Synthesis, characterization and applications of 3D porous graphene hierarchical structure by direct carbonization of maleic acid

This work reports the synthesis of a novel 3D porous graphene (PG) from maleic acid (HO₂CCH=CHCO₂H) used as a carbon source through a simple one-step carbonization process. The sodium carbonate (Na₂CO₃) was used as the skeletal substrate for 3D PG preparation and we observed that the ideal mass ratio of maleic acid (MA) to Na₂CO₃ is 1:4, which gives the highest yield and net carbon content for 3D PG preparation. The Na₂CO₃ decomposition temperature is greater than 550 °C which causes the release of CO₂ and hence ultimately it produced 3D porous graphene (PG). The prepared 3D PG was characterized by X-Ray Diffraction (XRD), Raman Spectra, Transmission Electron Microscope (HRTEM), Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS), and Brunauer Emmett Teller (BET) Surface area. The synthesized 3D architectural frameworks of graphene offered well-defined pores with a large surface area amounting to 567.56 cm²g^-1. However, with increasing temperature above 700 °C, there is a decrease in surface area which can be attributed to the heat shrinkage and sintering or collapse of smaller diameter pores. Also at higher temperatures, Na₂CO₃ decomposes quickly which impart less effect on the morphology of synthesized graphene. In addition, electrochemical and adsorptive properties were also studied and a comparison is made with 3D rGO synthesized separately. The unique porous structure of 3D PG showed an excellent adsorption capacity of 433.3 (mg g^-1) towards emerging pharmaceutical compound Atenolol and it further increases up to 642.4 (mg g^-1) towards organic dye Rhodamine B, which is much higher than the 3D reduced graphene oxide rGO obtained by the chemical reduction process. Similarly, the as-synthesized 3D PG depicted enhanced oxidation and reduction properties as compared to 3D rGO as is evident from sharp anodic and cathodic peaks for the 3D PG prepared at 700 °C.