Controllable fabrication and characterization of graphene oxide layers and quantum-dot-like structures from rice husk ash-derived carbon

The utilization of agricultural waste and the development of sustainable technologies for producing engineering advanced materials such as graphene oxides are of critical scientific and economic importance. In this work, graphene oxide materials high quality, improved structural features, and potential for scalable production were prepared using rice husk–derived activated carbon. By tuning the type and strength of oxidizing agents, the graphitic structure was selectively transformed into few-layer graphene oxide nanosheets (GO-1 and GO-2) or graphene quantum dots (GQDs). The resulting materials exhibited well-exfoliated structures with preserved sp² domains and abundant oxygen-containing functional groups. The samples were characterized using field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption at − 196 °C. The adsorption performance of the synthesized GO samples toward methylene blue (MB) dye was systematically evaluated with respect to solution pH, adsorbent dosage, and Langmuir equilibrium isotherm modeling. It was found that few-layer graphene oxides and graphene quantum dots could be obtained with tailored oxidation processes. The optimal adsorption conditions were observed at pH 6, using an adsorbent dosage of 0.1 g/L, with an initial dye concentration of 100 mg/L and at a temperature of 25 °C. The GQDs exhibited the highest monolayer adsorption capacity of 100 mg/g, which can be attributed to their higher specific surface area and abundant oxygen-containing functional groups, enhancing electrostatic interactions and surface adsorption sites. Therefore, the controllable modified Hummers’ method with adjustable oxidation degrees applied to rice husk-derived activated carbon offers an environmentally friendly and cost-effective route for the synthesis of graphene-based materials.