Theoretical studies on pillared covalent organic frameworks for the hydrogen storage material

Abstract

Pillared covalent organic frameworks (PCOFs) have been studied with the density functional theory (DFT) calculations. Based on the COF-1 structure, one of covalent organic frameworks (COFs), synthesized by the condensation reactions of phenyl diboronic acid {C6H4[B(OH)2]2}, we inserted pillar molecules between the organic layers for the improvement of physisorption ability for the hydrogen molecules. Pyridine, pyrazine and DABCO, 1,4-diaza-bicyclo[2.2.2]octane, were considered as the candidates of pillar molecules. The binding sites and orientations of the pillar molecules were investigated on cluster models of COFs and the system was extended to the solid state for the estimation of the effect of insertion, inter-layer distance and energetic stability. We also considered the effect of packing method for COF layers in the presence of pillar molecules; two packing structures of staggered and eclipsed forms which influence the morphology of the crystal structure. With this calculation, we proposed new PCOF structures to enhance hydrogen storage capacity.