Iohexol Degradation Research Articles

Photocatalytic degradation of iohexol by photo-driven double Z heterojunction photocatalyst under strong internal electric field in synergy with peroxymonosulfate (PMS)

This paper describes the preparation of a double Z heterojunction photocatalyst, g-C3N4/Bi2O2CO3/MnWO4 (CBCM), with a potent internal electric field using the hydrothermal method. The degradation efficiency can be further improved by combining photocatalytic technology with activated persulfate (PMS) technology. The synthesis of CBCM-7 was validated through XRD and TEM analyses, while XPS provided evidence of electron transfer and the establishment of heterojunctions within its structure. Additionally, PL, PC, and EIS measurements underscored CBCM-7′s proficient rate of photogenerated charge separation and robust charge transfer properties. The experimental results showed that the photocatalytic degradation of the iodinated contrast agent was substantially enhanced by this catalyst coupled with PMS. The degradation rate of Iohexol was up to more than 90 % within 40 min. After the completion of the recycling experiment, the degradation efficiency of this system remained above 80 %. Mechanistic analyses, including EPR tests, indicate that the main active groups generated by the degradation of this dual Z-scheme heterostructured photocatalyst coupled with activated PMS were superoxide radicals and hydroxyl radicals.

Activation of peroxymonosulfate (PMS) by rGO supported Co3O4 catalyst for iohexol degradation

Sulphate radical (SO4·-) -based advanced oxidation process (SR-AOP) is a promising sewage treatment technology. Reduced graphene oxide (rGO) supported Co3O4 composites were synthesized by a hydrothermal method for the degradation of iohexol (IOH) in the rGO/Co3O4/peroxymonosulfate (PMS) system. Experimental results show that rGO/Co3O4 possessed much better PMS activated ability than pure GO or Co3O4, which is ascribed to the summation of rGO and Co3O4. The efficiency of rGO/Co3O4 composite, single GO and Co3O4 nanocrystals for the degradation of IOH were 98.7%, 15.8% and 79.8% at 15 min, and their corresponding reaction rate constants (kapp) were 0.21 min−1, 0.0077 min−1 and 0.080 min−1, respectively. The results of active species capture experiment and electron paramagnetic resonance (EPR) experiment, showed that singlet oxygen is the main active species, which is non-radical degradation. rGO is conducive to the electron conduction of Co3O4, thus improving the efficiency of PMS activation. The system is simple and efficient, which is an effective technology to remove IOH.

Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol

Iodinated X-ray contrast media (ICM) are ubiquitously present in water sources and challenging to eliminate using conventional processes, posing a significant risk to aquatic ecosystems. Ultraviolet light-emitting diodes (UV-LED) emerge as a promising technology for transforming micropollutants in water, boasting advantages such as diverse wavelengths, elimination of chemical additives, and no induction of microorganisms’ resistance to disinfectants. The research reveals that iohexol (IOX) degradation escalates as UV wavelength decreases, attributed to enhanced photon utilization efficiency. Pseudo-first-order rate constants (kobs) were determined as 3.70, 2.60, 1.31 and 0.65 cm2 J−1 at UV-LED wavelengths of 255, 265, 275 and 285 nm, respectively. The optical properties of dissolved organic matter (DOM) and anions undeniably influence the UV-LED photolysis process through photon competition and the generation of reactive substances. The influence of Cl− on IOX degradation was insignificant at UV-LED 255, but it promoted IOX degradation at 265, 275 and 285 nm. IOX degradation was accelerated by ClO2−, NO3−and HA due to the formation of various reactive species. In the presence of NO3−, the kobs of IOX followed the order: 265 > 255 > 275 > 285 nm. Photosensitizers altered the spectral dependence of IOX, and the intermediate photoactivity products were detected using electron spin resonance. The transformation pathways of IOX were determined through density functional theory calculations and experiments. Disinfection by-products (DBPs) yields of IOX during UV-LED irradiation decreased as the wavelength increased: 255 > 265 > 275 > 285 nm. The cytotoxicity index value decreased as the UV-LED wavelength increased from 255 to 285 nm. These findings are crucial for selecting the most efficient wavelength for UV-LED degradation of ICM and will benefit future water purification design.

