Irreversible Change of Pore Structure of MCM-41 upon Hydration at Room Temperature

The pore structure stability of MCM-41 materials upon hydration/dehydration was studied by XRD, 29 Si MAS NMR, and gravimetric adsorption techniques. Results demonstrated that collapses of the pore structure of MCM-41 occurred upon rehydration at room temperature due to the hydrolysis of the bare Si−O−Si(Al) bonds in the presence of water vapor. Full structure collapses of MCM-41 were found to occur when a MCM-41 sample was left in air for three months. It is also suggested that care must be taken when XRD is used to evaluate the structure property of MCM-41 materials to avoid the possible adverse effects of water vapor.