Hierarchical Porous Carbon Synthesized from Novel Porous Amorphous Calcium or Magnesium Citrate with Enhanced SF₆ Uptake and SF₆/N₂ Selectivity

The emission of greenhouse gases such as CO2 and SF6 is believed to contribute significantly toward global warming. One way to reduce their release is by adsorption at point sources using a suitable adsorbent. In this work we present the synthesis of two hierarchical porous carbon materials (referred to as PC-CaCit and PC-MgCit) with a high uptake of SF6 (5.23 mmol/g, 0 °C, 100 kPa) and a reasonable uptake of CO2 (>3 mmol/g). PC-CaCit and PC-MgCit were obtained by pyrolysis of the most porous calcium citrate and magnesium citrate ever reported, which were synthesized by us. The Langmuir specific surface area of PC-CaCit and PC-MgCit was over 2000 m2/g (BET surface area also close to 2000 m2/g). We characterized PC-CaCit and PC-MgCit using a range of advanced characterization techniques including N2 adsorption, high-resolution electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. PC-CaCit and PC-MgCit also showed a SF6-over-N2 selectivity of ∼33 at 0 °C (100 kPa), good cyclic performance, and moderately low heat of adsorption. The porous carbons synthesized in this work are good candidate adsorbents for greenhouse gases.