Monoethanolamine enhanced iohexol degradation in the Co(II)/sulfite system: Nonnegligible role of complexation in accelerating cobalt redox cycling

Generation of sulfate radicals (SO4•−) from sulfite activation has emerged as a promising method for abatement of organic pollutants in the water and wastewater treatment. Co(II) has garnered attention due to its high catalytic activity in the sulfite activation, which is compromised by the slow Co(II)/Co(III) redox cycling. Regarding the regulation of Co(II) electronic structure via the complexation effect, monoethanolamine (MEA), a common chelator, is introduced into the Co(II)/sulfite system. MEA addition results in a significant improvement in iohexol abatement efficiency, increasing from 40% to 92%. The superior iohexol abatement relies on the involvement of SO4•−, hydroxyl radicals (HO•) and Co(IV). Hydrogen radical (•H) is unexpectedly detected, acting as a strong reducing agent, contributing to the reduction of Co(III). This enhancement of sulfite activation by MEA is due to the formation of the Co(II)-MEA complex, in which the complexation ratio of Co(II) and MEA is critical. Electrochemical characterization and theoretical calculations demonstrate that the complexation can facilitate the Co(II)/Co(III) redox cycling with the concomitant enhancement of sulfite activation. This work provides a new insight into the Co(II)/sulfite system in the presence of organic ligands.

Regulating >Fe(II)/>Fe(III) valence transformation in sulfite activation by oxygen vacancy enriched γ-Fe2O3 for efficient iohexol abatement

Sulfite activation with iron-based heterogeneous activators is a promising technology for the removal of organic contaminants from water. However, the slow valence transformation of >Fe(II)/>Fe(III) compromises sulfite activation efficiency. Regarding that the oxygen vacancy (Vo) can modulate the charge distribution and thus enhance >Fe(II)/>Fe(III) valence transformation via rapid electron transfer, Vo-enriched γ-Fe2O3 is constructed for sulfite activation (simplified as the γ-Fe2O3-Vo/sulfite system). The γ-Fe2O3-Vo/sulfite system exhibits excellent abatement performance for iohexol (IOX) with the efficiency as high as 90.2 % within 1 h of reaction at pH 8.5, in which sulfate radicals (SO4•−) and hydroxyl radicals (HO•) are the major species. Electrochemical and DFT calculations reveal that Vo-enriched γ-Fe2O3 possesses lower electrical impedance and the concomitant higher electron transfer efficiency. According to a series of characterizations, the enhance >Fe(II)/>Fe(III) valence transformation is confirmed to contribute to sulfite activation via the regulation of the electronic structure by the Vo. In addition, the degradation pathways of IOX are proposed by analyzing the degradation products of IOX by UPLC-QTOF-MS. Finally, the effects of different influencing factors on the degradation of IOX and the cyclic performance suggest the system shows strong resistance to interference and reusability, exhibiting superior application potential.

A comparative study on the degradation of iohexol and diatrizoate during UV/persulfate process: kinetics, degradation pathways and iodinated disinfection by-products

Iodinated X-ray contrast media (ICM) are widely used in medical imaging due to their stable properties, but they cannot be effectively removed in wastewater treatment plants (especially hospital wastewater).

Enhancing cationic superexchange interaction via adjustive lattice distortion in cobalt-based perovskite for improved Fenton-like decontamination

The cooperative mechanism of mixed transition metals (TMs) for heterogeneous peroxymonosulfate (PMS) based water treatment can be considered in the viewpoint of cationic superexchange interaction. Herein, Co-Fe cooperation towards PMS activation was studied by modulating octahedral TMO6 units in Fe-substituted LaCo1−xFexO3 perovskites. Certain lattice distortion formed at these reactive centers due to Co-Fe ionic radii mismatch, while LaCo0.95Fe0.05O3/PMS (0.136 min−1) achieved superior performance for iohexol degradation. Cobalt cations are identified as active sites by targeted poison and spectroscopic measurements, which prefer to accept electrons from Fe ions. Experimental and theoretical investigations illustrate that slight Fe-substitution induced lattice distortion leads to Co-O-Fe superexchange interaction, facilitating interfacial electron transfer and cationic valence exchange. And, the tolerance factor of catalysts is also indicated as an indicative descriptor to evaluate structure-dependent performance. Our work attempts to shed light on dual TM interactions for synergistic catalysis towards efficient Fenton-like decontamination.

