Seeding Layer Effect on the Microstructure of Hydrothermally Grown α-Manganese Dioxide Nanowires on Three-Dimensional Graphene Foam

Hydrothermal synthesis is a straightforward approach for producing high-yield manganese dioxide (MnO2) nanostructures with efficient morphological control at low temperatures. This study investigates the microstructural dependency of hydrothermally grown alpha-MnO2 nanowires (NWs) on pre-treatment conditions on the substrate surface. Within this scope, alpha-MnO2 NWs were synthesized on chemical vapor deposition (CVD)-based graphene foam (GF) substrates pre-treated via potassium permanganate (KMnO4) solution as a seeding layer with different concentrations (0.025, 0.050, 0.075, 0.1 M). A direct alpha-MnO2 NWs growth (without pre-treatment) was also performed on GF by hydrothermal method. The seeding layer effect on the NWs growth was elaborated to comprehend the process-structure correlations by characterizing the resultant graphene foam/alpha-MnO2 nanowires (GF/alpha-MnO2 NWs) nanocomposites through Scanning Electron Microscopy (SEM), Raman Spectroscopy, X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS). SEM, XRD, and Raman Spectroscopy revealed the successful acquisition of highly crystalline alpha-MnO2 in one-dimensional nanowire morphology on the high-quality GF. Moreover, XPS results confirmed that all nanocomposites comprise alpha-MnO2 and graphene without chemical degradation. Consequently, slight changes in solution concentration of seeding layers caused a noticeable alteration in the nanowire's structure, which could ensure effective control of nanocomposite properties without sacrificing the high purity of each component.

This study proposes a cost-effective and facile hydrothermal route to manage MnO2 nanowire growth on graphene foam for the first time. It is revealed that a slight change in solution concentration of the seeding layer caused a noticeable morphological, chemical, and structural alteration in alpha-MnO2, which could ensure a control of the growth through the user-friendly pre-treatment approach. image