A method for dispersing upconversion luminescent nanoparticles in a medium polarity solvent and a method for preparing a membrane material

Abstract

The invention discloses a method for dispersing nanoparticles in a medium polar solvent, and studies the dispersion of ligands with different functional groups in different types of solvents. The method comprises the following steps: synthesizing upconversion nanocrystals by coprecipitation method, wherein the solvents used for the synthesis are oleic acid and octadecene, and the obtained nanoparticles have oleic acid ligands attached to their surfaces, and are dispersed in cyclohexane after washing and collection. Then, appropriate ligands are selected to modify the surface of the nanoparticles so that they can be dispersed in medium polar solvents such as ethyl acetate, methyl acetate, butyl acetate, n-propanol, isopropanol, n-butanol, etc., and the relationship between the consistency of the functional groups of the ligands and the solvent and the dispersibility of the nanoparticles is studied. The nanoparticles dispersed in the medium polar solvent are also incorporated into a PDMS film, and the transmittance of the prepared PDMS film is greatly improved compared with the nanoparticles dispersed in cyclohexane without ligand exchange.

Description

Technical Field

[0001] The present application relates to the field of surface modification of nanoparticles, and in particular to a method for dispersing upconversion luminescent nanoparticles in a medium-polarity solvent and a method for preparing a film material. Background Art

[0002] Rare earth ions have a rich variety of electronic energy levels, and electrons have many transitions between energy levels. They have excellent upconversion luminescence characteristics, can absorb light in the near-infrared band, and emit light from the ultraviolet to the visible light region. They have broad application prospects in the fields of in vivo imaging, biological detection, disease treatment, anti-counterfeiting, etc. Among them, rare earth-doped fluorides have lower vibrational phonon energy, can reduce losses, have higher quantum efficiency, and have good physical and chemical stability. They are currently the most widely and deeply studied upconversion luminescent materials. The co-doping of several rare earth ions can achieve upconversion / downconversion emission in different bands. For example, through Yb 3+ , Er 3+ Co-doping can achieve the conversion of near-infrared to visible light. 3+ , Tb 3+ Down-conversion luminescence can be achieved. Some advantages of rare earth-doped up-conversion nanoparticles, such as low toxicity, good physical and chemical stability and biocompatibility, and narrow emission peak, can be utilized to achieve broad applications in the fields of biological detection, biological imaging, and fluorescent anti-counterfeiting.

[0003] After synthesis, upconversion nanoparticles have oleic acid ligands on their surfaces and are usually dispersed in non-polar solvents such as cyclohexane for storage. In polar solvents, the nanoparticles will aggregate and precipitate. This limits the use scenarios of upconversion nanoparticles. Therefore, it is necessary to disperse the upconversion nanoparticles in polar solvents and use the upconversion luminescence mechanism of rare earth elements to make fluorescent anti-counterfeiting materials, which have important practical value. Since the lanthanide ions in rare earth-doped upconversion nanoparticles can form complexes with carboxyl or amino groups, molecules with these functional groups are usually considered when selecting ligands.

[0004] Rare earth-doped upconversion nanoparticles have the characteristics of absorbing near-infrared light and emitting visible light. They are widely used in in vivo tumor treatment, biological detection and other fields by taking advantage of the strong biological penetration of near-infrared light and weak biological autofluorescence background. Therefore, the nanoparticles need to be dispersed in an aqueous solvent. "Upconversion Multicolor Fine-Tuning: Visible to Near-Infrared Emission from Lanthanide-Doped NaYF4 Nanoparticles" modifies the surface of nanoparticles with polyethyleneimine (PEI) so that they can be dispersed in strong polar solvents such as ethanol, ethylene glycol, DMF, and DMSO. It is also possible to remove the oleic acid modified on the surface of the nanoparticles and coat them with a layer of silica to make them hydrophilic. However, so far, no one has studied the dispersion of nanoparticles in solvents of medium polarity. Solvents with medium polarity include alcohol solvents with long hydrocarbon chains such as n-propanol, isopropanol, and n-butanol, and ester solvents such as methyl acetate, ethyl acetate, and butyl acetate. The polarity values ​​of these solvents are between non-polar solvents and strong polar solvents, and they are widely used in industry. They are good organic solvents and can be used as inks. Rare earth-doped upconversion luminescent nanoparticles have broad application prospects in luminescent display due to their excellent color tunability and full-color luminescence. We have noticed that many researchers choose polydimethylsiloxane (PDMS) as the matrix material when preparing display luminescent materials and incorporate nanoparticles into it. However, the light transmittance of the film prepared by directly mixing nanoparticles with oleic acid ligands dissolved in cyclohexane into PDMS is poor. In addition, upconversion luminescent nanoparticles also have broad applications in anti-counterfeiting, such as making anti-counterfeiting glue. However, the main components of glue commonly used in industry are epoxy resin or polyacrylate, and the commonly used solvent cyclohexane for nanoparticles has poor solubility with them.

