| 1. |
|
|
| 2. |
|
|
| 3. |
- El Jamal, Sawsan, et al.
(författare)
-
On the Stability of Uranium Carbide in Aqueous Solution-Effects of HCO3- and H2O2
- 2021
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 6:37, s. 24289-24295
-
Tidskriftsartikel (refereegranskat)abstract
- Uranium carbide (UC) is a candidate fuel material for future Generation IV nuclear reactors. As part of a general safety assessment, it is important to understand how fuel materials behave in aqueous systems in the event of accidents or upon complete barrier failure in a geological repository for spent nuclear fuel. As irradiated nuclear fuel is radioactive, it is important to consider radiolysis of water as a process where strongly oxidizing species can be produced. These species may display high reactivity toward the fuel itself and thereby influence its integrity. The most important radiolytic oxidant under repository conditions has been shown to be H2O2. In this work, we have studied the dissolution of uranium upon exposure of UC powder to aqueous solutions containing HCO3- and H2O2, separately and in combination. The experiments show that UC dissolves quite readily in aqueous solution containing 10 mM HCO3- and that the presence of H2O2 increases the dissolution further. UC also dissolves in pure water after the addition of H2O2, but more slowly than in solutions containing both HCO3- and H2O2. The experimental results are discussed in view of possible mechanisms.
|
|
| 4. |
- El Jamal, Sawsan
(författare)
-
Stability of Alternative Nuclear Fuel Materials in Aqueous Systems
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nuclear power produces a large portion of the electricity worldwide. It has been the largest low-carbon energy source for more than 30 years and has played an essential role in the security of energy supplies for many countries. However, despite its advantages, its future is unknown mainly because of accidents that can happen under reactor operation and the high radioactivity of the fuel after use. Therefore, Generation IV nuclear power has been introduced as it promises a sustainable and economical way of producing energy and reduces some of the risks observed in current reactors. UC and UN have advantageous properties compared to conventional UO2-based fuel which makes them promising fuel candidates for Generation IV nuclear reactors. Even though the fuel for Generation IV reactors is planned to be reprocessed, unexpected political decisions may change these plans, and the used fuel could end up in a geological repository. Therefore, the behavior of these new fuel materials must be understood in accident scenarios in reactors as well as under deep geological repository conditions. The radioactivity of the used fuel will induce radiolysis of water that comes in contact with it. This will lead to oxidative dissolution of the fuel and this is one of the potential routes for radionuclide release in the environment.In the first part of this thesis, UC and UN have been investigated in aqueous solutions under anoxic conditions, and under the influence of external γ-radiation and H2O2, the latter mimicking the impact of α-radiolysis. The hydrolysis of these materials in aqueous systems resulted in matrix dissolution which is not observed for UO2. The oxidative dissolution induced by H2O2 is more prominent than hydrolysis in water with or without added HCO3- where higher concentrations of dissolved uranium can be detected. In addition, the differences in reactivity are discussed for these materials and H2O2 is most reactive towards UN followed by UC and finally UO2, yet the dissolution yield is the lowest for UN. The change in UC and UN behavior with consecutive exposure to H2O2 was attributed to a change in surface reactivity where catalytic decomposition of H2O2 becomes possible. As it was observed for H2O2 additions, radiation induced oxidative dissolution also dominates over hydrolysis. Unexpectedly high concentrations of H2O2 were observed in the irradiated systems. This was found to be due to formation of nano-particulate studtite that could not be separated from the solutions samples by filtration. Hence, it turned out to be impossible to determine the free U(VI) and H2O2 concentrations in these systems.Finally, the stability of pure and ZrN containing UN pellet fragments was investigated in aqueous system under external γ-radiation or H2O2 exposure. The behavior of these pellet fragments was similar to the UN powder where the dissolution of uranium was enhanced under oxidizing conditions if compared with anoxic conditions (hydrolysis). Consecutive exposures of UN pellet fragments to H2O2 showed a change in surface reactivity. This change is attributed to the formation of an oxide layer on the surface of UN, as UO2 is less reactive towards H2O2 and UO2 pellets display lower dissolution yields than UN pellets. In addition, the impact of ZrN as a stabilizing additive to UN pellets was studied. The addition of ZrN to UN is expected to stabilize the UN matrix and thus render a more accident tolerant fuel. Interestingly, it was shown that under oxidizing conditions, ZrN did not have a significant impact on the stability of UN pellets in aqueous systems
|
|
| 5. |
- Hansson, Niklas, 1992, et al.
(författare)
-
Geometrical aspects of alpha dose rates from UO2 based fuels
- 2022
-
Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 199, s. 110336-
-
Tidskriftsartikel (refereegranskat)abstract
- Models for calculating dose rates of spherical particles as well as in fuel cracks are important for radionuclide source term estimations. Dose rates from UO2 based fuels were calculated for planar, spherical, and crack geometries. The escape probability for a-particles in spherical UO2 particles was derived as a continuous equation. The dose rate increased with increasing spherical radius due to the decreasing relative volume of the surrounding water layer. The model produced escape probabilities that were closely predicted by the theoretical derivation. It was shown that the dose rate in water filled fuel cracks with width smaller than the range of an alpha-particle led to dissolution rates that were lower per unit surface area.
|
|
| 6. |
|
|
| 7. |
- Puranen, Anders, 1977-, et al.
(författare)
-
A study on the immobilization of selenium oxyanions by H2/Pd(s) in aqueous solution : Confirmation of the one-electron reduction barrier of selenate
- 2010
-
Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 116:1-4, s. 16-23
-
Tidskriftsartikel (refereegranskat)abstract
- Selenium is a trace element of concern in several geochemical contexts, due to the potentially high mobility of the selenium oxyanions and the narrow range between deficiency and toxicity of the element. For high level nuclear waste repositories the long-lived fission product 79Se has been identified as a potential key dose contributor for the long-term safety. This paper deals with the catalytic effect of Pd(s) on the H2 reduction of selenium oxyanions which was studied experimentally in aqueous solutions containing bicarbonate and chloride. Pd-catalysts and hydrogen have been proposed for the remediation of various groundwater contaminants and can also serve as a model substance for catalytic noble metal inclusions present in spent nuclear fuel. In this study selenite (SeO32−) was found to adsorb on Pd. In the presence of hydrogen the rate of selenite removal increased yielding elemental Se. However, no adsorption or reduction of selenate (SeO42−) was observed. A simple radiation chemical experiment revealed a notable barrier towards stepwise one-electron reduction of selenate to selenite. This provides an explanation for the lower reactivity of selenate in systems where reductive immobilization of selenite as well as selenate is thermodynamically favorable.
|
|
| 8. |
- Yang, Yi, et al.
