Quasi-full-visible-light absorption by D35-TiO₂/g-C₃N₄ for synergistic persulfate activation towards efficient photodegradation of micropollutants

To utilize the excellent charge separation efficiency of the g-C₃N₄/TiO₂ photocatalyst and broaden its narrow visible-light absorption range, D35 dye-sensitization was employed to synthesize a novel D35-TiO₂/g-C₃N₄ photocatalyst. Due to the complementary co-absorption ability of g-C₃N₄ and the D35 dye, the D35-TiO₂/g-C₃N₄ nano-composite exhibits a quasi-full-visible-light harvesting range up to 675 nm, and the simultaneous electron injection from the D35 and g-C₃N₄ to TiO₂ synergistically activates persulfate (PS) to produce the active oxidizing species more efficiently. In the D35-TiO₂/g-C₃N₄/PS photocatalytic system, 10 mg/L bis-phenol A (100 mL) could be completely removed in only 15 min with 0.5 g/L photocatalyst and 2 mM PS under visible-light illumination (λ > 400 nm); meanwhile, nearly 50% of BPA was mineralized into nontoxic substances. Radical quenching experiments and electron paramagnetic resonance (EPR) spectra revealed that ^[rad]OH, SO₄^[rad]−, ^[rad]O₂- and h⁺ all contributed to organics elimination, and the radical process was the main degradation pathway. The efficient photodegradation of other typical micropollutants, such as caffeine, phenol, acetaminophen and methylene blue, indicating that the D35-TiO₂/g-C₃N₄/PS photocatalytic system has a strong non-selective oxidative ability to remove micropollutants. Therefore, it has great potential to be applied in water environment remediation.