Preparation of Metal–Organic Frameworks and Their Application as Flame Retardants for Polystyrene

Green preparation of highly transparent nano-NH2-UiO(Zr)-66/cellulose composite films with high-strength, superior flame retardant and UV to high-energy blue light shielding performance

From the perspective of sustainable development and practical applications, there is a significant demand for the design of advanced cellulose-based film materials with superior mechanical, optical, and functional properties utilizing environmentally friendly strategies. Herein, biodegradable, mechanically robust and flame-retardant cellulose films with adjustable optical performance were successfully fabricated by in situ synthesis of NH2-UiO(Zr)-66 via a DMF-free green process at room temperature. The results indicate that the introduction of NH2-UiO(Zr)-66 enables films to realize a desirable flame retardancy (the limiting oxygen index (LOI) increased significantly from 19.2 % to 32.9 %). The film self-extinguish quickly once removed from the flame, demonstrating a prominent flame resistance. Compared to the original film, the modified films demonstrate a significant reduction in the peak heat release rate and total heat released, decreasing from 186.6 to 26.8 W/g and 19.7 to 1.2 kJ/g, respectively. Encouragingly, the incorporation of nano-NH2-UiO(Zr)-66 enabled films to achieve excellent UV to high-energy blue light (HEBL) shielding competence (90.8-100 %, 99.6-100 %, and 60.9-89 % for UVB, UVA and HEBL) meanwhile retaining low haze (1.9-2.6 %) and high transmittance (86.2-90.9 %). Furthermore, the incorporation of nano-NH2-UiO(Zr)-66 was observed to enhance the mechanical strength. Overall, this film presents a promising alternative to conventional plastics used in various applications, including electronic devices and packaging materials.

Cocklebur-Inspired Robust Non-flammable Polymer Thermo Conductor for CPU Cooling

Efficient computer central processing units (CPUs) heat dissipation demands polymer-based thermal interface materials that combine high thermal conductivity with strong mechanical properties, eliminating the need for additional fasteners. However, polymers with high thermal conductivity often suffer from insufficient mechanical strength and other challenges, including high production costs, elevated interfacial thermal resistance, and flammability. Inspired by the 3D "spininess-seeds-bark" structure of cocklebur, cast polyurethane (PUC) composites are developed using copper ethylenediamine methylene-phosphonate as the "spininess" and functionalized alumina microspheres as the "seeds" filler. This spininess configuration prevents organophosphate self-polymerization, imparting self-extinguishing properties to the polymer, while also enhancing the mechanical strength and thermal conductivity by connecting the "seeds" to the matrix. The bark-like structure enables effective interlocking of functional particles, optimizing the synergy within the composite. The elevated surface reduces interfacial thermal resistance, leading to enhanced thermal conductivity. The resulting PUC composites demonstrate impressive performance, with a tensile strength of 15.9 MPa and thermal conductivity of 2.51 W m⁻¹ K⁻¹, providing effective continuous cooling for high-power CPUs. These composites offer low density, broad availability, and environmental sustainability, making them promising candidates for sustainable electronics and new energy applications, aligned with global development strategies.

Synergistic Effect of Amino-Modified Co-MOF and APP on Improvement of the Fire Safety of the Rigid Polyurethane Foam

The combustion of rigid polyurethane foam (RPUF) generates significant amounts of toxic and high-temperature smoke, which restricts its application. Here, an amino-modified Co-MOF (NH2-Co-MOF) was synthesized and it was used in conjunction with ammonium polyphosphate (APP) to decrease the flammability of RPUF. We obtained the expected results: the fire safety of RPUF was greatly enhanced by the addition of NH2-Co-MOF and APP. Compared to neat RPUF, the peak heat release rate (pHRR) and total heat release (THR) values of N-C/A/RPUF decreased by 22.5 and 37.4%, respectively. Based on the analysis of combustion products of the gaseous and condensed phases, it can be seen that the synergistic use of NH2-Co-MOF with APP enhances the barrier effect, dilutes combustible gases, and quenches the combustion chain reaction.