Passivating surface states of graphitic carbon nitride for improved photocatalytic Fenton-like decontamination

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for peroxymonosulfate (PMS) activation towards water treatment, but its inherent surface defects always lead to serious recombination wasting charge carriers. Herein, we constructed cobalt doped aluminum oxide overlayer (AlOx-Co) on g-C3N4 nanosheets, passivating surface states for accelerated photocatalytic PMS activation. The AlOx coating prevents dangling bonds associated with surface recombination, and the Co doping reduces dynamic barrier. Thus, g-C3N4/AlOx-Co (0.0745 min−1) exhibits a 3.5 times higher activity than bare g-C3N4 (0.0168 min−1) towards iohexol degradation. Systemic spectroscopic and photoelectrochemical measurements reveal that AlOx-Co overlayer could weaken in-band recombination and relieve Fermi level pinning, which facilitate the charge transfer. Meanwhile, this overlayer has suitable thickness (3 ∼ 5 nm) for feasible tunneling effects to generate surface-bound radicals. Our work attempts to overcome inefficient surface charge separation and transfer simultaneously for improved contaminant removal via photocatalytic Fenton-like catalysis.

Degradation of iohexol in the Co(II)/peracetic acid system under neutral conditions: Influencing factors, degradation pathways and toxicity

Advanced oxidation processes based on peracetic acid (PAA) activation have received more attention in water treatment recently. In this study, the degradation of iohexol (IOH, a classical iodinated X-ray contrast media) in the Co(II)/PAA system under neutral conditions, which mainly produced carbon-centric radicals, was investigated. Results showed that IOH decomposition follows the pseudo-first-order kinetic with a rate constant of 0.283 min−1. Appropriately increasing concentrations of PAA or Co(II) could promote the removal of IOH, while elevating the dosage of H2O2 inhibits the elimination of IOH in the Co(II)/PAA system. The IOH elimination was affected by pH, with the best response in pH between 5 and 7 in the Co(II)/PAA system. Additionally, low Cl− doses have negligible effects whereas high Cl− impeded the breakdown of IOH. Br−, I−, HCO3−, H2PO4− and humic acid suppressed the degradation of IOH. Removal of IOH was significantly inhibited in three selected real water samples. Furthermore, six IOH degradation pathways, including H-abstraction, amide hydrolysis, amino oxidation, deiodination reaction, hydroxylate and elimination reaction, were proposed on the basis of the liquid chromatography-tandem mass spectrometry, ion chromatography and DFT theoretical calculations (Frontier electron densities and fukui functions) results. Finally, the ECOSAR assessment showed that some degradation byproducts were much more toxic than IOH parent, but were much more biodegradable. Overall, this study indicates a potential risk when applying the carbon-centric radicals involved in PAA-based AOPs to remediate halogenated organic pollutants in water.

Acid-tailored self-assembled perylene diimide supramolecular for visible-light-driven activation of peroxymonosulfate towards efficient degradation of iohexol

The presence of iohexol (IOX) in the environment has attracted widespread attention. Acetic acid, hydrochloric acid, and nitric acid tailored self-assembled perylene diimides (PA, PC and PN) were prepared and utilized in different visible-light-driven activation of peroxymonosulfate (PMS/Vis) systems for the degradation of IOX. As an electron acceptor, PMS can significantly hinder the recombination of photogenerated electron-hole pairs. The removal rate of 5 mg/L IOX by PC/PMS/Vis system reached 99.1% at 30 min, which was 2.0 times and 1.3 times higher than that of PA/PMS/Vis and PN/PMS/Vis system. The boosted oxidation activity with PC was due to the pH dependence of perylene diimide (PDI) self-assembly and the small amount of Cl− (0.56%) absorbed on PC, which can promote the transfer of electron-hole pairs, change the surface charge distribution and energy band position, and enhance π-electron conjugation. Based on density functional theory and electrostatic potential calculation, the Cl− adsorbed on the surface of PDI brings an effect on the electrostatic potential distribution. Furthermore, the built-in intermolecular electric field leads to accelerated charge transfer of PDI. In the PC/PMS/Vis system, holes, singlet oxygen and superoxide radical were perceived as the dominant contributors. The degradation of IOX carried out via pathways of amide hydrolysis, amino oxidation, hydrogen abstraction, deiodination reaction, and OH attack. This work provides a new method for the pollution control of IOX and scientific guidance for the tailored self-assembly of organic supramolecules.

