Unusually large microporous HKUST-1 via polyethylene glycol-templated synthesis: enhanced CO2 uptake with high selectivity over CH4 and N2.

Abstract

Porous solids with highly microporous structures for effective carbon dioxide uptake and separation from mixed gases are highly desirable. Here we present the use of polyethylene glycol (20,000g/mol) as a soft template for the simple and rapid synthesis of a highly microporous Cu-BTC (denoted as HKUST-1). The polyethylene glycol-templated HKUST-1 obtained at room temperature in 10min exhibited a very high Brunauer-Emmett-Teller (BET) surface area of 1904 m2/g, pore volume of 0.87 cm3/g, and average micropore size of 0.84nm. However, conventional HKUST-1 exhibits a BET surface area of 700-1700 m2/g confirming the advantages of using this method. X-ray powder diffraction and electron microscopy analysis confirm the formation of highly crystalline and uniform octahedral particles with sizes ranging from 100nm to 120µm. Adsorption isotherms recorded at temperatures between 273 and 353K and pressures up to 40bar revealed a more favorable adsorption capacity of HKUST-1 for CO2 vs. CH4 and N2 (708mg (CO2)/g, 214mg (CH4)/g and 177mg (N2)/g at 298K and 40bar). The Langmuir, isotherm model, and isosteric heats of adsorption were evaluated. The CO2 interaction at PEG-templated HKUST-1 is physical, exothermic, and spontaneous with DH° = - 6.52kJ/mol, DS° = - 13.72J/mol, and DG° = - 2.43kJ/mol at 298K at 40bar. The selectivities in equimolar mixtures were determined as 53 and 24, respectively, for CO2 over N2 and CH4. CO2 adsorption-desorption tests reveal high adsorbent reusability. The cost-effective and quickly prepared PEG-templated HKUST-1 demonstrates high efficacy as a gas adsorbent, particularly in selectively capturing CO2.