MOFs-Based Materials with Confined Space: Opportunities and Challenges for Energy and Catalytic Conversion

Metal-Organic Frameworks (MOFs) are a very promising material in the fields of energy and catalysis due to their rich active sites, tunable pore size, structural adaptability, and high specific surface area. The concepts of "carbon peak" and "carbon neutrality" have opened up huge development opportunities in the fields of energy storage, energy conversion, and catalysis, and have made significant progress and breakthroughs. In recent years, people have shown great interest in the development of MOFs materials and their applications in the above research fields. This review introduces the design strategies and latest progress of MOFs are included based on their structures such as core-shell, yolk-shell, multi-shelled, sandwich structures, unique crystal surface exposures, and MOF-derived nanomaterials in detail. This work comprehensively and systematically reviews the applications of MOF-based materials in energy and catalysis and reviews the research progress of MOF materials for atmospheric water harvesting, seawater uranium extraction, and triboelectric nanogenerators. Finally, this review looks forward to the challenges and opportunities of controlling the synthesis of MOFs through low-cost, improved conductivity, high-temperature heat resistance, and integration with machine learning. This review provides useful references for promoting the application of MOFs-based materials in the aforementioned fields.

In Situ-Generated Heat-Resistant Hydrogen-Bonded Organic Framework for Remarkably Improving Both Flame Retardancy and Mechanical Properties of Epoxy Composites

In this study, the heat-resistant hydrogen-bonded organic framework (HOF) material HOF-FJU-1 was synthesized via in situ generation and then used as flame retardants (FRs) to improve the flame retardancy of epoxy resin (EP). HOF-FJU-1 can maintain high crystallinity at 450 °C and thus function as a flame retardant in EP. The study found that HOF-FJU-1 facilitates the improvement of char formation in EP, thus inhibiting heat transfer and smoke release during combustion. For EP/HOF-FJU-1 composites, the in situ-generated HOF-FJU-1 can remarkably improve both the mechanical properties and the flame retardancy of EP. Furthermore, the in situ-generated HOF-FJU-1 has better fire safety than the ex situ-generated HOF-FJU-1 at the same filling content. Thermal degradation products and flame retardation mechanisms in the gas and condensed phases were further investigated. This work demonstrates that the in situ-generated HOF-FJU-1 is promising to be an excellent flame-retardant candidate.

A biomimetic design for efficient petrochemical spill disposal: CoFe-PBA modified superhydrophobic melamine sponge with mechanical/chemical durability and low fire risk

Due to frequent petrochemical spills, environmental pollution and the threat of secondary marine fires have arisen, necessitating an urgent need for petrochemical spill treatment strategies with high-performance oil-water separation capabilities. To address the challenges of poor durability, instability in hydrophobic conditions, and difficulty in absorbing high-viscosity crude oil associated with hydrophobic absorbent materials, the authors of this study took inspiration from the unique micro and nanostructures of springtails' water-repellent skin. We engineered a superhydrophobic melamine sponge using interfacial assembly techniques designated as Si@PBA@PDA@MS. This material demonstrated improved mechanical and chemical durability, enhanced photothermal performance, and reduced fire risk. The metal-organic framework (MOF)-derived cobalt-iron Prussian blue analog (CoFe-PBA) was firmly anchored to the sponge framework by the chelation of cobalt ions using polydopamine (PDA). The results demonstrated that Si@PBA@PDA@MS demonstrated excellent superhydrophobicity (WCA=163.5°) and oil absorption capacity (53.4-97.5 g/g), maintaining high durability even after 20 cycles of absorption-squeezing. Additionally, it could still exhibit excellent mechanical properties, hydrophobic stability, and absorption performance across a wide temperature range (0-100 °C), pH range (1-14), and high compression strength (ε = 80%), with excellent mechanical/chemical durability. Furthermore, Si@PBA@PDA@MS demonstrated remarkable photothermal performance and low fire risk, offering efficient, safe, and sustainable practical value for effective petrochemical spill treatment.

Recent advances in metal-family flame retardants: a review

The use of polymer materials is inextricably linked to our manufacturing life. However, most of them are easily combusted in the air and the combustion process generates a large amount of toxic fumes and dangerous smoke. This can result in injuries and property damage, as well as limiting their use. It is essential to enhance the flame-retardant properties and smoke suppression performance by using multiple flame retardants. Metal-based flame retardants have a unique chemical composition. They are environmentally friendly flame retardants, which can impart good smoke suppression, flame retardancy to polymers and further reduce the production of toxic gases. The differences in the compounds formed between the transition metals and the main group metals make them act differently as flame retardants for polymers. As a result, this study presents the research progress and flame-retardant mechanism of flame-retardant polymers for flame retardants from different groups of metals in the periodic table of elements in a systematic manner. In view of the differences between the main group metals and transition metals, the mechanism of their application in flame retardant polymer materials is carefully detailed, as are their distinct advantages and disadvantages. And ultimately, prospects for the development of transition metals and main group metals are outlined. It is hoped that this paper will provide valuable references and insights for scholars in the field.