(författare)
-
Gamma-radiation induced synthesis of freestanding nickel nanoparticles
- 2021
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 50:1, s. 376-383
-
Tidskriftsartikel (refereegranskat)abstract
- A versatile method to produce metallic nickel nanoparticles is demonstrated. Metallic Ni nanoparticles have been synthesized from aqueous solution of NiCl2 using gamma-radiation induced reduction. To prevent Ni re-oxidation, post-irradiation treatment was elaborated. Structural and compositional analyses were executed using X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. These studies reveal that the synthesized material consists of fcc Ni particles having size of 3.47 +/- 0.71 nm. The nanoparticles have a tendency to agglomerate to the larger clusters. The latter are partially oxidized to form thin amorphous/poor-crystalline Ni(OH)(2)/NiO layers at the surface. Magnetization measurements demonstrate that the nanomaterial exhibit ferromagnetic-like behaviour with magnetization 30% lower than that in bulk Ni. The large active surface area (ECSA, 39.2 m(2) g(-1)) and good electrochemical reversibility, confirmed by the electrochemical studies, make the synthesized material a potential candidate as an active component for energy storage devices.
|
|
| 9. |
- Ahlsson, Fredrik, 1967-, et al.
(författare)
-
Adipokines and their relation to maternal energy substrate production, insulin resistance and fetal size
- 2013
-
Ingår i: European Journal of Obstetrics, Gynecology, and Reproductive Biology. - : Elsevier BV. - 0301-2115 .- 1872-7654. ; 168:1, s. 26-29
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE:The role of adipokines in the regulation of energy substrate production in non-diabetic pregnant women has not been elucidated. We hypothesize that serum concentrations of adiponectin are related to fetal growth via maternal fat mass, insulin resistance and glucose production, and further, that serum levels of leptin are associated with lipolysis and that this also influences fetal growth. Hence, we investigated the relationship between adipokines, energy substrate production, insulin resistance, body composition and fetal weight in non-diabetic pregnant women in late gestation.STUDY DESIGN:Twenty pregnant women with normal glucose tolerance were investigated at 36 weeks of gestation at Uppsala University Hospital. Levels of adipokines were related to rates of glucose production and lipolysis, maternal body composition, insulin resistance, resting energy expenditure and estimated fetal weights. Rates of glucose production and lipolysis were estimated by stable isotope dilution technique.RESULTS:Median (range) rate of glucose production was 805 (653-1337)μmol/min and that of glycerol production, reflecting lipolysis, was 214 (110-576)μmol/min. HOMA insulin resistance averaged 1.5±0.75 and estimated fetal weights ranged between 2670 and 4175g (-0.2 to 2.7 SDS). Mean concentration of adiponectin was 7.2±2.5mg/L and median level of leptin was 47.1 (9.9-58.0)μg/L. Adiponectin concentrations (7.2±2.5mg/L) correlated inversely with maternal fat mass, insulin resistance, glucose production and fetal weight, r=-0.50, p<0.035, r=-0.77, p<0.001, r=-0.67, p<0.002, and r=-0.51, p<0.032, respectively. Leptin concentrations correlated with maternal fat mass and insulin resistance, r=0.76, p<0.001 and r=0.73, p<0.001, respectively. There was no correlation between maternal levels of leptin and rate of glucose production or fetal weight. Neither were any correlations found between levels of leptin or adiponectin and maternal lipolysis or resting energy expenditure.CONCLUSION:The inverse correlations between levels of maternal adiponectin and insulin resistance as well as endogenous glucose production rates indicate that low levels of adiponectin in obese pregnant women may represent one mechanism behind increased fetal size. Maternal levels of leptin are linked to maternal fat mass and its metabolic consequences, but the data indicate that leptin lacks a regulatory role with regard to maternal lipolysis in late pregnancy.
|
|
| 10. |
- Ahlstrand, Christina, 1957, et al.
(författare)
-
Reliabilitetstestning av Purdue Pegboard® (finmotoriktest).
- 2009
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I MQ-FAS studien, vars syfte var att ändra muskelspänningsmönstret hos kvinnor med kroniska nackbesvär, ingick ett besticktorkningsmoment som en standardiserad arbetsuppgift i hemmet. För validering av denna besticktorkning har en pilotstudie genomförts, 12 personer torkade bestick vid två tillfällen. I studien, som utfördes av 2 testledare, ingick även ett finmotorikstest (Purdue Pegboard), ansträngningsskattning (Borg RPE-skalan) samt ett frågeformulär. Detta test kan med vissa justeringar troligen vara användbart som ett mått på arbetsförmåga av övre extremiteter vid utförande av arbetssyssla i hemmet, och jämföra individ med sig själv, för att mäta om funktionsnedsättning eller ökning har skett. Dock skall poängteras att detta var en pilotstudie och ytterligare studie av reliabilitet och validitet rekommenderas innan testet används i stor utsträckning för att mäta om funktionsnedsättning eller ökning har skett.
|
|
| 11. |
|
|
| 12. |
- Bajor, Antal, 1962, et al.
(författare)
-
Normal or increased bile acid uptake in isolated mucosa from patients with bile acid malabsorption.
