Experimental and Theoretical Investigations into the Performance and Mechanism of CO Capture by 3D and 2D ZnAl Layered Double Hydroxides.

Two-dimensional (2D) materials have a wide range of applications in adsorption and catalysis because of their high specific surface areas and large number of surface active sites. In this paper, bulk ZnAl layered double hydroxides (ZnAl-LDHs or bulk-LDHs) and 2D monolayer ZnAl-LDHs (monolayer-LDHs) were constructed and used for CO capture at temperatures of 298-573 K. The experimental results show that monolayer-LDHs have a large specific surface area (455 m g) and shows an excellent CO capture performance (4.5 mmol g). The CO adsorption capacity of monolayer-LDHs decreases greatly with an increase of the temperature, while bulk-LDHs are less affected by the temperature. Moreover, the parameters of charge distribution, density of states, and charge transfer of bulk-LDHs and monolayer-LDHs were studied in detail by density functional theory, and the difference of the adsorption mechanism between two LDH materials in CO capture was compared. It is found that monolayer-LDHs have better electronic activity than bulk-LDHs. At low temperature, CO is more likely to be physically adsorbed on the surface of monolayer-LDHs, and the adsorption process is more likely to occur. CO is more easily adsorbed on the surface of bulk-LDHs in the form of chemisorption, the adsorption energy is larger (-1.01 eV), but the CO capture capacity is quite stable at high temperature.