Metal organic frameworks (MOFs) are porous crystalline materials composed of metal ions or clusters of metal ions coordinated with organic linkers (such as terephthalic acid, 1,3,5-benzenetricarboxylic acid, or imidazoles) MOFs exhibit tunable structures, low density, ultrahigh surface area and have various potential applications in catalysis, hydrogen storage, and adsorption/separation of liquid or gaseous mixtures Among the MOFs structures, the zeolitic imidazolate frameworks (ZIFs) have recently attracted considerable attention In these materials, metal atoms such as Zn2+ are linked through N atoms by the ditopic 2-methylimidazolate ligand to form neutral frameworks ZIF-8 has a sodalite zeolite-type topology with cages of 116 A and pores of 34 A in diameter ZIF-8 are characterized by high thermal stability (550 oC in N2), large surface area (BET: 1630 m2/g) and high resistance to various solvents Concerning ZIF-8 chemical properties, these materials can successfully be used for hydrogen, carbon dioxide and iodide storage, Knoevenagel condensations, cycloadditions, oxidations, trans-esterification, and Friedel-Crafts alkylations Variations of synthetic parameters (solvent, concentration, temperature, time, molar ratio of reactants) are commonly used to manipulate the morphology and size of ZIF-8 crystals In this work, we demonstrate that the reactivity of the Zn(+2) salt in the growth solution can also markedly affect the size and the morphology of ZIF-8 particles Small ZIF-8 nanocrystals with diameters varying between ca 50 and 200 nm were obtained with reactive zinc salts like Zn(acac)2, Zn(NO3)2, ZnSO4 or Zn(ClO4)2 The use of ZnCl2, Zn(OAc)2 or ZnI2 afforded crystals with sizes varying between ca 350 and 650 nm Finally, the low reactive ZnBr2 was found to generate microsized crystals These significant changes in particle size induced distinctive changes in adsorption properties as demonstrated by BET measurements but also in the catalytic performances of ZIF-8 crystals in a Knoevenagel condensation used as model The small sized crystals produced from Zn(NO3)2 exhibit the highest surface area and the best catalytic activity

Controlling ZIF-8 nano and microcrystal formation and reactivity through zinc salts variations

Development of metal-organic framework (MOF) decorated graphene oxide nanoplatforms for anti-corrosion epoxy coatings

Recent advances in magnesium/lithium separation and lithium extraction technologies from salt lake brine

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.

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

Epoxy composite coating with excellent anticorrosion and self-healing performances based on multifunctional zeolitic imidazolate framework derived nanocontainers

Functionalized graphene with Co-ZIF adsorbed borate ions as an effective flame retardant and smoke suppression agent for epoxy resin.

ZIF@MgAl-LDH hybrids were synthesized by zeolitic imidazolate frameworks (ZIF) and MgAl-layered double hydroxide (MgAl-LDH) via electrostatic interactions. Their structure and morphology were systematically characterized. Then, ZIF@MgAl-LDH hybrids were added to epoxy resin (EP) to study their effects on the thermal properties and fire resistance of the material. The results of TGA showed that ZIF@MgAl-LDH could improve the char yield of the EP composites. The cone calorimetry, smoke density tests, limiting oxygen index (LOI) and UL94 vertical burning test showed that ZIF@MgAl-LDH effectively improved the flame retardancy and smoke suppression of EP. Furthermore, the laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS) results of the char residue showed that ZIF@MgAl-LDH promoted the formation of a char layer with high graphitization and thermal oxidation resistance, which was conducive to the reduction of the fire hazards. This simple treatment of EP may expand its fire safety applications.

Fabrication of zeolitic imidazolate frameworks on layered double hydroxide nanosheets to improve the fire safety of epoxy resin

A material (ZIF-8@SiO2) with a nuclear shell structure was synthesized to improve the flame retardancy and smoke suppression of epoxy resin (EP) through a synergetic catalytic effect. Zeolitic imidazolate framework-8 (ZIF-8) was synthesized and its surface was coated with SiO2 by hydrolyzing tetraethyl orthosilicate. Core–shell structured ZIF-8@SiO2 was obtained. Then ZIF-8@SiO2 was added to EP to explore its effect of flame retardancy and smoke suppression on the EP composite. The results of a cone calorimeter test showed that the peak heat release rate, total heat release, smoke production rate and total smoke production of the material were decreased by 75.9%, 38.9%, 51.1% and 39.8%, respectively, after 2 wt% ZIF-8@SiO2 was added to EP. Besides, through the analysis of char residue, the mechanism of ZIF-8@SiO2/EP's flame retardancy and smoke suppression was determined to be due to the physical barrier effect of SiO2 and the co-effect of SiO2 and ZnO decomposition by ZIF-8.

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Zeolitic imidazolate framework-8 was coated with silica and investigated as a flame retardant to improve the flame retardancy and smoke suppression of epoxy resin

A novel flame retardant (CuMoO4@h-BN) was synthesized through the co-precipitation method, and its structure and morphology were systematically characterized. CuMoO4@h-BN was added to polyurethane elastomer (PUE) to investigate the effect of thermal, flame retardancy and smoke suppression properties on the PUE composites. The results showed that 2 wt% CuMoO4@h-BN increased the residual char yield of the PUE composite notably to 9.8%. CuMoO4@h-BN exhibited an excellent charring effect. Compared with pure PUE, 2 wt% CuMoO4@h-BN decreased the peak heat release rate, total heat release and smoke density of the PUE composite by 73.6, 52.4 and 28.2%, respectively. CuMoO4@h-BN performed well in flame retardancy and smoke suppression. It may be attributed mainly to the physical barrier effect of h-BN and catalytic carbonization effect of CuMoO4. It is expected that this simple and inexpensive treatment of PUE may help expand the fire safety applications of the material.

Wu Li

Papers

Functionalized graphene with Co-ZIF adsorbed borate ions as an effective flame retardant and smoke suppression agent for epoxy resin.

Fabrication of zeolitic imidazolate frameworks on layered double hydroxide nanosheets to improve the fire safety of epoxy resin

Zeolitic imidazolate framework-8 was coated with silica and investigated as a flame retardant to improve the flame retardancy and smoke suppression of epoxy resin

CuMoO4@hexagonal boron nitride hybrid: an ecofriendly flame retardant for polyurethane elastomer

Improving fire safety of epoxy filled with graphene hybrid incorporated with zeolitic imidazolate framework/layered double hydroxide