UCNPs modified AgNPs (at) MgAl LDH composite material and preparation and application thereof

Abstract

The invention discloses a UCNPs modified AgNPs (at) MgAl LDH composite material and a preparation method of the UCNPs modified AgNPs (at) MgAl LDH composite material. According to the preparation method, MgAl LDH is synthesized through a solvothermal method, AgNPs is loaded on the MgAl LDH through a reduction precipitation method, and the AgNPs-coated MgAl LDH composite material is successfully prepared; liYF4: Yb and Tm-coated LiYF4 UCNPs are prepared at the same time, the LiYF4: Yb and Tm-coated LiYF4 UCNPs are subjected to hydrophilic modification by adopting a ligand exchange method, and finally the LiYF4: Yb and Tm-coated LiYF4 UCNPs and the LiYF4: Yb and Tm-coated LiYF4 UCNPs are compounded to prepare the AgNPs-coated MgAl LDH / According to the ternary composite system, through surface plasma resonance (SPR) of AgNPs, the up-conversion luminescence effect of UCNPs and the layered structure synergistic effect of MgAl LDH, efficient degradation of TCH can be achieved, and meanwhile a new thought is provided for the near-infrared driven environment restoration technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic materials, and particularly relates to a lithium-based core-shell structure LiYF4:Yb,Tm@LiYF4 upconversion nanoparticle (UCNP) modified AgNPs@MgAl LDH composite material photocatalyst, a preparation method thereof and application thereof. BACKGROUND

[0002] Tetracycline hydrochloride (TCH) is a dangerous colorless pollutant, which is a chemically stable and non-biodegradable tetracycline antibiotic, and widely exists in many water bodies in the world, such as drinking water and groundwater. The degradation methods for TCH in water include biodegradation, physical adsorption, complex oxidation and photocatalytic degradation. Among them, photocatalytic degradation has been proved to be an effective means to remove organic antibacterial pollutants.

[0003] Compared with other types of semiconductor photocatalysts, layered double hydroxides (LDHs) have their unique properties, such as adjustable chemical composition, high specific surface area and ability to intercalate various anions, which significantly improve their adsorption performance and catalytic efficiency. However, there are still some gaps in the stability and universality of these materials in practical applications. In the process of pursuing sustainable and efficient environmental remediation solutions, the development and optimization of LDH-based nanomaterials are particularly important. SUMMARY

[0004] The purpose of the application is to provide a UCNPs modified AgNPs@MgAl LDH composite material and a preparation method and application thereof. The application introduces silver nanoparticles (AgNPs) to regulate the light response range of MgAl LDH, so as to match the emission spectrum of lithium-based core-shell LiYF4:Yb,Tm@LiYF4 upconversion luminescent particles (UCNPs), thereby widening the light response range of the ternary composite material.

[0005] To achieve the above-mentioned purpose, the application adopts the following technical solutions: A UCNPs modified AgNPs@MgAl LDH composite material, and a preparation method thereof, includes the following steps: (1) Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea are added to a mixed solvent of ethylene glycol and water, stirred for 1 hour, and then subjected to hydrothermal reaction. After the reaction is completed, the reaction system is cooled to room temperature, and then washed with deionized water and ethanol for multiple times, and dried, to obtain MgAl LDH; (2) dispersing the MgAl LDH obtained in step (1) into deionized water, then dropping AgNO3 aqueous solution, and adding NaBH4, stirring for 3 hours in dark condition, then washing with deionized water and ethanol for several times, drying to obtain AgNPs@MgAl LDH; (3) adding YbCl3·6H2O, TmCl3·6H2O, YCl3·6H2O into the mixed solvent of oleic acid and 1-octadecene, then adding methanol solution of NH4F and methanol solution of LiOH after high temperature treatment, naturally cooling to room temperature after twice high temperature treatment, then adding ethanol to precipitate the product, and centrifuging and washing to obtain LiYF4:Yb,Tm@LiYF4 UCNPs; (4) mixing sodium citrate dihydrate, diethylene glycol and deionized water for heat treatment, then adding the dispersion liquid of LiYF4:Yb,Tm@LiYF4 UCNPs, continuing to heat treat twice, then cooling to room temperature, centrifuging and washing to obtain modified UCNPs, and dispersing the UCNPs in deionized water; (5) dispersing the AgNPs@MgAl LDH prepared in step (2) in anhydrous ethanol / deionized water mixed solution, adding the modified UCNPs aqueous dispersion liquid in step (4), stirring, centrifuging and drying to obtain AgNPs@MgAl LDH / UCNPs ternary composite material.

[0006] Further, the molar ratio of Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea used in step (1) is 2:1:15.

