A Fe3O4@SiO2@ upconversion material with controllable shell thickness and its preparation method

Abstract

The invention discloses a Fe3O4@SiO2@ upconversion material with controllable shell thickness and a preparation method thereof. The invention comprises the following steps: dissolving iron salt and polyacrylic acid in organic alcohol, reacting at 200-250°C for 1-2 hours, adding alkaline solution and continuing the reaction for 1-2 hours, collecting the product and washing and drying it; dispersing the product in water, adding alkaline solution, ethanol and silicon precursor, reacting for 20-40 minutes, collecting the product and washing and drying it; adding water and alcohol to the product, adding yttrium precursor, ytterbium precursor and thulium precursor, and then adding amide, 50-80 o The reaction is carried out at 160-200°C for 2-4 hours, and the product is collected, washed, and dried. The product is then dispersed in water, and ethylene glycol and NaF are added for a hydrothermal reaction at 160-200°C for 2-4 hours. The product is then collected, washed, and dried to obtain an Fe3O4@SiO2@ upconversion material with controllable shell thickness. This method achieves controllable spacing between the Fe3O4@ and the upconversion material by controlling the SiO2 shell thickness, facilitating research into the influence of distance in magneto-optical modulation. Adjusting the water-to-alcohol ratio during the coating process of the upconversion material prevents agglomeration and enables control of the coating thickness.

Description

Technical Field

[0001] The present invention belongs to the field of material technology, and in particular relates to an Fe3O4@SiO2@ upconversion material with controllable shell thickness and a preparation method thereof. Background Art

[0002] As one of the basic functional materials, magnetic materials have excellent physical, chemical and electromagnetic properties, which determine their wide application in fields such as medicine, environmental protection, information technology, and new energy. Patent CN114778528 A discloses an electrochemiluminescence sensor based on the co-enhanced luminescence of cadmium selenide quantum dots by ferroferric oxide and molybdenum disulfide. The invention uses CdSe quantum dots as the luminescent body, and Fe3O4@MoS2 catalyzes the co-reactant K2S2O8 to generate more SO4 •- , thereby enhancing the luminescence intensity of CdSe quantum dots.

[0003] Among photoluminescent materials, upconversion materials exhibit superior chemical and photostability, low toxicity, and long luminescence lifetimes compared to traditional quantum dots and organic dyes. They are widely used in fields such as anti-counterfeiting, biomedicine, sensing, and lasers. Patent CN115991994 A discloses a red rod-shaped core-shell upconversion nanoluminescent material and its preparation method. This invention uses a solvothermal method to prepare a rod-shaped core-shell structure, NaErF4:Tm@NaYF4, which emits high-purity red light.

[0004] Core-shell, as an orderly encapsulated assembly structure, integrates the properties of internal and external materials, complementing each other's deficiencies. Chinese patent CN108620100 A discloses a highly efficient magnetic near-infrared light composite catalyst and its preparation method. Nano-Fe3O4 is prepared by a solvothermal method. Then, a modified Stöber method is used to wrap the Fe3O4 with a silicon dioxide layer to form Fe3O4@SiO2. The Fe3O4@SiO2 is then used as the core to further prepare a magnetic high-efficiency near-infrared light composite catalyst Fe3O4@SiO2 / β-NaYF4:Yb with a core-shell structure by a hydrothermal method. 3+ ,Tm 3+ While this method combines magnetic and upconversion materials via a core-shell structure, the upconversion and magnetic materials are in direct contact, and the distance between them is uncontrollable, making it difficult to study the effect of distance on magneto-optical modulation. Furthermore, the thickness of the upconversion material is uncontrollable. Summary of the Invention

[0005] In response to the problems in the prior art that the distance between the upconversion material and the magnetic material and the thickness of the upconversion material are uncontrollable, the present invention provides a Fe3O4@SiO2@ upconversion material with controllable shell thickness and a preparation method thereof. By controlling the thickness of the SiO2 shell, the distance between the Fe3O4@ and the upconversion material is controllable. By adjusting the water-alcohol ratio, not only is agglomeration avoided during the coating process, but the coating thickness is also controllable.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a Fe3O4@SiO2@ upconversion material with controllable shell thickness comprises the following steps:

[0008] (1) Dissolve iron salt and polyacrylic acid in organic alcohol, react at 200-250°C for 1-2 hours, then add alkali solution and continue to react for 1-2 hours. After the reaction is completed, collect the product and wash and dry it;

[0009] (2) Dispersing the product in step (1) in water, adding alkali solution, ethanol, and silicon precursor, stirring and reacting at room temperature for 20 to 40 minutes, collecting the product after the reaction is completed, washing, and drying;

[0010] (3) Add water and alcohol to the product obtained in step (2), then add yttrium precursor, ytterbium precursor and thulium precursor, stir evenly and add amide, o C, stirring for 2-4 hours, after which the product was collected, washed and dried;

[0011] (4) The product in step (3) was dispersed in water, and ethylene glycol and NaF were added in sequence. After stirring evenly, the mixture was transferred to a reactor and subjected to a hydrothermal reaction at 160-200 °C for 2-4 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ upconversion material with controllable shell thickness.

