Zeolitic imidazolate frameworks-based flame retardants for polymeric materials

Metal-organic frameworks (MOFs) are an emerging family of coordination compounds, with zeolitic imidazolate frameworks (ZIFs) being an excellent member of the family. They possess a large specific surface area, high porosity, high chemical activity, a customizable structure, a simple preparation process, and low production costs, thus showing great application potential in the field of scientific research. In recent years, many researchers have studied the application of ZIFs in the field of flame retardancy, demonstrating their good flame retardant effects in different polymer matrices. Over the past five years, the number of articles related to ZIFs in the field of flame retardancy has greatly exceeded other MOFs, making it crucial to separately sort out ZIFs used for flame retardancy. To our knowledge, there has not been a comprehensive report on ZIFs as flame retardants yet. This article reviews the research progress on pure ZIFs, ZIFs as synergists, modified ZIFs, nanohybrids based on ZIFs, and ZIF derivatives. It shows the significant improvement in the flame retardancy of polymer composites such as epoxy resins by ZIFs and their derivatives. It focuses on the application of nanohybrids based on ZIFs in the field of flame retardancy, revealing the importance of nanohybrids for enhancing the performance of ZIFs. Furthermore, nanohybrids can also play a substantial role in expanding the functionality of ZIFs and greatly improving their mechanical, optical, and thermal properties, potentially promoting the development of ZIFs in higher-end fields. Finally, it concludes and looks forward to the future development direction and existing problems of flame retardant based on ZIFs.