Impact of hydrofluoric acid treatment on the composition, electrical conductivity, and structure of carbonized metal–organic frameworks

Metal–organic frameworks (MOFs) containing V, Cr, Mn, Fe, Co, Ni, Cu, and Zr were pyrolyzed under nitrogen flow. The products of carbonized MOFs (CMOFs) contain metal oxides and carbonaceous residues, which were characterized by powder X-ray diffraction (PXRD), electrical conductivity (EC), and Raman spectroscopy. To remove the metallic components in CMOFs, hydrofluoric acid (HF) treatment was performed. PXRD analysis showed that only Mn, Co, Ni, and Zr, but not V, Cr, Fe, and Cu, could be completely removed from CMOFs after HF treatment. In fact, PXRD analysis also revealed that during the formation of CMOFs, not only metal oxides, but also metal carbides were formed. The change of the EC of CMOFs after HF treatment was found to be mainly contributed from the metal components, whereas the carbon (graphitic) components played minor roles. The effect of HF treatment on the structure of CMOF was not significant as verified by the Raman analysis of the intensity ratio between D band and G band.