Graphene/Fe@N-doped carbon hybrid derived from spent MOF adsorbent as efficient persulfate activator for degradation of tetracycline hydrochloride

Abstract

• Spent MOF adsorbent was successfully recycled and reused by one-step pyrolysis. • Fe x NC displayed higher catalytic activity than the pristine MOF-derived. • Wide pH applicability and kinetics of 0.042 min −1 for TCH degradation was achieved. • The iron species in Fe x NC for PS activation was limited by the core–shell structure. • Non-radical oxidation was dominant for TCH degradation in Fe x NC/PS system. Metal-organic frameworks (MOF) have shown significant potential as efficient adsorbing materials for treating antibiotic wastewater. However, little attention has been paid to the proper disposal of dangerous antibiotic-polluted MOF adsorbents. In this study, tetracycline hydrochloride (TCH)-saturated MIL-100(Fe) as spent MOF adsorbent was converted into graphene/Fe@N-doped carbon hybrid (Fe x NC) by one-step pyrolysis to activate persulfate (PS) for TCH degradation. The existence of the TCH adsorbate on the MIL-100(Fe) precursor significantly affected the physicochemical properties of the obtained Fe@carbon product, which can be responsible for the higher catalytic activity of Fe x NC than the pristine MIL-100(Fe)-derived. Fe x NC was shown to have wide pH applicability (2–10) and the kinetics of TCH (96.2 mg/L) degradation was 0.042 min −1 with 0.3 g/L Fe x NC, 1 mM PS and pH 6. During TCH degradation, the carbon matrix and doped nitrogen in Fe x NC were more important than the iron species. Because of the inaccessibility of iron species encapsulated by carbon, 1 O 2 and O 2 •— were the dominant reactive oxygen species in Fe x NC/PS, with less contribution from SO 4 •— and •OH. Importantly, interfacial electron transfer was revealed to dominate the TCH oxidation process. This study provides not only a practical way for the disposal and reuse of waste MOF materials but also new ideas for the design of MOF-derived heteroatoms doping metal@carbon hybrids.