Unusual large pore copper silicate for CO2 adsorption

The variable ratio of tetrahedrally coordinated atoms with different valences in the zeolite framework determines the amount and distribution of extraframework cations, thereby regulating properties such as adsorption, separation, and catalysis. However, similar control is not possible for stoichiometric microporous mixed coordination polyhedra silicates. Here we identify synthesis conditions that reduce or completely eliminate the alkali cations in the 12-ring channels of a copper silicate while preserving the original framework stoichiometry that enables CO2 adsorption. Furthermore, despite the absence of cation positions, the emptied channels can undergo ion exchange and accommodate substantial amounts of Cs+ and Sr2+ ions. These results introduce a pioneering example of cation-free large pores in transition metal silicates and demonstrate how the same framework heteropolyhedral silicates can exhibit significantly distinct pore composition and adsorption properties controlled by the synthesis.