[0007] Further, the volume ratio of ethylene glycol and water in the mixed solvent in step (1) is 9:1.

[0008] Further, the temperature of the hydrothermal reaction in step (1) is 160℃, and the time is 6 hours.

[0009] Further, the mass ratio of AgNO3 and NaBH4 used in step (2) is 1:8.

[0010] Further, the mass ratio of AgNPs in the AgNPs@MgAl LDH obtained in step (2) is 0.25%~2%.

[0011] Further, the molar ratio of YbCl3·6H2O, TmCl3·6H2O, YCl3·6H2O, NH4F and LiOH used in step (3) is 7:0.05:2.95:40:15.

[0012] Further, the volume ratio of oleic acid and 1-octadecene in the mixed solvent in step (3) is 8:12.

[0013] Further, the high-temperature treatment in step (3) is performed at 160℃ under a nitrogen atmosphere and a vacuum degree of 0.08 MPa for 30 minutes.

[0014] Further, the concentration of the NH4F methanol solution used in step (3) is 0.8 mmol / ml, and the concentration of the LiOH methanol solution used is 0.3 mmol / ml.

[0015] Further, the secondary high-temperature treatment in step (3) is performed by increasing the temperature from room temperature to 50℃ under a nitrogen atmosphere, maintaining the temperature for 30 minutes, then increasing the temperature to 70℃, maintaining the temperature for 15-30 minutes, and then increasing the temperature to 300℃, maintaining the temperature for 60 minutes.

[0016] Further, the centrifugal washing in step (3) uses a mixed solution of cyclohexane and anhydrous ethanol in a volume ratio of 1:4 as the washing agent.

[0017] Further, the amount ratio of sodium citrate dihydrate, diethylene glycol, deionized water, and LiYF4:Yb,Tm@LiYF4UCNPs used in step (4) is 0.588 g:15 mL:1 mL:0.28 g.

[0018] Further, the dispersion liquid of LiYF4:Yb,Tm@LiYF4UCNPs in step (4) is prepared by dispersing 1 mmol of LiYF4:Yb,Tm@LiYF4UCNPs in 5 ml of cyclohexane.

[0019] Further, the heat treatment in step (4) is performed by increasing the temperature to 110℃ under a nitrogen atmosphere, maintaining the temperature for 40 minutes, and then cooling to room temperature.

[0020] Further, the secondary heat treatment in step (4) is performed by increasing the temperature to 130℃, maintaining the temperature for 30 minutes, and then further increasing the temperature to 175℃, maintaining the temperature for 2 hours.

[0021] Further, the volume ratio of anhydrous ethanol to deionized water in the anhydrous ethanol / deionized water mixed solution in step (5) is 1:1.

[0022] Further, the amount of the modified UCNPs water dispersion liquid used in step (5) is calculated according to the mass ratio of the modified UCNPs therein to the AgNPs@MgAl LDH used, which is 1.12:1.

[0023] The obtained UCNPs-modified AgNPs@MgAl LDH composite material can be used for photocatalytic degradation of tetracycline.

[0024] Furthermore, its application method involves using the UCNPs-modified AgNPs@MgAl LDH composite material as a photocatalyst to degrade tetracycline in water under visible-infrared light irradiation.

[0025] like Figure 1 As shown, when the catalyst is irradiated with light in the 420-2500 nm range, some of the light is directly absorbed by the material, and MgAl LDH generates photogenerated electron-hole pairs. Although MgAl LDH itself has weak absorption capacity for visible light, the deposition of AgNPs on the MgAl LDH surface produces a plasmonic resonance (SPR) effect, which significantly enhances the overall absorption capacity of the material for light sources, especially in the visible light range of 400-500 nm. For infrared irradiation in the 980 nm range, the sensitizer Yb in the active core of LiYF4:Yb,Tm@LiYF4UCNPs... 3+ When excited by 980 nm light, electrons move from the ground state. 2 F 7 / 2 Excited to metastable state 2 F 5 / 2 Yb is in the excited state 3+ The photon on the ion relaxes back to the ground state, and the energy is transferred nonradiatively to Tm outside the nucleus. 3+ of 3 H5 3 F2 and 1 G4 energy level. When a photon returns from a high-energy state to the ground state ( 1 G4→ 3 The process of H6 will emit light with wavelengths of 472 and 483 nm in the form of radiative transitions. Because 1 G4 and 1 The energy difference between the D2 levels is relatively large, requiring two Tm levels. 3+ ion 3 H4+ 1 G4→ 1 D2+ 3 F4 and 1 G4+ 3 H4→ 1 D2+ 3 F4 cross-relaxation triggers the arrival 1 It enters the D2 energy level and then decays to a lower energy state. 1 D2→ 3 F4 emits light at 452 nm. 1 D2→ 3H6 will emit ultraviolet light at 361 nm. At this point, both ultraviolet light and strong blue light fall within the absorption range of AgNPs@MgAl. Excited by this light source, electrons are excited from the semiconductor valence band to the conduction band, migrate to the catalyst surface, and undergo reduction. The oxidation reaction occurs directly from the holes left in the valence band. The CB position of MgAl LDH is -1.25 eV, much lower than the potential of O2 / ·O2- (-0.33 eV), allowing it to reduce O2 to ·O2⁻. Similarly, the VB position of MgAl LDH is 3.03 eV, much higher than the oxidation potential of ·OH / OH- (1.99 eV), thus enabling it to oxidize OH- to ·OH. When a certain amount of AgNPs is introduced onto the MgAl LDH surface, due to electron flow, the interfacial contact between AgNPs and the MgAl LDH semiconductor leads to the formation of a Schottky junction. Electrons will continuously migrate from the semiconductor to the AgNPs until equilibrium is reached with the AgNPs that create the potential barrier. At this point, AgNPs act as electron traps, capturing a large number of electrons from the CB of MgAlLDH. The Schottky barrier effectively prevents electrons from flowing back into the semiconductor, successfully inhibiting the recombination of electron-hole pairs within MgAlLDH itself, resulting in more active groups in the material as a whole. Subsequently, the available active groups and the h located in VB... + It can attack the molecules of organic pollutants and degrade them into smaller molecular products, and can also react with hydroxide ions (OH-) on the catalyst surface to generate a small amount of ·OH.

[0026] In summary, this invention introduces AgNPs and MgAl LDH to construct a Schottky junction, thereby suppressing electron backflow and broadening the photoresponse range of MgAl LDH. Simultaneously, it combines AgNPs@MgAl LDH with modified LiYF4:Yb,Tm@LiYF4 upconversion nanoparticles (UCNPs) via electrostatic interactions to construct a ternary composite system AgNPs@MgAl LDH / UCNPs. Since UCNPs can absorb near-infrared light and emit ultraviolet-visible light, the photoresponse range can be extended from the ultraviolet region to the visible and near-infrared regions, significantly improving light energy utilization.

[0027] The beneficial effects of this invention are as follows: (1) The UCNPs modified AgNPs@MgAl LDH composite material prepared in this invention has excellent photocatalytic performance, good stability and reusability.

[0028] (2) The UCNPs-modified AgNPs@MgAl LDH composite material prepared in this invention can extend the light response range from the ultraviolet region to the visible and near-infrared regions due to the introduction of silver nanoparticles (AgNPs) and upconversion luminescent particles (UCNPs). Under visible-infrared light (420-2500nm) irradiation, the degradation rate of 50mg / LTCH by the 0.5%AgNPs@MgAl LDH / UCNPs ternary composite material can reach 90.8%; under infrared light (800-2500nm) irradiation alone, its degradation rate of TCH can also reach 52.7%, which is 1.6 times that of 0.5%AgNPs@MgAl LDH (31.5%), significantly improving the light energy utilization rate. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the photocatalytic degradation mechanism of TCH by the AgNPs@MgAl LDH / UCNPs ternary composite material prepared in this invention.

[0030] Figure 2 X-ray diffraction (a) and FTIR spectra (b) of the MgAl LDH prepared in Example 1 and the AgNPs@MgAlLDH composites with different AgNPs loadings prepared in Example 2.

[0031] Figure 3 X-ray diffraction patterns of the 0.5AL composite material prepared in Example 2, the UCNPs prepared in Example 4, and the 0.5ALU-1 composite material prepared in Example 5.

[0032] Figure 4 The UV-Vis absorption spectra (a) of the MgAl LDH prepared in Example 1 and the Tauc diagram of the AgNPs@MgAlLDH composites with different AgNPs loadings prepared in Example 2, and (b) of the MgAl LDH.

[0033] Figure 5 Fluorescence spectra of UCNPs prepared in Example 3, modified UCNPs prepared in Example 4, and 0.5 ALU-1 prepared in Example 5 (a, inset is an enlarged view of 0.5 ALU-1), and fluorescence spectrum of UCNPs-OA and UV-Vis absorption spectrum of 0.5 ALU-1 (b).

[0034] Figure 6 The photocatalytic TCH degradation curves (a) and (b) of the MgAl LDH prepared in Example 1, the UCNPs prepared in Example 3, and the different photocatalyst samples prepared in Example 5 in the visible-infrared band (420-2500nm) are shown.

