The iron-based biochar activating chlorite (ClO2-) driven by mechanochemical ultrasonic: piecewise kinetics, biomimetic catalytic-mechanism, and novel advanced redox process

Chlorite (ClO2- or COI) is used to establish the advanced reduction and oxidation process (AROP). The iron/biochar-based particles (iron-based hydrothermal carbon with hinge-like structure, FebHCs, 20 mg/L) can be utilized to activate COI (2 mmol/L) to present selective oxidation in removing triphenylmethane derivatives (15 min, 90%). The protonation (H+ at similar to 102 mu mol/L level) played a huge role (k-2nd = 0.136c-H+ - 0.014 (R2-adj = 0.986), and rapp = - 0.0876/c-H+ + 1.017 (R2-adj = 0.996)) to boost the generation of the active species (e.g., high-valent iron oxidizing species (HVI=O) and chlorine dioxide (ClO2)). The protonation-coupled electron transfer promoted Fe-substances in Feb/HCs activating COI (the calculated kobs ranging from 0.066-0.285 min-1). The form of ClO2 mainly attributed to proton-coupled electron transfer (1e/1H+). The HVI=O was generated from the electron transfer within the coordination complex. Moreover, carbon particles in FebHCs serve as the bridge for electron transfer. The above roles contribute to the fracture and formation of coordination-induced bonds between Lx-FeII/III and ClO2- at phase interface to form AROP. The ultrasonic (US) cavitation enhanced the mass transfer of active species in bulk solution, and the HVI=O and ClO2 attack unsaturated central carbon atoms of triphenylmethane derivatives to initiate selective removal. Furthermore, the scale-up experiment with continuous flow (k values of approximately 0.2 min-1, COD removal efficiency of approximately 80%) and the reactor with COMSOL simulation have also proved the applicability of the system. The study offers a novel AROP and new insights into correspondingly heterogeneous interface activation mechanisms.