Zeolite imidazate framework and black phosphorus nanosheet compounded multifunctional flame retardant as well as preparation method and application thereof
By preparing a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets, the shortcomings of traditional flame retardant materials in fire resistance, heat insulation and electromagnetic compatibility among high-performance materials have been solved. This has achieved a synergistic improvement in high-efficiency flame retardancy, broadband wave absorption and thermal conductivity, and is suitable for aerospace, electronic equipment and other fields.
Patent Information
- Application Number
- CN202610009076.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-06
- Publication Date
- 2026-04-07
AI Technical Summary
Existing flame-retardant materials cannot simultaneously meet the requirements of high-performance materials for fire resistance, heat insulation, and electromagnetic compatibility. Traditional microwave absorbing materials have problems such as narrow bandwidth, high density, and poor compatibility, and cannot meet the multi-functional needs of high-end fields such as aerospace and electronic equipment.
By preparing a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets, the flame retardant efficiency is improved and broadband wave absorption capability is imparted by the synergistic effect of ferrocene-modified zeolite imidazole ester framework and black phosphorus nanosheets. The multifunctional synergistic optimization is achieved by combining porous and layered structures.
It achieves a synergistic improvement in high-efficiency flame retardancy, broadband wave absorption and thermal conductivity, reduces the generation of toxic gases, conforms to the development trend of green materials, and broadens the application scope.
Smart Images
Figure CN121801160A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets, its preparation method, and its application, belonging to the field of flame retardant technology. Background Technology
[0002] With the rapid development of modern industry, the demand for high-performance materials in aerospace, electronic equipment, construction and other fields is constantly increasing. These fields place extremely high demands on the fire resistance and electromagnetic compatibility of materials.
[0003] Traditional flame-retardant materials are mainly divided into two categories: organic flame retardants and inorganic flame retardants. Organic flame retardants, such as halogen compounds (bromines, chlorides) and phosphorus compounds (phosphate esters, phosphonates), while exhibiting good flame-retardant effects, produce large amounts of toxic and harmful gases (such as hydrogen halides) during combustion, posing serious threats to the environment and human health. Furthermore, organic flame retardants have poor thermal stability, making them unsuitable for applications in high-temperature environments. Inorganic flame retardants, such as aluminum hydroxide and magnesium hydroxide, are environmentally friendly and have good thermal stability, but their flame-retardant efficiency is low, and their compatibility with matrix materials is poor, making it difficult to meet the flame-retardant performance requirements of high-performance materials. Therefore, nanocomposite materials are gradually gaining attention as novel flame-retardant materials. For example, metal-organic frameworks (MOFs) materials, due to their unique pore structure and tunable chemical composition, are widely studied and used in the field of flame retardancy.
[0004] Coatings play a vital role in the field of material surface protection, with widespread applications in aerospace, electronics, construction, and automotive industries. Traditional coatings primarily provide corrosion resistance, abrasion resistance, and decorative properties; however, with technological advancements, their functionality is expanding towards multi-functionality. For example, coatings with flame-retardant, heat-insulating, and electromagnetic shielding properties have been developed to meet the comprehensive needs of high-performance materials. However, existing coatings still have shortcomings in flame-retardant and wave-absorbing properties, making it difficult to simultaneously meet the requirements of fire resistance, heat insulation, and electromagnetic compatibility. Meanwhile, the multi-functionality of flame-retardant materials is gradually becoming a research hotspot. For instance, by adding nanomaterials (such as nanoclay and carbon nanotubes) or modifiers, the flame-retardant properties of materials can be significantly improved, while simultaneously endowing them with new functions such as heat insulation, conductivity, and wave absorption. Furthermore, phosphorus-nitrogen-silicon synergistic flame-retardant technology inhibits combustion through multiple mechanisms (such as char formation, gas-phase flame retardancy, and dilution of combustible gases), while reducing the amount of traditional flame retardants used, thus improving the environmental performance of materials.
