Hydroxyl-rich Fe(II)–FeNi-LDH nanosheet arrays anchored on carbon felt as a bifunctional cathode for efficient norfloxacin degradation

During the electro-Fenton (EF) process, the in-situ activation of H 2 O 2 at the cathode is an important strategy to minimize the ineffective consumption of H 2 O 2 and enhance the reaction efficiency. Accordingly, a structurally ordered FeNi-layered double hydroxide (FeNi-LDH) nanosheet array was in-situ grown on carbon felt (CF) by a simple hydrothermal method. A Fe 2+ -based aliovalent substitution strategy was employed to modulate the morphology and active sites of FeNi-LDH. On one hand, Fe 2+ facilitated the formation of abundant open reactive microspaces by regulating the nucleation rate, which was conducive to the exposure of active sites and the mass transfer process. On the other hand, the aliovalent substitution of Fe 2+ introduced more low-valent metal sites and surface defects (–OH), thereby activating the in-plane metal sites of FeNi-LDH. As a result, the bifunctional Fe(II)-FeNi-LDH/CF-0.5 cathode exhibited an excellent performance. At a low current density of 5 mA cm −2 and with NFX concentrations up to 40 mg L −1 , the EF system removed 92.59% of NFX within 15 min, with a pseudo-first-order kinetic constant of 11.67 × 10 −2  min −1 . As the dominant reactive species, hydroxyl radicals (•OH) originated from the combined contributions of both homogeneous and heterogeneous catalytic pathways. The density functional theory (DFT) calculations further revealed that the abundant surface hydroxyl groups were conducive to the adsorption and activation of H 2 O 2 . This work provides a novel material option for EF systems.