Efficient iron oxide/expanded graphite nanocomposites prepared by underwater plasma discharge for removing heavy metals

Recent studies have shown that expanded graphite (EG) is a suitable substrate for combining iron oxide nanoparticles (IONPs). However, the low density and insignificant hydrophobicity of pristine EG hinder its applicability in wastewater treatment systems. Herein, iron oxide (IO)-combined EG nanocomposites (IO/EGs) were prepared using an underwater plasma discharge process, which is a fast and simple method for synthesizing composites. The IO/EGs produced by this method are complex combinations of the FeOOH and γ –Fe 2 O 3 phases, whose compositions vary as the IO precursor content changes between 20 and 60 wt.%. Compared with pristine EG, the IO/EGs with varying IO precursor contents (IO x /EGs) exhibited approximately six times higher surface areas (>100 m 2 /g), nearly double zeta potential values (>39 mV), and excellent heavy-metal removal efficiencies. The excellent heavy-metal removal efficiencies (>80% within 10 min, [ k ] = 2.30 h −1 , q e ; ≥ 125 mg/g) of IO 20 /EGs are attributed to their high specific surface areas (117.5 m 2 /g), relatively positive surface potentials (41.76 mV), and abundant reactive active sites (hydroxyl group). Overall, this study demonstrates that the simple and fast combined IO x /EGs are suitable adsorbents for removing heavy metals from polluted solutions.