A method for rapid detection of water content in solvents based on color change of CsPbBr3 perovskite nanocrystals

Abstract

The present invention discloses a method for rapidly detecting the water content in a solvent based on the color change of CsPbBr3 perovskite nanocrystals. The method comprises: adding PbBr2 and CsBr as precursors to a good solvent for dissolution, then adding a ligand and mixing uniformly to obtain a precursor solution; adding a poor solvent to the precursor solution to obtain a CsPbBr3 and PAA composite colloid; dripping solvents of varying water contents and volumes into equal amounts of the CsPbBr3 and PAA composite colloids to obtain mixtures; measuring the fluorescence spectra of the mixtures after standing for the same period of time, obtaining the CIE coordinate colors corresponding to the fluorescence spectra, and obtaining a colorimetric chart; dripping a solvent to be tested into the CsPbBr3 and PAA composite colloid, measuring its fluorescence spectrum to obtain the corresponding CIE coordinate colors or obtaining its luminescent color under ultraviolet light, and comparing the color with the colorimetric chart to determine the water content of the solvent to be tested. The method can determine the water content of a solvent by visually observing the photoluminescent color of the perovskite colloid after the solvent has been added, thereby enabling rapid and convenient perovskite detection of the water content of the solvent.

Description

Technical Field

[0001] The present invention belongs to the field of perovskite technology, and more specifically, relates to a method for quickly detecting the water content in a solvent based on the color change of CsPbBr3 perovskite nanocrystals. Background Art

[0002] The moisture content in organic solvents or pharmaceuticals is one of the important indicators in the quality control process. The increase in moisture content directly leads to changes in their properties. For example, in the Grignard reaction, the solvent must be strictly dehydrated to ensure the smooth progress of the reaction.

[0003] All-inorganic perovskite nanocrystals CsPbBr3 have unique optical advantages, but are also sensitive to moisture. Exploiting their disadvantage of being sensitive to water can develop their potential in moisture detection.

[0004] Common moisture detection methods include drying, toluene, chromatography, and Karl Fischer. The drying method involves placing the sample in an oven at a constant temperature and calculating the moisture content based on the change in sample weight before and after drying. This method is simple and inexpensive, but is not suitable for volatile solvents. The toluene method exploits the immiscibility of toluene and water, forming an azeotrope. This azeotrope removes the moisture and collects it through condensation. The moisture content in the sample is then calculated based on the volume of the water. This method is simple and inexpensive, but suffers from large operational errors, poor accuracy, toluene toxicity, and the requirement for a large sample volume. The chromatography method uses a gas chromatograph to determine moisture content, offering high sensitivity and accuracy. However, its disadvantages are the high requirements for instrumentation and chromatographic columns, and the cumbersome operation. The Karl Fischer method relies on the redox reaction of water with iodine and sulfur dioxide in the presence of pyridine and methanol, consuming the iodine generated by electrolysis at the anode until all the water is depleted. According to Faraday's law of electrolysis, the amount of iodine generated by electrolysis is directly proportional to the amount of electricity consumed. This method has the advantages of wide applicability and high accuracy. The disadvantages are that it requires instruments, has high requirements for ambient temperature and humidity, and the Karl Fischer reagent contains toxic reagents such as pyridine.

[0005] It can be seen that the above methods all require certain instrument conditions, and the operations are cumbersome and time-consuming. Summary of the Invention

[0006] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for quickly detecting the water content in a solvent based on the color change of CsPbBr3 perovskite nanocrystals. The purpose is to judge the water content in the solvent by observing the photoluminescence color of the perovskite colloid after adding the solvent with the naked eye, thereby realizing the rapid and simple detection of the water content of the solvent by perovskite.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for rapidly detecting the water content in a solvent based on the color change of CsPbBr3 perovskite nanocrystals is provided, comprising the following steps:

[0008] (1) PbBr2 and CsBr as precursors were added to a good solvent and dissolved. Oleylamine and polyacrylic acid were then added as ligands and mixed evenly to obtain a precursor solution. A poor solvent was added to the precursor solution, and CsPbBr3@PAA colloid with blue-purple photoluminescence was obtained by supersaturated recrystallization at room temperature. Hereinafter, the composite colloid of CsPbBr3 and PAA is referred to as "CsPbBr3@PAA" or "drug".

