General routes to porous metal oxides via inorganic and organic templates

Abstract

The generation of porous metal oxides by removal of template molecules from inorganic polymers formed by sol-gel type hydrolysis and condensation of metal alkoxides is described. The template molecules include organic polymers, copper (II) ions in hybrid copper oxide/silica sols and copper (II) bis(hexafluorocetylacetonate) (hfac). Neutron scattering experiments on the system in which polyacrylic acid (Mw=2,000 Daltons) is used as an organic template to generate microporous tin oxide show that removal of the template generates skeletal voids. In a second series of experiments, mixed copper/silicon oxide xerogels were prepared by hydrolysis of mixtures of Si(OEt)4 and Cu(OCH2CH(CH3)N(CH3)H)2 in the ratios of Si:Cu=2:1, 4:1, 9:1. Selective removal (etching) of the copper component generates porous silica. Neutron scattering data and BET surface area measurements are consistent with the creation of pores with molecular dimensions (micropores, 10 A or less). In the third strategy, Si(OEt)4 is hydrolyzed in the presence of Cu(hfac)2, a volatile, inert inorganic template, in a 4 to 1 molar ratio. Removal of the template from the xerogel at 100°C in vacuo affords microporous silica.