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Review

Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants

by
Ping Lyu
1,
Yongbo Hou
1,
Jinhu Hu
1,
Yanyan Liu
1,*,
Lingling Zhao
1,
Chao Feng
1,
Yong Ma
2,
Qin Wang
1,
Rui Zhang
1,
Weibo Huang
1 and
Mingliang Ma
1,*
1
School of Civil Engineering, Qingdao University of Technology, Qingdao 266520, China
2
School of Material Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
*
Authors to whom correspondence should be addressed.
Polymers 2022, 14(23), 5279; https://doi.org/10.3390/polym14235279
Submission received: 13 September 2022 / Revised: 20 November 2022 / Accepted: 28 November 2022 / Published: 2 December 2022
(This article belongs to the Special Issue Metal–Organic Frameworks–Polymer Composites)
Browse Figures
Versions Notes

Abstract

:
Polymer matrix is vulnerable to fire hazards and needs to add flame retardants to enhance its performance and make its application scenarios more extensive. At this stage, it is more necessary to add multiple flame-retardant elements and build a multi-component synergistic system. Metal organic frameworks (MOFs) have been studied for nearly three decades since their introduction. MOFs are known for their structural advantages but have only been applied to flame-retardant polymers for a relatively short period of time. In this paper, we review the development of MOFs utilized as flame retardants and analyze the flame-retardant mechanisms in the gas phase and condensed phase from the original MOF materials, modified MOF composites, and MOF-derived composites as flame retardants, respectively. The effects of carbon-based materials, phosphorus-based materials, nitrogen-based materials, and biomass on the flame-retardant properties of polymers are discussed in the context of MOFs. The construction of MOF multi-structured flame retardants is also introduced, and a variety of MOF-based flame retardants with different morphologies are shown to broaden the ideas for subsequent research.

1. Introduction

Fire is the beacon that lights up human life, and fire is a major hidden danger that threatens natural society and human life. Fire protection is not limited to traditional flammable materials such as wood, paper, and cotton, but also to new polymer materials. With the advantages of wear resistance, corrosion resistance, and good insulation, traditional steel products have been replaced by polymers in some fields. However, they display a large fire load and release a significant amount of heat and smoke when burning, which will cause property damage and personal injury [1,2]. Polymer flame retardants have been researched, but with them comes the possibility of environmental pollution [3,4,5,6]. In line with the green and environmental protection advocated at this stage, high-efficiency and environment-friendly flame retardants are bound to become a hot spot for research. The functionalization of metal organic frameworks (MOFs) has therefore drawn attention [7].
MOFs are coordination networks with organic ligands containing potential voids [8]. Due to their structural diversity and tunability, they continue to be widely used, including in, but not limited to, high-performance sensing materials [9,10], high-activity catalyst development [11,12], supercapacitors [13,14], microwave absorption [15,16], drug delivery [17], luminescent materials, nanomaterial carriers, polymerization, and imaging [18]. Tens of thousands of MOFs have been designed and synthesized since MOFs were explicitly proposed in the 1990s [19]. At the same time, MOF-based hybrids and MOF-derived materials are emerging one after another, which also provides a variety of strategies and approaches to better utilize the properties of MOF structures [20,21]. MOFs, also known as porous coordination networks (PCNs), have a robust structure that can generate permanently stable pores with tunable and controllable properties [22]. In connection with the fact that the smoke released when the polymer is burned is the most deadly hazard to humans in a fire, the rich mesh structure can delay the release of smoke [23]. Therefore, the porous structure of MOFs provides potential for their use as flame retardants. Smoke release retardation is good, but flame retardants can further inhibit heat transfer and smoke release by generating a good residual as a barrier, directly effectively reducing the release with high quality and abundant amounts of residual char. There have been some reports that transition metals can catalyze carbonization and reduce the rate of heat release [24,25]. Transition metals could form C-C bonds during combustion, which helps to convert the polymer matrix into char with considerable stability, thereby improving the flame-retardant efficiency. On the one hand, the above transition metal elements can just fit the metal nodes of MOFs, and various MOF structures also prompt researchers to have more choices for metal sites. On the other hand, the presence of organic ligands, another important component of MOFs, can provide partial flame-retardant elements and groups, while also enhancing compatibility with the polymer matrix. Hou et al. proposed possible flame-retardant mechanisms for organic ligands: condensed-phase catalysis into carbon, increased barrier effect, gas-phase dilution of combustible gases, and quenching of free radicals [26]. It is the mutual agreement of the two aspects that makes MOF-based flame retardants combined with the advantages of organic and inorganic flame retardants full of more possibilities. In addition, superior performance flame retardants may also be accompanied by excellent thermal stability, high limiting oxygen index (LOI), and low dripping.
In 2017, the addition of MOFs to polystyrene (PS) as flame retardants was first reported by Hu et al. [27]. The synthesized iron-based and cobalt-based MOFs could significantly improve the flame-retardant properties of PS composites, and the corresponding MOF’s flame-retardant mechanisms were proposed: thermal barrier effect and catalysis. During the pyrolysis of the PS matrix, the gaseous products of MOFs reduce the concentration of degradation products and reactive oxygen species, whereas the porous metal oxides act as heat and fuel transfer barriers. The flame-retardant mechanism is shown in Figure 1.
Since then, researchers have carried out a significant amount of research on the flame retardancy of MOFs, and pristine MOFs are naturally the primary target of research. Therefore, MOF derivatives, combined with phosphorus and nitrogen compounds or carbon-based materials, have been explored in greater depth. This work organizes the above categories and organizes the number of publications about MOF flame retardants in each year. It can also be confirmed from Figure 2 that research regarding MOF flame retardants is increasing each year, indicating that they have received more and more attention. It is hoped that this review can provide some reference and guidance for future research related to flame retardancy in MOFs based on the classification.

2. Pristine MOFs Directly as Flame Retardants

Because some of the MOFs whose own metal sites belong to transition metal elements (often Zn, Co, Zr, etc.) have catalytic carbonization properties, pristine MOF monomers can be added directly to the polymer matrix as flame retardants. During combustion, the metal sites of MOFs generate metal oxides that promote the formation of a continuous dense char layer to insulate part of the combustible gases and heat [28]. Shi et al. added synthetic zeolitic imidazolate framework-8 (ZIF-8) nanoparticles directly into poly (lactic acid) (PLA), and an addition of 0.2 wt% could increase the limiting oxygen index value from 20.5% to 23.5% [29]. Similarly, on polyvinyl alcohol aerogel (PVA) [30], flexible polyurethane foam (MFPU) [31], and even PLA non-woven fabric [32], the LOI has been significantly improved after adding ZIF monomer. Among them, when 1:1 ZIF-8 was added to the PVA aerogel, the peak heat release rate (pHRR) was significantly reduced by 44.2%. ZIFs had synthetic and structural similarities, and some of their microscopic morphologies are shown in Figure 3. The properties of ZIFs applied in flame retardants may also show similarity, as can be demonstrated by the performance tests of ZIF composites synthesized by some researchers [26,33,34]. Considering the excellent thermal stability and mechanical properties of zirconium-based MOFs [35,36], Sai et al. [37] directly blended UiO-66 with different mass fractions with polycarbonate (PC). The samples with 4 wt% UiO-66 added could reach the V-0 level. Time to ignite (TTI) and t-pHRR (time to reach pHRR) were delayed by 90 and 75 s, respectively, which would provide significantly more time for help for personnel rescue in real fires. Chen et al. [38] added UiO-66 directly to PS, and the smoke suppression effect was obvious. The total smoke release (TSR) of the PS/UiO-66-5 wt% composite was reduced by 35% compared with pure PS. In addition, compared to the large amount of dripping and black smoke from pure PS, the PS/UiO-66 composite does not have a similar situation because the heat-resistant material ZrO2 is generated during the reaction and acts as a good barrier.
To explore the different metals used as flame-retardant materials for unmodified MOFs, several MOFs, including Fe [26], Cr [39], Cu [40], and rare earth elements have been synthesized and blended directly into a polymer matrix to investigate their thermal stability. Mo-MOF was prepared and incorporated into epoxy (EP) by Zhang et al. [41]. Probably due to its good dispersion state and compatibility, the appropriate amount of Mo-MOF helped to enhance the mechanical properties of EP. The EP composites with the addition of 6 wt% Mo-MOF could reduce the pHRR and peak CO production (PCOP) by 44.7% and 42.9%, respectively. Some rare earth elements have thermal stability and toxic fume inhibition, and can be tried as flame retardants [42,43]. Li et al. [44] investigated three rare earth elements (La, Ce, and Y) as metal sites for MOFs (RE-MOF). The EP composites were tested for flame retardancy using the cone calorimeter test (CCT) while comparing the reasons for the high and low flame retardancy of the three RE-MOF. The best performing Y-MOF has excellent catalytic charring and radical trapping ability, thus blocking the EP degradation process, and the possible flame-retardant mechanism is shown in Figure 4. Specifically, Y can catalyze the formation of carbon layers possessing a higher degree of graphitization, and the formed Y2O3 can trap the free radicals in the chain reaction.
The direct blending of some of the initial MOFs into a polymer matrix has demonstrated the indispensable ability of MOF materials for flame-retardant applications. However, because the gains obtained are from their own structure, they partly require higher additions while causing a loss of mechanical properties. If people want to further improve the fire performance of polymers, it is inevitable to consider combining them with other materials.

3. Hybrid of Phosphorus–Nitrogen Compounds and MOFs as Flame Retardants

Phosphorus and nitrogen elements belong to the same group of elements, and both belong to the common non-halogen flame-retardant elements. At the same time, because halogens are regarded as substances that are toxic and affect environmental permanence, halogen-free flame retardants will naturally receive more attention [45,46,47]. Traditional phosphorus-based flame retardants include red phosphorus, phosphate, ammonium polyphosphate (APP), etc., while nitrogen-based flame retardants contain melamine and dicyandiamide [48,49,50,51]. Because phosphorus-based flame retardants and nitrogen-containing compounds are found to have a good synergistic effect, the two elements are also often combined in the design of flame retardants to bring into play the P-N synergistic effect. On the one hand, phosphorus flame retardants can release PO· and PO2· radicals and other reactive radicals such as H·, HO·, and O· generated in the combustion chain reaction burst reaction. On the other hand, phosphorus flame retardants can release some phosphoric acid-containing to promote the dehydration of polymer substrates into carbon, as shown in Figure 5. As the mechanism diagram shows, most conventional phosphorus flame retardants have a single flame-retardant mechanism, while P-N flame retardants can effectively improve the thermal stability and fire safety performance of polymers [52]. The compatibility exhibited by inorganic flame-retardant fillers with polymers is poor, while MOFs can form mutual attraction with polymer chains to improve the compatibility. The metal oxides generated from MOFs during pyrolysis also further promote catalytic carbonization [53].

3.1. Ammonium Salts and MOFs as Flame Retardants

In recent years, ammonium salt flame retardants have attracted attention due to their ease of preparation, clean production, application and disposal with less harm to the environment; they mainly include APP, melamine phosphate (MP), and melamine polyphosphate (MPP). APP, also known as ammonium polyphosphate, is used quite widely as the main type of non-halogen flame retardant. However, due to its limited flam- retardant effect alone, it is often used in combination with other halogen-free flame retardants. When used in combination, they can not only reduce the amount of APP but also improve the flame retardants efficiency. At the same time, compound flame retardants can reduce the loss of mechanical properties [54]. Chen et al. [55] first prepared Cu-based MOF materials and then used the Cu-MOF and APP mass fractions added as controls according to the differences. The effect of physical mixing of MOF materials with APP as a flame retardant for thermoplastic polyurethane (TPU) has been investigated. CCT and LOI tests showed that the flame-retardant property of TPU composites was further enhanced when Cu-MOF was used in combination with APP. When Cu-MOF was added, only 0.0625 wt%, the LOI level reached 28%, and the pHRR and total heat release (THR) values were reduced by 19.2% and 63.4% compared with TPU/APP. Table 1 also summarizes the currently reported data of MOF/APP synergistic flame retardants, as well as the combustion data of pure polymer matrix and no MOFs. Through the data analysis in Table 1, it can be confirmed that adding a certain amount of MOFs compared to only adding APP as a flame retardant shows a trend of improving the flame-retardant performance. However, the improved effect is different, which may be caused by the different types of substrates and MOFs. In addition to physical mixing, Wang et al. [56] assembled ZIF-67 onto the APP surface, which opened new avenues for MOFs while obtaining excellent flame-retardant properties. The synthesized APPZ4 was added to Ethylene-vinyl acetate (EVA) as a flame-retardant composite, and with the increase of temperature, APPZ4 could be converted to cobalt phosphate nanocatalyst and formed di-micro nano-films and aggregated nano-skeletons. It exerts catalytic graphitization on the surface of the EVA matrix and generates a large amount of graphite-like carbon as a barrier.
Melamine is also an important member of the halogen-free flame-retardant system, and it can be used alone or in combination with other flame retardants [60,61]. Nabipour et al. [62] applied isoreticular-MOF-3 to fire safety for the first time and obtained novel flame retardants by covalent hybridization with melamine. The addition of 2% heterocyanide to EP resulted in an LOI level up to 30.5% and decreases in pHRR, THR, and SPR by 74.0%, 71.4%, and 35.6%, respectively. By CCT and residual char analysis, they analyzed the flame-retardant smoke suppression mechanism from the condensed phase and gas phase, respectively. On the one hand, the ZnO generated by MOF-3 would enhance the thermal stability of the residual char while catalyzing the formation of char residues. On the other hand, melamine could generate non-combustible gas to dilute the combustible gas concentration and produce melam and melem to improve the heat resistance of char yield.

