Sulfate promotes the photocatalytic degradation of antibiotics by porphyrin MOF: The electron-donating effect of the anion

It has been a pressing challenge to treat saline wastewater with advanced oxidation techniques due to the inhibition of reactive oxygen species in the actual wastewater by co-existing ions. Herein, we synthesized TCPP@UiO-66(Hf) catalysts enriched with deletion linker defects by doping meso-tetra (4-carboxyphenyl) porphine (H₂TCPP) in UiO-66(Hf) to modulate its performance for the removal of ofloxacin (OFL) from complex aqueous environment. TCPP@UiO-66(Hf)-250 promoted the removal efficiency of OFL from 13.4% to more than 96%. The adsorption and photocatalytic properties of TCPP@UiO-66(Hf)-250 with defects were significantly enhanced in various anionic environments. The electron-donating role of coexisting anions was investigated with SO₄²⁻ as a representative. Quenching tests and electron paramagnetic resonance (EPR) revealed that in the TCPP@UiO-66(Hf)-250/Na₂SO₄/visible light (TCPP@UiO-66(Hf)-250/Na₂SO₄/VIS) system, O₂^∙− and ¹O₂ dominated the removal of OFL with increasing levels. And SO₄^∙− was generated after the addition of SO₄²⁻, confirming the electron-donating role of sulfate in the photocatalytic system. The TCPP@UiO-66(Hf)-250/visible light (TCPP@UiO-66(Hf)-250/VIS) system maintained excellent OFL removal efficiency over a broad pH range of aqueous solutions, in high co-existing ion concentrations and actual aqueous matrices, and exhibited good performance in cycling tests. It demonstrates that the coexisting anions play an electron-donating role in the photocatalytic system and further reveals the synergistic mechanism between the photocatalyst and coexisting anions, which offers the possibility of contaminant removal in highly saline water.