Monodispersed MCM-41 large particles by modified pseudomorphic transformation: Direct diamine functionalization and application in protein bioseparation

Direct diamine functionalization of large spherical MCM-41 (uniform particle diameter of 15 μm) was achieved via the co-condensation of pre-shaped spherical silica gel and [3-(2-aminoethyl aminopropyl)] triethoxysilane (ATMS) using a modified pseudomorphic transformation approach. The functionalized MCM-41 spheres exhibited ordered hexagonal mesostructure, narrow pore size distribution, and high-loadings of diamine group (1.785 mmol/g). The morphology of parent silica gel was well preserved during the simultaneous pseudomorphic transformation and diamine functionalization. Various characterization techniques such as thermogravimetric (TG), ultra violet-visible-near infrared (UV-vis-NIR), and solid state ²⁹Si and ¹³C MAS NMR, demonstrated that the diamine groups were successfully incorporated in the spherical MCM-41 silica framework. Benzaldehyde adsorption results proved that the distribution of diamine groups was concentrated on the pore wall surface of MCM-41, and they were active and accessible for further post-treatment. The surface density of diamine groups can be easily controlled by changing the ATMS content in the initial synthesis mixture, while the order of mesoporous MCM-41 structure was maintained in appropriate extent of ATMS/SiO₂ molar ratio. This preparation method provides a new synthesis protocol to modify large particle mesoporous materials with different functional groups. Furthermore, it was demonstrated that this diamine functionalized MCM-41 large particle can be used to separate native proteins efficiently.