[0035] Figure 7 The curves show the photocatalytic degradation of TCH by 0.5% AgNPs@MgAl LDH modified with NaGdF4:Yb,Tm@NaGdF4UCNPs as a comparative example in the visible-infrared band (420-2500nm). Detailed Implementation

[0036] A UCNPs-modified AgNPs@MgAl LDH composite material is prepared by the following steps: (1) Preparation of MgAl LDH Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea were added to a mixed solvent of ethylene glycol and water (9:1, v / v) in a molar ratio of 2:1:15. After stirring for 1 hour, the mixture was hydrothermally reacted at 160℃ for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, washed repeatedly by centrifugation with deionized water and ethanol, and dried at 100℃ for 15 hours to obtain MgAl LDH. (2) Preparation of AgNPs@MgAl LDH The MgAl LDH obtained in step (1) was dispersed in deionized water, and then AgNO3 aqueous solution was added dropwise. The mixture was stirred for 2 hours, and then NaBH4 was added at a mass ratio of AgNO3 to NaBH4 of 1:8. The mixture was stirred in the dark for 3 hours, collected by centrifugation, washed repeatedly with deionized water and ethanol, and then dried in a drying oven for 15 hours to obtain AgNPs@MgAl LDH, wherein the mass percentage of AgNPs was 0.25%~2%. (3) Preparation of LiYF4:Yb,Tm@LiYF4UCNPs: YbCl3·6H2O, TmCl3·6H2O, and YCl3·6H2O were added to a mixed solvent of oleic acid and 1-octadecene (8:12, v / v). The mixture was slowly heated to 160°C under a nitrogen atmosphere and a vacuum of 0.08 MPa, held at this temperature for 30 minutes, and then cooled to room temperature. Finally, a methanol solution of 0.8 mmol / ml NH4F and a 0.3 mmol / ml... The methanol solution of LiOH was heated from room temperature to 50°C under a nitrogen atmosphere, held for 30 minutes, then heated to 70°C and held for 15-30 minutes, and then heated to 300°C and held for 60 minutes. After naturally cooling to room temperature, an equal volume of ethanol was added to precipitate the product. The product was then washed by centrifugation with a mixed solution of cyclohexane and anhydrous ethanol (1:4, v / v) to obtain LiYF4:Yb,Tm@LiYF4UCNPs. The molar ratio of YbCl3·6H2O, TmCl3·6H2O, YCl3·6H2O, NH4F and LiOH used was 7:0.05:2.95:40:15. (4) Hydrophilic modification of LiYF4:Yb,Tm@LiYF4UCNPs 1 mmol (0.28 g) of LiYF4:Yb,Tm@LiYF4UCNPs was added to 5 mL of cyclohexane to prepare a dispersion of LiYF4:Yb,Tm@LiYF4UCNPs. 0.588 g of sodium citrate dihydrate was mixed with 15 mL of diethylene glycol and 1 mL of deionized water. The mixture was heated to 110 °C under a nitrogen atmosphere and held for 40 minutes before cooling to room temperature. The prepared dispersion of LiYF4:Yb,Tm@LiYF4UCNPs was then added and mixed thoroughly. The mixture was heated to 130 °C and held for 30 minutes before being further heated to 175 °C and held for 2 hours. After cooling to room temperature, the mixture was centrifuged and washed to obtain the modified UCNPs, which were then dispersed in deionized water. (5) Preparation of AgNPs@MgAl LDH / UCNPs: The AgNPs@MgAl LDH obtained in step (2) was dispersed in a mixed solution of anhydrous ethanol / deionized water (1:1, v / v), and then the modified UCNPs aqueous dispersion from step (4) was added at a mass ratio of 1.12:1 between modified UCNPs and AgNPs@MgAl LDH. After stirring, the mixture was centrifuged and dried to obtain the AgNPs@MgAl LDH / UCNPs ternary composite material.

[0037] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] Example 1: Preparation of MgAl LDH 8 mmol Mg(NO3)2·6H2O, 4 mmol Al(NO3)3·9H2O and 60 mmol urea were added to a mixed solvent of 45 mL ethylene glycol and 5 mL water. After stirring at room temperature for 1 hour, the mixture was transferred to a high-pressure reactor and reacted at 160 °C for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, washed repeatedly by centrifugation with deionized water and ethanol, and dried at 100 °C for 15 hours to obtain a white powder of MgAl LDH, labeled as L.

