Graphene oxide composite aerogels fabricated by supercritical CO2 technologycharacterization and applications

Abstract

For the past few decades, materials science has been living in a golden age, with the emergence of nanomaterials and, especially, because of porous nanomaterials. There is plenty of research being carried out on both ordered (zeolites and MOFs) and disordered (ceramics, polymers and aerogels) porous media. The discovery of aerogels by S. Kistler on 19311 and the exhaustive work on MOFs by O. Yaghi during the 1990's2 have inspired many research groups to focus on these two groups of materials. The Supercritical Fluids and Functional Materials (SFFM) group, in which this Thesis has been carried out, has a long solid research history of working with both porous materials, including the main motifs of this Thesis (aerogels and MOFs), with the particularity of being synthetized and/or processed in supercritical CO2 (scCO2).3 On the topic of MOFs, the supercritical technology has been used in the SFFM laboratory to synthetize compounds already known (e.g., ZIF-8),4 for the preparation of new coordination polymers based on different bi- or tri- pyridines,5,6 for the discovery of new curcumin-based bioMOFs,7 9 and, last but not least, in the work with flexible carborane-based MOFs in which the scCO2 played the role of solvent extractor.10 Concerning the aerogels subject, the SFFM team has gained extensive experience in organic aerogels.11,12 This Thesis extends the work on aerogels to the family of graphene derived materials, including graphene oxide (GO) and reduced graphene oxide (rGO). Graphene, GO and rGO are relatively new materials. Even so, all of them have been on a non-stop research during the last couple of decades, mostly to corroborate the plethora of their impressive properties or to discover new ones. Actually, scCO2 initial experiments performed with GO dispersions revealed the methodology to produce a fascinating aerogel material, yielding an early patent, which is the basis of this work.13 In this Thesis both aerogels and MOFs are synthesized, either pristine or as a composite, characterized and used in different applications. The preparation of these materials all have in common the use of scupercritical technology. Supercritical fluids and nanoporous materials are closely related, as the properties of these solvents, mainly their gas-like viscosity, high diffusivity and null surface tension, are crucial for drying materials avoiding pore collapse.14 The Thesis starts with an Introduction section in which the used materials and the fabrication methods are described. Actually, the introduction illustrates all the topics that are discussed in this work, which are further elaborated later in the following chapters. The Experimental section describes the used equipment, methodologies and characterization techniques. All of the performed experiments were carried out following green methodologies based on scCO2.