3.2. DOPO and MOFs as Flame Retardants

9,10dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is a phosphorus-containing flame-retardant intermediate that contains P-H bonds in its structure and has good activity against olefins, epoxy bonds, and carbonyl groups, and can react to generate a variety of derivatives [63,64]. The thermal stability of both DOPO and its derivatives is higher compared to uncycled organophosphate esters because of the benzene and phenanthrene ring structures in DOPO and its derivatives. Meanwhile, the modification of MOFs by DOPO can retain the original structure well, as shown in Figure 6. Some studies have shown that DOPO gives good flame-retardant performance, but the smoke suppression improvement is low [65,66,67]. Wang et al. [68] modified the synthesized bimetallic organic backbone (W-Zr-MOF) using DOPO to introduce a large amount of P elements while retaining the hollow octahedral morphology. The porous graded structure of the modified MOFs was used to efficiently absorb the released smoke and volatile gases, and it was able to significantly suppress the smoke and heat release. At the same time, the pyrolysis of DOPO produced a large amount of polyphosphate, which promoted the carbonization and dehydration of EP, thus inducing the formation of a dense and phosphorus-rich carbon layer. The TSP and pHRR were reduced by 36% and 58%, respectively, when 3 wt% of W-Zr-MOF-DOPO was added, and the residual char integrity was much higher than that of pure EP, as evidenced by visual inspection alone, a result also confirmed by Raman spectroscopy. It is shown that the multiple coordinated effects of multi-level pores, metals, and P elements improve the fire safety of EP composites. Liu et al. [69] used a derivative of DOPO (DMZ) to modify ZIF-8 to obtain dZIF-8, which was added to EP as a flame retardant. The dZIF-8EP composites containing 2 wt% of dZIF-8 reduced the total smoke release rate (TSRR) and maximum smoke density by 47% and 36%, respectively, compared to pure EP. It was shown that MOFs and DOPO have synergistic effects to enhance the smoke suppression performance of the polymer. In addition to the graft modification of DOPO on the original MOFs, some MOFs were coated on DOPO [70,71]. The metal elements in MOFs were also used to promote catalytic carbonization, forming a denser char layer and providing a more effective barrier effect.

3.3. Phosphonitrile Compounds and MOFs as Flame Retardants

Phosphonitrile polymers are a class of inorganic–organic polymers with alternating P and N double bonds as the main chain structure, which can be generally divided into two categories: cyclic polyphosphonitrile and linear polyphosphonitrile. Among the cyclic polyphosphonitrile, cyclotriphosphonitrile and cyclotetrakisphosphonitrile are the most common. Hexachlorocyclotriphosphonitrile (HCCP) is a very important intermediate and the most basic compound in phosphonitrile chemistry, and it plays a pivotal role in the development of phosphonitrile chemistry. Polyphosphonitrile compounds have outstanding light stability, thermal stability, good resistance to high and low temperatures, and high LOI value [73,74,75]. The main chain of polyphosphonitrile molecules is structurally stable and has a very high heat resistance temperature. What determines the physicochemical properties of polyphosphonitrile compounds is the nature and number of side chain species of phosphorus atoms in the phosphonitrile. Polyphosphazene has excellent flame-retardant applications because of its low smoke emissions and low toxicity of the gases emitted during combustion [76]. Polyphosphazene has similar customizable properties to MOFs, so when combined with MOFs, it is possible to customize a wider variety of structures with MOFs as well as to satisfy the need to avoid a single flame-retardant function. On this basis, the MOFs can be further modified by combining them with other materials to form a multi-synergistic flame-retardant effect [77,78].
According to researchers, MOFs and phosphonitrile compounds are mostly combined in the form of encapsulation or surface modification. Xu et al. [79] synthesized a Co-based MOF (MOF-71-NH2) and obtained organic–inorganic hybridization products by modification with phosphonitrile trimer (PCT). PS composites doped with PCT only, MOF-71-NH2, and PCT@MOF-71-NH2 were compared with pure PS using 3 wt% as a reference. With the synergistic effect of MOF and PCT, both heat release and smoke release were lower than adding only one of them, and THR and pSPR were reduced by 31.7% and 41%, respectively, compared to pure PS. Meanwhile, the increased yield and denseness of the residual char could be clearly seen by digital photographs and SEM of the residual char. Some CCT data for MOFs and phosphonitrile compounds as flame retardants are shown in Table 2. The selected flame-retardant additions are all 3%, and the polymer matrix is mostly EP, which is convenient as a comparison. It can be seen from the table that there are large differences in the degree of decrease of THR and TSP, compared to the pure resin matrix part of the composite, which is not significantly decreased, probably because of the different catalytic ability shown by different MOFs. This is also in response to the need for different matrixes to take different kinds of MOF composite attempts to compare. Among them, the decrease of Fe-MOF@PZS as a flame retardant is particularly significant, which is mainly attributed to the Fe2O3 and phosphide produced during the combustion process, and the char formed a dense and hard char ceramic layer, which effectively protected the unburned EP composites [80].

3.4. Other Phosphorus and Nitrogen Compounds and MOFs as Flame Retardants

In addition to the above-mentioned phosphine and nitrogen compounds that are used more synergistically with MOFs, there are some others that have been explored by researchers and have shown good results, such as phosphonates [85], α-zirconium phosphate [86], and polyaniline [87]. Some of the organic ligands in MOFs contain -NH2. On the one hand, -NH2 helps to increase the compatibility with EP. On the other hand, due to the presence of -NH2, NH3 is released during the combustion of EP, which dilutes the combustible gas and acts as a flame retardant in the gas phase. Wang et al. [88] modified NH2-MIL-101(Al) with polyethyleneimine (PEI) and used adsorbed dye as a further modification step to achieve sustainable application of MOF materials. Meanwhile, the synergistic effect of adsorbed dyes, MOF, and PEI enhanced the flame-retardant properties of EP. An ionic liquid (IL) containing phosphorus and nitrogen elements was synthesized, and the composite was obtained with NH2-MIL-101(Al) [89]. Combining the respective flame-retardant characteristics of both, the advantages are exerted in both the condensed phase and the gas phase, as shown in Figure 7. In addition, some researchers have constructed lamellar structures containing phosphorus and nitrogen elements and combined or modified them with MOFs in the form of two-dimensional/three-dimensional structures to obtain flame-retardant composites with fire and smoke suppression [90,91]. Zhang et al. [92] designed flame-retardant hybrids with specific functions using UiO-66 as the core and Prussian blue analogues (PBA) and poly(dopamine) (PDA) as custom components of the laminate structure. The composite of EP/UiO66-PDA-PBA-3 showed by CTT results that pHRR and CO production (COP) were reduced by 50% and 66%, respectively, and the residual char increased from 10.6% to 19.8%. This indicates that the constructed layered structure could be used as a new method of effective fire protection.

4. Carbon-Based Materials and MOFs as Flame Retardants

The development of carbon-based materials has a long history, as carbon is an element that is very commonly found in nature. Because carbon atoms can be bonded into numerous isomers of molecules and atomic-type crystals, they can be stacked and aggregated in different ways and orientations at the micron and nanometer scales, forming a wide variety of weaves. Carbon as a single element can form many substances with completely different structures and properties. With the advancement of characterization techniques in recent years, fullerenes (C60) [93], carbon nanotubes (CNTs) [94], and graphene [95] have been discovered one after another, and since then a new chapter of exploring carbon nanomaterials has been opened. Researchers have modified carbon materials at the microscopic and mesoscopic scales to prepare carbon materials with various novel functions for applications such as wave absorption [96,97,98], medical treatment [99], electrochemical supercapacitors [100,101], catalysis [102], and flame retardancy [103]. Carbon materials mostly have high thermal stability and thermal conductivity and partially enhance the mechanical properties of the polymer matrix. On the one hand, the carbon material itself acts as a physical barrier and provides a barrier effect. On the other hand, it contributes to the formation of a dense protective layer and helps to insulate heat and combustible gases.

4.1. Graphene and MOFs as Flame Retardants

Graphene is a two-dimensional material composed of a single layer of carbon atoms that possesses a great specific surface area and exhibits excellent thermal, electrical, and mechanical properties. Both graphene and its derivatives have good flame-retardant potential [104,105]. The flame-retardant mechanism based on graphene is vividly illustrated in Figure 8. However, due to the strong van der Waals and π-π gravitational forces between the graphene nanosheets, it is easy to agglomerate in the polymer matrix and difficult to disperse uniformly, resulting in the flam-retardant effect being affected [106]. The modification functionalization required by this problem associates the advantages of MOFs.
To improve flame retardancy by solving agglomeration problems, Hou et al. [108] used ZIFs as templates for layered double hydroxides (LDHs) while allowing in situ synthesis on the surface of graphene oxide (GO) or CNTs, which directly inhibited the agglomeration behavior of carbon materials. Compared with pristine GOs or CNTs, the composites combined with ZIF-derived hybrids exhibited extraordinary flame-retardant properties in unsaturated polyester resin (UPR). In addition, they were the first group to combine GO with MOF as a flame retardant for PS. By combining with GO, the agglomeration of vertically grown Ni-MOF sheets was significantly suppressed, and the resulting GOF hybrids had a large specific surface area and pore volume, which promoted the adsorption of volatile pyrolysis products. In studying the release of toxic gases during combustion, a steady-state tube furnace (SSTF) was used to evaluate the CO release. The COP of the PS/GOF composite was reduced by 52.3% compared to pure PS. Unlike agglomerated rGO sheets and NiO particles, the nanoscale NiO on the rGO surface provides a larger surface area and more active sites for the catalytic reduction of CO, thus reducing the COP of the composite [109]. The combustion data of graphene alone as a flame retardant and in combination with MOFs as a flame retardant are shown in Table 3. It is easy to see that when only graphene material is added as a flame retardant, the flame-retardant performance has improved compared with the pure polymer material. However, after compounding with MOFs, the flame-retardant data were further improved on this basis, which is sufficient to show that the combination of MOFs and graphene materials is the right choice to explore the improvement of flame-retardant performance.
Because graphene is a sheet structure with large surface area and abundant functional groups, most MOFs combined with it are grown directly on the surface of the sheet. It can be clearly seen from Figure 9 that MOF nanoparticles grow uniformly on the surface, and MOF nanoparticles can better catalyze the carbonization while the graphene sheet acts as barrier. In addition, it can be combined with other materials for modification and grafting to build ternary or even more multi-component flame-retardant materials. Xu et al. [111] doubly modified RGO with LDH and ZIF-67, and the flake LDH improved the RGO stacking phenomenon. The test results showed that RGO-LDH/ZIF-67 could effectively improve the smoke suppression effect, and the maximum smoke density (Ds,max) was reduced by 56.2% compared with pure EP, and the graphitization of residual carbon was significantly improved. Xu et al. [113] also synthesized leaf-type Co-ZIF-modified graphene and incorporated it into TPU together with conventional flame retardants. The thermogravimetric-infrared (TG-IR) test showed a significant reduction in the release of CO and HCN, etc. compared to pure TPU. The pHRR, THR, and TSP of TPU composites were significantly reduced by 84.4%, 70.1%, and 62.5%, respectively. On the one hand, the metallic cobalt provided by MOFs facilitates catalytic carbonization. On the other hand, the flake RGO and the catalytically formed carbon together play a physical barrier role.

