CN109932326B - Method for measuring coverage rate of ligand on surface of quantum dot - Google Patents
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Abstract
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot. Measuring the coverage rate K of the organic ligand containing sulfydryl on the surface of the quantum dot by a redox methodiAnd the method can be used for quality assessment of the quantum dots. If K isiLess than 2 x 10‑10mol/cm2If the quantum dot quality is not good enough, K should be addediAfter the value is increased, the application such as solution or ink preparation is carried out. The method for determining the coverage rate of the ligand on the surface of the quantum dot has the advantages of accurate result and simple operation, and further can ensure the stability of the content of the ligand on the surface of the quantum dot, ensure the solubility of the quantum dots in different batches, avoid the coffee ring effect caused by different drying rates when the quantum dot solution is prepared into a film, and improve the pixel resolution, the starting voltage and the uniformity of the photoelectric efficiency of the quantum dot display panel.
Description
Technical Field
The invention relates to the technical field of quantum dots, in particular to a method for measuring the coverage rate of a ligand on the surface of a quantum dot.
Background
Quantum dots, refers to semiconductor nanocrystals whose geometric dimensions are smaller than the exciton bohr radius. The quantum dots have excellent optical properties such as wide absorption band, narrow fluorescence emission band, high quantum efficiency, good light stability and the like, and have great potential application in the fields of biomedicine, environmental energy, illumination display and the like. In recent years, the display technology based on quantum dot light emission receives high attention from the display industry, and compared with liquid crystal display and organic light emitting display, quantum dot light emission has the advantages of wider color gamut, higher color purity, simpler structure and higher stability, and is considered as a new generation display technology.
The preparation technology of the quantum dot display device comprises spin coating, ink jet printing and the like. The specific process of the two methods is to spray the quantum dot solution on the substrate material, and form a quantum dot film at a specific position after drying. The viscosity, surface tension and charge transport capacity of the quantum dot solution determine the wetting capacity, drying rate, coffee ring effect and photoelectric property of the film of the quantum dot liquid drop in the device preparation process, so that the quality of the quantum dot solution plays an important role in device preparation. In the preparation process of the quantum dot solution, the surface ligand of the quantum dot has an important influence on the quantum dot solution, and the surface ligand not only influences the photoelectric property of the quantum dot, but also influences the solubility and stability of the quantum dot solution. Common quantum dot surface ligands are carboxylic acids, amines, alkyl phosphides, alkyl phosphine oxides, alkyl phosphoric acids, thiols, and the like. The influence of the surface ligand on the optical performance of the quantum dot per se is shown as follows: the average particle diameter of the quantum dots is smaller than the bohr radius of excitons, excitons are exposed on the surface to a certain extent, and the surface is easily influenced to reduce the optical performance of the excitons; when the surface atomic number of the quantum dot is increased, the surface dangling bonds are also increased rapidly, the surface of the quantum dot has many defects due to insufficient atom coordination, the probability of non-radiative recombination is increased due to the existence of the defects such as electrons or holes, and the recombination efficiency of normal radiative recombination is greatly reduced. When a proper surface ligand is added, the surface dangling bonds of the quantum dots can be effectively reduced, excitons are not exposed on the surface any more, and the optical performance of the quantum dots is improved. The influence of the surface ligand on the solubility and stability of the quantum dot is shown as follows: the increase of dangling bonds on the surface of the quantum dot leads the surface free energy to be very large, the surface becomes abnormally active, the system is unstable, the quantum dot tends to aggregate to reduce the surface area, and the solubility of the quantum dot solution is reduced. After the surface ligand is introduced, one end of the ligand is connected to the surface atoms of the quantum dots, and the other end of the ligand is dissolved in the solution, so that the surface energy of the quantum dots can be reduced, the solubility of the quantum dots can be improved, and the generation of precipitation in the quantum dot solution can be effectively inhibited.
