Revealing the synergistic effect in the BDD-based quadruple coupling system via active radical and non-radical species for efficient removal of refractory organic contaminant

Boron-doped diamond (BDD)-based advanced oxidation processes featured exceptional advantages in treating refractory organic contaminants. Herein, we reported, for the first time, the BDD-based quadruple coupling system, namely (+)BDD|PMS + CoAl2O4+Air|GF(−), by fully integrating the advantages of electrochemical oxidation, peroxymonosulfate (PMS), CoAl2O4 and electro-Fenton-like process, to degrade tetracycline (TC) via active radicals (i.e., O2∙−, SO4∙−, ∙OH) and non-radical singlet oxygen (1O2). In the quadruple system, CoAl2O4 particles could be polarized into suspended particle electrodes, promoting PMS activation to form active radicals by homo- and heterogeneous pathways and expanding the reaction regions to a broad spatial range; meanwhile, aeration is the key to the electro-Fenton-like process and an indispensable source of 1O2. Interestingly, high concentrations of 1O2 existed both on the BDD surface and in the bulk solution whereas other active species only existed on the former, indicating the crucial role of 1O2 in the TC removal. Leveraging the synergistic effect, the quasi-first-order kinetic constant of the coupling system for TC removal was 8 times that of the single EO system at only the cost of one-seventh of its electric energy consumption. Finally, the proposed coupling system exhibited long-term stability and practical application potential. [Display omitted] •BDD-based quadruple coupling system is reported for the first time.•Non-radical and radical pathways are responsible for contaminant removal.•Low energy consumption is achieved in the quadruple coupling system.•Long-term stability and practical application potential are verified.