A pH-responsive phase transformation of a sulfonated metal-organic framework from amorphous to crystalline for efficient CO2 capture

We report a pH-responsive phase transformation of a sulfonated MOF from amorphous UiO-66-SO3H to crystalline UiO-66-SO3M (M = Li, Na, K). Such transformation is obtained via neutralizing UiO-66-SO3H with the according alkali hydroxide solutions. EXAFS and FTIR results suggest that the recovered crystallinity can be attributed to the breakage of strong hydrogen bonds among the sulfonic acids in UiO-66-SO3H as well as the subsequent charge repulsion in UiO-66-SO3M to expand the collapsed framework.