Therefore, the solubility of the quantum dots greatly affects the preparation and performance of the device. Besides the solubility of the quantum dots and the types of the quantum dots, another important influence factor is the coverage rate of the ligands on the surfaces of the quantum dots. If the coverage rate of the surface of the quantum dot is low, the solubility of the quantum dot is poor, the uniformity of the quantum dot solution is poor, and the drying rate of the quantum dot solution and the coffee ring effect affect the quality of the luminescent layer film, which directly causes the problems of uneven quality of the printed panel, low pixel resolution, uneven lighting voltage, uneven photoelectric efficiency, and the like.
Disclosure of Invention
In view of the defects of the prior art, in order to ensure the stability of the film forming quality of the QLED device prepared by using the quantum dot ink in the later period, the invention firstly provides a method for measuring the coverage rate of the quantum dot surface ligand.
A method for measuring the coverage rate of a ligand on the surface of a quantum dot comprises the following steps:
providing sample particles, wherein each particle in the sample particles comprises a quantum dot and a sulfydryl-containing organic ligand bound on the surface of the quantum dot, and sulfur element is not contained in the quantum dot;
determining the average particle size of the particles in the sample particles;
mixing the sample particles with an oxidant to oxidize the sulfydryl-containing organic ligand on the surface of the quantum dot to generate sulfur dioxide, and introducing the generated sulfur dioxide into absorption liquid to obtain a solution to be detected;
mixing a solution to be detected with a color developing agent to form a mixed solution, developing the mixed solution, and measuring the absorbance of the mixed solution;
providing an absorbance standard curve of sulfur concentration, obtaining the sulfur concentration of the solution to be detected by contrasting the standard curve, converting the sulfur concentration into the mass of the S element in the sample particles, and calculating to obtain the coverage rate K of the ligand on the surface of the quantum doti。
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot. Measuring the coverage rate K of the organic ligand containing sulfydryl on the surface of the quantum dot by a redox methodiAnd the method can be used for quality assessment of the quantum dots. If KiLess than 2 x 10-10mol/cm2If the quantum dot quality is not good enough, K should be addediAfter the value is increased, the application such as solution or ink preparation is carried out. The method for determining the coverage rate of the ligand on the surface of the quantum dot has accurate result and simple operation, and further can ensure the stability of the content of the ligand on the surface of the quantum dot,the solubility of quantum dots in different batches can be ensured, the coffee ring effect caused by different drying rates in the process of preparing a film by using a quantum dot solution is avoided, and the pixel resolution, the turn-on voltage and the photoelectric efficiency uniformity of the quantum dot display panel can be improved.
Detailed Description
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
A method for measuring the coverage rate of a ligand on the surface of a quantum dot comprises the following steps:
s10 providing sample particles, wherein individual particles in the sample particles comprise quantum dots and organic ligands containing sulfydryl and bound on the surfaces of the quantum dots, and the quantum dots do not contain sulfur element;
s20 determining the average particle size of the particles in the sample particles;
s30, mixing the sample particles with an oxidant to oxidize the sulfydryl-containing organic ligand on the surface of the quantum dot to generate sulfur dioxide, and introducing the generated sulfur dioxide into absorption liquid to obtain a solution to be detected;
s40, mixing the solution to be detected with the color developing agent to form a mixed solution, developing the color, and measuring the absorbance of the mixed solution;
s50, providing an absorbance standard curve of sulfur concentration, obtaining the sulfur concentration of the solution to be measured by contrasting the standard curve, converting the sulfur concentration into the mass of the S element in the sample particles, and calculating to obtain the coverage rate K of the ligand on the surface of the quantum doti。
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot. Measuring the coverage rate K of the organic ligand containing sulfydryl on the surface of the quantum dot by a redox methodiAnd the method can be used for quality assessment of the quantum dots. If KiLess than 2 x 10-10mol/cm2If the quantum dot quality is not good enough, K should be addediAfter the value is increased, the application such as solution or ink preparation is carried out. Determining the surface of a quantum dot by the methodThe method can ensure the stability of the ligand content on the surface of the quantum dot, can ensure the solubility of quantum dots in different batches, avoids the coffee ring effect caused by different drying rates when the quantum dot solution is prepared into a film, and can improve the pixel resolution, the starting voltage and the photoelectric efficiency uniformity of the quantum dot display panel.
