Reductive removal of diatrizoate via catalytic hydrodeiodination over Pd/MnFe2O4 catalysts

In this study, we synthesized a series of Pd-based catalysts supported on spinel ferrites including MnFe2O4, CuFe2O4 and CoFe2O4 using the deposition-precipitation method and evaluated their performance in the catalytic hydrodeiodination (HDI) of iodinated contrast media (ICMs), with diatrizoate (DTZ) as the model compound. The deiodination rates were approximately 90 %, 50 %, and 15 % within 10 min over MnFe2O4, CoFe2O4, and CuFe2O4 supported Pd catalysts, respectively. The Pd2/MnFe2O4 catalysts exhibited superior Pd dispersion and an optimal Pd2+/Pd0 ratio, and the HDI of DTZ followed a stepwise deiodination pathway, with 3,5-diacetamidobenzoic acid (DABA) and iodide (I-) as the final products. Release of I- from catalyst surface was extremely important for deep deiodination, thus, the reduction of DTZ was strongly pH-dependent, with higher pH levels promoting the release of I- and accelerating DTZ reduction. Coexisting substances, such as Cl- , HA, and HCO3- facilitated the deiodination by depressing the adsorption of I-, whereas NO3- and I- inhibited DTZ reduction. Furthermore, we used the ECOSAR program to calculate the biotoxicity of the reduction products and found that deiodination effectively reduced the hazard of the pollutant to aquatic organisms. Additionally, the H2/Pd2/MnFe2O4 system maintained good robustness for DTZ deiodination during continuous operation.