Green approach for fabrication of high-quality graphene nanosheet from the waste of PET bottle plastic and wood sawdust by co-pyrolysis technology for dye adsorption from aqueous solution

Among carbon-based nanoparticles, graphene has garnered significant attention since its discovery as a carbon allotrope, owing to its unique two-dimensional structure and outstanding characteristics. In this research study, we present an environmentally friendly, cost-effective technique with the potential for mass production of valuable products such as graphene nanosheets. Graphene was derived from a mixture of wood sawdust and polyethylene–terephthalate bottles as the feedstock, along with a combination of sand and plant fertilizer that was modified by oxalic acid acting as a catalyst. The feedstock was successfully converted to graphite using a two-step fluidized-bed co-pyrolysis technology. Firstly, an experiment was conducted under a nitrogen atmosphere, subjecting the mixture to 500 °C for 30 min at a ramping rate of 5 °C/min, resulting in the synthesis of a black-charged residue. In the second step, graphite was obtained by subjecting the residue to 800 °C for 2 h at a ramping rate of 10°C/min, using the acid-modified catalyst in a nitrogen atmosphere. Finally, graphene nanosheets were produced from graphite through microwave-assisted liquid phase exfoliation. Due to the exceptional features of the synthesized graphene, it was used as an adsorbent for the removal of two organic dyes rhodamine B (RB) and malachite green (MG) from an aqueous solution. The effects of various factors on the adsorption capacity were studied in detail. The chemical structure and morphology of the synthesized samples were analyzed using advanced characterization techniques like XRD, FTIR, EDX, TGA, DTGA, and ZETA to determine the structure of graphene nanosheets and the degree of graphitization. The two models (Freundlich and Langmuir) were used to explain the experimental data obtained three different temperatures (298, 318, and 338 K) with a certain amount of graphene concentrate (0.04 g); the result showed the maximum adsorption capacity of RB and MG solution are 6.25 mg/g and 3 mg/g, respectively. The percentage of dye adsorbed for RB and Mg is 62.5 and 30%, respectively, in the optimum temperature 338 K, and optimum concentration for RB and MG is 25 and 12 ppm, respectively; as a result, the graphene considers as an ideal adsorbent (environmentally friendly and cost-effective) for removal of cationic types of dyes.