Simultaneously Achieving Fast Intramolecular Charge Transfer and Mass Transport in Holey D−π–A Organic Conjugated Polymers for Highly Efficient Photocatalytic Pollutant Degradation

Abstract

Simultaneously realizing efficient intramolecular charge transfer and mass transport in metal-free polymer photocatalysts is critical but challenging for environmental remediation. Herein, we develop a simple strategy to construct holey polymeric carbon nitride (PCN)-based donor−π−acceptor organic conjugated polymers via copolymerizing urea with 5bromo-2-thiophenecarboxaldehyde (PCN−5B2T D−π−A OCPs). The resultant PCN−5B2T D−π−A OCPs extended the πconjugate structure and introduced abundant micro-, meso-, and macro-pores, which greatly promoted intramolecular charge transfer, light absorption, and mass transport and thus significantly enhanced the photocatalytic performance in pollutant degradation. The apparent rate constant of the optimized PCN−5B2T D−π−A OCP for 2-mercaptobenzothiazole (2-MBT) removal is ∼10 times higher than that of the pure PCN. Density functional theory calculations reveal that the photogenerated electrons in PCN−5B2T D−π−A OCPs are much easier to transfer from the donor tertiary amine group to the benzene π-bridge and then to the acceptor imine group, while 2-MBT is more easily adsorbed on πbridge and reacts with the photogenerated holes. A Fukui function calculation on the intermediates of 2-MBT predicted the realtime changing of actual reaction sites during the entire degradation process. Additionally, computational fluid dynamics further verified the rapid mass transport in holey PCN−5B2T D−π−A OCPs. These results demonstrate a novel concept toward highly efficient photocatalysis for environmental remediation by improving both intramolecular charge transfer and mass transport.

B←N bonds alter the photo-generated electron/hole separation ability of conjugated polymers to promote photocatalytic performance

“…4 and Table 1). 25,59 This is consistent with the previous experimental characterization results on the ability of carrier separation and transport.…”

“…To better describe the charge separation and transport ability of these conjugated polymers, we examine the electron leap process of S 0 → S 1 and define S 0 as the hole and S 1 as the electron. 25,57–59 As shown in Fig. 4, we can visualize that the electrons (red) and holes (blue) of M29 without B←N bonds are concentrated in pyrimidine.…”

Charge Density Modulation of Pyrene-Related Small Molecules by Nitrogen Heteroatoms Precisely Regulates Photocatalytic Generation of Hydrogen

“…Specifically, the electrostatic potential around the N atom is more negative compared to that around the pyrene ring, signifying an accumulation of charge near the N atom. This suggests that the N atom effectively extracts localized electrons from the pyrene ring, facilitating the separation and migration of photogenerated charge carriers. , Notably, an increase in the number of introduced N atoms leads to a more pronounced electron enrichment in the bulk phase, potentially favoring the hydrogen production reaction at the N active sites and thereby enhancing the catalytic activity. Additionally, Py-p-N exhibits a more positive charge density at the center of the pyrene compared to Py-m-N.…”

Organic Donor‐Acceptor Systems for Photocatalysis

“…Reproduced with permission. [ 166 ] Copyright 2023, American Chemical Society. c) Chemical and electronic structure of COF‐TD1.…”