[0012] Furthermore, in step (1), the iron salt is ferric nitrate, ferric chloride or a hydrate thereof; the molecular weight of the polyacrylic acid is 2000-4000; the organic alcohol is diethylene glycol or ethylene glycol; and the alkali solution is an organic alcohol solution of sodium hydroxide or potassium hydroxide, and the concentration of the alkali solution is 1-5 mol / L.

[0013] Furthermore, the molar ratio of the iron salt, polyacrylic acid and alkali in the alkali solution in step (1) is 1:7~15:8~12.

[0014] Furthermore, in step (1), each 1 mL of organic alcohol contains 0.02-0.04 mmol of iron salt.

[0015] Furthermore, the alkali solution in step (2) is ammonia water or ethylenediamine; and the silicon precursor is ethyl orthosilicate or sodium silicate.

[0016] Furthermore, in step (2), the volume ratio of alkali solution, water and ethanol is 1:1:6-15; and the molar ratio of the silicon precursor to the iron salt is 0.5-2.5:1.

[0017] Furthermore, the alcohol described in step (3) is one of ethylene glycol, diethylene glycol, polyethylene glycol 400, polyethylene glycol 200, propylene glycol, and triethylene glycol; the yttrium precursor is yttrium nitrate, yttrium chloride or a hydrate thereof, the ytterbium precursor is ytterbium nitrate, ytterbium chloride or a hydrate thereof, and the thulium precursor is thulium nitrate, thulium chloride or a hydrate thereof; and the amide is carbonamide or N-N-dimethylformamide.

[0018] Furthermore, in step (3), the volume ratio of water to alcohol is 1~9:9~1; the molar ratio of the yttrium precursor, ytterbium precursor and thulium precursor is 9~11:2:4~1; and the molar ratio of the yttrium precursor to amide is 1:40~90.

[0019] Furthermore, in step (4), the volume ratio of water to ethylene glycol is 1:2-7; and the molar ratio of yttrium precursor to NaF is 1:2.5-5.

[0020] In the present invention, the Fe3O4@SiO2@ upconversion material with controllable shell thickness is prepared by the above-mentioned preparation method.

[0021] The beneficial effects achieved by the present invention are:

[0022] The present invention achieves controllable spacing between Fe3O4@ and the upconversion material by controlling the thickness of the SiO2 shell, which is conducive to studying the influence of distance in magneto-optical regulation; secondly, during the coating process of the upconversion material, by adjusting the water-alcohol ratio, not only agglomeration during the coating process is avoided, but also the coating thickness is controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 1;

[0024] Figure 2 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 2;

[0025] Figure 3 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 3;

[0026] Figure 4This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 4;

[0027] Figure 5 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 5;

[0028] Figure 6 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 6;

[0029] Figure 7 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 7;

[0030] Figure 8 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 8;

[0031] Figure 9 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 9;

[0032] Figure 10 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 10;

[0033] Figure 11 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Comparative Example 1;

[0034] Figure 12 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Comparative Example 2;

[0035] Figure 13 This is a transmission electron micrograph of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Comparative Example 3;

[0036] Figure 14 This is the emission spectrum of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 3 under 980 nm light excitation;

[0037] Figure 15 This is the emission spectrum of the Fe3O4@SiO2@ upconversion material with controllable shell thickness prepared in Example 8 under 980 nm light excitation. DETAILED DESCRIPTION

[0038] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0039] Example 1

[0040] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0041] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0042] (3) Add 50 mL of deionized water and 50 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0043] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 1 As shown, the thickness of the SiO2 shell layer is 22 nm and the thickness of the upconversion material shell layer is 14 nm.

[0044] Example 2

[0045] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0046] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0047] (3) Add 60 mL of deionized water and 40 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C, stirred and reacted for 2 h. After the reaction was complete, the product was collected, washed and dried;

[0048] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 2 As shown, the thickness of the SiO2 shell layer is 25 nm, and the thickness of the upconversion material shell layer is 25 nm.

[0049] Example 3

[0050] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 diethylene glycol solution) and continue the reaction for 1 hour. After the reaction is completed, the product is collected, washed and dried;

[0051] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0052] (3) Add 70 mL of deionized water and 30 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 .6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0053] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 3 As shown, the thickness of the SiO2 shell is 20nm, the thickness of the upconversion material shell is 35nm, and the emission spectrum of the prepared Fe3O4@SiO2@ upconversion material with controllable shell thickness under 980 nm light excitation is shown in Figure 14 shown.

