Construction of high reduction potential Fe-POMs/LDHs Z-scheme heterojunction: Variable valence state-assisted photocatalytic activation of persulfate radical for synergistic degradation of tetracycline

Semiconductor photocatalytic activation of persulfate for synergistic degradation of pollutants is a hotspot, but the activation effect is insufficient due to the slow carrier transport and the limited strength of the reduction potential. In this paper, Fe-POMs/LDHs Z-scheme heterojunction photocatalyst was constructed for the degradation of tetracycline (TC). Under optimal conditions, the heterojunction degraded tetracycline up to 90.7 %, which was 2.9 and 3.0 times higher than that of single-phase PS versus Fe-POMs/LDHs (unactivated PS), and the degradation rate still reached more than 80 % after four recycles. Material characterization and theoretical calculations revealed that the excellent photocatalytic activity was attributed to the composite constructed as a Z-Scheme heterojunction. On the one hand, the high-intensity built-in electric field promotes carrier transport; meanwhile, the material possesses a high reduction potential, which promotes the activation of Na2S2O8(PS) to generate sulfate radicals, which creates a synergistic effect in the photodegradation of tetracycline (TC). In addition, elements such as Co(II), Fe(II), and W(IV) provide additional electrons to accelerate the activation of PS, and a portion of the photogenerated electrons and PS activation intermediates can promote the cycling between Co(II)/Co(III), Fe(II)/Fe(III), and W(IV)/W(VI) to continuously activate PS.