The quantum dot surface ligand coverage rate test and calculation principle is as follows:
the sample particles are a collection of a plurality of single particles, each single particle comprises a quantum dot and a ligand bound on the surface of the quantum dot, and the ligand in the invention is an organic ligand containing sulfydryl. Surface ligand coverage K in the present inventioniThe amount of substances which are combined with surface ligands in unit area on the surface of the quantum dot is determined, the surface ligands are directly combined with the quantum dot through special functional groups, and the surface ligand coverage rate K can be calculated through the amount of substances of characteristic elements in the special groups combined with the quantum doti. Surface ligand coverage KiThe passing surface can be obtained by the following formula:
Ki＝ml/(0.74MlmQSq/ρQVq) (formula 1)
Specifying the mass m of a specific atom (sulfur element in the present invention) in a specific functional group (mercapto group in the present invention) in the surface ligand of the quantum dot in the sample particlelMolar mass MlTotal mass of sample particles is mQDensity of ρQSurface area S of individual particles in sample particlesqVolume is VqThe sample particles were densely packed with a space utilization of 0.74, assuming spherical particles with an average particle size of d.
Wherein the volume of single particles
Surface area of individual particles
Calculated after being substituted into a formula
Ki＝mlρQd/4.44MlmQ(formula 2) when the organic ligand is a polydentate ligand, the ligand denticity is removed, for example, 2 when it is a dithiol.
In the above formula 2, [ rho ]QThe method can be obtained by searching the density of related substances or testing by using an Archimedes principle, and the d can be obtained by testing the size of the quantum dot according to a TEM. Therefore, m is required to be tested by adopting a proper methodl/mQThus obtaining the ligand coverage rate on the surface of the quantum dot.
In step S10, the selected quantum dots may be unary quantum dots, binary quantum dots, or ternary quantum dots.
For example, the unary quantum dots may be selected from Au, Ag, Cu, Pt, or C quantum dots, but are not limited thereto;
the binary quantum dots can be selected from CdSe, ZnSe, PbSe, CdTe, ZnO, MgO, CeO2、NiO、TiO2InP or CaF2Quantum dots, but not limited thereto;
the ternary quantum dots can be selected from CdZnSe and NaYF4、NaCdF4ZnCdTe, CdZnSe/ZnSe, CdSe/CdZnSe/CdZnSe/ZnSe or CdZnSe/CdZnSe/ZnSe quantum dots, but is not limited thereto.
The organic ligand containing sulfydryl, which is combined on the surface of the quantum dot, can be the same or different, and is selected from one or more of mono-thiol, dithiol, sulfydryl alcohol, sulfydryl amine and sulfydryl acid.
Preferably, the monothiol is selected from one or more of hexanethiol, octanethiol, nonanethiol, decanethiol, undecanethiol, dodecanethiol, tridecanethiol, tetradecanethiol, hexadecanethiol and octadecanethiol;
preferably, the dithiol is selected from one or more of 1, 2-ethanedithiol, 1, 3-propanedithiol, 1, 4-butanedithiol, 1, 5-pentanethiol, 1, 6-hexanedithiol, 1, 8-octanethiol and 1, 10-decanedithiol;
preferably, the mercaptoalcohol includes 2-mercaptoethanol, 3-mercapto-1-propanol, 4-mercapto-1-butanol, 5-mercapto-1-pentanol, 6-mercapto-1-hexanol, or 8-mercapto-1-octanol;
preferably, the mercapto acid comprises one or more of 2-mercaptoacetic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptosuccinic acid, 6-mercaptohexanoic acid, 4-mercaptobenzoic acid and cysteine;
preferably, the mercaptoamine includes one or more of 2-mercaptoethylamine, 3-mercaptopropylamine, 4-mercaptobutylamine, 5-mercaptopentylamine, 6-mercaptohexylamine, 2-amino-3-mercaptopropionic acid, 2-aminothiophenol, and mercaptoundecanamine.
In one embodiment, in step S20 of the present invention, the transmission electron microscope analyzer may be used to determine the average particle size of the particles in the sample particles.
Specifically, the test conditions for determining the average particle size of particles in the sample particles by using a transmission electron microscope analyzer are as follows: the accelerating voltage is 200-300kV, the emission current is 7-20 muA, the working distance is 10-20mm, and the dead time is 20-40%.
The step of determining the average particle size of the particles in the sample particles using a transmission electron microscope analyzer comprises: and (3) dissolving the sample particles in a nonpolar solvent to prepare a quantum dot solution with the concentration of 1-5mg/mL, dripping 5-10 drops of a small amount of quantum dot solution on a copper mesh after the solution is completely dissolved, and placing the copper mesh in a transmission electron microscope analyzer for test analysis d. Specifically, a sample is amplified and analyzed by the magnification factor of 70000-150000 times, a TEM picture is obtained by focusing a region with concentrated and uniformly dispersed quantum dots, then the TEM picture is analyzed by software, the length of a ruler is set, then 30-80 quantum dots are calibrated, and finally the average particle size d of sample particles is obtained by calculation.
The method adopts the redox method to determine the mass m of the sulfur element in the sample particlesl. The method adopts a redox method test principle that sulfur element in a sulfydryl-containing ligand on the surface of a quantum dot is oxidized by a strong oxidant to generate sulfur dioxide, the sulfur dioxide is dissolved in water to generate sulfurous acid, then absorption liquid is utilized to react with the sulfurous acid, a reaction product and a color developing agent are subjected to a color development reaction, the quality of the sulfur is determined by the change of the absorbance of the color development reaction product, and thus the S element content is obtainedContent ratio of sub-points.
Specifically, in an embodiment, the absorption liquid prepared from formaldehyde, potassium mercuric chloride or triethanolamine may be used in step S30. Specifically, the absorption liquid can be 10-20% formaldehyde solution, 0.03-0.05mol/L potassium tetrachloromercuric chloride or 0.08-1mol/L triethanolamine solution. In order to ensure that sulfurous acid generated by dissolving sulfur dioxide in water reacts with the absorption liquid and other side reactions do not occur, the p value of the absorption liquid is 6-8. In a particular embodiment, the pH of the absorption solution may be adjusted by adding a buffer to the absorption solution, said buffer being selected from potassium hydrogen phthalate or from 0.3 to 0.4g disodium ethylenediaminetetraacetate.
Furthermore, a strong oxidant is required to be selected to oxidize sulfur elements in the sulfydryl-containing organic ligands on the surfaces of the quantum dots to generate sulfur dioxide, because the strong oxidant is used, the quantum dots in the detected sample particles cannot contain the sulfur elements, and if the quantum dots contain the sulfur elements, the sulfur elements can be oxidized by the strong oxidant to generate the sulfur dioxide, so that the detection result is influenced. Preferably, the oxidant is selected from one or more of perchloric acid, concentrated nitric acid and aqua regia. And after sulfur element in the sulfhydryl-containing organic ligand is oxidized to generate sulfur dioxide, introducing the sulfur dioxide into the absorption liquid to prepare a solution to be detected for subsequent detection and analysis.
In the step S40, the solution to be measured and the color-developing agent are reacted to generate a color-developing reaction, the quality of sulfur is determined by using the change of the absorbance of the color-developing reaction product, specifically, the mixed solution formed by the solution to be measured and the color-developing agent is transferred into a colorimetric tube, the absorbance of the colorimetric tube is measured by using water as a reference, and the absorbance at the position of 570nm is obtained. Preferably, the developer is chosen, by way of example and without limitation, from pararosaniline hydrochloride.
