Synergistic Fe and polyimide dual-modification of g-C3N4 for enhanced photocatalytic degradation of tetracycline.

Pristine g-C3N4 typically suffers from rapid recombination of photogenerated charge carriers and a narrow visible light absorption range, severely restricting its practical photocatalytic applications. In this work, a one-step pyrolysis strategy that co-incorporates Fe and polyimide (PI) into g-C3N4 as a dual-modification approach is proposed. The resulting Fe/PI co-doped g-C3N4 composites (FPICN) displayed a significantly enhanced specific surface area, extended visible light absorption, and improved charge separation. These enhancements are attributed to the electron-deficient PMDA units and the coordination of Fe within the g-C3N4 framework. Structural and spectroscopic analyses confirmed the successful incorporation of Fe and PI, the partial exfoliation of g-C3N4 layers, and favorable modulation of electronic structure. FPICN demonstrated outstanding photocatalytic performance, degrading 86.98% of tetracycline within 80 min under simulated solar light irradiation. The apparent rate constant was approximately 8.7 times higher than that of pristine g-C3N4. Moreover, FPICN retained over 80% of its initial activity after four cycles, demonstrating excellent stability. Radical trapping experiments and band structure analyses revealed that photogenerated holes (h+) and superoxide radicals (˙O2 - were the primary reactive species in the degradation pathway. This work provides a rational design strategy for high-performance photocatalysts based on synergistic transition metal doping and conjugated polymer modification, and offers insights into the efficient visible light-driven degradation of pollutants.