Physicochemical surface properties of Fe, Co, Ni, and Cu-doped monolithic organic aerogels

Fe, Co, Ni, and Cu-doped monolithic organic aerogels were prepared by the sol-gel method through the polymerization of a resorcinol formaldehyde mixture containing the metal acetates as polymerization catalysts. The aerogels were supercritically dried with carbon dioxide, and their surface morphology and pore texture were characterized by means of scanning electron microscopy, N-2 adsorption at -196 degreesC, and mercury porosimetry. The dispersion, distribution, and chemical nature of the metal-containing phase were analyzed by X-ray diffraction, backscattering electron imaging, energy-dispersive X-ray, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. According to these analyses, the surface morphology and pore texture were influenced by the metal acetate present because of its different catalytic activity and pH of the initial mixtures. The metal-containing phase was very highly dispersed in Co and Ni-doped monolithic organic aerogels, and it was homogeneously distributed in Fe and Cu-doped monolithic organic aerogels although not so highly dispersed. XPS studies provided experimental evidence of the chelation of iron and cobalt ions by the phenolic groups of the polymeric matrix but no clear evidence of the chelation of nickel and copper ions.