Green synthesis of templated carbon porous materials from simple raw materials

Abstract

Templated porous carbon materials (TPCMs) have recently received attention due to their many applications. In this context, this work focused on the development of a simple synthesis method to produce highly porous carbon materials, by applying commercial sugar as a carbon source, pyrolyzed silica (as a template) and deionized water. The synthesis of the materials consisted of: (i) gel formation, wherein the mass ratio sugar/template (S/T) was evaluated as well as the deionized water volume; (ii) carbonization: the gels were carbonized under an N₂ inert atmosphere at a heating rate of 10 °C min⁻¹ and a temperature of 700 °C for 1 h; and (iii) template leaching, in which two leaching agents were evaluated (NaOH and HF) for silica template removal. In order to evaluate the potential and characteristics of the TPCMs, morphological, textural and chemical characterization were carried out through N₂ and CO₂ physisorption, Raman spectroscopy, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Overall, the NaOH-leached materials reached similar chemical and textural properties when compared to the HF, which is interesting from the economical, safety and environmental points of view. The N₂ physisorption analyses evidenced the synthesis of a highly porous material after the removal of the template; C1-I (NaOH leaching) showed a specific surface area of 462 m² g⁻¹ and a micropore area of 610 m² g⁻¹, and elevated pore volume (1.04 cm³ g⁻¹), wherein micropores (0.21 cm³ g⁻¹) and mesopores (0.83 cm³ g⁻¹) were identified – most interesting values for the best TPCM amongst the studied conditions. An average diameter value of ultramicropores and supermicropores (2.9 Å) was also identified by CO₂ physisorption. The XRD diffractograms and Raman analyses indicated the formation of a semi-crystalline structure in the templated porous carbon material (TPCM), with large domains of graphite and graphene oxide sheets in a random pattern (turbostratic), along with amorphous carbon. From the FT-IR analysis it was possible to determine that the carbonized samples underwent partial oxidation and to identify the presence of bonds and vibrations of the aromatic skeleton (νOH, νC–H and νCC). Overall, the characterization of the TPCMs, produced from simple raw materials, have demonstrated the great potential of this synthesis method for highly porous carbonaceous materials.