Atmosphere-controlled thermal pathways of ZIF-67 and ZIF-8: From framework collapse to Co2C, Co0 and Zn(CN)2 formation

This study maps the thermal conversion pathways of ZIF-67 and ZIF-8 under oxidative and reducing atmospheres. Identical sodalite ZIFs were tracked in situ by temperature-resolved synchrotron XRD and Co K-edge XAS, and characterized by TG, FTIR, N 2 physisorption and electron microscopy. Under reducing conditions, ZIF-67 maintains tetrahedral Co-N coordination up to ≈523-673 K, collapses between ≈703-723 K, and converts at higher temperatures to a mixture of orthorhombic Co 2 C and metallic Co 0 . XAS indicates loss of the Co-N pre-edge and growth of low-coordination Co-Co scattering consistent with sub-nanometer, undercoordinated Co clusters embedded in a carbonaceous matrix. Oxidative calcination of ZIF-67 produces crystalline spinel Co 3 O 4 , which reduces stepwise (Co 3 O 4 → CoO → Co 0 ) under H 2 . ZIF-8 decomposes at lower temperatures (onset ≈623 K) and yields stable wurtzite ZnO under oxidative conditions or Zn(CN) 2 at high temperature under reducing flow, consistent with imidazolate fragmentation and cyanide capture by zinc. Thermal treatment causes pronounced loss of surface area and pore structure for both ZIFs. These findings clarify atmosphere- and temperature-dependent routes from ZIF precursors to oxide, metallic and carbidic products and offer guidance for tailoring ZIF-derived catalysts and functional nanomaterials via controlled thermal programs.