Experimental Study On The Effect And Mechanism Of Potassium Ferrate Oxidizing Contrast Agent (iohexol)

In recent years,iodinated X-ray contrast media（ICMs）have been continuously detected in water and have become a representative drug at relatively high concentrations（ie,μg/L level）in the water environment.Although ICMs are considered not to cause direct harm to the human body,the ICMs in the source water can be used as potential precursors of disinfection by-products（DBPs）and react with disinfectants to form highly toxic DBPs,such as iodinated disinfection by-products（I-DBPs）and high molecular weight disinfection by-products with unknown toxicity have great potential threats to drinking water safety,and iohexol is one of the highest levels of ICMs detected in China.Therefore,it is necessary to remove iohexol from the source to ensure the safety of drinking water.As a new green water treatment agent with synergistic effect of oxidation-adsorption-flocculation in the removal of pollutants,potassium ferrate（K₂Fe O₄）has good application potential in the treatment of water environment iohexol.In this experiment,laboratory-made potassium ferrate was used to process simulated water samples containing iohexol and actual water samples spiked to study the effect and mechanism of potassium ferrate on the degradation of iohexol.In this experiment,a quantitative analysis method for iohexol was established and the methodology was evaluated.The effect of the reaction time,the dosage of potassium ferrate and the p H on the removal rate of iohexol in the reaction process of potassium ferrate and iohexol was investigated.By adding humic acid,anions(HCO₃^-/PO₄^3-/SO₄^2-),and cations(NH₄⁺/Mg²⁺/Ca²⁺),the effect of a single coexisting substance in natural water on the removal of iohexol by potassium ferrate was simulated and further studied The effect of potassium ferrate on the removal of iohexol in the presence of complex coexisting substances in actual water.Since potassium ferrate self-decomposes slowly in an alkaline environment,it can avoid the influence of potassium ferrate self-decomposition on absorbance.Therefore,the kinetic law of potassium ferrate and iohexol under the condition of p H=9 was studied and the high iron content was inferred.The reaction pathway of potassium acid degrading iohexol.The results are as follows:（1）Establish the specific chromatographic conditions of the iohexol detection method using high performance liquid chromatography:C₁₈analytical column,mobile phase acetonitrile/ultrapure water（4:96,v:v）;elution procedure:isocratic elution,flow rate:1.0m L/min,the injection volume is 100μL,the column temperature is 30°C,and the detection wavelength is 254 nm.Methodological evaluation showed that when iohexol was in the range of50-1000μg/L,the correlation coefficient R-square between peak area and concentration was0.99939,and the detection limit was 0.75μg/L.The recovery rate of iohexol was100.87%-103.13%,and the relative standard deviation was less than 2%.（2）The reaction of potassium ferrate and iohexol basically ends after 10 minutes.When the mass ratio of potassium ferrate to iohexol is 100:1,the removal efficiency is the highest,and the removal rate reaches 72%.p H has a great influence on the reaction of potassium ferrate and iohexol.When a buffer solution is used to make the p H value unchanged during the reaction,the optimal p H for the reaction of potassium ferrate and iohexol is 8,which is The removal rate can reach 90%;when only the initial p H value is changed by using acid and alkali,the p H value changes during the reaction process.At this time,the optimal initial p H value of the reaction between potassium ferrate and iohexol is 6,iodine The removal rate of sea alcohol is 91.6%.（3）Humic acid can inhibit the reaction of potassium ferrate and iohexol,and the inhibitory effect increases as the concentration increases.HCO₃^-/PO₄^3-/NH₄⁺/Mg²⁺/Ca²⁺can inhibit the degradation of iohexol by potassium ferrate to varying degrees,while SO₄^2-has no obvious effect on the reaction of potassium ferrate and iohexol.（4）When potassium ferrate was used to degrade the iohexol in the actual water sample spiked,it was found that when the mass ratio of potassium ferrate to iohexol was 100:1,the removal effect of iohexol was still ideal,and potassium ferrate was effective in removing iohexol.Part of the dissolved organic matter in the actual water sample can also be removed.（5）The kinetic study of potassium ferrate and iohexol found that the reaction is a secondary reaction under p H=9,and the secondary reaction constant is 0.515 M^-1s^-1.（6）Using UPLC-MS/MS,a total of 6 intermediate products of potassium ferrate degradation of iohexol were detected,the molecular structures of these 6 products were inferred,and the pathways for potassium ferrate to degrade iohexol were finally inferred,including:dehydrogenation reaction,Amide hydrolysis reaction,degradation reaction,deiodination reaction,hydroxyl addition reaction.