Rational fabrication of Z-scheme heterojunction ZnFe2O4-seed@TpTt-COF for the visible-light-driven photocatalytic degradation of bisphenol A in food waste leachate boosted by primitive humic acid

Herein, we proposed a method by pre-embedding organic covalent organic framework TpTt-COF(TpTt) (consisting of the electron donor 1,3,5-triazine-2,4,6-triamine (Tt) and electron acceptor 2,4,6-triformylphloroglucinol (Tp) aldehyde) within inorganic ZnFe2O4 core to serve as seed for the in-situ grafting of organic TpTt shell tightly. The as-formed ZnFe2O4-seed@TpTt-COF (Z-S@TpTt) core–shell structure exhibited visible-light-driven photocatalytic degradation of BPA effectively. This may stem from the rationally tuned energy band structure of ZnFe2O4-seed via TpTt pre-anchoring, thus enabled a Z-scheme electron transfer way within the heterojunction to broaden the light adsorption, accelerate the charge transfer and maintain their thermodynamic redox capacity. More strikingly, humic acid (HA) in the actual wastewater (food waste leachate (FWL), where BPA highly frequently presented) could even boost the photocatalytic degradation of BPA. Comprehensive characterizations and DFT calculations revealed that HA acts as a critical "electron shuttle" to further promote the separation of electron-hole pairs via the formation of an EDA complex with the Z-S@TpTt. The gathered electrons on CB of ZnFe2O4-seed and holes on VB of TpTt may generate more •O2– and 1O2, thus the improved performance of Z-S@TpTt core–shell heterojunction in BPA degradation was achieved. Besides the promoted catalytical activity, the convenient separation ability and extraordinary chemical/thermal stability inherited from the magnetic core and the COF shell also enabled robust reuse of Z-S@TpTt heterojunction in FWL. All of these properties endowed Z-S@TpTt heterojunction with the practical application potential to remove BPA in an economical and environment-friendly way, which is also compatible with the "waste control by waste" strategy today.