CN109932405B - Method for measuring content of ligand on surface of quantum dot and method for preparing quantum dot ink - Google Patents
Method for measuring content of ligand on surface of quantum dot and method for preparing quantum dot ink Download PDFInfo
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Abstract
The invention provides a method for measuring the content of a ligand on the surface of a quantum dot and a method for preparing quantum dot ink. The preparation method of the quantum dot ink is adopted to prepare the quantum dot ink, so that the uniformity of the quality of the quantum dot ink can be ensured, the solubility, the drying rate and the coffee ring effect of quantum dot inks in different batches can be ensured to be the same, and the pixel resolution, the lighting voltage and the uniformity of the photoelectric efficiency of a quantum dot display panel can be improved.
Description
Technical Field
The invention relates to the technical field of quantum dot ink, in particular to a method for measuring the content of a ligand on the surface of a quantum dot and a method for preparing the quantum dot ink.
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. Compared with liquid crystal display and organic light emitting display, the display technology based on quantum dot light emitting has been highly emphasized by the display industry in recent years, and quantum dot light emitting technology 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 spraying, ink-jet printing, slit coating, gravure printing, screen printing and the like. The method is characterized in that the specific process of ink-jet printing is to spray quantum dot ink on a printing stock and form a quantum dot film at a specific position after drying. Compared with other preparation technologies, the ink-jet printing has the characteristics of low cost, convenience, high printing quality, suitability for manufacturing large-size panels and the like. The preparation of the quantum dot ink is to dissolve quantum dots in a specific solvent to form a solution with certain viscosity, surface tension and charge transport capacity. The viscosity, surface tension and charge transport capacity of the quantum dot ink determine the wetting capacity, drying rate, coffee ring effect and photoelectric properties of the film of ink droplets during ink-jet printing, and therefore, the quality of the quantum dot ink plays a crucial role in the ink-jet printing effect. In the process of preparing the quantum dot ink, the ligand combined on the surface of the quantum dot has an important influence on the quantum dot ink, so that the photoelectric property of the quantum dot is influenced, and the solubility and the stability of the quantum dot ink are also influenced. Common surface ligands are carboxylic acids, amines, alkyl phosphorus, 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 size of the quantum dot is smaller than the bohr radius of the exciton, the exciton is exposed on the surface to a certain extent, and the surface is easily influenced to reduce the optical performance of the exciton; 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.
In the current quantum dot ink-jet printing process, a common problem exists, that is, the properties of inks prepared by the same ink formula conditions are different from one another by different batches of the same quantum dots prepared by the same process. The reason is mainly caused by different ligand contents on the surface of the quantum dot. If the amount of the ligand on the surface of the quantum dot is too small, the quantum dot is not easily dissolved in the ink solvent, and thus ink jet printing cannot be performed. If the quantum dot surface ligand exchange rates of different batches are different, the solubility, drying rate and coffee ring effect of the quantum dot ink are different, so that the quality of a luminescent layer film is affected, and the problems of uneven quality of a printed panel, low pixel resolution, uneven lighting voltage, uneven photoelectric efficiency and the like are directly caused.
Disclosure of Invention
In view of the defects of the prior art, in order to ensure the quality stability of the quantum dot ink, the invention firstly provides a method for measuring the content of the ligand on the surface of the quantum dot, and further provides a method for preparing the quantum dot ink.
A method for measuring the content 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 an organic ligand bound on the surface of the quantum dot, the organic ligand is selected from a sulfydryl-containing organic ligand or a nitrogen-containing organic ligand, the organic ligand is one or more, and when the organic ligands are multiple, the molar molecular mass of each organic ligand is different from that of each other by no more than 5%;
measuring the mass percentage of sulfur element or nitrogen element in the sample particles by using a potentiometric titration method, and calculating the mass percentage as the content of the quantum dot surface ligand;
when the organic ligand on the surface of the quantum dot is a sulfydryl-containing organic ligand, the quantum dot does not contain sulfur element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements.
