Mechanisms and efficiency of CO2 absorption in polyamidoamine dendrimers: Experiments and theoretical calculations

To investigate the effect of amino number and viscosity on the absorption properties of PAMAM dendrimers and CO2, different initiation cores and different generations of PAMAM dendrimers were used to absorb the CO2. Molecular simulations were also employed to explain the regulatory mechanisms governing CO2 absorption, and an evaluation method of the absorption capacity was constructed for PAMAM dendrimers. The results exhibited that the viscosity of PAMAM dendritic polymers increased according to the increase of the initiator carbon chain length and nitrogen-containing functional groups. The high viscosity of G1.0 PAMAM-T and G2.0 PAMAM-D resulted in absorption loadings that were only slightly higher than those of G1.0 PAMAM-D and much lower than the theoretical capacity. The molecular simulations confirm that increasing the number of amino groups enhances the ability of PAMAM dendrimers to bind CO2, the correlation is not entirely linear. The increase in viscosity increases the resistance to mass transfer of CO2 molecules in the absorption system, thus limiting diffusion and reducing absorption efficiency. Consequently, the optimal benefits of PAMAM dendrimers are achieved only by balancing the advantages of multi-amino groups with the disadvantages of increased viscosity. 13C NMR confirms that the CO2 absorption mechanism of the PAMAM dendrimers follows the zwitterionic mechanism in which primary and secondary amines react with CO2 to produce carbamate.