Process Intensification of Mesoporous Material's Synthesis by Microwave-Assisted Surfactant Removal

Abstract

Mesoporous materials are of vital importance for use in separation, adsorption, and catalysis. The first step in their preparation consists of synthesizing an organic-inorganic hybrid in which a structuring directing agent (SDA, normally a surfactant) is used to provide the desired porosity. The most common method to eliminate the SDA, and generate the porosity, is high-Temperature calcination. Such a process is energy-intensive and slow. In this study, we investigated alternative nonthermal surfactant removal methods on a soft MCM-41 material, aiming at reducing the processing time and temperature, while maximizing the material's properties. The choice of a soft MCM-41 is critical since it is hydrothermally unstable, whereas the SDA removal is troublesome. Microwave processing yielded outstanding performance in terms of surfactant removal, structural preservation, and textural features; the surfactant was fully removed, the hexagonal structure was preserved, and the surface was highly rich in Si-OH groups. It is suggested that H2O2 is the dominant oxidant. In terms of the process features, the processing time is significantly reduced, 14 h (calcination) versus 5 min (microwaves), and the applied temperature is much lower. The energy savings were estimated to be 72% lower as compared to calcination; therefore, this approach contributes to the process intensification of a very relevant material's production.