The method for measuring the content of the ligand on the surface of the quantum dot has the advantages of simplicity, wide application range and strong operability, can be used for evaluating the synthesis quality of quantum dots in different batches, and particularly provides reliable guarantee for guaranteeing the quality of quantum dots synthesized in different batches in the same preparation process.
A method for preparing quantum dot ink comprises the following steps:
providing sample particles, wherein each particle in the sample particles comprises a quantum dot and an organic ligand bound on the surface of the quantum dot, the organic ligand is selected from a sulfydryl-containing organic ligand or a nitrogen-containing organic ligand, the organic ligand is one or more, and when the organic ligands are multiple, the molar molecular mass of each organic ligand is different from that of each other by no more than 5%;
respectively measuring the surface ligand content of the sample particles of different batches according to the measuring method of the surface ligand content of the quantum dots;
selecting one batch of sample particles as a reference batch of sample particles;
when the surface ligand content of other batch of sample particles is different from the surface ligand content of the reference batch of particles by no more than 10%, using the other batch of sample particles for preparing ink;
when the surface ligand content of other batch of sample particles is different from the surface ligand content of the reference batch of particles by more than 10%, adjusting the surface ligand content of the other batch of particles to be within 10% of the surface ligand content of the reference batch of particles, and then using the other batch of sample particles after adjusting the surface ligand content for preparing ink.
In order to ensure the stability of the quantum dot ink, the invention provides a preparation method of the quantum dot ink. Specifically, aiming at the same quantum dots of different batches, determining the surface ligand content of the quantum dots of the reference sample and recording the surface ligand content as omega1Determining the surface ligand content omega of other sample particles prepared from different batches (for example, other sample particles obtained based on the same method or the same preparation process)2If ω is2=【90%ω1, 110%ω1The content of the ligand on the surface of the quantum dots of the sample particles in batches is consistent, and the preparation of the quantum dot ink can be carried out; if omega2<90%ω1Regulation of omega by ligand-exchange2To 90% omega1~110%ω1Then preparing quantum dot ink; if omega2>110%ω1Firstly, the omega is adjusted by adopting a ligand removal method2To 90% omega1~110%ω1And preparing the quantum dot ink. The method for preparing the quantum dot ink can ensure the uniformity of the quality of the quantum dot ink, ensure the solubility, the drying rate and the coffee ring effect of quantum dot inks of different batches to be the same, and improve the uniformity of the pixel resolution, the turn-on voltage and the photoelectric efficiency of the quantum dot display panel.
Detailed Description
The invention provides a method for measuring the content of a ligand on the surface of a quantum dot and a method for preparing quantum dot ink, 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 content 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 bound on the surfaces of the quantum dots, the organic ligands are selected from mercapto-containing organic ligands or nitrogen-containing organic ligands, the organic ligands are one or more, and when the organic ligands are multiple, the molar molecular mass between each organic ligand is different by no more than 5%;
s20, measuring the mass percentage of sulfur or nitrogen in the sample particles by using a potentiometric titration method, and calculating the mass percentage as the content of the quantum dot surface ligand;
when the organic ligand on the surface of the quantum dot is a sulfydryl-containing organic ligand, the quantum dot does not contain sulfur element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements.
The invention provides a method for determining the percentage content of characteristic elements in organic ligands in sample particles by using a potentiometric titration method, wherein one or more organic ligands are adopted, when the organic ligands are multiple, the molar molecular mass difference between the organic ligands is not more than 5%, and the percentage content of the characteristic elements in the organic ligands in the sample particles can be presumed to be the content of the quantum dot surface ligands. When the organic ligand on the surface of the quantum dot is an organic ligand containing sulfydryl, the characteristic element in the organic ligand is sulfur element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the characteristic element in the organic ligand is a nitrogen element. When the organic ligand on the surface of the quantum dot is a sulfydryl-containing organic ligand, the quantum dot does not contain sulfur element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements.
