Effect of surface modifications on the adsorption and hydrothermal stability of MCM-41 material

Abstract

For mesoporous materials (M1, M2, M3, and M4) synthesized in different ways, the α values (hydrophobic index) were found to decrease in the following order: M1(4.57) > M2(2.57) > M3(1.36) > M4(0.92) > ZSM-5 (0.63). The surface -OH groups on mesoporous materials M1 and M2 were removed through different surface treatments, such as fluorination, silylation, alkoxylation, and TiO2 deposition. The variation of hydrophobicity could be placed in the descending order: silylated M1(17.43) > carbonized M1(14.20) > fluorinated M1(11.71) > fresh M1(4.57) > TiO 2/M1(3.55) ≫ ZSM-5(0.63). Surface fluorination largely increased the hydrophobic property of the material, but strikingly retarded the hydrothermal stability in boiling water. The hydrothermal stability of fresh M1 and carbonized SM1 were behaving similar. The enhanced hydrothermal stability of SM1 in boiling water has been ascribed to the hindrance of surface Si-O-Si(CH3)3 units on MCM-41 for the silicate hydrolysis.