Electrochemical Reduction of X-ray Contrast Iohexol at Mixed Metal Oxide Electrodes: Process Optimization and By-product Identification
2018
Turkay, Ozge | Barisci, Sibel | Ulusoy, Ebru | Dimoglo, Anatoly
The reduction of commonly used X-ray contrast iohexol (IOX) by the electrooxidation process is presented in this study. To begin with, the effect of anode material was examined, and different mixed metal oxide electrodes (MMOs) such as Ti/RuO₂, Ti/Pt, Ti/IrO₂-RuO₂, Ti/IrO₂-Ta₂O₅, Ti/Ta₂O₅-SnO₂-IrO₂, and Pt/SnO₂ were used. To assess experimental conditions at Ti/RuO₂ anode, provided the highest removal efficiency, the response surface method was applied and the key influencing parameter was the process time. The determined optimal conditions were triplicated with real wastewater samples, and the average degradation efficiency of IOX was found to be 99%. By-products of the IOX degradation on the Ti/RuO₂ anode have been identified using density functional theory and LC/MS-MS analysis. The results showed that IOX degradation opened with OH group detachment and resulted in the formation of a by-product with a molecular mass of 804 g mol⁻¹. Further degradation mechanism took place due to the breakup of C₄-C₁₀ and C₅-I₇ bonds with a by-product formed as 603 g mol⁻¹. Iodide atom replacement by OH groups caused the formation of a molecular fragment with 375 g mol⁻¹ molecular weight. The further disintegration of C₂-C₁₁ and C₆-N₁₆ σ- bonds led to the formation of molecular masses of 133, 126, and 119 g mol⁻¹, respectively.
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