[0040] Example 2: Preparation of AgNPs@MgAl LDH by Reduction Precipitation Method a) Take 0.3 g of MgAl LDH prepared in Example 1, disperse it in 30 mL of deionized water, add 1 mL of AgNO3 aqueous solution of different concentrations dropwise, and stir for 2 hours; b) Add the corresponding amount of NaBH4 at a mass ratio of AgNO3 to NaBH4 of 1:8, and stir for 3 hours in the dark. c) Collect by centrifugation, wash several times with deionized water and ethanol, and dry in a drying oven for 15 hours to obtain AgNPs@MgAl LDH, which are labeled as 0.25AL, 0.5AL, 1AL and 2AL according to the AgNPs loading.

[0041] Example 3: Preparation of LiYF4:Yb,Tm@LiYF4UCNPs a) Using 0.7 mmol ytterbium chloride hexahydrate (YbCl3·6H2O), 0.005 mmol thulium chloride hexahydrate (TmCl3·6H2O) and 0.295 mmol yttrium chloride hexahydrate (YCl3·6H2O) as raw materials, it was mixed with 12 mL 1-octadecene and 8 mL oleic acid. The mixture was slowly heated to 160 °C under a nitrogen atmosphere, a rotation speed of 480 r / min and a vacuum degree of 0.08 MPa, held at this temperature for 30 minutes, and then allowed to cool naturally to room temperature. b) Mix 5 mL of 0.8 mmol / mL NH4F methanol solution and 5 mL of 0.3 mmol / mL LiOH methanol solution, shake for 30 seconds and then inject into the solution obtained in step a). Then raise the temperature from room temperature to 50°C, keep the temperature for 30 minutes, raise the temperature to 70°C, keep the temperature for 15-30 minutes, raise the temperature to 300°C, keep the temperature for 60 minutes and then let it cool naturally to room temperature. c) Add an equal volume of ethanol to the reaction solution obtained in step b) to precipitate the product, then centrifuge at 10,000 rpm for 10 min, and then wash the product by centrifugation with a mixed solution of cyclohexane and anhydrous ethanol (1:4, v / v) to obtain LiYF4:Yb,Tm@LiYF4UCNPs, labeled as UCNPs-OA. The obtained LiYF4:Yb,Tm@LiYF4UCNPs are dispersed in cyclohexane.

[0042] Example 4: Hydrophilic modification of LiYF4:Yb,Tm@LiYF4UCNPs a) Mix 0.588 g of trisodium citrate dihydrate with 15 mL of diethylene glycol and 1 mL of deionized water in a three-necked flask. Heat the mixture to 110 °C under a nitrogen atmosphere and a rotation speed of 480 r / min. Hold the mixture at this temperature for 40 min and then cool it to room temperature.

[0043] b) 1 mmol (0.28 g) of LiYF4:Yb,Tm@LiYF4UCNPs obtained in Example 3 was added to 5 ml of cyclohexane to obtain a dispersion of LiYF4:Yb,Tm@LiYF4UCNPs; c) The obtained dispersion of LiYF4:Yb,Tm@LiYF4UCNPs was added dropwise to the three-necked flask of step a), heated to 130°C, held for 30 min, and then further heated to 175°C. After holding at this temperature for 2 hours, it was cooled to room temperature. The flask was washed twice by centrifugation with a mixture of 20 mL of ethanol and 5 mL of water to obtain 0.28 g of modified UCNPs, labeled as UCNPs-Cit, and dispersed in 5 mL of deionized water for later use.

[0044] Example 5: Preparation of AgNPs@MgAl LDH / UCNPs a) Disperse 0.1 g of 0.5% AgNPs@MgAl LDH (0.5AL) in 30 mL of anhydrous ethanol / deionized water (1:1, v / v) mixed solution, and add 0.25 mL, 0.5 mL, 1 mL and 2 mL of UCNPs-Cit aqueous solution prepared in Example 4 respectively, and stir at room temperature for 12 hours; b) The product was collected by centrifugation and dried thoroughly at 60°C to obtain ternary composite materials of different proportions of AgNPs@MgAl LDH / UCNPs. According to the amount of UCNPs-Cit aqueous solution used, they were labeled as 0.5ALU-0.25, 0.5ALU-0.5, 0.5ALU-1 and 0.5ALU-2, respectively.

