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Page 12 of 17 Hou et al. Microstructures 2023;3:2023039 https://dx.doi.org/10.20517/microstructures.2023.37

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Figure 6. Microstructures of (A) ZHS@NCH (Reproduced with permission . Copyright 2019, American Chemical Society); (B)
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ZIF@LDH@PZS (Reproduced with permission . Copyright 2022, American Chemical Society); (C) m-CBC-P@LDH (Reproduced with
[79] [80]
permission . Copyright 2023, Elsevier); (D) m-CBC@LDH (Reproduced with permission . Copyright 2023, Elsevie); (E) MPOFs
(Reproduced with permission [81] . Copyright 2022, American Chemical Society); (F) ZNs-B/CP (Reproduced with permission [82] .
Copyright 2022, Elsevier).
effectiveness in preventing flame spread. Therefore, to enhance the compatibility of LDH, it is typically
necessary to further modify or combine it with other flame retardants. Wang et al. modified LDH by
toluene diisocyanate, 2-hydroxyethyl acrylate, and vinyl triethoxysilane (LDH-TDI-HEA-VTES) to improve
its compatibility with organic matrix, resulting in better dispersion of modified LDH in matrix compared
with LDH . The experimental results showed that with the increase of LDH-TDI-HEA-VTES content, the
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thermal stability, mechanical properties, flame retardant properties, and shear resistance of LDH-TDI-
HEA-VTES-Acrylate composites were improved.

Moreover, acid etching can be employed to generate a novel ligand that substitutes the initial one.
Wang et al. used a modified version of core-shell ZIF-67@ZIF-8, where phytic acid was added to the
structure . The new phytate-metal ion hybrids are formed to improve the flame retardancy of EP. Our
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group also utilized carboxyl POSS to modify ZIF-67 and successfully synthesized Metal-POSS Organic
Frameworks (MPOFs). Thioglycolic acid was employed to replace the original imidazole ligand and
complex with metal ions. Additionally, We have synthesized hollow nanocage structures with a greater
number of active sites by utilizing ZIF as a sacrificial template and employing stepwise etching in the
sequence of phytic acid and boric acid. Another technique is thermal treatment. This involves exposing the
MOF to high temperatures, which can cause structural changes that improve their ability to act as flame
retardants. Hou et al. developed a method that involves utilizing HKUST-1, a MOF, as a sacrificial template
to synthesize Oxygen-Rich Covalent C N (CNO) nanosheets through thermal treatment and chemical vapor
2
deposition .
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In summary, conventional MOF ligands are often composed of organic compounds that possess
flammability. Additionally, the limited presence of flame-retardant elements in MOFs may result in reduced
flame-retardant effects and decreased practicality. The method of post-treatment MOFs is simple and
controllable and has the following advantages: (1) Endowing MOFs with more flame-retardant elements: by