Elliptical KAP crystal and preparation method thereof

Abstract

The invention relates to the field of KAP crystals, in particular to an elliptical KAP crystal and a preparation method thereof. Through MOFs in-situ growth, atomization spraying induced molecular orientation assembly and ultraviolet light initiated crosslinking, the mechanical strength, the super-hydrophobicity and the irradiation stability are improved, meanwhile, the optical performance of the crystal is kept, and a brand new solution is provided for application of the KAP crystal in the emerging fields of ocean sensing, flexible photoelectricity and the like.

Description

Technical Field

[0001] The present invention relates to the field of KAP crystals, and specifically to an elliptical KAP crystal and a preparation method thereof. Background Art

[0002] KAP crystal (potassium dihydrogen phosphate crystal, chemical formula KH2PO4), as a classic nonlinear optical material, due to its high nonlinear coefficient (d 36 ≈0.39 pm / V), wide light transmission band (200 - 1500 nm) and excellent frequency conversion efficiency, occupies an irreplaceable position in laser frequency conversion systems (such as frequency doubling of Nd:YAG lasers) and electro-optic modulation devices (such as high-speed optical switches). However, with the development of optoelectronic systems towards miniaturization, high power and extreme environment adaptability, the performance shortcomings of traditional KAP crystals have become increasingly prominent. The single crystal compressive strength of traditional KAP crystals is generally lower than 150 MPa, and it is prone to fragmentation in high-pressure packaging or mechanical vibration scenarios, resulting in device failure; moreover, the crystal surface is prone to deliquescence, severely restricting its application in high-humidity environments such as ocean exploration and tropical regions; in addition, its radiation tolerance is poor. When exposed to X-rays or high-energy particle beams for a long time, lattice defects rapidly accumulate, and the optical uniformity significantly decreases, restricting its service life in radiation imaging and space optical systems.

[0003] In the prior art, researchers have tried to improve the performance through composite reinforcement (such as adding ceramic particles) or surface hydrophobic coating (such as modification with silane coupling agents), but both have significant limitations: First, ceramic particles (such as Al2O3, ZrO2) or metal-organic framework (MOFs) materials (such as ZIF-8) are incorporated through mechanical mixing. However, the physical mixing method results in weak interfacial bonding force between the reinforcement phase and the matrix, low stress transfer efficiency, and limited improvement in compressive strength. More seriously, micron-sized pores are easily formed at the heterogeneous interface, which instead become rapid migration channels for deliquescent ions (such as K + , PO4 3- ), and the deliquescence rate is even higher than that of pure KAP crystals. The traditional hydrophobic coating process is prone to cause disordered molecular arrangement, the water contact angle is difficult to exceed 110°, and the bonding strength between the coating and the matrix is low, and it is easy to peel off during long-term use; Second, silane coupling agents or long-chain alkane coatings are applied by impregnation or spin coating. Although such processes can temporarily improve the hydrophobicity, the coating molecules are arranged disorderly, and they are only physically adsorbed to the crystal surface, and are easy to peel off under thermal and humid cycling or mechanical friction; Finally, heavy metal ions (such as Pb 2+ , Bi 3+ ) are introduced for doping to absorb high-energy radiation. However, heavy metal doping will significantly change the crystal energy band structure, resulting in a decrease in optical transmittance and inducing secondary radiation damage, which runs counter to the low-loss requirements of high-precision optical devices.

[0004] In recent years, due to their tunable pore sizes and surface chemical properties, metal-organic framework (MOF) materials have been regarded as potential solutions for enhancing crystal performance. However, the interfacial compatibility with inorganic crystals and the structural integration design remain technical challenges. How to achieve the in-situ construction of MOF networks, the chemical bonding of hydrophobic interfaces, and the synchronous repair of crystal defects through process innovation has become the key to breaking through the performance bottleneck of KAP crystals.

[0005] In view of the above problems, the present invention proposes a multi-step collaborative regulation strategy. Through in-situ growth of MOFs, atomized spraying-induced molecular orientation assembly, and ultraviolet light-induced crosslinking, while enhancing mechanical strength, superhydrophobicity, and radiation stability, the optical properties of the crystals are maintained, providing a new solution for the application of KAP crystals in emerging fields such as marine sensing and flexible optoelectronics. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides an elliptical KAP crystal and a preparation method thereof.

