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

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 CO2 (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 hydro-phobic 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.

Automated summary

This work demonstrates the use of supercritical CO2 technology as a generic processing aid for the synthesis of composites involving non-reduced graphene oxide (GO) and metal organic frameworks (MOFs). The composites are in the form of aerogels with hierarchical porosity and can be prepared using either the ex situ or in situ methods. The study also highlights the importance of adjusting the scCO2 methodology for each MOF in terms of the organic solvent used for dispersing the nanoentities in the composite.