Efficiency And Product Analysis Of Photocatalytic Degradation Of Iopamidol Based On UV₃₆₅

In recent years,as the demand for medical imaging diagnosis and contrast agent use increases,more and more iodine-substituted contrast agents（ICMs）are frequently detected in sewage plants,surface water and even drinking water,causing environmental pollution and posing a threat to human health.For the removal of ICMs,conventional water treatment processes have general performance or many limitations.While advanced oxidation processes（AOP_S）is a better choice in comparison,especially advanced oxidation technology based on UV catalysis,which has been a popular research topic in recent years.Therefore,iopamidol（IPM）,an ICM with high detection frequency,was selected as the target contaminant in this thesis.The commonly used persulfate（PDS）and hypochlorite（NaClO）were chosen as oxidants,and LED lamp materials were selected to construct a 365 nm wavelength-based UV photocatalytic system.The efficacy of UV₃₆₅/PDS and UV₃₆₅/NaClO systems in degrading IPM was investigated in this thesis.The experimental results indicate that PDS alone and NaClO alone basically did not degrade IPM,and the degradation efficiency of IPM by UV₃₆₅ alone was also low,while IPM could be efficiently degraded in UV₃₆₅/PDS and UV₃₆₅/NaClO systems,and the degradation processes were all consistent with pseudo primary reactions.Moreover,compared to UV₃₆₅/PDS,the UV₃₆₅/NaClO system is more efficient.The contribution of active components in the system was investigated through methods such as quenching agents and degradation of probe compounds.The presence of quenching agents significantly inhibited the degradation effect of IPM in the UV₃₆₅/PDS system,HO·was the most dominant active component in this system,and ¹O₂+O₂^-·and SO₄^-·also played an important role.The contribution of ozone to IPM degradation in the UV₃₆₅/NaClO system was extremely low,and the contribution rates of Cl O·,HO·,and Cl·+Cl₂^-·to the removal of IPM are 41.31%,34.45%,and 22.96%,respectively.The steady-state concentration of Cl O·（[Cl O·]ss）in the standard group was the highest,followed by[HO·]ss and the lowest is[Cl·]ss in the UV₃₆₅/NaClO system.The effects of experimental operating parameters and background composition of water were also examined.Especially,it is in the UV₃₆₅/NaClO system that the changes in steady-state concentration and contribution rate of free radicals under different conditions were compared.The experimental results indicate that the increase in oxidant concentration promoted the degradation of IPM in both systems,mainly because the steady-state concentration of the active ingredient resulting from the system would be gradually increased.However,the increase of k_obsin the UV₃₆₅/NaClO system tends to level off with the increase of oxidant concentration,and it is known that the increase of oxidant concentration makes the contribution of Cl O·significantly higher while the contribution of HO·and Cl·+Cl₂^-·from relevant calculations.This is mainly because the excess HCl O/Cl O^-captures HO·and Cl·,and it is further speculated that Cl·has a weaker effect on IPM degradation in the UV₃₆₅/NaClO system.The degradation of IPM was promoted to some extent by the UV₃₆₅/PDS system under both acidic and alkaline conditions.While the UV₃₆₅/NaClO system favored the degradation of IPM at low p H and inhibited the degradation of IPM at high p H.The calculation results showed that the steady-state concentrations of each radical,the contribution of HO·and Cl O·decreased with the increase of p H in the UV₃₆₅/NaClO system,mainly because the various radicals were more easily trapped under alkaline conditions.However,the contribution of Cl·+Cl₂^-·increased significantly,presumably because Cl₂^-·played a greater role in the degradation of IPM under alkaline condition.The presence of NOM has a strong inhibitory effect on the degradation of IPM in both systems,mainly because of the internal filtering effect of NOM leading to competing photons and NOM quenching the active component of the system.In the UV₃₆₅/NaClO system,the contribution of Cl O·was significantly reduced due to the quenching effect of NOM on Cl O·and its precursor radicals（HO·and Cl·）,while Cl·+Cl₂^-·had a significant increase in contribution,and it was further speculated that Cl₂^-·played the most important role in the degradation of IPM at this time.The addition of Cl^-and HCO₃^-/CO₃^2-in both systems only slightly inhibited the degradation of IPM,mainly because they generated CO₃^-·and various secondary reactive radicals after capturing the active components in the system,although their activity was slightly lower than that of HO·,the accumulation of their concentrations also made a certain contribution to the removal of IPM.After the addition of Cl^-to the UV₃₆₅/NaClO system,the[Cl·]ss decreased significantly,mainly because most of the Cl·would be converted to Cl₂^-·,but Cl·+Cl₂^-·to IPM is basically unaffected,and it is again speculated that the degradation of IPM by Cl·at UV₃₆₅/NaClO system is weak,while Cl₂^-·has some reactivity with IPM and plays appropriate role.The degradation products of IPM in both systems were detected and the relevant degradation pathways were speculated.During the degradation of IPM in UV₃₆₅/PDS system,14 possible organic products were obtained.It is speculated that IPM was gradually degraded mainly through rearrangement reaction,hydrogen extraction reaction,deiodination reaction,substitution reaction（-OH）,amide hydrolysis,and amine oxidation.15 possible organic products were obtained in the UV₃₆₅/NaClO system.It is speculated that IPM was gradually degraded mainly through hydrogen extraction reaction,deiodination reaction,substitution reaction（-OH,-Cl）,etc.,and TOC gradually decreased with the reaction.In addition,inorganic products of IPM were detected during the degradation process,where HOI rapidly accumulated,while the concentration of IO₃^-with non-toxic and iodine rich gradually increased slowly.The degradation effects of two systems on IPM in three actual water were compared and studied.The results showed that IPM was inhibited to varying degrees in all three actual water,with the inhibition effect being surface water>groundwater>tap water,and the inhibition effect in the UV₃₆₅/PDS system was more significant than that in the UV₃₆₅/NaClO system.According to the energy consumption calculation results,the unit energy consumption（EE/O）of IPM degradation by the UV₃₆₅/PDS system was more affected by the background composition of the water,and overall,the UV₃₆₅/NaClO system is more energy-saving.Therefore,compared to the UV₃₆₅/PDS system,UV₃₆₅/NaClO system has better application potential.There is almost no acute toxicity during the degradation of IPM in both systems,but the potential risks in actual water treatment should be taken seriously.