Study on Flame Retardancy Behavior of Epoxy Resin with Phosphaphenanthrene Triazine Compound and Organic Zinc Complexes Based on Phosphonitrile

A novel flame retardant phosphorus-containing organozinc complex (Zn-PDH) was prepared using zinc and iron as the metal center and 4-aminopyridine, with low steric hindrance, as the organic ligand, then using phosphazene to modify the organometallic complex (Zn-4APD). The flame retardant properties and mechanism of Zn-PDH/Tris-(3-DOPO-1-propyl)-triazinetrione (TAD) in epoxy resin (EP) were investigated. Flame inhibition behavior was studied by the vertical combustion test (UL94), while limiting oxygen index (LOI) measurement and flame retardant properties were studied by the cone calorimeter test (CONE). The flame retardant modes of action were explored by using the thermogravimetry–Fourier transform infrared (TG-FTIR) test, X-ray photoelectron spectrometer (XPS), and Raman spectroscopy (LRS). When TAD and Zn-PDH were added to the epoxy resin in the ratio of 3:1, the system achieved a balance between the gas-phase and condense-phase actions of the flame retardant effects, and the 3%TAD/1%Zn-PDH/EP composite system achieved not only good flame inhibition but also obtained good smoke and heat suppression performance, showing a comprehensive flame retardant performance. The gas phase and Zn-PDH mostly promoted charring with a barrier and protective effect in the condensed phase. As for the mechanism, TAD released the phosphorus-containing radicals and phenoxy radicals during decomposition and mainly exerted a gas-phase quenching effect. While in the condense phase, Zn-PDH promoted the decomposition of the polymer matrix to produce more aromatic structures and rapidly formed a complete and dense carbon layer rich in P-O-C crosslinked structures at high temperatures. Meanwhile, more N entered the gas phase in the form of inert gas, which diluted the concentration of the combustible fuel and helped to inhibit the combustion reaction.

Pyrolysis Kinetics of Lignin-Based Flame Retardants Containing MOFs Structure for Epoxy Resins

This study describes the preparation of a lignin-based expandable flame retardant (Lignin-N-DOPO) using grafting melamine and covering 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) using the Mannich reaction. Then, through in situ growth, a metal-organic framework (MOF) HKUST-1 (e.g., Cu3(BTC)2, BTC = benzene-1,3,5-tricarboxylate)/lignin-based expandable flame retardant (F-lignin@HKUST-1) was created. Before that, lignin epoxy resin containing phosphorus (P) and nitrogen (N) components had been created by combining epoxy resin (EP) with F-lignin@HKUST-1. Thermogravimetric analysis was used to examine the thermal characteristics of epoxy resin (EP) composite. The findings indicate that the thermal stability of EP is significantly affected by the presence of F-lignin@HKUST-1. Last but not least, the activation energy (E) of EP/15% F-lignin@HKUST-1 was examined using four different techniques, including the Kissinger-SY iteration method, the Ozawa-SY iteration method, the Lee-Beck approximation-iteration method, and the Gorbatchev approximation-iteration method. It was discovered that the activation energy was significantly higher than that of lignin. Higher activation energy suggests that F-lignin@HKUST-1 pyrolysis requires more energy from the environment, which will be significant about the application of lignin-based flame retardants.

Thermal Degradation and Carbonization Mechanism of Fe-Based Metal-Organic Frameworks onto Flame-Retardant Polyethylene Terephthalate

Currently, the metal-organic framework (MOF) is a promising candidate for flame-retardant polymers. In this study, a Fe-based MOF, MIL-88B(Fe), was introduced to polyethylene terephthalate (PET) and 3-hydroxyphenylphosphinyl-propanoic acid copolymer (P-PET) to reduce the fire hazard involved in using PET. The limiting oxygen indexes (LOIs) of MIL-PET and MIL-P-PET improved by 27% and 30%, respectively. The UL-94 level achieved for MIL-P-PET was V-0 rating. The thermal degradation and carbonization mechanisms of MIL-PET and MIL-P-PET were systematically investigated through thermogravimetric analysis coupled with a Fourier transform infrared spectroscopy (TG-IR), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), x-ray photoelectron spectroscopy (XPS), and Raman spectrum combined with quantum chemical molecular dynamics simulation. With the addition of MIL-88B(Fe), high graphitization and a hard flammability char residual were generated. Compared with neat PET, the ferric ions efficiently catalyzed the homolytic cleavage and dehydrogenation of PET to produce a large amount of CO₂ and terephthalic acid for MIL-PET in gas phase. Rough and hierarchical char residual with ferric oxide was also generated when temperatures exceeded 600 °C. However, the carbonization process was inhibited due to the coordinated complex between phosphorus and ferric ions in MIL-P-PET, invaliding the decarboxylation and generating more benzoic acid and its precursor, which led to heavy smoke.

