Graphene encapsulated Fe-based nanoparticles synthesized from iron(II) sulfate heptahydrate containing precursors: Influence of chemical vapor deposition parameters

Importance of process parameters on thermal, microstructural, and magnetic properties of synthesized core/shell nanoparticles was investigated during their production via chemical vapor deposition (CVD). Herein, iron(II) sulfate heptahydrate and fumed silica powders were mixed in ethanol, and the solution was used for precursor preparation by utilizing spray dryer. These prepared precursors were treated in the CVD process under methane/hydrogen (CH₄/H₂) gas flow to synthesize graphene-encapsulated core/shell nanoparticles. CVD studies were performed at various temperatures (900–1000 °C), holding times (60, 90 min), and gas flow rates (100, 200 mL/min). After CVD studies, purification was applied to remove uncoated nanoparticles, and remaining fumed silica phases originated from the precursor via selective acid leaching using hydrofloric acid (HF) and hydrochloric acid (HCl) solutions. X-ray diffractometry, Raman and Mössbauer spectroscopy, Zeta potential measurement, thermogravimetry combined with differential scanning calorimetry, scanning and transmission electron microscopy/energy-dispersive spectroscopy, and vibrating sample magnetometry (VSM) results yielded the optimized CVD parameters as 950 °C, 60 min, CH₄/H₂: 1/1 and 50 mbar. The characterization results proved that multilayer graphene (d-spacing: 0.34 nm) encapsulated Fe/Fe₃C nanoparticles (average core size: ∼46.9 nm, shell thickness: ∼16.6 nm) can be successfully synthesized by using CVD process followed by a leaching treatment. VSM results revealed that synthesized nanoparticles had soft ferromagnetic properties (M_s: 90.6–185 emu/g; H_c: 255.4–301.6 Oe). Characterization results deepen the understanding of process parameters of CVD system on characteristics of core/shell nanoparticles.