Carbon Dioxide Adsorption Performance and the Kinetic Properties of the Zirconium and Poly(ethyleneimine) Bifunctionalized Molecular Sieve of KIT-6

Porous materials of PEI(n)/Zr(N)-KIT-6 were prepared by doping zirconium to the KIT-6 framework and introducing poly(ethylenimine) (PEI) to the pore channels (n is the weight percentage of PEI to Zr(N)-KIT-6, and N is the molar ratio of Zr/Si). The adsorbents were characterized and tested at a 20% CO2 concentration to investigate the influence of Zr and PEI on CO2 adsorption. The results display that Zr–O–Si bonds are formed after the doping of Zr species. In addition, PEI is loaded on the surface through the formation of hydrogen bonds and Zr–N bonds. The synthesized PEI(n)/Zr(N)-KIT-6 materials keep stable when the temperature is lower than 210 °C. In addition, the materials exhibit good CO2 adsorption performance, which is attributed to the existence of Zr and PEI. The Lewis acidity of KIT-6 is improved after the doping of Zr heteroatoms, leading to the immobilization of more PEI and the enhancement of CO2 adsorption properties. The adsorption includes two steps: diffusion of CO2 in the pore channels and the reaction between CO2 and amine groups. When the gas flow rate is 40 mL/min, the maximum CO2 adsorption capacity of 174.7 mg/g is achieved. After 20 cycles, the adsorption value keeps stable.