Removal of tetracycline by a Fe doped BiMnO3/N doped RGO composite through activating PMS in a nonradical-dominated pathway

BMFO/N-RGO activated PMS through multiple pathways. • The redox of Mn(III) and Fe(II) favored the regeneration of active sites. • Doping Fe into BMO and N in RGO were beneficial for the electron transfer. • TC was effectively decomposed by BMFO/N-RGO through PMS activation. Activating persulfate with catalysts has become an efficient way to remove organic pollutants. In particular, the use of dual transition-metal catalysts can not only further increase the quantity of active sites for persulfate activation but also promote the recycling of active sites. In this study, a bimetallic catalyst composed of iron-doped BiMnO 3 and nitrogen-doped RGO (denoted as BMFO/N-RGO) was synthesized by a one-step hydrothermal method. The dual metals (Mn and Fe) and N-RGO provided abundant active sites and multiple pathways for activating peroxymonosulfate (PMS). So the prepared BMFO/N-RGO could activate PMS to effectively decompose tetracycline (TC) with η = 93.31% in 60 min. The removal efficiency of TC was still above 85.53% after five cycles. Based on ESR, trapping experiments, and electrochemical measurements, BMFO/N-RGO activated PMS via a combined radical-nonradical pathway, with the nonradical pathway predominating. In the radical pathway, O 2 •- , •OH, and SO 4 •- attacked TC; while in the nonradical pathway, 1 O 2 , Fe(IV)=O, Mn(IV)=O, and electron transfer dominated TC removal. Furthermore, DFT calculations demonstrated that PMS was more readily adsorbed on BMFO/N-RGO, that l o-o was stretched, and that the Bader charge increased. The redox between Mn 3+ /Fe 2+ and Mn 2+ /Fe 3+ favored the recycling and regeneration of active sites. The BMFO/N-RGO/PMS system showed good resistance to most inorganic ions and HA. A mechanism of TC removal by BMFO/N-RGO/PMS system was proposed. HPLC-MS elucidated the degradation pathway of TC. This study proposed a new approach to construct multiple pathways to activate PMS on bimetallic oxide surfaces for TC removal in complex aqueous environments. A composite BMFO/N-RGO catalyst was synthesized via a one-step hydrothermal method. BMFO/N-RGO activated peroxymonosulfate (PMS) through the radical and nonradical pathways to degradate TC, in which the nonradical pathway were predominating. Doping Fe into BMO and N in RGO led to higher E ads , larger Bader charge, and longer l O-O of PMS, all of which were beneficial for the decomposition of TC via electron transfer. In the radical pathway, O 2 ▪- and SO 4 ▪- attacked TC; While in the nonradical pathway, 1 O 2 , Fe(IV)=O, Mn(IV)=O, and electon transfer dominated TC elimination. And the redox reaction between Mn 3+ /Fe 2+ and Mn 2+ /Fe 3+ favoured the recycling and regeneration of active sites, thereby sustainably activating PMS. The removal rate of TC reached 93.31% within 60 min in BMFO/N-RGO/PMS system. Download: Download high-res image (72KB) Download: Download full-size image