ZIF-8 modified by Pluronic P123 copolymer with enlarged pores and enhanced textural properties for CO2/CH4 and CO2/N2 separations

The effect of non-ionic copolymer surfactant Pularonic P123 on textural and structural properties of ZIF-8 at different conditions was investigated. The varied synthesis parameters were the molar ratio of surfactant to precursors, synthesis temperature and required synthesis time of ZIF-8. Different molar ratios of Pluronic P123 to a mixture of 2-methyl imidazole (MeIM) and Zinc nitrate hexahydrate, (Pluronic P123/Zn(NO3)2. 6 H2O ​+ ​MeIM): 4/1, 2/1, 1/1, 1/2, 1/4) were used as precursors for the synthesis of Zeolitic Imidazolate Framework-8 (ZIF-8). The synthesis of the smallest ZIF-8 sample particles was also performed at temperatures of 30, 40, 50 and 60 ​°C. ZIF-8 particles were also synthesized with different duration of nucleation and growth (30, 60, 120, 240 and 480 ​min). XRD, SEM, gravimetric analysis of crystallinity degree, zeta potential and Laser particle size analysis, were applied to characterize the synthesized samples. The effects of different parameters and synthesis environments on the gas sorption capacity of ZIF-8 were also investigated using N2 adsorption-desorption isotherms, BET and DFT analysis. The overall results showed that the increases of surfactant concentration, time and temperature had an increasing effect on the pore size, pore volume and BET surface area of ZIF-8. Compared with the pure ZIF-8 sample, the increased mesoporosity of modified samples did not lead to superior sorption capacity of ZIF-8 except for two samples synthesized at the highest temperatures due to the heightened hydrophobicity of PPO and PEO groups of Pluronic P123 in those samples. The modification using Pluronic P123 has successfully enlarged the pores of ZIF-8 up to 2.7 ​nm. This enlargement in pore size together with an increase in the pore volume of ZIF-8 samples were identified as the main reason for the increase in CO2/CH4 and CO2/N2 solubility selectivity of the modified samples in adsorption experiments conducted at 298 ​K.