Charge transfer mechanism through S-scheme heterojunction in in-situ synthesized TiO/Fe-doped hydroxyapatite for improved photodegradation of xanthate.

The heterojunction structure of the photocatalyst composite, which necessitates a robust interface and sufficient contact areas, holds the key to obtaining high charge carrier migration efficiency. Here, a novel composite, TiO nanoparticles/Fe-doped hydroxyapatite (TONPs/FH_CS), is fabricated using a two-step synthetic technique, in which FH_CS is synthesized from artificial converter slag enriched with Fe and Ca. The unique nanorod@plate structure of FH_CS enables the uniform immobilization of TONPs onto FH_CS. Thereby, an n-n type heterojunction exhibits a highly intimate Ti-O-Fe heterointerface. Kelvin probe testing demonstrates the formation of an interfacial electric field oriented from FH_CS to TONPs, which serves as the driving force for interfacial electron transfer through the Ti-O-Fe channels. The photoacoustic signals provide information on electron trap levels and densities, indicating the formation of the electron transfer channels. •O and •OH species are responsible for being the active species in this system. A photoexcited carrier transfer pathway exhibiting an S-scheme mechanism with high separation efficiency significantly enhances the utilization of charge carriers in each phase. Thus, improved xanthate degradation has been achieved using a heterojunction containing a photocatalyst derived from industrial solid waste. This work demonstrates the significant potential of steel-making byproduct utilization in industrial wastewater treatment.