Enhanced NH3 permeation of bis[3-(trimethoxysilyl)propyl] amine membranes via coordination with metals

Bis[3-(trimethoxysilyl)propyl] amine (BTPA) membranes doped with different metals, including Fe, Ni, and Ag, were applied to evaluate the permeation properties of H2, N2, and NH3. All metal-coordinated BTPA gels showed superior NH3 adsorption and desorption capacity via NH3 temperature-programmed desorption (NH3-TPD), which benefits from the coordination between metal and NH3. The single-gas permeation and activation energy of permeance were measured to evaluate NH3 separation performance, which occurred in the following rank: Ni-BTPA > Fe-BTPA > Ag-BTPA > BTPA. These results are consistent with NH3-TPD data. The Ni-BTPA membrane showed NH3 permeance at ∼2.8 × 10−6 and ∼1.5 × 10−6 mol m−2 s−1 Pa−1 with ideal NH3/H2 selectivities of 11 and 27, and NH3/N2 selectivities of 102 and 277 at 200 and 50 °C, respectively. Intermolecular interaction energies and types between Ni-BTPA and NH3 were calculated by Density functional theory and Independent gradient model based on Hirshfeld partition in order to uncover the affinity mechanism for NH3. The results indicate that the interaction of Ni-BTPA with NH3 is significantly enhanced via metal-induced coordination and hydrogen bonds and/or van der Waals interactions caused by N–H, Si–OH, and NO functional groups.