A Fast and Efficient Ion-Exchange Procedure To Remove Surfactant Molecules from MCM-41 Materials

A pure silica MCM-41 and two aluminosilicates with Si/Al = 1.25 and 30 have been synthesized hydrothermally under basic conditions in the presence of cationic surfactants. Organic molecules could be completely extracted from the mesopores by treating as-made compounds with an ethanolic solution of ammonium nitrate at 333 K. The procedure is particularly efficient for the low-silica compound: all surfactant molecules are removed within less than 15 min. After treatment, NH4+ cations, which balance the charge of aluminum atoms in aluminosilicates, can be removed by heating extracted Al-MCM-41 at moderate temperature. In the pure-silica material, the in-situ decomposition of NH4+ cations directly forms silanol groups on the surface of the mesopores. Extracted materials possess highly ordered structures with properties similar to those of directly calcined materials. The procedure reported here is fast, cheap, and efficient to remove completely surfactant molecules from the pores of MCM-41 materials with various compositions.