[0009] (2) Solvents with different water contents and volumes were added dropwise to equal amounts of CsPbBr3@PAA colloid to obtain mixtures. After standing for the same amount of time, the fluorescence spectra of the mixtures were measured to obtain the CIE coordinate colors corresponding to the fluorescence spectra and obtain a colorimetric card.

[0010] (3) Dropping the solvent to be tested into the CsPbBr3@PAA colloid, measuring its fluorescence spectrum to obtain the corresponding CIE coordinate color or obtaining its luminescent color under ultraviolet light, comparing the color with a colorimetric card to determine the water content of the solvent to be tested; wherein the solvent to be tested is a solvent that can dissolve polyacrylic acid.

[0011] In step (3), the fluorescence spectrum of the sample has a luminescence range of 380-540 nm. The variation in luminescence color involves the increase and decrease of four fluorescence peaks, located at wavelengths of 430-440 nm, 455-465 nm, 470-490 nm, and 500-525 nm, respectively. The combination of the four fluorescence peaks and the variation in peak intensity affect the overall luminescence. The fluorescence data is converted to CIE coordinate color, and the color is compared with a colorimetric chart to determine the water content of the solvent to be tested.

[0012] The principle of the perovskite luminescence color change in the present invention is: compared with non-polar solvents and other polar solvents (such as alcohol solvents), CsBr has better solubility in water, and the solvents detected in the present invention can dissolve polyacrylic acid. For example, alcohol solvents have a certain solubility for PAA. When the cubic phase CsPbBr3@PAA complex colloid with blue-violet photoluminescence at around 437nm encounters a small amount of such aqueous solvent, such as ethanol with a volume fraction of 95%, ethanol, as a good solvent for PAA, slowly dissolves the PAA in the complex and opens it. The point-like nanocrystals break away from the protection and restriction of PAA and grow in a directionally attached manner to become strip-shaped and sheet-shaped nanocrystals. At the same time, water dissolves CsBr, and CsPbBr3 loses CsBr and transforms into tetragonal phase CsPb2Br5. New peaks around 463nm and 478nm appear in the fluorescence spectrum. The mixing of multiple luminescence peaks shifts the apparent luminescence color to blue. When the water content of the solvent increases to a certain level, the tetragonal CsPb2Br5 phase gradually transforms into the monoclinic CsPbBr3 phase, which emits light at around 519nm. The luminescence of the monoclinic CsPbBr3 at around 519nm, along with the luminescence at 437nm, 463nm, and 478nm, forms a cyan color. As the 519nm peak strengthens and the other peaks weaken, the overall color shifts to cyan and then green. Further increases in water content result in green photoluminescence at only 519nm. That is, at the same added volume, higher water content in the solvent increases the likelihood of the monoclinic CsPbBr3 phase, which in turn causes the luminescence to shift to green. Therefore, the color change is directly related to the water content of the solvent. Therefore, the technical solution of the present invention can directly determine the water content of the tested solvent through the above obvious color change discernible to the naked eye and comparison with a color chart.

[0013] Preferably, the solvent to be tested is at least one of methanol, ethanol, ethylene glycol, n-propanol, isopropanol, propylene glycol, n-butanol, isobutanol, sec-butanol, tert-butanol, glycerol, tetrahydrofuran, pyridine, acetonitrile, acetone, methylamine, ethylamine, triethylamine, aniline, formamide, N-methylformamide, DMF, DMA, and DMSO.

