Selective CO2 adsorption at low pressure with a Zr-based UiO-67 metal–organic framework functionalized with aminosilanes

Abstract

Selective CO₂ capture from offgas of various sources is very significant against global warming. Here, we modified a Zr-based MOF (UiO-67), for the first time, with aminosilanes by utilizing μ-OH of the MOF in order to increase the performances in CO₂ adsorption under a low pressure of up to 100 kPa. Although the MOF does not have open metal sites (OMSs) that are effective in grafting Lewis bases like diamines, aminosilanes could be loaded facilely onto the MOF. Importantly, one modified UiO-67 showed a remarkable selectivity (based on ideal adsorbed solution theory, IAST S_CO2/N2) of 407 (at 100 kPa) which is 163 times that of the pristine UiO-67. This IAST selectivity is higher than any result observed with MOFs having amino groups (excluding only a handful of results obtained for MOFs having very small pores). Moreover, the adsorbed quantity of CO₂ at 15 kPa over the modified UiO-67 was around 2.6 times that of the pristine UiO-67. Interestingly, the nitrogen content to show the most effective CO₂ adsorption (in both the selectivity and adsorbed quantity) was nearly constant at ca. 5.7 mmol g⁻¹ irrespective of the type of applied aminosilane; and there is little difference between primary and secondary amino groups in increasing the performances in CO₂ capture under low pressure. This study will pave the way to functionalize a MOF (although there is no OMS) with aminosilanes, providing a very effective adsorbent to capture CO₂ from offgas.