[0005] Until now, little research has been done on how to select ligands that can give nanoparticles the ability to disperse in various types of solvents. Summary of the invention

[0006] In view of this, the embodiments of the present application provide a method for dispersing upconversion luminescent nanoparticles in a medium-polarity solvent and a method for preparing a film material.

[0007] According to a first aspect of an embodiment of the present application, there is provided a method for dispersing upconversion luminescent nanoparticles in a medium polar solvent, comprising:

[0008] Step 1: Select an organic molecule with an amino or carboxyl group but without a hydroxyl or ester group as the exchange ligand;

[0009] Step 2: Disperse the ligand to be exchanged in a DMF solution, add the upconversion luminescent nanoparticles dissolved in cyclohexane, perform ultrasound, add toluene to the solution, centrifuge, remove the supernatant, add toluene, disperse the precipitate at the bottom by ultrasound, and then centrifuge again, repeat several times to obtain nanoparticles;

[0010] Step 3: dispersing the ligand-exchanged nanoparticles into a medium-polarity solvent, wherein the medium-polarity solvent is selected from one of n-propanol, isopropanol, n-butanol, methyl acetate, ethyl acetate, and butyl acetate.

[0011] Preferably, 2-naphthyloxyacetic acid or α-hydroxyhippuric acid is selected as the ligand.

[0012] Preferably, the molar concentration of the ligand in the DMF solution is 0.1-0.5 mmol / mL;

[0013] The concentration of the upconversion luminescent nanoparticles dissolved in cyclohexane is 10-20 mg / mL;

[0014] The volume ratio of the DMF solution to the cyclohexane is 1:1;

[0015] The volume ratio of the DMF solution to toluene is 1:2;

[0016] The concentration of the nanoparticles in the medium polarity solvent is 5-20 mg / mL.

[0017] Preferably, the ultrasonic time is 20-30 minutes.

[0018] Preferably, the centrifugation time is 10-20 minutes.

[0019] According to a second aspect of an embodiment of the present application, a method for preparing a membrane material is provided, comprising: adding nanoparticles dispersed in a medium polar solvent into a PDMS precursor to prepare the membrane material.

[0020] Preferably, the method comprises: adding 5 mL of organosilicon matrix, 0.5 mL of curing agent, adding 0.5 mL of solution containing 10 mg of nanoparticles into the container, evacuating for 1 hour, and keeping warm at 80 degrees for 0.5 hour.

[0021] The technical solution provided by the embodiments of the present application may have the following beneficial effects:

[0022] As can be seen from the above embodiments, the present application adopts a ligand selection method that does not conform to the principle of like dissolves like, and selects organic molecules with amino or carboxyl groups, but without hydroxyl or ester groups as ligands for exchange, so that nanoparticles can be dispersed in a medium polar solvent. The ligand to be exchanged is then dispersed in a DMF solution, and then upconversion luminescent nanoparticles dissolved in cyclohexane are added, ultrasonicated, and then toluene is added to the solution, centrifuged, and after removing the supernatant, toluene is added, and the precipitate at the bottom is ultrasonically dispersed, and then centrifuged again, and repeated multiple times to obtain nanoparticles; the nanoparticles after ligand exchange are dispersed in a medium polar solvent, and the medium polar solvent is selected from one of n-propanol, isopropanol, n-butanol, methyl acetate, ethyl acetate, and butyl acetate. The above method disperses upconversion luminescent nanoparticles in a medium polar solvent, and the steps are simple and easy to industrialize and batch. A method for preparing a membrane material is also provided. In this method, nanoparticles dispersed in a medium polar solvent are added to a PDMS precursor to prepare the membrane material. The prepared membrane material can generate up-conversion luminescence and the light transmittance is increased by more than 40%.