Improved degradation of iohexol using electro-enhanced activation of persulfate by a CuxO-loaded carbon felt with carbon nanotubes as an interlayer

Persulfate (PS) activation by means of transition metals has been extensively applied to eliminate persistent organic pollutants, but the slow rate of metal redox cycling between high-valence and low-valence states inhibits the degradation reaction. Here, a CuxO-loaded carbon felt with carboxylated multi-walled carbon nanotubes (MWCNT-COOH) as an interlayer (CuxO/CNT/CF) has been successfully prepared. This assembly was then employed in a process of peroxymonosulfate (PMS) activation with the assistance of an electric field (CuxO/CNT/CF-PMS-EC). PMS could be effectively activated by the electrically enhanced CuxO/CNT/CF due to faster metal redox cycling, and the system could be applied over a broad pH range (3.0–11.0). The degradation efficiency of iohexol (IOH) could reach 100 % within 25 min, and around 62.7 % of total organic carbon (TOC) was removed within 120 min in the CuxO/CNT/CF-PMS-EC system. Both non-radical (1O2)- and radical-mediated (·SO4-, ·O2–, and ·OH) PS activation are involved in the degradation process. According to the results of DFT calculations and LC-MS, the degradation of IOH involves deiodination, amide hydrolysis, amine oxidation, C-OH oxidation, addition of –OH, hydrogen abstraction, and elimination reactions. The present study shows electrocatalysis coupled with transition-metal-activated PS to be a highly efficient technique for the removal of iodinated contrast media (ICMs).

Degradation of iohexol by potassium ferrate in synthetic water and wastewater effluent: Influencing factors, kinetics, and potential intermediates

Degradation of iohexol by potassium ferrate in synthetic water and wastewater effluent: Influencing factors, kinetics, and potential intermediates

A Gd3+-doped blue TiO2 nanotube array anode for efficient electrocatalytic degradation of iohexol

A Gd3+-doped blue TiO2 nanotube array anode (Gd-BTNA) was successfully fabricated by the processes of anodization, Gd doping and cathodization. The electrocatalytic activity of a blue TiO2 nanotube array anode (BTNA) can be improved by Gd doping, which introduced oxygen vacancies into the material and increases the specific surface area of the anode. Gd-BTNA is used to eliminate iohexol (IOH) in water, and the optimal operating parameters for electrochemical degradation of IOH are a current density of 15 mA cm−2, initial solution pH of 6.5 and initial IOH concentration of 10 ppm. Coexisting components in wastewater have adverse effects on the treatment process, including Cl–, HCO3–, NH4+ and humic acid. Under the optimal conditions, complete degradation of IOH was obtained within 18 min and more than 52.1% total organic carbon (TOC) was removed after 60 min of reaction time, which outperforms the BTNA and several commercial electrodes. The excellent efficiencies in electrochemical degradation of iohexol show that Gd-BTNA was a promising anode to treat iodinated contrast media contaminants.

