The effects of surface acidity on CO2 adsorption over amine functionalized protonated titanate nanotubes

In this paper, an infrared study has been performed on CO2 adsorption over polyethylenimine (PEI) functionalized protonated titanate nanotubes (PTNTs) prepared by a simple wet impregnation method. It was found that PTNTs had a large amount of acidity sites, which had strong interaction with the amino groups of the loaded PEI. This interaction could lead to good dispersion of PEI molecules, resulting in good performance in adsorption capacity, amine efficiency and adsorption kinetics. Both weakly and strongly adsorbed CO2 species formed under CO2 exposure, which were attributed to hydrogen-bonded species and carbamate groups, respectively. The existence of strong surface acidity increased the proportion of weakly adsorbed CO2 on the protonated amine species, which was beneficial to the adsorption–desorption cyclic performance. Furthermore, it was confirmed that the interaction between the support surface and amine also resulted in the superior thermal stability of amine-modified sorbents. Overall, our results suggested that suitably tuning surface acidity of the support could effectively facilitate CO2 adsorption.