- 2006
-
Ingår i: Eur J Gastroenterol Hepatol. - 0954-691X. ; 18:4, s. 397-403
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Bile acid malabsorption as reflected by an abnormal 75Se-labelled homocholic acid-taurine (75SeHCAT) test is associated with diarrhoea, but the mechanisms and cause-and-effect relations are unclear. Objectives: Primarily, to determine whether there is a reduced active bile acid uptake in the terminal ileum in patients with bile acid malabsorption. Secondarily, to study the linkage between bile acid malabsorption and hepatic bile acid synthesis. Methods: Ileal biopsies were taken from patients with diarrhoea and from controls with normal bowel habits. Maximal active bile acid uptake was assessed in ileal biopsies using a previously validated technique based on uptake of 14C-labelled taurocholate. To monitor the hepatic synthesis, 7[alpha]-hydroxy-4-cholesten-3-one, a bile acid precursor, was assayed in blood. The 75SeHCAT-retention test was used to diagnose bile acid malabsorption. Results: The taurocholate uptake in specimens from diarrhoea patients was higher compared with the controls [median, 7.7 (n=53) vs 6.1 [mu]mol/g per min (n=17)] (P<0.01) but no difference was seen between those with bile acid malabsorption (n=18) versus diarrhoea with a normal 75SeHCAT test (n=23). The 75SeHCAT values and 7[alpha]-hydroxy-4-cholesten-3-one were inversely correlated. Conclusions: The data do not support bile acid malabsorption being due to a reduced active bile acid uptake capacity in the terminal ileum. (C) 2006 Lippincott Williams & Wilkins, Inc.
|
|
| 13. |
- Barreiro Fidalgo, Alexandre
(författare)
-
Experimental studies of radiation-induced dissolution of UO2 : The effect of intrinsic solid phase properties and external factors
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dissolution of the UO2 matrix is one of the potential routes for radionuclide release in a future deep geological repository for spent nuclear fuel. This doctoral thesis focuses on interfacial reactions of relevance in radiation-induced dissolution of UO2 and is divided in two parts:In the first part, we sought to explore the effects of solid phase composition:The impact of surface stoichiometry on the reactivity of UO2 towards aqueous radiolytic oxidants was studied. H2O2 reacts substantially faster with stoichiometric UO2 than with hyperstoichiometric UO2. In addition, the release of uranium from stoichiometric UO2 is lower than from hyperstoichiometric UO2. The behavior of stoichiometric powder changes with exposure to H2O2, approaching the behavior of hyperstoichiometric UO2 with the number of consecutive H2O2 additions.The impact of Gd-doping on the oxidative dissolution of UO2 in an aqueous system was investigated. A significant decrease in uranium dissolution and higher stability towards H2O2 for (U,Gd)O2 pellets compared to standard UO2 was found.In the second part, we sought to look at the effect of external factors:The surface reactivity of H2 and O2 was studied to understand the overall oxide surface reactivity of aqueous molecular radiolysis products. The results showed that hydrogen-abstracting radicals and H2O2 are formed in these systems. Identical experiments performed in aqueous systems containing UO2 powder showed that the simultaneous presence of H2 and O2 enhances the oxidative dissolution of UO2 compared to a system not containing H2.The effect of groundwater components such as bentonite and sulfide on the oxidative dissolution of UO2 was also explored. The presence of bentonite and sulfide in water could either delay or prevent in part the release of uranium to the environment. The Pd catalyzed H2 effect is more powerful than the sulfide effect. The poisoning of Pd catalyst is not observed under the conditions studied.
|
|
| 14. |
|
|
| 15. |
- Barreiro Fidalgo, Alexandre, et al.
(författare)
-
Radiation induced dissolution of (U, Gd)O-2 pellets in aqueous solution - A comparison to standard UO2 pellets
- 2019
-
Ingår i: Journal of Nuclear Materials. - : ELSEVIER SCIENCE BV. - 0022-3115 .- 1873-4820. ; 514, s. 216-223
-
Tidskriftsartikel (refereegranskat)abstract
- The behavior of spent nuclear fuel exposed to groundwater is crucial in the safety assessment of a deep geological repository for spent nuclear fuel. For this reason, leaching experiments on spent nuclear fuel as well as non-radioactive analogues have been conducted for several decades. Although the processes involved can be considered to be fairly well understood, there is a need for further experimental studies whenever new fuel types are introduced. Fuels with burnable absorbers are now in use but very little is known about their behavior under repository conditions. In this work, the impact of burnable absorbers doping (Gd, 3-8%wt.) on the oxidative dissolution of UO2 in an aqueous system was studied in H2O2 and gamma-irradiation induced dissolution experiments. The results showed a significant decrease in uranium dissolution and lower reactivity towards H2O2 for (U,Gd)O-2 pellets compared to standard UO2. The resulting decrease in the final oxidative dissolution yield was mainly attributed to decreased redox reactivity of the UO2-matrix upon doping. The results of the gamma radiation exposures display an even larger effect of Gd-doping. These findings indicate that other processes are involved in the radiation-induced dissolution of Gd-doped UO2 compared to pure UO2.
|
|
| 16. |
- Barreiro Fidalgo, Alexandre, et al.
(författare)
-
Radiation induced dissolution of (U, Gd)O2 pellets in aqueous solution : A comparison to standard UO2 pellets
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this work, the impact of burnable absorbers doping (Gd, 3-8%wt.) on the oxidative dissolution of UO2 in an aqueous system was studied by H2O2 and γ-irradiation induced dissolution experiments. The results showed a significant decrease in uranium dissolution and higher stability towards H2O2 for (U,Gd)O2 pellets compared to standard UO2. The resulting decrease in the final oxidative dissolution yield was mainly attributed to decreased redox reactivity of the UO2-matrix upon doping. During gamma radiation induced experiments, the difference in uranium release was even more pronounced compared to H2O2 induced dissolution experiments.
|
|
| 17. |
- Barreiro Fidalgo, Alexandre, et al.
(författare)
-
The role of surface-bound hydroxyl radicals in the reaction between H2O2 and UO2
- 2018
-
Ingår i: Journal of coordination chemistry (Print). - : Informa UK Limited. - 0095-8972 .- 1029-0389. ; 71:11-13, s. 1799-1807
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we have studied the reaction between H2O2 and UO2 with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of H2O2 consumption and uranium dissolution at different initial H2O2 concentrations. The results show that the consumption rates at a given H2O2 concentration are different depending on the initial H2O2 concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The dissolution yield given by the amount of dissolved uranium divided by the amount of consumed hydrogen peroxide was used to compare the different cases. For all initial H2O2 concentrations, the dissolution yield increases with reaction time. The final dissolution yield decreases with increasing initial H2O2 concentration. This is expected from the mechanism of catalytic decomposition of H2O2 on oxide surfaces. As the experiments were performed in solutions containing 10mM H2O2 and a strong concentration dependence was observed in the 0.2-2.0mM H2O2 concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.
|
|
| 18. |
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
- Carlsson, Celice, et al.