[0045] Performance testing: Figure 2X-ray powder diffraction (a) and FTIR spectra (b) of the samples synthesized in Examples 1 and 2 are shown. As seen in Figure (a), all samples exhibit diffraction peaks at 2θ values ​​of 11.7°, 23.4°, 34.9°, 39.4°, 46.8°, 53.1°, 60.9°, 62.3°, 75.0°, and 80.8°, consistent with the PDF#35-1275 card, corresponding to the (003), (006), (009), (015), (018), (1010), (110), (113), (0018), and (1112) crystal planes of pure MgAl LDH, respectively. The strong peaks at 2θ values ​​of 11.7° and 23.4° are characteristic peaks of the layered structure. Furthermore, the peaks at 60.9° and 62.3° indicate the presence of carbonate anions in the interlayer. Meanwhile, in the 2AL composite material, three additional peaks appeared at 2θ values ​​of 38.0°, 44.3°, and 64.5°, corresponding to the (111), (200), and (220) crystal planes of face-centered cubic silver metal (corresponding to PDF#01-1167). This indicates the successful synthesis of xAL, and that the loading of AgNPs did not change the crystal structure integrity of LDH. However, due to the deposition of AgNPs on the LDH surface, the intensity of the diffraction peaks in the composite material is lower than that of the L sample. As shown in Figure (b), the synthesized sample has a peak intensity of 3442 cm⁻¹. -1 The strong broadband observed nearby is due to the stretching vibrations of the hydroxide layer and the OH groups embedded in water molecules. At 1359 cm⁻¹ -1 and 782cm -1 The two strong peaks at 500–800 cm⁻¹ correspond to the antisymmetric stretching vibration and out-of-plane bending vibration of the embedded carbonate anion, respectively. -1 The absorption bands within this range originate from MO, MOM, and OMO (where M is Mg). 2+ Or Al 3+ The bending and stretching vibrations of MgAl were observed. However, for a series of xAL complexes, no significant changes in the FTIR spectra were observed after depositing silver nanoparticles on L. This result indicates the successful preparation of the samples and further demonstrates that the deposition of AgNPs did not affect the overall structure of MgAl LDH.

[0046] Figure 3The figures show the X-ray diffraction patterns of 0.5AL synthesized in Example 2, UCNPs synthesized in Example 4, and 0.5ALU-1 synthesized in Example 5. As can be seen from the figures, due to the fact that the AgNPs loading in 0.5AL is only 0.5% of the total mass, the characteristic peaks of AgNPs are almost invisible in this pattern (the LDH patterns of 0.5AL and MgAL are not significantly different). The diffraction pattern of UCNPs matches the diffraction peaks of the LiYbF4 standard card (PDF # 77-0816), indicating a tetragonal phase with no obvious impurity peaks, proving that the prepared UCNPs belong to the pure LiYF4 phase and have good crystallinity. Meanwhile, observation of the 0.5ALU-1 pattern shows that the 0.5ALU-1 composite material exhibits the diffraction peaks of both L and UCNPs, with no impurity peaks and no change in the position of the diffraction peaks, proving that no other impurities are generated after the 0.5AL and UCNPs are combined.

[0047] The light absorption capacity of a photocatalyst is an important factor in evaluating its degradation capacity. Figure 4 The UV-Vis diffuse reflectance spectra (a) and Tauc plots (b) of MgAl LDH are shown for the MgAlLDH prepared in Example 1 and the AgNPs@MgAl LDH composites with different AgNPs loadings prepared in Example 2. Figure (a) shows that L itself exhibits strong absorption in the UV region at approximately 250 nm, but almost no absorption in the visible region. Compared to L, the xAL composite shows a redshift in the absorption edge of the visible region due to the introduction of AgNPs. Simultaneously, the interaction between free electrons in AgNPs and the electric field of light induces collective oscillations at 400-500 nm, resulting in surface plasmon resonance (SPR), which improves the overall light absorption of the composite. Furthermore, the absorption in the visible region becomes sufficiently broad, reaching 600 nm. This indicates that the interaction between AgNPs and L enhances the visible light response of the composite, and among the xAL samples, 0.5AL exhibits the highest absorption intensity in both the UV and blue regions. Meanwhile, the Tauc plot of MgAl LDH shows (αhν). 2 The relationship between L and photon energy (hν) was used to determine that the band gap value of L is 4.18 eV.

[0048] The upconversion emission spectra of UCNPs-OA, UCNPs-Cit, and the 0.5ALU-1 composite material were systematically characterized using fluorescence spectroscopy under 980 nm near-infrared excitation. Figure 5Experimental results show that the fluorescence intensity of UCNPs-Cit modified with sodium citrate is lower than that of unmodified UCNPs-OA, while the fluorescence intensity of the 0.5ALU-1 composite material further decreases. This is attributed to the fact that the MgAl LDH matrix accounts for the majority of the mass fraction in the composite system, while the proportion of UCNPs is relatively low. Meanwhile, all three materials exhibit Tm... 3+ The characteristic emission spectra are as follows: the 361 nm ultraviolet emission peak corresponds to the 1D2→3H6 radiative transition; the 452 nm and 483 nm blue light emissions originate from the 1D2→3F4 and 1G4→3H6 energy level transitions, respectively; and the 647 nm red light emission originates from the 1G4→3F4 transition process. As shown in the inset, compared to UCNPs-Cit, the fluorescence intensity ratio of the blue to red bands in the 0.5ALU-1 composite material shows a significant decreasing trend, a phenomenon closely related to the spectral modulation effect of the 0.5AL support. As shown in Figure (b), the ultraviolet-visible diffuse reflectance spectrum of 0.5ALU-1 exhibits a significant absorption peak in the 400-500 nm wavelength range, and this characteristic peak effectively overlaps with the ultraviolet and blue emission bands of UCNPs. This band-matching characteristic promotes the secondary absorption of emitted light from UCNPs by 0.5ALU-1, thereby improving the light energy utilization efficiency of the composite system and ultimately realizing the synergistic response characteristics of the material under near-infrared excitation, increasing the overall material's utilization rate of the light source.

