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Page 6 of 17 Hou et al. Microstructures 2023;3:2023039 https://dx.doi.org/10.20517/microstructures.2023.37

Table 3. Combination of MOFs with other flame retardants
MOF Other flame retardants Example applications
Ni-MOF [13] Ammonium polyphosphate Flame-retardant additives for polymers and textiles
[44]
MOF-Cu Ammonium polyphosphate Flame-retardant additives for plastics and textiles
[46]
ZIF-67 Ammonium polyphosphate Flame-retardant coatings and polymer formulations
[47]
ZIF-8 Phosphorus-based flame retardants Flame-retardant coatings, textiles, and polymer matrices
[48]
UiO-66 Cyclotriphosphazene Flame-retardant composites and polymer formulations

Xu et al. employed a solvothermal method to synthesize a specific type of MOF using cobalt ions and
organic ligands, resulting in a porous material with high surface area and thermal stability. Subsequently,
the Co-MOF was compounded with PP after being mixed with melamine polyphosphate (MPP), which is
another flame retardant. The results indicate that the incorporation of Co-MOF into MPP/PP composite
significantly enhances its flame retardancy, as compared to PP alone or with only MPP. This improvement
is attributed to the release of water and gases from Co-MOF upon heating, which can effectively cool and
dilute flames . Quan et al. explore the synergistic effects of ZIFs (ZIF-67 and ZIF-8) with different
[43]
transition metals on intumescent flame-retarded PP composites . Overall, MOFs have the potential to be
[49]
used as a synergist for intumescent flame retardants in polymers, which could lead to the development of
more effective and efficient flame-retardant materials for a wide range of applications.

Escobar-Hernandez and Quan et al. provided valuable insights into the large-scale synthesis of MOFs [50,51] .
They present a promising method for the sustainable and efficient production of MOF-based polymer
nanocomposites . The process utilized for the production of these materials is known as reactive extrusion,
[52]
which involves blending MOF particles and polymers in an extruder. During this mixing procedure,
chemical reactions take place between the MOFs and polymers, leading to the formation of robust chemical
bonds between both materials. The sustainability and efficiency of this manufacturing process are
emphasized by researchers. Reactive extrusion was utilized to produce MOF-based polymer
nanocomposites with reduced energy consumption and waste generation compared to conventional
methods for similar materials. Moreover, the incorporation of MOFs in these composites enhances their
sustainability as they can be easily recycled and reused.

Despite their unique properties and potential for industrial applications, there are several challenges that
must be overcome before MOFs can be widely adopted in the industry. MOFs are often susceptible to
degradation or collapse when exposed to environmental factors such as moisture, heat, or mechanical stress.
This can limit their long-term stability and durability, which is a crucial consideration for industrial
applications. The cost of MOFs can be relatively high compared to traditional materials, which can limit
their adoption in certain applications. Additionally, the cost of MOF synthesis and production can vary
depending on the specific MOF and the synthesis method used, which can further complicate cost
considerations. Addressing these challenges will require continued research and development in the
synthesis, characterization, and integration of MOFs into industrial applications.

The industrialization of MOFs may follow a trajectory similar to that of graphene, which has demonstrated
unique properties and potential for various industrial applications such as electronics, energy storage, and
[53]
biomedical devices since its discovery in 2004 . However, the slow pace of industrialization can be
attributed to challenges in achieving mass production and cost-effective synthesis. Nevertheless, recent
advancements in graphene research have resulted in the development of various scalable production
methods, including chemical vapor deposition , liquid-phase exfoliation , and reduction of graphene
[55]
[54]
oxide (GO) . These methods have enabled the production of high-quality graphene in large quantities at a
[56]