Layered Double Hydroxide Nanoparticles/Microparticles (Mg/Al = 2) as Adsorbents for Temperature Swing Adsorption: Effect of Particle Size on CO₂ Gas Evolution Behavior

Mg–Al layered double hydroxide (LDH, Mg/Al ≈ 2) nanoparticles/microparticles with systematically controlled sizes were prepared using a hydrothermal method, and their performance as CO2 adsorbents for temperature swing adsorption (TSA) cycling was investigated. During continuous heating, gas evolution occurred in three distinct steps for all samples. During the second step of the multistep structural transformations (i.e., partial dehydroxylation of the layers followed by the coordination of carbonate ions to the metal ions), relatively large amounts of CO2 were evolved without the collapse of the layered crystal structure, whereas most of the interlayer CO32– ions were retained in the interlayer spaces. The amount of CO2 evolution increased as the particle size decreased. Subsequently, the amount of CO2 desorption was measured over repeated TSA cycles in the temperature range 463–603 K. All samples exhibited considerable CO2 desorption capacities, wherein water vapor enhanced the performance. In situ Fourier transform infrared spectroscopy revealed that the adsorption–desorption cycles were almost reversible. A slight change in the interlayer distance detected by in situ X-ray diffraction suggested that the insertion and removal of some carbonate species partly occurred in the interlayer spaces of the LDHs. The present study indicates the potential of LDH nanoparticles/microparticles for TSA adsorbents