[0023] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0025] Figure 1 (a) to (f) are transmission electron micrographs of the synthesized nanoparticles dispersed in various medium solvents without ligand exchange. (a) to (f) are transmission electron micrographs of the nanoparticles dispersed in n-propanol, isopropanol, n-butanol, methyl acetate, ethyl acetate, and butyl acetate, respectively.

[0026] Figure 2 The thermogravimetric analysis diagrams of different ligands after ligand exchange in Examples 1-6 and Comparative Examples 1-4 are shown. The ligands include 2-naphthoxyacetic acid, 4-methoxymandelic acid, 2-hydroxyoctanoic acid, mono-tert-butyl succinate, 2-phenoxybenzoic acid, and α-hydroxyhippuric acid.

[0027] Figure 3 The Fourier transform infrared spectra of different ligands after ligand exchange in Examples 1-6 and Comparative Examples 1-4 are shown.

[0028] Figure 4 TEM images of nanoparticles modified with different ligands and dispersed in medium polar solvents. (a)-(c) Nanoparticles modified with 2-naphthoxyacetic acid are dispersed in n-propanol, isopropanol, and n-propanol, and (d)-(f) Nanoparticles modified with α-hydroxyhippuric acid are dispersed in methyl acetate, ethyl acetate, and butyl acetate.

[0029] Figure 5 The hydrated particle sizes of nanoparticles modified with different ligands in n-propanol and butyl acetate, (a) in n-propanol, (b) in butyl acetate.

[0030] Figure 6 The transmittance of the film prepared by incorporating the nanoparticles dispersed in a medium polar solvent into PDMS in Example 7. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. In addition, it should be understood that after reading the contents disclosed in the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope of protection defined by the present invention.

[0032] Instruments and equipment:

[0033] In the present invention, the testing instrument model of the X-ray powder diffraction pattern is LabXXRD-6000, and the radiation wavelength of the copper target is λ=0.154184nm.

[0034] In the present invention, the transmission electron microscope image testing instrument model is FEITecnaiF20

[0035] In the present invention, the up-conversion emission spectrum test instrument model is FLSP920 (Edinburgh), and the excitation light source is a 980nm laser.

[0036] Select an organic molecule with an amino or carboxyl group but without a hydroxyl or ester group as the exchange ligand;

[0037] When selecting ligands, it is necessary to consider the functional groups carried by the ligands. Lanthanide ions can form coordination with carboxyl and amino groups, so molecules containing these two ligands are easy to connect to the surface of nanoparticles. At the same time, the medium-polarity reagents to be dispersed are alcohol or ester solvents, which contain hydroxyl groups and ester groups, respectively. According to common sense, based on similar solubility, there is a possibility that ligands containing hydroxyl groups are easier to disperse in alcohol reagents, and ligands containing ester groups are easier to disperse in ester reagents. At the same time, we also selected ligands that do not contain these two functional groups to study whether this inference is correct.

[0038] Through comparison, 2-naphthoxyacetic acid or α-hydroxyhippuric acid was finally selected as the ligand.

[0039] Example 1: Take 0.1mmol of 2-naphthyloxyacetic acid, dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 10mg of upconversion luminescent nanoparticles, and ultrasonicate for 30 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of n-propanol.

[0040] Embodiment 2:

[0041] Take 0.1mmol of 2-naphthyloxyacetic acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 10mg of upconversion luminescent nanoparticles, and ultrasonicate for 20 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 20 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of isopropanol.

[0042] Embodiment 3:

[0043] Take 0.5mmol of 2-naphthyloxyacetic acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 30 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 15 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of n-butanol.

