Synergistic dual-Li+ sites for CO2 separation in metal-organic framework composites

Although Li incorporation into adsorbent has been considered as an efficient method to enhance the selectivity for CO2 capture, the reported results are not desired. Herein, we proposed a dual-Li+ sites synergistic strategy to boost CO2 affinity and selectivity. The synergistic dual-Li+ sites in MOF are constructed by incorporating polyacrylic acid (PAA) with rich flexible carboxyl sites into stable UiO-66 framework, followed by neutralization with LiOH solution. Interestingly, 0.1 M Li+@PAA@UiO-66 composites exhibit steep absorption isotherm at low pressure range, which has never been observed in any other Li doped adsorbent, suggesting ultrahigh CO2 affinity. Meanwhile, 0.1 M Li+@PAA@UiO-66 composites show very high selectivity for CO2 over N-2 or CH4 (6341 and 1904 at 298 K, respectively) at zero coverage, surpassing all the reported Li doped adsorbents. The DFT calculations reveal that synergistic dual-Li+ sites show much stronger interactions with CO2 than that of traditional single Li+ site. This work not only proposes a strategy of constructing synergistic dual-Li+ sites in MOF to boost CO2 adsorption and separation, but also provides a promising CO2 adsorbent with high efficiency, high water stability and recyclability, low cost and commercially available raw materials, as well as simple and feasible preparation process.