4.2. Other Carbon-Based Materials and MOFs as Flame Retardants

In addition to graphene, researchers have also combined other carbon-based materials with MOFs in order to investigate the effect of different carbon-based materials and MOFs exerting synergistic effects on flame-retardant properties. Some design options of MOF loading on carbon-based materials, such as electrostatic interaction, hydrothermal reaction, and in situ growth, are provided in Figure 10, which can provide ideas for future modification designs. Graphite carbon nitride (g-C3N4) as an emerging two-dimensional material with a unique electronic structure, thermal stability, and high nitrogen content has some advantages for flame-retardant applications [118,119]. Chen et al. [120] constructed MIL-53 (Fe)@C/g-C3N4 by hydrothermal reaction and added it to UPR. The pHRR, pSPR, and CO2Y of the UPR composites decreased by 39.8%, 33.3%, and 37.3% compared to the pure UPR when the addition amount was 4%. The addition of MOFs helped catalyze the formation of stable carbon layers more than the UPR composites with the addition of g-C3N4 alone, and the suppression of smoke was significantly enhanced. Xu et al. [121] successfully prepared ZIF-67/g-C3N4@SiO2 hybrids and enhanced the flame-retardant properties of EP. ZIF-67 generated cobalt oxides during combustion, and the smoke index decreased significantly due to the large specific surface area that could adsorb smoke and volatile particles. Compared with pure EP, the pores of residual char became smoother and denser after combustion, and the ID/IG values from Raman spectra (ID and IG represent the D peak of amorphous carbon and G peak of crystalline graphitic carbon, respectively) indicated the enhancement of graphitization. The assembly of MXenes material (Ti3C2Tx) and the combination of carbon spheres (CS) and MOFs can also be seen in Figure 10. The advantages of being two-dimensional and three-dimensional carbon-based materials for the barrier of combustible gases, heat, and smoke, coupled with the catalytic effect of MOFs, exhibit the synergistic effect of both to enhance the flame-retardant properties of the polymer [122,123,124].

4.3. MOFs and Biomass Materials as Flame Retardants

Able to fit the concept of a green environment, biomass as a flame retardant has become a research hotspot. Because biomass as a biological resource is a renewable resource, it is not toxic and is also in line with the concept of sustainable development. Biomass as a flame retardant is broadly available in proteins, amino acids, oils, and sugars. The reason why bio-based flame retardant is included in this part of carbon-based materials is to consider that biomass and carbon are inseparable. Some biomasses can be used as a carbon source in flame retardants, and there are other biomasses that can promote carbon formation during combustion [126,127]. Among them, the modification of MOFs with phosphorus-rich phytic acid (PA) not only regulates the degradation of polymers but also promotes the cross-linking of EP combustion decomposition products into carbon. β-cyclodextrin (β-CD) is a natural source of carbon, and Zhang et al. [128] functionalized MOFs with PA and formed layered hybrids with β-CD to be added to EP as flame retardants. pHRR and SPR were reduced by 41% and 62%, respectively. The modified MOFs can act as both an acid and gas source and can promote more carbon production from β-CD, enhancing co-efficient flame retardancy. The combination of naturally derived cellulose and MOFs to construct gas barrier gels is not only economical and environmentally friendly, but also has a clear cross-linked network structure [129,130]. It also has certain adsorption abilities due to the mesh structure and great specific surface area, which can improve the handling of gaseous products by MOFs during the combustion process.
For the combination of biomass and MOFs, the structure is not limited to simple encapsulation and growth, but to build a multifaceted composite structure with more flame-retardant elements [61,114,131]. In terms of application, it is not only limited to flame retardants, but also to increase mechanical properties, adsorption applications, and hydrophobicity, etc. [132,133]. Xie et al. [134] used direct melt blending of dry wine lees, ZIF-8 and PP, and the mechanical properties of the obtained composites were significantly improved, with tensile strength and strain at break values of 34.2 MPa and 24.8%, respectively. This was due to the introduction of ZIF-8 as an interfacial modifier and energy-absorbing nanocrystals. In addition, the LOI value reached 25.0% at the ZIF-8 addition of 3 wt%, and the residual carbon not only became smooth and dense but also had a significant increase.

5. MOFs as Derivatize Templates and Hybrids with LDHs as Flame Retardants

In recent years, due to the rise of MOFs, their derivatives have been increasingly discovered and studied. The properties and advantages of MOFs have been mentioned above, because these structural properties can be preserved in derived materials, which can have a wider scope of application if they are suitably tuned (morphology, porosity size, and crystal size, etc.). Moreover, MOFs have been demonstrated as highly versatile precursors capable of deriving a wide variety of nanostructures, including carbon materials, metal oxides, metal phosphides, metal carbides, and LDHs [135,136]. These MOFs-derived materials are often used in batteries [137], supercapacitors [138], electrocatalysis, photocatalysis [139], and sensing, etc. Flame-retardant applications are relatively rare, and LDHs are mostly used for flame-retardant applications at this stage.

5.1. MOFs as Templates to Derivatize LDHs as Flame Retardants

LDH is a nano-filler, which combines the characteristics of traditional metal oxides and layered silicates and is widely used as a halogen-free flame retardant. On the one hand, LDHs with abundant oxygen-containing groups are well dispersed in polymers. On the other hand, the H2O decomposed by LDHs during combustion is beneficial to reduce the heat release rate, and the transition metal elements contained can generate metal oxides to promote the catalytic effect [140]. Li et al. [141] anchored ZIFs on LDH as flame retardants mixed into EP and made a comparison between ZIF-8 and ZIF-67 regarding flame-retardant properties. While showing the good flame-retardant performance of LDH, it could be presumed that the derivation of LDH from MOFs will have better results. MOFs have been shown to be ideal templates for the preparation of LDHs, and ZIFs can be used as precursors for the construction of different LDHs on a variety of materials [142,143]. Pan et al. [144] constructed a sandwich-type three-dimensional hybrid structure using ZIF-67 by growing NiCo-LDH in situ on both sides of graphene nanosheets, which avoided agglomeration on the graphene nanosheets and provided high specific surface area. The pHRR and TSP after addition to EP showed a significant decrease compared to pure EP, and the residual char amount increased from 11.9% to 21.6%. It was easy to see from the digital photos of each residue that rGO had poor fire performance due to stacking agglomeration, which also indicated that the catalytic effect of nickel-iron ions in LDH promoted the formation of carbon layers, thus reducing the heat and mass transfer in the gas and solid phases. Hou et al. [108] adjusted the Zn/Co ratio of bimetallic ZIF, which would keep the original structure better and be beneficial to the growth and arrangement of derivatives on the carrier. Sandwich structures and necklace structures were constructed using GOs and CNTs as carriers, respectively. UPR/GO@LDHs and UPR/CNTs@LDHs had a 27.4% and 24.6% reduction in THR and 46.1% and 33.9% reduction in TCO compared to pure UPR. In addition to 3D multilayer structures [145], there were LDHs grown on hollow nanomicrospheres [146], loaded on different carriers with flower-like structures derived from MOFs [147]. The variety of forms was to make the hybrids more functionalized and introduced more elements or groups. The multilayer structure helped physical barrier and hierarchical progressive catalysis, and the hollow microspheres were surface-modified to facilitate charring at the filler-substrate interface. While discussing LDHs as flame retardants, attention was also paid to their effects on the mechanical properties of polymers. Some data of pure polymer matrix and composites are listed in Table 4. It can be seen in the table that, after the addition of flame retardant, the tensile strength of each composite basically shows a trend of strengthening, which also confirms the good dispersion of the derived LDH flame retardant in the matrix.

5.2. MOFs as a Template for Other Derivatives as Flame Retardants

In addition to serving as templates for the derivation of LDHs, MOFs also have other derivatives added as flame retardants. Zhang et al. [152] proposed the concept of “secondary agglomeration” based on carriers and loadings, which was further investigated based on the ease of aggregation of nanoparticles in polymers. To solve this problem, zinc hydroxystannate (ZHS) nanoparticles were encapsulated by ZIF-67 and then layered Ni-Co hydroxides nanocages (NCH) were obtained using ZIF-67 as a template. Due to the confinement of ZHS by the egg yolk shell-like structure formed by NCH, the possible detachment of ZHS from the carrier due to weak loading force was avoided. In order to compare the performance differences, flame retardant tests of ZHS@NCH, ZHS, and NCH were carried out, respectively. Figure 11 shows the process of ZHS@NCH preparation and the flame-retardant mechanism. Both the external NCH and the internal ZHS could catalyze the carbonization of EP, thus exempting the lower substrate from further combustion. There was also a simple hydrothermal reaction using Ni-MOF as a template to introduce P elements, and the surface was composed of microspheres while retaining the original nanorod morphology. CCT showed that both THR and TSP are reduced, and the mechanical properties are improved [153]. In addition, there are studies to introduce more metallic elements or flame-retardant elements, and some other properties will be taken into account while enhancing the flame-retardant properties [154,155]. It is suggested that the use of MOFs as derivatives to combine other hybrids, in connection with many other application scenarios, broadens the limits of single use.

6. Conclusions and Future Perspectives

In conclusion, MOF-based flame retardants, as a material developed in recent years, can take the responsibility of flame-retardant applications for polymers. Through the structural analysis of MOFs, both organic ligands and metal sites have certain flame-retardant functions, but the specific question of which plays a greater role is inconclusive. There are also large differences in the role of metal oxides formed by different transition metals in the combustion process to play a catalytic carbonization of different polymers, and a large number of comparisons are still needed to facilitate further analysis. Aggregation and agglomeration of nanomaterials is a major issue, and the organic ligands of MOFs have the function of promoting compatibility with polymers, and the morphologies of the original MOFs used at this stage are regular and ordered. However, what type of ligand is more effective is still inconclusive, but this can be solved by introducing other conventional materials as carriers.
At this stage, there is limited research on MOFs as flame retardants directly, and the inorganic–organic characteristics of MOFs themselves are used to construct multi-faceted flame-retardant systems. By introducing inorganic flame-retardant elements and transition metal elements, MOFs are modified to introduce organic flame-retardant groups to construct different core-shell structures, three-dimensional multilayer structures, and sheet carrier structures, etc. All of them are designed to take advantage of the synergistic effect of components or structural advantages on the basis of the original ones, and to carry out flame-retardant functions from the gas phase and the condensed phase, respectively.
More attempts are needed to see if new MOFs can be applied to flame-retardant polymers in the future, and research on existing MOFs can be combined with other new materials containing flame-retardant elements or moieties. The combination of biomass materials and MOFs is still in the initial stage, and the construction of green flame-retardant systems could enhance the combination of both. Although some types of MOFs are now commercially available, the price is not enough to be used in flame retardants. Moreover, a single MOF does not meet our expectation of flame-retardant effect, and further modification is needed. Therefore, we believe that the future commercialization of MOF flame retardants requires the following conditions: (1) The need for innovative approaches to the production of large quantities of MOFs. (2) The search for materials that synergistically demonstrate excellent flame-retardant effect with MOFs, and at the same time this material should show the advantage of reasonable price. (3) Avoid overly complex functionalization of MOFs.