[0014] It should be noted that the CsPbBr3@PAA colloid prepared in step (1) of the method provided by the present invention is a CsPbBr3@PAA colloid mixed in a non-polar solvent without drying. The non-polar solvent is at least one of toluene, benzene, petroleum ether, n-hexane, cyclohexane, dichloromethane, chloroform, carbon tetrachloride, dibromomethane, carbon disulfide, ether, ethyl acetate, and isopropyl ether. The CsPbBr3@PAA colloid mixed in the non-polar solvent can be stored at low temperatures, for example, at 4-10°C. More conveniently, 2 mL of the CsPbBr3@PAA colloid mixed in the non-polar solvent can be injected into a 3 mL vial, sealed with a rubber stopper and an aluminum cap, and stored in a refrigerator for use.

[0015] The CsPbBr3@PAA colloid prepared in step (1) of the method provided by the present invention can also be dried. The dried CsPbBr3@PAA colloid is more convenient for storage. When used, the dried CsPbBr3@PAA colloid can be redispersed in the above-mentioned non-polar solvent.

[0016] Preferably, the volume ratio of CsPbBr3@PAA colloid to the solvent to be tested is (1-50):200.

[0017] Preferably, the colorimetric card in step (2) is obtained by plotting the water content of the solvent as variable 1, the volume of the solvent as variable 2, and the CIE coordinate color of the mixture as the result.

[0018] Preferably, the ordinate of the colorimetric card is a solvent with a volume fraction of 94% to 99.8%, and the abscissa of the colorimetric card is a solvent with a volume of 10 to 500 μL. When drawing the colorimetric card, the amount of CsPbBr3@PAA colloid dispersed in the non-polar solvent is 2 to 10 ml, wherein the concentration of CsPbBr3@PAA colloid is quantified by the Pb concentration, and the concentration of [Pb] in the non-polar solvent is 1 to 200 mg L -1 .

[0019] It should be noted that in step (2), a specific colorimetric card needs to be drawn for a specific solvent. When drawing the colorimetric card, the amount of CsPbBr3@PAA colloid used is the same. In order to ensure the consistency and accuracy of the water content test of the solvent to be tested in the subsequent step (3), the amount of CsPbBr3@PAA colloid used in step (3) is the same as the amount of CsPbBr3@PAA colloid used when drawing the colorimetric card. For example, in step (2), when drawing the colorimetric card, for 40μL 95% methanol and 100μL 95% methanol, a volume of 2mL of CsPbBr3@PAA colloid is used. The CsPbBr3@PAA colloid is CsPbBr3@PAA colloid dispersed in a non-polar solvent, wherein the Pb concentration [Pb] = 1-200mg L -1 In step (3), when testing the water content of the solvent to be tested, similarly, a volume of 2 mL of CsPbBr3@PAA colloid was used, wherein the Pb concentration [Pb] = 1-200 mg L -1 .

[0020] Preferably, the step (3) comprises the following steps:

[0021] (301) Select the solvent volume V1 in the colorimetric card that can show different colors at different water contents,

[0022] (302) A volume of the solvent to be tested, V1, is dropped into the CsPbBr3@PAA colloid, and its color under ultraviolet light is obtained. The color is compared with a colorimetric card to determine the water content or water content range of the solvent to be tested.

[0023] Preferably, the step (3) further includes a step (303), when the color of the solvent to be tested in step (302) can be further distinguished by the solvent with a volume of V2 in the color block of the corresponding volume on the colorimetric card, the solvent to be tested with a volume of V2 is dropped into the CsPbBr3@PAA colloid, and its fluorescence spectrum is measured to obtain the corresponding CIE coordinate color or its luminescent color is obtained under ultraviolet light, and the CIE coordinate color or luminescent color is compared with the colorimetric card to further determine the water content of the solvent to be tested.

[0024] Preferably, when the solvent volume is the same, as the water content in the solvent increases, the color of the color card changes from blue-purple, dark blue, cyan, turquoise to green in sequence; when the water content in the solvent is the same, as the solvent volume increases, the color of the color card changes from blue-purple, dark blue, cyan, turquoise to green in sequence.

