Studies on low-temperature degradation for sulfur hexafluoride over sulfidated nanoscale zero-valent iron supported on zeolite ZSM-5: heterostructures, interfacial activation and fluorine migration.

Owing to its strong chemical inertness, sulfur hexafluoride (SF6) is intrinsically resistant to degradation. Accordingly, a composite material was developed by coupling sulfidated nanoscale zero-valent iron (S-nZVI) with fly ash-derived zeolite ZSM-5, forming a multi-level heterostructure for efficient SF6 degradation. Experimental results confirmed that the composite exhibited exceptional low-temperature degradation performance, achieving complete removal of 2 vol% SF6 at 600 °C with a specific degradation amount of 206.1 mL/g. Remarkably, effective degradation was still maintained at 300 °C, surpassing the previously reported minimum temperature limit (∼450 °C) for SF6 degradation. Kinetic analysis revealed a near-zero-order reaction behavior with an apparent activation energy of only 27.61 kJ/mol, indicating that the initial stage was dominated by adsorption, diffusion, or interfacial electron transfer rather than SF bond cleavage. Comprehensive characterization showed that the composite possessed Fe0/FeS and FeS/ZSM-5 dual heterointerfaces, serving simultaneously as adsorption carriers, electron donors and acceptors. Specifically, the microporous framework of ZSM-5 physically confines nonpolar SF6 molecules through van der Waals and confinement effects, enriching their local concentration and forming a favorable adsorption-activation interface. Electrons released by Fe0 migrate directionally to these enrichment sites under the drive of the multi-level heterostructure, enabling concurrent adsorption and electron-induced activation of SF6, and thereby facilitating SF bond cleavage. The resulting fluoride ions initially react with Fe0 to generate FeF3, which subsequently interacts with the silicate framework to produce SiF4, establishing a mediated fluorine migration pathway from SF6 to SiF4 and enabling deep degradation with sustained reactivity.