Investigation of the factors influencing the structural stability of mesoporous silica molecular sieves

Structural stability of mesoporous molecular sieves synthesized under various conditions were investigated. The effect of synthesis temperature, compositions, and silica source was examined. The MCM-41 synthesized from fumed silica and FSM-16 synthesized from kanemite was the most stable towards water, retaining the regularity for more than 90 days; the sample synthesized from TEOS at room temperature was less structurally stable. It is considered that the regularity loss involves the adsorption of water onto the surface silanol groups, which causes the nearby Si–O–Si bond cleavage, eventually resulting in the structural collapse. The X-ray powder diffraction, N2 adsorption, and NMR study revealed that the structural stability has a strong correlation with the ratio of pore wall thickness t to the amount of SiOH, while such stability is weakly correlated with each parameter. [Copyright &y& Elsevier]