Interactive impacts of organic-inorganic modifiers on surface characteristics of Cu+-doped activated carbon for stable CO-adsorptive separation from CO2

Abstract

Conventional Cu+-doped activated carbon (C) materials are problematic in carbon monoxide (CO)-selective adsorption from carbon dioxide (CO2) due to their CO2-friendly surface basicity and microporosity. In this study, boehmite (AlOOH) film modified-carbon composite (AlC) was hydrothermally synthesized to dope with 30 wt% Cu+ ions by the impregnation-calcination method. The functional hydroxyl groups of Boehmite behaved as metallic anchoring sites for better Cu+ ion dispersion, enhancing the CO adsorption uptake to 38.84 cm3/g at 25 °C and ∼ 100 kPa in isotherm analysis. Additionally, the improved Lewis acidity of AlC surface interface together with pore widening impact reduced the CO2 uptake to 14 cm3/g, around half that of Cu+-doped activated carbon, by undergoing Lewis acid-acid repelling interaction between boehmite film and CO2. However, to address rapid oxidation of Cu+ ions in the hygroscopic AlC structure, iron (II) chloride (FeCl2) surface modification on the Cu+-doped AlC composite created a Fe3+-Cu+ bimetallic interface with high Cu+ immobilization, enriching the CO adsorption stability to 92 % even after 30 day-air exposure. Noticeably, pre-complexation of FeCl2 with thiourea (NH2CSNH2) before its dispersion over the doped Cu+ ions led to distinct Cu+ stabilization mechanisms without bimetallic redox interaction. This involves developing auto-redoxable iron (II) sulfides as barrier coatings for Cu+ species against oxidation and raising the Cu2+ reducibility via cyanide-ligands of thiourea. These combined preservation effects for Cu+ ions ensured CO adsorption stability of 91 %, underlining higher CO adsorption uptake (39.38 cm3/g) and CO/CO2 selectivity (67.49 at 0.2 kPa and 3.09 at ∼ 100 kPa) than modification effects of boehmite and FeCl2.