Introducing oxygen vacancy in TiO/R-TiO2 via non-stoichiometric engineering for chloride-resistant sensitive COD electrochemical detection

The rapid and accurate electrochemical detection of COD in water faces numerous challenges due to the abundance of chloride ions at high levels and insufficient conductivity of the electrodes. In this work, the TiO/R-TiO₂ composite material was innovatively constructed by introducing oxygen vacancies through non-stoichiometric engineering. The TiO/R-TiO₂ composite material possesses abundant oxygen vacancies and the resultant ultralow-valent titanium species, which can generate a large number of hydroxyl radicals via electrochemical oxidation of water and exhibit a rapid electron transfer rate. The introduced oxygen vacancies alter the surface charge distribution, endowing the material with excellent conductivity and resistance to chloride ion interference. Glucose was employed as a standard substance to evaluate the electrochemical response of the material, which exhibited a COD detection limit of 0.07 mg L⁻¹ and a broad detection range of 1–500 mg L⁻¹. Seawater was selected as actual water samples for detection, and the results demonstrated good consistency with the standard potassium permanganate method, thereby validating the constructed electrochemical sensing method's capability for direct and sensitive detection of water containing 0.5 M (17725 mg L⁻¹) chloride ions. By addressing the chloride ion interference problem, our work contributed to the development of robust electrochemical COD detection methods that can be widely applied in various water environments, ensuring the protection of water resources and the sustainability of aquatic ecosystems.