Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl, SO2, and NO2

Two different Mg–Al layered double hydroxides (LDHs), OH⋅Mg–Al LDH and CO3⋅Mg–Al LDH, are prepared and utilized for the efficient removal of acidic gases. The former contains OH− anions intercalated between the Mg–Al layers, whereas the latter contains CO32−. The synthesized Mg–Al LDHs were characterized via X-ray diffraction (XRD) and tested for their ability to remove three important acidic gases, HCl, NO2, and SO2 via chemical reaction with the intercalated OH− and CO32− anions (for HCl and NO2) and surface adsorption (in case of SO2). Both OH⋅Mg–Al LDH and CO3⋅Mg–Al LDH showed appreciable gas removal abilities with respect to HCl and NO2. However, in case of OH⋅Mg–Al LDH, a higher gas removal efficiency was observed due to the facile reaction between the acidic gases and the intercalated OH− anions between the LDH layers. Briefly, the HCl removal amount was 0.53 mmol for OH⋅Mg–Al LDH and 0.49 mmol for CO3⋅Mg–Al LDH in 90 min. The NO2 removal amount was 0.09 mmol for OH⋅Mg–Al LDH and 0.07 mmol for CO3⋅Mg–Al LDH in 90 min. The SO2 removal amounts by the LDHs were comparable since the gas was adsorbed on the surface of the LDHs. The SO2 removal amount was 0.04 mmol for OH⋅Mg–Al LDH and 0.04 mmol for CO3⋅Mg–Al LDH in 90 min. The XRD results indicated that the LDHs retained their structures after gas removal, despite attenuation of the XRD peak intensities. Thus, two easily synthesized LDHs with efficient acidic gas removal characteristics have been developed via judicious utilization of the reactions that dictate gas removal by LDHs.