(författare)
-
On the Selectivity of Radical Scavengers Used To Probe Hydroxyl Radical Formation in Heterogeneous Systems
- 2022
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:30, s. 12435-12440
-
Tidskriftsartikel (refereegranskat)abstract
- Tris and methanol have been used quite extensively as probes for surface-bound hydroxyl radicals in heterogeneous systems, such as TiO2 photocatalysis and catalytic decomposition of H2O2. Recent studies have indicated that the selectivity for surface-bound hydroxyl radicals is questionable and that the yield of the stable detectable product, formaldehyde, may be different for different reactive species. In this work, we have explored the selectivity as well as the formaldehyde yield of these two probes by experimentally studying formaldehyde formation in homogeneous (gamma radiolysis) and heterogeneous (TiO2 photocatalysis) systems, where hydroxyl radicals and Br-2.- can be formed. The latter is formed in the reaction between hydroxyl radicals and Br- at relatively high concentrations of Br-. The experiments clearly show that the formaldehyde yield is reduced by 85% when comparing hydroxyl radicals and Br2 & BULL;- in a homogeneous methanol system and increased by 50% when making the same comparison for the homogeneous Tris system. The increased yield is attributed to a change in the reaction mechanism as Br2 & BULL;- is mainly expected to produce a nitrogen-centered radical cation, while the hydroxyl radical mainly produces carbon-centered radicals. The radical cation appears to produce formaldehyde with a higher yield. In the photocatalysis system, the trends are similar but even more emphasized. The rationale for this is discussed, as well as the suitability of methanol and Tris as probes for surface-bound hydroxyl radicals in heterogeneous systems.
|
|
| 25. |
- Chen, Shangzhi, et al.
(författare)
-
Conductive polymer nanoantennas for dynamic organic plasmonics
- 2020
-
Ingår i: Nature Nanotechnology. - London : Nature Publishing Group. - 1748-3387 .- 1748-3395. ; 15
-
Tidskriftsartikel (refereegranskat)abstract
- Being able to dynamically shape light at the nanoscale is oneof the ultimate goals in nano-optics1. Resonant light–matterinteraction can be achieved using conventional plasmonicsbased on metal nanostructures, but their tunability is highlylimited due to a fixed permittivity2. Materials with switchablestates and methods for dynamic control of light–matterinteraction at the nanoscale are therefore desired. Here weshow that nanodisks of a conductive polymer can supportlocalized surface plasmon resonances in the near-infraredand function as dynamic nano-optical antennas, with their resonancebehaviour tunable by chemical redox reactions. Theseplasmons originate from the mobile polaronic charge carriersof a poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf)polymer network. We demonstrate complete and reversibleswitching of the optical response of the nanoantennasby chemical tuning of their redox state, which modulatesthe material permittivity between plasmonic and dielectricregimes via non-volatile changes in the mobile chargecarrier density. Further research may study different conductivepolymers and nanostructures and explore their usein various applications, such as dynamic meta-optics andreflective displays.
|
|
| 26. |
- Chen, Song, et al.
(författare)
-
Incorporation of strontium and europium in crystals of α-calcium isosaccharinate
- 2019
-
Ingår i: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 364, s. 309-316
-
Tidskriftsartikel (refereegranskat)abstract
- The final repository for short-lived, low and intermediate level radioactive waste in Sweden is built to act as a passive repository. Already within a few years after closure water will penetrate the repository and conditions of high alkalinity (pH 10.5―13.5) and low temperature (< 7 °C) will prevail. The mobility of radionuclides in the repository is dependent on the radionuclides distribution between solid and liquid phases. In the present work the incorporation of strontium (II) and europium (III) in α-calcium isosaccharinate (ISA) under alkaline conditions (pH ~10) at 5 °C and 50 °C have been studied. The results show that strontium and europium are incorporated into α-Ca(ISA)2 when crystallized both at 5 °C and 50 °C. Europium is incorporated to a greater extent than strontium. The highest incorporation of europium and strontium at 5 °C rendered the phase compositions Ca0.986Eu0.014(ISA)2 (2.4% of Eu(ISA)3 by mass) and Ca0.98Sr0.02(ISA)2 (2.2% of Sr(ISA)2 by mass). XPS spectra show that both trivalent and divalent Eu coexist in the Eu incorporated samples. Strontium ions were found to retard the elongated growth of the Ca(ISA)2crystals. The incorporation of Sr2+ and Eu3+ into the solid phase of Ca(ISA)2 is expected to contribute to a decreased mobility of these ions in the repository.
|
|
| 27. |
- Chen, Shangzhi, et al.
(författare)
-
Unraveling vertical inhomogeneity in vapour phase polymerized PEDOT:Tos films
- 2020
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 8, s. 18726-18734
-
Tidskriftsartikel (refereegranskat)abstract
- The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) forms a promising alternative to conventional inorganic conductors, where deposition of thin films via vapour phase polymerization (VPP) has gained particular interest owing to high electrical conductivity within the plane of the film. The conductivity perpendicular to the film is typically much lower, which may be related not only to preferential alignment of PEDOT crystallites but also to vertical stratification across the film. In this study, we reveal non-linear vertical microstructural variations across VPP PEDOT:Tos thin films, as well as significant differences in doping level between the top and bottom surfaces. The results are consistent with a VPP mechanism based on diffusion-limited transport of polymerization precursors. Conducting polymer films with vertical inhomogeneity may find applications in gradient-index optics, functionally graded thermoelectrics, and optoelectronic devices requiring gradient doping.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
- Chernyshev, Alexander N., et al.
(författare)
-
Characterization and degradation of a polyaryl ether based superplasticizer for use in concrete barriers in deep geological repositories
- 2018
-
Ingår i: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 95, s. 172-181
-
Tidskriftsartikel (refereegranskat)abstract
- Superplasticizers are important additives used in concrete barriers in geological waste repositories. Superplasticizers have been a major concern in the long-term assessments of safe geological disposal for radioactive waste since superplasticizers and their degradation products can act as complexing ligands and thereby increase the mobility of radionuclides. In this work a new type of superplasticizer, based on a polyaryl ether polymer, has been characterized. It was found that the superplasticizer combines the structural features of polycarboxylate ether based superplasticizers and sulfonated naphthalene-formaldehyde based superplasticizers and that it contains organophosphatecharged groups. A novel method for evaluating the rate of degradation of the superplasticizer under alkaline conditions was elaborated and the degradation products and rate constant of the process was determined. The results demonstrate that degradation occurs rapidly compared to the typical lifetime of a repository.
|
|
| 32. |
- Chernyshev, Alexander N., et al.
