Correlations of acidity-basicity of solvent treated layered double hydroxides/oxides and their CO2 capture performance

Abstract

The basicity and acidity of solvent-treated layered double hydroxide (ST-LDHs) and their layered double oxides (ST-LDOs) have been fully studied using Hammett titration, in situ FTIR, CO₂-TPD and NH₃-TPD. Five solvents (ethanol, acetone, isopropanol, ethyl acetate and 1-hexanol) were selected to treat [Mg_0.72Al_0.28(OH)₂](CO₃)_0.14 (Mg_2.5Al-CO₃ LDH) and compared with traditional LDH co-precipitated from water. The Brønsted basicity strength of the ST-LDHs and ST-LDOs increased but was accompanied by a decrease in basic site density. In addition, the Lewis acidity of ST-LDOs also changes significantly, with medium strength Lewis acid sites dissapearing after solvent treatment. We found that the CO₂ capture capacity of solvent treated LDOs is 50% higher than that of traditional co-precipitated LDO sample. The ethanol treated LDO exhibited the highest CO₂ uptake of 1.01 mmol g⁻¹. The observed CO₂ capture performance of the ST-LDOs correlates linearly with the ratio of total acid sites to total basic sites.