[0044] Embodiment 4:

[0045] Take 0.1mmol of α-hydroxyhippuric acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 10mg of upconversion luminescent nanoparticles, and ultrasonicate for 30 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of methyl acetate.

[0046] Embodiment 5:

[0047] Take 0.5mmol of α-hydroxyhippuric acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 30 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of ethyl acetate.

[0048] Embodiment 6:

[0049] Take 0.5mmol of α-hydroxyhippuric acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 20 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of butyl acetate.

[0050] Comparative Example 1:

[0051] Take 0.5mmol of 4-methoxymandelic acid, dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 20 minutes. After the end of the ultrasound, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeat 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of n-propanol. Then compare the dispersibility of upconversion luminescent nanoparticles in n-propanol using 2-naphthyloxyacetic acid as a ligand.

[0052] Comparative Example 2:

[0053] Take 0.5mmol of 2-hydroxyoctanoic acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 20 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of n-propanol.

[0054] Comparative Example 3:

[0055] Take 0.5mmol of 2-phenoxybenzoic acid and dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 20 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 10 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeating 2-3 times. The nanoparticles obtained are finally dispersed in 1mL of isopropanol.

[0056] Comparative Example 4:

[0057] Take 0.5mmol of mono-tert-butyl succinate, dissolve it in 1mL of DMF solution, then add 1mL of cyclohexane solution containing 20mg of upconversion luminescent nanoparticles, and ultrasonicate for 20 minutes. After the ultrasonication is over, add 2mL of toluene to the solution and centrifuge at 20000rpm for 20 minutes. After removing the supernatant, add 2mL of toluene, ultrasonically disperse the precipitate at the bottom, and then centrifuge again, repeat 2-3 times. The nanoparticles finally obtained are dispersed in 1mL of butyl acetate.

[0058] The synthesized nanoparticles were subjected to ligand exchange and dispersed in various medium-polarity solvents to compare the dispersion of ligands with different functional groups in different types of solvents. It was also verified whether ligand exchange improved the dispersibility of nanoparticles in medium-polarity solvents.

[0059] Figure 1 These are TEM images of upconversion luminescent nanoparticles without ligand exchange dispersed in various medium polar solvents. Anhydrous ethanol is added to the cyclohexane solution of the nanoparticles, centrifuged, and the resulting precipitate is added to various medium polar solvents and ultrasonically dispersed. (a)-(f) are nanoparticles dispersed in n-propanol, isopropanol, n-butanol, methyl acetate, ethyl acetate, and butyl acetate, respectively.

[0060] Figure 2 This is the thermogravimetric analysis of six ligands exchanged onto the surface of nanoparticles. The ligands used are 2-naphthoxyacetic acid, 4-methoxymandelic acid, 2-hydroxyoctanoic acid, mono-tert-butyl succinate, 2-phenoxybenzoic acid, and α-hydroxyhippuric acid. It can be seen that the ligands account for 3-12% in the nanomaterial.

[0061] Figure 3 Fourier transform infrared spectra of nanoparticles with the above six ligands.

[0062] Figure 4The TEM images of nanoparticles modified with different ligands and dispersed in medium polar solvents, where (a)-(c) are nanoparticles modified with 2-naphthoxyacetic acid and dispersed in n-propanol, isopropanol, and n-propanol, and (d)-(f) are nanoparticles modified with α-hydroxyhippuric acid and dispersed in methyl acetate, ethyl acetate, and butyl acetate. It can be seen that after using 2-naphthoxyacetic acid as a ligand for modification, the nanoparticles have good dispersibility in these alcohols. Similarly, after using α-hydroxyhippuric acid as a ligand for modification, the nanoparticles have good dispersibility in ester solvents.

[0063] Figure 5 (a) is the hydrated particle size of nanoparticles modified with different ligands in n-propanol, and (b) is the hydrated particle size in butyl acetate. It can be seen that compared with 4-methoxymandelic acid and 2-hydroxyoctanoic acid with hydroxyl groups, nanoparticles modified with 2-naphthyloxyacetic acid without hydroxyl groups have smaller hydrated particle size and better dispersibility in alcohol solvents, which is inconsistent with the well-known principle of like dissolves like. Similarly, the hydrated particle size of α-hydroxyhippuric acid without ester group in ester solvents is smaller than that of mono-tert-butyl succinate with ester group. This also proves that our habitual thinking is wrong.