Specifically, in step S10, the quantum dots may be selected from unary quantum dots, binary quantum dots, ternary quantum dots, or quaternary quantum dots. For example: the unitary quantum dots are 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 CdZnS, CdZnSe, CdSeS, PbSeS, ZnCdTe, CdS/ZnS, CdZnS/ZnS, CdZnSe/ZnSe, CdSeS/CdSeS/CdS, CdSe/CdZnSe/CdZnSe/ZnSe, CdS/CdZnS/CdZnS/ZnS, NaYF4Or NaCdF4Quantum dots; the quaternary quantum dots comprise CdSZnSeyS, CdSe/ZnS, CdSe/CdS/ZnS, CdSe/ZnSe/ZnS, CdSZnSe/CdS/ZnS or InP/ZnS quantum dots.
Specifically, in step S10, the thiol-group-containing organic ligand is selected from one or more of mono-thiol, di-thiol, thiol-alcohol, thiol-amine, and thiol-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 is selected from one or more of 2-mercaptoethanol, 3-mercapto-1-propanol, 4-mercapto-1-butanol, 5-mercapto-1-pentanol, 6-mercapto-1-hexanol and 8-mercapto-1-octanol;
preferably, the mercapto acid is selected from 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 is selected from one or more of 2-mercaptoethylamine, 3-mercaptopropylamine, 4-mercaptobutylamine, 5-mercaptopentylamine, 6-mercaptohexylamine, 2-amino-3-mercaptopropionic acid, 2-aminothiophenol, and mercaptoundecanamine.
Specifically, in step S10, the nitrogen-containing organic ligand is selected from one or more of primary amine, secondary amine and tertiary amine.
Preferably, the primary amine is selected from one or more of benzylamine, n-butylamine, n-propylamine, cyclohexylamine, phenethylamine, n-hexylamine, isopropylamine, aniline, p-toluidine, p-chloroaniline, p-bromoaniline, p-methoxyaniline, 1, 4-butanediamine and 1, 5-pentanediamine;
preferably, the secondary amine is selected from one or more of dimethylamine, diphenylamine, diisooctylamine, ditridecylamine and N-methylaniline;
preferably, the tertiary amine is selected from one or more of dimethyl octylamine, dimethyl decylamine, dimethyl dodecylamine, dimethyl tetradecylamine, dimethyl hexadecylamine, dimethyl octadecylamine, dimethyl oleylamine, bis octylmethylamine, bis decylmethylamine and trioctylamine.
In one embodiment, in step S20 of the present invention, the content of sulfur or nitrogen in the sample particles is measured by the potentiometric titration method, and the measured content is the content of the ligand on the surface of the quantum dot. The potentiometric titration test principle is that a metal inert electrode is used as an indicating electrode, and a working battery is formed by the reference electrode and a tested sample particle solution. With the addition of the titrant, the titrant chemically reacts with the measured ions, and the concentration of the measured ions changes during the titration process, so that the indicating electrode is caused to changeAnd the potential of the reference electrode is changed, and finally the titration endpoint is determined by the jump of the indicating electrode potential. In the titration process, mercaptan sulfur and silver ions on the organic ligand form mercaptan sulfur silver precipitate, and the mass percentage of the S element in the sample particles is obtained according to the usage amount of the titrant; ClO in perchloric acid4 -And Cl in pH glass electrode-Forming electrode reaction, and obtaining the mass percentage of the N element in the sample particles according to the usage amount of the titrant;
wherein the electrode potential equation is:
。
specifically, in one embodiment, the step S20 includes:
s201, dissolving the sample particles to obtain a sample particle solution;
s202, inserting an indicating electrode and a reference electrode into the sample particle solution, dropping a titrant into the sample particle solution for potentiometric titration, drawing an E-V titration curve, obtaining the titrant usage amount of a titration end point according to the titration curve, converting the titrant usage amount into the mass percentage content of sulfur or nitrogen elements in the sample particles and the sample particles, and calculating the mass percentage content of the sulfur or nitrogen elements in the sample particles and the mass percentage content of the sample particles as the content of the quantum dot surface ligand, wherein E is the potential, and V is the volume consumed by the titrant.
