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

Ammonia hydrothermal treatment provides a novel and convenient method for r efining the structural order and pore size uniformity of the acid-made meso porous silica synthesized from different quaternary ammonium surfactants an d acid sources. The post-synthesis treatment provokes transformation of sil ica wall-surfactant interactions within the mesostructure from the weaker h ydrogen bonding ((S+X-I0)) to the stronger electrostatic (S+I-) interaction s. 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 lat tice and pore size, as well as an extrusion of silica nanotubes from both s ides of the silica ropes, was observed. The extent of such silica nanotubes extrusion and lattice parameters is closely related to the hydrothermal co nditions, such as temperature. ammonia concentration and aging time. (C) 20 01 Elsevier Science B.V. All rights reserved.