Optimization of Ni-amine coordination for improving NH3 permeation through nickel-doped bis[3-(trimethoxysilyl)propyl] amine membranes

Nickel-coordinated bis[3-(trimethoxysilyl)propyl] amine (BTPA) xerogels and membranes reportedly showed excellent NH3 adsorption, permeance, and permselectivity. To study the H2, N2, and NH3 permeation properties of Ni-BTPA membranes in detail, the nickel doping amount in BTPA should be optimized. In this work, Ni-BTPA sols/gels with nickel/propylamine (Ni/N-H) mole ratios of 0, 0.125, 0.25, 0.50, and 1.00 were prepared and characterized via DLS, FT-IR, UV-vis, TG-MS, and XRD, indicating that the sol size and the interactions between nickel and N-H/N=O were increased with an increase in the Ni/N-H mole ratio. The large NH3 adsorption and desorption amounts were obtained with 0.50 and 1.00 Ni-BTPA xerogels via NH3-TPD measurement, additionally, the competitive interactions between nickel and NH3/other functional groups, such as N-H and N=O, were found in 1.00 Ni-BTPA, which could negatively affect the NH3 affinity. The pore sizes of membranes were gradually enlarged in Ni-BTPA with increases in the nickel content, which improved gas permeation. Due to the enlargement of the pore size and the sufficient NH3 affinity, the 0.50 Ni-BTPA membrane recorded the optimal performance with a NH3 permeance of ∼2.8 × 10-6 mol m-2 s-1 Pa-1, an ideal NH3/H2 selectivity of 11, and NH3/N2 selectivity of 102 at 200 °C.