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

Carbon nitride (C 3 N 4 ) 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 C 3 N 4 , but remains a huge challenge. Herein, a novel C 3 N 4 -based D-A conjugated copolymer is synthesized by incorporating aromatic ring into the C 3 N 4 skeleton by copolymerization of melamine with terephthalic acid from the in-situ controlled degradation of recycled poly(ethylene terephthalate) catalyzed by ZnO at 360 °C. The results of X-ray diffraction, solid-state 13 C cross-polarization magic-angle spinning nuclear magnetic resonance, thermodynamics analysis, and X-ray photoelectron spectroscopy confirm the structure of C 3 N 4 -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 C 3 N 4 -based D-A conjugated copolymer displays shorter lifetime of light-induced charge carriers, lower photoluminescence emission, and larger photocurrent response than pristine C 3 N 4 , certifying that the D-A conjugated system significantly promotes the separation efficiency of light-induced charge carriers. As such, the C 3 N 4 -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 C 3 N 4 . Lastly, reactive oxygen species including · OH, · O 2 - and 1 O 2 are proved to be the main active sites. This work not only offers new insights into the synthesis of efficient C 3 N 4 -based D-A conjugated copolymers, but also will inspire new paradigms toward sustainable transformation of waste plastics into value-added products for environmental remediation. • A C 3 N 4 -based D-A conjugated copolymer is prepared from melamine and waste polyester. • The copolymer shows lower photoluminescence emission and larger photocurrent signal. • The D-A conjugated system promotes the separation efficiency of charge carriers. • The copolymer displays high performance in photocatalytic degradation of pollutants. • Reactive oxygen species including · OH, · O 2 - and 1 O 2 are proved as main active sites.