Author Contributions

Conceptualization, P.L., Y.H. and M.M.; methodology, Y.L. and W.H.; investigation, Y.H., J.H., L.Z. and Q.W.; resources, C.F., R.Z. and Y.M.; writing—original draft preparation, Y.H.; writing—review and editing, P.L., Y.H. and M.M.; supervision, P.L. and W.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work is financially supported by Natural Science Foundation of Shandong Province (Grant No. ZR2021ME019, ZR2019BB063).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Fu, T.; Guo, D.M.; Chen, L.; Wu, W.S.; Wang, X.L.; Wang, Y.Z. Fire hazards management for polymeric materials via synergy effects of pyrolysates-fixation and aromatized-charring. J. Hazard. Mater. 2020, 389, 122040. [Google Scholar] [CrossRef] [PubMed]
  2. Geyer, R.; Jambeck, J.R.; Law, K.L. Production, use, and fate of all plastics ever made. Sci. Adv. 2017, 3, e1700782. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  3. Wang, X.; Zhu, Q.Q.; Yan, X.T.; Wang, Y.W.; Liao, C.Y.; Jiang, G.B. A review of organophosphate flame retardants and plasticizers in the environment: Analysis, occurrence and risk assessment. Sci. Total Environ. 2020, 731, 139071. [Google Scholar] [CrossRef]
  4. Besis, A.; Samara, C. Polybrominated diphenyl ethers (PBDEs) in the indoor and outdoor environments—A review on occurrence and human exposure. Environ. Pollut. 2012, 169, 217–229. [Google Scholar] [CrossRef] [PubMed]
  5. Liu, K.; Li, J.; Yan, S.J.; Zhang, W.; Li, Y.J.; Han, D. A review of status of tetrabromobisphenol a (TBBPA) in China. Chemosphere 2016, 148, 8–20. [Google Scholar] [CrossRef] [PubMed]
  6. Aschberger, K.; Campia, I.; Pesudo, L.Q.; Radovnikovic, A.; Reina, V. Chemical alternatives assessment of different flame retardants—A case study including multi-walled carbon nanotubes as synergist. Environ. Int. 2017, 101, 27–45. [Google Scholar] [CrossRef] [PubMed]
  7. Furukawa, H.; Ko, N.; Go, Y.B.; Aratani, N.; Choi, S.B.; Choi, E.; Yazaydin, A.O.; Snurr, R.Q.; O’Keeffe, M.; Kim, J.; et al. Ultrahigh porosity in metal-organic frameworks. Science 2010, 329, 424–428. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  8. Batten, S.R.; Champness, N.R.; Chen, X.-M.; Garcia-Martinez, J.; Kitagawa, S.; Öhrström, L.; O’Keeffe, M.; Paik Suh, M.; Reedijk, J. Terminology of metal–organic frameworks and coordination polymers (iupac recommendations 2013). Pure Appl. Chem. 2013, 85, 1715–1724. [Google Scholar] [CrossRef] [Green Version]
  9. Lustig, W.P.; Mukherjee, S.; Rudd, N.D.; Desai, A.V.; Li, J.; Ghosh, S.K. Metal-organic frameworks: Functional luminescent and photonic materials for sensing applications. Chem. Soc. Rev. 2017, 46, 3242–3285. [Google Scholar] [CrossRef]
  10. Yang, G.L.; Jiang, X.L.; Xu, H.; Zhao, B. Applications of MOFs as luminescent sensors for environmental pollutants. Small 2021, 17, e2005327. [Google Scholar] [CrossRef]
  11. Konnerth, H.; Matsagar, B.M.; Chen, S.S.; Prechtl, M.H.G.; Shieh, F.-K.; Wu, K.C.W. Metal-organic framework (MOF)-derived catalysts for fine chemical production. Coord. Chem. Rev. 2020, 416, 213319. [Google Scholar] [CrossRef]
  12. Sun, Y.M.; Xue, Z.Q.; Liu, Q.L.; Jia, Y.L.; Li, Y.L.; Liu, K.; Lin, Y.Y.; Liu, M.; Li, G.Q.; Su, C.Y. Modulating electronic structure of metal-organic frameworks by introducing atomically dispersed Ru for efficient hydrogen evolution. Nat. Commun. 2021, 12, 1369. [Google Scholar] [CrossRef] [PubMed]
  13. Wang, K.; Wang, S.; Liu, J.; Guo, Y.; Mao, F.; Wu, H.; Zhang, Q. Fe-based coordination polymers as battery-type electrodes in semi-solid-state battery-supercapacitor hybrid devices. ACS Appl. Mater. Interfaces 2021, 13, 15315–15323. [Google Scholar] [CrossRef] [PubMed]
  14. Nagaraju, G.; Sekhar, S.C.; Ramulu, B.; Yu, J.S. High-performance hybrid supercapacitors based on MOF-derived hollow ternary chalcogenides. Energy Storage Mater. 2021, 35, 750–760. [Google Scholar] [CrossRef]
  15. Shu, J.C.; Cao, W.Q.; Cao, M.S. Diverse metal–organic framework architectures for electromagnetic absorbers and shielding. Adv. Funct. Mater. 2021, 31, 2100470. [Google Scholar] [CrossRef]
  16. Ma, M.L.; Bi, Y.X.; Tong, Z.Y.; Liu, Y.Y.; Lyu, P.; Wang, R.Z.; Ma, Y.; Wu, G.L.; Liao, Z.J.; Chen, Y. Recent progress of MOF-derived porous carbon materials for microwave absorption. RSC Adv. 2021, 11, 16572–16591. [Google Scholar] [CrossRef] [PubMed]
  17. Lawson, H.D.; Walton, S.P.; Chan, C. Metal-organic frameworks for drug delivery: A design perspective. ACS Appl. Mater. Interfaces 2021, 13, 7004–7020. [Google Scholar] [CrossRef]
  18. Fan, Z.J.; Liu, H.X.; Xue, Y.H.; Lin, J.Y.; Fu, Y.; Xia, Z.H.; Pan, D.M.; Zhang, J.; Qiao, K.; Zhang, Z.Z.; et al. Reversing cold tumors to hot: An immunoadjuvant-functionalized metal-organic framework for multimodal imaging-guided synergistic photoimmunotherapy. Bioact. Mater. 2021, 6, 312–325. [Google Scholar] [CrossRef]
  19. Liu, C.; Wang, J.; Wan, J.; Yu, C. MOF-on-MOF hybrids: Synthesis and applications. Coord. Chem. Rev. 2021, 432, 213743. [Google Scholar] [CrossRef]
  20. Wang, Q.; Astruc, D. State of the art and prospects in metal-organic framework (mof)-based and mof-derived nanocatalysis. Chem. Rev. 2020, 120, 1438–1511. [Google Scholar] [CrossRef]
  21. Hou, C.C.; Wang, H.-F.; Li, C.; Xu, Q. From metal–organic frameworks to single/dual-atom and cluster metal catalysts for energy applications. Energy Environ. Sci. 2020, 13, 1658–1693. [Google Scholar] [CrossRef]
  22. Li, J.R.; Kuppler, R.J.; Zhou, H.C. Selective gas adsorption and separation in metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1477–1504. [Google Scholar] [CrossRef] [PubMed]
  23. Wang, H.; Qiao, H.; Guo, J.; Sun, J.; Li, H.; Zhang, S.; Gu, X. Preparation of cobalt-based metal organic framework and its application as synergistic flame retardant in thermoplastic polyurethane (TPU). Compos. B Eng. 2020, 182, 107498. [Google Scholar] [CrossRef]
  24. Wang, J.L.; Yuan, B.H.; Cai, W.; Qiu, S.L.; Tai, Q.L.; Yang, H.Y.; Hu, Y. Facile design of transition metal based organophosphorus hybrids towards the flame retardancy reinforcement and toxic effluent elimination of polystyrene. Mater. Chem. Phys. 2018, 214, 209–220. [Google Scholar] [CrossRef]
  25. Zhang, W.Y.; Zhang, W.C.; Pan, Y.T.; Yang, R.J. Facile synthesis of transition metal containing polyhedral oligomeric silsesquioxane complexes with mesoporous structures and their applications in reducing fire hazards, enhancing mechanical and dielectric properties of epoxy composites. J. Hazard. Mater. 2021, 401, 123439. [Google Scholar] [CrossRef] [PubMed]
  26. Hou, Y.B.; Qiu, S.L.; Xu, Z.M.; Chu, F.K.; Liao, C.; Gui, Z.; Song, L.; Hu, Y.; Hu, W.Z. Which part of metal-organic frameworks affects polymers’ heat release, smoke emission and CO production behaviors more significantly, metallic component or organic ligand? Compos. B Eng. 2021, 223, 109131. [Google Scholar] [CrossRef]
  27. Hou, Y.B.; Hu, W.Z.; Gui, Z.; Hu, Y. Preparation of metal-organic frameworks and their application as flame retardants for polystyrene. Ind. Eng. Chem. Res. 2017, 56, 2036–2045. [Google Scholar] [CrossRef]
  28. Liu, Y.; Xu, W.; Chen, R.; Cheng, C.; Hu, Y. Effect of different zeolitic imidazolate frameworks nanoparticle-modified β-FeOOH rods on flame retardancy and smoke suppression of epoxy resin. J. Appl. Polym. Sci. 2020, 138, 49637. [Google Scholar] [CrossRef]
  29. Shi, X.; Dai, X.; Cao, Y.; Li, J.; Huo, C.; Wang, X. Degradable poly(lactic acid)/metal–organic framework nanocomposites exhibiting good mechanical, flame retardant, and dielectric properties for the fabrication of disposable electronics. Ind. Eng. Chem. Res. 2017, 56, 3887–3894. [Google Scholar] [CrossRef]
  30. Nabipour, H.; Nie, S.; Wang, X.; Song, L.; Hu, Y. Zeolitic imidazolate framework-8/polyvinyl alcohol hybrid aerogels with excellent flame retardancy. Compos. Part A Appl. Sci. Manuf. 2020, 129, 105720. [Google Scholar] [CrossRef]
  31. Zhao, S.; Yin, L.; Zhou, Q.; Liu, C.; Zhou, K. In situ self-assembly of zeolitic imidazolate frameworks on the surface of flexible polyurethane foam: Towards for highly efficient oil spill cleanup and fire safety. Appl. Surf. Sci. 2020, 506, 144700. [Google Scholar] [CrossRef]
  32. Wang, X.; Liu, C.; Meng, D.; Sun, J.; Fei, B.; Li, H.; Gu, X.; Zhang, S. Surface integration of polyelectrolyte and zeolitic imidazolate framework-67 for multifunctional poly (lactic acid) non-woven fabrics. Appl. Surf. Sci. 2021, 569, 151039. [Google Scholar] [CrossRef]
  33. Zheng, Y.; Lu, Y.S.; Zhou, K.Q. A novel exploration of metal-organic frameworks in flame-retardant epoxy composites. J. Therm. Anal. Calorim. 2019, 138, 905–914. [Google Scholar] [CrossRef]
  34. Cheng, J.; Ma, D.; Li, S.; Qu, W.; Wang, D. Preparation of zeolitic imidazolate frameworks and their application as flame retardant and smoke suppression agent for rigid polyurethane foams. Polymers 2020, 12, 347. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  35. Ramezanzadeh, M.; Tati, A.; Bahlakeh, G.; Ramezanzadeh, B. Construction of an epoxy composite coating with exceptional thermo-mechanical properties using Zr-based NH2-UiO-66 metal-organic framework (MOF): Experimental and DFT-D theoretical explorations. Chem. Eng. J. 2021, 408, 127366. [Google Scholar] [CrossRef]
  36. Hou, Y.; Xu, Z.; Yuan, Y.; Liu, L.; Ma, S.; Wang, W.; Hu, Y.; Hu, W.; Gui, Z. Nanosized bimetal-organic frameworks as robust coating for multi-functional flexible polyurethane foam: Rapid oil-absorption and excellent fire safety. Compos. Sci. Technol. 2019, 177, 66–72. [Google Scholar] [CrossRef]
  37. Sai, T.; Ran, S.; Guo, Z.; Fang, Z. A Zr-based metal organic frameworks towards improving fire safety and thermal stability of polycarbonate. Compos. B Eng. 2019, 176, 107198. [Google Scholar] [CrossRef]
  38. Chen, W.L.; Jiang, Y.; Qiu, R.; Xu, W.; Hou, Y.B. Investigation of UiO-66 as flame retardant and its application in improving fire safety of polystyrene. Macromol. Res. 2020, 28, 42–50. [Google Scholar] [CrossRef]
