Developing ordered mesoporous silica superacids for high-precision adsorption and separation of ammonia

Abstract

NH3 reversible adsorption and separation show great significance during its production and utilization, traditional adsorbents show either complex synthetic procedures or unsatisfied separation precision. We report here a class of sulfonic group functionalized and ordered mesoporous silica superacids (OMS-SO3H-xs) via enhanced host–guest assembly between copolymer templates and silica precursors without additional solvent. The OMS-SO3H-xs have large surface areas (463.7–910.5 m2/g), abundant micropores tandem well-ordered mesopores, high concentration of –SO3H (2.5 mmol/g) with extremely-high acid strength. Consequently, the OMS-SO3H-xs exhibit ultra-high precision for NH3 reversible adsorption and separation, giving high NH3 capacity (9.0 & 7.6 mmol/g at 25 & 50 °C and 1.0 bar) with extraordinary NH3/N2 (0.1/0.9) Ideal Adsorption Solution Theory (IAST) selectivities (1200 & 2235). The room temperature saturated breakthrough NH3 capacities of OMS-SO3H-xs were up to 3.38 mmol/g (3.0v%NH3/24.75v%N2/72.25v%H2), which can be well-maintained after 8th cycling without attenuation. The above features found in the OMS-SO3H-xs were resulted from their high density of –SO3H superacid sites those were homogeneously anchored into the ordered mesoporosity, which not only enhances their interaction with NH3, but also achieves the controllable NH3 interaction and transportation inside the mesochannels.