[0025] Preferably, in step (1), the good solvent is at least one of DMF, DMA, DMSO, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, glycerol, formamide and acetonitrile; and the poor solvent is at least one of toluene, benzene, petroleum ether, n-hexane, cyclohexane, dichloromethane, chloroform, carbon tetrachloride, dibromomethane, carbon disulfide, ether, ethyl acetate and isopropyl ether.

[0026] The good solvent is dimethylformamide, and the poor solvent is toluene or ether.

[0027] Preferably, the molar ratio of CsBr to PbBr2 is 1:2-2:1; the volume ratio of the poor solvent to the good solvent is (10-200):1; the concentration of CsBr in the precursor liquid is 0.02mmol / mL-0.04mmol / mL, and the concentration of PbBr2 in the precursor liquid is 0.02mmol / mL-0.04mmol / mL; the concentration of polyacrylic acid in the precursor liquid is 0.10mmol / mL-1.6mmol / mL; and the concentration of oleylamine in the precursor liquid is 0.038mmol / mL-0.6mmol / mL.

[0028] According to another aspect of the present invention, there is provided a method for preparing a colorimetric card, comprising the following steps:

[0029] (1) PbBr2 and CsBr as precursors were dissolved in a good solvent, and then oleylamine and polyacrylic acid were added as ligands and mixed evenly to obtain a precursor solution. A poor solvent was added to the precursor solution, and CsPbBr3@PAA colloid with blue-purple photoluminescence was obtained by supersaturated recrystallization at room temperature;

[0030] (2) Solvents with different water contents and volumes were added dropwise to equal amounts of CsPbBr3@PAA colloid to obtain mixtures. After standing for the same amount of time, the fluorescence spectra of the mixtures were measured, and the CIE coordinates corresponding to the fluorescence spectra were obtained to obtain a colorimetric card. The solvent to be tested was a solvent capable of dissolving polyacrylic acid.

[0031] According to yet another aspect of the present invention, a colorimetric card is provided.

[0032] In general, the above technical solutions conceived by the present invention can achieve at least the following beneficial effects compared with the prior art.

[0033] (1) The method for detecting the water content of a solvent provided by the present invention only requires dropping a water-containing solvent into a drug and observing the luminescent color with the naked eye. The luminescent color is then compared with a colorimetric card to determine the water content of the tested water-containing solvent. This method does not require instrument operation, is portable, is low-cost, and takes little time. It is applicable to moisture detection in various scenarios, such as laboratories, factories, and daily life. This solves the technical problems of the drying method, toluene method, chromatography, and Karl Fischer method, which require certain instrument conditions, are cumbersome to operate, and contain toxic reagents such as pyridine.

[0034] (2) The solvent water content detection method provided by the present invention can be flexibly used according to the need for detection accuracy. For example, if only the approximate range of the water content of the solvent to be tested is needed, a single test can be performed to determine it. If an accurate value is needed, a two-step operation can be performed. This method has high accuracy and resolution. Taking ethanol as an example, the lowest detectable ethanol concentration is 99.8%, and concentrations of 99.8%, 99%, 98%, 97%, 96%, 95%, and 94% can be accurately distinguished. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 (a) and (b) are the fluorescence spectrum and CIE coordinate position of the CsPbBr3@PAA complex solution, respectively;

[0036] Figure 2 Colorimetric card for testing the water content of methanol;

[0037] Figure 3 (a) and (b) show the fluorescence spectra and CIE coordinate changes after adding 40 μL of 95%-99.8% methanol to 2 mL of the drug, respectively.

[0038] Figure 4 Colorimetric card for testing the water content of ethanol;

[0039] Figure 5 (a) and (b) show the fluorescence spectra and CIE coordinate changes after adding 80 μL of 94%-99.8% ethanol to 2 mL of the drug, respectively.

