Effect of LiNO3 Modification on UiO-66-nLiNO3 for CO2, CH4, and N2 Adsorption Performance from Low to High Pressures

This study systematically investigates the influence of lithium nitrate (LiNO 3 ) modification on the gas adsorption characteristics of UiO-66. The adsorption isotherms for carbon dioxide (CO 2 ), methane (CH 4 ), and nitrogen (N 2 ) were acquired within a pressure range of 0 to 20 bar. The results from the cyclic testing indicate that the UiO-66–0.05LiNO 3 variant exhibits commendable stability. Notably, the incorporation of LiNO 3 enhances the CO 2 adsorption capacity by 29.48%, reaching 2.24 mmol·g –1 at a pressure of 1 bar. This is attributed to the introduction of lithium ions, which enhance the electrostatic interaction between CO 2 and the MOF. Analysis of the high-pressure data reveals that the Langmuir–Freundlich model provides the most robust fit, whereas the Langmuir and Dual-site Langmuir models demonstrate increased discrepancies as pressure escalates. According to calculations based on the Ideal Adsorption Solution Theory (IAST), the maximum selectivity of the material for the CO 2 /CH 4 and CO 2 /N 2 mixtures is 11.5 and 56.0, respectively. These results suggest that LiNO 3 modification significantly enhances both the adsorption capacity and the selectivity for CO 2 separation.