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

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.

Advanced Flame-Retardant Methods for Polymeric Materials

Most organic polymeric materials have high flammability, for which the large amounts of smoke, toxic gases, heat, and melt drips produced during their burning cause immeasurable damages to human life and property every year. Despite some desirable results having been achieved by conventional flame-retardant methods, their application is encountering more and more difficulties with the ever-increasing high flame-retardant requirements such as high flame-retardant efficiency, great persistence, low release of heat, smoke, and toxic gases, and more importantly not deteriorating or even enhancing the overall properties of polymers. Under such condition, some advanced flame-retardant methods have been developed in the past years based on "all-in-one" intumescence, nanotechnology, in situ reinforcement, intrinsic char formation, plasma treatment, biomimetic coatings, etc., which have provided potential solutions to the dilemma of conventional flame-retardant methods. This review briefly outlines the development, application, and problems of conventional flame-retardant methods, including bulk-additive, bulk-copolymerization, and surface treatment, and focuses on the raise, development, and potential application of advanced flame-retardant methods. The future development of flame-retardant methods is further discussed.

Barrier Effects of Cellulosic Fibers with Hybrid Coating Based on Zirconium Metal-Organic Framework

Metal-organic frameworks (MOFs) have great potential for the development of fire barriers for flammable materials. Accordingly, zirconium-based metal-organic framework (Zr-MOF), branched polyethyleneimine (BPEI), and vinyltriethoxysilane (VTES) were deposited to produce composites assembled on cellulosic fibers to investigate their barrier effects. The structure, morphology, and thermal properties of the cellulosic fibers were characterized using FTIR spectroscopy, SEM, and TGA. Compared with the untreated cotton sample, the temperature of the maximum rate of weight loss (T_max) of C-Zr-MOF/BPEI/VTES increased from 479 to 523.3 °C and the maximum weight loss rate (R_max) at T_max decreased from 37.6 to 17.2 wt%/min. At 800 °C, the pristine cotton was burned out without residues whereas the residual char content of the C-Zr-MOF/BPEI/VTES sample was 7.2355 wt%. From the vertical burning tests, the results suggested that the C-Zr-MOF/BPEI/VTES sample had better barrier effects by reducing the flame-spread speed and generating more protective char layers.

Core-Shell ZIF67@ZIF8 Modified with Phytic Acid as an Effective Flame Retardant for Improving the Fire Safety of Epoxy Resins

Despite many important industrial applications, epoxy resin (EP) suffers from high flammability and toxicity emission, extremely hampering their applications. To circumvent the problem, core-shell structured ZIF67@ZIF8 is successfully synthesized and further functionalized with phytic acid (PA) to obtain PA-ZIF67@ZIF8 hybrids. Then, it is used as an efficient flame retardant to reduce the fire risk of EP. The fire test results show a significant reduction in heat and smoke production. Compared with EP, incorporating 5.0 wt % PA-ZIF67@ZIF8 into EP, the peak heat release rate, total heat release, and peak carbon monoxide production are dramatically reduced by 42.2, 33.0, and 41.5%, respectively. Moreover, the EP/PA-ZIF67@ZIF8 composites achieve the UL-94 V-0 rating and the limiting oxygen index increases by 29.3%. These superior fire safety properties are mainly attributed to the excellent dispersion and the catalytic effect of metal oxide and phosphorus-containing compounds. This work provides an efficient strategy for preparing a promising ZIF-based flame retardant for enhancing flame retardancy and smoke toxicity suppression of EP.

Comparative Study on the Flame Retardancy and Retarding Mechanism of Rare Earth (La, Ce, and Y)-Based Organic Frameworks on Epoxy Resin

In this work, a series of rare earth-based metal-organic frameworks (RE-MOFs) with the same organic ligand were synthesized and studied as flame retardants on epoxy. Through thermogravimetric analysis, limiting oxide index, UL-94, and cone calorimeter tests, a Y-based MOF (Y-MOF) showed the best flame retardancy compared with a La-based MOF (La-MOF) and Ce-based MOF (Ce-MOF). Further research with Raman, X-ray photoelectron spectroscopy, and theoretical calculation revealed that the reasons for the different flame retardance performances of RE-MOFs resulted from the catalytic carbonizing abilities and the radical-trapping abilities of La, Ce, and Y.

