Characterization and structure evolution of Ca-Al-CO3 hydrotalcite film for high temperature CO2 adsorption

In this work, monodispersed layered double hydroxide (Ca-Al LDHs) nanoparticles were synthesized by hydrothermal coprecipitation. Uniform thin films of layered double hydroxide on porous anodic aluminum oxide (AAO) substrates were formed by a direct precipitation process in a homogeneous suspension containing monodispersed Ca-Al layered double hydroxide nanoparticles. It was found that the formation of a designed hydrotalcite-like phase is strongly dependent on the [Ca(2+)]/[Al(3+)] ratios, and that a minor CaCO3 phase could possibly form simultaneously, which is attributed to the greater insolubility of CaCO3 and the incompatibility of the ionic size of Al and Ca. The optimal CO2 adsorption capacity appears in the layered Ca-OH-Al structure with the composition ratio of 3:1. Furthermore, the CO2 adsorption mechanism varies with treatment temperature. Below 400 degrees C, the CO2 adsorption is attributed to the LDH structure with a large surface area and pore volume, but above that the adsorption is due to the formation of CaCO3 and CaO. The permeation behavior and CO2 absorption can be explained by a preferable chemical and physical absorption of CO2 on the layered double hydroxide and porous structure of the membrane.