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.