Anchoring highly dispersed FeCo/C nanoparticles within zeolite 13X to promote 1O2 generation in the degradation of tetracycline hydrochloride

Abstract

This paper reports the preparation of a FeCo/C@13X catalyst derived from FeCo/ZIF using Na-13X molecular sieves as substrates through the ion-exchange method, followed by in situ FeCo/ZIF growth and a carbonization step. Compared with FeCo/ZIF@13X and Co/C@13X, FeCo/C@13X exhibited an improved peroxymonosulfate (PMS) activation effect owing to the well-dispersed FeCo sites embedded in the carbon@13X matrix, as confirmed by high-resolution transmission electron microscopy, Fourier transform infrared spectra and X-ray diffraction. The cobalt loading in the FeCo/C@13X catalysts was up to 15.32 wt% as determined by ICP-OES. FeCo/C@13X, prepared by the introduction of organic Fe and calcining FeCo/ZIF@13X, exhibited good reusability and stability, viz. 92 % degradation efficiency after five cycles compared to 84 % of Co/C@13X and 79 % of FeCo/ZIF@13X. The FeCo/C@13X/PMS system was highly stable over a wide pH range and showed excellent tolerance for background substances in aqueous environments because of non-radical-dominated degradation. Quenching experiments and electron paramagnetic resonance analysis demonstrated that singlet oxygen (1O2) primarily facilitated the tetracycline hydrochloride (TCH) removal during the FeCo/C@13X catalytic process. The electron transfer and free radicals (SO4∙−, ∙OH, and O2∙−) were engaged in the TCH degradation. Through electrochemical measurements and in situ Raman spectroscopy, electrons were rapidly transferred from FeCo/C@13X to PMS, consuming HSO5− to generate metastable active species (FeCo/C@13X-PMS* complexes), which can efficiently accelerate the cycling of Fe3+/Co3+ to Fe2+/Co2+ and enhance 1O2 production. This study provides a suitable method for designing heterogeneous Fenton-like catalysts with high and stable catalytic performances for the continuous production of 1O2.