[0005] Meanwhile, electromagnetic wave absorbing materials are experiencing rapid development. With the continuous advancement of military stealth technology and the increasing demand for electromagnetic compatibility in civilian fields such as 5G communication and intelligent transportation, the application scenarios of electromagnetic wave absorbing materials are becoming increasingly widespread. Although traditional magnetic metal powders, carbon materials, and conductive polymers can absorb electromagnetic waves, they suffer from problems such as narrow absorption bandwidth, high density, and poor compatibility, making it difficult to meet the needs of modern electronic equipment and military stealth technology.
[0006] In most applications of microwave absorbing coatings, there are also high standards of fire resistance and flame retardancy requirements. For example, electronic devices release a large amount of heat during operation, posing a significant fire hazard. To minimize fire damage, effectively suppressing the spread of fire is crucial. Furthermore, MOFs possess a porous structure and considerable microwave absorption potential. Therefore, synthesizing excellent flame-retardant microwave absorbing coatings has become a highly challenging and significant research direction.
[0007] The inventor's team has previously conducted related research and published results (Adv. Funct. Mater., 2500800 (2025)): Based on the zeolite imidazole ester framework (ZIF-67), an acidic polymer DHPPC was anchored onto the ZIF-67 surface using an ice bath slow etching process to prepare a ZIF@DHPPC composite coating with a core-pore structure. This coating, after being loaded onto the surface of flexible polyurethane (FPUF) using a solution immersion method, exhibited excellent flame-retardant properties. Meanwhile, this coating also endows FPUF with excellent noise reduction performance. Unmodified FPUF can only reduce everyday noise levels greater than 100dB to approximately 80dB, with a sound absorption coefficient of less than 0.3 in the 2000-3000Hz range. In contrast, FPUF-3 (5g / 100mL) modified with the ZIF@DHPPC coating can reduce noise to 60.5-66.4dB (noise reduction >35%), with a sound absorption coefficient exceeding 0.95 in this frequency band, significantly improving the noise reduction effect of FPUF. This preliminary work verifies that the porous structure of MOFs can achieve efficient sound absorption through multi-path reflection and absorption of sound waves, laying a theoretical foundation for the development of MOF-based multifunctional coatings.
[0008] However, previous research on ZIF@DHPPC coatings only focused on sound wave absorption, without addressing electromagnetic wave shielding or absorption, thus failing to meet the critical electromagnetic compatibility requirements of high-end fields such as aerospace and electronic equipment. In these high-end fields, the requirements for "fire resistance" and "wave absorption" often coexist—for example, stealth coatings for military equipment need to possess both broadband wave absorption capabilities and fire safety, while electronic device casings need to balance flame retardancy and electromagnetic interference protection. Traditional wave-absorbing materials (such as magnetic metal powders and carbon nanotubes) can absorb electromagnetic waves, but they suffer from high density and poor compatibility with flame-retardant components, easily leading to a decrease in coating flame-retardant efficiency or damage to lightweight performance after addition. Existing MOFs-based flame-retardant materials do not consider electromagnetic performance design and lack a technical solution to achieve integrated "flame retardancy-wave absorption" dual functions through component synergy. Summary of the Invention
[0009] In view of this, the purpose of this invention is to provide a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets, its preparation method, and its application.
[0010] To achieve the above objectives, the technical solution of the present invention is as follows.
[0011] A multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets is disclosed. The flame retardant is first obtained by reacting and calcining ferrocene formaldehyde with an aminated zeolite imidazole ester framework to obtain a ferrocene zeolite imidazole ester framework, and then combining the ferrocene zeolite imidazole ester framework with black phosphorus nanosheets.
