Intramolecular engineering of defective terminations within triazine-based conjugated polymers for augmented photocatalytic H2 production and Cr(VI) reduction

Abstract

In this study, enhanced intramolecular polarization of π-conjugated electrons in triazine-based conjugated polymers (TCPs) was modulated by incorporating –NH2/-CN terminations. The electron-abundant –NH2 groups and the electron-deficient –CN groups lead to the delocalization of the π-conjugated electrons on the plane of the conjugated polymer by the push-and-pull effect. The resultant A-TCP-C configuration expands the photoresponsive regions and form spatially separated electron-hole centers as the charge-transfer channels for electron shuttling. The π-conjugated electrons polarized delocalization system induces the asymmetrical distribution of electrostatic potential and creates intramolecular electric field to facilitate the activation of the conjugated electrons over the plane from π to π* states by accumulating valence electrons on the benzene ring near –NH2 terminals, which reduce the activation energy barrier and thus offer profitably condition for the visible light excitation process. Additionally, the exposed –NH2/-CN terminal defects create high-energy adsorption sites for the preconcentration of target substances. This optimization of thermodynamically and kinetically accessible pathways enabled preferential reactant accumulation and charges transfer. The as-synthesized A-TCP-C20 polymer exhibits a photocatalytic activity of removing 95.8% Cr(VI) within 40 min and a H2 production ability of 1919.0 μmol g−1 h−1, which is 6 folds and 260 folds over the pristine TCP, respectively. Our work presents a facile and directional structure arrangement can be devised to simultaneously optimize active species binding, transfer, and activation on TCPs surface sites.