Template-free preparation of mesoporous silica and alumina from natural kaolinite and their application in methylene blue adsorption

A facile top-down strategy of preparing mesoporous materials directly from natural minerals by selective-etching was proposed. Kaolinite (Al2O3·2SiO2·2H2O), a cheap and abundant clay mineral, was chosen and processed into mesoporous materials with well-defined mesopores (2–6 nm) and high specific surface areas (170–430 m2/g). In the process, kaolinite was activated by heat-treatment, and then etched by an acid or alkali solution according to its chemical and crystalline features. The activated amorphous alumina or silica component was selectively etched by acid or alkali, respectively, and nanopores were generated in-situ as a result. The pore sizes and specific surface areas can be controlled by the calcination and etching conditions. The as-prepared mesoporous silica and alumina materials showed favorable adsorption abilities towards methylene blue with the monolayer adsorption capacity up to 362 mg/g. The template-free preparation of mesoporous materials directly from natural clay minerals may help to promote not only the development of clay products but also the wide application of mesoporous materials with encouraging economic and environmental benefits.