Identifying the role of oxygen vacancy on cobalt-based perovskites towards peroxymonosulfate activation for efficient iohexol degradation

Oxygen vacancy (VO) is attracting extensive interest in heterogeneous peroxymonosulfate (PMS) activation, but its role remains elusive for water treatment. Herein, we constructed VO-tuned cobalt-based perovskite LaCoO3-VO, achieving superior activity (0.335 min−1) than LaCoO3 (0.124 min−1) for iohexol degradation. Nevertheless, VO did not directly serve as reactive sites, indicated by prohibited contaminant degradation via targeted poisoning of cobalt sites. Systemic electrochemical and spectroscopic measurements illustrate facile transformation of cobalt ions, increased charge density of depletion layer and low transfer resistance are attributed to VO manipulation. DFT calculations suggest reactant HSO5− is prone to attach defect site for elongated O-O bond. Experimental and theoretical results reveal the contributions of VO include adjusting PMS adsorption configuration, weakening lattice restraining of cobalt ions, reducing reaction barrier and optimizing electronic structures on perovskites. Our work attempts to understand energetic and kinetic factors of deficiency strategy for rational PMS-based degradation.

Effective sulfite activation with atomically dispersed cobalt loaded SBA-15 for iohexol abatement

Cobalt-based heterogeneous catalysts receive research interests in the sulfite activation to generate reactive radicals for abatement of organic contaminants in the aquatic environments, yet the sulfite activation efficacy is compromised by the limited utilization of available active cobalt sites. To address this problem, the atomically dispersed cobalt loaded on mesoporous silica SBA-15 (simplified as Co/SBA-15) is constructed for sulfite activation process regarding the incorporation of cobalt species into the confined space abundant with silicon hydroxyl groups in SBA-15. Co/SBA-15 exhibits excellent sulfite activation efficacy, in which iohexol can be completely degraded within 30 min. Sulfate radical (SO4•−) and hydroxyl radical (HO•) are the dominant reactive radicals responsible for iohexol abatement, in which 7.15 μM of SO4•− and 2.23 μM of HO• are produced. The excellent electron transfer efficiency of Co/SBA-15 is demonstrated by electrochemical impedance spectroscopy (EIS). Structural characterization and valence analysis suggest that the formation of atomically dispersed cobalt species facilitates the sulfite activation and Lewis acid sites on Co/SBA-15 can adsorb organic molecular fragments to realize the rapid conversion from >Co(III) to >Co(II) by electron transfer. The iohexol degradation pathways are also proposed based on UPLC-QTOF-MS analysis. In addition, the effects of various influencing factors including the reactant dosage, coexisting anions, humic acid and the different real water backgrounds on iohexol abatement are systematically investigated. This study is expected to provide an efficient heterogeneous catalyst for sulfite activation to achieve the rapid abatement of organic contaminants.

Toward efficient electrocatalytic degradation of iohexol using active anodes: A laser-made versus commercial anodes

The X-ray iodinated contrast medium iohexol is frequently detected in aquatic environments due to its high persistence and the inefficiency of its degradation by conventional wastewater treatments. Hence, the challenge faced in this study is the development of an alternative electrochemical treatment using active anodes. We investigate the oxidation of iohexol (16.42 mg L−1) using different operating conditions, focusing on the role of different mixed metal oxide anodes in the treatment efficiency. The electrocatalytic efficiency of the Ti/RuO2–TiO2 anode prepared using a CO2 laser heating and an ionic liquid is compared with Ti/RuO2–TiO2–IrO2 and Ti/IrO2–Ta2O5 commercial anodes. The hypochlorite ions generated by the anodes are also analyzed. The effect of the electrolyte composition (NaCl, Na2SO4, and NaClO4) and current density (15, 30, and 50 mA cm−2) on the iohexol degradation is also studied. The Ti/RuO2–TiO2 laser-made anode is more efficient than the commercial anodes. After optimizing experimental parameters, this anode removes 95.5% of iohexol in 60 min and displays the highest kinetic rate (0.059 min−1) with the lowest energy consumption per order (0.21 kWh m−3order−1), using NaCl solution as the electrolyte and applying 15 mA cm−2. Additionally, iohexol-intensified groundwater was used to compare the efficiency of anodes. The Ti/RuO2–TiO2 is also more efficient in removing the organic charge from the real water matrix (21.7% TOC) than the commercial anodes. Notably, the iohexol removal achieved is higher than all electrochemical treatments already reported using state-of-the-art non-active anodes in lower electrolysis time. Therefore, data from this study indicate that the electrochemical degradation of iohexol using the Ti/RuO2–TiO2 anode is efficient and has excellent cost-effectiveness; thus, it is a promising approach in the degradation of iohexol from wastewater. Furthermore, the Ti/RuO2–TiO2 active anode is competitive and can be an excellent option for treating effluents contaminated with recalcitrant organic compounds such as iohexol.