Synthesis and application of low-cost layered double hydroxides intercalated by gluconic acid anion for flame retardancy and tensile strength conservation of high filling epoxy resin

Epoxy resin (EP) is a polymer that is widely used in different aspects of life, but its flammability property limits its fields of applications. Most flame retardants at present cannot be applied practically in scale due to their toxicity, incompatibility in polymers, degraded mechanical property or high cost of raw materials and comprehensive preparation process. Layered double hydroxides intercalated by gluconic acid anion (GLDHs) may serve as a new approach. GLDHs with Mg/Al ratio of 3/1 and 2/1 were first coprecipitated with low-cost green reactants, MgCl₂·6H₂O, AlCl₃·6H₂O, NaOH and sodium gluconate. Their structures were confirmed by X-ray diffractions (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and elemental analysis; their thermal properties were analyzed by thermo gravimetric analysis (TGA). Composites containing 40 wt.% GLDHs were easily manufactured with normal magnetic stirring without any filler precipitation. The combustion properties of the composites filled with 40 wt.% GLDHs2 are as follows: the limit oxygen index (LOI) could rise to 29.8% from 25.2% of pristine EP; UL-94 can reach V-1 level with total burning time of only 12.1 s without dropping; compared to pristine EP, the heat release rate peak (PHRR) could drop to 30% with heavy decrease in the smoke production rate and CO production rate. Dynamic mechanical thermal analysis (DMA) tests showed that the addition of 40 wt.% GLDHs had little impact on the glass transition temperature of the composites and could slightly improve their rigidity and toughness. Tensile strength of the composites filled with 40 wt.% GLDHs2 was almost close to 88% of the tensile strength of pristine EP. Above all, GLDHs with good compatibility in polymers can serve as a promising environmental friendly and low-cost flame retardant for EP and other heterochain polymers.

Waste to resource: preparation of an efficient adsorbent and its sustainable utilization in flame retardant polyurethane composites

In order to realize the comprehensive utilization of industrial solid waste and the treatment of water eutrophication, the flower-like magnesium hydroxide (MH) was synthesized from phosphorus tailings by sulfuric acid hydrolysis and a hydrothermal method and then was modified with a metal organic framework (MOF) to remove the phosphates enriched in water through adsorption. Both MH and MOF-modified MH (MH@MOF) presented good removal performance of phosphates. The phosphate-adsorbed composites (MH-P and MH@MOF-P) were sustainably used as effective flame retardants for thermoplastic polyurethane (TPU) at low loadings by a solution blending method. The cone calorimetry test results showed that MH@MOF-P can significantly reduce the heat release rate (HRR), smoke production rate (SPR), total smoke release (TSR), CO release rate and CO2 release rate of TPU composites, compared with those of neat TPU. The novel strategy proposed in this work is of great significance for resource recycling, environmental governance and improving fire safety of polymer materials.

The effects of DOPO modified Co-based metalorganic framework on flame retardancy, stiffness and thermal stability of epoxy resin

In this work, the effect of a modified metal organic framework material on the fire resistance and mechanical properties of epoxy resin (EP) has been explored. The cobalt based metal organic framework (ZIF-67) was synthesized from an organic ligand with a Schiff base structure. Then DOPO@ZIF-67 was synthesized by modifying ZIF-67 with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and its effect on EP modification was explored. Compared with the pure EP, 4% DOPO@ZIF-67/EP passed the UL94 V-0 level and the ultimate oxygen index (LOI) reached 32.1%. The SEM pictures of carbon residue indicated that DOPO@ZIF-67 formed a more continuous and dense microstructure, which can enhance the thermal barrier and the physical barrier effect. The addition of DOPO@ZIF-67 also can effectively improve the stiffness and damping coefficient of EP composite material. The porous skeleton structure of DOPO@ZIF-67 can endow EP with rigidity and flame-retardant properties. Furthermore, the existence of DOPO made the combination of ZIF-67 with EP better. The results of this study suggest that DOPO@ZIF-67 may be a good additive for modification of the properties of epoxy thermosetting materials.