[0007] A preparation method of an elliptical KAP crystal includes the following steps: (1) Mix potassium dihydrogen phosphate and an ethanol aqueous solution of 65 - 75 wt% according to a mass ratio of (30 - 40):(60 - 70), heat to 54 - 56 °C to form a solution with a concentration of 34 - 36 wt%. Add a zinc-based MOF precursor and a dispersant to the solution, and ultrasonically oscillate for 30 - 40 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, start cooling from 54 - 56 °C at a rate of 0.7 - 0.9 °C / day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 42 - 44 °C, inject an aqueous sodium benzoate solution at 42 - 44 °C, and continue to cool at a rate of 0.7 - 0.9 °C / day to 39 - 41 °C to obtain a solution containing KAP crystals; (3) Use a nitrogen-assisted atomized spraying system to inject an ethanol solution containing 0.9 - 1.1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2). Subsequently, heat the system to 59 - 61 °C at a rate of 1 - 3 °C / min and keep it at a constant temperature for 5 - 7 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.4 - 0.6 wt% benzophenone photoinitiator according to a mass ratio of 1:(4 - 6), stir, irradiate with ultraviolet light for 14 - 16 min, take out, wash, and dry to obtain the elliptical KAP crystal.

[0008] The zinc-based MOFs precursor described in step (1) is formed by mixing zinc nitrate and 2-methylimidazole at a molar ratio of 1:(3.9 - 4.1), and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is (1 - 3):100.

[0009] The dispersant described in step (1) is at least one of polyvinylpyrrolidone, cetyltrimethylammonium bromide, and hydroxypropyl methylcellulose, and the addition amount of the dispersant is 0.1 - 0.2 wt% of the solution mass.

[0010] The frequency of the ultrasonic wave described in step (2) is 9 - 11 kHz and the power is 45 - 55 W.

[0011] The concentration of the sodium benzoate aqueous solution described in step (2) is 0.04 - 0.06 mol / L, and the addition amount is 1 - 3% of the volume of solution A obtained in step (1).

[0012] The carrier for atomizing and spraying described in step (3) is nitrogen at 0.19 - 0.21 Mpa; the spraying distance is 10 - 15 cm; the spraying rate is 0.5 - 1 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to KAP crystals is (40 - 50):1.

[0013] The wavelength of the ultraviolet light described in step (4) is 365 nm and the power is 19 - 25 mW / cm².

[0014] In the present invention, through in-situ growth of MOFs, atomizing spraying to induce molecular orientation assembly, and ultraviolet light-induced crosslinking, while improving mechanical strength, superhydrophobicity, and irradiation stability, the crystal optical properties are maintained. First, in step (1), the present invention introduces the zinc-based MOFs precursor prepared from zinc nitrate and 2-methylimidazole into the KAP solution, and uses the nano-porous characteristics of MOFs and its surface charge distribution (isoelectric point pH 6.8) to form uniform heterogeneous nucleation sites under ultrasonic assistance. Zn in the MOFs framework 2+ and the carboxylic acid group (-COOH) in the KAP molecule are preferentially adsorbed on a specific crystal plane ({010} plane) of the crystal through coordination, inhibiting the growth rate in this direction, thereby breaking the cubic symmetry of the traditional KAP crystal and inducing the formation of an ellipsoidal morphology.

[0015] Secondly, in step (2), ultra-slow cooling combined with low-frequency ultrasonic intervention is adopted to precisely control the solution supersaturation. The micro-jet generated by the ultrasonic wave can remove the adsorbed impurities on the crystal surface and maintain an atomically flat growth interface of the {100} and {001} planes; and the timely introduction of the sodium benzoate aqueous solution, its Na + and K of KAP +Competitive adsorption occurs, further regulating the interfacial energy difference of different crystal planes, and finally achieving a stable size ratio of the long axis (along the

[100] direction) to the short axis (along the

[001] direction) of 1.5:1.

