Degradation of iodinated X-ray contrast media by advanced oxidation processes:A literature review with a focus on degradation pathways

Available online Iodinated X-ray contrast media (ICMs) are clinical drugs used to enhance the imaging effect.Triiodobenzene ring structures of ICMs lead to its extremely high chemical stability,biological inertness,which makes it difficult to be completely removed by traditional water treatment processes.Hence,considerable concentration of ICMs can be frequently detected in aquatic environment.Relying on the strong oxidation capacity of HO·or SO_(4)^(·-),various advanced oxidation processes (AOPs) have demonstrated substantial removal efficiency for ICMs.It is evident that ICMs can be decomposed mainly through(1) deiodination,(2) dehydration,(3) decarboxylation,(4) H-abstraction,(5) hydroxyl addition,(6) hydroxyl substitution,(7) oxidation of alcohol groups,(8) cleavage of amide bond,and (9) amino oxidation.However,during the ICMs removal process,the C-I bonds of ICMs molecules are broken,giving rise to the formation of cytotoxic iodination disinfection by-products (I-DBPs) that are potentially more harmful to the ecosystem and human health than their parent compounds.To better understand the technology gaps,this review elaborates the major AOPs which are effective for ICMs removal and emphasizes on the main degradation routes of ICMs in different oxidation system.Some prevailing concerns and challenges are discussed for optimizing the ICMs treatment process.

A chronological review of photochemical reactions of ferrioxalate at the molecular level:New insights into an old story

Owing to its outstanding photoactivity,ferrioxalate is originally used as an actinometer and subsequent work has discovered that photochemistry of ferrioxalate is also fundamentally or technically important in atmospheric chemistry and water treatment.While the overall products generated from photolysis of ferrioxalate are known to include Fe(Ⅱ),a series of oxidizing(e.g.,·OH,O_(2)^(·-)/HO_(2)^(·-))or reducing(C_(2)O_(4)^(·-)/CO_(2)^(·-))radicals and H_(2)O_(2),however,at the molecular level,the primary step of the photoreaction of ferrioxalate remains as an unsolved mystery due to the difficulty in examining such ultrafast processes.Benefiting from the development of time-resolved spectroscopy,this old question has been studied with increasing vigor recently,by means of such ever-more-sophisticated techniques(e.g.,flash photolysis,time-resolved X-ray absorption spectroscopy(XAS),femtosecond infrared(IR)absorption spectroscopy,ultrafast photoelectron spectroscopy(PES)).There are two contrary views on the primary reaction mechanism:(1)Intramolecular electron transfer(ET)precedes the cleavage of the metal-ligand bond;(2)The dissociation of C-C or Fe-O bond occurs before intramolecular ET.Thus,this review presents a comprehensive summary about the overall reaction mechanism and molecular level mechanism of ferrioxalates.In chronological order,we have elaborated two predominant but controversial views from the perspectives of different experimental approaches.Some challenges and research opportunities in this active field are also briefly discussed.