(författare)
-
Solubilization of Ni(II) and Eu(III) through complexation with a polyaryl ether based superplasticizer in alkaline media
- 2021
-
Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 263
-
Tidskriftsartikel (refereegranskat)abstract
- Solubilisation of Ni(II) and Eu(III) by complexation with a polyaryl ether based superplasticizer (PAE SP) in alkaline solutions was studied. The solubilization was investigated in two types of artificial cement pore waters simulating different stages of cement degradation at a pH of 12.4 and 13.3, respectively. The solubility of Ni(II) and Eu(III) increased as the concentration of superplasticizer was increased from 0.04 to 0.4 wt%. When the concentration of SP was increased from 0.4 to 4%, the solubility of Eu(III) and Ni(II) increased in the pore water with a pH of 12.4, while the concentrations decreased in the pore water with a pH of 13.3. This is explained by a more rapid degradation of the superplasticizer at higher pH leading to a release of phosphate groups and thereby precipitation of Eu(III) and Ni(II) as phosphates. Based on results of the solubilisation of Ni(II) and Eu(III) by model compounds (anisole and PEG 400) and 31P NMR spectroscopy it was confirmed that the complexation of the studied metals with the PAE polymer occurs via the phosphate group of the superplasticizer.
|
|
| 33. |
- Dahlgren, Björn, et al.
(författare)
-
Numerical Simulation of the Kinetics of Radical Decay in Single-Pulse High-Energy Electron-Irradiated Polymer Aqueous Solutions
- 2019
-
Ingår i: Journal of Physical Chemistry A. - : AMER CHEMICAL SOC. - 1089-5639 .- 1520-5215. ; 123:24, s. 5043-5050
-
Tidskriftsartikel (refereegranskat)abstract
- A new method for the numerical simulation of the radiation chemistry of aqueous polymer solutions is introduced. The method makes use of a deterministic approach combining the conventional homogeneous radiation chemistry of water with the chemistry of polymer radicals and other macromolecular species. The method is applied on single-pulse irradiations of aqueous polymer solutions. The speciation of macromolecular species accounts for the variations in the number of alkyl radicals per chain, molecular weight, and number of internal loops (as a consequence of an intramolecular radical-radical combination). In the simulations, the initial polymer molecular weight, polymer concentration, and dose per pulse (function of pulse length and dose rate during the pulse) were systematically varied. In total, 54 different conditions were simulated. The results are well in line with the available experimental data for similar systems. At a low polymer concentration and a high dose per pulse, the kinetics of radical decay is quite complex for the competition between intra- and intermolecular radical-radical reactions, whereas at a low dose per pulse the kinetics is purely second-order. The simulations demonstrate the limitations of the polymer in scavenging all the radicals generated by water radiolysis when irradiated at a low polymer concentration and a high dose per pulse. They also show that the radical decay of lower-molecular-weight chains is faster and to a larger extent dominated by intermolecular radical-radical reactions, thus explaining the mechanism behind the experimentally observed narrowing of molecular weight distributions.
|
|
| 34. |
- Dahlgren, Björn, et al.
(författare)
-
Numerical Simulations of Nanogel Synthesis Using Pulsed Electron Beam
- 2020
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley. - 1022-1344 .- 1521-3919. ; 29:1, s. 1900046-
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, a new method for numerical simulation of the radiation chemistry of aqueous polymer solutions exposed to a sequence of electron pulses is presented. The numerical simulations are based on a deterministic approach encompassing the conventional homogeneous radiation chemistry of water as well as the chemistry of polymer radicals. The multitude of possible reactions in the macromolecular system is handled by allowing for a large number of macromolecular species. The speciation of macromolecular species is done to account for variations in molecular weight, number of alkyl radicals per chain, number of peroxyl radicals per chain, number of oxyl radicals per chain, and number of internal loops. As benchmarking, previously published results from a series of experiments on pulsed irradiation of aqueous poly(N-vinylpyrrolidone) (PVP) solutions are used. The numerical simulations clearly show that the pulsed nature of the radiation must be accounted for. The simulations qualitatively reproduce the experimentally observed impact of initial gas saturation (air and N2O) and polymer concentration on the molecular chain length upon irradiation. The formation of double bonds as a function of dose as well as the impact of effective dose rate on the final chain length are also qualitatively reproduced in the simulations.
|
|
| 35. |
|
|
| 36. |
- Dispenza, Clelia, et al.
(författare)
-
Micro- to Nanoscale Bio-Hybrid Hydrogels Engineered by Ionizing Radiation
- 2021
-
Ingår i: Biomolecules. - : MDPI. - 2218-273X. ; 11:1
-
Forskningsöversikt (refereegranskat)abstract
- Bio-hybrid hydrogels consist of a water-swollen hydrophilic polymer network encapsulating or conjugating single biomolecules, or larger and more complex biological constructs like whole cells. By modulating at least one dimension of the hydrogel system at the micro- or nanoscale, the activity of the biological component can be extremely upgraded with clear advantages for the development of therapeutic or diagnostic micro- and nano-devices. Gamma or e-beam irradiation of polymers allow a good control of the chemistry at the micro-/nanoscale with minimal recourse to toxic reactants and solvents. Another potential advantage is to obtain simultaneous sterilization when the absorbed doses are within the sterilization dose range. This short review will highlight opportunities and challenges of the radiation technologies to produce bio-hybrid nanogels as delivery devices of therapeutic biomolecules to the target cells, tissues, and organs, and to create hydrogel patterns at the nano-length and micro-length scales on surfaces.
|
|
| 37. |
- Dispenza, C., et al.
(författare)
-
On the nature of macroradicals formed upon radiolysis of aqueous poly(N-vinylpyrrolidone) solutions
- 2020
-
Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 174
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we have explored the nature of macroradicals formed upon radiolysis of aqueous poly(N-vinylpyrrolidone) (PVP) solutions using pulse radiolysis, density functional theory (DFT) and literature data. On the basis of literature data on site-specific kinetics of hydrogen abstraction from simple amides and spectra corresponding to specific radical sites on the same amides we have assessed the distribution of H-atom abstraction by •OH radicals from different positions on the pyrrolidone ring and the polymer backbone. Pulse radiolysis experiments performed at different doses per pulse and different PVP concentrations demonstrate that the H-abstracting radiolysis products are not quantitatively scavenged by the polymer when the dose per pulse exceeds ≈40 Gy. The implications of this are discussed in the context of radical-initiated crosslinking reactions. At a mass fraction of 0.1% PVP and doses per pulse ranging from 7 Gy to 117 Gy, the overall radical decay observed at 390 nm follows second order kinetics with rate constants on the order of 109 dm3 mol-1 s-1.
|
|
| 38. |
- Ditta, L. A., et al.