  39. Jouyandeh, M.; Tikhani, F.; Shabanian, M.; Movahedi, F.; Moghari, S.; Akbari, V.; Gabrion, X.; Laheurte, P.; Vahabi, H.; Saeb, M.R. Synthesis, characterization, and high potential of 3D metal-organic framework (MOF) nanoparticles for curing with epoxy. J. Alloys Compd. 2020, 829, 154547. [Google Scholar] [CrossRef]
  40. Dai, Y.; Tang, Q.; Zhang, Z.; Yu, C.; Li, H.; Xu, L.; Zhang, S.; Zou, Z. Enhanced mechanical, thermal, and UV-shielding properties of poly(vinyl alcohol)/metal–organic framework nanocomposites. RSC Adv. 2018, 8, 38681–38688. [Google Scholar] [CrossRef]
  41. Zhang, F.; Li, X.T.; Yang, L.Q.; Zhang, Y.N.; Zhang, M.J. A Mo-based metal-organic framework toward improving flame retardancy and smoke suppression of epoxy resin. Polym. Adv. Technol. 2021, 32, 3266–3277. [Google Scholar] [CrossRef]
  42. Yin, Z.; Lu, J.; Yu, X.; Jia, P.; Tang, G.; Zhou, X.; Lu, T.; Guo, L.; Wang, B.; Song, L.; et al. Construction of a core-shell structure compound: Ammonium polyphosphate wrapped by rare earth compound to achieve superior smoke and toxic gases suppression for flame retardant flexible polyurethane foam composites. Compos. Commun. 2021, 28, 100939. [Google Scholar] [CrossRef]
  43. Sai, T.; Su, Y.K.; Shen, H.F.; Ran, S.Y.; Huo, S.Q.; Guo, Z.H.; Fang, Z.P. Fabrication and mechanism study of cerium-based P, N-containing complexes for reducing fire hazards of polycarbonate with superior thermostability and toughness. ACS Appl. Mater. Interfaces 2021, 13, 30061–30075. [Google Scholar] [CrossRef] [PubMed]
  44. Li, X.; Zhang, F.; Zhang, M.; Zhou, X.; Zhang, H. Comparative study on the flame retardancy and retarding mechanism of rare earth (La, Ce, and Y)-based organic frameworks on epoxy resin. ACS Omega 2021, 6, 35548–35558. [Google Scholar] [CrossRef]
  45. Cheng, F.Y.; He, J.L.; Li, C.; Lu, Y.; Zhang, Y.N.; Qu, J. Photo-induced degradation and toxicity change of decabromobiphenyl ethers (BDE-209) in water: Effects of dissolved organic matter and halide ions. J. Hazard. Mater. 2021, 416, 125842. [Google Scholar] [CrossRef]
  46. Wang, P.; Chen, L.; Xiao, H.; Zhan, T.H. Nitrogen/sulfur-containing DOPO based oligomer for highly efficient flame-retardant epoxy resin. Polym. Degrad. Stab. 2020, 171, 109023. [Google Scholar] [CrossRef]
  47. Feng, J.B.; Sun, Y.Q.; Song, P.G.; Lei, W.W.; Wu, Q.; Liu, L.N.; Yu, Y.M.; Wang, H. Fire-resistant, strong, and green polymer nanocomposites based on poly(lactic acid) and core-shell nanofibrous flame retardants. ACS Sustain. Chem. Eng. 2017, 5, 7894–7904. [Google Scholar] [CrossRef]
  48. Liu, H.T.; Guo, Y.; Tian, H.F.; Yao, Y.N.; Liu, Q.; Xiang, A.M.; Zhou, H.F. Fabrication of polyimide foams with superior mechanical and flame resistance properties utilizing the graft copolymerization between red phosphorus and graphene oxide. Mater. Sci. Eng. B-Adv. Funct. Solid-State Mater. 2022, 275, 115498. [Google Scholar] [CrossRef]
  49. Qiu, X.Q.; Li, Z.W.; Li, X.H.; Zhang, Z.J. Flame retardant coatings prepared using layer by layer assembly: A review. Chem. Eng. J. 2018, 334, 108–122. [Google Scholar] [CrossRef]
  50. Hu, X.C.; Sun, Z.; Sun, Z.Q. Synthesis of a novel macromolecular carbon-nitrogen-phosphorous intumescent flame retardant. Adv. Powder Technol. 2021, 32, 1341–1349. [Google Scholar] [CrossRef]
  51. Huo, S.; Song, P.; Yu, B.; Ran, S.; Chevali, V.S.; Liu, L.; Fang, Z.; Wang, H. Phosphorus-containing flame retardant epoxy thermosets: Recent advances and future perspectives. Prog. Polym. Sci. 2021, 114, 101366. [Google Scholar] [CrossRef]
  52. Wang, G.Y.; Nie, Z.B. Synthesis of a novel phosphorus-containing epoxy curing agent and the thermal, mechanical and flame-retardant properties of the cured products. Polym. Degrad. Stab. 2016, 130, 143–154. [Google Scholar] [CrossRef]
  53. Panapitiya, N.P.; Wijenayake, S.N.; Huang, Y.; Bushdiecker, D.; Nguyen, D.; Ratanawanate, C.; Kalaw, G.J.; Gilpin, C.J.; Musselman, I.H.; Balkus, K.J.; et al. Stabilization of immiscible polymer blends using structure directing metal organic frameworks (MOFs). Polymer 2014, 55, 2028–2034. [Google Scholar] [CrossRef]
  54. Lv, X.Y.; Zeng, W.; Yang, Z.W.; Yang, Y.X.; Wang, Y.; Lei, Z.Q.; Liu, J.L.; Chen, D.L. Fabrication of ZIF-8@Polyphosphazene core-shell structure and its efficient synergism with ammonium polyphosphate in flame-retarding epoxy resin. Polym. Adv. Technol. 2020, 31, 997–1006. [Google Scholar] [CrossRef]
  55. Chen, X.L.; Chen, X.H.; Li, S.X.; Jiao, C.A.M. Copper metal-organic framework toward flame-retardant enhancement of thermoplastic polyurethane elastomer composites based on ammonium polyphosphate. Polym. Adv. Technol. 2021, 32, 2829–2842. [Google Scholar] [CrossRef]
  56. Wang, J.; Shi, H.; Zhu, P.; Wei, Y.; Hao, J. Ammonium polyphosphate with high specific surface area by assembling zeolite imidazole framework in EVA resin: Significant mechanical properties, migration resistance, and flame retardancy. Polymers 2020, 12, 534. [Google Scholar] [CrossRef] [Green Version]
  57. Wang, X.G.; Wang, S.H.; Wang, W.J.; Li, H.F.; Liu, X.D.; Gu, X.Y.; Bourbigot, S.; Wang, Z.W.; Sun, J.; Zhang, S. The flammability and mechanical properties of poly (lactic acid) composites containing Ni-MOF nanosheets with polyhydroxy groups. Compos. B Eng. 2020, 183, 107568. [Google Scholar] [CrossRef]
  58. Samiee, R.; Montazeri, S.; Ramezanzadeh, B.; Mahdavian, M. Ce-MOF nanorods/aluminum hydroxide (AITH) synergism effect on the fire-retardancy/smoke-release and thermo-mechanical properties of a novel thermoplastic acrylic intumescent composite coating. Chem. Eng. J. 2022, 428, 132533. [Google Scholar] [CrossRef]
  59. Shao, Z.-B.; Zhang, J.; Jian, R.-K.; Sun, C.-C.; Li, X.-L.; Wang, D.-Y. A strategy to construct multifunctional ammonium polyphosphate for epoxy resin with simultaneously high fire safety and mechanical properties. Compos. Part A Appl. Sci. Manuf. 2021, 149, 106529. [Google Scholar] [CrossRef]
  60. Li, Y.Y.; Li, X.M.; Pan, Y.T.; Xu, X.Y.; Song, Y.Z.; Yang, R.J. Mitigation the release of toxic PH3 and the fire hazard of PA6/AHP composite by MOFs. J. Hazard. Mater. 2020, 395, 122604. [Google Scholar] [CrossRef]
  61. Xu, W.Z.; Wang, G.S.; Xu, J.Y.; Liu, Y.C.; Chen, R.; Yan, H.Y. Modification of diatomite with melamine coated zeolitic imidazolate framework-8 as an effective flame retardant to enhance flame retardancy and smoke suppression of rigid polyurethane foam. J. Hazard. Mater. 2019, 379, 120819. [Google Scholar] [CrossRef] [PubMed]
  62. Nabipour, H.; Wang, X.; Song, L.; Hu, Y. Organic-inorganic hybridization of isoreticular metal-organic framework-3 with melamine for efficiently reducing the fire risk of epoxy resin. Compos. B Eng. 2021, 211, 108606. [Google Scholar] [CrossRef]
  63. Wang, H.; Li, S.; Zhu, Z.M.; Yin, X.Z.; Wang, L.X.; Weng, Y.X.; Wang, X.Y. A novel DOPO-based flame retardant containing benzimidazolone structure with high charring ability towards low flammability and smoke epoxy resins. Polym. Degrad. Stab. 2021, 183, 109426. [Google Scholar] [CrossRef]
  64. Shi, Y.Q.; Yu, B.; Zheng, Y.Y.; Yang, J.; Duan, Z.P.; Hu, Y. Design of reduced graphene oxide decorated with DOPO-phosphanomidate for enhanced fire safety of epoxy resin. J. Colloid Interface Sci. 2018, 521, 160–171. [Google Scholar] [CrossRef]
  65. Chi, Z.Y.; Guo, Z.W.; Xu, Z.C.; Zhang, M.J.; Li, M.; Shang, L.; Ao, Y.H. A DOPO-based phosphorus-nitrogen flame retardant bio-based epoxy resin from diphenolic acid: Synthesis, flame-retardant behavior and mechanism. Polym. Degrad. Stab. 2020, 176, 109151. [Google Scholar] [CrossRef]
  66. Yang, S.; Hu, Y.F.; Zhang, Q.X. Synthesis of a phosphorus-nitrogen-containing flame retardant and its application in epoxy resin. High Perform. Polym. 2019, 31, 186–196. [Google Scholar] [CrossRef]
  67. Shen, D.; Xu, Y.J.; Long, J.W.; Shi, X.H.; Chen, L.; Wang, Y.Z. Epoxy resin flame-retarded via a novel melamine-organophosphinic acid salt: Thermal stability, flame retardance and pyrolysis behavior. J. Anal. Appl. Pyrolysis 2017, 128, 54–63. [Google Scholar] [CrossRef]
  68. Wang, X.; Wu, T.; Hong, J.; Dai, J.; Lu, Z.; Yang, C.; Yuan, C.; Dai, L. Organophosphorus modified hollow bimetallic organic frameworks: Effective adsorption and catalytic charring of pyrolytic volatiles. Chem. Eng. J. 2021, 421, 129697. [Google Scholar] [CrossRef]
  69. Liu, D.; Cui, Y.; Zhang, T.; Zhao, W.; Ji, P. Improving the flame retardancy and smoke suppression of epoxy resins by introducing of DOPO derivative functionalized ZIF-8. Polym. Degrad. Stab. 2021, 194, 109749. [Google Scholar] [CrossRef]
  70. Cai, L.Y.; Xin, F.; Zhai, C.C.; Chen, Y.; Xu, B.; Li, X.M. The effects of DOPO modified Co-based metalorganic framework on flame retardancy, stiffness and thermal stability of epoxy resin. RSC Advs. 2021, 11, 6781–6790. [Google Scholar] [CrossRef]
  71. Hou, Y.B.; Liu, L.X.; Qiu, S.L.; Zhou, X.; Gui, Z.; Hu, Y. DOPO-modified two-dimensional Co-based metal-organic framework: Preparation and application for enhancing fire safety of poly(lactic acid). ACS Appl. Mater. Interfaces 2018, 10, 8274–8286. [Google Scholar] [CrossRef] [PubMed]
  72. Yang, J.; Zhang, A.; Chen, Y.; Wang, L.; Li, M.; Yang, H.; Hou, Y. Surface modification of core–shell structured ZIF-67@cobalt coordination compound to improve the fire safety of biomass aerogel insulation materials. Chem. Eng. J. 2022, 430, 132809. [Google Scholar] [CrossRef]
  73. Qiu, S.L.; Ma, C.; Wang, X.; Zhou, X.; Feng, X.M.; Yuen, R.K.K.; Hu, Y. Melamine-containing polyphosphazene wrapped ammonium polyphosphate: A novel multifunctional organic-inorganic hybrid flame retardant. J. Hazard. Mater. 2018, 344, 839–848. [Google Scholar] [CrossRef] [PubMed]
  74. Zhou, X.; Qiu, S.; Mu, X.; Zhou, M.; Cai, W.; Song, L.; Xing, W.; Hu, Y. Polyphosphazenes-based flame retardants: A review. Compos. B Eng. 2020, 202, 108397. [Google Scholar] [CrossRef]
  75. Zhang, Z.; Han, Z.; Pan, Y.-T.; Li, D.; Wang, D.Y.; Yang, R. Dry synthesis of mesoporous nanosheet assembly constructed by cyclomatrix polyphosphazene frameworks and its application in flame retardant polypropylene. Chem. Eng. J. 2020, 395, 125076. [Google Scholar] [CrossRef]
