Improvement of CO2 adsorption on ZIF-8 crystals modified by enhancing basicity of surface

The imidazolate framework ZIF-8 samples were modified separately by using ammonia impregnation and thermal treatment in atmosphere of N2 or H2 in order to improve its adsorption property toward CO2, and the modified samples A-ZIF-8, N-ZIF-8 and H-ZIF-8 were correspondingly available. The modified ZIF-8 samples were characterized, and the surface chemical properties of the ZIF-8 samples were determined separately by FTIR, CO2-TPD, NH3-TPD and H2O-TPD. The isotherms of CO2 on the modified ZIF-8 samples were measured. Results showed that after surface modification, the total amounts of basicity of the modified samples significantly increased, and followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The uptakes of CO2 increased proportionally with the basic groups on the surfaces of the ZIF-8 samples due to CO2 being an acidic molecule. As a consequence of that, the CO2 adsorption capacity of the samples followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The amount adsorbed of CO2 on the modified ZIF-8 sample by ammonia impregnation is the highest, having an increase.