Nitrogen sorption measurements were performed to examine the poros­ity of the different materials obtained by the reaction pathway shown in Figure 1 (EP, BEP, EP-(CH2)3-SH and EP-(CH2)3-SO3H). The nitrogen adsorption and desorption isotherms are shown in Figure 2. The type IV isotherms with the condensation step at relative pressures between 0.55 and 0.75 and the H1 hysteresis of the solids clearly indicate that the ma­terials are mesoporous and possess cylindrical pores with a narrow pore size distribution.

A summary of the properties of these materials is shown in Table 1. The materials exhibit high specific surface areas (SBET) ranging from 850

to 523 m2 g-1 and large total pore volumes around 0.84 mL g-1. The SBET decreases when the material is functionalized due to the decoration of the pore walls with the bromine and later on with the propylthiol functionality but also due to the overall weight gain of the functionalized materials. The pore diameter of all the materials lies in the range of 6 to 5 nm. Only a mi­nor shift to smaller pore diameters and a slight broadening of the pore size distribution is observed (Figure 2 and Table 1). The structural characteris­tics of the commercially available resin Amberlyst-15 are also presented in Table 1 for comparison. This ethenylbenzenesulfonic acid polymer is a strong acid ion exchange resin with unordered macropores. The material is also prone to swelling.

The XRD patterns of the materials in Figure 3 reveal three well-resolved signals originating from the low angle (100) and second-order (110) and (200) reflections. This evidently indicates that the materials possess a 2D — hexagonal ordered structure and thus retain their P6mm space group order­ing throughout the syntheses. Only a slight broadening can be observed at the patterns of sample BEP, EP-(CH2)3-SH and EP-(CH2)3-SO3H.

It is quite remarkable that all the materials discussed in this study, show outstanding structural stability. The materials retain porosity and ordering after three consecutive reactions as can be seen from the nitrogen sorption and XRD data. These results also confirm the reported stability of Periodic Mesoporous Organosilicas [20,23].

Table 2 presents an overview of the chemical characterization of the solids after the different synthetic procedures. The bromination of the eth- ene bridge is a very straightforward reaction and approximately 25%-30% of the double bonds are brominated as the remaining fraction of double bonds are buried inside the walls and are unavailable for further reaction [45]. The subsequent substitution with the Grignard reagent results in thiol functionalities. The amount of thiol functionalities is determined using a silver titration [44,46]. After oxidation of the thiol groups using sulfuric acid and a thorough washing step, a total amount of 0.60 mmol H+ per gram of material has been observed. This also includes the intrinsic acid­ity of the PMO material originating from the surface silanols (—0.15 mmol g-1), as we described earlier [49]. It is clear that the conversion of the thiol containing PMO into the sulfonic acid containing-material has occurred via the oxidation process. This is also confirmed by Raman spectroscopy by the appearance of two signals in the region between 1160 and 1190 cm-1 (See figure S1 in supplementary information). Also, the thiol titration after oxidation showed a zero concentration of remaining thiol groups. Amberlyst-15 exhibits a high acidity of 4.7 mmol H+ g-1.