Tailor-Made Aerogels Based on Carbon Nanofibers by Freeze-Drying

Abstract

The synthesis of aerogels based on carbon nanofibers (CNF aerogels) by a freeze-drying process has been studied. The influence of the polyvinyl alcohol/carbon nanofibers mass ratio (PVA/CNFs), the type of polymer and the use of functionalized CNFs on the physical properties of the resulting CNF aerogels have been evaluated. The morphology and textural properties of the resulting carbon aerogels were characterised by scanning electron microscopy (SEM) and nitrogen adsorption/desorption techniques. The thermal stability of the synthesized materials under nitrogen and oxygen atmospheres was also evaluated by TGA. Lower amounts of PVA gave rise to CNF aerogels with thicker and more amorphous structure due to CNF aggregation. Furthermore, the surface area and the total pore volume decreased on increasing the PVA/CNF mass ratio. It was found that the nature of the polymer had a marked influence on the morphology of the resulting CNF aerogels. The use of polyvinyl pyrrolidone (PVP) enhanced both the ignition characteristics and thermal stability of the CNF aerogels. Aerogels containing functionalized CNFs showed a high density and a low porosity due to the strong interaction of the latter with the polymer. The CNF aerogels described here could have potential uses as ultralight structural materials, thermal insulators and supercapacitors.

CNF-reinforced polymer aerogels: Influence of the synthesis variables and economic evaluation

“…The incorporation of CNF significantly increased the specific surface areas of the PVA aerogels [21,49]. According to Skaltsas et al [16], PVA acted as a carbon nanofibers binding and/or tip-blocking agent, then penetrating into the CNF pores during the freeze-drying process.…”

“…The CNF-reinforced polymer aerogel was prepared following a procedure based on that reported by Sánchez-Silva et al [21]. Fig.…”

“…According to previous studies [21], polyvinyl alcohol (PVA) was selected as the structural binder to improve the structure of the CNF-reinforced polymer aerogels [16,21].…”

“…10 shows the TGA-MS profiles for sample GEL PVA(0.25% CNF). According to some authors [67,21], the thermal degradation of PVA can be regarded as two degradation steps. Sample GEL PVA(0.25% CNF) showed a first weight loss of 18% in the temperature range of 180-250°C, which could be associated to the evaporation of water and/or splitting of monomers.…”

“…In this sense, very few studies have been focused on the lyophilization or freeze-drying process to obtain organic polymer aerogels [18][19][20]. In a previous work [21], aerogels based on carbon nanofibers were successfully prepared by the freeze-drying method. In addition, the influence of the mass ratio of PVA/CNF, the polymer use and the functionalization of CNF on the physical properties of the resulting aerogels was evaluated.…”