Manipulation of n → π* electronic transitions via implanting thiophene rings into two-dimensional carbon nitride nanosheets for efficient photocatalytic water purification

The photocatalytic performance of polymeric carbon nitride (C₃N₄) is heavily restricted by insufficient n → π* electronic transitions and limited active sites. To this end, we adopted an integrated copolymerization and repyrolysis approach to fabricate two-dimensional thiophene ring implanted (C₃N₄) nanosheets (2D Th_ing-CNNS). Advanced characterization studies demonstrated that the fusion of thiophene rings and the formation of 2D nanosheets significantly collectively elevated the n → π* electronic transitions and enlarged the specific surface areas of 2D Th_ing-CNNS, leading to a dramatically extended π-conjugated system and accelerated charge migration. Transmission electron microscopy, X-ray diffraction, and solid-state ¹³C NMR proved the existence of the thiophene ring. Additionally, quantum computations of the highest occupied and lowest unoccupied crystal orbitals implied that the 2D Th_ing-CNNS are more favorable for carrier migration than pristine (C₃N₄). The finite element method (FEM) analysis indicates that 2D Th_ing-CNNS have a stronger surface electric field and radiation absorption, which is consistent with the enhanced n → π* transition. Consequently, 2D Th_ing-CNNS exhibit a 42.7-fold enhancement in photocatalytic performances for bisphenol A oxidation accordingly, compared with pristine C₃N₄. This work provides a novel strategy for engineering the electronic structure of C₃N₄ for highly efficient water purification.