Stable ZIF-8-derived iron-immobilized ZnFe/NC catalyst for RhB degradation via persulfate activation

Abstract

Nitrogen-doped carbon materials have attracted extensive attention in the field of wastewater treatment due to their unique structural advantage, environmental friendliness and versatility. However, the limited catalytic activity of carbon-based materials during the recycling process is far from satisfactory. Herein, we firstly found that Zn could immobilize Fe and reported a stable ZIF-8-derived iron-immobilized ZnFe/NC catalyst with preferably activity for Rhodamine B (RhB) degradation via persulfate (PS) activation. It was found that Zn could make more active iron stabilized in the frame of ZIF-8 and inhibited the leaching of active iron, thus effectively promoted the stability of ZnFe/NC. Additionally, the physicochemical properties and performance of ZnFe/NC were closely related with the relative content of residual Zn and Fe. The ZnFe/NC-3 with the least Zn/Fe ratio performed the best. It could achieve 92.20% RhB removal rate and 66.04% of mineralization within 30 min, and maintain its activity after 10 catalytic cycles. This is mainly due to the most active Fe species produced and the most Fe coordination when the least Zn is remained. Further study found that residual Zn has a negative impact on the activity, but a small amount of Zn would greatly improve the stability of the ZnFe/NC catalyst. A mechanism study showed that the degradation process of RhB is a non-radical pathway dominated by singlet oxygen (1O2) and electron transfer. The Fe-Nx and graphitic N all acted as active catalytic sites to promote the generation of 1O2 and electron transfer between RhB and PS.