Unblocking Ion-occluded Pore Channels in Poly(triazine imide) Framework for Proton Conduction

Poly(triazine imide) or PTI is an ordered graphitic carbon nitride hosting angstrom-scale pores attractive for selective molecular transport. AA'-stacked PTI layers are synthesized by ionothermal route during which ions occupy the framework and occlude the pores. Synthesis of ion-free PTI hosting AB-stacked layers has been reported, however, pores in this configuration are blocked by the neighboring layer. The unavailability of open pore limits application of PTI in molecular transport. Herein, we demonstrate acid treatment for ion depletion which maintains AA' stacking and results in open pore structure. We provide first direct evidence of ion-depleted open pores by imaging with the atomic resolution using integrated differential phase-contrast scanning transmission electron microscopy. Depending on the extent of ion-exchange, AA' stacking with open channels and AB stacking with closed channels are obtained and imaged for the first time. The accessibility of open channels is demonstrated by enhanced proton transport through ion depleted PTI.