In one embodiment, in step S50, the standard curve may be obtained by: weighing 0.2g of sodium sulfite, dissolving in newly boiled and cooled water to prepare a sodium sulfite solution, diluting the absorption solution and the sodium sulfite solution into standard solutions with different concentrations, adding 0.4-1g of an alkaline regulator into the standard solutions with different concentrations, wherein the alkaline regulator can be selected from sodium hydroxide and potassium hydroxide but is not limited thereto, uniformly mixing the solutions, transferring the solutions into a colorimetric tube, adding a color developing agent (preferably pararosaniline hydrochloride solution), immediately covering the colorimetric tube, turning over the colorimetric tube, uniformly mixing the solutions, and standing the solutions for 5-20 min for color development. And (3) measuring the absorbance of each colorimetric tube by taking water as a reference, and drawing a standard curve by taking the absorbance at 570nm as an abscissa and the S concentration as an ordinate.
Further, according to the absorbance obtained in the step S40, the concentration of S in the solution to be measured can be obtained by comparing with the standard curve in the step S50, the concentration is converted into the mass of the S element in the sample particles, and the mass is calculated according to Ki＝mlρQd/4.44MlmQCalculating to obtain the coverage rate K of the quantum dot surface ligandi。
The research shows that the coverage rate K of the ligand on the surface of the quantum dotiIf less than 2 x 10-10mol/cm2The solubility of the quantum dots is poor, and the quality of a film prepared into the film subsequently is influenced. Require to be connected with KiAfter the value is increased, the application such as solution or ink preparation is carried out. Increase KiValues can be carried out using the ligand re-exchange method. The specific process is as follows: the quantum dots are firstly dissolved in a nonpolar solvent, and then the same surface ligand is added for exchange at the temperature of 25-150 ℃. The nonpolar solvent comprises chloroform, normal hexane, heptane, octane, toluene, chlorobenzene, dichlorobenzene, carbon tetrachloride, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, cyclodecane, cycloundecane, octadecene and the like. The amount of ligand added during said ligand re-exchange should not be less than (2 x 10)-10-K1)n1/K1(formula 3, K)0Representing the coverage rate of the ligand on the surface of the target quantum dot, K1Representing the coverage rate of the quantum dot ligand measured for the first time, and n1 is the amount of ligand added for the first time in the preparation process of the quantum dot). By using the process, KiThe value is increased to more than 2 x 10-10mol/cm2The quantum dots can be applied to other solution properties.
The present invention will be described in detail below with reference to examples.
Example 1
A method for measuring the coverage rate of a ligand on the surface of a quantum dot comprises the following steps:
(1) the average size d of the particles was determined to provide several sample particles comprising CdSe quantum dots and octanethiol ligands bound to the CdSe quantum dots surface. And (3) dissolving the sample particles in a normal hexane solution to prepare a solution of 5mg/ml, taking a small amount of sample particle solution drops 5 drops on a copper mesh after the solution is completely dissolved, and placing the copper mesh in a transmission electron microscope analyzer for test analysis. The acceleration voltage was set at 200kV, the emission current was set at 10. mu.A, the working distance was set at 15mm, and the dead time was 20%. And (3) carrying out amplification analysis on the sample particles, firstly setting the amplification factor to be 70000 times, carrying out focusing analysis on the concentrated and uniformly dispersed areas of the sample particles, and taking TEM pictures of the sample particles. Analyzing the TEM picture, firstly setting the length of a ruler, then calibrating 30-80 sample particles, and calculating to obtain the average size d of the sample particles to be 7.98 nm;
(2) the method for determining the mercaptan ligand coverage rate on the surface of the quantum dot by using a redox method comprises the following steps:
firstly, preparing an absorption liquid, namely weighing a certain amount of formaldehyde, dissolving the formaldehyde into water, mixing to obtain 100ml of 10% formaldehyde solution by mass fraction, then adding 1.58g of potassium hydrogen phthalate and 0.3g of disodium ethylene diamine tetraacetate into the absorption liquid, and adjusting the pH value of the absorption liquid to be neutral;
preparing standard solution, namely weighing 0.2g of sodium sulfite to be dissolved in newly boiled and cooled water, and then diluting the sodium sulfite solution into standard solution with different concentrations by using the absorption solution in the step I;
and thirdly, drawing a standard curve, and adding 0.4g of sodium hydroxide into the standard solution with different concentrations in the step II. After the solution is mixed evenly, adding pararosaniline hydrochloride solution, immediately covering and turning over the mixture, evenly mixing the mixture, and standing the mixture for 5min for color development. Measuring absorbance of the solution with water as reference, and measuring absorbance at 570nm as abscissa, SO3 2-The concentration is plotted on the ordinate, and a standard curve is drawn.
