CNT Microtubes with Entrapped Fe3O4 Nanoparticles Remove Micropollutants through a Heterogeneous Electro-Fenton Process at Neutral pH

Abstract

Catalyst-coated carbon electrodes require two preparation stages: electrode assembly using carbon and polymeric binders and subsequent catalyst immobilization on the porous carbons electrode. Such conventional coating methods require several steps, which is time-, chemical-, and energy-consuming. Also, polymeric binders can impair the porosity and block catalytic sites of final electrodes. This study introduces a novel one-pot synthesis method in which Fe3O4 nanoparticles are entrapped within a multi-walled carbon nanotube network, the latter being templated with microtubular geometry. Such carbon microtubes (CMT) represent a standalone geometry, serving as a binder-free electrode for an energy-efficient heterogeneous electro-Fenton (HEF) process. Fe3O4-containing CMTs remove carbamazepine (CBZ), a frequently detected pharmaceutical micropollutant in water bodies. While almost all literature reports degradation at acidic conditions requiring the use of acid, this material system functions at pH 7 ± 0.3 with lengthy reusability. The remarkable mineralization of the total oxidized CBZ emerges from the confinement of oxidation by-products in CMTs’ 3D framework, where unselective radicals are formed once the electro-generated H2O2 reacts with embedded Fe3O4. Additionally, the 3D network prevents the entrapped catalysts from leaching in acidic environments because of the increased local pH during electrolysis.