Insights into the Plasma-Assisted Fabrication and Nanoscopic Investigation of Tailored MnO<sub>2</sub> Nanomaterials

Among transition metal oxides, MnO<sub>2</sub> is of considerable importance for various technological end-uses, from heterogeneous catalysis to gas sensing, owing to its structural flexibility and unique properties at the nanoscale. In this work, we demonstrate the successful fabrication of supported MnO<sub>2</sub> nanomaterials by a catalyst-free, plasma-assisted process starting from a fluorinated manganese­(II) molecular source in Ar/O<sub>2</sub> plasmas. A thorough multitechnique characterization aimed at the systematic investigation of material structure, chemical composition, and morphology revealed the formation of F-doped, oxygen-deficient, MnO<sub>2</sub>-based nanomaterials, with a fluorine content tunable as a function of growth temperature (<i>T</i><sub>G</sub>). Whereas phase-pure β-MnO<sub>2</sub> was obtained for 100 °C ≤ <i>T</i><sub>G</sub> ≤ 300 °C, the formation of mixed phase MnO<sub>2</sub> + Mn<sub>2</sub>O<sub>3</sub> nanosystems took place at 400 °C. In addition, the system nano-organization could be finely tailored, resulting in a controllable evolution from wheat-ear columnar arrays to high aspect ratio pointed-tip nanorod assemblies. Concomitantly, magnetic force microscopy analyses suggested the formation of spin domains with features dependent on material morphology. Preliminary tests in Vis-light activated photocatalytic degradation of rhodamine B aqueous solutions pave the way to possible applications of the target materials in wastewater purification.