Mesopore expansion of surfactant-directed nanomorphic zeolites with trimethylbenzene

• Mesopore diameters of nanomorphic zeolites can be expanded by TMB when the Na+ content is sufficiently high.
• The mesopore expansion occur through recrystallization of the zeolite framework.
• The Na+ promotes the recrystallization process.
• The large-mesopore zeolites are suitable as supports for bulky biomolecules.

The synthesis of zeolite using multiammonium surfactants as the hierarchical structure-directing agent has been investigated with a particular focus on mesopore expansion by trimethylbenzene (TMB) addition during the synthesis of nanosponge beta, MTW and MRE zeolites. The results showed that mesopore diameters of these zeolites could be increased according to the amount of TMB added to the zeolite synthesis reaction mixture but only when the Na+ content was sufficiently high. The expansion was reversed when the synthesis mixture was reheated following TMB removal by solvent extraction. The thickness of the mesopore walls did not change during the consecutive pore expansion and shrinking processes. A transmission electron microscopic investigation revealed that the process is likely occurring through recrystallization of the zeolite frameworks, as promoted by Na+. The mesopore diameter of the nanosponge beta zeolite could be increased to 15 nm using this method. This zeolite exhibited four times the adsorption capacity for lysozyme (molecular dimension: 2.0 × 2.5 × 4.3 nm3) at 298 K, compared to the TMB-untreated zeolite, which possessed 3.8 nm mesopores.

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