Insights into the Plasma-Assisted Fabrication and Nanoscopic Investigation of Tailored MnO2 Nanomaterials

Among transition metal oxides, MnO2 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 MnO2 nanomaterials by a catalyst-free, plasma assisted process starting from a fluorinated manganese(II) molecular source in Ar/O-2 plasmas. A thorough multi technique characterization aimed at the systematic investigation of material structure, chemical composition, and morphology revealed the formation of F-doped, oxygen deficient, MnO2-based nanomaterials, with a fluorine content tunable as a function of growth temperature (T-G). Whereas phase-pure beta-MnO2 was obtained for 100 degrees C <= T-G <= 300 degrees C, the formation of mixed phase MnO2 + MnO2O3 nanosystems took place at 400 degrees 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.