Specifically, in step S201, 10 to 30mg of the sample particles are weighed and placed in a 250 mL conical flask or a titration cup matched with a potentiometric titrator with a corresponding range, 30 to 50mL of isopropanol is added as a solvent, and the sample particles are shaken to be completely dissolved in the solvent, so as to obtain the sample particle solution.
Specifically, in step S202, when the organic ligand on the surface of the quantum dot is a thiol-containing organic ligand, the titrant is a silver nitrate alcohol standard titration solution, the indicator electrode is a silver-silver sulfide electrode, and the reference electrode is a glass reference electrode. The preparation process of the silver nitrate alcohol standard titration solution is as follows: dissolving 1.7-8.5 g of silver nitrate in 10 mL of deionized water in a 1000mL volumetric flask, and diluting with isopropanol to a scale mark to obtain 0.01-0.05mol/L silver nitrate alcohol standard titration solution. The preparation process of the silver-silver sulfide electrode is as follows:
(1) preparing an alkaline titration solvent, namely absorbing 1.6-3.2 g of anhydrous sodium acetate to dissolve in 25 mL of oxygen-free water, and then injecting into 975 mL of isopropanol to obtain 0.02-0.04mol/L of the alkaline titration solvent;
(2) firstly, polishing a silver electrode silver terminal by using abrasive paper, then immersing the polished silver electrode silver terminal in 100 mL of alkaline titration solvent containing 5-8 mL of 1 wt% sodium sulfide solution, then slowly dripping 70-100 mL of silver nitrate alcohol standard titration solution from a burette under the condition of stirring, and rotating an electrode to ensure that a silver sulfide coating is uniformly plated on the electrode silver terminal, wherein the titration time is controlled to be 1-2 min.
Specifically, in step S202, when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the titrant is a perchloric acid standard titration solution, the indicator electrode is a pH glass electrode, and the reference electrode is a glass reference electrode. Wherein the perchloric acid standard titration solution is prepared by the following process: adding 8.5-17 mL of perchloric acid (70%) into a 1000mL volumetric flask, adding 100 mL of isopropanol to dissolve, and then adding dioxane to dilute to a scale mark to obtain 0.1-0.2mol/L perchloric acid standard titration solution.
In step S202, the specific potentiometric titration test conditions are: setting potential preset values dE (set) = 15-18mV, potential balance allowable values dE = 4-5mV, potential value recording time dt = 0.5-1s, minimum potential value recording time dt (min) = 0.5-1s, maximum potential value recording time dt (max) =5-10 s, and threshold value =200 mV/mL. Wherein, the potential value recording time means that after each drop of titrant is dripped, the titrant reacts with the sample for 0.5 to 1s and then the potential value is recorded, so that the titrant and the sample fully react, and the value is read after the potential value is stabilized. The minimum potential value recording time is the time required for the electrode to be fully contacted with the sample after the installation device is inserted into the electrode, and the initial minimum potential to be stable. The maximum potential value recording time means that after titration is finished, the potential value reaches the maximum value and waits for 5-10s until the potential does not change any more. The specific potentiometric titration test process is as follows: inserting a reference electrode and an indicating electrode into a container filled with the sample particle solution, and carrying out potentiometric titration by using the prepared silver nitrate alcohol standard titration solution or perchloric acid standard titration solution; adding a proper amount of titrant, and recording millivolts and milliliters after the potential is constant; when the end point is approached, the potential is constant after 5-10 min; in order to avoid the oxidation of the measured object by air during the titration, the titration time is shortened, and the titration cannot be interrupted; and finally, drawing an E-V titration curve by taking the E potential as a vertical coordinate and the volume V consumed by the titrant as a horizontal coordinate, obtaining the volume consumed by the titrant according to the potential jump point of the titration curve, converting the volume into the mass percentage of the sulfur or nitrogen elements in the sample particles, and calculating the mass percentage as the surface ligand content of the quantum dots.
