Homojunction-Incorporated\nOxygen Vacancy Functionalized\nSpherical TiO<sub>2</sub> Nanocrystals for the Electrochemical Detection\nof Chemical Oxygen Demand

Chemical oxygen demand (COD) is a critical criterion\nfor the analytical\nassessment of the degree of organic contaminants in an aqueous system.\nTypically, toxic and expensive reagents are employed in standardized\nCOD analysis methods, leading to secondary pollution. In this work,\nwe developed a rapid electrochemical method for COD detection based\non the oxidation of hydroxyl radicals for organics in water by using\noxygen vacancy doped anatase/rutile-TiO<sub>2</sub> nanoparticles\nas electrooxidation catalysts. Homojunction interface generated increasing\noxygen vacancies for enhancing electron-transfer rate and accelerating\nH<sub>2</sub>O oxidation to substantially improve ·OH yield.\nOxygen vacancy further increased the oxygen evolution potential of\nthe material. Initially, glucose was chosen as a standard analyte\nto evaluate electrochemical responses, and water from urban wastewater\ntreatment plants was assessed as real samples subsequently. Excellent\nanalytical characteristics were achieved with the A/R-TiO<sub>2</sub> sensor under the optimal conditions, exhibiting a linear range from\n1 to 300 mg L<sup>–1</sup> and detection limit of 0.1 mg L<sup>–1</sup> COD. The estimated COD values obtained from the samples\nwere highly consistent with those determined using the conventional\nstandard dichromate method. We have presented a fast, cost-effective,\nand ecologically sustainable method that outperforms the standard\nCOD analysis method and holds great potential for the accurate determination\nof COD and boasts high detection sensitivity and a broad linear range.