mL of a 10 mg / L CIP aqueous solution was added. The solutions were then magnetically stirred in the dark for 30 min to reach equilibrium, followed by continuous irradiation with a visible light source. Water samples were collected at predetermined time intervals. At each time point, 3 mL of solution was taken, centrifuged to remove adsorbent particles, and the absorbance of the supernatant was measured using a Shimadzu UV-2600 spectrophotometer with a wavelength of 272 nm. The adsorption efficiency of CIP (… E Calculate using the following formula: , in, C 0 and C The concentrations of CIP solution before and after degradation are shown below. A 0 and A The absorbance values ​​of CIP before and after degradation are shown below.

[0050] Figure 6 The graphs show the degradation performance of samples from Examples 1-3 of this invention. This invention investigated the degradation performance of Examples 1-3 under different influencing factors, such as... Figure 6 As shown in ac. Catalysts with different La contents (PO4). 3- -LaWO4 (X=5), PO4 3- -LaWO4 (X=10) and PO4 3- The photocatalytic CIP degradation performance of -LaWO4 (X=20) is as follows: Figure 6 As shown in a, PO4 can be found 3- -LaWO4 (X=10) exhibited the best degradation performance, a result consistent with previous characterization findings using SEM, TEM, and UV-Vis-DRS. The catalyst showed excellent degradation performance against various typical pollutants, including ciprofloxacin (CIP), norfloxacin (NOR), ofloxacin (OFX), enrofloxacin (ENR), and lomefloxacin (LOM). Figure 6(b) All showed excellent degradation ability. Among them, enrofloxacin (ENR) had the highest degradation performance. Regarding the influence of inorganic anions ( Figure 6 c), CO3 2- This process promotes the photocatalytic degradation of CIP in this invention. This phenomenon may originate from CO3. 2- It interacts with reactive species (such as hydroxyl radicals –OH) generated in the reaction system to produce carbonate radicals (CO3), which have strong oxidizing power and higher stability. –- This free radical can attack pollutant molecules more efficiently; meanwhile, CO3 2- It is possible to enhance the adsorption and charge transfer processes of pollutants by adjusting the pH of the solution and optimizing the surface charge state of the catalyst. - SO4 2- and NO3 - The catalyst had a relatively small impact on degradation efficiency, exhibiting no obvious promoting or inhibiting effect. This indicates that the catalyst has good anti-interference ability in complex aquatic environments containing common inorganic anions, especially in environments containing CO3. 2- Its performance can be improved in water bodies, significantly enhancing its potential for practical water remediation applications.

[0051] Figure 7 PO4 of Example 4 3- – Morphology and degradation performance of GdWO4 (X=10). Figure 7 a shows PO4 3- –GdWO4 (X=10) has a nanosheet structure and exhibits excellent photocatalytic degradation performance on fluoroquinolone antibiotics such as ciprofloxacin (CIP), norfloxacin (NOR), ofloxacin (OFX), enrofloxacin (ENR), and lomefloxacin (LOM). Figure 7 (b) The degradation rate exceeds 90%.

[0052] Figure 8 PO4 of Example 5 3- – Morphology and degradation performance of CeWO4 (X=10). Figure 8 a shows PO4 3- –GdWO4 (X=10) has a nanosheet structure, but is slightly aggregated. It also exhibits excellent photocatalytic degradation performance against fluoroquinolone antibiotics such as ciprofloxacin (CIP), norfloxacin (NOR), ofloxacin (OFX), enrofloxacin (ENR), and lomefloxacin (LOM). Figure 8 b).

[0053] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the invention, even when only a single embodiment is described with respect to a particular feature. The feature examples provided in this disclosure are intended to be illustrative and not limiting, unless otherwise stated. In practice, one or more technical features of the dependent claims may be combined with the technical features of the independent claims as needed and where technically feasible, and may be derived from the technical features of the respective independent claims in any suitable manner rather than solely by the specific combinations listed in the claims.

[0054] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A rare earth metal tungstate nanosheet material, characterized in that, Including PO4 3- –LnWO4 nanosheets, wherein Ln is at least one of the lanthanide rare earth metals.

2. The rare earth metal tungstate nanosheet material according to claim 1, characterized in that, The PO4 3- –LnWO4 nanosheets have a two-dimensional sheet-like structure containing PO4 3- Doping with Ln 3+ Doped WO4 2- Basic lattice.

