Manganese-nitrogen co-doped biochar (MnN@BC) as particle electrode for three-dimensional (3D) electro-activation of peroxydisulfate: Active sites enhanced radical/non-radical oxidation

A novel manganese-nitrogen co-doped biochar (MnN@BC) was synthesized and used as particle electrodes in three-dimensional (3D) electro-activation of peroxydisulfate (PDS) for the degradation of refractory organic pollutants. All the spectroscopy (EDS, XRD, XPS, FTIR, and Raman) results indicated that Mn-N nanoclusters were successfully deposited and embedded in BC. The material appeared graphitized structure with more defects after Mn-N doping. MnN@BC in 3D electro-activation of PDS (E/MnN@BC/PDS) exhibited excellent performance in carbamazepine (CBZ) removal, with removal efficiency and degradation rates of 96.84% and 0.0582 min^-1, respectively. Besides, MnN@BC was favorable for adsorption, electron transfer, and reactive oxidizing species (ROS) formation. MnN@BC had good recyclability in the E/MnN@BC/PDS system by the recycled experiments and characterization. Furthermore, quenching experiments, probe experiments, and electron paramagnetic resonance (EPR) analyses suggested that •OH and ¹O₂ were the main ROS in the E/MnN@BC/PDS system, and the non-radical oxidation take a key part. In addition, this system achieved excellent CBZ degradation under wide pH range of 3-11, had good tolerance to natural organic matter and inorganic ions, and was efficient to various water matrices and other refractory organic pollutants. These findings provided new insights into particle electrode design and mechanisms enhancement in electro-activated PDS systems.