Further, a preparation method of the quantum dot ink is provided, which comprises the following steps:
s101, providing sample particles, wherein each particle in the sample particles comprises a quantum dot and an organic ligand bound on the surface of the quantum dot, the organic ligand is selected from a sulfydryl-containing organic ligand or a nitrogen-containing organic ligand, the organic ligand is one or more, and when the organic ligands are multiple, the molar molecular mass of each organic ligand is different from that of each other by no more than 5%;
s102, respectively measuring the surface ligand content of the sample particles of different batches according to the measuring method of the surface ligand content of the quantum dots;
s103, selecting one batch of sample particles as a reference batch of sample particles;
s104, when the content of the surface ligand of the quantum dots of the other batch of samples is not more than 10% different from the content of the surface ligand of the reference batch of particles, using the other batch of sample particles for preparing ink;
s105, when the content of the surface ligand of the other batch of sample quantum dots is different from the content of the surface ligand of the reference batch of particles by more than 10%, adjusting the content of the surface ligand of the other batch of quantum dots to be within 10% of the content of the surface ligand of the reference batch of particles, and then using the other batch of particles with the adjusted content of the surface ligand for preparing ink.
In the step S104, in order to ensure the stability of the quantum dot ink, the invention provides a method for preparing the quantum dot ink. Specifically, for a plurality of different batches of same-kind sample particles, a potentiometric titration method is utilized to select a reference batch of sample particles and determine the content of the organic ligand on the surface of the quantum dot of the reference batch of sample particles as omega1Determining the organic ligand content omega on the surface of other quantum dots prepared in other batches (for example, the organic ligand content omega on the surface of other quantum dots obtained based on the same method or the same preparation process2According to ω1And omega2The relationship between the sample particles in the other batches is used for determining whether the sample particles in the other batches can be directly mixed with the sample particles in the other batches for preparing the ink. If omega2=【90%ω1, 110%ω1】（ω2Value of (d) is at 90% omega1~110%ω1And (b) the organic ligand content on the surface of the quantum dot of the other batch of sample particles is consistent with the organic ligand content on the surface of the quantum dot of the reference sample particle, and the quantum dot ink can be prepared. In the process, the step of using the other batch of sample particles to formulate an ink comprises: using the other batch of sample particles directly for preparing ink; or mixing the other batch of sample particles with other sample particles satisfying the condition (the reference particle and/or surface ligand content is 90% omega)1~110%ω1Sample particles in between) are mixed for formulating the ink.
In the step S105, if ω is2<90%ω1Regulation of omega by ligand re-exchange2To 90% omega1~110%ω1Then preparing quantum dot ink; if omega2>110%ω1The omega is regulated by a ligand-removing method2To 90% omega1~110%ω1And preparing the quantum dot ink. The method for preparing the quantum dot ink can ensure the uniformity of the quality of the quantum dot ink, ensure the solubility, the drying rate and the coffee ring effect of quantum dot inks of different batches to be the same, and improve the uniformity of the pixel resolution, the turn-on voltage and the photoelectric efficiency of the quantum dot display panel. The other batch of sample particles with the adjusted surface ligand content are used for preparing inkThe method comprises the following steps: using the other batch of sample particles directly for preparing ink; or mixing the other batch of sample particles with other sample particles satisfying the condition (the reference particle and/or surface ligand content is 90% omega)1~110%ω1Sample particles in between) are mixed for formulating the ink.
