The elemental analysis using scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy (TEM-EDX) confirms a homogeneous distribution of Si in the KPHI-Si sample as well as in the hydrophobized materials (See Supplementary Information Figure ). Nevertheless, it also evidences some inhomogeneities in the distribution of K and Cl atoms within the hydrophobically modified PHIs corresponding to the formation of KCl salt during the silylation which was not completely removed by washing with organic solvents (See Supplementary Information Figure ). These observations are consistent with the results of SEM-EDS elemental analysis (see Supplementary Information, Figure and Figure ).