  76. Rothemund, S.; Teasdale, I. Preparation of polyphosphazenes: A tutorial review. Chem. Soc. Rev. 2016, 45, 5200–5215. [Google Scholar] [CrossRef] [Green Version]
  77. Jiang, J.; Huo, S.; Zheng, Y.; Yang, C.; Yan, H.; Ran, S.; Fang, Z. A novel synergistic flame retardant of hexaphenoxycyclotriphosphazene for epoxy resin. Polymers 2021, 13, 3648. [Google Scholar] [CrossRef] [PubMed]
  78. Duan, R.; Wu, H.; Li, J.; Zhou, Z.; Meng, W.; Liu, L.; Qu, H.; Xu, J. Phosphor nitrile functionalized UiO-66-NU2/graphene hybrid flame retardants for fire safety of epoxy. Colloids Surf. A 2022, 635, 128093. [Google Scholar] [CrossRef]
  79. Xu, Z.M.; Xing, W.Y.; Hou, Y.B.; Zou, B.; Han, L.F.; Hu, W.Z.; Hu, Y. The combustion and pyrolysis process of flame-retardant polystyrene/cobalt-based metal organic frameworks (MOF) nanocomposite. Combust. Flame 2021, 226, 108–116. [Google Scholar] [CrossRef]
  80. Sang, L.; Cheng, Y.M.; Yang, R.; Li, J.; Kong, Q.H.; Zhang, J.H. Polyphosphazene-wrapped Fe-MOF for improving flame retardancy and smoke suppression of epoxy resins. J. Therm. Anal. Calorim. 2021, 144, 51–59. [Google Scholar] [CrossRef]
  81. Meng, W.; Wu, H.; Bi, X.; Huo, Z.; Wu, J.; Jiao, Y.; Xu, J.; Wang, M.; Qu, H. Synthesis of ZIF-8 with encapsulated hexachlorocyclotriphosphazene and its quenching mechanism for flame-retardant epoxy resin. Microporous Mesoporous Mater. 2021, 314, 110885. [Google Scholar] [CrossRef]
  82. He, T.; Guo, J.; Qi, C.; Feng, R.; Yang, B.; Zhou, Y.; Tian, L.; Cui, J. Core–shell structure flame retardant Salen-PZN-Cu@Ni-MOF microspheres enhancing fire safety of epoxy resin through the synergistic effect. J. Polym. Res. 2021, 29, 27. [Google Scholar] [CrossRef]
  83. Wang, R.Z.; Chen, Y.; Liu, Y.Y.; Ma, M.L.; Tong, Z.Y.; Chen, X.L.; Bi, Y.X.; Huang, W.B.; Liao, Z.J.; Chen, S.L.; et al. Metal-organic frameworks derived ZnO@MOF@PZS flame retardant for reducing fire hazards of polyurea nanocomposites. Polym. Adv. Technol. 2021, 32, 4700–4709. [Google Scholar] [CrossRef]
  84. Hou, B.; Song, K.; Ur Rehman, Z.; Song, T.; Lin, T.; Zhang, W.; Pan, Y.T.; Yang, R. Precise control of a yolk-double shell metal-organic framework-based nanostructure provides enhanced fire safety for epoxy nanocomposites. ACS Appl. Mater. Interfaces 2022, 14, 14805–14816. [Google Scholar] [CrossRef]
  85. Qi, X.L.; Zhou, D.D.; Zhang, J.; Hu, S.; Haranczyk, M.; Wang, D.Y. Simultaneous improvement of mechanical and fire-safety properties of polymer composites with phosphonate-loaded MOF additives. ACS Appl. Mater. Interfaces 2019, 11, 20325–20332. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  86. Xu, B.L.; Xu, W.Z.; Liu, Y.C.; Chen, R.; Li, W.; Wu, Y.; Yang, Z.T. Surface modification of -zirconium phosphate by zeolitic imidazolate frameworks-8 and its effect on improving the fire safety of polyurethane elastomer. Polym. Adv. Technol. 2018, 29, 2816–2826. [Google Scholar] [CrossRef]
  87. Ma, S.C.; Hou, Y.B.; Xiao, Y.L.; Chu, F.K.; Cai, T.M.; Hu, W.Z.; Hu, Y. Metal-organic framework@polyaniline nanoarchitecture for improved fire safety and mechanical performance of epoxy resin. Mater. Chem. Phys. 2020, 247, 122875. [Google Scholar] [CrossRef]
  88. Wang, J.; Liu, Y.S.; Guo, X.Y.; Qu, H.Q.; Chang, R.; Ma, J. Efficient adsorption of dyes using polyethyleneimine-modified NH2-MIL-101(Al) and its sustainable application as a flame retardant for an epoxy resin. Acs Omega 2020, 5, 32286–32294. [Google Scholar] [CrossRef]
  89. Huang, R.; Guo, X.Y.; Ma, S.Y.; Xie, J.X.; Xu, J.Z.; Ma, J. Novel phosphorus-nitrogen-containing ionic liquid modified metal-organic framework as an effective flame retardant for epoxy resin. Polymers 2020, 12, 108. [Google Scholar] [CrossRef] [Green Version]
  90. Sai, T.; Ran, S.Y.; Guo, Z.H.; Yan, H.Q.; Zhang, Y.; Song, P.G.; Zhang, T.; Wang, H.; Fang, Z.P. Deposition growth of Zr-based mofs on cerium phenylphosphonate lamella towards enhanced thermal stability and fire safety of polycarbonate. Compos. B Eng. 2020, 197, 108064. [Google Scholar] [CrossRef]
  91. Yang, X.; Zhao, L.; Peng, F.; Zhu, Y.; Wang, G. Co-based metal-organic framework with phosphonate and triazole structures for enhancing fire retardancy of epoxy resin. Polym. Degrad. Stab. 2021, 193, 109721. [Google Scholar] [CrossRef]
  92. Zhang, J.; Li, Z.; Shao, Z.B.; Zhang, L.; Wang, D.Y. Hierarchically tailored hybrids via interfacial-engineering of self-assembled UiO-66 and prussian blue analogue: Novel strategy to impart epoxy high-efficient fire retardancy and smoke suppression. Chem. Eng. J. 2020, 400, 125942. [Google Scholar] [CrossRef]
  93. Kroto, H.W.; Heath, J.R.; O’Brien, S.C.; Curl, R.F.; Smalley, R.E. C60: Buckminsterfullerene. Nature 1985, 318, 162–163. [Google Scholar] [CrossRef]
  94. Iijima, S. Helical microtubules of graphitic carbon. Nature 1991, 354, 56–58. [Google Scholar] [CrossRef]
  95. Novoselov, K.S.; Geim, A.K.; Morozov, S.V.; Jiang, D.; Zhang, Y.; Dubonos, S.V.; Grigorieva, I.V.; Firsov, A.A. Electric field effect in atomically thin carbon films. Science 2004, 306, 666–669. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  96. Tong, Z.Y.; Liao, Z.J.; Liu, Y.Y.; Ma, M.L.; Bi, Y.X.; Huang, W.B.; Ma, Y.; Qiao, M.T.; Wu, G.L. Hierarchical Fe3O4/Fe@C@MoS2 core-shell nanofibers for efficient microwave absorption. Carbon 2021, 179, 646–654. [Google Scholar] [CrossRef]
  97. Bi, Y.X.; Ma, M.L.; Liao, Z.J.; Tong, Z.Y.; Chen, Y.; Wang, R.Z.; Ma, Y.; Wu, G.L. One-dimensional Ni@Co/C@PPy composites for superior electromagnetic wave absorption. J. Colloid Interface Sci. 2022, 605, 483–492. [Google Scholar] [CrossRef]
  98. Liao, Z.J.; Ma, M.L.; Tong, Z.Y.; Bi, Y.X.; Chung, K.L.; Qiao, M.T.; Ma, Y.; Ma, A.J.; Wu, G.L.; Zhong, X.; et al. Fabrication of one-dimensional CoFe2/C@MoS2 composites as efficient electromagnetic wave absorption materials. Dalton Trans. 2021, 50, 11640–11649. [Google Scholar] [CrossRef]
  99. Islam, M.; Lantada, A.D.; Mager, D.; Korvink, J.G. Carbon-based materials for articular tissue engineering: From innovative scaffolding materials toward engineered living carbon. Adv. Healthc. Mater. 2022, 11, 2101834. [Google Scholar] [CrossRef]
  100. Li, Z.H.; Xu, K.; Pan, Y.S. Recent development of supercapacitor electrode based on carbon materials. Nanotechnol. Rev. 2019, 8, 35–49. [Google Scholar] [CrossRef]
  101. Ren, J.C.; Huang, Y.L.; Zhu, H.; Zhang, B.H.; Zhu, H.K.; Shen, S.H.; Tan, G.Q.; Wu, F.; He, H.; Lan, S.; et al. Recent progress on MOF-derived carbon materials for energy storage. Carbon Energy 2020, 2, 176–202. [Google Scholar] [CrossRef] [Green Version]
  102. Ma, M.L.; Yang, Y.Y.; Chen, Y.; Jiang, J.B.; Ma, Y.; Wang, Z.F.; Huang, W.B.; Wang, S.S.; Liu, M.Q.; Ma, D.X.; et al. Fabrication of hollow flower-like magnetic Fe3O4/C/MnO2/C3N4 composite with enhanced photocatalytic activity. Sci. Rep. 2021, 11, 2597. [Google Scholar] [CrossRef] [PubMed]
  103. Zhan, Y.Y.; Shang, S.; Yuan, B.H.; Wang, S.S.; Chen, X.F.; Chen, G.Q. Carbonization mechanism of polypropylene catalyzed by Co compounds combined with phosphorus-doped graphene to improve its fire safety performance. Mater. Today Commun. 2021, 26, 101792. [Google Scholar] [CrossRef]
  104. Nabipour, H.; Wang, X.; Song, L.; Hu, Y. Graphene oxide/zeolitic imidazolate frameworks-8 coating for cotton fabrics with highly flame retardant, self-cleaning and efficient oil/water separation performances. Mater. Chem. Phys. 2020, 256, 123656. [Google Scholar] [CrossRef]
  105. Huang, Y.L.; Yuan, B.H. Reduced graphene oxide/iron-based metal-organic framework nano-coating created on flexible polyurethane foam by layer-by-layer assembly: Enhanced smoke suppression and oil adsorption property. Mater. Lett. 2021, 298, 129974. [Google Scholar] [CrossRef]
  106. Xu, B.L.; Xu, W.Z.; Wang, G.S.; Liu, L.C.; Xu, J. Zeolitic imidazolate frameworks-8 modified graphene as a green flame retardant for reducing the fire risk of epoxy resin. Polym. Adv. Technol. 2018, 29, 1733–1743. [Google Scholar] [CrossRef]
  107. Sang, B.; Li, Z.W.; Li, X.H.; Yu, L.G.; Zhang, Z.J. Graphene-based flame retardants: A review. J. Mater. Sci. 2016, 51, 8271–8295. [Google Scholar] [CrossRef]
  108. Hou, Y.; Qiu, S.; Hu, Y.; Kundu, C.K.; Gui, Z.; Hu, W. Construction of bimetallic ZIF-derived Co-Ni LDHs on the surfaces of GO or CNTs with a recyclable method: Toward reduced toxicity of gaseous thermal decomposition products of unsaturated polyester resin. ACS Appl. Mater. Interfaces 2018, 10, 18359–18371. [Google Scholar] [CrossRef]
  109. Hou, Y.; Hu, W.; Zhou, X.; Gui, Z.; Hu, Y. Vertically aligned nickel 2-methylimidazole metal–organic framework fabricated from graphene oxides for enhancing fire safety of polystyrene. Ind. Eng. Chem. Res. Res. 2017, 56, 8778–8786. [Google Scholar] [CrossRef]
  110. Xu, W.Z.; Wang, X.L.; Wu, Y.; Li, W.; Chen, C.Y. Functionalized graphene with Co-ZIF adsorbed borate ions as an effective flame retardant and smoke suppression agent for epoxy resin. J. Hazard. Mater. 2019, 363, 138–151. [Google Scholar] [CrossRef]
  111. Xu, W.Z.; Wang, X.L.; Liu, Y.C.; Li, W.; Chen, R. Improving fire safety of epoxy filled with graphene hybrid incorporated with zeolitic imidazolate framework/layered double hydroxide. Polym. Degrad. Stab. 2018, 154, 27–36. [Google Scholar] [CrossRef]
  112. Zhang, J.; Li, Z.; Zhang, L.; Molleja, J.G.; Wang, D.Y. Bimetallic metal-organic frameworks and graphene oxide nano-hybrids for enhanced fire retardant epoxy composites: A novel carbonization mechanism. Carbon 2019, 153, 407–416. [Google Scholar] [CrossRef]
  113. Xu, W.Z.; Cheng, C.M.; Qin, Z.Q.; Zhong, D.; Cheng, Z.H.; Zhang, Q.Q. Improvement of thermoplastic polyurethane’s flame retardancy and thermal conductivity by leaf-shapedcobalt-zeolitic imidazolate framework-modified graphene andintumescent flame retardant. Polym. Adv. Technol. 2021, 32, 228–240. [Google Scholar] [CrossRef]
