New improved mesoporous nanocomposite CO, adsorbents IMSiNTs-PEI (IMP) were synthesized by improved pretreatment of natural halloysite nanotubes (HNTs) and impregnation of improved mesoporous silica nanotubes (IMSiNTs) with polyethylenimine (PEI). The new improved mesoporous morphology remained the same as the HNTs morphology, but the specific surface area (340.61 m(2)/g) and pore volume (0.499 m(3)/g) after treatment, respectively, were about 7 times and 2.5 times more than those values for HNTs. The results indicate that more active groups were created on the IMSiNTs surface compared with HNTs. Also, an adsorption apparatus was used for analyzing the impact of various ranges of pressure, temperature, and loaded PEI amount on adsorption capacity. The results showed an increase in uptake capacity with increasing pressure and also a decrease in uptake capacity with increasing temperature exhibiting that the nature of the processes is exothermic. On the other hand, the proper PEI dispersion inside the IMSiNTs could improve the adsorption capacity and the highest adsorption capacity of 7.84 mmol/g was obtained at 20 degrees C and 9 bar for IMP-30 PEI. It was also demonstrated that these adsorbents have high thermal stability, good reversibility, and stability during adsorption/desorption cycles.