Porous organic–inorganic hybrid aerogels based on Cr3+/Fe3+and rigid bridging carboxylates

A general method to prepare organic–inorganic hybrid aerogels has been presented. A series of organic–inorganic hybrid aerogels were successfully produced from 3d trivalent transition metals (Cr3+, Fe3+) and bridging carboxylic acids. Gelation of the Cr(III) gels was achieved by heating the precursor solution to temperatures above 80 °C, which is in sharp contrast to usual supramolecular gels. Among a range of ligands used, highly porous aerogels could be prepared from rigid carboxylate, e.g.1,4-benzenedicarboxylate and 1,3,5-benzenetricarboxylate. The porous aerogels can be described as a coherent, rigid spongy network of continuous nanometre-sized particles, which is significantly different from the usual fibrous network of supramolecular gels. The aerogels have tunable porous structures with micro- and mesoporosity depending on their reactant concentrations. Their surface areas, pore volumes, and average pore sizes were analysed by using nitrogen sorption, and the accessibility of the pores to bulky molecules was also evaluated. It represents a strategy to prepare hybrid materials with large porosity utilising structurally simple building blocks as precursors.