Post-synthesis treatment of acid-made mesoporous silica materials by ammonia hydrothermal process

Ammonia hydrothermal treatment provides a novel and convenient method for refining the structural order and pore size uniformity of the acid-made mesoporous silica synthesized from different quaternary ammonium surfactants and acid sources. The post-synthesis treatment provokes transformation of silica wall-surfactant interactions within the mesostructure from the weaker hydrogen bonding (S⁺ X^-I°) to the stronger electrostatic (S⁺I^-) interactions. The morphology of the mesoporous silica material remains unchanged after the ammonia hydrothermal treatment at 373 K. Such treatment resulted in an increase in both thermal and hydrothermal stability of the mesostructure. Whereas at higher treatment temperatures (>373 K), a marked increase in lattice and pore size, as well as an extrusion of silica nanotubes from both sides of the silica ropes, was observed. The extent of such silica nanotubes extrusion and lattice parameters is closely related to the hydrothermal conditions, such as temperature, ammonia concentration and aging time.