Porous macrobeads composed of metal oxide nanocrystallites and with percolated porosity

Abstract

In this work, we report a method of preparing porous metal oxide macrobeads using a cation-exchange resin with sulfonic acid groups as templates and aqueous solutions of metal salts as precursors. The metal–resin complexes formed on the pore surface of resins were firstly transformed into metal hydroxide precipitates in the pores after a treatment of ammonia, and then the metal oxide macrobeads were produced by calcination. In our experiment, Fe₂O₃, Al₂O₃ and TiO₂ macrobeads were prepared from FeCl₂, Al(NO₃)₃ and Ti(SO₄)₂. Our findings show that the loading content of metal ions plays a key role in the preparation of metal oxide macrobeads with conformability and integrity. If metal ions in the precursors have higher valence, the amount of metal ions that can be loaded to the resins is fewer. Therefore, repeating the ion-loading and ammonia-precipitation cycle is necessary to increase the loading content of metal species. Complete macrobeads can be obtained from one cycle for Fe₂O₃, two cycles for Al₂O₃ and three cycles for TiO₂. The as-synthesized metal oxides are spherical in shape, over 200 µm in size, have relatively high surface area, contain both mesopores and macropores and are crystalline. These properties make them potentially useful as catalysts, catalyst supports, absorbents and separation materials, especially for fixed-bed reactors or chromatography columns.