Intramolecular D-A structure and n-π* transition co-promoted photodegradation activity of carbon nitride: Performance, mechanism and toxicity insight

The weak visible-light harvest, limited active-site exposure and sluggish charge separation/migration are three bottlenecks faced by carbon nitride (CN) photocatalyst, which seriously hinder CN for environmental water remediation utilizing solar energy. Herein, focusing on the above defects, an ultrathin CN nanosheet with intramolecular D-A structure and awaken n-π* transition was fabricated via a fully ground reaction followed one-pot thermal-induce copolymerization of urea and 2,5-thiophenedicarboxylic acid. Series characterization tests verify that the optimized 2,5-thiophenedicarboxylic acid doped CN (0.02-TACN) sample possesses absorption edge of 670 nm, superior specific surface area of 98.3 m2 g−1 and evidently improved charge behaviors in contrast to single CN. The three merits endow 0.02-TACN boosted activity with photodegradation efficiency of 92.1 % for tetracycline (100 % for rhodamine B), and significant TOC removal efficiency of 77.5 % for TC, which is significantly higher than that of CN (4.8 %). Quench tests and ESR affirm that h+, ·O2– and 1O2 dedicate to photodegradation, which benefit by upshifted conduction band and the existence of midgap state. The LC-MS, toxicity prediction and online FTIR investigated intermediate, route and toxicity, as well as in-situ monitor the variation of functional groups during photodegradation. Finally, DFT theoretical calculation further affirm the generation of intramolecular D-A structure and clarify conceivable propel mechanism of photodegradation.