CNT encapsulated MnOx for an enhanced flow-through electro-Fenton process: the involvement of Mn(IV)

This study reports a nanoconfined flow-through electro-Fenton system for highly efficient degradation of aqueous micropollutants. The key to such a system is a functional electroactive carbon nanotube (CNT) cathodic filter with encapsulated MnOx nanoparticles (MnOx-in-CNT). The nanohybrid filter, assisted by an electric field, generated hydrogen peroxide (H2O2) in situ, followed by its subsequent conversion to reactive oxygen species (ROS) accompanied by the redox cycling of Mn(IV)/Mn(III). Compared with the filter consisting of MnOx coated on the surface of CNT (MnOx-out-CNT), the MnOx-in-CNT filter demonstrated a 2.9 times higher k(L) value (0.050 min(-1) vs. 0.017 min(-1)) toward the degradation of bisphenol A (BPA). Density functional theory (DFT) computation and experimental studies revealed that the dominant ROS in the confined MnOx-in-CNT system were high-valent metal-oxo species (Mn(IV)) rather than the traditional hydroxyl or superoxide radicals in the unconfined MnOx-out-CNT system. The flow-through configuration outperformed a conventional batch reactor in BPA degradation due to convection-enhanced mass transport. These findings may provide a novel strategy for environmental remediation using highly efficient and integrated systems based on materials science, Fenton chemistry, and microfiltration techniques.