[0016] In step (3), in the crystal-solution coexistence system, the 11-Phosphonoundecylacrylate ethanol solution is uniformly dispersed into the mother liquor by nitrogen atomization spraying. The 11-Phosphonoundecyl acrylate molecules migrate to the surface of the KAP crystal by the confined diffusion effect of the MOFs pores. At a constant temperature of 60 °C, the intermolecular van der Waals force drives the hydrophobic chains (-CH 2- CH 2- ) to be vertically arranged to form a dense monolayer film, and this film layer is anchored to the crystal surface through hydrogen bonds, significantly improving the moisture resistance of the crystal.

[0017] In step (4), benzophenone generates active free radicals under ultraviolet light excitation, triggering the cross-linking reaction of the terminal double bonds of 11-Phosphonoundecylacrylate molecules to form a three-dimensional network structure. This step converts the physically adsorbed monolayer film into a chemically bonded protective layer, enabling the crystal to maintain surface integrity in an environment with a humidity of 90% RH.

[0018] Advantages of the present invention: Through in-situ growth of MOFs, atomization spraying-induced molecular orientation assembly, and ultraviolet light-induced cross-linking, the present invention improves the mechanical strength, superhydrophobicity, and irradiation stability while maintaining the optical properties of the crystal, providing a new solution for the application of KAP crystals in emerging fields such as ocean sensing and flexible optoelectronics. Specific embodiments

[0019] Potassium dihydrogen phosphate, CAS No.: 7758-11-4, product number: S24278, Shanghai Yuanye Bio-Technology Co., Ltd.

[0020] 11-Phosphonoundecyl acrylate, CAS No.: 915376-49-7.

[0021] Polyvinylpyrrolidone, purity: K-30, molecular weight 40000, product number: S30268, Shanghai Yuanye Bio-Technology Co., Ltd.

[0022] Example 1

[0023] A preparation method of an elliptical KAP crystal, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution at a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 43 °C, inject an aqueous sodium benzoate solution at 43 °C, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) using a nitrogen-assisted atomization spraying system. Subsequently, heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator at a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystals.

[0024] The zinc-based MOFs precursor described in step (1) is composed of zinc nitrate and 2-methylimidazole mixed at a molar ratio of 1:4, and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is 2:100.

[0025] The dispersant described in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0026] The frequency of the ultrasonic wave described in step (2) is 10 kHz and the power is 50 W.

[0027] The concentration of the aqueous sodium benzoate solution described in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0028] The carrier of the atomization spraying described in step (3) is 0.2 MPa nitrogen; the nitrogen spraying distance is 12 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to KAP crystals is 50:1.

[0029] The wavelength of the ultraviolet light described in step (4) is 365 nm and the power is 20 mW / cm².

[0030] Example 2

[0031] A preparation method of an elliptical KAP crystal, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution at a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, start cooling from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 43 °C, inject an aqueous sodium benzoate solution at 43 °C, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) by using a nitrogen-assisted atomization spraying system, then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator at a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystal.

[0032] The zinc-based MOFs precursor described in step (1) is composed of zinc nitrate and 2-methylimidazole mixed at a molar ratio of 1:4, and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is 1:100.

[0033] The dispersant described in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0034] The frequency of the ultrasonic wave described in step (2) is 10 kHz and the power is 50 W.

[0035] The concentration of the aqueous sodium benzoate solution described in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0036] The carrier of the atomization spraying described in step (3) is 0.2 MPa nitrogen; the nitrogen spraying distance is 12 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to KAP crystals is 50:1.

[0037] The wavelength of the ultraviolet light described in step (4) is 365 nm, and the power is 20 mW / cm².

[0038] Example 3

[0039] A method for preparing an elliptical KAP crystal, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution in a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 43 °C, inject an aqueous sodium benzoate solution at 43 °C, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) using a nitrogen-assisted atomization spraying system, then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator in a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystal.

[0040] The zinc-based MOFs precursor described in step (1) is composed of zinc nitrate and 2-methylimidazole mixed in a molar ratio of 1:4, and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is 3:100.

[0041] The dispersant described in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0042] The frequency of the ultrasonic wave described in step (2) is 10 kHz and the power is 50 W.

[0043] The concentration of the aqueous sodium benzoate solution described in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0044] The carrier for the atomizing spray in step (3) is nitrogen gas at 0.2 MPa; the nitrogen gas spraying distance is 12 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to the KAP crystals is 50:1.