[0064] Embodiment 7:

[0065] Nanoparticles modified with 2-naphthyloxyacetic acid were dispersed in n-propanol, isopropanol, and n-propanol, and nanoparticles modified with α-hydroxyhippuric acid were dispersed in methyl acetate, ethyl acetate, and butyl acetate, and then these solvents were mixed into the PDMS precursor to prepare the membrane material. 5 mL of silicone matrix, 0.5 mL of curing agent, and 0.5 mL of solution containing 10 mg of nanoparticles were added to the culture dish, vacuumed for 1 hour, and kept warm at 80 degrees for 0.5 hours.

[0066] Figure 6 The transmittance of the prepared film shows that compared with the nanoparticles dispersed in cyclohexane without ligand exchange, the transmittance of the film prepared after dispersing the nanoparticles in a medium polar solvent has been significantly improved, which is not much different from the PDMS film without any nanoparticles doped.

[0067] In summary, the present invention provides a simple ligand exchange process for rare earth-doped upconversion nanoparticles, which is easy to operate and suitable for large-scale industrial production. In addition, we have a new understanding of the method of selecting ligands. We cannot simply infer that ligands with the same functional groups can disperse nanoparticles in organic solvents based on the principle of like dissolves like. Specific problems should be analyzed specifically. In addition, in response to the problem of poor film transmittance when upconversion nanoparticles were added to PDMS as anti-counterfeiting materials to prepare thin films in previous studies, we tried for the first time to disperse the nanoparticles in a medium-polarity solvent and prepared a thin film material with greatly improved transmittance.

[0068] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0069] Those skilled in the art will readily appreciate other embodiments of the present application after considering the description and practicing the contents disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The description and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the claims.

[0070] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for dispersing upconversion luminescent nanoparticles in a medium polar solvent, characterized in that: include: Step 1: Select 2-naphthyloxyacetic acid or α-hydroxyhippuric acid as a ligand; Step 2: Disperse the ligand to be exchanged in a DMF solution, add the upconversion luminescent nanoparticles dissolved in cyclohexane, perform ultrasound, add toluene to the solution, centrifuge, remove the supernatant, add toluene, disperse the precipitate at the bottom by ultrasound, and then centrifuge again, repeat several times to obtain nanoparticles; Step 3: dispersing the ligand-exchanged nanoparticles into a medium-polarity solvent, wherein the medium-polarity solvent is selected from one of n-propanol, isopropanol, n-butanol, methyl acetate, ethyl acetate, and butyl acetate.

2. The method according to claim 1, characterized in that The molar concentration of the ligand in the DMF solution is 0.1-0.5 mmol / mL; The concentration of the upconversion luminescent nanoparticles dissolved in cyclohexane is 10-20 mg / mL; The volume ratio of the DMF solution to the cyclohexane is 1:1; The volume ratio of the DMF solution to toluene is 1:2; The concentration of the nanoparticles in the medium polar solvent is 5-20 mg / mL.

3. The method according to claim 1, characterized in that The ultrasonic time is 20-30 minutes.

4. The method according to claim 1, characterized in that The centrifugation time is 10-20 minutes.

5. A method for preparing a membrane material, characterized in that: include: Nanoparticles dispersed in a medium polar solvent are incorporated into a PDMS precursor to obtain a membrane material; the medium polar solvent is selected from one of n-propanol, isopropanol, n-butanol, methyl acetate, ethyl acetate, and butyl acetate; the nanoparticles are the nanoparticles after ligand exchange in claim 1.

6. The method for preparing a membrane material according to claim 5, characterized in that: include: 5 mL of silicone matrix, 0.5 mL of curing agent, and 0.5 mL of a solution containing 10 mg of nanoparticles were added to the container, and the solution was evacuated for 1 hour and kept warm at 80 degrees for 0.5 hour. The solvent in the solution was a medium polar solvent.

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