Controlled hierarchical porosity of hybrid ceramics by leaching water soluble templates and pyrolysis

Hybrid ceramics, polysiloxane-derived materials, feature adjustable surface characteristics and high specific surface areas, making the material promising for applications such as gas separation. For increased permeability in gas separation processes or accessibility of active sites, additional porosity on multiple length scales is desired. In this study, we demonstrate how water soluble templates can be utilized to obtain a controlled hierarchical porosity. KCl sieving fractions are used for adjusting the macroporosity and a polysiloxane precursor, aminopropyltriethoxysilane, to create mesopores. The generation of micro- and mesopores is characterized by nitrogen adsorption while the macroporosity is examined by scanning electron microscopy and mercury intrusion. Water and n-heptane vapor sorption experiments show the control of the surface characteristics of the material by the pyrolysis temperature. In summary, leaching of water soluble templates for meso- and macropores combined with micro pore generation by pyrolytic decomposition enables pore size control on three different length scales.