[0045] The wavelength of the ultraviolet light in step (4) is 365 nm, and the power is 20 mW / cm².

[0046] Example 4

[0047] A method for preparing elliptical KAP crystals, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% aqueous ethanol solution in a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically vibrate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C per day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 43 °C, inject an aqueous sodium benzoate solution at 43 °C, and continue to cool at a rate of 0.8 °C per day to 40 °C to obtain a solution containing KAP crystals; (3) Use a nitrogen-assisted atomizing spray system to inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2), then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator in a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the said elliptical KAP crystals.

[0048] The zinc-based MOFs precursor in step (1) is composed of zinc nitrate and 2-methylimidazole mixed in a molar ratio of 1:4, and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is 2:100.

[0049] The dispersant in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0050] The frequency of the ultrasonic wave in step (2) is 10 kHz and the power is 50 W.

[0051] The concentration of the sodium benzoate aqueous solution described in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0052] The carrier for atomized spraying described in step (3) is nitrogen gas at 0.2 MPa; the nitrogen spraying distance is 15 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to the KAP crystal is 50:1.

[0053] The wavelength of the ultraviolet light described in step (4) is 365 nm, and the power is 20 mW / cm².

[0054] Example 5

[0055] A method for preparing an elliptical KAP crystal, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution in a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool down from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 43 °C, inject a sodium benzoate aqueous solution at 43 °C, and continue to cool down to 40 °C at a rate of 0.8 °C / day to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) by using a nitrogen-assisted atomized spraying system, then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator in a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystal.

[0056] The zinc-based MOFs precursor described in step (1) is composed of zinc nitrate and 2-methylimidazole mixed in a molar ratio of 1:4, and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is 2:100.

[0057] The dispersant described in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0058] The frequency of the ultrasonic wave described in step (2) is 10 kHz and the power is 50 W.

[0059] The concentration of the sodium benzoate aqueous solution described in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0060] The carrier for atomizing and spraying described in step (3) is nitrogen gas at 0.2 MPa; the nitrogen gas spraying distance is 10 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to the KAP crystal is 50:1.

[0061] The wavelength of the ultraviolet light described in step (4) is 365 nm and the power is 20 mW / cm².

[0062] Comparative Example 1

[0063] A preparation method of an elliptical KAP crystal, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution according to a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add ZIF-8 and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave to assist nucleation. When the temperature drops to 43 °C, inject a sodium benzoate aqueous solution at 43 °C, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) by using a nitrogen-assisted atomizing spraying system, then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator according to a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystal.

[0064] The mass ratio of ZIF-8 to potassium dihydrogen phosphate described in step (1) is 2:100.

[0065] In step (1), the dispersant is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0066] In step (2), the frequency of the ultrasonic wave is 10 kHz and the power is 50 W.

[0067] In step (2), the concentration of the sodium benzoate aqueous solution is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0068] In step (3), the carrier for atomizing spraying is nitrogen at 0.2 MPa; the nitrogen spraying distance is 12 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to the KAP crystal is 50:1.

[0069] In step (4), the wavelength of the ultraviolet light is 365 nm and the power is 20 mW / cm².

[0070] Comparative Example 2

[0071] A method for preparing an elliptical KAP crystal, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution at a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave-assisted nucleation. When the temperature drops to 43 °C, inject water at 43 °C, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) by using a nitrogen-assisted atomizing spraying system, then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator at a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystal.

[0072] The zinc-based MOF precursor described in step (1) is formed by mixing zinc nitrate and 2-methylimidazole at a molar ratio of 1:4, and the mass ratio of the zinc-based MOF precursor to potassium dihydrogen phosphate is 2:100.

[0073] The dispersant described in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0074] The frequency of the ultrasonic wave described in step (2) is 10 kHz and the power is 50 W.

[0075] The addition amount of water described in step (2) is 2% of the volume of solution A obtained in step (1).

[0076] The carrier for atomization spraying described in step (3) is nitrogen gas at 0.2 MPa; the nitrogen spraying distance is 12 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to KAP crystals is 50:1.

[0077] The wavelength of the ultraviolet light described in step (4) is 365 nm and the power is 20 mW / cm².

