The electrochemical preparation and characterization of sulfur-free expanded graphite

The environmentally friendly preparation of sulfur-free expanded graphite (EG) remains a great challenge. A large amount of strong acids and strong oxidants were used to prepare expandable graphite, resulting in environmental pollution problems. Herein, a novel and green preparation method for EG has been developed. Sulfur-free EG was fabricated using natural flake graphite (NFG), sodium perchlorate (NaClO₄), and oxalic acid (C₂H₂O₄) as raw materials. The electrochemical oxidation method was applied to prepare sulfur-free expandable graphite, and microwave irradiation technology was adopted to prepare sulfur-free EG. Sulfur-free expandable graphite was heated to generate sulfur-free EG through microwave irradiation technology. The optimum weight ratio was as follows: NFG:NaClO₄:C₂H₂O₄ = 1.5:10:2. The anodic oxidation occurred under a constant current density of 47 mA/cm², and the intercalation reaction lasted for 60 min at ambient temperature. The largest expanded volume (EV) of sulfur-free EG was 290 mL/g. The FTIR spectrum proved that the ClO₄⁻ and COO⁻ groups had entered the graphite layers. The SEM images showed that the graphite layers were completely opened, and the pore structure was clearly observed. The sulfur-free EG prepared by the method does not cause environmental pollution and has broad application prospects.

Graphical abstract

Natural flake graphite is composed of carbon atoms and has a layered structure. Oxidant oxidizes the edges of the graphite layer, causing the interplanar spacing to increase, and the intercalation agent molecules could enter the layers. The expandable graphite was synthesized, and microwave irradiation technology was adopted to prepare expanded graphite.