[0040] Figure 6 Color card for testing the water content of isopropyl alcohol;

[0041] Figure 7 (a) and (b) show the fluorescence spectrum and CIE coordinate changes after adding 150 μL of 94%-99.8% isopropanol to 2 mL of the drug, respectively. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0043] Example 1

[0044] This embodiment provides a method for rapidly detecting the water content in a solvent based on perovskite color change, the method comprising:

[0045] Weigh 0.4 mmol CsBr and 0.4 mmol PbBr2 into a centrifuge tube, add 10 mL DMF, and sonicate to dissolve most of the CsBr and PbBr2. Measure 0.5 mL OAm into the above centrifuge tube and continue sonicating. Then weigh 5 g PAA and add it to the above centrifuge tube. Sonicate to dissolve all the above components to obtain a uniform, transparent, and viscous precursor liquid.

[0046] The concentrations of the components in the precursor solution were: [CsBr] = [PbBr2] = 0.04 mmol / mL, [PAA] = 0.5 g / mL, and [OAm] = 0.15 mmol / mL. 2.6 g of the precursor solution was weighed into a flask using an electronic balance. 100 mL of toluene was added under vigorous stirring, and blue-purple fluorescence immediately appeared.

[0047] The obtained drug luminescence position and CIE coordinates can be found in Figure 1 (a)-(b). Figure 1 (a) is the fluorescence spectrum of the drug at an excitation wavelength of 330 nm. Since it is partially broadened in the blue light and purple light regions, the drug exhibits blue-purple photoluminescence. Figure 1 (b) shows that its CIE coordinates are (0.1622, 0.0345).

[0048] The drug prepared by the above method was injected into 3 mL vials at a rate of 2 mL per vial. The vials were sealed with rubber stoppers and aluminum caps and stored in a refrigerator for use. In this example, the concentration of the 2 mL CsPbBr3@PAA colloid was determined by [Pb], where Pb concentration [Pb] = 1-200 mg L -1 .

[0049] Take the above drugs, take 40 μL of 95%-99.8% (V%) methanol, inject it into the drugs at one time, shake it quickly, and measure the fluorescence spectrum after leaving it at room temperature for 1 minute. Figure 3 As shown in (a), the corresponding CIE coordinates are Figure 3As shown in (b), the drug turns green and cyan respectively after adding 95% (V%) and 96% (V%) methanol, and turns blue after adding 97%-99.8% (V%) methanol.

[0050] By changing the added volume, we can get Figure 2 The colorimetric card of the methanol solvent shown in FIG. 1 and the corresponding CIE coordinate values ​​are shown in Table 1:

[0051] Table 1 Methanol detection color card corresponding to CIE coordinates

[0052]

[0053] When testing the water content of a solvent with an unknown water content, first take 40 μL of the unknown solvent, inject it into the medicine at one time, shake it quickly, and compare the colorimetry under a 365nm ultraviolet lamp after one minute. If it is cyan, the water content is 95% (V%), if it is cyan, the water content is 96% (V%), if it is blue, the water content range is 97%-99.8% (V%), then take the medicine again, take 50 μL of the unknown solvent and test it again according to the same method. If it is cyan, the water content range is 97%-98% (V%), if it is blue, the water content range is 99%-99.8% (V%).

[0054] Example 2

[0055] The difference between this embodiment and embodiment 1 is that ethanol is used as the test solvent, and 80 μL of 95%-99.8% (V%) ethanol is added. The fluorescence spectrum and CIE coordinates change as shown in FIG. Figure 5 As shown in (a)-(b) in the figure. Figure 4 The ethanol solution colorimetric card shown in FIG. 1 and the corresponding CIE coordinate values ​​are shown in Table 2.

[0056] Take 80 μL of ethanol for testing. When the ethanol concentration is 94%-95% (V%), it displays green, 96% displays cyan-blue, 97%-98% displays blue, and 99%-99.8% displays bluish-purple. If you need to accurately determine the water content, test it a second time. For example, if the first test is green, that is, the water content is determined to be between 94% and 95% (V%), then take another 40 μL test. If it turns cyan-green, it is 94% ethanol, and blue, it is 95% ethanol. If the first test is blue, take a second 100 μL test. If the result is cyan, it is judged to be 97% (V%), and blue, it is judged to be 98% (V%). If the first test is bluish-purple, take a second 200 μL test. If the result is cyan, it is judged to be 99% (V%), and blue, it is judged to be 99.8% (V%).

