Thermal Decomposition of Molybdenum(II) Acetate as a Controlled Route to MoO2 and Mo2C Nanostructures: Structural, Morphological, and Atomic-Scale Insights

Abstract

Developing reproducible synthetic routes for reduced molybdenum-based nanostructures remains challenging due to the strong sensitivity of Mo–O systems to temperature, processing atmosphere, and precursor chemistry. Here, we demonstrate that the controlled thermal decomposition of molybdenum(II) acetate under vacuum provides a simple solid-state route for obtaining monoclinic MoO2 nanoparticles and hexagonal β-Mo2C with tunable morphology. Structural, morphological, and thermal analyses revealed a three-stage transformation pathway: (i) precursor degradation and amorphization between 300 and 400 °C; (ii) nucleation and crystallization of monoclinic MoO2 between 500 and 700 °C, yielding spherical nanoparticles with an average diameter of 23 ± 7.9 nm; and (iii) formation of vertically oriented MoO2/β-Mo2C microflakes at 800 °C, evidencing nanoparticle coalescence and the partial conversion of MoO2 into the β-Mo2C phase. Time-Differential Perturbed Angular Correlation (TDPAC) spectroscopy, using the 111In(111Cd) probe, provided atomic-scale information on local electric field gradients, enabling the direct identification of amorphous and crystalline MoO2 environments while revealing the role of defects, oxygen vacancies, and surface heterogeneities during phase evolution. These findings establish molybdenum(II) acetate as an effective precursor for the synthesis of molybdenum-based nanostructures and provide a multiscale understanding, spanning atomic to micrometer length scales, of the mechanisms governing the formation of MoO2 and β-Mo2C. Furthermore, the results indicate that carbonaceous species generated during precursor decomposition promote a coupled carbothermal reduction–carburization pathway, leading to the formation of β-Mo2C.