Efficient adsorption of ammonia by incorporation of metal ionic liquids into silica gels as mesoporous composites

The emerging of ionic liquids (ILs) provides a promising way to efficiently separate ammonia (NH 3 ) and simultaneously recover NH 3 due to their negligible volatility, good affinity with NH 3 and designable structures. However, the relatively high viscosities of ILs and the limited gas-liquid interface severely affect gas diffusion in ILs, which hinders their practical use in industries. In this work, in order to overcome the mass-transfer limitations of ILs in gas separation, three metal ILs (MILs), [Bmim] 2 [CuCl 4 ], [Bmim] 2 [NiCl 4 ] and [Bmim] 2 [Co(NCS) 4 ], with good affinity toward NH 3 were incorporated into porous silica gels with large surface area and abundant hydroxyl groups, by an impregnation-vaporization method to form novel MIL@silica gel composites for rapid, efficient and reversible adsorption of NH 3 . The FT-IR and BET results indicated that the prepared adsorbents with different loadings of MILs are mesoporous composites. The [Bmim] 2 [Co(NCS) 4 ]@silica gel composites not only show much higher NH 3 capacity and NH 3 selectivity than pristine silica gel and faster adsorption rate than the corresponding pure MILs, but also exhibit excellent reversibility. The highest capacity of NH 3 adsorption up to 99.808 mg NH 3 ·(g adsorbent) −1 in 15 min was obtained when the loading of [Bmim] 2 [Co(NCS) 4 ] in the MIL@silica gel composite was 48.89 wt%, which could be attributed to the synergistic interaction of the complexation and hydrogen bonding between cobalt coordinated anion and NH 3 as well as mesoporous structures. Moreover, the NH 3 absorbed by the [Bmim] 2 [Co(SCN) 4 ]@silica gel can be completely released in 15 min, and no obvious losses in NH 3 capacity were detected during five adsorption and regeneration cycles, indicating great potentials as adsorbents for NH 3 separation applications.