Silicalite-1 zeolite encapsulated Fe nanocatalyst for Fenton-like degradation of methylene blue

Abstract

Encapsulation of Fe nanoparticles in zeolite is a promising way to significantly improve the catalytic activity and stability of Fe-based catalysts during the degradation process of organic pollutants. Herein, Fe nanocatalysts were encapsulated into silicalite-1 (S-1) zeolite by using a ligand-protected method (with dicyandiamide (DCD) as an organic ligand) under direct hydrothermal synthesis condition. High-resolution transmission electron microscopy (HRTEM) results confirmed the high dispersion of Fe nanocatalysts which were successfully encapsulated within the voids among the primary particles of the S-1 zeolite. The developed S-1 zeolite encapsulated Fe nanocatalyst (Fe@S-1) exhibited significantly improved catalytic activity and reusability in the catalytic degradation process of methylene blue (MB). Specifically, the developed Fe 0.021 @S-1 catalyst showed high catalytic degradation activity, giving a high MB degradation efficiency of 100% in 30 min, outperformed the conventional impregnated catalyst (Fe/S-1). Moreover, the Fe@S-1 catalyst afforded an outstanding stability, showing only ca. 7.9% activity loss after five cycling tests, while the Fe/S-1 catalyst presented a significantly activity loss of 50.9% after only three cycles. Notably, the encapsulation strategy enabled a relatively lower Fe loading in the Fe@S-1 catalyst in comparison with that of the Fe/S-1 catalyst, i.e., 0.35% vs. 0.81 %(mass). Radical scavenging experiments along with electron spin resonance (ESR) measurements confirmed that the major role of ·OH in the MB degradation process. Specifically, Fe@S-1 catalyst with high molar ratio of [Fe(DCD)]Cl 3 is beneficial to form Fe complexes/nanoclusters in the voids (which has large pore size of 1–2 nm) among the primary particles of the zeolite, and thus improving the diffusion and accessibility of reactants to Fe active sites, and thus exhibiting a relatively higher degradation efficiency. This work demonstrates that zeolite-encapsulated Fe nanocatalysts present potential applications in the advanced oxidation of wastewater treatment.