Experimental evaluation of eco-friendly exfoliation strategies for Tour-method graphene oxide.

The exfoliation of graphite oxide (GrO) represents a critical stage prior to processes such as the reduction or functionalisation of graphene oxide (GO), directly affecting its final properties. In particular, GrO synthesised by the Tour method, which offers advantages over conventional methods such as the Hummers method (higher safety, better oxidation degree and homogeneity of the material), has been scarcely studied in terms of the control of its specific surface area (SSA), a fundamental parameter for its performance in technological applications. In this work, the optimisation of the exfoliation process of GrO prepared by the Tour method is proposed through the systematic comparison of different eco-friendly techniques: ultrasonic bath, ultrasonic probe, ball milling and glucose-assisted ball milling. A rigorous Design of Experiments (DE) and a comprehensive statistical analysis were carried out, using carbon content, C (%), and SSA as main responses. In addition, complementary characterisations by X-ray diffraction (XRD, for number of stacked layers, "n", crystal size, L, and diffraction peak position, 2θ) were performed to deepen the structural analysis. The results reveal that ball milling without additives achieved the highest SSA (~ 71 m² g−1), followed by glucose-assisted milling (~ 54 m² g−1), while ultrasonic techniques offered significantly lower values (6–30 m² g−1). This study provides a solid and rigorous basis for understanding and optimizing the properties of GO according to the requirements of the specific applications for which it is intended and a study of the differences between ball milling and ultrasonic exfoliation in GO normally applied in graphite exfoliation.