Hydrophobic high quality ring PMOs with an extremely high stability

Abstract

Ordered mesoporous organosilicas with a high organic loading lead to a more hydrophobic character and can result in better mechanical, hydrothermal and chemical stability. In this paper, we first present an optimized synthesis method of periodic mesoporous organosilicas containing interconnected [Si(CH₂)]₃ rings in the presence of surfactant Brij-76. Therefore, two important synthesis parameters, which are the acid and surfactant concentration, were systematically varied. This optimization method results in highly ordered mesoporous materials with very high surface areas, high pore volumes, uniform cylindrical pores and thick walls. Further, it was found that the porosity can be controlled by the surfactant concentration without changing the pore diameter. In the second part, it is demonstrated that a post modification with HMDS or an auto-hydrophobization step leads to PMOs which are totally hydrophobic without losing their mesoporosity. In the last part, the impact of the hydrophobization on the (a) hydrothermal, (b) mechanical and (c) chemical stability is investigated. The results reveal that post modification with HMDS creates ordered materials that can withstand (a) steaming at 130 °C, (b) a mechanical compression of 272 MPa and (c) a treatment with 1 M NaOH for 2.5 h without any degradation of the silica network.