Design and synthesis of Mg-HKUST-1/solid ionic liquid composites for CO2 capture with improved water stability

The water sensitivity HKUST-1, is a critical concern for realizing practical CO2 capture. Water stability and high CO2 adsorption are difficult to achieve simultaneously. Mg and piperazinium-based solid ionic liquids (SoILs) were incorporated into HKUST-1 to enhance its water stability and selective CO2 capture performance, respectively. The eco-friendly route was utilized for the synthesis of bimetallic Mg(x)-HKUST-1, employing water as the sole solvent with stirring and microwave treatment. The SoILs were incorporated into the pore structure of Mg (15)-HKUST-1 by wet impregnation. Among the different ratios of Mg used for the synthesis, 15 % Mg exhibited the highest improvement in CO2 capacity (5.32 mmol/g) and CO2/N2 selectivity (27) compared to the parent HKUST-1 (CO2 capacity, 4.2 mmol/g; CO2/N2 selectivity, 17). Once Mg(15)-HKUST-1 was impregnated with 10 % SoIL, the CO2 capture performance was further improved. In the stability study, 10 % SoIL/Mg(15)-HKUST1 and Mg(15)-HKUST-1 preserved respectively 92.4 % and 85.3 % CO2 adsorption capacity after 20 days of exposure to a humid environment (60 % RH) at 298 +/- 5 K, an improvement compared to the HKUST-1 (26 %). The CO2 and N2 adsorption capacities of HKUST-1, Mg-HKUST-1, and SoIL/Mg-HKUST-1 composite were measured using a volumetric method and characterized using Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA).