Unusually large microporous HKUST-1 via polyethylene glycol-templated synthesis: enhanced CO₂ uptake with high...

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 (20,000 g/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 10 min 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 0.84 nm. 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 100 nm to 120 µm. Adsorption isotherms recorded at temperatures between 273 and 353 K and pressures up to 40 bar revealed a more favorable adsorption capacity of HKUST-1 for CO₂ vs. CH₄ and N₂ (708 mg (CO₂)/g, 214 mg (CH₄)/g and 177 mg (N₂)/g at 298 K and 40 bar). 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° =  - 6.52 kJ/mol, DS° =  - 13.72 J/mol, and DG° =  - 2.43 kJ/mol at 298 K at 40 bar. 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.