Construction of Charring-Functional Polyheptanazine towards Improvements in Flame Retardants of Polyurethane

Nitrogen-containing flame retardants have been extensively applied due to their low toxicity and smoke-suppression properties; however, their poor charring ability restricts their applications. Herein, a representative nitrogen-containing flame retardant, polyheptanazine, was investigated. Two novel, cost-effective phosphorus-doped polyheptazine (PCN) and cobalt-anchored PCN (Co@PCN) flame retardants were synthesized via a thermal condensation method. The X-ray photoelectron spectroscopy (XPS) results indicated effective doping of P into triazine. Then, flame-retardant particles were introduced into thermoplastic polyurethane (TPU) using a melt-blending approach. The introduction of 3 wt% PCN and Co@PCN could remarkably suppress peak heat release rate (pHRR) (48.5% and 40.0%), peak smoke production rate (pSPR) (25.5% and 21.8%), and increasing residues (10.18 wt%→17.04 wt% and 14.08 wt%). Improvements in charring stability and flame retardancy were ascribed to the formation of P-N bonds and P=N bonds in triazine rings, which promoted the retention of P in the condensed phase, which produced additional high-quality residues.

Engineering MXene surface with POSS for reducing fire hazards of polystyrene with enhanced thermal stability

High-performance MXene-based polymer nanocomposites are highly desirable for diverse industry applications due to their exceptional mechanical, thermal and other properties. Nevertheless, it remains an intractable challenge to create flame retardant polymer/MXene nanocomposites due to the difficulty to achieve uniform dispersion of MXenes. Here, we reported a facile strategy for the surface manipulation of two-dimensional titanium carbide nanosheets (Ti₃C₂T_x) with 3-aminopropylheptaisobutyl-polyhedral oligomeric silsesquioxane (AP-POSS) (POSS-Ti₃C₂T_x) through electrostatic interactions. The POSS-Ti₃C₂T_x is steadily dispersed in many polar solvents. Upon incorporated into polystyrene (PS), the combined effect of AP-POSS and MXene makes the resultant PS nanocomposites exhibit significantly improved thermal and thermoxidative stability, e.g. 22 °C and 39 °C increases in the temperature at 5 wt% mass loss under nitrogen and air, respectively. Meanwhile, a 39.1 % reduction in the peak heat release rate, a respective 54.4 % and 35.6 % reduction in the peak CO production rate and the peak CO₂ production rate was achieved, which are superior to those of its own and previous counterparts. This outstanding fire safety is attributed to the combination of adsorption, catalytic and barrier effects of POSS-Ti₃C₂T_x. Hence, as-designed functionalized MXenes can be effectively applied in PS to formulate multifunctional polymer nanocomposites attractive for wide potential applications.

Plasmonic metal-organic framework nanocomposites enabled by degenerately doped molybdenum oxides

Metal-organic frameworks (MOFs) nanocomposites are under the limelight due to their unique electronic, optical, and surface properties for various applications. Plasmonic MOFs enabled by noble metal nanostructures are an emerging class of MOF nanocomposites with efficient solar light-harvesting capability. However, major concerns such as poor photostability, sophisticated synthesis processes, and high fabrication cost are raised. Here, we develop a novel plasmonic MOF nanocomposite consisting of the ultra-thin degenerately doped molybdenum oxide core and the flexible iron MOF (FeMOF) shell through a hydrothermal growth, featuring low cost, facile synthesis, and non-toxicity. More importantly, the incorporation of plasmonic oxides in the highly porous MOF structure enhances the visible light absorbability, demonstrating improved photobleaching performances of various azo and non-azo dyes compared to that of pure FeMOF without the incorporation of oxidative agents. Furthermore, the nanocomposite exhibits enhanced sensitivity and selectivity towards NO₂ gas at room temperature, attributed to the electron-rich surface of plasmonic oxides. This work possibly broadens the exploration of plasmonic MOF nanocomposites for practical and efficient solar energy harvesting, environmental remediation, and environmental monitoring applications.

Improved mechanical, water vapor barrier and UV-shielding properties of cellulose acetate films with flower-like metal-organic framework nanoparticles

Flower-like metal-organic frameworks (Cu-MOF) nanoparticles are successfully synthesized and incorporated into cellulose acetate (CA) matrix to prepare CA-based functional nanocomposite films via a simple solution-casting method. The effect of the incorporation of flower-like Cu-MOF on the morphological, mechanical, thermal, surface wettability, water vapor barrier, cytotoxicity, photostability and UV-shielding properties of CA films is fully investigated. Results reveal that the flower-like Cu-MOF has good compatibility with CA, providing uniform and compact nanocomposite films. The as-prepared nanocomposite films show improved mechanical properties, surface hydrophobicity, water vapor barrier ability compared to neat CA film, and exhibit super UV-shielding capability through the entire UV regions meanwhile retaining a high visible transparency. Moreover, the high transparency and UV-shielding ability of the nanocomposite films can be still maintained even after continuous UV-light (365 nm) irradiation for 12 h. In addition, MTT cytotoxicity assays towards normal human liver cells (HL-7702) reveal high cell viability (over 80%) and good biocompatibility for the CA/Cu-MOF nanocomposite films. These results indicate that the CA/Cu-MOF nanocomposite films with obviously improved physical and functional performances hold significant potential for transparent packaging and UV-protection applications.

Destruction of Metal-Organic Frameworks: Positive and Negative Aspects of Stability and Lability

Metal-organic frameworks (MOFs), constructed from organic linkers and inorganic building blocks, are well-known for their high crystallinity, high surface areas, and high component tunability. The stability of MOFs is a key prerequisite for their potential practical applications in areas including storage, separation, catalysis, and biomedicine since it is essential to guarantee the framework integrity during utilization. However, MOFs are prone to destruction under external stimuli, considerably hampering their commercialization. In this Review, we provide an overview of the situations where MOFs undergo destruction due to external stimuli such as chemical, thermal, photolytic, radiolytic, electronic, and mechanical factors and offer guidelines to avoid unwanted degradation happened to the framework. Furthermore, we discuss possible destruction mechanisms and their varying derived products. In particular, we highlight cases that utilize MOF instability to fabricate varying materials including hierarchically porous MOFs, monolayer MOF nanosheets, amorphous MOF liquids and glasses, polymers, metal nanoparticles, metal carbide nanoparticles, and carbon materials. Finally, we provide a perspective on the utilization of MOF destruction to develop advanced materials with a superior hierarchy for various applications.

Recent Progress on Metal-Organic Framework and Its Derivatives as Novel Fire Retardants to Polymeric Materials

High flammability of polymers has become a major issue which has restricted its applications. Recently, highly crystalline materials and metal-organic frameworks (MOFs), which consisted of metal ions and organic linkers, have been intensively employed as novel fire retardants (FRs) for a variety of polymers (MOF/polymer). The MOFs possessed abundant transition metal species, fire-retardant elements and potential carbon source accompanied with the facile tuning of the structure and property, making MOF, its derivatives and MOF hybrids promising for fire retardancy research. The recent progress and strategies to prepare MOF-based FRs are emphasized and summarized. The fire retardancy mechanisms of MOF/polymer composites are explained, which may guide the future design for efficient MOF-based FRs. Finally, the challenges and prospects related to different MOF-based FRs are also discussed and aim to provide a fast and holistic overview, which is beneficial for researchers to quickly get up to speed with the latest development in this field.

Mitigation the release of toxic PH3 and the fire hazard of PA6/AHP composite by MOFs

Aluminum hypophosphite (AHP) is a high-efficiency phosphorus-based flame retardant with high P content, which is widely used in Polyamide 6 (PA6). However, AHP releases phosphine gas (PH₃) at high temperatures, which is highly toxic to human's health and environment. Metal-organic frameworks (MOFs) have porous structure exhibiting high performance in gas adsorption. Therefore, mesoporous iron (III) carboxylate [MIL-100 (Fe)] was synthesized in this work and employed to study the adsorption capacity of toxic PH₃ in PA6/AHP composite during processing. AHP was combined with melamine cyanurate (MCA) and MIL-100 (Fe) followed by blending with PA6 to prepare PA6 composites (PA6/MA and PA6/MAF). PA6/MAF with the weight ratio of 5:5 performed well in inhibiting the release of PH₃ during the processing of composite as well as the accelerated thermal experiment devised by our group. Besides, PA6/MAF (5:5) showed relatively low fire hazard reflected by the reduction of the peak of heat release rate of PA6 composite from 962 to 260 kW/m² compared with that of pure PA6 in the cone calorimeter test, and MIL-100 (Fe) along with MCA also presented synergistic effect in suppressing the emission of carbon monoxide. The subtle selection of MOFs herein has the potential to be used as a promising synergist for hazardous gases released from polymer composites to improve the occupational and fire safety in the society.

Metal-Organic Framework (MOF)/Epoxy Coatings: A Review

Epoxy coatings are developing fast in order to meet the requirements of advanced materials and systems. Progress in nanomaterial science and technology has opened a new era of engineering for tailoring the bulk and surface properties of organic coatings, e.g., adhesion to the substrate, anti-corrosion, mechanical, flame-retardant, and self-healing characteristics. Metal-organic frameworks (MOFs), a subclass of coordinative polymers with porous microstructures, have been widely synthesized in recent years and applied in gas and energy storage, separation, sensing, environmental science and technology, and medicine. Nevertheless, less attention has been paid to their performance in coatings. Well-known as micro- and nanoporous materials, with a tailorable structure consisting of metal ions and organic linkers, MOFs have a huge loading capacity, which is essential for the delivery of corrosion inhibitors. This review paper attempts to highlight the importance of epoxy/MOF composites for coating applications. A particular emphasis was explicitly placed on the anti-corrosion, flame-retardant, mechanical, and dielectric properties of epoxy/MOF coatings.