Fourthly, collecting a sample, weighing 5mg of sample particles into a flask, adding aqua regia, reacting to generate gas, and collecting volatile gas by using absorption liquid with a certain volume;
measuring the sample, mixingAnd fourthly, transferring the absorption liquid after the gas is collected into a colorimetric tube. Measuring absorbance according to the third step, and obtaining SO according to a standard curve3 2-The mass of the sulfur element is obtained by conversion according to the volume of the solution, and the content ratio of the S element in the sampled particles is calculated to be 3.8%.
Sixthly, calculating the coverage rate Ki of the ligand on the surface of the quantum dot, wherein the density of the CdSe quantum dot is 5.2g/cm3According to the test results, the CdSe quantum dot size is 7.98nm, the mass ratio of S element in the thiol ligand in the quantum dot to the ligand is 3.8%, and K is calculated to be 1.1 x 10-9mol/cm2. K value greater than 2 x 10-10mol/cm2The method can be directly applied without ligand re-exchange.
Example 2
A method for measuring the coverage rate of a quantum dot ligand comprises the following steps:
(1) the average size d of the particles was determined to provide several sample particles comprising CdSe quantum dots and octanethiol ligands bound to the CdSe quantum dots surface. Dissolving sample particles in n-octane solution, preparing 5mg/ml solution, after the solution is completely dissolved, taking a small amount of sample particle solution to drop 8 drops on a copper mesh, placing the copper mesh in a transmission electron microscope analyzer for test analysis, setting the acceleration voltage to be 300kV, the emission current to be 20 muA, the working distance to be 20mm and the dead time to be 30%, carrying out amplification analysis on the sample particles, firstly setting the amplification factor to be 100000 times, carrying out focusing analysis on a region where the sample particles are concentrated and uniformly dispersed, and taking a TEM picture of the sample particles. Analyzing the TEM picture, firstly setting the length of a ruler, then calibrating 30-80 sample particles, and calculating to obtain the average particle size d of the sample particles to be 8.9 nm;
(2) determining the coverage rate of the ligand on the surface of the quantum dot by using a redox method, which comprises the following steps:
firstly, preparing an absorption liquid, weighing a certain amount of triethanolamine, dissolving the triethanolamine in water, and mixing to obtain 0.09mol/L triethanolamine absorption liquid. Then 2.95g of potassium hydrogen phthalate and 0.38g of disodium ethylene diamine tetraacetate are added into the absorption liquid, and the pH value of the absorption liquid is adjusted to be neutral;
preparing standard solution, namely weighing 0.2g of sodium sulfite to be dissolved in newly boiled and cooled water, and then diluting the sodium sulfite solution into standard solution with different concentrations by using the absorption solution in the step I;
and thirdly, drawing a standard curve, and adding 0.8g of potassium hydroxide into the standard solution with different concentrations in the step II. And (3) after the solutions are uniformly mixed, adding a pararosaniline hydrochloride solution, immediately covering and sealing, reversing and uniformly mixing, and standing for 5-20 min for color development. Measuring absorbance of each tube with water as reference, and measuring absorbance at 570nm as abscissa, SO3 2-The concentration is a vertical coordinate, and a standard curve is drawn;
collecting a sample, weighing a 30mg quantum dot sample in a flask, adding perchloric acid for reaction to generate gas, and collecting volatile gas by using a certain volume of absorption liquid;
fifthly, measuring the sample, transferring the absorption liquid after collecting the gas in the step IV into a colorimetric tube, measuring the absorbance according to the process in the step 3, and obtaining SO by contrasting a standard curve3 2-The content of (3) is 0.28% by volume of the absorbent solution;