(författare)
-
The role of molecular oxygen in the formation of radiation-engineered multifunctional nanogels
- 2019
-
Ingår i: European Polymer Journal. - : Elsevier. - 0014-3057 .- 1873-1945. ; 114, s. 164-175
-
Tidskriftsartikel (refereegranskat)abstract
- Nanogels are very promising biomedical nanodevices. The classic “radiation chemistry-based” approach to synthetize nanogels consists in the irradiation with pulsed electron beams of dilute, N 2 O-saturated, aqueous solutions of water-soluble polymers of the “crosslinking type”. Nanogels with controlled size and properties are produced in a single irradiation step with no recourse to initiators, organic solvents and surfactants. This paper combines experimental syntheses, performed with two e-beam irradiation setups and dose-ranges, starting from poly(N-vinyl pyrrolidone) solutions of various concentrations, both in N 2 O-saturated and air-saturated initial conditions, with the numerical simulations of the radiation chemistry of aqueous solutions of a radical scavanger exposed to the same irradiation conditions used in the experiments. This approach provides a methodology to predict the impact of system and irradiation conditions on the water radiation chemistry, which in turn affect the nanogel features in terms of molecular and physico-chemical properties. In particular, the crucial role of initial and transient concentration of molecular oxygen is revealed. This work also proposes a very simple and effective methodology to quantitatively measure the double bonds formed in the systems from disporportionation and chain scission reactions, competing with inter-/intra-molecular crosslinking.
|
|
| 39. |
|
|
| 40. |
- El Jamal, Ghada, et al.
(författare)
-
Estimating the Radical Character of Surface Bound Hydroxyl Groups through an in-situ Ultra-Violet Photoelectron Spectroscopy study of UO2, U2O5 and UO3 exposed to H2O and H.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ultraviolet Photoelectron Spectroscopy (UPS) has been used to study the reactions of H2O and atomic hydrogen with UO2, U2O5 and UO3 at low temperatures and low dosages (below 50 Langmuir). The aim was to compare the formation and characteristics of surface hydroxyl species, either by dissociation of the water (surface hydration) or by reduction of the oxide by atomic hydrogen (surface hydrogenation). In addition, the charge state of the OH (neutral-radical or anion) was investigated. On UO2 and U2O5, water adsorbs molecularly and little surface OH was formed. Atomic hydrogen reduces U2O5, by forming OH species but reduction yield is low compared to that of UO3. On UO3 water only weakly adsorbs and already at -110°C it desorbs. Hydrogen reduces UO3, from U(VI) to U(V). Photochemical reduction of the oxides by water was observed for both UO3 and U2O5. The influence of the termination layer on the adsorption of water has been investigated for UO3. UPS has been used to characterize the chemisorbed H2O and OH via their molecular orbitals (MOs), for H2O 1b2, 3a1 and 1b1 for OH the 1and 1. The 3a1-1b1 binding energy difference was taken as measure for the bond strength. The 1 /1 intensity ratio was tentatively used to determine the charge state of the surface hydroxyl.
|
|
| 41. |
- El Jamal, Ghada, et al.
(författare)
-
H2O2-Induced Oxidative Dissolution of UO2 in Saline Solutions
- 2021
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2021:40, s. 4175-4182
-
Tidskriftsartikel (refereegranskat)abstract
- H2O2 is one of the oxidants responsible for driving the process of radiation-induced dissolution of spent nuclear fuel in geological repositories for spent nuclear fuel. As the groundwater composition will vary depending on geographical location as well as on the age of the repository (in relation to glacial cycles, etc.), it is important to elucidate the impact of different groundwater constituents. While several studies have addressed the impact of HCO3− and halide ions on the radiation chemistry of water in general and radiation-induced oxidative dissolution of spent nuclear fuel in particular, very few studies have addressed the impact of halide ions on the mechanism of the reaction between H2O2 and UO2. In this work, the impact of Cl−, Br− and ClO4− on the mechanism and kinetics of H2O2-induced oxidative dissolution of UO2-powder in aqueous suspensions with and without added HCO3− has been studied experimentally. The experiments reveal both ionic strength effects and specific ion effects on the kinetics of the reactions involved. These are discussed in connection to the results.
|
|
| 42. |
- El Jamal, Ghada, et al.
(författare)
-
How inorganic anions in groundwater influence the mechanism of oxidativedissolution of nuclear fuels in geological repositories in case of barrier failure.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- H2O2 has previously been shown to be the main oxidant responsible for driving the process of radiation-induced dissolution of spent nuclear fuel in geological repositories for spent nuclear fuel. As the groundwater composition will vary depending on geographical location as well as on the age of the repository (in relation to glacial cycles, etc.), it is important to elucidate the impact of different groundwater constituents. While several studies have addressed the impact of HCO3- and halide ions on the radiation chemistry of water in general and radiation-induced oxidative dissolution of spent nuclear fuel in particular, very few studies have addressed the impact of halide ions on the mechanism of the reaction between H2O2 and UO2. In this work, the impact of Cl-, Br- and ClO4- on the mechanism and kinetics of H2O2-induced oxidative dissolution of UO2-powder in aqueous suspensions with and without added HCO3- has been studied experimentally. The experiments show that for systems containing 10 mM HCO3- and an initial H2O2-concentration of 0.15 mM, the presence of 1 M Cl-, Br- or ClO4- does not influence the kinetics of the reaction. At higher initial H2O2-concentrations, the presence of 1 M Br- appears to increase the rate of H2O2 consumption as well as the rate of UO22+ release. In solutions without added HCO3-, the presence of 1 M Cl-, Br- or ClO4- has an impact on the overall kinetics of the process at all initial H2O2-concentrations. This is partly attributed to an ionic strength effect enhancing adsorption of UO22+ to UO2 and partly attributed to stabilization of soluble uranyl-peroxo complexes mainly by Cl- and Br-.
|
|
| 43. |
|
|
| 44. |
- El Jamal, Ghada, et al.
