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–Fe2O3 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 (IOx/EGs) exhibited approximately six times higher surface areas (>100 m2/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, qe;≥ 125 mg/g) of IO20/EGs are attributed to their high specific surface areas (117.5 m2/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 IOx/EGs are suitable adsorbents for removing heavy metals from polluted solutions.