[0057] Table 2 CIE coordinates of ethanol detection colorimetric card

[0058]

[0059] Example 3

[0060] The difference between this example and Example 1 is that isopropanol is used as the test solvent. 150 μL of 95%-99.8% (V%) isopropanol is added to 2 mL of CsPbBr3@PAA colloid. The fluorescence spectrum and CIE coordinates change as shown in the following figure. Figure 7 As shown in (a)-(b), change the added volume and draw the Figure 6 The colorimetric card of the isopropyl alcohol solvent shown in FIG. 1 and the corresponding CIE coordinate values ​​are shown in Table 3.

[0061] Take 150 μL of isopropyl alcohol for testing. When the isopropyl alcohol concentration is 94%-95% (V%), it will appear green, 96% will appear cyan, 97%-98% will appear blue, and 99%-99.8% will appear bluish purple. If the water content needs to be accurately determined, a second test is required. For example, if the first test is cyan, it is determined that the water content is 94%-95% (V%). Then take another 50μL test. If it turns cyan, it is 94% ethanol, and if it turns blue, it is 95% ethanol. If the first test is bluish-purple, take 300μL for the second test. If the result is blue, it is judged to be 99% (V%), and if it is bluish-purple, it is judged to be 99.8% (V%). If the first test is blue, there are two options: ① Take 80μL for the second test. If the result is blue, it is judged to be 97% (V%), and if it is bluish-purple, it is judged to be 98% (V%); ② Take 500μL for the second test. If the result is cyan, it is judged to be 97% (V%), and if it is blue, it is judged to be 98% (V%).

[0062] Table 3 Isopropyl alcohol detection color chart corresponding to CIE coordinates

[0063]

[0064] Example 4

[0065] The difference between this embodiment and embodiment 2 is that this embodiment uses a fluorescence spectroscopy method to obtain the color of the mixture after the test solvent is added to the CsPbBr3@PAA colloid, measures its fluorescence spectrum, converts the spectral data into CIE coordinate color, and compares the color with a colorimetric chart to determine the water content of the test solvent.

[0066] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for rapidly detecting the water content in a solvent based on the color change of CsPbBr3 perovskite nanocrystals, characterized in that: The following steps are involved: (1) PbBr2 and CsBr as precursors are added to a good solvent and dissolved, and then oleylamine and polyacrylic acid are added as ligands and mixed evenly to obtain a precursor liquid, and a poor solvent is added to the precursor liquid, and a CsPbBr3 and PAA composite colloid with blue-purple photoluminescence is obtained by supersaturated recrystallization at room temperature; the good solvent is at least one of DMF, DMA, DMSO, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, glycerol, formamide and acetonitrile; the poor solvent is at least one of toluene, benzene, petroleum ether, n-hexane, cyclohexane, dichloromethane, chloroform, carbon tetrachloride, dibromomethane, carbon disulfide, ether, ethyl acetate and isopropyl ether; (2) Solvents with different water contents and volumes were added dropwise to equal amounts of CsPbBr3 and PAA composite colloids to obtain mixtures. After standing for the same amount of time, the fluorescence spectra of the mixtures were measured to obtain the CIE coordinate colors corresponding to the fluorescence spectra and obtain a colorimetric card. (3) Dropping the solvent to be tested into the CsPbBr3 and PAA composite colloid, measuring its fluorescence spectrum to obtain the corresponding CIE coordinate color or obtaining its luminescent color under ultraviolet light, comparing the CIE coordinate color or luminescent color with a colorimetric card to determine the water content of the solvent to be tested; wherein the solvent to be tested is a solvent that can dissolve polyacrylic acid.

