Monolithic nickel(II)-based aerogels using an organic epoxide: the importance of the counterion

Abstract

The synthesis and characterization of nickel(II)-based aerogel materials prepared using the epoxide addition method is described. The addition of the organic epoxide propylene oxide to an ethanolic solution of NiCl2·6H2O resulted in the formation of an opaque light green monolithic gel and subsequent drying with supercritical CO2 gave a monolithic aerogel material of the same color. This material has been characterized using powder X-ray diffraction, electron microscopy, elemental analysis, and nitrogen adsorption/desorption analysis. The results indicate that the nickel(II)-based aerogel has very low bulk density (98kgm−3 (∼98% porous)), high surface area (413m2g−1), and has a particulate-type aerogel microstructure made up of very fine spherical particles with an open porous network. By comparison, a precipitate of Ni3(NO3)2(OH)4 is obtained when the same preparation is attempted with the common Ni(NO 3)2·6H2O salt as the precursor. The implications of the difference of reactivity of the two different precursors are discussed in the context of the mechanism of gel formation via the epoxide addition method. The synthesis of nickel(II)-based aerogel, using the epoxide addition method, is especially unique in our experience. It is our first example of the successful preparation of a metal-oxide-based aerogel using a divalent metal ion and may have implications for the application of this method to the preparation of aerogels or nanoparticles of other divalent metal oxides. To our knowledge this is the first report of a monolithic pure nickel(II)-based aerogel materials.