Engineering low-valence Mo^δ+ (0<δ<4) sites on MoS₂ surface: Accelerating Fe³⁺/Fe²⁺ cycle, maximizing H₂O₂ activation efficiency, and extending applicable pH range in photo-Fenton reaction

Fenton/photo-Fenton reaction was limited by slow Fe³⁺/Fe²⁺ cycle, low H₂O₂ activation efficiency, and narrow applicable pH range. Here, Fe atoms doped MoS₂ (Fe–MoS₂) with abundant of low-valence Mo^δ+ (0 < δ < 4) was prepared. Benefiting from the powerful reduction capacity of Mo^δ+, the rate-limiting step of Fe³⁺ reduction was significantly accelerated. Nearly 100% of H₂O₂ utilization efficiency was realized. Importantly, 90% of H₂O₂ was effectively activated to be ^•OH. As a result, tetracycline degradation rate in photo-Fenton reaction catalyzed by Fe–MoS₂ was 5.8 and 4.2 times higher than those of MoS₂ and Fe–MoS₂-Hyd (prepared by hydrothermal reaction). In comparison with MoS₂ and Fe–MoS₂-Hyd whose efficient work range were limited in acidic condition, Fe–MoS₂ was a pH-universal catalyst (pH = 2.6–14.0) by taking advantage of the exposed Mo^δ+ and photoinduced electrons, largely improving the environmental tolerance. This work simultaneously addressed three bottlenecks in Fenton/photo-Fenton reaction, and provided a new strategy for the preparation of catalysts with powerful catalytic performance and high environmental adaptability.