Unveiling the role of titania at the hollow core of multi-walled carbon nanotubes in peroxydisulfate activation: Confinement-induced interfacial electron transfer route

Abstract

This study demonstrates that titania embedded in the hollow core of multi-walled carbon nanotubes (TiOx@MWCNT, TCNT) evolves into a core-shell structure during sintering, thereby enabling efficient peroxydisulfate (PDS) activation via a non-radical pathway. The TCNT/PDS system effectively degraded sulfamethoxazole (SMX; initial 10 μM) within 60 min (10.9 times synergistic effect versus control experiments), which was 2-fold faster than the combined system of hollow MWCNT and PDS. Given the inertness of TiO2 toward PDS activation, the intrinsic defects on the TiOx shell (oxygen vacancies and Ti3 +) were identified as key driving forces facilitating a novel electron transfer pathway, generated through interactions with the inner walls of carbon nanotubes. This mechanism was confirmed through multiple lines of evidence, including electron paramagnetic resonance, electrochemical analyses, (in situ) Raman spectroscopy, and density functional theory calculations. The spent TCNT was effectively regenerated through thermal treatment, and its degradation performance was completely restored to the level of the as-synthesized TCNT. The catalytic performance was further assessed under various water quality parameters (pH, inorganic ions, and humic acid), and the degradation pathway of SMX was proposed. Overall, the insights gained through this study provide a competitive design strategy for developing heterogeneous catalysts for effective activation of persulfates. © 2026 Elsevier B.V.