Fe3O4 catalytic ozonation of iohexol degradation in the presence of 1-hydroxybenzotriazole: Performance, transformation mechanism, and pathways

This study explored the degradation of an iodine X-ray contrast media, iohexol, under heterogeneous ozone-catalyzed oxidation by adding Fe3O4 and 1-hydroxybenzotriazole (HBT). Results show that increasing the dosages of Fe3O4 catalyst and ozone as well as solution pH were beneficial to the degradation of iohexol. The presence of low background humic acid (HA) concentration (≤10 mg/L) promoted iohexol degradation, but high HA concentration (≥20 mg/L) inhibited it. Adding HBT exhibited a similar effect on iohexol degradation as HA. The degradation rate constant of iohexol was calculated as 0.07108 min−1 in the Fe3O4/O3/HBT process ([HBT] = 5 μM) at pH 7.0, which was approximately 1.5 times higher than that in the Fe3O4/O3 process (0.04533 min−1), and 4 times higher than that in the O3 process (0.01742 min−1). Fe3O4/O3/HBT process was pH-dependent with high degradation efficiency of iohexol at pH 5 or 7. Singlet oxygen (1O2), hydroxyl radical (OH∙), and superoxide radical (O2-∙) have been identified in the Fe3O4/O3/HBT process, and the conversion of Fe2+ to Fe3+ was more obvious on the surface of Fe3O4 compared to that in the Fe3O4/O3 process. Transformation intermediates were identified, and the degradation pathways of iohexol were proposed. Overall, Fe3O4/O3 could enhance iohexol degradation compared with ozone-only system, and adding trace HBT in Fe3O4/O3 system can further enhance heterogeneous ozone-catalyzed process for rapid organic matter degradation.

Visible-light activation of persulfate ions by Z-scheme perylene diimide/MIL-101(Cr) heterojunction photocatalyst towards efficient degradation of iohexol

Persulfate (PS) is widely used as an oxidant in sulfate radical-based advanced oxidation process for contaminants degradation. A novel Z-scheme perylene diimide (PDI)/MIL-101(Cr) (PM) heterojunction was fabricated via a one-pot process and employed for PS activation assisted with visible light. PDI self-assembly, surface Cr reduction, and heterojunction formation were achieved simultaneously. Under visible light irradiation, rapid degradation of iohexol (IOH) was realized by PS/PM-7 (PDI:MIL-101(Cr) = 9:7, w/w, 0.5 g/L) with reaction rate 8.8 times that of PDI/PS/Vis system. The radical quenching tests showed that h+ and •OH were perceived as the dominant contributors. According to experimental results and density functional theory calculation, IOH experienced oxidation, hydrolysis, deiodination, and hydrogen extraction reactions in the PM-7/PS/Vis system. The PM-7/PS/Vis system also demonstrated promising efficiency for IOH elimination either in treatment of real water body or irradiated by natural sunlight. The Z-scheme PM heterojunction possessed high charge-transportation efficiency with induced-electrons injected from the conduction band of MIL-101(Cr) to the valence band of SA-PDI. PS can be employed as a photogenerated electron acceptor to boost the migration of charge carriers and promote the production of more reactive oxygen species, thereby accelerating IOH oxidation. This work provides new perspectives into the synergistic effects between photocatalysis and PS activation, constructing an eco-friendly system for removal of organic pollutants.

Activation of Peroxymonosulfate (Pms) by Rgo Supported Co3o4 Catalyst for Iohexol Degradation

Activation of Peroxymonosulfate (Pms) by Rgo Supported Co3o4 Catalyst for Iohexol Degradation

Identifying the Role of Oxygen Vacancy on Cobalt-Based Perovskites Towards Peroxymonosulfate Activation for Efficient Iohexol Degradation

Identifying the Role of Oxygen Vacancy on Cobalt-Based Perovskites Towards Peroxymonosulfate Activation for Efficient Iohexol Degradation