Meso/microporous MOF@graphene oxide composite aerogels prepared by generic supercritical CO2 technology

Abstract

The increasing complexity in composition and structure of modern porous nanocomposite materials requires the development of advanced technologies that allow the simultaneous treatment of dissimilar compounds, not only with unlike composition but also involving different classes of pores, e.g., micro and mesopores. This work shows that supercritical CO 2 (scCO 2 ) technology can be used as generic processing aid to obtain composites involving non-reduced graphene oxide (GO) and metal organic frameworks (MOFs) in the form of aerogels with hierarchical porosity. Hybrid aerogels are formed by either depositing ( ex situ ) or growing ( in situ ) MOF nanocrystals onto the surface of 2D GO nanosheets. The archetypal hydrophilic HKUST-1 and UiO-66 and hydrophobic ZIF-8 microporous MOFs are chosen to exemplify the method possibilities. The ex situ route was adequate to prepare hydrophilic MOFs@GO homogeneous composites, while the in situ approach must be used to prepare hydrophobic MOFs@GO aerogels. Moreover, the scCO 2 methodology should be adjusted for each studied MOF in regard of the organic solvent used to disperse the nanoentities constituting the composite. The end-products are obtained in the form of aerogels mimicking the shape of the recipient in which they are contained. The products are characterized in regard of structure by X-ray diffraction, textural properties by low temperature N 2 adsorption/desorption and morphology by electronic microscopy. • scCO 2 as a synthetic platform for fabrication of meso/microporous MOF@GO aerogels. • MOF hydrophobic/hydrophilic nature defines the choice of ex situ/in situ scCO 2 method. • The ex situ route can be applied to a large number of MOFs with hydrophilic nature. • The in situ method can be also applied to hydrophobic MOFs to reduce time/resources. • MOF@GO composites were homogenous with hierarchical micro/meso porosity.