(författare)
-
Mixed H2O/H2 Plasma-Induced Redox Reactions of Thin Uranium Oxide Films under UHV Conditions
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- X-Ray Photoelectron Spectroscopy (XPS) has been used to study the effect of mixed H2O/H2 gas plasma on the surface of UO2, U2O5 and UO3 thin films at 400 °C. The experiments were performed in-situ under ultra-high vacuum conditions. Deconvolution of the U4f7/2 peaks into the U(IV), U(V) and U(VI) components revealed the surface composition of the films after 10 minutes plasma exposure as a function of the H2 concentration in the feed gas of the plasma. Some selected films (unexposed and exposed) were also analysed using Grazing-Incidence X-Ray Diffraction (GIXRD). The XPS results show that U(V) is formed as a dominating product upon 10 minutes exposure of UO3 by a mixed H2O/H2 plasma in a fairly wide H2 concentration range. When starting with U(V) (U2O5), rather high H2 concentrations are needed to reduce U(V) to U(IV) in 10 minutes. In the plasma induced oxidation of UO2, U(V) is never observed as a major product after 10 minutes and it would seem that once U(V) is formed in the oxidation of UO2 it is rapidly oxidized further to U(VI). The Grazing Incidence X-Ray Diffraction analysis shows that there is a considerable impact of the plasma and heating conditions on the crystal structure of the films in line with the change of the oxidation state. This structural difference is proposed to be the main kinetic barrier for plasma induced transfer between U(IV) and U(V) in both directions.
|
|
| 45. |
- El Jamal, Ghada, et al.
(författare)
-
Mixed H2O/H2plasma-induced redox reactions of thin uranium oxide films under UHV conditions
- 2021
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 50:36, s. 12583-12591
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) has been used to study the effect of mixed H2O/H2gas plasma on the surfaces of UO2, U2O5and UO3thin films at 400 °C. The experiments were performedin situunder ultra-high vacuum conditions. Deconvolution of the U4f7/2peaks into U(iv), U(v) and U(vi) components revealed the surface composition of the films after 10 min plasma exposure as a function of H2concentration in the feed gas of the plasma. Some selected films (unexposed and exposed) were also analysed using grazing-incidence X-ray diffraction (GIXRD). The XPS results show that U(v) is formed as a major product upon 10 minutes exposure of UO3by a mixed H2O/H2plasma in a fairly wide H2concentration range. When starting with U(v) (U2O5), rather high H2concentrations are needed to reduce U(v) to U(iv) in 10 minutes. In the plasma induced oxidation of UO2, U(v) is never observed as a major product after 10 minutes and it would seem that once U(v) is formed in the oxidation of UO2it is rapidly oxidized further to U(vi). The grazing incidence X-ray diffraction analysis shows that there is a considerable impact of the plasma and heating conditions on the crystal structure of the films in line with the change of the oxidation state. This structural difference is proposed to be the main kinetic barrier for plasma induced transfer between U(iv) and U(v) in both directions.
|
|
| 46. |
- El Jamal, Ghada, et al.
(författare)
-
Monitoring the gradual change in oxidation state during surface oxidation or reduction of uranium oxides by photoemission spectroscopy of the 5f states.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Photoelectron spectroscopy study of the U5f emission gives valuable insight into the surface oxidation mechanism of uranium oxides. Their intensity is directly related to the electron count nf, which decreases with increasing oxidation number (U(IV): nf=2; U(V): nf=1; U(VI): nf=0). n5f can be quantified by analysing the U5f/U4f intensity ratio and using a standard of known composition. In addition, the 5f emission has a characteristic multiplet shape, directly related to n5f, which can be used to distinguish the 5f2 and 5f1 configuration of U(IV) and U(V), respectively. Three independent methods are used to determine the surface oxidation state: the U5f/U4f intensity ratio, the relative intensities of the U4f oxide shifted peaks, and the O1s/U4f intensity ratio. The first two reveal the concentration of the U different oxides, the last indicates the total concentration of oxygen. These methods are applied to follow the surface modification of UO2 films when exposed to various oxidative conditions: molecular and atomic oxygen and water plasma at 400°C. In addition, the reduction of UO3 by atomic H is studied. Molecular oxygen oxidizes UO2 to UO2+x(x=0.22), containing both U(IV) and U(V). Atomic oxygen also oxidizes U(IV) to U(V) at low dosages, but then continues oxidizing U(V) to U(VI) (UO3). Conversely, atomic hydrogen reduces UO3. In the early phase of reduction exclusively U(V) forms – no U(IV) is observed. Water plasma first transforms almost all UO2 (surface and subsurface) into U(V). With further plasma exposure the surface is oxidized to about 80% U(VI) and 20% U(V). Up to this point, a small fraction of U(IV) remains at the surface. Once it disappears, the surface oxidation stops and further water plasma exposure now leads to surface reduction into U(V) (the 5f1 peak increases again). Despite the reduction at high dosage, the O1s/U4f intensity ratio keeps increasing.
|
|
| 47. |
- El Jamal, Ghada, et al.
(författare)
-
Monitoring the gradual change in oxidation state during surface oxidation or reduction of uranium oxides by photoemission spectroscopy of the 5f states
- 2022
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 560
-
Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectroscopy study of the U5f emission gives valuable insight into the surface oxidation mechanism of uranium oxides. Its intensity is directly related to the electron count n(f), which decreases with increasing oxidation number (U(IV): n(f)= 2; U(V): n(f) = 1; U(VI): n(f)= 0). n5f can be quantified by analysing the U5f/U4f intensity ratio and using a standard of known composition. In addition, the 5f emission has a characteristic multiplet shape, directly related to n5f, which can be used to distinguish the 5f 2 and 5f 1 configuration of U(IV) and U(V), respectively. Three independent methods are used to determine the surface oxidation state: the U5f/U4f intensity ratio, the relative intensities of the U4f oxide shifted peaks, and the O1s/U4f intensity ratio. The first two reveal the concentration of the U in each oxide, the third indicates the total concentration of oxygen. These methods are applied to follow the surface modification of UO2 films when exposed to various oxidative conditions: molecular and atomic oxygen and water plasma at 400 C. In addition, the reduction of UO3 by atomic H is studied. Molecular oxygen oxidizes UO2 to UO2 +x(x = 0.22), containing both U(IV) and U(V). Atomic oxygen also oxidizes U(IV) to U(V) at low dosages, but then continues oxidizing U(V) to U(VI) (UO3) at high dosages. Conversely, atomic hydrogen reduces UO3. In the early phase of reduction U(V) forms exclusively - no U(IV) is observed. Water plasma first transforms almost all UO2 (surface and subsurface) into U(V). With further plasma exposure the surface is oxidized to about 80% U(VI) and 20% U(V). Up to this point, a small fraction of U(IV) remains at the surface. Once it disappears, the surface oxidation stops and further water plasma exposure now leads to surface reduction into U(V) (the 5f 1 peak increases again). Despite the reduction at high dosage, the O1s/U4f intensity ratio keeps increasing.
|
|
| 48. |
- El Jamal, Ghada
(författare)
-
Redox Reactions of Uranium-Based Materials in Aqueous Systems and Under UHV Conditions. : Two models mimicking radiation-induced oxidation of spent nuclear fuel.
