Characterization of MCM-41 mesoporous materials derived from polish fly ashes

Abstract

The synthesis of mesoporous molecular sieves from fly ashes is an interesting direction of use of the values of fly ash, and specifically its chemical composition (Si, Al), for obtaining high-quality porous materials offering wide possibilities of utilization. An attempt was made in the present work to obtain the MCM-41 mesoporous materials from 10 different fly ashes originating from Polish Power Stations. The synthesis was carried out by the hydrothermal method using the supernatants of coal fly ashes (fused fly ash solutions) and cationic cetyltrimethylammonium bromide (CTAB) surfactants as the structure-directing agents. Fly ashes were chemically analyzed and used to prepare mesoporous materials (MCM-41). The current work uses powder X-ray diffraction (XRD), TG/DTG, FTIR, SEM, TEM, nitrogen adsorption and 27Al MAS NMR, 29Si MAS NMR techniques to characterize physico-chemical properties of fly ash-based MCM-41 materials. The properties of the synthesized mesoporous materials were compared with those prepared from pure silica sources. Studies have shown that extracts suitable for the synthesis of the MCM-41 mesoporous material cannot be obtained from all fly ash types (even those with a very high Si content and a very high Si/Al ratio).