sixthly, calculating the coverage rate K of the ligand on the surface of the quantum dot1The density of ZnO quantum dots is 5.9g/cm3According to the test results, the size of the ZnO quantum dot is 8.9nm, the mass ratio of S element in the thiol ligand in the quantum dot to the ligand is 0.28%, and K is calculated to be 1.03 x 10-10mol/cm2。K1Value less than 2 x 10-10mol/cm2Ligand re-exchange is required;
seventhly, exchanging the ligand on the surface of the quantum dot, wherein if hexanethiol is added into ZnO in the preparation process to be 4mmol, the adding amount of the hexanethiol in the ligand exchange process cannot be less than 3.88 mmol. And (3) dissolving the ZnO quantum dots in a normal hexane solution, adding 4mmol of hexanethiol into the ZnO normal hexane solution, heating and stirring at 40 ℃ for 4h, and cleaning to obtain the quantum dots after ligand re-exchange. Detecting and analyzing the content of the surface ligand of the ZnO subjected to ligand re-exchange in the process 2 to obtain K2Is 2.03 x 10-10mol/cm2. Therefore, ZnO can be used for preparing ink solution after ligand re-exchange.
While the method for measuring the coverage of the quantum dot surface ligand provided by the embodiment of the present invention has been described in detail, for those skilled in the art, there may be variations in the specific implementation and application scope according to the concept of the embodiment of the present invention, and in summary, the content of the present specification should not be construed as a limitation to the present invention, and any variation made according to the design concept of the present invention is within the protection scope of the present invention.
Claims (13)
1. A method for measuring the coverage rate of a ligand on the surface of a quantum dot is characterized by comprising the following steps:
providing sample particles, wherein each particle in the sample particles comprises a quantum dot and a sulfydryl-containing organic ligand bound on the surface of the quantum dot, and the quantum dot does not contain sulfur element;
determining the average particle size of the particles in the sample particles;
mixing the sample particles with an oxidant to oxidize the sulfydryl-containing organic ligand on the surface of the quantum dot to generate sulfur dioxide, and introducing the generated sulfur dioxide into absorption liquid to obtain a solution to be detected;
mixing the solution to be detected with a color developing agent to form a mixed solution, then developing the color, and measuring the absorbance of the mixed solution;
providing an absorbance standard curve of sulfur concentration, obtaining the sulfur concentration of the solution to be detected by contrasting the standard curve, converting the sulfur concentration into the mass of the S element in the sample particles, and calculating to obtain the coverage rate K of the ligand on the surface of the quantum dotiWherein, the coverage rate K of the ligand on the surface of the quantum dotiThe amount of substance binding to the surface ligand per unit area of the surface of the quantum dot, Ki=ml/(0.74MlmQSq/ρQVq) The mass of sulfur element in the sulfydryl-containing organic ligand on the surface of the quantum dot is mlThe molar mass of sulfur element in the sulfydryl-containing organic ligand on the surface of the quantum dot is MlTotal mass of sample particles is mQDensity of sample particles is rhoQSurface area of individual particles in the sample particle is SqVolume of individual particles in sample particles is Vq。
2. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 1, wherein the quantum dot is a univariate quantum dot, a binary quantum dot or a ternary quantum dot.
3. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 2, wherein the univalent quantum dot is selected from Au, Ag, Cu, Pt or C quantum dots;
the binary quantum dots are selected from CdSe, ZnSe, PbSe, CdTe, ZnO, MgO and CeO2、NiO、TiO2InP or CaF2Quantum dots;
the ternary quantum dots are selected from CdZnSe and NaYF4、NaCdF4ZnCdTe, CdZnSe/ZnSe, CdSe/CdZnSe/CdZnSe/ZnSe or CdZnSe/CdZnSe/ZnSe quantum dots.