[0078] Comparative Example 3

[0079] A method for preparing elliptical KAP crystals, comprising the following steps: (1) Mix potassium dihydrogen phosphate and 70 wt% ethanol aqueous solution at a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOF precursor and a dispersant to the solution, and ultrasonically oscillate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C / day, and simultaneously apply ultrasonic wave to assist nucleation. When the temperature drops to 43 °C, inject an aqueous solution of sodium benzoate at 43 °C, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2), then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) Mix the 11-Phosphonoundecyl acrylate-modified KAP crystals obtained in step (3) and a toluene solution containing 0.5 wt% benzophenone photoinitiator in a mass ratio of 1:5, stir, irradiate with ultraviolet light for 15 min, take out, wash, and dry to obtain the elliptical KAP crystals.

[0080] The zinc-based MOF precursor in step (1) is formed by mixing zinc nitrate and 2-methylimidazole in a molar ratio of 1:4, and the mass ratio of the zinc-based MOF precursor to potassium dihydrogen phosphate is 2:100.

[0081] The dispersant in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0082] The frequency of the ultrasonic wave in step (2) is 10 kHz and the power is 50 W.

[0083] The concentration of the sodium benzoate aqueous solution in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0084] The wavelength of the ultraviolet light in step (4) is 365 nm and the power is 20 mW / cm².

[0085] Comparative Example 4

[0086] A method for preparing elliptical KAP crystals, comprising the following steps: (1) Mix potassium dihydrogen phosphate and a 70 wt% ethanol aqueous solution in a mass ratio of 35:65, heat to 55 °C to form a solution with a concentration of 35 wt%, add a zinc-based MOF precursor and a dispersant to the solution, and ultrasonically vibrate for 30 min to obtain solution A; (2) Place solution A in a programmable temperature-controlled crystallization tank, cool from 55 °C at a rate of 0.8 °C / day, and apply ultrasonic wave-assisted nucleation at the same time. When the temperature drops to 43 °C, inject a 43 °C sodium benzoate aqueous solution, and continue to cool at a rate of 0.8 °C / day to 40 °C to obtain a solution containing KAP crystals; (3) Inject an ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) by using a nitrogen-assisted atomization spraying system, then heat the system to 60 °C at a rate of 2 °C / min and keep it at a constant temperature for 6 h. Finally, filter, wash, and dry to obtain the elliptical KAP crystals.

[0087] The zinc-based MOF precursor in step (1) is formed by mixing zinc nitrate and 2-methylimidazole in a molar ratio of 1:4, and the mass ratio of the zinc-based MOF precursor to potassium dihydrogen phosphate is 2:100.

[0088] The dispersant described in step (1) is polyvinylpyrrolidone, and the addition amount of the dispersant is 0.1 wt% of the solution mass.

[0089] The frequency of the ultrasonic wave described in step (2) is 10 kHz and the power is 50 W.

[0090] The concentration of the sodium benzoate aqueous solution described in step (2) is 0.05 mol / L, and the addition amount is 2% of the volume of solution A obtained in step (1).

[0091] The carrier for atomizing spraying described in step (3) is nitrogen at 0.2 MPa; the nitrogen spraying distance is 12 cm; the spraying rate is 0.8 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to KAP crystals is 50:1.

[0092] Test Example 1

[0093] Mechanical property test (micro-indentation test) Instrument: AntonPaar MCT3 Sample preparation: Cut the elliptical KAP crystals prepared in the examples and comparative examples into 5×5×2 mm³ thin slices, and polish the surface to a mirror surface (Ra < 0.1 μm); Parameter setting: Select a Vickers indenter, with a loading force of 100 mN, a loading / unloading rate of 10 mN / s, and a holding time of 10 s; Test procedure: Randomly select 10 test points on the crystal surface, avoiding the edge and defect areas; record the load-displacement curve, and calculate the elastic modulus (E) and hardness (H) by the Oliver-Pharr method; The compressive strength (σ) is converted by the formula: σ = H × 3.3 (applicable to brittle materials); Data screening: Eliminate outliers (deviation > 15%), and take the average value of the remaining data.

[0094] The results are shown in Table 1.