2. The method according to claim 1, wherein The solvent to be tested is at least one of methanol, ethanol, ethylene glycol, n-propanol, isopropanol, propylene glycol, n-butanol, isobutanol, sec-butanol, tert-butanol, glycerol, tetrahydrofuran, pyridine, acetonitrile, acetone, methylamine, ethylamine, triethylamine, aniline, formamide, N-methylformamide, DMF, DMA, and DMSO.

3. The method according to claim 1 or 2, wherein: In the step (2), the colorimetric card is obtained by plotting the water content of the solvent as variable 1, the volume of the solvent as variable 2, and the CIE coordinate color of the mixture as the result.

4. The method according to claim 1 or 2, wherein: The step (3) includes the following steps: (301) Select the solvent volume V1 in the colorimetric card that can show different colors at different water contents. (302) A volume of V1 of the solvent to be tested is dropped into the CsPbBr3 and PAA composite colloid, and its fluorescence spectrum is measured to obtain the corresponding CIE coordinate color or obtain its luminescent color under ultraviolet light. The CIE coordinate color or luminescent color is compared with a colorimetric card to determine the water content of the solvent to be tested.

5. The method according to claim 4, wherein The step (3) further includes a step (303), when the color of the solvent to be tested in step (302) can be further distinguished from the water content of the solvent by the solvent with a volume of V2 in the color block of the corresponding volume on the colorimetric card, the solvent to be tested with a volume of V2 is dropped into the CsPbBr3@PAA colloid, its fluorescence spectrum is measured to obtain the corresponding CIE coordinate color or its luminescence color is obtained under ultraviolet light, and the CIE coordinate color or luminescence is compared with the colorimetric card to further determine the water content of the solvent to be tested.

6. The method according to claim 1, wherein When the solvent volume remains the same, as the water content in the solvent increases, the color of the color card changes from blue-purple, dark blue, cyan, turquoise to green in sequence; when the water content in the solvent remains the same, as the solvent volume increases, the color of the color card changes from blue-purple, dark blue, cyan, turquoise to green in sequence.

7. The method according to claim 1, wherein The molar ratio of CsBr to PbBr2 is 1:2-2:1; the volume ratio of the poor solvent to the good solvent is (10-200):1; the concentration of CsBr in the precursor liquid is 0.02 mmol / mL-0.04 mmol / mL, and the concentration of PbBr2 in the precursor liquid is 0.02 mmol / mL-0.04 mmol / mL; the concentration of polyacrylic acid in the precursor liquid is 0.10 mmol / mL-1.6 mmol / mL; and the concentration of oleylamine in the precursor liquid is 0.038 mmol / mL-0.6 mmol / mL.

8. A method for preparing a colorimetric card, characterized in that: The following steps are involved: (1) PbBr2 and CsBr as precursors are added to a good solvent and dissolved, and then oleylamine and polyacrylic acid are added as ligands and mixed evenly to obtain a precursor liquid, and a poor solvent is added to the precursor liquid, and a CsPbBr3 and PAA composite colloid with blue-purple photoluminescence is obtained by supersaturated recrystallization at room temperature; the good solvent is at least one of DMF, DMA, DMSO, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, glycerol, formamide and acetonitrile; the poor solvent is at least one of toluene, benzene, petroleum ether, n-hexane, cyclohexane, dichloromethane, chloroform, carbon tetrachloride, dibromomethane, carbon disulfide, ether, ethyl acetate and isopropyl ether. (2) Solvents with different water contents and volumes were added dropwise to equal amounts of CsPbBr3 and PAA composite colloids to obtain mixtures. After standing for the same period of time, the fluorescence spectra of the mixtures were measured to obtain the CIE coordinate colors corresponding to the fluorescence spectra and obtain a colorimetric card, wherein the solvent to be tested is a solvent that can dissolve polyacrylic acid.

9. A colorimetric card, characterized in that: It is prepared by the method according to claim 8.

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