Size tunable carbon-encapsulated nickel nanoparticles synthesized by pyrolysis of nickel acetate tetrahydrate

In this study, size control of carbon-encapsulated nickel nanoparticles (CENiNPs) synthesized by direct thermal decomposition of Ni(CH3COO)2.4H2O (NiAc) was possible by varying systematically the initial amount of the precursor during its pyrolysis. The reaction was conducted inside a thermogravimetric analyzer coupled to a quadrupole mass spectrometer for evolved gas analysis. By heating non-isothermally different initial amounts of NiAc (100-400 mg) in an argon flow at 10 °C/min from room temperature to 500 °C, CENiNPs were readily obtained, in which a thin layer of carbon resulting from the breakdown of the anion protects their metallic core from spontaneous oxidation. High resolution transmission electron microscopy and methane catalytic decomposition tests revealed that this encapsulating layer can also exert a significant role in the control of the size distribution (40-140 nm) and catalytic activity of the resultant CENiNPs. Temperature programmed oxidation of the CENiNPs identified preliminary some surface carbon species responsible for the packing of the catalytically-active metallic core. This simple and cost-effective method emerges as a competitive way to manufacture and conserve highly active CENiNPs.