Specifically, the surface ligand content of the reference batch of particles is noted as ω1And the content omega of the ligand on the surface of the quantum dots of other batches of samples2Less than 90% omega1When in use, the content of the surface ligand of the quantum dots of other batches of samples can be increased by a quantum dot ligand re-exchange method, which comprises the steps of dissolving other batches of sample particles in a non-polar solvent, and then adding the original surface ligand to carry out exchange at 25-100 ℃. The nonpolar solvent can be selected from one or more of chloroform, n-hexane, heptane, octane, toluene, chlorobenzene, dichlorobenzene, carbon tetrachloride, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, cyclodecane and cycloundecane. The ligand is added in the exchange process in an amount of (90% omega) of substance1-ω2)n~(110%ω1-ω2) And n, wherein n is the mass amount of the ligand added in the preparation process of the quantum dot.
Specifically, the surface ligand content of the reference batch of particles is noted as ω1And the content omega of the ligand on the surface of the quantum dots of other batches of samples2Higher than 110% omega1In the method, the ligand content on the surface of the quantum dots of other batches of samples can be reduced by a ligand removal method. For example, the ligand removal method may be an acid treatment method, in which the other batch of sample particles is mixed with a mineral acid solution to remove the ligands on the surfaces of the other batch of sample particles. At this time, the inorganic acid solution ionizes to give H+And anions, surface ligands and H+The binding generates a weak acid, thereby removing the ligand. The inorganic acid is preferably selected from hydrochloric acid, nitric acid or sulfuric acid, and the inorganic acid solution is an aqueous solution, a methanol solution or an ethanol solution with the volume concentration of the acid being 1.25% -5%. The amount of the material of the de-ligand agent added in the de-ligand process is mQ(ω2-110%ω1)/Ml~mQ(ω2-90%ω1)/MlWherein m isQThe mass of the other batch of sample particles, MlIs the molar molecular mass of the characteristic element.
The present invention will be described in detail below with reference to examples.
Example 1
1. Determining the relative content of the characteristic element S in the surface ligand of the standard particle CdSe quantum dot (the surface ligand is decamercaptan) to be omega1。
Preparing 0.0L mol/L silver nitrate alcohol standard titration solution, dissolving 1.7 g of silver nitrate in 10 mL of deionized water in a 1000mL volumetric flask, and diluting with isopropanol to a scale mark;
preparing an alkaline titration solvent, namely absorbing 1.6 g of anhydrous sodium acetate to dissolve in 25 mL of oxygen-free water, and then injecting into 975 mL of isopropanol;
preparing a silver-silver sulfide electrode, and 1) polishing a silver terminal of the silver electrode by using abrasive paper. 2) The polished silver electrode silver terminal was immersed in 100 mL of an alkaline titration solvent containing 7 mL of a 1 wt% sodium sulfide solution. 3) Under the condition of stirring, 80 mL of 0.01 mol/L silver nitrate alcohol standard titration solution is slowly added into the burette, and the electrode is rotated, so that the silver sulfide coating is uniformly plated on the silver terminal of the silver electrode. Controlling the titration time to be 2 min;
and fourthly, measuring the sample, namely accurately weighing 20 mg of sample particles, putting the sample particles into a 250 mL conical flask or a titration cup matched with an instrument with a corresponding measuring range, adding 40 mL of isopropanol, and shaking to disperse the sample particles in the solvent. Potential preset values dE (set) = 17 mV, minimum titrant addition dv (min) = 0.01 mL, maximum titrant addition dv (max) = 0.2 mL, potential equilibrium allowed value dE = 5mV, potential value recording time dt = 1s, minimum potential value recording time dt (min) = 0.5 s, maximum potential value recording time dt (max) =6 s, threshold value =200 mV/mL are set. Filling a glass reference electrode and the silver-silver sulfide electrode prepared in the step 3) into a container filled with sample particles, and titrating by using 0.01 mol/L silver nitrate alcohol standard titration solution prepared in the step 1); adding a proper amount of titrant, and recording millivolts and milliliters after the potential is constant; when the end point is approached, the potential is constant after 7 min; in order to avoid oxidation of sulfide by air during titration, the titration time should be shortened, and titration cannot be interrupted; and finally, drawing an E-V titration curve by taking the E potential as a vertical coordinate and the volume V consumed by the titrant as a horizontal coordinate, obtaining the volume consumed by the titrant according to the potential jump point of the titration curve, and converting the volume into the content of sulfur element in the sample particles, which accounts for 4.5% of the mass of the sample particles.
