Hybrid silsesquioxane-based porous polymer/chitosan aerogel for visible-light-driven degradation of antibiotics and reduction of Cr (VI)

A new organic semiconductor molecule 9, 9', 9″, 9‴-(4-(trifluoromethyl)-4'-vinyl-[1, 1'-biphenyl]-2, 3, 5, 6-tetrayl) tetrakis-carbazole (StTCbzCF3), was synthesized and subsequently copolymerized with octavinylsilsesquioxane (OVS) and 9-vinylcarbazole via azobisisobutyronitrile (AIBN)-initiated free-radical polymerization, yielding organic-inorganic hybrid porous polymers (PCS-SC-x (x = 1, 2, and 3; where x denotes the mass percentage of StTCbzCF3 in the synthesized polymers: 20% (x = 1), 40% (x = 2), 60% (x = 3)). Among these materials, PCS-SC-3 exhibited a high specific surface area (478 m2 g-1), a large Stokes shift (115 nm), and stable fluorescence. Notably, in the absence of sacrificial agents, 93% of Cr (VI) was photocatalytically reduced to the less toxic Cr (III) within 95 min under simulated sunlight, while >90% removal was retained after five cycles. In addition, PCS-SC-x (x = 1, 2, 3) was also demonstrated to function as a visible-light-driven photocatalyst for tetracycline hydrochloride (TCH) degradation. More than 95% of TCH was degraded within 75 min under visible light irradiation, with an initial pseudo-first-order rate constant of 0.0641 min-1, which was higher than most previously reported photocatalysts. In the coexisting Cr (VI)/TCH system, the removal of both pollutants was enhanced; with the Cr (VI) reduction rate constant reaching 0.0713 min-1, which was 2.05 times that obtained in the single-component system, indicating enhanced simultaneous remediation of the two pollutants. Radical-trapping experiments revealed that superoxide radicals (·O₂-) played a dominant role in the degradation pathway. PCS-SC-3 was further integrated with chitosan to fabricate a monolithic aerogel (PCS-SCA), which enabled efficient antibiotic degradation in a continuous-flow system and maintained a TCH removal efficiency of >96% after five cycles. This work provides a scalable, metal-free strategy for the integrated remediation of Cr (VI) and antibiotic contaminants and offers a facile and environmentally friendly route for the fabrication of flexible hybrid aerogels for practical water-treatment applications.