Dual S-Scheme g-C 3 N 4 /Ag 3 PO 4 /g-C 3 N 5 photocatalysts for removal of tetracycline pollutants through enhanced molecular oxygen activation

A dual S-scheme g-C 3 N 4 /Ag 3 PO 4 /g-C 3 N 5 heterojunction was prepared by decomposition methods, and it displayed enhanced performance to degrade tetracycline hydrochloride with the ideal stability under different water substrates and ions. Comparing with three single components, as g-C 3 N 4, g-C 3 N 5, and Ag 3 PO 4, the dual S-scheme g-C 3 N 4 /Ag 3 PO 4 /g-C 3 N 5 heterojunction displayed 4.4-, 3.4-, and 2.5-times enhancements in the tetracycline hydrochloride removal. Based on the dynamics analyses for charge carriers and band structure calculations, two channels of molecular oxygen activation (MOA) between Ag 3 PO 4 and g-C 3 N 4 (and g-C 3 N 5 ) were confirmed. More importantly, according to this double consumption process of excited electrons, dual S-scheme g-C 3 N 4 /Ag 3 PO 4 /g-C 3 N 5 could suppress the charge recombination, which was the key point to boosting photocatalytic activity. Moreover, the determination of intermediates also supported the vital role of MOA during these photocatalytic reactions. this report of two reactive sites in MOA that generate reactive oxygen species in a “V” type band structure. The electronic dynamic in the reaction was also testified by several detections, indicating the enhanced charge separation and migration from internal field effect and electron trapping from dual S-scheme mechanism. This work provides a new research direction for the design and mechanism analysis of dual S-scheme photocatalysts