A study on singlet oxygen generation for tetracycline degradation via modulating the size of α-Fe2O3 nanoparticle anchored on g-C3N4 nanotube photocatalyst

Photocatalysis is considered as an effective technique for mitigating ecological risks posed by residual tetracycline (TC). To improve the efficiency of this technique, it is necessary to enable photocatalysts to produce highly reactive species, such as singlet oxygen ( 1 O 2 ). However, due to the high activation energy of 1 O 2 , photocatalysts can hardly produce 1 O 2 without assistance from external oxidants. Herein, we find that the size-reduced α-Fe 2 O 3 nanoparticles (∼ 4 nm) that anchored on g-C 3 N 4 nanotube (α-Fe 2 O 3 @CNNT) can spontaneously generate 1 O 2 for degradation of TC. In comparison, only hydroxyl radical (·OH) can be produced by g-C 3 N 4 nanotube loaded with ∼ 14 nm α-Fe 2 O 3 nanoparticles (α-Fe 2 O 3 /CNNT). Owing to the high reactivity of the 1 O 2 species, the photocatalytic degradation rate ( K app ) of TC with α-Fe 2 O 3 @CNNT (0.056 min −1 ) was 1.8 times higher than that of α-Fe 2 O 3 /CNNT. The experimental results and theoretical calculations suggested that reducing the size of α-Fe 2 O 3 nanoparticles anchored on g-C 3 N 4 nanotube decreased the surface electron density of α-Fe 2 O 3 , which induces the generation of high-valent Fe(IV) active sites over α-Fe 2 O 3 @CNNT and turns the degradation pathway into a unique 1 O 2 dominated process. This study provides a new insight on the generation of 1 O 2 for effective degradation of environmental pollutant.