[0012] A method for preparing a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets, as described in this invention, includes the following steps: (1) The zeolite imidazole ester framework was aminated and the resulting aminated zeolite imidazole ester framework was dispersed in methanol to obtain a dispersion. (2) Add the methanol solution of ferrocene formaldehyde to the dispersion, heat at 55-65℃ for 12-24h, cool after the reaction, centrifuge, separate, wash, and dry to obtain the solid; (3) The solid is placed in a tube furnace and heated to 400-800℃ under nitrogen conditions and kept at that temperature for 2-4 hours to obtain a calcined zeolite imidazole ester skeleton grafted with ferrocene. (4) Preparation of black phosphorus nanosheets; (5) The ferrocene-grafted zeolite imidazole ester skeleton and black phosphorus nanosheets are dispersed in ethanol, sonicated for 1-2 hours, centrifuged, separated, washed, and dried to obtain the precursor; wherein, the ratio of the ferrocene-grafted zeolite imidazole ester skeleton to black phosphorus nanosheets and ethanol is 80-90 mg: 10-20 mg: 1-10 ml. (6) The precursor is placed in a tube furnace and heated to 200-300℃ under nitrogen conditions and kept at that temperature for 0.5-1h to obtain a multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets.
[0013] Preferably, in step (1), the zeolite imidazole ester framework is ZIF-67; more preferably, the ratio of the aminated zeolite imidazole ester framework to methanol is 0.5g:50-100ml.
[0014] Preferably, in step (2), the ratio of ferrocene formaldehyde to methanol in the ferrocene formaldehyde solution is 0.5g: 50-100ml; Preferably, in step (2), the ratio of ferrocene formaldehyde to the aminated zeolite imidazole ester framework is 1g:0.5-1.5g.
[0015] Preferably, in steps (2) and (5), the drying temperature is 50-60℃ and the drying time is 12-24h.
[0016] Preferably, in steps (3) and (6), the heating rate is 5-10℃ / min.
[0017] Preferably, in step (4), black phosphorus is dispersed in N-methylpyrrolidone and ultrasonically dispersed evenly to obtain a black phosphorus nanosheet dispersion. The black phosphorus nanosheet dispersion is centrifuged at 3000-4000 rpm for 8-12 min, and the supernatant is centrifuged at 10000-12000 rpm for 8-12 min. The filter cake is washed with ethanol and then dried in an oven at 50-60℃ for 12-24 h to obtain black phosphorus nanosheets. More preferably, the ratio of black phosphorus to N-methylpyrrolidone is 1 mg: 50-100 ml.
[0018] The application of a multifunctional flame retardant, which is a composite of zeolite imidazole ester framework and black phosphorus nanosheets as described in this invention, in flexible polyurethane.
[0019] Beneficial effects This invention provides a multifunctional flame retardant composed of a zeolite imidazolium ester framework and black phosphorus nanosheets. It fully utilizes the synergistic effect of ferrocene-modified zeolite imidazolium ester framework and black phosphorus nanosheets, improving flame retardant efficiency while also exhibiting high thermal conductivity and excellent microwave absorption properties, thus broadening its application range in high-performance materials. The specific advantages of this flame retardant are as follows: (1) Higher flame retardant efficiency: The flame retardant performance of the material is significantly improved by combining the ferrocene-modified zeolite imidazole ester framework with black phosphorus nanosheets, while avoiding the problem of toxic gas generation during the combustion of traditional halogen flame retardants. The zeolite imidazole ester framework used in this invention is a metal-organic framework material with high porosity and tunable chemical composition. By introducing ferrocene groups into the zeolite imidazole ester framework, not only is the thermal stability of the material enhanced, but free radical scavengers are also generated during combustion, thereby more effectively inhibiting the combustion reaction. In addition, the porous structure of MOFs can adsorb and isolate combustible gases, further improving the flame retardant effect.
[0020] (2) Excellent microwave absorption performance: The introduction of black phosphorus nanosheets endows the material with broadband microwave absorption capability, solving the problems of narrow bandwidth and poor compatibility of traditional microwave absorbing materials. In this invention, black phosphorus nanosheets, as a two-dimensional material, have a unique electronic structure and excellent electromagnetic properties. Its high specific surface area and layered structure can effectively absorb electromagnetic waves and convert them into heat energy through dielectric loss and magnetic loss. In addition, the layered structure of black phosphorus nanosheets forms multi-path reflection and absorption in the composite material, further enhancing the microwave absorption effect. At the same time, the porous structure of the zeolite imidazole ester framework can synergistically work with black phosphorus nanosheets to broaden the microwave absorption bandwidth. Its pore structure can adjust the propagation path of electromagnetic waves and increase the residence time of electromagnetic waves in the material, thereby improving the microwave absorption efficiency.
