Intra- and intermolecular charge transfer control of symmetric A1-D-A2-D-A1 ladder-like small molecules/g-C3N4 heterojunctions for efficient photocatalytic sterilization and degradation from visible to near-infrared

Conjugated donor (D)-acceptor (A) polymer heterojunctions have developed as attractive photocatalysts. However, it is a great difficulty in precisely keeping the batch-to-batch reproducibility of polymers and con-trolling the related photocatalytic activity. Herein, three ladder-like small molecules BTx (BT2F, BTORCAE, and BTORIC2Cl) are synthesized via molecular engineering and the corresponding BTx/g-C3N4 heterojunctions are developed as photocatalysts for sterilization and contaminant degradation. It is demonstrated that employing another A unit into the D-A-D backbones of the small molecule could promote its intramolecular charge transfer and also improve the intermolecular charge transfer. Notably, BTORIC2Cl employing 2-(5,6-Dichloro-3-oxo-2,3 dihydro-1H-inden-1-ylidene)malononitrile as A1 unit in its symmetric A1-D-A2-D-A1 structure displays near -infrared absorption and extends the absorption edge of BTORIC2Cl/g-C3N4 to 850 nm. With the synergy of efficient intermolecular charge transfer, BTORIC2Cl/g-C3N4 contributes the champion photocatalytic activity of 98.9 % and 99.6 % antibacterial rates for Staphylococcus aureus and Escherichia coli. Moreover, the highest degradation reaction rate constant for Rhodamine B obtained by BTORIC2Cl/g-C3N4 is 5.7 times that of g-C3N4. This study proposes new ideas of fabricating small molecules/g-C3N4 OSHJs as photocatalysts via rational mo-lecular engineering.

Automated summary

Conjugated donor-acceptor (D-A) polymer heterojunctions have been developed as efficient photocatalysts, but maintaining reproducibility and controlling photocatalytic activity are challenging. In this study, ladder-like small molecules BTx were synthesized and used to develop BTx/g-C3N4 heterojunctions for sterilization and contaminant degradation. By introducing an additional acceptor unit into the small molecule, intramolecular and intermolecular charge transfer were enhanced, resulting in improved photocatalytic performance. Specifically, BTORIC2Cl/g-C3N4 exhibited near-infrared absorption and achieved high photocatalytic activity and antibacterial rates. The study proposes a novel approach for fabricating small molecule/g-C3N4 heterojunctions as efficient photocatalysts via molecular engineering.