Nitroaromatic Compounds to Induce a Partial Positive Charge on the Silver Nanoparticle Surface for Facilitated Transport Membranes for Olefin/Paraffin Separation

Two nitroaromatic compounds (NACs), 1,2-dinitrobenzene (DNB) and 3,4-dinitrotoluene (DNT), were utilized as polarizers to induce a partial positive charge on the silver nanoparticle (Ag NP) surface with the help of the strong electron withdrawing property of the nitro group. Membranes containing surface-charged Ag NPs dispersed in poly( N -vinyl pyrrolidone) showed remarkably high separation performance for propylene/propane mixtures. The mixed-gas selectivity was higher than 170, which is the highest among polymer-based membranes ever reported including composite membranes, and the propylene permeance was about 0.9 gas permeance unit (GPU). This high separation performance is due to the facilitated olefin transport, where Ag NPs with a positive charge, as an olefin carrier, interact specifically and reversibly with propylene, but not with propane. Therefore, it was found that the facilitated olefin transport yielding extremely high separation performance is strongly associated with the binding energy of silver atoms, which is a measure of the positive charge density on the Ag NP surface.