[0021] (3) Multifunctional synergistic optimization: The composite material of the present invention not only has efficient flame retardant properties, but also has good thermal conductivity and wave absorption properties, realizing the synergistic optimization of multiple functions and broadening its application range in high-performance materials.
[0022] (4) Environmental friendliness: By optimizing the material composition and preparation process, the use of traditional flame retardants is reduced, thus lowering the negative impact on the environment and conforming to the development trend of green materials. The zeolite imidazole ester framework and black phosphorus nanosheets used in this invention are both environmentally friendly materials. The synthesis process of the zeolite imidazole ester framework does not require the use of toxic and harmful organic solvents, and its decomposition products are non-toxic metal oxides and small organic molecules. Black phosphorus nanosheets are a naturally occurring two-dimensional material, and no harmful byproducts are generated during their production and use.
[0023] This invention provides a method for preparing a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets. The method involves amylating the zeolite imidazole ester framework, modifying it by grafting ferrocene, and finally compositing it with black phosphorus nanosheets. Attached Figure Description
[0024] Figure 1 The image shown is a transmission electron microscope (TEM) image of the flame retardant prepared in the examples.
[0025] Figure 2 This is a mapping diagram of the Fe element in the flame retardant prepared in the examples.
[0026] Figure 3 This is a mapping diagram of the P element in the flame retardant prepared in the examples.
[0027] Figure 4 Three-dimensional reflection loss curves for pure FPUF (a) and FPUF with added FZ / BPNS (b).
[0028] Figure 5 shows the two-dimensional reflection loss curves of pure FPUF (a) and FPUF with added FZ / BPNS (b). Detailed Implementation
[0029] The present invention will be further described in detail below with reference to specific embodiments.
[0030] Example 1 A method for preparing a nanofunctional flame retardant composed of a ferrocene-modified zeolite imidazole ester framework and black phosphorus nanosheets includes the following steps: Preparation of S1 and ZIF-67: 2.91g of cobalt nitrate hexahydrate and 3.28g of 2-methylimidazole were dissolved in 100ml of methanol respectively. After mixing, the mixture was stirred for 1 hour, then allowed to stand for 24 hours. The solid was separated by centrifugation, washed three times with methanol, and dried in an oven at 60℃ for 24 hours to obtain ZIF-67. S2, Aminated ZIF-67: 0.5 g of ZIF-67 was dispersed in 50 ml of methanol by sonication in a water bath for 10 minutes. Then, 0.5 g of 3,5-diamino-1,2,4-triazole was dissolved in 50 ml of methanol. The mixture was stirred and reacted for 12 hours. The solid was separated by centrifugation, washed three times with methanol, and dried in a 60°C oven for 24 hours to obtain aminated ZIF-67 (NH2-ZIF). S3, Aminated ZIF-67-supported ferrocene derivatives: 0.5 g of NH2-ZIF was dispersed in 50 ml of methanol by ultrasonication in a water bath for 10 minutes. Then, 50 ml of a methanol solution containing 0.5 g of ferrocene formaldehyde was added, and the mixture was stirred at room temperature for 1 hour. Next, the mixture was refluxed at 60 °C for 24 hours and then cooled to room temperature. The solid was separated by centrifugation, washed three times with methanol, and dried in a 60 °C oven for 24 hours to obtain an aminated ZIF-67-supported iron-containing compound composite flame retardant (Fc-ZIF). S4. The calcined grafted ferrocene zeolite imidazole ester skeleton: 2g of Fc-ZIF was placed in a crucible and heated to 600℃ under nitrogen atmosphere for 3h. The heating rate was 10℃ / min to obtain the calcined zeolite imidazole ester skeleton (FZ) grafted with ferrocene. S5, Black Phosphorus Nanosheets: 200 mg of black phosphorus was placed in 200 ml of N-methylpyrrolidone and sonicated in an ultrasonic cell disruptor for 6 h. After centrifugation at 3000 rpm for 10 min, the supernatant was collected and centrifuged at 10000 rpm for 10 min. The supernatant was washed three times with ethanol and dried in an oven at 60 ℃ for 24 h to obtain black phosphorus nanosheets (BPNS). S6, a mixture of ferrocene-modified zeolite imidazole ester framework and black phosphorus nanosheets: Take 80 mg FZ and 10 mg BPNS in 40 ml ethanol, sonicate for 1 h, centrifuge to collect the product, wash three times with ethanol, and dry in an oven at 60 ℃ for 24 h to obtain a mixture of ferrocene-modified zeolite imidazole ester framework and black phosphorus nanosheets. S7, Ferrocene-modified zeolite imidazole ester framework and black phosphorus nanosheet hybrid: Take 2g of ferrocene-modified zeolite imidazole ester framework and black phosphorus nanosheet mixture in a crucible, heat to 300℃ under nitrogen atmosphere, calcine for 30min, heating rate is 10℃ / min, to obtain ferrocene-modified metal-organic framework composite black phosphorus nanosheet functional flame retardant (FZ / BPNS).
[0031] The transmission electron microscopy results of the flame retardant are as follows: Figure 1 As shown, the recombination state of FZ and BPNS can be clearly observed using transmission electron microscopy.
[0032] The Fe element mapping diagram in the flame retardant is as follows: Figure 2 As shown, the results indicate that ferrocene has been stably and uniformly grafted onto ZIF-67.
[0033] The P element mapping diagram in the flame retardant is as follows: Figure 3 As shown, the results indicate that the distribution of P elements from BPNS in the flame retardant is uniform.
[0034] Application of the prepared flame retardant in FPUF: Using chitosan (CS) as an interfacial binder, FZ / BPNS was dispersed into a dispersion with a concentration of 5 mg / mL. Finally, the FPUF was immersed in the dispersion for 30 minutes and then freeze-dried at -50°C for 48 hours to obtain composite foam.
[0035] Flame retardant properties were tested on the prepared FPUF composite material and unmodified FPUF: direct combustion tests were conducted in air at 25°C to evaluate the material's combustion behavior and self-extinguishing characteristics; thermogravimetric analysis (TGA) was used to determine the material's thermal stability and residual carbon formation; cone calorimetry was performed according to ISO 5660 standard, with a heat flux set at 35 kW / m², to quantify the heat release, smoke release, and toxic gas release characteristics during the material's combustion process. The test results are shown in Table 1. Table 1 Flame retardant properties of FPUF composite materials
[0036] As can be seen from Table 1, the FPUF composite material obtained by using the functional flame-retardant coating prepared in the embodiments of the present invention exhibits excellent flame-retardant and smoke-suppressing properties.
[0037] The three-dimensional reflection loss curves of pure FPUF and FPUF with added FZ / BPNS are as follows: Figure 4 As shown, RL is the core indicator for evaluating the performance of microwave absorbing materials. The core function of this 3D graph is to comprehensively present the microwave absorption performance of the composite flame-retardant coating under the dual variables of "frequency (GHz) - thickness (mm)". The vertical axis of the graph represents the reflection loss value, and the horizontal axis represents the frequency and the coating thickness, respectively. The microwave absorption effect of the composite flame retardant at different thicknesses and frequencies can be intuitively observed through the 3D curves.
[0038] Two-dimensional reflection loss curves of pure FPUF and FPUF with added FZ / BPNS are shown below. Figure 5 As shown.
