Insightful Understanding of Shear-Assisted Supercritical CO₂ Exfoliation for Fabricating Graphene Nanosheets through the Combination of Kinetics and Process Parameters

Abstract

The exfoliation of graphene in organic solvents with shear has been proved to be effective and easy to scaleup. However, there are a few studies focusing on the structure of the agitator or flow circulation. An improved approach for producing defect-free graphene using different agitators (type, diameter) in N-methyl pyrrolidone was developed herein, with the assistance of supercritical CO 2 intercalation. Then, different from the reported stator−rotor structure, an innovative structure with combined impellers and a draft tube was utilized, and the energy consumption of the two methods was compared. When a straight impeller combined with a nonperforated draft tube was used, the concentration of graphene was as high as 0.653 mg/mL, and the energy consumption was reduced under the dual effects of fluid shear and molecular intercalation. Raman spectroscopy revealed that the exfoliated flakes were free from basal-plane defects, and the transmission electron microscopy (TEM) and atomic force microscopy (AFM) images showed that the percentage of few-layer graphene (1−3 layers) was about 56.4%. Finally, the shear rate formula was derived from hydrodynamic methods, and it was found that the concentration of graphene was directly proportional to the shear rate.

Graphene Synthesis: Method, Exfoliation Mechanism and Large-Scale Production

“…The exfoliation method, using flake graphite or pyrolytic graphite with high crystallinity as raw material, separates the stacked sheets through external forces such as impact, [35], shear [36], friction [37], airflow expansion [38], blasting [39], chemical intercalation [40], redox [41], and electrode reactions [42], which significantly weaken and destroy the Van der Waals forces between graphite sheets to form single-layer, doublelayer, or few-layer graphene. According to the "power source" in the peeling process, it is categorized into electrochemical exfoliation [8,12,13,[25][26][27][28], oxide-assisted liquid phase exfoliation [6,9,43], mechanical exfoliation [27,[44][45][46][47], and three other categories.…”

Investigating The Effect of Various Parameters on The Yield of Graphene Obtained Through Graphite Exfoliation Using CO2 Supercritical Fluid

“…Since the discovery of graphene in 2004, graphene has attracted attention due to its attractive electronic, thermal, optical, and mechanical properties in various applications such as electronics, food industry, energy, etc. [1][2][3][4]. Currently, various methods for preparing graphene have been reported, all with the general goal of exploring the unique properties of graphene to increase potential practical applications.…”