Electrocatalytic activities of electrochemically reduced tubular titania arrays loaded with cobalt ions in flow-through processes

This study examines the electrocatalytic activity of disordered titania nanotube arrays modified with Co²⁺ for the oxidation of (in)organic substrates and inactivation of E. coli in a flow-through electrochemical device. As-anodized TiO₂ nanotubes (TNTs) on perforated Ti foils are electrochemically reduced to create Ti³⁺ states and oxygen vacancies. The electrochemically reduced TNTs (r-TNTs) are capable of adsorbing Co²⁺ in ~7 times larger amounts than the bare TNTs. Among the bare and modified TNT samples (TNTs, r-TNTs, Co-TNTs, and Co-r-TNTs), Co-r-TNTs exhibit the lowest interfacial charge-transfer resistance and fastest internal charge-transfer kinetics. The electron spin resonance analysis further reveals an enhanced production of OOH radicals in Co-r-TNTs. The combined effect of the excellent charge-transfer behavior and the radical production of Co-r-TNTs leads to faster decomposition of N,N-dimethyl-p-nitrosoaniline, higher current efficiency in the oxidation of iodide to triiodide, and greater inactivation of E. coli as compared to r-TNTs. Details on the surface characterization of the bare and modified TNTs samples are presented and the role of the adsorbed Co²⁺ is discussed.