3. The rare earth metal tungstate nanosheet material according to claim 1, characterized in that, Ln 3+ It is at least one of the following substances: La 3+ Gd 3+ Ce 3+ Pr 3+ 、Nd 3+ 、Sm 3+ Eu 3+ 、Tb 3+ .

4. The rare earth metal tungstate nanosheet material according to claim 1, characterized in that, Through Ln precursor and PW 12 PO4 was prepared 3- –LnWO4 nanosheets; Ln precursor and PW 12 The molar ratio is X:1, where X ranges from 1 to 10, or from 3 to 30, or X is 5, 10, or 20.

5. A method for preparing rare earth metal tungstate nanosheet material as described in claim 1, characterized in that, Includes the following steps: Step 1: Dissolve phosphotungstic acid and rare earth metal salt Ln(CH3COO)3·xH2O together in a mixed nonpolar solvent composed of cyclohexane and long-chain alcohol; stir continuously at 30-50°C for 30-60 minutes to form a homogeneous suspension; this step utilizes the weak coordination ability of long-chain alcohol to conduct preliminary interactions with rare earth ions, thereby regulating the subsequent nucleation kinetics; Step 2: Add a complex organic amine ligand, which consists of a host amine and an auxiliary diamine, to the system from Step 1. Stir vigorously at 60-80°C for 1-2 hours under an inert atmosphere until a homogeneous, transparent amber solution is formed. Then, allow the solution to stand at room temperature for 2-4 hours to promote the formation of a more stable metal-organic precursor complex. Step 3: Transfer the aged solution to a high-pressure reactor lined with polytetrafluoroethylene (PTFE), maintaining a filling level of 60%-75%; proceed with the reaction using a stepwise heating program. First stage: Heat to 140-160°C at a rate of 2-3°C / min and hold for 2-4 hours to achieve slow nucleation; Second stage: Continue heating to the target temperature of 180-200°C and hold the temperature for 12-20 hours to promote anisotropic growth and crystallization of the nanosheet structure; Step 4: After the reaction is complete, allow it to cool naturally to room temperature; collect the product by centrifugation and purify it using an alternating washing method: first wash twice with a mixed solvent of cyclohexane and acetone to completely remove long-chain organic amines and residual organic matter; then wash twice with anhydrous ethanol; dry the obtained product in a vacuum drying oven to obtain fluffy powdered rare earth metal tungstate nanosheets.

6. The method for preparing rare earth metal tungstate nanosheets according to claim 5, characterized in that, The molar ratio X of the rare earth metal precursor to phosphotungstic acid is Ln:PW. 12 Keep it between 1 and 50; In step 1: the long-chain alcohol is n-hexanol or n-octanol; the volume ratio of cyclohexane to the long-chain alcohol is 1:1 to 4:1; In step 2: the main amine is selected from oleylamine or hexadecylamine; the auxiliary diamine is selected from ethylenediamine; the auxiliary diamine accounts for 5%-15% of the volume of the complex organic amine ligand; In step 4: the volume ratio of cyclohexane to acetone is 1:1; the resulting product is dried in a vacuum drying oven at 80°C for 8-12 hours.

7. The method for preparing rare earth metal tungstate nanosheets according to claim 6, characterized in that, The rare earth metal Ln is selected from at least one of the following elements: La, Gd, Ce, Pr, Nd, Sm, Eu, Tb; The mixed nonpolar solvent is cyclohexane and n-hexanol, with a volume ratio of cyclohexane to n-hexanol of 3:

1. The composite organic amine ligand is a mixture of oleylamine and ethylenediamine, wherein ethylenediamine accounts for 10% of the total volume; In step 3, the solvothermal reaction is carried out in two stages: first, the temperature is maintained at 150°C for 3 hours, and then the reaction is carried out at 190°C for 16 hours. The molar ratio X is 10.

8. An application of rare earth metal tungstate nanosheet material as described in any one of claims 1-4 in the photocatalytic degradation of antibiotics or drug-like pollutants containing heterocyclic structures.

9. The application according to claim 8, characterized in that, The antibiotics include fluoroquinolone antibiotics; fluoroquinolone antibiotics are at least one of the following substances: CIP, NOR, OFX, ENR, LOM.

10. The application according to claim 8, characterized in that, In CO3 2- Photocatalytic degradation is carried out in the system.

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