Ammonium Polyphosphate with High Specific Surface Area by Assembling Zeolite Imidazole Framework in EVA Resin: Significant Mechanical Properties, Migration Resistance, and Flame Retardancy

A zeolite imidazole framework (ZIF-67) was assembled onto the surface of ammonium polyphosphate (APP) for preparing a series multifunctional flame-retardant APP-ZIFs. The assembly mechanism, chemical structure, chemical compositions, morphology, and specific surface area of APP-ZIFs were characterized. The typical APPZ1 and APPZ4 were selected as intumescent flame retardants with dipentaerythritol (DPER) because of their superior unit catalytic efficiency of cobalt by thermogravimetric analysis. APPZ1 and APPZ4 possessed 6.8 and 92.1 times the specific surface area of untreated APP, which could significantly enhance the interfacial interaction, mechanical properties, and migration resistance when using in ethylene-vinyl acetate (EVA). With 25% loading, 25% APPZ4/DPER achieved a limiting oxygen index value of 29.4% and a UL 94 V-0 rating, whereas 25% APP/DPER achieved a limiting oxygen index value of only 26.2% and a V-2 rating, respectively. The peak of the heat release rate, smoke production rate, and CO production rate respectively decreased by 34.7%, 39.0%, and 40.1%, while the char residue increased by 91.7%. These significant improvements were attributed to the catalytic graphitization by nano cobalt phosphate and the formation of a more protective char barrier comprised of graphite-like carbon.

Novel Phosphorus-Nitrogen-Containing Ionic Liquid Modified Metal-Organic Framework as an Effective Flame Retardant for Epoxy Resin

Metal-organic frameworks (MOFs) have shown great potential in flame retardant applications; however, strategies for fully exploiting the advantages of MOFs in order to further enhance the flame retardant performance are still in high demand. Herein, a novel MOF composite was designed through the generated cooperative role of MOF (NH₂-MIL-101(Al)) and a phosphorus-nitrogen-containing ionic liquid ([DPP-NC₃bim][PMO]). The ionic liquid (IL) was composed of imidazole cation modified with diphenylphosphinic group (DPP) and phosphomolybdic acid (PMoA) anions, which can trap the degrading polymer radicals and reduce the smoke emission. The MOF acts as a porous host and can avoid the agglomeration of ionic liquid. Meanwhile, the -NH₂ groups of NH₂-MIL-101(Al) can increase the compatibility with epoxy resin (EP). The framework is expected to act as an efficient insulating barrier to suppress the flame spread. It was demonstrated that the MOF composite (IL@NH₂-MIL-101(Al)) is able to effectively improve the fire safety of EP at low additions (3 wt. %). The LOI value of EP/IL@NH₂-MIL-101(Al) increased to 29.8%. The cone calorimeter results showed a decreased heat release rate (51.2%), smoke production rate (37.8%), and CO release rate (44.8%) of EP/IL@NH₂-MIL-101(Al) with respect to those of neat EP. This strategy can be extended to design other advanced materials for flame retardant.

Nanoreinforcements of Two-Dimensional Nanomaterials for Flame Retardant Polymeric Composites: An Overview

Polymer materials are ubiquitous in daily life. While polymers are often convenient and helpful, their properties often obscure the fire hazards they may pose. Therefore, it is of great significance in terms of safety to study the flame retardant properties of polymers while still maintaining their optimal performance. Current literature shows that although traditional flame retardants can satisfy the requirements of polymer flame retardancy, due to increases in product requirements in industry, including requirements for durability, mechanical properties, and environmental friendliness, it is imperative to develop a new generation of flame retardants. In recent years, the preparation of modified two-dimensional nanomaterials as flame retardants has attracted wide attention in the field. Due to their unique layered structures, two-dimensional nanomaterials can generally improve the mechanical properties of polymers via uniform dispersion, and they can form effective physical barriers in a matrix to improve the thermal stability of polymers. For polymer applications in specialized fields, different two-dimensional nanomaterials have potential conductivity, high thermal conductivity, catalytic activity, and antiultraviolet abilities, which can meet the flame retardant requirements of polymers and allow their use in specific applications. In this review, the current research status of two-dimensional nanomaterials as flame retardants is discussed, as well as a mechanism of how they can be applied for reducing the flammability of polymers.