  114. Wang, H.; He, Z.; Li, X.; Wang, Y.; Yao, D.; Zheng, Y. Improving the flame retardancy of epoxy resin with ZIF-67@GO-PA nanohybrid as filler. J. Appl. Polym. Sci. 2022, 139, 52211. [Google Scholar] [CrossRef]
  115. Zhang, J.; Li, Z.; Qi, X.L.; Zhang, W.; Wang, D.Y. Size tailored bimetallic metal-organic framework (mof) on graphene oxide with sandwich-like structure as functional nano-hybrids for improving fire safety of epoxy. Compos. B Eng. 2020, 188, 107881. [Google Scholar] [CrossRef]
  116. Zhang, M.; Ding, X.; Zhan, Y.; Wang, Y.; Wang, X. Improving the flame retardancy of poly(lactic acid) using an efficient ternary hybrid flame retardant by dual modification of graphene oxide with phenylphosphinic acid and nano mofs. J. Hazard. Mater. 2020, 384, 121260. [Google Scholar] [CrossRef]
  117. Zhang, M.; Shi, X.; Dai, X.; Huo, C.; Xie, J.; Li, X.; Wang, X. Improving the crystallization and fire resistance of poly(lactic acid) with nano-ZIF-8@GO. J Hazard. Mater. 2018, 53, 7083–7093. [Google Scholar] [CrossRef]
  118. Shang, S.; Yuan, B.H.; Sun, Y.R.; Chen, G.Q.; Huang, C.Y.; Yu, B.; He, S.; Dai, H.M.; Chen, X.F. Facile preparation of layered melamine-phytate flame retardant via supramolecular self-assembly technology. J. Colloid Interface Sci. 2019, 553, 364–371. [Google Scholar] [CrossRef]
  119. Li, J.; Wu, W.; Meng, W.; Zhang, W.; Zhou, Z.; Wang, T.; Xu, J.; Qu, H. Nickel ammonium phosphate nanowires modified g-C3N4 for improving the fire safety of epoxy resin. Fibers Polym. 2021, 22, 2664–2672. [Google Scholar] [CrossRef]
  120. Chen, Z.W.; Chen, T.T.; Yu, Y.; Zhang, Q.W.; Chen, Z.Q.; Jiang, J.C. Metal-organic framework MIL-53 (Fe)@C/graphite carbon nitride hybrids with enhanced thermal stability, flame retardancy, and smoke suppression for unsaturated polyester resin. Polym. Adv. Technol. 2019, 30, 2458–2467. [Google Scholar] [CrossRef]
  121. Xu, W.Z.; Yan, H.Y.; Wang, G.S.; Qin, Z.Q.; Fan, L.J.; Yang, Y.X. A silica-coated metal-organic framework/graphite-carbon nitride hybrid for improved fire safety of epoxy resins. Mater. Chem. Phys. 2021, 258, 123810. [Google Scholar] [CrossRef]
  122. Yin, Z.; Lu, J.; Hong, N.; Cheng, W.; Jia, P.; Wang, H.; Hu, W.; Wang, B.; Song, L.; Hu, Y. Functionalizing Ti3C2Tx for enhancing fire resistance and reducing toxic gases of flexible polyurethane foam composites with reinforced mechanical properties. J. Colloid Interface Sci. 2022, 607, 1300–1312. [Google Scholar] [CrossRef] [PubMed]
  123. Wang, M.; Peng, G.; Chen, C.; Zhang, L.; Xie, Y. Synergistic modification of ZIF and silica on carbon spheres to enhance the flame retardancy of composites coatings. Colloids Surf. A. 2022, 642, 128645. [Google Scholar] [CrossRef]
  124. Wang, G.; Xu, W.; Chen, R.; Li, W.; Liu, Y.; Yang, K. Synergistic effect between zeolitic imidazolate framework-8 and expandable graphite to improve the flame retardancy and smoke suppression of polyurethane elastomer. J. Appl. Polym. Sci. 2019, 137, 48048. [Google Scholar] [CrossRef]
  125. Zou, Z.; Wang, K.; Zhang, Z.; Cao, X.; Lin, J.; Yang, D.; Li, J.; Zhu, Y.; Wang, X. Preparation of (Fe)MIL-101 on short carbon fibers to improve the flame retardancy, smoke suppression, and mechanical of epoxy resin. Polym. Adv. Technol. 2021, 33, 400–410. [Google Scholar] [CrossRef]
  126. Liu, B.W.; Zhao, H.B.; Wang, Y.Z. Advanced flame-retardant methods for polymeric materials. Adv. Mater. 2022, 34, 2107905. [Google Scholar] [CrossRef] [PubMed]
  127. Li, S.; Wang, X.H.; Xu, M.J.; Liu, L.B.; Wang, W.B.; Gao, S.L.; Li, B. Effect of a biomass based waterborne fire retardant coating on the flame retardancy for wood. Polym. Adv. Technol. 2021, 32, 4805–4814. [Google Scholar] [CrossRef]
  128. Zhang, J.; Li, Z.; Yin, G.Z.; Wang, D.Y. Construction of a novel three-in-one biomass based intumescent fire retardant through phosphorus functionalized metal-organic framework and beta-cyclodextrin hybrids in achieving fire safe epoxy. Compos. Commun. 2021, 23, 100594. [Google Scholar] [CrossRef]
  129. Zhou, S.Y.; Apostolopoulou-Kalkavoura, V.; da Costa, M.V.T.; Bergstrom, L.; Stromme, M.; Xu, C. Elastic aerogels of cellulose nanofibers@metal-organic frameworks for thermal insulation and fire retardancy. Nano-Micro Lett. 2020, 12, 9. [Google Scholar] [CrossRef] [Green Version]
  130. Nabipour, H.; Nie, S.; Wang, X.; Song, L.; Hu, Y. Highly flame retardant zeolitic imidazole framework-8@cellulose composite aerogels as absorption materials for organic pollutants. Cellulose 2019, 27, 2237–2251. [Google Scholar] [CrossRef]
  131. Yin, L.; Gong, K.; Zhou, K.; Qian, X.; Shi, C.; Gui, Z.; Qian, L. Flame-retardant activity of ternary integrated modified boron nitride nanosheets to epoxy resin. J Colloid Interface Sci. 2022, 608, 853–863. [Google Scholar] [CrossRef]
  132. Huang, J.; Guo, W.; Wang, X.; Niu, H.; Song, L.; Hu, Y. Combination of cardanol-derived flame retardant with SiO2@MOF particles for simultaneously enhancing the toughness, anti-flammability and smoke suppression of epoxy thermosets. Compos. Commun. 2021, 27, 100904. [Google Scholar] [CrossRef]
  133. Zhang, J.; Li, Z.; Zhang, L.; Yang, Y.X.; Wang, D.Y. Green synthesis of biomass phytic acid-functionalized UiO-66-NH2 hierarchical hybrids toward fire safety of epoxy resin. ACS Sustain. Chem. Eng. 2020, 8, 994–1003. [Google Scholar] [CrossRef]
  134. Xie, J.; Shi, X.; Zhang, M.; Dai, X.; Wang, X. Improving the flame retardancy of polypropylene by nano metal–organic frameworks and bioethanol coproduct. Fire Mater. 2019, 43, 373–380. [Google Scholar] [CrossRef]
  135. Kaneti, Y.V.; Tang, J.; Salunkhe, R.R.; Jiang, X.C.; Yu, A.B.; Wu, K.C.W.; Yamauchi, Y. Nanoarchitectured design of porous materials and nanocomposites from metal-organic frameworks. Adv. Mater. 2017, 29, 1604898. [Google Scholar] [CrossRef]
  136. Dang, S.; Zhu, Q.L.; Xu, Q. Nanomaterials derived from metal-organic frameworks. Nat. Rev. Mater. 2018, 3, 17075. [Google Scholar] [CrossRef]
  137. Salunkhe, R.R.; Kaneti, Y.V.; Yamauchi, Y. Metal-organic framework-derived nanoporous metal oxides toward supercapacitor applications: Progress and prospects. ACS Nano 2017, 11, 5293–5308. [Google Scholar] [CrossRef]
  138. Salunkhe, R.R.; Kaneti, Y.V.; Kim, J.; Kim, J.H.; Yamauchi, Y. Nanoarchitectures for metal-organic framework-derived nanoporous carbons toward supercapacitor applications. Acc. Chem. Res. 2016, 49, 2796–2806. [Google Scholar] [CrossRef]
  139. Chen, Y.Z.; Zhang, R.; Jiao, L.; Jiang, H.L. Metal-organic framework-derived porous materials for catalysis. Coord. Chem. Rev. 2018, 362, 1–23. [Google Scholar] [CrossRef]
  140. Yu, J.F.; Wang, Q.; O’Hare, D.; Sun, L.Y. Preparation of two dimensional layered double hydroxide nanosheets and their applications. Chem. Soc. Rev. 2017, 46, 5950–5974. [Google Scholar] [CrossRef]
  141. Li, A.J.; Xu, W.Z.; Chen, R.; Liu, Y.C.; Li, W. Fabrication of zeolitic imidazolate frameworks on layered double hydroxide nanosheets to improve the fire safety of epoxy resin. Compos. Part A Appl. Sci. Manuf. 2018, 112, 558–571. [Google Scholar] [CrossRef]
  142. Zhang, J.T.; Hu, H.; Li, Z.; Lou, X.W. Double-shelled nanocages with cobalt hydroxide inner shell and layered double hydroxides outer shell as high-efficiency polysulfide mediator for lithium-sulfur batteries. Angew. Chem. Int. Ed. 2016, 55, 3982–3986. [Google Scholar] [CrossRef] [PubMed]
  143. Wang, J.; Wei, Y.; Wang, Z.; He, X.; Wang, C.; Lin, H.; Deng, Y. MOFs-derived self-sacrificing template strategy to double-shelled metal oxides nanocages as hierarchical interfacial catalyst for suppressing smoke and toxic gases releases of epoxy resin. Chem. Eng. J. 2022, 432, 134328. [Google Scholar] [CrossRef]
  144. Pan, Y.T.; Wan, J.T.; Zhao, X.L.; Li, C.; Wang, D.Y. Interfacial growth of MOF-derived layered double hydroxide nanosheets on graphene slab towards fabrication of multifunctional epoxy nanocomposites. Chem. Eng. J. 2017, 330, 1222–1231. [Google Scholar] [CrossRef]
  145. Guo, H.L.; Wang, Y.F.; Li, C.F.; Zhou, K.Q. Construction of sandwich-structured coal-layered double hydroxide@zeolitic imidazolate framework-67 (CoAl-LDH@ZIF-67) hybrids: Towards enhancing the fire safety of epoxy resins. RSC Adv. 2018, 8, 36114–36122. [Google Scholar] [CrossRef] [Green Version]
  146. Zhang, L.; Zhang, J.; Wang, D.Y. Hierarchical layered double hydroxide nanosheets/phosphorus-containing organosilane functionalized hollow glass microsphere towards high performance epoxy composite: Enhanced interfacial adhesion and bottom-up charring behavior. Polymer 2020, 210, 123018. [Google Scholar] [CrossRef]
  147. Zhou, Y.; Qiu, S.; Chu, F.; Yang, W.; Qiu, Y.; Qian, L.; Hu, W.; Song, L. High-performance flexible polyurethane foam based on hierarchical BN@MOF-LDH@APTEs structure: Enhanced adsorption, mechanical and fire safety properties. J Colloid Interface Sci. 2022, 609, 794–806. [Google Scholar] [CrossRef]
  148. Zhang, Z.D.; Qin, J.Y.; Zhang, W.C.; Pan, Y.T.; Wang, D.Y.; Yang, R.J. Synthesis of a novel dual layered double hydroxide hybrid nanomaterial and its application in epoxy nanocomposites. Chem. Eng. J. 2020, 381, 122777. [Google Scholar] [CrossRef]
  149. Zhou, X.; Mu, X.W.; Cai, W.; Wang, J.L.; Chu, F.K.; Xu, Z.M.; Song, L.; Xing, W.Y.; Hu, Y. Design of hierarchical NiCo-LDH@PZS hollow dodecahedron architecture and application in high-performance epoxy resin with excellent fire safety. ACS Appl. Mater. Interfaces 2019, 11, 41736–41749. [Google Scholar] [CrossRef]
  150. Zhou, Y.; Chu, F.; Ding, L.; Yang, W.; Zhang, S.; Xu, Z.; Qiu, S.; Hu, W. Mof-derived 3D petal-like CoNi-LDH array cooperates with MXene to effectively inhibit fire and toxic smoke hazards of fpuf. Chemosphere 2022, 297, 134134. [Google Scholar] [CrossRef]
  151. Wang, R.; Chen, Y.; Liu, Y.; Ma, M.; Hou, Y.; Chen, X.; Ma, Y.; Huang, W. Synthesis of sugar gourd-like metal organic framework-derived hollow nanocages nickel molybdate@cobalt-nickel layered double hydroxide for flame retardant polyurea. J. Colloid. Interface Sci. 2022, 616, 234–245. [Google Scholar] [CrossRef] [PubMed]
