Ning Liu, Zhen Hu, Liang Hao, Huiying Bai, Panpan He, Ran Niu*, Jiang Gong*

Trash into treasure: Converting waste polyester into C₃N₄-based intramolecular donor-acceptor conjugated copolymer for efficient visible-light photocatalysis

Journal of Environmental Chemical Engineering (2022) Accept. (IF2021 = 5.909)

Carbon nitride (C3N4) is regarded as one of the most prospective photocatalysts for environmental remediation. The design of intramolecular donor-acceptor (D-A) conjugated structure has aroused particular interest for improving visible-light photocatalytic activity of C3N4, but remains a huge challenge. Herein, a novel C3N4-based D-A conjugated copolymer is synthesized by incorporating aromatic ring into the C3N4 skeleton by copolymerization of melamine with terephthalic acid from the in-situ controlled degradation of recycled poly(ethylene terephthalate) catalyzed by ZnO at 360 oC. The results of X-ray diffraction, solid-state 13C cross-polarization magic-angle spinning nuclear magnetic resonance, thermodynamics analysis, and X-ray photoelectron spectroscopy confirm the structure of C3N4-based D-A conjugated system, consisting of terminal amino group of the tri-s-triazine unit as electron-donating group and aromatic ring as acceptor. Notably, the C3N4-based D-A conjugated copolymer displays shorter lifetime of light-induced charge carriers, lower photoluminescence emission, and larger photocurrent response than pristine C3N4, certifying that the D-A conjugated system signi?cantly promotes the separation efficiency of light-induced charge carriers. As such, the C3N4-based D-A conjugated copolymer displays high performance in the photocatalytic degradation of Amido black 10B upon visible light illumination, of which the kinetic constant is 101 times that of unmodified C3N4. Lastly, reactive oxygen species including ·OH, ·O2- and 1O2 are proved to be the main active sites. This work not only offers new insights into the synthesis of efficient C3N4-based D-A conjugated copolymers, but also will inspire new paradigms toward sustainable transformation of waste plastics into value-added products for environmental remediation.