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

Abstract

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 MnO_x nanoparticles (MnO_x-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 MnO_x coated on the surface of CNT (MnO_x-out-CNT), the MnO_x-in-CNT filter demonstrated a 2.9 times higher k_L value (0.050 min⁻¹vs. 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 MnO_x-in-CNT system were high-valent metal-oxo species (Mn(IV)) rather than the traditional hydroxyl or superoxide radicals in the unconfined MnO_x-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.