An upgraded electro-Fenton treatment of wastewater using nanoclay-embedded graphene composite prepared via exfoliation of pencil rods by submerged liquid plasma

In this work, two types of electrochemical electrodes were synthesized using two types (i.e., 4 black (4B) and hard black (HB)) of pencil rods during submerged liquid plasma (SLP) process. At high potential (3 kV) electrons, the SLP process offered an effective exfoliation route for the disorientation of the graphite sp² domain to produce two nanoclay-graphene composite electrodes with a few graphene layers (thickness = 4–9 layers) and high dispersibility (< 19% settlement: 4 h) in polar/non-polar solution (52–53.1% settlement: 4 h). Their performance was then evaluated towards the electro-Fenton (EF) degradation of lindane using a coated Fe₃O₄ plate (as Fenton catalyst). Accordingly, both 4B- and HB-ENcGe electrodes showed high specific capacitance values (473 and 363 F g⁻¹) at 0.05 A g⁻¹ and excellent triangular charge-discharge patterns (< 9% and 35% reduction of capacitance, respectively after 1000 cycles (charging rate: 0.2 A g^-1)). At pH 3 and current density of 6.5 mA cm^-2, 4B-ENcGe exhibited superior EF degradation performance (99.4% after 60 min) against 2.5 mg L^-1 lindane (H₂O₂ generation capacity: 2.53 mmol. h⁻¹, current efficiency: 89.4%, and stability: up to 5th cycles). The complete EF-based mineralization of lindane suggests that these electrodes should offer one-step cost-effective treatment for wastewater contaminants.