[0049] 20 mg of the catalyst was placed in 50 mL of 50 mg / L TCH solution and dark-treated for 30 min to ensure adsorption equilibrium was reached. Then the solution was irradiated with a light source of a certain wavelength. Figure 6 The photocatalytic TCH degradation curves of MgAl LDH prepared in Example 1, UCNPs prepared in Example 3, and different photocatalyst samples prepared in Example 5 are shown in (a) the visible-infrared band (420-2500 nm) and (b) the infrared band (800-2500 nm). 1 mL (0.2 mmol) of UCNPs-modified MgAl LDH (labeled LU-1) and a sample solution without catalyst (labeled WC) are used as controls. Figure 6As shown, after irradiation at wavelengths of 420-2500 nm for 60 min, the degradation rates of TCH by L and 0.5AL were 73.4% and 86.7%, respectively. The degradation properties of the composite materials formed with UCNPs were all improved, with 0.5ALU-2 showing the best degradation performance, reaching a degradation rate of 90.8% (a). Under irradiation at 800-2500 nm for 60 min, in the control experiment without a photocatalyst, the absorbance of the TCH solution showed an increasing trend. This phenomenon was mainly attributed to the increase in solution temperature caused by infrared light irradiation, which led to an accelerated solvent evaporation rate. In the system with the added photocatalyst, the degradation rate of 0.5ALU-2 was 52.7%, which was approximately 1.67 times that of 0.5AL (31.5%) (b).

[0050] Comparative Example a) Mix 0.588 g of trisodium citrate dihydrate with 15 mL of diethylene glycol and 1 mL of deionized water in a three-necked flask. Heat the mixture to 110 °C under a nitrogen atmosphere and a rotation speed of 480 r / min. Hold the mixture at this temperature for 40 min and then cool it to room temperature.

[0051] b) Add 1 mmol NaGdF4:Yb,Tm@NaGdF4 to 5 ml of cyclohexane to obtain a dispersion of NaGdF4:Yb,Tm@NaGdF4; c) Add the obtained dispersion dropwise to the three-necked flask of step a), heat to 130°C, maintain for 30 min, then further heat to 175°C, maintain for 2 hours, cool to room temperature, and centrifuge twice with a mixture of 20 mL ethanol and 5 mL water to obtain the modified UCNPs, and disperse them in 5 mL deionized water for later use. d) Disperse 0.1 g of 0.5% AgNPs@MgAl LDH in 30 mL of anhydrous ethanol / deionized water (1:1, v / v) mixed solution, and add 0.25 mL, 0.5 mL, 1 mL and 2 mL of the modified UCNPs aqueous dispersion prepared in step c) respectively, and stir at room temperature for 12 hours; e) The product was collected by centrifugation and dried thoroughly at 60°C to obtain 0.5% AgNPs@MgAl LDH modified with different proportions of NaGdF4:Yb,Tm@NaGdF4UCNPs, which were labeled as N-0.5ALU-0.25, N-0.5ALU-0.5, N-0.5ALU-1 and N-0.5ALU-2, respectively.

[0052] Figure 7The figures show the degradation efficiency of 0.5% AgNPs@MgAlLDH modified with different NaGdF4:Yb,Tm@NaGdF4UCNPs prepared in comparative proportions in the visible-infrared band (420-2500 nm) for 50 mL of 50 mg / L TCH solution. As can be seen from the figures, after dark treatment for 30 min and irradiation at 420-2500 nm for 60 min, 0.5ALU-0.5 exhibits the best degradation efficiency, but its degradation rate is only about 75%, significantly lower than that of 0.5% AgNPs@MgAlLDH modified with LiYF4:Yb,Tm@LiYF4UCNPs.