4. The method for measuring the ligand coverage rate on the surface of the quantum dot according to claim 1, wherein the organic ligand containing sulfydryl is selected from one or more of mono-thiol, dithiol, sulfydryl alcohol, sulfydryl amine and sulfydryl acid.
5. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 4,
the monothiol is selected from one or more of hexanethiol, octanethiol, nonanethiol, decanethiol, undecanethiol, dodecanethiol, tridecanethiol, tetradecanethiol, hexadecanethiol and octadecanethiol;
the dithiol is selected from one or more of 1, 2-ethanedithiol, 1, 3-propanedithiol, 1, 4-butanedithiol, 1, 5-pentanethiol, 1, 6-hexanedithiol, 1, 8-octanethiol and 1, 10-decanedithiol;
the mercapto alcohol comprises 2-mercaptoethanol, 3-mercapto-1-propanol, methyl mercaptan, ethyl mercaptan, 3-mercapto-1-propanol, methyl mercaptan, ethyl mercaptan, 2-mercaptoethanol, 3-mercapto-1-propanol, and,4-mercapto-1-butanol5-mercapto-1-pentanol, 6-mercapto-1-hexanol and8-mercapto-1-octanolOne or more of;
the mercapto acid comprises 2-mercaptoacetic acid and 3-mercaptoPropionic acid, 4-mercaptobutyric acid, mercaptosuccinic acid, 6-mercaptohexanoic acid,4- Mercapto benzoic acidAnd cysteine;
the mercaptoamine comprises one or more of 2-mercaptoethylamine, 3-mercaptopropylamine, 4-mercaptobutylamine, 5-mercaptopentylamine, 6-mercaptohexylamine, 2-amino-3-mercaptopropionic acid, 2-aminothiophenol and mercaptoundecanamine.
6. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 1, wherein the absorption solution is one selected from a 10-20% formaldehyde solution, 0.03-0.05mol/L potassium tetrachloromercuric chloride or 0.08-1mol/L triethanolamine solution, and the pH value of the absorption solution is 6-8.
7. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 6, wherein the absorption solution is prepared by the following method: the absorption liquid is prepared by adding potassium hydrogen phthalate and/or disodium ethylene diamine tetraacetate into 10-20% formaldehyde solution, 0.03-0.05mol/L potassium tetrachloromercuric or 0.08-1mol/L triethanolamine solution, and adjusting the pH value to 6-8.
8. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 1, wherein the color-developing agent is pararosaniline hydrochloride.
9. The method for measuring the ligand coverage rate on the surface of the quantum dot according to claim 1, wherein the oxidant is one or more selected from perchloric acid, concentrated nitric acid and aqua regia.
10. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 1, wherein a transmission electron microscope analyzer is used for measuring the average particle size of particles in the sample particles.
11. The method for determining the coverage rate of the ligand on the surface of the quantum dot according to claim 10, wherein the conditions for determining the average particle size of the particles in the sample particles by using a transmission electron microscope analyzer are as follows: the accelerating voltage is 200-300kV, the emission current is 7-20 muA, the working distance is 10-20mm, and the dead time is 20-40%.
12. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 10 or 11, wherein the step of measuring the average particle size of the particles in the sample particles by using a transmission electron microscope analyzer comprises the following steps: and (3) carrying out amplification analysis on the sample, wherein the amplification factor is 70000-150000 times, focusing the concentrated and uniformly dispersed area of the sample particles to obtain a TEM picture of the sample particles, analyzing the TEM picture by using software, calibrating 30-80 quantum dots, and calculating to obtain the average particle size of the sample particles.
13. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to any one of claims 1 to 11, wherein a standard curve of the absorbance of the sulfur element is provided, the concentration of the sulfur element in the solution to be measured is obtained by referring to the standard curve, the concentration is converted into the mass of the S element in the sample particle, and the coverage rate K of the ligand on the surface of the quantum dot is calculatediIf K isiLess than 2 x 10-10mol/cm2The method also comprises the following steps: and the ligand re-exchange method is adopted to improve the coverage rate of the ligand on the surface of the quantum dot.
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