Efficient photo-degradation of BPA in textile wastewater assisted by primitive carbonate: the exceptional contribution of PMS in magnetic Cu⁰–CuFe₂O₄@TpPzDa COF S-scheme heterojunctions

Herein, the magnetic Cu⁰–CuFe₂O₄ core was rationally embedded into a donor–acceptor (D–A) COF shell composed of pyrazine-2,5-diamine (PzDa) and 2,4,6-triformylphloroglucinol (Tp) to form Cu⁰–CuFe₂O₄@TpPzDa S-scheme heterojunctions for photo-degradation of BPA in textile wastewater. However, the photocatalytic performance of Cu⁰–CuFe₂O₄@TpPzDa was almost completely annihilated (the degradation efficiency of BPA remained only 5%) due to the adverse effects of the coordination between the interfacial Cu²⁺ in the Cu⁰–CuFe₂O₄ core and the organic units in the TpPzDa shell. Interestingly, when PMS was introduced, the Cu⁰–CuFe₂O₄@TpPzDa/vis system was reactivated to achieve 100% degradation of BPA (20 mg L⁻¹) with a degradation rate constant of 0.1672 min⁻¹. A series of experiments and DFT calculations revealed exceptional contributions of PMS. It may coordinate with Cu²⁺ to positively revise the band structure and recover the D–A charge transfer within TpPzDa; moreover, the adsorption of PMS on pyrazine (PzDa) strongly minimizes the exciton binding energy. The promoted electron–hole separation of TpPzDa, as well as the facilitated S-scheme charge transfer within Cu⁰–CuFe₂O₄@TpPzDa, led to the generation of more active species h⁺, O₂˙⁻ and ¹O₂. In addition, the primitive carbonate commonly co-existing in textile wastewater would further protect Cu⁰ from oxidation, ensuring the emphasized electron-bridge role of Cu⁰, which further accelerated the photo-degradation kinetics of BPA to 0.2189 min⁻¹. This property, along with the convenient magnetic separation ability and remarkable stability inherited from the core and COF shell, offers a great opportunity for BPA degradation in line with the concept of “treating waste with waste”.