Enhancement Effect of Nano-scaled White Silica on the Hydrothermal Stabilities of Mesoporous Montmorillonite

Poor stabilities of synthesized mesoporous sieves inhibit their applications. In present work nanoa2sized high crystalline mineral, natural montmorillonite, was introduced into the synthetic system in order to improve the stability of mesoporous sieve. Two additional siliceous sources, Na2SiO3 and nano-sized white silica, were employed to widen the gallery space of montmorillonite into nano-scale. The resultant mesoporous montmorillonite was charactered by XRD, FTIR, TEM and N2 adsorption-desorption isotherms. Moreover, the influences of milling conditions, stirring time, and type of siliceous sources on the porous structures and the hydrothermal stabilities of mesoporous montmorillonite were also discussed. The results show that intensive milling of raw materials is necessary to achieve longa2range ordered mesopores in the structure. Furthermore, the multi siliceous sources make significant improvements on the hydrothermal stabilities of the samples, due to the cooperation effects between the Na2SiO3, white silica, and montmorillonite sheets. The highest hydrothermal stability exists in the sample synthesized from multi siliceous sources, whose original specific surface area is up to 772m2/g. After hydrothermal treatment for 10d, the sample keeps the long-range ordered mesoporous structure with specific surface area above 580m2/g.