[0054] Example 4

[0055] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0056] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0057] (3) Add 80 mL of deionized water and 20 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0058] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 4 As shown, the thickness of the SiO2 shell layer is 27 nm and the thickness of the upconversion material shell layer is 40 nm.

[0059] Example 5

[0060] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 diethylene glycol solution) and continue the reaction for 1 hour. After the reaction is completed, the product is collected, washed and dried;

[0061] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 90 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction, the product was collected, washed, and dried.

[0062] (3) Add 70 mL of deionized water and 30 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C, stirred and reacted for 2 h. After the reaction was complete, the product was collected, washed and dried;

[0063] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 5 As shown, the thickness of the SiO2 shell layer is 32nm and the thickness of the upconversion material shell layer is 28nm.

[0064] Example 6

[0065] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 diethylene glycol solution) and continue the reaction for 1 hour. After the reaction is completed, the product is collected, washed and dried;

[0066] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 40 μL of ethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction, the product was collected, washed, and dried.

[0067] (3) Add 70 mL of deionized water and 30 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C, stirred and reacted for 2 h. After the reaction was complete, the product was collected, washed and dried;

[0068] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 6 As shown, the thickness of the SiO2 shell layer is 8 nm, and the thickness of the upconversion material shell layer is 30 nm.

[0069] Example 7

[0070] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 diethylene glycol solution) and continue the reaction for 1 hour. After the reaction is completed, the product is collected, washed and dried;

[0071] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0072] (3) Add 95 mL of deionized water and 5 mL of propylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C, stirred and reacted for 2 h. After the reaction was complete, the product was collected, washed and dried;

[0073] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 7 As shown, the thickness of the SiO2 shell layer is 35nm and the thickness of the upconversion material shell layer is 28nm.

[0074] Example 8

[0075] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 diethylene glycol solution) and continue the reaction for 1 hour. After the reaction is completed, the product is collected, washed and dried;

[0076] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0077] (3) Add 50 mL of deionized water and 50 mL of ethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 .6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0078] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 8 As shown, the thickness of the SiO2 shell is 30nm, the thickness of the upconversion material shell is 14nm, and the emission spectrum of the prepared Fe3O4@SiO2@ upconversion material with controllable shell thickness under 980nm light excitation is shown in Figure 15 shown.

[0079] Example 9

[0080] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0081] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0082] (3) Add 80 mL of deionized water and 20 mL of polyethylene glycol 200 to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0083] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 9 As shown, the thickness of the SiO2 shell layer is 35 nm and the thickness of the upconversion material shell layer is 42 nm.

[0084] Example 10

[0085] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 diethylene glycol solution) and continue the reaction for 1 hour. After the reaction is completed, the product is collected, washed and dried;

[0086] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0087] (3) Add 40 mL of deionized water and 60 mL of triethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C, stirred and reacted for 2 h. After the reaction was complete, the product was collected, washed and dried;

[0088] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 10 As shown, the thickness of the SiO2 shell layer is 25 nm and the thickness of the upconversion material shell layer is 33 nm.

[0089] Comparative Example 1

[0090] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0091] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0092] (3) Add 100 mL of deionized water to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0093] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 11 As shown, the sample is severely aggregated.

[0094] Comparative Example 2

[0095] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0096] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0097] (3) Add 100 mL of diethylene glycol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0098] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain Fe3O4@SiO2. Transmission electron microscopy of the prepared Fe3O4@SiO2 Figure 12 As shown, the SiO2 shell thickness is 30nm.

[0099] Comparative Example 3

[0100] (1) 0.0648 g FeCl3 and 0.2881 g polyacrylic acid (molecular weight 2000) were dissolved in 16 mL diethylene glycol and reacted at 230 °C for 2 h. Then 1 mL NaOH (2.5 mol . L -1 The reaction was continued for 1 hour, and the product was collected, washed and dried after the reaction was completed;

[0101] (2) The product in step (1) was dispersed in 3 mL of deionized water, and 1 mL of 25% ammonia water, 20 mL of anhydrous ethanol, and 60 μL of tetraethyl orthosilicate were added in sequence. The mixture was stirred at room temperature for 40 min. After the reaction was completed, the product was collected, washed, and dried.

