https://doi.org/10.1016/j.ces.2011.09.052
“Layered doubled hydroxides (LDH), also known as hydrotalcite-like compounds, are composed of positively charged layers with charge balancing anions located in the interlayer region. LDH have the general formula [M1−xIIMxIII(OH)2][Xx/qq−⋅nH2O] with x typically in the range between 0.10 and 0.33 (Forano et al., 2006). These materials can be readily and inexpensively synthesized with the desired characteristics for a particular application. LDH and calcined LDH (oxides) are widely used in the areas of catalysis, anion exchange and adsorption.
The use of LDH for adsorption of CO2 has been investigated, but mainly under conditions of elevated temperature. Yong et al. (2001) reported several commercial hydrotalcite-like compounds with adsorption capacities of 0.2–0.5 mmol g−1 at 300 °C and 1 bar of CO2. They also found that the carbonate anion favours CO2 adsorption compared to OH−, and a low content of water can improve adsorption capacity. CO2 adsorption capacities higher than 1.0 mmol g−1 have been reported by Hutson and Attwood (2008). A CO2 adsorption capacity of 3.55 mmol g−1 was achieved by Ca–Al LDH with ClO4− anion at 330 °C and 1 bar. The adsorption capacity of LDH adsorbents can also be enhanced by promotion with potassium salts (Walspurger et al., 2008, Lee et al., 2007).
Amine modified LDHs have been prepared by several different methods. Park et al. (2005) used dodecyl sulfate (DS) intercalated LDH as precursor and added (3-aminopropyl)triethoxysilane (APTS) together with N-cetyl-N,N,N-trimethylammonium bromide (CTAB). The key step for the process was the formation of insoluble DS-CTAB salts and DS molecules were simultaneously replaced by APTS moieties. A process of exfoliation of LDHs followed by grafting of the single layers with aminosilanes has also been proposed (Wypych et al., 2005, Wypych and Satyanarayana, 2005). In-situ grafting of APTS onto the surface of LDHs with the assistance of DS was also reported by Tao et al., 2009a, Tao et al., 2009b.”