2. Determining the relative content omega of the characteristic element S element in other batches of CdSe quantum dot surface ligands prepared in the same preparation process2. Obtaining the content omega of the S element in the surface ligand of another batch of CdSe quantum dots according to the process of the step 124.9%, omega2At 90% omega1~110%ω1In the range, the method can be directly used for preparing quantum dot ink.
Example 2
1. Determination of the Standard particle CeO2The relative content of the characteristic element N in the surface ligand of the quantum dot (the surface ligand is N-hexylamine) is omega1。
Firstly, preparing 0.1 mol/L perchloric acid standard titration solution, taking 8.5 mL perchloric acid (70%) in a 1000mL volumetric flask, adding 100 mL isopropanol to dissolve, and then adding dioxane to dilute to a scale mark;
secondly, testing the sample, namely accurately weighing 30mg of sample particles, placing the sample particles into a 250 mL conical flask or a titration cup matched with an instrument with a corresponding measuring range, adding 50mL of isopropanol, and shaking to disperse the sample particles in the solvent. Potential preset values dE (set) = 16 mV, minimum titrant addition dv (min) = 0.02 mL, maximum titrant addition dv (max) = 0.2 mL, potential equilibrium allowed value dE = 5mV, potential value recording time dt = 0.5 s, minimum potential value recording time dt (min) = 1s, maximum potential value recording time dt (max) =5 s, threshold value =200 mV/mL are set. Loading a glass reference electrode and a pH glass electrode into a container filled with sample particles, and titrating by using 0.1 mol/L perchloric acid standard titration solution calibrated in the step 1); adding a proper amount of titrant, and recording millivolts and milliliters after the potential is constant; when the end point is approached, the potential is constant after 6 min; and finally, drawing an E-V titration curve by taking the E potential as a vertical coordinate and the volume V consumed by the titrant as a horizontal coordinate, obtaining the volume consumed by the titrant according to the potential jump point of the titration curve, and converting the volume into the content of the N element in the sample particles accounting for 5.1 percent of the mass of the sample particles.
2. Determination of other batches of CeO of the same preparation Process2Relative content omega of characteristic element N element in quantum dot surface ligand2. Obtaining another batch of CeO according to the process of the step 12Content omega of N element in surface ligand of quantum dot24.7%, omega2At 90% omega1~110%ω1In the range, the method can be directly used for preparing quantum dot ink.
The above detailed description is provided for the method for determining the content of the ligand on the surface of the quantum dot and the method for preparing the quantum dot ink, and a person skilled in the art may have changes in the specific implementation and application scope according to the ideas of the embodiments of the present invention.
Claims (15)
1. A method for preparing quantum dot ink is characterized by comprising the following steps: providing sample particles, wherein each particle in the sample particles comprises a quantum dot and an organic ligand bound on the surface of the quantum dot, the organic ligand is selected from a sulfydryl-containing organic ligand or a nitrogen-containing organic ligand, the organic ligand is one or more, and when the organic ligands are multiple, the molar molecular mass of each organic ligand is different from that of each other by no more than 5%;
respectively measuring the surface ligand content of the sample particles of different batches by the following measuring method of the surface ligand content of the quantum dots; selecting one batch of sample particles as a reference batch of sample particles;
when the surface ligand content of other batch of sample particles is different from the surface ligand content of the reference batch of particles by no more than 10%, using the other batch of sample particles for preparing ink;
when the surface ligand content of other batch of sample particles is different from the surface ligand content of the reference batch of particles by more than 10%, adjusting the surface ligand content of the other batch of particles to be within 10% of the surface ligand content of the reference batch of particles, and then using the other batch of sample particles after adjusting the surface ligand content for preparing ink;
the method for measuring the content of the ligand on the surface of the quantum dot comprises the following steps:
providing sample particles;
measuring the mass percentage of sulfur element or nitrogen element in the sample particles by using a potentiometric titration method, and calculating the mass percentage as the content of the quantum dot surface ligand;
when the organic ligand on the surface of the quantum dot is a sulfydryl-containing organic ligand, the quantum dot does not contain sulfur element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements.