[0102] (3) Add 60 mL of deionized water and 60 mL of ethanol to the product obtained in step (2), and then add 0.3033 g of YCl3 . 6H2O, 0.0174 g YbCl3 . 6H2O and 0.0019 g TmCl3 . 6H2O, stir evenly and add 1.1 g of carbonamide, o C and stirred for 2 h. After the reaction, the product was collected, washed and dried;

[0103] (4) The product in step (3) was dispersed in 7.5 mL of deionized water, and 25 mL of ethylene glycol and 0.015 g of NaF were added in sequence. After stirring evenly, the mixture was transferred to a polytetrafluoroethylene reactor and subjected to hydrothermal reaction at 190 °C for 2 h. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ conversion material with controllable shell thickness. Transmission electron microscopy of the prepared Fe3O4@SiO2@ conversion material with controllable shell thickness was performed. Figure 13 As shown, the sample was severely aggregated.

[0104] By comparing the transmission electron microscopy results of the Fe3O4@SiO2@ upconversion materials prepared in the examples and comparative examples, it can be seen that in comparative example 1, no alcohol was added and the sample underwent severe agglomeration; in comparative example 2, no water was added and the upconversion material failed to be coated and agglomeration occurred; in comparative example 3, water and ethanol were added and the sample underwent severe agglomeration. Therefore, alcohol substances can prevent agglomeration during the upconversion coating process. By comparing the thickness of the SiO2 shell and the thickness of the upconversion material shell, in Examples 1 to 4, as the ratio of water to diethylene glycol changes, the thickness of the upconversion material shell also gradually changes, and the trend of change is that the thickness of the layer gradually increases with the increase in the amount of water. By comparing Examples 3, 5, and 6, it can be seen that changes in the amount of ethyl orthosilicate can significantly affect the thickness of the SiO2 shell, thereby changing the distance between Fe3O4 and the upconversion material. By Figure 14 、 15 It can be seen that after absorbing near-infrared light, the sample emits green light with a central wavelength near 525.

Claims

1. A method for preparing a Fe3O4@SiO2@ upconversion material with controllable shell thickness, characterized in that: The following steps are involved: (1) Dissolve iron salt and polyacrylic acid in organic alcohol, react at 200-250°C for 1-2 hours, then add alkali solution and continue to react for 1-2 hours. After the reaction is completed, collect the product and wash and dry it; (2) Dispersing the product in step (1) in water, adding alkali solution, ethanol, and silicon precursor, stirring and reacting at room temperature for 20 to 40 minutes, collecting the product after the reaction is completed, washing, and drying; (3) Add water and alcohol to the product obtained in step (2), then add yttrium precursor, ytterbium precursor and thulium precursor, stir evenly and add amide, o C, stirring for 2-4 hours, after which the product was collected, washed and dried; (4) The product in step (3) was dispersed in water, ethylene glycol and NaF were added, and the reaction was carried out at 160-200 °C for 2-4 hours. After the reaction, the product was collected, washed, and dried to obtain a Fe3O4@SiO2@ upconversion material with controllable shell thickness; The alcohol described in step (3) is one of diethylene glycol, polyethylene glycol 200, propylene glycol, and triethylene glycol, and the volume ratio of water to alcohol is 1~9:9~1; The molar ratio of the yttrium precursor, ytterbium precursor and thulium precursor in step (3) is 9-11:2:4-1; the molar ratio of the yttrium precursor to the amide is 1:40-90.

2. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: In step (1), the iron salt is ferric nitrate, ferric chloride or a hydrate thereof; the molecular weight of the polyacrylic acid is 2000-4000; the organic alcohol is diethylene glycol or ethylene glycol; the alkali solution is an organic alcohol solution of sodium hydroxide or potassium hydroxide, and the concentration of the alkali solution is 1-5 mol / L.

3. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: The molar ratio of the iron salt, polyacrylic acid and alkali in the alkali solution in step (1) is 1:7~15:8~12.

4. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: In step (1), each 1 mL of organic alcohol contains 0.02-0.04 mmol of iron salt.

5. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: The alkali solution in step (2) is ammonia water or ethylenediamine; the silicon precursor is ethyl orthosilicate or sodium silicate.

6. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: In step (2), the volume ratio of alkali solution, water and ethanol is 1:1:6~15; the molar ratio of the silicon precursor to the iron salt is 0.5~2.5:

1.

7. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: The yttrium precursor in step (3) is yttrium nitrate, yttrium chloride or a hydrate thereof, the ytterbium precursor is ytterbium nitrate, ytterbium chloride or a hydrate thereof, and the thulium precursor is thulium nitrate, thulium chloride or a hydrate thereof; and the amide is carbonamide or N-N-dimethylformamide.

8. The method for preparing the Fe3O4@SiO2@ upconversion material with controllable shell thickness according to claim 1, characterized in that: In step (4), the volume ratio of water to ethylene glycol is 1:2-7; the molar ratio of yttrium precursor to NaF is 1:2.5-5.

9. An Fe3O4@SiO2@ upconversion material with controllable shell thickness, prepared by the preparation method according to any one of claims 1 to 8.

Images