Microwave-induced decomposition of nitrogen-rich iron salts and CNT formation from iron(III)–melonate Fe[C 9N 13

Abstract

Two nitrogen-rich iron salts, ferric ferrocyanide (Fe 4[Fe(CN) 6] 3, Prussian Blue, “PB”) and iron melonate (Fe[C 6N 7(NCN) 3], “FeM”), were thermally decomposed. A household microwave oven was used to heat a molybdenum wire after being coated with the precursor and protected from ambient atmosphere. The nanostructured products obtained were characterised with FTIR- and Raman-spectroscopy, XRD, SEM, EDX, EELS and TEM. While the PB-precursor did not give any nanotube-containing products, the FeM-precursor furnished tubular carbon nanostructures in a reproducible manner. This result may be due to the graphite-like nature of the [C 6N 7(NCN) 3] 3−-anions present in FeM. The C 6N 7-unit is aromatic and completely planar, while the cyanide anions in PB do not provide similar structures. Another significant difference is the high Fe:C-ratio in PB, which might prevent CNT-formation when this precursor is used. The nitrogen content of the tubes was found to be below the detection limit of EELS. This indicates that the synthesis temperatures were too high resulting in complete evaporation of all nitrogen present in the FeM-precursor forming volatile species such as N 2 or (CN) 2.