Sulfur vacancy-rich MoS₂ nanoflowers as electron shuttles boost Fe(VI) activation for efficient micropollutant degradation

Ferrate (Fe(VI)) has limited applications due to its slow reaction rate with micropollutants under neutral or alkaline conditions. This study presented sulfur-vacancy-rich nanoflower-structured MoS₂ synthesized via a simple hydrothermal method, which effectively activated Fe(VI) to rapidly degrade micropollutants. Almost complete removal (98.4–100%) of various micropollutants (e.g., diclofenac (DCF), trimethoprim (TMP), etc.) was achieved within 5 min after adding a low dose of MoS₂ (25 mg/L) to the Fe(VI) system, with the rate constants (k_obs) 5.3–27.3 times higher than those of Fe(VI) alone. Probe experiments indicated that MoS₂ promoted the generation of more intermediate iron species (Fe(V)/Fe(IV)) from Fe(VI), with Fe(V) accounting for 88.8% of the total contribution. Furthermore, by adjusting the concentration of sulfur vacancies (Sv) in MoS₂, a relationship between sulfur vacancy abundance and degradation efficiency was established, providing the evidence for the critical role of sulfur vacancies in the activation of Fe(VI). Sv-rich MoS₂ served as key electron-shuttling, facilitating the adsorption of Fe(VI) and accelerating electron transfer processes to promote Fe(V)/Fe(IV) generation. The MoS₂/Fe(VI) system exhibited outstanding performance across a wide pH range and demonstrated strong resistance to common aquatic components (Cl-, SO₄2-, etc.). Remarkably, increasing the concentration of humic acid (HA) from 0 to 5 mg/L led to a near-complete degradation of DCF within 2 min, accompanied by a 3.9-fold increase in the k_obs value. This phenomenon can be attributed to the electron-shuttling role of HA that synergistically enhanced interfacial electron transfer. Practical application results validated that this system could achieve excellent DCF removal efficiency (96.5-97.9%) in various real water. This work provides fundamental insight into the intrinsic mechanism of defect-engineered MoS₂ activating Fe(VI), offering a sustainable and efficient strategy for water purification.