  152. Zhang, Z.D.; Li, X.L.; Yuan, Y.S.; Pan, Y.T.; Wang, D.Y.; Yang, R.J. Confined dispersion of zinc hydroxystannate nanoparticles into layered bimetallic hydroxide nanocapsules and its application in flame-retardant epoxy nanocomposites. ACS Appl. Mater. Interfaces 2019, 11, 40951–40960. [Google Scholar] [CrossRef] [PubMed]
  153. Zhang, L.; Chen, S.Q.; Pan, Y.T.; Zhang, S.D.; Nie, S.B.; Wei, P.; Zhang, X.Q.; Wang, R.; Wang, D.Y. Nickel metal-organic framework derived hierarchically mesoporous nickel phosphate toward smoke suppression and mechanical enhancement of intumescent flame retardant wood fiber/poly(lactic acid) composites. ACS Sustain. Chem. Eng. 2019, 7, 9272–9280. [Google Scholar] [CrossRef]
  154. Zhou, Y.; Chu, F.; Yang, W.; Qiu, S.; Hu, Y. Mof-derived strategy to obtain CuCoOx functionalized HO-BN: A novel design to enhance the toughness, fire safety and heat resistance of bismaleimide resin. Chem. Eng. J. 2022, 431, 134013. [Google Scholar] [CrossRef]
  155. Xu, Z.; Chu, F.; Luo, X.; Jiang, X.; Cheng, L.; Song, L.; Hou, Y.; Hu, W. Magnetic Fe3O4 nanoparticle/ZIF-8 composites for contaminant removal from water and enhanced flame retardancy of flexible polyurethane foams. ACS Appl. Nano Mater. 2022, 5, 3491–3501. [Google Scholar] [CrossRef]
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Figure 1. Proposed mechanisms for illustration of the thermal stability flame retardancy of PS and its composites. Reprinted with permission from Ref. [27]. Copyright 2017, American Chemical Society.
Figure 1. Proposed mechanisms for illustration of the thermal stability flame retardancy of PS and its composites. Reprinted with permission from Ref. [27]. Copyright 2017, American Chemical Society.
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Figure 2. Number of publications vs. year for metal organic frameworks and their derivatives as flame retardants (until June 2022).
Figure 2. Number of publications vs. year for metal organic frameworks and their derivatives as flame retardants (until June 2022).
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Figure 3. SEM images of ZIF-7, ZIF-8, and ZIF-11 (above) and ZIF-8 and ZIF-67 (below). Reprinted with permission from Ref. [26]. Copyright 2021 Elsevier and Ref. [34].
Figure 3. SEM images of ZIF-7, ZIF-8, and ZIF-11 (above) and ZIF-8 and ZIF-67 (below). Reprinted with permission from Ref. [26]. Copyright 2021 Elsevier and Ref. [34].
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Figure 4. Schematic illustration of the proposed mechanism of EP/Y-BTC. Reprinted with permission from Ref. [44]. Copyright 2021, American Chemical Society.
Figure 4. Schematic illustration of the proposed mechanism of EP/Y-BTC. Reprinted with permission from Ref. [44]. Copyright 2021, American Chemical Society.
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Figure 5. The flame-retardant mechanism of P-containing flame retardants: radical capturing effect in the gaseous phase and char promotion effect in the condensed phase. Reprinted with permission from Ref. [51]. Copyright 2021, Elsevier.
Figure 5. The flame-retardant mechanism of P-containing flame retardants: radical capturing effect in the gaseous phase and char promotion effect in the condensed phase. Reprinted with permission from Ref. [51]. Copyright 2021, Elsevier.
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Figure 6. Schematic diagram of DOPO-NH2-ZIF-67 and W-Zr-MOF-DOPO structures. Reprinted with permission from Ref. [68]. Copyright 2021 Elsevier, and Ref. [72]. Copyright 2022 Elsevier.
Figure 6. Schematic diagram of DOPO-NH2-ZIF-67 and W-Zr-MOF-DOPO structures. Reprinted with permission from Ref. [68]. Copyright 2021 Elsevier, and Ref. [72]. Copyright 2022 Elsevier.
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Figure 7. Schematic illustration of the proposed mechanism of EP/IL@NH2-MIL-101(Al) [89].
Figure 7. Schematic illustration of the proposed mechanism of EP/IL@NH2-MIL-101(Al) [89].
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Figure 8. Schematic diagram showing the flame retarding mechanism of graphene-based flame retardant under ideal conditionReprinted with permission from Ref. [107]. Copyright 2016, Springer Nature.
Figure 8. Schematic diagram showing the flame retarding mechanism of graphene-based flame retardant under ideal conditionReprinted with permission from Ref. [107]. Copyright 2016, Springer Nature.
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Figure 9. (a) SEM image of Co/Zn-MOF@GO nano-hybrids with big crystal distributed; (b,c) TEM and SEM of GPZ; (d) TEM of nano-ZIF-8@GO; (e,f) SEM image of UiO-66-NH2, TEM image of the UiO-66-NH2/GnPs. Reprinted with permission from Ref. [78]. Copyright 2022 Elsevier, Ref [115]. Copyright 2020 Elsevier, Ref. [116]. Copyright 2020 Elsevier, and Ref. [117]. Copyright 2018 Springer Nature.
Figure 9. (a) SEM image of Co/Zn-MOF@GO nano-hybrids with big crystal distributed; (b,c) TEM and SEM of GPZ; (d) TEM of nano-ZIF-8@GO; (e,f) SEM image of UiO-66-NH2, TEM image of the UiO-66-NH2/GnPs. Reprinted with permission from Ref. [78]. Copyright 2022 Elsevier, Ref [115]. Copyright 2020 Elsevier, Ref. [116]. Copyright 2020 Elsevier, and Ref. [117]. Copyright 2018 Springer Nature.
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Figure 10. Scheme of MOFs loading on carbon-based materials. Reprinted with permission from Ref. [121]. Copyright 2021 Elsevier, Ref. [122]. Copyright 2022 Elsevier, Ref. [123]. Copyright 2022 Elsevier, and Ref. [125]. Copyright 2021 John Wiley & Sons Ltd.
Figure 10. Scheme of MOFs loading on carbon-based materials. Reprinted with permission from Ref. [121]. Copyright 2021 Elsevier, Ref. [122]. Copyright 2022 Elsevier, Ref. [123]. Copyright 2022 Elsevier, and Ref. [125]. Copyright 2021 John Wiley & Sons Ltd.
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Figure 11. Schematic illustration for preparation process of ZHS@NCH and Schematic illustration of flame-retardant mechanism for ZHS@NCH. Reprinted with permission from Ref. [152]. Copyright 2019, American Chemical Society.
Figure 11. Schematic illustration for preparation process of ZHS@NCH and Schematic illustration of flame-retardant mechanism for ZHS@NCH. Reprinted with permission from Ref. [152]. Copyright 2019, American Chemical Society.
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Table
Table 1. Data comparison of MOF/APP as flame retardant and pure matrix.
Table 1. Data comparison of MOF/APP as flame retardant and pure matrix.
SamplesTHRpHRRTSPpSPR *ResiduesReference
MJ/m2kW/m2m2m2/s%
TPU78135910.30.110.1[23]
TPU/6.0APP6526880.0611.0
TPU/4.5APP/1.5Co-MOF632577.10.0415.2
TPU138.9909.6--1.74[55]
TPU/APP117.0270.7--24.16
TPU/APP/Cu0.062542.6218.7--28.19
PLA81.7450.82.6-0.1[57]
PLA-5.0APP70.6396.62.4-4.1
PLA-3.3APP/1.7Ni-MOF65.9329.61.3-5.4
Blank100.82192552.110.56-[58]
Intu/Neat41.7273843.690.44-
Intu/MOF31.9252235.330.35-
EP1051254310.388.0[59]
5APP/EP103924310.2617.4
(ZIF-67+APP)/EP74495270.1623.8
* Peak of smoke production rate.
Table
Table 2. Data on MOFs and phosphonitrile hybrids as flame retardants.
Table 2. Data on MOFs and phosphonitrile hybrids as flame retardants.
SamplesTHRpHRRTSPpSPRResiduesReference
MJ/m2kW/m2m2m2/s%
EP88.851631.2-0.347-[54]
EP/ZIF-8@PZN-348.53819.2-0.319-
EP92.5107324.830.33416.2[80]
EP/3 Fe-MOF@PZS58.474914.550.21228.5
EP116.71408.936.70.432.7[81]
EP/ZIF-8@HCCP-ZP-50100.7745.328.70.2615.87
EP106.65160130.94-0.52[82]
3% Salen-PZN-Cu@Ni-MOF/EP95.17111428.84-3.55
PUA108.37935.4--1.13[83]
PUA/ZnO@MOF@PZS 3.087.13670.6--5.99
EP88.1112735.6-1.8[84]
EP/ZIF@PZS75.591328.1-8.7
Table
Table 3. Data on graphene and its compounding with MOFs as flame retardants.
Table 3. Data on graphene and its compounding with MOFs as flame retardants.
SamplesTHRpHRRTSPSPRResiduesReference
MJ/m2kW/m2m2m2/s%
EP41.294063.00.82-[106]
RGO/EP31.947356.40.72-
ZIF-8/RGO/EP27.333236.80.53-
EP57.21212590.869.9[110]
EP/RGO-254.583049.40.6412.7
EP/ZIF-67/RGO-B-233.542332.70.3720.7
EP58.6135559.00.7810.0[111]
EP/RGO-LDH43.358034.30.5215.7
EP/RGO-LDH/ZIF-6737.946429.90.3817.9
EP-99236.9-16.6[112]
EP/0.5GO-9.5IFR-81223.3--
EP/[email protected]-53218.3-33.1
TPU192.7157316.0-9.2[113]
TPU/IFR/RGO87.842210.4-18
TPU/IFR/Co-ZIF-L/RGO57.62456.0-18.4
EP96.91133--17.9[114]
EP/GO91.1919--20.2
EP/ZIF@GO75.4507--24.0
Table
Table 4. Data on MOFs-derived LDHs as flame retardants.
Table 4. Data on MOFs-derived LDHs as flame retardants.
SamplesTHRpHRRTSPTS *ResiduesReference
MJ/m2kW/m2m2MPa%
EP969613039.711.9[144]
EP/2% rGO@LDH803272145.321.6
EP88.9123524.159.6-[146]
EP/HGM@LDH@DOPO76.753922.948.4-
EP72.9136126.4ANE **4.9[148]
EP/2.5% MgAl@NiCo44.745519.810.9
EP44.6426.9--7.1[149]
EP-4.039.6294.9--11.2
FPUF33.8-1.7471.2-[150]
6 wt% Ti3C2Tx@MOF-LDH29.5-1.4677.1-
PUA108.4935.414.123.726.9[151]
PUA/NiMoO4@Co-Ni LDH3.094.6613.51125.6313.5
* Tensile strength, ** almost no effect.
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Lyu, P.; Hou, Y.; Hu, J.; Liu, Y.; Zhao, L.; Feng, C.; Ma, Y.; Wang, Q.; Zhang, R.; Huang, W.; et al. Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants. Polymers 2022, 14, 5279. https://doi.org/10.3390/polym14235279

AMA Style

Lyu P, Hou Y, Hu J, Liu Y, Zhao L, Feng C, Ma Y, Wang Q, Zhang R, Huang W, et al. Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants. Polymers. 2022; 14(23):5279. https://doi.org/10.3390/polym14235279

Chicago/Turabian Style

Lyu, Ping, Yongbo Hou, Jinhu Hu, Yanyan Liu, Lingling Zhao, Chao Feng, Yong Ma, Qin Wang, Rui Zhang, Weibo Huang, and et al. 2022. "Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants" Polymers 14, no. 23: 5279. https://doi.org/10.3390/polym14235279

APA Style

Lyu, P., Hou, Y., Hu, J., Liu, Y., Zhao, L., Feng, C., Ma, Y., Wang, Q., Zhang, R., Huang, W., & Ma, M. (2022). Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants. Polymers, 14(23), 5279. https://doi.org/10.3390/polym14235279

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