[0039] from Figure 4 , 5 As can be seen, the FPUF composite material obtained using the functional flame-retardant coating prepared in the embodiments of the present invention exhibits excellent microwave absorption performance. Compared with the original FPUF (whose microwave absorption performance in the 2~18GHz band is negligible), the FZ / BPNS modified FPUF achieves a significant improvement in microwave absorption performance: it exhibits excellent broadband microwave absorption capability in the 2~18GHz band, and when the coating thickness is in the range of 1~7.6mm, the reflection loss (RL) value is always below -20dB (corresponding to an electromagnetic wave absorption efficiency of over 99%), and minimum reflection loss values of -57.43dB and -63.78dB are observed at thicknesses of 1.49mm and 1.17mm, respectively. This fully demonstrates that the coating can effectively endow FPUF with high-efficiency microwave absorption performance.
[0040] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.
Claims
1. A multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets, characterized in that: The flame retardant is first obtained by reacting and calcining ferrocene formaldehyde with an aminated zeolite imidazole ester framework to obtain a ferrocene zeolite imidazole ester skeleton, and then the ferrocene zeolite imidazole ester skeleton is combined with black phosphorus nanosheets to obtain the flame retardant.
2. A method for preparing a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 1, characterized in that: The method steps include: (1) The zeolite imidazole ester framework was aminated and the resulting aminated zeolite imidazole ester framework was dispersed in methanol to obtain a dispersion. (2) Add the methanol solution of ferrocene formaldehyde to the dispersion, heat at 55-65℃ for 12-24h, cool after the reaction, centrifuge, separate, wash, and dry to obtain the solid; (3) The solid is placed in a tube furnace and heated to 400-800℃ under nitrogen conditions and kept at that temperature for 2-4 hours to obtain a calcined zeolite imidazole ester skeleton grafted with ferrocene. (4) Preparation of black phosphorus nanosheets; (5) The ferrocene-grafted zeolite imidazole ester skeleton and black phosphorus nanosheets are dispersed in ethanol, sonicated for 1-2 hours, centrifuged, separated, washed, and dried to obtain the precursor; wherein, the ratio of the ferrocene-grafted zeolite imidazole ester skeleton to black phosphorus nanosheets and ethanol is 80-90 mg: 10-20 mg: 1-10 ml. (6) The precursor is placed in a tube furnace and heated to 200-300℃ under nitrogen conditions and kept at that temperature for 0.5-1h to obtain a multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets.
3. The preparation method of the multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2, characterized in that: In step (1), the zeolite imidazole ester framework is ZIF-67.
4. A method for preparing a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2 or 3, characterized in that: The ratio of the aminated zeolite imidazole ester framework to methanol is 0.5g:50-100ml.
5. The preparation method of the multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2, characterized in that: In step (2), the ratio of ferrocene formaldehyde to methanol in the ferrocene formaldehyde solution is 0.5g: 50-100ml.
6. The preparation method of the multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2, characterized in that: In step (2), the mass ratio of ferrocene formaldehyde to the aminated zeolite imidazole ester framework is 1:0.5-1.
5.
7. The preparation method of the multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2, characterized in that: In step (4), black phosphorus is dispersed in N-methylpyrrolidone and ultrasonically dispersed evenly to obtain a black phosphorus nanosheet dispersion. The black phosphorus nanosheet dispersion is centrifuged at 3000-4000 rpm for 8-12 min, and the supernatant is centrifuged at 10000-12000 rpm for 8-12 min. The filter cake is washed with ethanol and then dried in an oven at 50-60℃ for 12-24 h to obtain black phosphorus nanosheets. The ratio of black phosphorus to N-methylpyrrolidone is 1 mg: 50-100 ml.
8. The preparation method of the multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2, characterized in that: In steps (2) and (5), the drying temperature is 50-60℃ and the drying time is 12-24h.
9. The preparation method of the multifunctional flame retardant composed of zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 2, characterized in that: In steps (3) and (6), the heating rate is 5-10℃ / min.
10. The application of a multifunctional flame retardant composed of a zeolite imidazole ester framework and black phosphorus nanosheets as described in claim 1 in flexible polyurethane.