2. The method for preparing quantum dot ink according to claim 1, wherein the surface ligand content of the reference batch of sample particles is recorded as ω1When the ligand content omega on the surface of other batches of sample particles2Higher than 110% omega1Reducing the ligand content on the surface of the other batch of sample particles by a de-ligand method, wherein the de-ligand method comprises the following steps: and mixing the other batch of sample particles with a mineral acid solution, and removing the ligands on the surfaces of the other batch of sample particles.
3. The method of claim 2, wherein the inorganic acid solution is selected from a hydrochloric acid solution, a nitric acid solution, or a sulfuric acid solution.
4. The method for preparing quantum dot ink according to claim 2, wherein the volume concentration of the inorganic acid solution is 1.25-5%.
5. The method for preparing quantum dot ink according to claim 2, wherein the solvent in the inorganic acid solution is water, methanol or ethanol.
6. The method of claim 2, wherein the amount of the inorganic acid is mQ(ω2-110％ω1)/Ml～mQ(ω2-90％ω1)/MlMixing the other batch of sample particles with a mineral acid solution, wherein mQIs the mass of the other batch of sample particles, MlIs the molar mass of S or N.
7. The method for preparing quantum dot ink according to claim 2, wherein different batches of the sample particles are prepared by the same preparation process.
8. The method for preparing quantum dot ink according to claim 1, wherein the step of measuring the content of sulfur or nitrogen in the sample particles in percentage by mass of the sample particles by potentiometric titration as the content of the ligand on the surface of the quantum dot comprises:
dissolving the sample particles to obtain a sample particle solution;
inserting an indicating electrode and a reference electrode into the sample particle solution, dropping a titrant into the sample particle solution for potentiometric titration, drawing an E-V titration curve, obtaining the use amount of the titrant according to the titration endpoint of the titration curve, converting the use amount into the mass percentage content of sulfur or nitrogen elements in the sample particles and the sample particles, and calculating the mass percentage content as the content of the quantum dot surface ligand, wherein E is the potential, and V is the volume used by the titrant.
9. The method for preparing quantum dot ink according to claim 8, wherein the test conditions of the potentiometric titration are as follows: setting a potential preset value of 15-18mV, a potential balance allowable value of 4-5mV, a potential value recording time of 0.5-1s, a minimum potential value recording time of 0.5-1s, a maximum potential value of 5-10s and a threshold value of 200 mV/mL.
10. The method for preparing quantum dot ink according to claim 8, wherein when the organic ligand on the surface of the quantum dot is a mercapto group-containing organic ligand, the titrant is a silver nitrate alcohol standard titration solution, and the indicator electrode is a silver-silver sulfide electrode.
11. The method for preparing quantum dot ink according to claim 8, wherein when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the titrant is a perchloric acid standard titration solution, and the indicator electrode is a pH glass electrode.
12. The method for preparing quantum dot ink according to claim 1, wherein the quantum dot is a unary quantum dot, a binary quantum dot or a ternary quantum dot.
13. The method for preparing quantum dot ink according to claim 12, wherein the unary quantum dots are 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.
14. The method for formulating a quantum dot ink according to claim 1, wherein the thiol-group-containing organic ligand is selected from one or more of mono-thiol, di-thiol, thiol alcohol, thiol amine, and thiol acid.
15. The method for formulating the quantum dot ink as claimed in claim 1, wherein the nitrogen-containing organic ligand is selected from one or more of primary amine, secondary amine and tertiary amine.
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