[0095] Table 1: Results of mechanical property determination

[0096] Hydrophobic and anti-deliquescence property test: Instrument: Contact angle measurement (DSA100) + humidity cycling chamber; Contact angle measurement: Place the crystal in a constant temperature and humidity environment (25 °C, 50% RH) to equilibrate for 24 h; deposit 5 μL of ultrapure water droplets on the surface with a micro syringe, and record the droplet morphology with a high-speed camera (30 frames per second); fit the contact angle through the Young-La equation, and take the average value at 5 different positions.

[0097] Humidity cycling experiment: Set the cycling conditions: 40°C / 95%RH (12h) → 25°C / 50%RH (12h), for a total of 10 cycles; After each cycle, weigh the mass of the crystal (precision 0.1 mg), and calculate the deliquescence rate: Deliquescence rate = ; is the total mass change; : exposed area; : total duration; The results are shown in Table 2.

[0098] Table 2: Test results of hydrophobic anti-deliquescence performance

[0099] Test Example 3

[0100] Functional stability test (full width at half maximum of X-ray diffraction peak): Instrument: Bruker D8 Advance; Sample fixation: Fix the crystal on the sample stage to ensure that the test surface is parallel to the incident angle of the X-ray; Parameter settings: CuKα ray (λ = 1.5406 Å), scanning range 5 - 50° (2θ), step size 0.02°, scanning speed 2° / min; Repeated scanning: Continuously scan the same area 200 times, and record the intensity change of the main diffraction peak (such as the KAP characteristic peak); Attenuation rate calculation: Attenuation rate = (1 - 200 / 1) × 100%; : peak intensity at the nth scan; Table 3: Stability test results

[0101] From the test results in Table 1, Table 2, and Table 3, it can be seen that the elliptical KAP crystal in Example 1 of the present invention exhibits the optimal comprehensive performance, and its compressive strength, water contact angle, deliquescence rate, and diffraction peak attenuation rate are all significantly better than those of the comparative examples. This performance advantage stems from the following three points: First, in the growth process of the elliptical KAP crystal in Example 1, ZIF-8 precursor is used for gradient penetration to form a through-type three-dimensional reinforcement framework, endowing the crystal with high compressive strength; Second, sodium benzoate is used to stagewise regulate the crystal growth, synchronously inhibiting internal cracks and surface adsorption defects, and reducing the deliquescence rate to 12.5% of that of traditional crystals; Finally, 11-Phosphonoundecyl acrylate is atomized and sprayed combined with ultraviolet crosslinking to achieve vertical and oriented arrangement of hydrophobic molecules, and covalent bonding is used to inhibit interface defects, enhancing its hydrophobic performance.

[0102] It was found by comparing Example 1 with Comparative Example 1 that in Comparative Example 1, commercial ZIF-8 was directly mixed, and its compressive strength decreased by 46.2% compared with Example 1, and the deliquescence rate increased to 3 times that of Example 1. The present invention believes that the in-situ infiltration process of the ZIF-8 precursor can interlock the ZIF-8 precursor with the KAP lattice through hydrogen bonds / van der Waals forces to form a continuous reinforcement network, block the migration path of deliquescent ions, and at the same time absorb X-ray energy to reduce the diffraction peak attenuation rate.

[0103] It was found by comparing Example 1 with Comparative Example 2 that in Comparative Example 2, sodium benzoate was not used to stagewise regulate crystal growth, and the deliquescence rate reached 0.062 mg / cm²·h.

[0104] It was found by comparing Example 1 with Comparative Example 3 that in Comparative Example 3, 11-Phosphonoundecyl acrylate was modified by the traditional impregnation method, and its water contact angle decreased by 25.7% compared with Example 1, and the elastic modulus decreased by 18.8%. The present invention found that atomized spraying can induce the ordered assembly of 11-Phosphonoundecyl acrylate molecules perpendicular to the crystal surface, and at the same time, the rapid solvent evaporation fills the surface microcracks. However, due to the flat laying of molecules in the impregnation method, the hydrophobicity and mechanical properties deteriorate.

