Scalable production of high-quality exfoliated graphene using mechanical milling in conjugation with supercritical CO2

Abstract

The progress of graphene (GNs) exfoliation by ball milling from laboratory to commercial scale is still facing formidable challenges due to the extremely long milling process, toxic auxiliaries, dispersant, and complex post-purification steps. Herein, a highly-efficient and green exfoliation process using the synergetic effect of high-energy planetary ball-milling coupled with supercritical carbon dioxide (scCO2) was developed. The collaborative effect of high-shear force (SF) of planetary ball mill and CO2 intercalation through the graphite crevices increased the yield of GNs up to 59% under the optimized parameters. The exfoliated GNs flakes were highly dispersible in different organic solvents (eg. N-methyl pyrrolidone, dimethylformamide, and ethanol) and ≈71.32 % of GNs were less than 5 layers. The exfoliated GNs revealed a large graphitic domain and micrometer-scale lateral dimension. The electrical conductivity (σ) of the GNs film was 5.76 × 105 S·m−1. Also, the in-plane and through-plane σ of the GNs/high-density-polyethylene (GNs/HDPE) nanocomposite achieved 3.59 and 1.37 S·m−1 at 3% (weight/weight, w/w) of GNs loading amount respectively, encompassing the excellent viability of GNs in a wide range of applications. This new process holds a strong potential to overcome the drawbacks of GNs exfoliation by the common ball milling procedure and could boost the commercial scale-up opportunity.