Schiff-Base Hybrid Porous Polymers as Additive-Free Photocatalysts for Efficient Photodegradation of Dyes and Antibiotics under Visible Light

The design and synthesis of photocatalysts with high activity, stability, and visible-light responsiveness remains a significant challenge in catalyst development. In this study, Schiff-base hybrid cross-linked porous polymers (TFBE-SHCP) were prepared through aldehyde–amine condensation reactions using octakis(4-aminophenyl)silsesquioxane (OAPS) as the building block and tetrakis[4-formyl-(1,1′-biphenyl)-4-yl]ethylene (TFBE) as the electron-donating linker. The introduction of TFBE monomers featuring a π-conjugated structure not only extends the light absorption into the visible-light region but also enhances the separation efficiency of photogenerated charge carriers. The porous structure of TFBE-SHCP further increases the number of catalytic active sites, significantly improving its photodegradation capability for water pollutants. Under visible-light irradiation, the polymer exhibits degradation efficiencies of 98% (3 min), 98% (30 min), and 72% (8 min) toward Congo red (CR), Rhodamine B (RB), and tetracycline hydrochloride (TH), respectively, when the degradation equilibrium is reached (20 ppm pollutant, additive-free). The corresponding apparent rate constants are 1.40, 0.07, and 0.19 min –1, which are 2.1–11.4 times higher than those of recently reported photocatalysts. Our findings reveal that the conjugated structure of TFBE, together with the extended π delocalization within the three-dimensional porous framework formed via C═N cross-linking, effectively promotes the separation of photogenerated electron–hole pairs, thereby enhancing the photocatalytic activity. This work provides fundamental insights into modulating delocalized π electrons to improve the photocatalytic performance.