Follow:

Stability of ZIF-94 for CO2 capture under wet and dry gases

https://doi.org/10.3390/molecules27175608

“In addition to the potential for large-scale synthesis of ZIF-94 at room temperature, we also needed to evaluate it in terms of structural stability and performance stability, so that it can be better used in the separation of CO2 in flue gas. In the structural stability assessment, as shown in Figure 4a, the PXRD pattern obtained after being exposed to air for half a year (Figure S6) was still in good agreement with the freshly synthesized sample and had no impurity peaks, indicating that the sample has excellent stability in air. Destruction of the sample structure is often caused by the presence of water molecules, so the stability test of ZIF-94 was conducted in a humid environment. The samples were immersed in water for 1 day, 3 days, 7 days, 1 month, and 2 months (Figure S7); the test results showed that the crystallinity of the sample basically did not change with the prolongation of soaking time. The PXRD patterns of the sample were analyzed after activation at different temperatures (Figure S8), and the PXRD patterns under these conditions are still consistent with the simulated peaks. Moreover, the chemical stability of ZIF-94 was evaluated by treating the samples under harsh conditions. Their PXRD patterns also remained intact after soaking in different pH solutions for 2 days (Figures S9 and S10), and there was no phase transition or structural collapse, demonstrating the material’s resistance to harsh chemical environments. The PXRD patterns of the samples after multiple adsorptions and dynamic breakthrough experiments were compared with those of the freshly synthesized samples, and the intensity of the diffraction peaks was still well-maintained, it can be seen that the above two processes could not destroy the crystal structure. In short, ZIF-94 exhibited satisfactory structural stability, excellent thermal stability, and exceptional recoverability in water and aqueous alkaline solutions. At the same time, ZIF-94 also preliminarily showed that it was a promising candidate for adsorption and separation under high humidity conditions by virtue of its water resistance.”

4HZzDjYL

Figure 4. (a) Corresponding PXRD patterns to show the maintained structure of ZIF-94 under different conditions. (b) Cycling adsorption isotherms for CO2 at 298 K and 1 bar. Cycling breakthrough experiments on CO2/N2 mixture (15/85, v/v) under two humidity conditions: (c) dry gas and (d) wet gas (99.2% RH).” https://doi.org/10.3390/molecules27175608

“In the performance stability assessment, first, we performed single-component adsorption cycle experiments of CO2 at 298 K and 1 bar. As shown in Figure 4b, the adsorption capacity of CO2 hardly decreased in adsorption cycling experiments, indicating its good structural stability and reusability. Furthermore, component adsorption of CO2 was performed on ZIF-94 under different conditions, as shown in Figure S11. It was found that the CO2 adsorption amount of the sample exposed to the air for 4 months was 49.59 cm3/g, and the sample soaked in water for 2 months at room temperature (56.33 cm3/g) was close to that of the freshly made sample (53.30 cm3/g), which further confirms that ZIF-94 maintains its original adsorption capacity in a high-humidity environment. Finally, Figure 4c,d displays cyclic breakthrough experiments using a CO2/N2 mixture (15/85, v/v) under the two humidity conditions three times, and the breakthrough time was almost constant, which confirms that the presence of water vapor has negligible influence on the CO2 enrichment process. The performed N2 adsorption–desorption experiments proved that the N2 adsorption amount of the material remained unchanged (Figure S12), and it maintained its initial porous structure. Moreover, ZIF-94 could repeatedly achieve separation of CO2/N2 without loss of performance in both dry and humid environments. The above test results indicated the excellent cycle performance of ZIF-94, coupled with its robust structural stability. The excellent cycle performance for CO2 adsorption and separation points to the enormous potential applications of ZIF-94 for CO2/N2 separation under humid conditions in industrial settings.” https://doi.org/10.3390/molecules27175608

Leave a Comment