Development of sulfonated (3-Mercaptopropyl)trimethoxysilane membranes with thermal stability and excellent NH3 perm-selectivity at 300 °C

(3-Mercaptopropyl)trimethoxysilane (MPTMS) sols, xerogels, and membranes with and without H2O2 oxidation were prepared to improve NH3 affinity and selectivity particularly at high temperatures. Mercaptan (S–H) in MPTMS precursor can be completely oxidized to transform SO originated from various sulfur oxidization groups by mixing H2O2 to sol solution for enhancing NH3 affinity, as proven by FT-IR and XPS analyses. Thermogravimetric mass spectrometer (TG-MS) and N2 adsorption respectively verified the thermal stability and the dense structure of unoxidized and oxidized MPTMS xerogels around 300 °C. Furthermore, NH3 temperature-programmed desorption (NH3-TPD) revealed that oxidized MPTMS xerogels showed a strong NH3 affinity (NH3 adsorption amount of ∼1.41 mmol g−1), twice higher than that of unoxidized MPTMS xerogels (0.75 mmol g−1) owing to the strengthened acidity and increased acidic sites. Finally, oxidized MPTMS membranes expressed an excellent selectivity for NH3/H2 of 6 and NH3/N2 of 18 with an NH3 permeance of ∼1.4 × 10−7 mol m−2 s−1 Pa−1 at 300 °C for single gas permeation. NH3 permeance and selectivity at 300 °C in NH3/H2 and NH3/N2 mixed gas permeation were almost constant without any mixing-effects, consistent with those in single gas permeation.