Ferrocene is an organometallic compound that is a derivative of cyclopentadiene and consists of iron atoms sandwiched between two cyclopentadienyl rings. Since its discovery in 1951, ferrocene has become one of the important compounds in organometallic chemistry. Ferrocene and its derivatives have a variety of applications, including as catalysts in chemical reactions, as fuel additives, and in the synthesis of drugs and materials.
In addition, ferrocene has also been proven to have broad application potential in the development of flame retardant materials due to its effective smoke suppression and catalytic cross-linking properties. Here, Alfa Chemistry summarizes the research and development of ferrocene and its derivatives in various flame retardant composite materials.
Through the peeling and restacking method, ferrocene can be embedded into the molybdenum disulfide (MoS2) layer to prepare Fe-MoS2 composite flame retardant. Further, Fe-MoS2 was introduced into the polystyrene (PS) matrix through a masterbatch-based melt blending method to obtain PS/ MoS2 composite materials. The results show that Fe-MoS2 significantly enhances the thermal stability, flame retardancy and smoke suppression performance of PS composite materials. This is due to the synergistic effect between ferrocene and MoS2 nanosheets, the physical barrier effect of MoS2 nanosheets, and the promotion of char formation by both.
Illustration for PS/Fe–MoS2 composites. 
An oligomer (PFDCHQ) containing ferrocene groups and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) has been successfully synthesized to improve bisphenol Flame retardant efficiency of diglycidyl ether of bisphenol A epoxy resin (DGEBA). This oligomer combines the advantages of DOPO and ferrocene groups and is a highly efficient flame retardant for epoxy resin (EP) materials. When the PFDCHQ loading amount is 5 wt%, the limiting oxygen index (LOI) of EP can be increased to 32.0%, reaching the UL-94 V-0 grade. Combined with the analysis of possible pyrolysis pathways, PFDCHQ exhibits significant flame retardant effects in both condensed and gas phases.
Possible pyrolytic route of PFDCHQ. 
The molecular structure of ferrocene-based polymer (PDPFDE) consists of ferrocene, benzene ring and ethylenediamine. PDPFDE has high carbonization properties and can eliminate the "popcorn effect" of expandable graphite (EG). In the PDPFDE/EG synergistic flame retardant system, PDPFDE not only has excellent autocatalytic carbonization ability, but also can be used as a reactive carbonization binder for EG to inhibit further expansion of EG, and ultimately obtain dense, hard, and highly graphitized carbon layer. 
Schematic illustrations of the fire retardant mechanism. 
β-Cyclodextrin@ferrocene@hollow mesoporous silica microspheres (β-CD@FE@HMS) were successfully prepared through a self-assembly method and can be used to improve the flame retardant properties of epoxy resin (EP). The results show that β-CD@FE@HMS can effectively improve the thermal stability of EP, increase the initial degradation temperature and carbon residue amount of EP. 
Preparation routes of β-CD@FE@HMS.