[0053] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a UCNPs-modified AgNPs@MgAl LDH composite material, characterized in that: Includes the following steps: (1) Add Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea to a mixed solvent of ethylene glycol and water, stir for 1 hour and carry out hydrothermal reaction. After the reaction is completed, cool to room temperature, centrifuge, wash and dry to obtain MgAl LDH. (2) Disperse the MgAl LDH obtained in step (1) into deionized water, then add AgNO3 aqueous solution, then add NaBH4, stir for 3 hours in the dark, centrifuge, wash, and dry to obtain AgNPs@MgAl LDH; (3) YbCl3·6H2O, TmCl3·6H2O and YCl3·6H2O were added to a mixed solvent of oleic acid and 1-octadecene. After high-temperature treatment, methanol solution of NH4F and methanol solution of LiOH were added. After two high-temperature treatments, the mixture was naturally cooled to room temperature, centrifuged and washed to obtain LiYF4:Yb,Tm@LiYF4 UCNPs; (4) Sodium citrate dihydrate was mixed with diethylene glycol and deionized water and subjected to heat treatment; then a dispersion of LiYF4:Yb,Tm@LiYF4 UCNPs was added and mixed well, and a second heat treatment was carried out. After cooling to room temperature, the mixture was centrifuged and washed to obtain modified UCNPs, which were then dispersed in deionized water. (5) Disperse the AgNPs@MgAl LDH obtained in step (2) in anhydrous ethanol / deionized water mixed solution, add the modified UCNPs aqueous dispersion from step (4), stir and centrifuge to dry to obtain AgNPs@MgAl LDH / UCNPs ternary composite material.

2. The method for preparing the UCNPs-modified AgNPs@MgAl LDH composite material according to claim 1, characterized in that: The molar ratio of Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea used in step (1) is 2:1:15; the volume ratio of ethylene glycol and water in the mixed solvent is 9:1; the hydrothermal reaction temperature is 160℃ and the time is 6 hours.

3. The method for preparing the UCNPs-modified AgNPs@MgAl LDH composite material according to claim 1, characterized in that: The mass ratio of AgNO3 to NaBH4 used in step (2) is 1:8, and the mass percentage of AgNPs in the obtained AgNPs@MgAl LDH is 0.25%~2%.

4. The method for preparing the UCNPs-modified AgNPs@MgAl LDH composite material according to claim 1, characterized in that: The molar ratio of YbCl3·6H2O, TmCl3·6H2O, YCl3·6H2O, NH4F and LiOH used in step (3) is 7:0.05:2.95:40:15; the volume ratio of oleic acid and 1-octadecene in the mixed solvent is 8:12; the high-temperature treatment is carried out in a nitrogen atmosphere at 160°C and a vacuum of 0.08 MPa for 30 minutes; the secondary high-temperature treatment is carried out in a nitrogen atmosphere by raising the temperature from room temperature to 50°C and holding it for 30 minutes, then raising the temperature to 70°C and holding it for 15-30 minutes, and then raising the temperature to 300°C and holding it for 60 minutes; the centrifugal washing uses a mixed solution of cyclohexane and anhydrous ethanol with a volume ratio of 1:4 as the washing agent.

5. The method for preparing the UCNPs-modified AgNPs@MgAl LDH composite material according to claim 1, characterized in that: In step (4), the ratio of sodium citrate dihydrate, diethylene glycol, deionized water, and LiYF4:Yb,Tm@LiYF4 UCNPs is 0.588 g:15 mL:1 mL:0.28 g; the dispersion of LiYF4:Yb,Tm@LiYF4 UCNPs is prepared by dispersing 1 mmol of LiYF4:Yb,Tm@LiYF4 UCNPs in 5 mL of cyclohexane; the heat treatment is carried out by heating to 110°C under a nitrogen atmosphere, holding for 40 minutes, and then cooling to room temperature; the secondary heat treatment is carried out by heating to 130°C, holding for 30 minutes, and then further heating to 175°C and holding for 2 hours.

6. The method for preparing UCNPs-modified AgNPs@MgAl LDH composite material according to claim 1, characterized in that: In step (5), the volume ratio of anhydrous ethanol to deionized water in the anhydrous ethanol / deionized water mixed solution is 1:1; the amount of modified UCNPs aqueous dispersion is calculated based on the mass ratio of modified UCNPs to AgNPs@MgAl LDH used being 1.12:

1.

7. A UCNPs-modified AgNPs@MgAl LDH composite material prepared by the method described in claim 1.

8. The application of the UCNPs-modified AgNPs@MgAl LDH composite material as described in claim 7 in the photocatalytic degradation of tetracycline.

9. The application according to claim 8, characterized in that: The UCNPs-modified AgNPs@MgAl LDH composite material was used as a photocatalyst to degrade tetracycline in water under visible-infrared light irradiation.

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