Advances in carbon nanostructure-silica aerogel composites: a review

Silica aerogels are amorphous materials with remarkable properties, such as very high porosity and specific surface area, and low bulk density and thermal conductivity. However, the potential applications of these materials are limited as they exhibit poor mechanical strength. Nevertheless, silica aerogels allow easy incorporation of different compounds into their structure, enabling the production of materials with distinct characteristics from those of the native silica aerogels. The addition of particles, polymers or fibers, for improving the mechanical, optical or thermal properties has been extensively investigated by several authors in the last decade. A relatively recent alternative is their modification with carbon nanomaterials, which include carbon nanotubes, carbon nanofibers, graphene and carbon aerogels. These nanostructures have well-known characteristics, such as high electrical conductivity and high mechanical strength. The combination of these carbon materials with silica aerogels can lead to new materials with unique electrochemical performance, and thermal and adsorption properties that can be useful in several fields such as electronics, insulation and wastewater treatment. This paper presents a literature review on the synthesis of composite systems containing silica aerogels and carbon nanostructures, and describes their new properties and applications. Examples are the treatment of oily water and removal of heavy metals from wastewater, as well as their application as thermal insulators or anode materials. Along with these new properties, very promising results in mechanical reinforcement were already observed with the inclusion of carbon nanostructures in silica aerogel matrices, but there is still room for further developments in this regard.