Enhanced electro-fenton degradation of tetracycline pharmaceutical wastewater by N-doped carbon modified titanium membrane aeration: Formation of highly selective singlet oxygen

Singlet oxygen (¹O₂), the lowest excited electronic state of molecular oxygen, plays an important role in advanced oxidation, but how to directionally enhance the generation of ¹O₂ is a challenge. In this study,we use membrane aeration electrode modified by carbon-nitrogen for the first time to enhance the generation of ¹O₂ in the EF (Electro-Fenton) system. The carbon-nitrogen supported tubular titanium membrane (TTM@CN) aeration electrode was prepared by a simple dopamine-loaded one-step sintering method. A membrane aeration EF system was designed with TTM@CN as cathode and netted ruthenium-iridium titanium electrode as anode, and the output of ¹O₂ was greatly improved. The results of quenching experiments show that the main way of singlet oxygen production is ³O₂ → H₂O₂ → ¹O₂. In addition, the results of density functional theory (DFT) show that the empty orbital of C above Fermi level in heterojunction is obviously filled, and the density of states tends to shift to the depth of valence band. The system with metal Ti as carrier can quickly transfer electrons to the layer of C, which makes the states density of C increase significantly near Fermi level. It can reduce ³O₂ to H₂O₂ more quickly, and H₂O₂ can be further converted to ¹O₂. The system showed excellent degradation performance in a wide pH range (1–12) and excellent stability in 20 cycle experiments, which provided a reference significance for promoting the development of sustainable EF technology.