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for clean electricity is a primary concern in Europe. Nuclear power isconsidered as a greenhouse gas-free technology for generation of electricity. However,compared to other energy sources, it generates a highly toxic waste.In Sweden, the long-term solution for the waste disposal issue is called the KBS-3 method.It is based on protective natural and engineered barriers surrounding the spent nuclear fuelin order to isolate it from the biosphere, thereby ensuring protection of the environmentfrom increased levels of radioactivity. The spent nuclear fuel problem also concernscountries that no longer make use of nuclear power but still have large amounts of wasteto deal with.In recent years, the safety research concerning deep geological repositories for spentnuclear fuel have attracted significant attention. Scientists have investigated differentaspects of the worst-case scenario where the integrity of the barrier system is lost. Ifgroundwater actually comes into contact with the fuel, water radiolysis will be induced andthe products formed have the potential of oxidizing and dissolving the fuel matrix whichwill risk spreading radionuclides into the environment.Not surprisingly, actinide oxides are at the heart of many experimental studies. In manyinstances, their surfaces interaction with water radiolysis products are key to explain thematrix response in different environments. The main goal is to understand the fuelcorrosion/dissolution process, however many of the studies were performed on fairlycomplex systems which makes it difficult to draw reliable detailed mechanisticconclusions.In this thesis, the chemical processes involved in radiation induced oxidative dissolutionof UO2 were experimentally modeled in two different ways: The H2O2-induced oxidativedissolution of UO2 in aqueous solution and the reactive plasma interaction with uraniumoxide thin films under UHV conditions. H2O2 is one of the main oxidants generated inwater radiolysis. The impact of groundwater components on the mechanism of H2O2consumption and UO2 oxidation were investigated.The plasma of water gas successfully generated products similar to the ones formed by theradiolysis of liquid water. Three different types of uranium oxide (UO2, U2O5 and UO3)were probed with X-ray and Ultra-Violet Photoelectron Spectroscopy before and after theexposure to water plasma, pure or mixed with H2. A comprehensive examination was madeof redox events which mimic the radiation effects. Analysis of U5f emission was used todetermine the surface oxidation state. The nature of hydroxyl species adsorbed to thedifferent uranium oxides was also investigated in order to identify the conditions underwhich hydroxyl radical binding to uranium oxide surfaces is favored.
|
|
| 49. |
- El Jamal, Ghada, et al.
(författare)
-
Study of Water Interaction with UO2, U2O5, and UO3 : Tracking the Unexpected Reduction of Uranium Cations and Characterization of Surface-Bound Hydroxyls
- 2023
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:29, s. 14222-14231
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of water with the surfaces of metal oxides is important to many fields of research, extending from nuclear science to catalysis to energy and biomedical materials. One intriguing phenomenon is the observation that, for a few oxides, water seems to reduce (not oxidize) the oxide substrate. In this work, ultraviolet photoelectron spectroscopy (UPS) has been used to study the reactions of H2O with prototype oxide nuclear fuels: UO2, U2O5, and UO3. On UO2, water adsorbs largely in a molecular state. On U2O5, water partially dissociates at −60 °C, thus forming surface −OH groups, and a fraction of the uranium cations are reduced from U5+ to U4+. On UO3, a similar reduction process is seen (reduction of a fraction of uranium cations from U6+ to U5+), albeit less pronounced. The chemisorbed H2O and −OH states via their molecular orbitals (MOs), 1b2, 3a1, and 1b1 for H2O and 1σ and 1π for −OH, were further analyzed. The 3a1-1b1 binding energy difference (ΔE) was taken as a measure of the bond strength. It was found to be larger on UO2 and U2O5 (2.9-3.0 eV) than on UO3 (2.2 eV). The charge state of the surface hydroxyl was found to be related to the 1π /1σ intensity ratio, from which, and in conjunction with the created U 5f states, electron transfer to the conduction band under UPS collection was facilitated by the hole trapping capacity of surface −OH groups, at least in the case of UO3. An energy band diagram is constructed that may explain the redox process observed on UO3 under UV photon excitation.
|
|
| 50. |
- El Jamal, Ghada, et al.
(författare)
-
Time-dependent surface modification of uraniumoxides exposed to water plasma
- 2021
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 50:14, s. 4796-4804
-
Tidskriftsartikel (refereegranskat)abstract
- Thin UO2 films exposed to water plasma under UHV conditions have been shown to be interestingmodels for radiation induced oxidative dissolution of spent nuclear fuel. This is partly attributed to the factthat several of the reactive oxidizing and reducing species in a water plasma are also identified as productsof radiolysis of water. Exposure of UO2 films to water plasma has previously been shown to lead to oxidationfrom U(IV) to U(V) and (VI). In this work we have studied the dynamics of water plasma inducedredox changes in UO2 films by monitoring UO2 films using X-Ray photoelectron Photoemission (XPS) andUltra-Violet Photoemission (UPS) spectroscopy as a function of exposure time. The surface compositionin terms of oxidation states obtained from U4f7/2 peak deconvolution could be retraced along theexposure time, and compared to the valence band. The spectral analysis showed that U(IV) is initially oxidizedto U(V) which is subsequently oxidized to U(VI). For extended exposure times it was shown that U(VI)is slowly reduced back to U(V). UPS data show that, unlike the U(V) formed on the surface upon oxidationof U(IV), the U(V) formed upon reduction of U(VI) is localized in the bulk of the film. It also displays adifferent reactivity than the initially formed U(V). The experiments can be reproduced using a simplekinetic model describing the redox processes involved.
|
|
