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 (NH3) and simultaneously recover NH3 due to their negligible volatility, good affinity with NH3 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) [CuCl4], [Bmim](2) [NiCl4] 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 NH3. 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 NH3 capacity and NH3 selectivity than pristine silica gel and faster adsorption rate than the corresponding pure MILs, but also exhibit excellent reversibility. The highest capacity of NH3 adsorption up to 99.808 mg NH3 center dot(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 NH3 absorbed by the [Bmim](2)[Co(SCN)(4)]@silica gel can be completely released in 15 min, and no obvious losses in NH3 capacity were detected during five adsorption and regeneration cycles, indicating great potentials as adsorbents for NH3 separation applications.