Hierarchical porous graphitic carbon monoliths with detonation nanodiamonds: synthesis, characterisation and adsorptive properties

The addition of nano-carbons to composite materials is an area of significant research interest, when their addition results in improved properties. This work reports on the use of detonation nanodiamond (DND) in the preparation of porous carbon monoliths and an investigation of the properties of the final carbon–nanocarbon composite material. Porous carbon–nanodiamond (CND) monoliths, with macro-, meso- and micropores were prepared by carbonisation of a resorcinol-formaldehyde (RF) polymeric rod with an Fe(III) catalyst and spherical silica template. Pore characteristics and BET surface areas were determined from N2 isotherms, with surface areas in the range of 214–461 m2 g−1, depending on DND content. SEM imaging further confirmed the hierarchical pore structure present, where there was a trimodal structure for monoliths containing nanodiamond following pyrolysis up to 900 °C. Thermogravimetric analysis, TEM imaging, energy dispersive X-ray electron spectroscopy and Raman spectroscopy were employed to evaluate the properties of this new composite material. The adsorptions of methylene blue (MB) and neutral red (NR) dyes from water onto the composite monoliths were investigated and compared with activated carbon in order to further evaluate their physical and adsorptive properties. CND materials adsorb these two cationic dyes more effectively than activated carbon, due to a more accessible pore network, and DND content had a direct effect on adsorption capacities for the dyes. The adsorption isotherms coincided with Langmuir and Freundlich adsorption models. Maximum adsorption capacities of 599 and 284 mg g−1 were achieved for NR and MB, respectively, on the CND composites.