[0105] It was found by comparing Example 1 with Comparative Example 4 that in Comparative Example 4, the photoinitiator was cancelled, and 11-Phosphonoundecyl acrylate was only cured by heating, and its deliquescence rate and attenuation rate were both significantly higher than those of Example 1. The present invention speculates that the covalent cross-linking of the terminal double bonds of 11-Phosphonoundecyl acrylate initiated by ultraviolet light can form a dense network, while thermal curing only relies on physical entanglement, and the interfacial pores lead to increased water molecule penetration and irradiation damage.

[0106] Compared with the complex processes of traditional KAP crystals that require multiple layers of coating or composite shielding layers, such as anti-deliquescence coating + mechanical reinforcement layer, this method simultaneously improves the mechanical properties, hydrophobicity and irradiation stability through integrated design, providing a new solution for the controllable preparation, performance customization and environmental adaptation of functional crystal materials.

Claims

1. A method for preparing an elliptical KAP crystal, characterized in that: The following steps are involved: (1) Potassium dihydrogen phosphate and 65-75 wt% ethanol aqueous solution were mixed in a mass ratio of (30-40): (60-70), heated to 54-56° C. to form a solution with a concentration of 34-36 wt%, added a zinc-based MOFs precursor and a dispersant to the solution, and ultrasonically vibrated for 30-40 min to obtain a solution A; (2) placing solution A in a programmable temperature-controlled crystallization tank, cooling the solution from 54-56°C at a rate of 0.7-0.9°C / day, and applying ultrasound to assist nucleation. When the temperature drops to 42-44°C, inject a 42-44°C sodium benzoate aqueous solution, and continue cooling the solution to 39-41°C at a rate of 0.7-0.9°C / day to obtain a solution containing KAP crystals. (3) injecting an ethanol solution containing 0.9-1.1 wt% 11-Phosphonoundecyl acrylate into the solution containing KAP crystals obtained in step (2) using a nitrogen-assisted atomization spray system, then heating the system to 59-61° C. at a rate of 1-3° C. / min and maintaining the temperature for 5-7 h, and finally filtering, washing, and drying to obtain 11-Phosphonoundecyl acrylate-modified KAP crystals; (4) The 11-Phosphonoundecyl acrylate modified KAP crystals obtained in step (3) and a toluene solution containing 0.4-0.6 wt % of a benzophenone photoinitiator are mixed and stirred in a mass ratio of 1:(4-6), irradiated with ultraviolet light for 14-16 min, taken out, washed, and dried to obtain the elliptical KAP crystals.

2. The method for preparing an elliptical KAP crystal according to claim 1, characterized in that: The zinc-based MOFs precursor in step (1) is prepared by mixing zinc nitrate and 2-methylimidazole in a molar ratio of 1:(3.9-4.1), and the mass ratio of the zinc-based MOFs precursor to potassium dihydrogen phosphate is (1-3):

100.

3. The method for preparing an elliptical KAP crystal according to claim 1, characterized in that: The dispersant in step (1) is at least one of polyvinyl pyrrolidone, hexadecyl trimethyl ammonium bromide and hydroxypropyl methylcellulose, and the amount of the dispersant added is 0.1-0.2 wt % of the solution mass.

4. The method for preparing an elliptical KAP crystal according to claim 1, characterized in that: The frequency of the ultrasonic wave in step (2) is 9-11 kHz and the power is 45-55 W.

5. The method for preparing an elliptical KAP crystal according to claim 1, characterized in that: The concentration of the sodium benzoate aqueous solution in step (2) is 0.04-0.06 mol / L, and the amount added is 1-3% of the volume of solution A obtained in step (1).

6. The method for preparing an elliptical KAP crystal according to claim 1, characterized in that: The carrier of the atomized spray in step (3) is 0.19-0.21 MPa nitrogen; the spraying distance is 10-15 cm; the spraying rate is 0.5-1 mL / min, and the mass ratio of the ethanol solution containing 1 wt% 11-Phosphonoundecyl acrylate to the KAP crystals is (40-50):

1.

7. The method for preparing an elliptical KAP crystal according to claim 1, characterized in that: The wavelength of the ultraviolet light in step (4) is 365 nm and the power is 19-25 mW / cm².

8. An elliptical KAP crystal, characterized in that: The elliptical KAP crystal is prepared by the preparation method of any one of claims 1 to 7.

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